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Sample records for exhumed permian mudstone-dominated

  1. Geochemical variability and sequence stratigraphic interpretation of the mudstone- dominated Lower Cretaceous succession in the eastern Lower Saxony Basin, Germany

    NASA Astrophysics Data System (ADS)

    Thöle, Hauke; Heimhofer, Ulrich; Erbacher, Jochen; Bornemann, André; Luppold, Friedrich-Wilhelm

    2017-04-01

    Fine-grained sedimentary rocks predominantly composed of silts and clays (mudstones) are currently a popular topic within industry and academia. Of particular interest is to better constrain the pervasive facies variability present within these rocks. Despite their apparent homogeneity at core and outcrop scale, mudstones can actually be highly heterogeneous when examined in detail. We used geochemical and palynofacies analyses to delineate the facies variability present within the mudstone-dominated Lower Cretaceous succession in the eastern Lower Saxony Basin (LSB). In addition, the data-set is used to establish a sequence stratigraphic framework based on X-ray fluorescence (XRF) chemostratigraphy and palynofacies within apparently homogeneous mudstone successions. Our study is based on three scientific drill cores (Scharnhorst 3, Scharrel 10 and Frielingen 9) which were drilled during 2012-2014. Because of their close geographical location and similar palaeoenvironmental setting, these cored sections can be considered as one complete, 510-m-thick composite section covering the late Berriasian to earliest Aptian interval. All cores have been analysed for major and minor elements (Al, Si, S, K, Ca, Ti, Mn, Fe) by X-ray fluorescence (XRF) core scanning analysis at 1 cm resolution. The resulting trends for each element were analysed in terms of facies variability and to capture relative shifts in shoreline trajectories. For example, elemental ratios indicative of coarser clastic input (e.g., Si/Al) are used to decipher proximal to distal trends within the studied sediments. In order to better understand the nature of geochemical variations, XRF core scanning analyses are compared with palynofacies results.

  2. Exhumed Craters

    NASA Technical Reports Server (NTRS)

    2004-01-01

    5 July 2004 Burial and exhumation is a theme that repeats itself, all over the surface of Mars. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows several north mid-latitude meteor impact craters with bouldery ejecta deposits. Each of the craters was once buried and later exhumed. Mesas on the floors of these craters are remnants of the materials that once filled and covered them. The craters are located near 39.7oN, 206.0oW. The image covers an area about 3 km (1.9 mi) wide; sunlight illuminates the scene from the lower left.

  3. Exhuming Landforms

    NASA Technical Reports Server (NTRS)

    2005-01-01

    26 October 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a crater and adjacent terrain that have been exhumed from beneath a wind-eroded material. The sharp, pointy ridges inside and immediately adjacent to the crater are the remains of a material that once covered the entire scene. Wind has stripped these materials away, forming yardangs. Inside the crater, the erosion has revealed an older, eroded layered material. This smooth-surfaced layered feature inside the crater was already eroded to nearly its present shape before the yardang-forming material was deposited (and then eroded away).

    Location near: 7.2oN, 156.4oW Image width: width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Winter

  4. Late Permian vertebrate community of the Pranhita Godavari valley, India

    NASA Astrophysics Data System (ADS)

    Ray, Sanghamitra; Bandyopadhyay, Saswati

    2003-03-01

    The Kundaram Formation of the Pranhita-Godavari valley yields the only Late Permian multispecies terrestrial vertebrate assemblage from India. This includes various medium and small dicynodonts such as Endothiodon, Oudenodon, Kingoria, Emydops, Cistecephalus and Pristerodon. At present two species of Endothiodon ( E. mahalanobisi and E. uniseries) are known. Apart from these dicynodonts, the Kundaram vertebrate fauna also contains a medium-sized gorgonopsian and a small captorhinid. The material, from the red mudstone dominated Kundaram Formation, includes numerous isolated, disarticulated skulls and lower jaws. Postcranial elements are relatively rare except for a few broken limb ends and vertebrae. The bones are encrusted by iron rich matrix and most of them had suffered deformation. This skull dominant accumulation is attributed to prolonged aerial exposure prior to burial resulting in disarticulation of the skeletons and subsequent inundation by floodwater. The limb bones and other postcranial elements of the already disarticulated skeletons were winnowed out by shallow competent flow while the relatively heavier skulls and lower jaws resisting transportation were buried near the site of death. The Late Permian scenario of the Pranhita-Godavari valley was characterised by the dominance of herbivores. This abundance of herbivores at the base and the presence of relatively few carnivores and omnivores at the top of the Kundaram food pyramid indicate a trophic structure similar to that of the modern-day terrestrial ecosystem.

  5. Modern Pearl River Delta and Permian Huainan coalfield, China: A comparative sedimentary facies study

    USGS Publications Warehouse

    Suping, P.; Flores, R.M.

    1996-01-01

    Sedimentary facies types of the Pleistocene deposits of the Modern Pearl River Delta in Guangdong Province, China and Permian Member D deposits in Huainan coalfield in Anhui Province are exemplified by depositional facies of anastomosing fluvial systems. In both study areas, sand/sandstone and mud/mudstone-dominated facies types formed in diverging and converging, coeval fluvial channels laterally juxtaposed with floodplains containing ponds, lakes, and topogenous mires. The mires accumulated thin to thick peat/coal deposits that vary in vertical and lateral distribution between the two study areas. This difference is probably due to attendant sedimentary processes that affected the floodplain environments. The ancestral floodplains of the Modern Pearl River Delta were reworked by combined fluvial and tidal and estuarine processes. In contrast, the floodplains of the Permian Member D were mainly influenced by freshwater fluvial processes. In addition, the thick, laterally extensive coal zones of the Permian Member D may have formed in topogenous mires that developed on abandoned courses of anastomosing fluvial systems. This is typified by Seam 13-1, which is a blanket-like body that thickens to as much as 8 in but also splits into thinner beds. This seam overlies deposits of diverging and converging, coeval fluvial channels of the Sandstone D, and associated overbank-floodplain deposits. The limited areal extent of lenticular Pleistocene peat deposits of the Modern Pearl River Delta is due to their primary accumulation in topogenous mires in the central floodplains that were restricted by contemporaneous anastomosing channels.

  6. Quantification of Exhumation from Sonic Velocity Data, Cooper Basin, Australia, and Implications for Hydrocarbon Exploration

    NASA Astrophysics Data System (ADS)

    Mavromatidis, Angelos

    2006-05-01

    Exhumation (defined as rock uplift minus surface uplift) in the Cooper Basin of South Australia and Queensland has been quantified using the compaction methodology. The sonic log, which is strongly controlled by the amount of porosity, is an appropriate indicator of compaction, and hence is used for quantifying exhumation from compaction. The traditional way of estimating exhumation based on the degree of overcompaction of a single shale unit has been modified and five units ranging in age from Permian to Triassic have been analysed. The results reveal that exhumation increases eastwards from the South Australia into the Queensland sector of the basin. The results show that exhumation in Late Triassic - Early Jurassic times, after the Cooper Basin deposition, seems to be 200-400 m higher than exhumation in Late Cretaceous - Tertiary times, after the Eromanga Basin deposition. This study has major implications for hydrocarbon exploration. Maturation of source rocks will be greater for any given geothermal history if exhumation is incorporated in maturation modelling. Exhumation values can also be used to improve porosity predictions of reservoir units in undrilled targets.

  7. Permian chronostratigraphic subdivisions

    USGS Publications Warehouse

    Yugan, Jin; Wardlaw, Bruce R.; Glenister, Brian F.; Kotlyar, Galina V.

    1997-01-01

    Names and boundary levels for series and stages of the Permian System, based on marine successions, have been approved by the Permian Subcommission, ICS. These are the Cisuralian, Guadalupian, and Lopingian Series and their constituent stages standardized respectively in the Urals, Southwest USA, and South China for the Lower; Middle, and Upper Permian.

  8. Exhumed Crater with Slope

    NASA Technical Reports Server (NTRS)

    2004-01-01

    MGS MOC Release No. MOC2-575, 15 December 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a crater in Arabia Terra that has been exhumed. The picture was acquired less than 1 week ago, on 9 December 2003. The crater was buried beneath layered material, but erosion later brought it back to the surface. A thick blanket of dust mantles the scene; dark streaks have formed as some of this dust slid down the crater walls. Old, dust-covered ripples of windblown sediment occur on the floor of the exhumed crater. The image is located near 20.9oN, 320.7oW, and covers an area 3 km (1.9 mi) wide; sunlight illuminates the scene from the lower left.

  9. Exhumed Craters near Kaiser

    NASA Technical Reports Server (NTRS)

    2004-01-01

    24 August 2004 The upper left (northwest) corner of this Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a crater within which are several layers of eroded material. This crater, and probably all of its degraded neighbors, was once filled and buried, and was later exhumed. The burial and exhumation theme is one that repeats all over the surface of Mars, as ancient rocks are eroded to expose previously filled and buried craters, valleys, and landscapes. This particular image is located near the northwest rim of Kaiser Crater, in Noachis Terra, near 45.2oS, 342.7oW. The image covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the upper left.

  10. Permian karst topography in the Wichita uplift, southwestern Oklahoma

    SciTech Connect

    Donovan, R.N. Busbey, A.B. . Geology Dept.)

    1993-02-01

    The Wichita uplift in southwestern Oklahoma is one part of a record of Pennsylvania and early Permian deformation that affected the Southern Oklahoma aulacogen. As a result of a partial inversion, the Lower Paleozoic section of this aulacogen was sequentially stripped off an uplift between the Wichita uplift and the Anadarko basin, resulting in the exposure of ultrabasic rocks deep in the Cambrian igneous fill of the aulacogen. Following the late Paleozoic tectonism, the topography of the uplift was entombed beneath Permian sediments and remained essentially undisturbed until exhumation during the present erosional cycle. Modern erosion is gradually exposing this topography, permitting morphometric analysis of the Permian hill forms. Because of the variation of lithology in the uplift, it is possible to isolate the effects of weathering processes such as intense hydrolysis of the igneous rocks (producing, among other features, or topography) and limestone dissolution, in the form of a surface and subsurface karst imprint. The latter process resulted in a network of small caves that are essentially fissures eroded along tectonic fractures. These small caves can be found in all the exposed areas of limestone. They are particularly noteworthy for three reasons: in at least five examples they contain a complex fauna of Permian vertebrates (mostly fragmentary), speleothems in some examples contain hydrocarbon inclusions, derived from the underlying Anadarko basin, some of the caves yield evidence of post burial evolution in the form of clay infiltration from the surface and brine flushing from the underlying Anadarko basin.

  11. Untold muddy tales: Paleoenvironmental dynamics of a ``barren'' mudrock succession from a shallow Permian epeiric sea

    NASA Astrophysics Data System (ADS)

    Simões, M. G.; Matos, S. A.; Warren, L. V.; Assine, M. L.; Riccomini, C.; Bondioli, J. G.

    2016-11-01

    During the late Paleozoic, the intracratonic Paraná Basin, Brazil, in central Gondwanaland, was covered by a huge (>1.600.000 km2), shallow and isolated epeiric sea. Within the Permian succession, oxygen-deficient facies are commonly recorded in the Mesosaurus-bearing Irati Formation (Cisuralian, Artinskian/Kungurian) and the overlaying Serra Alta Formation (Guadalupian, Wordian/Capitanian). Barren, dark-grey mudstones are the main facies preserved in this last unit, which has usually discouraged extensive and detailed stratigraphical and paleontological investigations. However, exhaustive sedimentological, taphonomic and paleontological surveys in those deposits reveal a dynamic and complex depositonal history. Based on sedimentary fabric, autochthonous to parautochthonous occurrences of shelly benthic invertebrates (bivalves) and the presence/absence of concretion-bearing and phosphate-rich layers, we report variations in the oxygen levels of bottom and pore waters, in bathymetry, sedimentation rates, and changes in benthic colonization. Our data indicate that the deposition of this ;apparently barren; mudstone-dominated succession was driven by a complex interplay of variations in sedimentation rate and oxygen pulses tied to tectonic and climate changes. Three distinct populations or invertebrate paleocommunities were recorded, which were adapted to (a) normal background low-oxygen (dysoxic) conditions (i.e., minute infaunal suspension-feeding bivalves associated with the trace fossil Planolites), (b) chemically toxic (anoxic/extreme dysoxic) substrates, including gigantic burrowing bivalves (probable chemosymbiotic taxa), and (c) oxic/dysoxic substrates following short-term bottom disruptions.

  12. Sedimentology and petroleum occurrence, Schoolhouse Member, Maroon Formation (Lower Permian), northwestern Colorado

    USGS Publications Warehouse

    Johnson, S.Y.; Schenk, C.J.; Anders, D.L.; Tuttle, M.L.

    1990-01-01

    The Lower Permian Schoolhouse Member of the Maroon Formation forms a partly exhumed petroleum reservoir in the Eagle basin of northwestern Colorado. The Schoolhouse consists mainly of yellowish gray to gray, low-angle to parallel bedded, very fine to fine-grained sandstone of eolian sand-sheet origin; interbedded fluvial deposits are present in most sections. Geological and geochemical data suggest that Schoolhouse Member oils have upper Paleozoic sources, including the intrabasinal Belden Formation. Late Paleozoic faults have served as local conduits for vertical petroleum migration. Large-scale (>200 km) lateral migration from sources in the Permian Phosphoria Formation is also possible but less likely. Belden oil was generated and migrated before about 75 Ma. Subsequently, the Schoolhouse Member reservoir was uplifted, then partly exhumed on the monoclinal flank of the Laramide (latest Cretaceous-Paleogene) White River uplift. -from Authors

  13. Permian chronostratigraphy in Kansas

    SciTech Connect

    Baars, D.L. )

    1990-08-01

    Correlations between the type Permian System of Russia and North American strata have been difficult for decades because of biostratigraphic and nomenclatural confusion. Consequently, a standard Permian section was established in west Texas that is widely accepted throughout North America. Series of the North American standard section are, in ascending order, Wolfcampian, Leonardian, Guadalupian, and Ochoan. This nomenclature was adopted for usage in Kansas in 1951, but was later abandoned in favor of local terminology. However, direct biostratigraphic correlations between Kansas and the west Texas standard section have now been firmly established, and local chronostratigraphic names, i.e., Big Blue, Lyon, Geary, Cimarron, and Custer, have not been widely accepted. The Kansas Geological Survey has now readopted usage of the Wolfcampian Series for rocks of the Admire, Council Grove, and Chase Groups; the Leonardian Series for rocks of the Summer and Nippewalla Groups; and the Guadalupian Series for rocks of the Whitehorse, Day Creek, and Big Basin Formations. The Wolfcampian Series in Kansas (and elsewhere in North America) contains post-Virgilian (latest Carboniferous) strata that predate the classical Permian System of the Russian type section. Consequently, the Pennsylvanian/Permian boundary will probably have to be raised stratigraphically to conform to global usage.

  14. A Comparative Study on Exhumed Seismogenic Faults and Modern Nankai Seismogenic Megathrust

    NASA Astrophysics Data System (ADS)

    Kimura, G.; Kitamura, Y.; Sakaguchi, A.; Ujiie, K.; Sato, K.

    2003-12-01

    One of the critical questions to understanding the seismogenic subduction zone is what controls the updip limit of the zone. The question is quite significant to address why the rupture zone stops in some case or propagates to shallow portion and results in the tsunamigenesis in another case. The Nankai trough is a single most unique subduction zone in the world, where historical repetition of large earthquakes and tsumani more than 700 years are well recorded and the updip limit is located enough shallow to drill by riser vessel. That is one of the reasons why drilling into the seismogenic plate boundary has been proposed in the Nankai Trough. Before drilling, we are conducting a comparative research on exhumed seismogenic fault in ancient accretionary complex on land, which was once located in the sesimogenic depth, and the modern Nankai Trough of targeted site for drilling. Several new findings from the exhumed rocks stimulate the understanding of the sesimogenic zone and sharpen the targets by drilling. 1. Break and involvement of oceanic basement into the accretionary complex as blocks of melange is suggested to be a seismic process because of ubiquitous brittle (cataclastic to ultracataclastic) breakage of the oceanic fragment in contrast to ductile deformation of underthrusted sediments. 2. A boundary fault such as sandstone dominated coherent unit (might be offscraped) and mudstone dominated chaotic one (might be underthrusted) is a clear seismogenic fault and a candidate for a major seismogenic plate boundary. A discovery of pseudotachyllyte from the fault strongly suggests a melting lubrication for rupture propagation around the updip limit of the sesimogenic zone. 3. Detailed analysis of the melange and the boundary fault suggests a repeated activity of pressure solution creep (interseismic) alternated with cataclastic or melting slip (coseismic) in a thick plate boundary zone. 4. Crack seal mineral veins are also developed in and around the fault. P

  15. Early Permian bipedal reptile.

    PubMed

    Berman, D S; Reisz, R R; Scott, D; Henrici, A C; Sumida, S S; Martens, T

    2000-11-03

    A 290-million-year-old reptilian skeleton from the Lower Permian (Asselian) of Germany provides evidence of abilities for cursorial bipedal locomotion, employing a parasagittal digitigrade posture. The skeleton is of a small bolosaurid, Eudibamus cursoris, gen. et sp. nov. and confirms the widespread distribution of Bolosauridae across Laurasia during this early stage of amniote evolution. E. cursoris is the oldest known representative of Parareptilia, a major clade of reptiles.

  16. Exhuming Craters in a Crater

    NASA Technical Reports Server (NTRS)

    2004-01-01

    12 December 2004 Burial and exhumation of impact craters, and their destruction by erosion, are common and repeated themes all over the surface of Mars. Many craters in western Arabia Terra exhibit light-toned, layered outcrops of ancient sedimentary rock. Like the sedimentary rocks explored further to the south in Meridiani Planum by the Opportunity Mars Exploration Rover (MER-B), these intracrater sedimentary rocks may have been deposited in water. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an example of light-toned sedimentary rocks outcropping in a crater that is much farther north than most of the similar examples in western Arabia. This one is located near 36.6oN, 1.4oW, and shows several old impact craters in various states of erosion and exhumation from beneath and within the sedimentary rock materials. The image covers an area approximately 3 km (1.9 mi) wide and is illuminated by sunlight from the lower left.

  17. Stratigraphy, biostratigraphy and C-isotopes of the Permian-Triassic non-marine sequence at Dalongkou and Lucaogou, Xinjiang Province, China

    NASA Astrophysics Data System (ADS)

    Metcalfe, I.; Foster, C. B.; Afonin, S. A.; Nicoll, R. S.; Mundil, R.; Xiaofeng, Wang; Lucas, S. G.

    2009-11-01

    Measured lithostratigraphic sections of the classic Permian-Triassic non-marine transitional sequences covering the upper Quanzijie, Wutonggou, Guodikeng and lower Jiucaiyuan Formations at Dalongkou and Lucaogou, Xinjiang Province, China are presented. These measured sections form the framework and reference sections for a range of multi-disciplinary studies of the P-T transition in this large ancient lake basin, including palynostratigraphy, vertebrate biostratigraphy, chemostratigraphy and magnetostratigraphy. The 121 m thick Wutonggou Formation at Dalongkou includes 12 sandstone units ranging in thickness from 0.5 to 10.5 m that represent cyclical coarse terrigenous input to the lake basin during the Late Permian. The rhythmically-bedded, mudstone-dominated Guodikeng Formation is 197 m and 209 m thick on the north and south limbs of the Dalongkou anticline, respectively, and 129 m thick at Lucaogou. Based on limited palynological data, the Permian-Triassic boundary was previously placed approximately 50 m below the top of this formation at Dalongkou. This boundary does not coincide with any mappable lithologic unit, such as the basal sandstones of the overlying Jiucaiyuan Formation, assigned to the Early Triassic. The presence of multiple organic δ13C-isotope excursions, mutant pollen, and multiple algal and conchostracan blooms in this formation, together with Late Permian palynomorphs, suggests that the Guodikeng Formation records multiple climatic perturbation signals representing environmental stress during the late Permian mass extinction interval. The overlap between the vertebrates Dicynodon and Lystrosaurus in the upper part of this formation, and the occurrence of late Permian spores and the latest Permian to earliest Triassic megaspore Otynisporites eotriassicus is consistent with a latest Permian age for at least part of the Guodikeng Formation. Palynostratigrahic placement of the Permian-Triassic boundary in the Junggar Basin remains problematic

  18. Permian potentiometric analysis

    SciTech Connect

    Devary, J.L.

    1983-09-01

    Pacific Northwest Laboratory (PNL) was requested to analyze potentiometric data from the Wolfcamp Formation of the Permian System to evaluate the recommendations by the University of Texas/Bureau of Economic Geology (UT/BEG) that additional geohydrologic boreholes be drilled into the Wolfcamp. The UT/BEG recommended that two stratigraphic and two geohydrologic borings be drilled into the Permian System during FY83 and that several shallow hydrologic tests be made in the Dockum Formation. A geostatistical technique known as kriging was applied to objectively evaluate these geohydrologic borehole recommendations. The Deaf Smith County location appears to be an excellent choice for a borehole. No high quality potentiometric data are available from Deaf Smith County and a borehole location immediately upgradient from the candidate repository site is needed. Adding this borehole location to the potentiometric data base will significantly reduce field data uncertainty near the location being studied. The Swisher County location does not appear to be the best choice. High quality data values H2206 and H2360 are located immediately upgradient from the proposed repository site. The best placement of additional geohydrological boreholes in the Wolfcamp Formation depends strongly upon the proposed repository location. The variability of the potentiometric data causes estimation errors to rapidly increase away from locations of field measurements. Suggested locations for additional boreholes for the Deaf Smith investigations are in northwest Randall or central Potter Counties. Ideal borehole locations for the Swisher county studies appear to be in southeast Randall and Armstrong Counties.

  19. Exhumation of Continental Ultrahigh-Pressure Terranes

    NASA Astrophysics Data System (ADS)

    Gilotti, J. A.

    2008-12-01

    Exhumation of continental ultrahigh-pressure (UHP) terranes is one of the most enigmatic processes associated with UHP metamorphism for at least two reasons: 1. the structures that must have been active during the UHP and high pressure part of the decompression path are overprinted by lower grade structures and are thus cryptic, and 2. felsic crust subjected to UHP conditions should become denser than lithospheric mantle and sink; however, we observe that slivers of UHP continental crust are buoyant enough to be exhumed to Earth's surface. Even when deformational fabrics demonstrably formed at UHP conditions are preserved, their geometric and kinematic significance are uncertain due to likely rotation during exhumation and subsequent deformation. In light of the partial structural record and limited understanding of what controls exhumation versus permanent subduction of continental material, models for exhumation must be based on alternate observations. Some common features of exhumed UHP terranes are: a tabular geometry with thicknesses on the order of 10 km; location in the lower plate of a subduction channel; formation and exhumation early in the collision history; and a two-stage process with rapid rise to the lower-middle crust and slower exhumation to the surface. Popular Chemenda-type analog models, where slab break-off of the subducting lithosphere leads to buoyant extrusion of UHP slivers at least to lower crustal levels, provide one mechanism for exhumation; but this type of model needs refinement to account for a wider range of geological circumstances under which UHP terranes form and are exhumed. This talk is meant to review and highlight current thinking on the exhumation of UHP terranes incorporating these alternate settings. Emphasis will be placed on the variation in the initial configuration of the subduction channel, the relative strengths of the colliding lithospheric margins, and large scale melt-enhanced exhumation by diapiric mechanisms. UHP

  20. Phanerozoic orogeny triggers reactivation and exhumation in the northern part of the Archean-Paleoproterozoic North China Craton

    NASA Astrophysics Data System (ADS)

    Zhang, Hong-Fu; Zou, Dong-Ya; Santosh, M.; Zhu, Bin

    2016-09-01

    Cratons and orogenic belts are integral components of ancient continents. In some cases, stable continents can be reactivated and even largely destroyed by younger events. The mechanisms of reactivation or destruction of ancient cratons remain equivocal. Here we compile zircon U-Pb data from the metamorphic rocks of the Hongqiyingzi Group in the northern part of the North China Craton (NCC) to evaluate this problem. The results reveal episodic tectonothermal events related to three major periods of Latest Neoarchean-Earliest Paleoproterozoic (2.6-2.4 Ga), Paleoproterozoic (1.85-1.95 Ma) and Phanerozoic (480-220 Ma, with peak at 360-320 Ma). The Neoarchean-Paleoproterozoic crust as represented by the Hongqiyingzi Group was subducted to eclogite facies at ca. 1.95 Ga, followed by the final collision between the Eastern and Western Blocks at ca. 1.85 Ga to produce the Trans-North China Orogen (TNCO). The ubiquitous presence of Phanerozoic concordant zircons in the Hongqiyingzi Group suggests the episodic exhumation of the TNCO in the northern segment during the Phanerozoic. The 460-420 Ma concordant zircons record the onset of exhumation, triggered by the Ordovician-Silurian southward subduction of the Paleoasian Ocean. Widespread occurrence of 360-320 Ma metamorphic and magmatic zircons in the Hongqiyingzi Group demonstrates that the Carboniferous-Permian was an important period of exhumation for the TNCO, possibly related to back-arc extension. A few Permian-Triassic concordant zircons record late Permian accretion and Triassic post-accretional uplifting. Our study demonstrates that the young orogeny during the formation of the Central Asian Orogenic Belt resulted in extensive reactivation of not only the Archean continental crust but also the Paleoproterozoic orogen in the northern NCC.

  1. Permian evaporites in the Permian basin of southwestern United States

    USGS Publications Warehouse

    Johnson, K.S.

    1997-01-01

    During Permian time, a broad and shallow inland sea covered much of southwestern United States, extending northward from west Texas into northwestern Kansas. Slow but continual subsidence beneath all parts of this vast Permian basin caused deposition of a thick sequence of Permian red beds and evaporites, including dolomite, gypsum/anhydrite, salt, and potash. Evaporite units are notably thick and laterally persistent throughout the Permian basin. The entire Permian System ranges up to 2,000 m thick in various parts of the basin, and individual formations, consisting mostly of gypsum/anhydrite and salt, commonly are 60-500 m thick. Evaporite deposits are oldest in the northern part of the Permian basin, and they generally are progressively younger toward the south. The site of principal salt deposition during early Leonardian time (Wellington evaporites) was in Kansas and northwestern Oklahoma; it then shifted southward into western Oklahoma and the Texas Panhandle during late Leonardian and early Guadalupian time (Lower Clear Fork/Lower Cimarron evaporites, Upper Clear Fork/Upper Cimarron evaporites, and San Andres/Blaine evaporites); and finally into west Texas and southeastern New Mexico during late Guadalupian and Ochoan time (Artesia, Castile, Salado, and Rustler evaporites). These evaporites comprise a significant resource for the region: rock salt is produced from dry mines, brine fields, and solar-salt operations at 18 locations; gypsum is mined at 13 sites; potash is produced from 5 underground mines in the world-famous Carlsbad potash district; and sulfur is produced by the Frasch process at one site.

  2. Early Cenozoic "dome like" exhumation around the Irish Sea

    NASA Astrophysics Data System (ADS)

    Doepke, Daniel; Cogné, Nathan; Chew, David; Stuart, Fin

    2016-04-01

    Despite decades of research the Early Cenozoic exhumation history of Ireland and Britain is still poorly understood and subject to contentious debate (see Davis et al., 2012 and subsequent comments). Previous studies have attributed the Cenozoic exhumation history of Ireland and Britain mainly to: (a) Paleogene - Neogene far-field stress between the opening of the North Atlantic Ocean and the Alpine collision (Ziegler et al., 1995; Hillis et al., 2008) or (b) early Paleogene mantle driven magmatic underplating associated with the development of the proto-Iceland mantle plume beneath the Irish Sea (Brodie and White, 1994; Al-Kindi et al., 2003). The major differences between the two hypotheses are the pattern and timing of spatial exhumation. This project thus seeks to investigate the timing and mechanisms of late Mesozoic - early Cenozoic exhumation on the onshore part of the British Isles by using a combination of apatite fission track (AFT) and apatite (U-Th-Sm)/He (AHe) data, which we then model using the QTQt program of Gallagher (2012) to better constrain the modelled thermal histories. Our studied area centres on the margins of the Irish Sea, but includes all Ireland and western Britain. Overall we analysed 74 samples for AFT and 66 samples for AHe dating. In particular, our results include ten pseudo-vertical profiles. The AFT ages display a wide range of ages from early Carboniferous in Scotland to early Eocene in central Ireland. Our AHe ages range from mid Permian on Shetland to Eocene Ft-corrected. The AFT data do not show any specific spatial distribution, however, the Ft-corrected AHe ages around the Irish Sea only focus around late Cretaceous to Eocene suggesting an important thermal event around this time. The modelled thermal histories of samples located around the Irish Sea and western Scotland show a clear late Cretaceous to early Paleogene cooling event which is not present elsewhere. The distribution of this cooling event is broadly consistent

  3. Early Permian Pangea `B' to Late Permian Pangea `A'

    NASA Astrophysics Data System (ADS)

    Muttoni, Giovanni; Kent, Dennis V.; Garzanti, Eduardo; Brack, Peter; Abrahamsen, Niels; Gaetani, Maurizio

    2003-10-01

    The pre-drift Wegenerian model of Pangea is almost universally accepted, but debate exists on its pre-Jurassic configuration since Ted Irving introduced Pangea 'B' by placing Gondwana farther to the east by ˜3000 km with respect to Laurasia on the basis of paleomagnetic data. New paleomagnetic data from radiometrically dated Early Permian volcanic rocks from parts of Adria that are tectonically coherent with Africa (Gondwana), integrated with published coeval data from Gondwana and Laurasia, again only from igneous rocks, fully support a Pangea 'B' configuration in the Early Permian. The use of paleomagnetic data strictly from igneous rocks excludes artifacts from sedimentary inclination error as a contributing explanation for Pangea 'B'. The ultimate option to reject Pangea 'B' is to abandon the geocentric axial dipole hypothesis by introducing a significant non-dipole (zonal octupole) component in the Late Paleozoic time-averaged geomagnetic field. We demonstrate, however, by using a dataset consisting entirely of paleomagnetic directions with low inclinations from sampling sites confined to one hemisphere from Gondwana as well as Laurasia that the effects of a zonal octupole field contribution would not explain away the paleomagnetic evidence for Pangea 'B' in the Early Permian. We therefore regard the paleomagnetic evidence for an Early Permian Pangea 'B' as robust. The transformation from Pangea 'B' to Pangea 'A' took place during the Permian because Late Permian paleomagnetic data allow a Pangea 'A' configuration. We therefore review geological evidence from the literature in support of an intra-Pangea dextral megashear system. The transformation occurred after the cooling of the Variscan mega-suture and lasted ˜20 Myr. In this interval, the Neotethys Ocean opened between India/Arabia and the Cimmerian microcontinents in the east, while widespread lithospheric wrenching and magmatism took place in the west around the Adriatic promontory. The general

  4. Exhumation of the Greater Himalayan Sequence Along the Zanskar Shear Zone, NW India

    NASA Astrophysics Data System (ADS)

    Basta, S.; Beck, E.; Burlick, T.

    2013-12-01

    The Zanskar Shear Zone (ZSZ), the western extent of the South Tibetan Detachment System, exposes high-grade metamorphic rocks of the Greater Himalayan Sequence (GHS) in its footwall. Granites and metapelites collected along the the ZSZ in the Suru River valley provide how and when the GHS rocks exhumed and were deformed. There are two suits of Paleozoic granites deformed within the ZSZ: Pan-African Cambrian-Ordovician granites at the cores of gneiss domes and Mississippian-Permian granites related to Panjal Traps magmatism. Age of Himalayan granites indicates 28-16 Ma which is concurrent with anatectic leucogranite crystallization. The metamorphic mineral assemblage indicates increasing metamorhic grade from NE to SW and comprises Qtz × Kfs + Pl + Bt × Ms × Sil × Ky × Grt × St × Chl × Tur × Rt. In addition to macroscopic evidence, strongly deformed quartz grains, deformation twins, pressure shadows, and kink bands have been observed to demonstrate micro-tectonics evidence. There are two different method to explain exhumation and deformation of the GHS metapelites: Electron backscatter diffraction (EBSD) crystallographic mapping and pseudosection modeling. While EBSD indicates the potential temperature of deformation, pseudosection modeling with Perple_X specifically presents the exhumation path of the GHS rocks. Pseudosection modeling with Perple_X , based on whole-rock geochemical analysis, is set pressure and temperature to 0.4-1.2 GPa and 300-900°C, and uses specific solution models, Bio(TCC), Chl(HP), St(HP), feldspar, Mica(CHA), Gt(HP), and hCrd, namely. These two methods are used by combining with geo/thermochronology data from U-Pb, 40Ar/39Ar, and (U-Th)/He, constraining the age of metamorphism, the cooling and exhumation time of the GHS rocks, and the end of shearing of deformation, respectively. 40Ar/39Ar dating on muscovite and biotite constrains cooling and exhumation ages of the GHS as ~20-19 Ma and 15 Ma, respectively. A metamorphic pressure

  5. Permian geology of Gondwana countries: An overview

    SciTech Connect

    Dickins, J.M. )

    1992-10-01

    Earliest Permian sequences of Antarctica, southern and east-central Africa, the southern part of the Arabian Peninsula, Pakistan, peninsular and Himalayan India, Tibet, western and eastern Australia, New Zealand, and South America are all characterized by glacial deposits and cold-water marine faunas. In the course of the Permian, considerable faunal (and floral) and climatic divergence occurred. Although folding is not necessarily present, the effects of the strong compressive tectonic phase (Hunter-Bowen Orogenic Folding Phase of Dickins) beginning in the mid-Permian (traditional two-fold subdivision) and of acidic and intermediate volcano-magmatic activity are apparent in all these regions as in other parts of the world. The progressive continentality of the Upper Permian (worldwide regression) culminates at the Permian-Triassic (Changxingian-Griesbachian) boundary.

  6. New Permian fauna from tropical Gondwana

    PubMed Central

    Cisneros, Juan C.; Marsicano, Claudia; Angielczyk, Kenneth D.; Smith, Roger M. H.; Richter, Martha; Fröbisch, Jörg; Kammerer, Christian F.; Sadleir, Rudyard W.

    2015-01-01

    Terrestrial vertebrates are first known to colonize high-latitude regions during the middle Permian (Guadalupian) about 270 million years ago, following the Pennsylvanian Gondwanan continental glaciation. However, despite over 150 years of study in these areas, the biogeographic origins of these rich communities of land-dwelling vertebrates remain obscure. Here we report on a new early Permian continental tetrapod fauna from South America in tropical Western Gondwana that sheds new light on patterns of tetrapod distribution. Northeastern Brazil hosted an extensive lacustrine system inhabited by a unique community of temnospondyl amphibians and reptiles that considerably expand the known temporal and geographic ranges of key subgroups. Our findings demonstrate that tetrapod groups common in later Permian and Triassic temperate communities were already present in tropical Gondwana by the early Permian (Cisuralian). This new fauna constitutes a new biogeographic province with North American affinities and clearly demonstrates that tetrapod dispersal into Gondwana was already underway at the beginning of the Permian. PMID:26537112

  7. Exhumation, cooling and deformation history of the necking zone of the fossil Adriatic rifted margin: the Campo/Grosina section (S-Switzerland and N-Italy)

    NASA Astrophysics Data System (ADS)

    Petri, Benoît; Mohn, Geoffroy; Wijbrans, Jan R.; Manatschal, Gianreto; Beltrando, Marco

    2016-04-01

    The Austroalpine units in SE Switzerland and N-Italy preserve remnants of the fossil Adriatic rifted margin. Notably the Campo-Grosina units represent the necking zone where major crustal thinning was accommodated during the Jurassic rifting. This contribution aims to unravel the complex tectonic evolution recorded in these units from the late Carboniferous - early Permian to the Jurassic rifting. The cooling and exhumation of the Campo and overlying Grosina units, separated by the Eita shear zone are explored by the acquisition of 40Ar/39Ar on hornblende, muscovite and biotite. New geochronological data on the Grosina unit present 40Ar/39Ar ages between 273 and 261 Ma for muscovite and between 248 and 246 Ma for biotite. The Campo unit shows clearly younger ages between 210 and 177 Ma on hornblende, between 186 and 176 Ma on muscovite and between 174 and 171 Ma on biotite. Numerous data were discarded due to frequent excess 40Ar on amphiboles, probably associated to the emplacement of the Sondalo gabbro with a high 40Ar/36Ar ratio in Permian times. These new ages, together with a compilation of existing ages obtained with different chronometers (U-Pb, Sm-Nd, Rb-Sr, K-Ar, 40Ar/39Ar) and performed on different lithologies from both the Campo and the Grosina units allow an estimation of the cooling rates for these units to be done. The new results show that both the Campo and the Grosina units underwent a cooling rate around 10°C/Ma in Permian time. The Grosina unit, being in a shallower crustal level, did not record the Jurassic cooling, reaching up to 50°C/Ma in the Campo unit. The notable difference in cooling rates between the Permian and the Jurassic events attests of a cooling without being associated to an exhumation in Permian times, whereas the Campo unit cooled rapidly in Jurassic times, due to an exhumation and an emplacement in shallow crustal levels. The latter tectonic event was likely caused by shearing along the Eita or other greenschist facies

  8. Low-temperature thermochronology of the northern Thomson Orogen: Implications for exhumation of basement rocks in NE Australia

    NASA Astrophysics Data System (ADS)

    Verdel, Charles; Stockli, Daniel; Purdy, David

    2016-01-01

    The Tasmanides of eastern Australia record much of the Phanerozoic tectonic development of the retreating Pacific-Australia plate boundary and are an oft-cited example of an orogen that has undergone "tectonic mode switching." To begin to constrain the timing of exhumation of basement rocks that are now exposed in portions of the NE Tasmanides, we measured apatite and zircon (U-Th)/He ages from the Thomson Orogen and overlying Paleozoic strata in the back-arc of the New England Orogen in NE Australia. Zircon (U-Th)/He ages from basement samples (including those recovered from boreholes at depths of up to 1.1 km) are characterized by large inter- and intra-sample variability and range from approximately 180 Ma (Early Jurassic) to 375 Ma (Late Devonian). (U-Th)/He zircon ages from several individual samples are negatively correlated with effective uranium (eU), a pattern that is also true of the dataset as a whole, suggesting that variations in U and Th zoning and radiation damage are partially responsible for the age variability. The oldest zircon (U-Th)/He cooling ages coincide with the formation of regionally extensive Late Devonian-early Carboniferous back-arc basins, suggesting that Late Devonian extension played a significant role in exhumation of parts of the northern Thomson Orogen. Apatite (U-Th)/He ages from a basement sample and a late Permian sandstone in the overlying Bowen Basin, which are also marked by intra-sample variability and age-eU correlations, span from the Early Cretaceous through Oligocene, in general agreement with previous apatite fission track data. In conjunction with observations of key geologic relationships and prior K-Ar and 40Ar/39Ar data, our results suggest four overall phases in the thermal history of the northern Thomson Orogen: (1) Cambrian-early Silurian metamorphism during the Delamerian and Benambran Orogenies; (2) protracted cooling during the Late Devonian through mid-Permian that likely resulted from extensional

  9. Late Paleozoic structural evolution of Permian basin

    SciTech Connect

    Ewing, T.E.

    1984-04-01

    The southern Permian basin is underlain by the NNW-trending Central Basin disturbed belt of Wolfcamp age (Lower Permian), the deep Delaware basin to its west, and the shallower Midland basin to its eat. The disturbed belt is highly segmented with zones of left-lateral offset. Major segments from south to north are: the Puckett-Grey Ranch zone; the Fort Stockton uplift; the Monahans transverse zone; the Andector ridges and the Eunice ridge; the Hobbs transverse zone; and the Tatum ridges, which abut the broad Roosevelt uplift to the north. The disturbed belt may have originated along rift zones of either Precambrian or Cambrian age. The extent of Lower and Middle Pennsylvanian deformation is unclear; much of the Val Verde basin-Ozona arch structure may have formed then. The main Wolfcamp deformation over thrust the West Texas crustal block against the Delaware block, with local denudation of the uplifted edge and eastward-directed backthrusting into the Midland basin. Latter in the Permian, the area was the center of a subcontinental bowl of subsidence - the Permian basin proper. The disturbed belt formed a pedestal for the carbonate accumulations which created the Central Basin platform. The major pre-Permian reservoirs of the Permian basin lie in large structural and unconformity-bounded traps on uplift ridges and domes. Further work on the regional structural style may help to predict fracture trends, to assess the timing of oil migration, and to evaluate intrareservoir variations in the overlying Permian giant oil fields.

  10. Permian of Southeast Asia: an overview

    NASA Astrophysics Data System (ADS)

    Fontaine, Henri

    2002-08-01

    Permian rocks are widely distributed throughout Southeast Asia. Because of the tropical-equatorial climate the rocks are commonly deeply weathered and covered by dense vegetation over much of the region. Elsewhere, Permian rocks are well exposed and easy to access, particularly where limestone outcrops have weathered to form spectacular, castellated, tower karst. Many limestone outcrops, containing abundant fusulinaceans, were early recognized to be of Permian age, but many outcrops without fusulinaceans, erroneously assigned to the Permian, were found subsequently to be of Triassic age, and more careful studies have established the Permian age of rocks of other lithologies. It is now recognized that different depositional environments are represented by the Permian deposits in various parts of the region. Massive limestones, widespread throughout the region, represent extensive carbonate platforms; local occurrences of thick bedded cherts indicate deposition in deep marine environments, coal, bauxite and clastic sediments with vertebrate remains in North Vietnam and Laos indicate deposition in a continental environment, and pebbly mudstones in Myanmar, Peninsular Thailand, northwest Malaysia and Sumatra, are considered to have been formed in a glacial environment. Volcanic rocks are absent in northwest Peninsular Malaysia and Peninsular Thailand, but are extensively developed in North Vietnam, Sumatra, the eastern Malay Peninsula and Timor. Fossils, representing many fossil groups, are often prolific in Permian sediments, with fusulinaceans, for example, occurring in astronomical numbers in many limestone outcrops. Age-diagnostic fossils demonstrate that the whole of the Permian is represented in different areas of Southeast Asia. Fossil faunal and floral assemblages have been used to establish climatic conditions and environments of deposition, to define distinct crustal blocks and to provide the basis for reconstructing the palaeogeography during Permian times.

  11. Zircon and apatite fission-track evidence for an Early Permian thermal peak and relatively rapid Late Permian cooling in the Appalachian Basin

    SciTech Connect

    Roden, M.K. . Dept. of Earth and Environmental Science); Wintsch, R.P. . Dept. of Geological Sciences)

    1992-01-01

    New zircon fission-track ages compliment published apatite fission-track ages in the Appalachian Basin to narrowly constrain its thermal history. Geologic evidence can only constrain timing of the thermal peak to be younger than late Pennsylvanian sediments ([approximately] 300 Ma) and older than Mesozoic sediments in the Newark and Gettysburg Basins ([approximately] 210 Ma). Apatite fission-track ages as old as 246 Ma require the Alleghanian thermal peak to have been pre-Triassic. Preliminary data on reset zircon fission-track ages from middle Paleozoic sediments range from 255 to 290 Ma. Zircon fission-track apparent ages from samples younger and structurally higher than these are not reset. Thus, the oldest reset zircon fission-track age constraints the time of the Alleghanian thermal peak to be earliest Permian. Rates of post-Alleghanian cooling have not been well-constrained by geologic data and could be very slow. The difference between apatite and zircon fission-track ages for most of the samples range from 100--120 m.y. reflecting Permo-Triassic cooling of only 1 C/m.y. However, one sample with one of the oldest apatite ages, 245 Ma, yields one of the younger zircon ages of 255 Ma. This requires cooling rates of 10 C/m.y. and uplift rates of [approximately] 0.5 mm/yr. Collectively, these data support an early Permian thermal peak and a two-stage cooling history, consisting of > 100 C cooling (> 8 km denundation) in the Permian followed by relatively slow cooling and exhumation throughout the Mesozoic.

  12. The exhumation of a World War II Jewish grave.

    PubMed

    Chagowski, W; Madro, R

    1999-01-01

    The results of the exhumation of a mass grave from the time of the World War II are presented. In the course of exhumation it was established that the subjects were 190 individuals (men, women and children) of Jewish origin. All had died a violent death due to gunshot or mechanical injury.

  13. Fluid Flow, Reactions and Exhumation of Mantle Peridotite Along a Serpentinite Fault Zone.

    NASA Astrophysics Data System (ADS)

    Tulley, C. J.; Smith, S. A. F.; Scott, J.; Tarling, M. S.; le Roux, P. J.

    2016-12-01

    The last phase of exhumation of a > 1000 km long belt of Permian mantle (Dun Mountain Ophiolite Belt) in New Zealand was achieved by movements along the Livingstone Fault. At Mt Raddle and Mt Richards in the Olivine Range, near-pristine mantle harzburgite shows a complete transition through to the serpentinite melange of the Livingstone Fault, which juxtaposes the ultramafics against quartzofeldspathic crust. A talc-tremolite-diopside reaction zone developed at the serpentinite-crustal contact, with diopside overgrowing tremolite. We suspect that the initial formation of frictionally weak talc helped to localise deformation within the reaction zone. The hydration of peridotite is intimately linked to fluid flow along the Livingstone Fault, since water-bearing phases increase with proximity to the fault melange. The transformation of harzburgite to serpentinite is marked by serpentinisation of clinopyroxene and olivine, development of chromite from Cr spinel (Cr# increases from 45 to 97) and overgrowths of secondary olivine ( Fo82-85) around orthopyroxene. As the melange is approached, magnetite forms at the expense of Fe-bearing mantle minerals. The replacement of primary spinel released Al and Mg, which now forms nano-scale intergrowths of chlorite and lizardite. The scaly serpentinite melange is up to 80 m wide at Mt Raddle and contains pods of massive serpentinite, some with remnant peridotite texture. At Mt Richards, 2 km along strike, the melange narrows and fresh peridotite is exposed within 20 m of the quartzofeldspathic rocks. This change in fault zone structure implies that fluid ingress into the ultramafics was highly variable during the exhumation process. The Livingstone Fault may provide insights in to the decoupling of crust and mantle above a subduction zone. The infiltration of fluid along the fault interface acted as a lubricant, driving hydration reactions and enabling adjacent fresh mantle peridotite to be brought towards the Earth's surface.

  14. Early Permian brachiopods from Perak, west Malaysia

    NASA Astrophysics Data System (ADS)

    Shi, G. R.; Waterhouse, J. B.

    A Permian brachiopod fauna from beds at the Nam Loong No. 1 Mine of Kinta Valley west of Kampar, Perak, west Malaysia is described. New taxa are Schizophoria kintaensis n. sp., Stictozoster lata n. sp., Kintathyris malayaensis n. gen. n. sp., and Brachythyrina gobbetti n. sp. The brachiopods indicate possible Sterlitamakian age of the Sakmarian Stage (Early Permian). Correlations with Thailand, Pamirs, Timor, Australia, and the Urals are discussed. It is also pointed out that the brachiopod provinciality of the Shan-Thai terrane changed rapidly in Early Permian from southern cold temperate to subtropical zone, probably implying either a rapid northward drift of the terrane or a rapid shift of climatic zone during the Early Permian times.

  15. Exhumation of the Shackleton Range, Antarctica

    NASA Astrophysics Data System (ADS)

    Lucka, Nicole; Lisker, Frank; Läufer, Andreas; Spiegel, Cornelia

    2013-04-01

    The Shackleton Range is situated between 80° - 81°S and 19° - 31°W, where it forms the continuation of the Transantarctic Mountains in the Weddell Sea sector of Antarctica. There, Precambrian igneous and metamorphic basement is overlain by (meta-) sedimentary rocks of an Early Paleozoic nappe stack and post-orogenic red beds. Nappe stacking resulted from the collision of East and West Gondwana due to the closure of the Mozambique Ocean in pan-African times. The uplift and exhumation history of the Shackleton Range has been analysed earlier based on a series of vertical fission track profiles (Schäfer, 1998; Lisker et al., 1999). Zircon ages range from ~160 to 210 Ma while apatite ages between ~95 and ~170 Ma comprise a break in slope of the altitude regression at ~110 Ma, and are accompanied by mean track lengths of 12.7 - 14.1 µm (standard deviation 1.0 - 1.4 µm). These data have been interpreted qualitatively in terms of two cooling/ exhumation stages during Jurassic and mid-Cretaceous times. However, the recognition of Jurassic volcaniclastic rocks associated with the ~180 Ma Ferrar event in the vicinity of the sample locations (Buggisch et al., 1994) challenges this exhumation concept. Moreover, new fission track proxy data (Dpar) and apatite (U-Th-Sm)/He ages between 88 and 171 Ma allow thermal history modelling of the combined thermochronological data. First tentative thermal history models suggest early Mesozoic cooling followed by (post-) Jurassic heating and final cooling since the Late Cretaceous. This scenario requires burial of the Shackleton Range region, and therefore the existence of a sedimentary basin at least during the Jurassic-Early Cretaceous, and subsequent basin inversion. The thickness of the now vanished sedimentary strata did unlikely exceed 2 - 3 km. Future work including additional apatite fission track analyses will help to quantifying geometry, depth and timing of this depocentre and evaluating potential links with the coeval

  16. Subduction and exhumation of continental crust: insights from laboratory models

    NASA Astrophysics Data System (ADS)

    Bialas, Robert W.; Funiciello, Francesca; Faccenna, Claudio

    2011-01-01

    When slivers of continental crust and sediment overlying oceanic lithosphere enter a subduction zone, they may be scraped off at shallow levels, subducted to depths of up to 100-200 km and then exhumed as high pressure (HP) and ultra-high pressure (UHP) rocks, or subducted and recycled in the mantle. To investigate the factors that influence the behaviour of subducting slivers of continental material, we use 3-D dynamically consistent laboratory models. A laboratory analogue of a slab-upper mantle system is set up with two linearly viscous layers of silicone putty and glucose syrup in a tank. A sliver of continental material, also composed of silicone putty, overlies the subducting lithosphere, separated by a syrup detachment. The density of the sliver, viscosity of the detachment, geometry of the subducting system (attached plate versus free ridge) and dimensions of the sliver are varied in 34 experiments. By varying the density of the sliver and viscosity of the detachment, we can reproduce a range of sliver behaviour, including subduction, subduction and exhumation from various depths and offscraping. Sliver subduction and exhumation requires sufficient sliver buoyancy and a detachment that is strong enough to hold the sliver during initial subduction, but weak enough to allow adequate sliver displacement or detachment for exhumation. Changes to the system geometry alter the slab dip, subduction velocity, pattern of mantle flow and amount of rollback. Shallower slab dips with more trench rollback produce a mantle flow pattern that aids exhumation. Steeper slab dips allow more buoyancy force to be directed in the up-dip direction of the plane of the plate, and aide exhumation of subducted slivers. Slower subduction can also aide exhumation, but if slab dip is too steep or subduction too slow, the sliver will subduct to only shallow levels and not exhume. Smaller slivers are most easily subducted and exhumed and influenced by the mantle flow.

  17. Late Permian to Early Triassic magnetostratigraphy

    NASA Astrophysics Data System (ADS)

    Haag, Maja; Heller, Friedrich

    1991-10-01

    A Late Permian to Early Triassic magnetostratigraphic reference section is presented. The Lower Triassic part is based on results from marine limestone sections in South China published earlier [1,2]. Reliable new Permian data are added here which have been collected in the Nammal gorge (Salt Range, Northwest Pakistan) where marine sediments have been deposited quasi-continuously with occasional minor hiatuses during the late Palaeozoic to early Mesozoic. About 50% of the Permian samples from the Nammal section contain, hidden beneath a strong recent or Tertiary overprint, a characteristic remanent magnetization (ChRM) which is very likely of Permian age. This component, which was imprinted on the southern hemisphere, has normal as well as reversed polarity with a normal mean direction (Decl. = 289.3°, Incl. = -50.3°, α 95 = 4.3° , N = 113) which is in close agreement with the palaeofield direction expected for a site belonging to the Indian plate as part of Gondwanaland during the Permian. In the lower Upper Permian several normal polarity zones are recognized. This contradicts the current assumption that rocks of this age belong to the long, reversely polarized Kiaman hyperzone. The Kiaman interval must end and the Illawarra hyperzone of mixed polarity must begin in or prior to the lowermost Upper Permian. The Permian/Triassic boundary at Nammal as well as in the Chinese sections is situated very close to a transition from a reversed to a normal polarity zone. The Upper Permian at Nammal together with the Lower Triassic South China sections is estimated to cover about 20 Ma. Nearly 30 polarity changes are observed which result in an average reversal frequency very similar to that observed during the early Tertiary. The reversal rate after the end of the long-lasting reversed Kiaman hyperchron apparently increases in a manner similar to that after the end of the Cretaceous Long Normal Superchron. Only a few polarity zones are found in the lower Upper Permian

  18. Permian Basin maturation: proof for pervasive magmatic heat flow in the Netherlands

    NASA Astrophysics Data System (ADS)

    Bonte, Damien; van Wees, Jan Diederik; Fattah, Rader Abdul; Nelskamp, Suzanne; Cloetingh, Sierd

    2014-05-01

    The area of the Permian Basin is marked by significant Stephanian-Permian magmatism that is related to the Variscanorogenic collapse, resulting in pervasive mantle upwelling. Large extrusive evidence is visible in the North German Basin and in the Central North Sea. Theoretical models for tectonic heat flow and maturity evolution show that mantle upwelling, underplating, and intrusions are likely to have a significant effect on maturity-depth trends. Tectonic modelling of selected wells shows that tectonic subsidence and exhumation can be reconciled with a significant heat flow pulse at the Stephanian-Permian, and this could well explain the widespread elevated depth gradient of maturity in Carboniferous rocks. The quantitative assessment of heat flow, which is based on a kinematic model of the process of orogenic collapse, shows that the mantle upwelling and underplating at the base of the crust proposed by earlier studies in fact provides insufficient heat flow to explain strongly elevated maturity-depth trends. However, the Southern part of the Texel IJsselmeer High shows unusually high maturation values that cannot be explained by the simple effect of burial alone. This area of high maturation is also associated with evidence of intrusive magmatic rocks. By modelling five wells in the Texel IJsselmeer High, we conclude that the burial of the sediments and a shallow intrusion in the upper crust provide an elevated heat flow mechanism that has a regional impact, consistent with observed high maturity-depth trends. In each well, the model that best matches the elevated maturity data of the Carboniferous demonstrates the impact of a large intrusion emplacement in the upper crust at the time of the collapse of the Variscan orogen. The impact of this magmatic intrusion at such a shallow depth is extremely likely to have brought the maturity to the gas window during the heat pulse, and, based on the tectonic subsidence record, the model allows us to position this

  19. Magnitude and spatial patterns of erosional exhumation in the Nevadaplano, eastern Nevada and western Utah: insights from a Paleogene paleogeologic map

    NASA Astrophysics Data System (ADS)

    Long, S. P.

    2011-12-01

    Neoproterozoic and Permian in the Central Nevada thrust belt (CNTB), indicating significant structural relief. Isolated segments of CNTB structures can be correlated by their subcrop patterns, and can be traced southward to connect with thrust faults in southern Nevada. The exhumation map can be divided into three zones that exhibit significant across-strike magnitude changes: 1) high exhumation magnitudes (4-8 km) characterize the deeply-eroded hanging wall of the DWC thrust system and Sevier Culmination, which display little variability for a 350 km along-strike distance; 2) the CNTB displays high magnitudes (4-8 km) in its southern extent, and moderate magnitudes (2-5 km) in its northern extent; 3) the DWC thrust system and CNTB bound a large region that exhibits low (1-3 km) exhumation magnitudes. The close spatial association of high exhumation magnitudes with the hanging walls of thrust faults highlights the first-order control deformation and structural elevation has on exhumation patterns, and suggests that erosional exhumation is a response to relief generation accompanying contractional deformation in orogenic plateaus. The lack of significant exhumation variability within each structural zone implies that relief generation was relatively uniform along-strike.

  20. Episodic slab rollback fosters exhumation of HP-UHP rocks

    NASA Astrophysics Data System (ADS)

    Husson, Laurent; Jean-Pierre, Brun; Philippe, Yamato; Claudio, Faccenna

    2010-05-01

    The burial-exhumation cycle of crustal material in subduction zones can either be driven by the buoyancy of the material, by the surrounding flow, or by both. High pressure - ultrahigh pressure rocks are chiefly exhumed where subduction zones display transient behaviors, which lead to contrasted flow regimes in the subduction mantle wedge. Subduction zones with stationary trenches (mode I) favor the burial of rock units, whereas slab rollback (mode II) moderately induces an upward flow that contributes to the exhumation, a regime that is reinforced when slab dip decreases (mode III). Episodic regimes of subduction that involve different lithospheric units successively activate all three modes and thus greatly favor the exhumation of rock units from mantle depth to the surface without need for fast and sustained erosion.

  1. Late Cenozoic Exhumation of the Terskey Range, Kyrgyz Tien Shan

    NASA Astrophysics Data System (ADS)

    Sobel, E. R.; Macaulay, E. A.; Mikolaichuk, A.; Kohn, B. P.

    2008-12-01

    The glaciated, granitic Terskey range and the associated foreland basin within the Kyrgyz Tien Shan is an ideal region to examine whether Plio-Pleistocene climate change has led to enhanced erosion. Three ca. 1000m vertical profiles were collected in the hanging wall of the main, north-vergent thrust, spaced 25 km apart along strike. AFT analysis have been conducted from the westernmost-transect; all profiles have been analyzed using apatite (U-Th-Sm)/He analysis. AFT and Helium data from the Barskoon gorge profile define parallel trends on the age-elevation plot with apparent exhumation rates of ca. 0.08 km/Myr. The uppermost AFT sample resided for a long period within the partial annealing zone (PAZ); hence, the onset of rapid exhumation defined by the base of the exhumed PAZ appears to be 31±5 Ma. This is earlier than expected from the known regional geology. An alternative interpretation is that the next lowest sample has also been partially reset, such that the onset of exhumation is later and the initial exhumation is more rapid. Helium data from the Kichikyzulsu and Turgenaksu profiles define linear trends on age-elevation plots with apparent exhumation rates of 0.1-0.25 km/Myr and 0.2 km/Myr, respectively. Much older ages at high elevations along the former profile suggest that the base of the Helium partial retention zone (PRZ) has been sampled; the onset of exhumation is roughly constrained to be between 10 and 20 Ma. The onset of rapid exhumation at the latter profile can only be constrained as prior to 11 Ma. Combining the apparent exhumation rate with the age of the youngest samples from each transect provides an estimate of the amount of exhumation since that sample cooled through the PRZ. For the 3 profiles, this implies 1 to 1.2 km, 0.7 to 1.8 km, and 1.5 km of exhumation, assuming that the exhumation rate remained constant. The observed small magnitude and slow rate of exhumation suggests that there has been only limited advection and hence

  2. Prolonged Permian Triassic ecological crisis recorded by molluscan dominance in Late Permian offshore assemblages.

    PubMed

    Clapham, Matthew E; Bottjer, David J

    2007-08-07

    The end-Permian mass extinction was the largest biotic crisis in the history of animal life, eliminating as many as 95% of all species and dramatically altering the ecological structure of marine communities. Although the causes of this pronounced ecosystem shift have been widely debated, the broad consensus based on inferences from global taxonomic diversity patterns suggests that the shift from abundant brachiopods to dominant molluscs was abrupt and largely driven by the catastrophic effects of the end-Permian mass extinction. Here we analyze relative abundance counts of >33,000 fossil individuals from 24 silicified Middle and Late Permian paleocommunities, documenting a substantial ecological shift to numerical dominance by molluscs in the Late Permian, before the major taxonomic shift at the end-Permian mass extinction. This ecological change was coincident with the development of fluctuating anoxic conditions in deep marine basins, suggesting that numerical dominance by more tolerant molluscs may have been driven by variably stressful environmental conditions. Recognition of substantial ecological deterioration in the Late Permian also implies that the end-Permian extinction was the climax of a protracted environmental crisis. Although the Late Permian shift to molluscan dominance was a pronounced ecological change, quantitative counts of 847 Carboniferous-Cretaceous collections from the Paleobiology Database indicate that it was only the first stage in a stepwise transition that culminated with the final shift to molluscan dominance in the Late Jurassic. Therefore, the ecological transition from brachiopods to bivalves was more protracted and complex than their simple Permian-Triassic switch in diversity.

  3. Onset of rapid exhumation in the Namche Barwa syntaxis

    NASA Astrophysics Data System (ADS)

    Govin, Gwladys; Najman, Yani; van der Beek, Peter; Huyghe, Pascale; Millar, Ian; Bernet, Matthias; Wijbrans, Jan; Gemignani, Lorenzo

    2017-04-01

    The evolution of Himalayan syntaxes is debated: they have been subjected to anomalously young ( 10 Ma) high-grade metamorphism, melting and unusually high rates of exhumation (up to 10 mm/yr), compared to the main arc of the range where peak metamorphism occurred in the Early Miocene and exhumation rates of ≤2 mm/yr are more common. The timing of metamorphism and the onset of rapid exhumation of the eastern Namche Barwa syntaxis is poorly constrained. Bedrock studies have been interpreted to imply rapid exhumation since either 3-4 Ma or 8-10 Ma. Previous studies focused on detrital deposits have suggested onset of rapid exhumation in the last 6 Myr. Several models have been proposed to explain the syntaxial evolution, invoking different controlling factors, such as compressive crustal-scale folding orthogonal to the strike of the mountain belt, subduction geometry in the indentor region, or tectonic-surface process interactions and crustal channel flow. In order to understand how and why the syntaxis formed, this study better constrains the exhumation of Namche Barwa using the proximal detrital record of material eroded from the syntaxis by the paleo-Siang River. The recently dated Sibo-Remi-Siang Siwalik section is located directly downstream of the syntaxis, and is therefore the most likely location to contain these sediments. We report new detrital zircon fission-track, white-mica 40Ar/39Ar and rutile U-Pb data, together providing a more precise age for the onset of rapid exhumation of the eastern syntaxis. Our results, along with published data from bedrock and detrital data from the eastern syntaxis region are incorporated in a 1D version of the thermokinematic model Pecube, to reconstruct the syntaxis evolution from Miocene to present day.

  4. Eclogite Facies Relicts and Decompression Assemblages; Evidence for the Exhumation of a Large Coherent Metabasite Block From > 40 km Depth; Central Metamorphic Terrane, Eastern Klamath Mountains, Northern California

    NASA Astrophysics Data System (ADS)

    Barrow, W. M.; Fairhurst, R. J.; Metcalf, R. V.

    2007-12-01

    Recent exhumation models for eclogite terranes have focused on the exhumation of sialic rocks. Exhumed high pressure terranes are typically > 85% - 90% sialic material with only minor amounts of mafic and ultramafic rock. Most known metabasitic eclogites are blocks in mélange rather than large coherent bodies. The Central Metamorphic terrane (CMt) is a large (~300 km3) coherent, fault-bounded package of metabasites thought to represent a remnant of a downing plate subducted in an intra-oceanic convergent margin. Thermochronology indicates that the CMt was metamorphosed and later accreted to the base of the Trinity ophiolite along the Trinity fault during Early Permian extension (Hbl and Musc 40Ar/39Ar ages of 275 Ma - 294 Ma). Previous work suggested that the peak metamorphic temperatures and pressures were ~650°C and 0.4 to 0.8 GPa (Peacock and Norris, 1989) which is consistent with the amphibolite facies mineral assemblage. Trace element data confirm the NMORB-like composition of CMt metabasite protoliths. Newly discovered relict textures, however, suggest that CMt amphibolites record much deeper subduction burial with subsequent decompression exhumation. A decompression sequence consisting of rutile cores within ilmenite crystals mantled by titanite is observed in CMt amphibolite samples. Zr-in-rutile thermometry (Watson et al., 2006) combined with experimental data for rutile stability in metabasites (Ernst and Lui, 1998) suggests that relict rutile crystals preserve early P-T conditions of ~600°C and > 1.3 GPa consistent with eclogite facies metamorphism. Transition from eclogite facies is further supported by ilmenite-plagioclase-amphibole symplectites suggesting replacement of garnet (Bhowmik and Roy, 2003) during decompression. Amphibole compositions vary significantly and reflect lower grade (low Na, Al, Ti actinolite) overprint of earlier amphibolite facies compositions (high Na, Al, Ti magnesio- hornblende). Application of the Al-Ti hornblende

  5. Temporal Constraints on Continental Rifting and the Exhumation of Pliocene Eclogites, SE Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Waggoner, A. G.; Baldwin, S. L.; Webb, L. E.; Little, T. A.; Fitzgerald, P. G.

    2008-12-01

    The youngest known HP-UHP rocks on Earth have been exhumed in the footwalls of the metamorphic core complexes (MCCs) of Goodenough and Fergusson Islands within the active Woodlark rift of southeast Papua New Guinea. What can the felsic and intermediate gneisses found in the lower plate of these metamorphic core complexes tell us about the thermal evolution of these HP-UHP rocks? Also, how does their exhumation during rifting temporally relate with the sea-floor spreading history of the Woodlark Basin? Ion-microprobe U-Pb zircon, 40Ar/39Ar amphibole, phengite, biotite, and K-feldspar analyses were performed on gneisses collected from the ductile shear zones of the MCCs of Goodenough and Fergusson Islands. The application of a broad range of thermochronometers permits the detailed determination of the thermal histories of these rocks from eclogite-facies conditions to their exhumation to middle and upper crustal levels. U-Pb zircon data from these lower plate gneisses indicate a period of zircon growth concordant with the timing of eclogite facies metamorphism as previously determined in mafic eclogites. This younger population of zircon occurs as rims on cores; the cores yield ages that range in age from Paleocene to Permian. These older ages indicate an inherited component likely reflecting the nature of the protolith of these gneisses. However, the abundance and degree of this inherited component is highly variable from sample to sample. New 40Ar/39Ar data from samples collected from the northern range-bounding Wakonai shear zone and the core of Goodenough Island MCC indicate rapid cooling of these rocks as recorded by Ar closure in amphibole, phengite, biotite, and K-feldspar (~500 to ~150 °C) at ~2-1.5 Ma. Samples from along the northern range front of the Goodenough MCC indicate a southeastward younging trend that parallels the active Wakonai normal fault from the northwest end of the island to the center of the island. However, no age gradient is apparent

  6. CONSTRAINTS ON EXHUMATION AND SEDIMENTS PROVENANCE DURING PALEOGENE IN THE NORTHERN PYRENEES (FRANCE) USING DETRITAL AFT, ZHe AND Z(U/Pb) THERMOCHRONOLOGY

    NASA Astrophysics Data System (ADS)

    Filleaudeau, P.; Mouthereau, F.; Fellin, M.; Pik, R.; Lacombe, O.

    2009-12-01

    The Pyrenees are a doubly vergent orogenic wedge built by the convergence between the subducting Iberian microplate and the European plate lasting from late Cretaceous to early Miocene. The backbone of the Pyrenean belt (Axial Zone) consists in a stack of thrusts units composed of Paleozoic series intruded by late-Variscan granitoids. Both pro- and retro-wedge sides of the Pyrenees are fold-and-thrust belts made of Meso-Cenozoic sediments thrusted onto the Ebro and Aquitaine foreland basins. The deep structure, highlighted by the ECORS profile, shows a strong asymmetry caused by the southward migration of deformation associated with the development of a Paleogene antiformal stack emplaced during wedge growth in the Iberian plate. The present study focuses on the synorogenic deposits of the retro-foreland basin in the northern part of the belt. To examine the source rocks and quantify the exhumation rates, we combine fission track thermochronometry on detrital apatites with Helium diffusion and U/Pb thermochronometry on zircons. Due to the very high closure temperature of the U/Pb system and the wide range of age distribution, the U/Pb method, that provides zircon crystallisation ages, is a powerful tool to distinguish the various eroded sources feeding the North Pyrenean basin. Thus, we can separate grains coming from Variscan intrusive basement with ages around 310 Ma from younger grains coming from Permian or Triassic to lower Jurassic volcanics. Zircon ages of 220 Ma found in the Paleocene sandstones point to the Triassic volcanic rocks (the so-called “ophites”) as the main source of detrital grains. We infer that Paleozoic units of the Axial Zone were not outcropping in the Paleocene catchments. Exhumation rates are estimated through apatite fission track grain-age distributions and (U-Th)/He dating for two Lutetian and Bartonian synorogenic sandstone samples of the North Pyenean foreland basin. The first results obtained with AFT dating show two main grain

  7. Permian insect wing from antarctic sentinel mountains.

    PubMed

    Tasch, P; Riek, E F

    1969-06-27

    A homopterous insect wing was found in micaceous graywacke from the Polarstar Formation, Sentinel Mountains. The unusual venation is reminiscent of family Stenoviciidae known from the Permian and Triassic of Eastern Australia and elsewhere. This first documented account of Paleozoic insects in Antarctica bears on drift questions.

  8. Starting a Business in the Permian Basin.

    ERIC Educational Resources Information Center

    Harrison, Danny

    The business and economic development center of Midland College provides assistance to small businesses. Written for use by future and current small business owners and entrepreneurs living in a 17-county area of the Permian Basin of Texas, this guidebook describes the procedures for developing a business plan and for successfully starting and…

  9. Permian depositional history, Leach Mountains, northeastern Nevada

    SciTech Connect

    Martindale, S.G. . EMA/Construction Div.)

    1993-04-01

    The 4,000 m thick Permian sequence in the Leach Mountains consists of carbonate rock, chert, terrigenous clastic rock and phosphatic rock. These rocks, in ascending order, comprise the Third Fork Fm., Badger Gulch Fm., Trapper Creek Fm., Grandeur Fm., Meade Peak Phosphatic Shale Tongue of the Phosphoria Fm., Murdock Mountain Fm. and Gerster Limestone. This sequence disconformably overlain by Triassic strata. Initial Permian deposition, represented by the late Wolfcampian to early Leonardian Third Fork Fm., was on a slope, at a water depth of about 50 m. Subsequently, a shallowing trend occurred during the early Leonardian to late Leonardian with deposition of the Badger Gulch, Trapper Creek and Grandeur Fms. The Trapper Creek and Grandeur Fms. were deposited on the shelf, in very shallow subtidal to supratidal environments. The shelf persisted through the remainder of the Permian. In the late leonardian, the Meade Peak Tongue was deposited in very shallow subtidal and intertidal environments. A supratidal environment was re-established in latest Leonardian( ) to early Guadalupian with deposition of the lower Murdock Mountain Fm. The upper Murdock Mountain Fm. was deposited in very shallow subtidal to supratidal environments. Later during the early Guadalupian, intertidal to shallow subtidal deposition of the Gerster Limestone occurred. Angular phosphatic pebbles that were derived from phosphatic strata at the top of the Gerster Limestone are contained in the Triassic basal conglomerate. These pebbles indicate that the last Permian event was probably emergence and erosion of the top of the Gerster Limestone.

  10. Exhumation of (ultra-)high-pressure terranes: concepts and mechanisms

    NASA Astrophysics Data System (ADS)

    Warren, C. J.

    2013-02-01

    The formation and exhumation of high and ultra-high-pressure, (U)HP, rocks of crustal origin appears to be ubiquitous during Phanerozoic plate subduction and continental collision events. Exhumation of (U)HP material has been shown in some orogens to have occurred only once, during a single short-lived event; in other cases exhumation appears to have occurred multiple discrete times or during a single, long-lived, protracted event. It is becoming increasingly clear that no single exhumation mechanism dominates in any particular tectonic environment, and the mechanism may change in time and space within the same subduction zone. Subduction zone style and internal force balance change in both time and space, responding to changes in width, steepness, composition of subducting material and velocity of subduction. In order for continental crust, which is relatively buoyant compared to the mantle even when metamorphosed to (U)HP assemblages, to be subducted to (U)HP conditions, it must remain attached to a stronger and denser substrate. Buoyancy and external tectonic forces drive exhumation, although the changing spatial and temporal dominance of different driving forces still remains unclear. Exhumation may involve whole-scale detachment of the terrane from the subducting slab followed by exhumation within a subduction channel (perhaps during continued subduction) or a reversal in motion of the entire plate (eduction) following the removal of a lower part of the subducting slab. Weakening mechanisms that may be responsible for the detachment of deeply subducted crust from its stronger, denser substrate include strain weakening, hydration, melting, grain size reduction and the development of foliation. These may act locally to form narrow high-strain shear zones separating stronger, less-strained crust or may act on the bulk of the subducted material, allowing whole-scale flow. Metamorphic reactions, metastability and the composition of the subducted crust all affect

  11. Exhumation and continental strike-slip fault systems: Introduction

    USGS Publications Warehouse

    Roeske, S.M.; Till, A.B.; Foster, D.A.; Sample, J.C.

    2007-01-01

    Metamorphic rocks adjacent to and within strike-slip faultsystems occur in a wide range of tectonic settings. Detailed studies show that for a number of these locales a significant part of the exhumation occurred during strike-slip fault motion, but the specific processes involved are often cryptic. Although some sites share characteristic features, such as metamorphic rocks exhumed in extensional step-overs within overall transtensional systems, no one common theme emerges from all of the studies. Our understanding of the variables that control continental strike-slip faults' interaction with mid- to lower-crustal structures is still primitive.

  12. Exhumational variability within the Himalaya of northwest India

    NASA Astrophysics Data System (ADS)

    Deeken, A.; Thiede, R. C.; Sobel, E. R.; Hourigan, J. K.; Strecker, M. R.

    2011-05-01

    In the Himalaya of Chamba, NW India, a major orographic barrier in front of the Greater Himalayan Range extracts a high proportion of the monsoonal rainfall along its southern slopes and effectively shields the orogen interior from moisture-bearing winds. Along a ~ 100-km-long orogen perpendicular transect, 28 new apatite fission track (AFT) and 30 new zircon (U-Th)/He (ZHe) cooling ages reveal marked variations in age distributions and long-term exhumation rates between the humid frontal range and the semi-arid orogen interior. On the southern topographic front, very young, elevation-invariant AFT ages of < 4 Ma have been obtained that are concentrated in a ~ 30-km-wide zone; 1-D-thermal modeling suggests a Plio-Pleistocene mean erosion rate of 0.8-1.9 mm yr - 1 . In contrast, AFT and ZHe ages within the orogen interior are older (4-9 and 7-18 Ma, respectively), are positively correlated with sample elevation, and yield lower mean erosion rates (0.3-0.9 mm yr - 1 ). Protracted low exhumation rates within the orogen interior over the last ~ 15 Myr prevailed contemporaneously with overall humid conditions and an effective erosional regime within the southern Himalaya. This suggests that the frontal Dhauladar Range was sufficiently high during this time to form an orographic barrier, focusing climatically enhanced erosional processes and tectonic deformation there. Thrusting along the two frontal range-bounding thrust, the Main Central Thrust and the Main Boundary Thrusts, was initiated at least ~ 15 Ma ago and has remained localized since then. The lack of evidence for localized uplift farther north indicates either a rather flat décollement with no ramp or the absence of active duplex systems beneath the interior of Chamba. Exhumational variability within Chamba is best explained as the result of continuous thrusting along a major basal décollement, with a flat beneath the slowly exhuming internal compartments and a steep frontal ramp at the rapidly exhuming

  13. The terminal Permian in European Russia: Vyaznikovian Horizon, Nedubrovo Member, and Permian-Triassic boundary

    NASA Astrophysics Data System (ADS)

    Lozovsky, V. R.; Balabanov, Yu. P.; Karasev, E. V.; Novikov, I. V.; Ponomarenko, A. G.; Yaroshenko, O. P.

    2016-07-01

    The comprehensive analysis of the data obtained on terrestrial vertebrata, ostracods, entomologic fauna, megaflora, and microflora in deposits of the Vyaznikovian Horizon and Nedubrovo Member, as well as the paleomagnetic data measured in enclosing rocks, confirms heterogeneity of these deposits. Accordingly, it is necessary to distinguish these two stratons in the terminal Permian of the East European Platform. The combined sequence of Triassic-Permian boundary deposits in the Moscow Syneclise, which is considered to be the most complete sequence in the East European Platform, is as follows (from bottom upward): Vyatkian deposits; Vyaznikovian Horizon, including Sokovka and Zhukovo members; Nedubrovo Member (Upper Permian); Astashikha and Ryabi members of the Vokhmian Horizon (Lower Triassic). None of the sequences of Permian-Triassic boundary deposits known in the area of study characterizes this sequence in full volume. In the north, the Triassic deposits are underlain by the Nedubrovo Member; in the south (the Klyazma River basin), the sections are underlain by the Vyaznikovian Horizon. The Permian-Triassic boundary adopted in the General Stratigraphic Scale of Russia for continental deposits of the East European platform (the lower boundary of the Astashikha Member) is more ancient than the one adopted in the International Stratigraphic Chart. The same geological situation is observed in the German Basin and other localities where Triassic continental deposits are developed. The ways of solving this problem are discussed in this article.

  14. Cenozoic deformation and exhumation of the Kampot Fold Belt and implications for south Indochina tectonics

    NASA Astrophysics Data System (ADS)

    Fyhn, Michael B. W.; Green, Paul F.; Bergman, Steven C.; Van Itterbeeck, Jimmy; Tri, Tran V.; Dien, Phan T.; Abatzis, Ioannis; Thomsen, Tonny B.; Chea, Socheat; Pedersen, Stig A. S.; Mai, Le C.; Tuan, Hoang A.; Nielsen, Lars H.

    2016-07-01

    Latest Mesozoic to earliest Cenozoic deformation affected SE Asia's Sundaland core. The deformation event bridges the Mesozoic SE Asian fusion with the Cenozoic era of rifting, translation, basin formation, and the creation of modern SE Asian oceans. Southern Cambodia and Vietnam are central to this shift, but geological investigations of the region are in their infancy. Based on apatite and zircon fission track analyses (AFTA and ZFTA), stratigraphic and structural observations, seismic data, thermal maturity, and igneous rock dating, the geological evolution of southern Cambodia and Vietnam is investigated. Diverse depositional styles, igneous activity, structural deformation and subsurface unconformities testify to a highly variable Phanerozoic tectonic setting. Major latest Cretaceous to Paleocene thrusting and uplift affected the Kampot Fold Belt and surrounding regions and the associated up to 11 km exhumation probably exceeds earlier denudation events since at least Permian time. The present relief of the Bokor Mountains rising high above the Kampot Fold Belt represents an artifact after differential erosion and only 2.5-4.5 km of erosion affected this area. The latest Cretaceous to Paleocene orogenesis affected much of greater Indochina probably owing to plate collision along eastern Sundaland or a combination of collisions along both east and west Sundaland. AFTA and ZFTA data document protracted cooling of Cretaceous granites and locally elevated thermal gradients persisting a few tens of million years after their emplacement. The thermal gradient had stabilized by early Miocene time, and Miocene cooling probably reflects a renewed denudation pulse driven by either regional tectonism or climate-enhanced erosion.

  15. 36 CFR 12.6 - Disinterments and exhumations.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... INTERIOR NATIONAL CEMETERY REGULATIONS § 12.6 Disinterments and exhumations. (a) Interment of an eligible... court orders and other pertinent documents in the national cemetery files as a permanent record of the... National Park Service and without direct participation by national cemetery employees. (h)...

  16. [Exhumations procedures for investigating the genetic link in bones].

    PubMed

    Melki, J A; Martin, C C; Simões, A L

    2001-08-01

    To identify technical problems in exhumations performed for DNA detection in bones and to propose solutions through a protocol. A prospective and qualitative study of exhumations was carried out according to the methods proposed in the medical legal literature. From 1995 to 1998, were performed 10 exhumations to collect human remains for DNA extraction. Of them, seven cases were of civil interest and three of criminal. Alternatives were sought to overcome technical difficulties found during the execution of these procedures. For all cases, there was scarcity of useful information to identify the human remains. In half of them, identification was based on the individual's morphological characteristics, given by their relatives. Individual morphological characteristics contributed to identification in 50% of cases. In three cases, it was possible to determine only the sex, and in one of them, only the age. Lack of infrastructure and police security in the cemeteries impaired the examination. To assure the reliability of the DNA molecular examination, it is necessary to identify the individual to whom the exhumed mortal remains belonged. To an efficacious investigation, it is paramount to have a working protocol that will cover, among other issues, those concerning identification, infrastructure and staff safety at the site of examination.

  17. Clarification and changes in Permian stratigraphic nomenclature in Kansas

    USGS Publications Warehouse

    Sawin, R.S.; Franseen, E.K.; West, R.R.; Ludvigson, Greg A.; Watney, W.L.

    2008-01-01

    This paper outlines Permian nomenclature changes to Zeller (1968) that have been adopted by the Kansas Geological Survey. The Permian System/ Period, Cisuralian Series/Epoch, and Asselian Stage/Age are established at the base of the Bennett Shale Member of the Red Eagle Limestone. Series/epoch names Wolfcampian, Leonardian, and Guadalupian are retained and usage of Gearyan, Cimarronian, and Custerian is abandoned. The repositioned Carboniferous-Permian boundary divides the Council Grove Group into Carboniferous (Upper Pennsylvanian Series/Epoch; Virgilian Stage/Age) and Permian (Wolfcampian Series Epoch) segments.

  18. Succession of Permian and Mesozoic metasomatic events in the eastern Pyrenees with emphasis on the Trimouns talc-chlorite deposit

    NASA Astrophysics Data System (ADS)

    Boutin, Alexandre; de Saint Blanquat, Michel; Poujol, Marc; Boulvais, Philippe; de Parseval, Philippe; Rouleau, Caroline; Robert, Jean-François

    2016-04-01

    Recent studies proposing pre-orogenic mantle exhumation models have helped renew the interest of the geosciences community in the Pyrenees, which should be now interpreted as a hyper-extended passive margin before the convergence between Iberia and Eurasia occurred. Unresolved questions of the Pyrenean geology, as well as the understanding of the formation of hyper-extended passive margins, are how the crust was thinned, and when, where and how the crustal breakoff occurred. The study of the Variscan and pre-Variscan Pyrenean basement is thus critical to document and understand this Cretaceous crustal thinning. In order to specify the timing of Mesozoic metasomatism and the associated deformation in the pre-Mesozoic basement of the Pyrenees, we carried out a U-Th-Pb laser ablation ICP-MS study on a large panel of REE and titanium-rich minerals (titanite and rutile) from talc-chlorite ores from the eastern Pyrenees, with a special emphasis on the Trimouns deposit, the world's largest talc quarry. Our results suggest that the Trimouns talc formation was restricted to the upper Aptian-Cenomanian time, while the talc and chlorite formation in the eastern Pyrenees occurred during several distinct Permian, Jurassic and Cretaceous episodes. These results give strong constraints on the tectonic setting of the Pyrenean domain during the transition between the Variscan and Alpine orogenic cycles, and particularly on when and how the upper crust was thinned before the crustal breakoff and the final mantle exhumation.

