LITHOSTRATIGRAPHY

Summary

The onsite scientific team provided preliminary descriptions of sedimentary textures, structures, colors, fossil content, identification of lithostratigraphic units (NJGS Information Circular 1, 1990), and lithologic contacts (Table 1; Figs. 2, 3, 4, 5, 6, and 7). Subsequent studies integrated preliminary descriptions with additional descriptions, biostratigraphy, benthic foraminiferal biofacies studies, Sr-isotopic stratigraphy, and geophysical well logs. For the nonmarine, nearshore, and shallow neritic sections (primarily the Miocene and younger section), lithofacies and gamma log interpretations provide the primary means of recognizing unconformities and interpreting paleoenvironments; Sr-isotopic ages also provide a means of recognizing hiatuses and paraconformities. For the middle to outer neritic sections (primarily the Paleogene), biostratigraphic and biofacies studies provide an additional means of recognizing unconformities and the primary means of interpreting paleoenvironments. Benthic foraminiferal biofacies were used to recognize inner (0-30 m), middle (30-100 m), and outer (100-200 m) neritic paleodepths. Unconformities were identified on the basis of physical stratigraphy, including irregular contacts, reworking, bioturbation, major facies changes, gamma-ray peaks, and paraconformities inferred from biostratigraphic and Sr-isotopic age breaks. Recognition of these surfaces allow identification of sequences at the Cape May borehole.

Cape May Formation

Age: Pleistocene to Holocene
Interval: 5-140? ft (1.5-42.7 m)

The top of the borehole penetrated fill to 5 ft (1.5 m; 0 ft above sea level). The fill dates to the 1940s and is recognized by a soil horizon at the top underlain by poorly sorted yellowish sands. Below this are the unconsolidated gravels, sands, silts, and clays of the upper Pleistocene to Holocene Cape May Formation.

The interval from 5 to 33 ft (1.5-10 m) is predominantly clayey medium sand and sporadic pebbly sand with a strong H2S odor. There is a shelly interval at 30.9 ft (9.4 m), an organic-rich (decayed marsh flora) sandy clay at 32.3-33.1 ft (9.8-10.1 m), and a pebbly sand at 33.2-33.5 ft (10.1-10.2 m) that overlies a contact at 33.5 ft (10.2 m). An inlet-marsh environment is inferred based on continuity of the upper section with the modern inlet and the association of marsh flora and marine shells in the lower section. An accelerator mass spectrometer radiocarbon date of 2740 yr was measured at the Woods Hole Oceanographic NOAMS facility on the marsh flora at 33 ft (10 m), indicating that this section is upper Holocene.

The dominant lithology from 33.5 to 55 ft (10.2-16.8 m) is a sandy, silty clay with sporadic wood fragments (1-2 mm) from 35 to 40 ft (10.7-12.2 m). The interval from 55 to 65 ft (16.8-19.8 m) consists of micaceous sandy silty clay and fine to very fine sand. From 65 to 75 ft (19.8-22.9 m) laminated clay becomes common. These clays contain virtually no silt/sand and have alternating dark and light bands. The clays from 33.5 to 75 ft (10.2-22.9 m) have high gamma log values, whereas the overlying sands have low values. We interpret the section from 5 to 75 ft (1.5-22.8 m) as a coarsening-upward, ?latest Pleistocene (<14 ka) to Holocene sequence (Fig. 2).

At 75 ft (22.9 m), the lithology changes to a massive medium quartz sand with a few percent dark minerals that may mark a disconformity. Shell fragments become locally abundant from 82.6 to 87 ft (25.2-26.5 m). The interval from 75 to 87 ft (22.9-26.5 m) may reflect an inlet-marsh environment, similar to the section above 33.5 ft (10.2 m). This interpretation is consistent with the presence of the brackish water diatom Nitzschia granulata (see "Biostratigraphy" section, this chapter) and the shallow-water benthic foraminifers Elphidium and Ammonia. Amino acid racemization indicates that 83.7 and 85.6 ft (25.5 and 26.1 m) are lower Pleistocene based on Mulinia D/L values (0.53 0.05; ~1-1.9 Ma; J. Wehmiller, pers. comm., 1995). This suggests that the section from 75 to 90 ft (22.8-27.4 m) represents an early Pleistocene sequence.

A lithologic change occurs at about 90 ft (27.4 m), with greenish gray clay below. This change represents a facies shift from inlet-marsh sands and clays above to estuarine clays below, and may mark the base of the Cape May Formation at this borehole. The contact occurs in the nonrecovered interval between 87 and 90 ft (26.5 and 27.4 m). The clay continues to 130.6 ft (39.8 m) and has virtually no silt/sand and sporadic shell material. The clay is thinly laminated with organic-rich and silty sand laminations. A sharp lithologic break at 132.95 ft (40.5 m) separates the laminated clay above from a medium sand below; a gravel marks the contact. A 4-ft-thick (1.2 m), medium sand (133-137 ft; 40.5-41.8 m) is bracketed by gravels; the lower gravel extends to 140 ft (42.7 m). We interpret the section from 90 to 140 ft (26.5-42.7 m) as estuarine, with the gravels and medium sands deposited in small channels. The common presence of diatoms in this section indicate a strong marine influence on the estuary (i.e., lower estuarine).

