Reports
Stratigraphy of Upper Cretaceous and Tertiary sediments in a core-hole drilled near Chesterville, Kent County, Maryland
1992, Harry J. Hansen
Open File Report 93-02-7
Abstract
A 480-ft core hole (Ken-Bf 180) located near Chesterville in Kent County, Maryland has provided new stratigraphic data bearing on the Lower Tertiary-Upper Cretaceous section that underlies the northern Delmarva Peninsula. Upper Cretaceous nonmarine beds cored between 422.3 ft and 476.3 ft include strata tentatively assigned to palynozone IV (middle Cenomanian), which correlates with the Raritan Formation of New Jersey; the unit is mainly comprised of two pebbly sands of fluvial origin separated by a thin silty clay. Underlying this unit is a mottled clay that contains Zone IIC (late Albian) palynomorphs assigned to the Elk Neck beds of the Patapsco Formation.
The Upper Cretaceous Magothy Formation (Santonian to Campanian) is a lignitic, blackish clay. It is relatively thin (19 ft) and may represent a marsh or back-bay facies. The fluvio-deltaic sand facies of the Magothy is absent at the test site. The Magothy occurs between 404 ft and 422.3 ft.
The Upper Cretaceous Matawan Group (Campanian) occurs between 295 ft and 404 ft. It consists of silty clay and very fine to fine sand with several coarsening upward cycles.
The Upper Cretaceous Monmouth Group can be divided into two formations. The Mt. Laurel Formation (217.9 ft to 295 ft) is chiefly a medium to fine, glauconitic sand. It contains Maestrichtian microfossils and the index cephalopod Belemnitella americana. The overlying Severn Formation (204.2 ft to 217.9 ft) is a glauconitic, clayey, very fine to fine sand. It contains dinoflagellates characteristic of the Severn Formation at its type locality (in Anne Arundel County, Maryland). The Cretaceous/Tertiary boundary is a sharp contact with 0.5 in. of relief.
A relatively thick, lower Paleocene section (109.1 ft-204.2 ft), assigned to the Hornerstown Formation, occurs at the test site. The Hornerstown contains Danian foraminifera; its age is bracketed between the last occurrence of Cretaceous ostracodes and the first occurrence of the brachiopod Oleneothyris harlani, an index fossil that occurs near the base of the upper Paleocene (Thanetian). The Hornerstown Formation is a glauconitic sand that coarsens upwards.
The upper Paleocene Aquia Formation (23.5 ft to 109.1 ft) is also a regressive sand. The upper part is coarser grained, less clayey and better sorted than the lower part. It has a weathered aspect with intensely iron-stained quartz grains, glauconites commonly altered to limonite, and a diminished suite of labile heavy minerals. The large contrast in weathering intensity across the Aquia-Old Church(?) contact suggests a pre-middle Oligocene weathering event.
A fine to medium glauconitic sand, containing middle to late Oligocene foraminifera, overlies the Aquia Formation in Ken-Bf 180. This unit is tentatively assigned to the Old Church(?) Formation (18.5 ft to 23 ft). At the test site it is overlain by the surficial Pensauken Formation of late Miocene to early Pliocene (?) age.
