美国Marcellus页岩与中国南方龙马溪组页岩地质特征对比及启示

Comparison of Marcellus Shale in United States and Longmaxi Formation Shale in Southern China

中国南方地区下志留统龙马溪组富有机质页岩与美国阿巴拉契亚盆地中泥盆统Marcellus页岩,在形成构造背景、沉积环境方面具有一定的相似性,均形成于前陆盆地构造背景下的陆棚-斜坡浅海,沉积环境具有半封闭性。同时,二者也存在一定差异性,Marcellus页岩形成于前陆盆地早期快速沉降阶段斜坡带,其后期经历的构造变形相对较弱;中国南方龙马溪组页岩形成于前陆盆地持续沉降背景下,但其后期经历的构造改造作用多期复杂,其中四川盆地处于距离造山带较远的隆后凹陷构造位置,其除经历了频繁的升降运动外,挤压、拉张改造相对其周缘地区较弱。二者在具体地质特征方面也具有一定差异,主要表现在龙马溪组页岩埋藏较深、有效厚度大、热演化程度相对较高以及有机质含量相对较低。二者形成沉积构造背景以及地质特征的对比研究,对中国南方志留系龙马溪组页岩气进一步的勘探评价以及研究工作具有重要的指导意义。

The comparison of Middle Devonian Marcellus shale of Appalachian Basin in United States and Lower Silurian Longmaxi Formation organic-rich shale in southern China shows their similarities in tectonic setting and sedimentary environment. They both deposited in semi-restricted shallow sea belonging to continental shelf or slope facies during the foreland basin formation. Marcellus shale deposited on the foredeep slope when an active orogenic phase led to the rapid subsidence in the foreland basin, and the post tectonic reworking of it was relatively weak. Longmaxi Formation shale deposited during the continuous subsidence of foreland basin, with complex and multiple post tectonic reworking. While Sichuan Basin was located in the backdeep far from the orogenic belt, where vertical movements were frequent, but the horizontal stress and relevant reformation were relatively weak. Compared with Marcellus shale in geological characteristics, Longmaxi Formation shale is of deep depth, large thickness, high thermal maturity and low TOC content. The comparative study of Marcellus shale and Longmaxi Formation shale is of important theoretical and practical significance for the further exploration and evaluation of Longmaxi Formation shale gas in southern China.