We tentatively retain the lower estuarine clays and gravels from 90 to 140 ft (27.4-42.7 m) in the Cape May Formation and infer that it is Pleistocene. At a borehole drilled at Cape May airport by the USGS Branch of Eastern Regional Geology (D. Powars, unpubl. data, 1994; Owens et al., 1995), the base of the Quaternary was placed at 183 ft (55.8 m) below land surface (163 ft [49.7 m] below sea level) based on pollen studies. This level at Cape May airport is associated with a change from predominantly sands below to predominantly silty clays above. We note a similar lithologic contact at the top of this unit at 140 ft (135 ft below sea level) at the Cape May borehole and tentatively draw the base of the formation at this level. (Note added in proof: L. de Verteuil [pers. comm., 1996] reports upper Miocene dinocysts below 92 ft [28.0 m].)

Unnamed Sands and Clays

Age: ?Pliocene
Interval: 140-357 ft (42.7-108.8 m)

Medium to fine sands with sporadic organic matter and sandy clays are found from 140 to 160 ft (42.7-48.8 m). At about 160 ft (48.8 m), muddy sands become notably organic rich and very dark gray to black, gradually becoming reddish black to black down to 181 ft (55.2 m). Below 181 ft, the sands are dark gray and micaceous, and they become coarser. Between 200 and 206.7 ft (60.9-63 m), two 3-ft-thick (0.9 m) fining-upward successions are noted (dark gray clay, fine muddy sands, and medium to very coarse sands). Below 207 ft (63.1 m), the section consists of micaceous, fine to very fine silty sands with sporadic parallel and cross laminations. These sands continue to 264.6 ft (80.7 m) where the clay content increases, with a pebble layer at 268.2 ft (81.8 m). A coarse sandy gravel from 271.4 to 273.3 ft (82.7-83.3 m) changes to a fine quartz sand (275-280 ft; 83.8-85.3 m) that grades down to medium and coarse pebbly sand (285-322.5 ft; 86.9-98.3 m). An environmental interpretation of fluvial channels/estuarine is supported by the rapid changes in lithology and bedforms and the general absence of diatoms; the brackish water diatom Nitzschia granulata is observed where diatoms are present (see "Biostratigraphy" section, this chapter).

A sharp change to predominantly clay occurs at 322.5 ft (98.3 m). An approximately 7-ft-thick (2 m) clay layer from 322.5 to 330 ft (98.3-100.6 m) exhibits laminations of darker, apparently organic rich layers (with peats at 326.2, 327.4, and 327.9 ft) and lighter gray layers. The interval from 330.4 to 335 ft (100.7-102.1 m) was not recovered, but it is apparently sand based on cuttings and the gamma log.

The age of the sands and clays is uncertain. A radiocarbon date at 156.4 ft (47.6 m) yields a background age of >62 ka. Pollen studies at the nearby Cape May airport borehole indicate that this section is probably Pliocene (L. Sirkin, pers. comm., 1994). At that borehole, the top of the Pliocene is placed at 183 ft (55.8 m) below land surface based on pollen studies (163 ft [49.7 m] below sea level; L. Sirkin, pers. comm., 1994). A ?Pliocene unit has been informally called the Manokin Formation at the Oh25-02 Lewes, Delaware well (Fig. 1), where it lies at similar depths (173-310 ft [52.7-94.5 m] at Lewes) to the clay-sand unit in the Cape May borehole (Benson, 1990).

From 335 to 357 ft (102.1-108.8 m), we recovered laminated green and brown clays and slightly sandy clays lacking fossils. Near the base of the section, laminations become thicker and pyritized burrows appear. The base of the section is lower estuarine-shallow marine, as indicated by the presence of a few pyritized diatoms and rare to common benthic foraminifers from 354.1 to 357 ft (107.9-108.8 m). This clay unit has a distinct high gamma log signature. It is possible that this clay unit could be part of the Kirkwood Formation (see below); however, we recognized the top of definite Kirkwood Formation by the appearance of shells at 357 ft (108.8 m) in a clayey sand. This clay unit has been assigned to the ?St. Marys Formation at the Oh25-02 Lewes, Delaware well (310-382 ft; 94.5-116.5 m; Benson, 1990). We are not certain of the age of this unit (the ?St. Marys Formation is inferred to be upper Miocene; Benson, 1990), and the unit could be assigned to either the Pliocene unnamed sands and clays or older Miocene formations. However, the environment of deposition of these clays is similar to the estuarine clays and sands between 140 and 335 ft (42.7 and 102.1 m) (albeit more marine influenced), and we retain them in the same lithostratigraphic unit.

Kirkwood Formation

Age: early to middle Miocene
Interval: 357-1062.3 ft (108.8-323.7 m)

Owens et al. (1995) have recently redefined the Kirkwood Formation, previously recognized as the lower to middle Miocene sands and clays in New Jersey (e.g., Sugarman et al., 1993). They recognized four formations increasing in age: Belleplain, Wildwood, Shiloh Marl, and Kirkwood, equivalent to the Kirkwood 3, Kirkwood 2a and 2b, Kirkwood 1b, and Kirkwood 1a and Kirkwood 0, respectively, of Sugarman et al. (1993), Miller and Sugarman (1995), and this report. We have retained the older use of the Kirkwood Formation (e.g., Kirkwood 0 to Kirkwood 3) in this report to be consistent with other Leg 150X site reports (Miller et al., 1994a, 1994b).

