Belleplain Member of the Kirkwood Formation (NJTkb;1)

Belleplain Member - Clay to silty clay at the base and sand at the top. Clay, massive to laminated, gray-brown, locally contains abundant diatoms and scattered small shell fragments. Sand, fine- to medium-grained, pale-gray to white, somewhat micaceous and woody with scattered shell fragments. Most Belleplain sand is quartz with lesser amounts of feldspar and mica. Pyrite is common in clayey strata. The Belleplain subcrops beneath surficial deposits where the overlying Cohansey Formation was eroded away. Along the Atlantic Ocean, the member is exposed on the southern sheet between Beach Haven Terrace, Ocean County, and Brigantine, Atlantic County, where the unit is overlain by thin to thick deposits of alluvium. The member is as much as 15 m (49 ft) thick. The basal contact with the underlying Wildwood Member is sharp and unconformable with a thin bed of reworked coarse-grained quartz sand at the base. A middle Miocene age for the Belleplain was determined from diatoms. Specifics of the diatom biostratigraphy are discussed in the Description of Subsurface Units. Shells from this unit had a strontium-isotope age estimate of 13.2 Ma (Sugarman and others, 1993).

State	New Jersey
Name	Belleplain Member of the Kirkwood Formation
Geologic age	middle Miocene, Serravallian
Original map label	Tkb
Comments	part of the Kirkwood Formation (described seperately, but not mapped): Kirkwood Formation (middle and lower Miocene, Serravallian to Aquitanian) - Consists of the Wildwood Member and an informal lower member on the central sheet and the Belleplain Member, Wildwood Member, Shiloh Marl Member, and lower member on the southern sheet. The Belleplain Member is a new member named for beds occurring in a corehole drilled by the U.S. Geological Survey at Belleplain State Forest Headquarters, Cape May County. The Wildwood Member is a new member named for beds occurring in a drillhole at Wildwood Beach, Cape May County.
Primary rock type	clay or mud
Secondary rock type	sand
Other rock types	silt
Lithologic constituents	Major Unconsolidated > Coarse-detrital > Sand (Bed)Sand, fine- to medium-grained, pale-gray to white, somewhat micaceous and woody with scattered shell fragments. Most Belleplain sand is quartz with lesser amounts of feldspar and mica. Unconsolidated > Fine-detrital > Clay (Bed)Clay to silty clay at the base and sand at the top. Clay, massive to laminated, gray-brown, locally contains abundant diatoms and scattered small shell fragments. Pyrite is common in clayey strata Minor Unconsolidated > Fine-detrital > Silt (Bed)silty clay
Map references	Dalton, R. F., Herman, G. C., Monteverde, D. H., Pristas, R. S., Sugarman, P. J., Volkert, R. A., 1999, New Jersey Department Of Environmental Protection, Bedrock Geology and Topographic Base Maps of New Jersey: New Jersey Geological Survey CD Series CD 00-1; ARC/INFO (v. 7.1) export file: geology.e00, scale 1:100,000, unit description files: cslegend.pdf and nlegend.pdf, metadata: metast.pdf.
Unit references	Dalton, R. F., Herman, G. C., Monteverde, D. H., Pristas, R. S., Sugarman, P. J., Volkert, R. A., 1999, New Jersey Department Of Environmental Protection, Bedrock Geology and Topographic Base Maps of New Jersey: New Jersey Geological Survey CD Series CD 00-1; ARC/INFO (v. 7.1) export file: geology.e00, scale 1:100,000, unit description files: cslegend.pdf and nlegend.pdf, metadata: metast.pdf. Owens, James P., Sugarman, Peter J., Sohl, Norman F., Parker, Ronald A., Houghton, Hugh F., Volkert, Richard A., Drake, Avery A., Jr., and Orndorff, Randall C., 1998, Bedrock Geologic Map of Central and Southern New Jersey: U.S. Geological Survey Miscellaneous Investigations Series Map I-2540-B, scale 1 to 100,000, 8 cross sections, 4 sheets, each size 58x41. [http://pubs.er.usgs.gov/publication/i2540B] Sugarman, P.J., Miller, K.G., Owens, J.P., and Feigenson, M.D., 1993, Strontium isotope and sequence stratigraphy of the Miocene Kirkwood Formation, southern New Jersey: Geological Society of America Bulletin, v. 105, no. 4, p. 423-436.