Carbonate Mud Mounds from Lower Ordovician Wah Wah Limestone, Ibex Area, Western Millard County, Utah: ABSTRACT

Abstract

Four carbonate lenses in the upper Wah Wah Limestone, western Utah, were core drilled. Thin sections and peels show that the lenses are mud mounds consisting primarily of micrite matrix, with some bioclastic debris, and minor (< 1%) intraclasts, pellets, iron minerals, and calcite fillings. Bioclastic debris consists of sponges, echinoderms, shell fragments (brachiopods and trilobites), and an encrusting problematic organism. Porosity is less than 1%; dolomitization averages less than 10%. The lenses are extremely burrowed. These fragments were transported to the buildups by currents which varied from fairly low energy to moderately high energy. The absence of frame-building organisms in growth position indicates that these buildups are mud mounds rather than reefs. Fo mation of the mud mounds could have resulted from sediment trapping by some organism, from sediment heaping by currents, or by a combination of both processes. The mud mounds are similar to those of other geologic periods. The mud mounds, although similar to reefs in external appearance, could have significance in that they serve as examples of what reefs are not. They also demonstrate that not all reeflike carbonate bodies offer potential for petroleum. Analysis of the interiors of carbonate lenses is required to distinguish reefs from mud mounds. End_of_Article - Last_Page 555------------