On continental margins, high saturation gas hydrate systems (>60% pore volume) are common in canyon and channel environments within the gas hydrate stability zone, where reservoirs are dominated by coarse-grained, high porosity sand deposits. Recent studies, including the results presented here, suggest that rapidly deposited, silt-dominated channel-levee environments can also host high saturation gas hydrate accumulations. Here we present several sedimentological data sets, including sediment composition, biostratigraphic age from calcareous nannofossils, grain size, total organic carbon (TOC), C/N elemental ratio, delta C-13-TOC CaCO3, total sulfur (TS), and delta S-34-TS from sediments collected with pressure cores from a gas hydrate rich, turbidite channel-levee system in the Gulf of Mexico during the 2017 UT-GOM2-1 Hydrate Pressure Coring Expedition. Our results indicate the reservoir is composed of three main lithofacies, which have distinct sediment grain size distributions (type A-silty clay to clayey silt, type B-clayey silt, and type C-sandy silt to silty sand) that are characteristic of variable turbidity current energy regimes within a Pleistocene (< 0.91 Ma) channel-levee environment. We document that the TOC in the sediments of the reservoir is terrestrial in origin and contained within the fine fraction of each lithofacies, while the CaCO3 fraction is composed of primarily reworked grains, including Cretaceous calcareous nannofossils, and part of the detrital load. The lack of biogenic grains within the finest grained sediment intervals throughout the reservoir suggests interevent hemipelagic sediments are not preserved, resulting in a reservoir sequence of silt dominated, stacked turbidites. We observe two zones of enhanced TS at the top and bottom of the reservoir that correspond with enriched bulk sediment delta S-34, indicating stalled or slowly advancing paleo-sulfate-methane transition zone (SMTZ) positions likely driven by relative decreases in sedimentation rate. Despite these two diagenetic zones, the low abundance of diagenetic precipitates throughout the reservoir allowed the primary porosity to remain largely intact, thus better preserving primary porosity for subsequent pore-filling gas hydrate. In canyon, channel, and levee environments, early diagenesis may be regulated via sedimentation rates, where high rates result in rapid progression through the SMTZ and minimal diagenetic mineralization and low rates result in the stalling of the SMTZ, enhancing diagenetic mineralization. Here, we observed some enhanced pyritization to implicate potential sedimentation rate changes, but not enough to consume primary porosity, resulting in a high saturation gas hydrate reservoir. These results emphasize the important implications of sedimentary processes, sedimentation rates, and early diagenesis on the distribution of gas hydrate in marine sediments along continental margins.

The objective of this report is to present both bulk sediment and organic carbon-free sediment grain size data from samples of UT-GOM2-1 pressure cores (Flemings et al, 2018). The majority of the samples measured for grain size were collected from UT-GOM2-1 cores stored at Ohio State University and sampled there during sediment core description (Johnson et al., 2020). These cores were not recovered under pressure during the UT GOM2-1 expedition. Additional samples for grain size analysis were collected from pressure cores recovered under pressure during the UT-GOM2-1 expedition and subsequently quantitatively degassed, either on-board or on-shore (UT-Austin) to determine the hydrate concentration and the gas composition. Samples from some of the quantitatively degassed pressure cores were mailed to us for grain size measurement at the University of New Hampshire. Sediment grain size measurements throughout the gas hydrate bearing reservoir at Site GC 955 is an important data set that serves to quantify the grain size distribution of the host reservoir materials, determine the degree of sorting, and identify the size fraction containing the TOC (total organic carbon). During the UT-GOM2-1 expedition, two holes were drilled in Green Canyon Block 955 (GC 955) in the deep-water Gulf of Mexico: Hole GC 955 H002 (H002) and Hole GC 955 H005 (H005). 21 10 ft (3.05 m) pressure cores were attempted in and near the methane hydrate reservoir at 409-450 mbsf. In the first hole, H002, 1 of the 8 cores were recovered under pressure and there was 34% recovery of sediment (both pressurized and depressurized). In the second hole, H005, 12 of the 13 cores were recovered under pressure and there was 72% recovery of sediment (Flemings et al., 2020; Thomas et al., 2020). The pressure cores were imaged and logged under pressure. To document the sediment grain size throughout the cored intervals in both Holes H002 and H005 at GC 955, we used the Malvern Mastersizer 2000 Laser Particle Size Analyzer with a Hydro 2000G wet dispersion unit at the University of New Hampshire.

