The Thrill to Drill in the Chill — 3.6 Million Years of Arctic Climate Change from Lake El’gygytgyn, NE Russia
Julie Brigham-Grette University of Massachusetts – Amherst
Martin Melles University of Koln
Pavel Minyuk Northeastern Interdisciplinary Scientific Research Institute (NEISRI) – Magadan
Christian Koeberl University of Vienna
After several years of preparation, pre-site survey work, and arduous logistical planning, Lake El’gygytgyn is now the focus of a challenging interdisciplinary multi-national drilling campaign as part of the International Continental Drilling Program (ICDP). With drilling initiated in Nov. 2008, the goal is to collect the longest time-continuous record of climate change in the terrestrial Arctic and to compare this record with those from lower latitude marine and terrestrial sites to better understand hemispheric and global climate change.
Figure 1 – Cross section of Lake El’gygytgyn showing drilling locations.
Coring objectives include replicate overlapping lake sediment cores of 330 m and 420 m length at 2 sites (D1 and D2 in Fig. 1; four cores total) near the deepest part of the lake. Coring shall be continued 300 m (D1) and 100 m (D2) into the underlying impact breccia and brecciated bedrock in order to investigate the impact process and the response of the volcanic bedrock to the impact event. One additional land-based core (site D3) to ca. 200 m in lake sediments now overlain by frozen alluvial sediments on the lake-shore will allow better understanding of sediment supply to the lake and spatial depositional heterogeneity since the time of impact. This latter drill site at the west edge of the lake outside the talik (unfrozen ground in an area of permafrost) will also be used for permafrost studies and be permanently instrumented for future ground temperature monitoring as part of the Global Terrestrial Network for Permafrost (www.gtnp.org/index_e.html). Drilling of the primary D1 and D2 sites will take place from February to the middle of May 2009 using the lake ice as a drilling platform. The project is using a new GLAD-800 drilling system modified for extreme weather conditions by Drilling, Observation and Sampling of the Earths Continental Crust Inc. (DOSECC). Moreover, the science and logistics involves close cooperation with the Russian Academy of Sciences (Far East Geological Institute-Vladivostok; and Northeast Interdisciplinary Scientific Research Institute-Magadan) and Roshydromet’s Arctic and Antarctic Research Institute-St. Petersburg.
In summer 2009, the cores will be flown by chartered cargo plane to St. Petersburg. Later they will be trucked to the University of Cologne, Germany, for sub-sampling starting in September by the international team and their students; the archive core halves will be shipped to the University of Minnesota LacCore Facility in the US for post-moratorium studies.
The impetus for deep drilling at Lake El’gygytgyn is largely based on field and laboratory studies carried out over the past decade. Seismic work in the lake and morphostratigraphic work in the catchment and surrounding region confirmed that the lake record is undisturbed, without evidence of glaciation or desiccation (Niessen et al., 2007; Glushkova and Smirnov, 2007). A 12.9-m-long sediment core retrieved from the deepest part of the lake in 1998 revealed a basal age of ~ 250 kyr and demonstrated, using a variety of proxies, the sensitivity of this lacustrine environment to record high-resolution climatic change across NE Asia at millennial timescales (Brigham-Grette et al., 2007; Melles et al., 2007; Nowacyzk et al., 2007; Forman et al., 2007; plus 7 other papers in same issue listed in supplemental references; Fig. 2). A 16.7-m-long sediment core taken nearby in 2003 dated to nearly 300 kyr and confirmed the reproducibility of the record (Juschus et al., 2007).
This research also showed that nearly every proxy can be systemically linked to changes in the duration of seasonal lake ice cover, regional temperature, and changes in hydrologic input driven largely by high latitude precessional cycles and feedbacks. For example, the magnetic susceptibility and sedimentology showed that perennial ice cover during glacial summers led to anoxia in the hypolimnion, which had a profound impact on the biogeochemistry at the sediment/water interface (Nowacyzk et al. 2007; Minyuk et al., 2007). Knowledge of the basin geomorphology and sedimentation processes informs us of likely changes in landscape weathering and sedimentation rates (Asikainen et al., 2007; Glushkova and Smirnov, 2007). We have also demonstrated that while gravitational sediment transport occurs in the basin, such events do not cause erosion of the continuous stratigraphy in the center of the lake where drilling is planned. Documenting the dynamics and controls on the lake’s seasonal ice cover (Nolan et al, 2003; Nolan and Brigham-Grette, 2007) has been key to understanding lake circulation and beach geomorphology. Moreover, this work has been critical to developing safety plans for ice thickening and engineering prior to drilling from the lake’s frozen surface.
Figure 2 – DOSECC’s drilling platform on Lake El’gygytgyn, March 2009.
