Holocene Core Logs and Site Methods for Modern Reef and 

Head-Coral Cores: Dry Tortugas National Park, Florida 

By Todd D. Hickey, Christopher D. Reich, Kristine L. Delong, Richard Z. Poore, and John C. Brock 

Open-File Report 2012–1095

U.S. Department of the Interior 

U.S. Geological Survey 
ii

U.S. Department of the Interior 

Ken Salazar, Secretary 

U.S. Geological Survey 

Suzette M. Kimball, Acting Director 

U.S. Geological Survey, Reston, Virginia 2013 

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Suggested citation: 

Hickey, T.D., Reich, C.D., Delong, K.L., Poore, R.Z., and Brock, J.C., 2013, Holocene core logs and site methods for 

modern reef and head-coral cores – Dry Tortugas National Park, Florida: U.S. Geological Survey Open-File Report 

2012–1095, 27 p. 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

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. 
iii

Contents 

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

Methods ......................................................................................................................................................................... 2

Coring ........................................................................................................................................................................ 2

Core-site Elevation Survey ......................................................................................................................................... 5

Results and Summary ................................................................................................................................................... 6

Coral-core Description ............................................................................................................................................... 6

Wireline Core Description .......................................................................................................................................... 6

Acknowledgments ......................................................................................................................................................... 7

References Cited ........................................................................................................................................................... 8

Appendix 1. Photographs of cored corals, Dry Tortugas National Park, Florida ............................................................ 9

Appendix 2. Lithologic logs and core photographs, Dry Tortugas National Park, Florida .............................................19

Figures 

1. Landsat image with wireline and coral coring locations. ........................................................................................ 2

2. Underwater photograph of tripod and wireline coring system. ................................................................................ 4

3. Diver operating the hand-held drill while coring a Montastraea faveolata coral at site C2. ..................................... 5

Tables 

1. Holocene core information from Dry Tortugas National Park, Florida. .................................................................... 3

2. Coral core information from Dry Tortugas National Park, Florida. .......................................................................... 7
iv

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)

mile, nautical (nmi) 1.852 kilometer (km)

Area

acre 0.4047 hectare (ha)

acre 0.004047 square kilometer (km2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: 

°F=(1.8×°C)+32 

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: 

°C=(°F-32)/1.8 

Horizontal coordinate information is referenced to North American Datum of 1983 (NAVD 83). 
1

Holocene Core Logs and Site Methods for Modern Reef 

and Head-Coral Cores: Dry Tortugas National Park, Florida 

By Todd D. Hickey, Christopher D. Reich, Kristine L. Delong, Richard Z. Poore, and John C. Brock 

Introduction 

The Dry Tortugas are a series of islands, banks, and channels on a carbonate platform off the 

west end of the Florida Keys. Antecedent topography of the Dry Tortugas reflects carbonate 

accumulations of the last interglacial (marine isotope substage 5e, ~ 125,000 years ago, ka) when sea 

level was ~ 6 to 7 meters (m) higher than present (Schrag and others, 2002). The substage 5e surface 

was subsequently lithified and modified during subaerial exposure associated with lower sea level from 

~ 120 ka to 8 ka. The lithified late Pleistocene carbonates are known as the Key Largo Limestone, a 

coral reef (Hoffmeister and Multer, 1964; Multer and others, 2002), and the Miami Limestone, a tidalbar oolite (Sanford, 1909; Hoffmeister, 1974). The Holocene and modern sediments and reefs of the Dry 

Tortugas then accreted during the rise of sea level associated with the end of the last glacial and the start 

of the current interglacial (marine isotope Stage 1). 

With the exception of a half dozen or so islands, the Dry Tortugas region has been submerged 

for approximately 8,000 years, allowing conditions suitable for coral reef formation once again. The 

Holocene reef accumulation varies in thickness due to the antecedent topography. The reefs are 

composed of massive head corals such as species of Montastraea, Siderastrea, and Diploria (Swart and 

others, 1996; Cohen and McConnaughey, 2003) and rest atop the Pleistocene Key Largo Limestone 

high (Shinn and others, 1977). The coral reefs within the Dry Tortugas represent a windward reef 

margin relative to dominant wind and wave energies (Hine and Mullins, 1983; Mallinson and others,

1997; Mallinson and others, 2003). 
2

Figure 1. Landsat image with wireline and coral coring locations. Inset shows Dry Tortugas National Park study 

site in Florida. 

