--> Depositional and Diagenetic Controls on Porosity in Permian Abo and Tubb Sandstones, Northeastern New Mexico, by M. K. Nelis and H. J. Wacker; #90986 (1994).

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Abstract: Depositional and Diagenetic Controls on Porosity in Permian Abo and Tubb Sandstones, Northeastern New Mexico

Mary K. Nelis, Herbert J. Wacker

Petrologic study of redbed sandstones of the (subsurface) Abo and Tubb formations in the Bravo Dome area indicate that sandstones deposited in three general depositional environments responded differently to changing diagenetic conditions.

The oldest Abo sandstones were derived from granitic highlands northwest of Bravo Dome. The arkoses are feldspar-rich, coarse-grained, poorly-sorted, and were deposited in an alluvial fan environment. Overlying coarse-grained deposits are moderate- to well-sorted and were deposited in braided stream environments as sediment moved southeast across a broad alluvial plain. The youngest Abo and Tubb arkoses are very fine-grained, very well-sorted, and quartz-rich. They were deposited in wadis and display wind-reworking fabrics. Marine transgression from the southeast over the Tubb alluvial plain capped the sequence with an evaporite seal.

The paragenetic sequence indicates that diagenesis took place in three pore fluid-geochemical settings: (a) alkaline + oxidizing; (b) alkaline + reducing; and (c) acid + reducing. The sequence consists of: (1) Hematite and I/S grain coating, cementation by evaporites and carbonates, and dissolution of feldspar (at the surface and shortly after burial); (2) Cementation by evaporites, progressively more Fe-rich carbonates, and chlorite (after marine transgression). Cementation by adularia and quartz spans stages 1 and 2; (3) Dissolution of detrital plagioclase and carbonate cements, and cementation by zeolites and kaolinite (after invasion of CO2 and faulting).

The pore system developed in older, feldspar-rich, coarse-grained units is mostly moldic and intragranular and formed in stages 1 and 2. Younger, quartzose, fine-grained units exhibit a complex intergranular pore system that reflects the primary fabric as well as stage 3 dissolution.

Understanding the response of each sandstone type to the changing pore fluids improves prediction of porosity trends at Bravo Dome.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994