托阿尔期大洋缺氧事件在中国陆相地层的碳循环扰动响应^*

Response to carbon cycle perturbation during the Toarcian oceanic anoxic event in terrestrial strata of China

摘要

早侏罗世托阿尔期早期的大洋缺氧事件(Toarcian Oceanic Anoxic Event,T-OAE)是中生代发生的一次剧烈的环境扰动事件,伴随着全球碳同位素负偏、快速升温、金属中毒等。然而,对这一事件的研究主要集中在特提斯洋等海相地层,陆相地层研究比较薄弱。前人运用沉积学、古生物学、同位素地层学等多学科交叉,发现T-OAE在中国四川盆地、金羊盆地、柴达木盆地等陆相地层中有明显的响应,并且碳同位素发生了-1.3‰~-7‰负偏,最大负偏移量达到-12.5‰,其偏移可能为Karoo-Ferrar 大火成岩省喷发,导致大量的¹²C释放,引起了一系列气候—环境—生态变化。换言之,Karoo-Ferrar大火成岩省(KFLIP)引起温度升高,甲烷水合物分解,进一步加剧变暖,使得大量的甲烷或CO₂进入大气中; 温度升高也伴随着从湿地、永久冻土、冰盖、植被野火中释放出大量的甲烷或CO₂作为碳源,从而引起了碳同位素负偏移。虽然这些机制与温度升高以及正反馈气候作用有关,但不是引起T-OAE碳同位素偏移的必然控制因素。总之,KFLIP可能是T-OAE的导火线,造成了碳循环出现幕式扰动。研究结果可以与同时期海相地层进行综合对比,为精确厘定T-OAE层位提供可靠依据; 进一步探讨碳循环扰动的影响因素,也可能为更全面地了解早侏罗世托阿尔期大洋缺氧事件在陆相地层中的气候—环境响应提供新的思路。

Abstract

The Early Jurassic Toarcian Oceanic Anoxic Event(T-OAE,ca.~183Ma)represents a significantly environmental perturbation in the Mesozoic and was associated with pronounced negative carbon isotope excursion(NCIE),increasing sea-surface temperatures,heavy metal poising,and so on. This event recording in the Marine strata such as the Tethys ocean,has been researched in detail,but it was paid little attention in the terrestrial strata. This review synthesizes data from the Sichuan,Jingyuan,and Qaidam basins,which preserve terrestrial responses to the T-OAE based on sedimentological,paleontological,and isotopic evidence. Terrestrial strata exhibit a carbon isotope excursion(CIE)of -1.3‰ to -7‰,whereas the Ordos Basin records an extreme CIE of -12.5‰. These anomalies suggest carbon-cycle perturbations linked to major environmental changes,likely triggered by massive volcanism from the Karoo-Ferrar Large Igneous Province(KFLIP). An alternatively hypothesis is that KFLIP-triggered climatic warming released unusually high fluxes of methane and /or carbon dioxide to the atmosphere. Rising temperatures during the early Toarcian would also have increased emission of large amounts of methane and /or carbon dioxide from wetlands,permafrost,ice caps,and vegetation wildfire. Although these mechanisms would have contributed to rising global temperatures via positive climate feedbacks,they may not represent the primary driver of the Toarcian CIE. By correlating terrestrial and marine records(e.g.,European Shelf and North China), this study refines the stratigraphic framework of the T-OAE. Furthermore, evaluating paleotemperature proxies, carbon-cycle dynamics, and their environmental couplings during the T-OAE offers insights into modern climate responses to light carbon emissions.

关键词

侏罗纪 / 托阿尔期大洋缺氧事件 / 碳循环扰动 / 陆相地层 / 中国

Key words

Jurassic / T-OAE / carbon cycle perturbation / terrestrial strata / China

基金资助

*国家自然科学基金(编号: 42272125,42241203,41572095)以及中国科学院地球化学研究所矿床地球化学国家重点实验室开放基金(编号: 202215)共同资助