Sedimentology and sequence stratigraphy of the Baker Lake sub-basin, Nunavut: Evolution of a Paleoproterozoic rift basin.

摘要

The northeast-trending Baker Lake sub-basin was a volcanically active half-graben during deposition of ca. 1.85-1.78 Ga Baker Lake Group. Transverse streamflow-dominated alluvial fans were concentrated along the southern margin of the sub-basin. These fed gravel- and sand-bed braided streams that merged with an axial drainage system. Alluvial dynamics were characterized by channel aggradation and abandonment. Abandoned channel belts were sites of floodplain and eolian deposition. Braided streams fed northeast and southwest to a depocentre located near Christopher Island, where eolian, playa, and lacustrine environments were intimately linked. Paleoflow patterns indicate that the sub-basin was hydrologically closed.; A model is derived for the alluvial sequence stratigraphy and is applied to the Baker Lake Basin. Discharge and sediment supply are considered boundary conditions. Primary control on alluvial facies changes is attributed to alluvial gradient. Graded profile is defined as the topographic profile of a graded stream linking a sediment source region to a subaqueous basin. It is proposed that coupled source uplift and basin subsidence exert primary control on alluvial systems at relatively large scales.; In Baker Lake Basin, high accommodation alluvial, low accommodation alluvial, and mixed fluvial-shallow-lacustrine sequences are interpreted as 3 rd-order depositional sequences of tectonic origin. The succession of 3rd order sequences illustrates basin evolution from rift initiation, rift climax accompanied by widespread volcanism, to immediate post-rift. These comprise the 2nd order Baker Sequence, representing a tectonic stage of intracontinental rifting.; The high accommodation stage of basin development may have been the result of intracontinental retro-arc extension during ca. 1.85-1.84 Ga formation of the Kisseynew back-arc basin of the Trans-Hudson orogen. The Baker Lake Basin probably marked the northeastern extent of a series of basins that trended along the Snowbird Tectonic Zone, correlative with the Martin Group in northwestern Saskatchewan. Closure of the Kisseynew basin and collision of the Superior Province with the Western Churchill Province coincided with a change to strike-slip dominated faulting in the Baker Lake Basin. This low accommodation stage of basin development probably was a response to lateral tectonic escape adjacent to the Saskatchewan-Manitoba and Baffin Island-Committee Bay foci of the Superior collision.