Characteristics of Falling Stage Systems Tract Slope Channels: An Example from the Neoproterozoic Isaac Formation, Windermere Supergroup, Canada

Abstract

Coarse sediment filled channels are ubiquitous features of continental slope turbidite systems that are active during parts of all of a relative sea level cycle. Less well known are any systematic lithological and/or geometrical differences that would help differentiate channels formed and/or filled at different positions within a relative sea level cycle. At the study area the intermittent occurrence of shallow-water carbonate clasts, in addition to slumps, slides and debrites, collectively termed mass transport deposits (MTD), suggest periods of heightened slope instability and mass wasting that most probably coincided with episodes of falling relative sea level. As a result studying the stratal attributes of intercalated channel deposits permits the identification of sedimentological features specific, or at least more common, to conditions of falling relative sea level. This study examines several channel fills in a ∼150 m thick MTD dominated interval of continental slope deposits. Channel fills, MTD and levee deposits in the lower half of the section contain anomalous carbonate detritus, both as primary carbonate fragments and carbonate-cemented sandstone clasts. Additionally, the lowermost channel fill is dominated by anomalously coarse sediment, pebble conglomerate. Combined, these characteristics are interpreted to represent the initiation of carbonate and coarse, possibly mobilized palimpsest and relict sediment input during the early stages of relative sea level fall. Stratigraphically upward channel fills become significantly finer grained and absent of carbonate detritus. These systematic changes are interpreted to be related to long-term, allogenic influences on sediment supply to the deep-water system. Additionally, several channel fills have stratal attributes interpreted to be related to autogenic processes that are more common in unstable slope settings. These channels have two lithologically distinct fills: a lower fill composed of amalgamated, coarse-grained sandstone and mudbreccia; and an upper fill made up of markedly finer-grained sandstone beds with anomalously thick (several dm) muddy sandstone caps that onlap a debrite. The sharp contact between the two fills and thick muddy sandstone caps in the upper fills are interpreted to be related to the partial plugging of the channel by the debrite, which resulted in the local diversion of the axis of general sediment transport and ponding of the tail part of the transiting flows.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016