Dry Tortugas National Park, established in 1992, occupies an area of approximately 259 square 

kilometers (km2) and is located 110 kilometers (km) west of Key West, Fla. The isolation and relatively 

low anthropogenic impacts make the Dry Tortugas an ideal area from which to collect Holocene and 

modern coral cores to be used as a proxy for multidecadal paleoclimate reconstructions. This report 

summarizes the 2008 Dry Tortugas core-collection project and provides information on the methods 

used. 

Methods 

Coring 

Northkey Harbor and East Key were core drilled with the U.S. Geological Survey (USGS) 

portable hydraulic drill to recover lithologic samples spanning the Holocene back into the late 

Pleistocene. Reich and others (2009) provide a complete description of the coring method. Three 

Holocene cores were recovered one from East Key and two from Northkey Harbor (fig. 1, table 1). The 

hydraulic drill was powered by an 18-horsepower (hp) Briggs and Stratton engine. Another 18-hp 

Briggs and Stratton engine was used to hydraulically power a water pump that forced water down the 
3

annulus of the drill stem to lubricate and clean the predominantly carbonate cuttings from the drill-stem 

annulus. The core barrel was a Longyear NQ2 wireline system (fig. 2). 

Table 1. Holocene core information from Dry Tortugas National Park, Florida. 

Date Site Reef Latitude Longitude Water Depth Core Length

Collected Name Name (°N) (°W) (meters) (meters)

8/10/08

EK 

shallow East Key 24.65372 -82.79980 5.3 18.3

8/11/08

NKH 

shallow Northkey Harbor 24.70702 -82.84075 3.9 12.2

8/12/08

NKH 

deep Northkey Harbor 24.71143 -82.83265 6.7 10.7

This system retrieved a 2-inch (in.)-diameter rock core and left a 3-in. open hole when the 

drilling was complete. Each piece of drill pipe was 5 feet (ft) long. Therefore, at each 5-ft depth interval, 

the drilling stopped and the inner barrel was retrieved. The drill head was removed, and the overshot (an 

inner barrel retrieval device) attached with line was sent down inside the drill string to engage and lock 

on the inner barrel. The inner barrel assembly consisted of two stainless-steel split barrels that were held 

together by a core catcher on the bottom end and a device referred to as the spearhead, which forms the 

contact at the upper end. Next, the overshot was connected to the spearhead, and the inner barrel was 

raised out of the drill stem. To keep the operation running smoothly, two inner barrels were used so the 

one removed could be replaced right away. Once the overshot and the full inner barrel were removed 

from inside the drill stem, the second inner barrel was immediately attached to the overshot and placed 

within the drill stem. The empty inner barrel was then lowered to the base of the drill stem, and a device 

called the messenger was sent down the line to disengage the overshot from the spearhead. After pulling 

the overshot out of the drill stem, another 5-ft section of drill pipe was added, and the drill head was 

screwed back onto the drill string. This process was repeated until the desired depth of penetration was 

acquired, which, in this case, was indicated by recovery of the Pleistocene Key Largo Limestone at ~ 35 

ft below the core top at the ground surface. 
4

Figure 2. Underwater photograph of tripod and wireline coring system. 

Coral coring methods were less labor intensive. The drill head was a DL07652 Stanley hydraulic 

drill with a 4-in.-diameter core barrel 24 in. in length attached to the drill (fig. 3). A small hole was 

made in the coral surface with a 1⁄4-in. starting bit to prevent the 4-in. drill bit from “walking” across the 

top of the head coral. To collect full coral cores, extension pieces were added after the coral core was 

recovered from the diamond-studded core barrel. This process was repeated until the base of the coral 

was penetrated. 
5

Figure 3. Diver operating the hand-held drill while coring a Montastraea faveolata coral at site C2. 

Core-site Elevation Survey 

Proper elevation control for each Holocene core was necessary for correlating the recovered 

cores. Elevations were acquired using a kinematic global positioning system (GPS) system at the 

wireline coring sites. Ashtech high-precision, dual-frequency GPS receivers coupled with Thales choke-
6

ring antennas were used for this survey. Seco GPS poles were used to mount the antenna to the drilling 

tripod and were leveled using a hand level. A base station was set up on top of the Civil War-era Fort 

Jefferson over a previously established benchmark. Minimal time (30 minutes) was needed to obtain the 

core-site elevation (sessions) due to the < 15-km distance between coring and base-station locations. 