Kirkwood-Cohansey Sequence

Age: 11.2-11.9 Ma, late middle Miocene
Interval: 357-432.2 ft (108.8-131.8 m)

The middle to lower Miocene Kirkwood Formation was first recovered at 356.9 ft (108.7 m) (the "357-ft unconformity"; Fig. 3), where it consists of a uniform medium quartz sand with shells. This lithology dominates to 395.3 ft (120.5 m) with sporadic thin laminated firm clays (e.g., 383-384.6 ft). We interpret these sands as neritic-nearshore; they contain diatoms and sporadic inner neritic foraminifers.

A tight greenish gray clay was penetrated below 395.3 ft (120.5 m). The contact between sands above and clays below is very sharp and marked by a shell bed. The clays are massive at the top but become laminated downsection with interbedded silts and clays with sporadic shell fragments. This lithology continues to 417.1 ft (127.2 m), where there is a shell bed (417.6-418.4 ft; 127.3-127.6 m) and a change to medium sand (418.4-421 ft; 127.6-128.4 m).

A possible sequence boundary occurs between 421.5 (128.5 m; the base of a shell bed from 421 to 421.5 ft) and 422 ft (128.6 m) (Fig. 3). From 422 to 422.5 ft (128.6-128.8 m), there is an indurated phosphatic fine sand; the sands are generally poorly sorted and contain abundant shell fragments and pebbles, indicating marine shelf deposition. Several sequences below this (e.g., 503, 576, 680, 710, and 850 ft; Fig. 3 and Fig. 4) show an upsection pattern of basal shell beds, silts, sands, and lithified slightly shelly sands overlain by the shell bed of the overlying sequence; we placed sequence boundaries at the top of the lithified units in these other sequences, consistent with 422 ft (128.6 m) being a sequence boundary. However, Sr-isotopes indicate no age break across the 422-ft surface (128.6 m) (Table 2).

The section from 422.5 to 432.2 ft (128.8-131.8 m) consists of shelly fine-medium sands and is included as part of one sequence from 357 to 432.2 ft (108.8-131.8 m). This sequence generally shallows upward from the shelly neritic sands at the base to medial prodelta clays to upper neritic-nearshore sands and interbedded clays.

We place the sequence between 357 and 432.2 ft (108.8 and 131.8 m) in the Kirkwood Formation; however, it is possible that this unit is the fully marine equivalent of the nearshore Cohansey Formation (e.g., Carter, 1978). The age of the Cohansey Formation is uncertain, and it may be upper middle Miocene (Owens et al., 1988) or lower upper Miocene (Olsson et al., 1987). The age of the section from 357 to 432.2 ft (108.8-131.8 m) is upper middle Miocene at Cape May based on numerous Sr-isotopic ages of 11.2-11.9 Ma (the age of 12.5 Ma at 358.4 ft [109.2 m] is anomalous and needs replication; Table 2, Fig. 3). However, the late middle to late Miocene Sr-isotopic/age calibration has relatively large errors (from 0.9 m.y. based on three analyses at 95% confidence interval; Oslick et al., 1994), and it is possible that the section may actually be partly upper Miocene (<10.4 Ma). Benson (1990) reported the upper Miocene planktonic foraminifer Neogloboquadrina acostaensis at 356-367 ft at the Oh25-02 Lewes, Delaware, well (first appearance = 10.2 Ma; Berggren et al., 1985). Similar gamma log and lithologic signatures indicate that this section at Oh25-02 correlates with the 357-432 ft sequence(s) at Cape May. Thus, it is not clear if the 357-432.2 ft (108.8-131.8 m) sequence at Cape May is uppermost middle Miocene (ca. 12-11 Ma) or if it spans the middle/upper Miocene boundary (ca. 11-10 Ma).

Kirkwood 3 Sequence

Age: ?13.3-13.7 Ma, middle Miocene by correlation to Atlantic City
Interval: 432.2-503 ft (131.8-153.4 m)

At 432.2 ft (131.8 m, the "432-ft unconformity"), there is a lithologic break between gray medium to coarse sands with abundant shell fragments above and dark greenish gray medium to fine muddy sands lacking in shell material below. Sr-isotopes indicate that the section down to 431 ft (131.4 m) is ca. 11.5 Ma, and we infer that there is an unconformity and significant hiatus at 432.2 ft (131.8 m). Sands continue down to 440.7 ft (134.4 m); below this, dark bluish gray clay beds (1-5 cm thick) are interbedded with clayey fine sands down to 460 ft (140.2 m). The clay beds vary in their spacing (0.1-0.8 ft; 3-9 cm spacing). Between 460 and 461.5 ft (140.2-140.7 m), we encountered an indurated fine sand above a stiff, fine sandy clay. We interpret the sands from 432.2 to 461.5 ft (131.8-140.7 m) as inner neritic to nearshore based on the presence of diatoms and foraminifers (including Elphidium). A clay unit from 461.5 to 501.35 ft (140.7-152.8 m) is interbedded with sandy clays and silts. The clay is interpreted as a prodelta deposited in inner neritic paleodepth based on the benthic foraminifers (Bulimina, Hanzawaia). The increasing clay content below 440 ft (134.1 m) results in increasing gamma log values downsection, with peak values from 458 ft (139.6 m, uncorrected; 460.5 ft corrected) to 490 ft (149.4 m). From 471 to 473 ft (143.6-144.2 m) and at about 475 ft (144.8 m), there are thin interbeds of sandier clays. Indurated beds of alternating silt and clay with progressively less sand continue down to 490 ft (149.4 m) and overlie a clayey medium sand that continues to 502.9 ft (153.3 m); this sand contains phosphate pellets, marks the base of a sequence, and yields a sharp gamma spike (due to the phosphates). Thus, this sequence follows a pattern of basal shelly sands, medial silts and clays, and upper sands, reflecting a shallowing-upward succession.

