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Home , Hudson Strait, Ice rafting, Laurentide Ice Sheet, Levee

Imaging Laurentide Sheet into the Deep : Impact on and Bottom

Reinhard Hesse*, Ingo Klaucke, Department of and Planetary Sciences, McGill University, Montreal, H3A 2A7, William B. F. Ryan, Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964-8000 Margo B. Edwards, Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, HI 96822 David J. W. Piper, Geological Survey of Canada—Atlantic, Bedford Institute of Oceanography, Dartmouth, B2Y 4A2, Canada NAMOC Study Group†

ABSTRACT the western Atlantic, some 5000 to 6000 State-of-the-art sidescan-sonar imagery provides a bird’s-eye view of the giant km from their source. submarine drainage system of the Northwest Atlantic Mid-Ocean Drainage of the involved (NAMOC) in the Sea and reveals the far-reaching effects of drainage of the repeated collapse of the ice dome over into the deep sea. Two large-scale depositional Hudson , releasing vast numbers of ice- systems resulting from this drainage, one mud dominated and the other sand bergs from the Hudson ice in dominated, are juxtaposed. The mud-dominated system is associated with the short time spans. The repeat interval was meandering NAMOC, whereas the sand-dominated one forms a giant submarine on the order of 104 yr. These dramatic ice- braid , which onlaps the eastern NAMOC levee. This dichotomy is the result of rafting events, named Heinrich events grain-size separation on an enormous scale, induced by ice-margin sifting off the (Broecker et al., 1992), occurred through- outlet. At the upslope end of the mud system, fine, suspended sedi- out the North Atlantic and flooded the ment was dispersed by buoyantly rising meltwater plumes and entrained by the ocean north of 40°N with . south-flowing Labrador Current. from the turbid surface plumes blan- Heinrich events were associated with keted the continental slope south of the strait, whose high relief was subsequently short-term change (Bond et al., created by retrograde . Remobilization of this fine-grained slope sed- 1993) because they caused suppression iment created the mud-rich NAMOC. In contrast, bedload-rich meltwater dis- of the conveyor-belt circulation. The charges generated sandy turbidity currents on the low-relief slope off the Hudson freshwater lid from the melting icebergs Strait, which basinward formed the braid plain. Periodic surging of the Hudson prevented deep-water formation in the Strait ice stream, possibly related to subglacial- outburst flooding that triggered Norwegian Sea, which stopped the Gulf extraordinary large, bedload-rich meltwater discharges, released unusual quantities Stream from penetrating northward, thus of icebergs that left their trace in Heinrich layers rich in ice-rafted debris and triggering short-term Northern Hemi- marked times of short-term climate cooling. The injection of large volumes of fresh sphere cooling (Broecker, 1994; Paillard or brackish water into the ocean bottom circulation may be a side effect of Hein- and Labeyrie, 1994). rich events in the deep sea. SEA-FLOOR MORPHOLOGY AND CHANNEL GEOMETRY INTRODUCTION change through the thermohaline circula- Establishing seascape morphology Pleistocene continental ice caps tion may be coupled with a similarly pro- with high precision by sonar imaging is a shaped the surface of Earth more pro- nounced impact on deep-sea sedimenta- fundamental first step in interpreting sea- foundly than any other geologic phe- tion for the Pleistocene Laurentide Ice floor evolutionary processes (e.g., Macdon- nomenon of comparable duration. Their Sheet and neighboring . ald et al., 1993). To do this, state-of-the-art geomorphic effects on land are best sidescan-sonar imagery and swath known from their smaller cousins, the HUDSON STRAIT AND THE bathymetry were acquired using the Alpine , but these give NAMOC SUBMARINE DRAINAGE HAWAII MR-1 (Hawaii Institute of Geo- no idea of the extent to which large, land- SYSTEM physics Acoustic Wide-Angle Imaging based ice sheets have shaped the ocean The Hudson Strait played a unique Instrument Mapping Researcher 1) system, floors adjacent to ice margins. The far- role during the as a single the successor of SeaMARC II (Rognstad, reaching marine influence of ice sheets, major ice-sheet outlet. Through this out- 1992), on Hudson cruise 93-025. The sys- which we have documented in sidescan let, the subglacial drainage system of the tem is towed 70-80 m below the water sur- sonar imagery, is little known. Our under- area, a 3–4 x 106 km2 area face at 8-9 kn with the sidescan sonar standing of the role of continental ice (Fisher et al., 1985; Hughes, 1987) com- operating at frequencies of 11 and 12 kHz, sheets in Pleistocene paleoclimate change posing the northeastern sector of the Lau- respectively on the and starboard has recently changed dramatically with rentide Ice Sheet, was connected with the sides. Simultaneous deployment of 3.5 recognition that ice sheets may control basin-wide submarine drainage system of kHz and airgun vertical seismic systems short-term climate variations through the Northwest Atlantic Mid-Ocean Chan- makes this the most efficient remote- direct ocean-atmosphere feedback nel (NAMOC) on the Labrador Slope and sensing package for deep-sea floor surveys. (Broecker, 1994), rather than merely basin floor (Hesse et al., 1987; Hesse and Approximately 7000 km of real-time data record orbitally forced climate change. Rakofsky, 1992). The NAMOC extends covering 140 000 km2 of seafloor were The role of ice sheets in short-term climate nearly 4000 km from 61°N off the Hudson obtained and used to construct up to six- Strait to 37°N in the North American Basin track-wide mosaics of parts of the NAMOC (Chough and Hesse, 1976). Combined (each track being 20 km wide). with the >2000-km-long subglacial part on The resulting 2500-km-long and up to *Also at: Institut für Allgemeine und Angewandte land, this is one of the world’s longest Geologie, Ludwig Maximilians Universität, Munich, 120-km-wide corridor of sidescan imagery interconnected Pleistocene land-sea . along the course of NAMOC (Figs. 1 and †Saeed Khodabakhsh, Larry A. Mayer, and shipboard drainage systems. Through its channels, 2) provides a bird’s-eye view of the ocean participants J.-F. Boily, B. Chapman, R. B. Davis, glacially derived sediments were trans- J. R. Erickson, D. J. Johnson, C. Keeley, B. Konyukhov, floor diagonally across the Labrador Sea. C. Olson Major, K. Parlee, A. Peslier, S. Renaud, ported as far as the Sohm Abyssal Plain in S. Ryan, K. L. Sender, R. Sparkes, K. Wagner, and J. S. Won. Ice Sheet Drainage continued on p. 4

