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New Geotechnnical Drilling Applications for Water-Saturated Soils

idras geotechnical core drilling services

Custom Engineered Scientific Drilling Tools for IDRAS Offer New Geotechnical Drilling Applications

idras geotechnical core drilling servicesWhen developing the custom core drilling equipment for the scientific drilling IDRAS project that enables quality core drilling services in water-saturated soils while leaving the water in situ, it was clear the new technology would also offer benefits in geotechnical drilling applications.  When designing, engineering and fabricating custom equipment, DOSECC engineers always seek to extend the extend its capability beyond the immediate apparent demands of the project to expand study capabilities across other disciples as well.

For example, when designing custom equipment to drill at any remote location, our team does not always have data to verify exactly how hard a rock is anticipated to meet the needs of the research,  so we fabricate the equipment to be able to drill through harder materials and collect core from more consolidated clays than anticipated.    In the case of IDRAS, it will likely be primarily sands or organic sediments, and may not require penetration of anything harder than clay material, yet the DOSECC team must factor in the uncertainty.  In addition, there are other geotechnical drilling applications for this tool that may require the equipment be prepared for harder soils.  As a result, the team has prepared the equipment for much harder soils and rock as part of the IDRAS project.

Accurately Measuring Soil Bearing Capacity with Geotechnical Drilling

When geotechnical engineers are tasked with determining the property of the soils which will support a new structure, the tool originally developed for IDRAS now may allow those researchers to better evaluate the saturation level of the sands they encounter.   With sand material, the soil bearing capacity fluctuates widely depending on the water saturation.  The sand alone may have a bearing capacity that is compromised by 2 or 3 times due to the water saturation.

Currently, geotechnical engineers use what call an SPT or CPT technology and then are left with making inferences as to how water affects the soil bearing-conditions. The geotechnical drilling tool DOSECC has  custom-developed for the IDRAS project may give them more of a direct approach to more readily make accurate assessments.

For more information on geotechnical drilling capabilities, including custom design, engineering, and fabrication of new drilling technologies, please contact us.

 

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IDRAS – International Drilling for the Recovery of Aquifer Sands

idras scientific drilling map

IDRAS Scientific Drilling Project Overview

The International Drilling for the Recovery of Aquifer Sands, or “IDRAS” Project, is a current DOSECC scientific drilling project that requires DOSECC’s unique capabilities of custom engineering and fabrication of a unique drilling tool.  The DOSECC team was tasked with providing geoscience researchers the ability to drill core samples in soft sediments that are saturated with water, with the water left in situ and undisturbed in the sample.  The ultimate goal of this tool is to allow researchers on the IDRAS project to better analyze high arsenic groundwater in Southeast Asia, including India, Vietnam, and Bangledesh, that poses a significant health risks.

idras scientific drilling map

 

Project Update: As of October, 2016, the custom-fabricated drilling equipment has been successfully tested at DOSECC headquarters and will next undergo a second test drill an area of the Great Salt Lake that offers similar soil saturation conditions as those to be tested in Southeast Asia. This proofing test will provide validation that the system will meet the goals on the ground in Asia. Earlier tests allowed the design team to make adjustments to the original tool design to optimize the performance of the tool and change some features before this next round of testing.

Project Details

Elevated groundwater arsenic (As) concentrations impact the health of over 100 million villagers across Pakistan, Nepal, India, Bangladesh, Myanmar, Cambodia, Vietnam, and China who rely on tube wells as their main source of drinking water. This ICDP project, likely to be the first of several devoted to groundwater quality over the next decade, seeks to identify the limited set of parameters that need to be considered in order to make meaningful predictions about the vulnerability of a low-As aquifer in the absence of a full-scale study. This is a crucial question from a public health perspective because selectively tapping low-As aquifers is the most effective way of lowering As exposure.

idras geotechnical core drilling servicesAs a first step towards this goal, proponents from 16 different countries will drill an unconsolidated aquifer in the US that is elevated in As. A new tool under development, the freeze-shoe sampler, will be deployed to recover groundwater in contact with aquifer sands from the same depth by sealing the bottom of a coring tube by in situ freezing. Participants, including 9 from affected Asia countries whose travel to the drill site is supported by the project, will process cores collected at three sites with the freeze-shoe sampler on-site in a mobile geomicrobiology laboratory where a suite of labile sediment and groundwater properties will be measured. In addition to setting the stage for future deployments of the freezeshoe sampler in Asia, the new data will shed light on the release of As to groundwater caused by the reductive dissolution of iron (Fe) oxyhydroxides, a process that is mediated by micro-organisms involved in the mineralization of reactive organic carbon.

The freeze-shoe sampler has been developed under separate funding from the U. S. National Science Foundation.  DES has performed this work under a subcontract from Columbia University.  Freeze-shoe technology is being adapted for use on DES’s suite of soft sediment sampling tools that have been used for many years to collect long cores in modern lakes.  This project is the first field test of these new tools.

A Multi-Disciplinary Project

The DOSECC project is led by Lead Project Engineer and Project Manager Brian Grzybowski. He reports:

“I’ve enjoyed working on the project because it spans a pretty broad range of engineering disciplines.  With the freeze properties, it involves the heat transfer and thermodynamics of freezing the core.  It involves electrical control systems, integration, and thermal science and HVCF applications.  Plus, the system has all equipment on board, so when we send it down-hole it is an independent assembly that functions remotely down there, so it must be designed as a stand-alone system.  We have the added challenge of requiring that it be able to survive the downhole conditions of low temperature and high pressure.  When we send the tool downhole on the wire line, and it acts as a hypodermic needle, so it collects a core sample below what the bit has disturbed.  This allows us to collect a 5’ long core sample undisturbed by the drilling process. We freeze 6” at the tip contained inside of a plastic, polycarbonate liner, then we pull it off the drill coring system and transfer it to the researchers at that point.  They then can employ a system that can freeze the top of the core and allow it to be put it into refrigeration storage vertically to avoid the water changing orientation.”

A number of key DOSECC staff members have collaborated on this effort to bring a wide array of expertise and backgrounds to bear in order to solve a unique geoscientific problem for the first time.  From field and drilling experience and engineering design to fabrication capability and geotechnical experience, our wide range of staff members and associates enables DOSECC to bring a great deal of experience to bear for the development of the product.

 

Learn more about the geotechnical drilling applications of the custom equipment designed for IDRAS.

Read more about this scientific drilling project at ICDP.

Related Publication: International Drilling to Recover Aquifer Sands (IDRAs) and Arsenic Contaminated Groundwater in Asia by Alexander van Geen, 12/6/2011

 

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NJ Shallow Shelf – Expedition 313

New Jersey Shallow Shelf Drilling

The New Jersey-Delaware Coastal Plain Drilling Project: Reconstructing Global Sea Level Changes

Kenneth G. Miller, J.V. Browning, and G.S. Mountain  Rutgers University

P.J. Sugarman New Jersey Geological Survey

P.P. McLaughlin Delaware Geological Survey

M.A. Kominz Western Michigan University

The passive continental margin of the Mid-Atlantic U.S. provides a natural laboratory for evaluating the effects of global sea level, thermoflexural subsidence, and sediment supply on the stratigraphic record of the past 100 million years. Drilling onshore in the New Jersey and Delaware Coastal Plains (onshore Ocean Drilling Program [ODP] Legs 150X and 174AX) has provided 13 continuously cored sites funded by NSF/EAR Continental Dynamics, NSF/OCE Ocean Drilling, the New Jersey Geological Survey, the Delaware Geological Survey, and the U.S. Geological Survey.

