Anton F.-J. Wroblewski¹

(1) University of Wyoming, Laramie, WY

ABSTRACT: Channel Belt Stacking Patterns and Tectonic Redirection of Paleocene Fluvial Systems, Hanna Basin Area, Southern Wyoming

Channelform sandstone bodies in the Ferris (late Maastrichtian-early Danian) and Hanna (Danian-Selandian) formations of Wyoming's Hanna Basin (HB) area (including the Carbon (CB) basin) represent three architectural types. The first (largest scale) is multistorey, amalgamated bodies (15-100 m-thick and 500-2500 m-wide) representing an axial system originating in the Green River Basin. The second (intermediate) architectural type is single or multistorey bodies (3-10 m-thick and 10's-100's m-wide) preserving more complete barforms and bedforms than the larger bodies and representing lacustrine and marginal marine deltaic systems. The smallest scale (1-5 m-thick and <100 m-wide) of sandstone body scours underlying overbank deposits, and represents trunk drainages flowing off local Laramide uplifts.

Significant differences in stratigraphic thickness, paleocurrents, clast composition, and stratigraphic relationships to underlying units throughout the HB area, coupled with biostratigraphy, permit reconstruction of tectonic histories (and influence upon local fluvial systems) of local Laramide uplifts.

Earliest Danian paleocurrent reversals reflect initial reorganization of fluvial drainages in response to tectonic partitioning of the HB area. Uplift of Simpson Ridge (SR) and the Rawlins Uplift is indicated by: 1) thinning of Maastrichtian-Selandian strata towards SR, into CB; 2) advent of drainages flowing down-structure off SR; and 3) lacustrine deposition in the southeastern HB as SR formed a sediment barrier.

Danian uplift of the eastern Granite Mountains (EGM) is suggested by: 1) erosion of older units during deposition of the Hanna Formation; 2) advent of drainages that flowed down-structure off the EGM; and 3) lacustrine deposition and sediment ponding in the northeastern HB.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado