Coastal Plain Rock Unit Descriptions

Coastal Plain Rock Unit Descriptions johncallahan Thu, 06/24/2010 - 23:44

Assawoman Bay Group

Assawoman Bay Group siteadmin Fri, 08/20/2010 - 11:45

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

The Assawoman Bay Group consists of the well-sorted sands, silts, and clays of the Omar, Ironshire, and Sinepuxent Formations found adjacent to and inland of the Atlantic Coast of Delaware and Maryland. These deposits in Delaware and Maryland were named from oldest to youngest: the Omar Formation (Jordan, 1962, 1964), the Ironshire Formation (Owens and Denny, 1979), and the Sinepuxent Formation (Owens and Denny, 1979).

The Assawoman Bay Group consists of transgressive deposits that were deposited along the margins of an ancestral Atlantic Ocean during middle to late Pleistocene highstands of sea level. It is named for the Little Assawoman Bay in Delaware and the Assawoman Bay in Maryland in the vicinity of where the Omar, Ironshire, and Sinepuxent Formations are best developed. In Delaware, the Assawoman Bay Group extends south of Indian River Bay to east of Gumboro. In Maryland, it is mapped south and west of Salisbury (Owens and Denny, 1979). It extends east of Salisbury into the Virginia portion of the Delmarva Peninsula (Mixon, 1985).

Subtitle

Coastal Plain - Primarily Surficial Unit

Geologic Unit Symbol
Qabg
Geologic Time Period
middle to late Pleistocene
Reference(s)

Jordan, R.R., 1962, Stratigraphy of the sedimentary rocks of Delaware: Delaware Geological Survey Bulletin No. 9, 51 p.

_____, 1964, Columbia (Pleistocene) sediments of Delaware: Delaware Geological Survey Bulletin No. 12, 69 p.

Mixon, R.B., Berquist, C.R., Jr., Newell, W.L., Johnson, G.H., et al., 1989, Geologic map and generalized cross sections of the Coastal Plain and adjacent parts of the Piedmont, Virginia: U.S. Geological Survey Miscellaneous Investigations Series Map I-2033, scale 1:250,000.

Owens, J.P., and Denny, C.S., 1979, Upper Cenozoic deposits of the Central Delmarva Peninsula, Maryland and Delaware: U.S. Geological Survey Professional Paper 1067-A, 28 p.

Beaverdam Formation

Beaverdam Formation johncallahan Mon, 07/27/2009 - 13:45

The following description was published in GM15 Geologic Map of the Georgetown Quadrangle, Delaware, Ramsey, K.W., 2010:

Heterogeneous unit ranging from very coarse sand with pebbles to silty clay. Predominant lithologies at land surface are white to mottled light-gray and reddish-brown, silty to clayey, fine to coarse sand. Laminae and beds of very coarse sand with pebbles to gravel are common. Laminae and beds of bluish-gray to light-gray silty clay are also common. In a few places near land surface, but more commonly in the subsurface, beds ranging from 2- to 20-ft thick of finely laminated, very fine sand and silty clay are present. The sands of the Beaverdam Formation commonly have a white silt matrix that gives drill cuttings a milky appearance (Ramsey, 2001, 2007). This white silt matrix is the most distinguishing characteristic of the unit and readily differentiates the Beaverdam Formation from the adjacent clean sands of the Turtle Branch Formation. Interpreted to be a fluvial to estuarine deposit of late Pliocene age on the basis of pollen assemblages and regional stratigraphic relationships (Andres and Ramsey, 1995a, 1996; Groot and Jordan, 1999; Groot et al., 1990). Ranges from 50 to 120 ft thick in the Georgetown Quadrangle.



The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Light gray to white coarse to very coarse sand with beds of fine to medium sand. Sands are quartzose, moderately feldspathic (

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Beaverdam
Geologic Unit Symbol
Tbd
Geologic Time Period
upper Pliocene
Reference(s)

Andres, A.S., and Ramsey, K.W., 1995a, <a href="/publications/gm9-geology-seaford-area-delaware">Geology of the Seaford area, Delaware: Delaware Geological Survey Geologic Map No. 9</a>, scale 1:24,000.

_____, 1995b, <a href="/publications/ofr39-basic-data-geologic-map-seaford-area-delaware">Basic data for the geologic map of the Seaford area, Delaware: Delaware Geological Survey Open File Report 39</a>, 39 p.

_____, 1996, <a href="/publications/ri53-geology-seaford-area-delaware">Geology of the Seaford area, Delaware: Delaware Geological Survey Report of Investigations No. 53</a>, 22 p.

Groot, J.J., Ramsey, K.W., and Wehmiller, J.F., 1990, <a href="/publications/ri47-ages-bethany-beaverdam-and-omar-formations-southern-delaware">Ages of the Bethany, Beaverdam, and Omar formations of southern Delaware: Delaware Geological Survey Report of Investigations No. 47</a>, 41 p.

Groot, J.J., and Jordan, R.R., 1999, <a href="/publications/ri58-pliocene-and-quaternary-deposits-delaware-palynology-ages-and-paleoenvironments">The Pliocene and Quaternary deposits of Delaware: palynology, ages, and paleoenvironments: Delaware Geological Survey Report of Investigations No. 58</a>, 19 p.

Ramsey, K. W., 2001, <a href="/publications/gm11-geology-ellendale-and-milton-quadrangles-delaware">Geologic map of the Ellendale and Milton quadrangles, Delaware: Delaware Geological Survey Geologic Map Series No. 11</a>, scale 1:24,000.

_____, 2007, <a href="/publications/gm14-geologic-map-kent-county-delaware">Geologic Map of Kent County, Delaware: Delaware Geological Survey Geologic Map Series No. 14</a>, scale 1:100,000.

Bethany Formation

Bethany Formation siteadmin Mon, 08/16/2010 - 11:03

The following description was published in RI67 The Cat Hill Formation and Bethany Formation of Delaware, Andres, A.S., 2004:

The composition, thickness, and geophysical log signature of the Bethany Formation vary with location and depth. In general, the Bethany Formation is a sequence of clayey and silty beds with discontinuous lenses of sand (Andres, 1986; Ramsey, 2003). The most common lithologies are silty, clayey fine sand; sandy, silty clay; clayey, sandy silt; fine to medium sand; sandy, clayey silt, and medium to coarse sand with granule and pebble layers. Thin gravel layers occur most frequently in updip areas and are rarer in downdip areas. Sands are typically quartzose. Lignite, plant remains, and mica are common, grains of glauconite are rare. In the Lewes area, Ramsey (2003) describes the Bethany Formation as consisting of gray, olive gray, bluish-gray clay to clayey silt interbedded with fine to very coarse sand. Lignitic and gravelly beds are common.