Drilling onshore at 12 sites of typically 1500 ft was done by the USGS Eastern Earth Surface Processes Team (EESPT). DOSECC was contracted in 1996 to drill one deep hole (2000 ft) at Bass River that provided the greatest insights due to its penetration of thick, downdip sections. Offshore drilling on the NJ shelf and slope as conducted by the ODP Legs 150 and 174A have shown that many of these sequences are regionally correlative.

Together, over 10,000 ft of core onshore yielded the following scientific accomplishments:

  • Ages and paleoenvironmental changes associated with 14 Miocene, 8 Oligocene, 12 Eocene, 7 Paleocene, and 15-17 Late Cretaceous sequences (Miller et al., 1996, 2004, 2005; Browning et al., 2006);
  • Causal links between the formation of sequence boundaries and the growth of ice sheets between ca. 42 and ca. 10 Ma, and suggestions that such a link exists in the older, supposedly ice-free world (e.g., ca. 71 Ma; Miller et al., 1996, 2003, 2004, 2005);
  • Estimates of the amplitudes of global sea-level changes (Miller et al., 2005, Kominz et al., 2008);
  • Timing of major sea level falls and generation of new sea level curves for the Late Cretaceous to Recent (Miller et al., 2005, Kominz et al., 2008);

 

New Jersey Shallow Shelf Drilling

Distribution of sediments in sequences as a function of time. Sea level curve in blue from Miller et al. (2005). Sea-level curve in brown from Kominz et al., (this volume). Red oxygen isotopic curve from Miller et al. (2005). Depositional phases are described in the text BB-Bethany Beach core, CM-Cape May core, CZ-Cape May Zoo core, OV-Ocean View core, AC-Atlantic city core, IB-Island Beach core, AN-Ancora core, SG-Sea Girt core, MV-Millville core, BR-Bass River core, FM-Fort Mott core. NHIS-Northern Hemisphere Ice Sheets.

New Jersey Shallow Shelf Drilling1

Bass River borehole K/T boundary core showing spherule layer separating uppermost Maastrichtian and lowermost Paleocene and microfossil biostratigraphy. Note burrows in the Maastrichtian and clay clasts in the lower 6 cm of the Paleocene (from Schultz and D’Hondt, 1996).

  • Evaluation of links among sequence stratigraphic architecture, global sea-level variations, and margin evolution (Miller et al., 1996, 2004, 2005; Browning et al., 2006); and
  • Constraints on the causes of major global events in Earth history, including the middle Eocene-earliest Oligocene global cooling (Miller et al., 2008), the late Paleocene thermal maximum (Cramer et al., 1999), the K/T boundary (Olsson et al., 1997, 2002), early and late Maastrichtian events (Olsson et al., 2002), and the Cenomanian/Turonian carbon extraction event (Sugarman et al., 1999).

DOSECC’s involvement in coastal plain drilling proved critical because the Bass River corehole provided the best representation of these global events and because DOSECC will be spearheading efforts on IODP Expedition 313 to drill the shallow NJ shelf.

References:

Browning, J.V., Miller, K.G., McLaughlin, P.P., Kominz, M.A., Sugarman, P.J., Monteverde, D., Feigenson, M.D., and Hernàndez, J.C., 2006, Quantification of the effects of eustasy, subsidence, and sediment supply on Miocene sequences, Mid-Atlantic margin of the United States: Geological Society of America Bulletin, v. 118, p. 567-588.

Cramer, B.S., Aubry, M.-P., Miller, K.G., Olsson, R.K., Wright, J.D., and Kent, D.V., 1999, An exceptional chronologic, isotopic, and clay mineralogic record of the latest Paleocene thermal maximum, Bass River, NJ, ODP 174AX: Geological Society of France, Bulletin, v. 170, p. 883-897.

Kominz, M.A., Miller, K.G., and Browning, J.V., 1998, Long-term and short-term global Cenozoic sea-level estimates: Geology, v. 26, p. 311-314.

Kominz, M.A., Browning, J.V., Miller, K.G., Sugarman, P.J., Misintseva, S., and Scotese, C.R., 2008, Late Cretaceous to Miocene sea-level estimates from the New Jersey and Delaware coastal plain coreholes: an error analysis: Basin Research, v. 20, p. 211-226.

Miller, K.G., Mountain, G.S., the Leg 150 Shipboard Party, and Members of the New Jersey Coastal Plain Drilling Project, 1996, Drilling and dating New Jersey Oligocene-Miocene sequences: Ice volume, global sea level, and Exxon records: Science, v. 271, p. 1092-1094.

Miller, K.G., Browning, J.V., Pekar, S.F., and Sugarman, P.J., 1997, Cenozoic evolution of the New Jersey Coastal Plain: Changes in sea level, tectonics, and sediment supply, in Miller, K.G., and Snyder, S.W. eds., Proceedings of the Ocean Drilling Program, Scientific results, Volume 150X: College Station, Texas, Ocean Drilling Program, p. 361-373.

Miller, K.G., Browning, J.V., Sugarman, P.J., McLaughlin, P.P., Kominz, M.A., Olsson, R.K., Wright, J.D., Cramer, B.S., Pekar, S.F., Van Sickel, W., 2003, 174AX leg summary: Sequences, sea level, tectonics, and aquifer resources: Coastal plain drilling, in Miller, K.G., Sugarman, P.J., Browning, J.V., et al., eds., Proceedings of the Ocean Drilling Program, Initial Reports, 174AX (Supplement): College Station TX (Ocean Drilling Program), 1-38.

Miller, K.G., Sugarman, P.J., Browning, J.V., Kominz, M.A., Olsson, R.K., Feigenson, M.D., Hernàndez, J.C., 2004, Upper Cretaceous sequences and sea-level history, New Jersey coastal plain: Geological Society of America Bulletin, v. 116, p. 368-393.

Miller, K.G., Kominz, M.A., Browning, J.V., Wright, J.D., Mountain, G.S., Katz, M.E., Sugarman, P.J., Cramer, B.S., Christie-Blick, N., and Pekar, S.F., 2005, The Phanerozoic record of global sea-level change: Science, v. 310, p. 1293-1298.

Miller, K.G., Browning, J.V., Aubry, M.-P., Wade, B.S., Katz, M.E., Kulpecz, A.A., Wright, J.D., 2008, Eocene-Oligocene global climate and sea-level changes: St. Stephens Quarry, Alabama: Geological Society of America Bulletin, v. 120, p. 34-53 doi: 10.1130/B26105.1.

Olsson, R.K., and Wise, S.W., Jr., 1987, Upper Paleocene to middle Eocene depositional sequences and hiatuses in the New Jersey Atlantic Margin, in Ross, C., and Haman, D., eds., Timing and depositional history of eustatic sequences: constraints on seismic stratigraphy: Special Publication of the Cushman Foundation for Foraminiferal Research 24, p. 99-112.

Olsson, R.K., Miller, K.G., Browning, J.V., Wright, J.D., and Cramer, B.S., 2002, Sequence stratigraphy and sea-level change across the Cretaceous-Tertiary boundary on the New Jersey passive margin: Geological Society of America Special Paper 356, p. 97-108.

Schultz, P. H., and S. D’Hondt, Cretaceous-Tertiary (Chicxulub) impact angle and its consequences, Geology, 24, 963-967, 1996.

