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Abstract: Relationship Of Middle Ordovician Late Stage Diagenesis To Diagenesis Of Lower Ordovician Upper Knox Carbonates In East Tennessee


The Lower Ordovician Knox group hosts Mississippi Valley-type deposits in carbonate rocks that underlie Middle Ordovician limestones in East Tennessee. Basin evolution modeling, Rb-Sr dating of sphalerites, and analysis of organic compounds extracted from sphalerite provide various age estimates for mineralizing fluid ages ranging from about 410 Ma to 265 Ma.

The petrography, paragenetic timing, 87Sr/86Sr, and stable isotopes of oxygen of ferroan baroque dolomite in the Middle Ordovician are similar to pre-ore zone 2 and 3 dolomite cements in the Upper Knox. In addition, the 87Sr/86Sr of late burial ferroan baroque dolomite in the Middle Ordovician is similar to values reported for pre- and post-ore dolomite in the Knox Group.

Could zone 2 and 3 dolomite cements in the Knox have been precipitated from the same fluid that precipitated late burial ferroan dolomite in Middle Ordovician rocks? Analysis of temperatures estimated from burial curves, an assumed range of likely brine compositions, and known stable isotopic values of oxygen for late ferroan sparry calcite and ferroan baroque dolomite suggest that the Sevier basin is the most likely source of burial fluid that precipitated these late burial phases. Our analysis suggests that the Sevier basin could have expelled hot metal bearing brines into the Knox Group and the Middle Ordovician platform before the end of the Middle Ordovician (ca. 450 Ma).

AAPG Search and Discovery Article #90939©1997 AAPG Eastern Section and TSOP, Lexington, Kentucky