Our ability to inform policy makers about global/regional climate and related environmental change and its uncertainties depends on our capacity to understand the role of the Arctic region in modulating past periods of change under different climate forcing conditions. Of prime interest to the scientific community is determining why and how the Arctic climate system evolved from a warm forested ecosystem into a cold permafrost ecosystem between 2 and 3 million years ago. A continuous depositional record in this unique lake provides a means of capturing the mechanisms and dynamics of glacial/interglacial and millennial-scale change from this region over the duration of the “41 kyr world” and late Cenozoic “100 kyr world”. This record will then be compared with other long records from around the world, but especially the low latitude ocean records, to evaluate polar amplification, model systemic teleconnections and leads/lags relative to insolation forcing. This record will also provide insight as to whether rapid change events identified during the last glacial cycle are typical of earlier glacial periods. We hope to provide the science community with an understanding of the poorly documented regional sensitivity of the NE Asian Arctic to millennial-scale abrupt change (Heinrich and D/O scale) and interglacial warmth detected at global vs. regional scales, within the timeframe of the EPICA ice cores, long Asian loess and lake records, and comparable marine records. Climate modeling is also an important aspect of the program to allow these relationships to be evaluated systematically.
The Lake El’gygytgyn Drilling Project is an international effort funded by the International Continental Drilling Program (ICDP), the US National Science Foundation Earth Sciences Division and Office of Polar Programs (NSF/EAR/OPP), the German Federal Ministry for Education and Research (BMBF), Alfred Wegener Institute (AWI), and GeoForschungsZentrum-Potsdam (GFZ), and the Russian Academy of Sciences Far East Branch (RAS/FEB). The leading Russian institutions include Roshydromet’s Arctic and Antarctic Research Institute (AARI), the Northeastern Interdisciplinary Scientific Research Institute (NEISRI) and the Far East Geological Institute (FEGI). The deep drilling system for Arctic operations was developed by DOSECC, Inc.
Brigham-Grette, J., Melles, M., Minyuk, P. and Scientific Party, 2007: Overview and Significance of a 250 ka Paleoclimate Record from El’gygytgyn Crater Lake, NE Russia, Journal of Paleolimnology, 37: 1-16.
Gebhardt, A.C., Niessen, F. and Kopsch, C., 2006: Central ring structure identified in one of the world’s best-preserved impact craters, Geology, 34: 145-148.
Melles, M., Brigham-Grette, J., Glushkova, O.Yu., Minyuk, P.S., Nowaczyk, N.R. and Hubberten, H.W., 2007: Sedimentary geochemistry of a pilot core from Lake El’gygytgyn – a sensitive record of climate variability in the East Siberian Arctic during the past three climate cycles, Journal of Paleolimnology, 37: 89-104.
Nowaczyk et al., 2002: Magnetostratigraphic results from impact crater Lake El’gygytgyn, northeastern Siberia: A 300 kyr long high resolution terrestrial paleoclimatic record from the Arctic, Geophysical Journal International, 150: 109-126.
Lake Potrok Aike scientific core drilling services project, located in Rio Gallegos, Argentina, a 2008 project that was ICDP, DFG-funded.
The research initiative “Potrok Aike Maar Lake Sediment Archive Drilling Project” (PASADO) within the framework of ICDP addresses several key issues related to the evolution of maar craters, to quantitative climatic and environmental reconstruction, fire history, tephra and dust deposition and palaeosecular variation of the Earth’s magnetic field for the last several glacial to interglacial cycles. Moreover, dust and tephra records provide links to marine sediment archives and ice cores. Obtained reconstructions of climate variability have been compared to climate simulations from GCM’s to detect signals of climatic forcing.
andrANDRILL (Antarctic geological DRILLing) is a multinational collaboration comprised of more than 250 scientists, students, and educators from five nations (Germany, Italy, New Zealand, the UK and the US) whose objective is to recover stratigraphic records from the Antarctic margin using drilling technology deployed from ice shelf and sea-ice platforms. ANDRILL’s primary objective is to drill back in time to recover a history of paleoenvironmental changes that will guide our understanding of how fast, how large, and how frequent glacial and interglacial changes were in Antarctica. Future scenarios of global warming and climate change require guidance and constraint from past history that will reveal potential timing frequency and site of future changes.
Figure 1 – Map of the Victoria Land Basin, showing the location of the MIS and SMS drillsites. Also shown are the locations of earlier drilling in the region as part of the Cape Roberts Project (CRP), and earlier drilling expeditions. The dark blue area represents the area covered by the McMurdo Ice Shelf, which is buttressed by Ross Island, while the lighter blue is the area covered by seasonal or perennial sea ice.
Operations and logistics for ANDRILL are managed by Antarctica New Zealand. The scientific research is administered and coordinated through the ANDRILL Science Management Office (SMO), located at the University of Nebraska-Lincoln. The overall international budget for ANDRILL is approximately $30 million US, with approximately $13 million US funding the activities managed by the ANDRILL SMO, which includes annual subcontracts with US academic institutions to provide services for each project, and funding for the participation of US scientists in ANDRILL and post-expedition research support through the ANDRILL US Scientist Support Program. The use of DOSECC tools by the ANDRILL drilling system was facilitated through the efforts of Alex Pyne, Victoria University of Wellington.
