MEDFORD SITE SUMMARY

The Medford Site (April–May 2007) was the twelfth continuously cored borehole drilled as part of the New Jersey Coastal Plain Drilling Project (NJCPDP) and the ninth site drilled as part of Leg 174AX (Fig. F1). Located on the property of Medford Township's South Street Maintenance Facility, drilling at Medford (395348.815N, 744915.904W; elevation 34.0 ft; Mount Holly U.S. Geological Survey [USGS] 7.5 minute quadrangle; Medford Township, Burlington County, New Jersey) targeted Cretaceous sequences and aquifers. Recovery was good (mean recovery = 70%), ending at a total depth (TD) of 1090 ft (332.23 m) in Lower Cretaceous sediments. A full suite of slimline logs was obtained on formation to 1086 ft (331.01 m), and a gamma log was obtained to 1088 ft (331.62 m). The scientific team provided descriptions of sedimentary textures, structures, colors, and fossil content and identified lithostratigraphic units, lithologic contacts, and sequences (unconformity-bounded units). A team of scientists from the New Jersey Geological Survey (NJGS), Rutgers University, the Delaware Geological Survey (DGS), and the USGS collaborated in drilling and stratigraphic studies of this corehole that was funded by the NJGS. The basic data sets on which this site report is based comprise onsite and postdrilling studies of lithology, sequence stratigraphy, biostratigraphy, hydrostratigraphy, and Sr isotopes.

Lowermost Eocene sediments are found below a thin soil horizon (0–2.5 ft; 0–0.8 m). A thin glauconitic sandy clay of the Manasquan Formation (2.5–6.3 ft; 0.8–1.9 m) overlies a white kaolinitic clay of the Marlboro Clay (6.3–10.2 ft; 1.9–3.1 m), a unit that is associated elsewhere with the earlier Eocene carbon isotopic excursion.

The upper Paleocene (Zones NP7–NP8) Vincentown Formation consists of a thick highstand systems tract (HST) of glauconite-quartz sand that fines downsection to a sandy clayey biomicrite and then becomes more glauconitic downsection in a transgressive systems tract (TST). The lower Paleocene (Zone NP4) Hornerstown Formation is poorly recovered and consists primarily of a glauconite sand broken into two sequences (Zones P1c and P3a).

The Cretaceous/Paleogene boundary separates the green clays of the Hornerstown Formation from the clayey glauconite sands of the Navesink Formation; it lacks the spherules and clay clasts found elsewhere (e.g., the Bass River corehole) at this boundary in New Jersey.

The Upper Cretaceous consists of primarily marine sequences to 493.4 ft (150.4 m): Navesink I/II; Marshalltown; Merchantville I, II, and III; and Cheesequake. The Navesink Formation (60.7–100.4 ft; 18.5–30.5 m) is a Maastrichtian clayey glauconite sand that may be tentatively divided into two sequences. The Marshalltown sequence is upper Campanian (Zone CC20–CC22; 72–76 Ma Sr isotopic ages) and consists of thick slightly glauconitic quartz sands of the Mount Laurel Formation deposited in shoreface environments (upper HST), an offshore silty very fine sand of the Wenonah Formation (lower HST), and silty clayey glauconite sands of the Marshalltown Formation (TST). The upper Englishtown sequence (224.4–329.4 ft; 68.4–100.4 m) is middle Campanian (Zone CC19–CC20; ~76–77 Ma Sr isotopic ages) and is thicker here updip than in downdip sections. This sequence consists of an upper sandy HST deposited in delta front environments, a thick medial micaceous silty clay to clayey silt deposited as the lower HST in offshore to lower shoreface environments, and a basal glauconitic quartz sand deposited as a TST in lower shoreface environments. The Merchantville III sequence (MeIII) (329.4–389.5 ft; 100.4–118.7 m) is lower Campanian (Zones CC18–CC19) and consists of a micaceous lignitic sand (lower Englishtown Formation; upper HST) deposited in shoreface environments, a medial thin sandy silty clay (Woodbury Formation; lower HST) deposited in offshore environments, and a basal clayey glauconite sand deposited in offshore environments (upper part of the Merchantville Formation; TST). The Merchantville II (MeII) (389.5–420 ft; 118.7–246.7 m) and Merchantville I (MeI) (420–434.5 ft; 246.7–374.8 m) sequences are thin glauconite-dominated Santonian sequences (Zones CC17–CC16 and CC16, respectively) deposited in middle neritic environments. The Cheesequake sequence is a thin (434.5–439.4 ft; 374.8–133.9 m), poorly dated ?lower Santonian silty sequence deposited in inner neritic environments.

The Magothy Formation (439.4–573.1 ft; 133.9–174.7 m) is a complex series of nonmarine (delta front and estuarine) to marginal (bay/lagoon and tidal channel) marine sands and clays deposited during the Turonian to ?Coniacian (pollen Zone V, possibly Zone IV at the base). The Magothy Formation is better developed updip at Medford and Sea Girt than it is downdip at Ancora and Bass River. In the updip sites, we tentatively identify five sequences (I–IVB) that appear to correlate with sequences and lithologies observed in outcrop (Kulpecz et al., 2008). Below a major subaerial unconformity with weathered subtropical clays deposited as paleosols, Magothy sequence IVB (439.4–470.3 ft; 133.9–143.3 m) consists of thick lignitic, fining upward medium to coarse sands deposited in tidal channel environments; it may correlate to the Cliffwood Beds. A muddy sequence IVA (470.3–485.7 ft; 143.3–148 m) was deposited in tidal delta environments and may correlate with the Morgan Beds, though pollen data indicate that it may be older at Medford (Zone V versus Zone VII elsewhere). A sandy Sequence III (485.7–523.35 ft; 148–159.5 m) with nonmarine stacked channels overlying tidal channel deposits fines down to a lagoonal clay with marine dinocysts at its base; it is assigned to pollen Zone V and correlated with the Amboy Stoneware Clay. Micaceous lignitic sands fine downsection in Sequence II (523.35–562.6 ft; 159.5–171.5 m), which was deposited in delta front environments, and are tentatively correlated with the Old Bridge Sand and South Amboy Fire Clay Members. The base of the Magothy (Sequence I; 562.6–573.1 ft; 171.5–174.7 m) consists of moderately well sorted, medium-grained quartz sand deposited in estuarine environments and correlated to the Sayreville Sand.

