The on-site scientific team provided preliminary descriptions of sedimentary textures, structures, colors, fossil content, identification of lithostratigraphic units (NJGS Information Circular 1, 1990), lithologic contacts, and core photographs illustrating sequence bounding unconformities and facies variation within sequences (Tables T1, T2; Figs. F2, F3, F4, F5, F6, F7, F8, F9, AF1, AF2, AF3, AF4, AF5, AF6, AF7, AF8, AF9, AF10, AF11, AF12, AF13, AF14, AF15, AF16, AF17, AF18). Subsequent studies integrated preliminary descriptions with additional descriptions, biostratigraphy (Tables T3, T4, T5, T6), biofacies studies, isotopic stratigraphy (Table T7), and the downhole gamma log. Unconformities were identified on the basis of physical stratigraphy, including irregular contacts, reworking, bioturbation, major facies changes, and gamma ray peaks. Paraconformities were inferred from biostratigraphic breaks.

For the nonmarine and near-shore sections, lithofacies interpretations and pollen biostratigraphy provide the primary means of recognizing unconformities and interpreting paleoenvironments and systems tracts. For the neritic sections, biostratigraphic studies and Sr isotopes provide an additional means of recognizing unconformities and interpreting paleoenvironments and systems tracts.

Cumulative percent plots of the sediments in the cores were computed from washed samples (Table T2). Each sample was dried and weighed before washing, and the dry weight was used to compute the percentage of sand. This differs from the method used in previous New Jersey coastal plain cores (Bass River, Island Beach, Atlantic City, and Cape May) in which the samples were not dried before washing.

Facies changes within onshore sequences generally follow repetitive transgressive–regressive patterns (Sugarman et al., 1993, 1995) that consist of (1) a basal transgressive glauconite (particularly Paleogene–Upper Cretaceous sections) or quartz sand (particularly Miocene sections) equivalent to the TST of Posamentier et al. (1988) and (2) a coarsening-upward succession of regressive medial silts and upper quartz sand equivalent to the HST of Posamentier et al. (1988). Lowstand systems tracts (LSTs) are usually absent in the coastal plain and TSTs are generally thin. Because TSTs are thin, maximum flooding surfaces (MFSs) are difficult to differentiate from unconformities. Shell beds and gamma-ray peaks can mark both TSTs and MFSs. Flooding surfaces, particularly MFSs, may be differentiated from sequence boundaries by the association of erosion and rip-up clasts at the latter, lithofacies successions, and benthic foraminifer changes. The transgressive surface (TS), marking the top of the LST, represents a change from generally regressive to transgressive facies; because LST are generally absent, these surfaces are generally merged with the sequence boundaries. Where present, LSTs are recognized as generally thin, regressive, fluvial-estuarine sediments underlying TSTs and overlying sequence-bounding unconformities.

Manasquan Formation

Age: early Eocene
Interval: 2.5–6.3 ft (0.8–1.9 m)

Below a thin soil horizon (1.5–2.5 ft; 0.5–0.8 m), a glauconitic sandy clay with scattered pyrite grains is assigned to the Manasquan Formation that outcrops in the adjacent Southwest Branch of Rancocas Creek. The unit is likely deposited in neritic environments. The section appears bioturbated, but this may reflect soil processes. Concretions (siderite?) appear at 3.4 ft (1.0 m). There is a coring gap from 4.4 to 6.0 ft (1.3 to 1.8 m), with the Manasquan Formation lithology extending to 6.3 ft (1.9 m). Poor recovery, lack of biostratigraphic information, and a thin truncated section prevent application of sequence stratigraphy.

Marlboro Clay

Age: earliest Eocene?
Interval: 6.3–10.2 ft (1.9–3.1 m)

There is a contact at 6.3 ft (1.9 m) with the olive-gray glauconitic sandy clay above and a white kaolinite clay below. There is a possible clay rip-up clast immediately above the contact. The lower clay contains a few percent glauconite, a trace of mica, and iron-stained slightly sandier laminae (0.5 cm thick) that occur every 2–3 cm. The thin (3.9 ft, 1.19 m) kaolinitic clay at Medford has been previously recognized in thick sections (>40 ft, >12 m) at Bass River and Ancora, where it has been associated with the Paleocene/Eocene Thermal Maximum (Cramer et al., 1999). The clay appears to immediately postdate the carbon isotope excursion (Cramer et al., 1999) and hence is earliest Eocene (Aubry et al., 2007). Unusual magnetic properties in the clay led Kent et al. (2003) to suggest that it was a product of an impact vapor cloud. Kaolinite clay also occurs in coreholes at Clayton (Gibson et al., 1993), Wilson Lake (Lippert and Zachos, 2007), Millville (Sugarman et al., 2005), and Sea Girt (Miller et al., 2006). This clay has been discussed as an unnamed clay in previous studies of New Jersey coreholes. It has not been reported from outcrop, though we note a thin clay bed (thickness) adjacent to the Medford corehole on Rancocas Creek. A similar clay was first reported in Virginia and Maryland (Darton, 1948) and named as a formation by Glaser (1971). More recent studies by Edwards (1996) indicate that the Marlboro Clay is earliest Eocene and therefore correlates with the widespread clay in New Jersey. Hence, we apply here the term Marlboro Clay to the thin bed found at Medford.

Based on correlation to other coreholes, the unit probably was deposited in middle neritic paleodepths. There is a coring gap from 7.1 to 10 ft (2.2 to 3.0 m). A clay from 10.0 to 10.2 ft (3.1 to 3.1 m) may be a continuation of the clay above, but it is grayer and apparently less kaolinitic, and with the poor recovery it cannot be determined if this is still the Marlboro Clay.

Vincentown Formation

Age: late Paleocene
Interval: 10.2–50 ft (3.1–15.2 m)

The greenish gray clay continues down to an iron-stained layer at 10.2 ft (3.1 m); there is a contact from 10.2 to 10.6 ft (3.1 to 3.2 m) with a gradation from white clay to black clayey glauconite-quartz sand below. Clay decreases below 11.5 ft (3.5 m) and glauconite increases at 13 ft (4.0 m). The section from 13 to 27.6 ft (4.0 to 8.4 m) consists of interbedded clayey sands and slightly clayey glauconite-quartz sands that are heavily and beautifully bioturbated. Small shells appear at 23 ft (7.0 m). Gamma log values are high above 25 ft (7.6 m) because of common glauconite. The environment of deposition was probably an inner neritic, lower shoreface environment. We interpret this section as the upper part of a HST with reworked glauconite (though none appears iron stained, as is often found with recycled glauconite in these environments). The coequal abundances of quartz and glauconite sand are typical of reworked glauconite in HSTs.

There is a lithologic change across a coring gap (27.6–30.0 ft; 8.4–9.1 m) with clayier quartz-glauconite sand below; gamma logs place the contact at the top of the gap. There is a change at 32 ft (9.8 m) to a clayey quartz-glauconite sandy packed biomicrite, where the sandy carbonate fraction consists mostly of shell debris (bryozoans and bivalves). We have not observed this facies in our cores previously, but it is probably equivalent to the patch reef biomicrites that crop out in the type Vincentown Formation section 5 miles to the northeast at Vincentown, New Jersey (Gallagher, 2002). Biomicrite (blue, Fig. F2) peaks from ~33 to 34.8 ft (10.1 to 10.6 m) in association with a gamma log minimum; carbonate decreases and glauconite increases downsection from 34.8 to 41 ft (10.6 to 12.5 m), where the facies consist of clayey biomicritic quartzose glauconite sand. From 41 to 43.8 ft (12.5 to 13.4 m) is a slightly whitish clayey glauconite sand that represents the deepest paleodepths; a gamma log peak at ~43.5 ft (13.3 m) near the base of this interval is interpreted as the MFS (Fig. F2), probably deposited in middle neritic environments. From 43.8 to 46 ft (13.4 to 14.0 m), the section fines up, consistent with a TST, and consists of clayey slightly quartzose biomicrite-glauconite sand. Distinct bluish green clay laminae occur at 44.5 and 45.8 ft (13.6 and 14.0 m). Interlaminations of clayey slightly quartzose glauconite sand and greenish blue glauconitic clay occur from 45.8 to 47.7 ft (14.0 to 14.5 m). There is a clayey shelly glauconite sand to clayey glauconitic shell bed at 47.7–48.4 ft (14.5–14.8 m) (Fig. AF1). There might be a sequence boundary at 48.4 ft (14.8 m) at the contact between the shell bed and a black more uniform clayey glauconite sand that differs from above by having less common quartz and shells. The gamma log suggests that the sequence boundary may occur slightly deeper at ~50 ft (15.2 m) in a coring gap from 48.6 to 55 ft (14.8 to 16.8 m). We prefer the placement of the sequence boundary, and the base of the Vincentown Formation, at ~50 ft (15.2 m), with the interval from ~43.5 to 50 ft (13.3 to 15.2 m) interpreted as the TST. Age control on this sequence is from nannofossil assignments to Zones NP7 and NP8 (see "Calcareous Nannofossils"). This suggests correlation to sequence Pa2b of Harris et al. (in press).

