Site report for USGS test holes drilled at Cape Charles, 

Northampton County, Virginia, in 2004 

By Gregory S. Gohn, Ward E. Sanford, David S. Powars, J. Wright Horton, Jr., Lucy E. Edwards, 

Roger H. Morin, and Jean M. Self-Trail 

Open-File Report 2007–1094 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 

2007 

For product and ordering information: 

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS 

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its natural and living resources, natural hazards, and the environment: 

World Wide Web: http://www.usgs.gov 

Telephone: 1-888-ASK-USGS 

Suggested citation: 

Gohn, G.S., Sanford, W.E., Powars, D.S., Horton, J.W., Jr., Edwards, L.E., Morin, R.H., 

and Self-Trail, J.M., 2007, Site report for USGS test holes drilled at Cape Charles, 

Northampton County, Virginia, in 2004: U.S. Geological Survey Open-File Report 2007-1094 

22 p.

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endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report. 

ii
Contents 

Contents ..............................................................................................................................................................................iii

Figures .................................................................................................................................................................................iv

Tables ..................................................................................................................................................................................iv

Conversion Factors ...........................................................................................................................................................iv

Abstract................................................................................................................................................................................1

Introduction .........................................................................................................................................................................1

Background .........................................................................................................................................................................2

Drill Site ................................................................................................................................................................................3

Drilling Operations..............................................................................................................................................................4

Drilling Equipment...........................................................................................................................................................4

Drilling and Logging History..........................................................................................................................................4

Drilling Rate .....................................................................................................................................................................6

Coring Runs......................................................................................................................................................................7

Geophysical Logging......................................................................................................................................................8

Well Installation ............................................................................................................................................................11

Preliminary Site Geology.................................................................................................................................................13

Crystalline-clast Breccia and Cataclastic Gneiss ..................................................................................................14

Sediment-Clast Breccia...............................................................................................................................................15

Postimpact Sediments .................................................................................................................................................16

Upper Eocene Section – Chickahominy Formation (1,163 ft to 993 ft).............................................................16

Oligocene Section - Delmarva Beds, Drummonds Corner Beds, Old Church Formation (993 to 955 ft) ...17

Lower and Middle Miocene Section – Calvert and Choptank Formations (955 ft to 606 ft) ........................17

Upper Miocene Section – St. Marys and Eastover Formations (606 ft to 168 ft)...........................................18

Pliocene Section – Yorktown and Chowan River Formations (168 ft to 32 ft)................................................18

Pleistocene Section – Nassawadox Formation (32 ft to 5 ft)............................................................................19

Modern Artificial Fill (5 ft to 0 ft).............................................................................................................................19

Acknowledgments............................................................................................................................................................19

References Cited ..............................................................................................................................................................20

Appendix A: Drill-Site Staff............................................................................................................................................22

Drillers.............................................................................................................................................................................22

Site Geologists and Biologists....................................................................................................................................22

Geophysical Loggers....................................................................................................................................................22

iii
Figures 

Figure 1. Regional map showing the location of the Chesapeake Bay impact structure and the USGS-STP 

drill site at Cape Charles (yellow circle).........................................................................................................................2

Figure 2. Topographic map showing the location of the USGS-STP drill site near Cape Charles, Va. ...............3

Figure 3. Photograph of the USGS-STP drill site during drilling operations in May 2004......................................4

Figure 4. Drill penetration rate for the USGS-STP2 test hole......................................................................................7

Figure 5. Composite of geophysical logs obtained in test hole USGS-STP2. See list of Conversion Factors 

(above) to convert SI units to Inch/Pound units. ..........................................................................................................9

Figure 6. Diagram showing water wells 62G-24 (deep well) and 62G-25 (shallow well) in the USGS-STP2 test 

hole......................................................................................................................................................................................13

Figure 7. Generalized geologic column, and gamma-activity and short-normal-resistivity logs, from the 

USGS-STP2 test hole. ......................................................................................................................................................14

Tables

Table 1. Data for coring runs in the USGS-STP2 test hole..........................................................................................8

Table 2. Record of geophysical logging activities in the USGS-STP2 test hole. ....................................................9

Conversion Factors 

Inch/Pound to SI 

Multiply By To obtain

Length 

inch (in.) 2.54 centimeter (cm) 

inch (in.) 25.4 millimeter (mm) 

foot (ft) 0.3048 meter (m) 

mile (mi) 1.609 kilometer (km) 

Volume 

gallon (gal) 3.785 liter (L) 

Flow rate 

gallon per minute (gal/min) 0.06309 liter per second (L/s) 

Pressure 

pound per square inch (lb/in2) 6.895 kilopascal (kPa) 

iv
SI to Inch/Pound 

Multiply By To obtain

Length 

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi) 

meter (m) 1.094 yard (yd) 

Horizontal coordinate information is referenced to the North American Datum of 1988 (NAD 88). 

v
Site report for USGS test holes drilled at Cape 

Charles, Northampton County, Virginia, in 2004 

By Gregory S. Gohn, Ward E. Sanford, David S. Powars, J. Wright Horton, Jr., Lucy E. Edwards, 

Roger H. Morin, and Jean M. Self-Trail 

Abstract

The U.S. Geological Survey drilled two test holes near Cape Charles, Virginia, during May 

and June 2004, as part of an investigation of the buried, late Eocene Chesapeake Bay impact 

structure. The first hole is designated as the USGS-Sustainable Technology Park test hole #1 

(USGS-STP1). This test hole was abandoned at a depth of 300 ft; cuttings samples were collected,

but no cores or geophysical logs were acquired. The second hole is designated as the USGSSustainable Technology Park test hole #2 (USGS-STP2). This test hole was drilled to a depth of 

2,699 ft. Cores were collected between depths of 1,401.7 ft and 1,420.7 ft and between 2,440.0 ft 

and 2,699.0 ft. Cuttings samples were collected from the uncored intervals below 280-ft depth. 

Interim sets of geophysical logs were acquired during the drilling operation, and one final set was 

acquired at the end of drilling. Two wells were installed in the USGS-STP2 test hole. The deep 

well (designated 62G-24) was screened between 2,260 ft and 2,280 ft, and the shallow well 

(designated 62G-25) was screened between 1,360 ft and 1,380 ft. Ground-water salinities 

stabilized at 40 parts per thousand for the deep well and 20 parts per thousand for the shallow well. 

The geologic section encountered in the test holes consists of three main units: (1) Eocene, 

Oligocene, Miocene, Pliocene, and Pleistocene sands and clays are present between land surface 

and a depth of 1,163 ft; (2) sediment-clast breccias of the impact structure are present between 

depths of 1,163 ft and 2,150 ft; and (3) crystalline-clast breccias and cataclastic gneiss of the impact 

structure are present between depths of 2,150 ft and 2,699 ft.

Introduction 

The U.S. Geological Survey (USGS) drilled two scientific test holes at Cape Charles, 

Northampton County, Virginia, during May and June 2004. These test holes are part of a multiagency study of the buried Chesapeake Bay impact structure, which underlies Northampton County 

and surrounding areas. Sanford and others (2004) published a brief summary of the drilling 

operations and results at Cape Charles. This report presents a more detailed operational summary, 

and a preliminary geologic summary, for the two test holes. 