Variations in thickness reflect spatial changes in depositional environments during filling of the sedimentary basin and post-depositional erosional truncation (Andres, 1986). The age of the Bethany Formation is reported to range from late middle Miocene (Owens and Denny, 1979; Hansen, 1981; Benson, 1990) to perhaps Pliocene (Miller et al., 2003), although the age estimates are poorly constrained because of a general lack of diagnostic fossils or other materials that can be age-dated.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
bethany
Geologic Unit Symbol
Tbt
Geologic Time Period
late Miocene to Pliocene
Reference(s)

Andres, A.S., 1986, <a href="/publications/ri42-stratigraphy-and-depositional-history-post-choptank-chesapeake-group">Stratigraphy and depositional history of the post-Choptank Chesapeake Group: Delaware Geological Survey Report of Investigations No. 42</a>, 39 p.

Benson, R. N., ed., 1990, with contributions by A. S. Andres, R. N. Benson, K. W. Ramsey, and J. H. Talley, <a href="/publications/ri48-geologic-and-hydrologic-studies-oligocene-pleistocene-section-near-lewes-delaware">Geologic and hydrologic studies of Oligocene-Pleistocene section near Lewes, Delaware: Delaware Geological Survey Report of Investigations No. 48</a>, 34 p.

Hansen, H. J., 1981, Stratigraphic discussion in support of a major unconformity separating the Columbia Group from the underlying upper Miocene aquifer complex in eastern Maryland: Southeastern Geology, v. 22, p. 123-138.

Miller, K. G., McLaughlin, P. P., Jr., Browning, J. V., Benson, R. N., Sugarman, P. J., Ramsey, K. W., Hernandez, J., Baxter, S. J., Feigenson, M. D., Monteverde, D. H., Cramer, B. S., Uptegrove, J., Katz, M. E., McKenna, T. E., Strohmeier, S. A., Pekar, S. F., Cobbs, G., Cobbs, G., III, Aubry, M.-P., and Curtin, S., 2003, Bethany Beach site report, in Miller, K.G., Sugarman, P. J., Browning, J.V., et al., Proc. ODP, Init. Repts., 174AX (Suppl.), 1-84 [Online]. Available at: http://www.odp.tamu.edu/publications/174AXSIR/VOLUME/CHAPTERS/174AXS_3….

Owens, J. P. and Denny, C. S., 1979, Upper Cenozoic deposits of the central Delmarva Peninsula, Maryland and Delaware: U.S. Geological Survey Professional Paper 1067-A, 28 p.

Ramsey, K. W., 2003, <a href="/publications/gm12-geology-lewes-and-cape-henlopen-quadrangles-delaware">Geologic Map of the Lewes and Cape Henlopen quadrangles, Delaware: Delaware Geological Survey Geologic Map Series No. 12</a>, scale 1:24,000.

Bridgeton Formation

Bridgeton Formation johncallahan Tue, 07/28/2009 - 12:07

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Reddish-brown to brown, medium to very coarse, poorly sorted sand to silty quartz sand containing scattered gravel beds. Less than 15 ft thick and underlies a relict terrace flat that has elevations between 170 ft and 180 ft and parallels the present Delaware River. More extensive to the north in Pennsylvania (Owens, 1999; Berg et al., 1980).

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
Bridgetown
Geologic Unit Symbol
Tbr
Geologic Time Period
Miocene
Reference(s)

Berg, T.M., Edmunds, W.E., Geyer, A.R., and others, compilers, 1980, Geologic map of Pennsylvania: Pennsylvania Geological Survey, 4th ser., Map 1, scale 1:250,000, 3 sheets.

Owens, J.P., 1999, Cretaceous and Tertialy, <em>in</em> Shultz, C.H., editor, The Geology of Pennsylvania: Pennsylvania Geological Survey Special Publication No. 1, p. 219-223.

Bryn Mawr Formation

Bryn Mawr Formation johncallahan Tue, 07/28/2009 - 12:10

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Reddish-brown to yellowish-brown silty quartz sand to sandy silt that interfingers with medium to coarse clayey sand with gravel. Sand fraction, where a sandy silt, is fine- to very fine-grained and angular to subangular. Iron-cemented zones are common. Gravel fraction is primarily quartz. Sands are quartzose with minor amounts of weathered feldspar. Opaque heavy minerals form up to 3 percent of the sand fraction. Unit ranges up to 70 ft thick but generally less than 30 ft thick and commonly less than 10 ft thick. Surface forms a distinctive terrace that has elevations between 350 ft and 425 ft, and it overlies saprolite of the Piedmont rocks. No macrofossils have been recovered. Fossil pollen from the York Pit in Cecil County, Maryland (Pazzaglia, 1993; unpublished DGS data) indicate a Miocene age. Owens (1999) considered the unit late Oligocene in Pennsylvania.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
Bryn-mawr
Geologic Unit Symbol
Tbm
Geologic Time Period
Miocene
Reference(s)

Owens, J.P., 1999, Cretaceous and Tertiary, <em>in</em> Shultz, C.H., editor, The Geology of Pennsylvania: Pennsylvania Geological Survey Special Publication No. 1, p. 219-223.

Pazzaglia, F.J., 1993, Stratigraphy, petrography, and correlation of late Cenozoic middle Atlantic Coastal Plain deposits: implications for late-state passive-margin geologic evolution: Geological Society of America Bulletin, v. 105, p. 1617-1634.

Calvert Formation

Calvert Formation johncallahan Mon, 07/27/2009 - 13:58

The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Gray to grayish-brown, clayey silt to silty clay interbedded with gray to light-gray silty to fine to coarse quartz sands. Discontinuous beds of shell are common in the sands and in the clayey silts. Found in the subsurface throughout Kent County. Interpreted to be a marine deposit. Rarely the surficial unit on the uplands in northwestern Kent County where the Columbia or Beaverdam Formations are absent. Outcrops are patchy and are too small to be shown on this map. Three major aquifers are found within the Calvert Formation in Kent County: the Frederica, Federalsburg, and Cheswold, from top to bottom, respectively (McLaughlin and Velez, 2006). Ranges up to 425 feet thick.



