Estimation of Source-to-Sink Mass Balance and Depositional Systems Dominated Sediment Budgets by a Fulcrum Approach Assessment Using Channel Paleohydrologic Parameters: Cretaceous Dunvegan Formation

Abstract

Trunk rivers transport the bulk of the sediment in a source-to-sink (S2S) system, and total mass passing through any cross section (i.e., fulcrum) of a trunk river over geologic time should allow matching of source area sediment delivery budgets, to the downstream sediment volumes deposited in the basin. We analyze the paleohydrology of ancient trunk channels and linked downstream deltaic strata of Allomember E of the Cretaceous Dunvegan Formation in the Western Canadian Sedimentary Basin to test the total mass balance fulcrum approach. Bankfull channel depth and width, grain size, paleoslope, velocity, and discharge are derived from outcrop, core, and well logs. Some parameter estimates use multiple methods providing a range of values and serving as a cross check of independent methods. Annual flood frequency and paleodischarge estimates, associated with long-term geologic time estimates, are derived from chronostratigraphic analysis and allow cumulative sediment discharge calculation. Isopach maps are used to estimate sink area sediment volumes. The results indicate that the trunk river of Allomember E was 10-20m deep and 150-250m wide, carried fine to medium-grained (average 180 microns) sand and flowed over a low-gradient paleoslope of 10-5. Annual total sediment discharge is estimated to range from 2.6×106 to 8.4×106 m³. Within 70,000 to 100,000 years, the river is estimated to have transported 1.83 × 1011 m³ – 8.39 × 1011 m³ of sediment into the basin. This is consistent with the 1.1×1011 m³ of sediment documented in the sink area. However the upper range estimate of sediment delivered into the sink is up to 8 times the measured sediment volumes, which, if accurate, suggests significant sediment escape. This supports the hypothesis that in Dunvegan time, mud was widely dispersed southward, along the Alberta Foreland Basin by geostrophic currents associated with storm processes and counterclockwise oceanic gyres in the Cretaceous Seaway.

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