期刊文献+

Palaeogeographic variation in the Permian-Triassic boundary microbialites:A discussion of microbial and ocean process esafter the end-Permian mass extinction 被引量:2

Palaeogeographic variation in the Permian——Triassic boundary microbialites:A discussion of microbial and ocean processes after the end-Permian mass extinction
原文传递
导出
摘要 Shallow marine carbonate sediments that formed after the end-Permian mass extinction are rich in a thin(maximum ca.15 m) deposit of microbialites.Microbial communities that constructed the microbialites have geographic variability of composition,broadly divisible into two groups:1) eastern Tethys sites are calcimicrobe-dominated(appearing as thrombolites in the field),with rare occurrence of sedimentconstructed microbialites and uncommon cements either within microbial structure or as inorganic precipitates,2) other Tethys sites are sediment-dominated structures forming stromatolites and thrombolites,composed of micrites and cements,with some inorganic precipitates.These other Tethys locations include western and central Tethys sites but their palaeogeographic positions depend on the accuracy of continental reconstructions,of which there are several opinions.In contrast to geographic variation of microbialites,the conodont Hindeodus parvus,which appeared after the extinction and defines the base of the Triassic,is widespread,indicating easy lateral migration throughout Tethys.Conodont animals were active nekton,although being small animals were presumably at least partly carried by water currents,implying active Tethyan surface water circulation after the extinction event.Post-extinction ammonoid taxa,presumed active swimmers,show poor evidence of a wide distribution in the Griesbachian beds immediately after the extinction,but are more cosmopolitan higher up,in the Dienerian strata in Tethys.Other shelly fossils also have poorly defined distributions after the extinction,but ostracods show some wider distribution suggesting migration was possible after the extinction.Therefore there is a contrast between the geographic differences of microbialites and some shelly fossils.Determining the cause of geographic variation of post-extinction microbialites is problematic and may include one or more of the following possibilities:1) because calcifying microbial organisms that create calcimicrobes were benthic,they may have lacked planktonic stages that would have allowed migration,2)eastern Tethyan seas were possibly more saturated with respect to calcium carbonates and microbes,so microbes there were possibly more able to calcify,3) significant reduction of Tethyan ocean circulation,perhaps by large-scale upwelling disrupting ocean surface circulation,may have limited lateral migration of benthic microbial communities but did not prevent migration of other organisms,and 4) microbes may have been subject to local environmental controls,the mechanisms of which have not yet been recognized in the facies.The difficulty of distinguishing between these possibilities(and maybe others not identified) demonstrates that there is a lot still to learn about the post-extinction microbialites and their controls. Shallow marine carbonate sediments that formed after the end-Permian mass extinction are rich in a thin(maximum ca.15 m) deposit of microbialites.Microbial communities that constructed the microbialites have geographic variability of composition,broadly divisible into two groups:1) eastern Tethys sites are calcimicrobe-dominated(appearing as thrombolites in the field),with rare occurrence of sedimentconstructed microbialites and uncommon cements either within microbial structure or as inorganic precipitates,2) other Tethys sites are sediment-dominated structures forming stromatolites and thrombolites,composed of micrites and cements,with some inorganic precipitates.These other Tethys locations include western and central Tethys sites but their palaeogeographic positions depend on the accuracy of continental reconstructions,of which there are several opinions.In contrast to geographic variation of microbialites,the conodont Hindeodus parvus,which appeared after the extinction and defines the base of the Triassic,is widespread,indicating easy lateral migration throughout Tethys.Conodont animals were active nekton,although being small animals were presumably at least partly carried by water currents,implying active Tethyan surface water circulation after the extinction event.Post-extinction ammonoid taxa,presumed active swimmers,show poor evidence of a wide distribution in the Griesbachian beds immediately after the extinction,but are more cosmopolitan higher up,in the Dienerian strata in Tethys.Other shelly fossils also have poorly defined distributions after the extinction,but ostracods show some wider distribution suggesting migration was possible after the extinction.Therefore there is a contrast between the geographic differences of microbialites and some shelly fossils.Determining the cause of geographic variation of post-extinction microbialites is problematic and may include one or more of the following possibilities:1) because calcifying microbial organisms that create calcimicrobes were benthic,they may have lacked planktonic stages that would have allowed migration,2)eastern Tethyan seas were possibly more saturated with respect to calcium carbonates and microbes,so microbes there were possibly more able to calcify,3) significant reduction of Tethyan ocean circulation,perhaps by large-scale upwelling disrupting ocean surface circulation,may have limited lateral migration of benthic microbial communities but did not prevent migration of other organisms,and 4) microbes may have been subject to local environmental controls,the mechanisms of which have not yet been recognized in the facies.The difficulty of distinguishing between these possibilities(and maybe others not identified) demonstrates that there is a lot still to learn about the post-extinction microbialites and their controls.
出处 《Journal of Palaeogeography》 SCIE CSCD 2017年第2期97-107,共11页 古地理学报(英文版)
关键词 STROMATOLITE Thrombolite MICROBIALITE Permian-Triassic boundary CONODONTS TETHYS Mass extinction Stromatolite Thrombolite Microbialite Permian-Triassic boundary Conodonts Tethys Mass extinction
  • 相关文献

同被引文献44

引证文献2

相关作者

内容加载中请稍等...

相关机构

内容加载中请稍等...

相关主题

内容加载中请稍等...

浏览历史

内容加载中请稍等...
;
使用帮助 返回顶部