Geological Association of Canada [GA]

 CC:Hall E  Tuesday  0800h

Recent Contributions From IODP and ICDP Scientific Drilling Expeditions II Posters

Presiding:  N R Banerjee, University of Western Ontario; D Schmitt, University of Alberta


Comparison of Seismic Anisotropy Measurements From the ICDP Outokumpu, Finland Borehole With Theoretical Model Results

* Schijns, H (, Institute for Geophysical Research, University of Alberta, Rm #238 CEB 11322-89 Ave, Edmonton, AB T6G 2G7, Canada
Schmitt, D R (, Institute for Geophysical Research, University of Alberta, Rm #238 CEB 11322-89 Ave, Edmonton, AB T6G 2G7, Canada
Kukkonen, I T, Geological Survey of Finland, P.O. Box 96, Espoo, 02151, Finland
Heikkinen, P, Institute of Seismology, University of Helsinki, PL 68 (Gustaf Hällströmin katu 2b), Helsinki, 00014, Finland

The 2.5 km deep ICDP (International Continental Scientific Drilling Program) borehole located in Outokumpu, Finland was drilled in order to gain a more complete understanding of the regional geology. Outokumpu is the site of a historic base metal mine, and large scale crustal seismic reflection surveys have previously been used to explore the geology of the area. Glacial deposits in the region overly a biotite-rich schist that extends to a depth of ~1300 m. The schist is expected to be strongly anisotropic as a result of lattice preferred orientation (LPO) of the biotite and of aligned fractures. In May 2006 the University of Alberta executed a multi-depth multi- azimuth walk-away VSP using the Outokumpu borehole in order to study the seismic anisotropy. In addition, the 2006 survey included a high resolution zero offset VSP, a far offset VSP and a reflection/refraction profile collected along the same seismic lines as the walk-away VSP. The walk-away VSPs included a three component receiver located at depths of 1000, 1750 and 2500 m, and were processed with static corrections, removal of powerline harmonics, polarization filtering and, finally, the application of a tau-p transform. The greatest anisotropy was observed in the southeastern walk-away VSPs, with the velocity ranging from ∼5330-5950 m/s between 50-1000 m in depth, and up to ∼6150 m/s between 1000-1750 m in depth. Laboratory measurements made by other researchers using schist core samples from the borehole indicate the schist has an intrinsic orthorhombic symmetry. Forward modeling of an orthorhombic media with fluid- filled cracks was done in an attempt to fully describe the velocity anisotropy of the schist observed between 50- 1000 m depth. Good agreement is found between the theoretical model and the walk-away VSP measured velocities. The theoretical model for this upper 1 km of the subsurface predicts the foliation plane of the schist to be nearly horizontal, which corresponds with the known geology of the area. The dip of the cracks in the theoretical model can be compared to the angles of fractures visible in borehole televiewer data, and the azimuthal orientation compared to the known geology of the region. Further, theoretical and walk-away VSP measured velocities can be compared to laboratory measurements made on a range of core samples from the depths of interest.


Seismic Modeling of Geological Heterogeneity: an Application to Gas Hydrate Reservoirs of ICDP Program

* Huang, J (, University of Toronto, Department of Physics, 60 St. George Street, Toronto, ON M5S1A7, Canada
Bellefleur, G (, Geological Survey of Canada, 615 Booth Street, Ottawa, ON K1A 0E9, Canada
Milkereit, B (, University of Toronto, Department of Physics, 60 St. George Street, Toronto, ON M5S1A7, Canada

Natural gas hydrates, a type of inclusion compound or clathrate, are composed of gas molecules trapped within a cage of water molecules. The occurrence of gas hydrates in permafrost regions has been confirmed by core samples recovered from the Mallik gas hydrate research wells located within Mackenzie Delta in Northwest Territories of Canada. In hydrate-bearing sediment, compressional and shear wave velocities, as well as the attenuation of seismic signals, depend sensitively on the spatial variability of both the hydrate distribution and the subsurface lithology. Therefore, seismic wave velocities and energy attenuation have been used to estimate gas hydrate concentrations. For those estimates to be accurate, a model is required that can account for the impact of both large- and small-scale heterogeneity on the transmission of seismic energy. An algorithm based on stochastic medium theory is developed to delineate the subsurface hydrate distribution and to assess the attenuative effects of local heterogeneities. Using a modified Biot-Gassmann theory, the statistical parameters obtained from Mallik 5L-38 borehole logs, and the horizontal correlation length estimated from acoustic impedance inversion, we constructed a heterogeneous model based on borehole log data from the Mallik permafrost gas hydrate research site in the Canadian Northwest Territories. The model can be used to estimate the volume of hydrate in place and results suggest a range of total hydrate content between (528 ∼ 768)× 106 m3/km2, nearly an order of magnitude lower than early estimates in which small-scale heterogeneities were not accounted for. The heterogeneous models were further used with parallel 3-D viscoelastic Finite Difference modeling software to simulate a near offset Vertical Seismic Profile and cross borehole numerical surveys. The synthetic results indicate that the observed attenuation of seismic energy may not represent the intrinsic attenuation of hydrate-bearing sediment, but instead can largely be attributed to scattering from small-scale heterogeneities, and the highly-attenuative, "leaky mode" propagation of energy through larger-scale heterogeneities.


