OVERVIEW OF THE MARINE TERTIARY AND QUATERNARY DEPOSITS BETWEEN CAPE FEAR AND CAPE LOOKOUT, NCFigure 7. A. Distribution of the Pliocene Duplin Formation andequivalents (TB3.6 Sequence) on the Onslow Block. Sequencedesignation is after Zullo and Harris (1992). B. Distribution ofthe Pliocene Chowan River/Bear Bluff Formations (TB3.8Sequence) on the Onslow Block (modified from Ward et al.,1991). Sequence designation is after Zullo and Harris (1992).also used for latest Pliocene sediments that occur on theAlbemarle Block, and the Bear Bluff for age equivalent sedimentson the Onslow Block. The Duplin Formation consistsof sand, sandy and silty clay, and very shelly sand commonlyoverlying a b<strong>as</strong>al phosphate pebble conglomerate. North ofthe Neuse Hinge the Rushmere and Mogarts Beach Membersof the Yorktown Formation (=Duplin Formation) are continuous;however, to south on the Onslow Block, the Duplin ispreserved <strong>as</strong> outliers. The thickest section of the Duplin Formationalso occurs to the south where almost 5 m are foundin Bladen County (Ward et al., 1991). However, most outlierson the Onslow Block contain less than 2 m of the DuplinFormation.The upper Pliocene Chowan River Formation is onlyused in North <strong>Carolina</strong> north of the Neuse Hinge; to thesouth, the Bear Bluff Formation of DuBar et al. (1974) isFigure 8. A. Distribution of lower Pleistocene Waccamaw/James City Formations (TB3.9 Sequence) on the Onslow Block(modified from Owens, 1989; Ward et al., 1991). Sequence designationis after Zullo and Harris (1992). B. Distribution of themiddle Pleistocene Soc<strong>as</strong>tee/Flanner Beach Formations on theOnslow Block (modified from Mixon and Pilkey, 1976; Owens,1989; Ward et al., 1991).recognized. The Bear Bluff Formation is known mainly fromthe area south of the Cape Fear River, and may occur adjacentto the Intraco<strong>as</strong>tal Waterway below the Waccamaw Formationon the central Onslow Block. The Bear BluffFormation consists of calcareous sandstone, sandy limestone,subarkosic sand, and calcareous silt and h<strong>as</strong> a maximumobserved thickness that exceeds 33 m (DuBar et al.,1974).QUATERNARYPleistocene {Figures 8a and 8b)Pleistocene geology along the seaward side of theOnslow Block south of the Neuse River is poorly known.5
W. Burleigh HarrisMixon and Pilkey (1976) mapped the geology of the CapeLookout area (Carteret-Craven Counties), Owens (1989)mapped the Florence, South <strong>Carolina</strong>, and North <strong>Carolina</strong>,10 x 20 Quadrangle (Brunswick and western New HanoverCounties), and Dockal (this volume) is currently examiningthe area of southern New Hanover and Brunswick Counties.However, no detailed geologic mapping of Pleistocene unitsh<strong>as</strong> been completed on the Onslow Block south of NewRiver. The following discussion is mainly of those are<strong>as</strong>marking the southern and northern parts of the OnslowBlock.The Waccamaw/James City Formations are used forearly Pleistocene sediments of similar lithology that occur onthe southern and northern parts of the Onslow Block, respectively(Figs. 5 and 8a). The Waccamaw Formation occursover most of the area south of the Cape Fear River, particularlyin low are<strong>as</strong> developed on older units (i.e., the PeedeeFormation), and north of the Cape Fear River in small pitsand dredge spoils just west of the Intraco<strong>as</strong>tal Waterway. Ith<strong>as</strong> also been identified in Burnt Mill Creek in New HanoverCounty and probably occurs at other lower elevation localitiesthat are <strong>as</strong>sociated with the margins of the OnslowBlock. The Waccamaw Formation consists of poorly to moderatelywell sorted fossiliferous fine to coarse sand whichgrades upward into unfossiliferous