贵州开阳龙水地区震旦系洋水组沉积特征及生物成磷作用*

贵州开阳磷矿以其厚而富的磷矿石资源备受关注。对开阳龙水地区含磷岩系(洋水组)剖面进行地层学、岩石学和沉积学研究,并讨论其沉积环境和成磷作用。区内含磷岩系岩性组合为黏土岩-白云岩-碎屑状磷块岩-硅质岩-泥晶磷块岩-叠层石磷块岩。龙水地区在震旦纪陡山沱期整体为靠近古陆边缘的滨岸潮坪沉积环境,并经历了2次海侵-海退。其沉积环境由初期的无障壁海滩转变为晚期的潮坪环境,表明陡山沱期古海洋处于较为动荡的环境,海平面升降频繁。富含生物化石的致密状泥晶磷块岩、圆柱状叠层石磷块岩和磷质生物团粒,均属于原生磷块岩。三者磷酸盐含量极高,属于高品位磷块岩,其形成环境可能是弱酸性至弱碱性的浅海陆棚。生物与高品位磷块岩的密切关系说明生物在高品位磷块岩形成过程中起重要作用。其形成具有3个必要条件: 海水富磷,生物大量繁殖,有利于生物繁殖及磷酸盐结晶的沉积环境。

Sedimentary characteristics and biophosphorization of the Sinian Yangshui Formation in Longshui,Kaiyang, Guizhou Province

The Kaiyang phosphate mine has attracted much attention due to its thick and rich phosphate ore resources. In this paper,stratigraphy,petrology and sedimentology are studied for the phosphorous-bearing Yangshui Formation in Longshui,Kaiyang,and the sedimentary environment and phosphorus formation are discussed. The lithologic assemblages of the phosphorous-bearing rock systems in the area are clay rock-dolomite-clastic phosphate rock-siliceous rock-micritic phosphate rock-stromatolite phosphate rock. In the Doushantuo age,the Longshui area was a coastal tidal flat close to the old landmass,and experienced transgression-regression twice. The sedimentary environment of the Doushantuo age changed from the barrier-free beach in the early stage to the tidal flat in the late stage,indicating a relatively dynamic environment with frequent sea-level fluctuations. The dense micritic phosphate rock,cylindrical stromatolite and phosphate biological aggregates rich in biological fossils belong to the original phosphate rock. The phosphate content of the three lithofacies is high,belonging to the high grade phosphate block rock. The depositional environment was likely a low-energy subtidal zone with medium-acidity to weak alkalinity. The close relationship between organisms and high grade phosphate rock suggests that organisms played an important role in the formation of high grade phosphate rock. Its formation has three prerequisite conditions: seawater rich in phosphorus,biological mass reproduction and conducive to biological reproduction and phosphate crystal environments.