The McMurdo Sound region was the first area for Antarctic drilling under the ANDRILL banner; however, future target areas for scientific drilling are located all around the Antarctic margin. Because of the wide range of proposed drilling targets, individual drilling objectives are grouped into portfolios based on logistical requirements. The first drilling portfolio was the McMurdo Sound Portfolio, with two specific projects being funded in this portfolio, namely, the McMurdo Ice Shelf (MIS) Project (drilled in 2006) and the Southern McMurdo Sound (SMS) Project (drilled in 2007).
The ANDRILL Program successfully recovered a 1285m-long succession of cyclic glacimarine sediment with interbedded volcanic deposits, in its first season of drilling from the McMurdo Ice Shelf (MIS). The MIS drillcore represents the longest and most complete (98% recovery) geological record from the Antarctic continental margin to date, and will provide a key reference record of climate and ice sheet variability through the Late Neogene (~13Ma to present). The DOSECC sediment coring tools (Figure 3) were used to recover shallow subsurface sediments near the seafloor-water interface prior to the installation of the ANDRILL riser system using push-, gravity- and piston-coring approaches. The outcomes of these operational and scientific activities are included in the contributions to the ANDRILL MIS Project’s Initial Results volume in Terra Antarctica (Naish, Powell, et al., 2007). The initial results of the ANDRILL SMS Project were assembled for publication in Terra Antarctica in early 2009.
Figure 2 – The ANDRILL MIS Project drillsite, showing the drill rig and the integrated systems that contribute to its operation, including equipment storage and laboratory vans.
Specific science objectives of the McMurdo Sound Portfolio include:
Obtain high-resolution sediment cores that record major glacial events and transitional periods over the past 40 million years;
Determine orbital and sub-orbital glacio-climatic fluctuations that vary on 100,000, 40,000, and 20,000 year cycles (e.g., Milankovitch cycles);
Obtain a refined record of the onset and development of the East Antarctic ice sheet (EAIS) from 40 million years ago;
Identify how the Antarctic region responded to past episodes of global warmth;
Derive a detailed history of Antarctic Holocene environmental change at the end of the last glaciation (since the last glacial maximum at 20,000 years ago); and,
Test global linkages between climate changes in the Northern and Southern hemispheres.
In 2006-2007, the ANDRILL Program drilled to a record depth of 1284.87 meters below seafloor, through an access hole in the 85 meter-thick McMurdo Ice Shelf. This is the deepest sub-bottom penetration a drilling rig has ever reached in the Antarctic region, and it is the first time a geological drilling system operated through a floating ice shelf over nearly 900 meters of water. These successes are amplified by the recovery of more than 98% of the drilled interval as sediment cores that represent a nearly unbroken geological history of substantial glacial and climatic variation. Alternations of clastic-rich glacial sediment and diatomaceous marine sediment indicate a dynamic history of West Antarctica’s ice shelf /sheet advancing and retreating more than 50 times during the last 5 million years.
Figure 3 – DOSECC coring tools used at ANDRILL
A team of fifty-eight scientists, technicians, educators and support staff from United States, New Zealand, Italy and Germany spent three months in the Crary Laboratory of McMurdo Station providing the initial description and characterization of the recovered core. Their initial results document how Antarctic ice sheets behaved during periods of global warmth greater than the present day. Volcanic ashes, microfossils and paleomagnetic stratigraphy provide ages of the sediments and a means to compare this high latitude climatic history with that of other regions. Climate and ice sheet models will extend these results and provide guidance regarding potential response by the West Antarctic Ice Sheet and Ross Ice Shelf to future scenarios of global warming. Frequency and apparent speed of the retreating ice shelf, leading to interglacial and open marine conditions in the Ross Embayment, will be one focus of future studies on these cores.
The ANDRILL drilling season began in early October 2007 with the deployment of the drilling system and remote camp at the start of the SMS Project, which is co-led by Drs. David Harwood (UNL) and Fabio Florindo (Italy). Several UNL Department of Geosciences faculty members are part of the SMS team, including Drs. Chris Fielding, Tracy Frank, and Richard Levy, as well as UNL graduate student Eva Tuzzi. UNL undergraduate student Jake Carnes is participating in the Mackay Sea Valley seismic survey, which is related to future ANDRILL proposal development activities.
Armand L.K., Crosta X., Romero O. & Pichon J.-J., 2005. The Biogeography of Major Diatom Taxa in Southern Ocean Sediments: 1. Sea Ice Related Species. Palaeogeogr., Palaeoclim., Palaeoecol., 223, 93–126.
Bannister S. & Naish T.R., 2002. ANDRILL Site Investigations, New Harbour and McMurdo Ice Shelf, Southern McMurdo Sound, Antarctica. Institute of Geological & Nuclear Sciences, Science Report 2002/01, 24 p.
