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Abstract

Deep marine rocks of the Windermere Supergroup record a several km-thick sedimentary pile that accumulated along the passive continental margin of Neoproterozoic Laurentia (ancestral North America). The succession comprises mostly siliciclastic sedimentary rocks intercalated with carbonate and mixed carbonate-siliciclastic intervals that range up to a few 100 m in thickness. Observations along a several 100 km-long depositional transect that stretches from upper slope canyons to deep basin-floor deposits shows a number of systematic changes that appear to be principally controlled by changes of eustasy. Significantly, these changes are only recognized in the slope part of the transect.

Slope deposits form a ~2 km-thick succession dominated by thin-bedded turbidites that locally are intercalated with up to >100 m-thick by several km-wide erosional and leveed channel complexes. Channels exhibit two end member kinds of fill: aggradational and laterally accreting. Aggradationally filled channels are flanked by well developed sandy levees compared to mud-rich levees in the case of laterally accreting channels. Unlike aggradationally filled channels and laterally accreting channels are associated with the input of carbonate sediment, typically in the form of carbonate-cemented sandstone and mudstone clasts. Additionally, evidence of mass wasting, evidenced by thickly developed and areally extensive debrites, slump, and slide deposits, become an important component in the stratigraphy. Fragments within these strata, namely stromatolite and oolite fragments, in addition to abundant carbonate-cemented sandstone and mudstone clasts, indicates the resedimentation of debris sourced from an upslope shallow-water carbonate platform under late transgressive, highstand and possibly also early falling stage conditions. Specifically, the rise of eustasy is interpreted to have not only initiated the development of a carbonate platform, and thereby the input of carbonate sediment, but more importantly changed the make-up of the siliciclastic sediment supply, principally in terms of its grain size and grain-size distribution.

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