  19. Rheologic Transitions During Exhumation of High-Pressure Metamorphic Rocks

    NASA Astrophysics Data System (ADS)

    Whitney, D. L.; Teyssier, C. P.; Rey, P. F.

    2015-12-01

    The exhumation of deeply buried rocks typically involves dynamic feedbacks between deformation and metamorphic reactions (+ fluid and/or melt) that influence rheology and facilitate or drive large-magnitude exhumation. The evolution of grain-scale to terrane-scale processes during decompression can be seen in rocks exhumed from oceanic and continental subduction and from orogenic crust. In the Sivrihisar (Turkey) high-P/low-T (oceanic subduction) complex, microstructures record deformation and syn-kinematic reactions during decompression from eclogite to blueschist facies conditions; this transformation resulted in dramatic strength reduction that promoted strain localization along the subduction interface. In quartz-rich rocks, qz was deformed in the dislocation creep regime and records transitions in microstructure and slip systems during near-isothermal decompression from 2.5 to 1.5 GPa; these transitions may be related to decreasing water fugacity over tens of km of decompression. High-to ultrahigh-P eclogite in exhumed continental subduction zones such as the Western Gneiss Region (Norway) record decompression from >2.5 GPa to <1 GPa. Eclogite shows dramatic textural evidence for decompression, including partial melting and decomposition into hbl-gneiss, resulting in weakening and strain localization. In collisional orogens that are underlain by partially molten crust, upper crustal extension/transtension drives rapid ascent of the deep crust to form migmatite-cored domes. The exhuming deep crust entrains HP relics such as eclogite (e.g. Montagne Noire dome, France) as it traverses much of the orogenic crust, from >1.2 GPa to (in some cases) <0.1 GPa in a single, geologically rapid event during which the partially molten crust reaches the near-surface. In summary, decompression of subducted or deeply buried crust systematically leads to rheologic transitions and feedbacks between deformation and metamorphism in the presence of aqueous fluid and/or melt.

  20. Patterns of deformation, exhumation and uplift across the Island of Timor: insights into the processes that control the early stages of orogenesis (Invited)

    NASA Astrophysics Data System (ADS)

    McQuarrie, N.; Tate, G. W.; Van Hinsbergen, D. J.; Harris, R. A.

    2013-12-01

    On the island of Timor, arc-continent collision between the Banda volcanic arc and the Australian continent since the late Miocene has uplifted a mountain range containing both deeply exhumed metamorphic rocks and deepwater synorogenic basins. These varied lithologies are separated by a few tens of kilometers, and provide us with an opportunity to examine the spatial patterns of differential uplift and exhumation and its links to the geometry and magnitude of deformation in an orogen that is still in its infancy. New mapping in Timor has provided a detailed view of how the Australian continental slope and shelf rocks are being structurally repeated below overriding Banda Arc material. In East Timor, a window though the Banda terrane shows Permian and Triassic rocks that are repeated by four NNE-striking thrust faults with ~3 km spacing and 50-75 km along-strike extent. The strike of these faults is rotated 50-60 degrees compared to structures to the east and west of this main window. In addition, mapped fold axes are shown to cut across and warp fault traces. These map patterns indicate that the duplex has been both refolded and tilted since its initial formation. In West Timor, Permian through Triassic stratigraphy is faulted and folded into an antiformal stack with 5 exposed thrusts repeating an ~ 3 km thick section. Both south of and adjacent to these structural highs are 10-20 km wide piggyback basins of deepwater, synorogenic marine limestones and clays that coarsen upward into turbidites. Deposition of these units initiated at 5.5 Ma at lower bathyal depths. Synorogenic deposition directly over the Bobonaro mélange, which acts as the décollement between the overthrust Banda Arc rocks and the structurally repeated Australian margin rocks, requires the removal of both Banda arc material and the Cretaceous and younger Kolbano sequence before deposition. These basins record rapid surface uplift to upper bathyal depths from 3.5-3 Ma with continual uplift to

  1. Late- and post-Variscan cooling and exhumation history of the northern Rhenish massif and the southern Ruhr Basin: new constraints from fission-track analysis

    NASA Astrophysics Data System (ADS)

    Karg, Harald; Carter, Andrew; Brix, Manfred R.; Littke, Ralf

    2005-04-01

    Apatite fission-track analyses were carried out on outcrop and core samples from the Rhenish massif and the Carboniferous Ruhr Basin/Germany in order to study the late- and post-Variscan thermal and exhumation history. Apatite fission-track ages range from 291±15 Ma (lower Permian) to 136±7 Ma (lower Cretaceous) and mean track lengths vary between 11.6 μm and 13.9 μm, mostly displaying unimodal distributions with narrow standard deviations. All apatite fission-track ages are younger than the corresponding sample stratigraphic age, indicating substantial post-depositional annealing of the apatite fission-tracks. This agrees with results from maturity modelling, which indicates 3500-7000 m eroded Devonian and Carboniferous sedimentary cover. Numerical modelling of apatite fission-track data predicts onset of exhumation and cooling not earlier than 320 Ma in the Rhenish massif and 300 Ma in the Ruhr Basin, generally followed by late Carboniferous-Triassic cooling to below 50-60°C. Rapid late Variscan cooling was followed by moderate Mesozoic cooling rates of 0.1-0.2°C/Ma, converting into denudation rates of <1 mm/a (assuming a stable geothermal gradient of 30°C/km). Modelling results also give evidence for some late Triassic and early Jurassic heating and/or burial, which is supported by sedimentary rocks of the same age preserved at the rim of the lower Rhine Basin and in the subsurface of the Central and Northern Ruhr Basin. Cenozoic exhumation and cooling of the Rhenish massif is interpreted as an isostatic response to former erosion and major base-level fall caused by the subsidence in the lower Rhine Basin.

  2. Permian age from radiolarites of the Hawasina nappes, Oman Mountains

    SciTech Connect

    Wever, P.D. ); Grissac C.B. ); Bechennec, F. )

    1988-10-01

    The Hawasina napper of the Oman Mountains yielded Permian radiolarians from cherts stratigraphically overlying a thick volcanic basement (Al Jil Formation) at the base of the Hamrat Duru Group. This fauna represents the first Permian radiolarians and radiolarites in the central and western Tethyan realm. A Permain age for pelagic sequences within the Hawasina Complex of Oman has major significance for regional paleogeographic reconstruction. A clear differentiation between platform (reefal sediments) and basin (radiolarites) from the base of the Late Permian (255 Ma) is implied. It suggests a flexure of the platform during Permian time; the present data implies that a zone of rifting was already developed adjacent to the northeast Gondwana platform margin during the Late Permian. The Hamrat Duru Basin corresponds to an opening intracontinental rift area (sphenochasm) between Arabia and northeast Gondwana, a reentrant of the paleo-Tethys.

  3. Sedimentology and petroleum occurrence, Schoolhouse Member, Maroon Formation (Lower Permian), northwestern Colorado

    SciTech Connect

    Johnson, S.Y.; Schenk, C.J.; Anders, D.L.; Tuttle, M.L. )

    1990-02-01

    The Lower Permian Schoolhouse Member of the Maroon Formation (formerly considered the Schoolhouse Tongue of the Weber Sandstone) forms a partly exhumed petroleum reservoir in the Eagle basin of northwestern Colorado. The Schoolhouse consists mainly of yellowish gray to gray, low-angle to parallel bedded, very fine to fine-grained sandstone of eolian sand-sheet origin; interbedded fluvial deposits are present in most sections. The sand-sheet deposits of the Schoolhouse Member are sedimentologically and petrologically similar to those in the underlying red beds of the main body of the Maroon Formation, and the Schoolhouse is considered the uppermost sand sheet in the Maroon depositional sequence. The bleached and oil-stained Schoolhouse member is distinguished from the underlying Maroon red beds on the basis of its diagenetic history, which is related to regional hydrocarbon migration and development of secondary porosity. Geological and geochemical data suggest that Schoolhouse Member oils have upper Paleozoic sources, including the intrabasinal Belden Formation. 13 figs., 1 tab.

  4. Concretions in Exhumed Channels Near Hanksville Utah: Implications for Mars

    NASA Technical Reports Server (NTRS)

    Clarke, Jonathan; Stoker, Carol R.

    2011-01-01

    The landscape near Hanksville, Utah, contains a diversity of Mars analogue features. These included segmented and inverted anatasomosing palaeochannels exhumed from the Late Jurassic Brushy Basin Member of the Morrison Formation that hosts abundant small carbonate concretions. The exhumed and inverted channels closely resemble many seen on the surface of Mars in satellite imagery and which may be visited by surface missions in the near future. The channels contain a wealth of palaeo-environmental information, but intrinsically difficult terrain would make their study challenging on Mars. We show that an unexhumed channel feature can be detected geophysically, this may allow their study in more easily accessed terrain. The concretions morphologically and in their surface expression parallel the haematite blue berries that are strewn across the surface of Meridiani Planum on Mars. They are best developed in poorly cemented medium to coarse channel sandstones and appear to have formed early in the diagenetic history.

  5. The Major-ion Composition of Permian Seawater

    SciTech Connect

    Lowenstein, T K.; Timofeeff, Michael N.; Kovalevych, Volodymyr M.; Horita, Juske

    2005-01-01

    The major-ion (Mg{sup 2+}, Ca{sup 2+}, Na{sup +}, K{sup +}, SO{sub 4}{sup 2-}, and Cl{sup -}) composition of Permian seawater was determined from chemical analyses of fluid inclusions in marine halites. New data from the Upper Permian San Andres Formation of Texas (274--272 Ma) and Salado Formation of New Mexico (251 Ma), analyzed by the environmental scanning electron microscopy (ESEM) X-ray energy-dispersive spectrometry (EDS) method, along with published chemical compositions of fluid inclusions in Permian marine halites from North America (two formations of different ages) and the Central and Eastern European basins (eight formations of four different ages) show that Permian seawater shares chemical characteristics with modern seawater, including SO{sub 4}{sup 2-} > Ca{sup 2+} at the point of gypsum precipitation, evolution into Mg{sup 2+}-Na{sup +}-K{sup +}-SO{sub 4}{sup 2-}-Cl{sup -} brines, and Mg{sup 2+}/K{sup +} ratios {approx} 5. Permian seawater, however, is slightly depleted in SO{sub 4}{sup 2-} and enriched in Ca{sup 2+}, although modeling results do not rule out Ca{sup 2+} concentrations close to those in present-day seawater. Na{sup +} and Mg{sup 2+} in Permian seawater are close to (slightly below) their concentrations in modern seawater. Permian and modern seawater are both classified as aragonite seas, with Mg{sup 2+}/Ca{sup 2+} ratios >2, conditions favorable for precipitation of aragonite and magnesian calcite as ooids and cements. The chemistry of Permian seawater was modeled using the chemical composition of brine inclusions for three periods: Lower Permian Asselian-Sakmarian (296--283 Ma), Lower Permian Artinskian-Kungurian (283--274 Ma), and Upper Permian Tatarian (258--251 Ma). Parallel changes in the chemistry of brine inclusions from equivalent age evaporites in North America, Central Europe, and Eastern Europe show that seawater underwent secular variations in chemistry over the 50 million years of the Permian. Modeled SO{sub 4}{sup 2

  6. Permian magmatism, Permian detachment faulting, and Alpine thrusting in the Orobic Anticline, southern Alps, Italy

    NASA Astrophysics Data System (ADS)

    Pohl, Florian; Froitzheim, Niko; Geisler-Wierwille, Thorsten; Schlöder, Oliver

    2014-05-01

    The Grassi Detachment Fault is located in the Orobic Alps east of Lake Como and was described by Froitzheim et al. (2008) as an Early Permian extensional structure. Many issues still remained unclear, like the exact timing of faulting and the extension from the well-exposed part of the detachment towards west. The Grassi Detachment Fault separates the Variscan Basement in its footwall from the volcanic and sedimentary rocks of the Early Permian Collio Formation within its hanging wall, marked by a mylonitic and cataclastic layer whose textures indicate top-to-the-southeast displacement. The footwall basement is formed by the Variscan Morbegno Gneiss and two granitic intrusions, the Val Biandino Quarz Diorite (VBQD) and the Valle Biagio Granite (VBG). The former is syntectonic with respect to the detachment, whereas for the latter, the relation to the detachment is unknown. The age of the VBQD is poorly defined as 312 Ma ± 48 Ma (Thöni et al. 1992); the VBG has not been dated. Volcanic rocks of the Collio Formation in the hanging wall may represent the extrusive part of the magmatic system. In our study area west of Val Biandino, several faults and shear zones are exposed: (1) The Grassi Detachment Fault is represented by mylonites and cataclasites with top-SE shear sense, between basement rocks and the Collio Volcanics. Towards NW, it is truncated by the unconformably overlying Late Permian Verrucano Lombardo. This may reflect the eroded culmination of a Permian metamorphic core complex. (2) A steeply NW-dipping, brittle normal fault is found further west in the footwall between VBQD and VBG. It is sealed by the basal unconformity of the Verrucano Lombardo and therefore should also be of Early Permian age (Sciunnach, 2001). It may represent an antithetic fault with respect to the detachment, accommodating the uplift of the magmatically inflated core complex. (3) The Biandino Fault is a steeply SE-dipping reverse fault, affecting also the Late Permian Verrucano

  7. Comparative Earth history and Late Permian mass extinction

    NASA Technical Reports Server (NTRS)

    Knoll, A. H.; Bambach, R. K.; Canfield, D. E.; Grotzinger, J. P.

    1996-01-01

    The repeated association during the late Neoproterozoic Era of large carbon-isotopic excursions, continental glaciation, and stratigraphically anomalous carbonate precipitation provides a framework for interpreting the reprise of these conditions on the Late Permian Earth. A paleoceanographic model that was developed to explain these stratigraphically linked phenomena suggests that the overturn of anoxic deep oceans during the Late Permian introduced high concentrations of carbon dioxide into surficial environments. The predicted physiological and climatic consequences for marine and terrestrial organisms are in good accord with the observed timing and selectivity of Late Permian mass extinction.

  8. Comparative Earth history and Late Permian mass extinction.

    PubMed

    Knoll, A H; Bambach, R K; Canfield, D E; Grotzinger, J P

    1996-07-26

    The repeated association during the late Neoproterozoic Era of large carbon-isotopic excursions, continental glaciation, and stratigraphically anomalous carbonate precipitation provides a framework for interpreting the reprise of these conditions on the Late Permian Earth. A paleoceanographic model that was developed to explain these stratigraphically linked phenomena suggests that the overturn of anoxic deep oceans during the Late Permian introduced high concentrations of carbon dioxide into surficial environments. The predicted physiological and climatic consequences for marine and terrestrial organisms are in good accord with the observed timing and selectivity of Late Permian mass extinction.

  9. Comparative Earth History and Late Permian Mass Extinction

    PubMed

    Knoll; Bambach; Canfield; Grotzinger

    1996-07-26

    The repeated association during the late Neoproterozoic Era of large carbon-isotopic excursions, continental glaciation, and stratigraphically anomalous carbonate precipitation provides a framework for interpreting the reprise of these conditions on the Late Permian Earth. A paleoceanographic model that was developed to explain these stratigraphically linked phenomena suggests that the overturn of anoxic deep oceans during the Late Permian introduced high concentrations of carbon dioxide into surficial environments. The predicted physiological and climatic consequences for marine and terrestrial organisms are in good accord with the observed timing and selectivity of Late Permian mass extinction.

  10. Comparative Earth history and Late Permian mass extinction

    NASA Technical Reports Server (NTRS)

    Knoll, A. H.; Bambach, R. K.; Canfield, D. E.; Grotzinger, J. P.

    1996-01-01

    The repeated association during the late Neoproterozoic Era of large carbon-isotopic excursions, continental glaciation, and stratigraphically anomalous carbonate precipitation provides a framework for interpreting the reprise of these conditions on the Late Permian Earth. A paleoceanographic model that was developed to explain these stratigraphically linked phenomena suggests that the overturn of anoxic deep oceans during the Late Permian introduced high concentrations of carbon dioxide into surficial environments. The predicted physiological and climatic consequences for marine and terrestrial organisms are in good accord with the observed timing and selectivity of Late Permian mass extinction.

  11. Early diagenetic pyrite morphology in a mudstone-dominated succession: the Lower Jurassic Cleveland Ironstone Formation, eastern England

    NASA Astrophysics Data System (ADS)

    Taylor, K. G.; Macquaker, J. H. S.

    2000-03-01

    Diagenetic pyrite in the mudstones and ironstones of the Lower Jurassic Cleveland Ironstone Formation of eastern England exhibits two distinct morphologies: framboidal pyrite, commonly associated with organic matter, and euhedral pyrite, associated with detrital clay pellets. These two morphologies are mutually exclusive in occurrence. Framboidal pyrite is present in clay-rich mudstones, ooidal ironstones, apatite-rich units and some silt-rich mudstones. Euhedral pyrite is present in silt-rich and sand-rich mudstones. δ34S isotopic analysis of six samples of pyrite suggests that both types of pyrite morphology precipitated during early diagenesis from porewaters with open access to overlying sea-water, although both probably acted as sites for continued pyrite precipitation during burial. It is proposed that framboidal pyrite precipitated from iron-dominated porewaters at sites of sulfide supply (i.e. in the region of organic matter as a result of bacterial sulfate reduction) where, locally, sulfide production rates were high enough for porewaters to reach supersaturation with respect to FeS. Euhedral pyrite also precipitated from iron-dominated porewaters, but sulfide production rates from organic matter was such that FeS saturation was not reached at the sites of sulfide production. Instead, euhedral pyrite was precipitated directly from porewater when FeS2 saturation was reached. The control over pyrite morphology was probably the amount and reactivity of the organic matter within the deposited sediments. The sand-rich mudstones contained less reactive organic matter due to clastic dilution and deposition in shallower environments with O2-rich bottom waters. The ironstones and apatite-rich units were deposited under very low sedimentation rates, and as a result organic matter contents were very low and iron reduction dominated early diagenesis, which inhibited sulfate-reduction. The presence of minor framboidal pyrite within these units, however, suggests that sulfide reduction took place in micro-environments during early diagenesis.

  12. Upper Permian fluviolacustrine deposits of southern Africa and the late Permian climate southern Gondwana

    SciTech Connect

    Yemane, K. . Dept. of Geology Bryn Mawr Coll., PA . Dept. of Geology)

    1993-03-01

    Upper Permian-age fluviolacustrine deposits are widespread throughout southern Africa. In the southern part of the subcontinent, where deposition took place in foreland basin settings, the sequences are thicker and fluvial-dominated whereas, lacustrine-dominated deposits accumulated in settings of low relief, broad warping and mild faulting at the northern end. The geographic extent and lateral correlatability of these deposits suggest the existence of concurrent, perhaps interconnected, giant lakes within major fluvial frameworks throughout the subcontinent, thousands of miles inland from the sea. This period of major lake development within fluvial depositional settings suggests climatic conditions that sustained a uniquely wet continental environment, deep in the heart of the Gondwanan supercontinent. Simulations based on various general circulation and energy balance climate models predict extreme seasonal temperatures and aridity for Gondwana at the palaeolatitudes of southern Africa during the Late Permian. On the other hand, distribution of climate-sensitive rocks, palynologic and palaeobotanic data and vertebrate fossils, coroborate the temperature climate documented by sedimentologic studies. The erroneous modeling results may have arisen from the fact that the models do not employ palaeogeographies that accommodate the existence of the vast lakes and rivers of Gondwana. The Late Permian palaeogeography of series of giant lakes within major fluvial frameworks would have had considerable influences on the regional climate. This suggests that it is imperative that numerical modeling studies incorporate accurate palaeogeographies, constructed based on available geological data, in order to recreate past climates with acceptable degree of accuracy.

  13. Upper Permian (Guadalupian) facies and their association with hydrocarbons - Permian basin, west Texas and New Mexico

    SciTech Connect

    Ward, R.F.; Kendall, C.G.S.C.; Harris, P.M.

    1986-03-01

    Outcrops of Guadalupian sedimentary rocks in the Permian basin of west Texas and southeastern New Mexico are a classic example of the facies relationships that span a carbonate shelf. In the subsurface, these rocks form classic hydrocarbon-facies taps. Proceeding from basin to the updip termination of the shelf, the facies are (1) deep-water basin, (2) an apron of allochthonous carbonates, (3) carbonate shelf margin or reef, (4) carbonate sand flats, (5) carbonate barrier islands, (6) lagoon, and (7) coastal playas and supratidal salt flats (sabkhas). Over a half century of exploration drilling has shown that hydrocarbons in the Permian rocks of the Permian basin have accumulated at the updip contact of the lagoonal dolomites and clastics with the coastal evaporites, and in the basinal channel-fill clastics. The shelf marginal (reef) facies contain cavernous porosity, but commonly are water saturated. These facies relationships and hydrocarbon occurrences provide an exploration model with which to explore and rank hydrocarbon potential in other carbonate provinces. 16 figures, 3 tables.

  14. Timing of Fluid Flow During Exhumation of Deeply Subducted Continent

    NASA Astrophysics Data System (ADS)

    Zheng, Y.; Gao, T.; Wu, Y.; Gong, B.

    2005-12-01

    Quartz veins are common within UHP eclogites in the Dabie-Sulu orogenic belt of China. While their formation has been linked to dehydration reactions, time of veining has been uncertain during either subduction or exhumation. SHRIMP U-Pb dating for zircons from kyanite-quartz vein and its host eclogite in the Dabie orogen yields two groups of age at 212±7 Ma and 181±13 Ma, respectively. They are significant younger not only than SHRIMP zircon U-Pb ages of 243±4 and 224±3 Ma for host eclogite, but also than known UHP metamorphic ages of 234±4 to 227±2 Ma as dated by the SHRIMP U-Pb technique for coesite-bearing domains of zircon. The U-Pb age of 224±3 Ma for the eclogite dates zircon growth at the onset of HP eclogite-facies recrystallization during exhumation. Corresponding temperatures may be about 670°C as estimated for both eclogite-facies recrystallization and veining from a petrological study. The second group of zircon U-Pb age at 181±13 Ma is much later than the HP-UHP-HP metamorphic events during the orogenic cycle and thus may not be relevant to post-collisional exhumation. Therefore, the two groups of vein age date the two episodes of fluid flow, respectively, due to decompression dehydration during exhumation and heating dehydration in response to breakup of supercontinent Pangea. This provides for the first time the radiometric dates for timing of fracture fluid flow that transports both mass and heat during plate collision. Laser fluorination O isotope analyses show the almost same δ18O values for the minerals of both vein and eclogite, indicating the same origin of fluid and material for them and thus internally derived fluid for veining. High O isotope temperatures of 695±20 to 715±35°C are obtained for Qz-Ky and Qz-Gt pairs, suggesting the attainment of O isotope reequilibration during the HP eclogite-facies recrystallization. On the other hand, low O isotope temperatures of 490±10 to 510±15°C occur in Qz-Rt and Qz-Zo pairs

  15. Zooidogamy in the Late Permian genus Glossopteris.

    PubMed

    Nishida, Harufumi; Pigg, Kathleen B; Kudo, Kensuke; Rigby, John F

    2004-08-01

    We describe details of anatomically preserved fossil glossopterid ovules from the Late Permian of Queensland, Australia, that contain several pollen tubes at various stages of releasing flagellated sperm. Each sperm is approximately 12.7 microm long and 13.9 microm wide, with a conspicuous spiral structure comprised of a series of dots that resemble the position of basal bodies of flagella aligned along the multilayered structure (MLS). This configuration is similar to the helically arranged flagella in the sperm of cycads, Ginkgo, and many pteridophytes. However, the motile gametes of Glossopteris are considerably smaller than those of Ginkgo and cycads, and more similar in size, number of basal bodies, and number of gyres in their helix to pteridophyte forms. Glossopteris thus shares the intermediate stage of motile male gamete formation and apparently that of haustorial pollen tubes with cycads and Ginkgo.

  16. Calibrating the end-Permian mass extinction.

    PubMed

    Shen, Shu-zhong; Crowley, James L; Wang, Yue; Bowring, Samuel A; Erwin, Douglas H; Sadler, Peter M; Cao, Chang-qun; Rothman, Daniel H; Henderson, Charles M; Ramezani, Jahandar; Zhang, Hua; Shen, Yanan; Wang, Xiang-dong; Wang, Wei; Mu, Lin; Li, Wen-zhong; Tang, Yue-gang; Liu, Xiao-lei; Liu, Lu-jun; Zeng, Yong; Jiang, Yao-fa; Jin, Yu-gan

    2011-12-09

    The end-Permian mass extinction was the most severe biodiversity crisis in Earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ(13)C over 90,000 years, and coincided with a δ(13)C excursion of -5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.

  17. Exhumation history of the Serra do Mar, southeast Brazil

    NASA Astrophysics Data System (ADS)

    Carina Siqueira-Ribeiro, Marli; Hackspacher, Peter; Stuart, Finlay M.

    2016-04-01

    The Serra do Mar (SM) mountain range located along the southeast Brazilian continental margin is characterized by a low-lying coastal plateau separated from the elevated inland plateau by a steep escarpment. This morphology is a result of reactivation of Precambrian shear zones since the break-up of the Western Gondwana and opening of the South Atlantic Ocean in Early Cretaceous (1). Previous Thermochronological data from southeast Brazilian highlands (2,3), indicates that the landscape evolution is associated with several distinct exhumation events. In order to clarify the intensity and duration of the post-break up tectonic processes that shaped the SM we have undertaken a low temperature thermochronology study of crystalline basement, from the plateaus and escarpments situated between south of Rio de Janeiro and São Paulo state. Apatite fission track (AFT) and (U-Th/He) and (AHe) dating has been combined with geologic information to generate precise thermal histories and make initial attempts to quantify the amount of exhumation. AFT ages range from 145 to 53 Ma whereas preliminary AHe ages range from 75 to 37 Ma. Forward modeling using QTQt confirms Late Cretaceous-Paleogene cooling identified earlier (4,5) and identifies a distinct cooling phase in Neogene, between 30 and 10 Ma. Neogene cooling rapid caused exhumation of rocks 1 km through of the crust mainly in south portion of the SM in Rio de Janeiro state. (1) Almeida, 1976. An. Academia Bras de Cien 48 (suppl.), 15-(2) (2) Hackspacher et al. 2004. Gondwana Research,vol.2, 91-101. (3) Hiruma et al. 2010. Gondwana Research,18,674-687. (4) Siqueira-Ribeiro et al. 2011. Revista Bras. de Geomorfologia, 13, 3-14 (5) Cogné et al. 2012. Journal Geophysical Research, vol.117,1-16.

  18. A long geoclimatic record from the Permian

    NASA Astrophysics Data System (ADS)

    Anderson, Roger Y.

    1982-08-01

    A 260,000-year, continuous, annual geoclimatic time series has been compiled from the varved Permian Castile and Bell Canyon Formations of the Delaware Basin, southeastern New Mexico, and southwestern Texas. The last 200,000 years of the record was obtained from calcite-laminated anhydrite and anhydrite-laminated halite, which formed as a result of seasonal and annual deposition in the evaporite basin. The time series is based on measured thickness of individual varves. Analyses of calcium sulfate, calcium carbonate, and organic matter were made on 50-year intervals in the evaporite part of the sequence. Time series of the major components were examined by using smoothed graphic plots, variance spectra, and moving correlation coefficients. The longest oscillation recorded in the series that may be of climatic origin has a period of about 100,000 years. The calcium sulfate record contains 9-11 distinct oscillations with an average period of about 20,000 years. The strongest oscillation has a preferred spectral period of 2700 years and is recorded throughout the series as thickness changes in calcium sulfate, as events controlling halite deposition, and as episodes of basin freshening. A broad spectral response near a period of about 200 years reflects changes in sulfate, carbonate, and halite thickness. Shorter periods do not have consistent spectra. The time series contains no preferred periods that have not already been identified in previously described records. The climatic changes appear to be the result of a deterministic response to orbital effects at the longer periods and stochastic processes at the shorter periods. An unusually strong response near 2700 years is associated with episodic freshening of the basin. This period has been well established in the Holocene paleoclimatic record, and its presence in the Permian suggests a deterministic origin.

  19. Permian of Norwegian-Greenland sea margins: future exploration target

    SciTech Connect

    Surlyk, F.; Hurst, J.M.; Piasecki, S.; Rolle, F.; Stemmerik, L.; Thomsen, E.; Wrang, P.

    1984-09-01

    Oil and gas exploration in the northern North Sea and the southern Norwegian shelf has mainy been concentrated on Jurassic and younger reservoirs with Late Jurassic black shale source rocks. New onshore investigations in Jameson Land, central East Greenland, suggest that the Permian of the Norwegian-Greenland Sea margins contains relatively thick sequences of potential oil source rocks interbedded with carbonate reefs. The East Greenland, Upper Permian marine basin is exposed over a length of 400 km (250 mi) from Jameson Land in the south to Wollaston Forland in the north, parallel with the continental margin. The Upper Permian black shale is relatively thick, widely distributed, has a high organic carbon content, and a favorable kerogen type. Consequently, the possibilities for a Permian play in the northern part of the Norwegian shelf and along parts of the Norwegian-Greenland Sea margins are worth evaluating.

  20. Life in the end-Permian dead zone.

    PubMed

    Looy, C V; Twitchett, R J; Dilcher, D L; Van Konijnenburg-Van Cittert, J H; Visscher, H

    2001-07-03

    The fossil record of land plants is an obvious source of information on the dynamics of mass extinctions in the geological past. In conjunction with the end-Permian ecological crisis, approximately 250 million years ago, palynological data from East Greenland reveal some unanticipated patterns. We document the significant time lag between terrestrial ecosystem collapse and selective extinction among characteristic Late Permian plants. Furthermore, ecological crisis resulted in an initial increase in plant diversity, instead of a decrease. Paradoxically, these floral patterns correspond to a "dead zone" in the end-Permian faunal record, characterized by a paucity of marine invertebrate megafossils. The time-delayed, end-Permian plant extinctions resemble modeled "extinction debt" responses of multispecies metapopulations to progressive habitat destruction.

  1. An exhumed Late Paleozoic canyon in the rocky mountains

    USGS Publications Warehouse

    Soreghan, G.S.; Sweet, D.E.; Marra, K.R.; Eble, C.F.; Soreghan, M.J.; Elmore, R.D.; Kaplan, S.A.; Blum, M.D.

    2007-01-01

    Landscapes are thought to be youthful, particularly those of active orogenic belts. Unaweep Canyon in the Colorado Rocky Mountains, a large gorge drained by two opposite-flowing creeks, is an exception. Its origin has long been enigmatic, but new data indicate that it is an exhumed late Paleozoic landform. Its survival within a region of profound late Paleozoic orogenesis demands a reassessment of tectonic models for the Ancestral Rocky Mountains, and its form and genesis have significant implications for understanding late Paleozoic equatorial climate. This discovery highlights the utility of paleogeomorphology as a tectonic and climatic indicator. ?? 2007 by The University of Chicago. All rights reserved.

  2. Spatial and temporal patterns of exhumation in the Greater Caucasus from low-temperature thermochronometry (Invited)

    NASA Astrophysics Data System (ADS)

    Avdeev, B.; Niemi, N. A.

    2009-12-01

    Results of a low-temperature thermochronometric study are presented that provide new constraints on the spatial and temporal patters of exhumation in the central and eastern Greater Caucasus. This study employed a range of thermochronomtric systems with thermal sensitivity below ~250°C, including ZFT, 40Ar/39Ar, AFT, and apatite and zircon (U-Th)/He. Granitic samples from the central Greater Caucasus in Russia were collected primarily along two N-S transects between Mt. Elbrus and Mt. Kazbek, at ~43.25°E and 43.75°E. ZFT and 40Ar/39Ar results from these samples are Late Paleozoic in age, consistent with regional igneous cooling ages perhaps related to the Variscan orogeny. AFT and (U-Th)/He results indicate slow (<4°C/Myr) cooling from at least 30 until ~5Ma, at which time the rate of cooling sharply increased to ~ 25°C/Myr. These data constrain total exhumation of the central Greater Caucasus to ~10 km, with at least half of this total having been exhumed since the end of the Miocene. The initiation of the first phase of slow exhumation in the central Greater Caucasus is poorly constrained by our rapidly exhumed sample suite, but one slowly cooled sample from the northern edge of the range suggests exhumation may have begun in the Oligocene. No evidence is preserved in the thermochronometric data for an Eocene exhumational event related to the proposed onset of continental-continental collision at this time, but pre-Oligocene exhumation can be constrained by our data to be less than 1-2 km, assuming simple, monotonic cooling. Low-temperature thermochronometry of volcaniclastic rocks from the eastern Caucasus in Azerbaijan (~48.25°E) yield a markedly different story. Cretaceous AFT ages are consistent with stratigraphic estimates of the eruptive age of the volcaniclastic sequence, while (U-Th)/He ages are reset, limiting burial and re-exhumation since the Mesozoic to ~3 km. Rapid exhumation of these rocks began ~3 Ma, and well-preserved post-Mesozoic thermal

  3. Quantification of tertiary exhumation in the United Kingdom southern North Sea using sonic velocity data

    SciTech Connect

    Hillis, R.R.

    1995-01-01

    Sonic velocities from the Upper and Middle Chalk (Upper Cretaceous), the Bunter Sandstone and the Bunter Shale (both Lower Triassic) were used to independently quantify apparent exhumation (height above maximum burial depth) in the United Kingdom (UK) southern North Sea. Apparent exhumation is the displacement, on the depth axis, of a given velocity/depth trend from the normal (unaffected by exhumation) trend. Apparent exhumation results derived from the Upper and Middle Chalk, the Bunter Sandstone, and the Bunter Shale are statistically similar. The consistency of results from carbonate and clastic units suggests that, at a formational and regional scale, over-compaction (i.e., anomalously high sonic velocity) in all three units analyzed reflects previously greater burial depth, rather than sedimentological and/or diagenetic processes, and validates the use of lithologies other than shale in maximum burial depth studies. The consistency of results from units of Early Triassic to Late Cretaceous age suggests that Tertiary exhumation was of sufficiently great magnitude to mask any earlier Mesozoic periods of exhumation, and the maximum Mesozoic-Cenozoic burial depth in the southern North Sea was attained prior to Tertiary exhumation. The proposed magnitudes of exhumation are generally greater than those previously published for the southern North Sea, but they are consistent with recent estimates from apatite fission track analysis. Cretaceous-Tertiary burial prior to exhumation must have been of great magnitude and more rapid than suggested by the preserved stratigraphy. The effect of this extra burial and subsequent exhumation on sedimentary rock decompaction procedure and thermal maturation modeling is illustrated for the Cleethorpes-1 and 44/7-1 wells, and must also be incorporated in modeling reservoir diagenesis. The regional, Tertiary tectonic uplift associated with exhumation must have had a thick-skinned origin.

  4. Exhumation of the southern Pyrenean fold-thrust belt (Spain) from orogenic growth to decay

    NASA Astrophysics Data System (ADS)

    Rushlow, Caitlin R.; Barnes, Jason B.; Ehlers, Todd A.; Vergés, Jaume

    2013-07-01

    The deformation and exhumation history of an orogen reflects the interactions between tectonic and surface processes. We investigate orogenic wedge deformation, erosion, and sedimentation in the Pyrenees by (a) quantifying the spatiotemporal patterns of exhumation across the southern fold-thrust belt (FTB) with bedrock apatite fission track (AFT) thermochronology and (b) comparing the results with existing deformation, exhumation, and sedimentation chronologies. Eighteen new samples record exhumation during and after orogenesis between 90 and 10 Ma. Rocks from the range core (Axial Zone) record rapid exhumation that progresses east to west and north to south, consistent with patterns of tectonically driven uplift. Synorogenic sediments shed into piggyback basins on the southern fold-thrust belt during mountain building retain a detrital exhumation signal from the Axial Zone. In contrast, samples from other structural positions record exhumation of the thin-skinned Pyrenean thrust sheets, suggesting sediment burial and heating of sufficient magnitudes to reset the AFT system (> 3 km). In some locations, exhumation of these fold-thrust structures is likely an erosional response to thrust-driven rock uplift. We identify an exhumation phase 25-20 Ma that occurs along the central and eastern Spanish Pyrenees at the boundary between thick- and thin-skinned portions of the wedge. We suggest that this distributed exhumation event records (a) a taper response in the southern orogenic wedge to sediment loading and/or (b) a shift to wetter, stormier climate conditions following convergence-driven uplift and full topographic development. A final exhumation phase between 20 and 10 Ma may record the excavation of the southern fold-thrust system following base level lowering in the Ebro Basin.

  5. Permian stratigraphy and correlation of Northeast China: A review

    NASA Astrophysics Data System (ADS)

    Shen, S.-Z.; Zhang, H.; Shang, Q. H.; Li, W.-Z.

    2006-03-01

    Palaeontological, lithostratigraphical data from the Permian strata and correlation of the Permian successions for different tectonic units in Northeast China are reviewed and summarized in this paper. Permian strata in Northeast China are dominated by brachiopods, fusulinoideans and land plants, with limited ammonoids, conodonts and bivalves. The Cisuralian (Early Permian) in the northern margin of the North China Block and in the Manchuride Belt is composed mostly of marine massive limestone with the characteristic Pseudoschwagerina Zone in the Asselian and Sakmarian and the Misellina claudiae Zone in the Kungurian. The Cisuralian in the Xing'an Block and the northeastern part of Inner Mongolia is dominated by huge terrestrial deposits with fossil plants. The Guadalupian (Middle Permian) in the Manchuride, Altaid and Yanbian Belts are characterized by bi-temperate Roadian or early Wordian Monodiexodina fauna and the late Wordian-Capitanian Codonofusiella- Schwagerina or Neoschwagerina- Yabeina faunas, the mixed brachiopod faunas between the Boreal/antitropical and the Palaeoequatorial Cathaysian forms, the Roadian or early Wordian solitary coral faunas, and the late Wordian-Capitanian compound Waagenophyllum- Wentzelella fauna. The Nadanhada Terrane contains some exotic limestone blocks with a typical Cathaysian Neoschwagerina- Yabeina fauna in a Late Jurassic-Early Cretaceous mélange, which is related to Mesozoic subduction in the western Circum-Pacific region. The Lopingian (Late Permian) in Northeast China is mostly characterized by terrestrial molasse deposits with a mixed flora between the Boreal Angaran and the palaeoequatorial Cathaysian Provinces, indicating the final closure of the Palaeo-Asian Ocean.

  6. Extreme mantle uplift and exhumation along a transpressive transform fault

    NASA Astrophysics Data System (ADS)

    Maia, Marcia; Sichel, Susanna; Briais, Anne; Brunelli, Daniele; Ligi, Marco; Ferreira, Nicolas; Campos, Thomas; Mougel, Bérengère; Brehme, Isa; Hémond, Christophe; Motoki, Akihisa; Moura, Denise; Scalabrin, Carla; Pessanha, Ivo; Alves, Eliane; Ayres, Arthur; Oliveira, Pedro

    2016-08-01

    Mantle exhumation at slow-spreading ridges is favoured by extensional tectonics through low-angle detachment faults, and, along transforms, by transtension due to changes in ridge/transform geometry. Less common, exhumation by compressive stresses has been proposed for the large-offset transforms of the equatorial Atlantic. Here we show, using high-resolution bathymetry, seismic and gravity data, that the northern transform fault of the St Paul system has been controlled by compressive deformation since ~10 million years ago. The long-lived transpression resulted from ridge overlap due to the propagation of the northern Mid-Atlantic Ridge segment into the transform domain, which induced the migration and segmentation of the transform fault creating restraining stepovers. An anticlockwise change in plate motion at ~11 million years ago initially favoured extension in the left-stepping transform, triggering the formation of a transverse ridge, later uplifted through transpression, forming the St Peter and St Paul islets. Enhanced melt supply at the ridge axis due to the nearby Sierra Leone thermo chemical anomaly is responsible for the robust response of the northern Mid-Atlantic Ridge segment to the kinematic change. The long-lived process at the origin of the compressive stresses is directly linked to the nature of the underlying mantle and not to a change in the far-field stress regime.

  7. How Orogen-scale Exhumed Strike-slip Faults Initiate

    NASA Astrophysics Data System (ADS)

    Cao, S.; Neubauer, F.

    2015-12-01

    Orogen-scale strike-slip faults present one the most important geodynamic processes affecting the lithosphere-asthenosphere system. In specific subtypes, faulting is virtually initiated along hot-to-cool boundaries, e.g. at such of hot granite intrusions or metamorphic core complexes to cool country rocks. Such fault zones are often subparallel to mountain ranges and expose a wide variety of mylonitic, cataclastic and non-cohesive fault rocks, which were formed at different structural levels of the crust and are stacked within each other ("telescoping"). Exhumation of rocks is, therefore, a common feature of such strike-slip faults implying major transtensive and/or transpressive processes accompanying pure strike-slip motion. The hot-to-cool thermal structure across the fault zone significantly influences the physical fault rock properties. One major question is how and where a major strike-slip initiates and further development. Here, we propose a model in which major continental exhumed strike-slip faults potentially evolve along rheologically weak zones such as plutons or margins of metamorphic complexes. As an example, we propose a model for the Ailao Shan-Red River (ASRR) fault, SE Asia, which initiated along the edge of a plutonic belt and evolved in response to India-Asia collision with four tectonic phases.

  8. Documenting deformation patterns and exhumation across Gianbul Dome, NW India

    NASA Astrophysics Data System (ADS)

    Bowman-Kamaha'o, M.; Lee, J.; Cosca, M. A.

    2012-12-01

    textures recorded within shear sense indicators yield a temperature range of 400-700°C indicating that shearing continued at or below peak metamorphic conditions. Together, the deformation textures, mineral growth relationships, and kinematic shear sense indicate development of the S2 foliation and Ls2 lineation and normal shearing syn- to post-peak metamorphic conditions at temperatures between 400-700°C. 40Ar/39Ar mica cooling ages in the middle crustal rocks young from ~22 Ma in the southwest to ~19 Ma in the northeast reflecting initiation of moderate temperature (350-450°C) exhumation along the Khanjar shear zone in the southwest followed by exhumation along the Zanskar shear zone in the northeast. Cooling ages provide a lower age limit for formation of the foliation, lineation, and shear sense indicators. Buoyancy driven doming of buried nappes and intrusion related heating in the NE has been proposed to explain the deformation and exhumation history of GD. The absence of a qua-quaversal S2 foliation and radially oriented Ls2 lineation, and an asymmetric exhumation history suggest that the buoyancy model may not be viable. We suggest that the domal deformation temperature profile above ~400°C that is parallel to the S2 foliation, the location of the dome in the footwall of the STDS, and the asymmetric exhumation history is consistent with the channel flow extrusion doming mechanism.

  9. Asymmetric exhumation across the Pyrenean orogen: implications for the tectonic evolution of a collisional orogen

    NASA Astrophysics Data System (ADS)

    Fitzgerald, P. G.; Muñoz, J. A.; Coney, P. J.; Baldwin, S. L.

    1999-11-01

    The Pyrenees are a collisional mountain belt formed by convergence between the Afro-Iberian and European plates. Apatite fission track thermochronology from three vertical profiles along the ECORS seismic line constrain the exhumation history of the Pyrenean orogen and hence tectonic models for its formation. In the Eocene there is relatively uniform exhumation across the Pyrenees, but significantly more exhumation occurs on the southern flank of the axial zone in the Oligocene. The variation in exhumation patterns is controlled by a change in how convergence is accommodated within the Pyrenean double-wedge. Accommodation of thrusting on relict extensional features that leads to inversion dominated thrust stacking resulted in relatively slow exhumation in the Eocene. However, subsequent crustal wedging and internal deformation in the upper crust under the stacked duplex of antiformal nappes resulted in extremely rapid exhumation on the southern flank in the Oligocene. The Maladeta profile in the southern axial zone records extremely rapid Early Oligocene exhumation followed by dramatic slowing or cessation of exhumation in the middle Oligocene and the formation of an apatite partial annealing zone (PAZ). This PAZ has subsequently been exhumed 2-3 km since the Middle Miocene, supporting the observations of Coney et al. [J. Geol. Soc. London 153 (1996) 9-16] that the southern flank of the range was buried by ≤2-3 km of syntectonic conglomerates in the Oligocene and subsequently re-excavated from Late Miocene to Recent. The present-day topographic form of the Pyrenees is largely a relict of topography that formed in the Eocene and the Oligocene. Comparison with paleoclimatic records indicates that the Eocene-Oligocene exhumation patterns are controlled by tectonic forces rather than resulting from an orographic effect due to uplift of the Pyrenees.

  10. Rapid Oligocene Exhumation of the Western Canadian Rocky Mountains

    NASA Astrophysics Data System (ADS)

    Szameitat, A.; Parrish, R. R.; Stuart, F. M.; Carter, A.; Fishwick, S.

    2014-12-01

    As part of the North American Cordillera the Rocky Mountains of Canada impact the deflection of weather systems and the jet stream and form a distinct barrier to Pacific moisture reaching the continental interior. The extent to which this climatic pattern extended into the past is at present uncertain, so improving our understanding of the elevation history of the Rockies is critical to determining the controls on climate change within the Northern Hemisphere. We have undertaken a comprehensive apatite (U-Th-Sm)/He and fission track study of the southeastern Canadian Cordillera, i.e. the southern Canadian Rocky Mountains, in order to provide insight into the mid to late Cenozoic uplift and exhumation history of this region. Thermal history and exhumation models of widespread low elevation samples in combination with 6 vertical profiles covering elevations from 500 up to 3100 m a.s.l. show at least 1500 m of rapid exhumation west of the Rocky Mountain Trench (RMT) during the Oligocene (Figure 1). In contrast, the ranges east of the RMT low elevation samples provide Eocene ages throughout. The data show a very different history of recent uplift of the Canadian Rockies compared to what is currently known from published work, which mostly infer that the eastern Canadian Cordillera has not experienced significant uplift since the Eocene. We propose that the most likely cause of this rock uplift was upwelling of asthenosphere around the eastward subducting Farallon Plate. This also led to the eruption of the nearby mainly Miocene Chilcotin Group flood basalts and could have caused underplating of the thin lithosphere west of the RMT, adding to the buoyancy of the plate and lifting the range. Because the Trench marks the edge of the normal thickness craton which was underthrust beneath the Rocky Mountains during the initial upper Cretaceous orogeny, the eastern Rockies have a normal lithosperic thickness. This would impede recent uplift and provides an explanation for the

  11. Late Cretaceous and Cenozoic exhumation history of the Malay Peninsula

    NASA Astrophysics Data System (ADS)

    François, Thomas; Daanen, Twan; Matenco, Liviu; Willingshofer, Ernst; van der Wal, Jorien

    2015-04-01

    The evolution of Peninsular Malaysia up to the collisional period in the Triassic is well described but the evolution since the collision between Indochina and the Sukhothai Arc in Triassic times is less well described in the literature. The processes affecting Peninsular Malaysia during the Jurassic up to current day times have to explain the emplacement multiple intrusions (the Stong Complex, and the Kemahang granite), the Jurassic/Cretaceous onland basins, the Cenozoic offshore basins, and the asymmetric extension, which caused the exhumation of Taku Schists dome. The orogenic period in Permo-Triassic times, which also formed the Bentong-Raub suture zone, resulted in thickening of the continental crust of current day Peninsular Malaysia due to the collision of the Indochina continental block and the Sukhothai Arc, and is related to the subduction of oceanic crust once present between these continental blocks. The Jurassic/Cretaceous is a period of extension, resulting in the onland Jurassic/Cretaceous basins, synchronous melting of the crust, resulting in the emplacement Stong Complex and the Kemahang granite and thinning of the continental crust on the scale of the Peninsular, followed by uplift of the Peninsular. Different models can explain these observations: continental root removal, oceanic slab detachment, or slab delamination. These models all describe the melting of the lower crust due to asthenospheric upwelling, resulting in uplift and subsequent extension either due to mantle convective movements or gravitational instabilities related to uplift. The Cenozoic period is dominated by extension and rapid exhumation in the area as documented by low temperature thermocrological ages The extension in this period is most likely related to the subduction, which resumed at 45 Ma, of the Australian plate beneath the Eurasian plate after it terminated in Cretaceous times due to the collision of an Australian microcontinental fragment with the Sunda margin in the

  12. Physicochemical analysis of Permian coprolites from Brazil.

    PubMed

    Rodrigues, M I C; da Silva, J H; Santos, F Eroni P; Dentzien-Dias, P; Cisneros, J C; de Menezes, A S; Freire, P T C; Viana, B C

    2018-01-15

    In this paper we performed the study of two coprolites (fossilized feces) collected from the exposed levels of the Pedra de Fogo Formation, Parnaiba Sedimentary Basin, and Rio do Rasto Formation, Paraná Sedimentary Basin, both of the Palaeozoic era (Permian age). They were characterized using X-ray diffractometry, infrared, Raman and energy dispersive spectroscopy techniques in order to aid our understanding of the processes of fossilization and to discuss issues related to the feeding habits of the animals which generated those coprolites, probably cartilaginous fishes. The results obtained using a multitechnique approach showed that although these coprolites are from different geological formations, 3000km away from each other, they show the same major crystalline phases and elemental composition. The main phases found were hydroxyapatite, silica, calcite and hematite, which lead to infer that those coprolites were formed under similar conditions and produced by a similar group of carnivore or omnivore fishes. Copyright © 2017 Elsevier B.V. All rights reserved.

  13. Extreme localized exhumation at syntaxes initiated by subduction geometry

    NASA Astrophysics Data System (ADS)

    Bendick, Rebecca; Ehlers, Todd A.

    2014-08-01

    Some of the highest and most localized rates of lithospheric deformation in the world are observed at the transition between adjacent plate boundary subduction segments. The initiating perturbation of this deformation has long been attributed to vigorous erosional processes as observed at Nanga Parbat and Namche Barwa in the Himalaya and at Mount St. Elias in Alaska. However, an erosion-dominated mechanism ignores the 3-D geometry of curved subducting plates. Here we present an alternative explanation for rapid exhumation at these locations based on the 3-D thermomechanical evolution of collisions between plates with nonplanar geometries. Comparison of model predictions with existing data reproduces the defining characteristics of these mountains and offers an explanation for their spatial correlation with arc termini. These results demonstrate a "bottom-up" tectonic rather than "top-down" erosional initiation of feedbacks between erosion and tectonic deformation; hence, the importance of 3-D subduction geometry.

  14. Basin development, petrology, and paleogeography - Early Permian carbonates, northwestern Bolivia

    SciTech Connect

    Canter, K.L.; Isaacson, P.E. )

    1990-05-01

    Early Permian carbonate rocks of the Yaurichambi Formation in northwestern Bolivia demonstrate in-situ, low-paleolatitude development within a complexly interbedded sequence punctuated by siliciclastics apparently derived from a western source. The Yaurichambi Formation (Copacabana Group) occurs above a regional caliche surface that caps Upper Carboniferous quartzarenites. Lower beds of the formation are characterized by interbedded carbonate and quartz-rich lithologies. This interval is gradationally overlain by a shallowing-upward, carbonate-dominated sequence. Mud-rich wackestones and packstones grade upward to bioclastic packstones and grainstones. Common allochems in bioclastic-rich lithologies include echinoderms, brachiopods, fenestrate bryozoans, intraclasts, and less common corals. Uppermost beds contain abundant siliciclastic interbeds. Where exposed, this carbonate sequence is terminated by the Tiquina Sandstone. Permian rocks were deposited in a northwest-southeast-oriented basin. Siliciclastic flooding from the western and southwestern margin of the basin dominated throughout the Carboniferous and occurred intermittently during the Permian, with apparent shallowing to the south. A low-latitude paleogeographic setting for these rocks is indicated by the carbonate lithologies dominating the Lower Permian sequence. Sedimentary and diagenetic features diagnostic of semi-arid warm-water deposition include penecontemporaneous dolomites, fenestral fabric, and calcretes. Furthermore, the faunas are similar to those found in equivalent strata of the Permian basin area of west Texas, indicating that deposition occurred at relatively low latitudes.

  15. Middle-Late Permian mass extinction on land

    SciTech Connect

    Retallack, G.J.; Metzger, C.A.; Greaver, T.; Jahren, A.H.; Smith, R.M.H.; Sheldon, N.D.

    2006-11-15

    The end-Permian mass extinction has been envisaged as the nadir of biodiversity decline due to increasing volcanic gas emissions over some 9 million years. We propose a different tempo and mechanism of extinction because we recognize two separate but geologically abrupt mass extinctions on land, one terminating the Middle Permian (Guadalupian) at 260.4 Ma and a later one ending the Permian Period at 251 Ma. Our evidence comes from new paleobotanical, paleopedological, and carbon isotopic studies of Portal Mountain, Antarctica, and comparable studies in the Karoo Basin, South Africa. Extinctions have long been apparent among marine invertebrates at both the end of the Guadalupian and end of the Permian, which were also times of warm-wet greenhouse climatic transients, marked soil erosion, transition from high- to low-sinuosity and braided streams, soil stagnation in wetlands, and profound negative carbon isotope anomalies. Both mass extinctions may have resulted from catastrophic methane outbursts to the atmosphere from coal intruded by feeder dikes to flood basalts, such as the end-Guadalupian Emeishan Basalt and end-Permian Siberian Traps.

  16. Permian paleoclimate data from fluid inclusions in halite

    USGS Publications Warehouse

    Benison, K.C.; Goldstein, R.H.

    1999-01-01

    This study has yielded surface water paleotemperatures from primary fluid inclusions in mid Permian Nippewalla Group halite from western Kansas. A 'cooling nucleation' method is used to generate vapor bubbles in originally all-liquid primary inclusions. Then, surface water paleotemperatures are obtained by measuring temperatures of homogenization to liquid. Homogenization temperatures ranged from 21??C to 50??C and are consistent along individual fluid inclusion assemblages, indicating that the fluid inclusions have not been altered by thermal reequilibration. Homogenization temperatures show a range of up to 26??C from base to top of individual cloudy chevron growth bands. Petrographic and fluid inclusion evidence indicate that no significant pressure correction is needed for the homogenization temperature data. We interpret these homogenization temperatures to represent shallow surface water paleotemperatures. The range in temperatures from base to top of single chevron bands may reflect daily temperatures variations. These Permian surface water temperatures fall within the same range as some modern evaporative surface waters, suggesting that this Permian environment may have been relatively similar to its modern counterparts. Shallow surface water temperatures in evaporative settings correspond closely to local air temperatures. Therefore, the Permian surface water temperatures determined in this study may be considered proxies for local Permian air temperatures.

  17. Gas hydrate contribution to Late Permian global warming

    NASA Astrophysics Data System (ADS)

    Majorowicz, J.; Grasby, S. E.; Safanda, J.; Beauchamp, B.

    2014-05-01

    Rapid gas hydrate release (the “clathrate gun” hypothesis) has been invoked as a cause for the rapid global warming and associated negative carbon isotope excursion observed during the Latest Permian Extinction (LPE). We modeled the stability of gas hydrates through a warming Middle to Late Permian world, considering three settings for methane reservoirs: 1) terrestrial hydrates, 2) hydrates on exposed continental shelves during glacial sea level drop, and 3) hydrates in deep marine settings. Model results show that terrestrial hydrates would rapidly destabilize over ∼400 ky after deglaciation for moderate heatflow (40 mW/m2), and more rapidly for higher heat flow values. Exposed continental shelves would lose hydrates even more rapidly, after being flooded due to loss of ice storage on land. These two major hydrate reservoirs would thus have destabilized during the Middle to Late Permian climate warming, well prior to the LPE event. However, they may have contributed to the >2‰ negative C-isotopic shift during the late Middle Permian. Deep marine hydrates would have remained stable until LPE time. Rapid warming of deep marine waters during this time could have triggered destabilization of this reservoir, however given the configuration of one super continent, Pangea, hydrate bearing continental slopes would have been less extensive than modern day. This suggests that any potential gas hydrate release would have had only a minor contributing impact to the runaway greenhouse during the Latest Permian extinction.

  18. Preservation/exhumation of ultrahigh-pressure subduction complexes

    NASA Astrophysics Data System (ADS)

    Ernst, W. G.

    2006-12-01

    Ultrahigh-pressure (UHP) metamorphic terranes reflect subduction of continental crust to depths of 90-140 km in Phanerozoic contractional orogens. Rocks are intensely overprinted by lower pressure mineral assemblages; traces of relict UHP phases are preserved only under kinetically inhibiting circumstances. Most UHP complexes present in the upper crust are thin, imbricate sheets consisting chiefly of felsic units ± serpentinites; dense mafic and peridotitic rocks make up less than ˜ 10% of each exhumed subduction complex. Roundtrip prograde-retrograde P- T paths are completed in 10-20 Myr, and rates of ascent to mid-crustal levels approximate descent velocities. Late-stage domical uplifts typify many UHP complexes. Sialic crust may be deeply subducted, reflecting profound underflow of an oceanic plate prior to collisional suturing. Exhumation involves decompression through the P- T stability fields of lower pressure metamorphic facies. Scattered UHP relics are retained in strong, refractory, watertight host minerals (e.g., zircon, pyroxene, garnet) typified by low rates of intracrystalline diffusion. Isolation of such inclusions from the recrystallizing rock matrix impedes back reaction. Thin-aspect ratio, ductile-deformed nappes are formed in the subduction zone; heat is conducted away from UHP complexes as they rise along the subduction channel. The low aggregate density of continental crust is much less than that of the mantle it displaces during underflow; its rapid ascent to mid-crustal levels is driven by buoyancy. Return to shallow levels does not require removal of the overlying mantle wedge. Late-stage underplating, structural contraction, tectonic aneurysms and/or plate shallowing convey mid-crustal UHP décollements surfaceward in domical uplifts where they are exposed by erosion. Unless these situations are mutually satisfied, UHP complexes are completely transformed to low-pressure assemblages, obliterating all evidence of profound subduction.

  19. Paleozoic exhumation history of the North Qinling terrane,China

    NASA Astrophysics Data System (ADS)

    Dong, Yunpeng; Genser, Johann; Neubauer, Franz; Liu, Xiaoming; Yang, Zhao; Zhang, Guowei; Heberer, Bianca

    2010-05-01

    The Qinling mountain range lies between the North and South China blocks, and is bounded on the north by the Lushan fault and on the south by the Mianlue-Bashan-Xiangguang fault (Dong et al., 2008). The Qinling-Dabie orogen can be subdivided, from north to south, into the Southern North China block with the North Qinling terrane, the Shangdan suture, the South Qinling microcontinent block, the Mianlue suture and the South China block (Zhang et al., 1995; Meng et al., 1999; Li SZ et al., 2007). A number of models for the Qinling tectonic evolution have been proposed. Controversies, however, still exist, in particular on the timing of the joining and the processes of convergence between the North and South China blocks along the Shangdan suture zone. Most authors believe that the collision between the North and the South China blocks occurred after the closure of the Shangdan ocean. However, an increasing body of data is not consistent with simple collision models. This paper reports new U-Pb age zircon and 40Ar/39Ar hornblende and biotite ages from magmatic and metamorphic rocks from the Northern Qinling Terrane. Based on this new dataset, we discuss the exhumation and cooling history of the Northern Qinling Terrane in order to advance the understanding of the tectonic processes that operated during convergence between the North and South China blocks along the Shangdan zone. The amphibolite-grade North Qinling metamorphic unit forms the centre of the Qinling orogenic belt. Results of LA-ICP-MS U-Pb zircon, 40Ar/39Ar amphibole and biotite dating reveal the Palaeozoic tectonic history. U-Pb zircon dating of migmatitic orthogneiss and granite dykes constrains the age of two possible stages of migmatization at 517 ±14 Ma and 445.4 ± 4.6 Ma. Subsequently, intrusion by granites occurred at 417.2 ± 1.6 Ma. 40Ar/39Ar plateau ages of amphibole, ranging from 397.1 ± 8.6 Ma to 432.3± 3.4 Ma constrain the cooling of the Qinling complex below ca. 540°C and biotite 40Ar/39

  20. Miocene exhumation of the Pamir revealed by detrital geothermochronology of Tajik rivers

    NASA Astrophysics Data System (ADS)

    Lukens, C. E.; Carrapa, B.; Singer, B. S.; Gehrels, G.

    2012-04-01

    The Pamir mountains are the western continuation of the Tibetan-Himalayan system, the largest and highest orogenic system on Earth. Detrital geothermochronology applied to modern river sands from the western Pamir of Tajikistan records the history of sediment source crystallization, cooling, and exhumation. This provides important information on the timing of tectonic processes, relief formation, and erosion during orogenesis. U-Pb geochronology of detrital zircons and 40Ar/39Ar thermochronology of white micas from five rivers draining distinct tectonic terranes in the western Pamir document Paleozoic through Cenozoic crystallization ages and a Miocene (13-21 Ma) cooling signal. Detrital zircon U-Pb ages show Proterozoic through Cenozoic ages and affinity with Asian rocks in Tibet. The detrital 40Ar/39Ar data set documents deep and regional exhumation of the Pamir mountains >30 Myr after Indo-Asia collision, which is best explained with widespread erosion of metamorphic domes. This exhumation signal coincides with deposition of over 6 km of conglomerates in the adjacent foreland, documenting high subsidence, sedimentation, and regional exhumation in the region. Our data are consistent with a high relief landscape and orogen-wide exhumation at ˜13-21 Ma and correlate with the timing of exhumation of the Pamir gneiss domes. This exhumation is younger in the Pamir than that observed in neighboring Tibet and is consistent with higher magnitude Cenozoic deformation and shortening in this part of the orogenic system.

  1. Revised exhumation history of the Wind River Range, WY, and implications for Laramide tectonics

    NASA Astrophysics Data System (ADS)

    Stevens, Andrea L.; Balgord, Elizabeth A.; Carrapa, Barbara

    2016-05-01

    A reanalysis of apatite fission track (AFT) thermochronology coupled with thermal-kinetic modeling of samples from the Wind River Range document Late Cretaceous to early Eocene episodic cooling and exhumation of one of the largest basement-cored ranges in the western United States. Three vertical transects taken at different latitudes along the length of the 145 km Wind River Range reveal that exhumation is uniform along strike suggesting steady displacement along the Wind River Fault, and significant exhumation and relief in the Wind River Range by the early Eocene. Thermal modeling of AFT ages, lengths, and compositional proxies document rapid exhumation from ~65 to 50 Ma. This rapid exhumation episode matches a period of accelerated subsidence in the adjacent Green River and Wind River basins. At ~50 Ma, exhumation dramatically slowed by an order of magnitude coincident with decreasing subsidence in the adjacent basins. No signal of Oligocene cooling is apparent in either AFT cooling ages or thermal modeling suggesting that a possible later phase of reactivation of structures and uplift, as previously suggested, was limited to less than approximately 1 km of exhumation.

  2. Interpretation of "fungal spikes" in Permian-Triassic boundary sections

    NASA Astrophysics Data System (ADS)

    Hochuli, Peter A.

    2016-09-01

    Abundant occurrences of the palynomorph Reduviasporonites have been described as ;fungal spike; from several Permian/Triassic boundary sections and related to the supposed destruction of woody vegetation by fungal pathogens during the Permian/Triassic extinction event. The biological affinity of this taxa considered by some authors of fungal origin is still controversially discussed since there is geochemical evidence that it is most probably related to algae. The abundance peak of this species is used by some authors as a stratigraphic marker, notably in terrestrial Permian/Triassic boundary sections from South China. Illustrations of the reported fungal remains however show potentially erroneous taxonomic identification of Reduviasporonites, and, based on differences in thermal maturation, they may represent recent contamination. Here Reduviasporonites chalastus of Early Triassic age is illustrated together with recent fungal remains originating from a strongly weathered and otherwise barren sample from a Middle Triassic section.

  3. An unusual, structurally preserved ovule from the Permian of Antarctica.

    PubMed

    Klavins, S D.; Taylor, E L.; Krings, M; Taylor, T N.

    2001-06-01

    Anatomically preserved ovules are described from silicified peat of Late Permian age collected from Skaar Ridge in the central Transantarctic Mountains, Antarctica. The small ovules are significant in possessing fleshy apical appendages and a funnel-shaped micropylar extension formed by the sarcotestal layer of the integument, by which they differ from all other Permian ovules described to date. The apical modifications may have functioned in pollination and/or seed dispersal. Similarity with the apical organization of earlier Paleozoic ovules is shown to be superficial, since the analogous structures are developmentally derived from different tissues. Although the ovules occur in rocks in which glossopterids are the only gymnosperms represented, there is insufficient evidence to assign them to a taxonomic group. These ovules are of particular importance because there are so few anatomically preserved gymnosperm reproductive structures known from the Permian and thus provide new data on the diversity of late Paleozoic gymnosperms.

  4. Exhumation of oceanic blueschists and eclogites in subduction zones: Timing and mechanisms

    NASA Astrophysics Data System (ADS)

    Agard, P.; Yamato, P.; Jolivet, L.; Burov, E.

    2009-01-01

    High-pressure low-temperature (HP-LT) metamorphic rocks provide invaluable constraints on the evolution of convergent zones. Based on a worldwide compilation of key information pertaining to fossil subduction zones (shape of exhumation P- T- t paths, exhumation velocities, timing of exhumation with respect to the convergence process, convergence velocities, volume of exhumed rocks,…), this contribution reappraises the burial and exhumation of oceanic blueschists and eclogites, which have received much less attention than continental ones during the last two decades. Whereas the buoyancy-driven exhumation of continental rocks proceeds at relatively fast rates at mantle depths (≥ cm/yr), oceanic exhumation velocities for HP-LT oceanic rocks, whether sedimentary or crustal, are usually on the order of the mm/yr. For the sediments, characterized by the continuity of the P- T conditions and the importance of accretionary processes, the driving exhumation mechanisms are underthrusting, detachment faulting and erosion. In contrast, blueschist and eclogite mafic bodies are systematically associated with serpentinites and/or a mechanically weak matrix and crop out in an internal position in the orogen. Oceanic crust rarely records P conditions > 2.0-2.3 GPa, which suggests the existence of maximum depths for the sampling of slab-derived oceanic crust. On the basis of natural observations and calculations of the net buoyancy of the oceanic crust, we conclude that beyond depths around 70 km there are either not enough serpentinites and/or they are not light enough to compensate the negative buoyancy of the crust. Most importantly, this survey demonstrates that short-lived (< ˜ 15 My), discontinuous exhumation is the rule for the oceanic crust and associated mantle rocks: exhumation takes place either early (group 1: Franciscan, Chile), late (group 2: New Caledonia, W. Alps) or incidentally (group 3: SE Zagros, Himalayas, Andes, N. Cuba) during the subduction history

  5. Tracking the multi-stage exhumation history of the western Chinese Tianshan by Apatite Fission Track (AFT) dating - Implications for the preservation of epithermal deposits in ancient orogenic belt

    NASA Astrophysics Data System (ADS)

    Wang, Yannan; Cai, Keda

    2017-04-01

    The western Chinese Tianshan, located in the southern domain of the Central Asian Orogenic Belt (CAOB), was originally constructed by multiple accretion-collision processes in the Paleozoic, and was superimposed by complex intracontinental tectonic evolution in the Mesozoic-Cenozoic. Understanding the timing and mechanism of the latter geological processes is critical to unravel the preservation conditions of the epithermal deposits in the western Chinese Tianshan. This work presents new apatite fission track (AFT) data for three mountain ranges of the western Chinese Tianshan to track their exhumation history. Our AFT data gave a wide range of ages from 76.8 ± 5.5 Ma to 182.3 ± 9.9 Ma, and the mean confined fission track lengths are between 9.8 ± 0.5 μm and 12.3 ± 0.2 μm. The new data, in combination with the thermal history modeling,enable us to attribute the exhumation history to three primary stages, including Early Permian (300-280 Ma), Late Triassic-Early Cretaceous (230-130 Ma), and Late Oligocene-Early Miocene (30-20 Ma). The first stage may be caused by the terrane accretion-collision in the late Paleozoic. The second stage was likely related to the closure of the Mongol-Okhotsk Ocean during the Mesozoic. The last one is regarded as the result of the collision between the Indian Plate and the Eurasia Plate in the Cenozoic. The extraordinary exhumation processes of these three major mountain ranges might have been responsible for sediment supply to the corresponding intra-mountain basins in the western Chinese Tianshan, and the particularly mountain-basin coupling evolution is ascribed to an essential condition for the preservation of epithermal deposits in ancient orogenic belt.

  6. Permian scorpions from the Petrified Forest of Chemnitz, Germany.

    PubMed

    Dunlop, Jason A; Legg, David A; Selden, Paul A; Fet, Victor; Schneider, Joerg W; Rößler, Ronny

    2016-04-07

    Paleozoic scorpions (Arachnida: Scorpiones) have been widely documented from the Carboniferous Period; which hosts a remarkable assemblage of more than sixty species including both putative stem- and crown-group fossils. By contrast the succeeding Permian Period is almost completely devoid of records, which are currently restricted to a trace fossil from the early Permian of New Mexico, USA and some limb fragments from the late Permian of the Vologda Region, Russia. ?Opsieobuthus tungeri sp. nov. from the Petrified Forest of Chemnitz, Germany represents the first complete body fossils of scorpions from the Permian. Explosive volcanism preserved these remarkable specimens in situ as part of the palaeosol horizon and bedrock of the Petrified Forest, immediately beneath the Zeisigwald tuff horizon. This dates to the early Permian (Sakmarian) or ca. 291 Ma. Intriguingly, the specimens were obtained from a palaeosol horizon with a compacted network of different-sized woody roots and thus have been preserved in situ in their likely life position, even within their original burrows. Differences in the structure of the comb-like pectines in the two fossils offer evidence for sexual dimorphism, and permit further inferences about the ecology and perhaps even the reproductive biology of these animals. As putative members of a Coal Measures genus, these fossils suggest that at least some Carboniferous scorpion lineages extended their range further into the Permian. This contributes towards a picture of scorpion evolution in which both basal and derived (orthostern) forms coexisted for quite some time; probably from the end of the Carboniferous through to at least the mid Triassic.

  7. Permian high pressure rocks—the basement of the Sierra de Limón Verde in Northern Chile

    NASA Astrophysics Data System (ADS)

    Lucassen, F.; Franz, G.; Laber, A.

    1999-03-01

    The gneisses and metabasites of the Sierra de Limón Verde were investigated by P-T-t determinations. The rocks are unique in the Central Andes because of their high pressure metamorphic conditions with P≈13±1 kbar at T≈660-720°C. Their age of metamorphism is ≈270 Ma, based on Sm-Nd mineral isochrons. Final uplift of the isolated basement block occurred in the Triassic with a K-Ar age of biotite at ca 235 Ma. In our interpretation, the protolith of the Permian metamorphic rocks is the crust that formed and stabilized during Early Paleozoic. The Sierra de Limón Verde rocks give insight into the lowermost part of the crust in Early Mesozoic. Its Sm-Nd isotopic composition is indistinguishable from the composition of the crust that formed in the Early Paleozoic metamorphic-magmatic cycle ( ca 500 Ma) in northern Chile and NW Argentina. The tectonic-geodynamic setting that triggered the high P (˜45 km depth) metamorphism and the locally restricted exhumation of the rocks remains speculative. Continental collision or a subduction related accretionary complex is unlikely considering the regional geological situation. Transpression-transtension in a strike slip system along the continental margin is suggested as a hypothesis for future investigations.

  8. Hypoxia, global warming, and terrestrial late Permian extinctions.

    PubMed

    Huey, Raymond B; Ward, Peter D

    2005-04-15

    A catastrophic extinction occurred at the end of the Permian Period. However, baseline extinction rates appear to have been elevated even before the final catastrophe, suggesting sustained environmental degradation. For terrestrial vertebrates during the Late Permian, the combination of a drop in atmospheric oxygen plus climate warming would have induced hypoxic stress and consequently compressed altitudinal ranges to near sea level. Our simulations suggest that the magnitude of altitudinal compression would have forced extinctions by reducing habitat diversity, fragmenting and isolating populations, and inducing a species-area effect. It also might have delayed ecosystem recovery after the mass extinction.

  9. Upper Permian (Late Changhsingian) marine strata in Nan Province, northern Thailand

    NASA Astrophysics Data System (ADS)

    Fontaine, Henri; Hoang, Thi Than; Kavinate, Sathaporn; Suteethorn, Varavudh; Vachard, Daniel

    2013-10-01

    In the Upper Permian of northeastern Thailand (Loei Province), continental plants have been found and to the north in Laos near Luang Prabang, continental vertebrates (Dicynodon species) have been discovered. The Middle Permian is in sharp contrast to this as it is represented only by marine sediments. West of these areas in the province of Nan in Thailand, the Upper Permian is represented by marine sediments which extend to a high level in the Upper Permian and continental beds appear to be entirely absent, at least at Pha Dang Khwai, a locality where limestone extends from the end of the Lower Permian to the Triassic.

  10. Unraveling tectonics and climate forcing in the late-Neogene exhumation history of South Alaska

    NASA Astrophysics Data System (ADS)

    Valla, Pierre; Champagnac, Jean-Daniel; Shuster, David; Herman, Frédéric; Giuditta Fellin, Maria

    2015-04-01

    The southern Alaska range presents an ideal setting to study the complex interactions between tectonics, climate and surface processes in landscape evolution. It exhibits active tectonics with the ongoing subduction/collision between Pacific and North America, and major active seismogenic reverse and strike-slip faults. The alpine landscape, rugged topography and the important ice-coverage at present reveal a strong glacial imprint associated with high erosion and sediment transport rates. Therefore, the relative importance of climatically-driven glacial erosion and tectonics for the observed late-exhumation history appears to be quite complex to decipher. Here, we first perform a formal inversion of an extensive bedrock thermochronological dataset from the literature to quantify the large-scale 20-Myr exhumation history over the entire southern Alaska. We show that almost half of the variability within the thermochronological record can be explained by modern annual precipitations spatial distribution, the residuals clearly evidencing localized exhumation along major tectonic structures of the frontal fold and thrust belt. Our results confirm high exhumation rates in the St Elias "syntaxis" and frontal zones for the last 0-2 Myr, where major ice fields and high precipitation rates likely sustained high exhumation rates; however the impact of late Cenozoic glaciations is difficult to constrain because of the low resolution on the exhumation history older than ~2 Myr. On the contrary, our inversion outcomes highlight that north of the Bagley Icefield the long-term exhumation has remained quite slow and continuous over the last ~20 Myr, with no late-stage signal of exhumation change since the onset of glaciations despite a clear glacial imprint on the landscape. We thus focus on the Granite Range (Wrangell-St Elias National Park, Alaska), an area presenting a strong glacial imprint but minor tectonic activity with only localized brittle deformation. We sampled four

  11. Timing and Mechanisms of Oceanic Blueschist and Eclogite Exhumation : Implications for Subduction Mechanics

    NASA Astrophysics Data System (ADS)

    Agard, P.; Yamato, P.; Monié, P.; Jolivet, L.; Burov, E.

    2008-12-01

    Understanding what controls the detachment and migration of oceanic crustal slices along the subduction channel is crucial to constrain subduction mechanics. For this reason, we compiled key information pertaining to the burial and exhumation of oceanic blueschists and eclogites worldwide (shape of exhumation P-T-t paths, exhumation velocities, timing of exhumation with respect to the convergence process, convergence velocities, volume of exhumed rocks). In contrast with the fast (> cm/yr), buoyancy-driven exhumation of continental rocks, oceanic exhumation velocities for high-pressure low-temperature oceanic rocks, whether sedimentary or crustal, are usually on the order of the mm/yr. The sediments are characterized by the continuity of the P-T conditions and the importance of accretionary processes, whereas blueschist and eclogite mafic bodies are systematically associated with serpentinites and/or a mechanically weak matrix and crop out in an internal position in the orogen. Oceanic crust rarely records P conditions > 2.0-2.3 GPa, which suggests the existence of maximum depths for the sampling of slab-derived oceanic crust. Natural observations and calculations of the net buoyancy of the oceanic crust suggest that beyond depths around 70 km there are either not enough serpentinites and/or they are not light enough to compensate the negative buoyancy of the crust. This survey demonstrates that short-lived (< 15 My), discontinuous exhumation is the rule for the oceanic crust. Exhumation takes place either early (group 1: Franciscan, Chile), late (group 2: New Caledonia, W. Alps) or incidentally (group 3: SE Zagros, Himalayas, Andes, N. Cuba) during the subduction history. This discontinuous exhumation is likely permitted by the specific thermal regime following the onset of a young, warm subduction (group 1), by continental subduction (group 2) or by a major, geodynamic modification of convergence across the subduction zone (group 3). In addition, we stress that

  12. Measuring plume-related exhumation of the British Isles in Early Cenozoic times

    NASA Astrophysics Data System (ADS)

    Cogné, Nathan; Doepke, Daniel; Chew, David; Stuart, Finlay M.; Mark, Chris

    2016-12-01

    Mantle plumes have been proposed to exert a first-order control on the morphology of Earth's surface. However, there is little consensus on the lifespan of the convectively supported topography. Here, we focus on the Cenozoic uplift and exhumation history of the British Isles. While uplift in the absence of major regional tectonic activity has long been documented, the causative mechanism is highly controversial, and direct exhumation estimates are hindered by the near-complete absence of onshore post-Cretaceous sediments (outside Northern Ireland) and the truncated stratigraphic record of many offshore basins. Two main hypotheses have been developed by previous studies: epeirogenic exhumation driven by the proto-Iceland plume, or multiple phases of Cenozoic compression driven by far-field stresses. Here, we present a new thermochronological dataset comprising 43 apatite fission track (AFT) and 102 (U-Th-Sm)/He (AHe) dates from the onshore British Isles. Inverse modelling of vertical sample profiles allows us to define well-constrained regional cooling histories. Crucially, during the Paleocene, the thermal history models show that a rapid exhumation pulse (1-2.5 km) occurred, focused on the Irish Sea. Exhumation is greatest in the north of the Irish Sea region, and decreases in intensity to the south and west. The spatial pattern of Paleocene exhumation is in agreement with the extent of magmatic underplating inferred from geophysical studies, and the timing of uplift and exhumation is synchronous with emplacement of the plume-related British and Irish Paleogene Igneous Province (BIPIP). Prior to the Paleocene exhumation pulse, the Mesozoic onshore exhumation pulse is mainly linked to the uplift and erosion of the hinterland during the complex and long-lived rifting history of the neighbouring offshore basins. The extent of Neogene exhumation is difficult to constrain due to the poor sensitivity of the AHe and AFT systems at low temperatures. We conclude that the

  13. South Primorye, Far East Russia—A key region for global Permian correlation

    NASA Astrophysics Data System (ADS)

    Kotlyar, Galina V.; Belyansky, Gennady C.; Burago, Valentina I.; Nikitina, Antonina P.; Zakharov, Yuri D.; Zhuravlev, Andrey V.

    2006-03-01

    Significant differences between faunal and floral associations existing in different paleogeographic realms in the Kungurian-Late Permian interval make it difficult to correlate the Permian deposits of the world. Resolving this problem is one of the main tasks of Permian stratigraphy. The global significance of Permian strata of the Primorye region of Far East Russia is enhanced by the specific Middle Permian mixed Tethyan, Boreal and Gondwanan-type brachiopod fauna, mixed Angara-Euromerican-Cathaysian flora, and their close spatial and stratigraphical association with fusulinids, bryozoans, ammonoids, conodonts. These facts permit tracing of global correlational levels of some Permian sequences within the different paleobiogeographical realms: for example, the Monodiexodina sutschanica- Metadoliolina dutkevichi fusulinid zone of the Wordian age and Parafusulina stricta fusulinid zone of the Capitanian age. The Late Permian fauna of the Primorye is mainly Tethyan in origin and provides correlation with similar aged sequences from South China.

  14. Rapid Exhumation of the Rand Schist: Constraints From Natural Garnet Diffusion Couples

    NASA Astrophysics Data System (ADS)

    Chapman, A. D.; Saleeby, J. B.; Luffi, P. I.

    2007-12-01

    Intensive study of the Rand schist (hereafter referred to as the "schist") of southern California demonstrate convincingly that it formed in the Late Cretaceous by subduction of Cordilleran eogeoclinal detritus along a shallow dipping segment of the Farallon plate. Comparatively little is known about the exhumation history of the schist. Recent thermochronologic and thermobarometric analyses suggest that, in some localities, the schist was deposited, underplated beneath western Sierra Nevada batholithic assemblages (the "upper plate"), and exhumed with the upper plate from 30 - 40 km depths in less than 3 million years. Such a rapid cycling interval implies exhumation rates in excess of 5 mm/yr. To corroborate these existing data on the exhumation rate of the schist, we exploit diffusional annealing of garnet zonation. Some garnets from the schist of the San Emigdio Mountains were broken during late stages of their growth. Overgrowth along broken margins resulted in natural diffusion couples ca. 25 μm inward from the rims, where peak metamorphic temperatures reached 610 °C. A maximum time interval, representing exhumation prior to diffusion cessation, of 1 Ma was estimated from the degree of annealing of the originally sharp compositional step. Similar time intervals were calculated from narrow (10 μm) retrograde zones at the rims of compositionally homogenized garnets belonging to the upper plate. Garnets from the schist conspicuously lack retrograde zonation patterns, likely due to exhumation rates exceeding those of retrograde diffusion. Both garnet-based geospeedometry and thermochronometric studies indicate that the schist was exhumed at rates comparable to lateral tectonic plate motions (> 5 mm/yr). This conclusion, in the context of field-based analyses suggestive of west-directed ductile transport of the schist relative to the upper plate during exhumation, reveals a profound Late Cretaceous extensional event. These results yield important insight into

  15. Chronological constraints on the Permian geodynamic evolution of eastern Australia

    NASA Astrophysics Data System (ADS)

    Li, Pengfei; Rosenbaum, Gideon; Vasconcelos, Paulo

    2014-03-01

    The New England Orogen in eastern Australia developed as a subduction-related orogen in the Late Devonian to Carboniferous, and was modified in the Permian by deformation, magmatism and oroclinal bending. The geodynamics associated with the development of the New England oroclines and the exact timing of major tectonic events is still enigmatic. Here we present new 40Ar/39Ar results from metasedimentary and volcanic rocks from the southern New England Orogen. Eight grains from four metasedimentary samples (Texas beds) that originated in the Late Devonian to Carboniferous accretionary wedge yielded reproducible plateau ages of ~ 293, ~ 280, ~ 270 and ~ 260 Ma. These results suggest a complex thermal history associated with multiple thermal events, possibly due to the proximity to Permian intrusions. Two samples from mafic volcanic rocks in the southernmost New England Orogen (Alum Mountain Volcanics and Werrie Basalt) yielded eruption ages of 271.8 ± 1.8 and 266.4 ± 3.0 Ma. The origin of these rocks was previously attributed to slab breakoff, following a period of widespread extension in the early Permian. We suggest that this phase of volcanism marked the transition from backarc extension assisted by trench retreat to overriding-plate contraction. The main phase of oroclinal bending has likely occurred during backarc extension in the early Permian, and terminated at 271-266 Ma with the processes of slab segmentation and breakoff.