GSA TODAY, September 1996 3 Ice Sheet Drainage continued from p. 3 depth. (called channels on the gradient 1:1000 or less). The channel rise and basinward) are dramatically fewer floor appears as a meandering 2- to 3-km- Four distinct morphologic regions can be in number and have less relief than on the wide band of low-backscatter energy with recognized. slope (Fig. 3B), and the NAMOC appears as low sinuosity ( radius ranges from Region 1: Continental slope in a discernible trunk channel of the 17 to 55 km, averages 25 km). <3000 m water depth (west of 57°N, drainage system. No upslope canyon can run parallel to the NAMOC for several sea-floor gradient >1:500). A dendritic be singled out as the main NAMOC feeder. hundred kilometers (Hesse, 1989) but pattern of closely spaced canyons On the sidescan mosaic in Figure 2, the eventually join the main channel (conflu- with increasingly complex upslope most prominent aspect between about 57° ence with tributary E/F at about 57°40'N; branching (Fig. 2) shows steep canyon and 54°30'W is the dichotomy between Fig. 1). Bright areas in the channel are with spectacular relief of up to 700 the high-backscatter-energy (light areas) interpreted as slumps or point bars. The m (Fig. 3A) alternating with low-relief sec- muddy levees of the NAMOC, and the point bars are concentrated on, but not tors. Canyons in the low-relief regions are low-backscatter (dark areas) sand and restricted to, inner meander bends on the <120 m deep and have broad floors gravel-rich to the northeast. right channel . We imaged washover flanked by broad or levees. Low- Lithologies were established by piston fans, hanging submarine valleys, and relief sectors occur in front of glacial out- coring (Fig. 4). chute pools in this region for the first time lets, seaward of the shelf break (Hesse and Region 3: Labrador Basin floor in the deep sea (Klaucke and Hesse, 1996). Klaucke, 1995), whereas high-relief sectors south of 59°45'N and below 3400 m The most surprising morphologic typically lie south of these outlets. water depth to with H feature of the entire mosaic is the curved Region 2: Continental rise tributary and Imarssuak Mid-Ocean alternating high- and low-backscatter- between 3000 and 3400 m water Channel at 56°N (average sea-floor energy streaks on the sand and gravel

Figure 1. Mosaic of HAWAII MR-1 sidescan sonar images (6 ship tracks, each 20 km wide) in the central Labrador Sea (for location see inset in Fig. 2, southern part of red corridor) showing submarine braid plain with curved ridges and sand and gravel bars (bright) immediately east of the meandering NAMOC with its muddy levees. The imagery is dis- played in normal polar- ity—i.e., low-backscatter reflectivity appears dark and high-backscatter reflectivity bright.

