End-Guadalupian extinction of larger fusulinids in central Iran and implications for the global biotic crisis

摘要

The end-Guadalupian (Capitanian) biotic crisis was less intense than its end-Permian counterpart but highly selective against certain groups of tropical organisms, such as rugose corals and keriothecal-walled fusulinid foraminifera. The causes of this event remain debated, in part due to apparent disagreement among stratigraphic sections in the timing of taxonomic losses. In order to further constrain the timing of extinction and assess the broader pattern of change in benthic marine ecosystems across the Guadalupian/Lopingian boundary (GLB), here we report the stratigraphic occurrence patterns of the large, keriothecal-walled fusulinid foraminifera as well as associated skeletal grains in the Abadeh section, central Iran, which contains a relatively complete record through the GLB interval. The last keriothecal-walled fusulinid occurs within the upper Wordian at Abadeh whereas smaller fusulinids continue to occur below and above the Guadalupian/Lopingian boundary (GLB). A lithologic change from carbonates toward chert and shale within the section suggests that the local disappearance of the keriothecal fusulinids prior to the GLB reflects a facies control rather than global extinction long prior to the GLB. Re-examination of the last occurrences of keriothecal-walled fusulinids in well-studied sections of South China, Japan, NE Thailand, and Transcaucasia reveals that facies change to organic-rich sediments can explain the local disappearance of these species prior to the GLB in both Japan and NE Thailand. Apparent diachroneity of extinction in this group appears best interpreted to reflect local facies effects rather than a protracted extinction event. Global, warming-induced failure of associations between fusulinids and photosymbionts following Emeishan volcanism is the scenario most consistent with available data.