Frankfort Field Trip

Cyclonema gastropod


The many roadcuts on Rt. 127 north of Frankfort are popular places to collect. On one particular cut, an exposure of the lower tongue of the Clays Ferry Formation (Middle Ordovician) has yielded beautiful and abundant Cyclonema gastropods, a partial starfish, one spectacular Paraglyptocrinus crinoid, a couple dozen Glyptocrinus crinoids (two with snails attached!), a Lebetodiscus edrioasteroid, about 25 small Dendrocrinus crinoid calyxes, and an Anomalocrinus crinoid. On another multi-bench cut, the Lexington Limestone (Logana Member) yielded well preserved clams and flattened Conularia. Further north on Rt. 127, a large multi-bench cut exposing the Middle Ordovician lower tongue of the Clays Ferry Formation produced many nice Ectenocrinus crinoids. Some slabs even had calyxes exposed on both sides of the slab!

In addition to fossils, one road cut shows a vivid example of a "seismite," which are layers of rock contorted by an ancient earthquake that occured before the sediment hardened and was still soft and waterlogged.

A fourth Frankfort locality (not on Rt. 127) exposes the Lexington Limestone (Devil's Hollow Member). This locality is a football-field sized area in a subdivision where the overlying soil has been removed. The exposed rock shows a spectacular series of large ripple marks. The Devil's Hollow Member is believed to be formed from a lagoonal area with a water depth of less than a few meters. These ripple marks would seem to support this conclusion. Fossils found here include bryozoans and crinoid holdfasts.

Lexington Field Trip

Ostracode from Lexington Limestone

Teichochilina jonesi, an isochilinid ostracode


There are two roadcuts on New Circle Rd. which yield beautifully preserved ostracodes (Teichochilina jonesi) 0.5 to 0.75 inches in size. Even the small eye tubercle bumps are well shown. The rock is mapped as Lexington Limestone (Tanglewood Member), but clearly it is not. It doesn't really correspond to any easily recognizable part of the Lexington Limestone. It is a greenish-gray glauconitic shale layer several feet thick. Only a small layer within it contains the ostracodes, and sometimes long spired gastropods (I have one with 9 revolutions). Another roadcut on Man-O-War Rd. exposes the Lexington Limestone (Millersburg Member) and many Cyclonema gastropods can be found.