The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Gray to grayish-brown clayey silt to silty clay interbedded with gray to light-gray silty to fine to coarse quartz sands. Discontinuous beds of shell are common in the sands and in the clayey silts. The unit ranges up to 100 ft in thickness.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
calvert
Geologic Unit Symbol
Tc
Geologic Time Period
lower to middle Miocene
Reference(s)

McLaughlin, P.P., and Velez, C.C., 2006, <a href="/publications/ri72-geology-and-extent-confined-aquifers-kent-county-delaware">Geology and extent of the confined aquifers of Kent County, Delaware: Delaware Geological Survey Report of Investigations No. 72</a>, 40 p.

Cat Hill Formation

Cat Hill Formation johncallahan Thu, 05/06/2010 - 18:05

The following description was published in GM15 Geologic Map of the Georgetown Quadrangle, Delaware, Ramsey, K.W., 2010:

Yellowish-brown to light-gray, medium to fine sand with thin beds and laminae of medium to coarse sand and scattered pebbles (B) that grades downward into bioturbated, gray, very fine sand to silt (A). Rare beds of light-gray to red silty clay are found near the contact with the overlying Beaverdam Formation. Laminae of opaque heavy minerals are present in the upper sands. Laminae of very fine organic particles are found in the lower sand as well as laminae to thin beds of coarse sand to gravel. The burrows in the lower sand are clay lined, and in some intervals, the sediment is completely bioturbated to the extent that no sedimentary structures are preserved. Sand is primarily quartz with less than 5% feldspar and a trace to less than 1% mica (in the very fine sand to silt). Glauconite is present only in trace amounts. Fragments of lignite are common to rare in the organic laminae. Interpreted to be a late Miocene, very shallow marine to marginal marine (shoreface) deposit (McLaughlin et al., 2008). About 100 to 120 ft thick in the Georgetown Quadrangle.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
Cat-hill
Geologic Unit Symbol
Tcat
Geologic Time Period
Late Miocene

Choptank Formation

Choptank Formation johncallahan Mon, 07/27/2009 - 13:54

Description published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Light gray to blue gray, fine to medium, shelly, silty, quartz sand and clayey silt. Discontinuous beds of fine sand and medium to coarse quartz sand are common. Base of the unit is marked by a coarse to granule sand that fines upwards to a medium to fine silty sand. This sand is the Milford aquifer (Ramsey, 1997; McLaughlin and Velez, 2006). In southern Kent County, can be subdivided into upper and lower unit. Lower unit consists of the fining-upward sequence from the basal sand to a hard clayey silt to silty clay that ranges in color from grayish brown to bluish gray. Upper unit consists of clean to silty, fine to medium, moderately shelly sands with thin silty clay beds. Rarely found in outcrop in the upper reaches of some of the more deeply incised streams. Outcrops are too small to be shown on this map. Found in the southern half of Kent County. Up to 140 feet thick in the southernmost part of the county.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
choptank
Geologic Unit Symbol
Tch
Geologic Time Period
middle to upper Miocene
Reference(s)

McLaughlin, P.P., and Velez, C.C., 2006, <a href="/publications/ri72-geology-and-extent-confined-aquifers-kent-county-delaware">Geology and extent of the confined aquifers of Kent County, Delaware: Delaware Geological Survey Report of Investigations No. 72</a>, 40 p.

Ramsey, K.W., 1997, <a href="/publications/ri55-geology-milford-and-mispillion-river-quadrangles">Geology of the Milford and Mispillion Quadrangles, Delaware: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Columbia Formation

Columbia Formation johncallahan Mon, 07/27/2009 - 13:43

The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Yellowish- to reddish-brown, fine to coarse, feldspathic quartz sand with varying amounts of gravel. Typically cross-bedded with cross-sets ranging from a few inches to over three feet in thickness. Scattered beds of tan to reddish-gray clayey silt are common. In places, the upper 5 to 25 feet consists of grayish- to reddish-brown silt to very fine sand overlying medium to coarse sand. Near the base, clasts of cobble to small boulder size have been found in a gravel bed ranging from a few inches to three feet thick. Gravel fraction primarily quartz with lesser amounts of chert. Clasts of sandstone, siltstone and shale from the Valley and Ridge, and pegmatite, micaceous schist, and amphibolite from the Piedmont are also present. Fills a topographically irregular surface, is less than 50 feet thick, and is interpreted to be primarily a body of fluvial glacial outwash sediment (Jordan, 1964; Ramsey, 1997). Pollen indicate deposition in a cold climate during the middle Pleistocene (Groot and Jordan, 1999). Ramsey (2010) considered the Columbia to be lower Pleistocene.



The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Yellowish- to reddish-brown, fine to coarse, feldspathic quartz sand with varying amounts of gravel. Typically cross-bedded with cross-sets ranging from a few inches to over three ft in thickness. Scattered beds of tan to reddish-gray clayey silt common. In places, the upper 5 to 25 ft a grayish- to reddish-brown silt to very fine sand overlying medium to coarse sand. Near base of unit, clasts of cobble to small boulder size found in gravel bed ranging from a few inches to three ft thick. Gravel fraction consists primarily of quartz with lesser amounts of chert. Clasts of sandstone, siltstone, and shale from the Valley and Ridge Province, and pegmatite, micaceous schist, and amphibolite from the Piedmont are present. The Columbia fills an eroded surface and ranges from less than 10 ft thick to over 100 ft. Primarily a body of glacial outwash sediment (Jordan, 1964; Ramsey, 1997). Pollen indicate deposition in a cold climate during middle Pleistocene (Groot and Jordan, 1999).

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Columbia
Geologic Unit Symbol
Qcl
Geologic Time Period
lower Pleistocene
Reference(s)

Groot, J.J., and Jordan, R.R., 1999, <a href="/publications/ri58-pliocene-and-quaternary-deposits-delaware-palynology-ages-and-paleoenvironments">The Pliocene and Quaternary deposits of Delaware: palynology, ages, and paleoenvironments: Delaware Geological Survey Report of Investigations No. 58</a>, 19 p.

Jordan, R.R., 1964, <a href="/publications/b12-columbia-pleistocene-sediments-delaware">The Columbia sediments of Delaware: Delaware Geological Survey Bulletin No. 12</a>, 69 p.

Ramsey, K.W., 1997, <a href="/publications/ri55-geology-milford-and-mispillion-river-quadrangles">Geology of the Milford and Mispillion River quadrangles: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Ramsey, K.W., 2010, Stratigraphy, correlation, and depositional environments of the middle to late Pleistocene interglacial deposits of southern Delaware: Delaware Geological Survey Report of Investigations No. 76, 43 p.

