The original version of this glossary was published almost 20 years ago in the landmark volume Glaciated Continental Margins: An Atlas of Acoustic Images (Bell et al. 1997). For the present volume, we have modified the text and added academically accepted terminology gleaned from the manuscripts submitted to the present Atlas of Submarine Glacial Landforms and from other sources. By its nature, an atlas that illustrates acoustic images of glacimarine features and environments will incorporate a specialized vocabulary that covers many earth science disciplines. This revised glossary contains abbreviated non-technical definitions of commonly used terms to help the reader, as needed, understand the Atlas contributions, and to facilitate communications between specialists and others in the broader scientific community. The majority of terms defined here are found in the papers contributed to the Atlas of Submarine Glacial Landforms . Other commonly used technical terms are also included to assist with wider reading, for example of papers in the cumulated bibliography to this Atlas . The glossary, therefore, provides a balanced sample of terminology currently used in technical publications. The context of the definitions that are provided is directed towards studies of past and present glacimarine environments and, in some cases, may not rigorously apply to other geological studies. In addition, we emphasize the common current usage of the terms, and do not state or attempt to trace their historical meanings. Internet resources are now commonly available to assist the reader, and we have listed a short selection at the end of the Glossary. In compiling the glossary, we have consulted the dictionaries and glossaries that are listed in the ‘Written Sources’ section extensively, and have modified some of the definitions listed therein. For this glossary, however, we accept responsibility for any errors.

High-resolution seismic-reflection data were collected across the upperand middle-continental slope of the northern Gulf of Mexico to study the distribution of gas and gas hydrate and their relation to seafloor slides. Seafloor gas vents and gas hydrate are widely reported near salt-related structures, but gas hydrate is only reported in one deep drill site. In our study area, the upper 1000 m subbottom, which includes the gas-hydrate-stability zone (GHSZ), has many high-reflectivity zones (HRZs) that lie at varied subbottom depths near shallow diapirs, faults and likely debris flows, and that are interbedded within layered sedimentary sections. HRZs occur near seafloor gas vents and along faults, lie below (more common) and within the GHSZ, and coincide with zones of shallow water-flows. Bottom simulating reflections are rare in the Gulf, and not seen in our data. We believe HRZs result largely from free gas in sandy beds. These beds would also contain hydrates within the GHSZ. We estimate base GHSZ for methane and two petrogenic gases, and on seismic sections the base GHSZ correlates reasonably with top of HRZs in some thick well-layered basin sections, but poorly where shallow sediments are thin and strongly deformed. The correlation is equivocal in part because the values used to calculate estimates of base GHSZ are poorly constrained and may vary widely, especially near areas of large waterand sediment-flows. HRZs may be a potential indicator for nearby gas hydrate. HRZs also lie at the base of at least two large seafloor slides (e.g., up to 250 sq. km.) that may be actively moving along decollement faults that sole within the GHSZ or close to the estimated base of the GHSZ. We suspect that water/gas flow along these faults and adjacent strata provide gas to source gas hydrate in the GHSZ, and flow weakens sediments that slide on saltoversteepened slopes when triggered by earthquakes.

We recorded high-resolution seismic-reflection data in the northern Gulf of Mexico to study gas and gas-hydrate distribution and their relation to seafloor slides. Gas hydrate is widely reported near the seafloor, but is described at only one deep drill site. Our data show high-reflectivity zones (HRZs) near faults, diapirs, and gas vents and interbedded within sedimentary sections at shallow depth (< 1 km). The HRZs lie below the gas-hydrate-stability zone (GHSZ) as well as within the zone (less common), and they coincide with zones of shallow water-flows. Bottom simulating reflections are rare in the Gulf, and not documented in our data.We infer HRZs result largely from free gas in sandy beds, with gas hydrate within the GHSZ. Our estimates for the base BHSZ correlate reasonably with the top of HRZs in some thick well-layered basin sections, but poorly where shallow sediments are thin and strongly deformed. The equivocal correlation results from large natural variability of parameters that are used to calculate the base of the GHSZ. The HRZs may, however, be potential indicators of nearby gas hydrate. The HRZs also lie at the base of at least two large seafloor slides (e.g. up to 250 km(2)) that may be actively moving along decollement faults that sole within the GHSZ or close to the estimated base of the GHSZ. We suspect that water/gas flow along these and other faults such as 'chimney' features provide gas to permit crystallization of gas hydrate in the GHSZ. Such flows weaken sediment that slide down salt-oversteepened slopes when triggered by earthquakes. Published by Elsevier Science Ltd.

