A cored well 1,422 feet (433 meters) deep drilled two miles southeast of Dover is the basis for this integrated study of the lithology and paleontology of the Cretaceous-Tertiary section in central Delaware. The section is subdivided into lithostratigraphic, biostratigraphic, chronostratigraphic, and heavy mineral units. Data and results are presented on a common base in three plates.
In the Coastal Plain of Delaware, the non-marine Cretaceous sands and clays are separated from the Tertiary formations by a series of marine formations of Upper Cretaceous age. The sedimentary and hydrologic characteristics of these formations deserve detailed study because some of them are water-bearing beds. whereas others act as confining beds. A clear understanding of their relative age. and the presence or absence of unconformities is needed for proper correlation with formations found in wells throughout the State. as well as in Maryland and New Jersey.
The Pollack Farm Site near Cheswold, Delaware, is named for a borrow pit excavated during highway construction. The excavation exposed a portion of the Cheswold sands of the lower Miocene Calvert Formation. Two sand intervals (Cheswold C-3 and C-4) yielded a diverse assemblage of land and marine vertebrate remains and more than 100 species of mollusks. An isolated occurrence of a sandy silt (the radiolarian bed) stratigraphically between the two macrofossil-bearing units yielded only siliceous microfossils—radiolarians, diatoms, and sponge spicules.
Minerals are naturally occurring, inorganic substances with characteristic physical and chemical properties. Common examples found in Delaware are quartz (hard, glassy luster), mica (cellophane like pieces), and feldspar (waxy or pearly luster, cleavage). In nature minerals are usually found in mixtures with other minerals. A natural specimen containing several minerals is called "a rock." A common example is granite, which is a mixture of quartz, feldspar, mica, and usually other dark minerals. Fossils are any evidence, direct or indirect, of a pre-existing plant or animal in the rock record. The most popular area for collecting fossils in Delaware is the Chesapeake and Delaware Canal area.
Fossil collectors have been attracted to Delaware since the late 1820s when the excavation of the Chesapeake and Delaware (C&D) Canal first exposed marine fossils of Cretaceous age. Since then, many technical and nontechnical works have been written about the fossils. However, there has not been a single source for casual or student collectors to turn to for help in the identification of typical finds. This paper is written to fill that void as well as provide general information about fossils and specific information on geologic formations and collecting localities at the Canal. This report is not designed to be an encyclopedia on the fossils of the Canal but focuses on those fossils found most frequently. The majority of the fossils collected today are from the spoil areas in the vicinity of the Reedy Point Bridge. Thus, the chapter on classification concentrates on the fossils of the Mount Laurel Formation, the stratigraphic unit dredged in that area.
Analyses of drillers' and geophysical logs, cuttings, and 29 core samples from well Nc13-3 near Greenwood, Sussex County, Delaware indicate that the 1500-foot section penetrated by the drill can be divided into seven rock-stratigraphic units: Matawan Formation, Monmouth Formation, unit A, Piney Point Formation, Chesapeake Group (undifferentiated), Staytonville unit, and the Columbia Formation. The rock units are identified on the basis of texture, mineralogy, color, and interpretation of electric and gamma-ray logs. The oldest rocks penetrated are Upper Cretaceous; Tertiary and Quaternary rocks were also encountered. Correlations of the units encountered in the Greenwood test well with subsurface formations in adjacent parts of the Coastal Plain are explored utilizing lithologies, ages, positions in the stratigraphic column, and geophysical characteristics as criteria. Major time boundaries (Cretaceous-Tertiary; Early-Late Paleocene; Paleocene-Eocene; and Eocene-Miocene) are established by a preliminary study of mainly planktonic foraminifera. The Miocene-Pleistocene boundary was determined on changes in lithology across the unconformable contact.
This guide contains illustrations of fossils from Delaware Geological Survey Bulletin No. 3 ("Marine Upper Cretaceous Formations of the Chesapeake and Delaware Canal") and Report of Investigations No. 7 ("An Invertebrate Fauna from the Upper Cretaceous of Delaware"). The identifications have been revised to be as accurate as possible so that this guide will be useful to those fossil collectors interested in classifying their "finds."
Recent erosion along the Chesapeake and Delaware Canal has exposed an unusually rich Upper Cretaceous fossiliferous outcrop at the Biggs Farm, near the eastern end of the Canal. Some III species of mollusks representing 72 genera have been identified. Coelenterata, Porifera, Annelida, Brachiopoda, Crustacea, and a few fragmentary vertebrate remains have also been found. Five species are being described as new, and there are 54 new records for the Cretaceous of Delaware.
The preservation of the material suggests that the animals lived on a sandy bottom in water between 50 and 100 feet in depth, possibly near the mouth of a bay.
Inasmuch as there is a mixing of some species characteristic of the Matawan Group and other species characteristic of the Monmouth Group, it is believed that the fauna at this locality lies near the Matawan-Monmouth boundary, perhaps in the lower part of the Monmouth Group.
The uppermost Cretaceous and lowermost Tertiary planktonic Foraminifera obtained from cores taken in a deep well near Dover, Delaware are studied. The Cretaceous foraminifers are of the Heterohelix-Globotruncana assemblage and are probably of late Maescrichtian age. The Danian Globorotalia compressa - Globigerinoides daubjergensis zone lies immediately above. The Cretaceous-Tertiary boundary is at a depth of approximately
980 feet and lies within a gray, glauconitic silt.
The core of much DGS work culminates in the release of data and findings in official DGS publications, including Open File Reports, Reports of Investigations, Geologic Maps, Hydrologic Maps, and Bulletins.