Sugarman, P.J., Miller, K.G., Olsson, R.K., Browning, J.V., Wright, J.D., De Romero, L., White, T.S., Muller, F.L., Uptegrove, J., 1999, The Cenomanian/Turonian carbon burial event, Bass River, NJ: Geochemical, paleoecological, and sea-level changes: Journal of Foraminiferal Research, v. 29, p. 438-452.

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Block Island, Rhode Island Coast

geotechnical-drilling-project-block-island

Geotechnical Drilling Project at Block Island

Geotechnical Drilling Project at Block Island

Source: Fortune.com

This geotechnical drilling project at Block Island off the coast of Rhode Island was done in tandem with the New Jersey Shallow Shelf Geotechnical Drilling Project – Expedition 313.  GZA GeoEnvironmental retained DOSECC geotechnical drilling services to conduct site studies for offshore wind development off of Rhode Island by Deepwater Wind.

Update 2016: This project went on to become the first offshore wind farm in the United States, going online in October, 2016.

North America Finally Has Its First Offshore Wind Farm – Huffington PostNov 3, 2016

Offshore Deepwater Wind Farm To Begin Operation This Month – Manufacturing.netNov 3, 2016

US offshore wind farm debuts, with lessons learned from oil industry – Agri-PulseNov 3, 2016

Rhode Island Gears Up For First Electricity From Block Island Wind … – CleanTechnicaOct 27, 2016

Providence’s Deepwater Wind leads the way in U.S. offshore power – The Providence JournalOct 28, 2016

Why the Country’s First Offshore Wind Farm Is Such a Big Deal – FortuneOct 26, 2016

Why Rhode Island Wind Power Leads the Nation – Efficient Gov (press release) (blog)Oct 26, 2016

AWEA Brings Industry Stakeholders Together To Talk Offshore Wind – North American WindpowerOct 28, 2016

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Plate Boundary Observatory

Plate Boundary Observatory2

The Plate Boundary Observatory Borehole Strainmeter Network

Meghan Miller and Mike Jackson UNAVCO

Plate Boundary Observatory

Drilling PBO borehole B005 near Port Angeles, WA

One of the objectives of NSF funded geodetic component of Earthscope, the Plate Boundary Observatory, is to capture the continuous three-dimensional deformation field across the Western United States plate boundary. To accomplish this, the observatory consists of a suite of instruments which when combined have the ability to measure strain transients with deformation rates of milliseconds out to decades. The observatory, installed by UNAVCO, was completed in October 2008 and consists of over 1100 permanent GPS stations and 74 borehole strainmeter installations. Borehole strainmeters were included because they are designed to record nanostrain-level signals over periods of hours to weeks. They therefore provide an improved ability to record the evolution of strain transients such as those associated with Episodic Tremor and Slip (ETS) events and slow fault slip. DOSECC drilled the first six PBO boreholes, B001, B003, B004, B005, B006, and B007, on the Pacific Northwest Olympic Peninsula. Strainmeters installed in those holes have successfully recorded ETS related strain transients in 2005, 2007 and 2008.

To get the best performance strainmeters must be isolated from thermal and human induced tectonic strains and to record tectonic strain, it is essential they be well coupled to the surrounding rock. Hence, PBO strainmeters were installed in steel-cased boreholes at depths of up to 800 feet. The instruments are installed below the cased section ideally in an unfractured 8-12 foot section of rock. Samples and cutting were collected every 20 feet during drilling to identify the change in lithology and hydrology with depth. When the target depth was reached the boreholes were logged with a full wave sonic tool, an acoustic televiewer, a natural gamma tool and calipers. The DOSECC holes were then cored to determine whether or not the installation zone consisted of competent enough rock to host a strainmeter. Once a strainmeter was installed additional instruments such as a seismometer and in some cases pore pressure sensors were installed it. The holes were then backfilled with cement. In the Pacific Northwest it took about 3 days to complete the coring of a hole, extracting about 30 feet of core each day at a rate of about 1.5 inches per minute. Information on how to access the core from each site is available from UNAVCO. Links to logging information, photos of drilling and the installations plus strain data recorded in each of the DOSECC drilled holes can be found at http://pboweb.unavco.org/strain_data.

Plate Boundary Observatory1

Schematic drawing of PBO borehole B004 at Hoko Falls, WA. The strainmeter is installed at the bottom of the borehole in a bath of grout. When the grout cures the strainmeter is bonded to the surrounding rock. Most PBO boreholes include a seismometer installed above the strainmeter and several include pore pressure sensors. After the equipment is installed the hole is backfilled with cement.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

List of 2007/2008 publications using data from DOSECC drilled holes:

Seismological Society of America 2007 Annual Meeting, Hawaii, April 11-13 2007:

Hodgkinson, K.M., Anderson, G., Jackson, M., Mencin, D., and Johnson, W. Plate boundary Observatory Borehole Strainmeters: Results from the Pacific Northwest, Parkfield, and ANZA.

Roeloffs, E. Monitoring Aseismic Deformation in Northern Cascadia with Plate Boundary Observatory Borehole Strainmeters.

Schmidt, D.A., Observations of the Recent Slow Slip Events in Cascadia Captured by the PBO Strainmeters.

Hasting, M.A., Johnson, W.C., Venator, S.C., Dittman, S.T., Stair, J.M., Tiedeman, A.P., Gottlieb, M.H., Stroeve, A.R., Mencin, D.J., and Jackson, M. The Deployment of a PBO Strainmeter Site: Four Steps to a Better Understanding of the Earth.

Fall AGU 2007, San Francisco, 10–14 December 2007:

Roeloffs, E., McCausland, W. Areal and Shear Strain Coupling of PBO Borehole Strainmeters From Teleseismic Surface Waves.

Hodgkinson, K., Anderson, G., Dittmann, T., Henderson, B., Jackson, M., Johnson, W., Matykiewicz, J., Mencin, D., Wright, J. PBO Borehole Strainmeters: Bridging the Gap Between Seismology and GPS.

McCausland, W., Roeloffs, E.,Detection of Slow Slip Events Along the Cascadia Subduction Zone Using Plate Boundary Observatory Borehole Strainmeters.

Dragert, H., Wang, K. Observing Episodic Slow Slip with PBO Borehole Strainmeters along the Northern Cascadia Margin.

UNAVCO Science Meeting, March 11-13, 2008, Boulder Colorado:

Roeloffs, E, McCausland, W. Calibration of PBO Borehole Strainmeters: Time and Frequency Dependence.

Seismological Society of America 2008 Annual Meeting, 16 – 18 April 2008, Santa Fe, New Mexico:

McCausland, W. Scanning for strain transients along the Cascadia subduction zone using Plate Boundary Observatory borehole strainmeters.

 

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PBO strainmeter borehole drilling, Washington.

 

 

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Chesapeake Bay Impact Structure

Chesapeake Bay Impact Scientific Core Drilling Services

The ICDP-USGS Chesapeake Bay Impact Structure Deep Drilling Project

Gregory S. Gohn  U.S. Geological Survey

Christian Koeberl  University of Vienna

Kenneth G. Miller Rutgers University

Wolf Uwe Reimold Humboldt University

The Chesapeake Bay Impact Structure Deep Drilling Project is a joint venture of the International Continental Scientific Drilling Program (ICDP) and the U.S. Geological Survey (USGS). Project activities began with a planning workshop in 2003 that was attended by 63 scientists from ten countries. In 2004, a funding proposal to ICDP was accepted, and the USGS authorized additional drilling funds. The NASA Science Mission Directorate, ICDP, and USGS provided important supplementary drilling funds in November 2005 that permitted coring of the deeper part of the impact structure. Studies of post-impact sediments were supported by the U.S. National Science Foundation (NSF), Earth Science Division, Continental Dynamics Program.

