B43E-1647
The geometry and lithology of the Cima Sandstone Lentil: a paleoseep-bearing interbed in the Moreno Formation, central California
The Cima Sandstone Lentil outcrops over a relatively small area on the western side of the San Joaquin Valley in central California. Here this unit can be found in the Panoche Hills in the northern portion of the field area and the Tumey Hills in the southern portion of the field area. The Cima Sandstone resides within the 800m Moreno Formation that spans the Maastrichtian to the Danian. The Moreno Formation comprises four members, which are the Dosados Member, the Tierra Loma Member, the Marca Shale Member, and the Dos Palos Shale Member (of which the Cima Sandstone is an interbed). The Cima Sandstone contains numerous large carbonate mounds, concretions, and pavements, indicating paleoseep activity. The Cima Sandstone has never been studied in detail, but recent interest in sandstone injectites as well as interest in paleoseeps has prompted us to examine this interbed more carefully. The Cima is an immature sandstone composed primarily of quartz along with small amounts of micas and feldspars as well as varying amounts of glauconite. These minerals are generally cemented by carbonate but, occasionally, iron oxide cement is present locally. Much variation exists within the Cima Sandstone Lentil and we seek to characterize and understand this variation. One of the most obvious sources of variability is the thickness of the unit itself. The thickness ranges from near 60m in the northern Panoche Hills to only 9m in the Tumey Hills. Induration also varies noticeably, from well cemented in the north, to unconsolidated in the south. Similarly, the sandstone is grain-supported and houses some depositional structures in the northern outcrops but becomes largely matrix-supported and lacking bedding in the southern outcrops. Preliminary data suggests that proximity to carbonate concretions, fluid conduits, and underlying injectites may have some influence over grain size and sorting.
B43E-1648
Distribution and Geochemistry of Methane-Derived Cold Seep Carbonates Panoche, California
Isolated authigenic carbonate concretions and pavements occur locally within fine grained siliciclastic rocks of the Tertiary Great Valley Sequence of western California. Outcrops in the Panoche and Tumey Hills region are a record of prolonged expulsion of methane- and H2S- rich fluids from a relict cold seep system at the sea floor of a paleo-forearc basin. The entire outcrop length of the seep horizons is at least 15 km along strike. Sandstone injectites underlie the main seep horizons and may have provided fluid pathways to the sea floor. The concretions found in this locality are commonly rounded and vertically elongate, up to 15 m in height and resembling pillars in current outcrop form. Discrete carbonate pavements crop out continuously for as much as 100 m, are generally less then 3 m thick, and lacking any discernable stratification. The entire surface expression of the cold seep carbonates follows along strike, as a series of discontinuous shale encased mounds. Faunal assemblages (tubeworms, bivalves, and textures suggestive of algal mats) are fossilized, commonly in living position, within the carbonate cements. Growth and cross cutting relations recorded in these carbonate cements provides a chronology of the geochemical evolution of fluid venting at the cold seep. The earliest cement phase typically encasing the fossils and sedimentary structures is generally a high magnesium, detritus rich, finely micritic calcite or protodolomite. Energy dispersive spectrometry indicates that these cements have Ca/Mg ratios ranging from 8:1 to nearly 1:1. Within this hosting matrix are commonly a series of circular or wavy planar precipitation bands indicating sequential cementation. These later cements tend to be low Mg calcite (Ca/Mg below 8:1) which precipitated into void spaces from edge to center as coarsely fibrous crystals as large as 1 mm in width and several mm long. Each of these cement types has evidence of multiple phases of dissolution and precipitation, including coatings of fine euhedral sulfide or sulfate which also tend to grow from edge to center The presence of sulfide or sulfate indicates changes in seep chemistry, possibly related to changing redox conditions, between carbonate precipitation events. The trend with younger cements is towards progressively lower Mg content in calcite. Late-stage fibrous gypsum, commonly containing bitumen, cuts across all previous structures and contacts.
