Shiloh Marl Member of the Kirkwood Formation

Shiloh Marl Member - Consists of (1) a lower laminated, micaceous, locally fossiliferous (typically thin-walled, small mollusks), dark-gray clay interbedded with very fine grained sand and (2) an upper medium- to coarse-grained, gravelly, massive, pale-brown to medium-gray sand with scattered thin-walled mollusks. Thin, dark-gray clay layers interbedded with thin layers of lignite are common in this upper interval. Like the Wildwood, this unit occurs mainly within the southern sheet and the southeastern part of the central sheet. Thicknesses vary within the basin but are a maximum of 55 m (180 ft). In the Island Beach corehole the unit is clayey at the base and sandy at the top. The basal contact with the underlying unit is sharp but there is little reworked debris along this contact. In detail, the lowest 4.5 m (15 ft) of the unit is a fine- to medium-grained, massive, micaceous, extensively bioturbated, somewhat clayey, quartz sand. Small wood fragments are common. This basal sand bed grades upward into a sequence of horizontally bedded, light- to dark-gray clay and very fine grained, somewhat micaceous quartz sand. Color banding in this interval is strong. A very coarse grained, pale-gray quartz sand with some granules is interbedded with this dominantly clayey sequence. The clayey sequence is overlain by a medium-grained, massive, bioturbated, medium-gray sand similar to the basal sand. This sand grades into a thin- to thick-bedded and crossbedded sequence of dark-gray and brown sand that increases in grain size from coarse to very coarse grained up section. Most of the sand is quartz with lesser amounts of potassium feldspar (6 to 16 percent of the sand fraction). Near the top of the unit, quartz gravel is a common constituent in the very coarse grained sand bed. The age of the Shiloh is early Miocene (Burdigalian) as determined from diatoms. The Shiloh contains Actinoptychus heliopelta (ECDZ 1 of Andrews, 1987, 1988). Strontium age determinations on shells from this unit yielded ages of 20.9 to 19.7 Ma confirming the early Burdigalian age. Pollen studies indicate that the Shiloh has unusually high concentrations of Fagus (beech). Other pollen includes Quercus (oak), Carya (hickory), Pinus (pine), and Ulmus (elm) along with exotics. Overall the assemblage, except possibly for the high concentration of Fagus, indicates a warm-temperate climate during the time of deposition.