Hornerstown Formation

Age: early–late Paleocene
Interval: 50–60.7 ft (15.2–18.5 m)

The Hornerstown Formation is poorly recovered in the Medford corehole, where it consists of a dark olive gray to black, slightly quartzose, and slightly shelly clayey-glauconite sand. The environment of deposition was probably middle neritic. We tentatively identify two thin truncated sequences within the Hornerstown at the Medford site: an upper sequence from 50 to 56.6 ft (15.2 to 17.22 m) and a lower sequence from 56.6 to 60.7 ft (17.22 to 18.5 m). Distinct clay beds (55.2–55.5 and 56.4–56.6 ft; 16.8–16.9 and 17.19–17.22 m) in the upper sequence may mark a MFS in association with a gamma log maximum. Planktonic foraminifer biostratigraphy places sample 56.1 ft (17.1 m) in Zone P3a and 57.4 ft (17.5 m) in Zone P1c (see "Planktonic Foraminifers"), suggesting that the base of the lower clay bed at 56.6 ft is a paraconformity with a hiatus of > 0.2 m.y. Both sequences are assigned to Zone NP4, though the lower might include Zone NP3 (see "Calcareous Nannofossils"). The excellent planktonic fauna in the lower sample suggest that the older sequence below 56.6 ft (17.2 m) is truncated with a MFS near the top of the sequence. The lower sequence (P1c) can be confidently correlated to sequence Pa1a (Zones P1a and NP4) of Harris et al. (in press). The upper sequence likely correlates with sequence Pa1b (Zones P3b and NP4/NP5), though the assignment to Zone NP3a suggests that this may be a previously unrecognized sequence. The base of the formation (60.35–60.7 ft; 18.4–18.5 m) is marked by pale green clay (5G6/1) that is bioturbated and has glauconite-filled burrows at the top and laminations at the base. The bright green clay matrix contains small (2–10 mm) iron-cemented concretions containing glauconite sand. The heavily bioturbated interval may be correlative with the "Burrowed Unit" of Landman et al. (2007).

The Cretaceous/Paleogene boundary (K/P) occurs at 60.7 ft (18.5 m) (Fig. AF1), separating the pale green clays above from the uniform clayey glauconite sands of the Navesink Formation below. The boundary lacks both spherules and clay clasts that are often found in the New Jersey coastal plain coreholes. The sample at 61.4 ft (18.7 m) contains a typical uppermost Maastrichtian planktonic foraminifer assemblage.

Navesink Formation

Age: Maastrichtian
Interval: 60.7–97.05 ft (18.5–29.6 m)

The Navesink Formation at Medford is a clayey glauconitic sand and sandy glauconitic clay deposited in a middle neritic environment. Glauconite is mainly black with lesser dark green grains. A sharp contact at 75.9 ft (23.1 m) is marked by a lithologic change to brownish clayey medium glauconite sand with mica and quartz. This may be the contact between the Navesink I and Navesink II sequences (although poor recovery above 75.9 ft [23.1 m] makes this pick very tentative). The glauconite sand extends from 75.9 to 85.6 ft (23.1 to 26.1 m) with a gradational contact to heavily bioturbated glauconitic clay at 85.6 ft (26.1 m). The clay content increases toward the base of the Navesink Formation, where it becomes whiter and more calcareous; it reacts strongly with hydrochloric acid. Shells first appear at 82 ft (25.0 m) and are more common downsection. The MFS of this sequence is placed at 90 ft (27.4 m), where clay content is at a maximum. The contact with the Mount Laurel Formation is at 97.05 ft (29.6 m) at the top of an indurated zone consisting of phosphatized Mount Laurel lithology. This contact also represents the TS (Fig. AF1) within the Navesink I sequence.

Mount Laurel Formation

Age: Campanian
Interval: 97.05–180 ft (29.6–54.9 m)

The uppermost part of the Mount Laurel Formation is medium sand in the Medford corehole. The top 3.35 ft (1.02 m) of the Mount Laurel Formation is a lag deposit (located at the base of the Navesink I sequence; Fig. F3), with a sequence boundary at 100.4 ft (30.6 m) separating the Navesink I above from the Marshalltown sequence below. At the top (97.05–97.35 ft; 29.6–29.7 m), the lag deposit consists of an indurated phosphate nodule. The nodule reacts with acid and may have siderite cement. Below the nodule is a very poorly sorted clayey shelly granuliferous fine to medium sand (97.35–100.2 ft; 29.7–30.5 m) deposited in proximal upper shoreface environments. Large shell and belemnite fragments measure up to 3 cm across. The sand is interrupted at 98.5–98.7 ft (30.0–30.1 m), where there is a shell bed with 1–2 cm shells with granules. At 100.2–100.4 ft (30.5–30.6 m) there is a shift to silty quartz sand deposited in distal upper shoreface environments. Thus, the section from 97.35 to 100.4 ft (29.7 to 30.6 m) shallows upsection and is interpreted as a thin, regressive LST. At 100.4 ft (30.6 m) there is a shift to very slightly clayey, slightly glauconitic, slightly shelly medium quartz sand deposited in proximal upper shoreface environments (Fig. AF2). These typical yellow Mount Laurel sands continue to 108.2 ft (33.0 m) with clay- and silt-filled burrows throughout. There is a large oyster shell at 101.7–101.75 ft (31.00–31.01 m) and a very shelly and heavily burrowed section from 102 to 102.7 ft (31.1 to 31.3 m).

Glauconite increases downsection from 108.2 to 109.5 ft (33.0 to 33.4 m), and the section from 109.5 to 118.2 ft (33.4 to 36.0 m) consists of burrowed shelly glauconite-quartz sand with numerous fine, thin, whole shells. The glauconite-quartz sand is semi-indurated. There are two possible interpretations to the section: (1) this is the upper HST with reworked glauconite deposited in upper shoreface environments, as suggested by the high abundance of and covariance with quartz sand, or (2) the glauconite is in situ and represents deeper water, middle neritic environments with a sequence boundary at 118.2 ft (36.0 m). We favor the former interpretation.

Typical Mount Laurel Formation shelly medium quartz sand returns from 118.2 to 122.7 ft (36.0 to 37.4 m) deposited in proximal upper shoreface environments. There is a coring gap from 122.7 to 130 ft (37.4 to 39.6 m). Below this gap, the sand is slightly micaceous fine–medium sand. There is a change downsection at 133.2 ft (40.6 m) to muddy, micaceous fine sand with mud laminae as thick as 1 cm deposited in lower shoreface environments (Fig. AF2). This fine sand continues to 178.3 ft (54.3 m), where there is a coring gap to 180 ft (54.9 m). Below this, the section becomes silty very fine sand that we assign to the Wenonah Formation.

Wenonah Formation

Age: Campanian
Interval: 180–212.3 ft (54.9–64.7 m)

Micaceous, silty, glauconitic very fine sand with scattered lignite and shells was deposited in offshore environments (Fig. AF2) and is assigned to the Wenonah Formation, which is differentiated from the Mount Laurel Formation here by the finer grain size (silty fine versus fine–medium sand) and more common mica. Mica increases slightly downsection within the Wenonah Formation. The formation is heavily bioturbated, with extensive burrowing below 192 ft (58.5 m) along with evidence of gypsum. There may have been a deltaic influence on this shelf, though laminated silty clays typical of prodelta environments in this region are largely absent. Shells increase slightly downsection below 192 ft (58.5 m), and clay content increases downsection below 196 ft (59.7 m) in otherwise uniform micaceous, silty, glauconitic very fine sand. Clay is at a maximum at 210.3–210.7 ft (64.1–64.2 m) where we place the MFS at 209 ft (63.7 m) (Fig. F3). At the top of a section with high gamma log values, there is a shell zone from 211.9 to 212.3 ft (64.6 to 64.7 m) at the base of the Wenonah Formation.

Marshalltown Formation

Age: Campanian
Interval: 212.3–224.4 ft (64.7–68.4 m)

The contact of the Marshalltown with the overlying Wenonah Formation is a gradational contact recognized by the downhole increase in the amount of glauconite in the core. Below 210 ft (64.0 m), the amount of glauconite starts to exceed 15%. From 210 to 210.3 ft (64.0 to 64.1 m), the burrowing changes downsection to large clay-lined and glauconite-filled burrows; we placed the Wenonah/Marshalltown Formation contact here. The Marshalltown Formation is generally a highly bioturbated, shelly, silty clayey quartz and glauconite sand that is approximately correlative to the TST of the Marshalltown sequence. An alternative MFS to the one placed at 210.3–210.7 ft (64.1–64.2 m) could be at 217.5 ft (66.3 m) at the base of a clay-rich section, with more glauconite sand below. Shell concentrations occur at 212.7 and 215.9 ft (64.8 and 65.8 m). The Marshalltown Formation contains more silt and clay here than it has in outcrop; the amount of glauconite sand in the Marshalltown Formation never exceeds 50% in the Medford corehole. This unit was primarily deposited in an offshore environment. The base of the formation below 221 ft (67.4 m) is more heavily laminated and probably represents shallower water environments than the section above.

There is a contact at 222.5 ft (67.8 m) with a clayey glauconite sand above and a lag zone from 222.5 to 224.4 ft (67.8 to 68.4 m). The contact is interpreted as a TS. The lag deposits consist of glauconitic sandy silt with laminae and scattered blebs of yellow Englishtown quartz sand lithology. A large shell occurs at 223.6–223.7 ft (68.15–68.18 m). The formational placement of the lag unit from 222.5 to 224.4 ft (67.8 to 68.4 m) is uncertain but is placed here in the Marshalltown Formation because of the predominance of glauconite. At the base of the lag unit is a sharp irregular contact representing a sequence boundary at 224.4 ft (68.4 m) (Fig. AF2) with the underlying yellow Englishtown quartz sandstone below. Log values suggest the contact might be lower at ~228 ft (69.5 m) in an interval of no recovery (Fig. F4).