The Raritan Formation (573.1–623.8 ft; 573.1–190.1 m) is sandy at the top, giving way to tightly laminated, slightly sandy silty clay deposited in marsh to swamp environments (in outcrop the equivalent section was interpreted as mangrove swamp by Owens and Sohl [1969] to ~600 ft [182.9 m]). Below this, the Raritan Formation is laminated sandy dark gray clay with disseminated plant debris deposited in lower delta plain environments. The Raritan Formation at Medford is assigned to Zone III (lower Cenomanian); it appears truncated relative to Sea Girt and downdip coreholes, with Zone IV sediments lacking.

The majority of the sediments recovered (566.2 ft; 172.6 m) at Medford were from the Potomac Formation, including Potomac Units I?, II, and III (Lower to Upper Cretaceous; ?Barremian–lower Cenomanian). The Potomac is composed of fluvial sediments that were deposited in anastomosing and braided systems. The deposits overall consist of fluvial channel sand and gravel and finer grained levee, oxbow lake, swamp, and overbank sediment. The fine-grained silt and clay overbank and levee deposits have commonly been overprinted by ancient soil-forming processes, leaving thick paleosol deposits.

Although the Potomac has been successfully divided in the coastal plain using a palynological zonation, most of the samples from Medford yielded meager spore and pollen preservation, and many samples were essentially barren. In addition, stratigraphically diagnostic forms were generally absent. Consequently, the exact stratigraphic contacts between these pollen zones in the core were difficult to place at Medford.

The youngest Potomac subdivision, Potomac Unit III (623.8–681.2 ft; 190.1–207.6 m), is a thick section (163 ft; 49.7 m) of fluvial sediments that is informally divided into two sequences. The upper sequence from 623.8 to 681.2 ft (189.9 to 207.6 m) consists of two distinct fluvial channel sand bodies sandwiched between lignitic sandy clays and clays that were deposited in adjacent overbank, swamp, and oxbow lake environments.

The lower sequence is much thicker (681.2–786.8 ft; 207.6–239.8 m), with a ~25 foot thick paleosol (681.2–706.5 ft; 207.6–215.3 m) at the top of the sequence. Below this paleosol, fluvial facies are present to the base of the sequence. Below a thin clay deposited in oxbow lake environments is a ~14 ft (4.3 m) thick fluvial channel plant-rich sand that fines upward from very coarse to fine sand at the top. Below the channel is a thin ~5 ft (1.5 m) layer of colluvium which sits above a thicker (26 ft; 7.9 m), dominantly overbank clay that has been largely altered to paleosols. Thin oxbow lake clays and overbank clays cap a ~20 ft (6.1 m) succession of fluvial channel sands that lie at the base of the sequence. Pollen assigns the section from 623.8 to 790 ft (190.1 to 240.8 m) to Zone III (lower Cenomanian) and possibly Zone IIC (upper Albian) at the base, consistent with the assignment of the sequence to the Potomac Unit III.

Potomac Unit II is tentatively divided into two sequences. The upper sequence from 786.8 to 844.7 ft (239.8 to 257.5 m) is 57.9 ft (17.65 m) thick and contains predominantly medium- to coarse-grained fluvial channel sands (816–844.7 ft; 248.7–257.5 m) overlain by levee and overbank silt and clay (786.8–816 ft; 239.8–248.7 m) that are overprinted by soil processes.

The lower Potomac II sequence (844.7–983.15 ft; 257.5–299.7 m) is 138.45 ft (42.2 m) thick and, similar to the upper sequence, fines upward from fluvial channels at the base to overbank deposits on top. The overbank deposits consist of 24.6 ft (7.5 m) of thick clayey silts and silty clays. Below this is an interbedded complex of channel sands with a maximum thickness of 10 ft (3 m) and thinner clays and clayey sands deposited in oxbow lake and overbank levee environments that extend to 922.5 ft (281.2 m). The lower part of this sequence is composed of a ~25 ft (7.6 m) thick fluvial channel deposit consisting of poorly sorted sand ranging from fine to medium to very coarse. At the base of the sequence (to 983.15 ft; 299.7 m) is a thin (3.15 ft; 0.96 m) interlaminated clay, silt, and fine sand bed interpreted as a levee deposit. Limited pollen biostratigraphy from this sequence is assigned to Zone IIB (Albian).

The Potomac Unit I sequence (983.15 ft to TD at 1090 ft; 299.7 to 332.2 m) is sand dominated with two thin clay beds deposited in braided stream environments, with the coarsest beds possibly representing colluvium. Sands generally contain dark laminae and are coarse to very coarse with pebbly and gravelly zones. True basement was not reached. The sands are assigned to Zone I (lowermost Albian to Aptian/Barremian) or possibly Zone IIA (lower Albian).

The Medford corehole penetrated 12 distinct water-bearing sands that comprise potential aquifers. Though no hydrologic studies were conducted at this site, sedimentological and log analyses suggest that the Mount Laurel is shallow but a good aquifer, the two Englishtown aquifers are relatively poor, three sandy zones within the Magothy Formation are excellent aquifers, and six sandy zones in the Potomac are good potential aquifers.

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