Lithospheric flexure as a control on stratal geometry and fades distribution in Upper Cretaceous rocks of the Alberta foreland basin

Abstract

Facies distributions, stratal geometry and regional erosional bevelling surfaces in Upper Cretaceous (Cenomanian‐Santonian) strata of the Alberta foreland basin are interpreted in terms of high‐frequency (probably eustatic) relative changes in sea level, superimposed on longer‐term basin‐floor warping, related to episodic tectonic loading. Thick marine shales correspond to periods of rapid subsidence whereas thin but extensive strandplain sandstones record rapid progradation during slow subsidence. Westward‐thickening wedges of coastal plain strata were deposited during initial downwarping of a near‐horizontal strandplain, prior to marine transgression. Surfaces of erosional bevelling beneath which between 40 and >160m of strata have been removed extend at least 300 km from the present deformation front and are interpreted to reflect forebulge uplift in the east. Uplift appears to have lagged about 0.25‐0.5 Myr behind the onset of accelerated loading. Thin marine sandstones which grade westward into mudstone are interpreted as material winnowed from the crest of the rising forebulge. Subsidence and/or westward migration of the forebulge allowed the sea to flood westward across the eastern flank of the eroded forebulge. The transgressive shoreface cut asymmetric notches which were later blanketed by marine shales which lap out from east to west. The two unconformities which embody the largest erosional vacuity are veneered locally with oolitic ironstone which accumulated in a shallow, sediment‐starved setting on the crest of the forebulge. The consistent pattern of erosional bevelling and lap‐out of transgressive shales might be interpreted as evidence that the forebulge migrated towards the thrust load over a period of <1 Myr.

Retroarc foreland systems––evolution through time

“…As documented in a series of case studies in the Western Interior foredeep of Canada and the United States (e.g., Hart and Plint, 1993;Plint et al, 1993;Pang and Nummedal, 1995;Donaldson et al, 1998), flexure over reactivated crustal faults resulted in varying rates of subsidence across basement block boundaries, explaining localized incision, paleogeographic trends, and thickness and facies patterns that parallel terrane boundaries in the basement. The importance of basement tectonics on sedimentation was challenged by Aitken (1993), who noted that many basement features are only occasionally reflected, if at all, in the sedimentary cover overlying the basement.…”

Evolution of the northern Cordilleran foreland basin during the middle Cretaceous

“…However, Ross and Eaton (1999) suggested that there is little direct relationship between the Precambrian basement and presence and orientation of faults in the sedimentary section in the Alberta basin. In addition, in an earlier study by Plint et al (1993) it was suggested that at the British Columbia-Alberta border a forebulge zone controlled deposition of the Doe Creek and Pouce Coupe sandstones. Therefore, we interpret the hinge zone as a migratory forebulge (Fig.…”

Evolution of the passive margin of the peripheral foreland basin: an example from the Lower Miocene Carpathian Foredeep (Czech Republic)

“…18B). This situation probably mainly reflects the gradual sea-level rise, although early phases of the forebulge retreat might also play a role (Plint et al, 1993;Lesczyński & Nemec 2014). The interplay between sediment supply, basement relief, eustatic sea-level changes, and tectonics affected the frequent bathymetric changes and shoreline trajectory (dynamic stratigraphy of foredeep peripheral unconformity -see Lesczyński & Nemec 2014).…”