Characterization of Lateral and Vertical Trends in Deep Marine Distal Levee Deposits of the Neoproterozoic Isaac Formation, Windermere Supergroup, British Columbia, Canada

Abstract

Channel-levee slope complexes are prominent features of deep-marine turbidite systems. To date, much research has been devoted to the channel part of the complexes, and less to the adjacent levees. This is partly because levee deposits in the ancient sedimentary rock record are typically poorly exposed and seismic studies of ancient, or even modern systems, cannot capture cm- to dm-scale details of these strata. At the Castle Creek study area, levee deposits of the Neoproterozoic Windermere Supergroup are glacially polished and completely exposed, allowing for detailed examination and description of lateral and vertical lithological variation and stratal geometries, which is critical to understanding reservoir geometry and continuity. Previous work at Castle Creek has shown that levee deposits are considerably more complex than simply laterally thinning beds forming a wedge-shaped geometry. Based on detailed description of a 100% exposed 250m wide by 40m thick succession, preliminary results indicate that although there was a general thinning trend away from the channel, several beds display the opposite trend. These latter beds are interspersed throughout the section and in addition to thinning towards the channel often pinch out. Levee deposits are dominated by thin-bedded T_c-e turbidites, with the T_c unit subdivided into 3 kinds: multi set, single set, or starved sets that form bedsets composed of self-similar ripple sets. The lateral thinning of beds, irrespective of direction (i.e. away or toward the channel) is due to changes in the thickness of the T_c unit, but notably grain size changes little. In contrast, the overlying T_de unit shows negligible grain size or thickness change. Starved ripple sets are the finest grained and range from lower fine to upper very fine sand, whereas multi-set turbidites are the coarsest grained and range from lower fine to lower medium sand. Single-set turbidites are of intermediate grain size and range from lower fine to upper fine sand. Bedsets, which typically comprise between 5 and 30 individual turbidites and range in thickness from 10cm to 250cm thick, do not appear to show any systematic stacking pattern. Nevertheless, the sharply-bounded contacts of individual bedsets suggests that instead of being more or less random, depositional conditions remained fairly constant for some length of time and then changed abruptly with the deposition (i.e. superposition) of a different kind of ripple cross-stratified bedset.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018