科研之友
微信
新浪微博
Facebook
分享链接
摘要
Bone is susceptible to early diagenesis, and its carbon and oxygen isotopic compositions have been suggested to reflect conditions in the soil environment and shallow subsurface during fossilization. This implies open-system recrystallization involving mass exchange of carbon and oxygen among bioapatite, soil water, and DIC. Such recrystallization would also redistribute isotopic clumping (including C-13-O-18 bonds), leading to the possibility that the carbonate clumped isotope compositions of fossil bone record ground temperature during early diagenesis. We assess this possibility by studying Quaternary mammalian fossil bone from subtropical to polar latitudes: if recrystallization is early and pervasive, clumped isotope derived temperatures, T(Delta(47)), should closely mirror latitudinal gradients in ground temperature. Excluding results from a mummified specimen yielding T(Delta(47)) = 38 degrees C (that is, indistinguishable from mammalian body temperature), we find that T(Delta(47)) values are intermediate between mammalian body temperature and ground temperature, suggesting partial recrystallization of bone carbonate. XRD analyses show that the nature and extent of diagenesis varies among the samples and does not relate in a straightforward manner to T(Delta(47)). No clear correlation exists between T(Delta(47)) and mean annual temperature or mean warm season temperature. Furthermore, bone tends to retain the O-18-enriched signature of body water, suggesting incomplete oxygen isotope exchange with meteoric waters. %26lt;br%26gt;Incomplete carbon and oxygen isotope exchange between bone carbonate and soil waters is also indicated for a set of late Miocene bone-enamel pairs from a sequence of stacked paleosols in northern China. Analysis of bone as old as Early Cretaceous shows that bone carbonate is susceptible to later diagenesis at elevated burial temperatures, although T(Delta(47)) does not closely conform to maximum burial temperature, again suggesting partial recrystallization, or recrystallization during different stages of the burial and exhumation circuit. These results show that carbon, oxygen, and %26apos;clumped%26apos; isotopes in fossil bone are capable of recording aspects of early diagenesis and the subsequent burial and exhumation history, but that distinguishing among different effects is challenging. However, clumped isotopes in bone can provide useful directional constraints on past temperatures. For example, T(Delta(47)) values higher than body temperature necessarily place lower limits on maximum burial temperatures, and those lower than body temperature place upper limits on minimum fossilization temperatures.
- 出版日期2014-9-1
