Abstract: Burial Diagenesis of Cambro-Ordovician Platform Carbonates, Southern Appalachians

K. Srinivasan, K. R. Walker, D. M. Steinhauff

Southern Appalachian Cambro-Ordovician platform carbonates experienced different burial diagenesis. The timing and origin of the burial phases were determined by petrographic and geochemical analyses. Late stage burial fluids evolved in separate basinal sequences and migrated at different times to the platform interiors.

Dolomite is the principal burial phase in the Middle Cambrian Maryville Limestone. Four different types of dolomite formed during shallow (Types I and II), intermediate (Type III), and deep burial (Type IV). Intermediate and deep burial dolomite (Types III and IV) increases in abundance downslope and show lateral trends in Fe and Mn abundance. Fe and Mn values in Type IV dolomite decrease from west (basin) to east (shelf). This suggests west-east fluid flow during late burial diagenesis. ⁸⁷Sr/⁸⁶Sr values for Type III and Type IV dolomite range from 0.7111 to 0.7139, radiogenic compared to Cambrian seawater. Temperatures calculated from dolomite ^dgr¹⁸O values are 75-160°C. The distribution of facies indicates a Cambrian shale source, and burial cu ves suggest an Ordovician age for fluid movement.

Middle Ordovician intermediate and late stage diagenetic phases were studied in a 400 m thick succession at shelf-edge and on-shelf localities. At the shelf-edge, these phases have more depleted ¹⁸O values, higher Fe and Mn contents, and higher ⁸⁷Sr than on the shelf, suggesting a siliciclastic fluid source. Using a range of likely brine compositions and ^dgr¹⁸O values for late ferroan calcite and dolomite allows estimation of temperatures of their formation. A comparison with temperatures derived from burial curves for platform vs basin indicates that the Sevier basin SE of the platform was the source of burial fluids.

These fluids may have moved as early as late Middle Ordovician.

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