豫西登封寒武系第三统张夏组凝块石灰岩及其控制因素

依据宏观生长形态和成因环境,豫西登封寒武系第三统张夏组凝块石灰岩可划分为三种型式。小柱状凝块石灰岩以发育分散小柱状凝块为主,形成于潮下带上部中—高能交替的沉积环境;块状凝块石灰岩以不规则块状凝块为特征,形成于潮下带下部低能环境,并受动荡水流影响;树枝状凝块石灰岩以发散的树枝状凝块为特征,形成于正常浪基面之下的深水低能环境。凝块石灰岩发育以风暴成因的竹叶状砾屑灰岩开始,以持续高能环境中发育的厚层鲕粒灰岩的出现为结束。凝块石灰岩形成的水深和水动力条件、依附基底特征和陆源泥质供给等影响凝块石灰岩内部结构和宏观形态,控制着凝块石灰岩的特征发育和整体演化。

THROMBOLITES AND CONTROLLING FACTORS FROM THE ZHANGXIA FORMATION OF CAMBRIAN SERIES 3 IN DENGFENG,WESTERN HENAN PROVINCE

Three typies of thrombolites can be recognized from the Zhangxia Formation(Cambrian Series 3)of Dengfeng,western Henan Province on the basis of macroscopic growth morphology and genetic environments.The smallcolumnar thrombolites are dominated by irregular,dispersive column mesoclots and are formed in the alternating medium-high energy upper subtidal zone.The massive thrombolites are characterized by irregular massive mesoclots and are formed in the low-energy,lower subtidal zone,occasionally affected by the agitating water.The dendritic thrombolites display the divergent dendritic mesoclots and are formed in the deep low-energy environment under normal wave base.The development of thrombolites begin with the storm-induced flat-pebble limestones and end with the occurrence of thickbedded oolitic limestones in sustained high-energy environment.The internal structures and macro morphology of thrombolites and their origin and evolution are controlled by water depth and hydrodynamic conditions,attached substrates and the influx of terrigenous clays.