Bypass Margins, Basin-Restricted Wedges, and Platform-to-Basin Correlation, Upper Devonian, Canadian Rocky Mountains: Implications for Sequence Stratigraphy of Carbonate Platform Systems

Abstract

Carbonate platforms can commonly keep up with relative sea-level rise because of high rates of sediment accumulation and platform aggradation. Surrounding basinal environments are commonly starved but can receive variable extrabasinal siliciclastic input and episodically deposited carbonate sediment. If accumulation rates in basinal settings lag behind those of the platform, a bypass or erosional margin can develop. Under these circumstances platform and basin depositional sequences become physically detached and direct correlation of basinal and platform sequences is hindered.We report here the results of high-resolution stratigraphic analyses of two Upper Devonian isolated carbonate platforms in western Alberta that provide insight into the sequence stratigraphy of bypass margins and criteria for accurate correlation of platform and basinal sequences. The slope and basin sequences surrounding the Miette and Ancient Wall platforms consist of basin-restricted, onlapping wedges of fine-grained background sediment deposited dominantly from suspension and coarse-grained platform-derived sediment redeposited by a variety of gravity-flow mechanisms. Sequence boundaries are identified within the redeposited carbonate intervals. Identification of sequence boundaries and differentiation of highstand and lowstand slope and basinal facies was based on the geometry, mineralogy, and clast content of redeposited carbonate units. Highstand carbonates contain sheet-like debris flows and turbidites with abundant slope-derived clasts and background facies with high total carbonate content. Lowstand carbonates contain sheet-like and channelized debris flows and turbidites with abundant platform-derived clasts and background facies with low carbonate content and locally high amounts of organic carbon. Transgressive facies are dominated by initially carbonate-poor and organic-rich background sediments that display a progressive increase in carbonate content and decrease in organic carbon content. These patterns are interpreted to record abundant background carbonate sedimentation during late transgression and highstand when the carbonate factory was robust. Highstand redeposited carbonates record slope erosion due to oversteepening and slope readjustment processes. Lowstand redeposited carbonates indicate platform and platform-margin erosion and low background carbonate sedimentation when the platform was either exposed or under very shallow peritidal conditions. High siliciclastic and organic contents during lowstand and early transgression may partly be the result of reciprocal sedimentation but alternatively may represent continuous siliciclastic supply during times with little dilution by fine-grained carbonate sediment.Successive stages of platform development at Miette and Ancient Wall were controlled by accommodation changes driven by relative sea-level fluctuations. Backstripping analyses of strata from both platforms confirm that significant differential subsidence was a major control on variations in platform thickness and...

Regressive-transgressive cyclothem with facies record of the re-flooding window in the Late Silurian carbonate succession (Podolia, Ukraine)

“…: Droxler and Schlager 1985;Schlager et al 1994), both in relation to modern reefs, as well as to fossil (e.g. Devonian) examples (Whalen et al 2000, Racki et al 2002.…”

Hydrothermal activities and seawater acidification in the Late Devonian F-F transition: Evidence from geochemistry of rare earth elements

“…At the Yangdi section, as indicated by concordant Ce negative anomaly in all measured samples, there are no significant changes in redox conditions in the F-F transition, which might be related with the carbonate platform margin deeper water environment where frequent turbidity currents took place. Besides the anoxic event, collapse of stromatoporoid-coral reef ecosystem and overall carbonate production break also took place near the Upper Kellwasser horizon [32,60]. Whalen et al [60] claimed that most carbonate-starved, organic-rich sediments were linked with lowstand and early flooding as a record of minimal carbonate production and off-shoal ooze input.…”

“…Besides the anoxic event, collapse of stromatoporoid-coral reef ecosystem and overall carbonate production break also took place near the Upper Kellwasser horizon [32,60]. Whalen et al [60] claimed that most carbonate-starved, organic-rich sediments were linked with lowstand and early flooding as a record of minimal carbonate production and off-shoal ooze input. Herein we suggest that the carbonate-starved is also linked with seawater acidification caused by hydrothermal activities.…”

Toe-of-slope deposits of a Givetian reef-rimmed platform: provenance of calcareous density-flow deposits (Rabat-Tiflet-Zone, Morocco)

“…Gravel-rich density-flow deposits are usually distributed in proximal parts of a carbonate apron (Cook 1983;Harris 1994;Melim and Scholle 1995;Whalen et al 2000b;Drzewiecki and Simó 2002). Exceptions are thin gravely density-flow deposits which can be commonly traced far into the basin plain (e.g.…”