Upper Englishtown Formation

Age: Campanian
Interval: 224.4–329.4 ft (68.4–100.4 m)

The upper Englishtown Formation (and sequence) consists of a wide variety of lithologies in the Medford corehole representing paleoenvironments ranging from nearshore (delta front) to open shelf (Fig. AF3). A fine to medium sandstone with scattered glauconite occurs from 224.4 to 226.6 ft (68.4 to 73.2 m); there is an interval of no recovery from 226.6 to 230 ft (69.1 to 70.1 m). Below 230 ft (70.1 m), the section consists of slightly clayey, slightly micaceous fine quartz sand to 232.5 ft (70.9 m) deposited in delta front environments. A concretion at 232.3 ft (70.8 m) separates mostly fine sand above from silty, clayey fine to very fine sand with clay laminae below (232.5–233.3 ft; 70.9–71.1 m). A dark greenish gray organic-rich clay occurs from 233.3 to 234.0 ft (71.1 to 71.3 m). From 234.0 to 234.2 ft (71.3 to 71.4 m) is a laminated lignite with clay, whereas 234.3–235.9 ft (71.4–71.9 m) consists of a micaceous sand with finely disseminated lignite. Lignitic clay with thin interbeds of sand is found from 233.5 to 235.9 ft (71.2 to 71.9 m). Faintly laminated micaceous, slightly shelly medium to mostly fine quartz sand returns from 235.9 to 237.5 ft (71.9 to 72.4 m). There is no recovery from 237.5 to 240.3 ft (72.4 to 73.2 m; sediments from 240.0 to 240.3 ft [73.15 to 73.24 m] may be caved as suggested by the logs). These rapidly changing, organic-rich sediments were deposited in delta front environments (Fig. AF3) and comprise the upper HST of the thick upper Englishtown sequence.

Beginning at 240.3 ft (73.2 m), sediments become increasingly marine (finer grained with shells appearing downsection at 242.6 ft) in nature. The section from 240.3 to 324 ft (73.2 to 98.8 m) is predominantly very dark gray sandy clayey silt to sandy silty clay with abundant fossils and shell fragments (Fig. AF3). The silty clay is slightly micaceous and contains pyritized burrows and concretions. Fine shells are common and consist of thin-shelled bivalves and occasional gastropods. Bedding is uniform with occasional laminae. Very fine to fine quartz sand is common in this interval, concentrated in several thin (2–3 cm thick) beds or sand-filled burrows. Lignite is common and becomes less common below 251 ft (76.5 m), and mica decreases below 264 ft (80.5 m). The section at 271 ft (82.6 m) is slightly glauconitic and at 271.4 ft (82.7 m) has gypsum crystals that may indicate carbonate dissolution and a minor flooding surface. A very sandy silt bed occurs at 290–295 ft (88.4–89.9 m) deposited in offshore to lower shoreface environments. Very slightly micaceous silty clay with numerous shell fragments (up to 2 mm) and scattered whole shells returns from 295 to 324 ft (89.9 to 98.8 m); bedding is largely burrowed with occasional laminae and sulfide-filled burrows every few cm.

The environment of deposition of the silty clays to clayey silts is lower shoreface (LSF) to offshore. There is some deltaic influence, although less than is typical of the upper Englishtown Formation in other New Jersey coastal plain cores; we assign this unit to the lower part of the upper Englishtown Formation. A similar thick clay was noted in the upper Englishtown Formation at Sea Girt (Miller et al., 2006); both clays are assigned to Zone CC19. We interpret the section above ~264 ft (80.5 m) with more common lignite, sand, and mica as delta front. The section from 264 to 324 ft (80.5 to 98.8 m) was deposited in offshore environments with a slight prodelta influence. The sand beds in this section may represent LSF environments or storm deposits.

Several laminated intervals are interspersed with moderately bioturbated zones, and the section becomes increasingly glauconitic (5%–10%) from 270 to 277.4 ft (82.3 to 84.6 m). The section from 280.0 to 288.3 ft (85.3 to 87.9 m) consists of laminated clayey silt to silty clay with several ammonite fossils (282.5 ft; 86.1 m). From 288.3 to 289.7 ft (87.9 to 88.3 m), there are common dark green to black glauconite sand-filled burrows. Below 290.0 ft (88.4 m), the section consists of finely laminated slightly silty clay with abundant shell fragments. Laminated, glauconitic (in sand-filled burrows), and slightly micaceous clayey silt grades into to a dark gray, slightly shelly laminated silty clay from 294 to 324 ft (89.6 to 98.8 m). The MFS is placed at 319–319.5 ft (97.2–97.4 m) in an interval with common gypsum crystals and a gamma log kick, with the section above this to ~240 ft (73.2 m) comprising the lower HST of the thick upper Englishtown sequence.

Sand increases in the silty clays from 324 to 329.4 ft (98.8 to 100.4 m), with more coarse mica, common quartz, and glauconite. The section is burrowed. Glauconite is in trace amounts from 300 to 324.7 ft (91.4 to 99.0 m) but begins to increase in abundance from 2% to 3% at 325 ft (99.1 m) to 5% at 327 ft (99.7 m) and 10%–12% below 329 ft (100.3 m). There is a contact at 329.4 ft (100.4 m) that coincides with a major gamma log decrease downsection. Below the contact is a fairly homogeneous, slightly glauconitic, slightly silty fine quartz sand deposited in distal lower shoreface environments. The contact at 329.4 ft (100.4 m; Figs. F4, AF3) is interpreted as a sequence boundary. The thick sequence from 224.4 to 329.4 ft (68.4 to 100.4 m) is correlated to the upper Englishtown sequence and formation based on nannofossil biostratigraphy and Sr isotope age estimates. It is significantly thicker at Medford than the downdip Ancora and Bass River sites (Fig. F10).

Lower Englishtown Formation

Age: Campanian
Interval: 329.4–366 ft (100.4–111.6 m)

Micaceous, slightly lignitic, silty, clayey fine sand with lesser medium sand fines downward from 329.4 to 335 ft (100.4 to 102.1 m) and represents distal upper shoreface environments (Fig. AF4). A shell hash occurs from 332.2 to 332.3 ft (101.25 to 101.29 m). From 335 to 366 ft (102.1 to 111.6 m), the section consists of heavily bioturbated, slightly shelly, micaceous silty fine to very fine sand and silty clay deposited in lower shoreface environments (Fig. AF4) that generally fines downsection. Shells become more obvious below 360 ft (109.7 m). The lower Englishtown Formation lacks a deltaic influence and is significantly thicker than seen in most other sites. Clay begins to dominate at 366 ft (111.6 m), and we place the base of lower Englishtown at this level at the top of a "hot" gamma log zone. The lower Englishtown Formation comprises the upper HST of the MeIII sequence.

Woodbury Formation

Age: Campanian
Interval: 366–377.0 ft (111.6–114.9 m)

The Woodbury Formation is a micaceous, heavily bioturbated, slightly sandy silty clay to clayey silt with traces of shells. The Woodbury Formation is much thinner and less laminated at Medford than at other sites (Fig. F10). It was deposited in lower shoreface to offshore environments (Fig. AF4). Glauconite occurs at the top, is largely missing in the middle, and increases toward the base of the formation at 377 ft (114.9 m), where glauconite increases above 50%. We place the MFS at the peak in clay and gypsum at 371 ft (113.1 m), with the gypsum reflecting dissolution and reprecipitation of carbonate. Thus, the Woodbury Formation comprises both the upper TST and lower HST of the MeIII sequence. It is assigned to nannofossil Zones CC19 and CC18.

Merchantville Formation

Age: Campanian and Santonian
Interval: 377.0–434.5 ft (114.9–133.9 m)

The transition to the Merchantville Formation is placed at 377 ft (114.9 m) where the amount of glauconite sand in the corehole first exceeds 50% (Fig. F4). The upper part of the Merchantville Formation consists of heavily bioturbated, clayey, fine-medium glauconite sand. Gray-clay lined burrows are common as are siderite concretions; shells are rare. The clayey glauconite sand (385.9–388.5 ft; 117.6–118.4 m) changes to clayey silty quartz sand and silt below 390.3 ft (119.0 m). The interval from 388.5 to 390.3 ft (118.4 to 119.0 m) is a contact zone, with a gamma log kick at the top (Fig. F4). Mica increases downsection from 388.5 ft (118.4 m) where it is trace to >3% at 389.5 ft (118.7 m). Scattered shells occur throughout the contact section. Glauconite decreases downsection in the contact zone, occurring mostly in burrows and disappears below 390.3 ft (119.0 m). Nannofossils assign 389.5 ft (118.7 m) to Zone CC18 and 389.85 ft (118.8 m) to Zone CC17. We place a sequence boundary (within the Merchantville Formation) at 389.5 ft (118.7 m) at an irregular surface and a change from clayier to sandier sediments. The sequence from 329.4 to 389.5 ft (100.4 to 118.7 m) is correlated to the MeIII of Miller et al. (2006) and assigned to lowermost Campanian Zones CC18 and CC19.

