The Medford corehole successfully recovered a thick Upper Cretaceous succession, allowing identification of potential aquifers and correlation to previously drilled holes. We constructed three cross sections that illustrate updip to downdip (Medford-Ancora-Bass River; Fig. F10) and along-strike variability (Medford-Sea Girt; Fig. F11). Medford recovered a thick Potomac Formation that can be compared with the first continually cored Potomac record along strike at Fort Mott (Fig. F12). We describe the facies and hydrogeologic significance top to bottom.
The Maastrichtian Navesink sequence(s) are thin at all three coreholes, comprised predominantly of glauconite sand (Medford) to clayey glauconite sand (Ancora) to glauconite marl (Bass River), thus fining downdip as expected (Fig. F10). The Marshalltown sequence is thicker downdip at Bass River than it is at Ancora or Medford, though all three have coarse sands in the Mount Laurel Formation (Fig. F10). The Bass River section is also finer grained than the updip sections, and the Wenonah Formation there is dominated by silt (Fig. F10). The upper Englishtown sequence (mid-Campanian) and formation is thick at Medford and thins downdip (Fig. F10), though it is thickest along strike at Sea Girt (Fig. F11). Environments in the upper Englishtown sequence change from lower shoreface and delta front at Medford and Sea Girt to inner neritic and lower shoreface at Ancora to middle neritic deposits at Bass River. The Merchantville III sequence is much thicker downdip at Bass River (~170 ft; 51.5 m) than it is at Medford (~100 ft; 30.3 m) (Fig. F10). In particular, the middle neritic and prodelta clays from the Woodbury Formation are very thick at Bass River, thick at Ancora, and thin at Medford. At Medford, the MeIII (Campanian) sequence is dominated by lower shoreface sands lacking a deltaic influence and assigned to the lower Englishtown Formation (Fig. F10). Thus, the MeIII sequence had a deltaic influence downdip, but in the Medford region, it was a storm-dominated shoreface. MeII and MeI (Santonian) sequences are thin glauconite sequences (Fig. F10), with the MeI absent at Ancora.
The largely nonmarine Magothy Formation is poorly represented downdip at Ancora and Bass River (Fig. F10) but is well represented at Medford and Sea Girt (Fig. F11). Five upper Turonian–Coniacian sequences occur at both sites, with the Medford site apparently reflecting more marine influences (tidal channel, lagoon, and estuarine environments, in addition to the distributary channel, overbank, paleosols, lower delta plain environments found at Sea Girt). These sequences appear to correlate with members identified in outcrop and correlated to Sea Girt.
Potomac sequences (?Barremian to lower Cenomanian) at Medford appear to be closer to the source than at Fort Mott (Fig. F12). Though both are fluvial and fluvial-lacustrine, Fort Mott is very fine grained and dominated by more floodplain/overbanks/paleosol environments, whereas Medford is sandier. The upper sequence, the Potomac III at Medford, has three sand bodies within it, versus on main lower sand at Fort Mott, though both appear to represent anastamosing river systems. The lower Potomac I at Medford was deposited in braided environments, whereas the medial Potomac II sequence also displays more braided environments at Medford than at Fort Mott. The sequence stratigraphy outlined here allows evaluation of the hydrostratigraphy and predictions about aquifer continuity and quality.
The Medford site penetrated several significant aquifer-quality sand bodies outlined by Sugarman et al. (2005) (Fig. F13). The Mount Laurel aquifer is ~33 ft (10.1 m) thick at Medford and is composed predominantly of medium sand grading downward to fine to medium sand. The Englishtown aquifer system contains an upper and lower aquifer at Medford. The upper sand (224.4–240.3 ft; 68.4–73.2 m) is thin (~15 ft; 4.6 m) and fine grained and probably a minor aquifer at best. The lower Englishtown aquifer is even thinner (329.4–340 ft; 100.4–108.2 m) and is also a minor aquifer because it fines downward from fine sand with lesser medium fine sand to a silty fine to very fine sand.
The Potomac-Raritan-Magothy aquifer system contains several major aquifers. The Magothy aquifer, or upper aquifer of Zapecza (1989), is ~128 ft (39 m) thick at Medford. The Magothy aquifer contains two thick (27 and 29 ft; 8.2 and 8.8 m) sand beds from 446 to 473 ft (135.9 to 144.2 m) and 487 to 516 ft (148.4 to 157.3 m) in the upper portion of the aquifer separated by a thinner (14 ft; 4.3 m) clay-silt bed from 473 to 487 ft (144.2 to 148.4 m) that may act as a minor confining unit. This upper sandy interval is separated from the lower part of the aquifer by a 14 ft (4.3 m) thick confining unit from 516 to 530 ft (157.3 to 161.5 m) correlative with the Amboy Stoneware Clay. The lower section of the Magothy aquifer from ~530 to 573.1 ft (157.3 to 174.7 m) at Medford contains more fine sand than the upper section and might be a less productive interval within the aquifer.
An ~67 ft (20.4 m) thick confining unit from 573.1 to 640 ft (174.7 to 195.1 m) separates the Magothy or upper aquifer from several sand intervals within the Potomac that may provide high-quality aquifers. There are three aquifers within the Potomac Unit III. The uppermost one, the IIIc aquifer, is from 640 to 681.2 ft (195.1 to 207.6 m) and is ~40 ft (12.2 m) thick. A 30.4 ft (9.3 m) confining unit from 681.2 to 711.6 ft (207.6 to 216.9 m) separates the IIIc above from the IIIb aquifer below. The IIIb is a thinner (16.4 ft; 5 m) aquifer than the IIIc. A thick 37 ft (11.3 m) confining unit separates the IIIb aquifer from the IIIa aquifer that is 21.8 ft (6.6 m) thick (765–786.8 ft; 233.2–239.8 m).
The uppermost aquifer within the Potomac Unit II is the IIb, and it is separated from the IIIa aquifer by a 29.2 ft (8.9 m) thick confining unit between 786.8 and 816 ft (239.8 and 248.7 m). The IIb aquifer is 26 ft (7.9 m) thick. A confining unit from 842 to 870 ft (256.6 to 265.2 m) sits above the 60 ft (18.3 m) thick IIa aquifer. A confining unit from 930 to 958.1 ft (283.5 to 292 m) separates the IIa aquifer from a thick interval of aquifer sands predominantly in the Potomac Unit I termed the Ia aquifer. The Ia aquifer extends to the base of the hole (1090 ft; 332.2 m).
The Medford corehole provided our second continuously cored view of Potomac sequences and hydrogeologic units and surprises as to remarkable differences along strike from Fort Mott (Sugarman et al., 2006). Both share a fluvial origin, but the Medford corehole was sandier, close to source, yet had more a a marine influence. It is clear that the Potomac Formation is a complex unit that will defy predictability, versus the Upper Cretaceous sequences that display predictable updip-downdip and along-strike variability.