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Distribution and Paleoecology of Algae from Missourian (Upper Pennsylvanian) Cyclic Sequences, Mid-Continent, USA

HOLTERHOFF, PETER F., University of Cincinnati, Cincinnati, OH

The objectives of this study are fourfold: (1) document the basinal to inner shelf and vertical distribution of marine algae from Missourian transgressive-regressive depositional sequences of the U.S. Mid-Continent; (2) integrate observed taphonomic and petrographic properties with the distribution patterns to produce empirically derived paleoecologic interpretations of these algae; (3) propose an algal-carbonate facies model for Upper Pennsylvanian depositional sequences; (4) indicate which facies could be potential reservoirs.

Preliminary results indicate that cyanobacteria, often intergrown with encrusting forams, are as abundant as oncoids and encrustations; this consortia is often associated with the encrusting rhodophyte Archaeolithophyllum lamellosum, creating boundstone hardgrounds. These algae are especially characteristic of transgressive/highstand shelf and basin facies, are not commonly associated with other calcareous algal groups, and are low-light tolerant.

The rhodophyte phylloid alga A. missouriense occurs as large prostrate blades in mudstones, as in situ broken blades with abundant isopachous and botryoidal fiborous cements and mudstone breccia, or as abraded fragments in grainstones associated with various chlorophytes. These occurrences range across shelf facies; thus A. missouriense is probably the most eurytopic of the skeletal algae.

Codiacean chlorophyte phylloid algae are characteristically associated with shelf buildups and inner shelf/late highstand shoal grainstones. Fragments of dasycladacean chlorophytes are often associated with the shoal facies codiaceans. These algae appear rather stenotopic, requiring well-lit conditions.

Potential porosity development involves dissolution of metastable algal blades and marine cements in buildup and grainstone facies.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)