This section apparently correlates with the Kirkwood 3 sequence (= East Coast Diatom Zone [ECDZ] 6 sequence) of Sugarman et al. (1993). Our correlations (Fig. 5) indicate that this sequence correlates to the Kirkwood 3 sequence at Atlantic City where it was dated as 13.3-13.7 Ma (Fig. 5) (Miller et al., 1994a), although no Sr-isotope data are available at Cape May to confirm this.

Unnamed Kirkwood Sequence

Age: ca. 14.3-14.8 Ma, middle Miocene
Interval: 503-576 ft (153.3-175.6 m)

A sequence boundary occurs at 502.9 ft (153.3 m; Fig. 3): the "503-ft unconformity." At 502.9-505.95 ft (153.3-154.3 m), there is a highly indurated medium sand containing pebbles; this indurated zone (Fig. 3) is associated with high neutron porosity log values. The indurated zone marks the top of the underlying sequence, similar to other sequences in this borehole (e.g., 576, 680, 710, and 850 ft). These indurated intervals are thicker (1-3 ft; 0.3-0.9 m) than most hardgrounds associated with unconformities in the coastal plain; we suggest that these hardgrounds may reflect cementation during subaerial exposure. The cement is carbonate, and we intend to test the hypothesis of subaerial exposure with stable isotopes. We interpret these indurated pebbly coarse sand facies as part of the regressive late HST of the underlying sequence.

Between 506 and 510 ft (154.3 and 155.5 m), the section is predominantly clayey fine sand with interbeds of sandy clays, interpreted as prodelta. From 510 to 535.8 ft (155.5-163.4 m), the section is shelly clayey sand, interpreted as inner neritic (shallow shelf). The transition from shelf below to prodelta above represents a shallowing-upward succession, although the facies fine upsection. At 535.8 ft (163.4 m), there is an abrupt change to a clean fine to medium sand with shells that continues to 563 ft (171. 6 m). There is little or no shell material below about 540 ft (164.6 m), probably due to dissolution. We also interpret these sands as neritic; the presence of sponge spicules and foraminifers indicate neritic (probably inner) environments. There is a lithologic change to a muddy fine sand with abundant shell fragments in an interval of no recovery (563-570 ft, 171.6-173.8 m). At 575 ft (175.3 m), there is a gradational contact with gray fine sandy clays with large shell fragments that marks the base of the sequence at 575.7 ft (175.5 m) (Fig. 8A).

The clayey sands and sandy clays between ~563 and 575.7 ft (171.6 and 175.5 m) correlate with a gamma log maximum between 554 and 566 ft (168.9-172.5 m) uncorrected; 556.5-568.6 ft corrected). This ~7 ft (2.1 m) discrepancy can be explained by the poor recovery throughout this interval; we support this by noting that a neutron porosity peak at 567.5 ft uncorrected; 570 ft corrected; Fig. 3) probably coincides with the indurated zone at 575.7-577 ft in the core (175.5-175.9 m; Fig. 8A; i.e., indurated zones noted in several sections below correspond with neutron porosity peaks).

The sequence between 503 and 576 ft (153.4-175.6 m) is middle middle Miocene (14.3-14.8 Ma with one anomalous age of 15.5 Ma at the top of the sequence; Table 2). It therefore represents a sequence not previously recognized in the Kirkwood Formation (Fig. 5) (Sugarman et al., 1993).

Kirkwood 2b Sequence

Age: ca. 15.9-16.3 Ma, early middle Miocene
Interval: 576-615 ft (175.6-187.5 m)

There apparently is a sequence between 575.7 ft (the "?576-ft unconformity"; Fig. 3 and Fig. 8A) and 615 ft (175.5-187.5 m), although recovery is poor. From 575.7 to 577 ft (175.5-175.9 m), the section consists of very indurated sandy clay and shells that mark the top of the sequence (Fig. 8A). Gray clayey sands with shell fragments are present at 580-584.4 ft. From 590 to 617.5 ft (179.8-188.3 m), we recovered a total of only 1.1 ft of core (shell hash in clayey sand) that may mark the base of the section. The section contains inner neritic benthic foraminifers. This sequence between 575.7 and 614 ft is early middle Miocene (16.2, 15.9, and 16.3 Ma Sr-isotopic ages at 582, 583, and 600 ft, respectively; Table 2). Thus, it correlates with the Kirkwood 2b sequence (= upper ECDZ 2) of Sugarman et al. (1993).

Kirkwood 2a Sequence

Age: ca. 16.9-18.1 Ma?, late early Miocene
Interval: 615-710 ft (187.5-216.5 m)

An unconformity separates the shell hash from sands below; the contact is in the unrecovered interval between 614 and 617.5 ft (187.2-188.3 m; the "615-ft unconformity"; Fig. 3). The sequence from 617.5 to 680.1 ft (188.3-207.3 m) represents a classic coarsening-upward succession: fine to medium sand (617.5-627 ft; 188.3-191.2 m), primarily fine to medium sands with sporadic sandy clay layers (627.4-647.5 ft; 191.2-197.4 m), interbedded fine to medium sands and laminated clay beds (648-658 ft; 197.5-200.6 m), and laminated clays with sporadic shells (658-673.2 ft; 200.6-205.2 m) extending to a shell bed at the base (676.2-680.1 ft; 206.2-206.8 m). These facies represent a prograding delta, with a more distal prodelta at the base and more proximal delta front sands at the top. The sediments were at least partly marine, as evidenced by the presence of diatoms, shells, and foraminifers below 638.7 ft (194.7 m); it is probably nonmarine above this. A distinct shell hash (including complete Turritella shells) was recovered from 676.2 to 678.3 ft; this shelly unit is found at the top of the next core (680-680.1 ft; ~207.3 m), marking the base of the succession. These lower beds are inner to middle neritic based on the presence of the foraminifers Globigerina, Cibicidoides, and Nonionellina.

