山旺盆地的成因及其地质意义

ON ORIGIN OF THE SHANWANG BASIN ANDITS GEOLOGICAL SIGNIFICANCE

前人一般认为山旺盆地是一个深度不大的封闭性淡水剥蚀盆地。笔者认为它是一个火山口成因的封闭—半封闭盆地。盆地的发展经历了3个发展阶段:早期为火山喷发作用形成火山口,并造成火山碎屑物堆积:中期堆积了较厚层的沉积物,主要为粘土质岩石,如硅藻质页岩、泥岩,此外,还有少量的砂岩、砾岩;晚期为玄武岩充填,致使整个盆地完全封闭。在盆地发展过程中,早期为封闭环境,中、晚期为半封闭环境。火山碎屑物的再堆积和分解对于生物死亡和埋藏可能具有重要的意义;该区第三纪中心式火山作用非常强烈,通过详细的区域地质调查,有可能找到更多的化石产地和硅藻土矿。

Shanwang, which is situated in Lingqu county, Shandong Province, is a wellknown Tertiary basin. In this basin there are many rock beds with rather thin layers (<0. 1mm) and have explored numerous beautiful fossils. Most of the research workers proclaim that the basin is an erosional basin with shallow fresh-water. Based on a large number of geological facts, the authors believe that it was a crater, in which deposited the pyroclasts and the other terrigenous clasts in a closed - half-closed environment. The basin was formed in three stages. In the early stage there occurred strong volcanic eruption and formed the crater with accumulation of pyroclasts. In the second stage, terrigenous clasts were strongly accumulated in it. In this period, the sedimentary environments change gradually from a closed to a half - closed one. The sediments are mainly clay, dialomaceous OOZE and a little of sands. Finally, basaltic lavas flowed from its surrounding area into the basin. The authors consider that the reaccumulation and decomposition of the pyroclasts may be strongly effected on the habilats of extinct animals and plants in the basin. By the way, giving a detailed survey and some special researches, it is possible to find out more species and diatomaceous de-posites in this field.