The Lake Petén-Itzá Scientific Drilling Project (Proyecto Paleoambiental Lago Petén-Itzá)
Mark Brenner University of Florida
Lake Petén-Itzá lies at 110 masl in the lowlands of northern Guatemala. The lake has a surface area of ~100 km2 and a maximum depth ~165 m. It was targeted for drilling because it may be the only lake in lowland Central America to have held
water and preserved a record of paleoclimate/paleoenvironment changes through the last Glacial. Plans to drill Lake Petén-Itzá were formulated in the late 1990s. A joint Swiss-US team conducted seismic-imaging campaigns in 1999 (3 kHz pinger) and 2002 (airgun) that demonstrated the basin possessed thick lacustrine deposits. The seismic images were used to identify 6 primary and 4 alternate drill sites. Preliminary coring of Holocene sections was done in 2002 using a Kullenberg gravity corer. With seismic images (Anselmetti et al. 2006) and Holocene cores in hand (Hillisheim et al. 2005), a planning workshop supported by the International Continental Scientific Drilling Program, was convened in Flores, Guatemala in 2003. Scientists from 12 countries attended the meeting.
The Lake Petén-Itzá Scientific Drilling Project (PISDP) was undertaken to achieve three major objectives:
Develop a high-resolution paleoclimate reconstruction for the lowland neotropics extending well into, and perhaps beyond the last Glacial. Explore correlations between climate changes at this tropical, low-altitude site, and marine/terrestrial paleoclimate records from tropical and extra-tropical regions (e.g. Cariaco Basin, Greenland)
Investigate shifts in vegetation that accompanied climate fluctuations in the region during glacial and interglacial times. Evaluate responses of vegetation to natural (climate) forcing and later Maya land clearance
Study sediment biogeochemistry to gain a better understanding of mineral production in the water column and sediments of the lake, in response to changing hydrologic conditions.
Figure 1 – Location of Lake Petén-Itzá, Guatemala.
Drilling was conducted by DOSECC in Lake Petén-Itzá between 3 February and 11 March, 2006 using the Global Lakes Drilling (GLAD800) rig mounted on the “superbarge” R/V Kerry Kelts. More than 60 people, including drillers, scientists, and students, participated in the field effort. Cores were retrieved at 7 sites in the lake, ranging in water depth from 30 to 150 m. A single core was collected at the shallow site (30 m), whereas three parallel holes were drilled at five sites, and five cores were taken at site PI-2 (water depth 54 m). In total, 1327 m of sediment were collected, with recovery at each site averaging between 86.3 and 94.9%.
Retrieved cores were analyzed in the field for magnetic susceptibility and gamma ray attenuation (density), using a multi-sensor core logger. Cores were ultimately shipped to the LacCore facility at the University of Minnesota for storage. Sampling parties visited Minneapolis in the summers of 2006 and 2007 to sample the cores and begin analyses. Composite Core PI-6 extended to 75.9 m below the lake floor and was chosen as the first candidate for study. The core was re-measured for magnetic susceptibility and gamma ray density at high-resolution. Next, core sections were opened, split, and imaged digitally, prior to sampling.
Core PI-6 represents ~85,000 years of continuous sediment accumulation, as determined from AMS 14C dating and tephra layers of known age. Pleistocene-age deposits possess alternating clay- and gypsum-rich sediments that reflect relatively wetter and drier conditions, respectively. Clay sections display higher magnetic susceptibility and lower density than gypsum deposits. Wetter times in lowland Central America were associated with interstadials and drier periods with stadials. Carbonate clays dominate the record from about 85 to 48 ka, suggesting relatively moist conditions. From 48 to 23 ka, the record displays wet-dry (clay-gypsum) alternations that resemble temperature inferences from Greenland ice cores and North Atlantic marine sediment cores, as well as rainfall reconstructions from the Cariaco Basin. A thick clay layer associated with the Last Glacial Maximum (LGM) chronozone (21+/-2 ka) indicates relatively moist conditions. This finding is at odds with previous inferences for arid LGM conditions in lowland Guatemala. The deglacial was marked by alternating moist and very dry conditions, with abundant gypsum precipitated from 18.0-14.7 ka, and 12.8-10.3 ka. Holocene conditions at 10.3 ka reflect increased rainfall and onset of more organic-rich sediment deposition.
Figure 2 – Drilling crew aboard the R/V Kerry Kelts (photo courtesy of ICDP).
Pollen analyses suggest 5 °C cooling at the LGM, at which time pine and oak co-existed with tropical forest elements in the region. Pollen data support geochemical analyses in pointing to times in the deglacial as the periods of greatest aridity. Changes in temperature/moisture availability throughout the deglacial (18-10.3 ka) are also being documented using stable oxygen isotope measurements on ostracod shells from the core.
Cores collected by the PISDP are providing the first well-dated, high-resolution records of Pleistocene climate and environmental change in lowland Central America. In addition to the preliminary information gleaned from core PI-6, investigation of ash layers in cores from site 7 suggest a >200 ka record was retrieved.