During June 1998 and April 1999, the U.S. Geological Survey (USGS) conducted two research cruises in the northern Gulf of Mexico to acquire high-resolution seismic reflection data across the upper and middle continental slope as part of an investigation of the seismic character, distribution, and potential effects of naturally-occurring marine gas hydrates and related free gas within the gas hydrate stability zone. Over 1600 km of two-dimensional multichannel seismic reflection profiles were acquired during these two cruises. The specific objectives of this investigation are (a) to produce high-resolution images of the gas hydrate stability zone; (b) to study the distribution and character of potential seafloor failures and their relationship to known and inferred gas hydrate deposits; (c) to look at systematic variations in subsurface structure in gas hydrate and non-hydrate areas; and (d) to estimate, if possible, the amounts of hydrates present within the gas hydrate stability zone. The multichannel profiles provide high-quality images with approximately 5 meters of vertical resolution and up to 2 km of penetration. This report gives an overview of the acquisition and data processing of the multichannel seismic reflection profiles and provides references and links to reports with more detailed information. Geologic interpretations of these seismic profiles regarding gas hydrate occurrence and distribution within the study areas of this investigation are given in Cooper and Hart (2002).

1999 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

During June 1998, the U.S. Geological Survey (USGS) and the University of Mississippi Marine Minerals Technology Center (MMTC) conducted a 12-day cruise in the Mississippi Canyon region of the Gulf of Mexico (Fig. 1). The R/V Tommy Munro, owned by the Marine Research Institute of the University of Southern Mississippi, was chartered for the cruise. The general objective was to acquire very high resolution seismic-reflection data across of the upper and middle continental slope (200-1200-m water depths) to study the acoustic character, distribution and potential effects of gas hydrates within the shallow subsurface, extending from the sea floor down to the base of the gas-hydrate stability zone. The Gulf of Mexico is well known for hydrocarbon resources that include petroleum and related gases. Areas of the Gulf that lie in waters deeper than about 250 m potentially have conditions (e.g., pressure, temperature, near-surface gas content, etc.) that are right for the shallow-subsurface formation of the ice-like substance (gas and water) known as gas hydrate (Kvenvolden, 1993). Gas hydrates have previously been sampled in sea-floor cores and observed as massive mounds in several parts of the northern Gulf, including the Mississippi Canyon region (e.g., Anderson et al., 1992). Extensive seismic data have been recorded in the Gulf, in support of commercial drilling efforts, but few very high resolution data exist in the public domain to aid in gas-hydrate studies. Studies of long-term interest include those on the resource potential of gas hydrates, the geologic hazards associated with dissociation and formation of hydrates, and the impact, if any, of gas-hydrate dissociation on atmospheric warming (i.e., via release of methane, a "greenhouse" gas). Several very high resolution seismic systems (surface-towed, deep-towed, and sea-floor) were used during the cruise to test the feasibility of using such data for detailed structural (geometric) and stratigraphic (physical property) analyses based on the acoustic data. The cruise was conducted in two regions, on opposite flanks of the Mississippi Canyon, where gas hydrates are known and suspected from prior coring and seismic operations (e.g., Neurauter and Bryant, 1989). The regions are also characterized by thick surficial, relatively young (Pleistocene and younger) sediments. Swath-bathymetry data (Fig. 2) show extensive sea-floor faults, piercement features, and slumps—features whose development could potentially be related to gas hydrates. The specific objectives of the cruise were (a) to image the gas-hydrate stability zone across the continental margin to document bottom-simulating reflections (BSRs) and changes in geometry of the hydrate stability zone; (b) to image known hydrate features (with several seismic systems) to estimate physical properties for hydrate and non-hydrate areas; (c) to outline the shallow structures of the hydrate stability zone to ascertain their potential effects on the formation/distribution of hydrates and on stability of the sea floor; and (d) to estimate, if possible, the amounts of hydrates present in the shallow sub surface. During the cruise about 850 km of multichannel and single-channel seismic data were recorded. Seismic measurements at nine ocean-bottom seismometer (OBS) stations were recorded for several of the multichannel tracklines (see Fig. 3 in report). The following report describes the field operations and equipment systems employed, gives two examples of ship-board seismic records, and outlines a few preliminary results.

In 1983, President Ronald Reagan established the Exclusive Economic Zone, an area of 3.9 billion acres (∼1.6 billion hectares) that gives the United States exclusive rights to energy and mineral resources on and under the seafloor for a distance of 200 nautical miles (∼370 km) from its coastline and in its territorial seas [Rowland et al., 1983]. The U.S. Geological Survey established a program, EEZ‐Scan, in spring 1984 to map this new undersea territory [Gardner, 1984; EEZ‐Scan Group, 1985]. The results of the first field season of mapping the EEZ off the conterminous west coast of the United States have been published as an atlas [EEZ‐Scan 84 Scientific Staff, 1986] that is the first volume of a series.