The Cape Charles test holes are designated as the USGS Sustainable Technology Park test 

hole #1 (USGS-STP1) and the USGS Sustainable Technology Park test hole #2 (USGS-STP2). 

USGS-STP1 had to be abandoned at a depth of 300 ft because of a nearsurface sediment washout. 

No cores or geophysical logs were collected from this hole; cuttings were collected from the entire 

300-ft section. USGS-STP2 reached a total depth of 2,699 ft. Cores were collected from two 

intervals in this hole, and four geophysical logging runs were completed; cuttings were collected 

from the uncored intervals below a depth of 280 ft. The two test holes are located about 65 ft apart, 

1
and their geologic sections are considered collectively in this report. This section consists of

postimpact sediments that overlie sediment-clast breccias, crystalline-clast breccias, and cataclastic

gneiss within the impact structure. 

Background 

The Chesapeake Bay impact structure formed about 35 million years ago during the late 

Eocene when a comet fragment or asteroid struck the U.S. Atlantic continental shelf in the area

now occupied by the southern part of Chesapeake Bay and adjacent landmasses in the Virginia 

Coastal Plain. The resulting structure is an approximately circular, 53-mile-diameter crater

centered near the town of Cape Charles, Va. (Fig. 1). The geologic materials within the structure 

now lie buried beneath hundreds of feet of younger Cenozoic marine sediments. Additional 

information about the Chesapeake Bay impact structure is available in numerous published studies, 

including Koeberl and others (1996), Poag (1997), Powars and Bruce (1999), Powars (2000), 

Edwards and others, (2004a), Poag and others (2004), and Horton and others (2005a, b). 

Figure 1. Regional map showing the location of the Chesapeake Bay impact structure and the 

USGS-STP drill site at Cape Charles (yellow circle). 

The Chesapeake Bay impact structure spatially coincides with a long known, but poorly 

explained inland zone of salty ground water. This spatial association strongly suggests a genetic 

association (Powars and Bruce, 1999; McFarland and Bruce, 2005). The presence of the inland 

salt-water zone has practical significance because rapid population and commercial growth in areas 

2
above and near to the salt-water zone requires an ever-increasing supply of fresh water (Emry and 

Miller, 2004). Detailed knowledge of the distribution of the salt-water zone and its formative 

processes are needed to determine whether increased ground-water pumping in adjacent areas will 

lead to migration of the salt water. 

Drill Site 

The USGS-STP test holes are located near the property line between the Cape Charles 

Sustainable Technology Park (STP) and the Bayshore Concrete Products plant, about 0.3 miles 

south of Cape Charles harbor (Fig. 2). The holes are located immediately west of the paved 

parking lot at the Sustainable Technology Park on a narrow grassy strip between the pavement and 

a wooded area to the west (Fig. 3). This location is near the southeastern corner of the Cape 

Charles 7.5-min topographic quadrangle (USGS, 1968). 

Figure 2. Topographic map showing the location of the USGS-STP drill site near Cape Charles, Va. 

The latitude and longitude of the USGS-STP2 test hole are 37°15’33.17” N and 

76°01’04.83” W. Coordinates were obtained using a Magellan ProMark X GPS receiver and were 

differentially post processed. The datum is NAD 88, and the accuracy is submeter (sub-yard). The 

surface elevation at the drill site is 7 ft (±1 ft), as estimated from the 1:24,000-scale topographic 

map of the Cape Charles 7.5-min quadrangle. 

3
Figure 3. Photograph of the USGS-STP drill site during drilling operations in May 2004. 

Drilling Operations 

Drilling Equipment

The USGS-STP test holes were drilled by crews from the USGS Central Region Research 

Drilling Project between May 8 and May 26, 2004. Well installation and development continued 

into early June 2004. The test holes were drilled, and the wells installed, using a Gardner-Denver 

17W hydraulic rotary rig. 

Most of the drilling was conducted using 4.5-inch-diameter drilling rods and variety of wing 

(drag), roller, and claw bits. Coring was conducted using 3.7-inch-diameter coring rods and a tenfoot-long, Christensen H-size core barrel. The nominal core diameter is 2.5 inches. Mud 

viscosities were measured periodically using a Marsh funnel viscometer. Mud temperatures were 

not recorded. 

Drilling and Logging History

The drill rig arrived at Cape Charles on Friday, May 7, 2004, and drilling commenced on 

the morning of May 8th. Drilling was halted at a depth of 18 ft, and 12-inch-diameter steel surface 

casing was installed to that depth by the end of work on May 8th. There was no overnight drilling 

on May 8-9. Drilling continued on the morning of May 9th, and a depth of 300 ft was reached by 

the end of work on that day. There was no overnight drilling on May 9-10. The crew returned to 

the drill site at 6:00 am on May 10th to discover that the surface casing had dropped slightly below 

land surface overnight and that a washout cavern had developed in the sandy surficial sediments. 

As a result, the drill rig was moved about 65 ft to the south. 

4
The 300-ft-deep hole is USGS Sustainable Technology Park test hole #1. No geophysical 

logs or cores were acquired in this hole; however, cuttings were collected at 20-ft intervals from the 

entire 300-ft section. 

The drilling of the second test hole, USGS Sustainable Technology Park test hole #2, started 

at 4:45 pm on May 10th and reached a depth of 60 ft by 5:30 pm. At that time, 56 ft of 12-inchdiameter, schedule 40, PVC casing was placed in the hole. About 220 gal of cement were placed

around the casing between land surface and a depth of about 37 ft. Work at the drill site ended at 

9:00 pm on May 10th; there was no overnight drilling on May 10-11. On the morning of May 11th

, 

the crew repaired the pump on the shaker trailer and installed the side-discharge tube and cuttings 

trough to facilitate sample collection. Round-the-clock drilling started at 1:55 pm using a 10 and 

5/8-inch-diameter roller bit. Drilling continued to a depth of 394 ft at 11:12 pm on May 11th

without significant mechanical problems or weather delays. The collection of cuttings samples 

began at a depth of 280 ft; no cuttings were collected above this depth in USGS-STP2. 

The drill crew began to pull the rods from the hole at 11:14 pm on May 11th in preparation 

for geophysical logging and casing installation. The first logging probe (caliper) was lowered into

the hole at 12:30 am on May 12th, and the borehole size was measured from about 390-ft depth to

the land surface. The caliper log indicated that the borehole necked down to a diameter of about 2 

inches at depths of 126 ft to 130 ft. The multifunction and sonic-velocity probes could not pass this 

constriction, and data were collected with those tools only above 125-ft depth. At 4:45 am, the 

drillers started reaming the borehole to allow additional geophysical logging to the total depth of

the hole. Reaming was completed at 9:00 am, and the crew began to pull the rods from the hole at

that time. Geophysical logging resumed at 9:55 am, and the full length of the open borehole was 

logged with the caliper, multifunction, sonic-velocity, neutron-porosity, and gamma-gamma 

density tools. 