Findings of the PISDP of interest to a broad range of scientists, including paleoclimatologists, climate modelers, palynologists, biogeographers, sedimentologists, microbiologists, paleoecologists, and others. The public should also take interest, as the high-resolution paleoclimate records from the PISDP will provide information on the range of natural climate variability in the lowland neotropics prior to human impact.
Anselmetti, F.S., D. Ariztegui, D.A. Hodell, A. Gilli, M.B. Hillesheim, M. Brenner, and J.A. McKenzie. 2006. Late Quaternary climate-induced lake level variations in Lake Petén Itzá, Guatemala, inferred from seismic stratigraphic analysis. Palaeogeography, Palaeoclimatology, Palaeoecology 230:52-69.
Bush, M.B., Correa-Metrio, A., Hodell, D.A., Brenner, M., Anselmetti, F.S., Ariztegui, D., Mueller, A.D., Curtis, J.H., Grzesik, D., Burton, C., and Gilli, A. In press. The Last Glacial Maximum in lowland Central America. In: F. Vimeux, F. Sylvestre, and M. Khodri (Eds.), Past Climate Variability from the Last Glacial Maximum to the Holocene in South America and Surrounding Regions. Developments in Paleoenvironmental Research (DPER) Series. Springer, Dordrecht, Berlin, Heidelberg, New York.
Escobar, J., D.A. Hodell, M. Brenner, J.H. Curtis. In prep. Climate change in the northern neotropics during the last deglaciation. Geology.
Hillesheim, M.B., D.A. Hodell, B.W. Leyden, M. Brenner, J.H. Curtis, F.S. Anselmetti, D. Ariztegui, D.G. Buck, T.P. Guilderson, M.F. Rosenmeier, and D.W. Schnurrenberger. 2005. Lowland neotropical climate change during the late deglacial and early Holocene. Journal of Quaternary Science 20:363-376.
Hodell, D.A., Anselmetti, F.S., Ariztegui, D., Brenner, M., Curtis, J.H., Gilli, A., Grzesik, D.A., Guilderson, T.J., Muller, A.D., Bush, M.B., Correa-Metrio, Y.A., Escobar, J., and Kutterolf, S. 2008. An 85-ka Record of climate change in lowland Central America. Quaternary Science Reviews. 27:1152-1165.
Hodell, D., Anselmetti, F., Brenner, M., Ariztegui, D., and the PISDP Scientific Party. 2006. The Lake Petén-Itzá Scientific Drilling Project (PISDP). Scientific Drilling 3: 25-29.
Hodell, D., Anselmetti, F.S., Ariztegui, D. Brenner, M., Curtis. J., and the PISDP Scientific Party. 2006. Preliminary results of the Lake Petén-Itzá Scientific Drilling Project. DOSECC News 4:5-6.
Hodell, D., Anselmetti, F.S., Ariztegui, D. Brenner, M., Curtis. J., and the PISDP Scientific Party. 2006. 1.3 km of sediment recovered by the Lake Petén-Itzá Scientific Drilling Project. DOSECC News 4:1-2.
Mueller, Andreas D.. 2009. Late Quaternary Environmental Change in the Lowland Neotropics: The Petén-Itzá Scientific Drilling Project, Guatemala. PhD Dissertation ETH No. 18349.
Anselmetti, F.; Hodell, D.; Ariztegui, D.; Brenner, M.; Curtis, J.; Escobar, J.; Gilli, A.; Grzesik, D.; Kutterolf, S.; Mueller, A.D. 2008. The Peten Itza Scientific Drilling Project: A 200-ka record of climate change in lowland Central America. International Geological Congress. Oslo, Norway. August 2008.
Brenner, M., Hodell, D.A., Curtis, J.H., Escobar, J., Anselmetti, F.S., Ariztegui, D., Muller, A.D., Grzesik, D.A. 2008. Proyecto Paleoambiental Lago Petén-Itzá: nuevas perspectivas sobre el paleoambiente y paleoclima de Centroamerica. I Congreso Nacional de Cienagas y Lagunas. Medellin, Colombia. Sept 2008.
Escobar, J., Hodell, D.A., Anselmetti, F.S., Ariztegui, D., Brenner, M., Curtis, J.H., Gilli, A., Grzesik, D.A., Guilderson, T.J., Muller, A.D., Bush, M.B., Correa-Metrio, Y.A., Kutterolf, S. 2008. An 85-ka paleoclimate record from lowland Central America. Joint Assembly of the American Geophysical Union (AGU). Fort Lauderdale, Florida. May 2008.
Escobar, J., Hodell, D.A., Brenner, M., Curtis, J.H., Gilli, A., Anselmetti, F.S., Ariztegui, D., Grzesik, D.A., Mueller, A.D. 2008. Paleoclimate of lowland Central America during the last deglaciation. European Geophysical Union (EGU). Vienna, Austria. April 2008.
Hodell, D., Anselmetti, F., Ariztegui, D., Brenner, M., Curtis, J., Escobar, J., Gilli, A., Grzesik, D., Kutterolf, S., Mueller, A.D. 2008. The Petén-Itzá Scientific Drilling Project: A 200-ka record of climate change in lowland Central America. European Geophysical Union (EGU). Vienna, Austria. April 2008.