Sessions were processed using the NovAtel GrafNet program. 

Results and Summary 

Coral-core Description 

 Three different coral genera were selected for coring: Montastraea, Siderastrea, and Diploria. 

Coral cores were recovered near Middle Key and on Pulaski Reef (fig. 1). Photographs of the cored 

heads are presented in appendix 1. Nine coral cores were recovered (table 2). 

Wireline Core Description 

One objective of this study was to recover complete Holocene cores in the Dry Tortugas to 

facilitate and expand paleoclimate studies within the USGS. Previous USGS drilling expeditions in the 

Dry Tortugas (1976, 1997, and 2004) provided valuable information about the depth of penetration for 

complete recovery of the Holocene section. Three long cores were attempted in this study with varying 

degrees of success. Core logs were generated using LogPlot99 and Adobe Illustrator software. The logs 

(accompanied with Holocene and Pleistocene core photographs) are shown in appendix 2. The core logs 

include depth of recovery, sedimentary structure, lithologic description, core-recovery percentages, 

location coordinates, site elevation, and other pertinent observations. 
7

Table 2. Coral core information from Dry Tortugas National Park, Florida. 

Date Site Photo Reef Coral Latitude Longitude

Water 

Depth Core Length

Collected Name ID Name Species (N°) (W°) (meters) (centimeters)

8/6/08 08MK-A1 A1

Middle 

Key

Diploria

strigosa 24.64530 -82.83205 3.4 23

8/6/08 08PS-A1 A2 Pulaski

Siderastrea

siderea 24.69883 -82.79745 4.3 113

8/6/08 08PS-A2 A3 Pulaski

Siderastrea

siderea 24.69883 -82.79745 4.3 83

8/7/08 08PS-B1 B1 Pulaski

Siderastrea

siderea 24.69887 -82.79810 3.4 46

8/7/08 08PS-C1 B2 Pulaski

Diploria

strigosa 24.69887 -82.79810 3.4 60

8/7/08 08PS-B3 B3 Pulaski

Montastraea 

faveolata 24.69857 -82.79862 3.4 142

8/7/08 08PS-B4 B4 Pulaski

Montastraea 

faveolata 24.69847 -82.79835 3.4 110

8/8/08 08PS-F1 C1 Pulaski

Siderastrea

siderea 24.69495 -82.79465 3.7 64

8/8/08 08PS-C2 C2 Pulaski

Montastraea 

faveolata 24.69460 -82.79490 3.7 156

 Previous work has indicated the Holocene accretion is approximately 15 m thick regionally 

(Hoffmeister and Multer, 1964; Multer and others, 2002). This study is in agreement. Evidence is 

observed in the shallow Northkey Harbor site where a subaerial unconformity is found 35 ft below the 

seafloor. The three Holocene cores provided similarities and differences with respect to lithologies 

down core. Carbonate muds were prevalent near East Key and were reduced at the shallow Northkey 

Harbor site. All three sites included boulder corals as the main reef builders throughout the region, with 

little or no presence of branching or finger corals. The cores show that reefs of the Dry Tortugas have 

geologically evolved through predominantly boulder/massive head-coral accretion and not as much due 

to branching or finger corals. Other lithologic matrices observed include mudstones, packstones, and 

grainstones, but are few and far between in relation to the head-coral assemblages. Some of the common 

biogenic participants observed in all the cores include coralline algae, calcareous worm tubes, 

bioeroders, and bivalves. 

Acknowledgments 

We thank P.J. Walker of Everglades National Park for permission and access to Dry Tortugas 

National Park. Captains Clay Douglass, Janie Douglass, and John Spade of Dry Tortugas National Park 

provided logistical support above and beyond that necessary to help make the coring a success, and for 

that, we are most appreciative. Thanks are extended to Jordan Sanford and B.J. Reynolds of the USGS 

and Michèle LaVigne of Rutgers University for assistance in the collection of the cores. The USGS 

Coastal and Marine Program funded the project. 
8

References Cited 

Cohen A, and McConnaughey, T.A., 2003, Geochemical perspectives on coral mineralization: Reviews 

in Mineralogical and Geochemistry, v. 54, p. 151-187. 