The drill crew began placing 8-inch (inside diameter) steel casing into the borehole at 4:45 

pm. The casing reached a depth of 394 ft at 8:25 pm, and cementing of the casing began at the 

time. By 10:30 pm on May 12th, 442 gal of cement had been placed in and around the steel casing. 

Drilling was suspended until 3:15 pm on May 13th to allow the cement to harden. At that time, the 

crew began replacing the drill rods fitted with a 7 and 7/8-inch-diameter wing bit into the hole to 

drill out the cement plug. 

Normal drilling with the wing bit resumed at 5:30 pm on May 13th at the previously reached 

depth of 394 ft. Drilling proceeded only to a depth of 400 ft and was then halted at 6:00 pm to 

await the arrival of a shipment of drilling mud additives. Drilling resumed at 7:59 pm, and a depth

of 500 ft was reached at about midnight on May 13th. Drilling continued on May 14th and reached a 

depth of 940 ft at 9:35 pm. At that time, the crew began pulling the rods from the borehole in 

preparation for repairing the mast-line cable. The cable was replaced, and drilling resumed at 

12:14 pm on May 15th using a 7 and 7/8-inch-diameter, three-cone roller bit. Drilling continued 

until 8:00 pm on that day when a depth of 1,100 ft was reached. At 8:15 pm, the crew began 

pulling the rods from the borehole in order to change bits. The roller bit was replaced with a 7 and 

7/8-inch-diameter wing bit, and the rods were back to the bottom of the hole by 2:55 am on May 

16th. The borehole was reamed where needed and extensively flushed during the replacement of the 

rods into the hole. 

A depth of 1,340 ft was reached at 7:28 pm on May 16th at which time the crew began 

pulling the rods to change back to the 7 and 7/8-inch-diameter roller bit in the hope of increasing 

the drilling rate. The roller bit was placed back to the previous depth of 1,340 ft at 2:10 am on May 

17th. At that time, the crew emptied the mud system and mixed new drilling mud. Drilling resumed 

at 3:40 am, and a depth of 1,400 ft was reached at 10:30 am. At that time, the drillers began pulling 

the rods from the hole in preparation for geophysical logging and wireline coring. 

5
Geophysical logging operations to 1,400 ft consisted of collecting caliper, density, 

multifunction and sonic-velocity logs and were completed at 9:10 pm on May 17th. Assembly of

the coring equipment began shortly thereafter, and the crew began placing the 3.7-inch-diameter 

coring rods with an H-size sampling system into the test hole at 10:27 pm. Placing the sampling 

system into the hole proved difficult as the coring bit was blocked repeatedly by sediment during its 

descent, and the rod string had to be raised to a shallower depth to re-establish mud flow on each 

occasion. The problem was corrected by removing the inner sample barrel from the outer barrel,

thereby allowing better mud flow through the drill bit. Subsequently the inner barrel was placed 

downhole inside the rods, and it latched into place within the outer barrel without further 

difficulties. Two 10-ft coring runs were then completed between 3:05 pm and 4:42 pm on May 18th

at depths of about 1,400 ft to 1,420 ft (Table 1). 

After the coring runs, the coring rods were removed from the hole, and the drilling rods 

were returned to the borehole with a 6 and 3/4-inch-diameter claw (carbide-tooth) bit attached. The 

rods reached the bottom of the hole at 1,420 ft at 11:50 pm on May 18th, and drilling resumed at 

1:17 am on May 19th. Drilling continued without equipment problems and only minor 

thunderstorm delays until a depth of 2,440 ft was reach at 6:44 pm on May 22nd. During this fourday period, the drill bit reached depths of 1,780 ft at about midnight on May 19th, 2,120 ft at about 

midnight on May 20th, and 2,240 ft at about midnight on May 21st. The decision to switch to 

continuous coring operations was made on May 22nd

. 

Wireline coring began at 9:44 pm on May 23rd. The crew completed twelve coring runs to a 

depth of 2,549 ft before midnight on May 24th. Eleven coring runs were completed on May 25th to 

a depth of 2,659 ft. Four coring runs were completed by 11:37 am on May 26th, thereby bringing 

the hole to its final depth of 2,699 ft. Drilling operations ended at about noon on May 26th. Drilling 

was followed immediately by the final stage of geophysical logging in the open-hole section, from 

the total depth of 2,699 ft to the bottom of casing at 394 ft. Caliper, multifunction, acoustic 

televiewer, sonic-velocity, neutron-porosity, and gamma-gamma density logs were acquired at that 

time. 

Drilling Rate 

The time needed to drill a given depth interval was recorded for most drilling runs in 

USGS-STP2. The recorded times are for 20-ft drilling runs above a depth of 2,440 ft and 10-ft 

coring runs below 2,440 ft. The 20-ft intervals correspond to the collection intervals for cuttings 

samples. Drill penetration rates varied between 0.4 and 1.8 ft/min in the postimpact sediments 

above a depth of 1,163 ft (Fig. 4). Typically slower penetration rates occurred in the sediment-clast 

breccias of the impact structure between depths of 1,163 ft and 2,150 ft, generally in the range of 

0.2 to 1.0 ft/min with faster rates in the sandier sections. Penetration rates in the crystalline-clast 

breccias below 2,150-ft depth were similar to those in the sediment-clast breccias. Coring runs 

below a depth of 2,440 ft had the slowest penetration rates, typically less than 0.3 ft/min. 

6
Figure 4. Drill penetration rate for the USGS-STP2 test hole. 

Coring Runs 

Twenty-nine coring runs were completed in the USGS-STP2 hole (Table 1). Two coring 

runs were conducted within sediment-clast breccias of the impact structure between depths of 

1,401.7 and 1,420.7 ft. Twenty-seven coring runs were conducted in a section of crystalline-clast 

breccia and cataclastic gneiss between depths of 2,440 and 2,699 ft. A total of 278 ft of section was 

drilled with the core-sampling system. 

Core recovery was moderately low (48.8 percent), owing in part to the alternation of hard 

and soft rocks within the breccia-gneiss section. Four coring runs recovered more than 70 percent 

of the drilled section, and five runs recovered less than 30 percent. 

Cuttings samples were collected from the uncored intervals in USGS-STP2 below a depth 

of 280 ft. Individual cuttings samples generally represent 20 ft of section, equivalent to the 20-ft 

lengths of the drilling rods. The depth reference point for all core and cuttings samples was the 

land surface.

7
Table 1. Data for coring runs in the USGS-STP2 test hole.

 [The indicated depths are listed as reported by the lead driller.] 

