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Early and Middle Permian Proximally to Distally Steepened Cool-Water Shelf-to-Basin Transition, Sverdrup Basin, Arctic Canada

Beauchamp, Benoit *1
(1) Department of Geoscience, University of Calgary, Calgary, AB, Canada.

Artinskian (Lower Permian) and Wordian (Middle Permian) cool-water heterozoan carbonates formed extensive shelves in the Sverdrup Basin, Arctic Canada, where they pass laterally into substantially deeper water sediments that accumulated in a slope to basinal setting. The cool-water sedimentary regime followed a Pennsylvanian-Early Permian interval of warm water sedimentation that led to extensive shelf and shelf margin reef development. The shallow-shelf to deep-basin transition in the less productive carbonate cool-water setting contrasts with the far more prolific warm-water carbonate factories and their transition to Deepwater settings that existed earlier in the basin. In addition to a major drop in sediment production, cool water shelves or shelf-margins are devoid of reefs (only isolated mud mounds in the Artinskian, none in the Wordian) and microbial fabrics that play an important role in stabilizing slopes in their warm-water counterpart. Furthermore, heterozoan carbonate sediments composed of echinoderms, bryozoans and brachiopods, ranging from whole fossils to bioclasts, remained uncemented on the sea floor and at shallow burial depth due to the cooler water setting. The sediments were thus much freer to be moved around than in their warm water counterparts. Cool-water carbonate shelves of the Sverdrup Basin thus bear much resemblance to later clastic shelves as the sedimentary accumulations expanded from a relatively narrow nearshore area following the large second-order transgressions to prograde in a basinward direction via a series of gently-inclined clinoforms. The recurrent pattern of progradation evolved from proximally-steepened shelf to distally-steepened shelf with relatively coarse heterozoan sediments avalanching in a basinal direction with time. Once the sediment was formed on the sea floor following the death of various organisms, the principal agent for the redistribution were storms that were free to sweep wide areas of the shelf as they were unimpeded by shelf margin or mid-shelf reef constructions as in the earlier warm water setting. Ultimately, sloping carbonates pass into spiculitic chert which represents sedimentation in a distal shelf, ramp and slope setting. Coarse-grained turbidities are relatively well developed in these cool-water settings owing to the availability of a rich supply of loose coarse grained material on the shelf, which is not the case in the older warmer setting.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California