Bioturbated clayey, micaceous, glauconitic fine quartz sand with scattered shell fragments occurs from 390.3 to 398.2 ft (119.0 to 121.4 m) and was deposited in a inner neritic, predominantly lower shoreface environment (Fig. AF5). This comprises the upper HST of the MeII sequence (Fig. F4). Mica drops out below ~399 ft (121.6 m). Heavily burrowed, glauconite clayey silt and clayey glauconite sand with numerous clay burrows becomes progressively clayey from 398.2 to 409.3 ft (121.4 and 124.8 m). There is a brownish siderite zone from 405.8 to 407.9 ft (123.7 to 124.3 m) with numerous siderite concretions; this interval is a bioturbated glauconitic clay that has been diagenetically altered. From 409.3 to 411 ft (124.8 to 125.3 m), the section consists of a brownish heavily bioturbated glauconitic clay. More typical Merchantville lithology deposited in middle neritic environments (Fig. AF5) occurs from 411 to 416 ft (125.3 to 126.8 m) with a glauconite clay to clayey glauconite sand; the section from 411 to 412.7 ft (125.3 to 125.8 m) is heavily bioturbated, whereas the section from 412.7 to 416 ft (125.8 to 126.8 m) is laminated with less obvious burrows. Obvious gypsum crystals occur at 411.9–412.2 and 413.5–413.9 ft (125.5–125.6 and 126.0–126.2 m), suggesting primary carbonate. We tentatively place the MFS at this level and the lower HST from 398.2 to 411.9 ft (121.4 to 125.6 m). Glauconite increases from 415 to 416 ft (126.5 to 126.8 m), with burrows filled by glauconite sand. There is a coring gap from 416.1 to 420 ft (126.8 to 128.0 m). We tentatively place the sequence boundary between the MeII and MeI sequences in the coring gap and the TST from 411.9 to 420 ft (125.6 to 128.0 m). Nannofossil biostratigraphy places the MeII sequence (389.5–416 ft; 118.7–126.8 m) in uppermost Santonian Zones CC17 to CC16; it was deposited primarily in middle neritic environments (Fig. AF5), though the sands of the upper HST were deposited in offshore to LSF, probably inner neritic environments (i.e., shallower than the glauconite sands and clays).

From 420 to 424 ft (128.0 to 129.2 m), the section consists of slightly micaceous burrowed glauconite sandy clay to clayey glauconite sand. The section from 424 to 425.6 ft (129.2 to 129.7 m) (Fig. AF5) is brown clay and glauconite clay burrowed together with a lower percentage of glauconite. There is a siderite concretion from 424.8 to 424.9 ft (129.48 to 129.51 m). Common to dominant glauconite returns in a clayey glauconite sand from 424.0 to 429.1 ft (129.2 to 130.8 m). Mica is obvious above ~430 ft (131.1 m) and occurs in trace abundance from 430 to 431.1 ft (131.1 to 131.4 m). We place the maximum flooding surface at 425.4 ft (129.7 m), near the top of this interval, where glauconite dominates. A cemented siderite zone occurs at 429.1–429.6 ft (130.8–130.9 m). The lithology from 429.6 to 431.1 ft (130.9 to 131.4 m) is similar to above, though it is slightly brownish, reflecting some post-depositional siderite diagenesis. Glauconite clay and sand continue to 434.5 ft (132.4 m) (Fig. AF5). We tentatively place the top of the Cheesequake Formation and possible sequence boundary at this level. The Merchantville I sequence (420–434.5 ft; 128.0–132.4 m) was deposited in middle neritic environments (Fig. AF5) and assigned to Zone CC16 (Santonian).

?Cheesequake Formation

Age: ?Santonian
Interval: 434.5–439.4 ft (114.9–133.9 m)

From 434.5 to 439.4 ft (114.9 to 133.9 m), the section consists of a slightly glauconitic micaceous clayey silt that grades to a gray clay with very little glauconite beginning at 434.5 ft (132.4 m); these fine-grained beds lacking glauconite may be equivalent to the Cheesequake Formation or the base of the Merchantville Formation (Figs. F4, AF5). If this section is the base of Merchantville, then the lithologic contact at 434.5 ft (114.9 m) might be a MFS within the MeI sequence. The clay coarsens downsection to a sandy clayey silt at 436 ft (132.9 m). The base of the unit (436–439.4 ft; 132.9–133.9) is clayey silt with gypsum crystals on the outside of the core. Thus, this thin unit (sequence) fines upsection from silts to clays. The depositional environment was offshore "dirty shelf" but shallower than glauconite sands (i.e., inner neritic). No primary age data are available, though it is bracketed by Zone CC16 (upper Santonian) above and pollen Zone V (?Turonian–Coniacian) below.

Magothy Formation

Age: ?upper Turonian–Coniacian
Interval: 439.4–573.1 ft (133.9–174.7 m)

An abrupt contact at 439.4 ft (133.9 m) (Fig. AF6) separates the Cheesequake (or Merchantville; see discussion above) and Magothy Formations. Above the contact (beginning at 438.9 ft; 133.8 m) scattered granules and pebbles up to 1 cm in length are found in a muddy matrix. Below the contact (439.4–443.1 ft; 133.9–135.1 m), clayey silt is intensely weathered to kaolinite with common to abundant microsphaerosiderite; from 439.4 to 439.5 ft (133.9 to 134.0 m), abundant coarse sand and granules are mixed into the silty clay. The section from 439.4 to 440.1 ft (133.9 to 134.1 m) is light gray clayey silt with abundant microsphaerosiderite and some larger hematitic concretions. From 440.1 to 442.7 ft (134.1 to 134.9 m) the microsphaerosiderite is larger (>1–2 mm diameter) and more weathered to hematite. The section from 442.7 to 443.1 ft (134.9 to 135.1 m) is the same weathered lithology without the microsphaerosiderite. Thus, the Magothy Formation represents a major subaerial unconformity with extensive subtropical weathering. From 443.1 to 443.6 ft (135.1 to 135.2 m) the light gray clays transition down to dark gray silts. From 443.6 to 445.2 ft (135.2 to 135.7 m) is an interval of clayey dark gray silt and silty clay with interlaminated very fine sand. These are paleosols deposited in a floodplain environment.

The lithology changes across a sharp contact at 445.2 ft (135.7 m; Fig. F5) from overlying clay into dark gray, fine-to-medium sand with numerous very coarse sand and granule-sized quartz grains. The sand from 445.2 to 470 ft (135.7 to 143.3 m) contains lignitic-rich layers and varies from medium quartz sand to medium-to-coarse sand with very coarse sand to granules comprising up to 25% of the sand fraction. From 469.0 to 470.0 ft (143.0 to 143.3 m) the sand is slightly muddier than the sand above 469.0 ft (134.0 m). The sand, possibly representing tidal channels (Fig. AF6) (Zeff, 1988), continues to 470 ft (143.3 m). From 470 to 470.3 ft (143.26 to 143.35 m) is dark brown-gray clay. The change from sand to clay is sharp, but there is no evidence for an erosional contact.

At a contact at 470.3 ft (143.4 m), dark clay above passes into light gray clayey sandy silt that continues to 485.7 ft (148.0 m). This contact could be a sequence boundary representing an exposure surface with a shift to more heavily weathered clay below 470.3 ft (143.3 m). This possible sequence from 439.4 to 470.3 ft (133.93 to 143.4 m) may be equivalent to the Magothy IVB of Kulpecz et al. (2008) and the Cliffwood Beach Beds, though definitive pollen data are lacking (i.e., this sequence is associated with pollen Zone VII elsewhere, which is Coniacian to Santonian) (Fig. F5).

The muddy interval from 470.3 to 485.7 ft (143.3 to 148.0 m) represents one unit that becomes increasingly altered by soil-forming processes upsection and can be divided into four parts.

  1. The upper part (470.3–477.6 ft; 143.4–145.6) is generally light gray, silty, sandy clay with vague mottling.

  2. From 477.6 to 477.8 ft (145.6 to 145.8 m) is a muddy sand zone with hematitic concretions.

  3. From 477.8 to 479.9 ft (145.8 to 146.3 m) is light gray, slightly sandy, silty clay with scattered microsphaerosiderite with hematite rinds. Microsphaerosiderite becomes smaller and less evident downsection.

  4. From 479.9 to 484.6 ft (146.3 to 147.7 m) is interlaminated, light gray clay, silt, and muddy, very fine sand.

The laminations are interpreted to represent lenticular bedding deposited in a tidal-delta environment. This interval was later overprinted by soil processes in an overbank setting. The section from 484.6 to 485.7 ft (147.7 to 148.0 m) is similar to the lithology above (479.9–484.6 ft; 146.3–147.7 m) but is darker and sandier. It probably represents a similar environment but is not as gleyed as the material above.

A contact at 485.7 ft (148.0 m) separates the interlaminated clay and sand above from a thick sand below. The contact is a gradual transition with the two lithologies mixed and interlaminated together. It is associated with a major gamma log peak. The unit from 439.4 to 485.7 ft (133.9 to 148.0 m) is interpreted as a sequence and tentatively correlated to the Magothy IVA sequence of Kulpecz et al. (2008), equivalent to the Morgan Beds. It is assigned to pollen Zone V (Turonian to Coniacian; see "Planktonic Foraminifers"), which is inconsistent with its assignment to Zone VII at Sea Girt (Coniacian to Santonian; Kulpecz et al., 2008).

The sand from 485.7 to 513.25 ft (148.0 to 156.4 m) represents two fining-upward cycles that we infer to represent channels separated by a break at 502.15 ft (153.1 m). The upper channel contains fine sand on top (485.7–494 ft; 148.0–150.6 m) with some preserved laminae consisting mainly of plant debris (e.g., 488 ft; 148.7 m). It transitions downsection to medium sand at 494 ft (150.6 m) and to coarse sand at 501–501.7 ft (152.7–152.9 m). It becomes gravel with clasts as large as 15 mm from 501.7 ft (152.6 m) to the contact at 501.8 ft (152.9 m). There are zones with bedded plant debris or lignite at 492.6, 493.0, 493.7, 494.2, and 494.8 ft (150.1, 150.3, 150.5, 150.6, and 150.8 m). Charcoal woody debris is concentrated at 501–501.1 ft (152.7–152.74 m) and scattered pieces of charcoal at 501.1–501.7 ft (152.7–152.9 m). From 501.8 to 502.15 ft (152.9 to 153.1 m) is a bed of gravelly, sandy clay with fragments of woody material. This channel looks nonmarine, and possibly is a distributary channel (Fig. AF7).