Core 

Top 

(ft) 

Bottom

(ft) 

Top 

(m) 

Bottom

(m) 

Recovery 

(ft) 

Recovery 

(m) 

Recovery 

(%) Comments

 1 1401.7 1410.7 427.24 429.98 8.6 2.62 95.6% Loss at bottom; short run 

 2 1410.7 1420.7 429.98 433.03 4.9 1.49 49.0% Loss at bottom

 3 2440.0 2450.0 743.71 746.76 4.6 1.40 46.0% Loss at bottom

 4 2450.0 2460.0 746.76 749.81 5.1 1.55 51.0% Loss at bottom

 5 2460.0 2470.0 749.81 752.86 6.3 1.92 63.0% Loss at bottom

 6 2470.0 2480.0 752.86 755.90 3.2 0.98 32.0% Loss at bottom

 7 2480.0 2490.0 755.90 758.95 5.2 1.58 52.0% Loss at bottom

 8 2490.0 2500.0 758.95 762.00 4.2 1.28 42.0% Loss at bottom

 9 2500.0 2510.0 762.00 765.05 3.5 1.07 35.0% Loss at bottom

10 2510.0 2515.0 765.05 766.57 3.1 0.94 62.0% Loss at bottom; short run 

11 2515.0 2522.0 766.57 768.71 3.0 0.91 42.9% Loss at bottom; short run 

12 2522.0 2529.0 768.71 770.84 1.0 0.30 14.3% Loss at bottom; short run 

13 2529.0 2539.0 770.84 773.89 3.4 1.04 34.0% Loss at bottom

14 2539.0 2549.0 773.89 776.94 3.5 1.07 35.0% Loss at bottom

15 2549.0 2559.0 776.94 779.98 0.2 0.06 2.0% Loss at bottom

16 2559.0 2569.0 779.98 783.03 9.0 2.74 90.0% Loss at bottom

17 2569.0 2579.0 783.03 786.08 6.6 2.01 66.0% Loss at bottom

18 2579.0 2589.0 786.08 789.13 5.1 1.55 51.0% Loss at bottom

19 2589.0 2599.0 789.13 792.18 1.9 0.58 19.0% Loss at bottom

20 2599.0 2609.0 792.18 795.22 6.3 1.92 63.0% Loss at bottom

21 2609.0 2619.0 795.22 798.27 2.7 0.82 27.0% Loss at bottom

22 2619.0 2629.0 798.27 801.32 4.3 1.31 43.0% Loss at bottom

23 2629.0 2637.0 801.32 803.76 2.3 0.70 28.8% Loss at bottom; short run 

24 2637.0 2649.0 803.76 807.42 3.9 1.19 32.5% Loss at bottom; long run 

25 2649.0 2659.0 807.42 810.46 5.3 1.62 53.0% Loss at bottom

26 2659.0 2669.0 810.46 813.51 6.7 2.04 67.0% Loss at bottom

27 2669.0 2679.0 813.51 816.56 9.0 2.74 90.0% Loss at bottom

28 2679.0 2689.0 816.56 819.61 9.0 2.74 90.0% Loss at bottom

29 2689.0 2699.0 819.61 822.66 3.8 1.16 38.0% Loss at bottom

Totals: 135.7 41.36 48.8% 

Geophysical Logging

Geophysical logging of the USGS-STP2 test hole was conducted in four stages at depths of 

394 ft, 1,400 ft and 2,699 ft (Table 2). Geophysical tools consisted of the caliper, multifunction, 

full-waveform sonic velocity, neutron porosity, and gamma-gamma density probes. More 

information regarding the principles of operation of these logging tools can be found in Hearst and

others (2000). A composite of the geophysical logs collected and analyzed from test hole USGSSTP2 is shown in Figure 5. The individual logs obtained from the four separate logging runs have 

been spliced together and have undergone a simple smoothing process to reduce high-frequency 

variations and improve visual recognition of trends at the scale of the plots. All log depths are 

referenced to land surface. 

8
Table 2. Record of geophysical logging activities in the USGS-STP2 test hole.

Logging Runs Run 1A Run 1B Run 2 Run 3 

Date May 12, 2004 May 12, 2004 May 17, 2004 May 26-27, 2004 

Start Time 12:30 AM 9:55 AM 10:30 AM 4:30 PM

Nominal top 

logged interval (ft) 0 0 400 1,400 

Nominal base 

logged interval (ft) 125/390 394 1,400 2,699 

Base drilled interval (ft) 394 394 1,400 2,699

Probes 

(depth interval, ft) 

Caliper 

(to 390)

Caliper 

(to 394)

Caliper 

(395-1,400)

Caliper 

(400-2,699)

- - - 

Density

(26-377)

Density

(140-1,400)

Density 

(1,360-2,430)

Multifunction

(to 125)

Multifunction

(to 394)

Multifunction 

(397-1,400)

Multifunction

(1,337-2,687)

- - - 

Porosity 

(26-394) - - - 

Porosity 

(80-2,655)

Sonic 

(to 120)

Sonic 

(180-390)

Sonic 

(404-1,400)

Sonic 

(1,390-2,440)

________________________________________________________________________________ 

Figure 5. Composite of geophysical logs obtained in test hole USGS-STP2. See list of Conversion 

Factors (above) to convert SI units to Inch/Pound units. 

9
An attempt was made during the final logging stage to record an acoustic televiewer log 

across a depth interval where the hole was reasonably intact and its diameter fairly uniform (2,380 

ft to 2,430 ft). This tool provides magnetically oriented images of the borehole wall from which 

fractures, bedding, and other features may be identified and oriented. Regrettably, this run was 

unsuccessful due to the presence of thick mud in the hole that inhibited the transmission of acoustic 

pulses to the wall and back again to the tool transmitter-receiver. In addition, data acquired from 

the gamma-gamma density tool generally were unreliable and of poor quality, primarily because of 

large variations in borehole diameter that could not be adequately compensated by the tool. 

Consequently, acoustic televiewer data and density values are not included in the plots of Figure 5.

The three-arm caliper tool provides an approximate measure of borehole diameter. The 

three arms do not operate independently, and the resulting response is considered to be an average 

estimate of hole diameter. The caliper log in Figure 5 displays substantial enlargements in borehole 

diameter within the postimpact sediments and the sediment-clast breccia that extend well beyond 

bit gauge. This is indicative of a very unstable borehole and mechanically weak geologic materials. 

Conditions improve markedly below 2,150 ft in the more competent breccia-gneiss section, and the 

replacement of the drilling bit with the coring bit near 2,440 ft is recognized as a step reduction in 

diameter at 2,444 ft. 

The multifunction tool is equipped to measure natural gamma activity, electrical resistivity, 

borehole fluid conductivity, and borehole fluid temperature. Borehole fluid conductivity and 

temperature data were not useful under these field conditions because of the significant 

disturbances to the fluid column imposed by numerous episodes of mud circulation required during 

drilling. Therefore, logs of borehole fluid properties are not included in this report. The gammaactivity log is a measure of natural gamma radiation being emitted by the surrounding rocks and 

sediments. Clays tend to accumulate radioisotopes through adsorption and ion-exchange processes, 

and zones of high gamma activity are typically interpreted as being clay rich. Feldspathic 

sandstones, phosphatic limestones, and glauconitic sands also are associated with high gamma 

responses. Two zones that display increased gamma counts in Figure 5 are present in the lower 

part of the postimpact sediments (940 ft to 1,150 ft) and the upper part of the breccia-gneiss section 

(2,150 ft to 2,220 ft). 

Electrical resistivity measurements consisted of short-normal (16-inch) and long normal 

(64-inch) resistivities, also referred to as near and far resistivities, respectively. Saturated 

formation resistivity is primarily a function of porosity, pore-fluid resistivity, and mineralogy. It 

typically correlates positively with grain size and negatively with porosity. A lower resistivity 

corresponds to higher porosity or to smaller grain size because the surface area associated with fine 

particles promotes the transmission of electric current (Biella and others, 1983; Kwader, 1985). In 

addition, resistivity profiles are often effective in identifying freshwater-seawater interfaces. 

