One of the major objectives of the Double Trouble corehole was to understand the distribution and environment of deposition of the Toms River Member (TRM) of the Shark River Formation. The TRM is an important aquifer in the coastal plain, but it has been difficult to determine whether the aquifer is a single unit or is slightly different units in different parts of the state.
The TRM was first named by Enright (1969), and the type locality was designated as 160–240 ft (48.8–73.2 m) below sea level (225–240 ft [68.6–73.2 m] below ground surface) in well no. 84 of the Toms River Chemical Company, Toms River, New Jersey (LM# 492; permit number 290085J). Enright (1969) described the unit as a slightly clayey, shelly, fine to medium quartz sand. The TRM is recognized as a coarse quartz-glauconite sand of middle Eocene age. Downdip it is found between the carbonate-rich clay of the Shark River Formation Squankum Member (also known as the "Blue Marl"; referred to in other ODP 174AX reports as the lower Shark River; see, e.g., Miller et al., 1998b) below and the clay-rich upper Eocene Absecon Inlet Formation above. At some sites the TRM is distinguished from an upper Shark River Formation, an informal unit less sandy than the TRM but much sandier than the lower Shark River Formation. Neither the TRM nor the Absecon Inlet Formations have been recognized in outcrop.
In the Double Trouble corehole the TRM is coarse to very coarse glauconitic quartz sand. Above a basal glauconite at 517.4 ft (157.7 m), the TRM coarsens upsection from predominantly clay below 475 ft changing to medium quartz sand between 365 and 475 ft (111.3 and 144.8 m) and to coarse to very coarse sand with granules and pebbles from 365 ft (111.3 m) to the top of the sequence at 293.8 ft (89.6 m). It is interpreted to have been deposited on a lower shoreface shallowing upsection to upper shoreface environments.
The TRM is found in other ODP New Jersey coastal plain wells. Analysis of these wells allows us to recognize the TRM on gamma logs in the absence of core control. The TRM is different thicknesses and different ages in different parts of the state. Browning et al. (1997a) recognized the TRM at Island Beach and found it represented two sequences, designated E8 and E9. Sequence E8 is planktonic foraminiferal Zone P12 and calcareous nannoplankton Zone NP16. Sequence E8 is thickest (~250 ft; 76.2 m) and coarsest at Double Trouble. At Sea Girt the sequence is ~100 ft (30.5 m) thick and predominantly marl at the base deposited in inner middle neritic environments below storm wave base grading up to muddy fine sand on top deposited in a lower shoreface environment. At Ancora, Millville, ACGS, Bass River, and Island Beach, Sequence E8 consists of 20–40 ft (6.1–12.2 m) of glauconite quartz sand. At Atlantic City and Ocean View, Sequence E8 consists of 40 ft (12.2 m) of carbonate-rich clay with little quartz or glauconite.
Sequence E9 has a distribution similar to E8. Sequence E9 is not present at the updip Sea Girt or Double Trouble coreholes. Sequence E9 is thickest at Ancora, where it consists of ~100 ft (30.5 m) of shelly medium quartz sand (Miller et al., 1999). It is the HST of a sequence that includes finer grained mud and glauconite at its base. Sequence E9 is also found at Millville, where it consists of ~70 ft (21.3 m) of medium- to coarse-grained glauconitic quartz sand. The sequence is finer at the base and contains progressively less mud upsection. The environments change from offshore middle neritic at the base grading to distal lower shoreface to proximal lower shoreface on top. At Island Beach, Sequence E9 consists of 30 ft (9.1 m) of pebbly medium to coarse glauconite quartz sand. At the ACGS#4 and Bass River coreholes, Sequence E9 is finer grained and consists of 20 ft (6.1 m) of glauconite sand with abundant fine quartz. At Atlantic City and Ocean View, Sequence E9 consists of ~30–40 ft (9.1–12.2 m) of slightly glauconitic clay.
Sequence E10 follows a similar pattern to E8 and E9. Sequence E10 is thickest at Millville, where it consists of 140 ft (42.7 m) of fine to medium quartz sand with scattered coarse to very coarse grains (Sugarman et al., 2005b). At ACGS#4 corehole, Sequence E10 consists of 40 ft (12.2 m) of very muddy glauconite quartz sand that coarsens upsection above a basal glauconite, suggesting it is a sequence. At Bass River, Sequence E10 is 150 ft (45.7 m) thick and is glauconite sandy mud with minor amounts of fine to very fine quartz sand. At Island Beach, Sequence E10 consists of ~40 ft (12.2 m) of glauconite sandy mud. Sequence E10 is finer grained and thicker at Cape May (>140 ft; 42.7 m), Ocean View (300 ft; 91.4 m), and Atlantic City (170 ft; 51.8 m), where it consists of slightly sandy mud.
Sequence E11 is only found thick and well exposed at the ACGS#4 corehole, where it consists 80 ft (24.4 m) of very fine grained silty clay. It represents a much deeper water facies than the underlying quartz and glauconite sands.
The pattern of facies outlined here is similar to that described for the Oligocene of New Jersey by Pekar et al. (2000). The coarse-grained quartz facies known as the TRM is the foreshore and upper shoreface deposits. The glauconite- and quartz-rich facies, informally known as the upper Shark River Formation, is transitional between the lower shoreface and the offshore middle neritic environment, and the thick slightly sandy to sandy clay, generally referred to as the Absecon Inlet Formation, represents middle to outer neritic clays. These units are then time transgressive and represent the first prograding sequences across the shelf. This is a very different environment from that of the underlying lower Shark River that accumulated as carbonate-rich marls on a ramp setting. The changeover from carbonate to marl to prograding siliciclastics occurred at ~40–42 Ma on the New Jersey coastal plain (Browning et al., 1996).