Dedolomitization, Dolomitization, and Chertification in Fort Payne Formation: Relative Timing and Mechanism: ABSTRACT

Abstract

Samples of the Fort Payne Formation (Lower Mississippian) of central Tennessee typically contain 50% or more chert, with the bulk of the balance consisting of replacive dolomite. Low-iron calcite and ferroan calcite are common and minor ankerite is also present. The relative sequence of diagenetic replacement was established by cross-cutting relations as: low-iron calcite replaced by chert replaced by dolomite, introduction of ankerite, and finally, replacement by ferroan calcite of both chert and dolomite (dedolomitization). Thus dedolomitization was the last diagenetic phase. Complete replacement, rim replacement, and replacement of cores of dolomite rhombs by ferroan calcite was observed. Ferroan calcite fills veins, vugs, and intergranular pores and replaces sponge sp cules. Dedolomite occurs in both surface and subsurface samples, and there is no evidence for an unconformity within or adjacent to the Fort Payne, suggesting that the dedolomite is not related to exhumation and weathering. Minor mineralogy and sedimentary structures suggest a subtidal shelf, quiet-water environment of deposition. Stratigraphic relations suggest shallow burial. Dedolomitization of the Fort Payne occurred after lithification, probably during shallow burial, when ferrous iron was derived from indigenous minerals. End_of_Article - Last_Page 501------------