Plots of the 16-inch (solid line) and the 64-inch (dashed line) resistivity logs are displayed 

in Figure 5 at a logarithmic scale. The separation between the two plots is attributed to the 

presence of a drilling mud that is more resistive than seawater but less resistive than fresh water. 

The far measurement (64-inch) has a greater volume of investigation beyond the borehole and is 

proportionally less influenced by drilling mud than is the near measurement (16-inch). The logs 

depict a gradual downward transition from freshwater to seawater in the upper 400 ft, with the far 

resistivity being slightly greater than the near one. Below this zone, the far measurement is 

consistently less than the near resistivity due to the salinity of the saturating pore fluid, although the 

difference is very small (logarithmic scale). Slight incremental increases in resistivity are seen at 

both major lithologic contacts (1,163 ft and 2,150 ft). 

The neutron probe used in this study was a single-detector epithermal tool that yields an 

estimate of saturated formation porosity. This tool has been calibrated in specially designed test 

10
pits, and the response of the neutron detector, in counts per second, can be accurately converted to 

quantitative values of total porosity provided the formation is saturated. This estimate of total 

porosity includes both free water and bound water on clay surfaces. The porosity profile presented 

in Figure 5 shows a marked shift at the sediment-breccia contact (1,163 ft) that clearly distinguishes 

between the high-porosity postimpact marine sediments (porosity ~ 60 percent) and the underlying

sediment-clast breccia (porosity ~ 20 percent). The porosity estimates for the postimpact 

sediments, in the range of roughly 50 to 65 percent, are in good agreement with laboratory 

measurements conducted on various core samples from other drillholes (W. E. Sanford, USGS); 

porosities of the sediment-clast breccia are also in general agreement with core-derived data from 

other drill holes (E.R. McFarland, USGS, written communication). 

The porosity and the resistivity logs were combined to arrive at estimates of pore-fluid 

resistivity using Archie’s law (Archie, 1942), after making some general assumptions about 

cementation and grain size and shape. The far resistivity was used in this calculation because it 

was considered to be less affected by drilling-mud invasion into the formation than was the near

resistivity. The resulting plot of resistivity of the saturating pore fluid is shown in Figure 5 at a 

logarithmic scale, and it tends to mimic the 64-inch resistivity log. The pore fluid appears to be

fresh water near the surface (~ 40 ohm-meters), but gradually changes to brackish water (~ 4 ohmmeters) and finally to seawater (~ 0.4 ohm-meter) below 500 ft. 

The full-waveform sonic tool is equipped with a variable frequency transmitter and three 

receivers. Logs were obtained at a frequency of 10 kHz and were later processed by means of a 

semblance technique (Paillet and Cheng, 1991) to arrive at estimates of sonic velocities. Plots of

compressional-wave velocity VP (solid line) and shear-wave velocity VS (dashed line) are presented 

in Figure 5. A log of the compressional-wave velocity was constructed from the full waveforms 

down to 2,440 ft. This profile clearly delineates the contact between the postimpact sediments and 

the underlying sediment-clast breccia at 1,163 ft and indicates that the value of VP in the sediments 

approaches that of water alone (~ 1.55 km/s). Below this contact, the compressional-wave 

velocities gradually increase downward in the sediment-clast breccia. Below 2,150 ft, VP increases 

to almost 5 km/s as the rocks become more indurated and mechanically competent. Because of 

poor sampling conditions (borehole enlargements, mud invasion), it was difficult to transmit 

enough energy into the surrounding rocks to generate a detectable shear wave in all but the hardest 

rocks. Consequently, the plot of VS is limited to only the lowermost breccia-gneiss section, where 

VS is roughly half the velocity of VP. These values fall within a well-constrained lithology band 

presented by Paillet and Cheng (1991). 

Well Installation

Well installation in USGS-STP2 began on May 27th following the geophysical logging and 

lasted about three days. Two wells were completed in this single borehole (Fig. 6). Both wells 

were constructed of 2.5-inch-diameter, schedule-80, flush-jointed PVC with 20-ft stainless-steel, 

wire-wrap screens and 5-ft stainless-steel sumps. The deep well and shallow well were assigned

USGS unique numbers 62G-24 and 62G-25, respectively. The screen of the deep well was 

installed between 2,260 ft and 2,280 ft with the sump extending to 2,285 ft. The screen of the 

shallow well was installed between 1,360 ft and 1,380 ft with the sump extending to 1,385 ft. The 

screen locations were chosen based on the formation lithologies and geophysical logs.

11
The annular spacing around the wells was filled with a combination of pea gravel, bentonite 

pellets, and bentonite grout. The section of the hole beneath the bottom screen, from 2,320 ft to 

2,699 ft, was plugged with abandonment bentonite grout. The section around the deep screen, from 

2,070 ft to 2,320 ft, was filled with pea gravel. A section above the pea gravel from 2,010 ft to 

2,070 ft was then filled using bentonite pellets with minor amounts of pea gravel. The section from 

there up to the shallow screen, from 1,415 ft to 2,010 ft, was filled with a high-solids abandonment 

bentonite grout. A short section below the shallow screen, from 1,400 ft to 1,415 ft, was filled 

using bentonite pellets with minor amounts of pea gravel. The area around the shallow screen, 

from 1,300 ft to 1,400 ft, was filled with pea gravel. Another short section above the gravel, from 

1,275 ft to 1,300 ft, was filled using bentonite pellets with minor amounts of pea gravel. The 

remaining hole down to 1,275 ft was filled with a high-solids abandonment bentonite grout, except 

for the top 10 ft, which was finished with cement. 

The wells were developed using air immediately following their installation. Air was 

injected at high flow rates at about 500 ft below land surface, which brought a combination of air, 

mud, and formation fluid to the land surface. The air development was continued for a time period 

of ten hours before the drilling crew returned to Denver for a break. The crew returned about a 

week later to pack their equipment and drive back to Denver. The drilling mud was made with 

fresh water, which was used as one indicator of the extent to which the wells were developing. The 

deep well produced water at a decent rate such that, after ten hours, salt water was the dominant 

fluid coming out of the hole. The shallow well, however, had a lower yield, such that after ten 

hours the fresh-water-based drilling fluid had not been completely purged from the well. 

Slug tests were performed on the wells on October 29, 2004, before the purging continued. 

At this point in time, the water level in the deep well was 5.83 ft bmp (below the measuring point, 

i.e., the top of the well casing), and the shallow well was shut in with a pressure of 5 psi. The 

artesian head on the shallow well was attributed to the fresh drilling fluid (less dense than the 

formation water) that remained in the well casing. The deep well was drawn down to 28 ft bmp 

after pumping for 15 minutes at a rate of about 1 gpm. The pump was then turned off and the water 

level recovered to 7.8 ft bmp after 45 minutes. The shallow well was drawn down to 31 ft bmp 

after pumping for 15 minutes at a rate of about 1 gpm. The pump was then turned off and the water 

level recovered to 11.6 ft bmp after 7 hours. 