The sands at the top of the Kirkwood 2a sequence (617.5-647 ft; 188.3-197.4 m) plus those of the overlying sequence correlate with the Rio Grande aquifer of Zapecza (1989) and Mullikin et al. (in press) (Fig. 5). The finer grained sediments of the lower part of the Kirkwood 2a sequence correlate with the confining unit of Zapecza (1989) and Mullikin et al. (in press) (Fig. 5).

We note a surface (the "680-ft" surface) below the shell layer at 680.1 ft (207.3 m) that may be a disconformity or a flooding surface. Immediately below this, there is an indurated sand (680.1-681.4 ft; 207.3-207.7 m), as found with unconformities at 503, 576, 710, and 850 ft. This surface is also associated with a distinct gamma log increase (677.5 ft [206.6 m] uncorrected; 680 ft corrected). The clayey medium sand continues to 687.6 ft (209.6 m). From 690 to 706.2 ft (210.4-215.3 m), there is a fairly uniform, firm, micaceous brownish ("chocolate") dark gray clay with sporadic thin silt laminations. At 706.2 ft (215.3 m), there is a change to dark gray gravely sands and shell hash below to 710 ft (216.5 m) that marks the base of the sequence.

Together, the sections between 615 and 710 ft (187.5 and 216.4 m) correlate with the Kirkwood 2a sequence (= lower ECDZ 2) of Sugarman et al. (1993). The upper part of the sequence (615-680 ft, 187.5-207.3 m) has a Sr-isotopic age of 16.9 Ma (Table 2) and correlates with the upper Kirkwood 2a at Atlantic City (Fig. 5); the lower part (680-710 ft, 207.3-216.5 m) has a single age estimate of 17.8 Ma at 706.4 ft (215.4 m), correlating it with the lower Kirkwood 2a dated as 17.7-18.1 Ma at Atlantic City (Fig. 5). Further studies are needed to determine if the Kirkwood 2a can be divided into two separate sequences or if the surface at 680 ft is a flooding surface separating two parasequences within the Kw2a.

Unnamed Kirkwood Sequence

Age: 18.6-19.5 Ma, late early Miocene
Interval: 710-850 ft (216.5-259.1 m)

A disconformity (the "710-ft unconformity"; Fig. 4) occurs below the shell hash in the unsampled interval between 706.4 and 710 ft (215.2-216.5 m), associated with a distinct gamma log increase (at 704-706 ft uncorrected; 706.5-708.5 ft corrected). An extremely hard gravel layer with broken thick shell fragments was encountered from 710 to 710.8 ft (216.5-216.7 m), similar to a lithified zone immediately below the unconformities cited above. The interval from 710.7 to 713.7 ft (216.6-217.6 m) is less consolidated clayey gravel to pebbly coarse sand without visible shells. Beneath 713.7 ft (217.6 m) and down to at least 740 ft (225.6 m) (note recovery is poor; Fig. 4), extremely hard, pebbly, coarse-grained sandstone recurs. Careful examination reveals molds of bivalves, indicating dissolution of shells by ground water. The paleoenvironment represented by the indurated pebbly sands from 710 to 740 ft (216.5-225.6 m) is probably inner neritic to nearshore. The lithologic change at 706.2-710 ft (215.4-216.5 m) marks an important sequence boundary with a hiatus of approximately 0.8 m.y. (17.8 Ma above, 18.6 Ma below based on Sr-isotopes; Table 2).

At 749-753.7 ft (228.3-229.8 m), there are two distinct shell layers separated by a medium to coarse clayey quartz sand. The upper shell bed (749-751.3 ft, 228.3-229.1 m) contains many molds of mollusk shells. The lower shell bed (751.9-753.7 ft, 229.2-229.8 m) contains thick bivalve shells and weathered and fresh fragments. A third shell bed from 760.2 to 760.9 ft (231.8-232.0 m) is associated with a gamma log kick and overlies an indurated zone at 764 ft (232.9 m) that may mark an unconformity (indicated as ?764 ft on Fig. 4) or a flooding surface.

Shell beds in muddy sands continue down to about 774 ft (236.0 m), where medium muddy sands (774-781.4 ft) and coarse gravelly sands (781.4-807.3 ft) appear; both generally lack shell material. Shelly, clayey medium sand returns at 810 to 823.2 ft (247-251 m). There is a coarsening-upward succession from 830 to 847 ft (253-258.2 m): clayey fine sands with sporadic fragmented shells (830-834 ft), sandy silty clay/clayey silt (834-840 ft), to sandy clays (840-847 ft). This coarsening-upward succession is shown on the gamma log by decreasing values.

The sands from 710 to 834 ft (216.4-254.3 m) and clays from 834 to 847 ft (254.2-258.2 m) apparently represent an aquifer-confining unit that is not present at Atlantic City (Fig. 6 and Fig. 7). We recognize the confining units here as tight clays with little or no sand (Fig. 7); physical properties studies are needed to determine the degree to which these confining units serve as aquacludes or aquitards.