Cypress Swamp Formation

Cypress Swamp Formation siteadmin Mon, 08/16/2010 - 10:31

The following description was published in RI62 The Cypress Swamp Formation, Delaware, Andres, A.S. and Howard, C.S., 2000:

The upper part of the Cypress Swamp Formation is a multi-colored, thinly bedded to laminated, quartzose fine sand to silty fine sand, with areally discontinuous laminae to thin beds of fine to coarse sand, sandy silt, clayey silt, organic silt, and peat. The lowermost 3 to 6 ft of the unit are commonly composed of thin beds of dark-colored, organic-rich, clayey silt with laminae to thin beds of fine sand and peat. Fine sand to fine sandy silt are present at the base of the unit in boreholes where the lower organic-rich beds are absent. Dark-colored, peaty, organic-rich silt and clayey silt with laminae of fine to medium sand as much as 4.5 ft thick are common within 5 ft of land surface, but may be absent in some locations. Colors are shades of brown, gray, and green where the unit contains visible organic matter, and orange, yellow, and red at shallow depths where the organic-rich beds are absent. Clay-sized minerals are a mixed suite that includes kaolinite, chlorite, illite, and vermiculite.

Subtitle

Coastal Plain - Primarily Surface Unit

Formation Type
Cypress-swamp
Geologic Unit Symbol
Qcs
Geologic Time Period
late Pleistocene to Holocene

Deal Formation

Deal Formation siteadmin Mon, 08/16/2010 - 11:52

The following description was published in Bulletin 20 Stratigraphy of the Post-Potomac Cretaceous-Tertiary Rocks of Central Delaware, Benson, R.N., and Spoljaric, N., 1996:

It is a clayey, calcareous, shelly, glauconitic (10-20 percent) silt. Its colors range from greenish-gray and gray-green to brownish-gray and light gray. It is rich in calcareous and siliceous microfossils. The matrix mineralogy shows a high calcite component, except in the lower part of the formation which is within a calcite dissolution interval. In the lower half of the formation quartz is predominant.

Aragonite is rare or several levels except for the uppermost part of the formation where it shows a significant peak as the Deal grades upward into the Piney Point Formation. Marcasite and, to a lesser extent, pyrite also show major peaks at the same level. Feldspar, dolomite, pyrite, siderite, hematite, analcine, jarosite, alunite, goethite, vivianitc, and phillipsite are present in trace amounts at various levels.

A significant feature of the opaque heavy mineral assemblage is the increase in the amount of andalusite, which replaces tourmaline as the dominant heavy mineral in much of the Upper (middle Eocene) part of the Deal. Kyanite, zircon, rutile and garnet are subordinate constituents, and silliminite increases in the uppermost Deal. Clay minerals are glauconite/smectite, kaolinite, chlorite/smectite, and illite/smectite.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
deal
Geologic Unit Symbol
Td
Geologic Time Period
Paleocene to middle Eocene

Delaware Bay Group

Delaware Bay Group johncallahan Tue, 07/28/2009 - 11:55

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

The Delaware Bay Group consists of transgressive deposits that were laid down along the margins of ancestral Delaware Bay estuaries during middle to late Pleistocene rises and highstands of sea level. The Delaware Bay Group was described in detail by Ramsey (1997).

The Delaware Bay Group deposits consist of light reddish-brown to gray, medium to medium-to-coarse sands with common beds of fine to medium sand and very fine to fine sand and very fine to fine sandy silt. Also present are beds of gray clayey silt and brown, organic-rich clayey silt that are commonly found in lensoid channel-fill bodies. Beds of gray, fine to very fine clayey sand to clayey silt with shell are found in its eastern extent near Rehoboth Beach. The sands are quartzose with varying amounts of feldspar, slightly less than quantities of feldspar found in the Columbia Formation. The deposits are heterogeneous both vertically and laterally. The general trend within the formations is a fining upwards of sediment textures. Geomorphology: The Delaware Bay Group deposits are found beneath terraces that have scarps roughly parallel to the Delaware River and Bay tributaries, and relatively flat treads that slope gently toward the modern Delaware Bay.

The Delaware Bay Group includes transgressive deposits consisting of stream, swamp, marsh, estuarine barrier and beach, tidal flat, lagoon, and shallow offshore estuary environments (Ramsey, 1997).

The Delaware Bay Group is comprised of the Lynch Heights Formation, the Scotts Corners Formation, and the Cape May Formation (undivided) in New Jersey. Ramsey (1997) suggested that the Pleistocene interglacial deposits on the New Jersey side of Delaware Bay be included in the Delaware Bay Group. The Cape May Formation has similar geomorphic characteristics, ages, and depositional environments (O’Neal and McGeary, 2002; Newell et al., 2001) to the Delaware Bay Group.

Subtitle

Coastal Plain - Primarily Surficial Unit

Geologic Unit Symbol
Qdb
Geologic Time Period
upper Pleistocene
Reference(s)

Newell, W.L., Powars, D.S., Owens, J.P., and Schindler, J.S. 2001, Surficial geologic map of central and southern New Jersey: U.S. Geological Survey Miscellaneous Investigation Series Map I-2540-D, scale 1:100,000.

O’Neal, M.L., and McGeary, S., 2002, Late Quaternary stratigraphy and sea-level history of the northern Delaware Bay margin, southern New Jersey, USA: a ground penetrating radar analysis of composite Quaternary coastal terraces: Quaternary Science Reviews, v. 21, p. 929-946.

Ramsey, K. W., 1997, <a href="/publications/ri55-geology-milford-and-mispillion-river-quadrangles">Geology of the Milford and Mispillion River quadrangles: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Englishtown Formation

Englishtown Formation johncallahan Tue, 07/28/2009 - 13:26

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Light-gray to white, micaceous, slightly silty to silty, fine-grained, slightly glauconitic quartz sand. In outcrop, it is extensively burrowed with Ophiomorpha burrows. Ranges from 20 to 50 ft in thickness. On the cross-section, the Englishtown is shown only where the sands are well developed. Interpreted to be nearshore marine to tidal flat in origin.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
englishtown
Geologic Unit Symbol
Ket
Geologic Time Period
Upper Cretaceous

Hornerstown Formation

Hornerstown Formation johncallahan Tue, 07/28/2009 - 12:15

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Glauconite sand that is silty and slightly to moderately clayey and contains scattered shell beds. Glauconite approximately 90 percent to 95 percent of the sand fraction and quartz 5 percent to 10 percent. Near the top of unit, silt-filled burrows are present. Lower, the unit is commonly laminated with silty sand and moderately clayey sand. Silt and clay matrix is calcareous. Uniformly a dark-greenish-gray. Interpreted to be marine in origin. The Cretaceous-Tertiary boundary is considered to lie within the formation. Rarely occurs in outcrop and where shown on the map is covered by colluvium along the stream valley bluffs. Ranges between 10 and 50 feet in thickness.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
Hornerstown
Geologic Unit Symbol
KTht
Geologic Time Period
Upper Cretaceous and Paleocene

Ironshire Formation

Ironshire Formation siteadmin Mon, 08/16/2010 - 11:17

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

The Ironshire Formation was described by Owens and Denny (1979) as consisting of a lower loose, pale-yellow to white, well-sorted, medium sand characterized by long, low-angle inclined beds with laminae of black minerals. The upper portion of the units was described as consisting of light-colored, trough cross-stratified, well-sorted sand with pebbles and a few Callianassa borings. They described the Ironshire Formation near Rehoboth in a stratigraphic section which is now considered to be a part of the Lynch Heights Formation.