The purging process was continued beginning in May 2005 using a remote system 

consisting of pumps, data loggers, pressure transducers, conductivity meters, on/off switches for the 

pumps, and a solar panel. The wells were purged remotely for over a month until the conductance 

of the discharging fluids stabilized. The wells were then sampled on June 28, 2005. Final salinities 

of the waters stabilized at 40 parts per thousand for the deep well and 20 parts per thousand for the 

shallow well. The water level in the shallow well eventually stabilized below the top of the well 

casing at some time during the summer of 2005. 

12
Figure 6. Diagram showing water wells 62G-24 (deep well) and 62G-25 (shallow well) in the USGSSTP2 test hole. 

Preliminary Site Geology 

The geologic section in the USGS-STP test holes consists of three major units (Sanford and 

others, 2004; Horton and others, 2004, 2005b): (1) a lower impact-structure section of crystallineclast breccia and cataclastic gneiss, (2) an upper impact-structure section of sediment-clast breccia, 

and (3) postimpact sediments (Figs. 5, 7). 

The lower and upper impact-structure sections are present from the base of the test hole at 

2,699-ft depth to 1,163-ft depth, for a total penetrated thickness of 1,536 ft. These sections are 

separated by a contact at 2,150-ft depth. Thus, the section of crystalline-clast breccia and 

cataclastic gneiss is at least 549 ft thick, and the section of sediment-clast breccia is 987 ft thick. 

The postimpact section extends from 1,163 ft depth to the land surface. 

13
Figure 7. Generalized geologic column, and gamma-activity and short-normal-resistivity logs, from 

the USGS-STP2 test hole. 

Crystalline-clast Breccia and Cataclastic Gneiss 

The deepest part of the USGS-STP2 section consists primarily of crystalline-clast breccia 

and cataclastic gneiss. The upper contact of this rock unit is defined at 2,150 ft depth by the 

appearance of abundant crystalline-rock chips in the drill cuttings. This contact also is coincident 

with down-hole increases in resistivity, compressional velocity, and natural gamma activity on the 

borehole geophysical logs (Figs. 5, 7). Drill cuttings below 2,150 ft contain chips of granitic rock, 

gneiss, slaty rock, and minor fine-grained mica schist, in addition to clay and sand from higher 

levels in the test hole. 

Drill cores were obtained from 2,440 ft to the base of the test hole at 2,699 ft depth. This 

cored section consists of polymict crystalline-clast breccia, cataclastic quartzofeldspathic gneiss, 

slate and slaty metasiltstone, and smaller amounts of cataclastic chlorite-rich mafic rock (Horton 

and others, 2005c). Some of the crystalline-clast breccia is suevite (Horton and others, 2004, 

14
2005c), meaning that it contains clasts of impact-melt rock (see Lee and others, 2006), although 

clasts of quartzofeldspathic gneiss and chloritic mafic rock are more abundant. The suevitic 

breccia is crumbly to moderately cohesive. 

 Minerals in the crystalline-clast breccia and cataclastic gneiss include plagioclase (mainly 

albite), quartz, chlorite, minor calcite, and traces of pyrite (Horton and others, 2005c). The rocks 

also contain shocked quartz and other shocked minerals (Horton and others, 2004, 2005c; Jackson 

and others, 2006). Secondary chlorite and albite are attributed to hydrothermal alteration (Horton 

and others, 2004, 2005b; Sanford, 2005). 

Sediment-Clast Breccia 

The central part of the test-hole section is interpreted to consist of sediment-clast breccias 

that are typical of the sediment-clast breccias found throughout the Chesapeake Bay impact 

structure (Powars and Bruce, 1999; Poag and others, 2004; Horton and others, 2005b). The top of 

this breccia in the USGS-STP2 test hole is marked by the first (highest) down-hole appearance of 

abundant loose granules and medium to very coarse sand that consist primarily of quartz, 

glauconite, and feldspar, along with drilling chips that consist of a wide variety of sediments and 

crystalline rocks. This first appearance is in the upper part of the cuttings sample from 1,160 to 

1,170 ft. The naturally heterogeneous composition of the sediment-clast breccia, combined with 

the mixing and caving of cuttings produced by rotary drilling, prevents the identification of all but 

the broadest lithologic trends within this section in USGS-STP2. 

Loose grains in the breccia cuttings consist of quartz, glauconite, and feldspar with minor 

amounts of shell fragments, white mica, and pyrite and trace amounts of microfossils, wood, 

phosphate, and fish teeth. Coherent chips of sediment in the cuttings primarily consist of silty clays 

and clayey silts in a wide variety of colors. Chips of oxidized clayey silts and sands from the 

Cretaceous Potomac Formation are particularly common, whereas soft chips of muddy glauconitic 

sand from the breccia matrix are rare. Caved chips from the postimpact sedimentary section 

encountered higher in the test hole also are common, including cemented quartz-glauconite sand, 

muddy quartz sand, and shelly limestone. 

Chips of crystalline rocks in the breccia cuttings primarily consist of granitic rocks and 

chert. Less common rock types include light-red or light-gray felsite, chloritic gneiss, diabase, 

slate, and finely crystalline or aphanitic mafic rocks. 

Two runs recovered 13.5 ft of core from the interval between depths of 1,401.7 ft to 1,420.7 

ft. The cored material is heterogeneous and contains: (1) glauconite-bearing quartz sand that 

contains mixed-age and impact-damaged microfossils and darkened plant debris, (2) massive

coarse to very coarse sand with granules and pebbles (possible fluidized Cretaceous sand), (3) 

medium to coarse sands that show high angle lamination (possible clasts of Cretaceous sediment), 

(4) sand with clay clasts up to 2 inches (possible fluidized Cretaceous sand or clast), (5) a one-footthick concentration of pebbles up to 1.2 inches, where the pebbles are rounded to angular and 

include quartz, rock fragments, and clasts of red silty clays. Contacts between these lithologies are 

sharp. 

The geophysical logs show general increases in resistivity and compressional velocity, and 

a general decrease in porosity, with increasing depth within the sediment-breccia section (Fig. 5, 7). 

Lithification of the clay cuttings from the sediment-clast breccia also progressively increases with

depth. These trends may indicate postimpact compaction, early postimpact hydrothermal 

alteration, or both. A more abrupt downward increase in compressional velocity and a more abrupt 

downward decrease in porosity near 1,650 ft depth may indicate increases in the number and size of 

sediment clasts that have retained their preimpact densities. Below about 1,650 ft, the log patterns 

15
suggest intervals of relatively uniform lithology that may represent sediments blocks that are tens 

of feet, to perhaps 100 ft, in thickness. 

Regionally within the impact structure, the lower part of the sediment-clast breccia consists 

of blocks and megablocks (tens to hundreds of feet in diameter) of pre-impact sediments within a 

matrix of exotic and (or) locally derived sediments (Powars and Bruce, 1999; Poag and others, 

2004; Gohn and others, 2005). In the outer part of the structure, the sediment blocks are primarily 

autochthonous to parautochthonous, having been disrupted in place by the impact. In the central 

part of the structure, the sediment blocks are allochthonous, having slumped into the central part of 

the impact structure during late-stage gravitational collapse. 