The lower channel extends from 502.15 to 513.25 ft (153.1 to 156.4 m). Coarse sand (502.15–512.7 ft; 153.1–156.3 m) at the top has zones containing granules and scattered gravel. There is a transition at 512.7 ft (156.3 m) to a granule-rich, somewhat gravelly, slightly clayey sand. There are clay blebs at ~503.7–503.8 ft (153.5–153.6 m) and at 502.8 ft (153.3 m) that are likely burrows. The overall fining-upward lithology in a thick structureless sand with burrows suggests a tidal channel (Fig. AF7) over which a distributary prograded.

Below a coring gap (513.25–520 ft; 156.4–158.5 m) a clay extends from 520 to 523.35 ft (158.5 to 159.5 m). The interval from 520.0 to 521.0 ft (158.5 to 158.8 m) is medium gray clay with some small thin wisps of very fine sand in laminae. Below an irregular contact at 521.0 ft (158.8 m) the lithology changes to darker, faintly laminated, more organic rich clay that changes color downhole from grayish to brownish gray (521.0–523.35 ft; 158.8–159.5 m). This darker, more organic rich (from plant debris) clay contains dinoflagellates and represents a bay environment.

A contact at 523.35 ft (159.5 m) (Fig. AF7) with 0.05 ft (1.5 cm) of relief on it separates clay above from burrowed micaceous marine–looking sands below. We interpret this as a sequence boundary. We tentatively correlate the sequence from 485.7 to 523.35 ft (148.0 to 159.5 m) with the Magothy III sequence (Kulpecz et al., 2008), though this sequence and its contained facies at Medford are more marine than at other New Jersey sites. It may be the sequence equivalent to the Amboy Stoneware Clay of the Magothy III, though the facies are sandier at Medford. The unit is assigned to pollen Zone V (Turonian–Coniacian).

The lithology from 523.35 to 525.2 ft (159.5 to 160.1 m) is sandy, very micaceous mud and muddy sand with sporadic lignite and cleaner sand in small (~1 mm diameter) burrows and a weakly cemented zone (probably hematite cement) from 523.5 to 523.6 ft (159.56 to 159.59 m). The interval from 525.2 to 530.05 ft (160.1 to 161.6 m) is lignitic, sandy clay with a few 1–3 cm thick laminations of muddy sand. The sandy clay has a somewhat irregular, mottled appearance probably due to burrowing. Red sandy micaceous hematite concretions are found at 525.6–525.8 ft (160.2–160.3 m), 527.8–528 ft (160.87–160.93 m), and 528.5–528.7 ft (161.09–161.15 m), and a thin concretion at 529–530.05 ft (161.2–161.6 m) separates the sandy clay above from sand below. This interval was probably deposited in a delta front environment and is tentatively correlated to the Old Bridge Sand/Magothy II sequence. A tentative assignment to pollen Zone IV is not entirely consistent with this correlation, as it has been assigned to pollen Zone V elsewhere (Kulpecz, 2008).

A thick fine–medium sand from 530.05 to 562.7 ft (161.6 to 171.5 m) is also correlated with the Old Bridge Sand Member and the Magothy II sequence (Kulpecz et al., 2008). This interval is interpreted as marine-influenced upper delta front environments (Fig. AF7). The top of the sand (530.05–542.2 ft; 161.6–165.3 m) is a micaceous medium-grained quartz sand that is muddy at the top (530.05–530.5 ft; 161.6–161.7 m), changing downhole into cleaner sand below. There are a few thin muddy laminae and common laminae with concentrations of plant debris in the muddy interval. Some of the laminations are inclined, suggesting cross-bedding. From 542.2 to 543.35 ft (165.3 to 165.6 m), there is a shift to micaceous very clayey fine sand with faintly preserved laminations and finely disseminated plant debris. The section from 543.35 to 548.3 ft (165.6 to 167.1 m) is micaceous medium sand with a few laminae with concentrations of plant debris and a few muddy laminae. From 547.5 to 547.7 ft (166.88 to 166.94 m) there is some rust-colored banding in the sand.

Micaceous very clayey fine sand with some faint lamination is found from 548.3 to 549 ft (167.1 to 167.3 m). The upper 548.3–548.4 ft (167.1–167.2 m) appears to be weathered under the contact with a slightly reddish brownish color and with slightly coarser sand mixed in. A reddish, micaceous hematite-cemented fine-grained sandstone extends from 549 to 549.5 ft (167.3 to 167.5 m). The interval from 549.5 to 555.2 ft (167.5 to 169.2 m) consists of sandy sediment that exhibits soft-sediment deformation. A thin (1.5 cm) dark clay laminae occurs at 549.5 ft (167.5 m) and is underlain by a contorted bed of light gray very micaceous very fine sandy silt (549.6–550.75 ft; 167.5–167.9) subvertically juxtaposed against dark gray clayey, very micaceous very fine to fine sand. From 550.75 to 551.6 ft (167.9 to 168.1 m) is very micaceous, very silty, slightly clayey, light gray sand that oxidizes to reddish hematite on the outside of the core. A contorted mixture of dark and light gray very clayey sand is observed from 551.7 to 552.55 ft (168.2 to 168.4 m), underlain by dark gray, very muddy (clay and silt), very micaceous fine sand from 552.55 to 553.8 ft (168.4 to 168.8 m). At 553.8–554.45 ft (168.8–169.0 m), a mottled light gray clayey silty, very micaceous very fine to fine sand grades to a silty very micaceous light gray sand with small clay blebs (~3–4 cm), possible clay lined burrows, and laminae of dark gray very fine sandy clay to 555.2 ft (169.2 m). From 555.2 to 558.95 ft (169.2 to 170.4 m) (Fig. AF8) the interval consists of intercalated beds of slightly clayey silty, very micaceous light gray fine sand and laminae of sandy, micaceous dark gray clay with streaking of plant debris concentrated on laminations and several small clay blebs that may represent burrows. This thick sand section is correlated with the Old Bridge Sand.

The section from 560 to 562.6 ft (170.7 to 171.5 m) consists of a bioturbated very sandy silty micaceous dark gray clay and very clayey sand with preserved laminations. Several laminae are hematite enriched and orange in color, and a hematite concretion is found at 560.8 ft (170.9 m). This interval is correlated to the South Amboy Fire Clay, consistent with its assignment to Zone V or possibly Zones III–IV (Cenomanian). Assignment to Zones III–IV is inconsistent with this correlation (Fig. F5; see "Pollen"). A contact at 562.7 ft (171.5 m) is tentatively interpreted as a sequence boundary separating the Magothy II sequence above from the Magothy I below (Fig. F5).

The interval from 562.6 to 572 ft (171.5 to 174.3 m) consists of moderately well sorted, subangular to subrounded, medium-grained quartz sand that is muddy in places (563.8–564.0 and 570.0–570.2 ft; 171.8–171.9 and 173.7–173.8 m). Predominantly clean quartz sand extends from 570.2 to 572.9 ft (173.8 to 174.6 m) except for a lignite bed 571.1–571.25 ft (174.07–174.12 m), a small (3 cm) hematite concretion at 571.8 ft (174.3 m), and increasing percentage of mud downsection from 572.6 to 572.9 ft (174.5 to 174.6 m). From 572.7 to 572.9 ft (174.56 to 174.62 m) is lignitic medium sand, and 572.9–573.1 ft (174.6–174.7 m) is micaceous clayey fine sand. The interval from 562.7 to 573.1 ft (171.5 to 174.7 m) is correlated with the Magothy I sequence and the Sayreville Sand and is tentatively interpreted as estuarine environments. Whereas correlations suggested by the pollen zonation are somewhat uncertain, it appears that the Magothy Formation at Medford can be broken into five distinct sequences as at Sea Girt (Miller et al., 2006; Kulpecz et al., 2008). Further pollen studies are warranted to test the correlations to Sea Girt (Fig. F11).

