Drilling at Fort Mott State Park, New Jersey (39°36´19.956''N, 75°33´07.175''W; elevation = 3.79 ft [1.2 m]; Delaware City, Delaware, 7.5´ quadrangle, Salem County, New Jersey) began in early October 2001. Drilling operations were superintended by Gene Cobbs, USGS Eastern Earth Surface Processes Team; Gene Cobbs III was the driller. Space, water, and electricity were provided by the New Jersey Department of Parks at the Fort Mott State Park maintenance yard (courtesy of Fort Mott State Park Chief Ranger Patricia Cianflone). On 1 October, an onsite laboratory was established in a garage bay and P. Sugarman and J. Browning (Staff Scientist) moved equipment on site. A Kodak DC260 digital zoom camera (38.4–115.2 mm lens; 1536 x 1024 megapixel resolution), Power Macintosh 7200, and photography stand were set up to photograph 2-ft (0.61 m) core segments; default settings (including flash) with wide angle (38.4 mm) were used, yielding the truest colors and ensuring uniformity among photographs. On 2 October, the USGS team arrived on site and began rigging up, testing the water well on site, and connecting electrical hookups.
All cores were measured in feet (all depths are given in feet below land surface), and all operations are described in feet only. We continued to adopt ODP convention of top-justifying depths for intervals with incomplete recovery for all field notes and photos.
The first core was obtained on 3 October 2001 using a Christensen 94-mm (HQ) system, with a 4.5-in (11 cm) Christensen drill bit, creating a 2.5-in (6.4 cm) core diameter. For unconsolidated sands, an extended shoe was used to contact the sample 1.5–2.5 in (3.8–6.4 cm) ahead of the bit. A coal-rich fill was encountered in the upper 0.5 ft (0.15 m). Drilling was smooth through the surficial units on the first day. A gravel unit at 19–24 ft (5.79–7.32 m) was difficult to recover, and it destroyed the shoe. In all, 39 ft (11.89 m) was drilled with 24.7 ft (7.53 m) recovered (recovery = 63%).
On 4 October, 5-in (13 cm) polyvinyl chloride surface casing (to be removed after completion of the drilling) was set to 32 ft (9.75 m) into a tight clay. Drilling resumed promptly at 0930 hr. The first run (40–45 ft; 12.19–13.72 m) came up empty. Because it was possible that the core had slipped out of the rock shoe, the inner core barrel was placed back in the hole to try to retrieve it but nothing more was recovered. Run 10 (40–45.5 ft; 12.19–13.87 m) hit a hard layer that flared the shoe. Although 2.8 ft (0.85 m) was recovered between 40 and 45.5 ft (12.19 and 13.72 m), the top 2.1 ft (0.64 m) was drilling slurry and the bottom 0.7 ft (0.21 m) was clay mixed with drilling mud. An attempt to push the hard layer into the softer sediments resulted in no recovery on run 11 (45–50 ft; 13.72–15.24 m) and poor to moderate recovery (1.4 ft; 0.43 m) on run 12 (50–55 ft; 15.24–16.76 m). Recovery improved (4.0 ft; 1.22 m) on run 13 (55–60 ft; 16.76–18.29 m), but the cores still showed heavy scoring and intrusion of drilling mud and a new shoe was destroyed. It appeared that indurated material was blocking the hole and it was decided to pull the rods. A cobble was extracted from the hole along with 3.4 ft (1.04 m) of good core by jamming the drill string without a bit on its end over the cobble and pushing through the sediment below the cobble to trap it. The cobble is believed to have fallen into the hole during reaming and casing. This core was logged as run 15 (60–63.6 ft; 18.29–19.39 m). The day ended with 11.8 ft (3.60 m) recovered from 23.6 ft (7.19 m) drilled (40–63.6 ft; 12.19–19.39 m; recovery = 50%).
No major problems were encountered on 5 October, coring from 63.6 to 140 ft (19.39 to 42.67 m). Run 22 (120–130 ft; 36.58–39.62 m) was blocked by a chert pebble at 4.8 ft (1.46 m), and the lower 5.2 ft (1.58 m) was lost. For the day, we recovered 55.45 ft (16.90 m) from 76.4 ft run (23.29 m; recovery = 72.6%).