Recognizing the importance of methane hydrate research and the need for a coordinated effort, the United States Congress enacted the Methane Hydrate Research and Development Act of 2000. At the same time, the Ministry of International Trade and Industry in Japan launched a research program to develop plans for a methane hydrate exploratory drilling project in the Nankai Trough. India, China, the Republic of Korea, and other nations also have established large methane hydrate research and development programs. Government-funded scientific research drilling expeditions and production test studies have provided a wealth of information on the occurrence of methane hydrates in nature. Numerous studies have shown that the amount of gas stored as methane hydrates in the world may exceed the volume of known organic carbon sources. However, methane hydrates represent both a scientific and technical challenge, and much remains to be learned about their characteristics and occurrence in nature. Methane hydrate research in recent years has mostly focused on: (1) documenting the geologic parameters that control the occurrence and stability of methane hydrates in nature, (2) assessing the volume of natural gas stored within various methane hydrate accumulations, (3) analyzing the production response and characteristics of methane hydrates, (4) identifying and predicting natural and induced environmental and climate impacts of natural methane hydrates, (5) analyzing the methane hydrate role as a geohazard, (6) establishing the means to detect and characterize methane hydrate accumulations using geologic and geophysical data, and (7) establishing the thermodynamic phase equilibrium properties of methane hydrates as a function of temperature, pressure, and gas composition. The U.S. Department of Energy (DOE) and the Consortium for Ocean Leadership (COL) combined their efforts in 2012 to assess the contributions that scientific drilling has made and could continue to make to advance our understanding of methane hydrates in nature. COL assembled a Methane Hydrate Project Science Team with members from academia, industry, and government. This Science Team worked with COL and DOE to develop and host the Methane Hydrate Community Workshop, which surveyed a substantial cross section of the methane hydrate research community for input on the most important research developments in our understanding of methane hydrates in nature and their potential role as an energy resource, a geohazard, and/or as an agent of global climate change. Our understanding of how methane hydrates occur in nature is still growing and evolving, and it is known with certainty that field, laboratory, and modeling studies have contributed greatly to our understanding of hydrates in nature and will continue to be a critical source of the information needed to advance our understanding of methane hydrates.

Multibeam bathymetry is being collected in exponentially increasing quantities, which are expected to be tens of terabytes per year in the near future. The National Geophysical Data Center (NGDC) is the national and international steward of marine geophysical data, including multibeam bathymetry, and has developed a MultiBeam Bathymetric Data Base (MBBDB) for acquiring, managing, and delivering these data over the Internet. NGDC manages a wide variety of geophysical data including trackline and survey data as two distinct types. Multibeam data tends to bridge these data models depending on scale and track pattern. The MBBDB system has been assembled from existing commercial, and government,-off-the-shelf (COTS and GOTS) software systems: ORACLE, ArclMS, Generic Napping Tools (GMT), MBSystem, and Autochart. The MBDDB will continue to grow and evolve, guided by feedback from our user community.

Detailed bathymetry of Lake Ontario reveals a small circular feature and adjoining SWtrending ridge associated with a small topographic high identified as Charity Shoal on nautical charts. The feature consists of a circular basin 1,000 m in diameter and 19+ m deep, completely surrounded by a low-relief rim that rises to within 5 m of the water surface over much of its extent. A N53E tapering ridge is contiguous with the feature and extends southwestward. Bedrock consists of middle Ordovician limestones 100-150 m thick overlying rocks of Precambrian age. The limited information available suggests that the feature may be an extraterrestrial impact crater, but other origins such as sinkhole, volcanic cone, or kettle, are not ruled out. Time of formation is not known, but likely times include the Pleistocene when the area was exposed by glacial erosion, the middle Ordovician near the time of deposition of limestones, or the Cambro-Ordovician or Precambrian when erosion surfaces of this age were exposed. A subtle negative magnetic anomaly coincides with the feature and is consistent with an impact origin, though not positively diagnostic. Relief of the feature is low compared to that typical of an impact crater of this size. Glaciation may have diminished relief by eroding the rim and filling the central basin with drift. Verification as an impact crater will require detailed geophysical surveys and collection and analyses of samples from in and around the structure.

Overdevelopment of shores and wetlands, dwindling sites on land for the disposal of human‐generated waste, contamination of estuaries and nearshore sediments, the disruption of coastal‐water ecosystems by dredging, and the specter of rising sea level due to anthropogenically induced global warming are but a few of the pressures humans are exerting on coastal environments around the world. In the United States, a lot is riding on the response of its coastal environments to these pressures. The majority of the U.S. population resides in the coastal states, where the country's largest cities and most popular recreation areas are located.If the United States is to sustain the health and beauty of its coastal environments, then they must be managed, not only on the federal scale, but also on the state and local scales. One of the most fundamental types of data required to conduct this management will be detailed elevation data. On land, topography dictates the flow of water and the maximum extent of flooding. Offshore, bathymetry is a major control on shallow‐water ocean currents and the dissemination of sediments eroded from the continent.

As part of a broad synthesis of geophysical data from passive continental margins bordering the South Atlantic, sediment sound‐velocity functions have been derived for the Cape Basin off southwest Africa using velocity/travel time information gathered from multichannel seismic reflection profiles and sonobuoys. These functions allow more accurate sediment thickness calculations than similar functions previously derived for this region solely from sonobuoy results. However, a single basin‐wide function is insufficient to predict thickness variations everywhere in the depocenter. Furthermore, sediment‐velocity equations developed for the southern Cape Basin do not precisely define sediment thicknesses in the north, and vice versa. Equations appropriate to both regional and previously published crustal subdivisions of the basin produce the most consistent results relative to available well control, although possible associations between underlying crustal type and overlying sediment distribution on this passive margin remain unclear. Instead, the location of the Orange Cone deltaic accumulation south of the present course of the Orange River may be the principal factor responsible for separate southern and northern sediment‐velocity provinces in the Cape Basin.