Chesapeake Bay Impact Drilling

Figure 1 – Chesapeake Bay drilling locations.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The late Eocene Chesapeake Bay impact structure (CBIS) is buried at moderate depths beneath continental-margin sediments in southeastern Virginia, USA. It is among the largest and best preserved of the known impact structures on Earth (Poag, et al., 2004; Horton et al., 2005). The CBIS consists of a ~35 to 40-km diameter, strongly deformed central crater surrounded by a ~25-km-wide, less deformed annular trough. Therefore, the full diameter of the structure is ~85 to 90 km. The Eyreville coreholes were drilled into the deepest part of the central crater, as determined from pre-drilling seismic surveys. This structure is perhaps unique among known impact structures as a locality where impact effects in a shallow-marine, rheologically layered, silicic target can be addressed by core drilling. Also, it is the source of one of only four known tektite strewn fields on Earth, the North American tektite strewn field (Koeberl et al., 1996).

 

Chesapeake Bay Impact Drilling1

Figure 2 – Drilling pad setup, including driller’s trailer (left) and USGS office (right)

Drilling Operations

Site preparations began in July 2005 at Eyreville Farm in Northampton County, Virginia, USA, and deep coring operations were conducted during September-December 2005. DOSECC, Inc., was the general contractor for the deep drilling operations, and Major Drilling America, Inc., was the contract drilling company. Two connected coreholes were drilled (Table 1). Eyreville corehole A was drilled to a depth of 940.9 m. Problems with swelling clays and the repeated loss of mud circulation led to deviation from Eyreville A to a new corehole, Eyreville B, at 737.6 m. Eyreville B was drilled to a final depth of 1,766.3 m. The USGS, Rutgers University, and the Virginia Department of Environmental Quality conducted shallow coring operations in May-June 2006 to a depth of 140.2 m (Table 1). The final result was a continuously cored section from land surface to a total depth of 1,766 m (Gohn et al., 2006).

Geologic Section

Table 1. Cored sections in the Eyreville coreholes
Eyreville A: 125.6 to 591.0 m, PQ core (85.0 mm diameter)
  591.0 to 940.9 m, HQ core (63.5 mm diameter)
Eyreville B: 737.6 to 1,100.9 m, HQ core (63.5 mm diameter)
  1,100.9 to 1,766.3 m, NQ core (47.6 mm diameter)
Eyreville C: 0 to 140.2 m, HQ core (63.5 mm diameter)

 

A total of 1,322 m of crater-fill materials and 444 m of overlying post-impact sediments were recovered in the Eyreville cores (Table 2.) The cored crater section consists of five major lithologic units. The lowest unit consists of 215 m of fractured mica schist, granite pegmatite and coarse granite, and several impact-breccia veins. These rocks could be the autochthonous crater floor, but, more likely, they are parautochthonous basement blocks.

Above these rocks, 158 m of melt-bearing and lithic breccias are considered to be fallback and (or) ground-surge deposits. Above these breccias, a thin interval of quartz sand (22 m) contains an amphibolite block and other lithic clasts of centimeter to decimeter size. This sand occurs below a 275-m-thick granite slab, which is unshocked, and thus must have been transported at least 10 km from the rim of the crater during collapse of the transient cavity. The uppermost and thickest impactite unit consists of 652 m of deformed sediment blocks and overlying sediment-clast breccia. This unit contains clasts of target sediments and crystalline rock, as well as a small component of impact melt, and it is interpreted to represent late-stage collapse of the marine water column and its catastrophic flow back into the crater.

In the post-impact section, the upper Eocene interval consists of silty clays that were deposited in deep water (~200-300 m). There is a major facies shift from the Eocene clays to glauconitic Oligocene sediments that are associated with a >5 myr hiatus that may be attributed to a combination of eustatic fall, tectonic uplift, and sediment starvation. The lower Miocene strata also are highly dissected and thin. Sedimentation rates increase dramatically in conjunction with another facies change to fine-grained biosiliceous middle Miocene sediments. A ~13 to 8 Ma was followed by deposition of shelly, sandy upper Miocene and Pliocene strata. The Pleistocene section consists of two paralic sequences.

 

Table 2. Generalized composite geologic section for the Eyreville cores (Gohn et al., 2008).
0 to 444 m Post-impact sediments
444 to 1,096 m Sediment-clast breccias and sediment blocks
1,096 to 1,371 m Granite slab
1,371 to 1,393 m Lithic blocks in sediment
1,393 to 1,551 m Suevite, melt rock, lithic breccia, cataclasite
1,551 to 1,766 m Schist, pegmatite and coarse granite, impact-breccia veins

 

Research Program and Selected Preliminary Results

The project has wide ranging scientific goals that include studies of impact processes and products, post-impact continental margin tectonics and sedimentation, hydrologic consequences of the impact, and the effects of the impact on the microbial biosphere (Gohn et al., 2008). International science teams established at the planning workshop began the research phase of the project in March 2006 with a sampling party at the USGS National Center in Reston, VA. About thirty project scientists from seven countries attended the sampling party, and over 1,800 samples were marked for future study. These samples were in addition to hundreds of samples collected at the drill site for hydrologic and biologic study. Suevitic and lithic impact breccias were popular intervals for sampling, as well as the thin interval that records the transition from syn-impact to post-impact sedimentation.

The release of detailed research results began in October 2007 with 53 oral and poster presentations in three sessions at the Geological Society of America Annual Meeting. A 43-chapter volume of research results is nearing completion (December 2008) and a 2009 publication date is expected.

Hydrology

Major-ion and stable-isotope chemical analyses for >100 pore-water samples from the Eyreville cores yielded salinities of 40-64 ppt over most of the 1,322-m-thick section of impact deposits. Chloride and 18O values in the post-impact sediments show a steady trend with depth that indicates vertical mixing of fresh and saline waters. The Ca/Mg ratio increases regularly with depth, suggesting water-rock interaction related to increasing temperatures with depth. Overall, the pore-water chemistry suggests that much of the ground water in the central crater has been there since the impact, and that much of the brine was likely present in the target coastal plain sediments before impact.

Microbial biosphere

Microbiological enumeration and other methods, combined with geochemical data, suggest that three microbiological zones are present in the Eyreville cores. The upper zone (0-700 m) is characterized by a logarithmic decline in microbial numbers from the surface through the post-impact section across the transition into the upper layers of the crater-fill sediments. The middle zone (700-1,400 m) corresponds to a region of low hydraulic conductivity that may have been sterilized, in part, by the impact thermal pulse. A lack of culturable organisms and extractable DNA, and microbiological enumerations below the limits of detection, suggest that the middle zone is a biologically impoverished environment. The lowest zone (>1,560 m) coincides with fractured, hydrologically conductive schist, pegmatite, and granite. It has microbial cell numbers that are higher than the middle zone, and heterotrophic organisms have been cultured. These results support the hypothesis that impact events cause disruption to the subsurface biosphere that can result in well-defined zones of microbiological colonization linked to the process of impact cratering.

Read more about this scientific core drilling project at ICDP.

Representative References:

Gohn, G. S., Koeberl, C., Miller, K.G., Reimold, W.U., Cockell, C.S., Horton, J.W., Jr., Sanford, W.E., and Voytek M.A., 2006, Chesapeake Bay impact structure drilled, Eos Transactions, American Geophysical Union, v. 87(35), p. 349, 355.