Kirkwood 1b Sequence

Age: 20.1-20.4 Ma, early Miocene
Interval: 850-942 ft (259.1-287.1 m)

A disconformity (the "850-ft unconformity"; Fig. 4) occurs in an unrecovered interval between 847 and 850 ft (258.2-259.1 m), with a micaceous sandy silty clay above and a medium clayey sand below (Fig. 8B). The gamma log predicts the contact at 847 ft (258.2 m uncorrected) to 849.5 ft (259 m corrected). The gamma log, facies shift, and Sr-isotope ages (19.5 Ma at 832 ft, 20.1 Ma at 851.3 ft; Table 2) indicate that this is a major disconformity. The top of the sequence (850-850.7 ft) is gravelly indurated sand (Fig. 8B), perhaps reflecting subaerial exposure and diagenesis.

Sporadic shelly sands predominate from 850.7 to 916.8 ft (259.3-279.5 m; Fig. 8B). There are lithified, hard, coarse-grained sandstone layers from 882.8 to 884, 885 to 891, 892 to 893, and 893.8 to 894 ft, with unconsolidated gravelly, clayey, fine-coarse sands in between. Below this, muddy fine sands with sandy gravel beds (894-895 ft, 910-912 ft) occur down to 916.8 ft (279.5 m).

Interbedded silty sands, sandy silts, and silty clays with sporadic shells (e.g., 920-927.65 ft, 280.4-282.7 m) predominate from 916.8 to 941.75 ft (279.4-287 m). This finer grained section yields higher gamma log values (Fig. 4) than the section above and is the basal lithologic unit in this sequence. Below this (941.75-952 ft), the section consists of uniform fine sand (60%-70%; Fig. 8). We interpret the rapid facies shift from uniform sands below to silty sands and sandy silts above (916-942 ft) as a disconformity (the "942-ft unconformity"; Fig. 4).

The sequence from 850 to 942 ft (259.1-287.2 m) has two Sr-isotope ages estimates of 20.1 Ma (Fig. 4) and thus correlates with the Kirkwood 1b sequence at Atlantic City (Fig. 5), where it is dated as 20.1-20.4 Ma (Fig. 5). Rare, sporadic benthic foraminifers in this unit indicate that it was deposited partly or entirely in an inner neritic environment.

Kirkwood 1a Sequence

Age: 20.4-20.9 Ma, early Miocene
Interval: 942-1062.3 ft (287.1-323.7 m)

Uniform fine sands at the top of the next sequence (941.75-952 ft, 287.1-290.2 m) overlie very dark gray, micaceous, sporadic, peaty silty clay (952-963.8 ft, 290.2-293.8 m). We interpret the clays as prodelta sediments. A bed (963.8-967.1 ft, 293.8-294.8 m) of heavily bioturbated, shelly, fine sandy silty clays grades down to sands. These, in turn, overlie a thick succession (967.1-1012.8 ft, 294.8-308.8 m) of very dark gray micaceous silty clay and clayey silts; they contain burrows, laminations, cross-bedding structures, and thin shell hash beds. This unit has a high gamma log signature (Fig. 4) and is shallow marine.

At 1012.8 ft (308.7 m), there is a color change to greenish gray, shelly, bioturbated clay that continues to 1016.6 ft (309.9 m); the minor sand fraction (~2% at 1014 ft) contains glauconite and planktonic foraminifers. Similar clays are found at 1020-1026 ft (310.9-312.8 m), 1030-1032 ft (314-314.6 m), and 1040-1048 ft (317-319.5 m) and are interbedded with micaceous sandy clays. At 1056.8 ft (322.2 m), dark gray firm clays overlie glauconitic sandy clay that coarsens to glauconite sand below. Shells increase in the greensands downsection from 1059 to 1061.8 ft (322.9-323.7 m); the section is dominated by thick bivalve shells from 1061.8 to 1062.3 ft (323.7-323.9 m; Fig. 8C), with an unconformity at 1062.3 ft (323.7 m, the "1062-ft unconformity"; Fig. 6 and Fig. 8C).

The interval from 942 to 1062.3 ft (287.2-323.7 m) represents the Kirkwood 1a sequence, dated using Sr-isotopes as 20.4-20.9 Ma. Using Sr-isotopes, no hiatus is discernible between the Kirkwood 1a and 1b sequences at Cape May (Fig. 4) or Atlantic City (Fig. 5), although a major disconformity clearly is indicated by gamma logs, facies shifts, and irregular surfaces at 942 ft (287.2 m) at Cape May and at 741 ft (225.9 m) at Atlantic City (Fig. 5).

The sands and sandstones of the Kirkwood 1a and 1b sequences (850-952 ft, 259.1-290.2 m) are correlated to the upper sand aquifer and "Atlantic City 800-ft sand" aquifer units (Zapecza, 1989; Mullikin et al., in press). The sandy silt and silty clay unit from 916.8 to 941.75 ft (i.e., the base of the Kirkwood 1b sequence) apparently correlates with a confining unit between the "Atlantic City 800-ft sand" and the upper sand aquifer units of Zapecza (1989), although our data indicate that this silt/clay unit is quite sandy at Cape May (Fig. 7). We suggest that the 800-ft sand and upper aquifer unit as recognized at Atlantic City (Fig. 5) may serve as one aquifer unit in the Cape May peninsula, although the indurated zones may act as confining units within this aquifer.