U.S. Antarctic Program Shallow Drilling Project (SHALDRIL) Cruises Completed Using DOSECC Tools
S. Wellner University of Houston
L. Holloway ConocoPhillips
SHALDRIL (for SHALlow DRILling) is a project of the United States Antarctic Program aimed at developing and demonstrating a system to obtain drill core from the Antarctic continental margin. The concept behind SHALDRIL is to drill through the stiff glacial overburden that covers nearly all of the Antarctic continental shelf and has historically inhibited piston coring, in order to sample older deposits where they come close to the seafloor. In addition to being able to sample older lithified material, the system developed must also have the ability to sample soft sediment. SHALDRIL is designed to operate between the continental slope, where traditional drill ships typically work, and the fast-ice zone, where ANDRILL is best suited. The success of the SHALDRIL method is dependent upon having a mobile drilling platform, capable of operating in ice-covered waters, and a drilling system that can retrieve high-quality core during an extremely short operating window.
Figure 1- Nathanial B. Palmer with drill rig installed, SHALDRIL project, Antarctica
In 1994, a workshop was convened at Rice University in Houston, TX. Fourteen scientists attended the workshop, which focused on new data from the continental shelf offshore of Seymour Island (Anderson et al., 1992; Sloan et al., 1995). There was strong consensus from the group that shallow drilling would yield key information about this critical region, the “Last Refugium of Antarctica.” The workshop participants also discussed drilling technology. In the final analysis, it was determined that the technology for SHALDRIL was not yet ready. A SHALDRIL committee was formed to monitor technical advances. The result of this work is several reports outlining different methods and techniques that might be utilized. In 2000, the SHALDRIL steering committee learned about improved drilling systems, including diamond coring, capable of drilling in water depths of several hundred meters and to core a few hundred meters beneath the seafloor. In 2003 a contract was signed with Seacore Limited (UK) to design and build a vessel specific drilling rig and to conduct the drilling operations for SHALDRIL. The rig was mounted over a small moonpool that was installed through the starboard deck of the RV/IB Nathaniel B. Palmer (Fig. 1).
SHALDRIL II was conducted in the northwestern Weddell Sea and the primary drilling targets were in the northern portion of the James Ross Basin, which contains one of the most complete Neogene successions anywhere in Antarctica (Anderson, 1999). Previous seismic investigations have revealed a virtually continuous succession of seaward-dipping strata on the continental shelf. The succession spans the late Eocene through Pleistocene.
Throughout both cruises the Seacore rig operated without difficulty and only minor adjustments were made to it between the cruises. The sampling tools for SHALDRIL I worked extremely well when taking push samples through soft Holocene sediments but were not so successful at getting through the stiff Pleistocene till. Thus, a change was made for the 2006 cruise to develop a modified set of sampling tools supplied to Seacore through DOSECC.
DOSECC Bottom Hole Assembly
The primary set of drilling hardware includes a suite of DOSECC tools that were designed to work within a common bottom hole assembly (BHA). The DOSECC tools were originally designed to operate with a drill bit with an internal diameter (ID) of 3.345″. However, for SHALDRIL, the bit throat was modified to accommodate a larger 3.85” ID. The larger throat would have allowed the Seacore piggy-back coring hardware (PBCH) to be deployed through the common BHA bit if material was encountered where high-speed diamond coring was required. This option was not deployed during the 2006 campaign. Since the time at any drill site was severely limited due to drifting ice, it proved important to have multiple tools fitting the same BHA in order to reduce tripping times to change the BHA.
Two coring assemblies and one non-coring tool were developed. These include an extended-nose spring-loaded corer and another DOSECC assembly known as the Alien corer. The extended nose corer is typically used for sediments after push or piston sampling is exhausted. The alien corer is similar to the extended nose corer but is designed to sample harder material and uses a triple core barrel inner tube assembly that is rotated in conjunction with the larger outer BHA. Due to increasing the bit and tools to accept the larger throat size in the primary BHA bit, all tools were then able to sample the same core size. The alien corer proved to be the tool used during the majority of the SHALDRIL II cruise. Sample recovery was high using this system. In addition, drilling through the subglacial and glacial-marine diamictons that form the overburden above most of the targeted strata was just as fast with the alien corer as with the non-coring tool (i.e., center bit installed in place of a coring assembly).
Figure 2- Alien drill bit with glacial diamicton collected during SHALDRIL
Drill-in Bottom Hole Assembly
As noted above, the first hardware option allowed up to three sampling systems to be deployed through the same BHA. Others tools are available but were not part of the suite of tools purchased by Seacore for SHALDRIL II. Should hard rock be encountered at a very shallow depth where the common BHA bit cannot be advanced easily, a different operating system can be deployed. This hardware, which was originally developed at ODP and slightly modified for SHALDRIL, uses a robust five roller-cone bit and a one-cone center bit latched into its throat. The center bit is removable via wire line once the BHA has been drilled to depth to allow a clear passage for the PBCH to be initiated. This hardware was not deployed during SHALDRIL II.