B43E-1649
Vesicomyid Clams Alter Biogeochemical Processes at Pacific Methane Seeps
There exists a close relationship between fluid flow, biogeochemistry, and biota in seep sediments. Upwelling of methane and sulfide-rich fluids supports abundant macrofauna species harboring thiotrophic or methanotrophic symbionts. Variations in fluid flow, thus supply of methane and sulfide, are considered key factors controlling benthic communities. Vesicomyid clams harbor thiotrophic symbionts in their gills, which are supplied with oxygen from the surrounding water and hydrogen sulfide from the sediment. The clams are capable of extending their foot into the sediment to tap sulfide sources in deeper layers, consequently affecting water-sediment solute exchange. Because seep fluids are generally depleted in sulfate compared to seawater, this bioturbation activity may enhance the supply of sulfate to otherwise sulfate-limited sediments, thus boosting microbial activity of sulfate reduction (SR) coupled to anaerobic oxidation of methane (AOM). The goal of this study was to investigate the activity of three species of vesicomyid clams ( Calyptogena pacifica, C. kilmeri, C. gigas) from three methane seep habitats (Eel River Basin, Hydrate Ridge, Monterey Bay Canyon) and to evaluate its effect on biogeochemical processes. Sediment cores and clams were collected using the submersible Alvin or the ROV Jason, during three cruises with the R/V Atlantis in July and October 2006 and July 2007 (AT 15-7, AT 15-11, and AT 15-20). We performed high-resolution measurements of geochemical gradients in intact sediment cores using microsensors (O2, H2S, pH, redox potential). The cores were then sliced (1 cm intervals) for detailed chemical and microbiological analyses. Parallel cores were used to determine microbial activity (AOM, SR) with radioactive tracers. For detailed laboratory investigations, clams were kept in narrow aquaria (15 cm x 20 cm x 5 cm) in the ship's cold room. The front of the aquaria was perforated with holes at 1 cm resolution. These silicone-filled holes served as sampling ports or for direct microsensor measurements. Vertical and horizontal microprofiles were measured, pore water samples were extracted, and small sediment cores were taken along the length of the aquaria for microbial rate measurements and chemical and microbiological analyses. We documented different bioturbation activity for the three species of vesicomyid clam that related to distinct geochemical gradients and differences in microbial activity. Sulfate reduction, thus sulfide production, was significantly enhanced in the presence of clams compared to the control.
B43E-1650
Evolutionary implications of endosymbiont diversity within lucinid bivalves
Bacterial endosymbiosis is widespread among Bivalvia. Symbiosis between lucinid bivalves and sulfur-oxidizing (thiotrophic) bacteria has received recent attention, as lucinids are one of the geologically oldest extant bivalve clades to possess endosymbionts. However, the ecological and evolutionary relationships between host and symbiont are poorly understood, and reconstructing the evolutionary history and geological significance of lucinid endosymbiosis requires additional knowledge and characterization of endosymbiont ecology and taxonomic diversity. Our goal was to characterize the bacterial diversity of a modern lucinid habitat in order to evaluate possible lucinid endosymbiont diversity. Host organisms ( Lucinisca nassula and Phacoides pectinatus) and sediment cores were collected from geochemically reducing and sulfide-rich sea grass beds. PCR amplification and sequencing of bacterial 16S rRNA genes from the sediment cores retrieved 13 major taxonomic groups, including equally dominant Chloroflexi, Delta-, and Gammaproteobacteria, and rare Bacteroides, Acidobacteria, Spirochaetes, and Firmicutes. Less than 2% of the sequences were affiliated with uncultured gammaproteobacterial symbiont groups, but were not closely related to the sequences retrieved from the lucinid gills. Moreover, our analyses uncovered multiple gene sequence populations within an individual, as well as across individuals within the same sampling site. Additional habitat-host-symbiont diversity from three other lucinid taxa and from six geographically distinct habitat sites is also expanding the previously understood diversity of thiotrophic endosymbionts, and specifically that the lucinid symbionts are probably not a monophyletic species. These data suggest that thiotrophic bacteria are recruitable for endosymbiosis and are widely distributed in reducing marine environments. But, because of the diversity of bacteria in any one habitat, symbionts may be metabolically and physiologically diverse. An implication of this work is that the possible geochemical record of the lucinid-symbiont association may not yield systematic results.
B43E-1651
Foraminiferal Ecology and Stable Isotope Geochemistry of Methane Seeps in Monterey Bay, California
In an ongoing effort to understand the factors that influence the stable isotopic composition of benthic foraminifera, clam beds associated with methane seepage in the Clam Flats area of Monterey Bay, California were sampled using the remotely operated vehicle Jason II. Pore water chemistry and vertical and spatial distributions and stable isotopic signatures of benthic foraminifera (stained with Rose Bengal or labled with Cell Tracker green) were examined in push cores in seeps and non-seep environments (about 990 m water depth). Pore water profiles of alkalinity and sulfide concentration reflect highly reduced environments within the seeps, but less than 30 cm from the edge of the seeps, these profiles are similar to the profiles from the non-seep environments. This result indicates that the seeps are highly localized. Microprofiles of oxygen and hydrogen sulfide measured in intact cores showed distinct differences of microhabitats within and between cores. Dominant taxa of foraminifera living in surface sediments of Clam beds included Cibicides, Bolivina, and Epistominella. Comparisons between these results and previous results from the area suggest that there is an influence of methane seepage on the carbon isotopic values of foraminiferal calcite. However, the carbon isotopic composition of DIC in pore water and those of the foraminifera associated with pore water can differ by as much as 40 per mil. Possible reasons for this disequilibrium will be explored.
