Some new and rarely documented late Cretaceous calcareous nannofossils from subsurface sediments in South Carolina

Journal of Paleontology, Sep 1999 by Self-Trail, Jean M

ABSTRAcT--One new calcareous nannofossil genus Senitatus; four new calcareous nannofossil species Calculites favosus, Lithraphidites? charactozorro Self-Trail and Pospichal, Rucinolithus oriens, and Watznaueria bybelliae; and one new combination, Senilatus zipperum n. gen. and comb., are described from Upper Cretaceous (upper Campanian to Maastrichtian) sediments of cast-central South Carolina. These new species were described from five coreholes located in marine coastal plain deposits. There is evidence that the presence of one species, Senilatus zipperum, is indicative of nearshore, restricted environments. Scanning electron and light microscope pictures are provided for two species, Cretarhabdus multicavus Bukry, 1969 and Retemediaformis teneraretis Varol, 1991, that have previously been documented only with the transmission electron microscope. The ranges of these two species have been extended beyond those stated in the original descriptions.

INTRODUCTION

THIS PAPER is a result of studies in progress by the U.S. Geological Survey, the South Carolina Department of Natural Resources, and the Department of Energy-Savannah River Site to document and describe the subsurface stratigraphy of Coastal Plain sediments in the state of South Carolina. Detailed calcareous nannofossil biostratigraphic analyses of corehole material from sites across the state were used in conjunction with geophysical logs and lithostratigraphic data to correlate sediments. Although numerous articles have documented the abundance and diversity of Late Cretaceous calcareous nannofossils in Gulf Coastal Plain sediments (e.g., Risatti, 1974; Dowsett, 1989; Farhan et al., 1994), there remains a paucity of information concerning southern Atlantic Coastal Plain sediments and biostratigraphy. Hattner and Wise (1980) and Hattner et al. (1980) studied the Upper Cretaceous calcareous nannofossils from the USGS Clubhouse Crossroads Core #1 (South Carolina), in which they documented several new species and noted ecologic preferences for the Broinsonia-Arkhangelskiella-Gartnerago lineages. Moshkovitz and Habib (1993) studied the calcareous nannofossil and dinoflagellate biostratigraphy from the USGS Davis Hopkins core in Georgia. Although the main thrust of their paper detailed the Cretaceous/Tertiary boundary extinction event, they also documented a series of shallowing-upward events for the upper Campanian and Maastrichtian of the Georgian coastal plain. Since these studies, however, very little research pertaining to calcareous nannofossil biostratigraphy of the coastal plain has been documented.

MATERIALS AND METHODS

Five cores examined by the author for calcareous nannofossil content are discussed in detail in this paper (Fig. 1). The Myrtle Beach (HO-1165) corehole is located at the Myrtle Beach Water Treatment Plant in Horry County, SC (33 deg 43'44"N; 78 deg 54'14"W). It was cored continuously to a depth of 131.8 m (432.4 ft). The Cannon Park (CHN-800) corehole is located in the city of Charleston, SC (32 deg 46'55"N; 79 deg 56'41"W) and was cored continuously to a depth of 308.5 m (1,012 ft). The Santee Coastal Reserve (CHN-803) corehole was also drilled in Charleston County (33 deg 9'21"N; 79 deg 21'50"W) and was cored continuously to a total depth of 165.2 m (542 ft). The Clubhouse Crossroads #1 corehole is located in Dorchester County (32 deg 53'25"N; 80 deg 21'41"W) and was drilled continuously to a total depth of 792 m (2,599 ft). The C-15 testhole is located in Jasper County (32 deg 37'04"N; 80 deg 59'45"W) and was drilled to a total depth of 893.9 m (2,900 ft) (Fig. 1), and material examined for calcareous nannofossil content was extracted from sidewall cores. Calcareous nannofossil biostratigraphy was based on the zonations of Perch-Nielsen (1985) and Sissingh (1977). Descriptive terminology used in the systematics section is based on Young et al. (1997).

Sediment was examined for calcareous nannofossil content using standard light microscope (LM) techniques. The scanning electron microscope (SEM) was used to observe the ultrastructure of selected calcareous nannofossil specimens. Samples were extracted from the central portion of core segments at the drill site for the Cannon Park, Santee Coastal Reserve, and Myrtle Beach cores. Material taken from the C-15 sidewall cores was carefully extracted from the central portion of chips to avoid contamination from drilling fluid. Slides were made using a settling procedure described by Bybell and Self-Trail (1995), designed to separate nannofossils from sandy sediments, for the Cannon Park, Santee Coastal Reserve, and Myrtle Beach cores. Due to the paucity of material available from the C-15 sidewall cores, it was necessary to use smear slides rather than settled slides, though this method uses unprocessed sediment and is usually avoided when examining Coastal Plain material due to the high percentage of sand in the sediments.

To examine material with both the LM and SEM, sediment was prepared as for SEM examination and then pipetted onto a 22 X 30 cm coverslip as a series of small dots. Each sediment dot was examined for desired calcareous nannofossil specimens using a light microscope and ethyl alcohol. Sediment dots containing desired specimens were numbered using silver colloidal paint, transferred to a SEM stub, gold coated, and examined using the SEM. The coverslip was removed from the SEM stub upon completion and attached to a glass slide using Norland Optical Adhesive (NOA-65). The sediment dots then were reexamined and photographed with the light microscope. It should be noted that specimens photographed with the SEM are inverted relative to those of the LM slide.