Early and Middle Triassic trends in diversity, evenness, and size of foraminifers on a carbonate platform in south China: Implications for tempo and mode of biotic recovery from the end-Permian mass extinction
Payne J.L.,Stanford University |
Summers M.,Stanford University |
Summers M.,University of California at San Diego |
Rego B.L.,Stanford University |
And 5 more authors.
Paleobiology | Year: 2011
Delayed biotic recovery from the end-Permian mass extinction has long been interpreted to result from environmental inhibition. Recently, evidence of more rapid recovery has begun to emerge, suggesting the role of environmental inhibition was previously overestimated. However, there have been few high-resolution taxonomic and ecological studies spanning the full Early and Middle Triassic recovery interval, leaving the precise pattern of recovery and underlying mechanisms poorly constrained. In this study, we document Early and Middle Triassic trends in taxonomic diversity, assemblage evenness, and size distribution of benthic foraminifers on an exceptionally exposed carbonate platform in south China. We observe gradual increases in all metrics through Early Triassic and earliest Middle Triassic time, with stable values reached early in the Anisian. There is little support in our data set for a substantial Early Triassic lag interval during the recovery of foraminifers or for a stepwise recovery pattern. The recovery pattern of foraminifers on the GBG corresponds well with available global data for this taxon and appears to parallel that of many benthic invertebrate clades. Early Triassic diversity increase in foraminifers was more gradual than in ammonoids and conodonts. However, foraminifers continued to increase in diversity, size, and evenness into Middle Triassic time, whereas diversity of ammonoids and conodonts declined. These contrasts suggest decoupling of recovery between benthic and pelagic environments; it is unclear whether these discrepancies reflect inherent contrasts in their evolutionary dynamics or the differential impact of Early Triassic ocean anoxia or associated environmental parameters on benthic ecosystems. © 2011 The Paleontological Society. All rights reserved.
Zhang X.-J.,Guizhou Geological Survey |
Yang S.-F.,Guizhou Geological Survey |
Zhang H.,Geological Party 113 |
Li J.-B.,Guizhou Geological Survey
Wutan Huatan Jisuan Jishu | Year: 2015
Guizhou iron(rare earth) polymetallic deposit resources reserves is rich. However, the exploration has certain challenging because of its special geological condition. In this place, developing experimental study of geophysical methods to explore iron (rare earth) polymetallic deposit, it has an important guiding significance for the future exploration work. This paper briefly introduces the AMT working methods, as well as the geological and geophysical characteristics of Guizhou Weining Changgou area. The application of the exploration iron(rare earth) polymetallic deposit using AMT is discussed in Changgou area. Through the comprehensive inference and interpretation on resistivity section diagram, it has divided between the Permian Wuanwei group, emei mountain basalt group strata interface. It has circled the ore bearing favorable position. The drilling re-sults showing, it has obtained better prospecting results.
Zhang J.,Guizhou Geological Survey |
Zhang J.,Chinese Academy of science |
Dai C.,Guizhou Geological Survey |
Huang Z.,Chinese Academy of science |
And 3 more authors.
Ore Geology Reviews | Year: 2015
Gejiu is geographically located near Gejiu city, SW China. It is one of the largest tin-polymetallic districts in the world and contains approximately 3milliontons (Mt) of Sn and smaller quantities of Cu, Pb, and Zn. The deposit primarily yields three different types of ore: skarn-hosted ore, basalt-hosted stratiform ore, and carbonate-hosted stratiform ore. Kafang is one of the primary ore deposits in the Gejiu district and is an unusual occurrence hosted in basaltic rocks. Genetic models of the Kafang deposit suggest that it is related either to Anisian (Lower stage of Middle Triassic) Gejiu basalts or to Cretaceous Gejiu granite. In this study, we performed zircon SIMS U-Pb dating, major and trace element analyses, and Sr-Nd-Pb isotopic analyses for the Gejiu basalts and S isotopic analyses for stratiform Cu ore. Our results and previous studies are used to interpret the petrogenesis of the Gejiu basalts and the origin of the basalt-hosted stratiform Cu deposit. The SIMS zircon U-Pb analyses of the Gejiu basalts yield an age of 244.4Ma. The trace element ratios of the Gejiu basalts are similar to those of ocean island basalt and have positive εNd(t) values (ranging from 0.6 to 2.5) and uniform (87Sr/86Sr)i values (ranging from 0.70424 to 0.70488). These ratios are close to those of the Permian Emeishan flood basalt. Thus, the Gejiu basalts may represent coeval volcanisms within the plate involving remelting of the Emeishan plume head through a stress relaxation process after the main plume event. The Pb and S isotopic compositions of the Gejiu basalts and the stratiform Cu ores indicate that the source of Cu and S is primarily derived from the Gejiu basalts. However, the age of sulfide mineralization (84.2-79.6Ma) and the age of hydrothermal alteration (85.5-81.9Ma) are temporally consistent with the age of the Cretaceous granite emplacement (85.5-83.3Ma). From a petrological and geochemical study, we determine that the Gejiu basalts may have been subjected to pervasive granite-related hydrothermal alteration during the emplacement of granite. These processes increase the K and Mg contents of basalt and probably caused the formation of the Cu ores. Thus, the Kafang stratiform Cu deposit can be considered as a granite-related hydrothermal deposit. © 2015 Elsevier B.V.