Coring was slowed by rain on the morning of 6 October. Moderate recovery in interbedded sand and clay (140–180 ft; 42.67–54.86 m) changed to excellent recovery in clays (180–200 ft; 54.86–60.96 m). The top 3 ft (0.91 m) of run 29 (170–180 ft; 51.82–54.86 m) was chewed up, with 6.6 ft (2.01 m) of solid core, whereas core 30 (180–190 ft; 54.86–57.91 m) had 1 ft (0.92 m) of "chew" at top. The day ended with 45.9 ft (13.99 m) recovered from 60 ft run (18.29 m; recovery = 76.5%).
Recovery on 7 October was excellent. We drilled from 200 to 245 ft (60.96 to 74.68 m), with 90% recovery (40.3 ft [12.28 m] recovered of 45 ft [13.72 m] drilled). Excellent recovery continued during the first 3 runs on 8 October (245–270 ft drilled; 25.15 ft recovered; 74.68–82.30 m drilled; 7.66 m recovered), but recovery dropped sharply on runs 40 and 41 (270–290 ft; 82.30–88.39 m). There were no obvious problems in run 40 (270–280 ft; 82.30–85.34 m), with 4.8 ft (1.46 m) of clay recovered. The core was lost from the barrel in the next coring run (280–290 ft; 85.34–88.39 m), but 3.1 ft (0.94 m) was recovered on 9 October by running the inner core barrel back in for the core. This core may represent material from anywhere between the bottom of the overlying recovered interval at 274.8 ft (83.76 m) and the bottom of this run at 290 ft (88.39 m), but its top is hung at 280 ft (85.34 m).
Coring continued on 9 October with a change from mottled clay to coarse sand and some gravel. Drilling was limited to 25 ft (7.62 m) for the day (19.45 ft [5.93 m]; recovery = 78%) because the inner core barrel became stuck ~100 ft (30.48 m) from the bottom of the hole. The core from run 44 (300–303.5 ft; 91.44–92.51 m) was intruded with drilling mud. The top 2 ft (0.61 m) of the core from run 45 (303.5–310 ft; 92.51–94.49 m) may be drilling slurry.
On 10 October we cored 50 ft (15.24 m) from 315 to 365 ft (96.01 to 111.25 m). Below 330 ft (100.58 m) the drillers added bentonite to the drilling mud to equalize the pressure inside and outside the core barrel. For all subsequent coring runs on this day, drilling was slightly faster to minimize drilling mud invasion into sands and extra care was taken to pump long enough to clear drilled sand from the hole. A hard bed was encountered during the drilling of the last core (run 53; 360–365 ft; 109.73–111.25 m), destroying a coring shoe. The day ended with 40.5 ft (12.34 m) recovered from 50 ft run (15.24 m; recovery = 81%). Pumping after each run to clean out sand, as well as increasing the mud weight, probably helped contribute to the excellent recovery in a sand-dominated interval.
Recovery on 11 October was excellent, although the dominant mottled clay lithology kept the drilling rate slow. The drillers had been using a modified shoe with long springs inside to help capture the core. Using the modified shoe allowed them to move the shoe back up inside of the bit, allowing the bit to cut faster. All of these modified shoes were expended and we were relegated to using a regular rock shoe. The rock shoe contacts the clay just behind the carbide cutters and in front of the diamonds, reducing the speed at which clay is cut. The lack of modified shoes resulted in slower drilling. Recovery was 100% for the day (45 ft [13.72 m] from 375 to 410 ft [114.3 to 124.97 m]).
On 12 October, clay gave way to sand and drilling speeds increased. Below 418 ft (127.41 m), the sand content increased in the core and drilling was much quicker to 474 ft (144.48 m). At 474 ft (144.48 m) the drillers encountered a lithified zone or large nodule in the hole, and they stopped the run after 5 ft (1.52 m) in a gray clay. The day ended with 59.2 ft (18.04 m) recovered from 65 ft run (21.33 m; recovery = 91%).