  16. Terrestrial Permian - Triassic boundary sections in South China

    NASA Astrophysics Data System (ADS)

    Bercovici, Antoine; Vajda, Vivi

    2016-08-01

    The Permian-Triassic boundary interval in China comprises a significant record of faunal and floral changes during this important extinction event. Here we discuss the details of palynomorph preservation at the classical Western Guizhou and Eastern Yunnan sections in an effort to expand the stratigraphy and paleontology from these earlier studies.

  17. Oceanic Anoxia and the End Permian Mass Extinction

    PubMed

    Wignall; Twitchett

    1996-05-24

    Data on rocks from Spitsbergen and the equatorial sections of Italy and Slovenia indicate that the world's oceans became anoxic at both low and high paleolatitudes in the Late Permian. Such conditions may have been responsible for the mass extinction at this time. This event affected a wide range of shelf depths and extended into shallow water well above the storm wave base.

  18. From source-to-sink: The Late Permian SW Gondwana paleogeography and sedimentary dispersion unraveled by a multi-proxy analysis

    NASA Astrophysics Data System (ADS)

    Alessandretti, Luciano; Machado, Rômulo; Warren, Lucas Veríssimo; Assine, Mario Luis; Lana, Cristiano

    2016-10-01

    The Late Permian sedimentary succession of the Paraná Basin, southern Brazil, provide a valuable source of information about sediment provenance, tectonic processes and, consequently, the paleogeography of the southwestern Gondwana supercontinent. In order to understand the patterns of sedimentary dispersal and reconstruct the Late Permian source-to-sink dynamic, we report a complete series of U-Pb ages and Hf isotopic compositions of detrital zircons from the Rio do Rasto Formation sandstones allied with detailed paleocurrent and sedimentologic data. Our integrated provenance study reveals a consistent sediment transport from the south to the north and northwest. According to the evaluation of zircon ages and Hf isotopes, it was possible to determine four distinct source areas: (i) a distant Late Paleozoic active magmatic arc located in the southwestern Gondwana margin (i.e. Gondwanides Orogen), corresponding to the North Patagonian Massif; (ii) recycling of orthoquartzites from the uplifted Paleozoic Ventania Fold Belt and immature sandstones from the Claromecó Foreland Basin in central-eastern Argentina and the Silurian-Devonian successions of the southern Paraná Basin (central-northern Uruguay) and North Patagonian Massif; (iii) exhumed areas of the Archean-Paleoproterozoic basement and Neoproterozoic to Early Paleozoic mobile belts of the Damara in southwestern Africa and Ribeira Fold Belt in Uruguay and southern Brazil; and (iv) southeastward provenance of Grenvillian (1.2-1.0 Ga) zircons coming from the mafic to intermediate Mesoproterozoic igneous units of the Namaqua-Natal Belt in South Africa and Namibia. These data allow us to argue that sediments deposited in the Paraná Basin during the Late Permian come from both short- and long-distance source areas. In this context, an important population of Permian detrital zircons comes from the Gondwanides Orogen in the south, probably carried by transcontinental alluvial systems. Close to the source area

  19. Exhumation by gravitational sliding up an inclined plane

    NASA Astrophysics Data System (ADS)

    Podladchikov, Yury; Schmalholz, Stefan; Burg, Jean-Pierre

    2015-04-01

    Gravity causes sliding down an inclined plane if pressure is near lithostatic. If metamorphic pressures are lithostatic pressures, the approximation is inconsistent with pressure-temperature exhumation histories of thrust nappes stacked during compression to form the thickened crust of mountain belts. Overthickened mountain roots and foreland basin-type sedimentation accompanying the downward movement component of the Moho require significant non-lithostatic pressure perturbations within the mountain belts. Relaxation of the subsequent pressure gradients can be achieved by nappe-like thrusting up an inclined plane recording near isothermal decompression and carrying young sediments to high altitudes. We present results of fully dynamic numerical modelling documenting feasibility of this process. Neither thrusting, nor large weakness zones nor S-point-type boundary conditions are kinematically prescribed in our models. Thrusting emerges spontaneously as an instability, strain localization process that may follow preexisting lithological layering or thermal gradients and able to form new zones of weakness by shear heating mechanism. The non-prescribed nature of our modeled deformation modes makes them feasible, even probable as a leading response to continental shortening. In that case, non lithostatic pressure 'cycle' is an alternative or a complement to the classical Wilson cycle invoked alone to explain elevated occurrences of deep-water sediments.

  20. The Permian of Timor: stratigraphy, palaeontology and palaeogeography

    NASA Astrophysics Data System (ADS)

    Charlton, T. R.; Barber, A. J.; Harris, R. A.; Barkham, S. T.; Bird, P. R.; Archbold, N. W.; Morris, N. J.; Nicoll, R. S.; Owen, H. G.; Owens, R. M.; Sorauf, J. E.; Taylor, P. D.; Webster, G. D.; Whittaker, J. E.

    2002-08-01

    The Permian of Timor in the Lesser Sunda Islands has attracted the attention of palaeontologists since the middle of the nineteenth century because of the richness, diversity and excellent state of preservation of its fauna. These abundant fossil data have been compiled and updated for the present account. The Permian rocks of Timor were deposited on the northern margin of Australia. At the present time the northern margin of Australia, in the region of Timor, is involved in a continent-arc collision, where Australia is colliding with the Banda Arcs. As a result of this collision, Permian rocks of the Australian margin have been disrupted by folding and faulting with the generation of mud-matrix mélange, and uplifted to form part of the island of Timor. Due to this tectonic disruption, it has proved difficult to establish a reliable stratigraphy for the Permian units on Timor, especially as the classic fossil collections were obtained largely from the mélange or purchased from the local people, and do not have adequate stratigraphic control. Detailed systematic, structural, stratigraphic and sedimentological studies since the 1960s have provided a firmer stratigraphic and palaeogeographic background for reconsideration of the significance of the classic fossil collections. Permian rocks on Timor belong either to a volcanic-carbonate sequence (Maubisse Formation), or to a clastic sequence (Atahoc and Cribas formations) in which volcanics are less prominent. The Permian sequences were deposited on Australian continental basement which was undergoing extension with spasmodic volcanic activity. Carbonates of the Maubisse Formation were deposited on horst blocks and volcanic edifices, while clastic sediments of the Atahoc and Cribas formations were deposited in grabens. The clastic sediments are predominantly fine-grained, derived from a distant siliciclastic source, and are interbedded with sediments derived from the volcanics and carbonates of adjacent horst blocks

  1. Origin and structure of major orogen-scale exhumed strike-slip

    NASA Astrophysics Data System (ADS)

    Cao, Shuyun; Neubauer, Franz

    2016-04-01

    The formation of major exhumed strike-slip faults represents one of the most important dynamic processes affecting the evolution of the Earth's lithosphere and surface. Detailed models of the potential initiation and properties and architecture of orogen-scale exhumed strike-slip faults and how these relate to exhumation are rare. In this study, we deal with key properties controlling the development of major exhumed strike-slip fault systems, which are equivalent to the deep crustal sections of active across fault zones. We also propose two dominant processes for the initiation of orogen-scale exhumed strike-slip faults: (1) pluton-controlled and (2) metamorphic core complex-controlled strike-slip faults. In these tectonic settings, the initiation of faults occurs by rheological weakening along hot-to-cool contacts and guides the overall displacement and ultimate exhumation. These processes result in a specific thermal and structural architecture of such faults. These types of strike-slip dominated fault zones are often subparallel to mountain ranges and expose a wide variety of mylonitic, cataclastic and non-cohesive fault rocks, which were formed at different structural levels of the crust during various stages of faulting. The high variety of distinctive fault rocks is a potential evidence for recognition of these types of strike-slip faults. Exhumation of mylonitic rocks is, therefore, a common feature of such reverse oblique-slip strike-slip faults, implying major transtensive and/or transpressive processes accompanying pure strike-slip motion during exhumation. Some orogen-scale strike-slip faults nucleate and initiate along rheologically weak zones, e.g. at granite intrusions, zones of low-strength minerals, thermally weakened crust due to ascending fluids, and lateral borders of hot metamorphic core complexes. A further mechanism is the juxtaposition of mechanically strong mantle lithosphere to hot asthenosphere in continental transform faults (e.g., San

  2. River Antecedence and the Onset of Rapid Exhumation in the Eastern Himalayan Syntaxis

    NASA Astrophysics Data System (ADS)

    Lang, K. A.; Huntington, K. W.; Burmester, R. F.; Housen, B. A.

    2014-12-01

    The peripheral Himalayan foreland basin preserves a rich archive of Himalayan landscape dynamics. In particular, high-resolution geochronology and thermochronology of sedimentary units provides unique perspectives on the evolution of river drainage patterns and source exhumation rates when conventional bedrock applications may be limited. A case example is the rapid exhumation of the Namche Barwa metamorphic massif within the eastern Himalayan syntaxis. Here, thermo-mechanical feedbacks between erosion by the Yarlung River and uplift of a crustal-scale antiform may have locally sustained exhumation rates as high as 10 km/Ma through the Plio-Quaternary. However, the origins of these feedbacks remain difficult to constrain from the extremely young (<4 Ma) cooling histories observed in bedrock samples. To extend the record of landscape evolution, we quantify the depositional age, provenance and cooling histories of detrital minerals from Neogene sedimentary units proximal to the eastern syntaxis. Specifically, we combine magnetostratigraphy, detrital muscovite 40Ar/39Ar thermochronology, zircon fission track thermochronology and U-Pb geochronology to test the hypothesis that the development of a thermo-mechanical feedback is related to capture of the Yarlung River by a Himalayan tributary to the Brahmaputra River. Thermal modeling of thermochronologic lag-times indicates that extremely rapid exhumation rates (5-10 km/Myr) have persisted in the syntaxis since 5 Ma, following a dramatic rate increase in the Late Miocene. However, the presence of Gangdese-age zircons in older sedimentary units requires connection of the Yarlung and Brahmaputra Rivers by at least 11 Ma, predating the onset of rapid exhumation. These results suggest that capture of the Yarlung River was not a potential mechanism to initiate rapid exhumation of the Namche Barwa massif. Instead, we propose that Late Miocene tectonic uplift locally steepened the antecedent river channel, increasing rock

  3. Into the subduction plate interface: insights from exhumed terranes (Invited)

    NASA Astrophysics Data System (ADS)

    Agard, P.; Angiboust, S.; Plunder, A.

    2013-12-01

    In order to place constraints on the still elusive lithological and physical nature of the subduction plate interface, we herein present critical petrological (and modelling) data from intermediate depths along the subduction interface. Their implications, ranging from long-term underplating and exhumation to short-lived seismic events, are confronted with the recent wealth of geophysical/chemical data from the literature. Emphasis is placed on findings from two major localities showing deeply subducted ophiolitic remnants (Zermatt-Saas, Monviso), which crop out in the classic, well-preserved fossil subduction setting of the Western Alps. Both ophiolite remnants in fact represent large, relatively continuous fragments of oceanic lithosphere (i.e., several km-thick tectonic slices across tens of km) exhumed from ~80 km depths and thereby provide important constraints on interplate coupling mechanisms. We show that pervasive hydrothermal processes and seafloor alteration promoting fluid incorporation in both mafic and associated ultramafic rocks was essential, together with the presence of km-thick serpentinite soles, to decrease the density of the tectonic slices and prevent them from an irreversible sinking into the mantle. The Monviso case sudy (particularly the Lago Superiore Unit) provides further insights on both seismicity and fluid flow along the subduction plate interface at ~80 km depths: (1) Eclogite breccias, reported here for the first time, mark the locus of an ancient fault zone associated with intraslab, intermediate-depth earthquakes at ~80 km depth. They correspond to m-sized blocks made of 1-10 cm large fragments of eclogite mylonite later embedded in serpentinite in a ~100m thick eclogite facies shear zone. We suggest that seismic brecciation (possibly at magnitudes Mw ~4) occurred in the middle part of the oceanic crust, accompanied by the input of externally-derived fluids. (2) Prominent fluid-rock interactions, as attested by ubiquitous

  4. Isotopic age constraints on provenance of exotic terranes, latest Permian collision and fast Late Triassic post-collisional cooling and tectonic exhumation of the Korean collision belt

    NASA Astrophysics Data System (ADS)

    de Jong, Koenraad; Han, Seokyoung; Ruffet, Gilles; Yi, Keewook

    2016-04-01

    The Korean peninsula is located in the eastern margin of the Eurasian continent where major late Palaeozoic to early Mesozoic continental collision zones, like the Central Asian Orogenic Belt and the Central China Orogen, merge with circum-Pacific subduction-accretion systems. We present an integrated view of the Korean collision belt using recent Ar/Ar laser-probe step-heating single grain ages from the uppermost Gyeonggi Massif, central Korea's Palaeoproterozoic high-grade granite-gneiss terrane affected by Permo-Triassic metamorphism, the bordering Hongseong zone and the overlying Imjingang belt and the correlative Taean Formation, as well as SHRIMP isotopic ages of detrital zircons from meta-sandstones from the latter metamorphic marine turbidite sequences. We show that early Paleozoic isolated exotic terranes form part of the collision belt and were reworked in Permo-Triassic time. Age spectra of zircons from mature meta-sandstones in the Misan Formation (Imjingang Belt) and Taean Formation do not match the age distribution of the Gyeonggi Massif, to which both are usually assigned, as they show only subordinate 1.9-1.8 Ga and ~2.5 Ga age modes but dominant 441-426 Ma and 978-919 Ma peaks. Much of the sediment appears to have been derived from distant, exotic middle Paleozoic and Early Neoproterozoic magmatic sources, not present in Gyeonggi or other Korean basement massifs. The youngest concordant zircon ages are: 394, 398 and 402 Ma, showing that both formations are at least of Early Devonian age. Terranes with a substratum with Early Neoproterozoic and Silurian-Devonian granitoids are present in the South Chinese Cathaysia Terrane and in the Qinling Terrane (Central China Orogen). Both formations may, hence, represent the submarine fan part of a routing system and a delta-shelf system originally situated in China. The Taean Formation and Imjingang Belt are thus exotic Paleozoic terranes tectonically emplaced in the Korean collision belt. Muscovite, biotite and amphibole from different units of the Imjingang Belt yielded tightly clustered Ar/Ar plateau ages between 255±1 and 249±1 Ma, dating fast cooling after peak temperature conditions. Slightly younger 243±1 and 240±1 Ma muscovite plateau ages in strongly retrogressed mylonites in the top of the Gyeonggi Massif and 241-237 Ma age components (Taean Formation) point to collisional tectonism. Concordant 233-229 Ma isotopic ages of titanite, hornblende and mica in Hongseong zone and Taean Formation, and detrital muscovite in Jurassic Gimpo sandstones reveal a regional thermal event affecting large portions of the peninsula's crust, also manifested in widespread 237-226 Ma mantle-sourced Mg-rich potassic magmatism and associated mafic dykes truncating folds and tectonic foliations. The Late Triassic thermal pulse implies rapid advective-conductive asthenospheric heat transport promoted by extension and magmatic underplating during post- or late-collisional lower crust and uppermost mantle delamination and/or oceanic slab break-off. The efficiency of cooling is underlined by identical biotite (228±1 Ma) and hornblende (230±1 Ma) plateau ages in Hongseong amphibolites that are partly concordant with 243-229 Ma (average: ˜235 Ma) U-Pb zircon ages in the Gyeonggi Massif and the Hongseong zone, in the literature. This indicates that the Gyeonggi Massif is a Late Triassic core complex.

  5. Concept of the exhumed partial annealing (retention) zone in thermochronology: An appraisal

    NASA Astrophysics Data System (ADS)

    Fitzgerald, P. G.

    2013-12-01

    The concept of an exhumed partial annealing zone (PAZ) in fission track (FT) thermochronology has been a widely used and successful interpretative tool since the 1980s. This 1D-interpretative approach is typically applied to samples collected over significant relief, with best results if the sampling is undertaken in steep short-wavelength topography and samples collected parallel to topography (perpendicular to curved isotherms), and for samples following a vertical exhumation path. While annealing of fission tracks occurs even at low ambient temperatures the PAZ is defined as the zone between where tracks are annealed 'geologically' instantaneously and where the rate of annealing slows dramatically; between ~60 and ~110°C for tracks in apatite depending on composition. The shape and average slope of a PAZ varies depending on the paleogeothermal gradient and its stability, and the length of time over which a PAZ forms. PAZs and partial retention zones (PRZ) are now known for different minerals for various techniques. Single grain age dispersion can be significantly magnified in a PAZ/PRZ depending on composition, grain size, [eU], radiation damage and zoning for the FT and (U-Th)/He methods. An exhumed PAZ/PRZ may be revealed in an age-elevation ('vertical') profile when, following a period of uplift/exhumation, the form of the PAZ/PRZ is retained with a 'sharp' convex inflexion (the 'break in slope') marking the base of the exhumed PAZ/PRZ with reset samples structurally beneath. The break in slope represents a minimal age for the transition from 'relative thermal stability' to rapid cooling, as the rock column has to cool through the PAZ/PRZ, with the underestimate greater if the change in cooling rate is not significant. The base of an exhumed PAZ/PRZ is a curve, but we approximate it with straight lines, with less precision with fewer samples. The break in slope may not be distinguishable if the cooling/exhumation was long ago and/or of low magnitude. The

  6. A Climatic Trigger for Enhanced Late Cenozoic Exhumation of the Chinese Pamir?

    NASA Astrophysics Data System (ADS)

    Sobel, E. R.; Thiede, R.; Schoenbohm, L.; Chen, J.

    2007-12-01

    In the Chinese Pamir mountains at the western end of the Tibetan Plateau, two high peaks (Kongur Shan at 7719 m and Muztagh Ata at 7546 m), rise >4000 m above the plateau, representing an area of significant anomalous topography. These mountains are situated below the Kongur detachment, correspond with domal structures cored by gneisses exhumed since 6-8 Ma from up to 27 km depth (Robinson et al., GSAB, 2004). Exhumation of these domal structures is undoubtedly related to movement along the Kongur detachment fault. However, the locally more rapid exhumation rates in the area of these two domes, their association with extensive glaciers with headwalls up to 2 km high, and with deeply incised river gorges immediately to the north and south of the massifs point to additional exhumation of the domes driven by positive feedback between focused fluvial and glacial erosion and thermal and mechanical weakening of the crust. It is possible that glaciation is a passive result of tectonic exhumation, in which tectonically produced high peaks lead to greater orographic precipitation, resulting in the development of larger glaciers, or that the peaks are the location of a "tectonic aneurysm," driven to greater exhumation and height by focused glacial erosion. New apatite fission track (AFT) and argon data from both the footwall and hanging wall along the length of the detachment provide a more detailed view of the latest Cenozoic cooling history. In the north, along the Muji segment, and in the middle, near Kongur Shan, hanging wall AFT ages are 4-6 Ma. Footwall AFT ages in the Muji segment and in the south, along the upper Yarkand river are ca. 3 Ma. However, the footwall of the western flank of Kongur Shan yields AFT ages between 1 and 2 Ma, very similar to our own and published argon ages on biotite and muscovite, the oldest of which is 2.5 Ma (muscovite). Published argon MDD modeling of three feldspars from the northern flank of Kongur Shan show a significant increase in

  7. Tectonics and surface processes interactions in exhumation history of South Alaska: insights from the thermochronological record

    NASA Astrophysics Data System (ADS)

    Valla, Pierre G.; Champagnac, Jean-Daniel; Shuster, David L.; Herman, Frederic; Giuditta Fellin, Maria

    2014-05-01

    The southern Alaska range presents an ideal setting to study complex interactions between tectonics, climate and surface processes in landscape evolution. It exhibits active tectonics with the ongoing of subduction/collision between Pacific and North America, and major active seismogenic reverse and strike-slip faults. The alpine landscape, rugged topography and the important present-day ice-coverage reveal a strong glacial imprint associated with high erosion and sediment transport rates. Therefore, the relative importance of glacial erosion and tectonics for the observed late-exhumation history appears to be quite complex to decipher. This problem partly arises from the fact that most studies have been focused on the southern coast of Alaska where both glacial erosion and tectonic processes are both very active and act together in driving high exhumation rates. Here, we first perform a formal inversion of an extensive bedrock thermochronological dataset collected in southern Alaska over the last decades to quantify the large-scale 20-Myr exhumation history. Our results confirm high exhumation rates in the St Elias "syntaxis" and frontal fold and thrust belts for the last 0-2 Myr, where major ice fields and high precipitation rates likely promoted high erosion rates. It also highlights localized exhumation in the last 4-6 Myr along major tectonic features such like the Fairweather and Border Ranges faults. Large-scale inverse modeling therefore suggests that the late-stage exhumation history of South Alaska has mainly been driven by tectonic processes; the impact of late Cenozoic glaciations impact being less visible there than in less active mountain ranges such as the European Alps, British Columbia or Patagonia. To overcome this potential bias in resolving the glacial impact on erosion history, we studied to the Granite Range (Wrangell-St Elias National Park, Alaska), an area presenting a strong glacial imprint but minor tectonic activity with only localized

  8. Style of exhumation and rheological evolution of a Mediterranean subduction complex

    NASA Astrophysics Data System (ADS)

    Behr, W. M.; Platt, J. P.

    2012-04-01

    We examine the style of exhumation and rheological evolution of a subduction complex forming part of the Betic Cordillera in the Western Mediterranean. Rocks within the Nevado-Filabride complex (NFC) were subducted and exhumed to the surface within ~10 m.y. in the Miocene. Ti-in-quartz thermobarometry, Raman spectroscopy on graphite, and chlorite thermometry indicate that the exhumation path of the NFC was close to linear, reaching peak T and P of 550 ± 50°C and 15 ± 3 kbar. Two-dimensional thermal modeling allows us to fit this P-T-t path using exhumation rate and exhumation geometry as free parameters. We find that the P-T-t path is best fit by a model in which the rocks are subducted to > 50 km depth, exhumed rapidly along the same trajectory within a subduction channel, then captured by a low angle detachment fault cutting through the overlying crust. This model can be reconciled with the thermal history preserved in the overlying plate and is supported by the kinematics recorded in high strain fabrics within the NFC itself. We also link the exhumation history of the NFC subduction channel to the rheology of quartz-rich rocks within it by tracking changes in deformation mechanism, stress, strain rate, water content, and crystallographic preferred orientation (CPO) over time. Increasing localization during cooling allowed earlier microstructures to be preserved, such that the rocks record several stages in their exhumation history. Early deformation during initial subduction was accommodated by pressure solution under low-stress (<6 MPa), low-strain-rate, variable T conditions, and produced an inverted metamorphic gradient within the NFC. At the early stages of exhumation, the deformation mechanism at the top of the channel switched to dislocation creep at stresses of ~6-20 MPa, strain rates of < 5E-13/s and temperatures of 500-550°C. Both stress and strain rate increased with decreasing T in the channel margin, culminating in stresses of ~180 MPa, strain

  9. Style of exhumation and rheological evolution of a Mediterranean subduction complex

    NASA Astrophysics Data System (ADS)

    Platt, J. P.; Behr, W. M.

    2011-12-01

    We examine the style of exhumation and rheological evolution of a subduction complex forming part of the Betic Cordillera in the Western Mediterranean. Rocks within the Nevado-Filabride complex (NFC) were subducted and exhumed to the surface within ~10 m.y. in the Miocene. Ti-in-quartz thermobarometry, Raman spectroscopy on graphite, and chlorite thermometry indicate that the exhumation path of the NFC was close to linear, reaching peak T and P of 550 ± 50°C and 15 ± 3 kbar. Two-dimensional thermal modeling allows us to fit this P-T-t path using exhumation rate and exhumation geometry as free parameters. We find that the P-T-t path is best fit by a model in which the rocks are subducted to > 50 km depth, exhumed rapidly along the same trajectory within a subduction channel, then captured by a low angle detachment fault cutting through the overlying crust. This model can be reconciled with the thermal history preserved in the overlying plate and is supported by the kinematics recorded in high strain fabrics within the NFC itself. We also link the exhumation history of the NFC subduction channel to the rheology of quartz-rich rocks within it by tracking changes in deformation mechanism, stress, strain rate, water content, and crystallographic preferred orientation (CPO) over time. Increasing localization during cooling allowed earlier microstructures to be preserved, such that the rocks record several stages in their exhumation history. Early deformation during initial subduction was accommodated by pressure solution under low-stress (<6 MPa), low-strain-rate, variable T conditions, and produced an inverted metamorphic gradient within the NFC. At the early stages of exhumation, the deformation mechanism at the top of the channel switched to dislocation creep at stresses of ~6-20 MPa, strain rates of < 5E-13/s and temperatures of 500-550°C. Both stress and strain rate increased with decreasing T in the channel margin, culminating in stresses of ~180 MPa, strain

  10. Quantitative thermochronology and interpretation of exhumation in the central Nepalese Himalaya

    NASA Astrophysics Data System (ADS)

    Whipp, David Michael, Jr.

    Quantifying erosional and tectonic processes that exhume rock in convergent orogens is an essential step toward understanding connections between climate and tectonics. This work utilizes 3-D numerical models to address the sensitivity of thermochronometer data to tectonic and surface processes and quantify exhumation rates from the Nepalese Himalaya. General results show that low-temperature thermochronometers, such as apatite (U-Th)/He (AHe) and fission-track (AFT) are strongly affected by variations in denudation rate, but are less sensitive to different faulting scenarios. Higher temperature thermochronometers, such as zircon fission-track (ZFT) and muscovite 40Ar/39Ar, have much greater sensitivity to faulting history. Surface processes significantly affect detrital thermochronometers across a range of effective closure temperatures, with bedrock landslides showing a substantial impact on age distributions, particularly for short landslide sediment residence times (˜1 year). For both bedrock and detrital thermochronometers in rapidly eroding regions, little sensitivity to rock thermophysical properties, basal temperature/heat flux or topographic evolution is observed. The impact of these processes is important because they affect the calculation of exhumation rates from both bedrock and detrital thermochronometer data. Compared to exhumation rate estimates that assume a 1-D thermal field from bedrock AFT data (-2.6-12 2 mm/y), the range of model-predicted exhumation rates is >200% smaller (1.8-5.0 mm/y). Low-temperature (AHe) detrital thermochronometers show potential for large (>300%) overestimates of exhumation rates when using 1-D data interpretation techniques. At higher temperatures (e.g., MAr), the overestimation decreases to ˜90%. The flow of groundwater is also an important influence on exhumation rate calculations, with AFT data showing potential for underestimation of true exhumation rates by >200% in regions with high groundwater flow rates

  11. Sub-horizontal channel flow: an exhumation mechanism during the Gondwana collision

    NASA Astrophysics Data System (ADS)

    Abu-Alam, Tamer; Stüwe, kurt

    2013-04-01

    The Arabian-Nubian Shield is made up of juvenile crust which was formed due to arc-arc accretion during the East- and West-Gondwana collision (Pan-African event) and the closing of the Mozambique Ocean. Thus the shield is composed of ophiolitic and volcanic material with oceanic affinity. However rocks with continental affinity can be found as high grade metamorphic complexes that were exposed from underneath the arc-related rocks during the late stages of the Pan-African event. Two tectonic models explain the exhumation mechanism of these metamorphic complexes. The first model is exhumation as core complexes in extension setting. This model appears to pertain to the metamorphic complexes of the Eastern Desert of Egypt. The second model is exhumation in oblique transpressional regime as it was found - for example - for the Feiran-Solaf complex of Sinai Peninsula. These models are correct with regard to the structural elements in the outer zones of the metamorphic complexes, which formed during the final exhumation mechanism during the later stages of the deformation history (e.g. D3 of the Feiran complex). However the models cannot explain the sub-horizontal lineations that formed during the early deformation phases and are still recorded in the core of the metamorphic complexes (e.g. D1 of the Feiran-Solaf complex). Here we propose sub-horizontal channel flow as a mechanism to exhume the metamorphic complexes and a mechanism that can account for both types of structural elements as part of one exhumation history. We suggest that the rocks flowed horizontally at mid-crustal levels to the NW of the Arabian-Nubian Shield. The front of the channel flows was then exhumed to the Earth surface in a transpression regime. This middle crustal flow will produce extensional tectonic regime in the upper crust (i.e. ?3 is horizontal and oriented in the NW-SE direction). This extensional setting produces low-angle detachments which assisted the middle crustal rocks to be exhumed

  12. Variable exhumation rates and variable displacement rates: Documenting recent slowing of Himalayan shortening in western Bhutan

    USGS Publications Warehouse

    McQuarrie, Nadine; Tobgay, Tobgay; Long, Sean P.; Reiners, Peter W.; Cosca, Michael A.

    2014-01-01

    We link exhumational variability in space and time to the evolving geometry of the Himalayan fold–thrust belt in western Bhutan. By combining new and published geochronologic and thermochronologic data we document the burial age, peak temperatures and complete cooling history from 20 Ma to the present over an across-strike distance of ∼125 km. These integrated cooling curves highlight windows of fast exhumation that vary spatially and temporally. We propose that pulses of fast exhumation are a result of structures that facilitate the vertical motion of material, illustrated in sequentially-restored cross sections. Due to a range of permissible geometries at depth, we explore and evaluate the impact of geometry on kinematics and rates of deformation. The linked cooling history and cross sections provide estimates of both magnitude and timing of thrust sheet displacement and highlight temporal variability in potential shortening rates. Structural and chronologic data illustrate a general north to south progression of Himalayan deformation, with emplacement of the Main Central thrust (MCT), Paro thrust and Shumar thrust by 12 to no later than 9 Ma. Two different geometries and kinematic scenarios for the Lesser Himalayan duplex are proposed. A north to south propagating duplex system requires that the southern portion of that system, south of the MCT, deformed and cooled by 9 Ma, leaving only the southernmost thrust sheets, including the Main Boundary and Main Frontal thrusts, to deform between 9 and 0 Ma. This limited post 9 Ma shortening would necessitate a marked slowdown in convergence accommodated on the Main Himalayan thrust. A two-tiered duplex system, which allows for the Paro window duplex and the southern Baxa duplex to form simultaneously, permits duplex formation and accompanying exhumation until 6 Ma. Limited cooling from ∼200 °C to the surface post 6 Ma suggests either a decrease in shortening rates from 6 to 0 Ma or that duplex formation and

  13. Palynostratigraphy of Permian succession in the Mand-Raigarh Coalfield, Chhattisgarh, India and phytogeographical provincialism

    NASA Astrophysics Data System (ADS)

    Murthy, Srikanta; Ram-Awatar; Gautam, Saurabh

    2014-12-01

    Palynofloras have been recorded from the Barakar Formation in the Borehole MBKW-3, Barpali-Karmitikra Block, Mand-Raigarh Coalfield, Chhattisgarh. Three distinct palynoassemblages have been identified and referred to the following palynoassemblage zones - Gondisporites raniganjensis (Latest Permian); Faunipollenites varius (latest Early Permian), and Scheuringipollenites barakarensis (late Early Permian). It is inferred that these deposits contain the representative palynoassamblages of Early to Late Permian in age. The First Appearance Datum (FAD)s of Arcuatipollenites pellucidus, A. ovatus, Guttulapollenites hannonicus, Lundbladispora microconata, Alisporites opii, Klausipollenites sp., and Goubinispora indica (at 41.95, 45.90, 98.35 m depth), indicate the closing phase of Permian, as these elements are the key species that mark a transition from Permian to the Lower Triassic. An attempt has been made here to reconstruct the phytogeographical provincialism on the basis of Guttulapollenites recorded in this basin.

  14. Direct observation of strain localization along the differentially exhumed SEMP fault system, Austria

    NASA Astrophysics Data System (ADS)

    Frost, E.; Dolan, J. F.; Hacker, B. R.; Ratschbacher, L.; Sammis, C. G.; Seward, G.; Cole, J.

    2009-12-01

    Structural analysis of key outcrops from ~5 to ~25 km exhumation depth along the Salzach-Ennstal-Mariazell-Puchberg (SEMP) fault-zone in Austria reveal highly localized deformation in the seismogenic crust down through the brittle-ductile transition (BDT), widening into a 2-km-wide mylonite at mid-crustal levels. Specifically, grain-size distribution analysis of brittley-deformed dolomite exhumed from the seismogenic crust reveals that strain progressively localized into a 10-m-wide fault core. Microstructural analysis of marbles and greywackes exhumed from the BDT shows off-fault ductile deformation only accommodated a minor portion of the displacement along the SEMP, with most of the strain localized along the contact between these two units. Similar analysis of gneisses and amphibolite-facies metasediments exhumed from just below the BDT shows that at this depth, the majority of displacement is focused into a 100-m-wide ductile shear zone, with further evidence for strain localization along grain boundaries, creating throughgoing shear zones at the grain-scale. At deeper exhumation levels (Rosenberg and Schneider, 2008), the SEMP is a 1-2-km-wide mylonite zone that extends to depths of at least 25 km. Collectively, these data indicate that slip along the SEMP was highly localized from throughout the seismogenic crust downward into at least the mid-crust.

  15. Time and mode of exhumation of the Cordillera Blanca batholith (Peruvian Andes)

    NASA Astrophysics Data System (ADS)

    Margirier, Audrey; Audin, Laurence; Robert, Xavier; Herman, Frédéric; Ganne, Jérôme; Schwartz, Stéphane

    2016-08-01

    The Cordillera Blanca batholith (12-5 Myr) forms the highest Peruvian summits and builds the footwall of the Cordillera Blanca normal fault (CBNF). Even if several models have been proposed, the processes driving both the exhumation of the Cordillera Blanca and extensional deformation along the CBNF are still debated. Here we quantify the emplacement depth and exhumation of the batholith of the northern Peru arc from the late Miocene to present. Based on a compilation of crystallization ages and new thermobarometry data in the Cordillera Blanca batholith, we propose that the batholith was emplaced at a depth of ~3 km in successive sills from 14 to 5 Ma. By contrast, the younger rocks exposed at the surface were emplaced the deepest (i.e., ~6 km) and are located close to the CBNF, suggesting post 5 Ma tilting. Furthermore, a formal inversion of the thermochronologic data indicates an increase of the exhumation rates in the Cordillera Blanca during the Quaternary. The higher predicted exhumation rates correlate with areas of high relief, both in the northern and central part of the Cordillera Blanca, suggesting that Quaternary valley carving by glaciations have a significant impact on the latest stage of the Cordillera Blanca exhumation (2-0 Ma).

  16. Environmental mutagenesis during the end-Permian ecological crisis.

    PubMed

    Visscher, Henk; Looy, Cindy V; Collinson, Margaret E; Brinkhuis, Henk; van Konijnenburg-van Cittert, Johanna H A; Kürschner, Wolfram M; Sephton, Mark A

    2004-08-31

    During the end-Permian ecological crisis, terrestrial ecosystems experienced preferential dieback of woody vegetation. Across the world, surviving herbaceous lycopsids played a pioneering role in repopulating deforested terrain. We document that the microspores of these lycopsids were regularly released in unseparated tetrads indicative of failure to complete the normal process of spore development. Although involvement of mutation has long been hinted at or proposed in theory, this finding provides concrete evidence for chronic environmental mutagenesis at the time of global ecological crisis. Prolonged exposure to enhanced UV radiation could account satisfactorily for a worldwide increase in land plant mutation. At the end of the Permian, a period of raised UV stress may have been the consequence of severe disruption of the stratospheric ozone balance by excessive emission of hydrothermal organohalogens in the vast area of Siberian Traps volcanism. Copyright 2004 The National Academy of Sciencs of the USA

  17. Environmental mutagenesis during the end-Permian ecological crisis

    PubMed Central

    Visscher, Henk; Looy, Cindy V.; Collinson, Margaret E.; Brinkhuis, Henk; van Konijnenburg-van Cittert, Johanna H. A.; Kürschner, Wolfram M.; Sephton, Mark A.

    2004-01-01

    During the end-Permian ecological crisis, terrestrial ecosystems experienced preferential dieback of woody vegetation. Across the world, surviving herbaceous lycopsids played a pioneering role in repopulating deforested terrain. We document that the microspores of these lycopsids were regularly released in unseparated tetrads indicative of failure to complete the normal process of spore development. Although involvement of mutation has long been hinted at or proposed in theory, this finding provides concrete evidence for chronic environmental mutagenesis at the time of global ecological crisis. Prolonged exposure to enhanced UV radiation could account satisfactorily for a worldwide increase in land plant mutation. At the end of the Permian, a period of raised UV stress may have been the consequence of severe disruption of the stratospheric ozone balance by excessive emission of hydrothermal organohalogens in the vast area of Siberian Traps volcanism. PMID:15282373

  18. Insect mimicry of plants dates back to the Permian

    NASA Astrophysics Data System (ADS)

    Garrouste, Romain; Hugel, Sylvain; Jacquelin, Lauriane; Rostan, Pierre; Steyer, J.-Sébastien; Desutter-Grandcolas, Laure; Nel, André

    2016-12-01

    In response to predation pressure, some insects have developed spectacular plant mimicry strategies (homomorphy), involving important changes in their morphology. The fossil record of plant mimicry provides clues to the importance of predation pressure in the deep past. Surprisingly, to date, the oldest confirmed records of insect leaf mimicry are Mesozoic. Here we document a crucial step in the story of adaptive responses to predation by describing a leaf-mimicking katydid from the Middle Permian. Our morphometric analysis demonstrates that leaf-mimicking wings of katydids can be morphologically characterized in a non-arbitrary manner and shows that the new genus and species Permotettigonia gallica developed a mimicking pattern of forewings very similar to those of the modern leaf-like katydids. Our finding suggests that predation pressure was already high enough during the Permian to favour investment in leaf mimicry.

  19. Insect mimicry of plants dates back to the Permian

    PubMed Central

    Garrouste, Romain; Hugel, Sylvain; Jacquelin, Lauriane; Rostan, Pierre; Steyer, J.-Sébastien; Desutter-Grandcolas, Laure; Nel, André

    2016-01-01

    In response to predation pressure, some insects have developed spectacular plant mimicry strategies (homomorphy), involving important changes in their morphology. The fossil record of plant mimicry provides clues to the importance of predation pressure in the deep past. Surprisingly, to date, the oldest confirmed records of insect leaf mimicry are Mesozoic. Here we document a crucial step in the story of adaptive responses to predation by describing a leaf-mimicking katydid from the Middle Permian. Our morphometric analysis demonstrates that leaf-mimicking wings of katydids can be morphologically characterized in a non-arbitrary manner and shows that the new genus and species Permotettigonia gallica developed a mimicking pattern of forewings very similar to those of the modern leaf-like katydids. Our finding suggests that predation pressure was already high enough during the Permian to favour investment in leaf mimicry. PMID:27996977

  20. Abrupt and gradual extinction among Late Permian land vertebrates in the Karoo basin, South Africa.

    PubMed

    Ward, Peter D; Botha, Jennifer; Buick, Roger; De Kock, Michiel O; Erwin, Douglas H; Garrison, Geoffrey H; Kirschvink, Joseph L; Smith, Roger

    2005-02-04

    The Karoo basin of South Africa exposes a succession of Upper Permian to Lower Triassic terrestrial strata containing abundant terrestrial vertebrate fossils. Paleomagnetic/magnetostratigraphic and carbon-isotope data allow sections to be correlated across the basin. With this stratigraphy, the vertebrate fossil data show a gradual extinction in the Upper Permian punctuated by an enhanced extinction pulse at the Permian-Triassic boundary interval, particularly among the dicynodont therapsids, coinciding with negative carbon-isotope anomalies.

  1. Petrified peat from a permian coal bed in Antarctica

    USGS Publications Warehouse

    Schopf, J.M.

    1970-01-01

    Petrified plant remains that composed a Permian peat deposit occur at a coal horizon in a local area of Mount Augusta near the Beardmore Glacier in Antarctica. This discovery is the first in the entire Gondwana area that yields plant materials as exquisitely preserved as the materials of the well-known coal-ball localities of the Northern Hemisphere. A sampling of anatomical details is illustrated.

  2. Mixed permian-triassic fauna, guryul ravine, kashmir.

    PubMed

    Teichert, C; Kummnel, B; Kapoor, H M

    1970-01-09

    At Guryul Ravine near Srinagar, Kashmir, a varied fauna of productid brachiopods, including Spinomarginifera, is associated in approximately 15 feet (about 4 meters) of strata with the typical Scythian (Lower Triassic) pelecypod Claraia. These faunas are interpreted as true associations of surviving "Permian" and Lower Triassic faunal elements. Similar mixed associations have previously been identified in the lowest Triassic strata of the Salt Range and Surghar Range of West Pakistan.

  3. The Alps 2: Controls on crustal subduction and (ultra)high-pressure rock exhumation in Alpine-type orogens

    NASA Astrophysics Data System (ADS)

    Butler, Jared P.; Beaumont, Christopher; Jamieson, Rebecca A.

    2014-07-01

    Building on our previous results, we use 2-D upper mantle-scale thermomechanical numerical models to explore key controls on the evolution of Alpine-type orogens and the Alps per se, focusing on (ultra)high-pressure ((U)HP) metamorphic rocks. The models show that UHP rocks form and exhume by burial and subsequent buoyant ascent of continental crust in the subduction conduit. Here we test the sensitivity of the models to surface erosion rate, crustal heat production, plate convergence/divergence rates, geometry of the subducting continental margin, and strength of the retrocontinent. Surface erosion affects crustal exhumation but not early buoyant exhumation. Metamorphic temperatures increase with crustal radioactive heat production. Maximum burial depth prior to exhumation increases with plate convergence rates, but exhumation rates are only weakly dependent on subduction rates. Onset of absolute plate divergence does not trigger exhumation in these models. We conclude that contrasting peak pressures, exhumation rates, and volumes of (U)HP crust exhumed in the Alps orogen primarily reflect along-strike contrasts in the geometry, thermal structure, and/or strength of the subducting microcontinent (Briançonnais) and continental (European margin) crust. The experiments also support the interpretation that the Western Alps (U)HP Internal Crystalline Massifs exhumed as composite, stacked plumes and that these plumes drove local crustal extension during orogen-scale shortening. For weak upper plate retrocrusts, postexhumation retrothrusting forms a retrowedge. Overall, these results are consistent with predictions using the exhumation number (ratio of buoyancy to side traction forces in the conduit), which expresses the combined parameter control of the depth/volume of crustal subduction and the transition to buoyant exhumation.

  4. Exhumation History Of Brasilian Highlands After Late Cretaceous Alcaline Magmatism

    NASA Astrophysics Data System (ADS)

    Doranti Tiritan, Carolina; Hackspacher, Peter Christian; Carina Siqueira Ribeiro, Marli; Glasmacher, Ulrich Anton; Françoso de Godoy, Daniel

    2017-04-01

    The southeast Brazilian margin recorded a long history of tectonic and magmatic events after the Gondwana continent break up. The drifting of the South American Platform over a thermal anomaly generated a series of alkaline intrusions that are distributed from the interior to the coast from west to east. Several exhumation events are recorded on the region and we are providing insights on the landscape evolution of the region since Late Cretaceous, comparing low temperature thermochronology results from two alkaline intrusions regions. Poços de Caldas Alkaline Massif (PCAM), is lied in the interior, 300km from the coastline, covering over 800km2 intruding the Precambrian basement around 83Ma, nepheline syenites, phonolites and tinguaites intruded in a continuous and rapid sequence lasting between 1 to 2 Ma. São Sebastião Island (SSI) on the other hand is located at the coast, 200 km southeast of São Paulo. It is characterized by an intrusion in Precambrian/Brazilian orogen and intruded by Early Cretaceous sub-alkaline basic and acid dykes, as well as by Late Cretaceous alkaline stocks (syenites) and dykes (basanite to phonolite). Will be presenting the apatite fission track (AFT) and (U-Th)/He results that shows the main difference between the areas is that PCAM region register older history then the coastal area of SSI, where thermal history starts register cooling event after the South Atlantic rifting process, while in the PCAM area register a previous history, since Carboniferous. The results are giving support to studies that indicate the development of the relief in Brazil being strongly influenced by the local and regional tectonic movements and the lithological and structural settings. The landscape at the Late Cretaceous was witness of heating process between 90 and 60Ma due the intense uplift of South American Platform. The elevation of the isotherms is associated with the mantellic plumes and the crustal thickness that caused thermal anomalies due

  5. Mechanisms of mantle exhumation at oceanic core complexes

    NASA Astrophysics Data System (ADS)

    MacLeod, C. J.; Escartin, J.; Dick, H. J. B.; Allerton, S.

    2003-04-01

    Mantle rocks are exposed on the seafloor at many slow-spreading mid-ocean ridges as well as at the ocean-continent transitions of rifted continental margins. Similarities in morphology are evident in the two environments and it is likely that the mechanisms that give rise to exhumation of the mantle are comparable to some degree. We review the processes of deformation and magmatism in two contrasting modern oceanic core complexes and compare it with observations from the Lizard Complex (SW England), which is variously interpreted either as an ancient fragment of slow-spread ocean lithosphere or as a piece of lithosphere from a rifted continental margin. Mantle and lower crustal rocks are exposed at Atlantis Bank, on the SW Indian Ridge, and on corrugated highs north of the Fifteen-Twenty fracture zone on the Mid-Atlantic Ridge. Wireline rock drilling has shown that these ‘oceanic core complex’ massifs are the footwalls of large detachment fault systems. Despite their general similarities the two examples exhibit very different mechanisms of strain localisation, and may represent end-members of a range of processes by which detachment faults may form. At Atlantis Bank widespread high-temperature crystal-plastic (and locally syn-magmatic) deformation of gabbros indicates that the detachment fault did not form and move only during amagmatic phases: instead, a continuous gabbro layer was being formed and accreting in the footwall at the same time as the detachment was active, implying that the 'hot' detachment rooted within or near an active magma chamber. In contrast, evidence for high-temperature deformation on the Fifteen-Twenty detachment fault is absent: fault rocks are instead composed of talc-chlorite-tremolite schists, indicating that deformation took place under greenschist facies conditions and suggesting that fluid circulation accompanied and assisted strain localisation. This 'cold' detachment fault must therefore have rooted and slipped in the shallow

  6. Looking Down a Plate Boundary - an Exhumed Fossil Subduction Channel

    NASA Astrophysics Data System (ADS)

    Bachmann, R.; Oncken, O.

    2005-12-01

    hydraulically fractured veins exhibiting chaotic mineralization. Additionally, a vast number of foliation parallel mineralized veins invade the matrix of the fossil subduction channel, pointing to transient changes in fluid pressure and stress system. The relationship of these coarse grained mineralized veins to seismic faulting has yet to be evaluated. They may mirror dehydration processes during prograde metamorphism within the subduction zone. Since the exposed ancient subduction channel has experienced flow and fracturing over several cycles (including some overprint during collision and exhumation) it still may bear resemblance to cumulative active margins that have been active over 10s of Myrs.

  7. Complex Burial and Exhumation of South Polar Cap Pitted Terrain

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This image is illuminated by sunlight from the upper left. The two prominent bright stripes at the left/center of the image are covered with bright frost and thus create the illusion that they are sunlit from the lower left.

    The large pits, troughs, and 'swiss cheese' of the south polar residual cap appear to have been formed in the upper 4 or 5 layers of the polar material. Each layer is approximately 2 meters (6.6 feet) thick. Some Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images of this terrain show examples in which older pitted and eroded layers have been previously buried and are now being exhumed. The example shown here includes two narrow, diagonal slopes that trend from upper left toward lower right at the left/center portion of the frame. Along the bottoms of these slopes are revealed a layer that underlies them in which there are many more pits and troughs than in the upper layer. It is likely in this case that the lower layer formed its pits and troughs before it was covered by the upper layer. This observation suggests that the troughs, pits, and 'swiss cheese' features of the south polar cap are very old and form over long time scales.

    The picture is located near 84.6oS, 45.1oW, and covers an area 3 km by 5 km (1.9 x 3.1 mi) at a resolution of about 3.8 meters (12 ft) per pixel. The image was taken during southern spring on August 29, 1999.

    Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  8. Lower Permian Dry Mountain trough, eastern Nevada: preliminary basin analysis

    SciTech Connect

    Schwarz, D.L.; Snyder, W.S.; Spinosa, C.

    1987-08-01

    The Lower Permian Dry Mountain trough (DMT) is one of several basins that developed during the Late Pennsylvanian to Permian along the western edge of the North American continent. A tectonic mechanism has been suggested for the subsidence of the DMT, possibly due to reactivation of the Antler orogenic belt during the waning stages of Ancestral Rocky Mountain deformation. The DMT records marked subsidence with the appearance during the Artinskian (latest Wolfcampian) of a deeper water facies that consists of thin-bedded silty micrites and micritic mudstones rich in radiolarians and sponge spicules, characterized by a relative abundance of ammonoids, and rarer conodonts and Nereites ichnofacies trace fossils. Taxa recovered from a distinctive concretionary horizon at various locations provide an Artinskian datum on which to palinspastically reconstruct the DMT paleogeography. These taxa include ammonoids: Uraloceras, Medlicottia, Marathonites, Crimites, Metalegoceras, properrinitids; and conodonts: Neogondolella bisselli, Sweetognathus whitei, S. behnkeni, and Diplognathodus stevensi. The western margin facies of the DMT consists of Permian Carbon Ridge/Garden Valley Formations. Here, lowermost black Artinskianage euxinic micrites, considered a potential source rock for petroleum generation, are overlain by base-of-slope carbonate apron deposits, which, in turn, are overlain by base-of-slope carbonate apron deposits, which, in turn, are overlain by a thick, eastwardly prograding conglomerate wedge. Seismic profiles across Diamond Valley indicate a 3.0-4.6-km thick Tertiary sequence above the Paleozoic strata.

  9. Pennsylvanian-Permian Antler foreland of eastern Nevada

    SciTech Connect

    Snyder, W.S. . Dept. of Geosciences); Trexler, J.H. Jr. . Dept. of Geological Sciences)

    1993-04-01

    Models for the Antler foreland generally assume that it was a Mississippian feature dominated by a single, large basin (the Antler foredeep). Recent work indicates that the foreland, as a tectonic region, is longer-lived, and is better described as a series of sub-basins separated by intervening structural highs. Long sections reveal space/time changes in depositional facies and sedimentologic features indicative or suggestive of this repeated tectonism. For example, in the southern Pancake Range, the fluvial-deltaic clastic units of the Late Mississippian-earliest Pennsylvanian Neward Canyon sequence are overlain by 540 m of cyclical Pennsylvanian Ely Limestone. The flooding event that marks the boundary between these units occurs during a long-term 2nd order eustatic low stand and thus reflects the regional tectonism that created the Ely basin'. Further, tectonically driven subsidence seems necessary to sustain deposition of the thick of marginal marine-open shelf Ely Limestone at this locality. Regionally, Early Permian deposition within the Dry Mountain trough was dominated by a complex series of local tectonic controls. Within eastern Nevada, tectonic influences on the stratigraphy continued through at least the Middle Permian, and this tectonism perhaps merged with that of the classic Late Permian-Early Triassic Sonoma orogeny. One consequence of this protracted tectonism was development or reactivation of zones of structural weakness that fragmented the foreland into a series of basins and highs and that accommodated differing geometries and styles of deformation.

  10. Hooked: Habits of the Chinese Permian gigantopterid Gigantonoclea

    NASA Astrophysics Data System (ADS)

    Seyfullah, Leyla J.; Glasspool, Ian J.; Hilton, Jason

    2014-04-01

    Based upon anatomical evidence, Permian aged gigantopterid fossils are in general reconstructed as climbing or scrambling plants. Gigantonoclea, a genus of adpressed gigantopterid foliage from the Permian of northern China, has been reported to co-occur with hook-like organs that were interpreted as indicating a scrambling/climbing habit. We reinvestigated these hook-like structures and re-evaluated the nature of the co-occurrences in context with the flora preserved in each plant-bearing fossil 'bed' in the North China sedimentary succession. New findings show that the species Gigantonoclea hallei probably climbed using specially adapted clusters of compound grappling hook-like shoots borne on the stems. This structural arrangement comprising shoots of hooks is new to the scrambling/climbing concept in gigantopterids. However, a key figured specimen previously reported as showing intermediate hook-tipped leaf morphology on a sole pinnule tip is discounted as such and is reinterpreted as a 'normal' pinnule partially hidden under sediment that results in an unusual appearance to this pinnule tip. Adaptations for climbing or scrambling based upon 'hooked leaves' observed in Gigantonoclea lagrelii are no longer supported and are reinterpreted as incompletely expanded leaves where the vernation process was interrupted. These data weaken prior interpretations of G. lagrelii as a climber/scrambler and raise doubts about the ubiquity of hooks amongst the gigantopterids as structures enabling them to climb or scramble their way through the Permian world.

  11. Smaller foraminifers of the Lower Permian from Western Tethys

    NASA Astrophysics Data System (ADS)

    Filimonova, T. V.

    2010-12-01

    Among the smaller foraminifers from the Lower Permian of Western Tethys (Pamir, Northern Afghanistan, Central and Eastern Iran, Armenia, and Turkey), foraminiferal assemblages characteristic of the Asselian, Sakmarian, Yakhtashian, Bolorian, and Kubergandian stages are distinguished. The first stratigraphic scheme based on smaller foraminifers is elaborated for the Lower Permian (Cisuralian Series) of Western Tethys. Eight biostratigraphic units distinguished in the Lower Permian and one in the Kubergandian Stage are ranked as beds with characteristic foraminiferal assemblages. At particular stratigraphic levels, the beds are recognizable in different paleogeographic provinces of the Tethyan Realm, which enables correlation between deposits concurrently accumulated under dissimilar climatic and facies conditions to be carried. Some of the distinguished beds are recognizable beyond the Tethyan Realm, for instance in the Donetsk basin, Cis-Urals, Pechora coal basin, and Spitsbergen. Among foraminifers that have been studied, 264 species and subspecies, including 16 new taxa, are identified. The following species and subspecies are identified and described for the first time: Hemigordius permicus beitepicus subsp. nov., H. pamiricus sp. nov., Neohemigordius afganicus sp. nov., N. carnicus sp. nov., N. bangi sp. nov., N. zulumarticus sp. nov., N. kubergandinicus sp. nov., Geinitzina grandella sp. nov., G. dentiformis sp. nov., G. bella sp. nov., Pachyphloia paraovata minima sp. nov., P. aucta sp. nov., Frondicularia porrecta sp. nov., Globivalvulina gigantea sp. nov., G. compacta sp. nov., and G. explicata sp. nov.

  12. Lower Permian sediment-gravity-flow sequence, eastern California

    USGS Publications Warehouse

    Stevens, C.H.; Lico, M.S.; Stone, P.

    1989-01-01

    The Lower Permian (middle Wolfcampian) Zinc Hill sequence, a 65- to 110-m-thick series of beds in the Owens Valley Group in east-central California, comprises sediment-gravity-flow deposits consisting of carbonate sediment that originated on, and siliciclastic sediment that may have been generally ponded behind, a carbonate shelf to the east and northeast. Thickness patterns and paleocurrent indicators show that the sediment forming this sequence was transported primarily southeastward and deposited in a southeast-trending, lobe-shaped body. Evidently, the sediment was carried from the shelf by sediment-gravity flows that travelled westward down the slope and then turned southeastward upon reaching a southeast-trending basin at the base of the slope. Data derived from the study of this basin, which paralleled the shelf edge and is thought to have formed parallel to a southeast-oriented segment of the Early Permian continental margin, constitute one of the most important arguments favoring a Pennsylvanian to Early Permian age of truncation of the western North American continental margin. ?? 1989.

  13. Thecamoebians from Late Permian Gondwana sediments of peninsular India.

    PubMed

    Farooqui, Anjum; Aggarwal, Neha; Jha, Neerja

    2014-02-01

    The evolutionary history of thecamoebians (testate amoebae) extends back to the Neoproterozoic Era. However, until now, these have had a restricted, discontinuous and modest record across the world. The studied sediment of Raniganj Formation (Godavari Graben), Andhra Pradesh, India has been assigned as Late Permian on the basis of co-occurring age-diagnostic Late Permian palynomorphs. About sixteen thecamoebian species and one taxon incertae sedis have been recorded here in the palynological slides on the basis of shell morphology and morphometry. Out of these, five belong to the family Arcellidae, seven to Centropyxidae, two to Trigonopyxidae, one to Difflugiidae, one to Plagiopyxidae, and one is regarded incertae sedis. The morphometric characteristics of fossil forms resemble their corresponding extant species studied from ecologically diverse fresh water wetlands in India. In general, the ratio of shell diameter and aperture diameter of Late Permian fossil and extant specimens show significant correlation in all the studied species. Except that, the ratio of shell length and breadth is the distinguishing feature between Centropyxis aerophila and C. aerophila 'sylvatica', rather than the ratio of shell length and longest diameter of the shell aperture in both fossil and extant forms. The study elucidates the minimal morphological evolution in thecamoebians and their survival during mass extinction periods and stressful environmental conditions over the geological timescale.

  14. Hot acidic Late Permian seas stifle life in record time

    NASA Astrophysics Data System (ADS)

    Georgiev, Svetoslav; Stein, Holly J.; Hannah, Judith L.; Bingen, Bernard; Weiss, Hermann M.; Piasecki, Stefan

    2011-10-01

    The end of Permian time (252-251 Ma) hosts the largest mass extinction in Earth history, yet events heralding this global catastrophe remain intensely disputed. We present a chemostratigraphic marker, the 187Re/ 188Os ratio, which soars to unprecedented levels approaching the Permo-Triassic boundary. These ratios are tied to profound trace element changes and a precise Re-Os time record at 252 Ma preserved in black shales from East Greenland and the mid-Norwegian shelf. Within a 36-meter shale section, an 80-fold increase in Re concentrations (two-fold for Os) signals seawater conditions that became increasingly inhospitable to life. Unwavering initial 187Os/ 188Os ratios of 0.6 preclude mafic volcanism and meteorite impact as the direct cause of Late Permian anoxia. We argue that extraordinarily high 187Re/ 188Os ratios are the hallmark of simultaneously rising ocean temperature and acidity, leading to loss of oxygen and the stifling of life in latest Permian time.

  15. Spiral-shaped graphoglyptids from an Early Permian intertidal flat

    NASA Astrophysics Data System (ADS)

    Minter, Nicholas J.; Buatois, Luis A.; Lucas, Spencer G.; Braddy, Simon J.; Smith, Joshua A.

    2006-12-01

    Spiral-shaped foraging trace fossils, assigned to the grapho glyptid cf. Spirorhaphe azteca, are reported from an Early Permian intertidal flat in the Robledo Mountains of southern New Mexico, USA. Remarkably similar spiral-shaped structures are produced in modern intertidal flats by the paraonid polychaete Paraonis fulgens, and function as traps to capture mobile microorganisms migrating in the sediment in response to tides. We envisage a similar function for the Early Permian trace fossils. Previous studies have suggested that the lack of P. fulgens type traces from ancient intertidal deposits indicates that such behavior only evolved geologically recently in such settings. However, this report demonstrates that such specialized foraging behavior was present in intertidal settings by at least the Early Permian. Graphoglyptids are typical of deep-marine settings, and characteristic of the Nereites ichnofacies. This represents their first undoubted occurrence in intertidal facies in the geological record. We postulate that the occurrence of graphoglyptids in deep-marine and intertidal settings is related to the predictability of resources. The scarcity of intertidal graphoglyptids in the geological record is most likely a preservational effect.

  16. Spatial and temporal patterns of exhumation across the Venezuelan Andes: Implications for Cenozoic Caribbean geodynamics

    NASA Astrophysics Data System (ADS)

    Bermúdez, Mauricio A.; Kohn, Barry P.; van der Beek, Peter A.; Bernet, Matthias; O'Sullivan, Paul B.; Shagam, Reginald

    2010-10-01

    The Venezuelan Andes formed by complex geodynamic interaction between the Caribbean Plate, the Panamá Arc, the South American Plate and the continental Maracaibo block. We study the spatial and temporal patterns of exhumation across the Venezuelan Andes using 47 new apatite fission track (AFT) ages as well as topographic analyses. This approach permits the identification of at least seven tectonic blocks (Escalante, Cerro Azul, Trujillo, Caparo, Sierra Nevada, Sierra La Culata and El Carmen blocks) with contrasting exhumation and cooling histories. The Sierra Nevada, Sierra La Culata and El Carmen blocks, located in the central part of the Venezuelan Andes and separated by the Boconó fault system, cooled rapidly but diachronously during the late Miocene-Pliocene. Major surface uplift and exhumation occurred in the Sierra Nevada block since before 8 Ma. A second phase of uplift and exhumation affected the El Carmen and Sierra La Culata blocks to the north of the Boconó fault during the late Miocene-Pliocene. The highest topography and steepest relief of the belt coincides with these blocks. The Caparo and Trujillo blocks, located at the northeastern and southwestern ends of the orogen, cooled more slowly from the Oligocene to the late Miocene. These blocks are characterized by significantly lower mean elevations and slightly lower mean slopes than the central blocks. Unraveling the cooling history of the individual blocks is important to better understand the control of preexisting faults and regional Caribbean geodynamics on the evolution of the Venezuelan Andes. Our data indicate a strong control of major preexisting fault zones on exhumation patterns and temporal correlation between phases of rapid exhumation in different blocks with major tectonic events (e.g., collision of the Panamá arc; rotation of the Maracaibo block).

  17. Effect of horseshoe crab spawning density on nest disturbance and exhumation of eggs: A simulation study

    USGS Publications Warehouse

    Smith, D.R.

    2007-01-01

    Because the Delaware Bay horseshoe crab (Limulus polyphemus) population is managed to provide for dependent species, such as migratory shorebirds, there is a need to understand the process of egg exhumation and to predict eggs available to foraging shorebirds. A simple spatial model was used to simulate horseshoe crab spawning that would occur on a typical Delaware Bay beach during spring tide cycles to quantify density-dependent nest disturbance. At least 20% of nests and eggs were disturbed for levels of spawning greater than one third of the average density in Delaware Bay during 2004. Nest disturbance increased approximately linearly as spawning density increased from one half to twice the 2004 level. As spawning density increased further, the percentage of eggs that were disturbed reached an asymptote of 70% for densities up to 10 times the density in 2004. Nest disturbance was heaviest in the mid beach zone. Nest disturbance precedes entrainment and begins the process of exhumation of eggs to surface sediments. Model predictions were combined with observations from egg surveys to estimate a snap-shot exhumation rate of 5-9% of disturbed eggs. Because an unknown quantity of eggs were exhumed and removed from the beach prior to the survey, cumulative exhumation rate was likely to have been higher than the snap-shot estimate. Because egg exhumation is density-dependent, in addition to managing for a high population size, identification and conservation of beaches where spawning horseshoe crabs concentrate in high densities (i.e., hot spots) are important steps toward providing a reliable food supply for migratory shorebirds. ?? 2007 Estuarine Research Federation.

  18. Kinematic and thermal evolution during two-stage exhumation of a Mediterranean subduction complex

    NASA Astrophysics Data System (ADS)

    Behr, W. M.; Platt, J. P.

    2012-08-01

    We examine the kinematic and thermal evolution of the Nevado-Filabride Complex (NFC), an Early to Middle Miocene subduction complex within the Betic Cordillera of southern Spain. Thermobarometry from the NFC in the Sierra Alhamilla reveals an inverted geothermal gradient, with peak temperatures and pressures of 560°C and 13 kbar reached in the uppermost tectonic unit. The NFC cooled during exhumation, defining a linear PT path that remained within the stability field of kyanite until the aluminosilicate breakdown reaction. Geo- and thermochronology suggest the NFC was subducted and exhumed to the surface within ˜10 m.y., recording an early stage of fast cooling from peak T through ˜250°C, followed by a late stage of slower cooling as the rocks approached the surface. The exhumation is associated with a progressive change in kinematics, with early co-axial fabrics showing NNE-SSW-trending stretching lineations, and late non-coaxial fabrics showing SSW-trending lineations. A new tectonic model is proposed to explain these data, in which rocks at the leading edge of the Iberian margin were subducted southeastward beneath the thin, hot, Alboran lithosphere to form the NFC. The rocks at the top of the slab began to be exhumed once they reached 48-67 km depth. They were initially exhumed rapidly along the top of the subducting slab, in a subduction channel geometry; then upon reaching the middle crust, were captured by a low-angle detachment fault with a WSW shear sense and final exhumation was accommodated more slowly in a core-complex geometry.

  19. Decoupling of long-term exhumation and short-term erosion rates in the Sikkim Himalaya

    NASA Astrophysics Data System (ADS)

    Abrahami, Rachel; van der Beek, Peter; Huyghe, Pascale; Hardwick, Elisabeth; Carcaillet, Julien

    2016-01-01

    Understanding the relative strengths of tectonic and climatic forcing on erosion at different spatial and temporal scales is important to understand the evolution of orogenic topography. To address this question, we quantified exhumation rates at geological timescales and erosion rates at millennial timescales in modern river sands from 10 sub-catchments of the Tista River drainage basin in the Sikkim Himalaya (northeast India) using detrital apatite fission-track thermochronology and cosmogenic 10Be analyses, respectively. We compare these rates to several potential geomorphic or climatic forcing parameters. Our results show that millennial erosion rates are generally higher and spatially more variable than long-term exhumation rates in Sikkim. They also show strongly contrasting spatial patterns, suggesting that the processes controlling these rates are decoupled. At geological timescales, exhumation rates decrease from south to north, with rates up to 1.2 ± 0.6 mm/yr recorded in southwest Sikkim and as low as 0.5 ± 0.2 mm/yr in the northernmost catchment. Long-term exhumation rates do not correlate with any geomorphic or climatic parameter. We suggest they are tectonically controlled: high rates in southwest Sikkim may be linked to the building of the Lesser Himalaya Rangit Duplex, whereas low rates in north Sikkim are consistent with cessation of extensional exhumation along the South Tibetan Detachment after 13 Ma. The highest apparent erosion rates recorded by cosmogenic nuclides (∼5 mm/yr) occur in catchments spanning the Main Central Thrust Zone, but these appear to be strongly influenced by recent landsliding. High millennial erosion rates (1-2 mm/yr) also occur in north Sikkim and may be climatically driven through strong glacial inheritance of the landscape, as attested by high channel-steepness values close to the maximum extent of glaciers during the Last Glacial Maximum. In contrast, variations in rainfall rate do not seem to strongly influence

  20. Late-Quaternary exhumation of Namche Barwa constrained using low-temperature multi-OSL-thermochronometry

    NASA Astrophysics Data System (ADS)

    King, Georgina; Herman, Frederic

    2016-04-01

    The influence of climate on tectonic processes remains a controversial concept. Exhumation rates of >5 mm/yr make Namche Barwa, Tibet, one of the most rapidly exhuming places on earth, and two main hypotheses have developed to explain the very high rates of exhumation there. The tectonic aneurysm model (Zeitler et al., 2001) proposes that crustal weakening coupled with extremely active surface processes causes a spatial stationarity of exhumation. Alternatively, a northward plunging antiform that is progressively migrating north-eastward (Seward and Burg, 2008) may explain the concentration of extremely low cooling ages and rapid exhumation that characterise the Namche Barwa massif. Here we use multi-OSL-thermochronometry of feldspar, which comprises a series of different systems with closure temperatures ranging from 30 to 70 C, to quantify spatial and temporal changes in exhumation rates. We have applied this new technique to a suite of samples from the Namche Barwa massif and inverting our data enables us to precisely resolve cooling histories over 0.1 Ma timescales. Our data indicate propagation of a knick-point along the Parlung river, which can be explained by progressive north-eastward migration of a northward plunging antiform. We suggest that river incision does not therefore feedback onto tectonics, as proposed by the aneurysm model. Zeitler, P.K., Meltzer, A.S., Koons, P.O., et al., 2001. Erosion, Himalayan Geodynamics, and the Geomorphology of Metamorphism. GSA Today 11, 4-9 Seward, D., Burg, J-P., 2008. Growth of the Namche Barwa Syntaxis and associated evolution of the Tsangpo Gorge: Constraints from structural and thermochronological data. Tectonophysics 451, 282-289.

  1. Significance of "stretched" mineral inclusions for reconstructing P- T exhumation history

    NASA Astrophysics Data System (ADS)

    Ashley, Kyle T.; Darling, Robert S.; Bodnar, Robert J.; Law, Richard D.

    2015-06-01

    Analysis of mineral inclusions in chemically and physically resistant hosts has proven to be valuable for reconstructing the P- T exhumation history of high-grade metamorphic rocks. The occurrence of cristobalite-bearing inclusions in garnets from Gore Mountain, New York, is unexpected because the peak metamorphic conditions reached are well removed (>600 °C too cold) from the stability field of this low-density silica polymorph that typically forms in high temperature volcanic environments. A previous study of samples from this area interpreted polymineralic inclusions consisting of cristobalite, albite and ilmenite as representing crystallized droplets of melt generated during a garnet-in reaction, followed by water loss from the inclusion to explain the reduction in inclusion pressure that drove the transformation of quartz to cristobalite. However, the recent discovery of monomineralic inclusions of cristobalite from the nearby Hooper Mine cannot be explained by this process. For these inclusions, we propose that the volume response to pressure and temperature changes during exhumation to Earth's surface resulted in large tensile stresses within the silica phase that would be sufficient to cause transformation to the low-density (low-pressure) form. Elastic modeling of other common inclusion-host systems suggests that this quartz-to-cristobalite example may not be a unique case. The aluminosilicate polymorph kyanite also has the capacity to retain tensile stresses if exhumed to Earth's surface after being trapped as an inclusion in plagioclase at P- T conditions within the kyanite stability field, with the stresses developed during exhumation sufficient to produce a transformation to andalusite. These results highlight the elastic environment that may arise during exhumation and provide a potential explanation of observed inclusions whose stability fields are well removed from P- T paths followed during exhumation.

  2. Potential links between porphyry copper deposits and exhumed metamorphic basement complexes in northern Chile

    NASA Astrophysics Data System (ADS)

    Cooper, Frances; Docherty, Alistair; Perkins, Rebecca

    2014-05-01

    Porphyry copper deposits (PCDs) are typically associated with magmatic arcs in compressional subduction zone settings where thickened crust and fractionated calc-alkaline magmas produce favourable conditions for copper mineralisation. A classic example is the Eocene-Oligocene PCD belt of Chile, the world's leading copper producing country. In other parts of the world, older late Cretaceous to early Tertiary PCDs are found in regions of former subduction-related magmatism that have undergone subsequent post-orogenic crustal extension, such as the Basin and Range province of western North America, and the Eurasian Balkan-Carpathian-Dinaride belt. In the Basin and Range there is a striking correlation between the location of many PCDs and exhumed metamorphic core complexes (isolated remnants of the middle to lower crust exhumed during extensional normal faulting). This close spatial relationship raises questions about the links between the two. For example, are their exhumation histories related? Could the presence of impermeable metamorphic rocks at depth affect and localise mineralising fluids? In Chile there appears to be a similar spatial relationship between PCDs and isolated outcrops of exhumed metamorphic basement. In northern Chile, isolated exposures of high-grade metamorphic gneisses and amphibolites are thought to be exhumed remnants of the pre-subduction Proterozoic-Paleozoic continental margin of Gondwana [2], although little is known about when they were exhumed and by what mechanism. For example, the Limón Verde metamorphic complex, exhumed from a depth of ca. 50 km, is situated adjacent to Chuquicamata, the largest open pit copper mine in the world. In northernmost Chile, another metamorphic exposure, the Belén complex, sits close to the Dos Hermanos PCD, a small deposit that is not actively mined. Comprising garnet-bearing gneisses and amphibolites, the Belén is thought to have been exhumed from a depth of ca. 25 km, but when and how is unclear [3

  3. [Approaches to setting up the Center for identification of exhumed bodies in Chechen Republic].

    PubMed

    Klevno, V A; Ivanov, P L

    2007-01-01

    The authors participated in the activity of a group of European experts who visited Moscow, Rostov-on-Don and Grozny in September 2005 to clarify situation with identification of exhumed unknown dead bodies of the civil population. The European experts recommend to set up Center for Identification in Chechen Republic (in Grozny). The authors propose to make DNA identification tests in the Russian Federation Center for Forensic Medical Evaluation in Moscow which has much experience and staff skilled in identification of unknown exhumed bodies and can solve the problem of genetic identification of unidentified bodies of people missed in the Chechen Republic more effectively.

  4. A zircon (U-Th)/He exhumation study in the lower Sutlej River valley; Northwestern Himalaya

    NASA Astrophysics Data System (ADS)

    Boyes, T.; Michalak, M.; Hourigan, J. K.

    2009-12-01

    In an actively deforming orogen, such as the Himalaya, erosion, uplift, and consequently, exhumation are variable across time and space. Recent studies suggest a direct link between erosion and exhumation, both spatially and temporally (e.g. Thiede et al. 2004; Clift et al. 2008; Vannay et al. 2004). However, the complexities of this relationship have yet to be characterized in the Himalaya (Thiede et al., 2009; Whipple, 2009). In the Northwest Himalaya, low temperature thermochronology shows that the Southern Himalayan Front (SHF) has been rapidly exhuming since the mid-Miocene (Thiede et al. 2009; and references therin). Fission track studies have been used to quantify exhumation rates in the Sutlej River valley in the Northwest Himalaya along the SHF (Thiede et al. 2009; Vannay et al. 2004; Schlup 2003; Jain et al. 2000). These studies indicate rapid exhumation within the Higher and Lower Himalayan Crystalline series. However, few rock samples in the Lesser Himalayan metasedimentary units have been analyzed with these methods. Because exhumation varies temporally, it is important to use several low-temperature thermochronometers to detect changes in exhumation rates. In this study we use the zircon (U-Th)/He method, which provides a cooling age (Dodson, 1973) since passing through a ~180 degree C closure isotherm. Seven new (U-Th)/He cooling-ages along a 2.2km vertical transect, within the Lesser Himalayan series, are presented. Young (~3 Ma), reproducible cooling-ages for the upper five samples indicate that this section of metasedimentary rocks exhumed rapidly, as a coherent block, in the mid-Pliocene. Two samples from lower elevations unexpectedly yielded older cooling ages, however, these data had larger associated reproducibility errors. The apparent negative age-elevation relationship of this transect could be explained by i) an unmapped fault, ii) recent tilting of a large block, or iii) a rapid decrease in recent relief that occurred faster than the

  5. Structure of the Anayet Permian basin (Axial Zone, Central Pyrenees)

    NASA Astrophysics Data System (ADS)

    Rodriguez, L.; Cuevas, J.; Tubía, J. M.

    2012-04-01

    The Anayet Permian basin was generated by strike-slip tectonics that opened subsident basins with pull-apart geometries in the western Spanish Axial Zone (between the Aragon and Tena valleys). A continental succession of Permian age, that represents the first post-variscan deposits in the area, fills the basin and covers discordantly Devonian to Carboniferous limestones, sandstones and slates. Permian deposits have been classically divided in four main detrital groups, with three basic volcanic episodes interbedded (Gisbert, 1984, Bixel, 1987): the Grey Unit (50-120 m, Estefanian to Kungurian) with slates, conglomerates, tobaceous slates, coal and pyroclastic deposits, the Transition Unit (50 m maximum) showing grey and red sandstones and lutites with oolitic limestones intercalated, the Lower Red Unit (250 m) composed of cross-bedded red sandstones and andesitic volcanic rocks at the top, and finally the Upper Red Unit (400 m minimum, top eroded) formed by three fining up megasequences of carbonates, red sandstones and lutites with lacustrine carbonates intercalated and alkali basalts at the top. Increasingly older rocks are found towards the western part of the basin, where its depocenter is located. South-vergent angular folds deform the Permian sedimentary succession. Fold axes are N115 °E-trending, almost horizontal and are characterized by a remarkably constant orientation. Folds exhibit a long limb dipping slightly to the north and a short vertical limb, occasionally reversed. In the Anayet basin four main folds, with a wavelength of 400 m, can be distinguished, two anticlines and two synclines, with minor folds associated. Related to the angular folds an axial plane foliation, E-trending and dipping 40 to 60° to the north, is developed in the lutites. The more competent rocks, conglomerates and breccias, only locally show a spaced fracture cleavage. No main thrusts have been detected in Permian rocks. However, minor scale decollements, usually low angle

  6. Episodic exhumation and relief growth in the Mont Blanc massif, Western Alps from numerical modelling of thermochronology data

    NASA Astrophysics Data System (ADS)

    Glotzbach, C.; van der Beek, P. A.; Spiegel, C.

    2011-04-01

    The Pliocene-Quaternary exhumational and topographic evolution of the European Alps and its potential climatic and tectonic controls remain a subject of controversy. Here, we apply inverse numerical thermal-kinematic modelling to a spatially dense thermochronological dataset (apatite fission-track and (U-Th)/He) of both tunnel and surface samples across the Mont Blanc massif in the Western Alps, complemented by new zircon fission-track data, in order to better quantify its Neogene exhumation and relief history. Age-elevation relationships and modelling results show that an episodic exhumation scenario best fits the data. Initiation of exhumation in the Mont Blanc massif at 22 ± 2 Ma with a rate of 0.8 ± 0.15 km/Myr is probably related to NW-directed thrusting during nappe emplacement. Exhumation rates decrease at 6 ± 2 Ma to values of 0.15 ± 0.65 km/Myr, which we interpret to be the result of a general decrease in convergence rates and/or extensive exposure of less erodible crystalline basement rocks from below more easily erodible Mesozoic sediments. Finally, local exhumation rates increase up to 2.0 ± 0.6 km/Myr at 1.7 ± 0.8 Ma. Modelling shows that this recent increase in local exhumation can be explained by valley incision and the associated increase in relief at 0.9 ± 0.8 Ma, leading to erosional unloading, isostatic rebound and additional rock uplift and exhumation. Given the lack of tectonic activity as evidenced by constant thermochronological ages along the tunnel transect, we suggest that the final increase in exhumation and relief in the Mont Blanc massif is the result of climate change, with the initiation of mid-Pleistocene glaciations leading to rapid valley incision and related local exhumation.

  7. 40 CFR 81.242 - Pecos-Permian Basin Intrastate Air Quality Control Region.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Air Quality Control Regions § 81.242 Pecos-Permian Basin Intrastate Air Quality Control Region. The Pecos-Permian Basin Intrastate Air Quality Control Region (New Mexico) consists of the territorial area... Quality Control Region. 81.242 Section 81.242 Protection of Environment ENVIRONMENTAL PROTECTION...

  8. Olson's Extinction and the latitudinal biodiversity gradient of tetrapods in the Permian.

    PubMed

    Brocklehurst, Neil; Day, Michael O; Rubidge, Bruce S; Fröbisch, Jörg

    2017-04-12

    The terrestrial vertebrate fauna underwent a substantial change in composition between the lower and middle Permian. The lower Permian fauna was characterized by diverse and abundant amphibians and pelycosaurian-grade synapsids. During the middle Permian, a therapsid-dominated fauna, containing a diverse array of parareptiles and a considerably reduced richness of amphibians, replaced this. However, it is debated whether the transition is a genuine event, accompanied by a mass extinction, or whether it is merely an artefact of the shift in sampling from the palaeoequatorial latitudes to the palaeotemperate latitudes. Here we use an up-to-date biostratigraphy and incorporate recent discoveries to thoroughly review the Permian tetrapod fossil record. We suggest that the faunal transition represents a genuine event; the lower Permian temperate faunas are more similar to lower Permian equatorial faunas than middle Permian temperate faunas. The transition was not consistent across latitudes; the turnover occurred more rapidly in Russia, but was delayed in North America. The argument that the mass extinction is an artefact of a latitudinal biodiversity gradient and a shift in sampling localities is rejected: sampling correction demonstrates an inverse latitudinal biodiversity gradient was prevalent during the Permian, with peak diversity in the temperate latitudes.

  9. Socioeconomic Impact of Infill Drilling Recovery from Carbonate Reservoirs in the Permian Basin, West Texas

    DTIC Science & Technology

    1994-05-01

    revenues of infill drilling and the creation of jobs in the Permian basin communities, and ( 3 ) develops a correlation between the increased tax...1 3 viii Page CHAPTER IV THE AMOUNT OF REVENUE FROM OIL PRODUCTION...the Permian Basin ........................ 32 4.5 Percent of Federal Income Tax ............................................ 3 33 4.6 Rule of Thumb in

  10. Tectonic significance of Cenozoic exhumation and foreland basin evolution in the Western Alps

    NASA Astrophysics Data System (ADS)

    Carrapa, Barbara; Di Giulio, Andrea; Mancin, Nicoletta; Stockli, Daniel; Fantoni, Roberto; Hughes, Amanda; Gupta, Sanjeev

    2016-08-01

    The Alps are the archetypical collisional orogenic system on Earth, and yet our understanding of processes controlling topographic growth in the Cenozoic remains incomplete. Whereas ideas and models on the Alps are abundant, data from the foreland basin record able to constrain the timing of erosion and sedimentation, mechanisms of basin accommodation and basin deformation are sparse. We combine seismic stratigraphy, micropaleontology, white mica 40Ar/39Ar, detrital zircon (U-Th)/He and apatite fission track thermochronology to Oligocene-Pliocene samples from the retrowedge foreland basin (Saluzzo Basin in Italy) and to Oligocene-Miocene sedimentary rocks from the prowedge foreland basin (Bârreme Basin in France) of the Western Alps. Our new data show that exhumation in the Oligocene-Miocene was nonuniform across the Western Alps. Topographic growth was underway since the Oligocene and exhumation was concentrated on the proside of the orogenic system. Rapid and episodic early Miocene exhumation of the Western Alps was concentrated instead on the retroside of the orogen and correlates with a major unconformity in the proximal retroforeland basin. A phase of orogenic construction is recorded by exhumation of the proximal proforeland in both the Central and Western Alps at circa 16 Ma. This is associated with high sedimentation rates, and by inference erosion rates, and suggests that an increase in accretionary flux associated with the dynamics of subduction of Europe under Adria controlled orogenic expansion in the Miocene.

