Stable isotopic signatures of the modern land snail Eremina desertorum from a low-latitude (hot) dry desert-A study from the Petrified Forest, New Cairo, Egypt

摘要

This study was conducted on recent desert samples-including (1) soils, (2) plants, (3) the shell, and (4) organic matter from modern specimens of the land snail Eremina desertorum-which were collected at several altitudes (316-360m above sea level) from a site in the New Cairo Petrified Forest. The soils and shelle(E.desertorum) were analyzed for carbonate composition and isotopic composition (delta O-18, delta C-13). The plants and organic matter(E.desertorum)were analyzed for organic carbon content and delta C-13. The soil carbonate, consisting of calcite plus minor dolomite, has delta O-18 values from -3.19 to -1.78%. and delta C-13 values -1.79 to -0.27%.; covariance between the two values accords with arid climatic conditions. The local plants include C3 and C4 types, with the latter being dominant. Each type has distinctive bulk organic carbon delta C-13 values: -26.51 to -25.36%. for C3-type, and -13.74 to -12.43%. for C4-type plants. The carbonate of the shells(E.desertorum) is composed of aragonite plus minor calcite, with relatively homogenous isotopic compositions (delta O-18(mean) = -0.28 +/- 0.22 parts per thousand; delta C-13(mean) = -4.46 +/- 0.58 parts per thousand). Most of the 6180 values (based on a model for oxygen isotope fractionation in an aragonite-water system) are consistent with evaporated water signatures. The organic matter (E.desertorum) varies only slightly in bulk organic carbon delta C-13 values (-21.78 +/- 1.20%.) and these values suggest that the snail consumed more of 0-type than C4-type plants. The overall offset in delta C-13 values (-1732%.) observed between shelle(E.desertorum) carbonate and organic matters(E.desertorum) exceeds the value expected for vegetation input, and implies that 30% of carbon in the shell(E.desertorum) carbonate comes from the consumption of limestone material. (C) 2014 Elsevier GmbH. All rights reserved.