AHC-800 (Active Heave Compensation to 800 m) Drilling on the New Jersey Shelf

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1 AHC-800 (Active Heave Compensation to 800 m) Drilling on the New Jersey Shelf John A. Goff Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin 4412 Spicewood Springs Rd., Bdlg., 600, Austin, TX phone: (512) fax: (512) James A. Austin, Jr. Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin 4412 Spicewood Springs Rd., Bdlg., 600, Austin, TX phone: (512) fax: (512) Award Number: N LONG-TERM GOALS (1) Establish the geologic history of sedimentary processes on the New Jersey shelf (Fig. 1) over the last ~50,000 years, particularly focusing on the nature of shelf-edge sedimentary wedges, including the formation and preservation of sand bodies (Gulick et al., 2005), the paleoclimate associated with outershelf channel formation and subsequent infilling (Nordfjord et al., 2005), cross-shelf transport of sediments at or near lowstand (Goff et al., 2005), and the influence on the preserved stratigraphy of large sediment outflows associated with postulated glacial lake collapses during the last deglaciation (Fulthorpe and Austin, 2004). (2) Interact with ONR-funded acoustic programs on the New Jersey shelf to provide the capability for modeling geoacoustic properties of the shallow seabed in three dimensions OBJECTIVES Seismic reflection profiles have been used for decades to survey stratigraphic geometries in continental margin settings. Stratigraphy in turn provides a wealth of information on important scientific and societally relevant issues, including sea-level variations and long-term sea-level rise, climate history and climate change, and tectonism. However, despite its analytical power, the interpretation of reflection data for Navy-relevant purposes is ambiguous without direct sampling to establish the geology, physical properties, absolute age and paleoenvironmental history of insonified strata. The tremendous success of scientific ocean drilling, the Deep-Sea Drilling Project (DSDP, ), Ocean Drilling Program (ODP, ) and now the Integrated Ocean Drilling Program (IODP, 2003-), is a result of the marriage of geophysical surveys with analysis of drilled cores. Unfortunately, for the study of shallowly buried (up to ~100 m depth below seafloor), spatially-complex stratigraphy in continental shelf settings, sampling of imaged features has been extremely difficult. Sampling to sub-seafloor depths beyond ~5 m has fallen within a technological gap between expensive, deeppenetration rotary drilling, used by IODP and the oil industry, and smaller, cheaper, shallowpenetration methods, such as piston- and vibra-coring. Coarse-grained sediments typical of shelves have proven particularly difficult to penetrate and recover; penetrations are generally <5 m and

2 recovery is often poor to nonexistent. This difficulty has been a primary stumbling block for making significant progress in prior Office of Naval Research (ONR)-funded studies, parts of the STRATAFORM and Geoclutter initiatives, integrating superb high-resolution seismic images of shallow stratigraphy and the geologic successions responsible for those images. These shelf-upper slope stratigraphic successions exhibit the greatest potential for unraveling the anthropogenicallyrelevant geologic record of the last ~50 kyrs. Figure 1. Location of important available seabed data and samples on the NJ outer shelf, superimposed on bathymetric map (depths in meters). The heavy dashed lines indicates the primary acoustic propagation lines planned for the SWA06 experiment in summer 2006, and the yellow box indicates area of additional chirp data to be collected by Dr. Turgut of NRL in support of the SWA06 experiment. Since the 1990 s, the Institute for Geophysics has been collaborating with ONR and DOSECC (Drilling, Observation and Sampling of the Earth s Continental Crust), Inc., in the development of a capability to drill/core shallow-water shelf-upper slope sediments to sub-seafloor depths of tens to hundreds of meters. DOSECC, of which The University of Texas at Austin is a member, is a nonprofit corporation whose mission is to provide leadership and technical support in subsurface sampling and monitoring technology for addressing topics of scientific and societal importance ( DOSECC s lake-drilling system, the GLAD-800 (Global Lake Drilling to 800 m), deployed from a barge, has been successful at recovering unconsolidated lake sediments of all types. The GLAD-800 is also powerful enough to drill through and sample bedrock. The GLAD-800 employs equipment and techniques similar to those used successfully by ODP. UTIG and DOSECC, working with Woods Hole Oceanographic Institution and with support from ONR, have developed both heave-compensation for the rig and combined inertial and GPS navigation systems for high-

3 tolerance dynamic positioning (<3% of ambient water depth) of the drilling platform (R/V Knorr); both are required to deploy from a ship on the open ocean. This modified system, named the AHC-800 (Active Heave Compensation to 800 m), was successfully tested by UTIG and collaborators aboard the R/V Knorr in 2001 and 2002 on the New Jersey shelf. With funding from ONR, the New Jersey middle-outer shelf and upper slope have been surveyed extensively in 2002 using an ultra-high resolution (1-4 and 1-15 khz), deep-towed chirp seismic system (Fig. 1); resultant images are providing detailed constraints on the stratigraphic geometry of the upper ~30 m of the sedimentary record. The primary scientific goals are: (1) to investigate the preserved, shallow subsurface stratigraphic record in order to unravel the detailed paleoenvironmental and temporal history of the latest Quaternary glacio-eustatic cycle, (2) to understand cross-shelf sediment transport in glacial and periglacial settings, and (3) to understand the relationship between physical properties relevant to Navy acoustic interests (i.e., velocity, density, porosity) and the geologic structure and history in a clastic, passive margin setting. Important targets for sampling have been identified: (1) a latest Pleistocene, time-transgressive basal unconformity of complex but as yet indeterminate origin (reflector R ), (2) prograding, shelf-edge sedimentary wedges that appear to be a record of Wisconsin sea-level regression, (3) a newly-discovered seismic facies contrast that is hypothesized to record catastrophic erosion linked to breaching of glacial lake dams in Area 2 (Fig. 1), (4) fluvial channel systems likely carved just prior to the Wisconsin glacial maximum (LGM), in areas 1 and 2 (Fig. 1), and (5) channel-fills that represent the only well-preserved sediment record of the latest (Holocene) sea-level transgression on this margin, in areas 1 and 2 (Fig. 1). Our primary objective is to sample the imaged stratigraphy with the AHC-800 drilling system, in order to establish lithology, physical properties, age and paleoenvironment. The intended synthesis of seismic data and core analyses should enable us to test important, globally applicable hypotheses regarding the latest Quaternary evolution of this and similar margins APPROACH We propose AHC-800 drilling on the New Jersey shelf aboard the R/V Knorr in the summer of 2007 (a UNOLS ship request has already been submitted.). We are planning for a 12-day duration, including 10 days of drilling operations and 1 day of transit each way (from/to Woods Hole, MA). If operations are unimpeded by weather or operational delays, we anticipate being able to drill ~1 hole/day to m penetration sub-seafloor. This sampling rate would be a great improvement when compared with our 2002 production, but that (test) cruise was, in large part, dedicated to solving critical issues associated with navigation, dynamic positioning and heave compensation. Furthermore, the 2002 field effort took place in October, not the optimal weather window for the New Jersey shelf. Those problems have largely been solved. For example, the R/V Knorr now has installed a far more modern and capable dynamic positioning system. We will also plan to conduct the 2007 cruise in June-July, far more likely to be optimal for weather. Cautiously optimistic, we expect that ~3-4 well-sampled deep drill holes would be a realistic expectation for 10 days of operations in such an optimal weather window. Careful prioritization of drill locations to maximize scientific information is therefore imperative. On-board processing of cores will closely follow established ODP procedures. Core sections will be: (1) logged as whole-rounds for geoacoustic properties, including gamma-ray density, P-wave velocity and attenuation; (2) split, described sedimentologically, and preliminary sub-samples collected (particularly any fresh, datable material, e.g., wood fragments); and (3) split cores will be sealed in

4 storage tubes for later shore-based sampling and analysis. Laboratory analysis of 2002 samples has thus far included AMS 14 C age-dating of appropriate carbon-bearing material (wood, shells, foraminifera), grain size analysis and micropaleontological investigation to ascertain biostratigraphy and paleoenvironment. Core analyses will ultimately be interpreted within the context of the existing seismic stratigraphy, e.g., core logs have been used to generate synthetic seismograms which, when compared with chirp seismic data at the identical locations, help to remove depth ambiguities and confidently match seismic horizons with geologic strata. AMS 14 C dates establish chronostratigraphy, and biostratigraphy and related analyses document paleoenvironments. Figure 2 provides a schematic representation of the principal stratigraphic elements of the shallow seabed on the mid- to outer shelf. The basal R reflecting horizon formed in the Pleistocene ~40 kya. Although recognized regionally in seismic data (e.g., Milliman et al., 1990; Knebel et al., 1979), the origin of R is uncertain, perhaps formed by a composite of subaerial and submarine processes, and likely time-transgressive (Duncan et al., 2000). Overlying R is a sequence of three prograding units, formed during the latest sea level regression, ~30-20 kya (Gulick et al., 2005). Gulick et al. (2005) hypothesize that these units originated as sediments that were rapidly eroded by subaerial exposure, and then deposited in the submarine environment. From oldest-to-youngest, these are identified as the outer shelf sediments, the outer shelf wedge, and the deep shelf wedge (Fig. 2). The latter two exhibit highly laminated internal structures, indicating alterations between denser sandy sediments and less dense muds. The top of the laminated outer shelf wedge is, in places, separated from an upper transparent unit by a highly erose boundary ~5-10 m below the seafloor (Fig. 3). This boundary has been documented by Fulthorpe and Austin (2004) in their interpretation of the dense chirp seismic data collected at Area 2 (Fig. 1), which was an important focus of Geoclutter and remains at the center of the SWA06 experiment. They entertain a number of speculative explanations for the origin of this surface, favoring the possibility that this pronounced seismic facies contrast was formed during a catastrophic flooding event associated with glacial lake collapse north and east of the Hudson River. Fluvial channels eventually formed during lowstand, cutting into the outer shelf sediments, the outer shelf wedge and the R horizon (Duncan et al., 2000; Nordfjord et al., 2005). The channels were filled by estuarine and marine sediments during the transgression, and these fill units represent the only preserved record of these sediments (Nordfjord et al., in press). A transgressive ravinement, the T horizon, planed the top of the channels, and forms the base of the Holocene sand sheet (e.g., Goff et al., 2005). Our four highest-priority scientific targets for drilling are (Fig. 2 numbered for identification, not for order of priority): (1) through a full channel-fill sequence in Area 1, including the part of the Holocene sand sheet and the transgressive ravinement surface; we drilled through the flank of one of these channel sequences in 2002; (2) through outer shelf sediments (the oldest post- R unit) within Area 1 and through the R horizon; (3) through the outer shelf wedge at Area 2, including the erose boundary at the top of the wedge and through the R horizon at its base (see Fig. 3); and (4) through the deep shelf wedge, across the boundary between the outer and deep shelf wedges, and through R.

5 Figure 2. Schematic of the shallow stratigraphy of the middle and outer New Jersey shelf (after Duncan et al., 2000, Fulthorpe and Austin, 2004, and Gulick et al., 2005). The approximate stratigraphic locations of Areas 1 and 2 (see Fig. 1) are identified. Although these areas, which form the end-points of the SWA06 strike line, are at similar water depths, their underlying stratigraphy is quite different owing to the along-strike geometry of the wedges. The SWA06 dip line will incorporate all these stratigraphic elements. Numbered, heavy dashed lines indicate highest priority targets for scientific drilling (see text descriptions). Thin dashed lines represent existing cores from the 2002 AHC-800 field program. These targets, in addition to our previously collected samples, will enable us to characterize, geologically and geoacoustically, the principal stratigraphic features of the outer shelf and test our evolving hypotheses regarding the Pleistocene and Holocene evolution of this margin. WORK COMPLETED Our field work for this project is scheduled for summer of RESULTS None yet. IMPACT/APPLICATIONS In the long term, by improving our understanding of complex sedimentary systems on the continental shelf, we improve our ability to predict sedimentary properties based on understanding of environmental and geologic conditions in a region. In the short term, the results of our coring will have immediate impact on the modeling work associated with the 2006 Shallow Water Acoustic program, which is focused in the same study area. These results, combined with the Geoclutter and SWA06 chirp data, will enable us to model sediment geoacoustic properties throughout the acoustics survey region.

6 Figure 3. Portion of a chirp seismic profile from Area 2, illustrating the erose boundary mapped by Fulthorpe and Austin (2004). This pronounced facies contrast may have been produced by erosion caused by flooding across the New Jersey shelf by collapsing glacial lakes during the last deglaciation. Drilling could sample this surface, bounding facies, and get to and through the R horizon with a ~22-m penetration using the AHC-800. RELATED PROJECTS This project is most closely tied to the ONR SWA06 program, which this last summer conducted a 4-ship acoustics experiment in the same study area. Understanding the seabed geoacoustic properties along the various propagation path is a critical need for the modeling component of this program. The SWA06 web site is: REFERENCES Duncan, C. S., Goff, J. A., Austin, J. A., Fulthorpe C. S., Tracking the last sea level cycle: seafloor morphology and shallow stratigraphy of the latest Quaternary New Jersey middle continental shelf. Mar. Geol. 170, Fulthorpe, C.S., and J.A. Austin, Jr., Shallowly buried, enigmatic seismic stratigraphy on the New Jersey outer shelf: Evidence for latest Pleistocene catastrophic erosion? Geology 32, Goff, J. A., J A. Austin, Jr., S. Gulick, S. Nordfjord, B. Christensen, C. Sommerfield, and H. Olson, C. Alexander, Recent and modern marine erosion on the New Jersey outer shelf. Mar. Geol. 216,

7 Gulick, S. P. S, Goff, J. A., Austin Jr., J. A., Alexander Jr., C. R., Fulthorpe, C. S., Shelf-edge wedges off New Jersey: the R paleo-surface as the primary conduit for seaward transport of sediment during the latest Pleistocene sea-level fall. Geology 33, Knebel, H. J., Wood, S. A., Spiker, E. C., Hudson River: Evidence for extensive migration on the exposed continental shelf during Pleistocene time. Geology 7, Milliman, J. D., Jiezao, Z., Anchun, L., Ewing, J. I., Late Quaternary sedimentation on hte outer and middle New Jersey continental shelf: Result of two local deglaciations? J. Geol. 98, Nordfjord, S., Goff, J. A., Austin, J. A. Jr., Sommerfield, C. K., Seismic geomorphology of buried channel systems on New Jersey shelf: assessing past environmental conditions. Mar. Geol. 214, Nordfjord, S., Goff, J. A., Austin, J. A., Jr., Gulick, S. P. S., Sommerfield, C., Alexander, C., Schock, S.. Seismic facies analysis of shallowly buried incised valleys, New Jersey continental shelf: understanding late Quaternary paleoenvironments during the last transgression. In press, J. Sed. Res.