Stratigraphic Architecture of Coal and Non-Marine Strata of the Mannville Group in the Western Canadian Sedimentary Basin, South Central Alberta

Abstract

The Mannville group is a clastic wedge deposited during Barremian to early Albian ages in the Western Canadian foreland basin. It is overlying a major regional unconformity and corresponds to a third order sequence. The lowstand and transgressive system tracts refer to the Lower Mannville, whereas the highstand tract refers to the Upper Mannville. The Mannville Group includes thick and extended non-marine deposits, which may be referred to as coal bearing strata with enormous reserves. The upstream continental part of the Upper Manville in Central Alberta remains stratigraphically undivided. It is however punctuated by several sequences, considered as 4th order sequences associated to relative sea level changes, causing the formation of incised valleys. The main objectives of this study is to characterize the occurrence of coal strata of the Mannville Group in South Alberta, by focusing on their geometry, extension and distribution. A well-constrained stratigraphic framework has been established through two regional transects, calibrated by core description interpretation, in order to better predict their occurrence in the basin. The Vail model has been applied, as the stratigraphic architecture resulting from the correlation work can be subdivided into system tracts: a lowstand system tract, that correspond to the Lower Mannville Fm.; a backstepping phase of marine transgression corresponding to the transgressive system tract; and finally a highstand system tract that correspond to the “undivided” Upper Mannville. The geometry, distribution and extension of the present coal layers is examined withinboth the 4th order sequences end the third order sequences. In the latter, four different zones can be distinguished: LST-TST, early HST, middle HST and late HST. Relative thin and more restricted coal layers are formed during the lowstand and transgressive system tracts and also during the late highstand system tract. Thicker, more extensive coal layers are created during early highstand, as a result of the interplay between the early third order highstand and the fourth order highstand period. In middle highstand system tract, the thick and extensive coal layers are positioned near the fourth order MFS, which creates enough time and space to establish and accumulate significant volumes of terrigenous, organic-rich material.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015