Subglacial bedforms and landscapes formed by an ice sheet of Ediacaran-Cambrian age in west Henan, North China

摘要

Diamictites of late Ediacaran to early Cambrian age (ca. 551-518 Ma) are widespread across Southeast-Central Asia, with the Luoquan Formation particularly well preserved along the southern margin of the North China craton. A basal unconformity, comprising striations and p-forms interpreted to have been produced subglacially, was cut into Mesoproterozoic basement. Integrating new observations on the basal unconformity with the stratigraphy and sedimentology of the Luoquan Formation, an unequivocal glacial origin is demonstrated. The succession evolves from massive or stratified diamictite at the base to laminated fine-siltstone with dropstones upward, and is capped by siltstone with or without dropstones on the top. These lithological combinations represent a glacial sedimentary succession deposited recording progressive retreat of the ice margin. Based on multiple palaeoflow measurements, data from 7 new measured sections, and facies analysis, a new paleogeo-graphic model is proposed. This model envisages the expansion of a large continental ice sheet from north to south at the southern flank of the North China Craton (NCC).