Genetic implications of the trace element distribution pattern in the upper knox carbonate rocks,copper ridge district,East Tennessee

The Lower Ordovician, Upper Knox Group rocks (the Kingsport and Mascot formations) in the Copper Ridge district consist predominantly of fine-grained dolostones, medium and coarser grained dolostones, and limestones. Dolomite crystals of medium and coarser grained dolostones show up to eight cathodoluminescent zones of variable width and intensity. Electron microprobe analyses indicate that the zoning is related to variation in Fe/Mn ratios, the brighter luminescent zones corresponding to lower ratios. Superposed on this growth zoning is a compositional zoning characterized by a general increase in Fe from core to rim of individual dolomite crystals.Field and petrographic studies (Churnet, 1979; Churnet et al., 1981) indicate that the fine-grained dolostones formed in supratidal to upper intratidal environments, whereas the precursor lime muds of the limestones as well as of the medium and coarser grained dolostones formed in shallow subtidal to lower intertidal environments. The large areal extent of the dolostones must have required a regionally abundant source of Mg such as marine water. Yet, both limestones and dolostones have low Na and Sr contents suggestive of their formation in solutions more dilute than normal marine water. It is proposed that the fine-grained dolostones formed by aggradation of initially very fine-grained dolostones in presence of fresh water, and that the limestones stabilized and the medium and coarser grained dolostones formed in environments of mixed marine and fresh waters. Considered in the light of ordering of partition coefficients, such a mixing model can account for the observed correlation pattern of trace elements (especially, SMn and SrFe) as well as the Fe distribution in the zoned dolomite crystals. Variation of the partition coefficient of Mn due to fluctuations in the relative proportions of fresh and marine waters in the diagenetic solution may explain the different Fe/Mn ratios observed in the growth zones (luminescence bands) of zoned dolomite crystals.     

Depositional environments of Lower Pennsylvanian coal-bearing siliciclastics of southeastern Tennessee, northwestern Georgia, and northeastern Alabama, U.S.A.

In the Cumberland Plateaus of southeastern Tennessee, northwestern Georgia, and northeast Alabama, Pennsylvanian strata are siliciclastics containing discontinuous coal seams. Above some of these coal seams, the shale deposits contain fossils of marine or brackish fauna. The entire sequence was deposited in an asymmetric foreland basin and is thickest in the southeast. Within this general trend there are locally thick deposits of lowermost Pennsylvanian Gizzard Group sequences that mark subbasins. Conglomeratic sandstone members of the Gizzard Group are discontinuous and tend to be thicker in the subbasins. In contrast, conglomeratic to sandy units are more laterally continuous in the overlying Crab Orchard Mountains Group. The Pennsylvanian sequence overlies paleosols with subjacent freshwater-neomorphosed shallow marine carbonates, or siliciclastics of the uppermost Mississippian Pennington Formation.A provenance discrimination diagram indicates that Pennsylvanian siliciclastics were derived from an orogenic source. Profile analysis of thick quartzose sandstone sequences indicates facies, architectural elements and bounding surfaces characteristic of braided stream deposits. A dominant southwest paleoflow direction is inferred from paleocurrent indicators in sandy braided and meandering stream deposits.