The informally defined Exmore beds (Powars et al., 1992) constitute the upper part of the 

sediment-clast breccia throughout the structure. As seen in other cored test holes, the Exmore beds

consist of abundant pebbles, cobbles, and small boulders of preimpact Cretaceous and lower 

Tertiary sediments and sparse pebbles and cobbles of preimpact crystalline rocks dispersed in an 

unstratified and unsorted matrix of calcareous, muddy, quartz-glauconite sand and granules 

(Powars and Bruce, 1999; Poag and others, 2004; Gohn and others, 2005). These materials are 

interpreted to represent ocean-resurge deposition within the impact structure. 

 The transition from synimpact to postimpact sedimentation is marked by a thin interval of 

laminated, clayey sands and silts in coreholes drilled within the impact structure (Poag and others, 

2004; Powars and others, 2005). A few laminated silt and clay chips found in the cuttings may 

indicate the presence of a similar transition zone in the USGS-STP2. 

Postimpact Sediments

Upper Eocene Section – Chickahominy Formation (1,163 ft to 993 ft) 

Upper Eocene sediments in the USGS-STP2 test hole were sampled only as cuttings from 

depths of about 1,163 ft to 993 ft. The lower contact with the sediment-clast breccia was picked on 

the basis of the first (highest) down-hole appearance of abundant glauconite and lithic fragments in 

the run from 1,180-ft to 1,160-ft depth. There also are sharp down-hole increases in resistivity and 

compressional velocity, and a sharp down-hole decrease in porosity, between depths of 1,165 ft and 

1,162 ft (Figs. 5, 7). 

The upper contact of the upper Eocene sediments with the overlying Oligocene sediments 

was difficult to pick during drilling because the Eocene lithology returned few cuttings and tended

to form “clay boots” (clay adhering to the drill bit and rods), particularly when a roller bit were 

used instead of a wing bit. The upper contact was placed at 993-ft depth by comparison of the 

USGS-STP2 gamma-activity log with the equivalent log from the USGS-Watkins School corehole, 

located in Newport News, Va. (Edwards and others 2004b), and the onsite observation of a sandier 

interval in the middle of the 1,000-ft to 980-ft interval. 

The upper Eocene sediments in the USGS-STP2 hole are approximately 179 ft thick and are 

assigned to the Chickahominy Formation. This unit is known only in the subsurface and only in the 

vicinity of the Chesapeake Bay impact structure (Powars and Bruce, 1999; Poag and others, 2004). 

Chickahominy cuttings from the USGS-STP2 test hole consist of very stiff, very clayey silt that 

contains sparse to abundant foraminifera, local shell fragments, and a trace to 2 percent of 

glauconite in the silt to very fine sand fraction. The sediment color is olive gray (5Y3/2) to grayish 

olive (10Y4/2). Minor variations in the drilling speed likely reflect minor variations in grain size 

(Fig. 4). 

16
Oligocene Section - Delmarva Beds, Drummonds Corner Beds, Old Church Formation (993 to 

955 ft) 

Three Oligocene units are recognized in the subsurface of the Virginia Coastal Plain 

(Edwards and others, 2005; Powars and others, 2005). These are, in ascending order, the informal 

Delmarva beds, the informal Drummonds Corner beds, and the Old Church Formation. The lower 

two units are known only from the subsurface; the Old Church crops out in a thin band in the 

eastern Virginia mainland and also is present in the subsurface. These Oligocene units are 

recognized from 993-ft to 955-ft depth in the USGS-STP2 test hole on the basis of cuttings 

lithologies and comparison of the gamma-activity log with the equivalent log from the Watkins 

School corehole (Edwards and others, 2004b). The contact between the base of the Oligocene 

section (base of Delmarva beds) and the underlying Chickahominy Formation is placed at the base 

of a small gamma spike at 993-ft depth. (Fig. 7) The upper contact of the Oligocene section at 955 

ft is placed at the base of the higher of two closely spaced, prominent gamma spikes (Fig. 7). 

Where dated by microfossils from corehole sections, sediments of the higher prominent gamma 

spike are early Miocene in age. Patterns of gamma spikes similar to the one seen in the USGSSTP2 log are typical of Oligocene sections in other drill holes in southeastern Virginia (Powars and 

Bruce, 1999). In the USGS-STP2 cuttings, a 0.24-inch phosphate pebble was recovered near the 

end of the run from 960 ft to 940 ft. 

Approximate depths for the Oligocene units in the USGS-STP2 hole are: Delmarva beds, 

993 ft to 980 ft; Drummonds Corner beds, 980 ft to 962 ft; and Old Church Formation, 962 ft to 

955 ft. Cuttings from the Delmarva beds and Drummonds Corner beds consist of clayey silt that 

contains less conspicuous foraminifera and more prominent glauconite and (or) phosphate than the 

silts from the underlying Chickahominy. Cuttings from the Old Church Formation consist of

brownish-black to olive-black glauconite-phosphate sand in a clayey silt matrix. Some of the 

recovered cuttings show burrows of sand into lighter colored clayey silt. 

Lower and Middle Miocene Section – Calvert and Choptank Formations (955 ft to 606 ft) 

Lower and middle Miocene sediments are present at depths of about 955 ft to about 606 ft 

in the USGS-STP2 test hole. This 349-ft-thick interval consists primarily of clayey silt. The lower 

contact at 955 ft is placed at the base of a characteristically large gamma-activity spike (Fig. 7) that 

is produced by phosphatic sediments and correlates well with the gamma-activity log from the 

nearby Kiptopeke corehole in Northampton County, Va. (Powars and Bruce, 1999). At Kiptopeke, 

this gamma spike represents the basal beds of the lower Miocene deposits that Powars and Bruce 

(1999) named the Newport News beds of the Calvert Formation. In the USGS-STP2 test hole, 

cuttings from the run at depths of 960 ft to 940 ft show the first down-hole appearance of shelly 

very fine to fine quartz sand with scattered fine to granular phosphate grains (fine pebbles). The 

upper contact is placed at 606-ft depth where an abrupt change in the drilling rate was recorded 

(Fig. 4). 

These shallow-marine deposits are distinctly olive gray (5Y3/2) to olive gray (5Y4/1) to 

grayish olive (10Y4/2). The clayey silt has abundant microfossils (mostly foraminifera and 

diatoms) and sparse, scattered shell fragments. Glauconite (<1% to 5%) is present locally, mica 

(1% to 3%) is present, and very fine to fine quartz sand and very thin slightly sandier intervals are

observable in cuttings. 

Most of the lower and middle Miocene section in the USGS-STP2 test hole is considered to 

be the lower and middle Miocene Calvert Formation (Newport News beds and Fairhaven, Plum 

Point, and Calvert Beach Members); however, approximately the upper 20 ft may represent the 

17
middle Miocene Choptank Formation. A thin Choptank Formation was identified in the updip 

Watkins School core (Edwards and others, 2004b) and correlation of the Watkins School gammaactivity log to the equivalent USGS-STP2 log suggests that the presence of the Choptank in the 

USGS-STP2 hole should be considered. Although Powars and Bruce (1999) did not identify a 

Choptank section in the Kiptopeke corehole, the dinocyst data of de Verteuil and Norris (1996; 

their highest sample assigned to the Calvert Formation) support the presence of the Choptank at 

Kiptopeke. 