Detailed mapping is needed to clearly describe the unit in Delaware. Based on limited investigation in Delaware by the author, the Ironshire Formation is a fine to medium, sugary sand overlying a gray, silty clay that is flaser- to wavybedded with fine to medium sand overlying gray, silty clay with scattered organic-rich laminae in its reference area. To the north toward Indian River Bay, the Ironshire Formation is a fine to medium sand with coarse laminae and scattered pebbles and rare, scattered shelly zones and silty clay beds. The sands are quartzose with less than 10 percent feldspar. The Ironshire Formation is rarely over 20 feet thick.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Ironshire
Geologic Unit Symbol
Qi
Geologic Time Period
late Pleistocene
Reference(s)

Owens, J.P., and Denny, C.S., 1979, Upper Cenozoic deposits of the Central Delmarva Peninsula, Maryland and Delaware: U.S. Geological Survey Professional Paper 1067-A, 28 p.

Kent Island Formation

Kent Island Formation siteadmin Mon, 08/16/2010 - 11:41

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

Owens and Denny (1979) named the Kent Island Formation for deposits bordering the Chesapeake Bay found underneath lowlands that ranged in elevation from 0 to 25 feet in elevation but most of the land surface area is less than 10 feet in elevation. These lowlands are bordered by a scarp with at toe at approximately 25 feet. In its type area, the Kent Island Formation was described as consisting of thick beds of loose, light colored, cross-stratified sand overlying dark-colored massive to thinly laminated clay-silt. Pebbles as much as 10 cm (4 in.) in diameter occur in thin beds with the sand or as scattered clasts in both the sand and clay-silt. Locally, large tree stumps in growth position are encased in the clay-silt. Maximum thickness of the Kent Island was about 12 m (40 feet).

The Kent Island Formation in Delaware consists of a lower, light-gray to reddish-brown, coarse sand to pebble gravel with scattered organic silty clay lenses; a middle, gray, clayey silt to silty clay; and an upper fine to medium, brownish-yellow sand with scattered clay laminae. Rare lenses of shell, most commonly the oyster Crassostrea, are found where the middle clay is at its thickest. The thickness of the Kent Island Formation in Delaware ranges from 0 to 25 feet.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Kent-island
Geologic Unit Symbol
Qki
Geologic Time Period
late Pleistocene
Reference(s)

Owens, J.P., and Denny, C.S., 1979, Upper Cenozoic deposits of the Central Delmarva Peninsula, Maryland and Delaware: U.S. Geological Survey Professional Paper 1067-A, 28 p.

Lynch Heights Formation

Lynch Heights Formation johncallahan Mon, 07/27/2009 - 13:36

The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Heterogeneous unit of light-gray to brown to light-yellowish brown, medium to fine sand with discontinuous beds of coarse sand, gravel, silt, fine to very fine sand, and organic-rich clayey silt to silty sand. Upper part of the unit commonly consists of fine, well-sorted sand. Small-scale cross-bedding within the sands is common. Some of the interbedded clayey silts and silty sands are burrowed. Beds of shell are rarely encountered. Sands are quartzose and slightly feldspathic, and typically micaceous where very fine to fine grained. Unit underlies a terrace parallel to the present Delaware Bay that has elevations between 50 and 30 feet. Interpreted to be a fluvial to estuarine unit of fluvial channel, tidal flat, tidal channel, beach, and bay deposits (Ramsey, 1997). Overall thickness ranges up to 50 feet.



The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Heterogeneous unit of light-gray to brown to light yellowish brown, medium to fine sand with discontinuous beds of coarse sand, gravel, silt, fine to very fine sand, and organic-rich clayey silt to silty sand. Upper part of unit commonly consists of fine, well-sorted sand. Small-scale cross- bedding within sands is common. Some interbedded clayey silts and silty sands are burrowed. Beds of shell rarely encountered. Sands are quartzose, slightly feldspathic, and typically micaceous where very fine to fine grained. Unit underlies a terrace parallel to present Delaware River that has elevations between 50 and 30 ft. Interpreted to be a fluvial to estuarine unit of fluvial channel, tidal flat, tidal channel, beach, and bay deposits (Ramsey, 1997). Overall thickness rarely exceeds 20 ft.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Lynch-heights
Geologic Unit Symbol
Qlh
Geologic Time Period
middle Pleistocene
Reference(s)

Ramsey, K. W., 1997, <a href="/publications/ri55-geology-milford-and-mispillion-river-quadrangles">Geology of the Milford and Mispillion River quadrangles: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Magothy Formation

Magothy Formation johncallahan Tue, 07/28/2009 - 13:30

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Dark-gray to gray silty clay to clayey silt that contains abundant fragments of lignite; grades downward into a very fine to fine sand with scattered and discontinuous thin beds of clayey silt with lignite fragments. Thickness ranges from 20 to 50 ft. Updip in the vicinity of the Chesapeake and Delaware Canal, the Magothy fills channels incised into the Potomac Formation and is discontinuous in its extent. Interpreted to have been deposited in coastal to nearshore environments.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
magothy
Geologic Unit Symbol
Km
Geologic Time Period
Upper Cretaceous

Marshalltown Formation

Marshalltown Formation johncallahan Tue, 07/28/2009 - 13:24

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Greenish-gray, slightly silty, fine-grained glauconitic quartz sand. Glauconite comprises 30 to 40 percent of the sand fraction. Ranges from 10 to 50 ft in thickness. Extensively burrowed. Interpreted to be marine in origin.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
marshallton
Geologic Unit Symbol
Kmt
Geologic Time Period
Upper Cretaceous

Manasquan Formation

Manasquan Formation johncallahan Tue, 07/28/2009 - 13:20

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Consists of 30 ft of silty, shelly, fine sands that are commonly glauconitic (Benson and Spoljaric, 1996). Deposited during the latest Paleocene to early Eocene (Benson and Spoljaric, 1996). Based on microfossils (unpublished DGS file data), it can be characterized as an open shelf deposit.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
manasquan
Geologic Unit Symbol
Tmq
Geologic Time Period
Paleocene to Eocene
Reference(s)

Benson, R.N., and Spoljaric, N., 1996, <a href="/publications/b20-stratigraphy-post-potomac-cretaceous-tertiary-rocks-central-delaware">Stratigraphy of the post-Potomac Cretaceous-Tertiary rocks of central Delaware: Delaware Geological Survey Bulletin 20</a>, 28 p.

