Dinoflagellate cysts of the Gymnodiniaceae, Peridiniaceae, and Gonyaulacaceae from the Upper Cretaceous Monmouth Group, Atlantic Highlands, New Jersey

The taxonomy, paleoecology, and biostratigraphy of fossil dinoflagellate cysts belonging to three families (Gymnodiniaceae, Peridiniaceae, and Gonyaulacaceae) are investigated from the Campanian-Maestrichtian Mount Laurel Sand, Navesink Fonnation, and Sandy Hook Member of the Red Bank Sand of Atlantic Highlands, New Jersey. Thirty-seven genera and 91 species belonging to these families were recovered of which 3 genera and 20 species are described as new.

Dinoflagellate peak zones, restricted ranges, relative frequencies, and species diversity suggest that environments changed four times during deposition of the units studied. The stratigraphic intervals representing these four paleoenvironments correspond closely to intervals assigned to particular paleoenvironments based on invertebrate fossils and lithology (Owens and Sohl, 1969; Sohl, 1969). Thus, correlation of this previously determined paleoecological data and that of the dinoflagellates allows for interpretation of dinoflagellate distribution relative to particular marine to brackish water paleoenvironments.

Cordosphaeridium varians n. sp. and Exochosphaeridium bifidum (Clarke and Verdier) Clarke et al. 1968 are shown to be highly variable in morphology, each having distinctively different morphologic end members. It is suggested that such variability is natural and that extreme morphologic end members be assigned to the same species, as is done with living populations. C. varians is also shown to grade morphologically upsection into forms similar to Trichodinium hirsutum Cookson 1965 and which are referred to in this study as T. cf. T. hirsutum.

Scanning electron microscopy of Dinogymnium pustulicostatum n. sp. and D. westralium (Cookson and Eisenack) Evitt et al. 1967 has revealed the fine structure at the cingulum-sulcus intersection, consisting of apparent flagellar pores (one anterior and one posterior) and associated ridges and grooves which may have confined or directed the passage of the flagella. The presence of flagellar pores suggests that motile stage dinoflagellate tests may be preserved as fossils. Scanning electron microscopy also illustrates the detailed morphology of Dinogymnium wall canals (Evitt, Clarke, and Verdier, 1967), which are interpreted here as being trichocyst pores, such as are found on several modern dinoflagellates.

Campanian and Maestrichtian age-indicating dinoflagellates suggest that the Campanian-Maestrichtian boundary lies within the uppermost Mount Laurel Sand or lower Navesink Formation. This stratigraphic interval is in agreement with the position of the Campanian-Maestrichtian boundary at the study area as indicated by Ammonites (Cobban, 1974). Above this interval the Navesink Formation and Sandy Hook Member contain dinoflagellate assemblages which are comparable to those observed by Wilson (1974) in lower Maestrichtian sediments of the Maestricht Region, Holland, and of Denmark. Below this interval the Mount Laurel Sand is considered of late Campanian age.