Gohn, G.S., Koeberl, C., Miller, K.G., Reimold, W.U., Browning, J.V., Cockell, C.S., Horton, J.W., Jr., Kenkmann, T., Kulpecz, A.A., Powars, D.S., Sanford, W.E., and Voytek, M.A., 2008, Deep drilling into the Chesapeake Bay impact structure: Science, v. 320, p. 1740-1745.

Horton, J.W., Jr., Powars, D.S., and Gohn, G.S., 2005, Studies of the Chesapeake Bay impact structure—Introduction and discussion, in Horton, J.W., Jr., Powars, D.S., and Gohn, G.S., Studies of the Chesapeake Bay impact structure—The USGS-NASA Langley corehole, Hampton, Virginia, and related coreholes and geophysical surveys: U.S. Geological Survey Professional Paper 1688, p. A1-A23.

Koeberl, C., Poag, C.W., Reimold, W.U., and Brandt, D., 1996, Impact origin of Chesapeake Bay structure and the source of North American tektites. Science v. 271, p. 1263-1266.

Poag, C.W., Koeberl, C., and Reimold, W.U., 2004, The Chesapeake Bay Crater—Geology and Geophysics of a Late Eocene Submarine Impact Structure: New York, Springer-Verlag, 522 p., CD-ROM.

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Brazos River K/T Boundary

Brazos River, TX Scientific Core Drilling Company Project

Brazos River, Texas: Drilling the K-T and Chicxulub Event Strata

Gerta Keller Princeton University

 

Project Objectives

The main objective of this project was to drill the Cretaceus-Tertiary (K-T) transition in the Brazos River area in order to recover a series of cores that span the late Maastrichtian and early Paleocene, including the K-T boundary horizon, the sandstone complex (event strata) and the Chicxulub impact spherule layer. We reasoned that by recovering these three events in stratigraphic order, it could be determined whether there was a cause-and-effect relationship between the Chicxulub impact on Yucatan and the K-T mass extinction. The Brazos River area was chosen because K-T deposition occurred in a shallow shelf environment, sediments are undisturbed by tectonics and sediment deposition is among the most complete worldwide. The Brazos sequences thus held the potential to solve the current controversy over the age of the Chicxulub impact, the biotic effects and whether this impact caused the mass extinction.

Methods

DOSECC drilled in two localities and recovered three 75 m long cores spanning from the early through the late Maastrichtian. The cores were sampled and analyzed by an international team of scientists (US, UK, Germany, Switzerland, France, Israel, Egypt). Analysis included sedimentology, mineralogy, stable isotoes, PGE and trace element analysis (ICP-MS), biostratigraphy and quantitative faunal and floral analyses (planktic foraminifera, nannofossils, palynomorphs).

Results

The K-T sequences along the Brazos River of Falls County, Texas, provide the most important and critical information regarding the age and biotic effects of the Chicxulub impact outside of Mexico. New investigations based on outcrops and new cores drilled by DOSECC and funded by the National Science Foundation reveal a complex history of three tectonically undisturbed and stratigraphically well-separated events: the Chicxulub impact spherule ejecta layer, a sea-level lowstand event deposit (sandstone), and the K-T mass extinction (Keller, 2007; Keller et al., 2007).

The newly discovered Chicxulub impact spherule layer is the oldest of the three events and marks the time of the impact about 300,000 years before the K-T boundary (base of zone CF1), consistent with similar observations from NE Mexico and the Chicxulub crater core Yaxcopoil-l. Paleontological analysis reveals that the Chicxulub impact caused no species extinctions or any other significant biotic effects (Keller et al., 2008). The subsequent sea level lowstand resulted in deposition of a sandstone complex, which predates the K-T boundary by about 100,000 years.

Reworked Chicxulub impact spherules and clasts with spherules in this sandstone complex were eroded from the original impact spherule layer. The third event is the K-T boundary mass extinction, which in the new cores is 80 cm above the sandstone complex and clearly unrelated to the Chicxulub impact.

These data reveal that the Chicxulub impact and K-T mass extinction are two separate and unrelated events, and that the biotic effects of this impact have been vastly overestimated. The K-T mass extinction was likely caused by massive volcanism in India, which marks the second catastrophe at the end of the Cretaceous.

Project Grants

NSF EAR Drilling was supported by the US National Science Foundation’s Continental Dynamics Program and Sedimentary Geology and Paleobiology Program under NSF-EAR Grants 0207407, 0447171 and 0750664.

Brazos River, TX Drilling

Figure 1 – Gerta Keller and Jerry Baum examine cores from DOSECC drilling along the Brazos River, which recovered an expanded sequence with the K-T boundary 80cm above the sandstone complex with three reworked upward fining impact spherule layers at the base. The original impact spherule layer was discovered 65 cm below.

 

References:

Keller, G., 2007. K-T mass extinction and Chicxulub impact in Texas. J.South Texas Geology, Geol. Soc. Amer., XLVII (9), p. 15-44.

Keller, G. Adatte, T.. Berner, Z Harting, M. Baum, G. Prauss, M. Tantawy, A. A. and D. Stueben., 2007. Chicxulub Impact Predates K-T Boundary: New Evidence from Texas. Earth and Planet. Sci. Letters 255, 339-356.

Keller, G., Abramovich, S., Berner, Z., Adatte, T., 2008. Biotic effects of the Chicxulub impact, K-T catastrophe and sea-level change in Texas. Paleogeogr., Paleoclimatol., Paleoecol., doi:10.1016/j.palaeo.2008.09.007

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Valles Caldera

Valles Caldera Scientific Core Drilling Services

Deep Coring of the Valles Caldera: Obtaining a Long-Term Paleoclimate Record from Northern New Mexico

Peter J. Fawcett and John W. Geissman University of New Mexico

Fraser Goff and Jeff Heikoop Los Alamos National Lab

Scott Anderson Northern Arizona University

Short History

The goal of this project was to obtain and analyze a deep (~100 m) sediment core from a lacustrine sequence in the Valles Caldera, northern New Mexico. Our work focused on determining the paleoenvironmental record of long-lived lakes in the caldera and developing a paleoclimatic record for this part of northern New Mexico for a substantial part of the middle Pleistocene. The core was drilled by DOSECC in May 2004 with the CS500 rig, and achieved a total depth of 82.1m. Most of this material was lacustrine clay with over 99% recovery. Recovery of the basal sands and gravels at the base of the core was significantly less, but we did capture a basal tephra that allowed for a constraining Ar-Ar age date. The core, VC-3, was archived at the LacCore Facility at the University of Minnesota and initial core description and sampling was conducted there.

Questions to be Answered

The questions we hoped to address with core VC-3 pertained to the paleoclimatic history of northern New Mexico over much longer time periods than the many late Pleistocene to Holocene records that are available in the area. In particular, we hoped to develop a long-term Pleistocene record that would span a significant portion of the middle Pleistocene, including some of the longer interglacials with a similar orbital forcing to today (e.g. MIS 11). The goal here was to examine natural climatic variability under such conditions as an analog for future climate change in the southwest.

What Samples were Collected?

We sampled the lacustrine mud portion of the core at a resolution of ~20 cm for a total of several hundred samples. The gravels were not sampled in detail, but the 3-cm thick basal tephra was sampled almost completely.

What Did We Do to the Samples?

