陕西渭北奥陶系放射虫硅质岩与火山凝灰岩的成因环境

通过对层状放射虫硅质岩的岩石学和火山凝灰岩岩石类型的特征研究，认为渭北奥陶系的放射虫硅质岩是由远源的火山喷发物提供了ＳｉＯ２的来源，造成有利于硅质生物大量繁殖的条件，死后堆积海底，最终转变为层状放射虫硅质岩。从而进一步推断，本区中、上奥陶统的沉积形成于海平面大规模上升的远洋或半远洋的深水环境。火山凝灰岩则是岛弧火山喷发的产物，反映本区曾一度是华北板块活动大陆边缘弧后盆地北部边缘部分。

GENETIC ENVIRONMENT OF ORDOVICIAN RADIOLARIAN CHERTS AND VOLCANIC TUFFS IN WEIBEI, SHAANXI PROVINCE

Petrological characteristics of bedded radiolarian cherts and different types of volcanic tuffs have been studied in the Ordovician of Weibei, Shaanxi. Distal eruptive materials supplied SiO 2. Radiolarians thrived largely in this condition, and gradually dead bodies of radiolarians were accumulated on sea bottom and turned finally into bedded radiolarian cherts with sediments. It is inferred further that the Middle Upper Ordovician were deposited in a pelagic or semipelagic deep water environment with a greatly rising sea level. Volcanic tuff is the product of island arc volcanic eruption. This area was once the north margin of a back arc basin which belonged to an active continental margin of the North China plate.