--> The Deposition and Diagenesis of the Caddo Phylloid Algal Mounds, Caddo Limestone (Pennsylvanian), Stephen County, Texas, by M. C. Miller; #90903 (2001)

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The Deposition and Diagenesis of the Caddo Phylloid Algal Mounds, Caddo Limestone (Pennsylvanian), Stephen County, Texas

M. C. Miller
Department of Geosciences, Texas Tech University, Lubbock, TX ([email protected])

The Pennsylvanian Caddo Limestone (Atokan?-Desmoinesian?) of Stephens County, Texas, is a thick-hydrocarbon bearing carbonate unit. The uppermost Caddo is an algal-mound structure formed by the sediment-baffling effect of phylloid algae. Two cores south and southeast of Breckenridge, Texas were investigated petrographically and using geophysical logs to determine whether deposition or diagenesis of the mound structures was the major control on porosity. Within the cored intervals, multiple shallowing-upward sequences can be recognized. A succession of siliceous and calcareous sponge spiculites grade up into a basal mound wacke/packstone, then into phylloid algae-dominated bafflestone. Two different phylloid bafflestone deposition types can be recognized. Variation from quiet water (large intact phylloid algal blades associated with trapped carbonate mud) and a more agitated, higher energy waters (small layered broken “chip” phylloid blades) can be seen in the bafflestones.

The depositional features of the mound facies are strongly over printed by diagenesis. Fluctuations of sea level have imprinted multiple digenetic signatures on the algal mounds. Early marine cementation, multiple phases of fresh water cementation, repetitive dissolution and neomorphism, as well as burial (baroque) dolomitization have modified the aragonitic phylloid algal blades, associated baffled muds and original and diagenetic pore space within the mound units. The most important controls of pore space in the Caddo algal mounds were the multiple diagenetic events.

AAPG Search and Discovery Article #90903©2001 AAPG Mid-Continent Meeting, Amarillo, Texas