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Non-marine carbon-isotope stratigraphy of the Triassic-Jurassic transition in the Polish Basin and its relationships to organic carbon preservation, pCO2 and palaeotemperature
Earth-Science Reviews ( IF 12.1 ) Pub Date : 2020-11-01 , DOI: 10.1016/j.earscirev.2020.103383
Grzegorz Pieńkowski , Stephen P. Hesselbo , Maria Barbacka , Melanie J. Leng

Abstract New carbon-isotope data obtained from homogenous organic material (separated microfossil wood; δ13Cwood) from the upper Rhaetian and entire Lower Jurassic permit chemostratigraphic correlation of these marginal/non-marine deposits with the biostratigraphically well-constrained Llanbedr (Mochras Farm) core in N Wales and other marine profiles, supported by sequence stratigraphic correlation and biostratigraphical markers. Statistically significant (Rs = 0.61) positive exponential correlation between δ13Cwood values and continental TOC (TOCcont) concentrations occurs and can be defined empirically by equation. Changes of δ13Cwood observed in C3 plants depends on δ13CO2 of atmosphere and can be modulated by other factors such as pCO2 causing fractionation (enrichment in 12C) of C isotopes in source C3 plants and, to lesser extent, by soil moisture content. Floral remains occurring in the relatively stable palaeolatitude and climatic zone of the Polish Basin in the time interval studied lend no support for significant precipitation impact on the δ13C fractionation, although enhanced precipitation could have had a limited impact during the Toarcian Oceanic Anoxic Event (T-OAE). We argue that the observed relation between δ13Cwood values and TOCcont reflects the global carbon cycle forcing. Such correlations may develop because fluxes of of 12C-enriched methane, mobilized from near-surface carbon sources, lead to global warming, decreased δ13Cwood and enhanced (usually fungally-mediated) decomposition of the terrestrial carbon pool, while subsequent massive burial of organic carbon results in higher δ13C values in all carbon cycle reservoirs, and the attendant drawdown of atmospheric CO2 leads to global cooling and promotes sequestration of soil organic matter. In turn, this relation can be used as an indirect indicator of atmospheric temperature trends, although organic carbon isotope records are potentially subject to many different influences. Based on the δ13Cwood /TOCcont relationship, an approximate qualitative estimation of general trends in air temperature is suggested for c. 40oN paleolatitude and the warm temperate climatic zone. The observed hypothetical trends in temperature are generally in concordance with pCO2 trends calculated from stomatal index. A weak δ13Cwood and TOCcont correlation in Rhaetian deposits is explained by local environmental factors (TOC concentration dependent on a more localized fluvial plain settings), while mostly deltaic – coastal deposits contain more representative, averaged material delivered from a large catchment area.

中文翻译:

波兰盆地三叠纪-侏罗纪转变的非海相碳同位素地层及其与有机碳保存、pCO2 和古温度的关系

摘要 从上雷蒂亚纪和整个下侏罗纪的同质有机材料(分离的微化石木材;δ13Cwood)获得的新碳同位素数据允许这些边缘/非海相沉积物与生物地层学上受到良好约束的 Llanbedr(莫克拉斯农场)岩心的化学地层相关性北威尔士和其他海洋剖面,得到层序地层相关性和生物地层标记的支持。δ13​​Cwood 值与大陆 TOC (TOCcont) 浓度之间存在统计显着性 (Rs = 0.61) 正指数相关性,并且可以通过方程根据经验定义。在 C3 植物中观察到的 δ13Cwood 的变化取决于大气中的 δ13CO2,并且可以受到其他因素的调节,例如 pCO2 导致源 C3 植物中 C 同位素分馏(在 12C 中富集),并且在较小程度上,由土壤含水量决定。在研究的时间间隔内,在波兰盆地相对稳定的古纬度和气候带中出现的植物遗骸不支持降水对 δ13C 分馏的显着影响,尽管在托亚西大洋缺氧事件 (T- OAE)。我们认为 δ13Cwood 值和 TOCcont 之间观察到的关系反映了全球碳循环强迫。这种相关性可能会发展,因为从近地表碳源动员的富含 12C 的甲烷的通量导致全球变暖、δ13Cwood 减少和陆地碳库的分解(通常是真菌介导的)增强,同时随后大量有机碳被埋藏导致所有碳循环库中的 δ13C 值更高,随之而来的大气 CO2 下降导致全球变冷并促进土壤有机质的固存。反过来,这种关系可以用作大气温度趋势的间接指标,尽管有机碳同位素记录可能会受到许多不同的影响。根据 δ13Cwood /TOCcont 关系,建议对 c 的气温总体趋势进行近似定性估计。40oN 古纬度和暖温带气候区。观察到的温度假设趋势通常与根据气孔指数计算的 pCO2 趋势一致。Rhaetian 矿床中 δ13Cwood 和 TOCcont 相关性较弱的原因是当地环境因素(TOC 浓度取决于更局部的河流平原环境),
更新日期:2020-11-01
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