Raritan Formation

Age: Cenomanian–Turonian
Interval: 573.1–623.8 ft (174.7–190.1 m)

A contact at 573.1 ft (174.7 m) (Fig. AF8) between medium with some coarse sand above and dark grayish brown clay with scattered sand-filled burrows below marks the contact between the Magothy and Raritan Formations. Below the contact, the section from 573.1 to 573.8 ft (174.7 to 174.9 m) is interlaminated clayey sand and sandy clay; some of this section appears to be burrowed with a few organic-rich laminae. The color in this interval is slightly lighter than the clays below and may represent soil alteration of the clays underneath. The interval from 573.8 to 578.5 ft (174.9 to 176.3 m) is mostly gray to slightly reddish brown clayey sand with some laminae of sandy clay. It is burrowed with faint lamination preserved and grades downward to become more clayey. Also present are scattered bits of charcoal fragments, along with siderite concretions at 576.9 and 578.1 ft (175.8 and 176.2 m). Light brown to predominantly gray laminated slightly sandy silty clay with common disseminated plant fragments/lignite occurs from 578.5 to 590.3 ft (176.3 to 179.9 m). There are hematite-cemented zones at 580.1–580.2 (176.81–176.84), 586.45–586.55 (178.75–178.78), and 587.2–587.3 ft (178.98–179.01 m) and a sandy lignitic zone at 586.85–586.95 ft (178.87–178.90 m). The interval from 590.3 to 592.8 ft (179.9 to 180.7 m) is similar to above but with regular laminae of very fine sand and concretions at 592.7 (180.65) and 592.8 ft (180.69 m). The environment of deposition was probably marsh to swamp (in outcrop the equivalent section was interpreted as mangrove swamp by Owens and Sohl [1969]). There is a coring gap from 592.8 to 600.0 ft (180.7 to 182.9 m). From 600 to 601 ft (182.9 to 183.2 m) is faintly laminated dark gray clay with red bands, along with charcoal. Laminated, micaceous, burrowed clayey fine–very fine sand fining downward to very fine sandy clay occurs from 601.0 to 604.3 ft (183.2 to 184.2 m); the upper part of this interval is heavily burrowed and is less burrowed as sand becomes less obvious. A hematite concretion occurs at 602.9 ft (183.8 m), and a sandy pyrite concretion occurs at 603.8 ft (184 m). A thin sand bed is registered above a coring gap at 604.3–604.6 ft; logs suggest that the sand occurs from 606 to 611 ft (184.7 to 186.2 m) and that there is a 2 ft (0.6 m) registry shift. A sequence boundary could be placed at the top of the sand, but much more likely the 5 ft (1.5 m) sand reflects a facies succession within a bay-fill, lower delta plain deposit (Fig. F6).

From 610 to 622.15 ft (185.9 to 189.6 m) (Fig. AF9) is sporadically laminated, dark gray clay with brownish red bands and disseminated plant debris. This interval also contains fine to very fine sand found in 1–2 mm diameter burrows. Hematite-cemented zones occur at 610.65, 617.2, 617.4–617.5, and 621.6–621.7 ft (186.1, 188.1, 188.18–188.2, and 189.3–189.5 m), a sandy lignite from 612.2 to 612.5 ft (186.6 to 186.7 m), a sulfur bloom at 621.6 ft (189.3 m), and gypsum crystals occur sporadically. The environment of deposition is interpreted as bay-fill deposits in the lower delta plain. Sand disappears at a contact at 622.15 ft (189.6 m) with sandy clay above and lignitic, fairly homogeneous dark gray clay below with gypsum crystals on the surface and charcoal chunks up to 1 cm (622.15–623.8 ft; 186.9–190.1 m). There is a faint irregular contact at 623.8 ft (190.1 m) with light gray (?kaolinitic) gleyed or weathered clay (623.8–624.9 ft; 190.1–190.5 m) below that is siltier than above with zones of very fine sand. This clay overlies a coring gap (624.9–627.0 ft; 190.5–191.1 m), below which there is a change to nonmarine, very lignitic clays. We tentatively place the Raritan/Potomac contact and a major sequence boundary at 623.8 ft (190.1 m) (Figs. F6, AF9) and interpret the gray clays as overbank deposits.

Potomac Formation

Age: Lower Cretaceous–lowermost Upper Cretaceous (?Barremian–?lower Cenomanian)
Interval: 623.8–1090 ft (190.1–332.2 m)

Potomac Formation Unit III

Interval: 623.8–786.8 ft (190.1–239.8 m)

Below the ?kaolinitic light gray clay at its top (that likely indicates subaerial subtropical weathering) (Fig. AF9), the Potomac Formation consists of interbedded, very lignitic and charcoal-rich micaceous very fine sandy clay interbedded with dark gray to medium gray clay with common charcoal, lignite, and plant debris (627.0–636.5 ft; 191.1–194 m). Bedding is faint, and there is scattered pyrite and sulfur. Some of the woody debris is >5 cm long. From 636.5 to 637.9 ft (194 to 194.4 m) is homogeneous, slightly mottled light gray clay and charcoal. From 637.9 to 639.8 ft (194.4 to 195 m) is medium dark gray clay with a few laminae of micaceous fine sand and scattered charcoal and plant debris. The environment of deposition is fluvial delta plain, probably overbank swamp/oxbow lake environments (Fig. AF10).

A sandy unit occurs from 639.8 to 651.8 ft (195 to 198.7 m). The sand consists of slightly micaceous fine quartz that coarsens slightly downsection to medium sand with thin clay from 646.2 to 646.6 ft (197 to 197.1 m). The sand has clay blebs 0.25–0.5 cm in width (e.g., 642.4–642.6, 643.7–644.0 ft) that gives it aspects of bioturbation, but it is likely that these are mud rip-up clasts. Fine to medium sand coarsens downsection from 646.6 ft (197.1 m), becoming coarse sand at 651 ft (198.4 m) that continues to the base of a channel at 651.8 ft (198.7 m). The sections from 647.2 to 647.7 ft (197.3 to 197.4 m) and 650.5 to 650.6 ft (198.27 to 198.3 m) are lignitic, which reveal cross-bedding in the upper section. The environment of deposition is fluvial channel (Fig. AF10).

The section from 651.8 to 662.3 (198.7 to 201.9 m) is primarily clay, albeit poorly recovered. Kaolinized clay with an orange medium sand laminae and charcoal chunks (651.8–652.1 ft; 198.7–198.8 m) marks the top of a weathered zone at the base of the channel. Interbedded, lignitic/charcoal-rich muddy sand, clay, and clean fine sand with scattered small (5 mm–2 cm) hematite concretions are found below the kaolinitic clay. Clays vary from dark to light gray. There is a sandstone concretion from 653.0 to 653.3 ft (199 to 199.1 m). The environment is interpreted as fluvial overbank including paleosols.

"Birch log" sands occur from 662.3 to 677.0 ft (201.9 to 206.3 m). They are micaceous very fine to medium-grained quartz sands that display several distinct fining successions (e.g., 662.3–670, 670–672, 672–674, 674.0–677.0 ft; 201.9–204.2, 204.2–204.8, 204.8–205.4, 205.4–206.3 m). There is a clay bed at 675.4–675.5 ft (205.86–205.89 m). The sands have distinct cross beds and have scattered lignite and mica. The section from 664.2 to 664.8 ft (202.4 to 202.6 m) has inclined clay laminae. The environment of deposition is fluvial channel (Fig. AF10).

The section from 677.0 to 678.8 ft (206.3 to 206.9 m) consists of laminated very fine sandy clay, with the sand in laminae and possibly burrows. Lignite occurs from 678.2 to 678.8 ft (206.7 to 206.9 m). The environment of deposition is probably a swamp or marsh (Fig. AF10).

There are significant contacts at 678.8 (206.9) and 681.2 ft (207.6 m). Between these contacts is a reworked zone (678.8–681.2 ft; 206.9–207.6 m) that transitions downward from a sandy clay–clast conglomerate to a coarse-grained sand. The conglomerate has mostly light gray silty clay clasts and a few red clay clasts in a matrix of red muddy sand. There is a possible break in the bedding at 680.9–680.95 ft (207.5–207.6 m) where a thin laminae of gray clay occurs immediately under a cemented zone. The reworked zone between these contacts is possibly colluvium; the surface at 681.2 ft (207.6 m) may represent a sequence boundary (Fig. F6).

Below the contact (681.2–706.5 ft; 207.6–215.3 m) is light gray silty clay to very clayey silt. Extensive mottling reflecting soil processes (Fig. AF11) is found from 681.2 to 696 ft (207.6 to 212.1 m) and 700 to 705 ft (213.4 to 214.9 m), with numerous subvertical reddish mottles (several centimeters in diameter) and lesser olive-brown mottles and banding that may be root traces. Microsphaerosiderite is common with high concentrations from 688.7 to 689.8 ft (209.9 to 210.3 m) and 702.3 to 703.5 ft (214.1 to 214.4 m). This mottled very silty clay was deposited as alluvial plain paleosols (Fig. AF11). At the base (705–706.5 ft; 214.9–215.3 m), the section becomes slightly darker downhole with suggestions of laminations increasingly preserved downcore.

Dark gray clay with common very thin laminae of fine to very fine sand (706.5–709.65 ft; 215.3–216.3 m) represents strikingly different facies. The clay contains lignite and sulfur, and its bedding is subtly contorted and wavy. Some sand-filled structures from 706.5 to 707 ft (215.3 to 215.5 m) may represent either burrows or root fillings. These sediments represent a beautiful example of an oxbow lake environment (Fig. AF11).

The interval from 709.7 to 731.9 ft (216.3 to 223.1 m) consists of plant-rich sand with common clay beds. From 709.7 to 711.6 ft (216.3 to 216.9 m) is interbedded fine-grained sand with common plant-rich laminations and dark gray clay with thin very fine sand laminae. From 710.1 to 710.2 ft (216.4 to 216.4 m) is a pyrite-cemented sand concretion. From 711.6 to 721.7 ft (216.9 to 220 m) is a sand bed that coarsens downsection from fine-to-medium to very coarse sand; there are scattered cross laminae from 712 to 714 ft (217 to 217.6 m) (Fig. AF12) and 720 to 720.2 ft (219.46 to 219.5 m) of plant debris. An erosional surface interpreted as the base of a channel occurs at 721.7 ft (220 m). A slightly micaceous, cross-bedded medium sand subtly coarsens downsection from 721.7 to 724 ft (220 to 220.7 m) with a few organic-rich laminae. There is a coring gap from 724 to 730 ft (220.7 to 222.5 m). The sands above the gap are fluvial channel sands with possible point bar deposits near the base (e.g., 711.6–721.7 ft; 216.9–220 m). Medium gray clay is found immediately below the coring gap (730.0–730.2 ft; 222.5–222.6 m). Below this clay is a zone of reworked paleosols from 730.2 to 731.9 ft (222.6 to 223.1 m) that includes clay clasts pressed together in thin clay beds, woody debris, concentrations of hematized microsphaerosiderite and red paleosol mud clasts, and sand. From 731.75 to 731.85 ft (223 to 223.1 m) is a bed of clay rip-up clasts interpreted as colluvium.