Upper Miocene Section – St. Marys and Eastover Formations (606 ft to 168 ft) 

Upper Miocene sediments in the USGS-STP2 test hole were sampled only as cuttings 

between depths of about 606 ft and 168 ft. The lower contact is marked by a dramatic down-hole 

color change from dark greenish gray (5GY5/1 to 5GY4/1) to olive gray (5Y3/2) and an abrupt 

down-hole change to much denser, more brittle clayey silt that drilled significantly more slowly 

than the upper Miocene sediments (Fig. 4). There may be a thin cemented bed at the top of the 

underlying middle Miocene sediments. The lower contact also is marked by the down-hole 

appearance of fine sand with phosphate chips in the lower few feet of the upper Miocene section. 

The upper contact was picked on the basis of similarities between the USGS-STP2 gamma-activity 

log and the gamma-activity log for the Langley corehole (Powars and others, 2005). This contact is 

placed at the base of a high-gamma spike in the lower part of the overlying Pliocene section in the 

USGS-STP2 test hole (Fig. 7). 

The lower 266 ft of the upper Miocene section is assigned to the St. Marys Formation (606 

ft to 340 ft depth). This formation consists, in part, of a basal fine sand that is only a few feet thick. 

The basal sand is overlain by 50 ft of very clayey silt, that is overlain, in turn, by silty clay that

grades upward at about 440-ft depth into a clayey silt. The upper 172 ft of the upper Miocene 

section is assigned to the Eastover Formation (340 ft to 168 ft depth). The Eastover sediments are 

well sorted, variably shelly, silty, very fine to fine sand. 

Pliocene Section – Yorktown and Chowan River Formations (168 ft to 32 ft) 

Sediments from depths of about 168 ft to 32 ft in the USGS-STP2 test hole are assigned to 

the Pliocene on the basis of cuttings descriptions and correlation of the geophysical logs with the 

nearby Kiptopeke corehole (Powars and Bruce, 1999). The lower contact with the underlying 

upper Miocene sediments was placed at 168-ft depth on the basis of comparisons with the 

Kiptopeke gamma-activity and resistivity logs. Cuttings logged at 180 ft to 160 ft included shelly 

(turritellids and Chesapecten), fine to medium quartz sand with bone fragments and phosphate and 

glauconite (up to 15%), as well as silty fine sand with phosphate and glauconite (up to 10%). The 

upper contact with the overlying Pleistocene Nassawadox Formation at a depth of 32 ft is obvious, 

with yellow pebbly sand of the Nassawadox overlying dark-greenish-gray (5GY4/1), finer grained, 

shelly sands of the Pliocene section. 

The Pliocene section is 136 ft thick. The lower 22 ft consists of grayish-green (10G4/2), 

variably shelly, fine to medium sand. The sediments above this basal sand are dark-greenish-gray 

(5GY4/1), clayey, silty, very fine to medium quartz sand with variable amounts of glauconite and 

phosphate (1% to 50 %). Fragmental and perhaps whole mollusks shells appear to be concentrated 

locally into thin beds (about 1-ft-thick), which also contain glauconite and phosphate as coarse 

sand, granules, and pebbles up to 0.6 inches, and which may contain bone chips and sharks teeth. 

Clay and silt cuttings from the Pliocene interval are typically medium dark gray (N4) and have less

shell material, but more common foraminifera and sponge spicules, than the sands. 

18
Following Mixon (1985) and Powars and Bruce (1999), most of the Pliocene section in the 

USGS-STP2 test hole is assigned to the Yorktown Formation. However, correlation with the 

Kiptopeke corehole (Powars and Bruce, 1999) suggests that the upper 28 ft of the USGS-STP2 

Pliocene section may represent the Chowan River Formation, which typically fills paleovalleys or 

overlies ravinements cut into the top of the Yorktown. 

Pleistocene Section – Nassawadox Formation (32 ft to 5 ft) 

Cuttings recovered from the interval between depths of 32 ft and 5 ft in the USGS-STP test 

holes consist of poorly sorted, yellow to tan, fine to coarse sand with organic fragments (up to 5%) 

and scattered shell fragments, which grades downward to a very coarse pebbly sand at the unit’s 

base. The sand and pebbles are subrounded to rounded. These lithologies are consistent with 

Mixon’s (1985) description of the marginal-marine, late Pleistocene Butlers Bluff Member of the 

Nassawadox Formation. The Butlers Bluff Member is mapped across the Franktown Plain (flat 

upland surface and adjacent bay-side terrace), which includes the Cape Charles area. The Butlers 

Bluff Member is interpreted as a southward-building complex of spit-platform sands and very 

shallow shoals. 

Modern Artificial Fill (5 ft to 0 ft) 

Poorly sorted, pebbly, fine to coarse sand is present from a depth of about 5 ft to the land 

surface. This material is interpreted as artificial fill that was emplaced during construction of the 

parking lot located adjacent to the drill site. 

Acknowledgments 

Wilma Aleman Gonzalez, James B. Murray, Joseph H. Murray, and Ellen L. Seefelt 

(USGS), and Daniel Larsen (Univ. of Memphis), worked as site geologists (Appendix A). Barbara 

Corland (USGS) assisted with the geophysical logging of the test hole. Mary Voytek and Julie 

Kirshtein (USGS) sampled the core for microbiological studies. Arthur C. Clark supervised the 

USGS drilling crew (Appendix A). We thank the Sustainable Technology Park, and especially Ray 

Otten, for access to their property and for their support during the drilling operations. We also 

thank T. Scott Bruce (Virginia Dept. of Environmental Quality) for sharing his expertise in the 

collection and description of drill cuttings and for acquiring the GPS location data. We thank 

Emily Phillips (USGS) for creating Figure 2. 

19
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de Verteuil, Laurent, and Norris, Geoffrey, 1996, Miocene dinoflagellate stratigraphy and 

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Appendix A: Drill-Site Staff 

Drillers 

USGS, Denver, Colo. Arthur C. Clark (Supervisor), Jeffery D. Eman (Field Foreman), 

Stephen J. Grant (Lead Driller), Robert R. Hunley (Lead Driller), Ronald A. Funkhouser, Michael 

J. Schulz, James O. Stull, and Michael E. Williams. 

Site Geologists and Biologists 

USGS, Reston, Va. Wilma B. Aleman Gonzalez, Lucy E. Edwards, Gregory S. Gohn, J. 

Wright Horton, Jr., Julie Kirshtein, James B. Murray, Joseph H. Murray, David S. Powars, Ward E. 

Sanford, Ellen L. Seefelt, Jean M. Self-Trail, and Mary A. Voytek. 

University of Memphis, Memphis, Tenn. Daniel Larsen 

Geophysical Loggers 

USGS, Denver, Colo. Roger H. Morin and Barbara S. Corland 

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