Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Stratal Stacking Patterns and Sandstone Body Dimensions in the Cretaceous Ferron Sandstone of the Henry Mountains, South-Central Utah
(1) Department of Earth & Atmospheric Sciences, University of Nebraska-Lincoln, Lincoln, NE.
A sedimentological and stratigraphic analysis of the Turonian Ferron Sandstone along the western limb of the Henry Mountains Syncline, south-central Utah was undertaken. 60 detailed sections were logged through the formation over a depositional strike-oriented transect 67 km long, and beds were correlated physically between sections. Facies analysis reveals the studied succession to be the product of repeated progradation of river-dominated but wave- and tide-influenced deltas into the Cretaceous Western Interior Seaway Basin. The regional paleoslope was eastward, but sediments were deflected towards the south once they entered the marine basin (Fielding, 2010, J.Sed.Res., 80, 455-479). Overall, the stratal stacking pattern in the depositional strike orientation is tabular, with local development of clinoform sets in mainly distal delta front heterolithic facies. Delta front sandstones are relatively thin (<10 m thick) and up to 10 km wide in the lower part of the formation, becoming thicker and broader upward. Some composite sandstone bodies in the middle part of the formation are continuous over >50 km north-south. The upper part of the Ferron preserves a number of coastal fluvial channel sandstone bodies. These are concentrated in at least three clusters each 6-8 km in width and separated by 6-12 km-wide belts that are dominated by floodbasin mudrocks and that contain concentrations of coal and carbonaceous shale. Two regionally extensive erosion surfaces have been traced throughout the transect in the upper half of the formation, and are interpreted as sequence boundaries. These surfaces are predominantly planar and show only modest erosional relief (<10 m deep channel forms inset into ~planar surfaces). Facies juxtapositions indicate 10-20 m of relative sea-level fall across these boundaries. Other such surfaces are probably also preserved within the formation but are more difficult to trace laterally. In general, proximal facies overlie distal facies abruptly in individual progradational cycles, suggesting an external forcing control on stratal architecture. The degree of facies truncation and erosional relief on key surfaces increases upward, and the facies are more proximal with mainly delta platform deposits in the upper third of the formation. This is suggestive of sediment accumulation under a regime of gradually diminishing accommodation, superimposed on which are numerous shorter-term cycles of modest relative sea-level fluctuation.