4 GSA TODAY, September 1996 plain beyond the distal edge of the eastern braid plain. The braid plain forms the and a few meters high. Evidence of ero- NAMOC levee. This pattern corresponds southern, distal continuation of the sion can be seen where the furrows start to the depositional low-amplitude chan- nonbraided sand-gravel plain in region 2. abruptly upstream. The prevalent curva- nel-and- or lobe, or the erosional - The ridges or bars (bright streaks) are up to and-furrow topography, of a submarine 10 km long, several hundred meters wide, Ice Sheet Drainage continued on p. 6

Figure 2. Mosaic of HAWAII MR-1 sidescan sonar images (4 ship tracks wide) starting at 61°W on the upper Labrador slope off the Hudson Strait. IMOC is Imarssuak Mid-Ocean Channel; PTB is submarine , SL is slump; SMT is .

Figure 3. Sleeve-gun (655 cm3 = 40 in.3) seismic profiles from Labrador slope and basin. Locations shown in Figure 5. A. Profile along the upper Labrador slope in about 1500 m water depth (segment 1). On the high-relief sector (southern half of profile), parallel undulating low-amplitude reflections, which are grouped into packages by a few higher-amplitude reflections, and deep sound penetration (up to 800 ms two-way traveltime or 720 m subbottom depth, assuming a sound veloc- ity of 1.8 km/s), are characteristic of turbid surface- plume and pelagic-dominated sedimentation (southern two to three tracks on upper slope, Fig. 2). In the low-relief sector to the north, more highly reflective beneath the canyon floors indicates sand as canyon fill. The ridges and levees consist of large pockets of weakly stratified to transparent sediment with a few distinct reflec- tions and deep sound penetration up to 900 ms. B: Mid-slope section (segment 2) showing reduced number and relief of tributary canyons compared with profile A. Canyon fill (SCF) is sand-rich, with the exception of canyons NBA and NCAA, which contain debris-flow deposits (DFD). Seismic reflec- tion character and penetration beneath the ridges are very similar to those of profile A (from Hesse, 1992, Fig. 3). C: Basin section (segment 3) showing the highly asymmetrical NAMOC levees, which return numerous parallel, low-amplitude reflections and reveal deep penetration, as in the high-relief sector of segment 1 in profile A, although the levee facies results from spillover by fine-grained turbidity currents. The sand facies of the eastern braid plain (BP) onlaps (OL) the muddy eastern NAMOC levee truncating it. Slight lateral migration of the meandering NAMOC is indicated by a former channel margin (CM); however, the thick sand facies (DCF) under the NAMOC floor suggests relative stability of the channel position.

