Date of Award

1997

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology and Geophysics

First Advisor

Arnold H. Bouma

Abstract

The present research was aimed at comparison and distinction between various deltaic subenvironments from Pennsylvanian deposits of the Arkoma Basin, Arkansas. Detailed facies analysis of deltaic deposits reveal significant variation in sedimentary characteristics between different subenvironments. A multi-pronged approach, including documentation of measured sections and gamma ray profiles in the field and subsequent laboratory analysis of samples, was undertaken. The Atoka Formation deltaic deposits have been established primarily as representing fluvially-dominated deltas. Interdistributary bay fill deposits are splintery shales with abundant siderite nodules. Crevasse splay sandstone units are ripple cross-laminated and coarsen and thicken upward to a maximum of 60cm thick beds. Distributary channel deposits have sharp erosive bases and are composed of either an active or a passive fill. Active fill is characterized by large scale cross-bedding while passive fill is predominantly parallely laminated. Distributary mouth bar deposits show coarsening and thickening-upward sequences with tabular beds grading upward into more lenticular beds with occasional well developed cross-bedding. Delta front deposits are heterolithic with ripple cross-laminations and intense bioturbation. Prodelta deposits are predominantly shales with laterally persistent silty laminations that occasionally form starved ripples. Zoophycos ichnofacies are well represented in distributary mouth bar and delta front deposits. Skolithos-Cruziana ichnofacies are represented in delta front and interdistributary bayfill deposits, the latter with the unique presence of Conostichus. Amorphous non-structured dominated kerogen assemblages are present in all the subenvironments suggesting long transport possibly by fluvial effluence. Lycospora spp. dominated palynomorphs suggest coal-forming, swampy vegetation in the lower deltaic plain. Anisotropy of isothermal remanent magnetization (IRMA) analysis was conducted which revealed systematic variations in magnetic grain long axis (K$\sb{\rm max}$) alignment. Distributary mouth bar deposits show flow normal, while delta front and crevasse splay deposits show flow parallel K$\sb{\rm max}$ orientations. Distributary mouth bar deposits have 19% and delta front and crevasse splay deposits have 8% and 13% anisotropies, respectively, associated with sedimentary fabrics. The Atoka Formation deltaic deposits have been placed within a sequence stratigraphic framework. The composite section of the Atoka Formation reveals retrogradational, progradational, and aggradational parasequence stacking patterns deposited in a transgressive to highstand systems tract.

ISBN

9780591591095

Pages

213

DOI

10.31390/gradschool_disstheses.6462

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