川西南荥经坳陷川荥页1井奥陶系沉积相与古生物特征及地层厘定

对川西南荥经坳陷内三口页岩气井尤其是川荥页1井奥陶系开展了系统的岩心观察和分析。三口钻井在梁山组之下均发育十余米厚的灰黑色泥岩,其中川荥页1井灰黑色泥岩厚近16m。沉积相分析认为灰黑色泥岩为浅水陆棚相,泥岩之下发育的大套砂岩为滨岸近滨亚相,总体向上海水逐渐变深。砂岩中发育丰富的沉积软变形构造及波状交错层理、浪成沙纹层理、平行层理、斜层理等构造。川荥页1井上部泥岩中见大量三叶虫、笔石和腕足等化石及其碎片,鉴定表明含有代表中下奥陶统的常见生物分子,如对笔石(Didymograotus sp.)、大洪山虫(Taihungshania sp.)等。该套砂泥岩组合在沉积相及古生物化石等方面明显区别于荥经坳陷周缘奥陶系五峰组—志留系龙马溪组,与研究区及邻区中下奥陶统红石崖组、湄潭组、大湾组、大官山组中段等层位相当。

Sedimentary facies, paleontological characteristics and stratigraphic delineation of the Ordovician strata through the CYY1 well in the Yingjing depression,southwestern Sichuan

A systematic core observation and analysis are carried out for the Ordovician strata through three wells, especially through the CYY1 well in the Yingjing depression,southwestern Sichuan. Below the Permian Liangshan Formation through the three wells,a succession of greyish black mudstones is developed,with a thickness of more than 10 m (16 m thick in the CYY1 well),and assigned to the shallow shelf facies. Then the nearshore sandstones are found below the greyish black mudstones in the shallow shelf facies,with some siltstone strips or lens interbedded,displaying an overall deepening-upward sequence. In the sandstones and siltstones of nearshore facies,there occur abundant sedimentary structures including wavy cross bedding,wave-built cross bedding, parallel bedding,oblique bedding,as well as plenty of soft-sediment deformational structures. In the upper greyish black mudstones through the CYY1 well,there occur numerous fossils and fossil fragments of trilobite,graptolite and brachiopods. In addition,there are also the Middle-Lower Ordovician members such as Didymograotus sp. and Taihungshania sp. The above-mentioned sandstone-mudstone successions are highly different in sedimentary facies and fossil from those in the Ordovician-Silurian Wufeng Formation and Longmaxi Formation around the Yingjing depression,but correspond with the stratigraphic horizons of the Middle-Lower Ordovician Hongshiya Formation, Meitan Formation,Dawan Formation and the middle member of the Daguanshan Formation.