Devonian Environment Inferred from Stable Carbon and Oxygen Isotope Records of Brachiopod Shells from South China
Abstract
This study analyzed stable carbon and oxygen isotope compositions of brachiopod shells and whole rocks collected from Guizhou, south China to reconstruct the Devonian palaeoenvironment of South China Block.
We thin sectioned brachiopod shells and rocks, evaluated the preservation of brachiopod shells using transmitted light and cathode ray microscopy. Trace element contents of selected brachiopod shells were further analyzed by using inductively coupled plasma spectroscopy (ICP-OES) to confirm that the Fe and Mn contents of well preserved fossils are low. This study analyzed 65 brachiopod samples and 321 rock matrix samples. A total of 497 carbon and oxygen isotope analyses were performed. The average oxygen isotope values of well-preserved brachiopod shells are -5.8±0.2‰ (1σ; N=2) for Eifelian stage, -6.4±0.7 ‰ (N=59) for the Givetian stage and -6.7 ±0.3 ‰ (N=8) for Frasnian stage. The average values of carbon isotopes were 1.0 ±0.3 ‰, 0.8 ±1.7 ‰ and -1.1 ±0.3 ‰, for Eifelian, Givetian and Frasnian stages, respectively. If the oxygen isotope value of Devonian seawater was -3‰ (Wallmann, 2001), the calculated seawater temperature were between 28~33°C. Although it may show the characteristics of tropical waters in South China during Devonian, the low Devonian seawater oxygen isotope values need to be further examined. Carbon isotope values in South China were similar to those of mid-latitude record from Eifelian to Frasnian reported in van Geldern's (2006). However, carbon isotope values of this study are less than those reported in van Geldern's (2006) in the Famennian may indicate regional difference in seawater characteristics.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP21D1644T
- Keywords:
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- 0419 Biomineralization;
- BIOGEOSCIENCES;
- 0454 Isotopic composition and chemistry;
- BIOGEOSCIENCES;
- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCES;
- 4994 Instruments and techniques;
- PALEOCEANOGRAPHY