Dissolution and Recrystallization of Disarticulated Crinoids in Fort Payne Formation (Mississippian), Tennessee

Abstract

The Fort Payne Formation is a 320-million-year-old unit of rocks containing limestones, shales, and other sedimentary rocks. One of the main components of this formation is a crinoidal packstone, a biochemical sedimentary rock that is grain-supported and has more than 10% matrix material. The crinoid fragments within this unit show petrographic signs of dissolution, and recrystallization as quartz and/or calcite. Field samples taken on the TN Highway 52 near Celina, TN have been processed into thin sections for microscope work, which have been analyzed to observe the evidence of recrystallization of silica in these normally calcite rich fossil fragments. Five thin section slides from different parts of the Fort Payne have been studied, specifically where crinoid fragments above .5 mm in size occur. Here, we observe that recrystallization of silica only happens in specific parts of the crinoid fragments, and more importantly, the process of silica recrystallization happens as multiple phases of growth. There are two phases observed; A coarser grained internal phase, and a finer grained phase that remains adjacent to calcite growths. By using cross-cutting relationships, the order in which these phases of crystallization and dissolution occurred in can be more accurately charted chronologically.