*WINNER* Bumped, Bruised and Broken: Mississippian Crinoids as Indicators of Paleoflow Conditions

Abstract

This won best undergraduate poster in Earth Sciences.

The Fort Payne Formation is a Middle Mississippian unit that outcrops in Kentucky and parts of northern Tennessee. The dominant lithologies of the Fort Payne are mixed carbonates and siliciclastic shale with abundant shallow marine fossils including disaggregated crinoids. This study focuses on using crinoid columnals to determine paleoflow conditions during deposition.

We use a two-fold approach combining field observations with subsequent flume analysis. First, we measured the trend and plunge of 128 crinoid columnals in two beds: one within a channel feature and one that was outside the channel. We found that, in general, crinoid stalk fragments within the channel showed a weak preferred orientation, while fragments located outside of the channel showed little preference towards a specific orientation.

We designed a series of flume experiments to test how crinoid fragments orient in a channel with respect to flow. We generated synthetic crinoid columnals using clay molds and published values for crinoid densities (~1.2 g/cm3 ) and performed a series of tests in a 10 foot-long recirculating flume. We documented the following key observations: (1) Crinoid fragments of similar densities but different diameters undergo hydraulic sorting; (2) Crinoid columnals, regardless of length and diameter, orient perpendicular with respect to flow when water velocity is appropriate; and (3) Larger crinoid fragments commonly stack against each other in channelized flow. Our results suggest that disaggregated crinoids in the Fort Payne Formation can be used as paleoflow indicators within channel features and record hydrodynamic conditions at the time of deposition.