  11. Pliocene eclogite exhumation at plate tectonic rates in eastern Papua New Guinea.

    PubMed

    Baldwin, Suzanne L; Monteleone, Brian D; Webb, Laura E; Fitzgerald, Paul G; Grove, Marty; Hill, E June

    2004-09-16

    As lithospheric plates are subducted, rocks are metamorphosed under high-pressure and ultrahigh-pressure conditions to produce eclogites and eclogite facies metamorphic rocks. Because chemical equilibrium is rarely fully achieved, eclogites may preserve in their distinctive mineral assemblages and textures a record of the pressures, temperatures and deformation the rock was subjected to during subduction and subsequent exhumation. Radioactive parent-daughter isotopic variations within minerals reveal the timing of these events. Here we present in situ zircon U/Pb ion microprobe data that dates the timing of eclogite facies metamorphism in eastern Papua New Guinea at 4.3 +/- 0.4 Myr ago, making this the youngest documented eclogite exposed at the Earth's surface. Eclogite exhumation from depths of approximately 75 km was extremely rapid and occurred at plate tectonic rates (cm yr(-1)). The eclogite was exhumed within a portion of the obliquely convergent Australian-Pacific plate boundary zone, in an extending region located west of the Woodlark basin sea floor spreading centre. Such rapid exhumation (> 1 cm yr(-1)) of high-pressure and, we infer, ultrahigh-pressure rocks is facilitated by extension within transient plate boundary zones associated with rapid oblique plate convergence.

  12. An Unexplained Pulse of Late Cretaceous Exhumation in Northern New England

    NASA Astrophysics Data System (ADS)

    Amidon, W. H.; Roden-Tice, M. K.; Anderson, A. J.; Shuster, D. L.

    2015-12-01

    The steep relief of northern New England has long puzzled geomorphologists. Although it is suggestive of recent tectonic rejuvenation, roughly 200 Myr has passed since the opening of the Atlantic. The timing of recent exhumation has proven difficult to constrain because the magnitude of Cenozoic unroofing is often insufficient to reset surface thermochronometers and associated sediments are not well preserved. This study attempts to better resolve the Mesozoic-Cenozoic exhumation history of the White Mountains (New Hampshire) by combining apatite fission track, (U-Th)/He, and 4He/3He thermochronology in a 700 m deep drill core from the White Mountains of New Hampshire. Forward (HeFTY) and inverse (QTQt) modeling of age-elevation profiles point to a period of accelerated exhumation from roughly 85 to 65 Ma. Cooling rates accelerated by a factor of 6-10 around this time, presumably translating to the removal of 2-3 km of overburden in the span of ~20 million years. The timing of this episode is in broad agreement with AFT cooling ages across major faults in the region, which suggest late Cretaceous reactivation. However, an analysis of regional AFT ages suggests that not all of the uplift can be explained by extensional faulting and that dynamic surface uplift might have played a role. Although external forcing mechanisms remain unclear, the timing of this exhumation corresponds well to a reorganization of seafloor spreading in the North Atlantic and to the timing of alkaline volcanism in Iberia.

  13. Focused exhumation along megathrust splay faults in Prince William Sound, Alaska

    USGS Publications Warehouse

    Haeussler, Peter J.; Armstrong, Phillip A; Liberty, Lee M; Ferguson, Kelly M; Finn, Shaun P; Arkle, Jeannette C; Pratt, Thomas L.

    2015-01-01

    Megathrust splay faults are a common feature of accretionary prisms and can be important for generating tsunamis during some subduction zone earthquakes. Here we provide new evidence from Alaska that megathrust splay faults have been conduits for focused exhumation in the last 5 Ma. In most of central Prince William Sound, published and new low-temperature thermochronology data indicate little to no permanent rock uplift over tens of thousands of earthquake cycles. However, in southern Prince William Sound on Montague Island, apatite (U–Th)/He ages are as young as 1.1 Ma indicating focused and rapid rock uplift. Montague Island lies in the hanging wall of the Patton Bay megathrust splay fault system, which ruptured during the 1964 M9.2 earthquake and produced ∼9 m of vertical uplift. Recent geochronology and thermochronology studies show rapid exhumation within the last 5 Ma in a pattern similar to the coseismic uplift in the 1964 earthquake, demonstrating that splay fault slip is a long term (3–5 my) phenomena. The region of slower exhumation correlates with rocks that are older and metamorphosed and constitute a mechanically strong backstop. The region of rapid exhumation consists of much younger and weakly metamorphosed rocks, which we infer are mechanically weak. The region of rapid exhumation is separated from the region of slow exhumation by the newly identified Montague Strait Fault. New sparker high-resolution bathymetry, seismic reflection profiles, and a 2012 Mw4.8 earthquake show this feature as a 75-km-long high-angle active normal fault. There are numerous smaller active normal(?) faults in the region between the Montague Strait Fault and the splay faults. We interpret this hanging wall extension as developing between the rapidly uplifting sliver of younger and weaker rocks on Montague Island from the essentially fixed region to the north. Deep seismic reflection profiles show the splay faults root into the subduction megathrust where there

  14. Efficient exhumation of (ultra) high-pressure rocks by slab extraction

    NASA Astrophysics Data System (ADS)

    Zhao, Zhongbao; Bons, Paul; Gomez-Rivas, Enrique; Soesoo, Alvar; Evgueni, Burov

    2015-04-01

    A range of mechanisms has been proposed for the enigmatic exhumation of (ultra) high-pressure (UHP) rocks from great depths. These include channel flow, wedge extrusion, diapiric rise, metamorphic core complexes and eduction. Most current models envisage exhumation to occur in a subduction setting, where exhumation of UHP rocks takes place in the context of the downward movement of the subducting slab. In addition, removal of the downward pull on the subducting slab (by slab break-off and slab retreat) may lead to buoyant rise of the UHP material, especially in case of subduction of continental crust. Here we consider the alternative scenario of slab extraction, where subduction is reversed and the slab is pulled up and away from the overriding plate, instead of sliding down into the mantle. UHP rocks are then exhumed together with the ascending plate. Slab extraction occurs when the downward pull of the subducted slab is exceeded by an opposite force, for example in case of plate divergence. Another case is a divergent double subduction zone (DDSZ), where the two hinges inevitably converge by rollback. At some point the pull of one slab can exceed that of the other one if it is short enough, leading to the extraction of the shorter slab and concomitant exhumation of UHP rocks. The evolution of a DDSZ with one short slab was modelled with the thermo-mechanical code FLAMAR, varying the relative movement of the two overriding plates. If the two overriding plates do not converge too fast, the short slab is pulled up and away from its suture and is eventually pulled down at the opposite suture. UHP rocks are exhumed at rates exceeding cms/yr in what is effectively a lithospheric-scale core complex. This mechanism may explain the exhumation of UHP rocks in the Tibetan Qiangtang Metamorphic Belt and the d'Entercasteaux Islands. If the sutures converge slower than the long slab slides down, an oceanic basin forms, which we suggest is the cause for the rapid opening of the

  15. Late-Quaternary exhumation rates constrained by OSL thermochronometry at the Franz Josef Glacier, New Zealand

    NASA Astrophysics Data System (ADS)

    Duverger, Arnaud; King, Georgina; Valla, Pierre; Cox, Simon; Herman, Frederic

    2016-04-01

    The Southern Alps of New Zealand are often cited as the primary example of a mountain range that has reached exhumation and topographic steady state, especially on the West Coast where exhumation rates reach up to about 10 mm/yr. However, cyclic climatic changes, throughout the Quaternary period have meant that the Alps cycled between being completely glaciated and ice free. The impact that such glacial cycles may have had on the spatial variability of erosion rates remains poorly constrained. Here we use Optically Stimulated Luminescence (OSL) as a very low temperature thermochronometer to constrain rock cooling histories at 10-100 kyr timescales on samples collected near the Franz Josef glacier. OSL-thermochronometry is based on the amount of electrons accumulated in the lattice defects of natural minerals such as quartz or feldspar, due to the competing effects of charge trapping due to the natural radioactivity within the rock and charge detrapping due to thermal loss during rock exhumation towards the surface. We collected 9 samples along the Waiho valley (crossing the Alpine Fault) and the Franz Josef glacier to quantify late-Quaternary exhumation rates and their potential spatial variations. Bedrock samples have been crushed to extract the light-safe rock interiors which have then been processed to isolate potassium-rich feldspars (K-feldspars). We used the Infra-Red Stimulated Luminescence at 50°C (IRSL50) protocol, including the measurement of the natural IRSL50 trapped charge population and the laboratory characterization of sample-specific thermal and athermal kinetic parameters. Once measured, the luminescence signal can be inverted into cooling histories. We also explored the potential of the recently developed multi-OSL-thermochronometer (King et al., accepted) to better constrain the cooling path. Our first OSL measurements show that samples are not in saturation and thus contain useful thermochronometric information over the last ~100 kyr. Inverse

  16. Feedback Between Rifting and Diapirism can Exhume Ultrahigh-Pressure Rocks

    NASA Astrophysics Data System (ADS)

    Ellis, S. M.; Little, T.; Wallace, L. M.; Hacker, B. R.; Buiter, S.

    2011-12-01

    Rapid exhumation of Earth's youngest (ultra-) high-pressure (UHP) rocks is occurring within an active rift in the D'Entrecasteaux Islands of the Woodlark Basin, Papua New Guinea. There, HP and coesite-bearing UHP eclogites have been exhumed at cm/yr rates in only the past few million years- a process that is thought to be continuing today, yet which is not compatible with the most commonly invoked class of UHP exhumation models: syn-convergent extrusion or return flow of the UHP rocks in a still-active subduction channel. Instead, we use 2D and 3D thermo-mechanical models to demonstrate that rapid vertical ascent of partially molten felsic crustal bodies within a rift setting is a mechanically feasible process that can account for the observed exhumation history and field structures of the rocks. We show that rifting of the overlying lithosphere and diapiric rise of quartzofeldspathic terranes positively reinforce each other in a kind of feedback loop to promote exhumation at plate-tectonic rates. Our models successfully reproduce: (1) the observed pressure-temperature evolution of HP and UHP rocks; (2) rapid exhumation rates of 2-3 cm/yr as a result of partial melt causing a reduction in density, and a complex feedback between viscosities, extension rates and melt fraction in the diapir; (3) flow patterns and structure of diapiric domes broadly consistent with that seen in the D'Entrecasteaux Islands; (4) buoyant support and high elevation of thinned crust due to the presence of an underlying partially molten UHP body and elevated temperatures in crust and mantle, consistent with observations from tomography; (5) asymmetry in initial rift structure (for an initially dipping subducted body, and as a result of 3D rotations); and (6) westward propagation of rifting and exhumation. The 3D model also illustrates how viscous flow associated with variable along-strike extension rates is consistent with observed ductile fabrics indicating rift margin-parallel stretching

  17. Cooling and exhumation of the Rieserferner Pluton (Eastern Alps, Italy/Austria)

    NASA Astrophysics Data System (ADS)

    Steenken, André; Siegesmund, Siegfried; Heinrichs, Till; Fügenschuh, Bernhard

    2002-03-01

    The Defereggen-Antholz-Vals (DAV) Line marks the southern border of alpine greenschist facies metamorphism within the Austroalpine basement to the south of the western Tauern window. During the Oligocene sinistral-strike slip, coeval with vertical displacement, was accompanied by the syntectonic emplacement of the Rieserferner Pluton along the north side of the fault. To the north of the DAV Line Rb/Sr as well as K/Ar-biotite cooling ages continuously increase from 16 Ma at the Rensen Pluton in the west to 30 Ma at the eastern end of the Rieserferner Pluton. Similar trends are apparent from zircon and apatite fission-track data, which increase eastward from 19 to 29 Ma, and 13 to 16 Ma, respectively. Low cooling rates allow a direct transformation into exhumation rates assuming an average geothermal gradient of 28 °C km-1. The resulting exhumation rates of less than 1 mm year-1 do not affect the depth of isotherms in a geologically significant manner. Hence, variable cooling rates within the basement north of the DAV Line are a result of differential exhumation of individual blocks. High exhumation rates bracketed between the intrusion age of the Rieserferner Pluton at 31+/-3 Ma and the apatite partial annealing zone (PAZ) range between 0.4 and 0.6 mm year-1, whereas final exposure takes place at reduced exhumation rates of 0.2 mm year-1. East-side-down tilting of the block north of the DAV Line, as indicated by variations in exhumation rates, strongly affects the western part of the area studied between the Rensen and the Central Rieserferner Pluton whereas, further east, block rotation becomes less important. A total difference in exhumation of about 2.2 km corresponding to 5° tilting between the Western and Eastern Rieserferner, as indicated by K/Ar-biotite and zircon fission-track data, occurred before going through the PAZ for apatite fission-tracks. Furthermore, the significance of the cooling ages, especially for biotite, is tested by calculating a finite

  18. Controls on reservoir development in Devonian Chert: Permian Basin, Texas

    SciTech Connect

    Ruppel, S.C.; Hovorka, S.D.

    1995-12-01

    Chert reservoirs of the Lower Devonian Thirtyone Formation contain a significant portion of the hydrocarbon resource in the Permian basin. More than 700 million bbl of oil have been produced from these rocks, and an equivalent amount of mobile oil remains. Effective exploitation of this sizable remaining resource, however, demands a comprehensive appreciation of the complex factors that have contributed to reservoir development. Analysis of Thirtyone Formation chert deposits in Three Bar field and elsewhere in the Permian basin indicates that reservoirs display substantial heterogeneity resulting from depositional, diagenetic, and structural processes. Large-scale reservoir geometries and finer scale, intra-reservoir heterogeneity are primarily attributable to original depositional processes. Despite facies variations, porosity development in these cherts is principally a result of variations in rates and products of early silica diagenesis. Because this diagenesis was in part a function of depositional facies architecture, porosity development follows original depositional patterns. In reservoirs such as Three Bar field, where the Thirtyone Formation has been unroofed by Pennsylvanian deformation, meteoric diagenesis has created additional heterogeneity by causing dissolution of chert and carbonate, especially in areas of higher density fracturing and faulting and along truncated reservoir margins. Structural deformation also has exerted direct controls on heterogeneity that are particularly noteworthy in reservoirs under waterflood. High-density fracture zones create preferred flow paths that result in nonuniform sweep through the reservoir. Faulting locally creates compartments by offsetting reservoir flow units. As such, the processes and models defined here improve understanding of the causes of heterogeneity in all Thirtyone chert reservoirs in the Permian basin and aid recovery of the sizable hydrocarbon resource remaining in these rocks.

  19. Forward stratigraphic modeling of the Permian of the Delaware Basin

    SciTech Connect

    Qiucheng, Ye; Kerans, C.; Bowman, S. )

    1996-01-01

    Permian platform-to-basin strata of the Delaware Basin In west Texas and New Mexico represent one of the world's most complete, best studied, and most hydrocarbon productive records of this geologic period in the world. This superb marriage of a refined stratigraphic framework and active exploration provided impetus to develop a forward stratigraphic model of this section to better predict the distribution of reservoir and seal relationships. The approximately 30 m.y. interval modeled is composed of 2 km of platform strata and 3 km of basinal strata divided into 8 composite sequences (average 3 m.y. duration) and 45 high-frequency sequences (400 ky m.y. duration). A 130 km dip section through the basin margin Guadalupe/Deleware Mountain outcrop is inversely modeled to derive local tectonic subsidence and a sea level curve for the Permian. In this process, the highest and lowest shoreline positions of each sequence are interpreted based on facies description which are assumed to approximate the highest and lowest relative sea level. A eustatic sea level curve is calculated by restoring these shoreline positions and removing local tectonic subsidence using a polynomial fit to the derived relative sea level curve. The quantitatively constrained curve for the Permian contains 2nd, 3rd, and 4th order 180m. This quantitatively constrained accommodation history (calculated eustatic curve and subsidence history) are input into the PHIL forward modeling program. Model variables of sediment supply are depositional system are adjusted to match known outcrop relations. The resulting model is potentially capable of predicting stratigraphy elsewhere in the basin using only subsidence history data from the inverse model.

  20. Forward stratigraphic modeling of the Permian of the Delaware Basin

    SciTech Connect

    Qiucheng, Ye; Kerans, C.; Bowman, S.

    1996-12-31

    Permian platform-to-basin strata of the Delaware Basin In west Texas and New Mexico represent one of the world`s most complete, best studied, and most hydrocarbon productive records of this geologic period in the world. This superb marriage of a refined stratigraphic framework and active exploration provided impetus to develop a forward stratigraphic model of this section to better predict the distribution of reservoir and seal relationships. The approximately 30 m.y. interval modeled is composed of 2 km of platform strata and 3 km of basinal strata divided into 8 composite sequences (average 3 m.y. duration) and 45 high-frequency sequences (400 ky m.y. duration). A 130 km dip section through the basin margin Guadalupe/Deleware Mountain outcrop is inversely modeled to derive local tectonic subsidence and a sea level curve for the Permian. In this process, the highest and lowest shoreline positions of each sequence are interpreted based on facies description which are assumed to approximate the highest and lowest relative sea level. A eustatic sea level curve is calculated by restoring these shoreline positions and removing local tectonic subsidence using a polynomial fit to the derived relative sea level curve. The quantitatively constrained curve for the Permian contains 2nd, 3rd, and 4th order 180m. This quantitatively constrained accommodation history (calculated eustatic curve and subsidence history) are input into the PHIL forward modeling program. Model variables of sediment supply are depositional system are adjusted to match known outcrop relations. The resulting model is potentially capable of predicting stratigraphy elsewhere in the basin using only subsidence history data from the inverse model.

  1. Development of the Permian Basin beam pump failure database

    NASA Astrophysics Data System (ADS)

    Rahman, Mohammed Mahbubur

    Artificial Lift Energy Optimization Consortium (ALEOC) was formed by eleven oil companies operating in the Permian Basin with the primary goal of improving oil field operations through sharing experiences. Beam pumping system received special attention because it is the most widely used artificial lift method in the Permian Basin as well as in the world. The combined effort to optimize beam pumping system calls for the creation of a central database, which will hold beam pump related data from diverse sources and will offer ways to analyze the data to obtain valuable insight about the nature, magnitude and trend of beam pump failure. The database mentioned above has been created as part of this work. The database combines beam pump failure data from about 25,000 wells owned by different companies into a single, uniform and consistent format. Moreover, two front-end computer applications have been developed to interact with the database, to run queries, and to make plots form the query results. One application is designed for desktop, while the other one is designed for the Internet. Both applications calculate failure frequencies of pump, rod, and tubing, and summarize the results in various ways. Thus the database and the front-end applications together provide a powerful means for analyzing beam pump failure data. Much useful information can be gathered from the database, such as the most vulnerable component in the system, the best and the worst performers, and the most troublesome operating area. Such information can be used for benchmarking performance, identifying best design/operational practices, design modification, and long term production planning. Results from data analysis show that the pump has the highest probability to fail in a beam pumping system, followed by the rod string and the tubing string. The overall failure in the Permian Basin shows a general decline with time.

  2. The paleoclimate of the Kazanian (early Late Permian) world

    SciTech Connect

    Moore, G.T. ); Peoples, C.J. )

    1990-05-01

    The Kazanian (early Late Permian, 258-253 m.y.) marked the onset of a unique interval in the Phanerozoic, distinguished by a classic end-member case of continental assembly, the megacontinent Pangaea. Compilation of biostratigraphic and lithofacies data indicate a warm, extensively arid world, largely ice free, and characterized by the onset of atmospheric conditions that were exceedingly stressful to the biosphere, the worst of the eon. Using Chevron's version of the Community Climate model, the authors report here on two Kazanian paleoclimate seasonal simulations, one using 200 ppm CO{sub 2} and the other with 2,000 ppm CO{sub 2}. The authors consider the knowledge of plate assembly back to the Permian accurate enough to allow employment of a seasonal model. Simulation of a warmer Earth with an elevated greenhouse effect (modeled as CO{sub 2}) fits the observed geology and isotope signals. The increased CO{sub 2} experiment warmed the entire planet with the greatest increases north of 50{degree} latitude and least changes in the tropics. The warming caused the poleward retreat of sea ice in both hemispheres. Precipitation and evaporation increased, but runoff was confined to areas of very intense rainfall. Monsoons are limited to the southern hemisphere, associated with the western Tethys sea and the eastern equatorial Panthalassa ocean. Extreme southeastern Pangaea (northern Australia) was a focus of precipitation throughout the year. Precipitation occurred in the higher latitudes (50-55{degree}) on the western coast, of Pangaea where storm tracks make landfall. High evaporation rates characterized the restricted Permian (US), Zechstein, and Perm (Soviet Union) basins, a time of evaporite, deposition. Interior Pangaea at middle to high latitudes endured frigid winters ({minus}40{degree}C) and torrid summers (60{degree}C).

  3. The Permian-Triassic boundary & mass extinction in China

    USGS Publications Warehouse

    Metcalfe, I.; Nicoll, R.S.; Mundil, R.; Foster, C.; Glen, J.; Lyons, J.; Xiaofeng, W.; Cheng-Yuan, W.; Renne, P.R.; Black, L.; Xun, Q.; Xiaodong, M.

    2001-01-01

    The first appearance of Hindeodus parvus (Kozur & Pjatakova) at the Permian-Triassic (P-T) GSSP level (base of Bed 27c) at Meishan is here confirmed. Hindeodus changxingensis Wang occurs from Beds 26 to 29 at Meishan and appears to be restricted to the narrow boundary interval immediately above the main mass extinction level in Bed 25. It is suggested that this species is therefore a valuable P-T boundary interval index taxon. Our collections from the Shangsi section confirm that the first occurrence of Hindeodus parvus in that section is about 5 in above the highest level from which a typical Permian fauna is recovered. This may suggest that that some section may be missing at Meishan. The age of the currently defined Permian-Triassic Boundary is estimated by our own studies and a reassessment of previous worker's data at c. 253 Ma, slightly older than our IDTIMS 206Pb/238U age of 252.5 ??0.3 Ma for Bed 28, just 8 cm above the GSSP boundary (Mundil et al., 2001). The age of the main mass extinction, at the base of Bed 25 at Meishan, is estimated at slightly older than 254 Ma based on an age of >254 Ma for the Bed 25 ash. Regardless of the absolute age of the boundary, it is evident that the claimed <165,000 y short duration for the negative carbon isotope excursion at the P-T boundary (Bowring et al., 1998) cannot be confirmed. Purportedly extraterrestrial fullerenes at the boundary (Hecker et al., 2001) have equivocal significance due to their chronostratigraphic non-uniqueness and their occurrence in a volcanic ash.

  4. Aerobic Marine Habitat Loss During the Late Permian Extinction

    NASA Astrophysics Data System (ADS)

    Penn, J. L.; Deutsch, C.; Payne, J.; Sperling, E. A.

    2016-12-01

    Rapid climate change at the end of the Permian is thought to have triggered the most severe mass extinction in Earth's history, but the precise mechanism of biodiversity loss is unknown. Geological evidence points to lethally hot equatorial temperatures and an expansion of anoxic ocean waters as likely culprits. However, previous climate model simulations of the warm Early Triassic exhibit weak tropical warming, and anoxic conditions require a massive and unconstrained increase in the ocean nutrient reservoir. Reconciling model predictions with the geologic record remains a key challenge to identifying the kill-mechanism, which must also take into account the role of animal physiology. Here we apply a recently developed index for the metabolic scope of marine animals to the first global climate simulations of the Permian-Triassic transition to quantify the effects of ocean warming and oxygen (O2) depletion on aerobic habitat availability. Forcing with extreme CO2 concentrations warms the surface ocean by over 10oC, consistent with paleoproxies for upper ocean temperature change. Warming depletes global O2, with greatest losses occuring in tropical deep waters as a result of their reduced ventilation. Together warming and deoxygenation would have constricted the occurrence of marine habitat by 80% globally, by decreasing the metabolic index of the Permian ocean. These changes are most pronounced in the tropics where the fossil record suggests recovery was severely inhibited. Fossil deposits also record changes in animal body size across the extinction. We find that adaptation via body size reductions can compensate for increasing hypoxia at high latitudes, and even prevent extinction there, but cannot maintain the habitability of the tropics.

  5. [Insects at the borderline between the Permian and the early triassic (Urzhum - Olenek age) and the problem of Permian-Triassic biodiversity crisis].

    PubMed

    Rasnitsyn, A P; Aristov, D S; Rasnitsyn, D A

    2013-01-01

    Distribution of 115 insect families is considered in 15 local assemblages of European Russia, Siberia, Australia and South Africa. The assemblage ages embrace the Urzhum stage of the Middle Permian, the Late Permian, and the transitional Permian-Triassic interval. The assemblages are ordered statistically using two criteria. Ordination after the appearance of a fauna, that is, relation of the number of younger vs. older families, is found to be generally consistent with the stratigraphic data. The method of minimizing the gaps (ghost ranges) in distribution of the families is useful in interpreting the results. Urzhum time is characterized by the balance of emergence and extinction of families (counted as their first and latest appearances, respectively). In Severodvinsk and particularly in Vyatka time, the number of first appearances was decreasing resulted in prevailing extinction. In the transitional Permian-Triassic interval, the emergence of new families accelerated. Initially, the appearance of assemblages was typically Paleozoic (with older families prevailed). It changed gradually, so as by the end of Vyatka time it turned to be quite post-Paleozoic. Diversity was the highest in Severodvinsk time, and it halved at Vyatka time and at the transition interval. However, if we consider transitional families (those not found on a particular interval, but known before and after), the extinction rate reduces to one-third. And when normalized after the material volume, the diversity drop decreases up to a quarter. There was no mass extinction found at the end of the Permian, and the less so at the Permian-Triassic boundary and during the Lower Triassic. Structure of the Permian-Triassic diversity crisis is similar to that of the Cretaceous crisis in many respects. Since the Middle Triassic and up to now, the biodiversity kept increasing quickly and continuously. This implies that the Permian-Triassic crisis resulted in profound modification of the biosphere

  6. Cenozoic Exhumation History and Evolutionary Model For The Central Catalan Coastal Ranges (ne Spain)

    NASA Astrophysics Data System (ADS)

    Gaspar-Escribano, J. M.; Garcia-Castellanos, D.; Roca, E.; Juez-Larre, J.; Cloetingh, S.

    We have studied the Cenozoic exhumation history of the Catalan Coastal Ranges (NE Spain) and propose a model for its kinematic evolution. Two difficulties appear when reconstructing the geological evolution of the study area: (1) Neogene fault extensional reactivation overrides former compressional structures, leading to uncertainties of fault slips and amounts of exhumation and hence misinter- pretation of basin evolution; (2) Absence of parts of the sedimentary record impedes a complete description of timing and significance of erosion-sedimentation during the corresponding time interval. We address these problems by using multiple data sets as constraints for a kinematic model. The observations accounted for in the model consist of: (1) Partially reconstructed geological sections based on seismics and/or sedimentological studies; and (2) New fission track data, that were translated in terms of exhumation to validate the evolu- tionary model. In order to quantitatively link these observations, we use a fault block model that as- sumes vertical shear and incorporates flexural isostasy and surface transport (erosion and sedimentation). Modifying input fault geometries and velocities we can adjust modeling predictions with the observed geometry and exhumation-time diagrams. A gradual variation of effective elastic thickness (low value~5 km offshore, higher value ~25 km in the Ebro Basin) is required to fit exhumation curves derived and the topog- raphy in the Littoral Range. Results of our model provide constraints on the evolution of the region in terms of topography and fault activity. The mass balance between deposition and erosion is also calculated, indicating significant out-of-plane surface transport.

  7. Late-Quaternary Exhumation of Namche Barwa Constrained Using Low-temperature Multi-OSL-thermochronometry

    NASA Astrophysics Data System (ADS)

    King, G. E.; Herman, F.

    2015-12-01

    Exhumation rates >5 mm a-1 have been reported for Namche Barwa, making it one of the most rapidly exhuming places on earth. The driver of such high exhumation rates has been highly debated, and two principle hypotheses have evolved: first the aneurysm model (Zeitler et al., 2001) which proposes that a weakening of the crust coupled with extremely active surface processes causes a spatially stationary locus of exhumation. Secondly a northward plunging antiform that is progressively migrating north-eastward (Seward and Burg, 2008) may instead explain the concentration of extremely low cooling ages and rapid exhumation. Distinguishing the effects of tectonic and surface processes, as well as climate is complex, especially given that most existing thermochronometric systems are unable to resolve late-stage cooling histories. Here we present multi-OSL-thermochronometry which comprises a series of different systems with closure temperature ranging from 30 to 70 oC. We have applied this new technique to a suite of samples from the Namche Barwa massif and are able to resolve cooling histories over 0.1 Ma timescales. Our data indicate propagation of a knick-point along the Parlung river, which can be explained by progressive north-eastward migration of a northward plunging antiform. We suggest therefore that river incision does not feedback onto tectonics, as proposed by the aneurysm model. References Seward, D., Burg, J-P., 2008. Growth of the Namche Barwa Syntaxis and associated evolution of the Tsangpo Gorge: Constraints from structural and thermochronological data. Tectonophysics 451, 282-289. Zeitler, P.K., Meltzer, A.S., Koons, P.O., et al., 2001. Erosion, Himalayan Geodynamics, and the Geomorphology of Metamorphism. GSA Today 11, 4-9.

  8. Post-breakup burial and exhumation of passive continental margins: nine propositions to inform geodynamic models

    NASA Astrophysics Data System (ADS)

    Green, Paul F.; Duddy, Ian; Japsen, Peter; Chalmers, James; Bonow, Johan

    2017-04-01

    Despite many years of study, the processes involved in the post-breakup development of passive margins remain poorly understood. Integration of apatite fission track analysis (AFTA) and stratigraphic landscape analysis (SLA) at a number of margins has provided new insights into the development of elevated passive continental margins (EPCMs). In particular, these studies have highlighted the importance of integrating evidence from the preserved rock record with information on the deposition and erosional removal of rock units which are no longer present ("missing section"). From these studies we have formulated nine propositions regarding the formation of EPCMs and the nature of the controlling processes, viz: 1: EPCMs are not the inevitable consequence of rifting and breakup 2: Elevated topography at present-day EPCMs developed long after breakup 3: Similar EPCM landscapes at different margins suggest similar controlling processes 4: EPCMs undergo episodic burial and exhumation rather than slow monotonic denudation, both before rifting and after breakup 5: Post-breakup exhumation at continental margins is not restricted to elevated onshore regions 6: Post-breakup burial and exhumation have affected low lying margins as well as EPCMs 7: Episodic km-scale exhumation and re-burial also affects cratonic regions 8: Exhumation events show a broad level of synchroneity across continents and oceans and correlate with plate boundary events and changes in plate motions. 9: EPCMs are located where there is an abrupt, lateral change in crustal or lithospheric thickness These propositions imply that positive and negative vertical motions at passive margins are controlled by plate-scale processes. Many of these key aspects are absent from current geodynamic models of passive margin development. Understanding the processes that control vertical movements at passive continental margins requires development of realistic geodynamic models that honour these propositions.

  9. New Permian durhaminid cerioid corals from east-central California

    USGS Publications Warehouse

    Stevens, C.H.; Stone, P.

    2009-01-01

    Permian colonial corals from Artinskian to Kungurian strata in the Conglomerate Mesa area, Inyo Mountains, east-central California, include five new species, one of which is assigned to a new genus. The new taxa are: Malpaisia maceyi n. gen. and n. sp., Pararachnastraea bellula n. sp., P. delicata n. sp., P. owensensis n. sp., and Cordillerastraea inyoensis n. sp. These species, several of which compare most closely with other Artinskian and Kungurian species from eastern Nevada and northern Mexico, represent three distinct stocks that differentiated on an isolated submarine uplift offshore from the main part of the Cordilleran carbonate shelf.

  10. Permian Tethyan Fusulinina from the Kenai Peninsula, Alaska

    USGS Publications Warehouse

    Stevens, C.H.; Davydov, V.I.; Bradley, D.

    1997-01-01

    Two samples from a large, allochthonous limestone block in the McHugh Complex of the Chugach terrane on the Kenai Peninsula, Alaska, contain species of 12 genera of Permian Fusulinina including Abadehella, Kahlerina, Pseudokahlerina?, Nankinella, Codonofusiella, Dunbarula, Parafusulina?, Chusenella, Verbeekina, Pseudodoliolina, Metadoliolina?, Sumatrina?, and Yabeina, as well as several other foraminiferans and one alga. The assemblage of fusulinids is characteristically Tethyan, belonging to the Yabeina archaica zone of early Midian (late Wordian) age. Similar faunas are known from the Pamirs, Transcaucasia, and Japan, as well as from allochthonous terranes in British Columbia, northwestern Washington, and Koryakia in eastern Siberia.

  11. A sudden end-Permian mass extinction (Invited)

    NASA Astrophysics Data System (ADS)

    Shen, S.

    2013-12-01

    The end-Permian mass extinction is the largest of the Phanerozoic. In the immediate aftermath the marine ecosystem was dominated by microbial and communities with disaster taxa. Plausible kill mechanism includes an extremely rapid, explosive release of gases such as carbon dioxide, methane and hydrogen sulfide. Siberian flood volcanism has been suggested as the most possible mechanism to trigger the massive release of greenhouse gases from volcanic eruptions and interaction of magmas with carbon from thick organic-rich deposits or rapid venting of coal-derived methane or massive combustion of coal. A sharp δ13C isotopic excursion, rapid disappearance of carbonate benthic communities and δ18O data from conodont apatite suggest rapid global warming. The end-Permian mass extinction occurred in less than 200,000 years. This extinction interval is constrained by two ash beds (Beds 25 and 28) at the Meishan section. However, the extinction patterns remain controversial largely due to the condensed nature of the Meishan sections. Geochemical signals and their interpretations are also contentious. Thus, the level of achievable stratigraphic resolution becomes crucial to determine the nature of the event and a detailed study of the extinction interval is essential to unravel the extinction pattern, chemostratigraphy, and the causes. However, the extinction interval at Meishan is only 26 cm thick and contains distinct gaps at the Permian-Triassic boundary (PTB) and possibly the base of Bed 25. Thus, it is impossible to resolve a detailed extinction pattern. Studying expanded sections is crucial to understand the detailed events before, during and after the main extinction. In this report, we show a highly-expanded Permian-Triassic boundary section in Guangxi Province, South China. The last 4.5 m between beds 22 and 28 of the Meishan sections is represented by a sequence of ~560 m at the section and the extinction interval between beds 24e and 28 at Meishan is represented

  12. Photic zone euxinia during the Permian-triassic superanoxic event.

    PubMed

    Grice, Kliti; Cao, Changqun; Love, Gordon D; Böttcher, Michael E; Twitchett, Richard J; Grosjean, Emmanuelle; Summons, Roger E; Turgeon, Steven C; Dunning, William; Jin, Yugan

    2005-02-04

    Carbon and sulfur isotopic data, together with biomarker and iron speciation analyses of the Hovea-3 core that was drilled in the Perth Basin, Western Australia, indicate that euxinic conditions prevailed in the paleowater column during the Permian-Triassic superanoxic event. Biomarkers diagnostic for anoxygenic photosynthesis by Chlorobiaceae are particularly abundant at the boundary and into the Early Triassic. Similar conditions prevailed in the contemporaneous seas off South China. Our evidence for widespread photiczone euxinic conditions suggests that sulfide toxicity was a driver of the extinction and a factor in the protracted recovery.

  13. Photic Zone Euxinia During the Permian-Triassic Superanoxic Event

    NASA Astrophysics Data System (ADS)

    Grice, Kliti; Cao, Changqun; Love, Gordon D.; Böttcher, Michael E.; Twitchett, Richard J.; Grosjean, Emmanuelle; Summons, Roger E.; Turgeon, Steven C.; Dunning, William; Jin, Yugan

    2005-02-01

    Carbon and sulfur isotopic data, together with biomarker and iron speciation analyses of the Hovea-3 core that was drilled in the Perth Basin, Western Australia, indicate that euxinic conditions prevailed in the paleowater column during the Permian-Triassic superanoxic event. Biomarkers diagnostic for anoxygenic photosynthesis by Chlorobiaceae are particularly abundant at the boundary and into the Early Triassic. Similar conditions prevailed in the contemporaneous seas off South China. Our evidence for widespread photic-zone euxinic conditions suggests that sulfide toxicity was a driver of the extinction and a factor in the protracted recovery.

  14. Putting it all together: Exhumation histories from a formal combination of heat flow and a suite of thermochronometers

    USGS Publications Warehouse

    d'Alessio, M. A.; Williams, C.F.

    2007-01-01

    A suite of new techniques in thermochronometry allow analysis of the thermal history of a sample over a broad range of temperature sensitivities. New analysis tools must be developed that fully and formally integrate these techniques, allowing a single geologic interpretation of the rate and timing of exhumation and burial events consistent with all data. We integrate a thermal model of burial and exhumation, (U-Th)/He age modeling, and fission track age and length modeling. We then use a genetic algorithm to efficiently explore possible time-exhumation histories of a vertical sample profile (such as a borehole), simultaneously solving for exhumation and burial rates as well as changes in background heat flow. We formally combine all data in a rigorous statistical fashion. By parameterizing the model in terms of exhumation rather than time-temperature paths (as traditionally done in fission track modeling), we can ensure that exhumation histories result in a sedimentary basin whose thickness is consistent with the observed basin, a physically based constraint that eliminates otherwise acceptable thermal histories. We apply the technique to heat flow and thermochronometry data from the 2.1 -km-deep San Andreas Fault Observatory at Depth pilot hole near the San Andreas fault, California. We find that the site experienced <1 km of exhumation or burial since the onset of San Andreas fault activity ???30 Ma.

  15. Continental breakup, back arc spreading and subsequent fast-rates of repeated mantle exhumation in the Tyrrhenian Basin

    NASA Astrophysics Data System (ADS)

    Ranero, César R.; Sallares, Valenti; Prada, Manel; Grevemeyer, Ingo; Zitellini, Nevio

    2017-04-01

    We present active seismic data backed up by geological sampling that shows that rifting of Variscan lithosphere during the opening of the Tyrrhenian basin produced a sequence of events that casts some doubts on the classical interpretation of magma-poor rifted margins. Extensive wide-angle seismic data crossing the basin in 7 transects (collected in 2010 and 2015) provide P-wave velocity models that support the presence of robust magmatism linked to an abrupt breakup and early backarc spreading. The magmatic phase stopped abruptly and was followed by a phase of mantle exhumation constrained by P and S wave velocity models, groundtruth by an existing ODP drill site. The wide-angle data supports that mantle exhumation has occurred in several episodes through time and that tectonically-exhumed mantle floors most of the Vavilov and Marsilli sub-basins of the Tyrrhenian basin. These areas of exhumed mantle have been soon after exhumation or event coeval to mantle exhumation been intruded by numerous basaltic diking events that currently form ridges and crop out at the seafloor in some locations where they have been sampled. Each sequence of events of mantle exhumation and basaltic diking was followed by the construction of large basaltic volcanic edifice that form three distinct structures in the area: The Magnaghi, the Vavilov and Marsilli Seamounts Extensive seismic stratigraphy with > 3000 km of 2D seismic lines across the entire basin calibrated by existing wells provides one of the most accurate kinematically constrained history of any rifted margin from the shelf to the deep basin. The stratigraphy supports that mantle exhumation (after backarc spreading) opened at fast rates comparable to the east Pacific Rise mid ocean ridge, where magmatism is robust and mantle exhumation has not been described.

  16. Permian dust in Oklahoma: Source and origin for Middle Permian (Flowerpot-Blaine) redbeds in Western Tropical Pangaea

    NASA Astrophysics Data System (ADS)

    Sweet, Alisan C.; Soreghan, Gerilyn S.; Sweet, Dustin E.; Soreghan, Michael J.; Madden, Andrew S.

    2013-02-01

    Analogous to many Permian units globally, the Middle Permian of Oklahoma (Flowerpot Shale and Blaine Formation) contains voluminous fine-grained redbeds. These units have long been interpreted to record marine to marginal-marine deposition owing to minor evaporite/dolomite strata; this interpretation, however, disregards the predominant siliciclastic material. Siltstone predominates, and all siliciclastic material is of inferred aeolian origin owing to the fine and remarkably uniform grain size, internally massive structure, blanket-like geometry, and common palaeosols, especially in the Flowerpot Shale. Previously suggested alternative environments for such abundant fine-grained material, such as distal deltaic deposition, are inconsistent with the absence of key sedimentary structures (e.g., graded beds), associated facies (e.g., channelised units), and vertical or lateral trends (e.g., upward coarsening). The minor claystone and associated evaporite and dolomite facies of the Blaine Formation exhibit evidence for subaqueous deposition, but with aeolian delivery of the siliciclastic component. An aeolian dust origin for the siliciclastic material reinforces the interpretation of generally semiarid conditions for this equatorial region of western Pangaea. Whole-rock geochemical and detrital-zircon geochronological data on the siliciclastic units indicate a mixed provenance that includes a mafic component exhibiting a composition similar to reference populations from the Ouachita orogen. The dominant zircon populations reflect transport from easterly/southeasterly directions, with fewer grains likely derived from basement located to the west. Combining an aeolian delivery with the provenance signal indicates predominant equatorial easterlies during deposition of the study units, and subordinate westerlies, consistent with Pangaean monsoonal circulation. Permian redbeds preserved in many parts of former low-latitude Pangaea bear attributes similar to those of the

  17. The end-Permian mass extinction: A complex, multicausal extinction

    NASA Technical Reports Server (NTRS)

    Erwin, D. H.

    1994-01-01

    The end-Permian mass extinction was the most extensive in the history of life and remains one of the most complex. Understanding its causes is particularly important because it anchors the putative 26-m.y. pattern of periodic extinction. However, there is no good evidence for an impact and this extinction appears to be more complex than others, involving at least three phases. The first began with the onset of a marine regression during the Late Permian and resulting elimination of most marine basins, reduction in habitat area, and increased climatic instability; the first pulse of tetrapod extinctions occurred in South Africa at this time. The second phase involved increased regression in many areas (although apparently not in South China) and heightened climatic instability and environmental degradation. Release of gas hydrates, oxidation of marine carbon, and the eruption of the Siberian flood basalts occurred during this phase. The final phase of the extinction episode began with the earliest Triassic marine regression and destruction of nearshore continental habitats. Some evidence suggests oceanic anoxia may have developed during the final phase of the extinction, although it appears to have been insufficient to the sole cause of the extinction.

  18. Flourishing ocean drives the end-Permian marine mass extinction.

    PubMed

    Schobben, Martin; Stebbins, Alan; Ghaderi, Abbas; Strauss, Harald; Korn, Dieter; Korte, Christoph

    2015-08-18

    The end-Permian mass extinction, the most severe biotic crisis in the Phanerozoic, was accompanied by climate change and expansion of oceanic anoxic zones. The partitioning of sulfur among different exogenic reservoirs by biological and physical processes was of importance for this biodiversity crisis, but the exact role of bioessential sulfur in the mass extinction is still unclear. Here we show that globally increased production of organic matter affected the seawater sulfate sulfur and oxygen isotope signature that has been recorded in carbonate rock spanning the Permian-Triassic boundary. A bifurcating temporal trend is observed for the strata spanning the marine mass extinction with carbonate-associated sulfate sulfur and oxygen isotope excursions toward decreased and increased values, respectively. By coupling these results to a box model, we show that increased marine productivity and successive enhanced microbial sulfate reduction is the most likely scenario to explain these temporal trends. The new data demonstrate that worldwide expansion of euxinic and anoxic zones are symptoms of increased biological carbon recycling in the marine realm initiated by global warming. The spatial distribution of sulfidic water column conditions in shallow seafloor environments is dictated by the severity and geographic patterns of nutrient fluxes and serves as an adequate model to explain the scale of the marine biodiversity crisis. Our results provide evidence that the major biodiversity crises in Earth's history do not necessarily implicate an ocean stripped of (most) life but rather the demise of certain eukaryotic organisms, leading to a decline in species richness.

  19. Calcium isotope constraints on the end-Permian mass extinction

    PubMed Central

    Payne, Jonathan L.; Turchyn, Alexandra V.; Paytan, Adina; DePaolo, Donald J.; Lehrmann, Daniel J.; Yu, Meiyi; Wei, Jiayong

    2010-01-01

    The end-Permian mass extinction horizon is marked by an abrupt shift in style of carbonate sedimentation and a negative excursion in the carbon isotope (δ13C) composition of carbonate minerals. Several extinction scenarios consistent with these observations have been put forward. Secular variation in the calcium isotope (δ44/40Ca) composition of marine sediments provides a tool for distinguishing among these possibilities and thereby constraining the causes of mass extinction. Here we report δ44/40Ca across the Permian-Triassic boundary from marine limestone in south China. The δ44/40Ca exhibits a transient negative excursion of ∼0.3‰ over a few hundred thousand years or less, which we interpret to reflect a change in the global δ44/40Ca composition of seawater. CO2-driven ocean acidification best explains the coincidence of the δ44/40Ca excursion with negative excursions in the δ13C of carbonates and organic matter and the preferential extinction of heavily calcified marine animals. Calcium isotope constraints on carbon cycle calculations suggest that the average δ13C of CO2 released was heavier than -28‰ and more likely near -15‰; these values indicate a source containing substantial amounts of mantle- or carbonate-derived carbon. Collectively, the results point toward Siberian Trap volcanism as the trigger of mass extinction. PMID:20421502

  20. Depositional Environment of Permian Tak Fa Formation, Nakhonsawan, Northern Thailand

    NASA Astrophysics Data System (ADS)

    Ketwetsuriya, Chatchalerm; Nützel, Alexander; Kanjanapayont, Pitsanupong

    2016-04-01

    The carbonate rocks of the study area at Amphoe Tak Fa and Amphoe Takhli, Changwat Nakhon Sawan belong to the Tak Fa Formation, Saraburi Group. This formation crops out in the Khao Khwang Platform and consists of late Palaeozoic carbonate platform deposits. It reaches a thickness of 900 meters and crops out in a vast area. The exposures have been measured and samples were collected for petrographic study. The rock consists of limestones, argillaceous limestones, mudstones and dolomites with nodular and banded cherts, which comprise many invertebrate fossils such as fusulinids, ammonoid, pelecypod, gastropod, coral and bryozoa. Many of the fossils are silicified. The gastropod assemblage is currently under study and represents one of the most diverse faunas reported from SE Asia. The age of the rock is Yakhtashian or Artinskian (late Early Permian) to Midian or Capitanian (late Middle Permian). The study of carbonate facies and fauna indicates that the depositional environment was on shelf lagoon within the carbonate platform varying from shallow marine to barrier bar.

  1. Dalhart's only Permian field gets best oil well

    SciTech Connect

    Not Available

    1992-07-20

    This paper reports that activity is picking up in Proctor Ranch oil field in the northwestern Texas panhandle, the only Permian producing field in the lightly drilled Dalhart basin. During the last 2 1/2 months, the field has a new operator and a new producing well, the best of five drilled since discovery in 1990. Corlena Oil Co., Amarillo, acquired the field from McKinney Oil Co. in May and tested its first well in early July. The 1-64 Proctor, 18 miles west of Channing, pumped at rates as high as 178 bd of oil and 6 b/d of water from Permian Wolfcamp dolomite perforations at 4,016-29 ft. Corlena plans to drill another well south of the field soon. The lease requires that the next well be spudded by early November. The field appears to be combination structural-stratigraphic trap in which the dolomite pinches out against the Bravo Domes-Oldham nose to the west.

  2. Wrench faulting in selected areas of Permian Basin

    SciTech Connect

    Bolden, G.P.

    1984-01-01

    Landsat and NASA High Altitude Special Mission Aircraft imagery have made it possible to define at least six separate lineament trends between the Amarillo-Wichita uplift (N62/sup 0/W) and the Texas lineament (N54/sup 0/W) that are 200 to 330 mi (320 to 530 km) long and oriented N54/sup 0/W to N62/sup 0/W. These long lineaments are thought to be P shears and are left-lateral wrench faults by definition. This left-lateral wrench fault system has been demonstrated at the Carta Valley fault zone. The Permian surface between Brown-Bassett and JM field of Terrell, Crockett, and Val Verde Counties along the Pecos River has a fracture system that is compatible with wrench faulting. In Garza and Borden Counties, the elements of left-lateral wrench faulting can be demonstrated from high altitude aircraft imagery and demonstrated on the surface and in the subsurface with seismic support. Surface lineaments are observed on Landsat imagery throughout the Permian basin and lead to the belief that the very long N54/sup 0/ to 62/sup 0/W lineaments are P shears. The set oriented N86/sup 0/ +/- E are the Riedel shears and the N36/sup 0/E are conjugate Riedel shears. These for high angle en echelon faults at the surface in Borden and Garza Counties, and with the surface alignments being documented on CDP seismic lines in the subsurface.

  3. Calcium isotope constraints on the end-Permian mass extinction.

    PubMed

    Payne, Jonathan L; Turchyn, Alexandra V; Paytan, Adina; Depaolo, Donald J; Lehrmann, Daniel J; Yu, Meiyi; Wei, Jiayong

    2010-05-11

    The end-Permian mass extinction horizon is marked by an abrupt shift in style of carbonate sedimentation and a negative excursion in the carbon isotope (delta(13)C) composition of carbonate minerals. Several extinction scenarios consistent with these observations have been put forward. Secular variation in the calcium isotope (delta(44/40)Ca) composition of marine sediments provides a tool for distinguishing among these possibilities and thereby constraining the causes of mass extinction. Here we report delta(44/40)Ca across the Permian-Triassic boundary from marine limestone in south China. The delta(44/40)Ca exhibits a transient negative excursion of approximately 0.3 per thousand over a few hundred thousand years or less, which we interpret to reflect a change in the global delta(44/40)Ca composition of seawater. CO(2)-driven ocean acidification best explains the coincidence of the delta(44/40)Ca excursion with negative excursions in the delta(13)C of carbonates and organic matter and the preferential extinction of heavily calcified marine animals. Calcium isotope constraints on carbon cycle calculations suggest that the average delta(13)C of CO(2) released was heavier than -28 per thousand and more likely near -15 per thousand; these values indicate a source containing substantial amounts of mantle- or carbonate-derived carbon. Collectively, the results point toward Siberian Trap volcanism as the trigger of mass extinction.

  4. The Permian and Triassic in the Albanian Alps

    NASA Astrophysics Data System (ADS)

    Gaetani, Maurizio; Meço, Selam; Rettori, Roberto; Henderson, Charles M.; Tulone, Accursio

    2015-09-01

    The sedimentary succession of the Permian to Middle Triassic of the Albanian Alps is described, as part of the eastern Adria passive margin towards the Tethys. A carbonate ramp deepening towards NE in present day coordinates developed during the Middle Permian and was affected by block faulting with the deposition of carbonate breccia. The Early Triassic was characterized by intense terrigenous deposition with several cobble conglomerate units up to 80 m-thick, and by oolitic carbonate shoals. The fine clastic deposition ended gradually during the earliest Anisian and a wide calcarenitic ramp occupied the area, with small local carbonate mounds. Basinward, the red nodular limestone of the Han Bulog Formation was interbedded with calcarenitic material exported from the ramp. Drowning to more open conditions occurred towards the end of the Pelsonian. Subsequently, cherty limestone and tuffitic layers spread over the entire area. Towards the end of the Ladinian, with the end of the volcanic activity, red pelagic limestone was deposited locally for a short period. By the latest Ladinian most of the area returned to shallow-water conditions, with a peritidal carbonate platform. In the Theth area, in contrast, a basin with black organic-rich dolostone and limestone developed which seems to be unique in that part of the Adria passive margin. The occurrence of cobble conglomerate units in the Lower Triassic testifies to very active block faulting and high accommodation, not yet described for the area.

  5. Low temperature thermochronometric constraints on exhumation and landscape evolution of the eastern Lhasa block, southern Tibet

    NASA Astrophysics Data System (ADS)

    Tremblay, M. M.; Shuster, D. L.; Schmidt, J. L.; Zeitler, P. K.; Harrison, M.

    2013-12-01

    Thermochronometric constraints on unroofing in the eastern Lhasa block--bound by the Bangong-Nujiang and Indus-Yarlung sutures to the north and south, respectively, and east of Nyainqentanglha Shan--are important to understanding the geodynamic evolution of the Himalaya-Tibet orogen. With the exception of the Yarlung-Tsangpo River, the eastern Lhasa block marks the westernmost reach of east-flowing rivers in the externally drained portion of the Tibetan Plateau and is characterized by 1-1.5 km of local relief. At the southern margin of Asia prior to collision with India, the Lhasa block has also experienced all stages of the India-Asia collision since its inception at ~50 Ma. However, we know relatively little about when externally drained rivers propagated, how much material has been denuded, or how tectonic and erosional processes have interacted throughout collision to develop the modern relief in the eastern Lhasa block. To address these questions, we conducted apatite (U-Th)/He and 4He/3He analyses on granites of the Gangdese batholith from a 1.1 km vertical transect at the eastern headwaters of the Lhasa River. Apatite (U-Th)/He ages range from 11.2 to 15.3 Ma and show an age elevation relationship with a sharp break in slope between higher elevation samples (exhumation rate = 0.7 mm/yr) and samples from the valley floor (constant exhumation rate < 0.1 mm/yr). Inverse modeling of 4He/3He ages and release spectra agrees well with conventional apatite (U-Th)/He data, predicting at least 2 km of exhumation over ~3 Myr in the middle Miocene, followed by slow to negligible exhumation rates up to the present. Rapid middle Miocene unroofing likely reflects an increase in local erosion rate, which may be associated with activity on the north-south trending Nari Yun Chu rift system 20 km east of the vertical transect. Additional 4He/3He analyses of the lowest elevation samples are required to constrain when the modern relief at the headwaters of the Lhasa River

  6. Slow steady exhumation of the high elevation Deosai Plateau (Northern Pakistan Himalaya) since 40 Ma

    NASA Astrophysics Data System (ADS)

    van Melle, J.; van der Beek, P.; Guillot, S.; Pecher, A.; Latif, M.

    2007-12-01

    Mountain ranges of the north-western Himalaya in Pakistan show strongly contrasting relief, opposing steep, deeply incised topography with extremely high peaks such as the Karakorum Range and Nanga Parbat Haramosh Massif (NPHM), to high-altitude, low-relief areas such as the Deosai Plateau located between the Karakorum and NPHM and the Tso-Morari Massif in Eastern Ladakh. In contrast, mean elevations of the different mountain ranges are comparable, the Deosai Plateau being on average even slightly higher than the adjacent NPHM. The aim of this study is to quantify the exhumation history the Deosai Plateau, in order to understand how to build such a high-altitude, low-relief plateau and how to preserve it over million-year timescales. Here, we report the first low-temperature thermochronologic data from the Deosai Plateau, to compare its exhumation history to that of the surrounding massifs. Apatite Fission Track (AFT) ages reported in the literature from the NPHM and Karakorum are extremely young (<1 Ma for the NPHM and between <1 and 7 Ma in Karakorum) implying exhumation rates >1 km/Ma. In contrast, our AFT ages from the Deosai Plateau are 15-27 Ma; an order of magnitude older than those of the surrounding massifs. Zircon and apatite (U-Th)/He ages (measured at U of Arizona, HeDWaAZ program) range from 23-45 Ma, and 12-15 Ma, respectively. Modeling the combined AFT and He ages requires continuous and very slow long term cooling rates (around 4 ° C/Ma), consistent with an exhumation rate of about 0.15 km/Ma for typical geothermal gradients. Our data thus suggest steady slow unroofing of the Deosai Plateau since at least 40 Ma. A clear link between cooling age patterns and the geomorphology is also evident, with strongly incised, high-relief massifs showing exhumation at rates an order of magnitude faster than the low-relief plateau. AFT and ZFT ages similar to our data have been reported from the Tso Morari massif further east, characterised by similar high

  7. Detrital mica 40Ar/39Ar dating approach for provenance and exhumation of the Eastern Alps.

    NASA Astrophysics Data System (ADS)

    Gemignani, Lorenzo; Sun, Xilin; Van Gerve, Thomas; Braun, Jean; Wijbrans, Jan Robert

    2017-04-01

    The use of thermochronological techniques on detrital minerals, such as (U-Th)/He on apatite and zircon, zircon fission-tracks and Ar-dating on mica and microcline, can be used to constrain the lateral variation of the exhumation rate and the sediment provenance of large sectors of an actively deforming mountain belt. Analysis of modern river sands yields an inventory of ages of rocks currently cropping out and eroding in the hinterland of a river drainage basin. So far, only few studies have focused on testing the consistency of the detrital mineral age distributions and the surface bed-rock thermochronology. We present here new detrital 40Ar/39Ar biotite and muscovite age distributions for nineteen modern river sands from rivers draining the Eastern Alps north of the Periadriatic line. The ages, interpreted to reflect cooling of the source rock under the closure temperature of muscovite and biotite respectively, were compared with the in-situ ages for the bedrock in the hinterland from literature. The results were generally comparable with the bedrocks ages for both the target minerals and represent three main clusters of ages that record the main exhumation pulses in this sector of the Alps. We have applied two numerical methods to the cooling ages to a) quantify the rates of exhumation of the Tauern Window during Paleocene-Miocene period of the Alpine orogeny, b) linearly compute the spatial variability of the present-day exhumation rates of a set of 4 detrital mineral sample drainage basins along the Inn river stream. Our results suggest a 0.17-0.52 mm/yr range in exhumation rates for the Tauern Window since the Miocene. The results from modelling constrained the downstream evolution of the detrital signal in the Inn river and realistically predicts higher erosion rates in the downstream basin where young cooling ages from the Penninic units of the Tauern are drained into the system, forming a characteristic peak. Our data define more inclusive trends in

  8. Evolution of a complex behavior: the origin and initial diversification of foliar galling by Permian insects

    NASA Astrophysics Data System (ADS)

    Schachat, Sandra R.; Labandeira, Conrad C.

    2015-04-01

    A central notion of the early evolution of insect galling is that this unique behavior was uncommon to rare before the diversification of angiosperms 135 to 125 m.yr. ago. However, evidence accumulated during recent years shows that foliar galls were diverse and locally abundant as early as the Permian Period, 299 to 252 m.yr. ago. In particular, a diversity of leaf galling during the Early Permian has recently been documented by the plant-damage record of foliar galls and, now, our interpretation of the body-fossil record of culprit insect gallers. Small size is a prerequisite for gallers. Wing-length measurements of Permian insects indicate that several small-bodied hemipteroid lineages originated early during the Permian, some descendant lineages of which gall the leaves of seed plants to the present day. The earliest foliar gallers likely were Protopsyllidiidae (Hemiptera) and Lophioneuridae (Thripida). Much of the Early Permian was a xeric interval, and modern galls are most common in dry, extra-tropical habitats such as scrubland and deserts. Plant-damage, insect body fossils, and the paleoclimate record collectively support the ecological expansion of foliar galling during the Early Permian and its continued expansion through the Late Permian.

  9. Evolution of a complex behavior: the origin and initial diversification of foliar galling by Permian insects.

    PubMed

    Schachat, Sandra R; Labandeira, Conrad C

    2015-04-01

    A central notion of the early evolution of insect galling is that this unique behavior was uncommon to rare before the diversification of angiosperms 135 to 125 m.yr. ago. However, evidence accumulated during recent years shows that foliar galls were diverse and locally abundant as early as the Permian Period, 299 to 252 m.yr. ago. In particular, a diversity of leaf galling during the Early Permian has recently been documented by the plant-damage record of foliar galls and, now, our interpretation of the body-fossil record of culprit insect gallers. Small size is a prerequisite for gallers. Wing-length measurements of Permian insects indicate that several small-bodied hemipteroid lineages originated early during the Permian, some descendant lineages of which gall the leaves of seed plants to the present day. The earliest foliar gallers likely were Protopsyllidiidae (Hemiptera) and Lophioneuridae (Thripida). Much of the Early Permian was a xeric interval, and modern galls are most common in dry, extra-tropical habitats such as scrubland and deserts. Plant-damage, insect body fossils, and the paleoclimate record collectively support the ecological expansion of foliar galling during the Early Permian and its continued expansion through the Late Permian.

  10. Permian and Triassic rocks near Quinn River Crossing, Humboldt County, Nevada

    NASA Astrophysics Data System (ADS)

    Ketner, Keith B.; Wardlaw, Bruce R.

    1981-03-01

    Permian and Triassic rocks near Quinn River Crossing, Humboldt County, Nevada, consist of four structural blocks: (1) a Lower Permian volcanic block; (2) a Permian(?) chert-arenite block; (3) a Lower Permian limestone block; and (4) a Permian and Triassic block. The contacts between the Permian volcanic block and the others are interpreted as thrust faults or glide surfaces. None of these rocks are metamorphosed, in contrast to those of the surrounding mountain ranges. Each of the blocks is lithically similar in some respects to rocks of the Osgood Mountains area 80 km to the southeast. The fusulinid and brachiopod faunas of two of the blocks display affinities to those of the McCloud Limestone of northern California and the Coyote Butte Limestone of central Oregon, and the fauna of another block has elements in common with autochthonous rocks of eastern Nevada and Utah. All four blocks probably are allochthonous with respect to the rocks exposed in the surrounding mountain ranges, but their points of origin remain obscure. The rocks at Quinn River Crossing provide a link among the Permian rocks of north-central Nevada, northern California, and central Oregon and a possible key to their original relations, but more comparative data are needed.

  11. Contrasting microbial community changes during mass extinctions at the Middle/Late Permian and Permian/Triassic boundaries

    NASA Astrophysics Data System (ADS)

    Xie, Shucheng; Algeo, Thomas J.; Zhou, Wenfeng; Ruan, Xiaoyan; Luo, Genming; Huang, Junhua; Yan, Jiaxin

    2017-02-01

    Microbial communities are known to expand as a result of environmental deterioration during mass extinctions, but differences in microbial community changes between extinction events and their underlying causes have received little study to date. Here, we present a systematic investigation of microbial lipid biomarkers spanning ∼20 Myr (Middle Permian to Early Triassic) at Shangsi, South China, to contrast microbial changes associated with the Guadalupian-Lopingian boundary (GLB) and Permian-Triassic boundary (PTB) mass extinctions. High-resolution analysis of the PTB crisis interval reveals a distinct succession of microbial communities based on secular variation in moretanes, 2-methylhopanes, aryl isoprenoids, steranes, n-alkyl cyclohexanes, and other biomarkers. The first episode of the PTB mass extinction (ME1) was associated with increases in red algae and nitrogen-fixing bacteria along with evidence for enhanced wildfires and elevated soil erosion, whereas the second episode was associated with expansions of green sulfur bacteria, nitrogen-fixing bacteria, and acritarchs coinciding with climatic hyperwarming, ocean stratification, and seawater acidification. This pattern of microbial community change suggests that marine environmental deterioration was greater during the second extinction episode (ME2). The GLB shows more limited changes in microbial community composition and more limited environmental deterioration than the PTB, consistent with differences in species-level extinction rates (∼71% vs. 90%, respectively). Microbial biomarker records have the potential to refine our understanding of the nature of these crises and to provide insights concerning possible outcomes of present-day anthropogenic stresses on Earth's ecosystems.

  12. Regional structural cross sections, mid-permian to quaternary strata, Texas Panhandle and Eastern New Mexico

    SciTech Connect

    McGookey, D.A.; Gustavson, T.C.; Hoadley, A.D.

    1989-01-01

    Twelve regional cross sections (with text) of the Palo Duro, Dalhart, and Anadarko Basins illustrating the tabular geometry of Permian evaporite beds, areas where salt has been lost by dissolution, and the effects of dissolution-induced subsidence on Permian and post-Permian strata. The authors identify areas of dissolution beneath the High Plains, the Caprock Escarpment, the Rolling Plains, the Pecos Plains, and along the Canadian River valley. The cross sections are printed at a vertical scale of 1 inch equals 400 feet and a horizontal scale of 1 inch equals approximately 8 miles and were constructed using geophysical logs, sample logs, and surficial geologic data.

  13. Permian brachiopods from new localities in northeast Thailand: Implications for paleobiogeographic analysis

    NASA Astrophysics Data System (ADS)

    Pérez-Huerta, Alberto; Chonglakmani, Chongpan; Chitnarin, Anisong

    2007-05-01

    A small Permian brachiopod fauna is described from new localities in northeastern Thailand. Brachiopods were collected from early Permian (Asselian) limestones of the Nam Maholan Formation and middle Permian (Murgabian) sandstones of the Nam Duk Formation and limestones of the Khao Khwang Formation. Analyses of taxa confirm preliminary hypotheses of Cathaysian affinities for brachiopods and fusulinids found in this part of Thailand. Fossils found in sandstones of the Nam Duk molasse facies, however, also show possible Gondwanan relationships with brachiopod taxa described in Australia. This has to be further tested with ongoing research in a better understanding of the paleobiogeography of this part of Southeast Asia.

  14. Western Tibet: Low-temperature thermochronology data and interpretation on exhumation history.

    NASA Astrophysics Data System (ADS)

    Gourbet, L.; Shuster, D. L.; Maheo, G.; Leloup, P. H.; Paquette, J.

    2013-12-01

    The Tibetan plateau is the highest and largest orogenic plateau in the world. Uplift of the plateau is related to the India-Asia collision. However, recent studies [1] suggest that peneplanation predates collision. This implies that a low-relief, low-elevation surface could have existed prior to the uplift and have therefore gained elevation following the India-Asia collision. Some models of long timescale, regional topographic evolution have been mostly based on low-temperature thermochronometry, but so far most data have been obtained in Central and Southern Tibet, where " plateau " conditions, (i.e. low exhumation rates), seem to have been reached prior to the collision [1,2]. Our study focuses on Western Tibet, where the landscape is internally drained and characterized by high local relief on the order of 2 km. We performed (U-Th)/He dating on 21 granitic samples collected in Western Tibet, between the Karakoram fault and the Pangong Co. Apatite (U-Th)/He ages from a vertical transect in the Rutog granite vary between 13.11 +/- 0.14 and 29.25 +/- 0.31 Ma and reveal a clear ages-elevation correlation. Based on the crystallization age of the sampled granite (74.4 +/- 1.9 Ma, U/Pb on zircons), apatite ages are not related to post-intrusion cooling but rather record exhumation or relief evolution. Mean apparent exhumation rate is ~67 m/Ma, which is significatively higher than rates estimated in central Tibet [1,2]. Western Tibet, as Central Tibet, is currently a cold, arid environment with low rates of river incision; modern exhumation rates are presumably similar to Central Tibet and extremely low (< 0.003 mm/a) [3]. Apparent exhumation rates are at least one-order-of-magnitude greater than modern exhumation rates; this suggests that exhumation slowed down after 13 Ma. A possible hypothesis to explain the cooling age difference between Central and Western Tibet is that internal drainage, responsible for low exhumation rates, was established later in Western Tibet

  15. Tracking Burial, Displacement and Exhumation in the Lesser Himalayas, Eastern Bhutan

    NASA Astrophysics Data System (ADS)

    McQuarrie, N.; Long, S. P.; Tobgay, T.; Reiners, P. W.; Coutand, I.

    2010-12-01

    We present data on the burial, displacement and exhumation history of Lesser Himalayan (LH) rocks in eastern Bhutan by presenting quartz deformation microstructure, U-Pb geochronology of zircon metamorphic rim growth, and zircon (U-Th)/He (ZHe) and apatite fission track (AFT) thermochronology combined with sequentially-restored geologic cross-sections. These data highlight the magnitude and timing of displacement of large, discrete structures such as the Main Central thrust (MCT), the Shumar thrust (ST) and a series of thrust faults that comprise the LH duplex, by first tracking the burial history of footwall rocks, and then their subsequent exhumation. ZHe ages (~200°C closure temperature) in LH rocks range from 11.9±1.1 Ma, to 5.65±0.27 Ma and display a general trend of increasing ages to the south with a slight decrease in age within 5 km of the MBT. AFT ages in LH rocks are uniformly young, ranging between 4.5 ± 0.73 to 3.38 ± 0.68 Ma, and do not show a N-S age progression. These LH AFT ages are all younger than previously reported AFT ages in proximal Greater Himalayan rocks exposed at structurally and topographically higher levels to the east and west. Quartz and feldspar deformation microstructures indicate that lower LH rocks were buried to temperatures of 400°-450° via thrust emplacement of the MCT. Half of the total burial depth is attributed to the thickness of the Paleoproterozoic LH section (assuming a 25-30° C/km geothermal gradient). Published prograde monazite ages suggest LH burial was underway by 20-18 Ma. Upper LH rocks were in turn buried by lower LH rocks. Zircon metamorphic rim ages (LA-MC-ICP-MS) ranging from 17-15 Ma date the timing of burial of the northern upper LH section by emplacement of the ST. Plastically-elongated and partially-recrystallized quartz porphyroclasts in the upper LH Baxa Group indicate both temperature of deformation (280°-400°) and synchronous layer normal flattening (LNF) strain. Corresponding burial depths

  16. Exhumation of high-pressure rocks beneath the Solund Basin, Western Gneiss Region of Norway

    USGS Publications Warehouse

    Hacker, B.R.; Andersen, T.B.; Root, D.B.; Mehl, L.; Mattinson, J.M.; Wooden, J.L.

    2003-01-01

    The Solund-Hyllestad-Lavik area affords an excellent opportunity to understand the ultrahigh-pressure Scandian orogeny because it contains a near-complete record of ophiolite emplacement, high-pressure metamorphism and large-scale extension. In this area, the Upper Allochthon was intruded by the c. 434 Ma Sogneskollen granodiorite and thrust eastward over the Middle/Lower Allochthon, probably in the Wenlockian. The Middle/Lower Allochthon was subducted to c. 50 km depth and the structurally lower Western Gneiss Complex was subducted to eclogite facies conditions at c. 80 km depth by c. 410-400 Ma. Within 100. Exhumation to upper crustal levels was complete by c. 403 Ma. The Solund fault produced the last few km of tectonic exhumation, bringing the near-ultrahigh-pressure rocks to within c. 3 km vertical distance from the low-grade Solund Conglomerate.

  17. Exhumation--Providing justice to victims of homicide: The Nigerian experience.

    PubMed

    Faduyile, Francis Adedayo; Taiwo, Olufemi Joshua; Soyemi, Sunday Sokuunle; Akinde, Olakanmi Raphael

    2015-01-01

    Forensic investigations have been embraced in many developed countries to help investigate homicidal cases in their legal system amongst others. It is however still in infancy state in many developing countries, including Nigeria, making the use of this very vital tool very limited to prosecute cases. Some of the reasons include the low knowledge base of the investigating officers, to the dearth of Forensic personnel and the inability to use the findings to prosecute the offenders. The few cases where proper investigation is done, anatomic pathologists and sometimes medical officers are usually called to provide the forensic evidence. Often this involves exhumation of corpse. Exhumation of corpses for death investigation is not a common occurrence in Nigeria and we present the findings seen in these cases.

  18. Fission track ages and Exhumation mechanisms of the Tauern Window, Eastern Alps

    NASA Astrophysics Data System (ADS)

    Bertrand, Audrey; Rosenberg, Claudio; Garcia, Sebastian

    2010-05-01

    The Tauern Window (TW) is a thermal and structural dome which exposes Penninic basement, its cover units as well as parts of the overlying Austroalpine basement in the central part of the Eastern Alps. The peak of metamorphism was attained approximately at 30Ma (Selverstone et .al, 1992), followed by cooling and exhumation throughout Miocene time. Most of the tertiary exhumation of the Eastern Alps was localized in the TW, from Early Oligocene to late Miocene time. A current debate centers on the exhumation mechanisms of Penninic rocks in the core of the TW, namely to assess whether orogen-parallel extension (e.g., Selverstone, 1988) or a combination of folding and erosion (eg., Rosenberg et al., 2004) with subordinate extension were the controlling processes. E-W extension is well documented at the western (Brenner Fault) and eastern (Katschberg Fault) margins of the window (e.g., Behrmann, 1988; Selverstone, 1988; Genser and Neubauer, 1989). In contrast, upright folding dominates the internal structure of the dome, and in particular along its western part, where fold amplitudes, mostly eroded during folding, attained up to 10 km. This study attempts to assess the relative importance of folding and erosion and of orogen-parallel extension during exhumation by analyzing the spatial and temporal cooling patterns of apatite and zircon fission track ages. The compilation of published apatite and zircon fission track ages indicates a concentric younging of both the apatite and zircon ages toward the core of the TW. The concentric isochrones follow the map trace of the axial planes of the upright folds of the western and eastern TW. This cooling pattern is in contrast to the one expected by a process of extensional unroofing, which in map view would results in isochrons parallel to the extensional faults and progressively younging towards them (e.g., Foster et al., 2001). We therefore propose that folding and erosion were primarily responsible for exhuming the Penninic

  19. Subduction dynamics and exhumation of eclogites and blueschists: The Cycladic Blueschist Unit (Cyclades, Greece)

    NASA Astrophysics Data System (ADS)

    Laurent, Valentin; Jolivet, Laurent; Scaillet, Stéphane; Lanari, Pierre; Augier, Romain

    2017-04-01

    Located in eastern Mediterranean, the Hellenic subduction zone results from the convergence between Apulia and Eurasia plates since the late Cretaceous. The Cycladic Blueschist Unit (CBU) is a HP-LT metamorphic unit that was buried and exhumed in the Hellenic subduction zone. Famous for its excellent preservation of HP-LT metamorphic rocks and tectonic structures, the CBU is considered as a natural laboratory to study subduction dynamics. Our study, mainly conducted on Syros Island, combines field structural observations, P-T thermodynamic modelling and 40Ar/39Ar dating that provide a detailed P-T-t-d path of the CBU. Our results show that the CBU was exhumed by an overall top-to-the east shearing during exhumation from eclogite- to greenschist-facies depths, localized along several retrograde shallow-dipping shear zones. Thermobarometry shows that three events of garnet growth have been recorded in the CBU. A first prograde event is recorded in garnets from eclogites at 17 ± 2 kbar and 450 ± 50 °C and a second one at peak P-T conditions around 22 ± 2 kbar and 550 ± 50 °C. A last garnet growth event is recorded only in retrograded samples between 10-12 kbar and 500-570 °C. We interpret this retrograde garnet growth event as the result of an almost isobaric heating previously highlighted on Tinos and Andros islands. Finally, 40Ar/39Ar ages constrain the timing of peak pressure conditions at 52-49 Ma, which is consistent with previous U/Pb, Sm/Nd, Lu/Hf and Rb/Sr ages. Our 40Ar/39Ar ages then constrain exhumation through blueschist-facies P-T conditions between 47 and 35 Ma and the final ductile exhumation in the greenschist-facies at 18-20 Ma. Syn-orogenic exhumation of the CBU, from eclogite- to blueschist-facies P-T conditions, was accommodated in ca. 15 Ma within the subduction channel between a top-to-the E detachment above (Vari Detachment) and a thrust below. Then, a change of subduction dynamics and the settling of a faster slab retreat, coeval with

  20. Structural and erosional controls on exhumation across the southern Himalayan front, NW India

    NASA Astrophysics Data System (ADS)

    Thiede, R. C.; Ehlers, T. A.; Strecker, M. R.

    2006-12-01

    One of the premier research questions in the study active orogens is the role of climate and its potential influence on tectonic processes. The Himalayan orogen comprises well developed topographic, climatic, and erosional gradients, as well as a distinct zonation of physiographic provinces. These characteristics, active faulting, uplift, and superposed extreme climatic gradients associated with high monsoonal rainfall impinging on the southern mountain front make this region an ideal setting to evaluate the interaction between tectonics and surface processes at the scale of the orogen. Since the Indian/Eurasian collision began about 50 Ma ago, deformation in the Himalaya has been concentrated within a 200-km-wide zone. This zone is composed of three major tectonic, climatic, and topographic regions where: (1) the northern and internal part are characterized by high elevation (3-6 km a.s.l), moderate to steep relief and arid climate; (2) the High Himalaya, which constitutes high elevations (1.0-7 km a.s.l), steep relief and a humid climate; and (3) the Lesser Himalaya, with moderate elevation (0.5-3 km a.s.l), moderate relief, and a humid climate. We quantify the distribution of exhumation along the southern front of the Himalaya between the Bhagirati River (upper Ganges) in the east and the Sutlej River in the west. Twenty-five new and 103 previously published apatite fission track (AFT) samples are integrated to quantify spatial variations in exhumation within a 200 (E- W) x 100 (N-S) km wide segment of the southern Himalayan mountain front. The new ages range between 18 and <1 Ma and clusters in two age groups with a specific regional distribution: (a) AFT ages ranging between 10 and 5 Ma are characteristic for the Lesser Himalaya, whereas (b) ages along the southern front of the High Himalaya cluster between 3 and 0.5 Ma. The very young, and elevation-independent AFT cooling ages (<3 Ma) indicate a distinct and laterally extensive region of rapid rock uplift

  1. Changing exhumation patterns during Cenozoic growth and glaciation of the Alaska Range: Insights from detrital thermochronology and geochronology

    USGS Publications Warehouse

    Lease, Richard O.; Haeussler, Peter J.; O'Sullivan, Paul

    2016-01-01

    Cenozoic growth of the Alaska Range created the highest topography in North America, but the space-time pattern and drivers of exhumation are poorly constrained. We analyzed U/Pb and fission-track double dates of detrital zircon and apatite grains from 12 catchments that span a 450 km length of the Alaska Range to illuminate the timing and extent of exhumation during different periods. U/Pb ages indicate a dominant Late Cretaceous to Oligocene plutonic provenance for the detrital grains, with only a small percentage of grains recycled from the Mesozoic and Paleozoic sedimentary cover. Fission-track ages record exhumation during Alaska Range growth and incision and reveal three distinctive patterns. First, initial Oligocene exhumation was focused in the central Alaska Range at ~30 Ma and expanded outward along the entire length of the range until 18 Ma. Oligocene exhumation, coeval with initial Yakutat microplate collision >600 km to the southeast, suggests a far-field response to collision that was localized by the Denali Fault within a weak Mesozoic suture zone. Second, the variable timing of middle to late Miocene exhumation suggests independently evolving histories influenced by local structures. Time-transgressive cooling ages suggest successive rock uplift and erosion of Mounts Foraker (12 Ma) through Denali (6 Ma) as crust was advected through a restraining bend in the Denali Fault and indicate a long-term slip rate ~4 mm/yr. Third, Pliocene exhumation is synchronous (3.7–2.7 Ma) along the length of the Alaska Range but only occurs in high-relief, glacier-covered catchments. Pliocene exhumation may record an acceleration in glacial incision that was coincident with the onset of Northern Hemisphere glaciation.

  2. Changing exhumation patterns during Cenozoic growth and glaciation of the Alaska Range: Insights from detrital thermochronology and geochronology

    NASA Astrophysics Data System (ADS)

    Lease, Richard O.; Haeussler, Peter J.; O'Sullivan, Paul

    2016-04-01

    Cenozoic growth of the Alaska Range created the highest topography in North America, but the space-time pattern and drivers of exhumation are poorly constrained. We analyzed U/Pb and fission-track double dates of detrital zircon and apatite grains from 12 catchments that span a 450 km length of the Alaska Range to illuminate the timing and extent of exhumation during different periods. U/Pb ages indicate a dominant Late Cretaceous to Oligocene plutonic provenance for the detrital grains, with only a small percentage of grains recycled from the Mesozoic and Paleozoic sedimentary cover. Fission-track ages record exhumation during Alaska Range growth and incision and reveal three distinctive patterns. First, initial Oligocene exhumation was focused in the central Alaska Range at ~30 Ma and expanded outward along the entire length of the range until 18 Ma. Oligocene exhumation, coeval with initial Yakutat microplate collision >600 km to the southeast, suggests a far-field response to collision that was localized by the Denali Fault within a weak Mesozoic suture zone. Second, the variable timing of middle to late Miocene exhumation suggests independently evolving histories influenced by local structures. Time-transgressive cooling ages suggest successive rock uplift and erosion of Mounts Foraker (12 Ma) through Denali (6 Ma) as crust was advected through a restraining bend in the Denali Fault and indicate a long-term slip rate ~4 mm/yr. Third, Pliocene exhumation is synchronous (3.7-2.7 Ma) along the length of the Alaska Range but only occurs in high-relief, glacier-covered catchments. Pliocene exhumation may record an acceleration in glacial incision that was coincident with the onset of Northern Hemisphere glaciation.

  3. Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria-Europe plate boundary (Western Alps, Calabria, Corsica)

    NASA Astrophysics Data System (ADS)

    Malusà, Marco G.; Faccenna, Claudio; Baldwin, Suzanne L.; Fitzgerald, Paul G.; Rossetti, Federico; Balestrieri, Maria Laura; Danišík, Martin; Ellero, Alessandro; Ottria, Giuseppe; Piromallo, Claudia

    2015-06-01

    Since the first discovery of ultrahigh pressure (UHP) rocks 30 years ago in the Western Alps, the mechanisms for exhumation of (U)HP terranes worldwide are still debated. In the western Mediterranean, the presently accepted model of synconvergent exhumation (e.g., the channel-flow model) is in conflict with parts of the geologic record. We synthesize regional geologic data and present alternative exhumation mechanisms that consider the role of divergence within subduction zones. These mechanisms, i.e., (i) the motion of the upper plate away from the trench and (ii) the rollback of the lower plate, are discussed in detail with particular reference to the Cenozoic Adria-Europe plate boundary, and along three different transects (Western Alps, Calabria-Sardinia, and Corsica-Northern Apennines). In the Western Alps, (U)HP rocks were exhumed from the greatest depth at the rear of the accretionary wedge during motion of the upper plate away from the trench. Exhumation was extremely fast, and associated with very low geothermal gradients. In Calabria, HP rocks were exhumed from shallower depths and at lower rates during rollback of the Adriatic plate, with repeated exhumation pulses progressively younging toward the foreland. Both mechanisms were active to create boundary divergence along the Corsica-Northern Apennines transect, where European southeastward subduction was progressively replaced along strike by Adriatic northwestward subduction. The tectonic scenario depicted for the Western Alps trench during Eocene exhumation of (U)HP rocks correlates well with present-day eastern Papua New Guinea, which is presented as a modern analog of the Paleogene Adria-Europe plate boundary.

