高精度海、陆T-J界线地层对比——基于C3植物碳同位素地层学

Due to few common fossils between marine and terrestrial strata, marine-terrestrial stratigraphic correlation has long been a great challenge. Recently, the terrestrial carbon-isotope stratigraphy based on C3 plants offers a theoretical and practical solution to this difficulty. C3 plants are composed of polymer, primarily including lignin and celluloses. The carbon-isotope kinetic fractionation resulted by C3 plant physiological effects remains a nearly constant offset of δ13C values between C3 plant and the atmospheric CO2. The δ13C values in the contemporary atmospheric CO2 are thus faithfully archived. On a geological scale, rapid global atmospheric CO2 equilibrium ensures a high-resolution and globally synchronous stratigraphic correlation. During the T-J boundary, there are significant carbon-isotope perturbations in Earth surface system and the records are widely witnessed in many marine and terrestrial strata across the world. An excellent terrestrial deposition occurs in the Kuqa, Tarim Basin, where continuous strata across T-J boundary are constrained by relatively well-studied biostratigraphy (chronology) and lithostratigraphy. The present study aims to acquire a high-resolution terrestrial carbon-isotope stratigraphic curve around the T-J boundary at the Kuqa Section; and then it serves for high-resolution stratigraphic correlation between terrestrial strata in the Kuqa and marine strata from Global Stratotype Sections and Points (GSSP) and other well-studied T-J boundary locations globally. Furthermore, it seeks for the kinetic mechanism of carbon perturbations in the various carbon reservoirs on Earth surface across T-J boundary; and an inferred impact event suggested by a potentially synchronous soft-sediment deformation over global scales.

因海、陆缺乏共同的生物化石，跨海、陆地层对比一直是地层学中的难题。基于C3植物的碳同位素地层学为此提供了理论和实践的路径。C3植物主要由高分子的木质素和纤维素组成，其碳源来自大气中的CO2，经植物生理作用的同位素动力分馏，C3植物的δ13C值与大气CO2的保持近恒定的差值，记录了同时代大气的δ13C值。在地史尺度上，全球大气平衡速率极快，赋予了C3植物的碳同位素地层学高分辨、全球等时性的基础。T-J之交时期，在全球表层系统中有巨大的碳循环波动，并记录于海、陆相T-J边界地层中。塔里木盆地库车剖面连续发育的陆相T-J界线地层，有很好的生物（年代）地层学基础。本项目拟在此开展，获取高分辨率的碳同位素地层曲线，完成首个中国陆相T-J界线地层与全球层型剖面点GSSP及国际其他海相地层的高分辨率等时对比，探索T-J界线时期海、陆和大气碳储库波动的动力学机制，考察该时段跨洲际尺度软沉积变形的等时性。

全球跨海、陆相地层的高精度对比一直是地层学中的难题。本研究以塔里木盆地库车河剖面的三叠系—侏罗系（T-J）界线与位于奥地利的GSSP高精度对比为例证研究，进行了尝试和探索。系统地采集以碳质的高等植物木质部为主的材料作为研究对象，获得可以指示当时的大气二氧化碳碳同位素值的有机碳同位素地层曲线；结合前人在该剖面取得的孢粉和大植物化石的数据进行统计分析，得到该剖面上生态系统波动的记录；综合以上数据，完成了该剖面T-J界线与GSSP的高分辨率对比，高精度地确定了新疆塔里木盆地北缘库车凹陷的库车河剖面等时T-J界线。本研究中，两次独立地、系统地采集碳同位素地层学样品，两次结果具有较好的可重复性，验证了地层中顺次随机采样方法的有效性和本研究数据结果的可靠性。另外，塔里木盆地库车河剖面与以天山为分隔的准噶尔盆地郝家沟剖面也有很好的可对比性。