Print this pageStratal Architecture of Highly Confined and Poorly Confined Deep-Marine Sinuous Channel Systems - from Outcrop Perspective
Deep-marine strata of the Neoproterozoic Windermere Supergroup, western Canada, exhibit two end-member kinds of sinuous channel fills - poorly-confined and highly confined. Poorly-confined channels are larger-scale composite features up to about 100 m thick and over 1 km wide. Channel deposits tend to amalgamate vertically. Highly-confined systems, on the other hand, are smaller-scale, typically isolated features that are of the order of 10 m thick and separated vertically by thin-bedded turbidites.
In both poorly- and highly-confined channel systems coarse-grained channel deposits are flanked on both sides by levee deposits, however the make-up of these latter deposits are starkly different. In poorly-confined channels, the outer levee, at least in its proximal reaches (<400 m from channel margin) tends to be sand rich, and was constructed by flow overspill and inertial run-up. The contact between coarser-grained channel deposits and sandy levee strata is erosive. On the inner-bend side, by contrast, channel strata grade laterally into finer, thinner levee deposits, suggesting continuity of the flows that deposited in the channel and over the inner-bend levee. In highly-confined channels the outer bend is similarly erosive, but everywhere in contact with fine-grained levee deposits (thin-bedded turbidites) related to an older (underlying) channel. Sandstone injection complexes are locally well developed. On the inner-bend side of the channel, a distinctive obliquely-upward interfingering pattern of coarse-grained channel deposits terminating abruptly where they onlap fine-grained levee deposits is observed. This intercalation suggests episodes of fine- and coarse-grained sediment deposition on the inner-bend levee related to recurring variations in local flow and/or channel conditions. Moreover, the abrupt upward termination of coarse levee deposits against conterminous fine-grained levee strata suggests emplacement from the lower part of highly stratified turbulent flows that at least locally were depositional on the inner bend of a deep-marine sinuous channel.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009