  4. Exhumation of Mid-Crustal Rocks in the Arabian-Nubian Shield. The Baladaya Complex of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Abu-Alam, Tamer; Hassan, Mahmoud; Stüwe, Kurt; Meyer, Sven; Passchier, Cees

    2013-04-01

    Upper amphibolite facies rocks from mid-crustal levels are exhumed in the Arabian-Nubian Shield as metamorphic complexes surrounded by low-grade rocks. These middle crustal level rocks were exhumed during the East- and West-Gondwana collision (Pan-African event) in a time interval of ca. 630 to 590 Ma. One of these metamorphic complexes (i.e. Baladaya complex) shows a complicated exhumation history. Four major rock types are found in the study area. They are: a) metamorphic rocks of upper-amphibolite facies which represent the core of the Baladaya complex. Angular unconformity separates the upper-amphibolite facies rocks away from other rock types in the complex, b) metamorphic rocks of greenschist-amphibolite facies transition. These rocks lie directly above the upper-amphibolite facies rocks (type: a) and below Thalbah molasse sediments (type: c). The lower section of the Thalbah sediments shows metamorphism in lower-greenschist facies. The types (a) and (b) were exhumed underneath the Thalbah sediments (type c) as a flower structure. This flower structure can be confirmed in the field by presence of granitic rocks (rock type: d) bounded by thrust planes. The thrust planes surround the Baladaya complex and dip toward the inner part of the complex while the Thalbah molasse sediments as a footwall to the thrust planes. This geological setting indicates that the complex was exhumed at least three times during the activity of the Pan-African event. The first exhumation was prior to the deposition of sediments, which metamorphosed later to be metamorphic rocks of greenschist-amphibolite facies transition (type: b). The second exhumation was prior the deposition of Thalbah molasse sediments. The third exhumation was by the formation of thrust planes and the regional flower structure of the Baladaya complex.

  5. Crustal Structure Linked to Ultra-High-Pressure Rock Exhumation: A Model for the Tso Morari Complex

    NASA Astrophysics Data System (ADS)

    Jamieson, R. A.; Beaumont, C.; Butler, J. P.; Warren, C. J.

    2009-05-01

    Many syn-collisional ultra-high-pressure (UHP) complexes display an array of upper-crustal structures suggesting that doming accompanied by coeval normal and thrust faulting is closely linked to UHP exhumation processes. We present a geodynamical model that accounts for structural, metamorphic, and geochronological data from UHP terranes in terms of crustal burial and exhumation in a subduction channel below an accretionary wedge. Competition between down-channel shear traction and up-channel buoyancy forces, expressed as the exhumation number, E, controls crustal subduction and exhumation, leading to rapid up-channel flow when E > 1. In some cases, transient slab rollback can lead to incorporation of deep mantle peridotite into the subduction channel. Exhuming UHP material forms a nappe stack and structural dome as it penetrates and destabilises the overlying wedge, driving thrusting and extension. The Tso Morari complex, Ladakh, is a structural dome cored by UHP rocks that were metamorphosed and exhumed during the early stages of the Himalayan collision (ca. 55-45 Ma). Results from a high-resolution numerical model, in which convergence velocity decreases from 15 cm/a to 5 cm/a during the early stages of collision, are consistent with a wide range of structural, metamorphic, and geochronological data from Tso Morari. We conclude that the model offers a viable explanation for the geological evolution of syn-collisional UHP complexes. Moreover, the model demonstrates that buoyant exhumation from deep in the subduction channel is responsible for observed upper-crustal structures, which therefore hold important (but commonly overlooked) clues to UHP exhumation processes.

  6. Thrusting and exhumation of the southern Mongolian Plateau: Joint thermochronological constraints from the Langshan Mountains, western Inner Mongolia, China

    NASA Astrophysics Data System (ADS)

    Feng, Li-Xia; Brown, Roderick W.; Han, Bao-Fu; Wang, Zeng-Zhen; Łuszczak, Katarzyna; Liu, Bo; Zhang, Zhi-Cheng; Ji, Jian-Qing

    2017-08-01

    The Mongolian Plateau has undergone multi-stage denudation since the Late Triassic, and the NE-trending Langshan Mountains in the southern margin of the Mongolian Plateau is crucial to unraveling the Meso-Cenozoic cooling and exhumation history of the Mongolian Plateau. The Langshan Mountains are dominated by Precambrian gneiss and Permian-Middle Triassic granitic plutons crosscut by a set of NE-striking thrust faults. A joint thermochronological study was conducted on 31 granitic and gneissic samples along the HQ and CU transects across the Langshan Mountains and other two samples from the BQ in the north of the Langshan Mountains. Four biotite/muscovite and three K-feldspar 40Ar/39Ar plateau ages range from 205 ± 1 to 161 ± 1 and 167 ± 1 to 131 ± 1 Ma, respectively. Thirty-three apatite fission track (AFT) ages are between 184 ± 11 and 79 ± 4 Ma, with mean track lengths from 11.1 ± 1.8 to 13.1 ± 1.4 μm of mostly unimodal distributions. Thirty-one single-grain raw AHe ages are in a range of 134 ± 8 to 21 ± 1 Ma. The AFT ages decrease monotonously from NW to SE until thrust faults along the two transects, with an age-jump across thrust F35. Joint thermal history modelling shows a three-stage cooling history as a result of denudation, especially with spatial differentiation in the first stage. Relative slow cooling at c. 0.6-1.0 °C/Ma occurred in the BQ and the northern part of the HQ transect during 220-100 Ma and the northern part of the CU transect during 160-100 Ma, respectively, with an amount of c. 2-3 km denudation between 160 and 100 Ma, implying little movement along the thrusts F13 and F33. In the middle and southern parts of the HQ transect and the southern part of the CU transect, rapid cooling at c. 4.0-7.0 °C/Ma, with c. 6-9 km denudation during 170-130 or 160-100 Ma, respectively, is probably influenced by thrusting of F35, F38 and F42 and the resultant tilting. A combination of thrusting, tilting, and denudation led to the youngering

  7. The Late Permian Ocean: What's the Big Stink?

    NASA Astrophysics Data System (ADS)

    Meyer, K. M.; Ridgwell, A.; Kump, L. R.

    2006-12-01

    Since the ocean is (and has been) sulfate rich, the development of basinal to global anoxia is often associated with the buildup of hydrogen sulfide in anoxic waters. Bacterial sulfate reduction begins to dominate after oxygen and nitrate have been depleted, producing hydrogen sulfide. Hence, low atmospheric oxygen content, warm surface ocean temperatures, and high O2 demand reduce oceanic oxygen content and favor the establishment of euxinia. Biomarker evidence for photic zone sulfide and biogeochemical calculations suggest that the end-Permian mass extinction was one interval during which extreme anoxia may have led to H2S buildup. We hypothesize that H2S release to the atmosphere would be possible if the upward flux of sulfide from deep water in a largely euxinic ocean exceeded the oxygen flux into the surface ocean from wind mixing. In this scenario, destabilization of the chemocline (oxygen-sulfide interface) would cause sulfide poisoning in both the marine and terrestrial realms and contribute to the extinction. We used the end-Permian configuration of GENIE (www.genie.ac.uk), an energy-moisture-balance atmosphere model coupled to a 3-D, non-eddy-resolving, frictional geostrophic model to evaluate this hypothesis. This model includes marine biogeochemistry and capably simulates processes associated with the transition to oceanic anoxia. We performed a series of simulations designed to identify the conditions necessary for widespread euxinia and chemocline destabilization. We characterized the magnitude of hydrogen sulfide flux as a function of increasing oceanic phosphate content resulting from P release from sediments in anoxic environments. Significant ocean-atmosphere fluxes of H2S result from 6- to 10-fold increases in ocean phosphate at modern oxygen levels. These fluxes are focused in upwelling regions, although toxic H2S concentrations are also observed in the surface waters of nearshore equatorial regions. Our initial simulations support the

  8. Appalachian Piedmont landscapes from the Permian to the Holocene

    USGS Publications Warehouse

    Cleaves, E.T.

    1989-01-01

    Between the Potomac and Susquehanna Rivers and from the Blue Ridge to the Fall Zone, landscapes of the Piedmont are illustrated for times in the Holocene, Late Wisconsin, Early Miocene, Early Cretaceous, Late Triassic, and Permian. Landscape evolution took place in tectonic settings marked by major plate collisions (Permian), arching and rifting (Late Triassic) and development of the Atlantic passive margin by sea floor spreading (Early Cretaceous). Erosion proceeded concurrently with tectonic uplift and continued after cessation of major tectonic activity. Atlantic Outer Continental Shelf sediments record three major erosional periods: (1) Late Triassic-Early Jurassic; (2) Late Jurassic-Early Cretaceous; and (3) Middle Miocene-Holocene. The Middle Miocene-Holocene pulse is related to neotectonic activity and major climatic fluctuations. In the Piedmont upland the Holocene landscape is interpreted as an upland surface of low relief undergoing dissection. Major rivers and streams are incised into a landscape on which the landforms show a delicate adjustment to rock lithologies. The Fall Zone has apparently evolved from a combination of warping, faulting, and differential erosion since Late Miocene. The periglacial environment of the Late Wisconsin (and earlier glacial epochs) resulted in increased physical erosion and reduced chemical weathering. Even with lowered saprolitization rates, geochemical modeling suggests that 80 m or more of saprolite may have formed since Late Miocene. This volume of saprolite suggests major erosion of upland surfaces and seemingly contradicts available field evidence. Greatly subdued relief characterized the Early Miocene time, near the end of a prolonged interval of tropical morphogenesis. The ancestral Susquehanna and Potomac Rivers occupied approximately their present locations. In Early Cretaceous time local relief may have been as much as 900 m, and a major axial river draining both the Piedmont and Appalachians flowed southeast

  9. Differential exhumation rates across the Longriba fault system : insights from low temperature thermochronology

    NASA Astrophysics Data System (ADS)

    Ansberque, Claire; Godard, Vincent; Bellier, Olivier; De Sigoyer, Julia; Bernet, Matthias; Ehlers, Todd; Stuebner, Konstanze; Wang, Mingming; Tan, Xibin; Xu, Xiwei

    2016-04-01

    The eastern Tibetan margin forms one of the steepest topographic escarpment in the world. Most of the current deformation of this area appears to be accommodated in the Longmen Shan thrust system whose major seismogenic potential is attested by the 2008 Wenchuan earthquake. Yet, the velocity gradient across the margin revealed by GPS measurements decreases significantly 200 km north the Longmen Shan. These observations suggest that other tectonic structures might contribute to the global deformation in eastern Tibet, in particular the Longriba fault system (LFS). For over fifteen years, the Longmen Shan have been the focus of many thermochronological investigations, which have gradually contributed to produce a large database and allowed to better constrain the history and patterns of exhumation of the eastern Tibetan margin. Comparatively, there is significantly fewer thermochronology data near the LFS. This structure has been recognized as a main structure of the margin accommodating much of the Aba block motion (with respect to the Longmen Shan). But, although its Holocene tectonic activity has been investigated, its long-term behavior remains unclear, and its present-day geodynamical role over Late Cenozoic timescales is still uncertain. To better constrain this issue, we used fission tracks and (U-Th)/He on apatites and zircons, on samples located across the two main faults of the LFS and more particularly on both sides of the Maoergai fault. The results show two very contrasted Late Cenozoic exhumation patterns: at the Oligocene, samples north but very close to the fault display an exhumation rate of 40 m/Ma, while at the Miocene, samples south the fault show an exhumation rate of 170 m/Ma. Such discrepancy could reflect two distinct incision periods of the margin and could also highlight the role of the Maoergai fault in the control of this incision pattern.

  10. Survival of Mycobacterium tuberculosis organisms for 8 days in fresh lung tissue from an exhumed body.

    PubMed

    Nolte, Kurt B

    2005-08-01

    Mycobacterium tuberculosis was isolated from the lung tissue of an 86-year-old unembalmed woman who was exhumed for an autopsy 8 days after her death. Autopsy prosectors should consider performing microbiological culture in all cases with a history or gross pathological findings suggestive of an infection even if the postmortem interval is extended. In addition, prosectors should still adhere to biosafety precautions for airborne pathogens, because a long postmortem interval does not necessarily provide assurance that these organisms are not viable.

  11. Burial, Uplift and Exhumation History of the Atlantic Margin of NE Brazil

    NASA Astrophysics Data System (ADS)

    Japsen, Peter; Bonow, Johan M.; Green, Paul F.; Cobbold, Peter R.; Chiossi, Dario; Lilletveit, Ragnhild

    2010-05-01

    We have undertaken a regional study of landscape development and thermo-tectonic evo-lution of NE Brazil. Our results reveal a long history of post-Devonian burial and exhuma-tion across NE Brazil. Uplift movements just prior to and during Early Cretaceous rifting led to further regional denudation, to filling of rift basins and finally to formation of the Atlantic margin. The rifted margin was buried by a km-thick post-rift section, but exhumation began in the Late Cretaceous as a result of plate-scale forces. The Cretaceous cover probably extended over much of NE Brazil where it is still preserved over extensive areas. The Late Cretaceous exhumation event was followed by events in the Paleogene and Neogene. The results of these events of uplift and exhumation are two regional peneplains that form steps in the landscape. The plateaux in the interior highlands are defined by the Higher Surface at c. 1 km above sea level. This surface formed by fluvial erosion after the Late Cretaceous event - and most likely after the Paleogene event - and thus formed as a Paleogene pene-plain near sea level. This surface was reburied prior to the Neogene event, in the interior by continental deposits and along the Atlantic margin by marine and coastal deposits. Neo-gene uplift led to reexposure of the Palaeogene peneplain and to formation of the Lower Surface by incision along rivers below the uplifted Higher Surface that characterise the pre-sent landscape. Our results show that the elevated landscapes along the Brazilian margin formed during the Neogene, c. 100 Myr after break-up. Studies in West Greenland have demonstrated that similar landscapes formed during the late Neogene, c. 50 Myr after break-up. Many passive continental margins around the world are characterised by such elevated plateaus and it thus seems possible, even likely, that they may also post-date rifting and continental separation by many Myr.

  12. Ancestral Rocky Mountian Tectonics: A Sedimentary Record of Ancestral Front Range and Uncompahgre Exhumation

    NASA Astrophysics Data System (ADS)

    Smith, T. M.; Saylor, J. E.; Lapen, T. J.

    2015-12-01

    The Ancestral Rocky Mountains (ARM) encompass multiple crustal provinces with characteristic crystallization ages across the central and western US. Two driving mechanisms have been proposed to explain ARM deformation. (1) Ouachita-Marathon collision SE of the ARM uplifts has been linked to an E-to-W sequence of uplift and is consistent with proposed disruption of a larger Paradox-Central Colorado Trough Basin by exhumation of the Uncompahgre Uplift. Initial exhumation of the Amarillo-Wichita Uplift to the east would provide a unique ~530 Ma signal absent from source areas to the SW, and result in initial exhumation of the Ancestral Front Range. (2) Alternatively, deformation due to flat slab subduction along a hypothesized plate boundary to the SW suggests a SW-to-NE younging of exhumation. This hypothesis suggests a SW-derived Grenville signature, and would trigger uplift of the Uncompahgre first. We analyzed depositional environments, sediment dispersal patterns, and sediment and basement zircon U-Pb and (U-Th)/He ages in 3 locations in the Paradox Basin and Central Colorado Trough (CCT). The Paradox Basin exhibits an up-section transition in fluvial style that suggests a decrease in overbank stability and increased lateral migration. Similarly, the CCT records a long-term progradation of depositional environments from marginal marine to fluvial, indicating that sediment supply in both basins outpaced accommodation. Preliminary provenance results indicate little to no input from the Amarillo-Wichita uplift in either basin despite uniformly westward sediment dispersal systems in both basins. Results also show that the Uncompahgre Uplift was the source for sediment throughout Paradox Basin deposition. These observations are inconsistent with the predictions of scenario 1 above. Rather, they suggest either a synchronous response to tectonic stress across the ARM provinces or an SW-to-NE pattern of deformation.

  13. Numerical modeling of mantle wedge processes and exhumation of UHP mantle in subduction zones

    NASA Astrophysics Data System (ADS)

    Gorczyk, W.; Gerya, T. V.; Guillot, S.; Connolly, J. A.; Yuen, D.

    2007-12-01

    The upwelling of subduction generated partially molten rocks is potentially a mechanism for the exhumation of UHP rocks through the mantle wedge. We investigated this processes using a 2-D coupled petrological- thermomechanical model that incorporates slab dehydration and water transport as well as partial melting of mantle and crustal rocks. This approach allows us to study the dynamics of mantle wedge processes including evolution of partially molten plumes and their interaction with surrounding dry mantle. To study the internal structure of the plumes we used ultra-high resolution numerical simulations with 10 billion active markers to detail the internal structure of natural plumes originating from the slab. The plumes consist of partially molten hydrated peridotite, dry solid mantle and subducted oceanic crust, which may comprise up to 12 volume % of the plume. As the plumes grow and mature these materials mix chaotically resulting in attenuation and duplication of the original layering on scales of 1-1000 m. Comparison of numerical results with geological observations from the Horoman ultramafic complex in Japan suggests that mixing and differentiation processes related to development of partially molten plumes above slabs may be responsible for strongly layered lithologically mixed (marble cake) structure of asthenospheric mantle wedges. The recent discovery of garnet bearing peridotites in the subduction zone of the Great Antilles in Hispaniola has raised questions about the process that leads to their exhumation. To evaluate whether upwelling plumes are a plausible exhumation mechanism we investigated the dynamics of subduction of slow spreading ridges. The results show that subduction of strongly serpentinized oceanic plate causes strong dehydration of the slab and leads to a rheological weakening of the interface between subducting and overriding plate. This weakening triggers trench retreat and massive asthenospheric upwelling into the gap between the

  14. Cooling, exhumation, and kinematics of the Kanchenjunga Himal, far east Nepal

    NASA Astrophysics Data System (ADS)

    Larson, Kyle P.; Camacho, Alfredo; Cottle, John M.; Coutand, Isabelle; Buckingham, Heather M.; Ambrose, Tyler K.; Rai, Santa Man

    2017-06-01

    New single crystal 40Ar/39Ar and apatite fission track ages from the Kanchenjunga region of far east Nepal yield insight into the timing of assembly of the Himalayan midcrust and the mechanisms that controlled its exhumation. The 40Ar/39Ar data are compared with new U(Th)/Pb zircon and monazite intrusive crystallization ages and existing metamorphic monazite ages from across the study area to test for internal consistency and potential excess Ar contributions. This new data set, which significantly enhances the density and spatial coverage available from the region, shows that inferred thrust-sense discontinuities within the now-exhumed former midcrustal rocks exposed therein must have ceased motion by 12 Ma. Furthermore, the spatial distribution of ages across the Kanchenjunga region, older ages ( 12-16 Ma) to the south and north and younger ages ( 8 Ma) in the middle portion of the transect, is compatible with simulations of tectonic-enhanced exhumation above a developing duplex system in nearby Bhutan.

  15. Burial and exhumation of the western border of the Ukrainian shield

    NASA Astrophysics Data System (ADS)

    Andreucci, Benedetta; Schito, Andrea; Aldega, Luca; Corrado, Sveva; Di Paolo, Lea; Zattin, Massimiliano; Szaniawski, Rafal; Jankowski, Leszek; Mazzoli, Stefano

    2015-04-01

    The Podolia region is located on the western border of the Eastern European Craton and it has been part, between the Paleozoic and the Miocene, of an epicontinental basin system. Using indicators of paleotemperature and low temperature thermochronometry, the burial and exhumation history of the Paleozoic succession has been reconstructed, in order to investigate the effects, on this region, of the orogenic cycles occurring along the plate margin. Maximum burial for Silurian and Devonian rocks occurred during the Devonian and Early Carboniferous at depths of 4-4.7 km, as constrained by vitrinite reflectance and mixed layers illite-smectite. Thermochronometric data indicate that exhumation through the 40-120°C temperature range occurred between the Late Triassic and the Early Jurassic, and that no significant burial occurred afterwards (temperatures remaining lower than ca. 60°C). These results point to a major exhumation event occurred at the same time of the Cimmerian orogenesis, taking place a few hundreds of Km away from this region. On the other hand no significant effect of the Alpine orogenesis was recorded, although the collisional front was located less than 100 Km from the Podolia region.

  16. Late Cretaceous extension and exhumation of the Stong Complex and Taku Schist, NE Peninsular Malaysia

    NASA Astrophysics Data System (ADS)

    François, Thomas; Afiq Md, Muhammad; Matenco, Liviu; Willingshofer, Ernst; Fatt Ng, Tham; Iskandar Taib, N.; Kamal Shuib, Mustaffa

    2017-04-01

    Dismembering large continental areas by post-orogenic extension requires favourable geodynamic conditions and frequently occurs along pre-existing suture zones or nappe contacts as exemplified by the Stong Complex and Taku Schist of northern Peninsular Malaysia. For this particular case we have employed a field and microstructural kinematic study combined with low temperature thermo-chronology to analyse the tectonic and exhumation history. The results show that the late Palaeozoic - Triassic Indosinian orogeny created successive phases of burial related metamorphism, shearing and contractional deformation. This orogenic structure was then dismembered during a Cretaceous thermal event that culminated in the formation of a large scale late Santonian - early Maastrichtian extensional detachment, genetically associated with crustal melting, the emplacement of syn-kinematic plutons and widespread migmatisation. The emplacement of these magmatic rocks led to an array of simultaneously formed structures that document deformation conditions over a wide temperature range, represented by amphibolite-facies mylonites and more brittle structures, such as cataclastic zones and normal faults that formed during exhumation in the footwall of the detachment. The formation of this detachment and a first phase of Late Cretaceous cooling was followed by renewed Eocene - Oligocene exhumation evidenced from our apatite fission track ages. We infer that an initial Cretaceous thermal anomaly was responsible for the formation of an extensional gneiss dome associated with simple shear and normal fault rotation. These Cretaceous processes played a critical role in the establishment of the presently observed crustal structure of Peninsular Malaysia.

  17. Methanogenic burst in the end-Permian carbon cycle

    PubMed Central

    Rothman, Daniel H.; Fournier, Gregory P.; French, Katherine L.; Alm, Eric J.; Boyle, Edward A.; Cao, Changqun; Summons, Roger E.

    2014-01-01

    The end-Permian extinction is associated with a mysterious disruption to Earth’s carbon cycle. Here we identify causal mechanisms via three observations. First, we show that geochemical signals indicate superexponential growth of the marine inorganic carbon reservoir, coincident with the extinction and consistent with the expansion of a new microbial metabolic pathway. Second, we show that the efficient acetoclastic pathway in Methanosarcina emerged at a time statistically indistinguishable from the extinction. Finally, we show that nickel concentrations in South China sediments increased sharply at the extinction, probably as a consequence of massive Siberian volcanism, enabling a methanogenic expansion by removal of nickel limitation. Collectively, these results are consistent with the instigation of Earth’s greatest mass extinction by a specific microbial innovation. PMID:24706773

  18. Methanogenic burst in the end-Permian carbon cycle

    NASA Astrophysics Data System (ADS)

    Rothman, Daniel H.; Fournier, Gregory P.; French, Katherine L.; Alm, Eric J.; Boyle, Edward A.; Cao, Changqun; Summons, Roger E.

    2014-04-01

    The end-Permian extinction is associated with a mysterious disruption to Earth's carbon cycle. Here we identify causal mechanisms via three observations. First, we show that geochemical signals indicate superexponential growth of the marine inorganic carbon reservoir, coincident with the extinction and consistent with the expansion of a new microbial metabolic pathway. Second, we show that the efficient acetoclastic pathway in Methanosarcina emerged at a time statistically indistinguishable from the extinction. Finally, we show that nickel concentrations in South China sediments increased sharply at the extinction, probably as a consequence of massive Siberian volcanism, enabling a methanogenic expansion by removal of nickel limitation. Collectively, these results are consistent with the instigation of Earth's greatest mass extinction by a specific microbial innovation.

  19. Karst in Permian evaporite rocks of western Oklahoma

    SciTech Connect

    Johnson, K.S. )

    1993-02-01

    Bedded evaporites (gypsum and salt) of Permian age have been dissolved naturally by ground water to form a major evaporite-karst region in western Oklahoma. The Blaine Formation and associated evaporites comprise 100--800 ft of strata that dip gently into broad, structural basins. Outcropping gypsum, dolomite, and red-bed shales of the Blaine display typical karstic features, such as sinkholes, caves, disappearing streams, and springs. Large caves are developed in gypsum beds 10--30 ft thick at several places, and a major gypsum/dolomite karst aquifer provides irrigation water to a large region in southwestern Oklahoma, where salt layers above and below the Blaine Formation have been partly dissolved at depths of 30--800 ft below the land surface. Salt dissolution causes development of brine-filled cavities, into which overlying strata collapse, and the brine eventually is emitted at the land surface in large salt plains.

  20. Methanogenic burst in the end-Permian carbon cycle.

    PubMed

    Rothman, Daniel H; Fournier, Gregory P; French, Katherine L; Alm, Eric J; Boyle, Edward A; Cao, Changqun; Summons, Roger E

    2014-04-15

    The end-Permian extinction is associated with a mysterious disruption to Earth's carbon cycle. Here we identify causal mechanisms via three observations. First, we show that geochemical signals indicate superexponential growth of the marine inorganic carbon reservoir, coincident with the extinction and consistent with the expansion of a new microbial metabolic pathway. Second, we show that the efficient acetoclastic pathway in Methanosarcina emerged at a time statistically indistinguishable from the extinction. Finally, we show that nickel concentrations in South China sediments increased sharply at the extinction, probably as a consequence of massive Siberian volcanism, enabling a methanogenic expansion by removal of nickel limitation. Collectively, these results are consistent with the instigation of Earth's greatest mass extinction by a specific microbial innovation.

  1. Latest Guadalupian (Middle Permian) conodonts and foraminifers from West Texas

    USGS Publications Warehouse

    Lambert, L.L.; Wardlaw, B.R.; Nestell, M.K.; Nestell, G.P.

    2002-01-01

    Clarkina, which characterizes Upper Permian (Lopingian Series) strata, evolved from Jinogondolella altudaensis in the Delaware basin of West Texas as demonstrated by transitional continuity. The West Texas section is significantly more complete in the uppermost Guadalupian interval than that of the probable GSSP reference section in South China, and clarifies the phylogenetic relationships among other conodont taxa as well. Jinogondolella granti clearly evolved into J. artafrons new species, both characterized by Pa elements with a distinctive fused carina. Representatives of Jinogondolella crofti are limited to the uppermost part of the altudaensis zone, and are interpreted as terminal paedomorphs. The associated foraminifer (non-fusulinid) fauna has some species in common with Zechstein faunas, possibly presaging the evaporitic basin that would develop following this latest Guadalupian marine deposition in West Texas.

  2. Cretaceous stem chondrichthyans survived the end-Permian mass extinction.

    PubMed

    Guinot, Guillaume; Adnet, Sylvain; Cavin, Lionel; Cappetta, Henri

    2013-01-01

    Cladodontomorph sharks are Palaeozoic stem chondrichthyans thought to go extinct at the end-Permian mass extinction. This extinction preceded the diversification of euselachians, including modern sharks. Here we describe an outer-platform cladodontomorph shark tooth assemblage from the Early Cretaceous of southern France, increasing the fossil record of this group by circa 120 million years. Identification of this material rests on new histological observations and morphological evidence. Our finding shows that this lineage survived mass extinctions most likely by habitat contraction, using deep-sea refuge environments during catastrophic events. The recorded gap in the cladodontomorph lineage represents the longest gap in the fossil record for an extinct marine vertebrate group. This discovery demonstrates that the deep-sea marine diversity, poorly known during most of the fish evolutionary history, contains essential data for a complete understanding of the long-term evolution of marine fish paleobiodiversity.

  3. No reff-rimmed margins to the Permian carbonate platforms of Thailand

    NASA Astrophysics Data System (ADS)

    Dawson, Orapin; Baird, Angus; Bosence, Dan

    In the central Thailand platform, marginal buildups (Early Permian) are formed mainly by fossiliferous grainstones with boundstones occurring only as small biostrome. Boundstones have a dominant skeletal element of encrusting Archaelithoporella and Tubiphytes with calcisponges and abundant syndepositional marine cements. This boundstone texture is similar to that of many other well documented Permian examples, such as El Capitan, U.S.A. and Trogkofel, Austria. In the Ratburi area of Peninsular Thailand, small bioherms (Middle Permian) are interbedded within grainstone shoals. Boundstone textures are matrix rich, with bryozoa, the main skeletal element and Tubiphytes, the main binding element. The Peninsular Thailand buildups formed on platform interior ridges and not in a shelf marginal position. These small biostromal and biohermal buildups in central and Peninsular Thailand did not form massive shelf-margin reef bodies as have been described from Permian platforms in western U.S.A. and southern China.

  4. Typical Triassic Gondwanan floral elements in the Upper Permian of the paleotropics

    NASA Astrophysics Data System (ADS)

    Kerp, Hans; Abu Hamad, Abdalla; Vörding, Birgit; Bandel, Klaus

    2006-04-01

    Permian floras of the Middle East often show a mixture of Euramerican, Cathaysian, and Gondwanan elements. We report several species of Dicroidium, a seed fern typical for the Triassic of Gondwana, from the Upper Permian of the Dead Sea region. This is the earliest unequivocal record and the most northerly occurrence of this genus, suggesting that it may have evolved during the Permian in the paleotropics. With the decline and eventual extinction of the typical Permian Glossopteris flora, Dicroidium may have migrated southward. As the climate ameliorated in the Triassic, Dicroidium could have spread farther, eventually colonizing all of Gondwana, where it became one of the dominant floral elements.

  5. U/Pb zircon geochronology and tempo of the end-permian mass extinction

    PubMed

    Bowring; Erwin; Jin M W Martin YG; Davidek; Wang

    1998-05-15

    The mass extinction at the end of the Permian was the most profound in the history of life. Fundamental to understanding its cause is determining the tempo and duration of the extinction. Uranium/lead zircon data from Late Permian and Early Triassic rocks from south China place the Permian-Triassic boundary at 251.4 +/- 0.3 million years ago. Biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the Changhsingian pulse of the end-Permian extinction, corresponding to the disappearance of about 85 percent of marine species, lasted less than 1 million years. At Meishan, a negative excursion in delta13C at the boundary had a duration of 165,000 years or less, suggesting a catastrophic addition of light carbon.

  6. Permian biogeography of the Indian subcontinent with special reference to the marine fauna

    NASA Astrophysics Data System (ADS)

    Singh, Trilochan

    Permian biogeography of the Indian subcontinent is discussed in the light of brachiopods and associated fossils from different localities. The discussion is based primarily on the Permian "biome" concept of Waterhouse and Bonham-Carter (1975), wherein three biomes are proposed: group A of subpolar, group B of temperate, and group C of tropical character. Data on the occurrence of Permian brachiopods and associated fossils are given for the Salt Range, Karakoram, and Himalayan regions of India, Nepal, Bhutan, Tibet, and Peninsular India with respect to the age of the fauna. Marine Permian localities of the Himalayan region include those of Ladakh, Zanskar, Lahaul and Spiti, Kashmir, Bhadarwah-Bhallesh-Chamba, Kinnaur, Garhwal, Kumaun, Darjeeling, Sikkim, and Arunachal Pradesh. Permian marine localities of Peninsular India, which forms a part of central Gondwanaland, include those of Bap, Badhaura, Umaria, Manendragarh, and Daltonganj, where marine transgression occurred in Early Permian time. The faunas of these localities are discussed with respect to their age, which falls into two groups, Early and Late Permian. It is suggested that widespread colder climatic conditions prevailed in the Indian subcontinent during the early Early Permian. Similar conditions continued in most of the localities until the late Early Permian, except at west Karakoram (Shaksgam valley), Zanskar, north Tibet (central and western part), and the Salt Range. However, during the Late Permian, climatic conditions were varied. Cold climatic conditions prevailed in north Tibet (central part), Kumaun Tethyan Himalaya, and south Tibet; temperate conditions occurred in west Karakoram (Shaksgam valley), Zanskar, Lahaul and Spiti, Bhadarwah-Bhallesh-Chamba, north Nepal, and north Sikkim; and tropical conditions occurred in the Salt Range, east Karakoram, Ladakh, Kashmir, and north Tibet (western and eastern parts). At a few localities there appear to be some anomalies that might be due to lack of

  7. Trace-element record in zircons during exhumation from UHP conditions, North-East Greenland Caledonides

    USGS Publications Warehouse

    McClelland, W.C.; Gilotti, J.A.; Mazdab, F.K.; Wooden, J.L.

    2009-01-01

    Coesite-bearing zircon formed at ultrahigh-pressure (UHP) conditions share general characteristics of eclogite-facies zircon with trace-element signatures characterized by depleted heavy rare earth elements (HREE), lack of an Eu anomaly, and low Th/ U ratios. Trace-element signatures of zircons from the Caledonian UHP terrane in North-East Greenland were used to examine the possible changes in signature with age during exhumation. Collection and interpretation of age and trace-element analyses of zircon from three samples of quartzofeldspathic gneiss and two leucocratic intrusions were guided by core vs. rim zoning patterns as imaged by cathodoluminesence. Change from igneous to eclogite-facies metamorphic trace-element signature in protolith zircon is characterized by gradual depletion of HREE, whereas newly formed metamorphic rims have flat HREE patterns and REE concentrations that are distinct from the recrystallized inherited cores. The signature associated with eclogite-facies metamorphic zircon is observed in coesite-bearing zircon formed at 358 ?? 4 Ma, metamorphic rims formed at 348 ?? 5 Ma during the initial stages of exhumation, and metamorphic rims formed at 337 ?? 5 Ma. Zircons from a garnet-bearing granite emplaced in the neck of an eclogite boudin and a leucocratic dike that cross-cuts amphibolite-facies structural fabrics have steeply sloping HREE patterns, variably developed negative Eu anomalies, and low Th/U ratios. The granite records initial decompression melting and exhumation at 347 ?? 2 Ma and later zircon rim growth at 329 ?? 5. The leucocratic dike was likely emplaced at amphibolite-facies conditions at 330 ?? 2 Ma, but records additional growth of compositionally similar zircon at 321 ??2 Ma. The difference between the trace-element signature of metamorphic zircon in the gneisses and in part coeval leucocratic intrusions indicates that the zircon signature varies as a function of lithology and context, thus enhancing its ability to aid in

  8. Cenozoic exhumation history of Sulu terrane: Implications from (U-Th)/He thermochrology

    NASA Astrophysics Data System (ADS)

    Wu, Lin; Monié, Patrick; Wang, Fei; Lin, Wei; Ji, Wenbin; Bonno, Michael; Münch, Philippe; Wang, Qingchen

    2016-03-01

    The Qinling-Dabie-Sulu orogen is the most prominent Phanerozoic orogenic belt in China. The discovery of ultra-high pressure (UHP) minerals in zircon inclusions suggests that the crust was subducted to deeper than 120 km into the mantle and then exhumed to shallow crustal. Recently, low temperature thermochronology has been applied to constrain the final exhumation of Dabie Shan, while there are few studies describing the Cenozoic exhumation history of the Sulu belt. Here we report some (U-Th)/He ages for various lithologies from Sulu Orogenic belt and its northern part-Jiaobei terrane. The single grain He ages range between 18 and 154 Ma, and most of the samples having large intra-sample age scattering. Several reasons such as invisible U/Th-rich inclusions, grain size effect, slow cooling rate, and zonation of parent nuclide or radiation damage effect may account for this dispersion. For all samples, the pattern of the single grain age data exhibits a peak at ~ 45 Ma which is consistent with the borehole fission-track age pattern in adjacent Hefei Basin. Both (U-Th)/He and fission track ages of the Sulu area suggest an enhanced exhumation/cooling in Early-Middle Eocene in the southern part of Tan-Lu fault zone. This enhanced cooling event coincides with rapid subsidence of North China Basin and rapid uplift of its surrounding reliefs, which indicates basin-mountain coupling. This Eocene event is widespread in central China and could be far-field consequence of India-Asia collision. The convergence rate between Pacific Plate and Eurasia decreased substantially during early Tertiary and reached a minimum in Eocene (~ 30-40 mm/yr) while at the same time the collision between India and Asia was completed. Therefore, the Cenozoic exhumation history of the Sulu Orogenic Belt was a combined result of far-field effect of India-Asia collision and declined subduction rate of the Pacific Plate under Eurasia.

  9. Eocene extensional exhumation of basement and arc rocks along southwesternmost Peru, Central Andes.

    NASA Astrophysics Data System (ADS)

    Noury, Mélanie; Bernet, Matthias; Sempéré, Thierry

    2014-05-01

    The overthickened crust of the current Central Andes is commonly viewed as the result of tectonic shortening. However, in the present-day terrestrial forearc and arc of southwesternmost Peru, crustal thickness increases from 30 km along the coastline to >60 km below the active arc, whereas the upper crust exhibits little to no evidence of crustal shortening and, in constrast, many extensional features. How (and when) crustal overthickness was acquired in this region is thus little understood. Because crustal overthickening often results in extensional collapse and/or significant erosion, here we address this issue through a regional-scale study of exhumation using fission-track thermochronology. The limited fission-track data previously available in the area suggested that exhumation began during the Mesozoic. In this study, we present new apatite and zircon fission-track data obtained along the current terrestrial forearc of southwesternmost Peru. This relatively restricted area presents the interest of providing extensive outcrops of Precambrian to Ordovician basement and Early Jurassic to Late Cretaceous arc plutons. In order to compare the chronology of exhumation of these units, we performed extensive sampling for fission-track dating, as well as structural mapping. Our results indicate that the basement rocks and Jurassic plutons that crop out in the Arequipa region, where the crust is now >50 km-thick, experienced a rapid cooling through the 240-110°C temperature range between ~65 and ~35 Ma. This period of rapid exhumation coincided in time with the accumulation of terrestrial forearc deposits (the Lower Moquegua Group), that exhibit many syn-sedimentary extensional features and are bounded by conspicuous normal faults, specifically along the region where intense activity of the main arc between ~90 and ~60 Ma had led to voluminous magma emplacement. This close succession of (1) intense magmatic activity and (2) regional-scale exhumation associated with

  10. The history of the Arabian platform evolution in the Late Permian and Triassic

    SciTech Connect

    Bebeshev, I.I.

    1995-03-01

    On the basis of comprehensive investigations of the Upper Permian and Triassic sequences of the Arabian platform, three stages were recognized, corresponding to distinct time intervals. The first stage corresponds to the Latest Permian-Early Triassic, the second - to the Early-Middle Triassic, the third - to the Late Triassic. Special maps were plotted for the second and third stages, reflecting major paleogeographic and paleotectonic events. An effort was made to test the oil potential of the sequences.

  11. Prolonged Permian–Triassic ecological crisis recorded by molluscan dominance in Late Permian offshore assemblages

    PubMed Central

    Clapham, Matthew E.; Bottjer, David J.

    2007-01-01

    The end-Permian mass extinction was the largest biotic crisis in the history of animal life, eliminating as many as 95% of all species and dramatically altering the ecological structure of marine communities. Although the causes of this pronounced ecosystem shift have been widely debated, the broad consensus based on inferences from global taxonomic diversity patterns suggests that the shift from abundant brachiopods to dominant molluscs was abrupt and largely driven by the catastrophic effects of the end-Permian mass extinction. Here we analyze relative abundance counts of >33,000 fossil individuals from 24 silicified Middle and Late Permian paleocommunities, documenting a substantial ecological shift to numerical dominance by molluscs in the Late Permian, before the major taxonomic shift at the end-Permian mass extinction. This ecological change was coincident with the development of fluctuating anoxic conditions in deep marine basins, suggesting that numerical dominance by more tolerant molluscs may have been driven by variably stressful environmental conditions. Recognition of substantial ecological deterioration in the Late Permian also implies that the end-Permian extinction was the climax of a protracted environmental crisis. Although the Late Permian shift to molluscan dominance was a pronounced ecological change, quantitative counts of 847 Carboniferous–Cretaceous collections from the Paleobiology Database indicate that it was only the first stage in a stepwise transition that culminated with the final shift to molluscan dominance in the Late Jurassic. Therefore, the ecological transition from brachiopods to bivalves was more protracted and complex than their simple Permian–Triassic switch in diversity. PMID:17664426

  12. Evolution and extinction of Permian fusulinid fauna in the Khao Tham Yai Limestone in NE Thailand

    NASA Astrophysics Data System (ADS)

    Hada, Shigeki; Khosithanont, Somboon; Goto, Hiroya; Fontaine, Henri; Salyapongse, Sirot

    2015-05-01

    The first detailed biostratigraphic investigation of a single limestone unit within the Khao Tham Yai Limestone shows it was deposited continuously in a shelf setting without any intercalation of clastic beds. It ranges from the Wordian (middle Middle Permian) up to the Wuchiapingian (lower Upper Permian). The limestone unit is divided in ascending order into three fusulinid zones, i.e. Colania, Lepidolina and Codonofusiella zones. The middle zone is characterized by an abundance of large-tested fusulinids characteristic of the Lepidolina Zone. Shell sizes of the fusulinid species in this zone display continuous rapid morphological change along a one-way evolutionary path from small, primitive species with simple structure to large, highly evolved species having a complicated wall structure. Fusulinid biostratigraphy in a single limestone unit elucidates evolution and extinction patterns of Permian fusulinids of the shallow-water Tethyan shelf area in the Indochina Block. Our study reveals that the boundary between the Guadalupian (Middle Permian) and Lopingian (Upper Permian) in the Khao Tham Yai Limestone is clearly defined as an abrupt change in the fusulinid assemblages from the elimination of large-tested Verbeekinids and Schwagerinids to the domination of small-shelled Schubertellids. The Schubertellids underwent slower evolutionary morphological change than earlier fusulinids and were decreasingly dominant through the Permian. A similar pattern of fusulinid evolution and extinction at the Guadalupian-Lopingian boundary occurs in shallow-water Tethyan shelf areas and mid-oceanic shallow-water environments in mid-Panthalassa. Eventually, even smaller fusulinids abruptly become extinct. Clastic deposits finally replace previous carbonate formations characterized by algae-foraminifera biota. It starts in the upper Middle Permian in the southern parts and spreads throughout the whole area in the lower Upper Permian in NE Thailand. These observations suggest

  13. Understanding the thermal history, exhumation patterns, and role of fault systems on Goodenough Island, Papua New Guinea: Insights from 3D thermo-kinematic modelling

    NASA Astrophysics Data System (ADS)

    Bermudez, M. A.; Baldwin, S.; Fitzgerald, P. G.; Braun, J.

    2012-12-01

    The world's youngest eclogites, exhumed from depths of ca. 90 km since 8 Ma, are located in the D'Entrecasteaux Islands in the active Woodlark rift of southeastern Papua New Guinea. These (U)HP rocks formed during/following subduction of Australian margin-derived volcaniclastic sediments, and were exhumed during rifting within the larger, obliquely convergent Australian-Pacific plate boundary zone. Several (U)HP exhumation mechanisms have been proposed including diapiric rise of buoyant crust from mantle to crustal depths, and rifting of heterogeneous crust ahead of the east-to-west propagating Woodlark seafloor spreading center. In order to constrain the relative importance of different exhumation mechanisms through time (i.e., timing and rates of diapirism vs crustal faulting), we apply 3D thermo-kinematic modeling (Pecube) to constrain cooling and exhumation histories derived from thermochronologic data from Goodenough Island, the western-most of the D'Entrecasteaux Islands. More than 500,000 Pecube inverse models were run to evaluate scenarios involving vertical exhumation velocities (i.e., simulating simple buoyancy due to diapirism), low-angle normal faulting and combinations of both processes. These preliminary models assume steady-state topography. Preliminary models (starting at 8 Ma) include: (i) continuous exhumation, (ii) two exhumation phases with different exhumation rates (increasing and/or decreasing), and (iii) three exhumation phases with variable exhumation rates. For buoyancy-only models, the first two scenarios (i and ii) result in poor fits between model-derived and observed (experimental) data. Notably, scenarios (i) and (ii) produce indistinguishable ages for all thermochronologic systems, uniformly long apatite fission-track (AFT) lengths, excessive temperatures at the Moho and geological starting parameters (depth, T) that are not consistent with other data. Scenario (iii) with three exhumation phases has the least misfit between model

  14. Neogene exhumation of the Internal Rif units (Northern Morocco) evidenced by low- temperature thermochronology

    NASA Astrophysics Data System (ADS)

    Romagny, Adrien; Munch, Philippe; Corsini, Michel; Azdimoussa, Ali; Arnaud, Nicolas; Monié, Patrick; Bonno, Michael; Vazquez, Mercedes

    2013-04-01

    The Rif Chain (Northern Morocco) belongs, with the Betic Cordillera (Southern Spain) to the westernmost part of the Alpine belt. There, the Beni Bousera peridotite massif is exhumed and corresponds to one of the deepest exhumed lithospheric rocks of the chain. Tectono-metamorphic studies showed that the internal units were subjected to very fast exhumation during the late Oligocene - early Miocene interval in relation with a crustal thinning and the Alboran sea rifting (synthesis in Chalouan et al., 2008). However, no data are available for the subsequent period despite that Neogene uplift sediments are well known in the internal domain since the work of Wildi and Wernli (1977) and predicted during the Messinian by thermomecanical modelling (Duggen et al., 2003). We present here for the first time a low temperature thermochronologic study (apatite (U-Th)/He and fission tracks; AHe and AFT) of these rocks in order to date and quantify the Neogene exhumation history of internal units of the Rif Chain. Most AHe ages are comprised between 14.25 ± 0.21 and 21.32 ± 0.31 Ma however some are younger (e.g. 6.92 ± 0.14 Ma). AHe ages are closed to fission tracks ages, indicating a very rapid cooling. Moreover they do not show any clear age-elevation relationship that is consistent with a very rapid cooling. Youngest ages correspond to apatite with low eU concentration and thus are interpreted in terms of lower closure temperatures. We performed thermal modelling with HeFTy software (Ehlers et al., 2005; Ketcham et al., 2007) on fission tracks lengths and He diffusion data as they provide a statistical but more complete temperature-time history for the samples. We also used available 40Ar/39Ar data on biotite and field data to better constrain thermal modelling. Exhumation occurred in two main steps: i) a very rapid cooling between 22 and 17 Ma until rocks reached the top of the PAZ (80 to 60°C) at a rate of ~70 to 120°C/Ma) and ii) a very slow cooling between 17 and 4 Ma

  15. Mesozoic burial, Mesozoic and Cenozoic exhumation of the Funeral Mountains core complex, Death Valley, Southeastern California

    NASA Astrophysics Data System (ADS)

    Beyene, Mengesha Assefa

    2011-12-01

    The Funeral Mountains of Death Valley National Park, CA, provide an opportunity to date metamorphism resulting from crustal shortening and subsequent episodic extensional events in the Sevier hinterland. It was not clear whether crustal shortening and thus peak temperature metamorphism in the hinterland of the Sevier-Laramide orogenic wedge have occurred whether in Late Jurassic, Early Cretaceous, Late Cretaceous or somewhere between. Particularly ambiguous is the timing of crustal shortening in the deep levels of the hinterland of the Sevier belt, now manifest in the metamorphic core complexes, and how and when these middle-to-lower crustal rocks were exhumed. A 6-point garnet and a whole rock Savillax isochron from middle greenschist facies pelitic schist of the southeastern Funeral Mountains core complex yields an age of 162.1 +/- 5.8 Ma (2sigma). Composite PT paths determined from growth-zoned garnets from the same samples show a nearly isothermal pressure increase of ˜2 kbar at ˜490°C, suggesting thrust burial at 162.1 +/- 5.8 Ma. A second sample of Johnnie Formation from the comparatively higher metamorphic grade area to the northwest (East of Chloride Cliff) yielded an age of 172.9 +/- 4.9 Ma (2sigma) suggesting an increase of thrust burial age towards the higher grade rocks (northwest part of the core complex), consistent with paleo-depth interpretation and metamorphic grade. 40Ar/ 39Ar muscovite ages along footwall of the Boundary Canyon detachment fault and intra-core Chloride Cliff shear zone exhibit significant 40Ar/39Ar muscovite age differences. For samples from the immediate footwall of BCD, the pattern of ages decreasing toward the northwest is consistent with differences in depth of metamorphism, and for Late Cretaceous, top-to-northwest exhumation by motion along the precursor BCD; consistent with mesoscopic and microscopic kinematic studies. Samples from the footwall of the structurally-lower Chloride Cliff shear zone yield Tertiary 40Ar/39Ar

  16. Multiple broadly synchronous km-scale exhumation episodes on different continents: implications for controlling processes

    NASA Astrophysics Data System (ADS)

    Green, Paul; Duddy, Ian; Japsen, Peter

    2015-04-01

    Numerous low temperature thermochronology studies have defined regional cooling episodes which imply removal of several km of section over areas of several 104 km2. The origin of such events has long been the subject of debate, while their reality has sometimes been questioned because of the lack of a viable mechanism. Kilometre-scale denudation at rifted margins has traditionally been interpreted as related to rifting and breakup, magnified by the flexural response to denudation of the uplifted rift flanks. But it is now clear that at many margins the post-breakup history is more complex, with km-scale uplift and erosion commonly post-dating breakup by 10s of Myr and often affecting regions many 100s of kilometres inland of the margins (Green et al., 2013; Brown et al., 2014). Numerous examples around the world of km-scale exhumation affecting regions distant from continental margins, including cratonic regions traditionally regarded as stable over Phanerozoic time (e.g. Ault et al., 2009; Flowers & Kelley, 2011), cannot be explained by margin-related mechanisms. It has also become clear that periods of exhumation are separated by episodes of burial, defining a series of positive and negative vertical movements. Previous studies have defined a broad synchroneity of Early, Middle and Late Cenozoic exhumation events in regions from Alaska to Greenland, Norway and Svalbard (Green and Duddy, 2010). New results from SE Australia define a series of exhumation episodes ranging in time from Carboniferous to Cenozoic which are broadly synchronous with similar events previously defined in Brazil and South Africa (Green et al. 2013). While estimates of the timing of exhumation in different areas are subject to some uncertainty, data across three southern hemisphere continents show a broad synchronicity in similar fashion to the northern hemisphere examples cited above. Dynamic topography has been invoked as a possible mechanism for producing uplift, the effects of which

  17. Feasibility study of heavy oil recovery in the Permian Basin (Texas and New Mexico)

    SciTech Connect

    Olsen, D.K.; Johnson, W.I.

    1993-05-01

    This report is one of a series of publications assessing the feasibility of increasing domestic heavy oil production. Each report covers select areas of the United States. The Permian Basin of West Texas and Southeastern New Mexico is made up of the Midland, Delaware, Val Verde, and Kerr Basins; the Northwestern, Eastern, and Southern shelves; the Central Basin Platform, and the Sheffield Channel. The present day Permian Basin was one sedimentary basin until uplift and subsidence occurred during Pennsylvanian and early Permian Age to create the configuration of the basins, shelves, and platform of today. The basin has been a major light oil producing area served by an extensive pipeline network connected to refineries designed to process light sweet and limited sour crude oil. Limited resources of heavy oil (10`` to 20`` API gravity) occurs in both carbonate and sandstone reservoirs of Permian and Cretaceous Age. The largest cumulative heavy oil production comes from fluvial sandstones of the Cretaceous Trinity Group. Permian heavy oil is principally paraffinic and thus commands a higher price than asphaltic California heavy oil. Heavy oil in deeper reservoirs has solution gas and low viscosity and thus can be produced by primary and by waterflooding. Because of the nature of the resource, the Permian Basin should not be considered a major heavy oil producing area.

  18. Feasibility study of heavy oil recovery in the Permian Basin (Texas and New Mexico)

    SciTech Connect

    Olsen, D.K.; Johnson, W.I.

    1993-05-01

    This report is one of a series of publications assessing the feasibility of increasing domestic heavy oil production. Each report covers select areas of the United States. The Permian Basin of West Texas and Southeastern New Mexico is made up of the Midland, Delaware, Val Verde, and Kerr Basins; the Northwestern, Eastern, and Southern shelves; the Central Basin Platform, and the Sheffield Channel. The present day Permian Basin was one sedimentary basin until uplift and subsidence occurred during Pennsylvanian and early Permian Age to create the configuration of the basins, shelves, and platform of today. The basin has been a major light oil producing area served by an extensive pipeline network connected to refineries designed to process light sweet and limited sour crude oil. Limited resources of heavy oil (10'' to 20'' API gravity) occurs in both carbonate and sandstone reservoirs of Permian and Cretaceous Age. The largest cumulative heavy oil production comes from fluvial sandstones of the Cretaceous Trinity Group. Permian heavy oil is principally paraffinic and thus commands a higher price than asphaltic California heavy oil. Heavy oil in deeper reservoirs has solution gas and low viscosity and thus can be produced by primary and by waterflooding. Because of the nature of the resource, the Permian Basin should not be considered a major heavy oil producing area.

  19. The relationship of the Indian and western Australian Permian marine faunas

    NASA Astrophysics Data System (ADS)

    Dickins, J. M.; Shah, S. C.

    At Gondwana Five, Wellington, New Zealand, 1980, the relationship of the Permian Peninsular and Himalayan India fauna and flora was explored. The authors concluded that Peninsular India could not have been far from southern Asia during the Permian. This conclusion has been confirmed by data presented at the Symposium on the Tibet Plateau, Beijing, China, 1980, and the recent discovery of Eurydesma and the Eurydesma fauna in northwest Tibet. The relationship of the marine faunas of Peninsular and Himalayan India with those of the western Australian region and the climatic implications have now been considered by the authors. Although the Lower Permian Gondwana cold- and cold-temperate-water faunas of both areas have important similarities, significant differences can be tabulated. Such differences are not apparent in the faunas from within the Peninsular-Himalayan Indian region, so that the faunas of this region are closer to each other than they are to the faunas of the western Australian region. In India the early faunas are overlain by warm-water faunas, whereas in the western Australian region temperate-water conditions prevail. Only in the Upper Permian, when the world as a whole became warmer, are closer faunal links established between the two areas. It is concluded that Western Australia was unlikely to have been close to India during the Permian, and that the faunal relationships indicate India cannot be placed alongside Western Australia. This conclusion is supported by the different geological development in the two areas during the Permian.

  20. Permian-Triassic boundary interval as a model for forcing marine ecosystem collapse by long-term atmospheric oxygen drop

    NASA Astrophysics Data System (ADS)

    Weidlich, O.; Kiessling, W.; Flügel, E.

    2003-11-01

    Ecological traits of reefs across the Permian-Triassic boundary interval coincide with a modeled decline of atmospheric oxygen throughout the Permian Period. Selective extinction and recovery patterns within the reef system are observed both at the end of the middle Permian (end-Guadalupian) and at the Permian-Triassic boundary. The end-Guadalupian event selectively affected corals and broke down the cool-water carbonate factory. Sponges, however, were largely unaffected and bloomed in reefs toward the end of the Permian. The end-Permian total destruction of the metazoan reef system only left behind poorly diverse microbial communities. The temporal reef patterns are thus similar to spatial patterns of modern benthic communities approaching oxygen minimum zones. This observation suggests that a decline in oxygen concentrations was at least partly involved in the destruction of reefs, even where there is no direct evidence of oceanic anoxia.

  1. Exhumation of Basement-cored Uplifts: Example of the Kyrgyz Range Quantified with Apatite Fission-track Thermochronology

    NASA Technical Reports Server (NTRS)

    Sobel, Edward R.; Oskin, Michael; Burbank, Douglas; Mikolaichuk, Alexander

    2005-01-01

    The Kyrgyz Range, the northernmost portion of the Kyrgyzstan Tien Shan, displays topographic evidence for lateral propagation of surface uplift and exhumation. The highest and most deeply dissected segment lies in the center of the range. To the east, topography and relief decrease, and preserved remnants of a Cretaceous regional erosion surface imply minimal amounts of bedrock exhumation. The timing of exhumation of range segments defines the lateral propagation rate of the range-bounding reverse fault and quantifies the time and erosion depth needed to transform a mountain range from a juvenile to a mature morphology. New apatite fission-track (AFT) data from three transects from the eastern Kyrgyz Range, combined with published AFT data, demonstrate that the range has propagated over 110 km eastwards over the last 7-11 Myr. Based on the thermal and topographic evolutionary history, we present a model for a time-varying exhumation rate driven by rock uplift and changes in erodability and the time scale of geomorphic adjustment to surface uplift. Easily eroded, Cenozoic sedimentary rocks overlying resistant basement control early, rapid exhumation and slow surface upliftrates. As increasing amounts of resistant basement are exposed, exhumation rates decrease while surface uplift rates are sustained or increase, thereby growing topography. As the range becomes high enough to cause ice accumulation and develop steep river valleys, fluvial and glacial erosion become more powerful and exhumation rates once again increase. Independently determined range-noma1 shortening rates have also varied over time, suggesting a feedback between erosional efficiency and shortening rate.

  2. Determining orogenic exhumation, steady state, and frontal accretion, using the sediment record: an example from the Himalayan foreland basin

    NASA Astrophysics Data System (ADS)

    Najman, Y.; Pringle, M.; Bickle, M.; Garzanti, E.; Ando, S.; Burbank, D.; Brozovic, N.

    2003-04-01

    The sediment archive can provide an invaluable record of a mountain belt's evolution, where information from rocks in the mountain belt itself has been lost by overprinting due to later metamorphism or removed by tectonism or erosion. In this study of the Himalayan foreland basin sediments, we demonstrate the use of Ar-Ar dating of detrital white micas to provide information on the cooling, exhumation and tectonic history of the source region. Calculation of lag times, defined as the difference between the detrital mica Ar-Ar age and its host sediment depositional age, allows: 1) Determination of cooling and exhumation rates in the orogen. Short lag times indicate periods of rapid exhumation. Exhumation rates can be quantified using a simple thermal model that allows for advection modification of the geotherm. 2) An assessment of the orogen's maturity in terms of its progress towards steady-state. Exhumational steady-state is defined as "when ages obtained from a specific thermochronometer in a specified thermal domain are time-invariant" (Willett &Brandon, Geology, 2002). Exhumational steady-state can be identified using the sediment record, represented by periods when lag times remain constant through time. Additionally, temporal variation in detrital mica Ar-Ar ages can be used to track provenance changes in the source region, the result of tectonic exhumation. This technique, combined with additional provenance tools of Sm-Nd whole rock isotopic analyses, petrographic and heavy mineral data, allows us to document a period of frontal accretion in the Himalaya, which can be interpreted in terms of critical wedge theory.

  3. Modern and Past Rock Exhumation in the St. Elias Mountains Revealed by Onshore and Offshore Detrital Thermochronology

    NASA Astrophysics Data System (ADS)

    Enkelmann, E.; Dunn, C. A.; Ridgway, K.; Allen, W. K.

    2016-12-01

    The St. Elias Mountains in southeastern Alaska provide a natural laboratory to study the interacting processes of tectonics and climate. Because of the high-latitude, coastal geography the surface processes in the St. Elias Mountains are dominated by glacial erosion that varied during late Cenozoic climate shifts. Sediment eroded from the St. Elias Mountains are transported into the Gulf of Alaska by large tidewater glaciers and rivers, where they are deposited on the shelf and in large deep-sea submarine fans. Surface uplift and erosion jointly results in exhumation of deep crustal rocks that has been quantified by thermochronology, revealing spatial variations in exhumation rates across the St. Elias Mountains. We present new thermochronology data (apatite and zircon fission-track ages) from offshore strata derived from boreholes drilled by IODP Expedition 341 in the Gulf of Alaska. This offshore record provides an integrated signal of rock exhumation from the St. Elias and southeast Alaska since 10 Ma. Integrating the offshore data with the existing onshore thermochronology reveals that very rapid exhumation (>2 km/Myr) from 8-10 km depths has been occurring in southeastern Alaska since 11­-10 Ma and thus prior to the onset of glaciation. The majority of our offshore data record the past 1 Myr of deposition related to the Bagley-Bering Glacier and allows assessing the long-standing question of the western limit of extreme exhumation observed at the St. Elias syntaxis in the Seward and Hubbard glacial drainages. The zircon fission-track ages from the Bering sediment reveal small age populations that peak between 15­-9 Ma, suggesting much slower exhumation beneath the Bagley Ice Valley than farther east underneath the Seward and Hubbard glacier. Our results point out the first-order role of tectonics in providing sustained uplift and crustal weakening in the upper plate that than serve as areas for focused exhumation due to secondary erosional/climate processes.

  4. Thermal history and differential exhumation across the Eastern Musgrave Province, South Australia: Insights from low-temperature thermochronology

    NASA Astrophysics Data System (ADS)

    Glorie, Stijn; Agostino, Kate; Dutch, Rian; Pawley, Mark; Hall, James; Danišík, Martin; Evans, Noreen J.; Collins, Alan S.

    2017-04-01

    Multi-method geo- and thermochronological data obtained for Palaeo- and Mesoproterozoic granitoids traversing the main structural architecture of the eastern Musgrave Province within South Australia reveal multiphase cooling histories. Apatite U-Pb dating on six samples yield consistent ages of 1075-1025 Ma, suggesting a thermal reset coinciding with mantle-derived magmatism of the greater Warakurna Large Igneous Province ( 1080-1040 Ma). Apatite fission track (AFT) analysis indicate that four discrete thermal events affected the study area, inducing cooling through the AFT partial annealing zone ( 60-120 °C), supported by apatite and zircon (U-Th-Sm)/He data. Late Neoproterozoic cooling from deep crustal levels to temperatures < 200 °C was discerned, which is thought to be related to exhumation and denudation during the Petermann Orogeny. Subsequent cooling events at 450-400 Ma (Silurian-Devonian) and 310-290 Ma (Late Carboniferous) are interpreted to represent exhumation associated with the Alice Springs Orogeny. The latter event exhumed the sampled plutons to shallow crustal depths. An additional Triassic - early Jurassic thermal event, likely recording elevated geothermal gradients at that time, was observed throughout the study area, however, more data is needed to further support this interpretation. The high sample density across the structural architecture of the study area furthermore reveals patterns of fault reactivation and resulting differential exhumation, indicating shallower exhumation levels in the centre and deeper exhumation towards the margins of the sampled transect. The observed differential exhumation patterns match with existing seismic data and fit a model of an inverted graben system for the Phanerozoic evolution of the eastern Musgraves. The results highlight a complex Phanerozoic thermal history for the eastern Musgraves and help to elucidate the poorly appreciated tectonic evolution of inland Australia. This study further demonstrates

  5. Seismic valve as the main mechanism for sedimentary fluid entrapment within extensional basin: example of the Lodève Permian Basin (Hérault, South of France).

    NASA Astrophysics Data System (ADS)

    Laurent, D.; Lopez, M.; Chauvet, A.; Imbert, P.; Sauvage, A. C.; Martine, B.; Thomas, M.

    2014-12-01

    During syn-sedimentary burial in basin, interstitial fluids initially trapped within the sedimentary pile are easily moving under overpressure gradient. Indeed, they have a significant role on deformation during basin evolution, particularly on fault reactivation. The Lodève Permian Basin (Hérault, France) is an exhumed half graben with exceptional outcrop conditions providing access to barite-sulfides mineralized systems and hydrocarbon trapped into rollover faults of the basin. Architectural studies shows a cyclic infilling of fault zone and associated S0-parallel veins according to three main fluid events during dextral/normal faulting. Contrasting fluid entrapment conditions are deduced from textural analysis, fluid inclusion microthermometry and sulfide isotope geothermometer: (i) the first stage is characterized by an implosion breccia cemented by silicifications and barite during abrupt pressure drop within fault zone; (ii) the second stage consists in succession of barite ribbons precipitated under overpressure fluctuations, derived from fault-valve action, with reactivation planes formed by sulphide-rich micro-shearing structures showing normal movement; and (iii) the third stage is associated to the formation of dextral strike-slip pull-apart infilling by large barite crystals and contemporary hydrocarbons under suprahydrostatic pressure values. Microthermometry, sulfide and strontium isotopic compositions of the barite-sulfides veins indicate that all stages were formed by mixing between deep basinal fluids at 230°C, derived from cinerite dewatering, and formation water from overlying sedimentary cover channelized trough fault planes. We conclude to a polyphase history of fluid trapping during Permian synrift formation of the basin: (i) a first event, associated with the dextral strike-slip motion on faults, leads to a first sealing of the fault zone; (ii) periodic reactivations of fault planes and bedding-controlled shearing form the main mineralized

  6. Accretion/underplating, detachment and exhumation: short/long-term rheology of the subduction plate interface

    NASA Astrophysics Data System (ADS)

    Agard, Philippe; Angiboust, Samuel; Plunder, Alexis; Guillot, Stéphane; Yamato, Philippe; Oncken, Onno; Ruh, Jonas; Burov, Evgueni; Bonnet, Guillaume

    2016-04-01

    The presence of km-scale accreted terranes/units in both ancient and present-day subduction zones attests to changes in strain localization along the plate interface, whereby these terranes/units get detached from the downgoing slab (or, in places, are eroded away from the tip of the upper plate) and either directly exhumed or accreted/underplated below the upper plate before final exhumation. The rock record (P-T-t data) indicates that, for a given subduction zone, exhumation is episodic: no more than a few My compared to the ~100 My lifetime of typical subduction zones. Not much is known, however, regarding this process and important open questions remain: what exactly is episodic (i.e., detachment from the slab and/or exhumation?), for how long and where? How is mechanical coupling impacted by the initial structure of the incoming plates (structural/lithological heterogeneities, thermo-fluid regime, geodynamic boundary conditions, etc...)? We herein present both new and literature structural and P-T-t data ranging from shallow (i.e., 15-20 km) to intermediate depths (~100 km) along the subduction interface, that span a range from long-term to short-lived events of underplating and/or exhumation, and confront them with the recent wealth of geophysical data gathered on subduction zones. Structural and petrological data indicate that the slicing of km-scale units mostly occurs at specific depths where major mechanical changes occur along the plate interface: at 30-40 km (downdip of the seismogenic zone) and 70-80 km (where mechanical coupling between the two plates resumes and where eclogites get critically dense). This suggests that switches in mechanical coupling (i.e., in the rheology of the material) are key in controlling the ability to detach pieces from the slab (and that later exhumation is rather controlled by large-scale, lithospheric-scale boundary conditions). The study of rock remnants detached from the slab and underplated during subduction infancy (i

  7. Brittle deformation and exhumation mechanisms in the core of the Eastern Alps, The Tauern Window

    NASA Astrophysics Data System (ADS)

    Bertrand, Audrey; Garcia, Sebastian; Rosenberg, Claudio

    2010-05-01

    The Tauern Window (TW) is a Tertiary structural and thermal dome located in the core of the Eastern Alpine orogen and in front of the Dolomite indenter. The Penninic basement and cover units within the TW attained their thermal peak about 30 Myr ago (e.g., Selverstone et al., 1992) followed by cooling and exhumation from Early Oligocene to late Miocene time (e.g., Grundmann and Morteani, 1985). Most exhumation was partly accommodated by two normal faults at the western and eastern ends of the TW (Brenner and Katschberg faults, respectively). Although these normal faults are well described in the literature, their roles in the exhumation of the TW are still under debate: Exhumation accommodated primarily by folding and erosion (e.g., Rosenberg et al., 2004) versus exhumation mainly accommodated by Brenner and Katschberg normal faulting (e.g., Selverstone, 1988; Ratschbacher et al., 1989). New fault-slip data from the TW allow us to reconstruct paleostress axes by inversion and to constrain the relative roles of the folding and orogen-parallel extension during the late deformation history of the TW, in the brittle-field. Our results show little evidence of compression and a clear zoning of the paleostress field in the TW. In the central part of the TW, the σ1 direction is sub-horizontal N-S to NE-SW (strike-slip), whereas it is steep in the footwall of the Brenner and the Katschberg normal faults. Local variability of the σ3 direction are observed; indeed, the σ3 direction varies from E-W to WNW-ESE along the Brenner fault, to NW-SE along the Jaufen fault, the inferred southern continuation of the Brenner fault (Schneider et al., this session). Along the Katschberg fault, the σ3 direction is mainly NNW-SSE oriented, which is consistent with extension in front of a triangular dead zone shape induced by the WSW-striking Dolomites indenter. Nearly no evidence of a stress field compatible with upright folding (D2 phase of deformation) was found in the brittle domain

  8. Exhumation with a twist: restoration of the Menderes Metamorphic core complex since the late Oligocene

    NASA Astrophysics Data System (ADS)

    van Hinsbergen, Douwe J. J.

    2010-05-01

    Here, I provide a restoration of the post-Oligocene unroofing history of the Menderes metamorphic massif of western Turkey. Exhumation of this massif - among the largest continental extensional provinces in the world - is generally considered to have occurred along extensional detachments with a NE-SW stretching direction. Restoration of the early Miocene history, however, shows that this simple history is impossible to reconstruct. Restoration back to ~15 Ma is relatively straightforward, and is mainly characterised by a previously reported ~25° vertical axis rotation difference between the northern Menderes Massif, and the Southern Menderes Massif, Lycian Nappes and Bey Dağları about a pole close to Denizli. To the west of this pole, the rotation was accommodated by exhumation of the Central Menderes core complex since middle Miocene times, and to the east by compressional deformation of the Lycian Nappes. Evidence for the latter is not abundant, but a dextral transpressional system in the heart of the Isparta Angle, and post-Oligocene thrusting in the Denizli basin are in line with this suggestion. At the end of the early Miocene, the Menderes Massif formed a rectangular, NE-SW trending tectonic window of ~150x100 km. Fission track- and cooling ages suggest unroofing between ~25 and 15 Ma. The northeastern Menderes Massif was exhumed along the early Miocene Simav detachment, over a distance of ~50 km. The accommodation of the remainder of the exhumation is enigmatic, but was presumed to also result from NE-SW extension. This, however, requires a transform fault along the eastern margin of the Menderes massif with an offset of ~150 km, cutting througth the Lycian Nappes, for which there is no evidence in the latter. The Lycian Nappes have been previously shown to thrust to the SE between 23 and 15 Ma over at least 75 km. This is contemporaneously with, and orthogonally to stretching along the Simav detachment. It is argued that the amount of emplacement was

  9. Paleomagnetism of Permian sediments and volcanic rocks from Sardinia

    NASA Astrophysics Data System (ADS)

    Moser, E.; Emmer, B.; Bachtadse, V.; Kent, D. V.; Muttoni, G.; Ronchi, A.

    2005-12-01

    During the Late Carboniferous, large granitic bodies were emplaced on Sardinia related to a change of the tectonic setting from compressional to extensional. Simultaneously the newly formed fault-bounded basins were filled with continental clastic sediments, paleontologoically and radiometrically dated to be Late Carboniferous to Early Permian in age. These basins provide an ideal testing ground for tectonic models such as the controversial Pangea B to A transition, which should have occurred prior to the opening of the Atlantic Ocean in the Jurassic. The mega-shear zone required for this transition has been postulated to be situated in today's Mediterranean (Arthaud and Matte, 1977). If this is valid, Sardinia should have been caught within this shear zone and suffered massive internal deformation. Here we report paleomagnetic data from six Permian basins from different Sardinian regions: in the NW (Nurra), N (Gallura), SW (Iglesiente-Sulcis) and SE (Gerrei-Sarcidano). About 200 samples from 23 sites covering mostly continental redbeds and subordinate acidic volcanics were thermally demagnetised. The overwhelming majority of the specimens studied displayed rather simple directional behaviour. A positive intraformational conglomerate test (Gerrei-Sarcidano) as well as the general improvement of the between-site scatter after correcting for minor tilt supports the primary character of the magnetisation. The resulting mean direction for five sites from Nurra (Dec: 126°, Inc: -24°, α95: 8°, k: 118) is in perfect agreement with data published earlier by Vigliotti et al. (1990). Three sites of the Gallura area farther to the east yield a mean site direction (Dec: 158°, Inc: -34°, α95: 23°, k: 28) which is rotated clockwise with respect to the data of Vigliotti et al. (1990). Seven sites from southern Sardinia (SW and SE) yield a mean direction with a declination of 82° and inclination of 12° (α95: 12°, k: 25). These results imply crustal coherence of Nurra

  10. Grain-rimming kaolinite in Permian Rotliegend reservoir rocks

    NASA Astrophysics Data System (ADS)

    Waldmann, Svenja; Gaupp, Reinhard

    2016-04-01

    Upper Rotliegend sediments of Permian age from the northeast Netherlands show moderate to good reservoir qualities. The predominant control is by the presence of authigenic grain-rimming kaolinite, which has a negative, but in some parts also a positive, effect on reservoir quality. To better understand the formation and distribution of grain-rimming kaolinite, reservoir rocks were studied in terms of composition and diagenetic processes. Petrographic evidence, summarized as a paragenetic sequence, is integrated with geochemical modeling results to identify early mesodiagenetic water-rock interactions under the participation of gases, i.e., CO2 and H2S, released from underlying Carboniferous source rocks. The sediments investigated were deposited at varying distance from the southern flank of the Southern Permian Basin. Sediments near the basin margin are mainly attributed to a fluvial environment and comprise medium to coarse-grained sandstones and conglomerates. There, vermicular kaolinite occurs with a lath-like structure. Distal to the basin margin, mainly in sandstones intercalated with fine-grained playa sediments, comparatively high amounts of grain-rimming kaolinite occur. There, the presence of this mineral has a significant influence on the rock properties and the reservoir quality. Geochemical modeling suggests that the formation of such kaolinites cannot be explained exclusively by in situ feldspar dissolution. The modeling results support evidence that kaolinite can be formed from precursor clay minerals under the presence of CO2-rich formation waters. Such clay minerals could be corrensite, smectite-chlorite mixed-layer minerals, or chlorite that is potentially present in Rotliegend sediments during early diagenesis. Furthermore, the geochemical modeling can reflect several mineral reactions that were identified from petrographic analysis such as the formation of illite and kaolinite at the expense of feldspar dissolution and consequent silica

  11. Exhumation of the Cordillera Blanca batholith (Peruvian Andes) constrained by amphibole barometry and low-temperature thermochronology modelling

    NASA Astrophysics Data System (ADS)

    Margirier, Audrey; Audin, Laurence; Robert, Xavier; Herman, Frédéric; Ganne, Jérôme; Schwartz, Stéphane

    2017-04-01

    The Cordillera Blanca batholith forms the highest Peruvian summits and builds the footwall of the Cordillera Blanca normal fault (CBNF). Even if several models have been proposed, the processes driving both the exhumation of the Cordillera Blanca and extensional deformation along the CBNF are still debated. We coupled barometric and thermochronologic data to quantify the emplacement and exhumation history of the Cordillera Blanca batholith from the late Miocene to present. Based on new thermobarometry data and a compilation of crystallization ages in the Cordillera Blanca batholith, we propose that the batholith was emplaced at a depth of 3 km in successive sills from 12 to 5 Ma. Close to the CBNF, the younger rocks that are emplaced the deepest (i.e., 6 km) are exposed at the surface, suggesting post 5 Ma tilting. In addition, a formal inversion of the barometric and thermochronologic data (apatite fission-track and apatite (U-Th)/He) indicates an increase of the exhumation rates in the Cordillera Blanca during the Quaternary. The higher predicted exhumation rates correlate with areas of high relief suggesting that Quaternary valley carving by glaciations have a significant impact on the latest stage of the Cordillera Blanca exhumation (2-0 Ma).

  12. [131 cases of exhumation in Hamburg and their significance for legal medicine and medical insurance (1971-1995)].

    PubMed

    Seibel, O; Heinemann, A; Hildebrand, E; Püschel, K

    1997-12-01

    The results of 131 forensic exhumations performed by the Institute für Legal Medicine in Hamburg from 1971 up to 1995 are presented and analysed. 50 exhumations have been ordered by legal authorities concerning criminalistic aspects. 81 cases have been commissioned by insurance companies. 7 categories of cases have been established which are separately analysed (e.g. suspicion of intoxication, accidental cases, occupational diseases). A synopsis presents the evidence of several pathological findings in regard to the body's lay-days in the grave compared with similar studies. The study gives evidence of the value of specific findings even if the body had been buried one or two years before exhumation. In 65 of 92 cases the suspected cause of death could be confirmed. In 121 cases the cause of death was definitely cleared up by autopsy. 125 exhumations (approximately 95%) have been successful concerning the underlaying question that gave reason for further examinations. Exhumations turned out to be very useful in order to clarify insurance-related medical questions.

  13. Exhumation history and faulting activity of the southern segment of the Longmen Shan, eastern Tibet

    NASA Astrophysics Data System (ADS)

    Tan, Xi-Bin; Lee, Yuan-Hsi; Chen, Wen-Yu; Cook, Kristen L.; Xu, Xi-Wei

    2014-02-01

    The Longmen Shan (LMS), which constitutes the eastern border of the Tibetan Plateau, is about 400 km in length and characterized by a steep topographic transition from the Sichuan Basin to the plateau. The 2008 Mw7.9 Wenchuan earthquake and 2013 Mw6.6 Lushan earthquake were associated with the central to northern segments and southern segment of the LMS fault belt, respectively. In this paper, zircon and apatite fission track (ZFT and AFT, respectively) dating in combination with previously published low temperature thermochronology studies are used to constrain both the exhumation history and fault activity along the LMS, with a special focus on the southern segment. In the southern segment of the LMS, the ZFT ages in the hanging wall of the Wulong-Yanjing fault 10-14 Ma, increasing to ca. 30 Ma to the northwest of the faults and to 100-200 Ma in the plateau region. The AFT ages are 3-5 Ma at the mountain front and increase to 8-26 Ma in the plateau. We show that these age distributions are controlled by fault geometry. Two stages of rapid exhumation were identified using apatite fission track length modeling and the age distributions in the southern segment of the LMS. The first stage is from ca. 30 Ma and the second stage is from 3-5 Ma to present. In contrast with the middle segment of the LMS, the Cenozoic exhumation rate is higher in the southern segment of the LMS, which may be due to the influence of the collision between the India and Eurasia plates and/or different faulting mechanisms in the different segments.

  14. Relating shortening, erosion, and exhumation to orogen width during Alpine collision

    NASA Astrophysics Data System (ADS)

    Rosenberg, Claudio; Berger, Alfons; Bellahsen, Nicolas; Bousquet, Romain

    2014-05-01

    The width of orogens may change through time depending on the amount of shortening, on the efficiency of erosion, on the strength and thickness of the plates, or on the occurrence of pre-existing and newly formed weaknesses within the plates. The effect of erosion rates on the width of the Alps was controversially discussed, based on estimates of paleo-erosion rates and paleo-widths of the orogen. However, both parameters are difficult to reconstruct. In this contribution we investigate the causes of present-day, along-strike changes of width of the Eastern and the Central Alps to understand its width changes through time. Based on a series of 6 orogen-scale cross-sections and their retro-deformation we set the width of the thickened accreted lower plate in relation to the amount of collisional shortening and exhumation. We conclude that higher amounts of shortening systematically coincide with smaller widths of the thickened, accreted lower plate, i.e. the width of the mountain chain north of the South-Alpine indenters. Changes of width by a factor 2 along orogen segments of less than 200 km length cannot result from long-term climatic differences and sedimentary or paleontological evidences suggesting such differences are lacking. Therefore, erosional processes did not directly control the width of the orogen, which did not behave as a critical taper. Higher amounts of shortening coincide with larger amplitudes of orogen-scale, upright folds, with larger amounts of exhumation, and with higher exhumation rates. Hence, erosion did play a major role in reducing by up to 35 km the vertical crustal thickness in order to accommodate and allow shortening by folding, but along-strike changes of erosion rates were governed by different amounts of shortening, not by different climate.

  15. Influence of paleo-heat flow variations on estimates of exhumation rates

    NASA Astrophysics Data System (ADS)

    von Hagke, Christoph; Luijendijk, Elco

    2016-04-01

    Deriving exhumation estimates from thermochronological data requires assumptions on the paleo-thermal field of the Earth's crust. Existing thermal models take into account heat transfer by diffusion and advection caused by the movement of the crust and erosion as well as changes in geothermal gradient over time caused by changes in structure or thermal properties of the crust, surface temperature and elevation. However, temperature field of mountain belts and basins may vary not only due to tectonic activity or landscape evolution. We present a high-resolution thermochronology data set from the foreland fold-and-thrust belt of the European Alps that shows substantial variation of cooling rates probably caused by hydrothermal flow in the subsurface in the past. Tectonic blocks with uniform exhumation history show variations in cooling of up to 50°C. In addition, changes in cooling between two different fault blocks show opposite trend than expected by models of their tectonic history. The observed historic changes in paleo-geothermal gradients are equal in magnitude to a present-day thermal anomaly caused by the upward flow of warm fluids in the distal part of the foreland basin. The strong variations in geothermal gradients by fluid flow imply that straightforward interpretation of landscape evolution rates using thermochronology is not possible, unless the thermal effects of fluid flow are taken into account. This is of particular importance to studies where the amount of thermochronology data is limited and local hydrothermal anomalies could easily be interpreted as regional exhumation signals. On the other hand, our findings suggest that thermochronology offers new opportunities to constrain magnitude and timing of paleo-heat flow variations in the upper crust.