B43E-1652
Natural Gas - Microbe Interactions in Southern California Bight Seep Environments
The microbial consumption of methane (C1), ethane (C2), propane (C3) and n-butane (nC4) was investigated by quantifying the distributions of these gases and other related chemicals in marine gas seeps, and through laboratory incubations of seep sediment. In-situ porewater samplers (peepers) were deployed in the sediments surrounding hydrocarbon seeps at Santa Monica Basin, Santa Barbara Basin and Coal Oil Point and were used along with traditional coring techniques to quantify the natural distributions of C1-C4 hydrocarbons. Chemical distributions display major distinctions based upon the distance to a gas vent, even over distances of only 30 cm. This data and preliminary methane oxidation rate measurements suggest high rates of methane oxidation in close proximity to natural gas vents and the possible preferential degradation of higher hydrocarbons at shallower depths. Additional sediment incubation experiments are underway, and results will be presented.
B43E-1653
A Geophysical Study of a Pockmark in the Nyegga Region, Norwegian Sea
Pockmarks are seabed expressions of gas/fluid escape chimneys which are thought to be of global significance as they are pathways for the escape of methane from beneath continental margins to the atmosphere and provide habitats for chemosynthetic communities of biota. Their formation and dynamics are poorly constrained due to the lack of proper three dimensional imaging of their internal structure. Numerous fluid escape features provide evidence for an active fluid-flow system on the Norwegian Margin in the Nyegga region. In June-July 2006 a high-resolution seismic experiment using Ocean Bottom Seismometers (OBS) was carried out to investigate the detailed 3D structure of two pockmarks (named CN03 and G11) in the region. The G11 pockmark is ~220 m wide and has a rugged topography with irregular ridges divided by a central sediment basin and carbonate piles. An array of eight 4-component and six 2-component OBS was deployed across the pockmark with a spacing of ~100 m and 1 m location accuracy. The source consisted of 13/35 and 24/24 cubic inch mini GI guns and the data were acquired on a grid of lines of minimum length 5000 m at 50 m and 100 m line- spacing corresponding to shot intervals of 4s and 6s. A pattern of circular lines was also shot to cover a full range of offsets and azimuths for the OBS array. The shots were also recorded on a short near-surface hydrophone streamer. Several reflectors of high amplitude and reverse polarity are observed on the profiles indicating the presence of gas. A pipe ascends from a gas charged zone at ~300 m below the seabed, to where it terminates in the investigated G11 pockmark at the seabed. An initial 2D raytraced forward model of some of the P wave data along a line running NE-SW across the G11 pockmark shows, a gradual increase in velocity between the seafloor and the gas charged zone. The traveltime fit is improved if the pockmark is underlain by velocities lower than in the surrounding layer. Gas hydrates were recovered with gravity cores from less than a meter below the seafloor during the cruise. Indications of gas at shallow depths in the hydrate stability field show that methane is able to escape through the water-saturated sediments in the chimney without being entirely converted into gas hydrate. Different possible geological processes will be examined to explain this phenomenon.
B43E-1654
Chronology of Methane Venting From Pockmarks on the Northern Flank of the Storegga Slide Complex
The northern flanks of the Storegga Slide complex on the Norwegian continental margin contains features that have been inferred to be associated with shallow methane. These include bottom simulating reflectors in seismic reflection profiles, that indicate free-gas below the base of gas hydrate stability and pockmarks which are commonly associated with seafloor gas venting. Four jumbo piston cores (JPC), three taken from separate pockmarks and one core taken near the pockmarks on the northern flank of the Storegga Slide (800m water depth), were sampled at 10 cm resolution. Radiocarbon ages indicate typical sedimentation rates of 40-70 cm/ka at these sites. Concentrated layers of Bathymodiolus mussels, an indicator of methane-rich environments, are found at 670-710 cmbsf and 780-790 cmbsf in one core. Radiocarbon dating indicates these mussel beds were deposited 18,212 +/-338 and 22,229 +/-338 calendar years before present respectively. Planktonic and benthic foraminifera (Neogloboquadrina pachyderma, Globigerina bulloides, and selected benthic species) were analyzed for stable isotopic composition. Oxygen isotopic values exhibit a classic glacial-interglacial sequence (d18O shift from 4.48 to 1.58 permil), including Terminations IA and IB. Carbon isotopic values from multiple cores depict negative excursions in planktonic foraminifera (-0.45 to < -2 permil), interpreted to reflect methane release to surface waters during the Last Glacial Maximum and early Holocene.