Magnetostratigraphy and Environmental Magnetism of Laguna Potrok Aike: Preliminary Results from the ICDP Project PASADO

* Lise-Pronovost, A (, ISMER-GEOTOP, 310, allee des Ursulines, Rimouski, QC G5L 3A1, Canada
Haberzettl, T (, ISMER-GEOTOP, 310, allee des Ursulines, Rimouski, QC G5L 3A1, Canada
St Onge, G (, ISMER-GEOTOP, 310, allee des Ursulines, Rimouski, QC G5L 3A1, Canada
Brown, L (, University of Massachusetts Amherst, 611 North Pleasant Street, Amherst, MA 01003, United States
Gebhardt, C (, Alfred Wegener Institute for Polar and Marine Research, Postfach 12 01 61, Bremerhaven, 27515, Germany
PASADO Science Team, P ( AB: Laguna Potrok Aike (51° 58'S, 70° 23'W), is a ~770 ka maar lake in southern Patagonia (Province of Santa Cruz, Argentina). In the austral spring 2008, the PASADO international team of scientists cored Laguna Potrok Aike using the GLAD800 equipment in order to obtain a high-resolution geological archive for paleoenvironmental reconstructions. Two long sedimentary sequences of approximately 100 meters each were recovered close to the center of the lake at 100 m water depth. In the field, the magnetic susceptibility was measured using a Multi Sensor Core Logger at 2 cm intervals. At the Paleo and Environmental Magnetism Laboratory of ISMER in Rimouski (Québec, Canada), core catcher samples (core 5022 2A) were analyzed using an alternating gradient force magnetometer to determine the magnetic mineralogy and grain size. In the framework of the PASADO project, the aim of this paleomagnetic study is to 1) reconstruct the first full paleomagnetic vector (inclination, declination and relative paleointensity) recorded from southern South America and presumably back to Oxygen Isotope Stage 5, 2) use magnetostratigraphy as a chronostratigraphic tool in Laguna Potrok Aike in addition to radiocarbon and optical (OSL) dating as well as tephrochronology and 3) develop high-resolution magnetic proxies of paleoenvironmental changes in southern Patagonia. Here we present the paleomagnetic study outline, the magnetic susceptibility profiles obtained in the field and preliminary laboratory results as a first step to characterize the magnetic mineralogy and grain size.


ICDP Lake Drilling at Laguna Potrok Aike, Argentina: a Progress Report of the PASADO Project

