Article: The palaeoecology of a transition zone across an Upper Cretaceous boundary in New Jersey

Sediments and fossils were sampled at one-foot intervals across the Mt. Laurel-Navesink boundary (Upper Cretaceous) at Marlboro, New Jersey; this sequence is of some interest as it contains the Exogyra cancellata Zone, which has been traced along the coastal plain from New Jersey to Texas. It is shown that weak bottom currents were present during the time represented by this sequence, that the oysters and sponges examined lived in non-turbid waters of normal salinity in which nutrients were provided in quantity, that water depth increased in the upper part of the sequence, and that an important break in sedimentation, indicated by electron microphotographs of the surface textures of sand grains and the presence of shallow-water crabs, is found at the Mt. Laurel-Navesink boundary and possibly represents a disconformity. Interlocked oyster shells with sponge borings found throughout the section indicate local periods of water turbulence followed by long periods of quiescence. Comparison of sediment and individual size frequency distributions implies that Guembelina ultimatumida was probably sorted by water currents after reaching the sea bottom.