An Ar-Ar age date of 552 ± 3 ka was obtained from the basal tephra, constraining the base of the core to the middle Pleistocene. To develop the paleoclimatic record, the lacustrine mud samples were split for a number of different analyses, conducted at multiple institutions (UNM, LacCore, LANL, NAU, UMN-Duluth). These analyses included organic carbon, C/N ratios, d13C, d15N, magnetic mineral properties (magnetic susceptibility MS, anisotropy of remanent magnetization, ARM), XRD of clay minerals, ICP OES (destructive elemental analysis) scanning XRF (non-destructive elemental analyses), compound specific dD, Methylated Branched Tetraether (MBT – a new paleotemperature analysis), pollen and charcoal content as well as a detailed sedimentologic description of the entire core.

What Did We Learn?

The 82-m deep lacustrine sediment core from the Valles Caldera, northern New Mexico reveals details of climate change over two glacial cycles in the middle Pleistocene. Core VC-3, taken from the Valle Grande, has a basal 40Ar/39Ar date of 552 ± 3 kyr from a tephra associated with the eruption of the South Mountain rhyolite which formed the lake. A variety of proxies including core sedimentology, organic carbon and carbon isotopic ratios, pollen, scanning XRF analysis and a new paleotemperature proxy, MBT (methylated branched tetraether) content of soil bacteria reveal two major warm periods above the basal tephra which we correlate with interglacials MIS 13 and MIS 11. This chronology is corroborated by the identification of two geomagnetic field ‘events’ which are correlated with globally recognized events (14α and 11α). The lacustrine record terminates at ~350 ka when the lake filled its available accommodation space behind the dam of rhyolite lava. Thus, the entire core spans two full glacial-interglacial cycles in the middle Pleistocene.

Valles Caldera Drilling

Figure 1: DOSECC CS500 rig operating in the Valle Grande, Valles Caldera, New Mexico

MBT temperature estimates show average glacial temperatures in core VC-3 of -4oC, and average interglacial temperatures of +4oC, and the general trends are well corroborated by multiple proxies including interglacial/glacial pollen ratios and lacustrine organic productivity estimates (organic carbon and Si/Ti ratios from the scanning XRF). A temperature increase of ~9oC occurs during Termination V, the largest glacial termination in the Pleistocene. Multiple proxies from VC-3 show significant structure during the two interglacials present in the core (MIS 13 and 11). Three warm substages (~ 2oC warmer) are recognized within MIS 11 based on organic productivity (Corg, Si/Ti ratios), pollen taxa, elevated charcoal from fires, and the MBT temperature estimates. These warm substages appear to be a strong response to precessional forcing in the SW continental interior even though the amplitude of eccentricity-modulated precession was at a minimum during MIS 11. These results suggest that future climate change in the SW may be characterized by similar natural temperature variability on precessional timescales, superimposed on future anthropogenic warming. Intervals of mudcrack facies representing significant drought conditions occur during or just after the warmest phases of the two interglacials. This past coupling between warm temperatures and extended drought in the SW as a natural feature of long interglacials is consistent with recent predictions of extended Dust-Bowl-like conditions in the SW as a response to global warming.

Where We Able to Answer These Questions & Why Should Society Care?

As a result of the multiple analyses and collaborations in this project, we were able to address the questions posed prior to the drilling project. We have generated a long, high-resolution terrestrial paleoclimate record for the middle Pleistocene, including important reconstructions of the variability within two long interglacials (MIS 11 and MIS 13). As these periods represent possible analogs for future climate change in the southwest, society should be very interested, particularly as the paleoclimate record appears to support the recent prediction of extended Dust-Bowl-like conditions in the SW as a response to global warming. The record also shows how vegetation and charcoal has changed in response to past climate change, potentially showing how vegetation and fire regimes might respond to future climate change.

Valles Caldera Drilling1

Figure 2: Representative core sections of glacials (MIS 14, MIS 12) and interglacials (MIS13).

 

References:

* denotes graduate student author

Fawcett, P.J., Heikoop, J., Goff, F., Anderson, R.S., Donohoo-Hurley, L., Geissman, J.W., WoldeGabriel, G., Allen, C.D., Johnson, C.M., Smith, S.J., and Fessenden-Rahn, J., 2007, Two Middle Pleistocene Glacial-Interglacial Cycles from the Valle Grande, Jemez Mountains, northern New Mexico; New Mexico Geological Society Guidebook, 58th Field Conference, Geology of the Jemez Mountains Region II, 2007, p. 409-417.

Johnson, C.M.*, Fawcett, P.J., and Ali, A.S., 2007, Geochemical Indicators of Redox Conditions as a Proxy for mid-Pleistocene Climate Change From a Lacustrine Sediment Core, Valles Caldera, New Mexico, New Mexico Geological Society Guidebook, 58th Field Conference, Geology of the Jemez Mountains Region II, 2007, p. 418-423.

Donohoo-Hurley, L.*, Geissman, J.W., Fawcett, P.J., Wawrzyniec, T., and Goff, F., 2007, A 200 kyr lacustrine record from the Valles Caldera: Insight from environmental magnetism and paleomagnetism, New Mexico Geological Society Guidebook, 58th Field Conference, Geology of the Jemez Mountains Region II, 2007, p. 424-432.

WoldeGabriel, G., Heikoop, J., Goff, F., Counce, D., Fawcett, P.J., and Fessenden-Rahn, J., 2007, Appraisal of post-South Mountain volcanism lacustrine sedimentation in the Valles Caldera using tephra units, New Mexico Geological Society Guidebook, 58th Field Conference, Geology of the Jemez Mountains Region II, 2007, p. 83-85.

 

Presentations

November 2008   Quaternary and Environmental Sciences and Department of Geology, Northern Arizona University (Fawcett)

March 2008 Valles Caldera Trust Public Forum, Albuquerque (Fawcett)

November 2007 IGPP Climate Study Group, LANL (Fawcett)

September 2007 Department of Geosciences, UNM (Fawcett)

September 2007 Fall Field Conference of the Geological Society of New Mexico, Jemez Mountains (Fawcett, Goff)

June 2007 IGPP Board Meeting, Santa Fe (Heikoop)

 

Presentation with Published Abstracts

Cisneros-Dozal, L, Heikoop, J., Fessenden, J., Fawcett, P., Kawka, O, and Sachs, J., 2007, Mid-Pleistocene lacustrine records of carbon and nitrogen elemental and isotopic data from Valles Caldera, New Mexico, USA, Eos Trans. AGU 88(52), Fall Meet. Suppl., Abstract PP43B-1253.

Dodd, J.P., Sharp, Z.D., Fawcett, P.J., Schiff, C., and Kaufman, D.S., 2007, A laser-extraction technique for oxygen isotope analysis of diatom frustules, Eos Trans. AGU 88(52), Fall Meet. Suppl., Abstract B13A-0893.

Donohoo-Hurley, L. L., Geissman, J.W., Fawcett, P. J., Wawrzniec, T. F., and Goff, F, 2005, Environmental magnetic record of lacustrine sediments of the Valles Caldera, New Mexico, New Mexico Geological Society Spring Meeting, Abstracts with Program

Donohoo-Hurley, L., Geissman, J.W., Fawcett, P.J., Wawrzyniec, T.F., and Goff, F., 2005, Preliminary results of the environmental magnetic record of Pleistocene Valles Caldera sediments, New Mexico, Geological Society of America Abstracts with Programs, Vol. 37, No. 7, p. 453

Donohoo-Hurley, L.L., Geissman, J.W., Fawcett, P.J., Wawrzyniec, T.F., and Goff, F, 2006, An environmental magnetism investigation of the Pleistocene lacustrine sediments from the Valle Grande, New Mexico, New Mexico Geological Society 2006 Spring Meeting, Socorro, NM, Abstract volume, p. 17.

