Carbon isotope chemostratigraphy of the Xiagou formation of Gansu Province, northwestern China

Date
2014
Authors
Milder, Timothy
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Abstract

Over the past decade, many significant paleontological finds have been unearthed from formations in Central Asia including northwestern China. As large areas of this region suffer from poor age-constraint, it is necessary to develop a stronger stratigraphic framework with which to contextualize the wealth of new paleontological data available. This study defines carbon isotopic signatures for samples from the Xinminpu Group of the Yujingzi Basin in Gansu Province of China, with the aim of correlating these strata to the well-defined global marine carbon isotope record, and thus more tightly constraining the age of this section. Samples were collected from the fluviolacustrine strata of the Xinminpu Group, at intervals of 25-100cm over a measured distance of 320 meters. 550 samples were decarbonated and analyzed for their carbon isotopic composition of sedimentary organic matter using IRMS. Sample ranges from -28.02 / to -20.90 / vs V-PDB. The section is correlated on the basis of a δ13C org increase (magnitude 7.12 /). The base of the section exhibits stratigraphic carbon isotope variation consistent with that observed for the Upper Barremian by some authors, while the variations within the middle and upper segments of the section are consistent with global carbon isotopic variations C3-C7 based on marine carbon isotope records. This constrains the Xinminpu Group strata within the Yujingzi Basin to the latest Barremian through Early Albian Stages (125-113 Ma), with specific segments from the middle and upper parts of the section correlated to the Selli Equivalent, associated with Ocean Anoxic Event 1a.

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Keywords
Earth sciences
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Department
Geosciences