  16. Exhuming Metamorphic Rocks: Constraints from Cooling of the Chugach Metamorphic Complex, southern Alaska

    NASA Astrophysics Data System (ADS)

    Gasser, Deta; Bruand, Emilie; Stüwe, Kurt; Rubatto, Daniela; Foster, David; Schuster, Ralf

    2010-05-01

    Exhumation mechanisms for metamorphic rocks include (a) erosion, (b) extension, (c) extrusion by channel flow, simple or pure shear, and - recently suggested - (d) slab extraction. Distinguishing in a particular case of a metamorphic complex between the different exhumation mechanisms is a much discussed subject in modern geodynamics. In order to add to this discussion, we adopt an interdisciplinary approach combining detailed petrological and structural field work with several geochronological and thermochronological systems. The Chugach Metamorphic Complex of southern Alaska is a ~600 km long and 10-30 km wide zone of upper amphibolite-facies metamorphic rocks. It lies in the outermost tectonic belt of the North American Cordillera, which is a vast and complex Phanerozoic orogen formed from the oblique collision of the Pacific, Kula and Farallon oceanic plates and the North American continent. The Chugach Complex developed in the Eocene in a Cretaceous to Paleocene accretionary prism while the Kula and Pacific plates were obliquely colliding with North America. We conducted detailed field work, U-Pb and 40Ar-39Ar geochronology and compiled all other geochronological data from the region in order to construct cooling histories for the whole metamorphic complex. These cooling histories vary along strike: The western and central parts of the Chugach Metamorphic Complex, where the metamorphic complex is wide, show very fast cooling to below ~300° C between 54-45 Ma, shortly after peak metamorphism, and then slowly cool to surface temperatures over the remaining 45 Ma. In contrast, the south-eastern part, where the metamorphic complex is very narrow, slowly and steadily cooled between 51-5 Ma only to increase its cooling rate in the last few Ma before present. Whether and how these cooling rates can be directly linked with exhumation rates and why they differ so grossly between the wide and the narrow parts of the complex is the current focus of our work.

  17. Deformation Processes of Subduction and Exhumation in Alpine Eclogites with Focus on the Tauern Window

    NASA Astrophysics Data System (ADS)

    Stipp, M.; Keppler, R.; Behrmann, J. H.; Heidelbach, F.

    2015-12-01

    Deformation processes inside subduction channels or during subduction and exhumation of HP and UHP nappes in collisional orogens are a matter of debate. Dehydration embrittlement, localized faulting and dissolution-precipitation creep have been suggested as major deformation processes. These processes, however, do not correspond to the field-based deformation record of penetrative foliations and stretching lineations in most HP and UHP nappes of the Central Alps, indicative of dislocation and diffusion creep processes including metamorphic reaction transfer. The Eclogite Zone of the Tauern Window (Eastern Alps) consists of fresh and retrogressed eclogites in a matrix of metasediments. Peak metamorphism was at 600°C and 2.0-2.5 GPa in the Oligocene followed by fast exhumation within a few million years. Eclogites and blueschists display a pronounced foliation and lineation fabric. Fresh and retrogressed samples have been investigated by neutron diffraction texture, electron backscatter diffraction and microprobe analysis. All investigated eclogites exhibit a pronounced crystallographic preferred orientation (CPO) of omphacite. In retrogressed eclogites the glaucophane CPO is strong as well and matches topologically always that of omphacite. Omphacite microstructures are characteristic of subgrain rotation recrystallization, identifying high-stress dislocation creep as main deformation mechanism. Diffusion and reaction transfer can be derived from the variable jadeite contents in omphacite porphyroclasts and recrystallized grains. The corresponding CPO of omphacite and glaucophane indicates that progressive CPO development spanned the whole high-pressure part of metamorphism and lasted until retograde blueschist grade. We propose that deformation in the Eclogite Zone was mostly distributed and continuous during subduction and exhumation and that dislocation and diffusion creep processes accommodated most of the strain below the frictional-viscous transition.

  18. Styles of continental subduction and collision and their effect on formation and exhumation of UHP rocks

    NASA Astrophysics Data System (ADS)

    Warren, C. J.; Beaumont, C.; Jamieson, R. A.

    2006-12-01

    Ultra-high pressure (UHP) metamorphic rocks are exposed in many Phanerozoic mountain belts. It is now widely accepted that they represent continental margin rocks that were subducted to ≥100km during the transition from oceanic subduction to continental collision. A range of subduction-collision mechanisms have been proposed to account for UHP formation and exhumation. A series of upper-mantle-scale geodynamic models is used to test the sensitivity of a subset of these mechanisms to variations in lithosphere density, radioactive heat production, and crustal strength. The subducting crust includes an oceanic domain, a continental margin domain with variable width, thickness, strength, and heat production, and a strong internal continental domain. The models involve dynamic subduction, constant convergence velocity, density changes that accompany the main phase changes during burial, and surface erosion in the collision zone. Results show that continental subduction without retro-continent deformation is favored by relatively dense mantle lithosphere. Subduction of the retro-continent (forearc subduction) is associated with shallow-dipping, low- density mantle lithosphere. Back-thrusting of retro-lithosphere is favored by relatively weak retro-continental crust. UHP material can be exhumed in all 3 model styles, depending on the evolving geometry of the subduction-accretion zone and the degree of decoupling between subducting upper and lower continental crust in this zone. Weaker and/or hotter margins decouple and accrete, and their subsequent exhumation is driven by bulk density contrast (buoyancy) and/or forced expulsion in response to advection of strong continental material into the subduction zone (plunger effect). Stronger and/or colder continental margin material is subducted without decoupling and is then transported laterally, underplating the retro-mantle lithosphere. Model results are compatible with observed geometries and PTt paths from some UHP

  19. Peneplains on Tibetan Plateau: a long-term archive of exhumation and slow erosion

    NASA Astrophysics Data System (ADS)

    Haider, Vicky; Dunkl, István; von Eynatten, Hilmar; Lin, Ding

    2010-05-01

    Peneplains are not only representative and well recognizable geomorphological features but also archives of slow erosion and long-term exhumation. In the Lhasa terrane between the Banggong Suture in the north and the Nyaingentangtha Mountain range in the south, especially in the area around lake Nam Co, peneplains were graved into Jurassic and Cretaceous granitic intrusions. Some peneplains are crossing massive Jurassic sandstone. Characteristic outstanding paleosurfaces are wide planar surfaces that extend over 1 km at different elevation. They are not to mix up with also present sub-recent, smaller sized plane surfaces which were formed by abrasion processes of the local lakes. We used low-temperature chronological methods such as (U-Th)/He and fission track (FT) for dating heavy minerals such as apatite and zircon to measure and extract information about processes like erosion and exhumation that are closely related to orogenic stacking and uplift. Around hundred samples in particular from Cretaceous to Eocene granites, volcanics and sedimentary rocks were taken from the peneplains and their surroundings. Apatite crystals from more than 25 samples and zircon crystals from ten samples have been successfully analysed by (U-Th)/He method. While (U-Th)/He apatite ages cluster in Paleocene and Eocene ranging from 38 to 60 Ma, apatite and zircon FT ages cluster in Late Cretaceous. The age clusters are internally consistent in areas smaller than 100 km2. This first thermochronological data lead us most surely to a Late Cretaceous to Early Tertiary thermotectonical event which is probably connected to erosion and planation of the paleosurface. The deposition of Late Cretaceous to Eocene siliciclastic sediments close to the currently exhumed peneplains are also evidence of such an event.

  20. Foundering and Exhumation of UHP Terranes: Race Car or School Bus?

    NASA Astrophysics Data System (ADS)

    Kylander-Clark, A. R.; Hacker, B. R.

    2008-12-01

    Recent geochronologic data from the giant ultrahigh-pressure (UHP) terrane, in the Western Gneiss Region of Norway, indicate that subduction and exhumation were relatively slow (a few mm/yr), and that the terrane was exhumed to the surface as a relatively thick, coherent body. These conclusions are in stark contrast to those reached in previous studies of some of the best-studied, smaller UHP terranes and suggest that the processes that form and/or exhume small UHP terranes are fundamentally different from the processes that affect large UHP terranes. These differences may be the result of variations in the buoyancy forces of different proportions of subducted felsic crust, mafic crust, and mantle lithosphere. Initial collision occurs via the subduction of smaller portions of continental material, such as microcontinents or ribbon continents. Because the proportion of continental crust is small, the processes involved in early UHP terrane formation are dominated by the oceanic slab; subduction rates are fast because average plate densities are high, and, as a result, subduction angles are steep. Because these smaller, thinner portions of crust are weak, they deform easily and mix readily with the mantle. As the collision matures, thicker and larger portions of continental material-such as a continental margin-are subducted, and the subduction regime changes from one that was ocean dominated to one that is continent dominated. The increased buoyancy of the larger volume of continental crust resists the pull of the leading oceanic lithosphere; subduction shallows and plate rates slow. Because the downgoing continent is thick, it is strong, remains cohesive and has limited interaction with the mantle. Although the subduction regime during early orogenesis is distinct from that during late orogenesis, the degree of mountain building and crustal thickening may be similar in both stages as small volumes and fast flow rates of buoyant material give way to large volumes

  1. Multi-mineral geochronology: insights into crustal behaviour during exhumation of an orogenic root

    NASA Astrophysics Data System (ADS)

    LaFlamme, Crystal; McFarlane, Christopher R. M.; Fisher, Christopher M.; Kirkland, Christopher L.

    2017-03-01

    Under rare conditions, reworked cratons and their margins preserve the orogenic roots of ancient mountain-building events. However, based on the preservation of high-temperature ( 800 °C), middle and lower crustal metamorphic assemblages, present day exposure of these terrains is not simply a result of protracted denudation, but also must reflect a multifaceted exhumational history. In situ analysis within thin section preserves the textural setting of target minerals that can be used as thermochronometers such as U-Pb of zircon, monazite, titanite and apatite, and Sm-Nd of apatite. In situ analyses of these chronometers has the potential to provide critical timing constraints on exhumation processes related to decompression, melting and cooling across large metamorphic terrains. The Repulse Bay block of the Rae craton preserves a large composite amphibolite-granulite area (50,000 km2) of Archean orthogneiss, migmatite, and slivers of Proterozoic metasediments that underwent high-grade metamorphism, partial melting, ductile flow and finally exhumation during the Paleoproterozoic Trans-Hudson Orogeny. The granulite domain preserves dry granitoid assemblages, whereas the amphibolite domain is dominated by hydrated migmatites and orthogneiss. Metasediments occur in both domains and preserve mineral assemblages that are consistent with having undergone tectonometamorphic conditions of 9 kbar/800 °C during burial. U-Pb thermochronometers document identical cooling histories of the granulite and amphibolite domains through the U-Pb closure temperatures of titanite ( 650 °C) and apatite ( 450 °C). This suggests that melt-loss from the underlying granulite domain and melt-gain to the amphibolite domain prior to cooling through 650 °C are a controlling factor of the metamorphic assemblages across the composite granulite-amphibolite terrains such as the Repulse Bay block, rather than significant differences in burial history, cooling history, and/or reorganization of

  2. Early and Middle Permian paleoclimates of the Baoshan Block, western Yunnan, China: insight from carbonates

    NASA Astrophysics Data System (ADS)

    Yan, Jiaxin; Liang, Dingyi

    2005-03-01

    In Permian times the Baoshan Block of western Yunnan, southwest China formed the eastern part of the Cimmerian Continent. Most biogeographical and sedimentological data indicate that the Early Permian Dingjiazhai Formation formed on the block under conditions strongly influenced by the Permo-Carboniferous glaciation. After Early Permian rifting, with post-glaciation climatic amelioration, and as the Baoshan Block drifted northwards to approach South China and Indochina, faunal elements characteristic of Gondwana affinity decreased, while those of Cathaysian affinity increased. Finally, Late Permian faunas are characterized by exclusively Cathaysian elements. This shift of marine provinciality becomes an important indicator in understanding the Permian paleoclimatic evolution of the region. This research investigated the composition of carbonate grain associations and the early diagenetic features of limestones from the upper part of the Dingjiazhai Formation, and from the overlying Yongde and Shazipo formations. A sharp distinction in petrological and diagenetic features is recognized between the Dingjiazhai Formation and the two overlying formations. The Dingjiazhai carbonates are characterized by the bryonoderm (bryozoan-echinoderm)-extended facies of the heterozoan association, with no non-skeletal grains. Because early diagenetic cement was rarely formed, the Dingjiazhai carbonates experienced strong diagenetic compaction. In contrast, the Yongde and Shazipo carbonates show a chloroforam facies of photozoan association, with the common occurrence of non-skeletal grains. These carbonates were well cemented during early diagenetic processes. From comparison with Permian cool-water carbonates from northern Pangea and Tasmania, Australia, the Dingjiazhai carbonates are interpreted as deposits of warm-temperate conditions, while the overlying carbonates are considered to be deposits of subtropical or tropical conditions. This climatic interpretation, based on the

  3. Trans-Siberian Permian rivers: A key to understanding Arctic sedimentary provenance

    NASA Astrophysics Data System (ADS)

    Ershova, Victoria B.; Khudoley, Andrey K.; Prokopiev, Andrei V.; Tuchkova, Marianna I.; Fedorov, Petr V.; Kazakova, Galina G.; Shishlov, Sergey B.; O'Sullivan, Paul

    2016-11-01

    Permian strata of northern Siberia contain a rich record of the late Paleozoic history of Siberia and surrounding fold and thrust belts (FTB). More than 850 uranium-lead (U-Pb) detrital zircon ages collected from the Permian strata provide vital information about sediment source areas and history of the sedimentary basins. The detrital zircon populations obtained from the Permian clastics of northern Siberia are characterized by large percentages of late Paleozoic and early Paleozoic zircons, whose ages can be correlated with magmatic events known from the Ural-Mongolian Orogen. Our data suggest that Permian clastics of northern Siberia were mainly sourced from orogens developed along the western and southwestern margins of the Siberian Craton (in present-day coordinates), with an additional sediment contribution from the reworked sedimentary cover and basement of Siberia. The contribution from Siberian sources is distinguished in the Precambrian part of the detrital zircon populations by wide distribution of ca. 1700-2000 Ma and 2500-2750 Ma zircons with an almost total lack of zircons ranging in age from 800 to 1700 Ma. We propose that a major fluvial system, which we here term the "Paleo-Khatanga", was the main sediment transport pathway along the western and northern margins of Siberia during the Permian. From a regional overview of detrital zircon populations in Permian deposits across the Arctic realm, we propose that the New Siberian Islands, Alexander and Farewell terranes were sourced from the western framework of the Ural-Mongolian Orogen and were located along the northern margin of Baltica during the late Paleozoic. The Arctic-Alaska-Chukotka Terrane on the other hand does not have Uralian signatures in the detrital zircon populations of the Permian sediments, and can be reconstructed adjacent to the northern margin of Laurentia. Our new data presented here help to better define the enigma of Arctic paleogeography during the Paleozoic.

  4. An Early Permian fusuline fauna from southernmost Peninsular Thailand: Discovery of Early Permian warming spikes in the peri-Gondwanan Sibumasu Block

    NASA Astrophysics Data System (ADS)

    Ueno, Katsumi; Arita, Michiko; Meno, Satomi; Sardsud, Apsorn; Saesaengseerung, Doungrutai

    2015-05-01

    An Early Permian fusuline fauna is reported from the Tarn To Formation of the Yala area in southernmost Peninsular Thailand, which geotectonically belongs to the peri-Gondwanan Sibumasu Block. The fauna consists of Pseudofusulina and Praeskinnerella? species, including forms closely resembling Tethyan and Panthalassan Pseudofusulina fusiformis and Pseudofusulina ex gr. kraffti. A Yakhtashian-Bolorian age is estimated for this fauna. In Sibumasu, shallow-marine biotas showing similar Tethyan affinities, such as the fusulines Misellina and alatoconchid bivalves, also occur in the Early Permian succession of the Kinta Valley area in western Peninsular Malaysia. These unusual Tethyan faunas within Early Permian peri-Gondwanan fossil records suggest episodic influences from paleo-tropical Tethyan biotas. They are here interpreted as showing short-term warming spikes during the late Yakhtashian-Bolorian transgression, which would facilitate sporadic migration and temporal inhabitation of warm-water dwellers into the eastern Cimmerian areas. The Yala and Kinta Valley fusuline and other invertebrate faunas would give us a new insight for the Permian geohistory and environmental change of the peri-Gondwanan Sibumasu Block.

  5. Subduction and exhumation of the Pelona-Orocopia-Rand schists, southern California

    USGS Publications Warehouse

    Jacobson, C.E.; Oyarzabal, F.R.; Haxel, G.B.

    1996-01-01

    The Pelona, Orocopia, and Rand schists of southern California and southwestern Arizona are thought to have formed in either the same east-dipping subduction zone as the Franciscan complex or in a southwest-dipping subduction zone related to collision of an outboard continental fragment with North America. The principal justification for the collision model has been the observation that continental rocks overlying the schists locally show transport to the northeast. Field and petrographic studies now confirm that the northeast movement occurred during exhumation of the schist, not during subduction. Combined with regional geologic relations, this evidence makes the collision model unlikely.

  6. Low temperature thermochronological constrains on the late exhumation of the Alpine foreland (Digne nappe, France).

    NASA Astrophysics Data System (ADS)

    Schwartz, S.; Gautheron, C.; Audin, L.; Dumont, T.; Nomade, J.; Pinna-Jamme, R.

    2015-12-01

    The frontal part of the southwestern Alpine belt is characterized by important compressional deformation marked by the emplacement of the Digne nappe and the formation of the Valavoire thrust-sheet. The final emplacement of this nappe is dated Late Miocene thanks to Tertiary continental molasses of the foreland basin that are involved in the famous Vélodrôme recumbent syncline and exposed in erosional windows. The stratigraphic series of the Digne nappe is made of ~5000 m thick Liassic to Eocene deposits, which overthrust the vélodrôme syncline. We performed a low temperature apatite fission tracks (AFT) and (U-Th)/He (AHe) study on detrital grains of Tertiary molasses in order to (i) characterize the thermal conditions during burial and exhumation and to (ii) propose a late tectonic evolution in the front of the European Alpine foreland. Tertiary molasses were sampled in two sites of the erosional windows at different elevations. Samples present dispersed AHe and AFT ages due to an incomplete resetting of both thermochronometers, expected for the lowest elevation samples. In detail, AHe ages ranges from 2±0.2 to 60.4±5.4 Ma, whereas central AFT ages range from 11±1 to 67±16 Ma. On both sites, the total and partial reset of the thermochronological data suggests a heating event after the sediment deposition. Using QTQt inverse modeling and He damage codes, we determined the samples thermal history. The results implied a common burial temperature at 110±5°C during ~5Ma and a similar exhumation starting at 6±1 Ma. From these results, we conclude that the thermal conditions during burial associated with the Digne nappe thrusting were sufficient to reset the detrital apatites. Using mean surface temperature of 10°C and typical thermal gradient from 25°C/km, our new data show that the Digne Nappe reached at least 4.5 to 3.6 km-thick on both sites before further erosion. We propose that the late exhumation occurred at ~6 Ma ago, before the Messinian incision

  7. Offshore Sedimentary Record of Exhumation in Southeast Alaska Using Detrital Zircon Fission Track Analysis

    NASA Astrophysics Data System (ADS)

    Bootes, N.; Enkelmann, E.; Lease, R. O.

    2016-12-01

    In this study, we investigate the Cenozoic exhumation of the mountain ranges in southeast Alaska using detrital zircon data from twenty-two samples collected from four offshore oil exploration wells in the Gulf of Alaska. The wells were drilled into the Cenozoic cover of the Yakutat Plate, which is subducting beneath the North American Plate and forming the St. Elias Range. The St. Elias Range is the primary source of detrital material today, but in the past, as the plate has moved to the northwest, coastal areas in the southeast dominated the sediment supply. In order to quantify how exhumation has changed both spatially and temporally, we double-dated individual zircon grains using fission-track dating (ZFT) to determine cooling ages as a signal for exhumation, and U/Pb dating to determine grain provenance. Two wells are located southwest of the Bering Glacier and include samples deposited between 8.5 and 0.5 Ma. The youngest ZFT age populations found in these samples range from 30-13 Ma with lag times ranging from 7-26 Myr. Most of the grains from these samples represent ZFT age populations ranging from 94-41 Ma. Another well, located 45 km west of Icy Bay includes four samples with deposition ages between 4 Ma and 0.5 Ma. The youngest ZFT age populations yield peaks of 27-12 Ma and the majority of grains compose ZFT age populations with peaks of 81-37 Ma. The easternmost well, located 60 km southwest of Yakutat, has three samples deposited between 3.5 Ma and 2 Ma, and seven samples deposited between 39 Ma and 18 Ma. The Pliocene and Pleistocene samples show young ZFT age populations (11-9 Ma) with lag times of 6-9 Myr. The percentage of young grains composing the youngest ZFT peaks increases through time, suggesting an increased importance of sediments from a rapidly exhuming area. The majority of the grains compose ZFT age populations with peaks of 94-20 Ma.

  8. Late Permian topography at the southern margin of the Northern Permian Basin: Paleogeography inferred from 3D seismic analysis

    NASA Astrophysics Data System (ADS)

    Clausen, Ole R.; Andresen, Katrine J.; Rasmussen, Jens A.

    2013-04-01

    The Top Pre Zechstein (TPZ) surface in the North Sea Basin is often mapped because it reveals the total basement tectonics in the area. In areas where Zechstein salt is present halokinetic processes, differential subsidence, and Mesozoic faulting however significantly alter the TPZ surface. The study area is located at the southern margin of the Northern Permian Basin in the eastern North Sea at the northern flank of the Ringkøbing-Fyn High. This area occurs approximately at the pinch-out line of the late Permian Zechstein salt and constitutes an excellent theater illustrating a range of salt-related problems. The TPZ surface is characterized by an overall NNW-ward dip defining the northern flank of the RFH and is transected by a set of NNW-SSE striking faults, and a E-W striking set of minor faults. Salt structures in the northern part of the study area introduce velocity pull-up (artefacts) at the TPZ surface and furthermore cause intense faulting of the Mesozoic and Cenozoic cover sediments. Pronounced isolated topographic highs similar to hills can be observed in the southern part of the study area where no to very little Zechstein evaporites are present. In the central part where Zechstein evaporites are present, small topographic highs similar to ridges can be observed at the footwall crest of minor faults. The Zechstein evaporites generally onlap towards the south in the study area but in the transitional zone around the hills, onlap from all directions onto the hills is observed. This suggests that the hills reflect paleo-topography developed during sub-aerial exposure before and perhaps during the deposition of the Zechstein sediments. The internal reflections within the hills show that they are composed of southward dipping sediments and very evident erosional truncations can be observed. The hills are aligned parallel to the major E-W striking basement fault, but are not directly associated to faults offsetting the TPZ surface. However, the alignment

  9. Complete tylosis formation in a latest Permian conifer stem

    PubMed Central

    Feng, Zhuo; Wang, Jun; Rößler, Ronny; Kerp, Hans; Wei, Hai-Bo

    2013-01-01

    Background and Aims Our knowledge of tylosis formation is mainly based on observations of extant plants; however, its developmental and functional significance are less well understood in fossil plants. This study, for the first time, describes a complete tylosis formation in a fossil woody conifer and discusses its ecophysiological implications. Methods The permineralized stem of Shenoxylon mirabile was collected from the upper Permian (Changhsingian) Sunjiagou Formation of Shitanjing coalfield, northern China. Samples from different portions of the stem were prepared by using the standard thin-sectioning technique and studied in transmitted light. Key Results The outgrowth of ray parenchyma cells protruded into adjacent tracheids through pits initially forming small pyriform or balloon-shaped structures, which became globular or slightly elongated when they reached their maximum size. The tracheid luminae were gradually occluded by densely spaced tyloses. The host tracheids are arranged in distinct concentric zones representing different growth phases of tylosis formation within a single growth ring. Conclusions The extensive development of tyloses from the innermost heartwood (metaxylem) tracheids to the outermost sapwood tracheids suggests that the plant was highly vulnerable and reacted strongly to environmental stress. Based on the evidence available, the tyloses were probably not produced in response to wound reaction or pathogenic infection, since evidence of wood traumatic events or fungal invasion are not recognizable. Rather, they may represent an ecophysiological response to the constant environmental stimuli. PMID:23532049

  10. Fullerenes and Interplanetary Dust at the Permian-Triassic Boundary

    NASA Astrophysics Data System (ADS)

    Poreda, Robert J.; Becker, Luann

    2003-01-01

    We recently presented new evidence that an impact occurred ~250 million years ago at the Permian-Triassic boundary (PTB), triggering the most severe mass extinction in the history of life on Earth. We used a new extraterrestrial tracer, fullerene, a third carbon carrier of noble gases besides diamond and graphite. By exploiting the unique properties of this molecule to trap noble gases inside of its caged structure (helium, neon, argon), the origin of the fullerenes can be determined. Here, we present new evidence for fullerenes with extraterrestrial noble gases in the PTB at Graphite Peak, Antarctica, similar to PTB fullerenes from Meishan, China and Sasayama, Japan. In addition, we isolated a 3He-rich magnetic carrier phase in three fractions from the Graphite Peak section. The noble gases in this magnetic fraction were similar to zero-age deep-sea interplanetary dust particles (IDPs) and some magnetic grains isolated from the Cretaceous-Tertiary boundary. The helium and neon isotopic compositions for both the bulk Graphite Peak sediments and an isolated magnetic fraction from the bulk material are consistent with solar-type gases measured in zero-age deep-sea sediments and point to a common source, namely, the flux of IDPs to the Earth's surface. In this instance, the IDP noble gas signature for the bulk sediment can be uniquely decoupled from fullerene, demonstrating that two separate tracers are present (direct flux of IDPs for 3He vs. giant impact for fullerene).

  11. Eolian permian deposits in west and northwest Argentina

    NASA Astrophysics Data System (ADS)

    Limarino, C. O.; Spalletti, L. A.

    1986-08-01

    The sedimentary and stratigraphic characteristics of eolian Permian deposits exposed in Mendoza, La Rioja and San Juan Provinces (west and northwest Argentina) are described in this paper. The eolianites are fine and medium sandstones with large-scale cross-bedding, multiple parallel truncation planes and some asymmetrical ripples. Three genetic types of deposits have been identified: dune facies, eolian sand-sheet facies and mixed fluvial-eolian facies. Fine and medium sandstones with large-scale cross-bedding and multiple parallel truncation planes are here interpreted as dune deposits (mainly crescentic dunes), and unstratified or flat-bedded sandstones as eolian sand-sheet deposits. Mixed fluvial and eolian sequences, composed of sandstones, mudstones and some matrix-supported conglomerates, represent a transitional facies between those formed in eolian and fluvial environments. This considerable deposition of eolian sediments was probably brought about by the existence of an extensive, medium to low-latitude continent and the withdrawal of marine environments. The environments with highest aridity occurred towards the south and west of the region. The eolian circulation pattern was controlled by a long ensialic volcanic arc emerging towards the west of the basin.

  12. Radon in the creswell crags Permian limestone caves.

    PubMed

    Gillmore, G K; Phillips, P S; Denman, A R; Gilbertson, D D

    2002-01-01

    An investigation of radon levels in the caves of Creswell Crags, Derbyshire, an important Site of Special Scientific Interest (SSSI) shows that the Lower Magnesian Limestone (Permian) caves have moderate to raised radon gas levels (27-7800 Bq m(-3)) which generally increase with increasing distance into the caves from the entrance regions. This feature is partly explained in terms of cave ventilation and topography. While these levels are generally below the Action Level in the workplace (400 Bq m(-3) in the UK), they are above the Action Level for domestic properties (200 Bq m(-3)). Creswell Crags has approximately 40,000 visitors per year and therefore a quantification of effective dose is important for both visitors and guides to the Robin Hood show cave. Due to short exposure times the dose received by visitors is low (0.0016 mSv/visit) and regulations concerning exposure are not contravened. Similarly, the dose received by guides is fairly low (0.4 mSv/annum) due in part to current working practice. However, the risk to researchers entering the more inaccessible areas of the cave system is higher (0.06 mSv/visit). This survey also investigated the effect of seasonal variations on recorded radon concentration. From this work summer to winter ratios of between 1.1 and 9.51 were determined for different locations within the largest cave system.

  13. Paleoyardangs: wind-scoured topography at Permian unconformity

    SciTech Connect

    Tewes, D.W.; Loope, D.B.

    1989-03-01

    At least 28 elongate, parallel ridges exhibiting 5-14 m of positive relief are preserved on the upper surface of the White Rim Sandstone (Permian) near its eastern stratigraphic pinch-out in Canyonlands National Park, southeastern Utah. The ridges show extreme consistency in size, shape, and directional trend. Ridges average 250 m in width, are less than one to possibly several kilometers in length, and trend N20/degree/W /plus minus/ 5/degree/. Ridge flanks dip as steeply as 30/degree/ and are commonly covered with a thin lag of coarse sand. Sand-filled polygonal fissures are abundant on ridges and intervening flats. The unimodal southeastward dip of the cross-strata within the White Rim and the relationship between eolian bounding surfaces and ridge morphology negate a depositional origin for the ridges. The presence of lag grains within polygonal fissures indicates that the lithification required for fissuring took place prior to deposition of the lag. The authors interpret the ridges as paleoyardangs that were shaped from partially lithified eolian sand by the same unidirectional winds that prevailed during deposition. Similar wind-eroded topography has been repeatedly documented from modern hyperarid regions with unimodal winds but has not been previously described from the stratigraphic record. Wind erosion as well as deposition must be considered when investigating ancient eolian sequences.

  14. Fullerenes and interplanetary dust at the Permian-Triassic boundary.

    PubMed

    Poreda, Robert J; Becker, Luann

    2003-01-01

    We recently presented new evidence that an impact occurred approximately 250 million years ago at the Permian-Triassic boundary (PTB), triggering the most severe mass extinction in the history of life on Earth. We used a new extraterrestrial tracer, fullerene, a third carbon carrier of noble gases besides diamond and graphite. By exploiting the unique properties of this molecule to trap noble gases inside of its caged structure (helium, neon, argon), the origin of the fullerenes can be determined. Here, we present new evidence for fullerenes with extraterrestrial noble gases in the PTB at Graphite Peak, Antarctica, similar to PTB fullerenes from Meishan, China and Sasayama, Japan. In addition, we isolated a (3)He-rich magnetic carrier phase in three fractions from the Graphite Peak section. The noble gases in this magnetic fraction were similar to zero-age deep-sea interplanetary dust particles (IDPs) and some magnetic grains isolated from the Cretaceous-Tertiary boundary. The helium and neon isotopic compositions for both the bulk Graphite Peak sediments and an isolated magnetic fraction from the bulk material are consistent with solar-type gases measured in zero-age deep-sea sediments and point to a common source, namely, the flux of IDPs to the Earth's surface. In this instance, the IDP noble gas signature for the bulk sediment can be uniquely decoupled from fullerene, demonstrating that two separate tracers are present (direct flux of IDPs for (3)He vs. giant impact for fullerene).

  15. Time-calibrated Milankovitch cycles for the late Permian

    PubMed Central

    Wu, Huaichun; Zhang, Shihong; Hinnov, Linda A.; Jiang, Ganqing; Feng, Qinglai; Li, Haiyan; Yang, Tianshui

    2013-01-01

    An important innovation in the geosciences is the astronomical time scale. The astronomical time scale is based on the Milankovitch-forced stratigraphy that has been calibrated to astronomical models of paleoclimate forcing; it is defined for much of Cenozoic–Mesozoic. For the Palaeozoic era, however, astronomical forcing has not been widely explored because of lack of high-precision geochronology or astronomical modelling. Here we report Milankovitch cycles from late Permian (Lopingian) strata at Meishan and Shangsi, South China, time calibrated by recent high-precision U–Pb dating. The evidence extends empirical knowledge of Earth’s astronomical parameters before 250 million years ago. Observed obliquity and precession terms support a 22-h length-of-day. The reconstructed astronomical time scale indicates a 7.793-million year duration for the Lopingian epoch, when strong 405-kyr cycles constrain astronomical modelling. This is the first significant advance in defining the Palaeozoic astronomical time scale, anchored to absolute time, bridging the Palaeozoic–Mesozoic transition. PMID:24030138

  16. Extremely acid Permian lakes and ground waters in North America

    USGS Publications Warehouse

    Benison, K.C.; Goldstein, R.H.; Wopenka, B.; Burruss, R.C.; Pasteris, J.D.

    1998-01-01

    Evaporites hosted by red beds (red shales and sandstones), some 275-265 million years old, extend over a large area of the North American mid- continent. They were deposited in non-marine saline lakes, pans and mud- flats, settings that are typically assumed to have been alkaline. Here we use laser Raman microprobe analyses of fluid inclusions trapped in halites from these Permian deposits to argue for the existence of highly acidic (pH < 1) lakes and ground waters. These extremely acidic systems may have extended over an area of 200,000 km2. Modern analogues of such systems may be natural acid lake and groundwater systems (pH ~2-4) in southern Australia. Both the ancient and modern acid systems are characterized by closed drainage, arid climate, low acid-neutralizing capacity, and the oxidation of minerals such as pyrite to generate acidity. The discovery of widespread ancient acid lake and groundwater systems demands a re-evaluation of reconstructions of surface conditions of the past, and further investigations of the geochemistry and ecology of acid systems in general.

  17. Time-calibrated Milankovitch cycles for the late Permian.

    PubMed

    Wu, Huaichun; Zhang, Shihong; Hinnov, Linda A; Jiang, Ganqing; Feng, Qinglai; Li, Haiyan; Yang, Tianshui

    2013-01-01

    An important innovation in the geosciences is the astronomical time scale. The astronomical time scale is based on the Milankovitch-forced stratigraphy that has been calibrated to astronomical models of paleoclimate forcing; it is defined for much of Cenozoic-Mesozoic. For the Palaeozoic era, however, astronomical forcing has not been widely explored because of lack of high-precision geochronology or astronomical modelling. Here we report Milankovitch cycles from late Permian (Lopingian) strata at Meishan and Shangsi, South China, time calibrated by recent high-precision U-Pb dating. The evidence extends empirical knowledge of Earth's astronomical parameters before 250 million years ago. Observed obliquity and precession terms support a 22-h length-of-day. The reconstructed astronomical time scale indicates a 7.793-million year duration for the Lopingian epoch, when strong 405-kyr cycles constrain astronomical modelling. This is the first significant advance in defining the Palaeozoic astronomical time scale, anchored to absolute time, bridging the Palaeozoic-Mesozoic transition.

  18. Structural evolution of zonal metamorphic sequences in the southern Chinese Altai and relationships to Permian transpressional tectonics in the Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Li, Pengfei; Sun, Min; Rosenbaum, Gideon; Jiang, Yingde; Cai, Keda

    2016-12-01

    The Chinese Altai in the Central Asian Orogenic Belt is characterized by the occurrence of kyanite- and andalusite-type metamorphic zones. However, the tectonic setting associated with these metamorphic zones is still debated. Here we present structural observations from the southern Chinese Altai (Aletai area), where a relict kyanite zone occurs within an andalusite-type metamorphic zonal sequence of sillimanite, andalusite-sillimanite, andalusite-staurolite, staurolite-garnet and biotite. We document two major phases of folding in this area. The earlier structures (D1) developed synchronously with kyanite growth and are represented by an axial planar fabric of tight folds. D1 fabric is mostly obliterated by later deformation, but is inferred to be penetrative as indicated by a profound intersection lineation (L21). The second generation of deformation (D2) is associated with superimposed F2 folds and a dominant axial planar foliation (S2) with NW-SE orientation. Microstructural observations show that D2 structures are associated with the andalusite-type metamorphic series, which is characterized by an early-D2 occurrence of sillimanite, staurolite-garnet and biotite zonal sequence overprinted by the late-D2 growth of andalusite. Combining with previous metamorphic data, we consider that these two folding events (D1 and D2) correspond with the development of kyanite- and andalusite-type metamorphic zones, respectively, which records the burial and exhumation history of metamorphic rocks possibly in response to Devonian-Carboniferous accretion/collision and Permian transpressional tectonics. The latter was associated with oblique convergence between the Chinese Altai and the intra-oceanic arc system of the East/West Junggar.

  19. The Alashan Terrane did not amalgamate with North China block by the Late Permian: Evidence from Carboniferous and Permian paleomagnetic results

    NASA Astrophysics Data System (ADS)

    Yuan, Wei; Yang, Zhenyu

    2015-05-01

    Rock magnetic and paleomagnetic studies have been carried out on the early Carboniferous limestones and the Late Permian purple sandstones sampled in the eastern Alashan Terrane (ALT), northwest of China. Two components were isolated from the Early Carboniferous limestone by thermal progressive demagnetisation: a low unblocking temperature component (LTC) of recent origin; a pre-folding medium temperature component (MTC) (the paleomagnetic pole is λ = 13.1°N, Ф = 11.0°E, A95 = 7.0°) that is probably the result of the hydrothermal fluids from the Qilian Orgenic Belt acquired during the Late Carboniferous-Early Permian. Also, two components were separated from the Late Permian purple sandstone by thermal progressive demagnetisation: the LTC with the recent viscous remanent magnetisation, and the higher temperature component (HTC) revealed from three sections which has passed a regional fold test at the 95% probability level and reversal test, suggesting a primary characteristic magnetisation. The corresponding paleomagnetic pole is λ = 27.2° N, Ф = 18.8° E, A95 = 12.0°. The apparent polar wander path (including early Carboniferous, late Carboniferous-Early Permian, Late Permian and Early-middle Triassic poles) of the ALT is significantly different with those of the NCB. Comparison of the APWPs between the ALT and NCB shows a strong similarity. If the APWP of Hexi Corridor-Alashan rotated counterclockwise around an Euler pole at 44°N, 84°E by 32°, then the coeval APW path of the ALT overlaps to that of the NCB. This result indicates that the ALT migrated to the NCB after the Early-Middle Triassic along a tectonic boundary located between Helanshan Mountain and Zhuozishan Mountain, and finally amalgamated to the NCB before the Early Cretaceous.

  20. CENOZOIC EXHUMATION OF THE ANTIOQUEÑO PLATEAU, NORTHERN ANDES, COLOMBIA, FROM APATITE LOW-TEMPERATURE THERMOCHRONOLOGY

    NASA Astrophysics Data System (ADS)

    Restrepo-Moreno, S. A.; Foster, D. A.; O'Sullivan, P. B.; Donelick, R.; Stockli, D. F.

    2009-12-01

    The Antioqueño plateau (AP), in the northernmost Cordillera Central, Colombia, is the most extensive and best preserved relict surface in the Northern Andes. Apatite (U-Th)/He (AHe) and fission track (AFT) results from twenty two samples, collected from paleocrustal depths along two vertical profiles in canyons dissecting the AP, constrain Cenozoic erosional exhumation of this segment of the Andean range. The two profiles exhibit excellent reproducibility of AHe and AFT data. Helium ages increase with elevation from ~22-49 Ma. A marked inflection point in the AHe age-elevation plots at 25 Ma defines the bottom of the post-Oligocene He partial retention zone (PRZ). Virtually invariant ages at ~25 Ma record onset of rapid exhumation in the AP. A more subtle slope change in the PRZ at ~43 Ma is interpreted as a minor exhumation pulse. AFT better defines timing and intensity of Eocene exhumation. AFT ages for both profiles vary from ~30-49 Ma and are consistently older than AHe ages. AFT data display invariant ages (±2σ) between 1500-2400 m elevations while confined track length data exhibit uni-modal distributions with a mean track length of ~14.2 μm. Both facts indicate rapid cooling. This is further supported by virtually concordant AFT and AHe ages for both profiles between 1500 to 2200 m implying that rocks were exhumed from temperatures >120°C to below AHe closure temperature 60°C. Assuming a geothermal gradient of ~25°C/km this corresponds to exhumation rates in the order of 0.5 mm/y, comparable in intensity to the Miocene pulse defined by AHe. Integrated thermal modeling show an episode of rapid cooling at ~43-49 Ma. AFT profiles show an apparent inflection point at ~1400 m, which defines the upper boundary of an apatite partial annealing zone (PAZ) exhumed during the 43-49 Ma cooling event. The position of the PAZ and PRZ relative to the present erosional surface point to average erosion rates of ~0.03 mm/yr, which constitute very low denudation rates

  1. Bioessential element-depleted ocean following the euxinic maximum of the end-Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Takahashi, Satoshi; Yamasaki, Shin-ichi; Ogawa, Yasumasa; Kimura, Kazuhiko; Kaiho, Kunio; Yoshida, Takeyoshi; Tsuchiya, Noriyoshi

    2014-05-01

    We describe variations in trace element compositions that occurred on the deep seafloor of palaeo-superocean Panthalassa during the end-Permian mass extinction based on samples of sedimentary rock from one of the most continuous Permian-Triassic boundary sections of the pelagic deep sea exposed in north-eastern Japan. Our measurements revealed low manganese (Mn) enrichment factor (normalised by the composition of the average upper continental crust) and high cerium anomaly values throughout the section, suggesting that a reducing condition already existed in the depositional environment in the Changhsingian (Late Permian). Other redox-sensitive trace-element (vanadium [V], chromium [Cr], molybdenum [Mo], and uranium [U]) enrichment factors provide a detailed redox history ranging from the upper Permian to the end of the Permian. A single V increase (representing the first reduction state of a two-step V reduction process) detected in uppermost Changhsingian chert beds suggests development into a mildly reducing deep-sea condition less than 1 million years before the end-Permian mass extinction. Subsequently, a more reducing condition, inferred from increases in Cr, V, and Mo, developed in overlying Changhsingian grey siliceous claystone beds. The most reducing sulphidic condition is recognised by the highest peaks of Mo and V (second reduction state) in the uppermost siliceous claystone and overlying lowermost black claystone beds, in accordance with the end-Permian mass extinction event. This significant increase in Mo in the upper Changhsingian led to a high Mo/U ratio, much larger than that of modern sulphidic ocean regions. This trend suggests that sulphidic water conditions developed both at the sediment-water interface and in the water column. Above the end-Permian mass extinction horizon, Mo, V and Cr decrease significantly. On this trend, we provide an interpretation of drawdown of these elements in seawater after the massive element precipitation event

  2. Permian-Triassic Osteichthyes (bony fishes): diversity dynamics and body size evolution.

    PubMed

    Romano, Carlo; Koot, Martha B; Kogan, Ilja; Brayard, Arnaud; Minikh, Alla V; Brinkmann, Winand; Bucher, Hugo; Kriwet, Jürgen

    2016-02-01

    The Permian and Triassic were key time intervals in the history of life on Earth. Both periods are marked by a series of biotic crises including the most catastrophic of such events, the end-Permian mass extinction, which eventually led to a major turnover from typical Palaeozoic faunas and floras to those that are emblematic for the Mesozoic and Cenozoic. Here we review patterns in Permian-Triassic bony fishes, a group whose evolutionary dynamics are understudied. Based on data from primary literature, we analyse changes in their taxonomic diversity and body size (as a proxy for trophic position) and explore their response to Permian-Triassic events. Diversity and body size are investigated separately for different groups of Osteichthyes (Dipnoi, Actinistia, 'Palaeopterygii', 'Subholostei', Holostei, Teleosteomorpha), within the marine and freshwater realms and on a global scale (total diversity) as well as across palaeolatitudinal belts. Diversity is also measured for different palaeogeographical provinces. Our results suggest a general trend from low osteichthyan diversity in the Permian to higher levels in the Triassic. Diversity dynamics in the Permian are marked by a decline in freshwater taxa during the Cisuralian. An extinction event during the end-Guadalupian crisis is not evident from our data, but 'palaeopterygians' experienced a significant body size increase across the Guadalupian-Lopingian boundary and these fishes upheld their position as large, top predators from the Late Permian to the Late Triassic. Elevated turnover rates are documented at the Permian-Triassic boundary, and two distinct diversification events are noted in the wake of this biotic crisis, a first one during the Early Triassic (dipnoans, actinistians, 'palaeopterygians', 'subholosteans') and a second one during the Middle Triassic ('subholosteans', neopterygians). The origination of new, small taxa predominantly among these groups during the Middle Triassic event caused a

  3. Permian and Triassic microfloral assemblages from the Blue Nile Basin, central Ethiopia

    NASA Astrophysics Data System (ADS)

    Dawit, Enkurie L.

    2014-11-01

    Palynological investigation was carried out on surface samples from up to 400 m thick continental siliciclastic sediments, here referred to as “Fincha Sandstone”, in the Blue Nile Basin, central Ethiopia. One hundred sixty species were identified from 15 productive samples collected along a continuous road-cut exposure. Six informal palynological assemblage zones have been identified. These assemblage zones, in ascending order, are: “Central Ethiopian Permian Assemblage Zone - CEPAZ I”, earliest Permian (Asselian-Sakmarian); “CEPAZ II”, late Early Permian (Artinskian-Kungurian); CEPAZ III - Late Permian (Kazanian-Tatarian); “CETAZ IV”, Lower Triassic (Olenekian Induan); “CETAZ V”, Middle Triassic (Anisian Ladinian); “CETAZ VI”, Late Triassic (Carnian Norian). Tentative age ranges proposed herein are compared with faunally calibrated palynological zones in Gondwana. The overall composition and vertical distribution of miospores throughout the studied section reveals a wide variation both qualitatively and quantitatively. The high frequency of monosaccate pollen in CEPAZ I may reflect a Glossopterid-dominated upland flora in the earliest Permian. The succeeding zone is dominated by straite/taeniate disaccate pollen and polyplicates, suggesting a notable increase in diversity of glossopterids. The decline in the diversity of taeniate disaccate pollen and the concomitant rise in abundance of non-taeniate disaccates in CEPAZ III may suggest the decline in Glossopteris diversity, though no additional evidence is available to equate this change with End-Permian extinction. More diverse and dominant non-taeniate, disaccate, seed fern pollen assignable to FalcisporitesAlisporites in CETAZ IV may represent an earliest Triassic recovery flora. The introduction of new disaccate forms with thick, rigid sacci, such as Staurosaccites and Cuneatisporites, in CETAZ V and VI may indicate the emergence of new gymnospermous plants that might have favourably

  4. The last "pelycosaur": a varanopid synapsid from the Pristerognathus Assemblage Zone, Middle Permian of South Africa

    NASA Astrophysics Data System (ADS)

    Modesto, Sean P.; Smith, Roger M. H.; Campione, Nicolás E.; Reisz, Robert R.

    2011-12-01

    We report on a partial varanopid skull and mandible from the Pristerognathus Assemblage Zone of the Beaufort Group, in the South African Karoo Basin, which is probably latest Middle Permian (Capitanian) in age. This mycterosaurine is not only the youngest known varanopid from the Southern Hemisphere, but it is also the youngest known "pelycosaur" (i.e., non-therapsid synapsid). Like all other members of this clade of hypercarnivores, the teeth are strongly flattened, recurved, and have finely serrated cutting edges. The anterior dentary teeth form a caniniform region, and the splenial features a foramen intermandibularis oralis, the first ever to be described in a "pelycosaur." The last varanopids were the smallest carnivores of latest Middle Permian continental faunas. Occupation of the small carnivore guild appears to have allowed varanopids to achieve a nearly cosmopolitan distribution throughout the Middle Permian, between the great Early Permian radiation of basal synapsids and the spectacular diversification of therapsid synapsids in the Late Permian and Early Triassic.

  5. Silicified wood from the Permian and Triassic of Antarctica: Tree rings from polar paleolatitudes

    USGS Publications Warehouse

    Ryberg, P.E.; Taylor, E.L.

    2007-01-01

    The mass extinction at the Permian-Triassic boundary produced a floral turnover in Gondwana in which Paleozoic seed ferns belonging to the Glossopteridales were replaced by corystosperm seed ferns and other seed plant groups in the Mesozoic. Secondary growth (wood production) in both plant groups provides information on plant growth in relation to environment in the form of permineralized tree rings. Techniques utilized to analyze extant wood can be used on fossil specimens to better understand the climate from both of these periods. Late Permian and early Middle Triassic tree rings from the Beardmore Glacier area indicate an environment where extensive plant growth occurred at polar latitudes (~80–85°S, Permian; ~75°S, Triassic). A rapid transition to dormancy in both the Permian and Triassic woods suggests a strong influence of the annual light/dark cycle within the Antarctic Circle on ring production. Latewood production in each ring was most likely triggered by the movement of the already low-angled sun below the horizon. The plants which produced the wood have been reconstructed as seasonally deciduous, based on structural and sedimentologic evidence. Although the Late Permian climate has been reconstructed as cold temperate and the Middle Triassic as a greenhouse, these differences are not reflected in tree ring anatomy or wood production in these plant fossils from the central Transantarctic Mountains.

  6. A new captorhinid reptile, Gansurhinus qingtoushanensis, gen. et sp. nov., from the Permian of China

    NASA Astrophysics Data System (ADS)

    Reisz, Robert R.; Liu, Jun; Li, Jin-Ling; Müller, Johannes

    2011-05-01

    Captorhinids, a clade of Paleozoic reptiles, are represented by a rich fossil record that extends from the Late Carboniferous into the Late Permian. Representatives of this clade dispersed from the equatorial regions of Laurasia into the temperate regions of Pangea during the Middle and Late Permian. This rich fossil record shows that there was an evolutionary trend from faunivorous to omnivorous and herbivorous feeding habits within this clade. The discovery of well-preserved captorhinid materials in the Middle Permian of China allows us to determine that the new taxon, Gansurhinus qingtoushanensis, gen. et sp. nov, is a member of Moradisaurinae, a clade of captorhinids with multiple tooth rows arranged in parallel. The presence of this moradisaurine in the Middle Permian of south central Asia leads us to suggest that paleogeographic changes during the Permian, with part of what is today China becoming a large peninsula of Pangea, allowed these early reptiles as well as other terrestrial vertebrates to extend their geographic ranges to this region of the Late Paleozoic supercontinent.

  7. Permian tectonism in Rocky Mountain foreland and its importance in Exploration for Minnelusa and Lyons sandstones

    SciTech Connect

    Moore, W.R.

    1985-05-01

    Permian sandstones are important producers of oil in the Powder River and Denver basins of the Rocky Mountain foreland region. In the Powder River basin, Wolfcampian Minnelusa Sandstone produces oil from structural and stratigraphic traps on both sides of the basin axis, whereas in Denver basin, the Leonardian Lyons Sandstone produces oil mainly from structural traps on the west flank of the basin. Two fields, North Fork-Cellars Ranch in the Powder River basin, and Black Hollow in the Denver basin, are examples of Permian growth of structural features. At North Fork-Cellars Ranch, a period of Permian structural growth and resultant differential sedimentation is documented by structure and isopach maps of the Minnelusa and overlying Goose Egg Formation. Structural growth began at the end of Minnelusa deposition and resulted in deposition of a much thicker Goose Egg section on the west flank of the field. At Black Hollow, mapping indicates structural growth was initiated before deposition of the Lyons Sandstone and continued throughout Leonardian time. In both fields growth abruptly ceased in the Late Permian. Both North Fork-Cellars Ranch and Black Hollow are located on structural highs, or arches, which trend east-west across the Powder River and Denver basins. These arches were present during the pre-Laramide migration of Paleozoic-sourced hydrocarbons into the basins and acted as pathways for migration. Exploration for Permian reservoirs in the two basins should be concentrated on the arches, as the early formed traps were present when migration began.

  8. Development of the Permian-Triassic unconformity in southwestern Utah, southeastern Nevada and northwestern Arizona

    SciTech Connect

    Nielson, R.L. . Dept. of Geology)

    1993-04-01

    Development of positive areas, that are oriented northwest-southeast in south-western Utah, southeastern Nevada, and northwestern Arizona, are indicated by the depositional patterns of the Rock Canyon Conglomerate and facies changes produced by on-lapping during the deposition of the Timpoweap, Lower Red, and Virgin Limestone Members of the Moenkopi Formation. The lack of facies change in the Kaibab Formation indicates that uplift of the positive areas did not start during the early Permian. The Fossil Mountain Member of the Kaibab Formation, is a marker of continuous shallow marine sedimentation across the area. The Harrisburg Member contains three limestone units, separated by gypsum and shale units, that represent regressions and transgressions. Where the gypsum in the Kaibab Formation thins, collapse breccia and deformed shale units are present indicating that the gypsum was deposited and then removed by dissolution. Channels cut during the late Permian and early Triassic Periods do not cut through the Harrisburg Member of the Kaibab Formation. West of St. George, Utah, where the gypsum deposits are thickest, is the location where Timpoweap, Lower Red, and Virgin Limestone members thin and are absent. Late Permian and early Triassic topography may have in part been controlled by dissolution of the gypsum deposits in the Kaibab Formation. The low angle of discordance between Permian and Triassic units indicated that the area was not subjected to major deformation during the late Permian and early Triassic, but was gently tilted and uplifted.

  9. 40Ar/ 39Ar dating of Late Permian evaporites, southeastern New Mexico, USA

    NASA Astrophysics Data System (ADS)

    Renne, Paul R.; Sharp, Warren D.; Montañez, Isabel P.; Becker, Tim A.; Zierenberg, Robert A.

    2001-12-01

    40Ar/ 39Ar dating of the potassium-magnesium sulfate mineral langbeinite from Permian evaporites of the Salado formation near Carlsbad, New Mexico, provides quantitative evidence that some salts in these deposits have not recrystallized for 251 Myr since deposition. Survival of Permian salts supports the possibility that Bacillus bacteria recovered from nearby halite was isolated in a closed system and represents a sample of uncontaminated Permian life. Local recrystallization of langbeinite and other nearby minerals is also indicated by the dating, suggesting both the need and the opportunity to document closed system behavior more rigorously. The shoaling and desiccation event recorded by the Salado formation began at least 1 Myr before the Permian-Triassic boundary. Temporal correlation of the Salado with the Zechstein evaporites of north-central Europe supports previously inferred regression models for the origin of these deposits. Significant paleoenvironmental change at the Permian-Triassic boundary thus occurred on a time scale more protracted than that implied by geologically instantaneous events such as bolide impacts.

  10. Eduction, extension, and exhumation of ultrahigh-pressure rocks in metamorphic core complexes due to subduction initiation

    NASA Astrophysics Data System (ADS)

    Petersen, Kenni Dinesen; Buck, W. Roger

    2015-09-01

    The controversy over the exhumation of ultrahigh-pressure (UHP) rocks centers on whether it involves rising of pieces of crust detached from subducted continental lithosphere or an entire subducted plate that undergoes "eduction," i.e., reverse subduction. We present a new thermomechanical model of continental subduction showing that these apparently contrasting mechanisms can occur together: crust subducted deep enough is heated and weakened, causing limited diapiric rise, while crust subducted to shallower depths retains strength and is exhumed only by eduction. The model also shows for the first time how eduction followed by seafloor spreading can occur in a zone of regional convergence. This occurs spontaneously when subduction of buoyant crust causes a subduction zone to "lock up" in one place causing a new subduction zone to form in another. The model is consistent with many features of the youngest region of UHP rock exhumation on earth: the D'Entrecasteaux Islands. UHP exhumation and the amount of regional extension, as well as the seismic structure around the islands, can be explained by eduction. Ductile flow fabrics, seen on the islands, would result from exhumation of the most deeply subducted crust heated enough to undergo partial melting. Reversal of motion on the north-dipping continental subduction zone, required by this model, was likely triggered by initiation of the New Britain Trench, as suggested previously. Our model implies that the crust of Goodenough Basin, south of the islands, was exhumed by eduction in the last 5 Ma and this hypothesis can be tested by drilling.

  11. Microstructural, textural and thermal evolution of an exhumed strike-slip fault and insights into localization and rheological transition

    NASA Astrophysics Data System (ADS)

    Cao, Shuyun; Neubauer, Franz; Liu, Junlai; Bernroider, Manfred; Genser, Johann

    2016-04-01

    The presence of deep exhumed crustal rocks with a dominant but contrasting mineralogy results in shear concentration in the rheological weakest layer, which exhibits contrasting patterns of fabrics and thermal conditions during their formation. We tested a combination of methodologies including microstructural and textural investigations, geochronology and geothermometry on deformed rocks from exhumed strike-slip fault, Ailao Shan-Red River, SE, Asian. Results indicate that the exhumed deep crustal rocks since late Oligocene (ca. 28 Ma) to Pliocene (ca. 4 Ma) typically involve dynamic microstructural, textural and thermal evolution processes, which typically record a progressive deformation and syn-kinematic reactions from ductile to semi-ductile and brittle behavior during exhumation. This transformation also resulted in dramatic strength reduction that promoted strain localization along the strike-slip and transtensional faults. Detailed analysis has revealed the co-existence of microfabrics ranging from high-temperatures (granulite facies conditions) to overprinting low-temperatures (lower greenschist facies conditions). The high-temperature microstructures and textures are in part or entirely altered by subsequent, overprinting low-temperature shearing. In quartz-rich rocks, quartz was deformed in the dislocation creep regime and records transition of microfabrics and slip systems during decreasing temperature, which lasted until retrogression related to final exhumation. As a result, grain-size reduction associated by fluids circulating within the strike-slip fault zone at brittle-ductile transition leads to rock softening, which resulted in strain localization, weak rock rheology and the overall hot thermal structure of the crust. Decompression occurred during shearing and as a result of tectonic exhumation. All these results demonstrate that the ductile to ductile-brittle transition involves a combination of different deformation mechanisms, rheological

  12. Tales from the grave: Opposing autopsy reports from a body exhumed.

    PubMed

    Gunasekera, R S; Brown, A B; Costas, E H

    2012-07-01

    We report an autopsy case of a 42-year-old woman who, when discovered, had been dead in her apartment for approximately 1 week under circumstances involving treachery, assault and possible drug overdose. This case is unique as it involved two autopsies of the deceased by two different medical examiners who reached opposing conclusions. The first autopsy was performed about 10 days after death. The second autopsy was performed after an exhumation approximately 2 years after burial. Evidence collected at the crime scene included blood samples from which DNA was extracted and analysed, fingerprints and clothing containing dried body fluids. The conclusion of the first autopsy was accidental death due to cocaine toxicity; the conclusion of the second autopsy was death due to homicide given the totality of evidence. Suspects 1 and 2 were linked to the death of the victim by physical evidence and suspect 3 was linked by testimony. Suspect 1 received life in prison, and suspects 2 and 3 received 45 and 20 years in prison, respectively. This case indicates that cocaine toxicity is difficult to determine in putrefied tissue and that exhumations can be important in collecting forensic information. It further reveals that the combined findings of medical examiners, even though contradictory, are useful in determining the circumstances leading to death in criminal justice. Thus, this report demonstrates that such criminal circumstances require comparative forensic review and, in such cases, scientific conclusions can be difficult.

  13. Exhumation and shortening distribution in the Taiwan orogen: insights from thermomechanical modeling

    NASA Astrophysics Data System (ADS)

    Mouthereau, F.; Yamato, P.; Burov, E.

    2007-12-01

    The Taiwan orogen has long been regarded as a case example for studying exhumation and erosion processes in association with mountain building. In the recent years, the increasing number of thermochronometric data (mainly ZFT and AFT ages) has allowed to better understanding the deep-seated tectonic processes. For instance, using thermomechanical wedge modelling, up to 50% of underplating has been proposed to explain the observed distribution of FT ages. So it would appear that a large amount of materials added to the orogen originated in more deeper and ductile parts of the crust. The nature of this additional flux (velocity, mechanism of deformation) is however poorly constrained in the current thermomechanical model. Our concern is to use a fully- coupled visco-elasto-plastic themomechanical numerical model to reproduce the observed FT ages and long- term distribution of shortening. To this aim we use the numerical code PARA(O)VOZ based on F.L.A.C. (Fast Lagrangian Analysis of Continua) algorithm. Our results show that the particular distribution of shortening across the Taiwan belt as well as the rapid exhumation and thermal conditions in the hinterland are well accounted for by two superimposed flows of upper and lower crustal rocks decoupled from the subducting Eurasian mantle.

  14. A method for evaluating basement exhumation histories from closure age distributions of detrital minerals

    SciTech Connect

    Lovera, Oscar M.; Grove, Marty; Kimbrough, David L.; Abbott, Patrick L.

    1999-12-10

    We have developed a two-dimensional, thermokinetic model that predicts the closure age distributions of detrital minerals from pervasively intruded and differentially exhumed basement. Using this model, we outline a method to determine the denudation history of orogenic regions on the basis of closure age distributions in synorogenic to postorogenic forearc strata. At relatively high mean denudation rates of 0.5 km m.y.-1 sustained over millions of years, magmatic heating events have minimal influence upon the age distributions of detrital minerals such as K-feldspar that are moderately retentive of radiogenic Ar. At lower rates, however, the effects of batholith emplacement may be substantial. We have applied the approach to detrital K-feldspars from forearc strata derived from the deeply denuded Peninsular Ranges batholith (PRB). Agreement of the denudation history deduced from the detrital K-feldspar data with thermochronologic constraints from exposed PRB basement lead us to conclude that exhumation histories of magmatic arcs should be decipherable solely from closure age distributions of detrital minerals whose depositional age is known. (c) 1999 American Geophysical Union.

  15. Conditions for lower lithosphere exhumation from continental collision: South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Cunje, A.; Pysklywec, R. N.

    2013-12-01

    The South Island of New Zealand provides a unique opportunity for the investigation of active deep crustal dynamics and the effects of surface processes during collision, as a fairly young and relatively well-constrained convergent plate boundary. One of the uncertainties of the orogenesis is the fate of the lower crust during the continental collision: portions of the crust are exhumed along the Alpine Fault, but the lowermost crust does not seem to follow. This work focuses on the fate of the mid- and lower-crust during the collision, investigating several of the primary controls - rheology, boundary conditions, temperature - that regulate the behaviour of the crust during an idealized continental collision event. We use forward thermo-mechanical numerical modelling of the mantle and lithosphere, with variable surface boundary conditions of erosion and deposition, to explore the deformation of the crust and mantle lithosphere via the collision; the 2D models are configured for a South Island-type system using available observational constraints. The models show several end member modes of behaviour of the lower crust from complete exhumation, to 'ponding'/ accumulation at the base of the orogen, to subduction and deep entrainment. The rheology of the lower crust is the dominant factor controlling these behaviours, although there is also modification of the dynamics depending on the rates of continental convergence, the presence of active and varying degrees of erosion, and the effects of differing ratios of deposition.

  16. From nappe stacking to exhumation: Cretaceous tectonics in the Apuseni Mountains (Romania)

    NASA Astrophysics Data System (ADS)

    Reiser, Martin Kaspar; Schuster, Ralf; Spikings, Richard; Tropper, Peter; Fügenschuh, Bernhard

    2016-05-01

    New Ar-Ar muscovite and Rb-Sr biotite age data in combination with structural analyses from the Apuseni Mountains provide new constraints on the timing and kinematics of deformation during the Cretaceous. Time-temperature paths from the structurally highest basement nappe of the Apuseni Mountains in combination with sedimentary data indicate exhumation and a position close to the surface after the Late Jurassic emplacement of the South Apuseni Ophiolites. Early Cretaceous Ar-Ar muscovite ages from structurally lower parts in the Biharia Nappe System (Dacia Mega-Unit) show cooling from medium-grade conditions. NE-SW-trending stretching lineation and associated kinematic indicators of this deformation phase (D1) are overprinted by top-NW-directed thrusting during D2. An Albian to Turonian age (110-90 Ma) is proposed for the main deformation (D2) that formed the present-day geometry of the nappe stack and led to a pervasive retrograde greenschist-facies overprint. Thermochronological and structural data from the Bihor Unit (Tisza Mega-Unit) allowed to establish E-directed differential exhumation during Early-Late Cretaceous times (D3.1). Brittle detachment faulting (D3.2) and the deposition of syn-extensional sediments indicate general uplift and partial surface exposure during the Late Cretaceous. Brittle conditions persist during the latest Cretaceous compressional overprint (D4).

  17. Forensic examination after exhumation: Contribution and difficulties after more than thirty years of burial.

    PubMed

    Nouma, Y; Ben Amar, W; Zribi, M; Bardaa, S; Hammami, Z; Maatoug, S

    2016-11-01

    We report a case of a Tunisian footballer who was found dead abroad under suspicious circumstances. The cause of death was, originally, attributed to a lightning strike. The corpse was buried without/autopsy. Over thirty years later, the family requested the exhumation to verify the identity and the cause of death. The exhumation was performed in 2011. DNA profiling from teeth and femur bone samples confirmed the identity of the deceased. The dry bone study revealed defects in the skull and the pelvis evoking firearm injuries. Post-mortem CT with three-dimensional (3-D) reconstruction allowed to confirm the characteristics of firearms injuries and to speculate about the number and the trajectories of potential shots. Nevertheless, the vitality of these injuries as well as the eventual fatal shot and the shooting distance could not be determined. Likewise, the type of the eventual weapon could not be clarified as there were no bullets or any metallic projectile fragments. Despite all doubts, the forensic explorations have allowed to verify the identity of the deceased, to evoke firearms injuries and, mainly, to deny the proposed cause of death after more than thirty years of burial. Moreover, the loss of soft tissues and bone fragility were the major obstacles.

  18. Exhumation along the Fairweather fault, southeastern Alaska, based on low-temperature thermochronometry

    USGS Publications Warehouse

    McAleer, R.J.; Spotila, J.A.; Enkelmann, E.; Berger, A.L.

    2009-01-01

    The southern Alaskan syntaxis marks the spectacular junction between the >1000-km-long Pacific-North America transform margin and the Chugach-St. Elias belt, where subduction and terrane accretion drive rapid convergent deformation and rock uplift. New low-temperature thermochronometry reveals that intense orogenic deformation is not restricted to one side of the syntaxis but extends nearly 300 km south along the dextral Fairweather fault. Apatite and zircon (U-Th)/He ages as young as 0.9 and 2.0 Ma suggest maximum exhumation rates of nearly 2 mm/a in close proximity (0.5 mm/a along the entire plate margin. We estimate that long-term rock uplift accommodates ???3 mm/a of fault-normal convergence in this area. This suggests that the Fairweather fault is slightly transpressive and highly partitioned, analogous to the central San Andreas fault. This convergence only accounts for ???1/5 of the obliquity between Pacific plate motion and the continental margin, however, implying the deficit is taken up by 1-2 cm/a thrust-sinistral motion along the offshore Transition fault. Additionally, thermochronometry shows a marked increase in bedrock cooling coincident with onset of heavy glaciation, similar to what has been observed in other parts of the Pacific Northwest. The tectonically active Fairweather corridor is distinguished, however, by the magnitude of the acceleration and the depth of exhumation since Pliocene climate change. Copyright 2009 by the American Geophysical Union.

  19. Toxicological Analysis of Opiates from Alternative Matrices Collected from an Exhumed Body.

    PubMed

    Cippitelli, Marta; Mirtella, Dora; Ottaviani, Giovanni; Tassoni, Giovanna; Froldi, Rino; Cingolani, Mariano

    2017-05-18

    In this case study, the body of a 45-year-old man was exhumed after 1 year at the request of the public prosecutor to assess whether the death was caused by drug consumption. Toxicological analyses were performed on several matrices, including liver, kidney, and the alternative matrices hair and teeth. The systematic toxicological analysis (STA), which consisted of basic and acid liquid/liquid extraction and gas chromatography-mass spectrometry (GC-MS) analysis, showed the presence of opiates in each of the matrices analyzed. Subsequently, to confirm and quantify the presence of opioids, samples of each of the matrices were subjected to solid-phase extraction and specific GC-MS analysis. The case presented demonstrates the possibility of drug detection in an exhumed body that has been buried for 1 year, despite the problems of quantitative interpretation of the data, and that toxicological results could be useful along with other forensic evidence. © 2017 American Academy of Forensic Sciences.

  20. Nb-Ta mobility and fractionation during exhumation of UHP eclogite from southwestern Tianshan, China

    NASA Astrophysics Data System (ADS)

    Zhang, Lijuan; Zhang, Lifei; Lü, Zeng; Bader, Thomas; Chen, Zhenyu

    2016-05-01

    In order to study the behavior of high field strength elements (HFSE) during retrograde overprint of ultrahigh-pressure (UHP) eclogites, analysis of Nb and Ta concentrations was carried out on bulk rock, rutile (in both veins and host rocks) and titanite in the host eclogite. The studied samples were collected from the UHP metamorphic belt of southwestern Tianshan, China. Petrographic observation and phase equilibria modeling show that the host eclogites have experienced UHP metamorphism and the rutile-bearing veins are thought to be originated from an internal fluid source, probably by lawsonite dehydration during exhumation. The presence of vein rutile indicates HFSE could be mobilized from host eclogites to veins, which is probably facilitated by complexation with dissolved Na-Al silicates and fluorine-rich fluids. Changes in fluid composition (e.g., F-1, X(CO2)) may trigger the precipitation of rutile. Rutile/fluid partitioning may be the key to fractionating Nb and Ta, with preference for Ta in the fluid, resulting in Nb/Ta ratio of rutile in the veins lower than that in the host eclogite. Besides, the transformation of rutile into titanite also might be an effective mechanism for fractionating Nb from Ta, resulting in the intra-grain Nb-Ta zonations in vein rutile. The Nb-Ta mobility and fractionation can happen during exhumation of the UHP eclogite, which should be very important for understanding the behavior of HFSE in subduction zone metamorphism.

  1. From nappe stacking to exhumation: Cretaceous tectonics in the Apuseni Mountains (Romania)

    NASA Astrophysics Data System (ADS)

    Reiser, Martin Kaspar; Schuster, Ralf; Spikings, Richard; Tropper, Peter; Fügenschuh, Bernhard

    2017-03-01

    New Ar-Ar muscovite and Rb-Sr biotite age data in combination with structural analyses from the Apuseni Mountains provide new constraints on the timing and kinematics of deformation during the Cretaceous. Time-temperature paths from the structurally highest basement nappe of the Apuseni Mountains in combination with sedimentary data indicate exhumation and a position close to the surface after the Late Jurassic emplacement of the South Apuseni Ophiolites. Early Cretaceous Ar-Ar muscovite ages from structurally lower parts in the Biharia Nappe System (Dacia Mega-Unit) show cooling from medium-grade conditions. NE-SW-trending stretching lineation and associated kinematic indicators of this deformation phase (D1) are overprinted by top-NW-directed thrusting during D2. An Albian to Turonian age (110-90 Ma) is proposed for the main deformation (D2) that formed the present-day geometry of the nappe stack and led to a pervasive retrograde greenschist-facies overprint. Thermochronological and structural data from the Bihor Unit (Tisza Mega-Unit) allowed to establish E-directed differential exhumation during Early-Late Cretaceous times (D3.1). Brittle detachment faulting (D3.2) and the deposition of syn-extensional sediments indicate general uplift and partial surface exposure during the Late Cretaceous. Brittle conditions persist during the latest Cretaceous compressional overprint (D4).

  2. From nappe stacking to exhumation: Cretaceous tectonics in the Apuseni Mountains (Romania).

    PubMed

    Reiser, Martin Kaspar; Schuster, Ralf; Spikings, Richard; Tropper, Peter; Fügenschuh, Bernhard

    2017-01-01

    New Ar-Ar muscovite and Rb-Sr biotite age data in combination with structural analyses from the Apuseni Mountains provide new constraints on the timing and kinematics of deformation during the Cretaceous. Time-temperature paths from the structurally highest basement nappe of the Apuseni Mountains in combination with sedimentary data indicate exhumation and a position close to the surface after the Late Jurassic emplacement of the South Apuseni Ophiolites. Early Cretaceous Ar-Ar muscovite ages from structurally lower parts in the Biharia Nappe System (Dacia Mega-Unit) show cooling from medium-grade conditions. NE-SW-trending stretching lineation and associated kinematic indicators of this deformation phase (D1) are overprinted by top-NW-directed thrusting during D2. An Albian to Turonian age (110-90 Ma) is proposed for the main deformation (D2) that formed the present-day geometry of the nappe stack and led to a pervasive retrograde greenschist-facies overprint. Thermochronological and structural data from the Bihor Unit (Tisza Mega-Unit) allowed to establish E-directed differential exhumation during Early-Late Cretaceous times (D3.1). Brittle detachment faulting (D3.2) and the deposition of syn-extensional sediments indicate general uplift and partial surface exposure during the Late Cretaceous. Brittle conditions persist during the latest Cretaceous compressional overprint (D4).

  3. Upper Permian (Guadalupian) coastal tidal flat and shelf lagoon deposits: outcrop model and subsurface examples of stratigraphic traps, Permian basin

    SciTech Connect

    Harris, P.M.; Ward, R.F.

    1986-05-01

    Over half a century of exploration and development drilling has shown that hydrocarbons reservoired in Upper Permian (Guadalupian) deposits of west Texas and southeastern New Mexico have accumulated at the contact between shelf-lagoon dolomites or siltstones and their updip coastal evaporite equivalents. Production from any of the Guadalupian shelf units similarly occurs from stacked reservoirs of dolomites or siltstones. Dolomites comprise shoaling cycles of deposition: intercrystalline and moldic porosities typify basal dolomudstones and dolowackestones as well as overlying dolopackstones, whereas capping dolomudstones may contain fenestral porosity but usually are tight and interlayered with anhydrite. Interparticle porosity occurs in siltstones that are interbedded with the dolomites. Reservoir development is more a problem of updip seal than porosity, as sediments other than lagoonal dolomites and siltstones are porous. Porous carbonate sands accumulated in a backreef position and the shelf margin reef and associated slope debris apron have developed porosity secondarily through solution, fracturing, and minor dolomitization. Hydrocarbons migrated from presumed basinal source rocks through the margin and backreef, and continued updip into shelf lagoon deposits that pinch out into tight anhydrite-cemented equivalents as well as interbedded evaporites of coastal tidal-flat origin.

  4. Plio-Pleistocene exhumation of the eastern Himalayan syntaxis and its domal 'pop-up'

    NASA Astrophysics Data System (ADS)

    Bracciali, Laura; Parrish, Randall R.; Najman, Yani; Carter, Andrew; Wijbrans, Jan R.; Smye, Andrew

    2016-04-01

    The eastern termination of the Himalayan orogen at the southern margin of the Tibetan Plateau forms a syntaxial antiform that folds the suture zone between the Indian and Asian plates and is characterised by 10 to < 1 Ma dates of various geo- and thermo-chronometers. These document Late Miocene to Pleistocene structural, metamorphic, igneous and exhumation events and a recent history of very rapid cooling. The northern third of the syntaxis corresponds to a steep domal 'pop-up' structure bounded by the India-Asia suture on three sides and a thrust zone to the south. One of the major rivers of the eastern Himalaya-Tibet region, the Yarlung Tsangpo, dissects the eastern syntaxis. The river becomes the Brahmaputra River in the Indian foreland basin before emptying into the Bay of Bengal. Exceptionally high relief and one of the deepest gorges on Earth have developed where the river's tortuous route crosses the Namche Barwa-Gyala Peri massif (> 7 km in elevation) in the core of the syntaxis. Downstream of the gorge very high erosion rates contribute ~ 50% of total detritus to the sediment load of the river. The initiation of the exceptional exhumation has been attributed either to the extreme erosive power of a river flowing across a deforming indentor corner and the positive feedback that would establish between the two, or to subduction geometry of a stiffened indentor corner. It has also been suggested that the growth of the antiformal structure and the exhumation of its high grade metamorphic core resulted from buckling as a means to accommodate shortening in the indentor corner. In this study [1] we provide new chronological data on the bedrock of the eastern syntaxis and its erosion products to date the inception of very rapid uplift and erosion and discuss its cause, with the ultimate aim to reconstruct the structural and exhumation history of the syntaxis. We use U-Pb zircon and rutile, white mica Ar-Ar and fission track zircon dating of bedrock, modern

  5. 78 FR 16569 - Iowa Pacific Holdings, LLC, Permian Basin Railways, and San Luis & Rio Grande Railroad-Corporate...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-03-15

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF TRANSPORTATION Surface Transportation Board Iowa Pacific Holdings, LLC, Permian Basin Railways, and San Luis & Rio Grande... Holdings, LLC (IPH), its wholly owned subsidiaries Permian Basin Railways (PBR) and San Luis & Rio Grande...

  6. Polish permian basin: Lithofacies traps for gas within the Rotliegende deposits as a new exploration potential

    SciTech Connect

    Karnkowski, P.H. )

    1993-09-01

    Rotliegende deposits are the most prospective reservoir gas rocks in the Polish Permian basin. Thirty years of their exploration have led to location of numerous gas fields in the upper-most part of these series, particularly in the area of the Fore-Sudetic monocline. Up to this time, exploration studies concentrated mainly on structural objects, and most of the structures were positive gas traps. Well and seismic data also indicate an occurrence of lithofacies gas traps; they occur mainly in the sandstone zones within the fanglomerates surrounding the Wolsztyn Ridge. When comparing the facies regularities in the known gas fields in the German Permian basin (interfingering sandstones and claystones) to the facies patterns of the Polish Permian basin, one may suspect similar exploration possibilities. These are the first promising results. Advances in analysis of the Rotliegende depositional systems will enable us to create a new exploration potential.

  7. Permian tetrapods from the Sahara show climate-controlled endemism in Pangaea.

    PubMed

    Sidor, Christian A; O'Keefe, F Robin; Damiani, Ross; Steyer, J Sébastien; Smith, Roger M H; Larsson, Hans C E; Sereno, Paul C; Ide, Oumarou; Maga, Abdoulaye

    2005-04-14

    New fossils from the Upper Permian Moradi Formation of northern Niger provide an insight into the faunas that inhabited low-latitude, xeric environments near the end of the Palaeozoic era (approximately 251 million years ago). We describe here two new temnospondyl amphibians, the cochleosaurid Nigerpeton ricqlesi gen. et sp. nov. and the stem edopoid Saharastega moradiensis gen. et sp. nov., as relicts of Carboniferous lineages that diverged 40-90 million years earlier. Coupled with a scarcity of therapsids, the new finds suggest that faunas from the poorly sampled xeric belt that straddled the Equator during the Permian period differed markedly from well-sampled faunas that dominated tropical-to-temperate zones to the north and south. Our results show that long-standing theories of Late Permian faunal homogeneity are probably oversimplified as the result of uneven latitudinal sampling.

  8. Permian reptilian fauna from the Kundaram Formation, Pranhita-Godavari Valley, India

    NASA Astrophysics Data System (ADS)

    Ray, Sanghamitra

    1999-07-01

    The Kundaram Formation of the Pranhita-Godavari Valley yields the only Permian reptilian fauna in India. It is composed essentially of a dicynodont assemblage and includes Endothiodon, Cistecephalus, Pristerodon, Oudenodon and Emydops-like forms. The only non-dicynodont member is a captorhinid reptile. These taxa allow the correlation of the Kundaram Formation with the Tropidostoma and/or Cistecephalus Assemblage Zones of the Beaufort Group of South Africa, the basal beds of Madumabisa Mudstones of Zambia, the Ruhuhu and lower part of the Kawinga Formation of Tanzania and the Morro Pelado member of the Rio do Rasto Formation of Brazil, indicating a Late Permian (Tatarian) age. The Kundaram fauna helps in fixing the upper age of the coal-bearing Damuda Group more precisely at Tatarian. The distribution of the Late Permian dicynodonts in the now widely separated geographic areas suggests the close proximity of the continents and a lack of endemism or provinciality.

  9. Trouble Upstairs: Reconstructing Permian-Triassic Climate during Siberian Traps Magmatism

    NASA Astrophysics Data System (ADS)

    Black, B. A.; Neely, R. R., III; Lamarque, J. F.; Elkins-Tanton, L. T.; Mills, M. J.

    2014-12-01

    The eruption of large igneous provinces can transfer significant masses of volatiles from Earth's interior to the atmosphere. What are the consequences of this degassing for habitability and extinction? In this presentation, we consider this question in the context of Siberian Traps magmatism, which has been shown to overlap within geochronologic uncertainty with catastrophic deterioration of Permian-Triassic marine and terrestrial ecosystems. To investigate the impacts of endogenic gases on climate, atmospheric chemistry, and ocean circulation, we conducted a series of numerical experiments with a comprehensive global model for the Permian-Triassic. Our simulations predict the intensity and distribution of acid rain and ozone depletion, with implications for terrestrial biota. We further explore feedbacks between sulfur emissions, transient cooling, and shifts in ocean circulation. We suggest that Siberian Traps magmatism may have triggered several distinct kill mechanisms in the oceans and on land, contributing to a complex combined pattern of environmental stress and latest Permian ecological failure.

  10. Good genes and good luck: ammonoid diversity and the end-Permian mass extinction.

    PubMed

    Brayard, Arnaud; Escarguel, Gilles; Bucher, Hugo; Monnet, Claude; Brühwiler, Thomas; Goudemand, Nicolas; Galfetti, Thomas; Guex, Jean

    2009-08-28

    The end-Permian mass extinction removed more than 80% of marine genera. Ammonoid cephalopods were among the organisms most affected by this crisis. The analysis of a global diversity data set of ammonoid genera covering about 106 million years centered on the Permian-Triassic boundary (PTB) shows that Triassic ammonoids actually reached levels of diversity higher than in the Permian less than 2 million years after the PTB. The data favor a hierarchical rather than logistic model of diversification coupled with a niche incumbency hypothesis. This explosive and nondelayed diversification contrasts with the slow and delayed character of the Triassic biotic recovery as currently illustrated for other, mainly benthic groups such as bivalves and gastropods.

  11. Chondritic meteorite fragments associated with the Permian-Triassic boundary in Antarctica.

    PubMed

    Basu, Asish R; Petaev, Michail I; Poreda, Robert J; Jacobsen, Stein B; Becker, Luann

    2003-11-21

    Multiple chondritic meteorite fragments have been found in two sedimentary rock samples from an end-Permian bed at Graphite Peak in Antarctica. The Ni/Fe, Co/Ni, and P/Fe ratios in metal grains; the Fe/Mg and Mn/Fe ratios in olivine and pyroxene; and the chemistry of Fe-, Ni-, P-, and S-bearing oxide in the meteorite fragments are typical of CM-type chondritic meteorites. In one sample, the meteoritic fragments are accompanied by more abundant discrete metal grains, which are also found in an end-Permian bed at Meishan, southern China. We discuss the implications of this finding for a suggested global impact event at the Permian-Triassic boundary.

  12. Altered river morphology in south africa related to the permian-triassic extinction

    PubMed

    Ward; Montgomery; Smith

    2000-09-08

    The Permian-Triassic transition in the Karoo Basin of South Africa was characterized by a rapid and apparently basin-wide change from meandering to braided river systems, as evidenced by preserved sedimentary facies. This radical changeover in river morphology is consistent with geomorphic consequences stemming from a rapid and major die-off of rooted plant life in the basin. Evidence from correlative nonmarine strata elsewhere in the world containing fluvial Permian-Triassic boundary sections suggests that a catastrophic terrestrial die-off of vegetation was a global event, producing a marked increase in sediment yield as well as contributing to the global delta(13)C excursion across the Permian-Triassic boundary.

