下侏罗统辛涅缪尔阶-普林斯巴阶界线地质事件研究进展

Sinemurian-Pliensbachian boundary event (Early Jurassic): Current status and future challenges

早侏罗世经历了赫塘期、辛涅缪尔期、普林斯巴期和土阿辛期,其中土阿辛期大洋缺氧事件(T-OAE)被广泛研究。但在辛涅缪尔阶-普林斯巴阶界线处,δ^(13)C_(org)及δ^(13)C_(carb)曲线均发生负偏,局部伴随黑色页岩沉积。其在英国、法国、意大利、葡萄牙以及中国等地区都有记录,碳同位素的变化伴随着环境、气候的变化,研究显示该事件可能是全球性的,被称为“S-P界线事件”(SPBE)。此次地质事件与T-OAE事件类似,也显示了一次大洋缺氧事件,其发生时有轻碳同位素被排入了大气系统中,但是轻碳同位素的来源尚不明确,部分学者认为是大火成岩省喷发时排放的轻碳物质注入了海洋-大气系统所致。目前对该事件的研究主要集中于欧洲海相地层,其对陆地生态系统的影响还知之甚少。我国四川盆地下侏罗统湖相沉积发育良好,下侏罗统自流井组东岳庙段沉积有与大安寨段(T-OAE发生层段)类似的黑色页岩及介壳灰岩,其有机碳同位素负偏,显示了S-P界线事件的影响,其与T-OAE类似也对四川盆地早侏罗世古湖泊产生了影响。

The Lower Jurassic is composed of the Hettangian, Sinemurian, Pliensbachian and Toarcian, among which the Toarcian oceanic anoxic events(T-OAE) have been widely studied. Depositions of black shales and negative excursions of both δ^(13)C_(org) and δ^(13)C_(carb) at the Sinemuiran-Primbalian boundary, which has been recorded in the United Kingdom, France, Italy, Portugal and China.This event, known as the "S-P boundary event"(SPBE), characterized by significant carbon isotope, environmental and climatic perturbations in global scale. It is considered to be similar to the T-OAE, a well-known oceanic anoxic event, during which light carbon was released into the atmospheric system, although it is still unknown the sources of the carbon inputs. Research has so far dominantly focused on the marine strata in Europe, while few studies have evaluated the Lower Jurassic terrestrial strata. The Lower Jurassic lacustrine deposits are well developed in the Sichuan Basin, China. Similar to the T-OAE in the Daanzhai Member of Ziliujing Formation, the negative excursion of δ^(13)C_(org) was recorded in the blackshales and shelly limestones of the Dongyuemiao Member, Ziliujing Formation, indicating that the SPBE likewise has an impact on the Early Jurassic ancient lake in the Sichuan Basin.