川西北江油马角坝地区黄龙组下部风暴沉积特征

The characteristics of storm deposits in the lower Huanglong Formatiom of Majiaoba area,northwestern Sichuan Provine

川西北江油马角坝地区上石炭统黄龙组下部发育典型的风暴沉积,包括介壳灰岩、砾屑灰岩、瘤块状灰岩、砂屑灰岩和正常沉积灰岩或泥岩等沉积类型,以及冲刷沟槽、瘤块状构造、粒序层理、水平层理、波状层理和生物扰动等沉积构造。根据野外观察和室内显微分析,结合风暴沉积标志组合,在江油马角坝地区2个剖面的黄龙组下部各识别出4层风暴层,并划分出5套风暴沉积组合。组合Ⅰ以冲刷沟槽、介壳滞留层、粗砾滞留层、块状层理、水平层理、波状层理、泥灰岩层和生物富集层为特征,沉积于正常浪基面以上强风暴作用的开阔台地环境。组合Ⅱ以瘤块状构造、粒序层理和块状层理的生物碎屑灰岩为特征,沉积于正常浪基面之上受重力流影响的局限台地环境。组合Ⅲ以冲刷沟槽、粗砾滞留层、粒序层理、块状层理为特征,沉积于浪基面以上持续风暴流作用的开阔台地边缘浅滩环境。组合Ⅳ由冲刷沟槽、正粒序层理和块状层理的生物碎屑灰岩组成,产出于组合Ⅲ之上,表明该组合在前一期风暴未完全结束时又遭到后一期风暴的侵袭,接受浪基面之上的浅滩沉积。组合V由冲刷沟槽、粗砾滞留层和泥岩层组成,沉积于晴天浪基面以上缺少物源的极浅水开阔台地环境。以上5种组合风暴岩都发育于台地中上部,与一般的斜坡风暴岩有明显的差别,均属于近源极浅水风暴岩。风暴岩的研究对地层对比、古气候、岩相古地理、沉积盆地演化和油气勘探具有重要的理论和现实意义。

There are many depositional characteristics of storm deposits in the lower Huanglong Formation around Majiaoba area, Jiangyou County, including storm shell limestone, storm calcirudite,storm nodular limestone, storm calcarenite, scouring structures, graded beddings, similar knotty structures, scale beddings, horizontal beddings, current beddings, bioturbate structures and so on. Through detailed field observation and laboratory study, four storm layers have been recognized in each of the two sections and a total of five combinations of stormdeposits systems have been divided. Combination Ⅰ ,which is deposited in normal weather wave base nearby open platform facies, is characterized by scouring structures, coarse gravel beddings, scale beddings, horizontal beddings, current beddings, bioturbate structures and dragonfly fossil concentration. Combination Ⅱ , formed by above normal wave base nearby restricted platform faicies, is represented by bioclastic limestone with similar knotty structures, graded beddings and massive beddings. Combination Ⅲ, which is deposited above normal weather wave base nearby winnowed open platform edge facies, is characterized by coarse gravel beddings, graded beddings and massive beddings. Combination Ⅳ located on combination Ⅲ, is characterized by graded beddings, hummocky cross stratifications and massive beddings. It is proven that the combination IV begins to deposit before storm flow Ⅲ completely ended and deposits in normal weather wave base nearby the storm fluid. Combination V ,which is formed at the place sunny weather wave base nearby open platform facies, is characterized by scouring structures, coarse gravel beddings and mudstone. These tempestite are wholly proximal storms rocks. The research of tempestite is useful in stratigraphic correlation, paleoclimate, lithofacies paleogeography, sedimentary evolution and oil-gas exploration.