  13. Permian-Triassic plutonism and tectonics, Death Valley region, California and Nevada

    SciTech Connect

    Snow, J.K.; Asmerom, Y. ); Lux, D.R. )

    1991-06-01

    Significant contractional structures that deform Permian rocks but predate an Early Triassic overlap sequence are recognized within the Cordilleran orogen, western US. Thrusting in the Death Valley region of the orogen, however, has been regarded as Middle Triassic or younger and thus kinematically distinct. The authors present new isotopic age limits on two posttectonic stocks that intrude major structures of the Death Valley thrust belt. The stocks are no younger than Middle Triassic, but are likely Late Permian in age, consistent with stratigraphic and structural data suggesting that thrusting predates the overlap sequence. The authors hypothesize that Permian shortening may have affected more than 700 km of the Cordilleran orogen at the same time arc activity began within cratonic North America but prior to Early Triassic emplacement of the structurally higher Sonomian arc terrane.

  14. Morphological disparity of ammonoids and the mark of Permian mass extinctions.

    PubMed

    Villier, Loïc; Korn, Dieter

    2004-10-08

    The taxonomic diversity of ammonoids, in terms of the number of taxa preserved, provides an incomplete picture of the extinction pattern during the Permian because of a strongly biased fossil record. The analysis of morphological disparity (the variety of shell shapes) is a powerful complementary tool for testing hypotheses about the selectivity of extinction and permits the recognition of three distinct patterns. First, a trend of decreasing disparity, ranging for about 30 million years, led to a minimum disparity immediately before the Permian-Triassic boundary. Second, the strongly selective Capitanian crisis fits a model of background extinction driven by standard environmental changes. Third, the end-Permian mass extinction operated as a random, nonselective sorting of morphologies, which is consistent with a catastrophic cause.

  15. Timing of mammal-like reptile extinctions across the Permian-Triassic boundary in South Africa

    NASA Astrophysics Data System (ADS)

    MacLeod, Kenneth G.; Smith, Roger M. H.; Koch, Paul L.; Ward, Peter D.

    2000-03-01

    The rate, timing, and pattern of change in different regions and paleoenvironments are critical for distinguishing among potential causes for the Permian-Triassic (P-T) extinction. Carbon isotopic stratigraphy can provide global chronostratigraphic control. We report a large δ13C excursion at the P-T boundary and no long-term Permian δ13C trends for samples from the interior of Pangea. Stratigraphic gaps between available samples limit the resolution of our δ13C curve, but the excursion is within a 15-m-thick zone of overlap between Permian and Triassic taxa. Sedimentological and taphonomic observations demonstrate that this 15 m interval does not represent geologically instantaneous deposition. Together these data support a rapid and globally synchronous P-T event, but suggest that it occurred over a geologically resolvable interval of time.

  16. Ocean anoxia did not cause the Latest Permian Extinction

    NASA Astrophysics Data System (ADS)

    Proemse, Bernadette C.; Grasby, Stephen E.; Wieser, Michael E.; Mayer, Bernhard; Beauchamp, Benoit

    2014-05-01

    The Latest Permian Extinction (LPE, ~252 million years ago) was a turning point in the history of life on Earth with a loss of ~96% of all marine species and ~70% of all terrestrial species. While, the event undoubtedly shaped the evolution of life its cause remains enigmatic. A leading hypothesis is that the global oceans became depleted in oxygen (anoxia). In order to test this hypothesis we investigated a proxy for marine oxygen levels (molybdenum isotopic composition) in shale across the LPE horizon located on the subtropical northwest margin of Pangea at that time. We studied two sedimentary records in the Sverdrup basin, Canadian High Arctic: Buchanan Lake (eastern Axel Heiberg Island; 79° 26.1'N, 87° 12.6'W), representing a distal deep-water slope environment, and West Blind Fiord (southwest Ellesmere Island; 78° 23.9'N, 85° 57.2'W), representing a deep outer shelf environment (below storm wave base). The molybdenum isotopic composition (δ98/95Mo) of sediments has recently become a powerful tool as a paleo-oceanographic proxy of marine oxygen levels. Sample preparation was carried out in a metal-free clean room facility in the isotope laboratory of the Department of Physics and Astronomy, University of Calgary, Canada, that is supplied by HEPA-filtered air. Molybdenum isotope ratios were determined on a Thermo Scientific multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) with an uncertainty better than ±0.10o for δ98/95Mo values. Results from the Buchanan Lake section show a large shift in δ98/95Mo values from 2.02o to +2.23o at the extinction horizon, consistent with onset of euxinic conditions. In contrast, West Blind Fiord shales, representing the sub-storm wave base shelf environment, show little change in the molybdenum isotopic composition (1.34o to +0.05), indicating ongoing oxic conditions across the LPE (Proemse et al., 2013). Our results suggest that areas of the Pangea continental shelf (North West Pangea) experienced

  17. Evolution of Permian evaporite basin in Texas panhandle

    SciTech Connect

    Presley, M.W. )

    1987-02-01

    Permian (Leonardian to Ochoan) evaporites in the Texas Panhandle were deposited in a range of marine shelf to supratidal environments along an arid coastline. Carbonates in these strata generally were deposited in inner shelf systems and include subtidal to supratidal facies. Landward of shelf environments, evaporites were deposited in brine pans and salt flats. Brine-pan facies are laminated anhydrite and banded salt that formed in shallow, hypersaline water such as restricted lagoons or supratidal salines. Salt-flat facies are mainly chaotic mixtures of mudstone and halite possibly formed by salt deposition on and within mud flats that bordered brine pans, or in brine-soaked mud-flat depressions. Periodically, mud flats built across the evaporite systems and were supplied with red terrestrial clastics, mainly mud and silt. These facies occur together in at least three different types of lithogenetic units. Strata in the Clear Fork Group (Leonardian) are considered deposits of a coastal evaporite basin that was progressively filled by terrestrial clastics. These rocks exhibit regressive cycles of brine-pan, salt-flat, and mud-flat facies. In contrast, San Andres strata (Guadalupian) were deposited in a broad marine embayment with persistent brine-pan conditions, and contain cycles of inner shelf and brine-pan facies. Post-San Andres strata (late Guadalupian and Ochoan) were deposited in the inner reaches of a broad interior salt basin and are composed mainly of mud-flat, salt-flat, and halite-rich brine-pan facies. 20 figs., 2 tabs.

  18. Flourishing ocean drives the end-Permian marine mass extinction

    PubMed Central

    Schobben, Martin; Stebbins, Alan; Ghaderi, Abbas; Strauss, Harald; Korn, Dieter; Korte, Christoph

    2015-01-01

    The end-Permian mass extinction, the most severe biotic crisis in the Phanerozoic, was accompanied by climate change and expansion of oceanic anoxic zones. The partitioning of sulfur among different exogenic reservoirs by biological and physical processes was of importance for this biodiversity crisis, but the exact role of bioessential sulfur in the mass extinction is still unclear. Here we show that globally increased production of organic matter affected the seawater sulfate sulfur and oxygen isotope signature that has been recorded in carbonate rock spanning the Permian−Triassic boundary. A bifurcating temporal trend is observed for the strata spanning the marine mass extinction with carbonate-associated sulfate sulfur and oxygen isotope excursions toward decreased and increased values, respectively. By coupling these results to a box model, we show that increased marine productivity and successive enhanced microbial sulfate reduction is the most likely scenario to explain these temporal trends. The new data demonstrate that worldwide expansion of euxinic and anoxic zones are symptoms of increased biological carbon recycling in the marine realm initiated by global warming. The spatial distribution of sulfidic water column conditions in shallow seafloor environments is dictated by the severity and geographic patterns of nutrient fluxes and serves as an adequate model to explain the scale of the marine biodiversity crisis. Our results provide evidence that the major biodiversity crises in Earth’s history do not necessarily implicate an ocean stripped of (most) life but rather the demise of certain eukaryotic organisms, leading to a decline in species richness. PMID:26240323

  19. Ochoan (upper Permian) stratigraphy and age determinations, southeastern New Mexico and west Texas

    SciTech Connect

    Lucas, S.G. ); Anderson, O.R. )

    1994-03-01

    Upper Permian strata, which are the stratotype of the Ochoan State (Series), have an extensive subsurface distribution and limited outcrop area in southeastern New Mexico and west Texas. The oldest strata are alternating laminae of anhydrite and calcite of the Castile Formation and are as much as 700 m thick. The closely related and overlying Salado Formation is a much as 600 m thick and is mostly halite and argillaceous halite with minor anhydrite. The overlying Rustler Formation is as much as 150 m thick and consists of anhydrite, red silty shale and magnesian limestone. Overlying red beds are the Quartermaster Formation (Dewey Lake Formation is a synonym, as is the term Pierce Canyon red beds), which is as much as 106 m thick and consist of fine sandstones, siltstones, and minor gypsum. The Castile rests disconformably on the Capitanian (middle Permian) Lamar Limestone Member of the Bell Canyon Formation and its equivalent, the Tansill Formation of the Artesia Group. Counting of Castile-Salado laminae and their posited relationship to astronomical cycles suggests that Castile-Salado deposition took only 200,000-300,000 yr. Limited assemblages of brachiopods and conodonts from the Rustler Formation indicate a Late Permian age, but are no more precise age indicators. A small assemblage of bivalves, K-Ar ages and magnetostratigraphy indicate a late Permian age for the Quartermaster Formation. There is no evidence to support a Triassic age assignment for the Quarter-master; it is disconformably overlain by the Upper Triassic (Carnian) Chinle group. Most workers us the Ochoan as a Late Permian Stage-Age, although its typical strata generally lack good age indicators and may represent relatively short and sporadic intervals of the Late Permian. We prefer recognition of the Ochoan as a lithostratigraphic unit (group) without regional or global geochronologial significance.

  20. Shallow marine ecosystem feedback to the Permian/Triassic mass extinction

    NASA Astrophysics Data System (ADS)

    Wang, Yongbiao; Meng, Zheng; Liao, Wei; Weng, Zeting; Yang, Hao

    2011-03-01

    Late Permian reefs developed widely on shallow marine carbonate platforms in South China but disappeared far below the main mass extinction level of the latest Permian. The collapse of reef ecosystem may be related to the enhanced volcanism at the end of Late Permian. Notably, some colony corals and reef-building sponges were found to occur near the mass extinction boundary, inferring the eclipse of reef ecosystem is ahead of the disappearance of reef-building organisms, and the triggers would be present long before the main mass extinction. As the primary producers, the calcareous algae are rich in platform limestones of Late Permian and played a very important role in maintaining the shallow benthic ecosystems. The calcareous algae were found to disappear synchronously with the great reduction of foraminifers, which were ecologically associated with these algae. The extinction of Late Permian calcareous algae greatly reduced the biodiversity of primary producers in the shallow marine environment and destroyed in part the structure and the base of the shallow marine ecosystems, which in turn cause the extinction of ecologically associated metazoan. Microbialites developed on carbonate platforms immediately after the end-Permian mass extinction, representing a simple and unique microbial ecosystem. Widespread occurrence of microbialites symbolized the deterioration of marine environmental conditions and the dramatic revolution of marine ecosystems. As the new primary producers instead of the extinguished calcareous algae, cyanobacteria in the microbialites were an important base of this peculiar ecosystem and contributed greatly to the survival of the remnant faunas after the mass extinction. Widespread occurrence of microbialites in shallow marine environment is suggested to be related to the elevated level of volcanism-induced greenhouse gases and enhanced evaporation and hypersaline condition in addition to the decrease of metazoan grazing pressure. The change

  1. Surface water paleotemperatures and chemical compositions from fluid inclusions in Permian Nippewalla Group halite

    SciTech Connect

    Benison, K.C. )

    1996-01-01

    Quantitative climatic data for the Permian have been determined from Nippewalla Group halite. The middle Permian Nippewalla Group of Kansas and Oklahoma consists of several hundred feet of bedded halite, anhydrite, and red beds. Study of core and surface samples suggest that this halite was deposited by ephemeral lakes. Fluid inclusions provide evidence for the geochemistry of these Permian saline lake waters, including temperatures, salinities, and chemical compositions. Primary fluid inclusions are well-preserved in the Nippewalla halite. They are 5 - 30 [mu]m cubic inclusions situated along chevron and cornet growth bands. Most are one phase aqueous inclusions, but some also contain anhydride [open quote]accidental[close quotes] crystals. Rare two phase liquid-vapor inclusions may have formed by subaqueous outgassing or trapping of air at the water surface. Fluid inclusion freezing-melting behavior and leachate analyses suggest that Nippewalla halite precipitated from Na-Cl-rich waters with lesser quantities of SO[sub 4], Mg, K, Al, and Si. This composition may be a product of long-term weathering. Surface water paleotemperatures were determined from one phase aqueous fluid inclusions. Homogenization temperatures range from 32 to 46[degrees]C in primary fluid inclusions and are consistent (within 3[degrees]C) along individual chevrons and cornets. These homogenization temperatures are interpreted to represent maximum surface water temperatures. These fluid inclusion data are significant in addressing global change problems. Temperatures and chemistries in these Permian lake waters agree with some modern shallow saline lake waters and with Permian climate models. This study suggests that this Permian environment was relatively similar to its modern counterparts.

  2. Surface water paleotemperatures and chemical compositions from fluid inclusions in Permian Nippewalla Group halite

    SciTech Connect

    Benison, K.C.

    1996-12-31

    Quantitative climatic data for the Permian have been determined from Nippewalla Group halite. The middle Permian Nippewalla Group of Kansas and Oklahoma consists of several hundred feet of bedded halite, anhydrite, and red beds. Study of core and surface samples suggest that this halite was deposited by ephemeral lakes. Fluid inclusions provide evidence for the geochemistry of these Permian saline lake waters, including temperatures, salinities, and chemical compositions. Primary fluid inclusions are well-preserved in the Nippewalla halite. They are 5 - 30 {mu}m cubic inclusions situated along chevron and cornet growth bands. Most are one phase aqueous inclusions, but some also contain anhydride {open_quote}accidental{close_quotes} crystals. Rare two phase liquid-vapor inclusions may have formed by subaqueous outgassing or trapping of air at the water surface. Fluid inclusion freezing-melting behavior and leachate analyses suggest that Nippewalla halite precipitated from Na-Cl-rich waters with lesser quantities of SO{sub 4}, Mg, K, Al, and Si. This composition may be a product of long-term weathering. Surface water paleotemperatures were determined from one phase aqueous fluid inclusions. Homogenization temperatures range from 32 to 46{degrees}C in primary fluid inclusions and are consistent (within 3{degrees}C) along individual chevrons and cornets. These homogenization temperatures are interpreted to represent maximum surface water temperatures. These fluid inclusion data are significant in addressing global change problems. Temperatures and chemistries in these Permian lake waters agree with some modern shallow saline lake waters and with Permian climate models. This study suggests that this Permian environment was relatively similar to its modern counterparts.

  3. Early Permian volcano-sedimentary successions, Beishan, NW China: Peperites demonstrate an evolving rift basin

    NASA Astrophysics Data System (ADS)

    Chen, Shi; Guo, Zhaojie; Qi, Jiafu; Zhang, Yuanyuan; Pe-Piper, Georgia; Piper, David J. W.

    2016-01-01

    The Lower Permian volcano-sedimentary Zhesi Group has been investigated in the Hongliuhe and Liuyuan areas in Beishan, China, which is significant for the reconstruction of Late Paleozoic evolution in the southern part of the Central Asian Orogenic Belt. A variety of volcanic facies were distinguished in the Upper Zhesi Group: pillow basalt with interstitial limestone, thin-interbedded limestone and basalt, closely packed pillows, pillow-fragmented hyaloclastite breccia, and peperite. Laser 40Ar/39Ar whole-rock dating of the basalt yielding an age of 277 ± 11 Ma, as well as Early Permian brachiopod fossils in the limestone interbedded with the basalt, indicate that basalt was erupted in the Early Permian. The identification of the peperite and other facies originating from magma-sediment mingling reveals that the basaltic lava flows were derived from autochthonous basaltic magmatism and formed as part of the Lower Permian succession. The peperite also indicates that these subaqueous basaltic lava flows are not dismembered ophiolitic components, but formed in an autochthonous extensional setting in the Early Permian. The clastic rocks in the Lower Zhesi Group underlying the basaltic flows and peperites in the Hongliuhe and Liuyuan areas show a general fining-upwards sequence, indicating that they were deposited in a progressively deepening basin overlying the Devonian Hongliuhe suture zone. Subaqueous volcanism in a rift basin or basins, accompanied by coeval deposition of carbonate sediment and mud, built up the peperite-bearing volcanogenic-sedimentary successions. From among the various tectonic hypotheses for the Beishan region, this study demonstrates that by Early Permian the region was developing post-collisional rift basins.

  4. Terrestrial paleoenvironment characterization across the Permian-Triassic boundary in South China

    NASA Astrophysics Data System (ADS)

    Bercovici, Antoine; Cui, Ying; Forel, Marie-Béatrice; Yu, Jianxin; Vajda, Vivi

    2015-02-01

    Well-preserved marine fossils in carbonate rocks permit detailed studies of the end-Permian extinction event in the marine realm. However, the rarity of fossils in terrestrial depositional environments makes it more challenging to attain a satisfactory degree of resolution to describe the biotic turnover on land. Here we present new sedimentological, paleontological and geochemical (X-ray fluorescence) analysis from the study of four terrestrial sections (Chahe, Zhejue, Mide and Jiucaichong) in Western Guizhou and Eastern Yunnan (Yangtze Platform, South China) to evaluate paleoenvironmental changes through the Permian-Triassic transition. Our results show major differences in the depositional environments between the Permian Xuanwei and the Triassic Kayitou formations with a change from fluvial-lacustrine to coastal marine settings. This change is associated with a drastic modification of the preservation mode of the fossil plants, from large compressions to small comminuted debris. Plant fossils spanning the Permian-Triassic boundary show the existence of two distinct assemblages: In the Xuanwei Formation, a Late Permian (Changhsingian) assemblage with characteristic Cathaysian wetland plants (mainly Gigantopteris dictyophylloides, Gigantonoclea guizhouensis, G. nicotianaefolia, G. plumosa, G. hallei, Lobatannularia heinanensis, L. cathaysiana, L. multifolia, Annularia pingloensis, A. shirakii, Paracalamites stenocostatus, Cordaites sp.) is identified. In the lowermost Kayitou Formation, an Early Triassic (Induan) Annalepis-Peltaspermum assemblage is shown, associated with very rare, relictual gigantopterids. Palynological samples are poor, and low yield samples show assemblages almost exclusively represented by spores. A ∼1 m thick zone enriched in putative fungal spores was identified near the top of the Xuanwei Formation, including diverse multicellular forms, such as Reduviasporonites sp. This interval likely corresponds to the PTB "fungal spike

  5. Two pulses of oceanic environmental disturbance during the Permian-Triassic boundary crisis

    NASA Astrophysics Data System (ADS)

    Shen, Jun; Feng, Qinglai; Algeo, Thomas J.; Li, Chao; Planavsky, Noah J.; Zhou, Lian; Zhang, Mingliang

    2016-06-01

    Pyrite morphology, iron speciation, and pyrite sulfur isotope data from the Xiakou section (Hubei Province, South China) were integrated to explore oceanic environmental variations through the Permian-Triassic transition and their possible relations to the largest mass extinction in Earth history. High ratios of highly-reactive iron to total iron (FeHR/FeT > 0.6) and pyrite iron to highly-reactive iron (FePy/FeHR > 0.7) together with a high abundance of small (mean diameter <5 μm) framboidal pyrite show that euxinic conditions existed in the late Permian (pre-extinction interval). High ratios of FeHR/FeT (mostly >0.6) along with lower values of FePy/FeHR (<0.7) and more variable framboid content among samples indicate anoxic but dominantly ferruginous conditions punctuated by episodic euxinic events in the latest Permian to earliest Triassic (post-extinction interval). The largest fluctuations of these redox proxies are observed in the ∼1.0 m of strata directly overlying the first (latest Permian) extinction horizon, indicating unsettled marine environmental conditions marked by frequent perturbations during the ∼60-kyr interval immediately following the mass extinction. The two largest redox events at Xiakou coincided with deposition of volcanic ash layers that have been correlated with Beds 25 and 28 of the Meishan D section, each of which was associated with an extinction pulse (the first and second extinction horizons of latest Permian and earliest Triassic age, respectively). Thus, our observations document two pulses of oceanic environmental change during the Permian-Triassic transition, each associated with a faunal crisis and possibly triggered by contemporaneous volcanic activity.

  6. Large perturbations of the carbon cycle during recovery from the end-permian extinction.

    PubMed

    Payne, Jonathan L; Lehrmann, Daniel J; Wei, Jiayong; Orchard, Michael J; Schrag, Daniel P; Knoll, Andrew H

    2004-07-23

    High-resolution carbon isotope measurements of multiple stratigraphic sections in south China demonstrate that the pronounced carbon isotopic excursion at the Permian-Triassic boundary was not an isolated event but the first in a series of large fluctuations that continued throughout the Early Triassic before ending abruptly early in the Middle Triassic. The unusual behavior of the carbon cycle coincides with the delayed recovery from end-Permian extinction recorded by fossils, suggesting a direct relationship between Earth system function and biological rediversification in the aftermath of Earth's most devastating mass extinction.

  7. Differential exhumation in response to episodic thrusting along the eastern margin of the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Arne, Dennis; Worley, Brenton; Wilson, Christopher; Chen, She Fa; Foster, David; Luo, Zhi Li; Liu, Shu Gen; Dirks, Paul

    1997-10-01

    Thermochronological data from the Songpan-Ganze˛Fold Belt and Longmen Mountains Thrust-Nappe Belt, on the eastern margin of the Tibetan Plateau in central China, reveal several phases of differential cooling across major listric thrust faults since Early Cretaceous times. Differential cooling, indicated by distinct breaks in age data across discrete compressional structures, was superimposed upon a regional cooling pattern following the Late Triassic Indosinian Orogeny. 40Ar/ 39Ar data from muscovite from the central and southern Longmen Mountains Thrust-Nappe Belt suggest a phase of differential cooling across the Wenchuan-Maouwen Shear Zone during the Early Cretaceous. The zircon fission track data also indicate differential cooling across a zone of brittle re-activation on the eastern margin of the Wenchuan-Maouwen Shear Zone during the mid-Tertiary, between ˜38 and 10 Ma. Apatite fission track data from the central and southern Longmen Mountains Thrust-Nappe Belt reveal differential cooling across the Yingxiu-Beichuan and Erwangmiao faults during the Miocene. Forward modelling of apatite fission track data from the northern Longmen Mountains Thrust-Nappe Belt suggests relatively slow regional cooling through the Mesozoic and early Tertiary, followed by accelerated cooling during the Miocene, beginning at ca. 20 Ma, to present day. Regional cooling is attributed to erosion during exhumation of the evolving Longmen Mountains Thrust-Nappe Belt (LMTNB) following the Indosinian Orogeny. Differential cooling across the Wenchuan-Maouwen Shear Zone and the Yingxiu-Beichuan and Erwangmiao faults is attributed to exhumation of the hanging walls of active listric thrust faults. Thermochronological data from the Longmen Mountains Thrust-Nappe Belt reveal a greater amount of differential exhumation across thrust faults from north to south. This observation is in accord with the prevalence of Proterozoic and Sinian basement in the hanging walls of thrust faults in the

  8. Cretaceous–Cenozoic burial and exhumation history of the Chukchi shelf, offshore Arctic Alaska

    USGS Publications Warehouse

    Craddock, William H.; Houseknecht, David W.

    2016-01-01

    Apatite fission track (AFT) and vitrinite reflectance data from five exploration wells and three seafloor cores illuminate the thermal history of the underexplored United States Chukchi shelf. On the northeastern shelf, Triassic strata in the Chevron 1 Diamond well record apatite annealing followed by cooling, possibly during the Triassic to Middle Jurassic, which is a thermal history likely related to Canada Basin rifting. Jurassic strata exhumed in the hanging wall of the frontal Herald Arch thrust fault record a history of probable Late Jurassic to Early Cretaceous structural burial in the Chukotka fold and thrust belt, followed by rapid exhumation to near-surface temperatures at 104 ± 30 Ma. This history of contractional tectonism is in good agreement with inherited fission track ages in low-thermal-maturity, Cretaceous–Cenozoic strata in the Chukchi foreland, providing complementary evidence for the timing of exhumation and suggesting a source-to-sink relationship. In the central Chukchi foreland, inverse modeling of reset AFT samples from the Shell 1 Klondike and Shell 1 Crackerjack wells reveals several tens of degrees of cooling from maximum paleo-temperatures, with maximum heating permissible at any time from about 100 to 50 Ma, and cooling persisting to as recent as 30 Ma. Similar histories are compatible with partially reset AFT samples from other Chukchi wells (Shell 1 Popcorn, Shell 1 Burger, and Chevron 1 Diamond) and are probable in light of regional geologic evidence. Given geologic context provided by regional seismic reflection data, we interpret these inverse models to reveal a Late Cretaceous episode of cyclical burial and erosion across the central Chukchi shelf, possibly partially overprinted by Cenozoic cooling related to decreasing surface temperatures. Regionally, we interpret this kinematic history to be reflective of moderate, transpressional deformation of the Chukchi shelf during the final phases of contractional tectonism in the

  9. Subduction and Slab Advance at Orogen Syntaxes: Predicting Exhumation Rates and Thermochronometric Ages with Numerical Modeling

    NASA Astrophysics Data System (ADS)

    Nettesheim, Matthias; Ehlers, Todd A.; Whipp, David M.

    2017-04-01

    The change in plate boundary orientation and subducting plate geometry along orogen syntaxes may have major control on the subduction and exhumation dynamics at these locations. Previous work documents that the curvature of subducting plates in 3D at orogen syntaxes forces a buckling and flexural stiffening of the downgoing plate. The geometry of this stiffened plate region, also called indenter, can be observed in various subduction zones around the world (e.g. St. Elias Range, Alaska; Cascadia, USA; Andean syntaxis, South America). The development of a subducting, flexurally stiffened indenter beneath orogen syntaxes influences deformation in the overriding plate and can lead to accelerated and focused rock uplift above its apex. Moreover, the style of deformation in the overriding plate is influenced by the amount of trench or slab advance, which is the amount of overall shortening not accommodated by underthrusting. While many subduction zones exhibit little to no slab advance, the Nazca-South America subduction and especially the early stages of the India-Eurasia collision provide end-member examples. Here, we use a transient, lithospheric-scale, thermomechanical 3D model of an orogen syntaxis to investigate the effects of subducting a flexurally stiffened plate geometry and slab advance on upper plate deformation. A visco-plastic upper-plate rheology is used, along with a buckled, rigid subducting plate. The free surface of the thermomechanical model is coupled to a landscape evolution model that accounts for erosion by fluvial and hillslope processes. The cooling histories of exhumed rocks are used to predict the evolution of low-temperature thermochronometer ages on the surface. With a constant overall shortening for all simulations, the magnitude of slab advance is varied stepwise from no advance, with all shortening accommodated by underthrusting, to full slab advance, i.e. no motion on the megathrust. We show that in models where most shortening is

  10. Evolution of Continental Lower Crust Recorded By an Exhumed Deep Crustal Intracontinental Shear Zone

    NASA Astrophysics Data System (ADS)

    Dumond, G.; Mahan, K. H.; Regan, S. P.; Williams, M. L.; Goncalves, P.; Wood, V. R.

    2014-12-01

    Exposures of deep crustal shear zones are fundamental records of strain localization and the temporal evolution of ductile to brittle behavior as these tectonites were exhumed to the surface. We present results from a decade of field-based research on a deeply exhumed (~35 km-paleodepths) strike-slip shear zone in the western Churchill province of the Canadian Shield. The Grease River shear zone is a >400 km-long and 7 km-thick structure that cuts the Athabasca granulite terrane, North America's largest exposure of continental lower crust (>20,000 km2). The shear zone is dominated by granulite- to amphibolite-grade L-S and L>S tectonites characterized by penetrative NE-striking steeply-dipping foliations with gently-plunging to sub-horizontal stretching and intersection lineations. These fabrics are locally overprinted by pseudotachylyte and narrow (<500 m-thick) greenschist-grade zones of cataclasite. Dextral kinematics are defined by deflected foliation trajectories, C' shear bands, and well-developed σ- and δ-type porphyroclasts of Kfs + Pl + Opx + Grt + Hb in felsic to intermediate granulite paragneisses and orthogneisses. Data collected along a well-exposed, nearly 150 km-long segment of the shear zone documents a >100 m.y. episodic record of transpressive to strike-slip intracontinental strain accumulation that coincided with two oppositely convergent orogenies: the east-vergent arc-continent collision of the 1.94-1.90 Ga Taltson orogen and the west-vergent continent-continent collision of the 1.9-1.8 Ga Trans-Hudson orogen. Deformation mechanisms evolved from distributed ductile dynamic recrystallization and grain-size reduction to localized pseudotachylyte development, cataclastic flow, and brittle faulting. Lower crustal behavior during strain localization was dynamic. Melt-weakened mono-cyclic crust was juxtaposed against strong isobarically-cooled poly-cyclic crust along the shear zone at 1.92-1.90 Ga. Brittle-ductile reactivation of the structure

  11. Glacial morphology in the Chinese Pamir: Connections among climate, erosion, topography, lithology and exhumation

    NASA Astrophysics Data System (ADS)

    Schoenbohm, Lindsay M.; Chen, Jie; Stutz, Jamey; Sobel, Edward R.; Thiede, Rasmus C.; Kirby, Benjamin; Strecker, Manfred R.

    2014-09-01

    Modification of the landscape by glacial erosion reflects the dynamic interplay of climate through temperature, precipitation, and prevailing wind direction, and tectonics through rock uplift and exhumation rate, lithology, and range and fault geometry. We investigate these relationships in the northeast Pamir Mountains using mapping and dating of moraines and terraces to determine the glacial history. We analyze modern glacial morphology to determine glacier area, spacing, headwall relief, debris cover, and equilibrium line altitude (ELA) using the area x altitude balance ratio (AABR), toe-to-headwall altitude ratio (THAR) and toe-to-summit altitude method (TSAM) for 156 glaciers and compare this to lithologic, tectonic, and climatic data. We observe a pronounced asymmetry in glacial ELA, area, debris cover, and headwall relief that we interpret to reflect both structural and climatic control: glaciers on the downwind (eastern) side of the range are larger, more debris covered, have steeper headwalls, and tend to erode headward, truncating the smaller glaciers of the upwind, fault-controlled side of the range. We explain this by the transfer of moisture deep into the range as wind-blown or avalanched snow and by limitations imposed on glacial area on the upwind side of the range by the geometry of the Kongur extensional system (KES). The correspondence between rapid exhumation along the KES and maxima in glacier debris cover and headwall relief and minimums in all measures of ELA suggest that taller glacier headwalls develop in a response to more rapid exhumation rates. However, we find that glaciers in the Muji valley did not extend beyond the range front until at least 43 ka, in contrast to extensive glaciation since 300 ka in the south around the high peaks, a pattern which does not clearly reflect uplift rate. Instead, the difference in glacial history and the presence of large peaks (Muztagh Ata and Kongur Shan) with flanking glaciers likely reflects

  12. Kinematics of post-orogenic extension and exhumation of the Taku Schist, NE Peninsular Malaysia

    NASA Astrophysics Data System (ADS)

    Md Ali, M. A.; Willingshofer, E.; Matenco, L.; Francois, T.; Daanen, T. P.; Ng, T. F.; Taib, N. I.; Shuib, M. K.

    2016-09-01

    Recent studies imply that the formation and evolution of many SE Asian basins was driven by extensional detachments or systems of low-angle normal faults that created significant crustal exhumation in their footwalls. In this context, the architecture of the Triassic Indosinian orogen presently exposed in Peninsular Malaysia is compatible with significant extension post-dating the orogenic event. In this study we performed a kinematic analysis based on fieldwork and microstructural observations in the Taku Schist, Kemahang granite and the surrounding Gua Musang sediments of northern Peninsular Malaysia in order to shed light on processes related to the build-up and subsequent demise of the Indosinian orogen. The first three phases of deformation were related to an overall period of E-W oriented contraction and burial metamorphism. These phases of deformation are characterized by isoclinal folding with flat lying axial plane cleavages (D1), asymmetrical folding, top-to-the-W-SW shearing (D2) and upright folding (D3). All are in general agreement with observations of the previously inferred Permo-Triassic Indosinian orogeny. During these times, the Taku Schist, a sequence of Paleozoic clastic sediments with mafic intercalations was metamorphosed to amphibolite facies. These rocks are most likely equivalent to the ones exposed in the Bentong-Raub suture zone. Structural relations suggest that the Triassic Kemahang pluton is syn-kinematic, which provides important constraints for the timing of these contractional events. We demonstrate that the overall shortening was followed by a hitherto undescribed extension in NW-SE direction resulting in the formation of a large-scale detachment, the Taku detachment, in northern Peninsular Malaysia. Extension probably reactivated the former subduction plane as a detachment and exhumed previously buried and metamorphosed rocks of similar lithological composition to the neighboring Bentong-Raub suture zone. Such a mechanism is

  13. Constraining the Quaternary exhumation of the Siwaliks using very low temperature OSL-thermochronometry

    NASA Astrophysics Data System (ADS)

    King, Georgina E.; Grujic, Djordje; Coutand, Isabelle; Herman, Frederic

    2017-04-01

    The Himalayan foreland fold-and-thrust belt is composed of Neogene synorogenic sediments of the Siwalik Group and accommodates 15-20% of the India-Eurasia convergence [1]. Along the strike of the 2500-km-long orogenic arc, despite homogenous lithology and erodibility, the fold-and-thrust belt narrows towards the east. This has been attributed to increasing annual rainfall and specific stream power, rather than to lateral changes in shortening rates [1]. However, exhumation/erosion rates of this unit remain unknown. Constraining these rates would allow estimation of the relative contributions of tectonic and climatic processes to the erosion of the youngest and frontal part of the Himalayan orogen as well as how shortening is distributed within the range. Here we present new OSL-thermochronometry data from western Nepal and eastern Bhutan. Thermochronometry enables the cooling histories, and therefore exhumation/erosion histories of rocks to be determined. However the cooling histories of the Siwalik Group, which have experienced limited burial heating not exceeding 100-50 °C remain very difficult to constrain using traditional thermochronometers. Optically stimulated luminescence (OSL)-thermochronometry is a recently developed very low temperature thermochronometer sensitive to temperatures of 40-100 °C. Consequently, its application to the Siwalik deposits may provide insights into their cooling and exhumation histories. K-feldspar extracts from 18 sandstones samples of the Siwalik Group were investigated using a multi-OSL-thermochronometry approach, whereby four different signals, with different thermal stabilities were measured for each sample. The sandstone samples were collected along two transects across the Himalayan fold-and-thrust belt in western Nepal, and eastern Bhutan. Using signals with different thermal sensitivities enables high precision Quaternary cooling histories to be derived. Inverting these data, results in erosion rates of 3 mm/yr, which

  14. Rifting of the Tyrrhenian Basin, a complex interaction among faulting , magmatism and mantle exhumation.

    NASA Astrophysics Data System (ADS)

    Ranero, C. R.; Sallarés, V.; Grevemeyer, I.; Zitellini, N.; Guzman, M.; Prada, M.; Moeller, S.; de Franco, R.; Medoc Cruise Party

    2012-04-01

    The Tyrrhenian basin has been created during the extension of continental lithosphere driven by the retreat of a Ionian slab across the mantle. The basin does not seem to be actively extending, but its preserved crustal structure provides information of the time evolution of the processes involved in rifting. The basin rifted from north to south, with rifting stopping after progressively larger stretching factor towards the south. The northern region stopped opening after a relatively low extension factor. Towards the south extension increased up to full crustal separation that produced mantle exhumation. The final structure displays two conjugate margins with asymmetric structures. Thus, the basin provides a natural laboratory to investigate a full rift system, that displays variable amounts of extension. We present observations from a two-ship seismic experiment that took place in spring 2010. The cruise took place on two legs. In the first leg, the Spanish R/V Sarmiento de Gamboa and the Italian R/V Urania collected five E-W trending wide-angle seismic (WAS) profiles across the entire basin using 17 Ocean Bottom Seismometers and 25 Ocean Bottom Hydrophones and a 4800 c.i. G-II gun array. The profiles were extended with land stations that recorded the marine shots. During a second leg the R/V Sarmiento de Gamboa collected 16 Multichannel Seismic Reflection (MCS) profiles using a 3.75 km-long streamer and a 3000 c.i. G-II gun array. MCS profiles were acquired coincident with the WAS profiles, and a number of additional lines concentrated in the central region of the basin where mantle exhumation took place. The seismic profiles were located to cover regions of the basin that displays different amount of extension, and the coincident wide-angle and MCS transects cross the entire basin to image the two conjugate margins. In this presentation we compare observations from different transects mapping the structures produced at different extension factors. A comparison

  15. Structural and exhumational response to oroclinal bending at the Eastern Alps - Western Carpathian transition

    NASA Astrophysics Data System (ADS)

    Heberer, Bianca; Neubauer, Franz

    2017-04-01

    Curvature is an intriguing feature within many mountain belts worldwide. Several proposals have been made for deciphering the origin of curvature, however, there is still significant debate about the bend-forming mechanisms, the consequences as well as on how bending is accommodated within the lithosphere. Only few of the worldwide oroclines have been studied in detail and a variety of alternative controlling factors, such as the role of inherited structures, the rheological coupling between lower and upper plates, the presence of a basement promontory in the foreland and its particular geometry, and lateral orogen-parallel extrusion are likely underestimated or not considered at all. This study focuses on oroclinal bending at the transition from the W-E trending Eastern Alps to the SW-NE oriented Western Carpathians. There, the orogenic front is concave towards the Alpine foreland and the greatest degree of curvature (ca. 55°) is found adjacent to the Bohemian massif. The oroclinal axis runs from the Bohemian promontory to the South Burgenland high. Various competing mechanisms occurred, i.e. rotation around a stiff foreland promontory and lateral extrusion induced by tectonic escape due to the indentation of a microplate and extensional collapse due to slab-rollback beneath the Carpathians. Little is known for such cases, where bending around as well as overriding of a promontory occurs, particularly on how it controls the exhumational and structural architecture within the orogen itself. Based on a synthesis of low-T thermochronology and structural data we find a significant impact of oroclinal bending on exhumation and structures: Highest amounts of erosion occur in the immediate vicinity of the Bohemian promontory and along its prolongation in the South Burgenland high, corroborating that shortening and exhumation are most pronounced there and should decrease along-strike of the orogenic front. In the outer bend strong Miocene extensional thinning parallel to

  16. Exhumation Histories Across an Ancient Arc-craton Boundary, Northern North American Cordillera

    NASA Astrophysics Data System (ADS)

    Fayon, A. K.; Kahn, M.; Tikoff, B.; Gaschnig, R. M.

    2016-12-01

    (U-Th)/He zircon ages obtained from samples along east-west IDOR seismic transect illustrate a cooling history from temperatures > 200 °C that spans 60 m.y. The IDOR transect crosses the Cretaceous-age North American margin near 44 °N latitude that is in part defined by steep geochemical and strain gradients, and a cooling history not shared by adjacent basement exposures. Coincident with this boundary is the western Idaho shear zone (WISZ), a transpression shear zone that records dextral translation that ceased at 90 Ma. The timing and rate of cooling across the IDOR transect varies considerably, as recorded by (U-Th)/He zircon ages. Regions with distinct exhumation histories correspond to: 1) the accreted terrane-North American craton boundary and 2) the Stanley Valley area. Within the Wallowa-Blue Mountain terrane, cooling ages range from 136 to 80 Ma. Within the North American craton, cooling ages range from 65 to 20 Ma. Cooling ages within WISZ are tightly constrained between 76.2 and 63.2 Ma and are consistent along the 300 km segment of the WISZ. Cooling ages in the Idaho batholith are distinctive from those affected by the WISZ, and record a more protracted cooling history that spans 40 m.y. The youngest ages are recorded in the Stanley Valley area. Here Miocene cooling is recorded by the Idaho batholith as exposed in the Sawtooth metamorphic complex. The thermochornologic data obtained from the IDOR EarthScope project reveal the evolution of a stable craton to the east that is disconnected in time from the rocks now exposed west of the WISZ. This break corresponds to a step in the Moho as identified by Davenport et al. (2016). The stable region of the Idaho batholith was then deformed by Miocene faulting. More dense sampling from the Wallowa Mountains to Lava Buttes at a latitude of 45.2 °N reveals recent burial and exhumation in Hells Canyon along the Snake River, as determined by paired (U-Th)/He zircon and apatite ages. In the accreted terranes, (U

  17. Slab vs. Slivers: U-Pb Geochronologic Constraints on the Exhumation of the Western Gneiss Region, Norway

    NASA Astrophysics Data System (ADS)

    Ginsburg, A. A.; Hacker, B. R.; Kylander-Clark, A. R.

    2011-12-01

    Ultrahigh-pressure (UHP) and high-pressure (HP) terranes, such as those exposed in the Western Gneiss Region (WGR), Norway, provide an excellent natural laboratory for studying collisional orogenesis and its subsequent effects on Earth processes. UHP terranes are thought to be a variety of thicknesses, ranging from small, thin (<10 km), poorly insulated, rapidly exhumed slabs to large, thick (>30 km), well insulated, slowly exhumed slabs. Resolving the true thickness, size, and timing of such terranes quantifies the amount of potentially recycled crustal material. Using the new LASS-ICP-MS method, a decreasing east to west gradient (~425 - 398 Ma) was established for U-Pb zircon (re)crystallization ages in eclogites, implying the persistence of one, coherent slab during exhumation. Additionally, the absence of old (> 425 Ma) U-Pb eclogite ages from western UHP domains in the data raises two questions: 1) Have prograde zircons in eclogite experienced lead loss at peak PT conditions? 2) Assuming no lead loss was experienced, why was zircon confined to (re)crystallizing during exhumation?

  18. Exhumation of Wistar rats experimentally exposed to the carbamate pesticides aldicarb and carbofuran: A pathological and toxicological study.

    PubMed

    de Siqueira, Adriana; Rodrigues, Karina Borges Almeida; Gonçalves-Júnior, Vagner; Calefi, Atilio Sersun; Fukushima, André Rinaldi; Cuevas, Silvia Elena Campusano; Spinosa, Helenice de Souza; Maiorka, Paulo César

    2016-06-01

    Exhumation is required for the investigation of suspicions deaths when a body is buried and is usually performed under court order. Exhumation of animals is not a routine practice in forensic pathology. In this study, 30 male 70-day-old Wistar rats were experimentally exposed to the carbamate pesticides aldicarb and carbofuran. Toxicological, macroscopic and microscopic examinations were performed. Groups of 3 animals (2 exposed and 1 control) were evaluated at 24h, 3days, 5days, 7days and 10days post-mortem. In histopathological examination, the brain, liver, lungs and kidneys were assessed, and for toxicological analysis, the gastric contents, liver, vitreous humor, skeletal muscle and larvae (when available) were collected. The pesticides were detected by HPLC and quantified in the analyzed matrices, and a possible delay in tissue putrefaction due to the pesticides was observed. This study has revealed that it is possible to exhume animals for investigations of possible poisoning by carbamates and has demonstrated that the exhumation of an animal in a suspected case of poisoning should not be ruled out. The increasing demand for investigations of suspicious animal deaths, e.g., in cases of poisoning, will likely lead to an increase in the use of this type of procedure in veterinary pathology.

  19. Tectonic evolution of a continental subduction-exhumation channel: Variscan structure of the basal allochthonous units in NW Spain

    NASA Astrophysics Data System (ADS)

    DíEz FernáNdez, RubéN.; MartíNez CataláN, José Ramón; Arenas MartíN, Ricardo; Abati Gómez, Jacobo

    2011-06-01

    A regional study starting from detailed geological mapping has been carried out in the Malpica-Tui Complex of Galicia in NW Spain. The complex is formed by two units representing pieces of the external edge of Gondwana, subducted and exhumed during the Variscan collision. The study shows that synsubduction and early synexhumation structures in continental subduction channels tends to be obscured and even erased once exhumation is complete. Detailed structural analysis, matched with the knowledge of the history, and available data for other Galician basal units have elucidated the major structures developed during the subduction-exhumation process. The results include evidence of the plate convergence causing early Variscan continental subduction of the Gondwana margin. Subduction was followed by exhumation driven by ductile thrusting within the subduction channel, which, in turn, provoked crustal duplication in the subducted slab and modified the initial tectonometamorphic architecture of the subduction wedge. The next step was accretion to the adjacent continental domains, placing the subduction wedge on top of unsubducted parts of the Gondwana margin via ductile thrusting. Thrusting was preceded by progressive propagation of a train of recumbent folds toward the foreland that affected the previous structural stack. Subsequent transference of oceanic (Rheic) and peri-Gondwanan terranes to the Gondwana margin took place by out-of-sequence thrusting followed by crustal extensional collapse and strike-slip tectonics.

  20. Exhumation history of the NW Indian Himalaya revealed by fission track and 40Ar/39Ar ages

    USGS Publications Warehouse

    Schlup, M.; Steck, A.; Carter, A.; Cosca, M.; Epard, J.-L.; Hunziker, J.

    2011-01-01

    New fission track and Ar/Ar geochronological data provide time constraints on the exhumation history of the Himalayan nappes in the Mandi (Beas valley) - Tso Morari transect of the NW Indian Himalaya. Results from this and previous studies suggest that the SW-directed North Himalayan nappes were emplaced by detachment from the underthrusted upper Indian crust by 55. Ma and metamorphosed by ca. 48-40. Ma. The nappe stack was subsequently exhumed to shallow upper crustal depths (<10. km) by 40-30. Ma in the Tso Morari dome (northern section of the transect) and by 30-20. Ma close to frontal thrusts in the Baralacha La region. From the Oligocene to the present, exhumation continued slowly.Metamorphism started in the High Himalayan nappe prior to the Late Oligocene. High temperatures and anatexis of the subducting upper Indian crust engendered the buoyancy-driven ductile detachment and extrusion of the High Himalayan nappe in the zone of continental collision. Late extrusion of the High Himalayan nappe started about 26. Ma ago, accompanied by ductile extensional shearing in the Zanskar shear zone in its roof between 22 and 19. Ma concomitant with thrusting along the basal Main Central Thrust to the south. The northern part of the nappe was then rapidly exhumed to shallow depth (<10. km) between 20 and 6. Ma, while its southern front reached this depth at 10-5. Ma. ?? 2010 Elsevier Ltd.

  1. River network evolution as a major control for orogenic exhumation: Case study from the western Tibetan plateau

    NASA Astrophysics Data System (ADS)

    Gourbet, Loraine; Mahéo, Gweltaz; Shuster, David L.; Tripathy-Lang, Alka; Leloup, Philippe Hervé; Paquette, Jean-Louis

    2016-12-01

    The westernmost Tibetan plateau, despite being internally drained, has a high topographic relief. Here, using apatite (U-Th-Sm)/He and 4He/3He thermochronometry, we reconstruct the exhumation history of the Rutog batholith during the Neogene. Thermal modeling in 1D using the QTQt program indicates that relatively slow cooling occurred from 30 Ma to 19 Ma, which we interpret as an exhumation rate of ∼10 m/Ma. This was followed by two pulses of moderate cooling from 19 to 17 Ma and ∼11 to 9 Ma that correspond to a total exhumation of about 1500 m. Cooling since 9 Ma has been negligible. This differs from exhumation patterns in central Tibet but reveals timing similarities with externally drained portions of southern Tibet. We interpret our cooling constraints as recording two different transitions in western Tibet from an externally to an internally drained system since the Oligocene. External drainage allowed this part of the Tibetan plateau, unlike internally drained portions of central Tibet, to record regional-scale processes. The first cooling event, at about 20 Ma, was likely related to a major geodynamic event such as slab breakoff that induced contemporaneous potassic and ultrapotassic magmatism. The second rapid cooling pulse from ∼11 Ma to 9 Ma and subsequent negligible cooling was most likely controlled by a local factor such as Indus and Shyok river network reorganization caused by dextral motion of the Karakorum fault. We discuss these interpretations and their limitations in this contribution.

  2. Records of Late Permian surface temperatures in continental Gondwana in isotope geochemistry of upper Permian early diagenetic calcite concretions

    SciTech Connect

    Yeman, E.; Kelts, K.

    1996-12-31

    We present geochemical and isotopic evidence of paleotemperatures from freshwater continental deposits from 55{degrees}S in interior southern Gondwana. Lacustrine shales host spheroidal concretions with abundant septarian cracks. Cement carbonate varies from 65% at the centre to 15% at the edges. Cistraccide remains are preserved. Septarian calcite occurs in dull and bright bands, with three distinct generations of vein-fills. Early-formed cement both in concretions and septarian veins is magnesium-rich whereas, later-formed carbonates are pure calcite. Carbon- and oxygen-isotope ratios (PDB) are: host shales, {delta}{sup 13}C= -4.36 to o.77{per_thousand}, {delta}{sup 18}O= -12.73 to -17.12{per_thousand}; concretion cements, {delta}{sup 13}C=+0.26 to {delta}{sup 18}O= -9.34{per_thousand}; and vein-fills, {delta}{sup 13}C= -7.05 to +1.09{per_thousand}, {delta}{sup 18}O= -8.28 to -18.24{per_thousand}. 13C and 18O ratios are depleted from the center of concretions to the periphery, as well as from the centre of veins to the tip. Near-surface cementation is suggested by textural evidence. {delta}18O in the range of -12.636{per_thousand} to -8.989 SMOW is calculated for the meteoric palaeowaters, from which average annual surface temperatures of 5-8{degrees}C are inferred. {delta}18O of early-formed cements also yields a mean annual surface temperature of 2-6{degrees}C. Based on continentality and palaeolatitudes of northern Malawi during the Late Permian, we propose that mean annual surface palaeotemperatures may have been as high as 10{degrees}C, similar to those found in modern continental temperate climates.

  3. Records of Late Permian surface temperatures in continental Gondwana in isotope geochemistry of upper Permian early diagenetic calcite concretions

    SciTech Connect

    Yeman, E. ); Kelts, K. )

    1996-01-01

    We present geochemical and isotopic evidence of paleotemperatures from freshwater continental deposits from 55[degrees]S in interior southern Gondwana. Lacustrine shales host spheroidal concretions with abundant septarian cracks. Cement carbonate varies from 65% at the centre to 15% at the edges. Cistraccide remains are preserved. Septarian calcite occurs in dull and bright bands, with three distinct generations of vein-fills. Early-formed cement both in concretions and septarian veins is magnesium-rich whereas, later-formed carbonates are pure calcite. Carbon- and oxygen-isotope ratios (PDB) are: host shales, [delta][sup 13]C= -4.36 to o.77[per thousand], [delta][sup 18]O= -12.73 to -17.12[per thousand]; concretion cements, [delta][sup 13]C=+0.26 to [delta][sup 18]O= -9.34[per thousand]; and vein-fills, [delta][sup 13]C= -7.05 to +1.09[per thousand], [delta][sup 18]O= -8.28 to -18.24[per thousand]. 13C and 18O ratios are depleted from the center of concretions to the periphery, as well as from the centre of veins to the tip. Near-surface cementation is suggested by textural evidence. [delta]18O in the range of -12.636[per thousand] to -8.989 SMOW is calculated for the meteoric palaeowaters, from which average annual surface temperatures of 5-8[degrees]C are inferred. [delta]18O of early-formed cements also yields a mean annual surface temperature of 2-6[degrees]C. Based on continentality and palaeolatitudes of northern Malawi during the Late Permian, we propose that mean annual surface palaeotemperatures may have been as high as 10[degrees]C, similar to those found in modern continental temperate climates.

  4. Inversion tectonics in the Anayet Permian basin (Axial Zone, Central Pyrenees)

    NASA Astrophysics Data System (ADS)

    Rodriguez, L.; Cuevas, J.; Tubía, J. M.

    2012-04-01

    During Permian times the Pyrenees were characterized by extensional tectonics that opened subsident basins with pull-apart geometries. The Anayet Permian basin crops out in the western Spanish Axial Zone between the Aragon and Tena valleys. It is WNW-trending and it is filled by a continental Permian succession that represents the first post-variscan deposits in the area. Permian deposits rest discordantly over Devonian to Carboniferous limestones, sandstones and slates. In the Anayet basin, Permian deposits have been classically divided in four main detrital groups, mainly composed of sandstones and conglomerates, with three basic volcanic episodes interbedded (Gisbert, 1984, Bixel, 1987). Due to the lithological characteristics of the Permian rocks in this region, there are almost no accurate age constraints for these units. A detailed structural study of the area, including mapping and balanced cross-sections, shows increasingly older rocks to the west of the Anayet basin. Moreover, it can be deduced a mean slope of around 11 % to the west for the basin. These data confirm that the basin depocenter was located to the west and that the Anayet basin was partitioned by N10 °E-trending normal faults. Although the contacts between the Permian and the Devono-Carboniferous rocks are covered by quaternary deposits in most of its extent, a fault contact can also be recognized. The fault contact is a 3 m thick shear zone oriented N120 ° E and dipping 60° to the North. It develops breccias, fault gouges and sigmoidal S-C tectonites indicating a reverse motion. The contact places Permian slates and sandstones over Carboniferous limestones and is almost parallel to the alpine cleavage deforming Permian rocks. The slope of the contact together with the presence of younger rocks in the hangingwall of the reverse fault points out that the original contact was a normal fault reactivated as a high-angle reverse fault during the positive inversion tectonics induced by the

  5. Glacial erosion, deep exhumation and the development of high topography along the Kongur detachment, Pamir Mountains, Western China

    NASA Astrophysics Data System (ADS)

    Schoenbohm, L.; Jie, C.; Sobel, E.; Thiede, R.; Strecker, M.

    2005-12-01

    Glacial erosion is linked to rapid exhumation and the formation of anomalously high peaks along the Kongur detachment fault in the Chinese Pamir. The footwall of the N-S detachment forms a high range along the eastern border of the Pamir that increases in elevation to the south, culminating in the twin peaks Kongur Shan (7719 m) and Muztagh Ata (7546m). The rocks underlying the peaks have experienced significantly more exhumation than those in the north (Robinson et al., 2004) and form broad domes. In the hanging wall valley to the west, the trunk river is forced to the west side of the valley by Quaternary/Holocene(?) debris shed from the footwall range. This observation and the relatively thinness of sediments in the valley indicate footwall uplift rather than hanging wall subsidence. This leads to higher peak elevations in the footwall, increasing the landscape area above the ELA. We suggest a scenario in which initial structural unroofing of the footwall, increased peak height and the resulting orographic focusing of precipitation may have led to increased glacial erosion. Glaciation would have been most significant in the south where the peaks were highest. The additional component of exhumation in the southern regions then drove greater structural exhumation, maintaining high topography and establishing a climate-moderated feedback loop. In order to understand the importance of glaciation in this scenario, we look to understanding temporal and spatial erosion and deposition in the valley. Three glacial sequences (moraine deposition, terrace formation, erosion) are recorded in the hanging wall valley, successively decreasing in extent. The extent of glaciation varies significantly from the north, where moraines are limited to the mouths of tributary valleys, to the south, where moraines completely filled the main valley. This variation is the result of the southward increasing range height and landscape area above the ELA. With moraine volume as a proxy for

  6. Early Acadian exhumation history of garnet-kyanite schists from western Massachusetts determined by LASS analysis of metamorphic monazite (Invited)

    NASA Astrophysics Data System (ADS)

    Peterman, E. M.; Snoeyenbos, D. R.; Kylander-Clark, A. R.

    2013-12-01

    Assessing the mechanics of exhumation (e.g. steady vs. episodic processes) requires constraints on the timing and rates of metamorphism and deformation, which can be accomplished by directly dating minerals that formed along the exhumation path. This research focuses on metamorphic monazites contained in restitic high-pressure garnet-kyanite schists from the Goshen Dome in western Massachusetts that record exhumation during the early Acadian. We employ the laser ablation split stream (LASS) technique to simultaneously collect geochronological and geochemical information from the same volume of material. By measuring in situ, LASS analysis allows coordination of petrology, geochemistry and geochronology to reconstruct the timing of metamorphic mineral growth concomitant with exhumation. The gar + ky × crd schists analyzed in this study contain monazite in a variety of petrographic contexts, some of which are interpreted to represent prograde metamorphism. Because we are concerned with exhumation, this contribution focuses on matrix monazite. Matrix monazites are generally aligned with their long axes parallel to foliation. All grains have at least one metamorphic overgrowth, and many grains have multiple generations of overgrowths, thus presenting a detailed record of events. The majority of the matrix monazite cores are 378 to 374 Ma with variable Y concentrations and REE trends. From 375 to 371 Ma, monazite depleted in Y with steep HREE profiles and higher LREE concentrations overgrew pre-existing cores or formed as neoblasts. Dates from most of these monazite domains cluster around 374 to 373 Ma. Neoblasts are typically elongated parallel to the foliation. From 370 to 369 Ma, overgrowths have intermediate Y concentrations with shallower HREE trends and intermediate LREE concentrations, indicating growth during garnet breakdown; these domains are commonly overgrowths with a consistent thickness (ca. 10-15 um), but some domains are more rounded. A pulse of

  7. Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars.

    PubMed

    Grotzinger, J P; Gupta, S; Malin, M C; Rubin, D M; Schieber, J; Siebach, K; Sumner, D Y; Stack, K M; Vasavada, A R; Arvidson, R E; Calef, F; Edgar, L; Fischer, W F; Grant, J A; Griffes, J; Kah, L C; Lamb, M P; Lewis, K W; Mangold, N; Minitti, M E; Palucis, M; Rice, M; Williams, R M E; Yingst, R A; Blake, D; Blaney, D; Conrad, P; Crisp, J; Dietrich, W E; Dromart, G; Edgett, K S; Ewing, R C; Gellert, R; Hurowitz, J A; Kocurek, G; Mahaffy, P; McBride, M J; McLennan, S M; Mischna, M; Ming, D; Milliken, R; Newsom, H; Oehler, D; Parker, T J; Vaniman, D; Wiens, R C; Wilson, S A

    2015-10-09

    The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp). Copyright © 2015, American Association for the Advancement of Science.

  8. Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars

    USGS Publications Warehouse

    Grotzinger, J.P.; Gupta, S.; Malin, M.C.; Rubin, D.M.; Schieber, J.; Siebach, K.; Sumner, D.Y.; Stack, K.M.; Vasavada, A.R.; Arvidson, R.E.; Calef, F.; Edgar, Lauren; Fischer, W.F.; Grant, J.A.; Griffes, J.L.; Kah, L.C.; Lamb, M.P.; Lewis, K.W.; Mangold, N.; Minitti, M.E.; Palucis, M.C.; Rice, M.; Williams, R.M.E.; Yingst, R.A.; Blake, D.; Blaney, D.; Conrad, P.; Crisp, J.A.; Dietrich, W.E.; Dromart, G.; Edgett, K.S.; Ewing, R.C.; Gellert, R.; Hurowitz, J.A.; Kocurek, G.; Mahaffy, P.G.; McBride, M.J.; McLennan, S.M.; Mischna, M.A.; Ming, D.; Milliken, R.E.; Newsom, H.; Oehler, D.; Parker, T.J.; Vaniman, D.; Wiens, R.C.; Wilson, S.A.

    2015-01-01

    The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).

  9. Early Tertiary exhumation of the flank of a forearc basin, southwest Talkeetna Mountains, Alaska

    USGS Publications Warehouse

    Bleick, Heather A.; Till, Alison B.; Bradley, Dwight C.; O’Sullivan, Paul; Wooden, Joe L.; Bradley, Dan B.; Taylor, Theresa A.; Friedman, Sam B.; Hults, Chad P.

    2012-01-01

    New geochronologic and thermochronologic data from rocks near Hatcher Pass, southwest Talkeetna Mountains, Alaska, record earliest Paleocene erosional and structural exhumation on the flank of the active Cook Inlet forearc basin. Cretaceous plutons shed sediments to the south, forming the Paleocene Arkose Ridge Formation. A Paleocene(?)-Eocene detachment fault juxtaposed ~60 Ma metamorphic rocks with the base of the Arkose Ridge Formation. U-Pb (analyzed by Sensitive High Resolution Ion Micro Probe Reverse Geometry (SHRIMP-RG)) zircon ages of the Cretaceous plutons, more diverse than previously documented, are 90.3±0.3 (previously considered a Jurassic unit), 79.1±1.0, 76.1±0.9, 75.8±0.7, 72.5±0.4, 71.9±0.3, 70.5±0.2, and 67.3±0.2 Ma. The cooling of these plutons occurred between 72 and 66 Ma (zircon fission track (FT) closure ~225°C). 40Ar/39Ar analyses of hornblende, white mica, and biotite fall into this range (Harlan and others, 2003). New apatite FT data collected on a west-to-east transect reveal sequential exhumation of fault blocks at 62.8±2.9, 54±2.5, 52.6±2.8, and 44.4±2.2 Ma. Plutonic clasts accumulated in the Paleocene Arkose Ridge Formation to the south. Detrital zircon (DZ) ages from the formation reflect this provenance: a new sample yielded one grain at 61 Ma, a dominant peak at 76 Ma, and minor peaks at 70, 80, 88, and 92 Ma. The oldest zircon is 181 Ma. Our apatite FT ages range from 35.1 to 50.9 Ma. Greenschist facies rocks now sit structurally between the plutonic rocks and the Arkose Ridge Formation. They are separated from plutonic rocks by the vertical Hatcher Pass fault and from the sedimentary rocks by a detachment fault. Ar cooling ages (Harlan and others, 2003) and new zircon FT ages for these rocks are concordant at 61-57 Ma, synchronous with deposition of the Arkose Ridge Formation. A cooling age of ~46 Ma came from one apatite FT sample. The metamorphic protolith (previously considered Jurassic) was deposited at or after

  10. Using Digital Topography to Differentiate Erosionally Exhumed and Tectonically Active Mountains Fronts

    NASA Astrophysics Data System (ADS)

    Frankel, K. L.; Pazzaglia, F. J.

    2003-12-01

    Mountain ranges in the southern Rocky Mountains have departed on unique landscape evolutionary pathways in the late Cenozoic that are directly dependent upon the degree of post-orogenic tectonic activity they have experienced. The topography of Sierra Nacimiento, a Laramide uplift in west-central New Mexico lacking an active range-front fault, is shaped primarily by erosional exhumation that is continuous, but not steady, being driven by distal base level fall from Rio Grande incision and resultant south to north knickpoint migration. In contrast, the topography of the Taos Range, a rift flank uplift in north-central New Mexico is shaped by contrasting active stream incision and aggradation astride an active range front normal fault. The distinction between exhumation-dominated and tectonically-dominated mountain fronts is best quantified by analyses of a new metric we call the drainage basin volume to drainage basin area ratio (V-A ratio) as well as the gradients of first-order streams. Drainage basin volume and area are calculated by constructing topographic envelope maps from 10 m resolution digital elevation models (DEM). The envelope maps are pinned by the watershed divide and cover the maximum elevations in each drainage basin. Subtracting the original DEM from the maximum elevation envelope map produces a topographic residual map from which area and volume data can be obtained. The erosionally exhumed Sierra Nacimiento has a mean V-A ratio of 88 m while the tectonically active Taos Range has a mean V-A ratio of 140 m. Similarly, there are systematic differences in the gradients of first order streams measured both in the range block and approximately 5 km of adjacent piedmont. Streams were defined and subsequently Strahler ordered by a flow accumulation threshold of 250 water-equivalent grid cell units. First order stream channel long profiles were extracted from the DEM at 30 meter increments and gradients were calculated by a FORTRAN program. Gradients of

  11. The exhumed ``Carlin-type'' fossil oil reservoir at Yankee Basin

    NASA Astrophysics Data System (ADS)

    Hulen, Jeffrey B.; Collister, James W.; Stout, Bill; Curtiss, David K.; Dahdah, Nicolas F.

    1998-12-01

    The Carlin-type disseminated gold orebodies of Yankee basin in the southern part of the Alligator Ridge mining district in Nevada contain widespread oil as smears, open-space fillings, and fluid inclusions in syn- and pre-mineral calcite veins. These unusual oils are the relicts of an exhumed and deeply oxidized oil reservoir that encom-passes the orebodies at the crest of a dissected, anticlinal trap. Results of fluid-inclusion microthermometry and organic geochemistry demonstrate that the oils experienced peak paleotemperatures of no more than about 150°C, a temperature unusually low for Carlin-type mineralization, but ideal for the transport, entrapment, and preservation of liquid hydrocarbon. Similar geothermal systems are actively circulating at three of Nevada’s producing oil fields—Grant Canyon, Bacon Flat, and Blackburn. Accordingly, concealed Carlin-type fossil hydrothermal systems of this type, even if subeconomic for gold, could contain commercial concentrations of oil.

  12. Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars

    NASA Astrophysics Data System (ADS)

    Grotzinger, J. P.; Gupta, S.; Malin, M. C.; Rubin, D. M.; Schieber, J.; Siebach, K.; Sumner, D. Y.; Stack, K. M.; Vasavada, A. R.; Arvidson, R. E.; Calef, F.; Edgar, L.; Fischer, W. F.; Grant, J. A.; Griffes, J.; Kah, L. C.; Lamb, M. P.; Lewis, K. W.; Mangold, N.; Minitti, M. E.; Palucis, M.; Rice, M.; Williams, R. M. E.; Yingst, R. A.; Blake, D.; Blaney, D.; Conrad, P.; Crisp, J.; Dietrich, W. E.; Dromart, G.; Edgett, K. S.; Ewing, R. C.; Gellert, R.; Hurowitz, J. A.; Kocurek, G.; Mahaffy, P.; McBride, M. J.; McLennan, S. M.; Mischna, M.; Ming, D.; Milliken, R.; Newsom, H.; Oehler, D.; Parker, T. J.; Vaniman, D.; Wiens, R. C.; Wilson, S. A.

    2015-10-01

    The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).

  13. Long-term coupling along the subduction plate interface: insights from exhumed rocks and models

    NASA Astrophysics Data System (ADS)

    Agard, P.; Angiboust, S.; Guillot, S.; Garcia-Casco, A.

    2012-04-01

    Fragments of subducted oceanic lithosphere returned along the plate interface convey crucial information regarding the thermal and rheological conditions of convergent plate boundaries. Combining evidence from exhumed rocks worldwide and the results of recently published thermo-mechanical models, we herein investigate how long-term mechanical coupling takes place along deep portions of the plate interface (40-80 km depth), for which there is no counterflow (unlike in accretionary prisms) and no other known mechanisms to return eclogites than interplate friction or buoyancy. Geological evidence indicates that, unlike subduction, exhumation is highly discontinuous. Besides, eclogites worldwide are found in essentially two types of tectonic setting, either as large scale (>km) slices with coherent PT estimates (W. Alps) or as isolated fragments (frequently m-hm) in a serpentinite- or sedimentary-rich matrix showing contrasting equilibration depths (with hints of punctuated exhumation and even reburial in some localities; Franciscan, Cuba, Sistan). This latter type tends to show warmer equilibration paths (although minor lawsonite-eclogite blocks can be found), whereas the larger tectonic slices from the former type remain systematically cold. Serpentinites are crucial for both in permitting decoupling and acting as a buoy, and fluid budget is important too in enhancing floatability and allowing large slices to survive. Numerical models implementing free migration of fluids in the subduction zone also show that the plate interface is strongly localized in the absence of fluids: mechanical decoupling efficiently occurs along the sediment veneer and/or at the top of the highly hydrothermalized crust. Whenever fluids are released in greater amounts (depending on initial fluid content and/or thermal structure), deformation becomes much more distributed and affects both the mantle wedge and the top of the downgoing lithosphere (hydrated crust and mantle top), thereby

  14. The global range of subduction zone thermal structures from exhumed blueschists and eclogites: Rocks are hotter than models

    NASA Astrophysics Data System (ADS)

    Penniston-Dorland, Sarah C.; Kohn, Matthew J.; Manning, Craig E.

    2015-10-01

    The maximum-pressure Psbnd T conditions (Pmax- T) and prograde Psbnd T paths of exhumed subduction-related metamorphic rocks are compared to predictions of Psbnd T conditions from computational thermal models of subduction systems. While the range of proposed models encompasses most estimated Pmax- T conditions, models predict temperatures that are on average colder than those recorded by exhumed rocks. In general, discrepancies are greatest for Pmax < 2 GPa, where only a few of the highest-T model paths overlap petrologic observations and model averages are 100-300 °C colder than average conditions recorded by rocks. Prograde Psbnd T paths similarly indicate warmer subduction than typical models. Both petrologic estimates and models have inherent biases. Petrologic analysis may overestimate temperatures at Pmax where overprinting occurs during exhumation, although Psbnd T paths suggest that relatively warm conditions are experienced by rocks on the prograde subduction path. Models may underestimate temperatures at depth by neglecting shear heating, hydration reactions and fluid and rock advection. Our compilation and comparison suggest that exhumed high-P rocks provide a more accurate constraint on Psbnd T conditions within subduction zones, and that those conditions may closely represent the subduction geotherm. While exhumation processes in subduction zones require closer petrologic scrutiny, the next generation of models should more comprehensively incorporate all sources of heat. Subduction-zone thermal structures from currently available models appear to be inaccurate, and this mismatch has wide-reaching implications for our understanding of global geochemical cycles, the petrologic structure of subduction zones, and fluid-rock interactions and seismicity within subduction zones.

  15. The Global Range of Subduction Zone Thermal Structures From Exhumed Blueschists and Eclogites: Rocks are Hotter than Models

    NASA Astrophysics Data System (ADS)

    Penniston-Dorland, S.; Kohn, M. J.; Manning, C. E.

    2015-12-01

    The maximum-pressure P-T conditions (Pmax-T) and prograde P-Tpaths of exhumed subduction-related metamorphic rocks are compared to predictions of P-Tconditions from computational thermal models of subduction systems. While the range of proposed models encompasses most estimated Pmax-Tconditions, models predict temperatures that are on average colder than those recorded by exhumed rocks. In general, discrepancies are greatest for Pmax< 2 GPa where only a few of the highest-Tmodeled paths overlap typical petrologic observations and model averages are 100-300 °C colder than average conditions recorded by rocks. Prograde P-Tpaths similarly indicate warmer subduction than typical models. Both petrologic estimates and models have inherent biases. Petrologic analysis may overestimate temperatures at Pmaxwhere overprinting occurs during exhumation, although P-Tpaths suggest that relatively warm conditions are experienced by rocks on the prograde subduction path. Models may underestimate temperatures at depth by neglecting shear heating, hydration reactions and fluid and rock advection. Our compilation and comparison suggest that exhumed high-P rocks provide a more accurate constraint on P-Tconditions within subduction zones, and that those conditions may closely represent the subduction geotherm. While exhumation processes in subduction zones require closer petrologic scrutiny, the next generation of models should more comprehensively incorporate all sources of heat. Subduction-zone thermal structures from currently available models appear to be inaccurate, and this mismatch has wide-reaching implications for our understanding of global geochemical cycles, the petrologic structure of subduction zones, and fluid-rock interactions and seismicity within subduction zones.

  16. Partial melting during exhumation of Paleozoic retrograde eclogite in North Qaidam, western China

    NASA Astrophysics Data System (ADS)

    Cao, Yu-ting; Liu, Liang; Chen, Dan-ling; Wang, Chao; Yang, Wen-qiang; Kang, Lei; Zhu, Xiao-hui

    2017-10-01

    Ultrahigh pressure (UHP) rocks are often overprinted by high pressure (HP) granulite-facies metamorphism during exhumation. Here we investigate retrograde eclogite from the Lvliangshan area in North Qaidam which is associated with abundant felsic veins. The eclogite adjacent to the vein shows conversion to garnet amphibolite. Petrographic, mineralogical, geochemical, geochronological data suggest that the eclogite has been experienced peak eclogite facies metamorphism at c. 440 Ma, followed by granulite facies retrogression at c. 420 Ma, and amphibolite facies overprinting at <420 Ma. The retrograde eclogite has microstructural records for partial melting with elongated plagioclase grains occurring as veinlets along the garnet-ilmenite grain boundaries and interspersed in clinopyroxene. Moreover, highly cuspate, wedge-shaped and triangular plagioclase grains are distributed along the garnet boundaries, and banded felsic veins (Pl + Qz) occur along the boundaries of amphibole in garnet amphibolite. Whole-rock geochemistry suggests that the felsic veins have 438.1-1106 ppm Sr and 2.87-12.18 ppm Y with Sr/Y ratios from 81.98-166.2, exhibit pronounced positive Eu anomaly, and depletion of HREE, resembling those of adakitic rocks. Felsic veins contain zircon grains with an U-Pb age of ∼422 Ma, similar to the age of HP granulite-facies metamorphism (420 Ma) of retrograde eclogite. Combined with the identical Hf isotope compositions between the granulite-facies zircon grains from the host retrograde eclogite and those from the felsic vein, we infer closed system partial melting during HP granulite facies retrogression of the retrograde eclogite. The tonalitic (high Sr/Y ratio and enrichment of LREE) chemical feature, low Rb/Sr and high Ba/Rb ratios of the felsic veins suggest that zoisite and sodic amphibolite dehydration-melting together account for the formation of felsic veins during exhumation from the eclogite-facies to granulite-facies stages.

  17. Large Influence of Subduction Geometry on Extreme Exhumation in Orogen Syntaxes

    NASA Astrophysics Data System (ADS)

    Ehlers, T. A.; Bendick, R. O.

    2014-12-01

    Some of the highest and most localized rates of lithospheric deformation in the world are observed at the transition between adjacent plate boundary subduction segments (syntaxes). The initiating perturbation of this deformation has long been attributed to vigorous, climate driven, erosional processes as observed at Nanga Parbat and Namche Barwa in the Himalaya and at Mt. St. Elias in Alaska. However, an erosion-dominated mechanism ignores the 3D geometry of curved subducting plates and changes in paleoclimate. Here we present an alternative explanation for rapid exhumation at these locations based on the 3D thermo-mechanical evolution of collisions between plates with nonplanar geometries. A set of numerical solutions and thermochronometer observations are presented for the interaction between a rigid indenter between subduction segments with an overriding viscous material. The model setup is intentionally simplified to identify how the 3D geometry of a subducting plate influences upper plate deformation, and therefore omits many of the complexities of collision interfaces, such as the transfer of mass between the downgoing and overriding plates. Temperatures are calculated using the 3D advection diffusion equation with radiogenic heat production and shear heating. The thermal and Stokes flow solutions are fully coupled and evolve throughout the simulation. Model predicted cooling ages are compared to observed cooling ages from published bedrock and detrital thermochronometer studies by calculating cooling rate dependent thermochronometer ages. Comparison of model predictions with existing thermochronometer data reproduces the defining characteristics of these mountains such as a localized "bulls-eye" pattern of rapid exhumation and young cooling ages above the rigid indenter between subduction segments. These results demonstrate a 'bottom up' tectonic rather than 'top down' erosional initiation of feedbacks between erosion and tectonic deformation. While the role

  18. Exhumation history of the Tatry Mountains, Western Carpathians, constrained by low-temperature thermochronology

    NASA Astrophysics Data System (ADS)

    Śmigielski, M.; Sinclair, H. D.; Stuart, F. M.; Persano, C.; Krzywiec, P.

    2016-01-01

    This study tests alternative models for the growth of the Tatry Mountains (Central Western Carpathians) by the application of low-temperature thermochronology. Zircon (U + Th)/He ages from the north of the range are mostly between 48 and 37 Ma and indicate cooling prior to the onset of fore-arc sedimentation in the region (42-39 Ma). In contrast, zircon (U + Th)/He ages in the south of the range are around 22 Ma. Apatite fission track ages across the sampled sites range from 20 to 15 Ma. Apatite (U + Th)/He ages range from 18 to 14 Ma with little variation with elevation or horizontal location. Based on thermal modeling and tectonic reconstructions, these Miocene ages are interpreted as cooling in the hanging wall of a northward dipping thrust ramp in the current location of the sub-Tatric fault with cooling rates of ~20°C/Myr at ~22-14 Ma. Modeled cooling histories require an abrupt deceleration in cooling after ~14 Ma to <5°C/Myr. This is associated with termination of deformation in the Outer Carpathians and is synchronous with the transition of the Pannonian Basin from a syn-rift to a postrift stage and with termination of N-S compression in the northern part of the Central Western Carpathians. Overall, the timing of shortening and exhumation is synchronous with the formation of the Outer Carpathian orogen and so the Miocene exhumation of the Tatry records retrovergent thrusting at the northern margin of the Alcapa microplate.

  19. Exhumation of Metamorphic rocks during the Taiwan Orogeny: A Study on the Soufeng Fault

    NASA Astrophysics Data System (ADS)

    Yi, D.; Lin, C. W.; McAleer, R. J.; Kunk, M. J.; Wintsch, R. P.

    2015-12-01

    Part of the exhumation history of eastern Taiwan is stored in the shear zone between the Yuli and Tailuko belts, the Daguan shear zone (Yi et al., 2012), which is a part of the Soufong fault named by Yen (1963). Our detailed fieldwork across this fault shows that it is marked by a sharp contact between the Yuli forearc metasediments and the Tailuko belt marbles and schists. As the boundary is approached from the eastern Yuli belt a moderate to strong slaty cleavage becomes phyllitic, with anastomosing S-C fabrics and local boudinage of stronger quartzites, subarkoses and graywackes. These fault rocks are characterized by abundant stretched lenticular quartz veins, locally intercalated with thin elongated meta-conglomerates. Across the fault to the west are massive marbles, layered quartz mica schists, chlorite schists, and meta-chert. Regional Ar dating of fine fraction of white micas in these rocks yields ages of ~1 to 16 Ma (Tsao, 1996). Ar ages of biotite in mylonitic Tananao schists range from 3.0-4.1 Ma (Wang, 1998). We separated and dated very fine-grained phyllitic folia of the phyllites and phyllonites approaching the fault zone, and find ages even younger than this. Our preliminary step heating experiments show age spectra with reproducible age steps less than 1 Ma. These spectra climb to ages as old as found by others, 12 to 14 Ma, demonstrating multiple age populations. However, our separates concentrating the youngest fabric-forming micas demonstrate that recrystallization during faulting persisted to the Middle Pleistocene. Thus differential movement between these belts probably played a critical role in driving the uplift and exhumation of these rocks.

  20. Thermochronologic constraints on Late Cretaceous to Cenozoic exhumation of the Bendeleben Mountains, Seward Peninsula, Alaska

    NASA Astrophysics Data System (ADS)

    McDannell, Kalin T.; Toro, Jaime; Hourigan, Jeremy K.; Harris, Daniel

    2014-10-01

    the Bendeleben Mountains, Seward Peninsula, mid-Cretaceous granites are exposed in an uplifted block bounded on its south side by an E-W striking normal fault. The Bendeleben fault has well-preserved scarps 4-7 m in height that offset Holocene moraines. Seismic activity, young normal faulting, and Quaternary basaltic volcanism are all evidence of active extension. South of the Bendeleben fault, there is a 3-4 km deep basin. Fifteen apatite (U-Th)/He ages from granitic samples of the footwall yield an Eocene weighted mean age of 41.3±4.8 Ma. Biotite 40Ar/39Ar ages from the country rock of the Bendeleben pluton are 81-83 Ma. In spite of the young fault scarps, HeFTy and Pecube thermal modeling results illustrate that rapid exhumation of the Bendeleben Mountains occurred in the Late Cretaceous-Eocene and slowed since the Oligocene. A weak age-elevation relationship of apatite He ages and a lack of correlation between age and distance from the fault indicate that exhumation was accomplished with minimal block rotation on a steeply dipping, long-lived normal fault. Timing of extension in the Seward Peninsula can be correlated with deformation in the offshore Hope Basin where seismic reflection lines document Early Tertiary large-magnitude normal faulting followed by minor post-Miocene reactivation. The faulting observed in the Bendeleben Mountains is part of an extensional system that spans a large portion of the Bering Strait region. The tectonic model proposed in previous studies suggests that clockwise rotation of the Bering block relative to North America is the cause of extensional deformation in western Alaska.

  1. Asymmetric Exhumation Patterns Revealed through Apatite-Zircon Thermochronology of the Santa Lucia Range, Central California

    NASA Astrophysics Data System (ADS)

    Mere, A.; Steely, A.; Hourigan, J. K.

    2016-12-01

    Previous thermochronological analyses of crystalline bedrock in the central Santa Lucia range have yielded surprisingly rapid rates of surface uplift and bedrock extrusion despite lack of modern seismicity along nearby faults. We use 8 new apatite and zircon (U-Th)/He dates in order to better constrain the history of bedrock extrusion in response to the transpressional North American-Pacific plate boundary. Granitic samples were collected along coastal fault blocks bounded by the Palo Colorado (PCF), Sur-Nacimiento (SNF), and San Gregorio Hosgri faults (SGHF); as well as one sample from Salinian Basement >25km NE of the SGHF. Helium was extracted and analyzed using a quadrupole equipped multi-sample laser microfurnace and U/Th content was measured using high precision isotope-dilution ICP mass spectrometry. Rapid late Cretaceous unroofing is captured in Salinian basement zircon and apatite by the respective 67Ma and 63Ma dates. Zircon along coastal silvers proximal to PCF and SNF record 28-31Ma dates while zircon in close proximity to SGHF record ages as young as 6.5Ma. Apatite ages proximal to PCF and SNF range between 6-9Ma and are as young as 1.5Ma directly NE of the SGHF. These data reflect increased exhumation beginning as recently as the Miocene and additionally indicate rates of modern (<2Ma) uplift exceeding 1.3 mm/yr. These results indicate that stresses caused by the active plate boundary are accommodated by the SGHF and associated faults as vertical deformation despite low rates of modern seismicity. We suggest that the SGHF and nearby faults are more active, or behave differently, that previously acknowledged. The pattern of focused exhumation within narrow fault blocks appears to be related to underplating of low strength schist that is thought to be synchronous with late Cretaceous unroofing of Salinian basement.