Kirkwood Equivalent Glauconite Sands and Clays

Kirkwood 0 Sequence

Age: 22.6-23.2 Ma; earliest Miocene
Interval: 1062.3-1180 ft (323.7-359.8 m)

A lithified sandstone of medium quartzose glauconite sand with leached shells occurs from 1062.3 to 1066.3 ft (Fig. 8C), associated with a gamma log minimum (Fig. 4). We place a sequence boundary at 1062.3 ft (323.7 m, the "1062-ft unconformity"; Fig. 6) at the top of the lithified unit separating the shelly medium quartzose glauconite sand from a medium to coarse glauconite quartz sand below (Fig. 8C).

From 1066.3 to 1180 ft (325.1-359.8 m), glauconite sands predominate with various secondary facies: they can be pebbly (with quartz pebbles up to 6 mm), clay-rich, bioturbated, lithified (1073.5-1073.9 ft, 1074.0-1074.9 ft; shown as distinct neutron density log peaks), and scattered with sporadic shells (1083.2-1100.4 ft). Quartz pebbles and sand are generally subdominant, except for coarse glauconite quartz sand beds at 1110.5-1112.8 ft (338.6-339.3 m) and at 1132.7-1137.4 ft (345.3-346.8 m). We did not recognize any additional sequences in the interval from 1066.3 to 1180 ft (325-359.7 m).

We initially correlated the greensands from 1062.3 to 1180 ft (323.7-359.8 m) with Oligocene glauconite sands elsewhere in the New Jersey subsurface (Olsson et al., 1980; Miller et al., 1994a, 1994b). However, Sr-isotopic ages (22.6, 22.7, and 23.1 Ma at 1085, 1098, and 1136 ft, respectively) establish that the glauconite sands and clays between 1062 and 1180 ft represent a lowermost Miocene sequence and are temporal equivalents of the Kirkwood Formation. We term this the Kirkwood 0 sequence and correlate it with a glauconite sand-shell bed sequence dated at Atlantic City as 21.9 to 24.1 Ma (Fig. 5). This is the oldest Miocene sequence sampled in the middle Atlantic coastal plain.

Unnamed Glauconite Sands and Clays

Age: Oligocene
Interval: 1180-1360 ft (359.8-414.6 m)

We place a sequence boundary (the "1180-ft unconformity"; Fig. 6) between the lower Miocene and unnamed Oligocene greensands and glauconitic silts in an unrecovered interval (1171-1180 ft, 357-359.8 m) (Fig. 6). The Sr-isotopic data are consistent with a hiatus from 23.1 Ma in the shelly glauconite sands at 1136 ft (lowermost Miocene; Table 2) to 25.5 Ma in the clayey glauconitic sands at 1209 ft (368.6 m, uppermost Oligocene).

The section from 1180 to 1210.1 ft (359.8-368.9 m) consists of clayey quartzose glauconite sands, as shown by higher gamma log values than the section above (Fig. 6). There is a biofacies change from middle neritic above (1171 ft, 357 m) to inner neritic (low-diversity N. pizarrensis-B. gracilis fauna) below the 1180-ft unconformity. Between 1180 and 1210.1 ft, there are few facies changes and the section is clayey quartzose glauconite fine sand. Distinct brown clay laminations occur at 1194.5-1194.6, 1194.7-1194.8, and 1195.3-1195.4 ft. Thin (~1 mm), sporadic green and brown clay laminations occur from 1200 to 1210 ft (365.9-368.9 m) in an otherwise uniform, clayey, fine to medium quartzose glauconite sand. This unit (1180-1210 ft) is uppermost Oligocene (Sr-isotope age of 25.0 1 Ma at 1209.9 ft [368.9 m]).

There is a stratal surface and lithologic contact at 1210.1 ft (368.9 m), which may represent an unconformity ("?1210 ft"; Fig. 6), with a distinct coarsening-upward sequence below. Very coarse (2-4 mm) quartz sands, with <10% glauconite, grade down to medium sands (1230-1242 ft) to clayey sands and sandy clay (1242-1246 ft). Sporadic altered shells and shell layers occur throughout the section. The glauconitic to medium coarse quartz sands probably represent the shallowest deposits (inner neritic) and the clayey glauconite fine-grained quartz sands represent the deepest environments (middle neritic). Sr-isotopes indicate this section is uppermost Oligocene (24.1 and 24.3 Ma at 1247.0 and 1249.0 ft, respectively). Further studies are needed to determine if these two uppermost Oligocene units (1180-1210 and 1210-1248.5 ft) are separate sequences.

There is a possible disconformity at 1248.5 ft (380.6 m, the "?1249-ft unconformity"; Fig. 6) with a shelly interval (dark greenish gray) overlying a laminated clay (olive gray) (Fig. 6). This surface may be a disconformity as indicated by (1) a sharp lithologic break from shelly glauconitic quartz sands above to clays below, (2) a change in inferred depositional environment from middle to outer neritic below to inner to middle neritic above, (3) a thin shell bed immediately above the surface, (4) a change in stratification from laminated below to massive above, (5) bioturbation of the sand down into the clays, and (6) a distinct gamma log peak (Fig. 6). Laminated, slightly shelly silty clay at the top (~1248.5-1262 ft) overlies a coarser grained clayey glauconite sand (1262-1267 ft). A shell bed (1267.0-1268.4 ft) consisting of nested bivalve shells in a clayey glauconite sand matrix marks the base of the possible sequence. This section is upper Oligocene (Subzone P21b). Further studies are needed to determine if this is a separate sequence from those above.