Coring in clay continued on 13 October from 475 to 530 ft (144.78 to 161.54 m), with 52.15 ft (15.90 m) recovered (95%). Coring was faster in the morning in gray, slightly micaceous silty clays, but slowed in the afternoon as we reencountered mottled red, green, and gray clays.
Drilling was suspended on 14 October as the drillers returned to Reston, Virginia, to get additional supplies. The rods were turned in the morning and in the evening to prevent binding in the hole. No problems were encountered on return from Reston and smooth coring resumed on 15 October. Drilling became easier on runs 73–74 (540–560 ft; 164.59–170.69 m) as we penetrated silts. Easy drilling continued, but recovery dropped in sands on runs 75–77 (560–590 ft; 170.69–179.83 m). The day ended at 590 ft (179.83 m) with 41.7 ft (12.71 m) recovered (69.5%).
On 16 October, run 78 (590–598 ft; 179.83–182.27 m) penetrated a harder zone at the top of the run and was stopped at a hard layer at 598 ft (182.27 m). Run 79 (598–605 ft; 182.27–184.40 m) recovered only 2 ft of sand and interbedded clay, whereas run 80 (605–610 ft; 184.40–185.93 m) became plugged with clay, blowing away the underlying sand. The interbedded sands and clays hindered recovery. Run 81 (610–616 ft; 185.93–187.76 m) slipped out of the core barrel. We went down with the 10-ft (3.05 m) barrel and drilled another 4 ft (1.22 m; 610–620 ft; 185.92–188.98 m), recovering 8.4 ft (2.56 m). The final run (620–630 ft; 188.98–192.02 m) obtained 8.1 ft (2.47 m). For the day, 26.9 ft (8.20 m) was recovered from 40 ft (12.19 m) drilled (recovery = 67.3%).
At the beginning of the day on October 17, runs 83–84 (630–650 ft; 192.02–198.12 m) penetrated silty sands. Drilling slowed near the end of run 84 at 644.1 ft (196.32 m) when we penetrated a very hard clayey silt. The drillers stopped the run after drilling 6.5 ft (1.98 m); only 4.7 ft (1.43 m) was recovered. The hard lithology continued in run 85, which was stopped after 4.5 ft (1.37 m) at 651 ft (198.42 m) with 6.0 ft (1.83 m) recovered. We believe the top 1.5 ft (0.46 m) of run 85 represents material from the bottom of run 84. Run 86 drilled very slowly, and the core catcher was destroyed during the run. Only 1.85 ft (0.56 m) of 9.0 ft (2.74 m) run was recovered (with the remainder probably still in the bottom of the hole, having slipped out of the core catcher). The same interval was re-run as run 86A, and an additional 1.2 ft (0.37 m) of core was recovered, likely from the bottom part of the run interval, making a total of 3.05 ft (0.93 m) recovered for this 9.0-ft (2.74 m) interval. For the day, 21.9 ft (6.68 m) was recovered from 30 ft (9.14 m) drilled (recovery = 73%).
On 18 October, drilling was slow with good recovery (>96.5%) as the mottled clays become harder. The drilling ended with 30 ft (9.14 m) drilled to 690 ft (210.31 m). The core was dropped on the last 10 ft (3.05 m) run, but completely recovered.
On 19 October, the rods were stuck in the hole because of swelling clays, so the mud was thinned and circulated until about 0900 hr. Drilling resumed with a 4-ft (1.22 m) run, with a recovery of 2.15 ft (0.66 m). The core was mangled (undercut) because the material was very hard. A 6-ft (1.83 m) run followed, and 6.1 ft (1.86 m) of core was recovered (693.9–700 ft; 211.50–213.36 m). The day finished with a 10-ft (3.05 m) run (700–710 ft; 213.36–216.41 m), from which 10.25 ft (3.12 m) was recovered. The drillers pulled the rods up 200 ft (60.96 m) at the end of the day to avoid the swelling clays that caused the rods to stick that morning. For the day, 16.5 ft (5.03 m) was recovered from 20 ft (6.10 m) drilled (recovery = 83%).