Fawcett, P J., Goff, F., Heikoop, J.,Allen, C.D., Donohoo-Hurley, L., Geissman, J.W., Wawrzyniec, T.F., Johnson, C., Fessenden-Rahn,J., WoldeGabriel, G. and Schnurrenberger, D., 2005, Deep coring in the Valles Caldera, New Mexico to obtain a long-term paleoclimatic record, New Mexico Geological Society Spring Meeting, Abstracts with Program.

Fawcett, P.J. Fawcett, Werne, J., Anderson, R.S, Heikoop, J., Brown, E., Hurley, L, Smith, S., Berke, M., Soltow, H., Goff, F., Geissman, J., WoldeGabriel, G., Fessenden, J., Cisneros-Dozal, M., and Allen, C.D., 2008, Coupled Warming and Drought in the American Southwest During Long mid-Pleistocene Interglacials (MIS 11 and 13), AGU Fall Meeting, 2008.

Fawcett, P.J., Goff, F., Heikoop, J., Allen, C.D., Donohoo-Hurley, L., Geissman, J.W., Johnson, C., WoldeGabriel, G., and Fessenden-Rahn, J., 2005, Climate change over a glacial-interglacial cycle during the middle Pleistocene: A long term record from the Valles Caldera, New Mexico, Earth System Processes 2, Calgary, Alberta, GSA Specialty Meetings Abstracts with Programs No. 1, p. 33.

Fawcett, P.J., Goff, F., Heikoop, J., Allen, Craig D., , Donohoo-Hurley, L., Wawrzyniec, T.F., Geissman J.W., Fessenden-Rahn, J., WoldeGabriel, G., and Schnurrenberger, D., 2004, Deep Coring in the Valles Caldera, Northern New Mexico to Obtain a Long-Term Paleoclimatic Record, EOS Transactions, American Geophysical Union, v. 85 T43C-1346.

Fawcett, P.J., Heikoop, J., Anderson, R.S., Donohoo-Hurley, L., Goff, F., Geissman, J.W., Johnson, C., Allen, C.D., WoldeGabriel, G., and Fessenden-Rahn, J., 2006, Two mid-Pleistocene glacial cycles from the Valles Caldera, New Mexico, 10th International Paleolimnology Symposium June 25-29, 2006, Duluth, Minnesota, USA, Abstracts Volume, p. 32.

Fawcett, P.J., Heikoop, J., Anderson, R.S., Hurley, L., Goff, F. WoldeGabriel, G., Geissman, J., and Allen, C.D., 2007, A long middle Pleistocene climate record (MIS 14 to 9) from lacustrine sediments in the Valles Caldera, New Mexico, Geological Society of America Abstracts with Programs, Vol. 39, No. 6, p. 270.

Fawcett, P.J., Heikoop, J., Anderson, R.S., Hurley, L., Goff, F., Johnson, C., Geissman, J.W., and Allen, C.D., 2007, Two mid-Pleisocene glacial cycles (MIS 14 to 10) from lacustrine sediments in the Valles Caldera, northern New Mexico, Abstract XVII INQUA Congress Cairns Australia; Quaternary International v. 167-168, p. 114.

Fawcett, P.J., Heikoop, J., Anderson, R.S., Hurley, L., Goff, F., Geissman, J.W., Johnson, C., WoldeGabriel, G., Allen, C.D., and Fessendeh-Rahn, J., 2006, Two mid-Pleistocene glacial cycles (MIS 14 to 10) from lacustrine sediments in the Valles Caldera, New Mexico, EOS Trans, 87(52) AGU, Fall Meet. Suppl., Abstract PP51B-1137.

Fawcett, P.J., Heikoop, J., Goff, F., Allen, C.D., Anderson, R.S., Donohoo-Hurley, L., Geismman, J.W., Johnson, C., WoldeGabriel, G., and Fessenden-Rahn, J., 2005, Climate change over a glacial-interglacial cycle from the mid Pleistocene: A lacustrine record from the Valles Caldera, New Mexico, American Geophysical Union Annual Fall Meeting. Eos Trans. AGU, 86(52), Fall Meet. Suppl., Abstract PP31A-1505

Fawcett, P.J., Heikoop, J., Goff, F., Anderson, R.S., Donohoo-Hurley, L., Geissman, J.W., Johnson, C., Allen, C.D., WoldeGabriel, G., and Fessenden-Rahn, J., 2006, A mid-Pleistocene glacial-interglacial cycle from the Valles Caldera, New Mexico, New Mexico Geological Society 2006 Spring Meeting, Socorro, NM, Abstract volume, p. 18.

Hurley, L., Geissman, J.W., Fawcett, P.J., Wawrzyniec, T., and Goff, F., 2006, An investigation of environmental magnetism of the Pleistoene Valle Grande lacustrine sediments, New Mexico, Geological Society of America Abstracts with Programs, Vol. 38, No. 7, p. 199

Hurley, L.L., Geissmann, J.W., Fawcett, P., Wawrzyniec, T., and Goff, F., 2007, Environmental magnetism of mid-Pleistocene lacustrine sediments of the Valles Caldera, New Mexico, Eos Trans. AGU 88(52), Fall Meet. Suppl., Abstract GP53B-1218.

Johnson, C.M., Fawcett, P.J., and Ali, A.S., 2006, Geochemical and mineralogical indicators of redox conditions of a mid-Pleistocene lake in the Valles Caldera, New Mexico, New Mexico Geological Society 2006 Spring Meeting, Socorro, NM, p. 23.

Johnson, C.M., Fawcett, P.J., and Ali, M., 2006, Geochemical Indicators of Redox Conditions as a Proxy for mid-Pleistocene Climate Change From a Lacustrine Sediment Core, Valles Caldera, New Mexico, EOS Trans, 87(52) AGU, Fall Meet. Suppl., Abstract PP51B-1143.

 

Valles Caldera Drilling2

Figure 3: Core VC-3 Stratigraphic section, Organic Carbon (%) in siderite free fraction, bulk magnetic susceptibility (SI x 10-6) and bulk sediment density (g/cm3). Age assignments are based on Ar-Ar dates, and correlation with geomagnetic field events and glacial terminations. MBT temperature estimates (in oC) and depths given in red, within the Organic Carbon plot.

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Lake Bosumtwi

Lake Bosumtwi Scientific Core Drilling Services Project

The 2004 ICDP Bosumtwi Impact Crater Drilling Project, Ghana

Christian Koeberl University of Vienna

Bernd Milkereit University of Toronto

Jonathan T. Overpeck University of Arizona

Christopher A. Scholz Syracuse University

The 10.5-km-diameter 1.07 Ma Bosumtwi impact crater was the subject of an interdisciplinary and international drilling effort of the International Continental Scientific Drilling Program (ICDP) from July to October 2004. Sixteen different cores were drilled by DOSECC at six locations within the lake, to a maximum depth of 540 m. A total of about 2.2 km of core material was obtained. 

Introduction and Geological Setting

Bosumtwi is one of only four known impact craters associated with a tektite strewn field. It is a well-preserved complex impact structure that displays a pronounced rim and is almost completely filled by the 8 km diameter Lake Bosumtwi. The crater is excavated in 2 Ga metamorphosed and crystalline rocks of the Birimian System; it is surrounded by a slight near-circular depression and an outer ring of minor topographic highs with a diameter about 20 km. The goal of the integrated drilling, rock property and surface geophysical study was to study the three-dimensional building blocks of the impact crater (delineate key lithological units, image fault patterns, and define alteration zones).