Merchantville Formation

Merchantville Formation johncallahan Tue, 07/28/2009 - 13:28

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Light- to dark-gray, very micaceous, glauconitic, very silty fine- to very fine-grained sand to fine sandy silt. Ranges from 20 to 120 ft in thickness. Marine in origin.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
merchantville
Geologic Unit Symbol
Kmv
Geologic Time Period
Upper Cretaceous

Mt. Laurel Formation

Mt. Laurel Formation johncallahan Tue, 07/28/2009 - 12:18

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Slightly calcareous, glauconitic, quartz sand that is medium to fine grained. Contains about 3 to 5 percent glauconite. Sand is subrounded to subangular and slightly silty with a few moderately silty zones. Scattered belemnites are present as well as a few scattered shell fragments or thin shell beds. Uniform dark olive gray or yellowish-brown where weathered. In outcrop, reported to be extensively burrowed (Owens, et al., 1970). Where it is the surficial deposit south of the Chesapeake and Delaware Canal, the Mt. Laurel can be confused with the Columbia Formation, especially where the color is similar. Can be differentiated by ubiquitous presence of glauconite and generally better sorted sands of the Mt. Laurel. Marine in origin. Ranges from 30 to 100 ft in thickness.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
Mount-laurel
Geologic Unit Symbol
Kml
Geologic Time Period
Upper Cretaceous
Reference(s)

Owens, J.P., Minard, J.P., Sohl, N.F., and Mello, J.F., 1970, Stratigraphy of the outcropping post-Magothy Upper Cretaceous Formations in Southern New Jersey and Northern Delmarva Peninsula, Delaware and Maryland: U.S. Geological Survey Professional Paper 674, 60 p.

Nanticoke River Group

Nanticoke River Group siteadmin Fri, 08/20/2010 - 12:34

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

The Nanticoke River Group consists of the Turtle Branch and Kent Island Formations. In Delaware, the Nanticoke River Group extends along the margins of the Nanticoke River and its tributaries. It continues along the Nanticoke River into adjacent Maryland.

The Nanticoke River Group consists of heterogeneous units of interbedded fine to coarse sand, clayey silt, sandy silt, and silty clay. Where the units are muddy, downstream of Seaford, the sequence consists of a lower fluvial to estuarine swamp to tidal stream deposits (coarse sand to gravelly sand with scattered organic-rich muddy beds) overlain by estuarine clayey silts and silty clays that contain rare to common Crassostrea (oyster) bioherms. The silts and clays are overlain by sands with clay laminae, to fine to coarse well-sorted, clean sand that are estuarne beach and eolian in origin. Upstream, the mud beds are rarer and restricted to the west side of streams and consist of organic rich clayey silt. Most of the stratigraphic section is dominated by clean, well-sorted sands.

The Nanticoke River Group consists of fluvial to estuarine, fine to coarse sand and estuarine clayey silts to silty clays that were deposited during highstands of sea level during the late Pleistocene. In Delaware, these deposits underlie terraces that flank the margins of the present Nanticoke River and its tributaries. Upstream the terraces become less distinct, and in places the surface of the Nanticoke River Group does not have a distinctive boundary scarp with the adjacent Beaverdam Formation. The Nanticoke River Group sands, however, are distinct and readily discernable from those of the Beaverdam Formation; the Nanticoke River Group sands are more well sorted, less feldspathic, and lack the distinctive white silty matrix of the Beaverdam Formation.

The informal term “Nanticoke deposits” was used by Andres and Ramsey (1995, 1996) for Quaternary sediments along the Nanticoke River in the vicinity of Seaford in western Sussex County. These deposits included estuarine sediments as well as eolian dunes along the margins of the Nanticoke River. More recent mapping in the Georgetown area in 2006 and 2007 (Ramsey, 2010), as well as along the Nanticoke River to the southwest of Seaford in 2005 (unpublished DGS data), has allowed for more detailed analysis of the deposits and for recognition of two stratigraphic units within what was mapped as the Nanticoke deposits.

Subtitle

Coastal Plain - Primarily Surficial Unit

Geologic Unit Symbol
Qnrg
Geologic Time Period
middle to upper Pleistocene
Reference(s)

Andres, A.S., and Ramsey, K.W., 1995, Geologic Map of the Seaford area, Delaware: Delaware Geological Survey Geologic Map Series No. 9, scale 1:24,000.

_____, 1996, Geology of the Seaford area, Delaware: Delaware Geological Survey Report of Investigations No. 53, 22 p.

Navesink Formation

Navesink Formation johncallahan Tue, 07/28/2009 - 13:22

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Generally a calcareous silt that is slightly to moderately sandy and slightly to moderately clayey. Sand is fine to very fine grained composed of about 50 percent glauconite, 40 percent peloids, and 10 percent quartz. Sediment is laminated, marked by varying amounts of clay and sand. Peloids are yellow to yellowish-brown flat to ovoid pellets that are calcareous and may contain flakes of chitin and grains of glauconite or quartz. Scattered shell fragments are present but form a minor constituent of the sediment. Uniformly dark-greenish-gray, slightly lighter in color than the overlying Hornerstown Formation. 10 to 20 ft thick.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
navesink
Geologic Unit Symbol
Knv
Geologic Time Period
Upper Cretaceous

Old College Formation

Old College Formation johncallahan Tue, 07/28/2009 - 12:05

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Reddish-brown to brown clayey silt, silty sand to sandy silt, and medium to coarse quartz sand with pebbles (Ramsey, 2005). Rock fragments of mica or sillimanite quartzose schist are common sand fraction. At land surface, a gray to grayish-brown clayey silt is present. Sands are cross-bedded with laminae of muscovite or heavy minerals defining the cross-sets. Silty beds tend to be structureless, or in the gray clayey silt beds, heavily bioturbated by roots. No fossils other than pollen have been recovered. Pollen indicate a cold climate during deposition of the upper clayey silt unit (unpublished DGS data). Stratigraphic relationships indicate either slightly younger than or contemporaneous with the Columbia Formation. Ranges from 5 to 40 ft in thickness.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Old-college
Geologic Unit Symbol
Qoc
Geologic Time Period
middle Pleistocene
Reference(s)

Ramsey, K.W., 2005, <a href="/publications/ri69-geology-old-college-formation-along-fall-zone-delaware">Geology of the Old College Formation along the Fall Zone of Delaware: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Omar Formation

Omar Formation siteadmin Mon, 08/16/2010 - 11:28

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

The Omar Formation was originally described (Jordan, 1962) as consisting of interbedded, gray to dark gray, quartz sands and silts with bedding ranging from a few inches to more than 10 feet thick. Thin laminae of clay are found within the fine, well-sorted sands. Silt mixed with sand generally contains some plant matter and where dark in color could be considered organic. Sands contain wood fragments, some of which are lignitic.

