贵州遵义松林寒武系底部热液喷口及与喷口相关生物群特征

贵州遵义寒武系底部黑色页岩中含Mo、Ni、U等重金属的富集层，它们一直被认为与热水沉积作用有关。本文通过对贵州遵义松林小竹一带的寒武系底部地层的系统的岩石、矿物、地球化学研究，认为遵义松林小竹一带寒武系底部黑色页岩中富含Mo、Ni、U等重金属层属于热液（水）喷流沉积，主要依据有：①含大量的黄铁矿、针镍矿、硫钼矿及较多的锑硫镍矿、黄铜矿、闪锌矿、重晶石、石英、石膏等矿物；②具有大量的同生砾屑，砾屑成分为黑色碳质体和碎屑状黄铁矿、针镍矿、硫钼矿等矿石，它们堆积成层状结构，碎屑呈被撕裂状、棱角状、熔蚀港湾状等结构，球状、脸盆状、枕头状等构造，它们类似海底喷流沉积；③硅同位素、锶同位素、Re／Os值、Th／Sc值、Th／U值都表明有深部物质加入；④黑色岩系中夹碳酸盐岩透镜体，碳同位素具有强烈负异常特征，表明有热液作用；⑤超强富集元素Mo、As、Se、Re和T1都属于典型的气相迁移元素，而钼是典型的高温气相迁移元素，暗示了可能存在火山射气作用；而强富集的Ni、U、Au、Ag、PGE元素组合是超基性岩浆活动的产物，表明有热液活动。研究发现在热液（水）喷流沉积形成的富集Mo、Ni、U等重金属硫化物层之上，产出丰度大、分异度低、含大型海绵类、双壳类、菌藻类和少量大型蠕虫化石的生物群，它的特征与现代太平洋海底热喷口附近的生物群类似，因此认为遵义小竹一带寒武系底部生物群属于与海底热喷口相关生物群，这一新发现对研究寒武纪生态和生物爆发具有重要意义。

A Study on Characteristics of the Hydrothermal Vent and Relating Biota at the Cambrian Bottom in Songlin, Zunyi County, Guizhou Province

Abundant Mo, Ni, U ore deposit within the black shales at the bottom of Cambrian in Zunyi, Guizhou Province was considered hydrothermal sediment. According to the lithological and mineral feature and geochemical characters of the black shales in Xiaozhu area, Zunyi County, writers suggest that Mo, Ni, U ore deposits belong to hydrothermal vent sediment. Major proofs are asfollows:(1) Abundant pyrite, capillose, molybdenite, and ullmannite, chalcopyrite, sphalerite, barite, quartz, gypsum. (2) Abundant syn-depositional gravel fragments, which are composed of black carbonaceous body and fragmental pyrite, capillose, molybdenite, and accumulated into beds. Thefragments show the features of rend-form and resorption form, orebeds show the globular structure, basin-shaped and pillow structure, belonging to sea floor hydrothermal vent sediment. (3)Si-isotope, Sm-isotope, Re-Os ratio value, Th/Sc and Th/U ratio value showing mantle materialintrusion. (4) Carbonate in the black shales has sharp negative carbon isotopic value. (5)Abundant Mo, As, Se, Re and Tl elements are typical gas-migration element, and Mo is typical high temperature gas-migration element, which hint that volcano eruptions happened at the beginning of Cambrian. Active ultrabasic magma supplies abundant Ni, U, Au, Ag, PGE elements. An abundant, but low diversity biota, including large-type spongia, bivalve, Cyanophyta, and a small amount of larger-type worm, similar to modern hydrothermal vent community in the pacific. Therefore,writers suggest that the biota in Mo, Ni, U ore deposit within the black rock series in Xiaozhu, Zunyi County, Guizhou Province is relative to hydrothermal vent community. The new discoveryis important for us to study the Cambrian explosion and the palaeoecology of early life.