Lake Bosumtwi Drilling

Figure 1 – Location map with ICDP boreholes and seismic profile shown in Fig. 2.

Paleoclimatic Studies at Bosumtwi

Owing to its impact origin, Bosumtwi possesses several important characteristics that make it well suited to provide a record of tropical climate change. In order to gain greater insight into the role of the tropics in triggering, intensifying and propagating climate changes, scientific drilling for the recovery of long sediment records from Lake Bosumtwi was undertaken. Five drill sites (Fig. 1) were occupied along a water-depth transect in order to facilitate the reconstruction of the lake level history. At these five drill sites, a total of 14 separate holes were drilled. Total sediment recovery was 1,833 m. For the first time the GLAD lake drilling system (a system specifically constructed for drilling at lakes) cored an entire lacustrine sediment fill from lakefloor to bedrock.

 

The complete 1 Ma lacustrine sediment fill was recovered from the crater ending in impact-glass bearing, accretionary lapilli fallout. This accretionary lapilli unit represents the initial post-impact sedimentation and provides an important age constraint for the overlying sedimentary sequence. The initial lacustrine sediment is characterized by a bioturbated, light-gray mud with abundant gastropod shells suggesting that a shallow-water oxic lake environment was established in the crater. Future study of the earliest lacustrine sediment will address important questions related to the formation of the lake and the establishment of biologic communities following the impact. Most of the overlying 294 m of mud is laminated thus these sediment cores will provide a unique 1 million year record of tropical climate change in continental Africa at extremely high resolution. The shallow water drill sites consist of alternating laminated lacustrine mud (deepwater environment), moderately-sorted sand (nearshore beach environment) and sandy gravel (fluvial or lake marginal environments). These sediments preserve a record of major lake level variability that will greatly advance the present Bosumtwi lake level histories obtained from highstand terraces and shorter piston cores. All of the drill sites will be used to produce a basin-scale stratigraphic framework for the crater sediment fill.

Geophysics and Impact Results

The two impactite cores, LB-07A and LB-08A, were drilled into the deepest section of the annular moat (540 m) and the flank of the central uplift (450 m), respectively. Samples from these cores have been studied by more than a dozen different research teams from around the world. The first set of peer-reviewed papers resulting from this work has just been published in a special issue of the journal “Meteoritics and Planetary Science”, which contains 27 papers on various aspects of the impact and geophysical studies at Bosumtwi.

At both impactite holes, drilling progressed through the impact breccia layer into fractured bedrock. LB-07A comprises lithic (in the uppermost part) and suevitic impact breccias with appreciable amounts of impact melt fragments. The lithic clast content is dominated by graywacke, besides various metapelites, quartzite, and a carbonate target component. Shock deformation in the form of quartz grains with planar microdeformations is abundant. First chemical results indicate a number of suevite samples that are strongly enriched in siderophile elements and Mg, but the presence of a definite meteoritic component in these samples cannot be confirmed due to high indigenous values. Core LB-08A comprises suevitic breccia in the uppermost part, followed with depth by a thick sequence of graywacke-dominated metasediment with suevite and a few granitoid dike intercalations. It is assumed that the metasediment package represents bedrock intersected in the flank of the central uplift.

Major results include the complete petrographic and geochemical record of the impactite fill. Major surprises in this regard include the, in comparison to suevites outside of the crater, small impact melt component and the record of shock metamorphism in the clast content of suevites, which are both at variance with earlier numerical modeling results. Also, impact-related hydrothermal overprint seems to be limited. These examples suffice to illustrate that further research on impact structures, accompanied by numerical modeling, is required to solve these and other problematics. Impactite geochemistry has also revealed that the impact breccias and the Ivory Coast tektite compositions can be satisfactorily modeled as mixtures of the known Birimian-age target rocks (metasedimentary rocks and granitoids). The geophysical studies, calibrated against the petrophysical data retrieved from the drill cores, have allowed to develop much improved three-dimensional models for the crater volume.

Lake Bosumtwi Drilling1

Figure 2 – Seismic section with deep boreholes.

Deep drilling results confirmed the general structure of the crater as imaged by the pre-drilling seismic surveys. Borehole geophysical studies conducted in the two boreholes confirmed the low seismic velocities for the post-impact sediments (less than 1800 m/s) and the impactites (2600-3300 m/s). The impactites exhibit extremely high porosities (up to 30 vol%), which has important implications for mechanical rock stability.

The statistical analysis of the velocities and densities reveals a seismically transparent impactite sequence (free of prominent internal reflections). Petrophysical core analyses provide no support for the presence of a homogeneous magnetic unit (= melt breccia) within the center of the structure. Borehole vector-magnetic data point to a patchy distribution of highly magnetic rocks within the impactite sequence.

Prior to drilling, numerical modeling estimated melt and tektite production using different impact angles and projectile velocities. The most suitable conditions for the generation of tektites are high-velocity impacts (>20 km/s) with an impact angle between 30 and 50° from the horizontal. Not all the melt is deposited inside the crater. In the case of a vertical impact at 15 km/s, 68% of the melt is deposited inside the crater. Results of the numerical modeling agreed well with the then-available geophysical data, crater size, and the distribution of tektites and microtektites of the tektite strewn field. The now observed situation for breccias within and around the crater is very different from these model results. The predicted amount of melt is much higher than the meager amounts observed. Clearly, much more melt has been incorporated in the suevite ejected outside of the structure, in comparison with the low amounts measured in the within-crater suevite occurrences. The lack of a coherent melt sheet, or indeed of any significant amounts of melt rock in the crater fill, is thus in contrast to expectations from modeling and pre-drilling geophysics, and presents an interesting problem for comparative studies and requires re-evaluation of existing data from other terrestrial impact craters, as well as modeling parameters. This research project provided important new data and improved our understanding of global change and impact processes.

Lake Bosumtwi Drilling2

Figure 3 – Bosumtwi Project Coring Team aboard DOSECC’s GLAD800 drilling platform, R/V Kerry Kelts.

 

Read more about this scientific core drilling services project at ICDP.

Acknowledgments

This work was supported by the International Continental Drilling Program (ICDP), the U.S. NSF-Earth System History Program under Grant No. ATM-0402010, Austrian National Science Foundation (project P17194-N10), the Austrian Academy of Sciences, and by the Canadian National Science Foundation. Drilling was performed by DOSECC.

References:

Koeberl C., Milkereit B., Overpeck J.T., Scholz C.A., Amoako P.Y.O., Boamah D., Danuor S.K., Karp T., Kueck J., Hecky R.E., King J., and Peck J.A.

(2007) An international and multidisciplinary drilling project into a young complex impact structure: The 2004 ICDP Bosumtwi impact crater, Ghana, drilling project – An overview. Meteoritics and Planetary Science 42, 483-511.

Ferrière, L., Koeberl, C., Ivanov, B.A., and Reimold, W.U. (2008) Shock metamorphism of Bosumtwi impact crater rocks, shock attenuation, and uplift formation. Science 322, 1678-1681.

Nowaczyk N.R., Melles, M. and Minyuk, P., 2007: A revised age model for core PG1351 from Lake El’gygytgyn, Chukotka, based on magnetic susceptibility variations correlated to northern hemisphere insolation variations, Journal of Paleolimnology, 37: 65-76.

Secondary References:

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