On the basis of regional mapping by Ramsey (2010), the description of the Omar Formation is modified from that of Jordan (1962). The Omar Formation consists of quartzose, greenish-gray to light-yellow, homogeneous, fine to very fine sand with scattered medium to coarse laminae commonly overlain by dark-greenish-gray, silty clay to clayey silt with scattered shell beds and bioherms of the oyster Crassostrea. The silty clay is overlain by a light-gray, fine to coarse sand. Coarse sand and gravel interspersed with organic-rich horizons that include stumps and logs of cypress trees is found both at the base of the Omar Formation and at the top of the silty clay.

The Omar Formation ranges from 10 to 80 feet thick. In the western portions of its extent in the vicinity of Cypress Swamp and to the north where it grades into the Lynch Heights Formation, the unit is typically a sheet of moderately well sorted to well sorted, fine to coarse sand.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
omar
Geologic Unit Symbol
Qo
Geologic Time Period
middle Pleistocene
Reference(s)

Jordan, R.R., 1962, <a href="/publications/b9-stratigraphy-sedimentary-rocks-delaware">Stratigraphy of the sedimentary rocks of Delaware: Delaware Geological Survey Bulletin No. 9</a>, 51 p.

Piney Point Formation

Piney Point Formation johncallahan Mon, 07/27/2009 - 14:03

Description published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Bright green, fine to coarse, shelly, glauconitic (20 to 40% glauconite), quartz sand. Silty and clayey toward the bottom and coarsens upwards. Considered to be a marine deposit (Benson, Jordan, and Spoljaric, 1985). The Piney Point aquifer coincides with the sandier portion of the unit. Ranges up to 250 feet thick in the southern portion of Kent County.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
piney-point
Geologic Unit Symbol
Tpp
Geologic Time Period
upper Eocene
Reference(s)

Benson, R.N., Jordan, R.R., and Spoljaric, N., 1985, <a href="/publications/b17-geological-studies-cretaceous-and-tertiary-section-test-well-je32-04-central-delawa">Geological study of the Cretaceous and Tertiary Section, Test Well Je32-04, Central Delaware: Delaware Geological Survey Bulletin No. 17</a>, 69 p.

Potomac Formation

Potomac Formation johncallahan Tue, 07/28/2009 - 12:21

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Dark-red, gray, pink, and white silty clay to clayey silt and very fine to medium sand beds. Beds of gray clayey silt to very fine sand that contain pieces of charcoal and lignite are common. Deposited in a fluvial setting in a tropical to subtropical environment as indicated by abundant paleosol horizons. Ranges from 20 ft updip to over 1600 ft thick in southern New Castle County.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
Potomac
Geologic Unit Symbol
Kpt
Geologic Time Period
Cretaceous

Scotts Corners Formation

Scotts Corners Formation johncallahan Fri, 07/24/2009 - 15:25

The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Heterogeneous unit of light-gray to brown to light-yellowish-brown, coarse to fine sand, gravelly sand and pebble gravel with rare discontinuous beds of organic-rich clayey silt, clayey silt, and pebble gravel. Sands are quartzose with some feldspar and muscovite. Commonly capped by one to two feet of silt to fine sandy silt. Laminae of opaque heavy minerals are common. Unit underlies a terrace parallel to the present Delaware River that has elevations less than 25 feet. Interpreted to be a transgressive unit consisting of swamp, marsh, estuarine channel, beach, and bay deposits. Climate during the time of deposition was temperate to warm temperate as interpreted from fossil pollen assemblages (Ramsey, 1997). Overall thickness of the unit rarely exceeds 20 feet.



The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Heterogeneous unit of light-gray to brown to light-yellowish-brown, coarse to fine sand, gravelly sand and pebble gravel with rare discontinuous beds of organic-rich clayey silt, clayey silt, and pebble gravel. Sands are quartzose with some feldspar and muscovite. Commonly capped by one to two ft of silt to fine sandy silt. Laminae of opaque heavy minerals common. Unit underlies a terrace parallel to the present Delaware River that has elevations less than 25 ft. Interpreted to be a transgressive unit consisting of swamp, marsh, estuarine channel, beach, and bay deposits. Climate during deposition was temperate to warm temperate as interpreted from fossil pollen (Ramsey, 1997). Overall thickness rarely exceeds 15 ft.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Scotts-corners
Geologic Unit Symbol
Qsc
Geologic Time Period
upper Pleistocene
Reference(s)

Ramsey, K.W., 1997, <a href="/publications/ri55-geology-milford-and-mispillion-river-quadrangles">Geology of the Milford and Mispillion Quadrangles, Delaware: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Shark River Formation

Shark River Formation johncallahan Tue, 07/28/2009 - 13:18

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Glauconitic clayey silt and clay, with some glauconite sand and fine glauconitic quartz sand. Deposited in the middle Eocene (Benson and Spoljaric, 1996), and is generally 60 to 70 ft thick. Based on the microfossils (unpublished DGS file data), it can be characterized as an open shelf deposit.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
shark-river
Geologic Unit Symbol
Tsr
Geologic Time Period
Eocene
Reference(s)

Benson, R.N., and Spoljaric, N., 1996, <a href="/publications/b20-stratigraphy-post-potomac-cretaceous-tertiary-rocks-central-delaware">Stratigraphy of the Post-Potomac Cretaceous-Tertiary Rocks of Central Delaware: Delaware Geological Survey Bulletin 20</a>, 28 p.