An integrated biostratigraphy (conodonts and foraminifers) and chronostratigraphy (paleomagnetic reversals, magnetic susceptibility, elemental chemistry, carbon isotopes and geochronology) for the Permian-Upper Triassic strata of Guandao section, Nanpanjiang Basin, south China
Lehrmann D.J.,Trinity University |
Stepchinski L.,Trinity University |
Altiner D.,Middle East Technical University |
Orchard M.J.,Geological Survey of Canada |
And 16 more authors.
Journal of Asian Earth Sciences | Year: 2015
The chronostratigraphy of Guandao section has served as the foundation for numerous studies of the end-Permian extinction and biotic recovery in south China. Guandao section is continuous from the Permian-Triassic boundary to the Upper Triassic.Conodonts enable broad delineation of stage and substage boundaries and calibration of foraminifer biostratigraphy as follows. Changhsingian-Griesbachian: first Hindeodus parvus, and first appearance of foraminifers Postcladella kalhori and Earlandia sp. Griesbachian-Dienerian: first Neospathodus dieneri, and last appearance of foraminifer P. grandis. Dienerian-Smithian: first Novispathodus waageni and late Dienerian first appearance of foraminifer Hoyenella ex gr. sinensis. Smithian-Spathian: first Nv? crassatus and last appearance of foraminifers Arenovidalina n. sp. and Glomospirella cf. vulgaris. Spathian-Aegean: first Chiosella timorensis and first appearance of foraminifer Meandrospira dinarica. Aegean-Bithynian: first Nicoraella germanica and first appearance of foraminifer Pilammina densa. Bithynian-Pelsonian: after last Neogondolella regalis, prior to first Paragondolella bulgarica and first appearance of foraminifer Aulotortus eotriasicus. Pelsonian-Illyrian: first Pg. excelsa and last appearance of foraminifers Meandrospira? deformata and Pilamminella grandis. Illyrian-Fassanian: first Budurovignathus truempyi, and first appearance of foraminifers Abriolina mediterranea and Paleolituonella meridionalis. Fassanian-Longobardian: first Bv. mungoensis and last appearance of foraminifer A. mediterranea. Longobardian-Cordevolian: first Quadralella polygnathiformis and last appearance of foraminifers Turriglomina mesotriasica and Endotriadella wirzi.The section contains primary magnetic signature with frequent reversals occurring around the Permian-Triassic, Olenekian-Anisian, and Anisian-Ladinian boundaries. Predominantly normal polarity occurs in the lower Smithian, Bithynian, and Longobardian-Cordevolian. Predominantly reversed polarity occurs in the upper Griesbachian, Induan-Olenekian, Pelsonian and lower Illyrian. Reversals match well with the GPTS. Large amplitude carbon isotope excursions, attaining values as low as -2.9‰ δ13C and high as +5.7‰ δ13C, characterize the Lower Triassic and basal Anisian. Values stabilize around +2‰ δ13C through the Anisian to Carnian. Similar signatures have been reported globally. Magnetic susceptibility and synthetic gamma ray logs show large fluctuations in the Lower Triassic and an overall decline in magnitude of fluctuation through the Middle and Upper Triassic. The largest spikes in magnetic susceptibility and gamma ray, indicating greater terrestrial lithogenic flux, correspond to positive δ13C excursions. High precision U-Pb analysis of zircons from volcanic ash beds provide a robust age of 247.28±0.12Ma for the Olenekian-Anisian boundary at Guandao and an age of 251.985±0.097Ma for the Permian-Triassic boundary at Taiping. Together, the new U-Pb geochronology from the Guandao and Taiping sections suggest an estimated duration of 4.71±0.15Ma for the Early Triassic Epoch. © 2015 Elsevier Ltd.
Fu H.,Hubei University |
Ma D.,Guizhou Geological Survey |
Wu T.,Guizhou Geological Survey |
Xiong X.,Guizhou Geological Survey |
Zeng Y.,Guizhou Geological Survey
Geological Bulletin of China | Year: 2015
Pollen fossils such as Classopollis, Annulispora, and Chasmatosporites as well as abundant dinoflagellates like Systematophora cf., and Ctenidodinium, which indicate Middle-Upper Jurassic strata with a typical significance, were found in the formerly-regarded Middle Permian Xiala Formation within the Tarezeng area, Tibet. The findings show that at least part of Middle-Upper Jurassic strata has not been identified previously in the Xiala Formation. The assemblage characteristics of the rock, basic sequence, and fossil comparison show that this set of strata belongs to the Ringtor Formation. The determination of this formation provides basic information for the correlation of regional strata, the establishment of the stratigraphic framework and the investigation of the evolution of the Mesozoic basin. © 2015, Science Press. All right reserved.