下扬子地区龙潭组煤系地层特征

STRATIGRAPHIC FEATURES OF THE COAL-BEARING LONGTAN FORMATION IN THE LOWER YANGTZE AREA

下扬子地区二叠系龙潭组既是重要的烃源岩,也是重要的储集层,局部含煤层。通过对下扬子陆域龙潭组的沉积特征、沉积层序研究以及陆域和海域龙潭组煤系地层特征的对比认为,龙潭组煤系地层从陆域到海域,沉积物的岩性从碳酸盐岩和碎屑岩逐渐演变为碎屑岩;煤层主要分布在龙潭组的中上部,但陆域煤层之上通常发育一套＂压煤灰岩＂,而海域通常缺少这一套＂压煤灰岩＂;陆域龙潭组烃源岩丰度较高（TOC为2%-4%）,厚度较大（200-600m）,以生油为主（Ro：0.5%-2%）;与南黄海盆地崂山隆起相邻的滨海隆起二叠系分布局限,但丰度可能较高,因此,推测南黄海盆地崂山隆起二叠系烃源岩分布局限,丰度较高。

The Permian Longtan Formation in the Lower Yangtze area contains not only important source rocks,but also high quality reservoirs,in addition to coal seams in some places.Based on the comparison of the depositional features and sedimentary sequences of the Formation between the land and sea areas,it reveals that the sequence starts with carbonate rock and gradually becomes clastic dominated deposits when coal-bearing strata expands from the land to the sea.Coal seams are mainly distributed in the middle and upper parts of the Longtan Formation.In the land area,there is always a covering limestone on the top of the coal,but it is missing in the marine area.The organic matters in the source rocks of the Longtan Formation are quite high（TOC：2-4%）.The source rocks are quite thick（200-600m）,and good for oil generation（Ro：0.5-2%）on land.However,the Permian source rocks around the coastal rifts next to the Laoshan uplift are restricted.Thus,we speculate that the Permian source rocks around the Laoshan uplift of the South Yellow Sea Basin is not very potential.