GSA TODAY, September 1996 5 Ice Sheet Drainage continued from p. 5 ture of the streaky pattern toward the main channel where the east NAMOC levee is absent (between 57° and 56°30'N) shows that the levee was eroded by currents flowing from the braid plain into the channel, not vice versa. The occurrence of the submarine braid plain distal to the upslope non- braided sand-and-gravel plain (region 2) is contrary to expectation and could be an artifact of sidescan penetration through mud cover. Piston cores from the braid plain show a 1–1.5-m-thick Holocene mud blanket above massive sand layers up to several meters thick. The sidescan signal could have penetrated the thinner “mud screen” in region 3, but not the thicker mud cover near the ice outlet in region 2. Region 4: NAMOC segment between 56°N and 44°30'N below 3800 m water depth (average sea- floor gradient: 1:2000). In this region (not shown in Fig. 1), NAMOC meander radii increase from 50 km north of 54°S, to >50 km farther south. Some channel Figure 4. Piston cores from the submarine braid plain showing massive or graded sand and gravel layers reaches are straight (in the sense of Clark up to several meters thick overlain by a 1-m-thick Holocene pelagic lutite layer. IRD is ice-rafted debris. et al., 1992), whereas in others, and basement structures cause sharp, gen- erally north-northwest–south-southeast to density barrier and form density under- or above the Labrador were west-east deflections as the channel enters flows (Mulder and Syvitski, 1995). These entrained by the south-flowing Labrador and leaves fracture zones. turbidity currents carried sandy sediment Current. Typical turbid-plume deposits well beyond the upper or mid-slope (as far (Fig. 6) have been identified in piston INTERPRETATION: EFFECTS OF as region 3 and probably beyond) and fed cores from within 20 km of the assumed SEDIMENT INPUT AND TRANS- the sand and gravel plains east of the ice-margin position. The remainder of the PORT MECHANISMS ON SEA- NAMOC. The plains adjacent to the slope is predominantly underlain by fine- FLOOR MORPHOLOGY NAMOC are best explained as forming grained sediments with equal parts of The profound changes and juxtaposi- by deposition of sand-rich sheet flows hemipelagic sediments and muddy tion of sea-floor morphologies described originating in Hudson Strait and circum- spillover turbidites. Subordinate con- above can be attributed to sediment deliv- venting the NAMOC and its tributaries, stituents are from ice rafting (Fig. 6, B, and ery and transport mechanisms during rather than by flooding from the trunk D), including distinct Heinrich layers glacial episodes. The transfer of the channel. Some of the flows were appar- (Wang and Hesse, 1996), and moving glacially derived sediment to the marine ently of unusually large volume (see bottom layers of suspended sediment environment requires two major steps: below). These currents overflowed the called nepheloid-layer deposits (Fig. 6). (1) delivery to the ice margin and upper low-relief slope in front of the strait and The modern high relief of the slope slope by primary transport mechanisms, cut shallow channels into the substrate has been generated by retrograde syn- and (2) slope erosion and redeposition by of the debris-flow deposits on the upper or postdepositional erosion involving secondary transport mechanisms. The slope (Fig. 3A). headward and sideward gullying in the upper-slope dichotomy of low- vs. high- canyons producing the present-day den- relief sectors (Fig. 3A), which is projected High-Relief Morphology: Turbid- dritic, high-relief canyon pattern. Remobi- basinward by the submarine braid-plain Plume Deposition, Slope Erosion lization of sediment by slumping, debris vs. leveed-channel dichotomy (Figs. 3B, 5) and Redeposition flow, and turbidity current formation has is the result of a giant grain-size fractiona- The normal mode of turbidity-current been the main sediment source for the tion process at the ice margin. When generation in an ice-marginal environ- NAMOC, whose muddy levees in regions detritus carried by the and its ment is secondary transport due to remo- 2 and 3 formed by spillover from the fine- reaches the sea, the is bilization of glacial-front upper-slope sedi- grained tops of turbidity currents (same separated from the bedload by processes ment, not meltwater flooding. To a large spillover turbidites as in Fig. 6D, but appropriately named ice-margin sifting. extent, the upper-slope region south of without ice-rafted debris). the Hudson Strait outlet received sediment Low-Relief Morphology: Transport as a mud blanket deposited by particle-by- Channelized Turbidity Currents by Debris Flows and “Primary” particle settling. Meltwater entering the The change from the depositional- Turbidity Currents sea, even when heavily loaded with sus- erosional topography of the slope to a The vast volumes of coarse material pended sediment, rose buoyantly to the mostly depositional topography on the melted from the huge Hudson Strait surface, forming turbid surface plumes—a rise is marked by the appearance of chan- glacier tongue led to the production of well-known phenomenon in modern - nels with true depositional levees built by giant debris flows that had a smoothing water glaciers (Syvitski et al., 1987; Pfir- deposition from turbidity cur- effect on the relief. Periodic meltwater man and Solheim, 1989; Lemmen, 1990). rents. Levee development peaked along peaks caused heavy sand-laden Meltwater plumes jetting out from under the upper NAMOC in regions 2 and 3 freshwater flows to break the seawater

6 GSA TODAY, September 1996 (upstream from the entrance of sandy flows from the braid plain) where levees reach a maximum height of 80 m above the adjacent basin plains, and widths up to 40 km to the west and 20 km to the east of the NAMOC (Fig. 3C). Down-channel decreases of levee relief from 80 to 30–10 m and channel depth from 200 to 140–75 m imply that flow parameters decreased down-flow. The difference in levee height between the west and east levees also decreases from a maximum of 90 m to 30 m in the proximal to the distal channel reaches, signaling the decreasing effect of Coriolis force with latitude together with decreasing flow velocities and densities in the distal channel. Quantification of flow parameters by using imaged channel geometry (width, meander radii) and a digital terrain model generated from the bathymetric data (channel depth, levee asymmetry) provide information on flow-velocity variation, both longitudinally along the flow path and vertically within the flows (Klaucke, 1995). Equilibrium-flow conditions have been established only for the first 350 km Figure 5. Facies distribution map, Labrador slope and basin, based on seismic profiles and ground- of region 3. Low flow velocities of 0.8 m/s truthing piston cores. that decrease to 0.05 m/s, calculated for region 3 bankfull flows, are flow-top veloc- ities (Klaucke, 1995). Gravel-sized chan- nel-fill sediments in the NAMOC along regions 2 and 3 (Chough et al., 1987) give maximum calculated bottom velocities of 6.5 to 8 m/s (for the lower 50 to 80 m of up to 200-m-thick flows). These higher bottom velocities apparently shaped the overall channel geometry, including the low-sinuosity meander pattern.

RELATION BETWEEN BRAID- PLAIN DEVELOPMENT, HEINRICH EVENTS, AND SHORT-TERM CLIMATE CHANGE The development of the submarine braid plain in the Labrador Basin adjacent to the NAMOC (Fig. 5) sheds light on a possible relation between the injection of sand-laden meltwater by turbidity currents AB C D and Heinrich ice-rafting events. Some of Figure 6. X-radiographs of glaciomarine depositional facies from the Labrador slope and basin. A: Tur- the turbidity currents that deposited sand bid surface-plume deposits; B: hemipelagic sediment with ice-rafted debris; C: nepheloid-layer deposits; on the braid plain must have been unusu- D: overbank levee spillover turbidites alternating with laminae of ice-rafted debris. ally large. After having traveled more than 1000 km from the Hudson Strait outlet, were dammed by end , or injected into the deep-ocean circulation. some of them were still powerful enough by the ice itself, surging of the Hudson This may have affected deep-water density to erode the east NAMOC levee between Strait ice stream during Heinrich events and, accordingly, the deep conveyor-belt 57° and 56°30’N. There, they entered the could have cut the barriers, causing the circulation in the Atlantic, at least tem- main channel and traveled down channel catastrophic emptying of the lakes. Alter- porarily. This possibility has not been an unknown distance, probably to the natively, rising lake levels may have lifted considered previously in the climate-feed- channel terminus on the Sohm Abyssal the ice and been the cause that trig- back scenarios, which have recently Plain. These flows deposited sandy over- gered ice surging and Heinrich events. The incorporated Heinrich events as short- sediment all along the east levee of ensuing outburst flooding term climate pacemakers. the distal channel (Klaucke, 1995). The events would have cut the gorges and only suitable of appropriate size canyons now subaerially exposed as ACKNOWLEDGMENTS that could have released such very large spillways on on We are grateful for a careful, in-depth volumes of sediment and water are sub- the north of the strait (Johnson and review of this paper by John E. Damuth, glacial lakes in Hudson Strait and its Lauritzen, 1995). Large volumes of fresh critical comments by Andrew Hynes and drainage area. The former existence of or brackish water entrained in the result- these lakes is indicated by large depres- ing turbidity currents could have been sions (e.g., in the floor of the strait). If the Ice Sheet Drainage continued on p. 8

GSA TODAY, September 1996 7 REPORT implies, only nuclear contamination was considered. This workshop documented Bruce F. Molnia that much less radioactive waste had been dumped into the far eastern marginal Washington Report provides the GSA membership with a window on the activities of the than into the Arctic marginal seas. One federal agencies, Congress and the legislative process, and international interactions that reason for this was that most of the high- could impact the geoscience community. In future issues, Washington Report will present level solid waste in the Russian Far East, summaries of agency and interagency programs, track legislation, and present insights into generally reactors and spent fuel rods of Washington, D.C., geopolitics as they pertain to the geosciences. mothballed nuclear submarines, were still in temporary storage at naval sites along the coastline. Even more problematic was the fact that a suitable reprocessing capa- tion-gathering activities. In 1992, after bility and the means to transport these Pristine No More learning that several million curies of highly radioactive materials do not exist. radioactive waste had been dumped by The proceedings of this workshop were Several recent reports have provided a the former Soviet Union into the Arctic’s released in May 1996, as the volume 9, variety of information indicating that marginal seas, the IARPC convened an fall/winter issue of Arctic Research of the human and natural changes are having a international workshop to identify the . significant impact on many of the north- breadth and sources of existing data and In June 1996, a follow-on workshop, ern and Arctic marginal seas. These areas information about Arctic contamination, cosponsored by the U.S. Geological include the Bering Sea, Kara Sea, Barents to identify major data gaps, and to deter- Survey, was held in Niigata, Japan. Its pur- Sea, Laptev Sea, Sea of Okhotsk, and Sea of mine whether specific Arctic contami- pose was to continue the multinational Japan. The human activities include nants present a risk to the environment, international dialogue on how to reduce dumping radioactive waste, overfishing, ecosystems, or human health in , the volume of radioactive waste stored in release of metals and other contaminants the Arctic, and the global environment. the Russian Far East. The proceedings of to the environment, and a variety of other The focus of the workshop was not only this workshop will be published early in actions. Radioactive waste has also been radioactive contamination, but also other 1997 in Arctic Research of the United States. dumped in the northernmost northwest contaminants that exist in and affect the The third report, “The Bering Sea Pacific Ocean. Arctic. Ecosystem,” 309 pages long, concluded Three reports—two released in the The result is a 311-page proceedings that during the past 50 years, natural past few months and one released last volume, which contains about 60 presen- changes in the ocean environment have year—clearly document what is known tations, including 12 papers and 10 combined with the effects of human har- about the extent of change to these north- abstracts by Russian experts. The work- vesting of whales, the taking of other ern areas. Two reports were released by the shop identified that a broad variety of marine mammals, such as seals, and over- U.S. Interagency Arctic Research Policy contaminants are found in the Arctic, fishing “to cause a cascading and possibly Committee (IARPC). They are “Workshop even though they are not used in that irreversible sequence of changes in the on Arctic Contamination” and “Proceed- area. For instance, natural transportation Bering Sea ecosystem.” These activities ings of the Japan—Russia—United States processes concentrate compounds like appear to have reduced the amount of Study Group on Dumped Nuclear Waste in DDT in the coastal Arctic even though high-quality food available to young the Sea of Japan, Sea of Okhotsk, and the they are not being used within a several marine mammals and birds. Nine recom- North Pacific Ocean.” The third report, thousand mile radius. The proceedings mendations are presented, including some “The Bering Sea Ecosystem,” released in volume, was released in May 1995, as the possible changes to the management of May 1996, was prepared by the Polar volume 8, issue of Arctic Research of the Bering Sea fishery. Research Board (PRB) of the National the United States. Both IARPC proceedings are available Research Council and published by the The second report, “Proceedings of at no cost from the Office of Polar Pro- National Academy Press. the Japan—Russia—United States Study grams at the National Science Foundation; The IARPC, a federal committee with Group on Dumped Nuclear Waste in the the PRB report may be purchased from the a membership composed of the 14 agen- Sea of Japan, Sea of Okhotsk, and the National Academy Press. For additional cies active in the Arctic, coordinates Fed- North Pacific Ocean,” expanded the geo- information, contact your Washington eral Arctic basic and applied research, graphic area of concern to the marginal Report editor ([email protected]). ■ monitoring efforts, and other informa- seas of the Russian Far East. As the title

Ice Sheet Drainage continued from p. 7 Broecker, W. S., Bond, G., Klas, M., Clark, E., and Hesse, R., 1989, “Drainage system” associated with mid- McManus, J., 1992, Origin of northern Atlantic’s Hein- ocean channels and submarine yazoos: Alternative to rich events: Climate Dynamics, v. 6, p. 265–273. submarine fan depositional systems: Geology, v. 17, Kirk Maasch, substantial editorial assis- p. 1148–1151. tance by Suzanne Kay, the cooperation of Chough, S. K., and Hesse, R., 1976, Submarine mean- dering talweg and turbidity currents flowing for 4000 Hesse, R., 1992, Continental-slope sedimentation adja- Captain Lewis, and the officers and crew km in the Northwest Atlantic Mid-Ocean Channel: cent to an ice margin. I. Seismic facies of Labrador of CSS Hudson, and major funding from Geology, v. 4, p. 529–533. Slope: Geo-Marine Letters, v. 12, p. 189–199. the Canadian Natural Science and Engi- Chough, S. K., Hesse, R., and Müller, J., 1987, The Hesse, R., and Klaucke, I., 1995, A continuous along- neering Research Council and the U.S. Northwest Atlantic Mid-Ocean Channel of the Labrador slope seismic profile from the Upper Labrador Slope, Sea. IV. Petrography and provenance of the sediments: in Pickering, K. T., et al., eds., Atlas of deep-water National Science Foundation. Canadian Journal of Earth Sciences, v. 24, p. 731–740. environments: Architectural style in turbidite systems: Chapman & Hall, p. 18–22. Clark, J. D., Kenyon, N. H., and Pickering, K. T., 1992, REFERENCES CITED Quantitative analysis of the geometry of submarine Hesse, R., and Rakofsky, A., 1992, Deep-sea Bond, G., Broecker, W., Johnson, S., McManus, J., channels: Geology, v. 20, p. 633–636. channel/submarine yazoo system of the Labrador Sea: A Labeyrie, L., Jouzel, J., and Bonani, G., 1993, Correla- new deep-water facies model: American Association of Fisher, D. A., Reeh, N., and Langley, K., 1985, Objective tion between climate records from North Atlantic sedi- Petroleum Geologists Bulletin, v. 104, p. 680–707. ments and Greenland ice: Nature, v. 365, p. 143–147. reconstruction of the Late Wisconsinan Laurentide Ice Sheet and the significance of deformable beds: Broecker, W. S., 1994, Massive discharges as triggers Géographie physique et Quaternaire, v. 39, p. 229–238. for global climate change: Nature, v. 372, p. 421–424. Ice Sheet Drainage continued on p. 9

8 GSA TODAY, September 1996 Penrose Conference Scheduled fax 505-255-5253, E-mail: haneberg@ nmt.edu; J. Casey Moore, Earth Sciences Board, University of , Santa Cruz, Faults and Subsurface Fluid Flow: CA 95064, (408) 459-2574, E-mail: casey@ rupture.ucsc.edu; Laurel B. Goodwin, Fundamentals and Applications to Department of Earth and Environmental Science, New Mexico Tech, Socorro, NM Hydrogeology and Petroleum Geology 87801, (505) 835-5178, E-mail: lgoodwin@ nmt.edu; Peter S. Mozley, Department of September 10–15, 1997 Earth and Environmental Science, New Mexico Tech, Socorro, NM 87801, (505) A Geological Society of America Pen- faults and subsurface fluid flow. Partici- 835-5311, E-mail: [email protected]. rose Conference, “Faults and Subsurface pants will be returned to the Albuquerque Application deadline is March 1, Fluid Flow: Fundamentals and Applica- airport before noon on September 15. 1997. Invitations will be mailed to partici- tions to Hydrogeology and Petroleum The conference will be limited to pants by April 1, 1997. We will have a lim- Geology,” will be held September 10–15, 70 participants, who will be selected to rep- ited number of invited oral presentations, 1997, in Albuquerque and Taos, New resent a broad range of disciplines and geo- so that a significant part of the meeting Mexico. The conference will be a synopsis graphic areas of expertise. We encourage can be devoted to poster presentations of state-of-the-art field, laboratory, and interested graduate students to apply, and and informal discussions. computer modeling studies of the role of we will be able to offer some partial stu- Potential participants should send a faults as barriers to and conduits for sin- dent subsidies. The registration fee, which letter of application to William Haneberg gle- and multiphase fluid flow. Topics to will cover lodging, meals (except for first (address above), including a brief state- be addressed will include deformation of night’s dinner), ground transportation dur- ment of interest, the relevance of the rocks and sediments in fault zones; the ing the conference, field trip, and all other applicant’s recent work to the themes influence of deformation on fluid flow costs except personal incidental expenses, of the meeting, and the subject of any and transport phenomena; diagenetic is expected to be approximately $600 to proposed poster presentation. Although alterations and their feedback into $700. Participants will be responsible for E-mail inquiries to any or all of the con- hydrologic and structural processes; and transportation to and from the conference. veners are welcome, potential participants geological and geophysical imaging of Co-conveners are: William C. should submit two paper copies of their fault properties. We will emphasize both Haneberg, New Mexico Bureau of Mines application. E-mail letters of application fundamental research and application to & Mineral Resources, 2808 Central Avenue will not be considered. ■ problems such as ground-water supply, SE, Albuquerque, NM 87106, (505) 262-2774, ground-water contamination, petroleum migration, and petroleum production. Participants will be picked up at the About People Albuquerque airport and spend the evening of September 10 in Albuquerque, GSA Fellow Wallace S. Broecker, Lamont-Doherty Earth Observatory, and assemble the next morning for a field Columbia University, Palisades, , has been awarded the National Medal of trip to examine the relation between faults Science for his pioneering contributions in understanding chemical changes in the and ground-water flow in the Albuquer- ocean and atmosphere. que basin. Planned stops will highlight the Fellow Farouk El-Baz, University, Boston, Massachusetts, is the 1996 structure and stratigraphy of the Cenozoic recipient of the AAPG Michel T. Halbouty Human Needs Award, for his contribu- basin-fill aquifer system; deformational tions in remote sensing to the search for natural resources in arid lands. features, paleoflow indicators, and zones Joining the Colorado School of Mines (Golden, Colorado) faculty are GSA of cementation along faults cutting Members Murray W. Hitzman (Charles Franklin Fogarty Distinguished Chair in unconsolidated basin-fill sediments; Economic Geology) and Neil F. Hurley (Charles Boettcher Distinguished Chair in and the hydrogeology of basin-bounding Petroleum Geology). faults. We will then travel to Taos, for Fellow John G. Vedder, Portola , California, is the fourth recipient three days of oral presentations, poster ses- of the Dibblee Medal, presented by the Thomas Wilson Dibblee, Jr., Geological sions, and discussions concerning current Foundation, in recognition of extraordinary accomplishment in geologic mapping. and future research on the interrelation of

Ice Sheet Drainage continued from p. 8 Klaucke, I., and Hesse, R., 1996, Fluvial features in the Pfirman, S., and Solheim, A., 1989, Subglacial meltwater deep sea: New insights from the glacigenic submarine discharge in the open-marine tidewater glacier environ- Hesse, R., Chough, S. K., and Rakofsky, A., 1987, The drainage system of the Northwest Atlantic Mid-Ocean ment: Observations from Nordaustlandet, Northwest Mid-Ocean Channel of the Labrador Sea. V. Channel in the Labrador Sea: Sedimentary Geology (in Archipelago: Marine Geology, v. 86, p. 265–281. Sedimentology of a giant deep-sea channel: Canadian press). Rognstad, M., 1992, HAWAII MR1: A new underwater Journal of Earth Sciences, v. 24, p. 1595–1624. Lemmen, D. S., 1990, Glaciomarine sedimentation in mapping tool: International Conference on Signal Pro- Hughes, T., 1987, Ice dynamics and mod- Disraeli , high Arctic Canada: Marine Geology, cessing Technology ‘92, p. 900–905. els when ice sheets collapsed, in Ruddiman, W. F., and v. 94, p. 9–22. Syvitski, J. P. M., Burrell, D. C., and Skei, J. M., 1987, Wright, H. E. J., eds., North America and adjacent Macdonald, K. C., Scheirer, D. S., Carbotte, S., and Fox, : Processes and products: New York, Springer - oceans during the last deglaciation: Boulder, Colorado, P. J., 1993, It’s only topography: GSA Today, v. 3, no. 1, Verlag, 375 p. Geological Society of America, Geology of North Amer- p. 1, p. 24-25, no. 2, p. 29-31, p. 34–35. ica, v. K-3, p. 183–220. Wang, D., and Hesse, R., 1996, Continental slope sedi- Mulder, T., and Syvitski, J.P.M., 1995, Turbidity currents mentation adjacent to an ice-margin. II. Glaciomarine Johnson, R. G., and Lauritzen, S.-E., 1995, Hudson Bay- generated at mouths during exceptional discharges to depositional facies on Labrador Slope and glacial cycles: Hudson Strait jökulhlaups and Heinrich events: A the world ocean: Journal of Geology, v. 103, p. 285–299. Marine Geology (in press). hypothesis: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 117, p. 123–137. Paillard, D., and Labeyrie, L., 1994, Role of the thermo- Manuscript received August 1, 1995; revisions received haline circulation in the abrupt warming after Heinrich Klaucke, I., 1995, The submarine drainage system of the October 31, 1995, January 18, 1996, June 11, 1996; events: Nature, v. 372, p. 162–164. ■ Labrador Sea: Result of glacial input from the Lauren- accepted June 18, 1996. tide Icesheet [Ph.D. thesis]: Montreal, Quebec, Canada, McGill University, 248 p.

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