秦岭北坡洛南地区上张湾组冰碛层岩石特征

东秦岭北坡,陕西洛南地区,有一套古老的冰碛层,在洛南县石门以北,洛(南)-华(县)公路23公里处、上张湾一带出露良好,该处地层剖面清晰,露头连续,顶底界限清楚,岩石变质轻微,岩性特殊,结构明显,便于观察研究。 自1958年杨志坚报告豫西“临汝冰碛层”以后,1963年王日伦指出,洛南地区有冰碛层存在,并与罗圈组对比。1976年陕西省地质局六队、区调队,进一步肯定了冰碛层的存在,并作了比较详细的研究和划分。其间,西北大学、西北地质研究所、河南省地质研究所等亦曾进行过一些零星的工作。

THE CHARACTERS OF TILLITES OF SHANGZHANGWAN FORMATION,LOUNAN COUNTY AT THE NORTHERN SLOPE OF QINLING RANGE

According to the recent investigation,the carbonate breccias with in the Sinian system of Shangzhangwan,Lounan County,Shanxi Province,are tillite,indeed.The coarse angular fragments in them are erratics made of diverse carbonates,the finegrained fragments have similar composition to the coarse ones,and the matrix consists of angular silty carbonate grains.Such a clastic material of multiple grades of grain size and with salient edges is mainly formed by glaciers of limited extent upon carbonate beds.Spreading along the southern margin of the North China Platform,i.e.from western Henan through Shanxi to Ningxia,this tillite may display a continuum of sedimentary facies as well as lithologic types from boulder clay to some ice-transported deposits,erratics-bearing dolomitic mudstones to drop stones from ice-bergs by the possible transition from subaerial to lacustrine and marine environment.All these sediments seems to be typical for their respective sedimentary environments.