During SHALDRIL II, the ice conditions along the existing seismic lines did not allow any of the proposed sites to be occupied in their exact locations. The ability to continue drilling into sections of the desired age was dependent on collection of new seismic data during the cruise. In effect, areas of open water were identified, then seismic data was collected and correlated, and then sites were selected and drilled before changes in ice conditions. Without this ability to follow the water, chances are none of the objectives would have been met.
While none of the planned sites were drilled, nearly all of the coring objectives were met by drilling in alternate locations. A total of five holes reached the targeted older material yielding samples from the Eocene, Oligocene, Miocene, and Pliocene, although only a few meters were recovered from any one hole due to being driven away by ice. Also during the SHALDRIL II cruise, a long Holocene core was recovered from the Firth of Tay that will complement other Holocene cores of the area, including that from Maxwell Bay collected during the 2005 SHALDRIL cruise. The only SHALDRIL drilling objective that was not met was to gain a continuous sample through a thick (80-100 m) grounding zone wedge deposit. This was simply not possible due constant problem of drifting ice. However, based on the samples obtained from the overburden at other sites, there is every reason to believe this would have been technically possible.
The sea ice conditions encountered during SHALDRIL II were the worst-case scenario, thick multiyear ice drifting at rates that were unpredicted. The fact that SHALDRIL is so mobile enabled us to improvise and overcome severe sea-ice conditions and exploit alternate sites, proving the efficacy of the “drill and run” strategy. The drilling and sampling system is capable of penetrating up to 20 meters of glacial overburden and sampling older strata within 24 hours time. Core recovery in partially lithified sedimentary material is quite good (greater than 80%). The fact that success was found in more ice, and thus much shorter windows for drilling, than predicted will allow future SHALDRIL plans to be made for a much broader set of conditions. We hope that this is the beginning of a long program of drilling from icebreakers in the Antarctic.
We thank the crew of the NBP and the dedicated staffs at Raytheon Polar Services Company and Seacore for helping to make SHALDRIL possible. We are supported by NSF Office of Polar Programs grant ANT-0125526 to John Anderson (Rice University), in collaboration with P. Manley (Middlebury College), S. Wise (Florida State University), and J. Zachos (University of California Santa Cruz.)
Anderson, J.B., S.S. Shipp, and F.P. Siringan (1992), Preliminary seismic stratigraphy of the northwestern Weddell Sea Continental Shelf, in Y. Yoshida, K. Kaminuma, and K. Shiraishi (Eds.), Recent Progress in Antarctic Earth Science, Terra Scientific Publishing, Tokyo, 603-612.
Sloan, B.J., L.A. Lawver, and J.B. Anderson (1995), Seismic stratigraphy of the Palmer Basin, in A.K. Cooper, P.F. Barker, and G. Brancolini (Eds.), Geology and Seismic Stratigraphy of the Antarctic Margin, American Geophysical Union, Antarctic Research Series, 68, 235-260.
The Plate Boundary Observatory Borehole Strainmeter Network
Meghan Miller and Mike Jackson UNAVCO
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.
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.
An Zisheng, Ai Li, and Song Yougui Institute of Earth Environment, Chinese Academy of Sciences
Steven M. Colman University of Minnesota-Duluth
Lake Qinghai in the People’s Republic of China covers 4400 km2 on the northeastern margin of the Tibetan Plateau, at an elevation of 3194 m (Fig. 1). The lake is extremely sensitive to changes in climate because it lies in a critical transitional zone between the humid climate region controlled by the East Asian monsoon and the dry inland region affected by westerly winds. Three major atmospheric circulation systems affect its climate: (i) the winter monsoon, induced by Siberian high pressure and associated high latitude ice cover, (ii) tropical moisture from low latitudes, carried by the East Asian summer monsoon, and (iii) climatic changes in the North Atlantic region, the effects of which are inferred to be transmitted via the westerlies. A study of drill cores from the lake and the surrounding area is critical for understanding the climatic, ecological, and tectonic evolution of the area, including the development of the East Asian monsoon system and its relationship to major global atmospheric circulation.
Figure 1. Satellite photograph of Lake Qinghai with sketch map of drilling sites.
Lake Qinghai occupies a closed tectonic depression, or piggy-back basin, on the upper plate of a major, active thrust fault. The basin is bound to the north by the Qilian Mountains, which constitute the northeastern margin of the Tibetan Plateau. The lake basin thus is intimately related to the active tectonics of the Tibetan Plateau. Seismic-reflection data show that the lake sediments are tectonically deformed in some parts of the basin and largely undeformed in other parts, where they should record at least the timing of regional tectonism. The seismic surveys indicate that the shallow lake is underlain by northern and southern sub-basins and that the southern sub-basin contains a continuous stratigraphic sequence of unconsolidated sediments more than 700 m thick.