sediments (Owens,1989). A local thin conglomerate of phosphate and quartzpebbles occurs at the b<strong>as</strong>e of the unit. Sediments that containtypical Waccamaw fossils range in thickness to almost 7 m(DuBar et al., 1974) in Brunswick County.The James City Formation of DuBar and Solliday(1963) is recognized along the Neuse River below NewBern. It extends to the north onto the Albemarle Blockalmost to Virginia, and to the south to the New River (Blackwelder,1981). Several small pits west of the Intraco<strong>as</strong>talWaterway between the New and Cape Fear Rivers indicatethat the unit extends to the southe<strong>as</strong>t eventually becomingthe Waccamaw Formation (Ward et al., 1991). AlthoughWard et al. (1991) indicate that the Waccamaw/James CityFormations extend west of the Hanover Scarp, I know of nolower Pleistocene marine sediments on the central OnslowBlock north of the Cape Fear River. The James City Formationis an unconsolidated shelly argillaceous sand and sandyclay (DuBar and Solliday, 1963). Although the unit is consideredto be early Pleistocene in age (Ward et al., 1991),Campbell (1993) suggested that it is late Pliocene b<strong>as</strong>ed onoxygen isotopes.Numerous lithostratigraphic names have been applied tomiddle and upper Pleistocene units between the Cape Fearand Neuse Rivers (Fig. 5). Middle Pleistocene units arereferred to the Soc<strong>as</strong>tee/ Canepatch and Flanner Beach Formations(Soller and Mills, 1991). The Soc<strong>as</strong>tee Formation,the major co<strong>as</strong>tal Pleistocene unit in the Cape Fear region,consists of b<strong>as</strong>al coarse sand, fine gravel and reworked shellsto 1 m in thickness, and interbedded sand and clay. The sandand clay are commonly peaty and contain upright tree trunks(Owens, 1989). The Soc<strong>as</strong>tee ranges up to 5 m in thickness(DuBar et al., 1974) in the northern co<strong>as</strong>tal area of South<strong>Carolina</strong>. Its extent between the Cape Fear and Neuse Riversis unknown; however, if present, it is probably restricted tothe seaward edge of the Onslow Block (Fig. 8b). The CanepatchFormation, named for exposures in the Myrtle Beach,South <strong>Carolina</strong> area by DuBar (1971), w<strong>as</strong> restricted to onesubsurface locality along the Intraco<strong>as</strong>tal Waterway byOwens (1989). Therefore, the name is not used in this paper.The Soc<strong>as</strong>tee Formation is middle Pleistocene in age b<strong>as</strong>edon isotopic dates (McCartan et al., 1982).In the Neuse River area, the Soc<strong>as</strong>tee Formation is correlatedto the Flanner Beach Formation of DuBar and Solliday(1963). The Flanner Beach Formation consists ofunconsolidated clay, sandy clay, argillaceous sand, and peatysand and clay, which reach almost 12 m in thickness; molluscanfossils are common in the lower part (DuBar and Solliday,1963). Although the Flanner Beach Formation w<strong>as</strong>restricted to exclude some of the originally defined parts ofthe unit by Mixon and Pilkey (1976), the unit occurs seawardof north-trending elements of the Suffolk Scarp. The FlannerBeach Formation is also considered to be middle Pleistocenein age; its distribution is shown in Figure 8b.Late Pleistocene units are poorly described and are<strong>as</strong>signed numerous lithostratigraphic names. Dockal (thisvolume) discusses upper Pleistocene stratigraphy in the CapeFear region.SCARPS AND PLAINS ON THE ONSLOWBLOCKSeveral scarps and <strong>as</strong>sociated terraces (plains) are recognizedon the Onslow Block between Cape Fear and CapeFigure 9. Relation of scarps and terraces to major structuralfeatures <strong>as</strong>sociated with the Onslow Block (modified from Zulloand Harris, 1979; and Harris and Laws, in press).6
Change language