On 20 October, a first attempt to core 5 ft (710–715 ft; 216.41–217.93 m) yielded no recovery. A rock shoe was used in this interval, and the core likely slipped through the metal core catcher because of undercutting. After some modification of the catcher, drilling resumed for an additional 5 ft (1.52 m; 715–720 ft; 217.93–219.46 m), targeted at recovering the lost core (710–715 ft; 216.41–217.93 m) as well as the additional footage (715–720 ft; 217.93–219.46 m). On attempting to retrieve this interval, the core again slipped through the catcher. The core barrel was lowered, this time with a short snout shoe and plastic core catcher, and the interval was drilled again, finally recovering 2.9 ft (0.88 m) of the 10-ft (3.05 m) interval cored (recovery = 29%). The following coring run (720–725 ft; 219.46–220.98 m) went fairly smoothly and recovered 2.8 ft (0.85 m) of 5 ft (1.52 m) drilled (recovery = 56%). The interval from 725 to 730 ft (220.98 to 222.50 m) was very hard; 5.5 ft (1.68 m) of core was recovered of 5 ft (1.52 m) drilled (recovery = 110%), including the bottom of the previous coring run. The final core for the day, 730–740 ft (222.50–225.55 m), began with a hard interval and concluded with a softer interval at its base. Recovery was 9.2 ft (2.80 m). For the day, 20.4 ft (6.22 m) was recovered from 30 ft (9.14 m) drilled (recovery = 68%).
There was no drilling on Sunday, 21 October. Drilling resumed on 22 October. Approximately 50% of the first run (740–748 ft; 225.55–227.99 m) was recovered. Recovery improved to 84% on the next run (748–753.5 ft; 227.99–299.67 m); this core cut faster than the previous run. Recovery between 753.5 and 760 ft (299.56 and 231.65 m) was 5.15 ft (1.57 m; recovery = 79%); the last 0.5 ft (0.15 m) was very hard. Recovery from 760 to 765 ft (231.65 to 233.17 m) was perfect. The last 0.7 ft (0.21 m) was much harder, resulting in a new shoe being fitted for the next run. The day concluded with a 10-ft (3.05 m) run from 765 to 775 ft (233.17 to 236.22 m) and 75% recovery (7.5 ft; 2.29 m). For the day, 26.35 ft (8.03 m) of core was recovered from 35 ft (10.67 m) drilled (recovery = 75%).
The final day of coring was 23 October, as we reached our target depth of 800 ft (243.84 m). The first run of the day had no recovery from 775 to 780 ft (236.22 to 237.74 m). When the core barrel was retrieved, we discovered that the core catcher was inside out. The next run (780–785 ft; 237.74–239.27 m) recovered 5.1 ft (1.55 m) of core, (recovery = 102%). Run 105 (785–795 ft; 239.27–242.32 m) recovered 7.7 ft (2.35 m). Another 10-ft (3.05 m) run (795–805 ft; 242.32–246.36 m) was attempted as penetration was easy, but only 4.5 ft (1.37 m) was recovered. The next 5-ft (1.52 m) section was drilled from 805 to 810 ft (245.36 to 246.89 m), with 5.2 ft (1.58 m) recovered. The run was stopped at 5 ft (1.52 m) to switch back to a hard rock shoe for the next run. The final core run (810–820 ft; 246.89–249.94 m) recovered 4 ft (1.22 m) of core. Drilling was easy, and basement saprolite or rock was never encountered.
At Fort Mott, we recovered 638.85 ft (194.7 m) from a total hole of 820 ft (249.9 m); mean recovery was 78% for the 820 ft (249.9 m) cored. Lithologies were described on site and subsequently at the Rutgers core facility; these descriptions form the basis for the preliminary lithologic descriptions. Samples were obtained at ~5-ft (1.52 m) intervals for biostratigraphic and coarse-fraction lithologic studies. Cores were cut into 2-ft (0.61 m) sections, labeled at top and bottom of each section, placed into split PVC pipe (3-in [7.6 cm] diameter), wrapped in plastic sheeting, and stored in 2-ft (0.61 m) wax boxes. A total of 119 core boxes were moved to permanent storage at the Rutgers University core library for further study.