The overall scientific objectives of the project include:
To obtain an improved understanding of the late Cenozoic environmental history of the Lake Qinghai region and the development of the East Asian monsoon climate
To understand the Late Cenozoic tectonic evolution of the Lake Qinghai basin and the growth of the northeastern margin of the Tibetan Plateau and its effects on regional climate
To correlate Lake Qinghai environmental records with other regional and global paleoclimatic records to obtain a better understanding of the connection between regional climatic change, the development of the East Asian monsoon system, prevailing westerlies, and, ultimately, the evolution of global climate
After several weeks of delay caused by poor weather and a regional outbreak of bird flu, drilling operations began in late July 2005 and continued to early September. The drilling was conducted from a barge with the Global Lake Drilling 800 m (GLAD800) coring system (Fig. 2), the modular ICDP drilling platform and drilling system operated by Drilling, Observation and Sampling of the Earth’s Continental Crust (DOSECC, Inc.). DOSECC’s coring operations were supported by the Qinghai Geology Survey and scientists from the Xi’an Institute of Earth Environment of the Chinese Academy of Sciences (IEECAS). The sediment cores were described initially onboard by observing through the plastic core liners and examining core-catcher samples. The maximum 1.5-m-long core segments were scanned for geophysical properties with a GEOTEK instrument at a shore base that was occupied throughout the drilling operations. In total, 324 core runs for 548 m of drilling acquired 323 m of core at an average recovery rate of 59%.
The upper few tens of meters of sediment were mainly gray clay and silty clay. Core recovery was excellent in this upper part of the lake bed, and these cores will serve for the planned high-resolution study of climatic changes extending through much of the last glaciation. The sediment below the clay-rich upper section was mainly rather fine-grained, unconsolidated sand with only a few clayey layers. The character of these sandy units plus the persistent rough wind and wave conditions experienced during the drilling operation greatly hindered the recovery of good cores. The principal investigators thus decided to postpone the proposed 700-m drilling for a future campaign and to focus on obtaining high-quality, overlapping cores of the upper 30–50 m of relatively fine-grained sediment at several sites (Fig. 1). Hole 2C penetrated the deepest (114.9 m), and the cores from this site may provide paleoenvironmental information through the late Quaternary.
Concurrently with offshore drilling, an onshore site was drilled successfully on Erlang Jian on the southeastern shore of the lake (Fig. 1) using Chinese equipment. The drill rig was deployed to its maximum drill string capacity, allowing coring down to 1108.9 m, with an average recovery of more than 90%. Comparisons to outcrop exposures suggests that the lowermost sediment recovered sediments with a maximum age of late Miocene. The onshore drilling was conducted by the Qinghai Geology Survey, in collaboration with the IEECAS. All drill cores were shipped in refrigerated trucks to the IEECAS in Xi’an, China for storage at 2–5°C. So far, about sixty scientists from China, Japan, Europe, and North America have expressed interest in participating in upcoming studies. The principal investigators (Z. An, S.M. Colman, G. Haug, P. Molnar, and T. Kawai) and the science team held a planning and sampling meeting in May of 2007 in Xi’an, China. Preliminary results of a wide variety of paleoenvironmental proxy analyses were presented at a special session on Asian monsoon history at the American Geophysical Union meeting in December of 2008.
Figure 2. The GLAD800 drilling system being towed away from the dock to the first drill site, Lake Qinghai, China.
About 500 scientists, engineers, and technicians from the People’s Republic of China and abroad worked at and visited the drilling sites, mainly from the Chinese Academy of Sciences, the Ministry of Science and Technology of China, the National Science Foundation of China, the China Meteorological Association, the ICDP, and several universities and research organizations, as well as local governments. China Central Television and other TV stations and newspapers gave enthusiastic attention to this scientific research. They are all thanked for their contributions.
Lake Malawi scientific core drilling project, located in Malawi, a 2005 project that was NSF, ICDP-funded.
LAKE MALAWI DRILLING PROJECT
East African Rift System, Malawi, Tanzania, Mozambique
The top scientific objective of the project was to obtain a continuous, high-resolution (annual-decadal) record of past climates in the continental tropics over the past ~800 kyr. Other primary scientific objectives of the drilling program intersect several fields, including extensional basin evolution and neotectonics, evolutionary biology, and the environmental background to human origins. The critical role of the tropics in driving global circulation is widely recognized, but the climatic linkage between tropical Africa and the high latitudes at decadal-centennial through orbital timescales, has yet to be established.
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.
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).
Figure 2 – Drilling pad setup, including driller’s trailer (left) and USGS office (right)
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).
Table 1. Cored sections in the Eyreville coreholes
125.6 to 591.0 m, PQ core (85.0 mm diameter)
591.0 to 940.9 m, HQ core (63.5 mm diameter)
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)
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
444 to 1,096 m
Sediment-clast breccias and sediment blocks
1,096 to 1,371 m
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.
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.
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.
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.
Brazos River, Texas: Drilling the K-T and Chicxulub Event Strata
Gerta Keller Princeton University
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.
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).
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.
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.
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.
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