晚三叠世卡尼期黑色页岩事件在龙门山地区的沉积学和古生物学响应

龙门山前缘地区卡尼阶-诺利阶马鞍塘组中部发育一套薄-中层状黑灰色、灰黑色、黑色（含介壳）钙质泥（页）岩，在该套岩石中瓣鳃类生物多见，原生二价金属硫化物（黄铁矿）发育，水平层理发育，显示着低能环境贫氧条件的典型特征。与马鞍塘组中部黑灰色、灰黑色钙质泥（页）岩相当层位的卡尼期晚期沉积，在松潘-甘孜地区、昌都地区、可可西里地区均可见到，多显示为黑色、灰黑色色调，岩性为泥（页）岩或粉砂质板岩、钙质板岩，反映了一次黑色页岩地质事件在中国西部古特提斯东部地区产生了大范围的影响。全球对比表明，该套深色泥（页）岩在西特提斯、印度喜玛拉雅等地均有分布，覆盖在卡尼期早期碳酸盐沉积之上。据此，作者认为晚三叠世卡尼期特提斯范围的黑色页岩事件，很有可能与卡尼期全球性的碳酸盐生产危机有关，马鞍塘组中部发育的深色泥（页）岩即是此次事件在扬子地台西缘的反映。根据对川西北地区绵竹汉旺、安县雎水、江油马鞍塘等剖面的实际考察与研究，认为代表缺氧事件沉积的马鞍塘组中部黑灰色泥（页）岩之下为卡尼阶灰岩段（即汉旺组中下部灰岩段，主要为鲕粒灰岩、海绵礁灰岩等），之上为诺利阶灰色粉、细砂岩夹灰岩、泥岩段（相当于石元组）。黑灰色钙质泥（页）岩不仅是该组岩性变化的转折点，亦是古生物、古生态急剧变化的转折点。在马鞍塘组下部广泛可见的六射海绵、海百合、苔藓虫、珊瑚等海相化石在马鞍塘组中上部地层（上卡尼阶至诺利阶底部）中很少看到，仅见丰富的瓣鳃类、菊石、腕足类等有壳类动物化石。
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Black shale event during the Late Triassic Carnian Age: Implications from sedimentary and palaeontological records in Longmen Mountains region

 A set of dark gray， grayish black or black calcareous shale(bearing shell sometimes)occurred at the Upper Triassic Carnian—Norian Maantang Formation in the Longmen Mountains region， Sichuan Province. Numerous bivalves， primary divalent metal sulfides(pyrite)， thin intermediate layers and horizontal bedding observed in the shale indicated an anoxic low energy environment. The Late Carnian sediments mainly mudstone，shale  or silty slate， calcareous slate which are time equvalent to this black shale，can be found in the east Paleotethys including Songpan—Ganzi Area， Changdu Area，and Hoh Xil Area. We considered that they reflected a black shale event which strongly influenced the marine sediments in the eastern Paleotethys of west China. The global correlation indicated that the dark color mudstone（shale）were widely distributed in western China， Indian Himalayas， Eastern Alps， and overlied on the Early Carnian carbonate rocks. Thus we proposed a Tethys wide black shale event， which caused the late Early Carnian global carbonate production crisis occurred， while the dark color mudstone(shale)developed in the middle part of the Maantang Formation is a reflection of this event along the western margin of the Yangtze Platform. Based on investigation and studies of the Upper Triassic sections in Hanwang， Jushui， and Maantang areas in northwestern Sichuan， it is concluded that the Carnian limestone(ie. oolid limestone， sponge reef limestone in the middle lower Maantang Formation)was deposited before the anoxic event， and the Norian gray siltstone and fine sandstone was laid down after the event. The black mudstone(shale)triggered by the event not only indicated the significant lithological change， but also was the turning point of sudden paleontological and paleoecological changes. Marine fossils such as hexactinellida， crinoid， bryozoa，and coral were abundant in the limestones of the lower Maantang Formation， but they suddenly disappeared in the black shales in the Maantang Formation. Shell fauna fossils such as rich bivalves， ammonoids，and brachiopods occurred in the middle upper Maantang Formation.