--> Abstract: Architecture of Lateral Accretion Deposits in Deep-Marine Sinuous Channel Fills, by R. William C. Arnott; #90039 (2005)

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Architecture of Lateral Accretion Deposits in Deep-Marine Sinuous Channel Fills

R. William C. Arnott
University of Ottawa, Ottawa, ON

At Castle Creek a 2.5 km-thick succession of basin-floor to continental slope Neoproterozoic rocks are superbly exposed. In part of that outcrop inner-bend deposits of three sharp-based, laterally-accreting sinuous channels, which, stratigraphically-upward, are oriented parallel, perpendicular, and moderately oblique to the outcrop surface. Lateral-accretion deposits, which are inclined at 7-12o to the channel base and are of the order of 120-140 m long, comprise subparallel but inclined, decimeter-thick beds composed of very coarse sandstone/granule conglomerate grading upward to medium sandstone -- grain size changes little along their length or stratigraphically upward, but beds generally do thin upward.

Mudstone (in reality silty slate) is generally absent. Where present, it occurs typically as isolated patches of intraclast breccia in the lower 1/3 of the channel fill. At the top of the channel fill mudstone interfingers with typically very coarse, poorly-sorted (lateral-accretion) sandstone that thin laterally and then pinch out, commonly abruptly, into the mudstone. Sandstone consists commonly of two sharp-based units: basal poorly-sorted, ungraded very coarse sandstone that locally is dune cross-stratified, overlain abruptly by planar-laminated medium sandstone. Beyond the pinch-out of both the upper and lower units, mudstone strata show no evidence of erosion, suggesting the flows that deposited the coarse lateral accretion layers formed only a featureless bypass surface beyond the sandstone pinch-out. In addition, the bipartite structure of the sandstone layer suggests that suspension deposition over much of the lateral accretion surface was succeeded, at least on the upper part of the lateral accretion surface, by sediment reworking and bed-load transport.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005