A distinct surface occurs in an unrecovered interval between 1268.4 and 1270 ft (386.7 and 387.2 m, the "1270-ft unconformity"; Fig. 6). This surface can be recognized by a gamma log kick (1266 ft uncorrected, 1268.5 ft corrected) and by a change from laminated silty clay below to the shell hash above. The disconformity separates the upper Oligocene sequence (<29 Ma; Subzone P21b) from the lower Oligocene (>32 Ma; Zones P19-P20) sequence, with an associated hiatus of greater than 3 m.y. (Note added in proof: Subsequent studies have shown that the upper/lower Oligocene contact is at 1304.8 ft [397.7 m].)

A well-developed sequence was penetrated between 1270 and 1350.8 ft (387.1 and 411.8 m). The general lithology of the sequence is clayey, silty, fine-grained glauconitic (up to 20% of sand fraction) sands and sandy clays. Generally, it comprises an coarsening-upward succession: (1) a basal middle to outer neritic glauconite sand (1350-1327 ft), (2) a medial laminated glauconitic silty clay (1326-1316.9 ft), and (3) an upper sandy clay and clayey glauconitic sand (1316.9-1270 ft). This succession is well represented on the gamma log (Fig. 6). It is lower Oligocene in age (Zones P19-P20; see "Biostratigraphy" section, this chapter) and probably correlates with the ca. 33-Ma sequence at Island Beach (Miller et al., 1994b).

The glauconite sand is underlain by a brownish firm clay (1350.8-1352.0 ft, 411.8-412.2 m; Fig. 8D). This sharp facies shift is associated with a gamma log kick and is interpreted as a possible sequence boundary ("?1350 ft"; Fig. 6 and Fig. 8D). Below this, the interval from 1352.0 to 1352.5 ft is a very dark glauconitic sandy clay. Freshly preserved and abundant thin shells within a brown colored clay matrix between 1352.5 and 1354.5 ft is interpreted as marking the base of a sequence (the "1360-ft unconformity"; Fig. 6). The 1360-ft disconformity is recognized on the gamma log at 1358 ft and in the cores by a sharp facies change between 1354.5 and 1360 ft (this interval was not recovered; Fig. 8E). The section from 1350 to 1358 ft is lowermost Oligocene Zone P18. Planktonic foraminifers indicate that the top of the underlying clays (1360 ft, 414.6 m) are uppermost Eocene.

Unnamed Uniform Clays and Silty Clays (= ACGS alpha Unit)

Age: late Eocene
Thickness: 1360 ft (414.6 m) to TD

A firm, laminated, greenish brown clay and silty clay begins at 1360 ft (414.6 m; Fig. 8F) and continues fairly uniformly down to total recovered depth of 1495.85 ft (456 m). The clay contains fossil fragments (bivalve shells, scaphopods, and abundant microfossils) and sporadic pyrite nodules (some up to 3 cm). Laminations vary from faint, <1-mm-thick color variations (Fig. 8E) revealed by drilling chatter (e.g., 1481-1482 ft) to thicker (centimeter scale) silt/clay laminations (e.g., 1484-1485 ft). Laminations are obscured by bioturbation in some intervals, particularly above 1416 ft (431.7 m).

The gamma log is fairly uniform from 1360 ft (414.6 m) to the base of the logged section at 1490 ft (454.3 m, Fig. 6); minor gamma peaks (e.g., 1480 ft, 1460-1450 ft) have no obvious expression in the cores. The sand content of the uniform clays is uniformly less than 9% (2.7% mean for 17 analyses). Alternations from heavily bioturbated to laminated do not have a gamma log expression.

A contact occurs at 1454.3 ft (443.1 m), with very dark gray (2.5Y 3/1) slightly sandy clay above to dark grayish brown (2.5Y 4/2) clay below. The section above this contact (from 1360 to 1454.25 ft) contains fewer visible macrofossils than below and has a greater number of heavily bioturbated intervals.

This clay was deposited in middle-outer neritic paleoenvironments. Benthic foraminifers indicate primarily middle neritic paleo depths. Planktonic foraminifers range from less than 10% above 1398 ft (426.2 m) to over 40% below 1450 ft (442.1 m), consistent with middle neritic paleodepths (Christensen et al., 1995). A sharp upsection decrease in percent planktonic foraminifers occurs across the lithologic contact at 1454.3 ft (443.1 m), probably caused by shallowing. It is not clear if this inferred shallowing represents the base of an HST or an unconformity.

The uniform clays below 1360 ft (414.6 m) are upper Eocene (Zones P16-P17, NP19/NP20; see "Biostratigraphy" section, this chapter), on the basis of the highest occurrence of Turborotalia cerroazulensis and Hantkenina spp. at 1360 ft (414.6 m).

The clay correlates lithologically and chronologically with the upper Eocene clays at Mays Landing ACGS#4, Island Beach, and Atlantic City boreholes (Owens et al., 1988; Miller et al., 1994a, 1994b). This unit is informally named the ACGS alpha unit, and it correlates with the Chickahominy Formation in Virginia and Maryland (Owens et al., 1988). Before Owens et al. (1988), upper Eocene strata were not recognized onshore in New Jersey north of Cape May, although Brown et al. (1972) and Poag (1985) noted the presence of upper Eocene strata at the Anchor-Dickinson well.

We did not penetrate the glauconitic sands and sandy marls of the middle to lowermost upper Eocene Shark River Formation at Cape May.

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