河北易县青白口群底部燧石角砾岩成因的探讨

引言 河北易县青白口群底部燧石角砾岩(下面简称“角砾岩”)系指震旦亚界蓟县群铁岭组之上、青白口群下马岭组下部之角砾岩。它在太行山北段、中段都有分布,厚度由二、三米至五、六十米不等,在易县南约十四公里的向阳、北考一带发育很好,厚达六十米,顶底接触关系清楚,是研究“角砾岩”成因的良好地段。

THE ORIGIN OF "CHERT BRECCIA"|IN THE BOTTOM OF QINGBAIKOU GROUP IN COUNTY YIXIAN, HEBEI PROVINCE

The "chert breccia" under study refers to the breccia forming the basal part of the Xiamaling Formation of Qingbaikou Group and overlying the Tieling Formation of Jixian Group of the Sinian suberathem in North China. As to its origin various opinions so far expressed include sedimentary, glacial and chiefly karstic. Despite these differences, it is generally agreed that the base of the breccia marks a deposi-tional gap, which forms boundary between the Jixian and Qingbaikou Groups.Investigations and observations on the "relic beds" from the brecciated strata, the breccia composition and the phenomena of strain as well as on the so-called transitional horizon between breceiated strata and the underlying indicate that the chert breccia was formed due to gravity from the overlying strata in the long geologic time. As a result, the brittle chert deposits were fractured to form breccia while some plastic argillo-arenaceous intercalations may have resulted from the viscous flow along fractures of breccia.