Dunham, R.J., 1962, Classification of carbonate rocks according to depositional texture, in Ham, W.E., 

ed., Classification of carbonate rocks: American Association of Petroleum Geologists Memoir, p. 

108-121. 

Hine, A.C., and Mullins, H.T., 1983, Modern carbonate shelf-slope breaks, in Stanley, D.J., and Moore, 

G.T., eds., The shelfbreak- Critical interface on continental margins: Society of Economic 

Paleotologists and Mineralogists Special Publication 33, p. 169-188. 

Hoffmeister, J.E., 1974, Land from the sea: The Geologic story of south Florida: University of Miami 

Press, 143 p. 

Hoffmeister, J.E., and Multer, H.G., 1964, Growth rate estimates of a Pleistocene reef of Florida: 

Geologic Society of American Bulletin, v. 75, no. 4, p. 353-357. 

Mallinson, D., Hine, A.C., Hallock, P., Locker, S., Shinn, E.A., Naar, D., Donahue, B., and Weaver, D., 

2003, Development of small carbonate banks on the south Florida platform margin- Response to sea 

level and climate change: Marine Geology, v. 199, p. 45-63. 

Mallinson, D., Locker, S., Hafen, M., Naar, D., Hine, A., Lavoie, D., and Schock, S., 1997, A highresolution geological and geophysical investigation of the Dry Tortugas carbonate depositional 

environment: Geo-Marine Letters, v. 17, p. 237-245. 

Multer, H.G., Gischler, E., Lundberg, J., Simmons, K., and Shinn, E.A., 2002, Key Largo Limestone 

revisited: Pleistocene shelf-edge facies, Florida Keys, USA: Facies, v. 46, p. 229–272.

Reich, C.D., Hickey, T.D., Delong, K.L., Poore, R.Z., and Brock, J.C., 2009, Holocene core logs and 

site statistics for modern patch-reef cores- Biscayne National Park, Florida: U.S. Geological Survey 

Open-File Report 2009-1246, 69 p., available at http://pubs.usgs.gov/of/2009/1246/. 

Sanford, S., 1909, The topography and geology of southern Florida: Florida Geologic Survey annual 

report, Florida Geological Survey, Tallahassee, Fla, p. 175-231. 

Schrag, D.P., Adkins, J.F., McIntyre, K., Alexander, J.L., Hodell, D.A., Charles, C.D., and McManus, 

J., 2002, The oxygen isotope of seawater during the last glacial maximum: Quaternary Science 

Reviews, v. 21, no. 1-3, p. 331-342. 

Shinn, E.A., 2001, Coral reefs and shoreline dipsticks: American Association of Petroleum Geologists 

Studies in Geology, v. 47, p. 251-264. 

Shinn, E.A., Hudson, J.H., Halley, R.B., and Lidz, B.H., 1977, Topographic control and accumulation 

rate of some Holocene coral reefs, South Florida and Dry Tortugas: Proceedings, Third International 

Coral Reef Symposium, v. 2, Geology, Miami, Fla., p. 1-7. 

Swart, P.K., Dodge, R.E., and Hudson, H.J., 1996, A 240-year stable oxygen and carbon isotope record 

in a coral from south Florida—Implications for the prediction of precipitation in southern Florida: 

PALAIOS, v. 11, no. 4, p. 362-375. 
9

Appendix 1. Photographs of cored corals, Dry Tortugas National Park, Florida 
10

Site 08MK-A1, Diploria strigosa. 
11

Site 08PS-A1, Siderastrea siderea. 
12

Site 08PS-A2, Siderastrea siderea. 
13

Site 08PS-B1, Siderastrea siderea. 
14

Site 08PS-C1, Diploria strigosa. 
15

Site 08PS-B3, Montastraea faveolata. 
16

Site 08PS-B4, Montastraea faveolata. 
17

Site 08PS-F1, Siderastrea siderea.
18

Site 08PS-C2, Montastraea faveolata. 
19

Appendix 2. Lithologic logs and core photographs, Dry Tortugas National Park, Florida 
20

Core log descriptions 
21

Core log for East Key 
22

East Key core. 
23

Core log for Northkey Harbor Shallow. 
24

Northkey Harbor Shallow core, box 1 of 2. 
25

Northkey Harbor Shallow core, box 2 of 2. 
26

Core log for Northkey Harbor Deep. 
27

Northkey Harbor Deep core.