Nada Member (Borden Formation) of Kentucky: Macrofauna

by Don Chesnut (chesnut<at>uky.edu)
ęDRC 2014

Outcrop of the Nada Member

Introduction

The Mississippian-age Nada Member is a fossiliferous shale found in the upper part of the Borden Formation in the western-belt of outcrop in eastern Kentucky. It consists of shale with interbeds of calcareous shale, and thin limestone and siltstone stringers. The Nada overlies the massive Cowbell Siltstone Member of the  Borden and unconformably underlies the Renfro Member of the Slade Formation, a predominantly limestone and dolostone unit. In the southern part of the belt of outcrop, in Madison and Rockcastle counties, Kentucky, the Nada is overlain by the thin interbedded siltone and shale Wildie Member of the Borden. The Osagian-age Nada has been cited as being equivalent to the uppermost Tournasian (Lee and others, 2005, Work and Mason, 2009) in Europe. The Cowbell Silstone has been interpreted as having been deposited as a subaqueous delta known as the Borden Delta (Chaplin, 1980). The glauconite- and phosphorite-bearing Nada is thought to have been deposited as part of a transgressive-system tract on top of the Borden Delta platform.
Glauconitic siltstone
Glauconitic siltstone [bar = 1cm]

Thin argillaceous limestone bed.
Crinoidal argillaceous limestone bed

Macrofauna

Identified macrofauna from the Nada Member include echinoderms, mollusks, brachiopods, bryozoans, cnidarians, arthropods and poriferans. Most abundant are bryozoans, brachiopods and echinoderms. Dissassociated fossiliferous shales yield fines composed of about 95% fenestrate bryozoan debris and 5% crinoid ossicles, other fossil debris, pyrite, glauconite and phosphorite. Thin argillaceous limestone beds contain abundant crinoid, brachiopod and fenestellid and ramose bryozoan fossils. See the following categories for more information.

References