In this report, the shelf (St.George basin) and deep-water (Umnak Plateau region) areas of the St. George basin OCS planning area are described separately, (Fig. 1) as was done with the previous resource reports of Marlow and others (1979c) and Cooper and others (1980).At the time of the writing of this report, information for two cost wells in St. George basin are in final preparation for

Recent seismic-reflection surveys reveal a frontier province of exceptional size--the Navarin basin province--beneath the northwestern Bering Sea shelf.Structure contours drawn on acoustic basement define three basins within the province; the basins contain strata 10 to 15 km thick and underlie more than 2 45,000 km (11 million acres) of the Bering Sea shelf.Tertiary mudstone dredged from the continental slope averages more than 0.33 percent (range of .33 to .88)organic carbon, and Cretaceous mudstone along the continental slope in Pribilof Canyon contains as much as 1 percent organic carbon.However, these mudstones may not be correlative with the lower Intense storms produce exceptionally large waves which are not only capable of eroding bottom sediments, but also are dangerous to surface structures and vessels.Gas-charged sediment, present throughout a large part of the basin, has reduced strength and bearing capacity as compared to strength of gas-free sediment.Volcanic activity is a hazard of low probability.Migratory pack ice is a yearly occurrence and could pose a significant problem during years of heavy concentrations.64 62 0 Multichannel Track Lines Figure 2. Trackline chart of 24-channel seismic reflection profiles across the Navarin basin province.High resolution seismic reflection, refraction, bathymetry, gravity, and limited magnetic data were also collected along the tracklines.Navarin basin province shown by stipple pattern.Albers equal area proj ection.'So-EXPLANATION CP Novonn bom '. ' complen X '-.< | | SuilKial dap*|ii> including ohK.01 drill * ' , Ou»t>nO>r on* Ta'liarf >*IC*

th ISAES in Santa Barbara, California, USA. The meeting agenda is given below. The meeting was held in the Corwin West room of University Centre, and eighteen people attended (see list below). Fred Davey gave the background for the CASP project, and then outlined the agenda and meeting objectives. The principal objective of this first CASP meeting was to organize the project, with later meetings and workshops then addressing procedural and science issues. Other meeting objectives were to: outline existing interests of investigators; discuss and achieve agreement by the community on data access and use; outline a work program for the next year; and select a Steering Committee and Convenor for the project. Meeting participants introduced themselves and briefly discussed the regions of the Antarctic margin where they are working, the seismic data bases that they had and whether these data bases were now loaded in a seismic interpretation package. They also described how much seismic data had been interpreted for regional stratigraphy, the interpretive package they used and what they hoped to be able to contribute to the project. During these presentations, two phases for the project were recognized and emphasized i) merging of data bases held in different interpretive systems, and ii)integration of seismic stratigraphies for different parts of the continental margin. Nearly 310,000 km of multichannel seismic data (MCS) now exist around the Antarctic margin from the continental shelf to the abyssal plain (e.g. Wardell et al., 2007), and many regional stratigraphic studies have been published. The former ANTOSTRAT project (1989 - 2003) compiled data in five principal areas around Antarctica and created regional data compilations, regional seismic stratigraphies and a seismic stratigraphic atlas of the Ross Sea (e.g., Cooper et al., 1995). Results of some of these studies are summarized in Cooper et al. (in press). Over the past decade, over 75,000 km of new MCS data have been collected principally by Australia, Russia, Norway, Germany, and Italy around the East Antarctic margin from the Weddell to Ross seas. German Leitchenkov indicated that Russian data have been entered into a Landmark system. Phil O'Brien noted that Australian data are entered into a GeoFrame system. The two groups together with an Italian group, are now working to merge the overlapping data sets and seismic stratigraphies. On the West Antarctic margin, Chiara Sauli described the extensive work being done by the ROSSMAP Project to reassess the seismic stratigraphy of the Ross Sea, based on new data collected since the ANTOSTRAT atlas was made. This work is being done by several groups using at least three different seismic interpretation systems. Lou Bartek noted the U.S. MCS data that were being contributed to the ROSSMAP project. Karsten Gohl noted that stratigraphic analysis of about 10,000 km of MCS data in the Bellingshausen Sea was being done using a Landmark system, which is the same system that German scientists used for the compilation of their Weddell Sea data. In the Antarctic Peninsula and western Weddell Sea regions, Andres Maldonado described efforts at the University of Granada to compile all of Spain's MCS data on a Landmark system. Michele Rebesco noted that only few of the Italian lines in the Antarctic Peninsula region were in their interpretive system. The presentations and follow-up discussion highlighted the high level of interest in regional seismic stratigraphic mapping, and the desire to integrate these interpretations into a unified circum-Antarctic stratigraphy. The general feeling was that such a project is now possible for large parts of the Antarctic margin if all existing seismic data sets are incorporated. This will be a massive undertaking and not possible by one research group, and will require a large