The Fossil Localities and Their Stratigraphy
The extensive deposits of Cretaceous age in eastern North America have been widely studied for over 150 years. These generally poorly consolidated sediments have provided valuable resources, notably glauconite, fire clay, and chalk. As the publications by Morton (1829), Vanuxem (1829), Conrad (1869), and other early authors showed, the sediments are also quite fossiliferous.
In the eastern United States, significant Cretaceous deposits occur from New Jersey to Texas ([Figure 1]), with extensive outcrop and subsurface records in both Atlantic and Gulf coastal plains. The surface distribution and correlations were first summarized by Stephenson et al. (1942). Subsequent works by various authorities have refined, but not substantially altered his views of outcrop stratigraphy. Petroleum exploration has encouraged more recent restudy of the subsurface stratigraphy, notably along the east coast (Minard et al., 1974; Perry et al., 1975; Petters, 1976).
Figure 1.—Distribution of Cretaceous rocks in the eastern United States. Arrow indicates New Jersey. (Modified after Moore, 1958, fig. 15.2).
In New Jersey, the latest Cretaceous deposits are remarkably rich in glauconite, especially the Navesink and Hornerstown formations. Besides providing a local industry in agricultural fertilizers, the glauconite greensands, locally called "marl," yielded many specimens to the fiercely competitive vertebrate paleontologists of the nineteenth century. Preservation of vertebrate fossils in a glauconite deposit may be excellent, apparently due to autochthonous formation of the mineral and the probable quiescence of the depositional environment. The Hornerstown Formation, for example, contains few grains of terrigenous origin and little evidence of disturbance by water currents. Such depositional environments were apparently favorable for the preservation of small and delicate bones. The accumulation of sediment occurred during a period of marine transgression with the shoreline not far to the northwest but at sufficient distance to prevent deposition of terrigenous material.
During their great rivalry, E.D. Cope and O.C. Marsh sought greensand fossils vigorously. Marsh, however, obtained all of the Cretaceous birds (Marsh, 1870, 1872), largely due to efforts of marl pit owner J.G. Meirs. Although in the years subsequent to Marsh's original descriptions of the New Jersey birds from the Navesink and Hornerstown formations there was some confusion regarding their probable age (Wetmore, 1930), this was later definitely established as Cretaceous by Baird (1967), who attributed the specimens to the Navesink and Hornerstown formations.
The summary of Petters (1976) represents current ideas of the Cretaceous stratigraphy of New Jersey. Baird's (1967) discussion is consistent with Petters's view that the Hornerstown Formation is regarded as partly Cretaceous and partly Tertiary. Some authors have used the term New Egypt Formation instead of Navesink in more southerly outcrops.
Cretaceous birds have been recovered from three geographically distinct localities in New Jersey ([Figure 2]). With the exception of Laornis, all of the specimens described by Marsh (1870, 1872) came from Upper Freehold Township, Monmouth County, in the area including the settlements of Hornerstown, Arneytown, and Cream Ridge. The Meirs family operated a number of pits in this area and it is no longer possible to ascertain the exact provenance of specimens labelled only as being from Hornerstown. These could have come either from the basal Hornerstown Formation or the underlying Navesink Formation, both of which are Maastrichtian in age. Baird (1967:261) ascertained that the holotype of Palaeotringa vetus, from "friable green marl near Arneytown" was from the lower (i.e., Cretaceous) part of the Hornerstown Formation. The holotypes of Telmatornis priscus and T. affinis, from the Cream Ridge Marl Company pits, on the other hand, are from the Navesink Formation. A more recently collected specimen from this area is the proximal end of an ulna (NJSM 11900) collected by Gerard R. Case from "marl piles near junction of Rtes. 537 and 539 in Upper Freehold Twp., Monmouth County, near Hornerstown." This definitely came from the Hornerstown Formation but it cannot be said whether from the Cretaceous or Paleocene sediments included therein.
Figure 2.—Localities in southern New Jersey of the main fossiliferous deposits that have yielded Cretaceous birds. (The bold line demarcates the inner and outer coastal plain physiographic provinces; B = Birmingham; H = Hornerstown; S = Sewell.)
The second general locality is near Birmingham, Burlington County, where the type of Laornis edvardsianus was obtained from "greensand of the upper, Cretaceous marl bed ... in the pits of the Pemberton Marl Company" (Marsh, 1870:208). There is nothing to be added to Baird's (1967) conclusion that this specimen is latest Cretaceous in age.
The third locality, and that yielding most of the recently obtained specimens, is the Inversand Company marl pit, located near Sewell, Gloucester County. In accordance with the wishes of the Inversand Company, the precise locality of this pit will not be disclosed, although this information is preserved in records sufficient in number and distribution to assure that it will not be lost. The Inversand specimens came from the main fossiliferous layer within the basal portion of the Hornerstown Formation ([Figure 3]). This layer is of late Maastrichtian age (latest Cretaceous), on the basis of invertebrate fossils, including three genera of ammonites, and a substantial vertebrate fauna, including mosasaurs (see Appendix). It is probable that the upper part of the Hornerstown Formation within the pit is of Paleocene age, as it is known to be elsewhere, but most paleontologists believe the basal portion to be Cretaceous in age (Gaffney, 1975; Koch and Olsson, 1977). One avian specimen is from an unknown level in the pit.
Figure 3.—Stratigraphic diagram of the Inversand Company marl pit at Sewell, Gloucester County, New Jersey.