Sinepuxent Formation

Sinepuxent Formation siteadmin Mon, 08/16/2010 - 11:10

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

Owens and Denny (1979) described the Sinepuxent Formation in Maryland as dark, poorly sorted, silty fine to medium sand with the lower part of the unit being fine grained with thin beds of black clay. The Sinepuxent Formation is described as being lithically distinct from the Omar and Ironshire Formations due to the presence gray, laminated, silty very fine to fine, quartzose, micaceous, sand to sandy silt. The base of the unit is typically a bluishgray to dark-gray clayey silt to silty clay. There are a few shelly zones within the Sinepuxent Formation in the vicinity of Bethany Beach (McDonald, 1981; McLaughlin et al., 2008). The Sinepuxent Formation is up to 40 feet thick.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Sinepuxent
Geologic Unit Symbol
Qsi
Geologic Time Period
late Pleistocene
Reference(s)

Owens, J.P., and Denny, C.S., 1979, Upper Cenozoic deposits of the Central Delmarva Peninsula, Maryland and Delaware: U.S. Geological Survey Professional Paper 1067-A, 28 p.

McDonald, K.A., 1981, Three-dimensional analysis of Pleistocene and Holocene coastal sedimentary units at Bethany Beach, Delaware: unpublished M.S. Thesis, University of Delaware, Newark, 205 p.

McLaughlin, P.P., Miller, K.M., Browning, J.V., Ramsey, K.W., et al., 2008, <a href="/publications/ri75-stratigraphy-and-correlation-oligocene-pleistocene-section-bethany-beach-delaware">Stratigraphy and Correlation of the Oligocene to Pleistocene Section at Bethany Beach, Delaware: Delaware Geological Survey Report of Investigations No. 75</a>, 41 p.

St. Marys Formation

St. Marys Formation johncallahan Mon, 07/27/2009 - 13:52

The following description was published in GM15 Geologic Map of the Georgetown Quadrangle, Delaware, Ramsey, K.W., 2010:

Bioturbated, dark-greenish-gray silty clay, banded light-gray, white, and red silty clay, and glauconitic, shelly, very fine sandy silt. In the Georgetown Quadrangle, the St. Marys Formation is capped by about 5 to 15 ft of bioturbated, dark-greenish-gray silty clay. A distinct burrowed horizon separates the clay from the underlying banded clay that consists of a 10- to 15-ft thick, compact, color-banded silty clay with scattered white clayey concretions. The banded clay has a sharp contact at its base with underlying glauconitic, very fine, sandy silt. The sandy silt contains shells of the gastropod Turritella. The entire thickness of the St. Marys Formation is less than 100 ft in the Georgetown Quadrangle, thinning from its thickest in the southeast corner to about 50 ft thick in the northwest corner of the map area. Interpreted to be a marine deposit of late Miocene age (McLaughlin et al., 2008).



The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Light reddish-brown to gray, fine to very fine, silty sand and clayey silt. Discontinuous beds of fine to medium quartz sand are common. Base of unit in the Milford area (Ramsey, 1997) is a medium sand bed ranging from 10 to 15 feet thick. Found in the southeastern portion of Kent County. Patchy in distribution where it occurs beneath Quaternary deposits. Thickness ranges up to 30 feet. Interpreted to be a shallow marine deposit.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
st-marys
Geologic Unit Symbol
Tsm
Geologic Time Period
upper Miocene
Reference(s)

McLaughlin, P.P., Miller, K.G., Browning, J.V., Ramsey, K. W., and others, 2008,<a href="/publications/ri75-stratigraphy-and-correlation-oligocene-pleistocene-section-bethany-beach-delaware"> Stratigraphy and Correlation of the Oligocene to Pleistocene section at Bethany Beach, Delaware: Delaware Geological Survey Report of Investigations No. 75</a>, 41 p.

Ramsey, K. W., 1997, <a href="/publications/ri55-geology-milford-and-mispillion-river-quadrangles">Geology of the Milford and Mispillion River quadrangles: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Turtle Branch Formation

Turtle Branch Formation johncallahan Mon, 07/27/2009 - 13:39

The following description was published in GM15 Geologic Map of the Georgetown Quadrangle, Delaware, Ramsey, K.W., 2010:

Fining-upward sequence of a thin (less than 1 ft thick), gravelly sand, to an interlaminated, medium to coarse sand with heavy mineral laminae, to a well-sorted fine to medium, fluffy sand that makes up the bulk of the unit. Near the present stream valleys, 1 to 5-ft thick beds of light-grayish-brown to brown, organic-rich, clayey silt are common. Along the margins of the unit where it is adjacent to the Beaverdam Formation, the unit commonly consists of pale-yellow to yellowish-brown, fine to very fine silty sand. The unit is less than 5 ft thick over much of its mapped area but can range up to 20 ft thick near the present stream valleys. The well-sorted sands of the Turtle Branch Formation are differentiated from those of the dune deposits by their slightly coarser texture, better developed soil profile, and common presence of heavy mineral laminae. Interpreted to be a sand-dominated fluvial to tidal and shoreline deposit associated with a high stand of sea level during the middle Pleistocene.



The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

One to five feet of gray coarse sand and pebbles overlain by one to ten feet of tan to gray clayey silt to silty clay that is in turn overlain by three to five feet of fine to medium sand. Laterally, finer beds are less common away from Marshyhope Creek and the deposit is dominated by fine to medium sand with scattered beds of coarse to very coarse sand with pebbles. Sands are quartzose with some feldspar and laminae of opaque heavy minerals. Underlies a terrace with elevations ranging from 35 to 50 feet and is interpreted to be fluvial to estuarine in origin. Found in the Marshyhope Creek drainage basin in Kent County and more extensively along the Nanticoke drainage basin in Sussex County. Thickness ranges up to 20 feet closer to the valley of the Marshyhope and thins away from the river.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Turtle-branch
Geologic Unit Symbol
Qtb
Geologic Time Period
middle Pleistocene

Vincentown Formation

Vincentown Formation johncallahan Tue, 07/28/2009 - 12:12

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Glauconitic sand that ranges from slightly silty to moderately silty and slightly to moderately clayey. Dominant constituent is subrounded to subangular clear quartz sand that ranges from medium to fine grained. Fine-grained glauconite is a secondary constituent, which ranges from 5 percent in the clayey zones to 15 percent where cleaner. Towards bottom of unit, glauconite percentages increase to about 50 percent of the sand fraction. Silty and clayey zones are thin to thick laminae ranging from 0.01 to 0.5 ft thick. Olive gray to dark-yellowish-brown in zones where iron cement is present. Interpreted to be marine in origin. Rarely occurs in outcrop and is covered by colluvium along the stream valley bluffs where shown on the map. Ranges from 50 to 100 ft in thickness in the subsurface and less than 50 ft thick where it is cut by younger deposits updip.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
vincentown
Geologic Unit Symbol
Tvt
Geologic Time Period
Paleocene