Paleosols return from 731.85 to 750.85 ft (223.1 to 228.9 m) (Figs. F7, AF12), consisting of clayey slightly sandy silt with zones of clay or sand. The upper 0.15 ft (0.05 m) is paleosol clay with clay clasts of light gray, medium gray, and reddish clay and is also interpreted as colluvium. Below this is light gray silt with medium gray mottles (732.0–733.0 ft; 223.1–223.4 m), silt with increasing amounts of fine–very fine sand downsection (733.0–733.6 ft; 223.4–223.6 m), a coring gap (733.6–740.0 ft; 223.6–225.6 m), and a thin bed of slightly muddy sand and hematized microsphaerosiderite (740.0–740.1 ft; 225.6 m). The section from 740.1 to 750.0 ft (225.6 to 228.6 m) consists of mottled silt that alternates from predominately light gray to red, with mottles suggestive of root traces (Fig. AF12). The bottom of this interval (750.0–750.85 ft; 228.6–228.9 m) is slightly muddy fine sand. These environments are interpreted as well-drained alluvial plain overbank.

There is a weathering contact at 750.85 ft (228.9 m), with a transition from weathered clay to increasingly dark gray clay below to 753.9 ft (229.8 m). The clay is organic rich, contains common laminae of very fine sand and zones with minor burrows/roots, and was deposited in oxbow lake environments (Fig. AF12). From 753.9 to 760.9 ft (229.8 to 231.9 m) are interbedded gray, organic-rich fine sand and clay beds with 0.2–0.4 ft (0.06–0.12 m) thickness deposited in cut-off channel/overbank sands.

From 760.9 to 786.8 ft (231.9 to 239.8 m) is an interval characterized by fining-upward sand successions with common cross-bedding and scattered plant debris–rich laminae. The uppermost succession (760.9–764.5 ft; 231.9–233 m) coarsens downward from fine-grained to poorly sorted medium- and coarse-grained sand. The next fining-upward sand succession from 764.5 to 772 ft (233 to 235.3 m) coarsens downward from a thin sandy clay to orange fine sand to coarse sand to a sandy conglomerate of light gray clay clasts that are mostly 0.5–2 cm in diameter. The contact below is not clear. From 772 to 786.8 ft (235.3 to 239.8 m) is micaceous medium cross-bedded sand with abundant lignitic laminae coarsening downward to cross-bedded medium to coarse sand. There are a few scattered clasts of white gray clay at 780–786.8 ft (237.7–239.8 m). The likely environment of deposition is a fluvial channel (Fig. AF13). We place a sequence boundary at 786.8 ft (239.8 m), separating the fluvial channels above from paleosols below (Fig. F7). This follows Benson (2006) and Sugarman et al. (2004, 2006) in placing the base of Potomac Unit III consistently below a relatively thick sand. 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 (see "Pollen"), consistent with the assignment to the Potomac Unit III sequence (Fig. F7).

Potomac Formation Unit II

Interval: 786.8–983.15 ft (239.8–299.7 m)

Below a coring gap (786.8–790 ft; 239.8–240.8 m), there is a change to stiff clayey silts alternating between red extensively mottled silt and light gray less mottled silt representing paleosols from 790 to 797.7 ft (240.8 to 243.1 m) (Figs. F8, AF14). Microsphaerosiderite is abundant through most of this interval. It appears to include root traces and soil cracks (cutains). There is coring gap from 797.7 to 800 ft (243.1 to 243.8 m). Below the coring gap from 800 to 803.9 ft (243.8 to 245 m) is an interesting heterolithic mix of dark to medium gray sandy clayey silt with abundant mud clasts ranging from 1 mm to 2 cm in diameter. They include dark gray clay, light gray clay, and a few reddish brown clay clasts, and rare pyrite. The mix also includes abundant charcoal that is more common upcore. The environment of this muddy bed is not clear but could possibly represent a debris flow in an alluvial plain environment (Fig. AF14).

A sharp contact at 803.95 ft (245 m) separates the clay above from an interval of mud and sand (803.9–814.4 ft; 245–248.2 m). The contact is a mixture of a large bleb of light gray silty clay that is mixed irregularly with the matrix of the dark gray material above. The interval changes from light gray, hard silty clay and clayey silt that has a number of cracks with scattered microsphaerosiderite that begins to pick up thin laminae of sand at 810 ft (246.9 m). It becomes increasingly sandy downcore with sand predominating at the base from 812.7 to 814.4 ft (247.7 to 248.2 m). There is a high abundance of plant debris from 813.9 to 814.4 ft (248.1 to 248.2 m), including a thin charcoal bed at 814.3 ft (248.2 m). From 814.4 to 816.0 ft (248.2 to 248.7 m) is organic-rich (plant debris and charcoal) laminated dark gray clay with thin laminae of slightly micaceous fine to very fine sand. Laminae are slightly irregular in places. The upper part down to 814.7 ft (248.3 m) is slightly sandier with more carbonaceous material mixed in. This unit was deposited in levee and overbank environments with basal levee sands overlain by overbank clays that are overprinted by soil processes (Fig. AF15).

There is a thick sandy interval from 816 to 844.7 ft (248.7 to 257.5 m) with mud increasing toward the base. Coarse and medium sand is found from 816 to 822 ft (248.7 to 250.6 m) with lignite-rich sand between 822 (250.5 m) and 823 ft (250.9 m). A 0.2 ft thick bed of clay occurs at 823.4 ft (251 m) that is underlain by a 0.1 ft thick bed of charcoal fragments at 823.6 ft (251 m). From 823.7 to 824 ft (251.1 to 251.2 m) is coarse sand with a charcoal bed at its base. Below a coring gap from 824 to 830 ft (251.2 to 253 m), sand (830–834 ft; 253–254.2 m) ranges from coarse to fine with clear cross-bedding in places and with several thin beds of clay and muddy sand and lignite. There is also a pyrite-cemented sand concretion (3 cm diameter) at 832.8 ft (253.8 m). From 834 to 841.4 ft (254.2 to 256.5 m), the section is sandy clay with some sand beds and laminae. In the lower part (840.7–841.4 ft; 256.2–256.5 m), it appears to be composed of clay rip-up clasts (0.1–1 cm diameter) in a sandy mud matrix. From 841.4 to 843.7 ft (256.5 to 257.2 m), the section exhibits a downward coarsening transition from poorly sorted medium to coarse sand to a sandy clay clast conglomerate with abundant chunks of hematite that are probably the remnants or microsphaerosiderite. From 843.7 to 844.3 ft (257.2 to 257.3 m) is mostly medium sand. The bottom of the unit (844.3–844.7 ft; 257.3–257.5 m) is sandy medium to dark gray clay with large chunks of lignite and charcoal. These sands represent deposition in and around fluvial channels. Some might be in a channel, and others might represent levee deposits.

We place a possible sequence boundary at 844.7 ft (257.5 m) in association with a downhole change to high gamma log values in a clayey silt and silty clay (Fig. F8). 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, fining upward from fluvial channels at the base to overbank deposits on top.

Below a coring gap from 844.7 to 848.6 ft (257.5 to 259.1 m), clayey silt and silty clay returns from 848.6 to 860.75 ft (258.7 to 262.4 m). The top of the interval is light gray that exhibits progressively redder mottling below 851.1 ft (259.4 ft). Much of the mottling is vertical to subvertical and several centimeters in diameter, suggestive of root traces (Fig. AF16). Microsphaerosiderite is common throughout. From 859 to 860.75 ft (261.8 to 262.4 m) the core is banded red, pink, light gray, and greenish brown with a few mottles and includes common small hematite concretions from 859 to 859.9 ft (261.8 to 262.1 m). Medium gray clayey sandy silt returns from 860.75 to 861 ft (262.4 to 262.4 m), below which is a coring gap to 869.3 ft (265 m). This is a gleyed soil versus the oxidized soils above. This section is interpreted as overbank deposits.

The section from 869.3 to 871.4 ft (265 to 265.6 m) is predominantly dark-to-light gray to black sandy mud with some muddy sand. The sandy mud is dark gray with faint lamination and common plant debris. The muddy sand is light–medium gray, predominantly medium grained, with common to abundant plant debris. The intervals from 869.8 to 869.9 ft (265.1 to 265.2 m) and 870.8 to 870.9 ft (265.4 to 265.5 m) are ligntic.

Poorly recovered intervals from 871.4 to 871.7 ft (265.6 to 265.7 m) and 879.3 to 881.55 ft (268 to 268.7 m) across a coring gap (871.7–879.3 ft; 265.7–268 m) consist of a gray sand that fines upward from medium coarse to medium fine and contains rare plant debris laminations and clay clasts; this is a fining-upward fluvial channel to overbank deposit.