* Francus, P (, GEOTOP, Univ. du Quebec a Montreal, C.P. 8888, Succ. Centre-Ville, Montreal, QC H3C 3P8, Canada
* Francus, P (, Institut National Recherche Scientitfique, 490 de la couronne, Quebec, QC G1K 9A9, Canada
Anselmetti, F (, Swiss Federal Institute of Aquatic Science & Technology, Ueberlandstrasse 133, Duebendorf, 8600, Switzerland
Aritztegui, D (, Univ. Geneva, Earth Sciences, rue des Maraichers 13, Geneva, 1205, Switzerland
Corbella, H (, Argentine Museum of Natural History, Av. Gallardo 470, Buenos Aires, 1007, Argentina
Gebhardt, C (, Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, Bremerhaven, 27576, Germany
Luecke, A (, Forschungszentrum Julich GmbH, ICG-5, Julich, 52425, Germany
Ohlendorf, C (, Institute of Geography (Geopolar), Univ. of Bremen, Bremen, 28359, Germany
Ross, P (, Institut National Recherche Scientitfique, 490 de la couronne, Quebec, QC G1K 9A9, Canada
Schaebitz, F (, Seminar for Geography and Education, Univ. Cologne, Gronewaldstr. 2, Cologne, 50931, Germany
St-Onge, G (, GEOTOP, Univ. du Quebec a Montreal, C.P. 8888, Succ. Centre-Ville, Montreal, QC H3C 3P8, Canada
St-Onge, G (, Institut des Sciences de la Mer, Univ. Quebec Rimouski, 310, Allee des Ursulines, Rimouski, QC G5L 3A1, Canada
Zolitschka, B (, Institute of Geography (Geopolar), Univ. of Bremen, Bremen, 28359, Germany
PASADO Science Team, ( AB: Within the framework of the ICDP-funded Potrok Aike maar lake sediment archive drilling project (PASADO), an international team of scientists carried out interdisciplinary research at the mid-Pleistocene (770 ka) maar lake of Laguna Potrok Aike in southern Patagonia (Province of Santa Cruz, Argentina). Previous studies on short cores revealed that this lake is very sensitive to variations in southern hemispheric wind and pressure systems. It holds a unique and continuous lacustrine record of climatic and ecological variability of global significance, potentially for the last 770ka. Three months of drilling activities that finished last November 2008 were carried out by DOSECC from the drilling platform R/V "Kerry Kelts". More than 500 m of lacustrine sediments were recovered. This sedimentary archive will provide (1) new insights into the processes of regional back arc volcanism within the Pali Aike Volcanic Field itself as well as the more distant explosive volcanism of the Andean mountain chains; and, (2) high-resolution (decadal) quantitative climate and environmental reconstructions supported by multiple dating and stratigraphic correlations. Marine - ice core - terrestrial linkages will be emphasized as well as the incorporation of results from global climate modeling simulations for the last ca. 100 ka. Two drilled sites in the central deep basin of Laguna Potrok Aike were selected based on four seismic surveys carried out between 2003 and 2005. Sediments were recovered at both drilled sites down to a subbottom depth of slightly more than 100 m using the GLAD800 drill rig with the hydraulic piston corer tool at water depths varying between 95 and 100 m. The total core recovery is 94%. On- site core logging with the multi sensor core logger documents an excellent correlation between the four recovered holes drilled at Site 1 as well as with the three holes obtained from Site 2 which is located ca. 700 m south of Site 1. Additionally, a variety of sedimentological, physical and geochemical analyses were carried out on the core catcher samples during fieldwork. Preliminary interpretation of all the available data before core opening indicates that the record may go back in time as far as oxygen isotope stage 5a.


Offset Vertical Seismic Profiling in the Bosumtwi Impact Crater, Ghana (ICDP)

* Bongajum, E (, University of Toronto, Dept. of Physics, Toronto, ON M5S 1A7,
Milkereit, B (, University of Toronto, Dept. of Physics, Toronto, ON M5S 1A7,
Meillieux, D (, Petroleum Geo-Services, Strandveien 4, Box 290 Lysaker 1366,
Schmitt, D R (, University of Alberta, Dept. of Physics, Edmonton, AB T6G 2G7,

Impact cratering processes are known to have contributed the earth's evolution. In recent years, geoscientific studies of impact craters have helped in our knowledge of the composition and evolution of the earth's continental crust and in providing insights to the essential processes associated to impact cratering. The Bosumtwi impact crater, located in central Ghana, is the largest young and well preserved impact crater in the world. Seismic studies were conducted as a part of an integrated drilling, geologic and geophysical program in order to understand the structure of the impact crater whose target rocks are concealed by a lake (Lake Bosumtwi) and sediments. Offset Vertical Seismic Profiling (VSP) data was acquired in borehole LB08A to provide information on the in situ wavefield and physical properties of the impact crater. Results from analyzing first break attributes of data from the borehole sensors suggest that offset VSP acquisition geometry with a single sensor fixed at depth can be used as a quality control tool for shot positioning and seismic spectral content in a seismic survey. Estimates of geometric spreading within the sediments were also obtained. Such information can be valuable for improving seismic imaging of the crater by accordingly accounting for amplitude losses caused by geometric spreading in surface seismic data. References: D. R. Schmitt, B. Milkereit, T. Karp, C. Scholz, S. Danuor, D. Meillieux, and M. Welz, 2007, In situ seismic measurements in borehole LB-08A in the Bosumtwi impact structure, Ghana: Preliminary interpretation, Meteoritics and Planetary Science 42, 755-768 Scholz, C. A., Karp, T., Brooks, K. M., Milkereit, B., Amoako, P. Y. O., and Arko, J. A., 2002, Pronounced Central Uplift identified in the Bosumtwi impact Structure, Ghana, using multichannel seismic reflection data: Geology, Vol. 30, No. 10, P. 939-942.