  2. Hydrous species in eclogitic omphacite: Implication for metamorphic dehydration during exhumation

    NASA Astrophysics Data System (ADS)

    Sheng, Ying-Ming; Gong, Bing

    2017-09-01

    Water contents were analyzed by infrared spectroscopy for structural hydroxyl in randomly oriented cuboids and doubly polished wafers of single crystal omphacite from an ultrahigh-pressure eclogite in the Dabie orogen. The results are quantitatively compared with bulk water contents measured by the TC/EA-MS continuous flow technique. This enables recognition of various hydrous species in omphacite and their bearings on metamorphic dehydration during continental subduction. The two cuboids yield constant maximal structural water contents of ∼378 ppm (H2O wt.) using the omphacite-specific infrared absorption coefficient, which are much lower than the bulk water contents of ∼1496 ppm. The excessive water is contributed by the presence of other hydrous species in the form of hydrous mineral inclusions, hydrous symplectite and submicron fluid inclusions. Since the hydrous mineral and/or fluid inclusions may be captured at different metamorphic stages during subduction and exhumation of continental crust and the hydrous symplectite is the secondary rather than the primary, it is suggested that the bulk water contents represent a mixing of various hydrous species with distinct origins. In this regard, it is critical to examine whether water in these secondary hydrous species is of internal origin; if not, it has nothing to do with the transport capacity of water in deeply subducted crustal rocks. Upon stepwise heating up to 700 °C, omphacite exhibits a gradual decrease in bulk water contents but an increase in δD values, indicating the preferential loss of D-depleted hydrous species as a whole due to the decompressional dehydration of UHP metamorphic rocks during exhumation. Therefore, the D-depleted hydrous species may be dominated in the hydrous symplectite and inclusion water.

  3. Spatial variations in focused exhumation along a continental-scale strike-slip fault: The Denali fault of the eastern Alaska Range

    USGS Publications Warehouse

    Benowitz, J.A.; Layer, P.W.; Armstrong, P.; Perry, S.E.; Haeussler, P.J.; Fitzgerald, P.G.; VanLaningham, S.

    2011-01-01

    40Ar/39Ar, apatite fission-track, and apatite (U-Th)/He thermochronological techniques were used to determine the Neogene exhumation history of the topographically asymmetric eastern Alaska Range. Exhumation cooling ages range from ~33 Ma to ~18 Ma for 40Ar/39Ar biotite, ~18 Ma to ~6 Ma for K-feldspar minimum closure ages, and ~15 Ma to ~1 Ma for apatite fission-track ages, and apatite (U-Th)/He cooling ages range from ~4 Ma to ~1 Ma. There has been at least ~11 km of exhumation adjacent to the north side of Denali fault during the Neogene inferred from biotite 40Ar/39Ar thermochronology. Variations in exhumation history along and across the strike of the fault are influenced by both far-field effects and local structural irregularities. We infer deformation and rapid exhumation have been occurring in the eastern Alaska Range since at least ~22 Ma most likely related to the continued collision of the Yakutat microplate with the North American plate. The Nenana Mountain region is the late Pleistocene to Holocene (~past 1 Ma) primary locus of tectonically driven exhumation in the eastern Alaska Range, possibly related to variations in fault geometry. During the Pliocene, a marked increase in climatic instability and related global cooling is temporally correlated with an increase in exhumation rates in the eastern Alaska Range north of the Denali fault system.

  4. Global taxonomic diversity of anomodonts (tetrapoda, therapsida) and the terrestrial rock record across the Permian-Triassic boundary.

    PubMed

    Fröbisch, Jörg

    2008-01-01

    The end-Permian biotic crisis (~252.5 Ma) represents the most severe extinction event in Earth's history. This paper investigates diversity patterns in Anomodontia, an extinct group of therapsid synapsids ('mammal-like reptiles'), through time and in particular across this event. As herbivores and the dominant terrestrial tetrapods of their time, anomodonts play a central role in assessing the impact of the end-Permian extinction on terrestrial ecosystems. Taxonomic diversity analysis reveals that anomodonts experienced three distinct phases of diversification interrupted by the same number of extinctions, i.e. an end-Guadalupian, an end-Permian, and a mid-Triassic extinction. A positive correlation between the number of taxa and the number of formations per time interval shows that anomodont diversity is biased by the Permian-Triassic terrestrial rock record. Normalized diversity curves indicate that anomodont richness continuously declines from the Middle Permian to the Late Triassic, but also reveals all three extinction events. Taxonomic rates (origination and extinction) indicate that the end-Guadalupian and end-Permian extinctions were driven by increased rates of extinction as well as low origination rates. However, this pattern is not evident at the final decline of anomodont diversity during the Middle Triassic. Therefore, it remains unclear whether the Middle Triassic extinction represents a gradual or abrupt event that is unique to anomodonts or more common among terrestrial tetrapods. The end-Permian extinction represents the most distinct event in terms of decline in anomodont richness and turnover rates.

  5. Sedimentology and cyclicity in the Lower Permian De Chelly Sandstone on the Defiance Plateau: eastern Arizona

    USGS Publications Warehouse

    Stanesco, J.D.

    1991-01-01

    The Lower Permian (Leonardian) De Chelly Sandstone crops out along a north-south trend on the Defiance Plateau of eastern Arizona. It is divided into lower and upper members separated by a tongue of the Supai Formation that pinches out to the north. Stratigraphy, and lateral and vertical facies relations within the lower and upper members, are discussed. -from Author

  6. Assessment of Permian tight oil and gas resources in the Junggar basin of China, 2016

    USGS Publications Warehouse

    Potter, Christopher J.; Schenk, Christopher J.; Tennyson, Marilyn E.; Klett, Timothy R.; Gaswirth, Stephanie B.; Leathers-Miller, Heidi M.; Finn, Thomas M.; Brownfield, Michael E.; Pitman, Janet K.; Mercier, Tracey J.; Le, Phuong A.; Drake, Ronald M.

    2017-04-05

    Using a geology-based assessment methodology, the U.S. Geological Survey estimated undiscovered, technically recoverable mean resources of 764 million barrels of oil and 3.5 trillion cubic feet of gas in tight reservoirs in the Permian Lucaogou Formation in the Junggar basin of northwestern China.

  7. Phosphatic Permian rocks of the Adobe Range, Nevada, and their environment of deposition

    USGS Publications Warehouse

    Ketner, Keith Brindley

    1979-01-01

    Permian sedimentary rocks in the Adobe range, northern Nevada, are phosphatic, and although the particles of phosphate are relatively more disseminated, they closely resemble the rocks of the Phosphoria Formation. In the northern Adobe Range, where the entire Permian sequence is approximately correlative with the Phosphoria Formation, it is 200 m thick and averages 1.7 percent P2O5 . In the southern Adobe Range, the Permian sequence is more than 1,700 m thick, and the upper half which is roughly correlative with the Phosphoria Formation averages more than 2 percent P2O5. Some thin beds in rocks of Permian age contain more than 20 percent P2O5. Phosphatic rocks of the Adobe Range were deposited in shallow water among islands in the western part of the epicontinental Phosphoria sea. The continental margin and the open ocean lay far to the west. At the same time, the Phosphoria Formation was being deposited in the eastern and central parts of the Phosphoria sea. Theories based on the work of Kasakov done in 1937 relating phosphate deposition directly to sites of upwelling oceanic waters are questioned. Nondeposition of diluent materials such as detritus and carbonate is probably of more importance in producing phosphate in economic concentrations than is geographic position with respect to upwelling waters.

  8. Some Permian corals from East Peninsular Malaysia: associated microfossils, paleogeographic significance

    NASA Astrophysics Data System (ADS)

    Fontaine, Henri; Lys, Maurice; Duc Tien, Nguyen

    A few Permian corals fromm East Peninsula Malaysia are described; associated microfossils are identified. These fossils belong to the Kubergandian and to the Upper Murghabian-Lower Midian boundary. The fossil assemblages of East Peninsular Malaysia are different from thoseof Northwest Peninsula Malaysia; they are richer and more diverse. The two paleogeographic areas are conspicuously different.

  9. Unayzah Formation: a new Permian-Carboniferous unit in Saudi Arabia

    SciTech Connect

    Al-Laboun, A.A.

    1987-01-01

    The sandstones, shales, and thin beds of argillaceous limestone previously included as the basal part of the Permian Khuff Formation were described as the Unayzah Formation by al-Laboun in 1982 and 1986. The type locality (stratotype.) of this formation is in the town of Unayzah, and a reference section was established in the Qusayba area, al-Qasim district, Saudi Arabia. Fossil flora collected from outcrops and palynomorphs obtained from boreholes support a Late Carboniferous-Early Permian age for these strata. The Unayzah Formation is conformably overlain by the massive carbonates of the Khuff Formation, whereas its basal contact is marked by a regional angular unconformity with various older units. The Unayzah Formation is widespread in the Greater Arabian basin. The formation represents cyclic transgressive and regressive deposits preceding the Permian regional marine transgression, during which the massive carbonates of the Khuff Formation were deposited. This Permian transgression marked a major change in the Sedimentation and evolution of the Greater Arabian basin. The porous sandstones of the Unayzah Formation are important exploration targets because several fields in the eastern and southeastern parts of the Greater Arabian basin produce hydrocarbons from the Unayzah. 11 figures, 1 table.

  10. Tectonic controls on Upper Permian lacustrine oil shales in the Junggar basin, NW China

    SciTech Connect

    Carroll, A.R.; Brassell, S.C.; Graham, S.A. )

    1991-03-01

    Collision of the Tarim craton with the southern margin of Asia during the Late Carboniferous-Early Permian resulted in uplift of an ancestral Tian Shan range and geographic isolation of the previously marine Junggar basin. Dramatic shifts from marine to nonmarine sedimentation took place in both the southern Junggar and northern Tarim basins during the Permina. Paleocurrent analysis indicate that by the Late Permian, coarse-grained sediments in both basins were being supplied predominantly from the area of the Tian Shan. During the Late Permian, the southern Junggar received in excess of 5,000 m of nonmarine sediments, including approximately 1,000 m of laminated, highly organic-rich lacustrine mudstones (oil shales). These deposits commonly have TOCs of 20-30%, and Rock-Eval pyrolitic yields reaching 2,000 mg/g, ranking them among the most prolific petroleum source rocks in the world. Based on a comparison of the distribution of steranes and extended tricyclic terpanes, these Upper Permian oil shales appear to be the primary source of oils in the giant Karamay field in the northwestern Junggar basin. Ancestral uplift of the Tian Shan thus produced a complex tectono-hydrologic partitioning of the Late Permina Junggar basin, which exerted a strong influence on the character of petroleum source rocks deposited within the basin.

  11. Permian and Pennsylvanian tectonic events in eastern California in relation to major plate motions

    SciTech Connect

    Stevens, C.H.; Sedlock, R. ); Stone, P. )

    1993-04-01

    Northwest-trending basins cutting across older northeast-trending facies belts in eastern California opened by Middle Pennsylvanian time and continued to develop and expand into the Early Permian. Basin development was accompanied by east-vergent thrust-faulting in the Early Permian and was followed by development of northeast-trending folds and regional uplift in middle and Late Permian time. These events have been considered products of long-tern sinistral truncation of the western North American continental margin. Later, in the Late Permian, extensional faulting created small northeast-trending basins in which deposition of terrestrial and shallow-marine rocks occurred. The author consider all late Paleozoic tectonism in eastern California to have been driven by plate interactions along the western margin of North America and to be only indirectly related to the late Paleozoic collision between North America and Gondwana. They propose that the truncated part of North America was part of the Paleo-pacific plate. In Nevada the margin of this plate, along which the Havallah assemblage eventually was emplaced, was convergent, but in California the margin bent sharply and became transform. This fault continued as the Mojave-Sonora mega-shear into Mexico where the oceanic part of the Paleopacific plate was subducted under Gondwana, forming an extensive arc now represented by rocks in S. America.

  12. Unique organic remains from an upper Permian coal bearing sequence in the Talcher Coalfield, Orissa, India

    SciTech Connect

    Tripathi, A.

    2004-07-01

    The playnological assemblage of coal bearing upper Permian sequence of Talcher Coalfield registers presence of some peculiar organic remains. These are described as Orissiella gen. nov., which is characterized by a vesicle with collar-like structure at the oral end, spines and or corrugations on the body. The affinity and palaeoecological significance of Orissiella is also discussed. 12 refs., 4 figs., 2 plates.

  13. Taeniopterid lamina on Phasmatocycas megasporophylls (Cycadales) from the Lower Permian of Kansas, U.S.A.

    USGS Publications Warehouse

    Gillespie, W.H.; Pfefferkorn, H.W.

    1986-01-01

    New specimens of Phasmatocycas and Taeniopteris from the original Lower Permian locality in Kansas demonstrate organic attachment of the two and corroborate Mamay's hypothesis that Phasmatocycas and Taeniopteris were parts of the same plant. These forms also suggest that cycads evolved from taxa with entire leaves; i.e. Taeniopteris, rather than from pteridosperms with compound leaves. ?? 1986.

  14. Marine anoxia and delayed Earth system recovery after the end-Permian extinction.

    PubMed

    Lau, Kimberly V; Maher, Kate; Altiner, Demir; Kelley, Brian M; Kump, Lee R; Lehrmann, Daniel J; Silva-Tamayo, Juan Carlos; Weaver, Karrie L; Yu, Meiyi; Payne, Jonathan L

    2016-03-01

    Delayed Earth system recovery following the end-Permian mass extinction is often attributed to severe ocean anoxia. However, the extent and duration of Early Triassic anoxia remains poorly constrained. Here we use paired records of uranium concentrations ([U]) and (238)U/(235)U isotopic compositions (δ(238)U) of Upper Permian-Upper Triassic marine limestones from China and Turkey to quantify variations in global seafloor redox conditions. We observe abrupt decreases in [U] and δ(238)U across the end-Permian extinction horizon, from ∼3 ppm and -0.15‰ to ∼0.3 ppm and -0.77‰, followed by a gradual return to preextinction values over the subsequent 5 million years. These trends imply a factor of 100 increase in the extent of seafloor anoxia and suggest the presence of a shallow oxygen minimum zone (OMZ) that inhibited the recovery of benthic animal diversity and marine ecosystem function. We hypothesize that in the Early Triassic oceans-characterized by prolonged shallow anoxia that may have impinged onto continental shelves-global biogeochemical cycles and marine ecosystem structure became more sensitive to variation in the position of the OMZ. Under this hypothesis, the Middle Triassic decline in bottom water anoxia, stabilization of biogeochemical cycles, and diversification of marine animals together reflect the development of a deeper and less extensive OMZ, which regulated Earth system recovery following the end-Permian catastrophe.

  15. Provincialization of terrestrial faunas following the end-Permian mass extinction

    PubMed Central

    Sidor, Christian A.; Vilhena, Daril A.; Angielczyk, Kenneth D.; Huttenlocker, Adam K.; Nesbitt, Sterling J.; Peecook, Brandon R.; Steyer, J. Sébastien; Smith, Roger M. H.; Tsuji, Linda A.

    2013-01-01

    In addition to their devastating effects on global biodiversity, mass extinctions have had a long-term influence on the history of life by eliminating dominant lineages that suppressed ecological change. Here, we test whether the end-Permian mass extinction (252.3 Ma) affected the distribution of tetrapod faunas within the southern hemisphere and apply quantitative methods to analyze four components of biogeographic structure: connectedness, clustering, range size, and endemism. For all four components, we detected increased provincialism between our Permian and Triassic datasets. In southern Pangea, a more homogeneous and broadly distributed fauna in the Late Permian (Wuchiapingian, ∼257 Ma) was replaced by a provincial and biogeographically fragmented fauna by Middle Triassic times (Anisian, ∼242 Ma). Importantly in the Triassic, lower latitude basins in Tanzania and Zambia included dinosaur predecessors and other archosaurs unknown elsewhere. The recognition of heterogeneous tetrapod communities in the Triassic implies that the end-Permian mass extinction afforded ecologically marginalized lineages the ecospace to diversify, and that biotic controls (i.e., evolutionary incumbency) were fundamentally reset. Archosaurs, which began diversifying in the Early Triassic, were likely beneficiaries of this ecological release and remained dominant for much of the later Mesozoic. PMID:23630295

  16. Invertebrate Biostratigraphy of an Early Permian Limestone in north-central Texas.

    NASA Astrophysics Data System (ADS)

    Shell, R.; Ciampaglio, C. N.

    2016-12-01

    Outcrops of the lower Leuders Formation in Shackleford County, Texas were investigated for Early Permian (Leonardian) fossils. While over 30 species were recovered, the lack of brachiopods in this Paleozoic limestone set the rocks apart from nearly all other Paleozoic carbonates, as well as other Permian units in Texas such as those of the Glass Mountains. Superficially, the lower Leuders Formation here can be divided into two sub sequences: an upper section of orange and tan limestones with brown mudstones and shales, and a lower gray sequence of limestones and black calcareous shales. Across this color boundary, the invertebrate biostratigraphy illustrates a community in transition from one dominated by animals common to the Pennsylvanian, to one more similar to typical Permian marine deposits. The alternating mudstone and limestone sequence here indicates small-scale marine transgressions and regressions, which may have driven the faunal overturn at this locality. A single productid brachiopod was found in the upper sequence here, suggesting that sea level changes at this locality may have influenced the local spread of brachiopods at this site in the Early Permian.

  17. Permian continental paleoenvironments in Southeastern Asia: New insights from the Luang Prabang Basin (Laos)

    NASA Astrophysics Data System (ADS)

    Bercovici, Antoine; Bourquin, Sylvie; Broutin, Jean; Steyer, Jean-Sébastien; Battail, Bernard; Véran, Monette; Vacant, Renaud; Khenthavong, Bounxou; Vongphamany, Sotsy

    2012-10-01

    In Laos (Southeastern Asia), Late Paleozoic sediments were identified by early French explorations across Indochina during the late 19th century (Pavie missions), but little work was undertaken to characterize the sedimentological and stratigraphical context until now. From detailed sedimentological and paleontological studies, we propose an interpretation of the depositional environment and of the stratigraphic context of series located on the right bank of the Mekong River in the Luang Prabang Basin where three main formations were described. The silicoclastic Red Claystone Formation, attributed to alluvial plain environment, contains large fragments of unidentified dicynodonts. The Limestones and Sandstones Formation preserves a new macrofloral assemblage displaying affinities with Middle to Late Permian Cathaysian floras of South China. This assemblage occurs as an intercalation within marine calcareous sandstones that have yielded a marine fauna, including the ammonoid Pseudotirolites sp. which indicates a Late Permian (Changhsingian) age. The well-developed Purple Claystones Formation yielded an abundant and well preserved Late Permian fauna composed of a carnivorous amphibian and numerous Dicynodon cranial and postcranial elements. This formation shows a vertical evolution from braided river to alluvial plain with sheet-flood sand bed and bed-load rivers, with a constant supply of volcanic clasts. Results from the analysis of the paleontological associations in the Luang Prabang Basin suggest that a continental communication between Laurussia and the Indochina Block existed during the Permian, allowing for migration of the terrestrial Dicynodon fauna.

  18. Carnivorous dinocephalian from the Middle Permian of Brazil and tetrapod dispersal in Pangaea

    PubMed Central

    Cisneros, Juan Carlos; Abdala, Fernando; Atayman-Güven, Saniye; Rubidge, Bruce S.; Şengör, A. M. Celâl; Schultz, Cesar L.

    2012-01-01

    The medial Permian (∼270–260 Ma: Guadalupian) was a time of important tetrapod faunal changes, in particular reflecting a turnover from pelycosaurian- to therapsid-grade synapsids. Until now, most knowledge on tetrapod distribution during the medial Permian has come from fossils found in the South African Karoo and the Russian Platform, whereas other areas of Pangaea are still poorly known. We present evidence for the presence of a terrestrial carnivorous vertebrate from the Middle Permian of South America based on a complete skull. Pampaphoneus biccai gen. et sp. nov. was a dinocephalian “mammal-like reptile” member of the Anteosauridae, an early therapsid predator clade known only from the Middle Permian of Russia, Kazakhstan, China, and South Africa. The genus is characterized, among other features, by postorbital bosses, short, bulbous postcanines, and strongly recurved canines. Phylogenetic analysis indicates that the Brazilian dinocephalian occupies a middle position within the Anteosauridae, reinforcing the model of a global distribution for therapsids as early as the Guadalupian. The close phylogenetic relationship of the Brazilian species to dinocephalians from South Africa and the Russian Platform suggests a closer faunistic relationship between South America and eastern Europe than previously thought, lending support to a Pangaea B-type continental reconstruction. PMID:22307615

  19. Conodont biostratigraphy of the Permian-Triassic boundary sequence at Lung Cam, Vietnam

    USGS Publications Warehouse

    Wardlaw, Bruce R.; Nestell, Merlynd K.; Nestell, Galina P.; Ellwood, Brooks B.; Lan, Luu Thi Phuong

    2015-01-01

    The occurrences of a few specimens of Clarkina and many specimens of Hindeodus at the Permian-Triassic boundary section at Lung Cam, Vietnam allow accurate graphic correlation to the P-T boundary stratotype at Meishan, China. One species of Clarkina, ten species and two subspecies of Hindeodus, and the apparatuses of Hindeodus latidentatus and Merrillina ultima are described and illustrated.

  20. Carnivorous dinocephalian from the Middle Permian of Brazil and tetrapod dispersal in Pangaea.

    PubMed

    Cisneros, Juan Carlos; Abdala, Fernando; Atayman-Güven, Saniye; Rubidge, Bruce S; Şengörc, A M Celâl; Schultz, Cesar L

    2012-01-31

    The medial Permian (~270-260 Ma: Guadalupian) was a time of important tetrapod faunal changes, in particular reflecting a turnover from pelycosaurian- to therapsid-grade synapsids. Until now, most knowledge on tetrapod distribution during the medial Permian has come from fossils found in the South African Karoo and the Russian Platform, whereas other areas of Pangaea are still poorly known. We present evidence for the presence of a terrestrial carnivorous vertebrate from the Middle Permian of South America based on a complete skull. Pampaphoneus biccai gen. et sp. nov. was a dinocephalian "mammal-like reptile" member of the Anteosauridae, an early therapsid predator clade known only from the Middle Permian of Russia, Kazakhstan, China, and South Africa. The genus is characterized, among other features, by postorbital bosses, short, bulbous postcanines, and strongly recurved canines. Phylogenetic analysis indicates that the Brazilian dinocephalian occupies a middle position within the Anteosauridae, reinforcing the model of a global distribution for therapsids as early as the Guadalupian. The close phylogenetic relationship of the Brazilian species to dinocephalians from South Africa and the Russian Platform suggests a closer faunistic relationship between South America and eastern Europe than previously thought, lending support to a Pangaea B-type continental reconstruction.

  1. Integrated Sr isotope variations and global environmental changes through the Late Permian to early Late Triassic

    NASA Astrophysics Data System (ADS)

    Song, Haijun; Wignall, Paul B.; Tong, Jinnan; Song, Huyue; Chen, Jing; Chu, Daoliang; Tian, Li; Luo, Mao; Zong, Keqing; Chen, Yanlong; Lai, Xulong; Zhang, Kexin; Wang, Hongmei

    2015-08-01

    New 87Sr/86Sr data based on 127 well-preserved and well-dated conodont samples from South China were measured using a new technique (LA-MC-ICPMS) based on single conodont albid crown analysis. These reveal a spectacular climb in seawater 87Sr/86Sr ratios during the Early Triassic that was the most rapid of the Phanerozoic. The rapid increase began in Bed 25 of the Meishan section (GSSP of the Permian-Triassic boundary, PTB), and coincided closely with the latest Permian extinction. Modeling results indicate that the accelerated rise of 87Sr/86Sr ratios can be ascribed to a rapid increase (>2.8×) of riverine flux of Sr caused by intensified weathering. This phenomenon could in turn be related to an intensification of warming-driven runoff and vegetation die-off. Continued rise of 87Sr/86Sr ratios in the Early Triassic indicates that continental weathering rates were enhanced >1.9 times compared to those of the Late Permian. Continental weathering rates began to decline in the middle-late Spathian, which may have played a role in the decrease of oceanic anoxia and recovery of marine benthos. The 87Sr/86Sr values decline gradually into the Middle Triassic to an equilibrium values around 1.2 times those of the Late Permian level, suggesting that vegetation coverage did not attain pre-extinction levels thereby allowing higher runoff.

  2. Development of the Permian-Triassic sequence in the basin Fringe area, southern Netherlands

    SciTech Connect

    Geluk, M.; Van Doorn, D.; Plomp, A.; Duin, E. )

    1993-09-01

    Geological studies in the fringe area of the southern Permian basin led to new insights in the distribution and development of the Permian-Triassic sequence. During the Permian, the fringe area formed a platform, attached to the London-Brabant Massif, while during the Triassic it is characterized by strongly subsiding half grabens. In the southern Netherlands, Rotliegende sandstones and conglomerates have a much wider distribution than previously recognized. The Rotliegende deposits are capped by claystones and carbonates of the Upper Permian Zechstein. In the offshore, an important feeder system of clastics from the London-Brabant Massif was active during deposition of the Rotliegende and the Zechstein. In course of time, the location of major sandstone deposition shifted westward. Deposition of the Triassic Buntsandstein was controlled by the development of a large feeder system, which transported clastics from the Vosges northward, through the Roer Valley Graben and West netherlands Basin into the Off Holland Low. This system was responsible for the deposition of the economically important sheet sandstones of the Volpriehausen, Detfurth, Hardegsen, and Solling formations. A regional unconformity occurs below the Solling Formation. The sandstones are capped by claystones, evaporites, and sandstones of the Rot Formation. During deposition of the Muschelkalk, the differences in subsidence decreased and shallow marine sediments are interbedded with evaporites. Several unconformities occur within the Keuper. In the previous half grabens in the southern Netherlands, the Keuper is incomplete, which may be indicative for a possible reversal of the tectonic movements during this period.

  3. Lower Permian Radiolaria from the Pos Blau area, Ulu Kelantan, Malaysia

    NASA Astrophysics Data System (ADS)

    Jasin, Basir; Aziz Ali, Che

    1997-08-01

    Twenty two species of Radiolaria were identified from a 30 mthick chert sequence exposed at a roadcut near Pos Blau, Ulu Kelantan. The radiolarian assemblage represents the top part of the Pseudoalbaillella lomentaria Zone, upper Wolfcampian which is equivalent to the Sakmarian, Lower Permian. These radiolarian faunas contain elements present in both Southern Urals and Japanese faunas.

  4. Controls on body size during the Late Permian mass extinction event.

    PubMed

    He, W-H; Twitchett, R J; Zhang, Y; Shi, G R; Feng, Q-L; Yu, J-X; Wu, S-B; Peng, X-F

    2010-12-01

    This study examines the morphological responses of Late Permian brachiopods to environmental changes. Quantitative analysis of body size data from Permian-Triassic brachiopods has demonstrated significant, directional changes in body size before, during and after the Late Permian mass extinction event. Brachiopod size significantly reduced before and during the extinction interval, increased for a short time in more extinction-resistant taxa in the latter stages of extinction and then dramatically reduced again across the Permian/Triassic boundary. Relative abundances of trace elements and acritarchs demonstrate that the body size reductions which happened before, during and after extinction were driven by primary productivity collapse, whereas declining oxygen levels had less effect. An episode of size increase in two of the more extinction-resistant brachiopod species is unrelated to environmental change and possibly was the result of reduced interspecific competition for resources following the extinction of competitors. Based on the results of this study, predictions can be made for the possible responses of modern benthos to present-day environmental changes.

  5. Pattern of marine mass extinction near the Permian-Triassic boundary in South China.

    PubMed

    Jin, Y G; Wang, Y; Wang, W; Shang, Q H; Cao, C Q; Erwin, D H

    2000-07-21

    The Meishan section across the Permian-Triassic boundary in South China is the most thoroughly investigated in the world. A statistical analysis of the occurrences of 162 genera and 333 species confirms a sudden extinction event at 251.4 million years ago, coincident with a dramatic depletion of delta13C(carbonate) and an increase in microspherules.

  6. Continuity of Permian Mengkareng formation through GPR interpretation in Merangin Geopark

    NASA Astrophysics Data System (ADS)

    Hanif, F.; Syahputra, R.; Kristyanto, T. H. W.; Tempessy, A. S.; Rokhmatuloh

    2017-07-01

    The Permian Mengkarang Formation was a part of the continental margin (Gondwana Land) which separated in the Devon Period. In this period, Gondwana Land experienced glaciation at the Paleo South Pole. However, the fossils found in Mengkarang Formation were tropical flora, had made the Merangin to be certified as one of the national geoparks. It also shows that the geological process (stratigraphy and tectonic) in the Merangin has occurred before the Indonesian archipelago was formed: namely the Permian to Triassic period. Ground Penetrating Radar (GPR) was chosen as an effective geophysical method to study shallow subsurface geology. GPR and seismic reflection method have the same common principle to identify the facies and sub-sequence stratigraphy but they are different in implementation. Therefore, this study aims to deliver the vertical continuity of the Permian Mengkarang Formation in high resolution unit. The GPR result showing the subsurface image is based on dielectric of the rock layers. The GPR sections show the absence of the unconformity delivered in the intercalation between mudstone, sandstone, and tuff. Thus, it can be concluded that the Permian Mengkareng Formation continues up to 20 m depth.

  7. Provincialization of terrestrial faunas following the end-Permian mass extinction.

    PubMed

    Sidor, Christian A; Vilhena, Daril A; Angielczyk, Kenneth D; Huttenlocker, Adam K; Nesbitt, Sterling J; Peecook, Brandon R; Steyer, J Sébastien; Smith, Roger M H; Tsuji, Linda A

    2013-05-14

    In addition to their devastating effects on global biodiversity, mass extinctions have had a long-term influence on the history of life by eliminating dominant lineages that suppressed ecological change. Here, we test whether the end-Permian mass extinction (252.3 Ma) affected the distribution of tetrapod faunas within the southern hemisphere and apply quantitative methods to analyze four components of biogeographic structure: connectedness, clustering, range size, and endemism. For all four components, we detected increased provincialism between our Permian and Triassic datasets. In southern Pangea, a more homogeneous and broadly distributed fauna in the Late Permian (Wuchiapingian, ∼257 Ma) was replaced by a provincial and biogeographically fragmented fauna by Middle Triassic times (Anisian, ∼242 Ma). Importantly in the Triassic, lower latitude basins in Tanzania and Zambia included dinosaur predecessors and other archosaurs unknown elsewhere. The recognition of heterogeneous tetrapod communities in the Triassic implies that the end-Permian mass extinction afforded ecologically marginalized lineages the ecospace to diversify, and that biotic controls (i.e., evolutionary incumbency) were fundamentally reset. Archosaurs, which began diversifying in the Early Triassic, were likely beneficiaries of this ecological release and remained dominant for much of the later Mesozoic.

  8. Carnivorous dinocephalian from the Middle Permian of Brazil and tetrapod dispersal in Pangaea

    NASA Astrophysics Data System (ADS)

    Cisneros, Juan Carlos; Abdala, Fernando; Atayman-Güven, Saniye; Rubidge, Bruce S.; Celâl Şengör, A. M.; Schultz, Cesar L.

    2012-01-01

    The medial Permian (∼270-260 Ma: Guadalupian) was a time of important tetrapod faunal changes, in particular reflecting a turnover from pelycosaurian- to therapsid-grade synapsids. Until now, most knowledge on tetrapod distribution during the medial Permian has come from fossils found in the South African Karoo and the Russian Platform, whereas other areas of Pangaea are still poorly known. We present evidence for the presence of a terrestrial carnivorous vertebrate from the Middle Permian of South America based on a complete skull. Pampaphoneus biccai gen. et sp. nov. was a dinocephalian "mammal-like reptile" member of the Anteosauridae, an early therapsid predator clade known only from the Middle Permian of Russia, Kazakhstan, China, and South Africa. The genus is characterized, among other features, by postorbital bosses, short, bulbous postcanines, and strongly recurved canines. Phylogenetic analysis indicates that the Brazilian dinocephalian occupies a middle position within the Anteosauridae, reinforcing the model of a global distribution for therapsids as early as the Guadalupian. The close phylogenetic relationship of the Brazilian species to dinocephalians from South Africa and the Russian Platform suggests a closer faunistic relationship between South America and eastern Europe than previously thought, lending support to a Pangaea B-type continental reconstruction.

  9. Permian-Triassic palynofacies and chemostratigraphy in a core recovered from central Spitsbergen.

    NASA Astrophysics Data System (ADS)

    van Soelen, Els; Hasic, Edi; Planke, Sverre; Svensen, Henrik; Sleveland, Arve; Midtkandal, Ivar; Twitchett, Richard; Kürschner, Wolfram

    2017-04-01

    The Late Permian biotic crisis is one of the most severe extinction events in the history of the Earth, affecting both terrestrial and marine environments. A large igneous province (LIP) in Siberia is thought to be linked with this global event; however, correlation between the volcanic event and the biotic crisis is difficult and requires well dated and high resolution Permian-Triassic boundary successions from the Arctic region. The Svalbard end-Permian drilling project is aimed at improved correlation of the Permian-Triassic sections in Svalbard with the Siberian Traps. The core was collected from Deltadalen, in central Spitsbergen, with additional samples collected from an outcrop close to the drilling site. As part of this collaborative project, carbon isotope geochemistry, palynofacies and palynomorphs were studied in order to learn more about the biostratigraphy and to understand changes in the source(s) of organic matter. Objectives were to reconstruct the paleo-environment; to correlate the core with other sites on Svalbard, and with global records; and to identify and characterize the Late Permian extinction event in the core. A carbon isotope shift is an important global stratigraphic marker in the latest Permian and occurs near the base of the Vikinghøgda Formation in the Deltadalen core, where bulk rock values change from -24.5 to -32.7‰. Palynomorph preservation was generally poor in both core and outcrop samples which prevented detailed examination of species and limited their usefulness for biostratigraphy. Still, palynofacies were useful for correlative purposes. AOM (amorphous organic matter) in the core increases at the lithological change from sandstones to siltstones, and is indicative of anoxic conditions. Similar high levels of AOM in the outcrop samples can be correlated with the core. Palynological analyses show that the spore/pollen ratio starts to increase before the negative shift in the isotope curve. Such an increase in spore

  10. Upper Permian vertebrates and their sedimentological context in the South Urals, Russia

    NASA Astrophysics Data System (ADS)

    Tverdokhlebov, Valentin P.; Tverdokhlebova, Galina I.; Minikh, Alla V.; Surkov, Mikhail V.; Benton, Michael J.

    2005-02-01

    Fossil fishes and tetrapods (amphibians and reptiles) have been discovered at 81 localities in the Upper Permian of the Southern Urals area of European Russia. The first sites were found in the 1940s, and subsequent surveys have revealed many more. Broad-scale stratigraphic schemes have been published, but full documentation of the rich tetrapod faunas has not been presented before. The area of richest deposits covers some 900,000 km 2 of territory between Samara on the River Volga in the NW, and Orenburg and Sakmara in the SW. A continental succession, some 3 km thick, of mudstones, siltstones, and sandstones, deposited on mudflats and in small rivers flowing off the Ural Mountain chain, span the last two stages of the Permian (Kazanian, Tatarian). The succession is divided into seven successive units of Kazanian (Kalinovskaya, Osinovskaya, and Belebey svitas, in succession) and Tatarian age, which is further subdivided into the early Tatatian Urzhumian Gorizont (Bolshekinelskaya and Amanakskaya svitas, in succession), and the late Tatarian Severodvinian (Vyazovskaya and Malokinelskaya svitas, of equivalent age) and Vyatkian gorizonts (Kulchumovskaya and Kutulukskaya svitas, of equivalent age). This succession documents major climatic changes, with increasing aridity through the Late Permian. The climate changes are manifested in changing sedimentation and the spread of dryland plants, and peak aridity was achieved right at the Permo-Triassic (PTr) boundary, coincident with global warming. Uplift of the Urals and extinction of land plants led to stripping of soils and massive run-off from the mountains; these phenomena have been identified at the PTr boundary elsewhere (South Africa, Australia) and this may be a key part of the end-Permian mass extinction. The succession of Late Permian fish and tetrapod faunas in Russia documents their richness and diversity before the mass extinction. The terminal Permian Kulchomovskaya and Kutulukskaya svitas have yielded

  11. Middle Miocene Hotspot-Related Uplift, Exhumation, and Extension north of the Snake River Plain: Evidence from Apatite (U-Th)/He Thermochronology

    NASA Astrophysics Data System (ADS)

    Foster, D. A.; Vogl, J.; Min, K. K.; Bricker, A.; Gelato, P. W.

    2013-12-01

    Passage of North America over the Yellowstone hotspot has had a profound influence on the topography of the northern Rocky Mountains. One of the most prominent topographic features is the Yellowstone crescent of high topography, which comprises two elevated shoulders bounding the eastern Snake River Plain (SRP) and converging at a topographic swell centered on the Yellowstone region. Kilometer-scale erosion has occurred locally within the topographic crescent, but it is unclear if rock exhumation is due to surface uplift surrounding the propagating hot spot, subsidence of the Snake River Plain after passage of the hot spot, or relief initiated by extension in the Northern Basin and Range Province. We have applied (U-Th/He) apatite (AHe) thermochronology to the Pioneer-Boulder Mountains (PBM) on the northern flank of the SRP, and the southern Beartooth Mountains (BM) directly north of the modern Yellowstone caldera, to constrain the timing, rates, and spatial distribution of exhumation. AHe ages from the PBM indicate that >2-3 km of exhumation occurred in the core of this topographic culmination since ~11 Ma. Age-elevation relationships suggest an exhumation rate of ~0.3 mm/yr between ~11 and 8 Ma. Eocene Challis volcanic rocks are extensively preserved and Eocene topographic highs are locally preserved to the north and south of the PBM, indicating minimal erosion adjacent to the PBM culmination. Spatial patterns of both exhumation and topography indicate that faulting was not the primary control on uplift and exhumation. Regional exhumation at 11-8 Ma was synchronous with silicic eruptions from the ~10.3 Ma Picabo volcanic field located immediately to the south and with S-tilting of the southern flank of the PBM that is likely the result of loading of the ESRP by mid-crustal mafic intrusions. AHe data from Archean rocks of the southern BM reveal Miocene-Pliocene cooling ages and include samples as young as ~2-6 Ma. Discordant single grain ages in samples with

  12. Cretaceous Exhumation of the North American Cordillera Measured through Mineral Multi-Dating: Insights into Basin Filling Models and Orogenic Architecture

    NASA Astrophysics Data System (ADS)

    Painter, C. S.; Carrapa, B.; DeCelles, P. G.; Gehrels, G. E.; Thomson, S. N.

    2015-12-01

    Apatite fission track (AFT) thermochronology is an effective thermochronometer to measure source exhumation in the North American Cordillera, western U.S.A. We use a combination of thermochronology and geochronology to measure lag times, i.e., the difference in time between the cooling and depositional ages of a mineral crystal. These lag-time measurements using source exhumation ages, measured with AFT thermochronology, and depositional ages, measured with biostratigraphy and detrital zircon U-Pb geochronology, indicate constant to decreasing lag times of 0-5 m.y. throughout the Cretaceous. These lag times are consistent with rapid exhumation rates of ~0.9->1 km/m.y. One pitfall of using detrital thermochronology to measure source exhumation is assuring that the apatite crystals are exhumed apatites and not volcanic apatites introduced into the system from the volcanic arc. To do this we use U-Pb geochronology to remove samples contaminated with young arc derived apatites and keep those with old exhumed apatites. Five of the seven detrital AFT samples were significantly contaminated with young volcanic apatites, showing that U-Pb geochronology should be a routine step in measuring lag times. Our findings demonstrate that coarse-grained foreland basin deposits in the Cretaceous Western Interior, in both the proximal and distal settings, were deposited during times of active tectonism and exhumation and that sediments are not stored in wedge-top and proximal foredeep settings for long periods of time, i.e. >5 m.y., and then subsequently reworked distally. Exhumation rates of ~0.9->1 km/m.y. are not sustainable over the entire orogenic belt for the duration of the Sevier orogeny, indicated by the lack of deep-crustal material exhumed in the North American Cordillera. High exhumation rates were likely concentrated over the eastward-propagating Sevier fold-thrust belt, whereas the Nevadaplano and hinterland experienced much slower rates of exhumation. This variation in

  13. Total petroleum systems of the Bonaparte Gulf Basin area, Australia; Jurassic, Early Cretaceous-Mesozoic; Keyling, Hyland Bay-Permian; Milligans-Carboniferous, Permian

    USGS Publications Warehouse

    Bishop, M.G.

    1999-01-01

    The Bonaparte Gulf Basin Province (USGS #3910) of northern Australia contains three important hydrocarbon source-rock intervals. The oldest source-rock interval and associated reservoir rocks is the Milligans-Carboniferous, Permian petroleum system. This petroleum system is located at the southern end of Joseph Bonaparte Gulf and includes both onshore and offshore areas within a northwest to southeast trending Paleozoic rift that was initiated in the Devonian. The Milligans Formation is a Carboniferous marine shale that sources accumulations of both oil and gas in Carboniferous and Permian deltaic, marine shelf carbonate, and shallow to deep marine sandstones. The second petroleum system in the Paleozoic rift is the Keyling, Hyland Bay-Permian. Source rocks include Lower Permian Keyling Formation delta-plain coals and marginal marine shales combined with Upper Permian Hyland Bay Formation prodelta shales. These source-rock intervals provide gas and condensate for fluvial, deltaic, and shallow marine sandstone reservoirs primarily within several members of the Hyland Bay Formation. The Keyling, Hyland Bay-Permian petroleum system is located in the Joseph Bonaparte Gulf, north of the Milligans-Carboniferous, Permian petroleum system, and may extend northwest under the Vulcan graben sub-basin. The third and youngest petroleum system is the Jurassic, Early Cretaceous-Mesozoic system that is located seaward of Joseph Bonaparte Gulf on the Australian continental shelf, and trends southwest-northeast. Source-rock intervals in the Vulcan graben sub-basin include deltaic mudstones of the Middle Jurassic Plover Formation and organic-rich marine shales of the Upper Jurassic Vulcan Formation and Lower Cretaceous Echuca Shoals Formation. These intervals produce gas, oil, and condensate that accumulates in, shallow- to deep-marine sandstone reservoirs of the Challis and Vulcan Formations of Jurassic to Cretaceous age. Organic-rich, marginal marine claystones and coals of the

  14. Uppermost Permian to Lower Triassic Conodont Zonation from Enshi area, western Hubei Province, South China

    NASA Astrophysics Data System (ADS)

    Lyu, Z.; Zhao, L.; Chen, Z. Q.; Ma, D.; Yan, P.; Zhan, P.

    2015-12-01

    The Permian-Triassic transition witnessed the largest biotic turnover of Earth life during the Phanerozoic history. Ecosystems in sea and on land have also experienced the most protected restoration following the end-Permian mass extinction. These biocrises were also associated with climatic and environmental extremes through the latest Permian to Middle Triassic. In order to uncover the links among these extreme events, we need to establish high-resolution biochronostratigraphy, which offers precise timescales for reconstructing event sequences and probing the possible causes. Of these, conodont biostratigraphy is an operational tool in enhancing stratigraphic resolution. Although their ancestors and phylogeny remain unclear, conodonts are a rapid evolutionary lineage and extremely abundant in the Triassic marine carbonate successions. Here, we present recent study results of the Lower Triassic conodont zonation from the Ganxi and Jianshi areas, western Hubei Province, South China, which were situated on a carbonate ramp at the southern northern margin of the Upper Yangtze Platform. Therein, the uppermost Permian to Lower Triassic successions are well exposed and yield abundant conodonts. A total of nine conodont zones was established: (1) Clarkina yini-Clarkina zhangi Zone, (2) Hindeodus changxingensis Zone, (3) Hindeodus parvus Zone, (4) Isarcicella staeschei Zone, (5) Clarkina planata Zone, (6) Neoclarkina discrete Zone, (7) Neospathodus dieneri Zone, (8) Novispathodus waageni Zone, and (9) Triassospathodus homeri Zone. The Ns. dieneri M1, Ns. dieneri M2 and Ns. dieneri M3 subzones have also been distinguished from the Ns. dieneri Zone. Both Nv. waageni eowaageni subzones and Nv. waageni waageni subzones are also recognizable from the Nv. waageni Zone. The first occurrence of H. parvus marks the Permian-Triassic boundary(PTB), while the first occurrence of Nv. waageni eowaageni defines the Induan-Olenekian boundary. These conodont zones correlate well with

  15. Tectonic rotations south of the Bohemian Massif from palaeomagnetic directions of Permian red beds in Hungary

    USGS Publications Warehouse

    Marton, E.; Elston, D.P.

    1987-01-01

    Palaeomagnetic studies were carried out in Permian red beds of the Balaton Highlands, the Mecsek Mountains and the Bu??kk Mountains of Hungary. Statistically well defined directions were obtained from six localities in the Balaton Highlands and two localities in the Mecsek Mountains. No meaningful results were obtained from the Bu??kk Mountains. Three magnetic components were identified from red beds of the Balaton Highlands: (1) in haematite with a very high unblocking temperature (700??C), interpreted as a Permian magnetization (Dc= 79??, Ic=-11??, k = 24, ??95 = 13.6 ??), in six samples from three beds in a single locality (2) a secondary but ancient component residing mainly inmaghemite (D = 314??, I = 49??, k = 48, ??95 = 10.0??), in 84 samples from six localities with a within-locality scatter increasing on unfolding; and (3) a direction parallel to the present field (D = 7??, I = 62??, k = 46, ??95 = 7.7 ??), in nine samples from a single locality. For the Balaton Highlands, the component 1 direction agrees with directions obtained from Permian red beds and volcanics in the eastern part of the Southern and Eastern Alps and the Inner West Carpathians. All show large, apparent rotations relative to stable Europe since the Permian. Component 2 is of post-folding (post-Aptian) age. Its direction agrees with known Late Cretaceous directions from the Transdanubian Central Mountains, which also show significant counterclockwise rotation relative to stable Europe. The characteristic magnetization for the Mecsek Mountains resides in haematite and may be primary. The directions indicate only a slight net counterclockwise rotation of the Mecsek Mountains with respect to stable Europe since the Permian. ?? 1987.

  16. Permian-Early Triassic tectonics and stratigraphy of the Karoo Supergroup in northwestern Mozambique

    NASA Astrophysics Data System (ADS)

    Bicca, Marcos Müller; Philipp, Ruy Paulo; Jelinek, Andrea Ritter; Ketzer, João Marcelo Medina; dos Santos Scherer, Claiton Marlon; Jamal, Daúd Liace; dos Reis, Adriano Domingos

    2017-06-01

    The Gondwana continent was the base of great basin inception, sedimentation and magmatism throughout the Cambrian to Middle Jurassic periods. The northwestern Mozambique igneous and metamorphic basement assemblages host the NW-trending Moatize Minjova Basin, which has great economic potential for coal and gas mining. This rift basin was activated by an S-SW stress field during the Early Permian period, as constrained by regional and field scale structural data. Tectonically induced subsidence in the basin, from the reactivation of NW-SE and NNE-SSW regional structures is well recorded by faults, folds and synsedimentary fractures within the Early Late Permian Moatize Formation. NW-SE, N-S and NE-SW field structures consist of post-Karoo reactivation patterns related to a NNE-SSW extension produced by the Pangea breakup and early inception stages of the Great East African Rift System. The Early Late Permian sequences of the Moatize-Minjova Basin are composed of fluvial meandering, coal-bearing beds of the Moatize Formation, which comprises mostly floodplain, crevasse splay and fluvial channel lithofacies associations, deposited in a cyclic pattern. This sequence was overlapped by a multiple-story, braided fluvial plain sequence of the Matinde Formation (Late Permian - Early Triassic). Lithofacies associations in the Matinde Formation and its internal relationships suggest deposition of poorly channelized braided alluvial plain in which downstream and probably lateral accretion macroforms alternate with gravity flow deposits. NW paleoflow measurements suggest that Permian fluvial headwaters were located somewhere southeast of the study area, possibly between the African and Antarctic Precambrian highlands.

  17. Microbialites and global environmental change across the Permian-Triassic boundary: a synthesis.

    PubMed

    Kershaw, S; Crasquin, S; Li, Y; Collin, P-Y; Forel, M-B; Mu, X; Baud, A; Wang, Y; Xie, S; Maurer, F; Guo, L

    2012-01-01

    Permian-Triassic boundary microbialites (PTBMs) are thin (0.05-15 m) carbonates formed after the end-Permian mass extinction. They comprise Renalcis-group calcimicrobes, microbially mediated micrite, presumed inorganic micrite, calcite cement (some may be microbially influenced) and shelly faunas. PTBMs are abundant in low-latitude shallow-marine carbonate shelves in central Tethyan continents but are rare in higher latitudes, likely inhibited by clastic supply on Pangaea margins. PTBMs occupied broadly similar environments to Late Permian reefs in Tethys, but extended into deeper waters. Late Permian reefs are also rich in microbes (and cements), so post-extinction seawater carbonate saturation was likely similar to the Late Permian. However, PTBMs lack widespread abundant inorganic carbonate cement fans, so a previous interpretation that anoxic bicarbonate-rich water upwelled to rapidly increase carbonate saturation of shallow seawater, post-extinction, is problematic. Preliminary pyrite framboid evidence shows anoxia in PTBM facies, but interbedded shelly faunas indicate oxygenated water, perhaps there was short-term pulsing of normally saturated anoxic water from the oxygen-minimum zone to surface waters. In Tethys, PTBMs show geographic variations: (i) in south China, PTBMs are mostly thrombolites in open shelf settings, largely recrystallised, with remnant structure of Renalcis-group calcimicrobes; (ii) in south Turkey, in shallow waters, stromatolites and thrombolites, lacking calcimicrobes, are interbedded, likely depth-controlled; and (iii) in the Middle East, especially Iran, stromatolites and thrombolites (calcimicrobes uncommon) occur in different sites on open shelves, where controls are unclear. Thus, PTBMs were under more complex control than previously portrayed, with local facies control playing a significant role in their structure and composition. © 2011 Blackwell Publishing Ltd.

  18. Paleoenvironment of the Permian rocks: a comparison between central and eastern Alborz, Iran

    NASA Astrophysics Data System (ADS)

    Lankarani, M.; Amini, A.; Mosadegh, H.

    2009-04-01

    The succession of Permian rocks in Alborz region is composed of siliciclastic and carbonate facies. All of the sediments were deposited in the Paleotethyan passive continental margin but they show different facies architecture and paleoenvironmental condition in various parts of the region. This study, as part of a wider project, has investigated sedimentary facies and paleoenvironment of the Permian rocks in central and eastern Alborz. The Permian rocks in central Alborz are dominated by siliciclastic facies (Doroud Formation) in the lower, and carbonate facies (Ruteh Formation) in the upper half. Field studies and laboratory measurements resulted in recognition of 4 terrigenous and 13 carbonate facies in the succession. A siliciclastic shallow marine system was determined as depositional environment of the terrigenous facies. A homoclinal carbonate ramp, with scattered patch reefs, was determined as depositional environment of the carbonate facies. Dasycladacean green algae, ancestral red algae, hermatypic corals and bryozoans were the major bioconstructors of the ramp. The abundance of skeletal shoals respect to ooidal shoals in the ramp margin was high. The Permian rocks in eastern Alborz are dominated by mixed siliciclastic-carbonate facies (Ruteh Formation) in the lower, and siliciclastic facies (Nesen Formation) in the upper half. The studies resulted in recognition of 5 terrigenous and 6 carbonate facies in the succession. A mixed siliciclastic-carbonate shelf with high sediment influx was determined as depositional environment of the mixed siliciclastic-carbonate facies. Occurrence of the small patch reefs with high coral diversity in this mixed shelf indicates normal marine (hyposaline) condition. Upper terrigenous facies were deposited in fluvial-flood plain system. Difference in paleoclimate and tectonic activity of two sub-basins seems to be the major cause of the differences between the Permian facies in central and eastern Alborz.

  19. Coring and High-Resolution Imaging of the Permian-Triassic Boundary in Deltadalen, Svalbard

    NASA Astrophysics Data System (ADS)

    Planke, Sverre

    2016-04-01

    The Permian-Triassic extinction was likely triggered by the voluminous igneous activity of the Siberian Traps. There are, however, limited information available about the effects of the Siberian Traps volcanism in Permian to Triassic sedimentary successions outside Siberia. We drilled two boreholes across the Permian-Triassic boundary (PTB) in Deltadalen, Svalbard, in August 2014, to better document the extinction event and environmental changes in the sedimentary succession in this region. Even though the PTB event is studied in several outcrops to varying degree if scrutiny on Svalbard, a scientific core is important for understanding the details of the PTB event, as outcrops may not permit studies at the appropriate levels of resolution, exposure or confidence. The Deltadalen site was chosen as an optimal drilling location after field work in the Isfjorden area in 2013 and early 2014. The almost 100 m deep holes were fully cored and penetrated the Triassic Vikinghøgda Formation (about 85 m recovered) and the Permian Kapp Starostin Formation (about 15 m). The main lithologies include Permian chert-rich green glauconitic sandstones and Triassic mudstones. A 10 m thick sedimentary reference outcrop section across the PTB was further logged and sampled in a nearby river valley. A comprehensive core analysis program is now underway. High-resolution XRF, MST and hyperspectral core scanning has been completed along the entire core surface, while high-resolution CT scanning has been carried out for whole core sections. The DD-1 core has subsequently been split, photographed, described, and sampled for geochemical, micropaleontological, petrological and magnetic analyses. Almost 10 bentonite layers have furthermore been sampled for volcanological and geochronological studies. Our goal is that the cores will become an important future reference section of the PTB in Svalbard and the high-Arctic, and help constrain the extent of the regional effects of explosive volcanism

  20. Stratigraphic and palaeoenvironmental framework of the Early Permian sequence in the Salt Range, Pakistan

    NASA Astrophysics Data System (ADS)

    Ghazi, Shahid; Mountney, Nigel P.; Butt, Aftab Ahmad; Sharif, Sadaf

    2012-10-01

    The Early Permian Gondwana regime succession of the Nilawahan Group is exposed only in the Salt Range of Pakistan. After a prolonged episode of non-deposition that spanned much of the Palaeozoic, the 350 m thick predominantly clastic sequence of the Nilawahan Group records a late glacial and post-glacial episode in which a range of glacio-fluvial, marine and fluvial environments evolved and accumulated. The Early Permian succession of the Salt Range has been classified into four formations, which together indicates a changing climatic regime during the Early Permian in the Salt Range region. The lower-most, Tobra Formation unconformably overlies a Cambrian sequence and is composed of tillite, diamictite and fresh water facies, which contain a floral assemblage ( Gangamopteris and Glossopteris) that confirms an Asselian age. The Tobra Formation is overlain by marginal marine deposits of the Dandot Formation (Sakmarian), which contain an abundant brachiopods assemblage ( Eurydesma and Conularia). Accumulation of the Dandot Formation was terminated by a regional sea-level fall and a change to the deposition of the fluvial deposits of the Warchha Sandstone (Artinskian). The Warchha Sandstone was deposited by high sinuosity meandering, avulsion prone river with well developed floodplains. This episode of fluvial sedimentation was terminated by a widespread marine transgression, as represented by the abrupt upward transition to the overlying shallow marine Sardhai Formation (Kungurian). The Early Permian Gondwana sequence represented by the Nilawahan Group is capped by predominantly shallow shelf carbonate deposits of the Tethyan realm. The sedimentologic and stratigraphic relationship of these four lithostratigraphic units in the Salt Range reveals a complex stratigraphic history for the Early Permian, which is mainly controlled by eustatic sea-level change due to climatic variation associated with climatic amelioration at the end of the major Gondwana glacial episode

  1. An integrated biomarker, isotopic and palaeoenvironmental study through the Late Permian event at Lusitaniadalen, Spitsbergen

    NASA Astrophysics Data System (ADS)

    Nabbefeld, Birgit; Grice, Kliti; Twitchett, Richard J.; Summons, Roger E.; Hays, Lindsay; Böttcher, Michael E.; Asif, Muhammad

    2010-03-01

    The largest extinction of the Phanerozoic occurred near the Permian/Triassic (P/Tr) boundary some 252 Ma ago. Several scenarios and drivers have been proposed for this event. Here we report for the first time an integrated study comprising sedimentological data, biomarker distributions/abundances and selected stable carbon and hydrogen isotopes along with bulk isotopes (δ 34S pyrite, δ 13C carb, δ 13C org) for a Late Permian section from Lusitaniadalen, Spitsbergen, Norway. Sedimentological and geochemical data support a marine transgression and collapse of the marine ecosystem in the Late Permian. Strong evidence for waxing and waning of photic zone euxinia throughout the Late Permian is provided by Chlorobiaceae-derived biomarkers (including δ 13C data) and δ 34S pyrite, implying multiple phases of H 2S outgassing and potentially several pulses of extinction. A rapid decrease in abundance of various land-plant biomarkers prior to the marine collapse event indicates a dramatic decline of land-plants during the Late Permian and/or increasing distance from palaeoshoreline as a consequence of sea level rise. Changes in δD of selected biomarkers also suggest a change in source of organic matter (OM) or sea level rise. We also found biomarker and isotopic evidence for a phytoplanktonic bloom triggered by eutrophication as a consequence of the marine collapse. Compound specific isotope analyses (CSIA) of algal and land-plant-derived biomarkers, as well as δ 13C of carbonate and bulk OM provide strong evidence for synchronous changes in δ 13C of marine and atmospheric CO 2, attributed to a 13C-depleted source. The source could be associated with isotopically depleted methane released from the melting of gas clathrates and/or from respired OM, due to collapse of the marine ecosystem.

  2. The Cannery Formation--Devonian to Early Permian arc-marginal deposits within the Alexander Terrane, Southeastern Alaska

    USGS Publications Warehouse

    Karl, Susan M.; Layer, Paul W.; Harris, Anita G.; Haeussler, Peter J.; Murchey, Benita L.

    2011-01-01

    The Cannery Formation consists of green, red, and gray ribbon chert, siliceous siltstone, graywacke-chert turbidites, and volcaniclastic sandstone. Because it contains early Permian fossils at and near its type area in Cannery Cove, on Admiralty Island in southeastern Alaska, the formation was originally defined as a Permian stratigraphic unit. Similar rocks exposed in Windfall Harbor on Admiralty Island contain early Permian bryozoans and brachiopods, as well as Mississippian through Permian radiolarians. Black and green bedded chert with subordinate lenses of limestone, basalt, and graywacke near Kake on Kupreanof Island was initially correlated with the Cannery Formation on the basis of similar lithology but was later determined to contain Late Devonian conodonts. Permian conglomerate in Keku Strait contains chert cobbles inferred to be derived from the Cannery Formation that yielded Devonian and Mississippian radiolarians. On the basis of fossils recovered from a limestone lens near Kake and chert cobbles in the Keku Strait area, the age of the Cannery Formation was revised to Devonian and Mississippian, but this revision excludes rocks in the type locality, in addition to excluding bedded chert on Kupreanof Island east of Kake that contains radiolarians of Late Pennsylvanian and early Permian age. The black chert near Kake that yielded Late Devonian conodonts is nearly contemporaneous with black chert interbedded with limestone that also contains Late Devonian conodonts in the Saginaw Bay Formation on Kuiu Island. The chert cobbles in the conglomerate in Keku Strait may be derived from either the Cannery Formation or the Saginaw Bay Formation and need not restrict the age of the Cannery Formation, regardless of their source. The minimum age of the Cannery Formation on both Admiralty Island and Kupreanof Island is constrained by the stratigraphically overlying fossiliferous Pybus Formation, of late early and early late Permian age. Because bedded radiolarian

  3. Spatiotemporal variation in exhumation of the Crystallines in the NW-Himalaya, India: Constraints from fission track dating analysis

    NASA Astrophysics Data System (ADS)

    Patel, R. C.; Adlakha, Vikas; Lal, Nand; Singh, Paramjeet; Kumar, Y.

    2011-05-01

    During Himalayan orogeny, coeval thrusting along the Main Central/Munsiari Thrust (MCT/MT) and extension along the South Tibetan-Detachment System (STDS) are widely responsible for rapid exhumation of the Higher Himalayan Crystalline (HHC) zone. Apatite and zircon fission-track data along the Kaliganga and Darma valleys in the Kumaon Himalaya serve to document the shallow bedrock exhumation history of the HHC. Taking into account sample location within the HHC with respect to the MCT/MT, the apatite fission track (AFT) data-sets along the Darma (1.0 ± 0.1 to 2.8 ± 0.3 Ma) and Kaliganga (1.4 ± 0.2 to 2.4 ± 0.3 Ma) which are sharing same structural setting and rock types and being separated by 40 km, show very similar patterns of exhumation histories since Plio-Quaternary in the Kumaon Himalaya. Data sets along Darma and Kaliganga are very similar to data set of adjacent traverse (50 km away) along the Goriganga valley studied by Patel and Carter (2009). Whole data sets within the HHC in Kumaon Himalaya provide clear evidence for Plio-Quaternary tectonic activity along the Vaikrita Thrust (VT). Precipitation in this region exerts a strong influence on erosional surface processes. Fluvial erosional unloading along the Himalaya is focused on the high mountainous region of the HHC, where the orographic barrier forces out the maximum percentage of annual rainfall. FT cooling ages reveal coincidence between rapid erosion and exhumation that is focused in a ~ 25-30 km wide sector of the HHC, rather than covering the entire orogen. Similarity of AFT age pattern and exhumation rates along all three major traverses (Goriganga, Darma and Kaliganga) indicates that the region has been experiencing constant rate of crustal uplift and erosion since long time. Comparison of fission track ages from the Kumaon Himalaya with other segments of the NW-Himalaya shows spatiotemporal variation in exhumation. It is described due to the development of local structures such as dome

  4. Episodic exhumation of the Greater Himalayan Sequence since the Miocene constrained by fission track thermochronology in Nyalam, central Himalaya

    NASA Astrophysics Data System (ADS)

    Wang, An; Garver, John I.; Wang, Guocan; Smith, Jacqueline A.; Zhang, Kexin

    2010-12-01

    The Greater Himalayan Sequence (GHS), which makes up the core of the Himalayan orogen, has an uppermost tectonic contact defined by the South Tibetan Detachment System (STDS) and a lower tectonic contact defined by the Main Central Thrust (MCT). The GHS occurs as one of the most important tectostratigraphic units for deciphering processes related to tectonic and climatic exhumation across the orogen. Zircon and apatite fission track (ZFT, AFT) dating were carried out along a transect in Nyalam, central Himalaya in southern Tibet to constrain cooling driven by orogenic process since the middle Miocene. The hanging wall of the STDS yields an essentially unreset Jurassic ZFT age in the Jurassic strata. However, below the STDS within the GHS there is a clear and distinct thermal signal of cooling related to exhumation. In the footwall and within the GHS, the rocks have ZFT ages of middle Miocene to Pliocene, and AFT ages of late Miocene to Quaternary that get younger downward and away from the STDS. In combination with thermal structure modeling, a two-part episodic model, which is widely compatible with existing thermochronological data, is proposed for cooling and exhumation of the GHS since the middle Miocene: [1] middle Miocene; and [2] Pliocene to Quaternary (Recent). The middle Miocene cooling is suggested to have resulted from a rapid tectonic unroofing by down-to-the-north slip on the STDS. The tectonic exhumation was also recorded by several other thermochronological systems (e.g. biotite 40Ar/ 39Ar) with concordant middle Miocene cooling ages in different structural positions across the GHS. Post middle Miocene ZFT and AFT cooling ages in the lower part of the GHS suggest accelerated cooling by climate-enhanced erosional exhumation, which was initiated in the late Miocene to Pliocene and was dramatic in the Quaternary to Recent. Thermochronological data and modeling further imply that the present Himalayan topographic front may have been shaped essentially by

  5. Rheo-speedometer: constraining the exhumation rate using inclusion-host system with visco-elastic rheology

    NASA Astrophysics Data System (ADS)

    Zhong, Xin; Moulas, Evangelos; Tajcmanová, Lucie

    2017-04-01

    Constraining the time scale of rock exhumation is of great interest in geology. Geochronology and diffusion chronometry have been applied to obtain the exhumation duration by using the radioactive isotope decay and the diffusion kinetics of the major/minor elements, respectively. Here, we present an approach based on visco-elastic mechanical solutions applied to inclusion-host systems, e.g. quartz-in-garnet. During cooling and decompression, the difference in the thermal-elastic moduli between the inclusion and host forms a "pressure-vessel" that can generate a gigapascal level pressure jump at the inclusion-host interface as confirmed with the laser Raman spectroscopy (Enami et al., 2007; Sobolev et al., 2000). In order to main the mechanical equilibrium, a differential stress in the host is applied that results in viscous creep and pressure relaxation. The relaxed inclusion pressure can be quantitatively linked to the exhumation rate using the experimentally calibrated viscous flow law of the host mineral. The newly developed, so called, "rheo-speedometer" thus allows to constrain the exhumation rate by measuring the residual pressure with Raman spectroscopy. The rheo-speedometer is applied to four geological case studies of the Stak eclogite (Pakistan), Kokchetav mica schist (Kazakhstan), Udachnaya Kimberlite (Russia), and Sifnos blueschist (Greece). We demonstrate that: 1) the exhumation rate can be quantitatively constrained with certain confidence interval; 2) rocks undergoing either rapid magmatic ascent or slower metamorphic exhumation can be qualitatively distinguished; 3) the elastic limit can be reached for a quartz-in-garnet system below 550°C. References Enami, M., Nishiyama, T., Mouri, T., 2007. Laser Raman microspectrometry of metamorphic quartz: A simple method for comparison of metamorphic pressures. Am. Mineral. 92, 1303-1315. doi:10.2138/am.2007.2438 Sobolev, N.V., Fursenko, B.A., Goryainov, S.V., Shu, J., Hemley, R.J., Mao, H.K., Boyd, F

  6. Cooling and Exhumation of the Coastal Batholith in the Peruvian Andes (5-12°S)

    NASA Astrophysics Data System (ADS)

    Michalak, M.; Hall, S. R.; Farber, D.; Hourigan, J. K.; Audin, L.

    2014-12-01

    The South American Andes exhibit strong morphological differences along strike, shaped by a combination of tectonic forces and surface processes. In the central Peruvian Andes (~12°S) a major morphological transition occurs; to the north, the spines of the Western and Eastern Cordilleras come together into a relatively narrow configuration of high topography. In Southern Peru, the region of high topography widens, where the Western and Eastern Cordilleras flank the broad, Altiplano plateau. Despite this morphological change, the Mesozoic-early Cenozoic Coastal Batholith outcrops continuously from 0°-18°S along the western margin of the Peruvian Andes, emplaced along a trench-parallel marginal basin in the Mesozoic. The Coastal Batholith is an ideal geologic setting to investigate potential differences in rock exhumation and cooling histories along the western margin of Peru. While the cooling history of the southern Coastal Batholith has been previously used to estimate timing and magnitude of rock exhumation in Southern Peru, north of 12°S it is poorly constrained. We present 16 zircon and 7 apatite (U-Th)/He mean-ages from three sites, across seven degrees of latitude (5°S to 12°S). In general, ZHe and AHe ages capture two stages of cooling, Oligocene-to-mid-Miocene and mid-to-late Miocene, respectively. We model time-temperature histories of samples with paired AHe and ZHe ages using a Monte-Carlo inversion of HeFTy® (Ketcham, 2005); best fit time-temperature pathways show cooling rates ranging from ~2-24°C/my, where fastest cooling rates are generally observed in the mid-Miocene. To estimate exhumation rates, we apply a simple thermal model to account for nonuniform geothermal gradients expected in a trench-arc setting. Exhumation rates range from ~0.2mm/yr in the north, to 0.4-0.7mm/yr in the south, and rates increase orogenward, where mean elevation is highest. These results, particularly the predominance of Miocene ZHe and AHe data, and the younging

  7. Total exhumation across the Beichuan fault in the Longmen Shan (eastern Tibetan plateau, China): Constraints from petrology and thermobarometry

    NASA Astrophysics Data System (ADS)

    Airaghi, Laura; de Sigoyer, Julia; Lanari, Pierre; Guillot, Stéphane; Vidal, Olivier; Monié, Patrick; Sautter, Benjamin; Tan, Xibin

    2017-06-01

    The deep structure and deformation mechanisms of the Longmen Shan thrust belt (Sichuan, China), at the eastern border of the Tibetan plateau, were largely debated after the devastating Mw 7.9 Wenchuan earthquake (2008). Recent geophysical studies and field investigations have been focused on the active motion of the major Beichuan fault, which ruptured during the earthquake. However, the total exhumation across the fault still remains unclear. In the hanging wall of the Beichuan fault, the South China block is exhumed in the Pengguan massif. Close to the Beichuan fault, the rocks of the Pengguan massif underwent greenschist facies metamorphism associated with brittle-ductile deformation. No metamorphism is observed in the footwall of the fault. In this study, we characterize and date the metamorphic history recorded in the hanging wall of the Beichuan fault in order to constrain the depth and timing of exhumation of the rocks of the Pengguan massif along the fault. A high-resolution petrological approach involving chemical analyses and X-ray maps was used to analyze the micrometric metamorphic minerals. The P-T conditions of the greenschist facies metamorphic event were estimated by an inverse multi-equilibrium thermodynamic approach. The results, 280 ± 30 °C and 7 ± 1 kbar, suggest that the rocks of the Pengguan massif were exhumed from ca. 20 km depth. Our results underline the importance of the thrusting component in the long-term behavior of the Beichuan fault and provide a minimal depth at which the fault is rooted. In situ laser ablation 40Ar/39Ar dating of metamorphic white mica revealed that the greenschist overprint occurred at 135-140 Ma. The Pengguan massif was therefore partially thrusted along the Beichuan fault during the Lower Cretaceous, long before the Eocene-Miocene exhumation phase which is well-constrained by low-temperature thermochronology. Our results provide the first independent depth information for the exhumation history of the

  8. Rheological Heterogeneity Along the Deep Subduction Interface: Insights from Exhumed HP Metamorphic Rocks Exposed on Syros Island, Greece

    NASA Astrophysics Data System (ADS)

    Kotowski, A. J.; Behr, W. M.; Stockli, D. F.; Ashley, K. T.

    2015-12-01

    Rheological properties of subduction interface shear zones control several aspects of subduction zone dynamics, including shear tractions along the plate interface, rates and amounts of exhumation, and depths and styles of seismicity. We document the rheological properties of a deep subduction interface using exhumed eclogite and blueschist-facies rocks from Syros Island, Greece. These rocks were subducted to ~60 km depth during the Eocene, were exhumed part way along the top of the subducting slab, and were then exhumed to upper-crustal levels beneath Miocene detachment faults. Localization of strain during exhumation allowed prograde fabrics to be preserved. The PT conditions (400-550°C, 12-16kb) of these fabrics are comparable to conditions of episodic tremor and slow slip (ETS) observed in some modern subduction zones, including Cascadia. Two types of prograde fabrics were distinguished after analyzing macro-scale distributions of strain and microphysical mechanisms of creep in metamafic rocks. Type 1 fabrics contain eclogite pods boudinaged within a blueschist matrix. The eclogites show brittle deformation with cross-cutting veins containing high-pressure minerals. Deformation in matrix blueschists is accommodated by rigid rotation of amphibole and diffusion creep in plagioclase. Type 2 fabrics contain blueschists and eclogites that are isoclinally folded at similar wavelengths, thus are approximately isoviscous. Deformation is again accommodated by diffusion creep in blueschists, but by dislocation creep of omphacite in eclogites. These deformation types characterizing boudin-matrix and isoviscous rheologies of blueschist-eclogite assemblages appear to reflect varying amounts of finite strain, but work is in progress to determine whether they also record different PT conditions. The transition from Type 1 to 2 fabrics represents a significant change in bulk viscosity and seismic anisotropy, and may correspond to a transition from ETS-type behavior

  9. Thermochronological constraints on the multiphase exhumation history of the Ivrea-Verbano Zone of the Southern Alps

    NASA Astrophysics Data System (ADS)

    Wolff, R.; Dunkl, I.; Kiesselbach, G.; Wemmer, K.; Siegesmund, S.

    2012-12-01

    The Ivrea-Verbano Zone of the western Southern Alps (NW Italy) exposes a well-preserved tilted section across the lower continental crust, making it a key region for studying deep crustal and exhumation processes. This paper refines the cooling and exhumation history of the Ivrea-Verbano Zone using K/Ar dating of mica and illite-rich fault gouges as well as zircon fission track and (U-Th)/He thermochronology. The adjacent Strona-Ceneri Zone, Sesia-Lanzo Zone and Lower Penninic nappes are included in the study to derive a broader picture of the low-temperature history of the area. In the Strona profile of the Ivrea-Verbano unit the biotite K/Ar, zircon fission track and (U-Th)/He geochronometers show well preserved, but unusually wide partial retention zones. The youngest ages, representing the formerly deepest position, are situated along the Insubric Line. The main foliation of the Ivrea-Verbano Zone is vertical. The exhumation of the Ivrea-Verbano Zone, which section has a horizontal position on the surface now - took place in three steps. During Jurassic time the Ivrea-Verbano Zone was exhumed to a shallow to mid-crustal position by continental-scale extension. In this displacement the Pogallo Line probably played a dominant role. The studied section occupied an oblique position with a calculated angle of ca. 15 to 23° in the Jurassic. Later the Ivrea-Verbano Zone experienced a minor cooling event in the Late Eocene (~ 38 Ma zircon fission track ages) that was probably related to thrusting and erosion. The final exhumation towards the surface took place in the mid-Miocene as documented by the ca. 14 Ma zircon (U-Th)/He ages and a 12.8 Ma K/Ar fault gouge age. The magnitude and the high rate of final exhumation suggest orogen-parallel extension as a driving force, which is widespread in the Alps in the Lower to Middle Miocene and is most probably connected to orogenic collapse.

  10. How does the distribution of orographic precipitation guide exhumation patterns along the Southern Himalayan front, NW India?

    NASA Astrophysics Data System (ADS)

    Thiede, R. C.; Bookhagen, B.; Strecker, M. R.; Arrowsmith, J.; Sobel, E. R.; McWilliams, M.

    2003-12-01

    A strong climatic contrast exist across the Himalaya, whereas the Southern Himalayan Front (SHF) is affected by strong monsoonal precipitation, the internal region between the High Himalaya and the Indus-Tsangpo suture zone to the north is dry. When during the Indian summer monsoon the humid airflow has to cross the Himalaya, it is controlled and funneled by the topography. This result in asymmetric precipitation distribution concentrated in elevations of 2000 to 4000 m along the southern termination of the High Himalaya and provides a high seasonal fluvial runoff, which enables an effective sediment evacuation out of the range. The High Himalaya is actively deforming as indicated by young cooling ages, micro-seismicity, and geodetic data. In the area of the Sutlej River (NW-India) the deeper high-grade metamorphic rocks of High Himayalan and Lesser Himalayan Crystalline are being exhumed as an extruding wedge. Active deformation of the orogen coincides with high monsoonal precipitation, pronounced relief contrasts, steep river gradients and slope angles that predispose these rocks to effective mass removal. But how and if this inhomogeneous distribution of precipitation affects mountain building processes of the Himalayan range is still controversial. New young apatite fission track (AFT) (<1-5 Ma; 30 dates) and 40Ar/39Ar (20 dates) ages from the greater Sutlej area document rapid exhumation of high-grade metamorphic Lesser and Higher Himalayan Crystalline units. Two AFT sample transects are sampled in the range between 1.5 and 4.5 km in elevation along tributaries perpendicular to the Sutlej River. The AFT samples yield ages between <1-4 Ma and correlate with elevation. Compiled regional distribution of AFT ages document a ˜50 km long sector where the Sutlej River is crossing the southern termination of the High Himalaya (main orographic barrier), and AFT samples provide young cooling ages of ˜1 Ma. Assuming uniform long-term steady-state erosion and exhumation

  11. Thermal evolution and exhumation of deep-level batholithic exposures, southernmost Sierra Nevada, California

    USGS Publications Warehouse

    Saleeby, J.; Farley, K.A.; Kistler, R.W.; Fleck, R.J.

    2007-01-01

    The Tehachapi complex lies at the southern end of the Sierra Nevada batholith adjacent to the Neogene-Quaternary Garlock fault. The complex is composed principally of high-pressure (8-10 kbar) Cretaceous batholithic rocks, and it represents the deepest exposed levels of a continuous oblique crustal section through the southern Sierra Nevada batholith. Over the southern ???100 km of this section, structural/petrologic continuity and geochronological data indicate that ???35 km of felsic to intermediate-composition crust was generated by copious arc magmatism primarily between 105 and 99 Ma. In the Tehachapi complex, these batholithic rocks intrude and are bounded to the west by similar-composition gneissic-textured high-pressure batholithic rocks emplaced at ca. 115-110 Ma. This lower crustal complex is bounded below by a regional thrust system, which in Late Cretaceous time tectonically eroded the underlying mantle lithosphere, and in series displaced and underplated the Rand Schist subduction assemblage by low-angle slip from the outboard Franciscan trench. Geophysical and mantle xenolith studies indicate that the remnants of this shallow subduction thrust descend northward through the crust and into the mantle, leaving the mantle lithosphere intact beneath the greater Sierra Nevada batholith. This north-dipping regional structure records an inflection in the Farallon plate, which was segmented into a shallow subduc-tion trajectory to the south and a normal steeper trajectory to the north. We combine new and published data from a broad spectrum of thermochronom-eters that together form a coherent data array constraining the thermal evolution of the complex. Integration of these data with published thermobarometric and petro-genetic data also constrains the tectonically driven decompression and exhumation history of the complex. The timing of arc magmatic construction of the complex, as denoted above, is resolved by a large body of U/Pb zircon ages. High

  12. Kinematics of syn- and post-exhumational shear zones at Lago di Cignana (Western Alps, Italy): constraints on the exhumation of Zermatt-Saas (ultra)high-pressure rocks and deformation along the Combin Fault and Dent Blanche Basal Thrust

    NASA Astrophysics Data System (ADS)

    Kirst, Frederik; Leiss, Bernd

    2017-01-01

    Kinematic analyses of shear zones at Lago di Cignana in the Italian Western Alps were used to constrain the structural evolution of units from the Piemont-Ligurian oceanic realm (Zermatt-Saas and Combin zones) and the Adriatic continental margin (Dent Blanche nappe) during Palaeogene syn- and post-exhumational deformation. Exhumation of Zermatt-Saas (U)HP rocks to approximately lower crustal levels at ca. 39 Ma occurred during normal-sense top-(S)E shearing under epidote-amphibolite-facies conditions. Juxtaposition with the overlying Combin zone along the Combin Fault at mid-crustal levels occurred during greenschist-facies normal-sense top-SE shearing at ca. 38 Ma. The scarcity of top-SE kinematic indicators in the hanging wall of the Combin Fault probably resulted from strain localization along the uppermost Zermatt-Saas zone and obliteration by subsequent deformation. A phase of dominant pure shear deformation around 35 Ma affected units in the direct footwall and hanging wall of the Combin Fault. It is interpreted to reflect NW-SE crustal elongation during updoming of the nappe stack as a result of underthrusting of European continental margin units and the onset of continental collision. This phase was partly accompanied and followed by ductile bulk top-NW shearing, especially at higher structural levels, which transitioned into semi-ductile to brittle normal-sense top-NW deformation due to Vanzone phase folding from ca. 32 Ma onwards. Our structural observations suggest that syn-exhumational deformation is partly preserved within units and shear zones exposed at Lago di Cignana but also that the Combin Fault and Dent Blanche Basal Thrust experienced significant post-exhumational deformation reworking and overprinting earlier structures.

  13. Exhumation of the Source Area of the Cameros Basin revealed by detrital zircon fission track analysis

    NASA Astrophysics Data System (ADS)

    Del Rio, Pedro; Barbero, Luis; Casas-Sainz, Antonio

    2010-05-01

    The Cameros Basin (NW of the Iberian Range, NE of the Iberian Peninsula) was an intracontinental basin during Mesozoic times, which was inverted during Alpine compression. Its formation was due to a main rifting stage during Thithonian-Albian times related with an extensional period due to the opening of the Bay of Biscay. This extensional period is characterized by high subsidence and the filling of the basin with up to 8 km of continental sediments. A very low-grade metamorphic event is recorded during Albian times reaching maximum temperatures of ~350°C. Although the Cameros Basin has been studied for several decades from different geological points of view, the source area for the Cameros Basin still remains unknown. Previous studies have given some information about the possible location and nature of the source area: (1) Paleocurrent data indicate that the main source area was located SW of the basin (Salas et al., 2001); (2) Calculated chemical alteration indices show no intense chemical weathering of the source area and no significant variations along the stratigraphic section (Mata et al., 2000); (3) mineralogical studies trace elements ratios indicate that the material source should be acid igneous rock or any rock derived from them (Mata et al., 2000). In this work we present new detrital zircon fission track (ZFT) data from samples collected in different stratigraphic units of the Cameros Basin. Five samples were not reset for ZFT during burial and the metamorphic episode that occurred during Albian times. Those samples have a thermal signal previous to their deposition in the Cameros Basin and reveal the cooling history of the source area. Youngest peak ages for ZFT are in a range of 149 to 214 Ma. Lag-time values for those samples show a break-in-slope at ~130 Ma. Older samples show a decrease in lag-time values (from 55 myr to 20 myr) which implies an increase in exhumation rate between 145 and 135 Ma coinciding with the beginning of the rifting

  14. Geochronological Constraints on the Exhumation and Emplacement of Subcontinental Lithospheric Mantle Peridotites in the Westernmost Mediterranean

    NASA Astrophysics Data System (ADS)

    Garrido, Carlos J.; Hidas, Károly; Marchesi, Claudio; Varas-Reus, María Isabel; Booth-Rea, Guillermo

    2017-04-01

    Exhumation of subcontinental mantle peridotite in the Western Mediterranean has been attributed to different tectonic processes including pure extension, transpression, or alternating contractive and extensional processes related with continental subduction followed by extension, before final their contractive intracrustal emplacement. Any model trying to explain the exhumation and emplacement of subcontinental lithospheric mantle peridotites in the westernmost Mediterranean should take into account the available geochronological constraints, as well as the petrological and geochemical processes that lead to internal tectono-magmatic zoning so characteristic of the Betic and Rif orogenic peridotites. Different studies have suggested a Hercynian, Cenozoic-Mesozoic or an Alpine age for the late tectono-magmatic evolution and intra-crustal emplacement of Betic-Rif peridotites. The pervasive presence of Mesozoic U-Pb zircon ages in Ronda UHP and HP garnet pyroxenites does not support a Hercynian age for the intracrustal emplacement o