The contact at the base of the sand at 881.55 ft (268.7 m) is sharp. From 881.55 to 882.5 ft (268.7 to 269 m) is a light to medium gray, vaguely laminated and mottled mix of sandy clay to clayey sand deposited as a paleosol in a gleyed overbank environment with mottles possibly reflecting rooting. From 882.5 to 894.15 ft (269 to 272.5 m including a 6.9 ft [2.1 m] core gap) is interbedded slightly silty sand, lignitic muddy sand, clayey sand, sandy clays, and clay; the sands are primarily fine grained. Beds range from 0.1 to 0.5 ft (0.03 to 0.2 m) in thickness and the sands appear cross-laminated. This likely represents deposition in a wet overbank to levee environment. There is a coring gap from 894.15 to 900 ft (272.5 to 274.3 m).

A fluvial channel deposit (Fig. AF16) occurs from 900 to 906.55 ft (274.3 to 276.3 m) and consists of coarse sand that fines up to medium sand in the top 1 ft (0.3 m) and contains a few thin (2 cm) beds of lignite. The sand is immature and poorly sorted at the base. The interval from 903.5 to 903.8 ft (275.4 to 275.5 m) is kaolintic.

An overbank-levee-channel complex occurs from 906.55 to 920.6 ft (276.3 to 280.6 m). From 906.55 to 910.2 ft (276.3 to 277.4 m including a coring gap [907.55–910.0 ft; 276.6–277.4 m]) is laminated and has thin beds of clay, silty clay, clayey silt, and clayey sand, with colors in bands from darker gray (more organic material) to lighter gray (lightly gleyed). These sediments represent an overbank environment. A levee deposit from 910.2 to 914.7 ft (277.4 to 278.8 m) consists of laminated to thinly bedded silty to clayey medium to fine sand with interbedded silty and clayey laminae. It coarsens downward to medium sand in the lower part. A channel deposit from 914.7 to 920.6 ft (278.8 to 280.6 m) consists of a coarsening-downward succession from silty poorly sorted medium-coarse to coarse sand with black charcoal and small (up to 4 cm) clay rip-up clasts. From 920.6 to 921.8 ft (280.6 to 281 m) is a sand that changes downward from a very clayey and silty white light gray poorly sorted medium–coarse sand (920.6–920.9 ft; 280.6–280.7 m) to slightly silty medium sand. This probably is a paleosol formed on a thin levee deposit. A wet overbank deposit from 921.8 to 922.5 ft (281 to 281.2 m) consists of thinly interbedded light gray and dark gray clay, clayey sand, clayey silt, and lignitic sand. There is a coring gap from 922.5 to 930.0 ft (281.2 to 283.5 m).

A varying complex of oxbow lakes, overbank levee, and small channels occurs from 930.0 to 958.1 ft (283.5 to 292 m), marked at its base by a sharp gamma log decrease (Fig. F9) and shift in depositional environments to braided river deposits below this contact. From 930.0 to 930.7 (283.5 to 283.7 m) is very muddy, poorly sorted, very coarse grained to fine-grained sands; the heterolithic nature may be due to paleosol mixing processes. From 930.7 to 932.4 ft (283.7 to 284.2 m) is a gray, silty micaceous clay that becomes darker downward, suggesting some gleying in the top. The section from 932.4 to 933.7 ft (284.2 to 284.6 m) consists of two light gray sand beds (upper coarse, lower medium) separated by darker gray sandy silty clay. The sediments from 930.7 to 933.7 ft (283.7 to 284.6 m) were deposited in an overbank environment (Fig. AF17). There is an interesting zone of dark gray clay from 933.7 to 937.75 ft (284.6 to 285.8 m) that changes from vaguely laminated to 934.7 ft (284.9 m) to homogeneous, mottled-looking sandy clay with sand burrows to 937.5 ft (285.8 m) to laminated at the base. The environment is enigmatic but is interpreted as an oxbow lake deposit perhaps influenced by bioturbation or later rooting (Fig. AF17). There is a coring gap from 937.7 to 940.1 ft (285.8 to 286.5 m). From 940.1 to 941.7 ft (286.5 to 287.0 m) is well-sorted medium sand that has a light gray clayey matrix and faint laminations from 940.3 to 940.8 ft (286.6 to 286.8 m). Interlaminated dark gray clay and sandy clay returns from 941.7 to 945.7 ft (287 to 288.2 m), with cleaner sand-filled root/burrow traces; this again is likely an oxbow lake. Sand reappears from 945.7 to 949.7 ft (288.2 to 289.5 m), comprising three fining-upward successions (945.7–947.2, 947.2–948.0, and 948.0–949.7 ft; 288.2–288.7, 288.7–289, and 289–289.5 m) from medium–coarse at the bases to well-sorted, medium–fine sand at the tops deposited in a proximal levee environment. The section from 950.0 to 953.5 ft (289.6 to 290.6 m) consists of a succession of interbedded/interlaminated slightly micaeous silty sand, clayey sand, and sandy clay where laminations have been somewhat homogenized by soil processes; the sand is primarily medium grained with some coarse- and fine-grained quartz laminae and scattered charcoal concentrations. A clayey interval from 953.5 to 958.1 ft (290.6 to 292 m) changes from sandy light gray silty clay at the top to mottled, brownish red–light gray clay from 954.7 to 955.5 ft (291 to 291.8 m); to increasing laminated, increasing dark gray clay from 955.5 to 957.3 ft (291.2 to 291.8 m); to increasingly lighter gray laminated silty clay from 957.3 to 958.1 ft (291.8 to 292 m). This clayey interval represents changes in depositional oxbow lake environments (Fig. AF17) upsection from gleyed, to ungleyed, to gleyed, to oxidized, and back to gleyed.

"Zebra" (alternating black–white) sands (Fig. AF17) occur from 958.1 to 972.2 ft (292 to 296.3 m). The sands are very poorly sorted with silt beds from 0.1 to 0.6 ft (0.03 to 0.18 m) in thickness that range from fine to medium to very coarse sand. Very coarse beds occur at 971.6 (296.1), 968 ft (295 m), and 964.3 ft (293.9 m). There are dark cross-laminae of dark organic-rich silt. This sandy interval appears to be a fluvial channel bar deposit. Though resistivity shows high values typical of sands, the gamma logs show two unexplained peaks at 964 ft (293.8 m) and 970 ft (295.7 m) that may reflect the mineralogy (Fig. F9). Pyrite concretions occur at 967–968 ft (294.7–295 m). There is a coring gap from 972.2 to 980 ft (296.3 to 298.7 m).

The section from 980 to 983.15 ft (298.7 to 299.7 m) consists of interlaminated clay, silt, and silty fine sand that varies from darker to light gray; the section below 982.5 ft (299.5 m) is lighter gray and may represent some gleying. This represents an overbank distal levee deposit. There is a possible sequence boundary at 983.15 ft (299.7 m) separating the finer grained fluvial deposits above from much coarser braided river deposits below. The surface also separates pollen Zone IIB (Albian) from I/IIA (lower Albian) (pollen resolution is poor in this interval of the core). We are tentatively assigning the remaining section below 983.15 ft (299.7 m) to the base of the hole (TD) to Potomac Unit I (Fig. F9).

Potomac Formation Unit I

Interval: 983.15–1090 ft (299.7–332.2 m)

Sand is present from 983.15 ft (299.7 m) to the base of the hole (TD at 1090 ft; 332.2 m) except for two thin clay beds at 1039–1039.8 ft (316.7–316.9 m) and 1043.7–1043.9 ft (318.1–318.2 m). There appears to be distinct sand-size patterns within several of the channels contained in this sandy interval. Sand with dark laminae ("zebra facies") and rare quartzite pebbles from 983.15 to 1020 ft (299.7 to 310.9 m) is predominantly coarse grained with gravelly zones. There are a few thin clay beds (maximum thickness 1 ft) from 990.6 to 991.6 ft (301.9 to 302.2 m; light gray), 1009.3 to 1009.5 ft (307.6 to 307.7 m), and 1011.5 to 1011.7 ft (308.3 to 308.4 m). The matrix is silty to slightly clayey in many places. This predominantly sandy section was deposited in a braided river system (Fig. AF18).

The facies from 1020 to 1025 ft (310.9 to 312.4 m) consist of poorly sorted very coarse to coarse sand with whitish blebs that appear to be weathered feldspars and give a speckled appearance. The sand is poorly sorted from predominantly coarse to pebble size. Pebbles concentrated from 1023 to 1023.5 ft (311.8 to 311.96 m) are mostly quartzite. This speckled facies was deposited either as braided river deposits or possible colluvium (slope wash).

Interbedded coarse–medium sands with dark laminae (zebra facies) and gravelly sands return from 1025 to 1079.2 ft (312.4 to 328.9 m) and again represent braided river deposits (Fig. AF18). They contain gravelly zones from 1026 to 1026.3 ft (312.7 to 312.8 m), 1026.8 to 1027.1 ft (312.97 to 313.06 m), 1027.8 to 1028.0 ft (313.27 to 313.33 m), 1029 to 1029.4 ft (313.64 to 313.76 m), 1050.0 to 1051.6 ft (320 to 320.53 m; the latter including cobbles), 1055 to 1056 ft (321.56 to 321.87 m), and 1080 to 1082.9 ft (329.18 to 330.07 m). The intervals in between consist of medium–coarse sands with dark laminae and coring gaps. Muddy sand occurs in the gravels from 1081.1 to 1081.6 ft (329.5 to 329.7 m). True basement was not reached. These sands are assigned to Zone I (lowermost Albian to Aptian/Barremian) or possibly IIA (lower Albian; see "Pollen").

As a general comment, the Potomac Formation at Medford differs from that at Fort Mott by the greater dominance of sand, the lesser amount of red soils, and the greater diversity of fluvial environments (Fig. F12).