34S/32S and 18O/16O ratios of dissolved sulfate from interstitial water samples above gas hydrate bearing sediments of IODP Expedition 311, Cascadia margin

* Wortmann, U G (, University of Toronto Dept. of Geology, 22 Russelstr., Toronto, ON M5S3B1, Canada
Chernyavsky, B M (, Institute for Integrated Energy Systems, University of Victoria, Victoria, BC V8W 3P6, Canada
TOrres, M (, College of Oceanic and Atmospheric Sciences, Oregon State University,
Kastner, M (, Scripps Institution of Oceanography, University of California San Diego,

Microbially mediated sulfate reduction affects the isotopic composition of dissolved and solid sulfur species in marine sediments. Although several details of the fractionation process remain controversial, the overall process is well understood and can be described as the sum of several mass dependent fractionations during the stepwise reduction of sulfate to sulfide. Experiments and field data show that the 18O/16O of sulfate is also modified in the presence of sulfate-reducing microorganisms. Here we use a reaction transport model to analyze these processes and to constrain the rates of organotrophic versus methanotrophic sulfate reduction. Our results show that even in cases where sulfate concentration decline in a linear fashion, up to 50% of all sulfate is consumed by organotrophic sulfate reduction.


Paleo-sea Surface Conditions in the NW North Atlantic During Recent Interglacials

* de Vernal, A (, GEOTOP, Universite du Quebec a Montreal, PO Box 8888, Montreal, QC H3C 3P8, Canada
Hillaire-Marcel, C (, GEOTOP, Universite du Quebec a Montreal, PO Box 8888, Montreal, QC H3C 3P8, Canada
Mayor, S (, GEOTOP, Universite du Quebec a Montreal, PO Box 8888, Montreal, QC H3C 3P8, Canada
Lamziouaq, R (, GEOTOP, Universite du Quebec a Montreal, PO Box 8888, Montreal, QC H3C 3P8, Canada
Preda, M (, GEOTOP, Universite du Quebec a Montreal, PO Box 8888, Montreal, QC H3C 3P8, Canada
Stevenson, R (, GEOTOP, Universite du Quebec a Montreal, PO Box 8888, Montreal, QC H3C 3P8, Canada

Sites IODP-1305, ODP-646 and IODP 1302/1303 are ideally located for the documenting of Pleistocene climatic and glacial history over Greenland and eastern Canada, in addition to providing information on thermohaline conditions notably with regard to convection in the Labrador Sea (LS) and deep North Atlantic Water (NADW) sources (see also Hillaire-Marcel et al., same meeting). At site 1305 (Eirik Ridge), at the entry of the modern Greenland current, North-East Deep Atlantic Water and Denmark Strait Overflow Water into the LS, clay minerals and Nd-isotopes indicate that sedimentary supplies during marine isotope stages (MIS) 1, 5e, 7 and 9 differed from those of earlier interglacials, for which sedimentary supplies suggest soil development over volcanic rocks from partly deglaciated eastern Greenland. Pollen analyses also indicate denser vegetational cover than at present over southern Greenland during most interglacials prior to MIS 1, with specific features for each of them. For example, rich pollen assemblages dominated by spruce suggest the spreading of boreal forest vegetation over an ice-free southern Greenland during MIS 11, thus a significantly reduced ice-volume in comparison to those of more recent interglacials. Sheltered from direct influence of the western boundary undercurrent, IODP Site 1302/1303 (Orphan Knoll) provides a ca. 700 kyrs, uniform and continuous record of linkages between the northeastern Laurentide Ice-Sheet surge area (cf. Heinrich events) and the North Atlantic. The site also provides critical information about the Atlantic Meridional Overturning Circulation (AMOC) since all water masses contributing to the modern NADW still preserve their identity in the overlying water column. For example during MIS 5e, benthic foraminiferal assemblages, oxygen and carbon isotope records of Site 1302/1303, compared to those of site 1305, indicate distinct bottom water masses in the inner vs. outer basins of the LS, thus a distinct AMOC. Similarly, isotopic measurements in Globigerina bulloides suggest a warming trend in surface water toward the end of MIS 5e, in contrast to the present interglacial that shows an early thermal optimum. During most of MIS 5e, dinocyst data also indicate sea- surface temperatures much higher than present (+3°C in winter and +5°C in summer), too high for convection to occur in the LS. It is concluded that beside specific features for each interglacial, the Holocene stands clearly out, both for the intense convection in the LS from mid- to late Holocene, and the relative stability of the Greenland ice-sheet until the Present.