Comparative Taphonomy of Echinoderms in Carbonate Facies: Fort Payne Formation (Lower Mississippian) of Kentucky and Tennessee

Abstract

Taphonomic analysis of more than 3000 specimens of crinoids and blastoids from 14 localities from south-central Kentucky and north-central Tennessee reveals differences in preservational style among five carbonate and associated clastic facies. Collections from each locality were sorted on the basis of a 9-point taphonomic scale ranging from fully articulated specimens with arms and column to isolated plates. Degree of skeletal articulation is used as a relative measure of burial rate and autochthony. Preservational style of a pelmatozoan assemblage is the product of both depositional processes and differential taphonomic behavior of different morphotypes. The taphonomic profile for an assemblage is strongly influenced by the preservational style of its dominant pelmatozoan taxa. Taking this taxonomic and morphologic bias into account, both autochthonous and allochthonous pelmatozoan-rich facies are recognized in the Fort Payne Formation. Carbonate facies judged to be chiefly autochthonous are 1) crinoidal packstone buildups showing a full range of preservation including articulated specimens, and 2) wackestone buildups dominated by complete calyxes lacking arms and column. Green shales associated with carbonate buildups are dominated by disarticulated specimens but include complete calyxes and arm segments, suggesting slow background deposition punctuated by periodic rapid influxes. Allochthonous carbonates include 1) sheetlike packstones dominated by complete and partial calyxes, and 2) channelform packstones dominated by disarticulated skeletal debris with occasional fully articulated crinoids. Fort Payne carbonate facies in north-central Tennessee are exclusively allochthonous, sheetlike packstones, whereas both allochthonous and autochthonous facies occur in Kentucky proximal to the Borden Front. The taphonomic character and distribution of pelmatozoan-rich facies in the Fort Payne in Kentucky and Tennessee are consistent with a progradational, basin-filling depositional model.