Different fossil brachiopod skeletal microstructure of different information on carbon and oxygen isotope contents  

作　　者：Xinqing Li Guojiang Wan Ronggui Huang 

机构地区：[1]Chinese Acad Sci, Inst Geochem, State Key Lab Environm Geochem, Guiyang 550002, Peoples R China [2]Chinese Acad Sci, Lanzhou Inst Glaciol & Geocryol, Lab Ice Core & Cold Reg Environm, Lanzhou 730000, Peoples R China

出　　处：《Chinese Science Bulletin》1999年第22期2087-2094,共8页

摘　　要：Whether there is isotope fractionation caused by metabolism (vital effect) of bra-chiopods in geologic time with their shells’ δ18O and δ13C has been studied intensively in the field of carbonate isotope geochemistry in the last decade. The approach to dealing with the problem is by comparing isotopic compositions between different fossil brachiopods with their secondary shells which usually consist of two kinds of layers: prismatic layer composed of pris-Whether there is isotope fractionation caused by metabolism (vital effect) of brachiopods in geologic time with their shells’ δ18O and δ13C has been studied intensively in the field of carbonate isotope geochemistry in the last decade. The approach to dealing with the problem is by comparing isotopic compositions between different fossil brachiopods with their secondary shells which usually consist of two kinds of layers: prismatic layer composed of prismatic low-Mg calcite crystals, and fibrous layer comprising fibrous ones. The isotopic compositions of the two secondary layers have been investigated by comparison of carbon and oxygen isotopic compositions between five genera of Atrypidae collected from Givetian, Middle Devonian in Longmenshan, Sichuan Province, China. Due to different microstructures of the two secondary layers, their abilities to prevent from being altered by diagenesis are also different, thus in their state of preservation. The fibrous layer is more susceptible to the diagenetic alternation than the prismatic one in the way of microfracture filling between fibrous crystals in the elongated direction. Consequently, the isotopic compositions of the fibrous layer are systematically lower than those of the prismatic layer in their δ18O and δ13C by (0.53 ± 0.08)‰ and (0.12 ±0. 04)‰, respectively. This suggests that further studies of vital effects with brachiopod in geological times by comparison of isotopic compositions in the secondary shell take into consideration of the different states of preservation between the fibrous and the prismatic layer.

关 键 词：FOSSIL BRACHIOPOD geochemistry stable isotope Longmenshan. 

分 类 号：Q915.816[天文地球—古生物学与地层学]