B43E-1655
Active Venting Sites On The Gas-Hydrate-Bearing Hikurangi Margin, Off New Zealand: ROV Measurements And Observations
During R.V. Sonne cruise SO191-3, part of the "New (Zealand Cold) Vents" expedition, RCMG deployed a CHEROKEE ROV "Genesis" on the Hikurangi Margin. This accretionary margin, on the east coast of New Zealand, is related to the subduction of the Pacific Plate under the Australian Plate. Several cold vent locations as well as an extensive BSR, indicating the presence of gas hydrates, have been found at this margin. The aims of the ROV-work were to precisely localize active methane vents, to conduct detailed visual observations of the vent structures and activity, and to perform measurements of physical properties and collect samples at and around the vent locations. The three investigated areas generally have a flat to moderate undulating sea floor with soft sediments alternating with carbonate platforms. The different sites were sometimes covered with dense fields of live clams or shell debris, often in association with tube worms, sponges and/or soft tissue corals. Active bubble- releasing seeps were observed at Faure's site and LM-3 site. Bubble-releasing activity was very variable in time, with periods of almost non-activity alternating with periods of violent outbursts. Bubble release occurred mainly from prominent depressions in soft-sediment sea floor. Bottom-water sampling revealed sometimes high concentrations of methane. Sediment-temperature measurements were largely comparable with the bottom- water temperature except for a "raindrop site" (with dense populations of polychaetes), where anomalous low sediment-temperature was measured. Further analysis of the ROV data together with the integration of other datasets will enable us to produce a model characterizing seep structure and environment.
B43E-1656
Multi-frequency Hydro-acoustic Imaging of Cold Seeps on the Hikurangi Margin Offshore New Zealand
The subduction of the Pacific plate underneath the Australian plate along the Hikurangi margin leads to intense fluid venting along the southeastern margin of New Zealand's North Island. In the framework of the NewVents project several areas, where active fluid venting was known or expected, have been mapped using shipborne multibeam bathymetry as well as deep-towed sidescan sonar. Among the areas investigated the area known as Wairarapa, located just north of the southern end of Cook Strait, is one of the most interesting because several sites showing different degrees of fluid venting have been identified on 75 kHz sidescan sonar data. The Wairarapa area is located in roughly 1000-m water depth on a southwest-northeast trending ridge that has a distinct cone-shaped elevation at its northern end. Relief on the ridge is rather small and erosive sediment pathways separate the area from direct input of coarse sediment. Sedimentation in the Wairarapa area is dominated by hemipelagic sedimentation together with probably only very fine-grained turbidite spill-over deposition. Distinct high backscatter features showing a rough surface on the ridge are consequently most likely the result of carbonate cementation and precipitation of authigenic carbonates, as ground-truthing by video observation and coring show. A minimum of seven such high backscatter patches with maximum diameters of several hundreds of meters can be distinguished. Active fluid venting in these areas is demonstrated by very distinct acoustic flares in the water column. Due to narrow spacing of mapping profiles and an increased swath width of the deep-tow sidescan sonar system several high backscatter patches have been surveyed several times within the space of a few hours. Interestingly the outline of the flares change over time as viewed in different profiles indicating the activity of the seeps.
B43E-1657
High-resolution seismic imaging of continental shelf and slope sediments and associated dynamic processes on the Otago Margin: East coast of the South Island, New Zealand
The seafloor off the southeastern coast of the South Island of New Zealand is characterised by a narrow (15- to 30-km-wide) shelf cut by a set of submarine canyons that feed into the Bounty Trough. On the outermost Otago Shelf, between the Papanui and Saunders submarine canyons, the regional shelf break is interrupted by a <1 km2 bench at a depth of ~220 m. Fishermen dredging for scallops on this bench discovered a collection of carbonate chimneys that are connected to one of several significant seafloor vents along the east coast of New Zealand. A strong correlation appears to exist between the location of the chimneys and the heads of submarine canyon systems. Our work investigates some of the geological processes in place on this continental margin that have led to the present vent system and its underlying fluid pathways. A series of high-resolution single-channel seismic reflection surveys has been undertaken over the last 18 years on the Otago Shelf to address a range of sedimentological, stratigraphic, structural and hydrogeological aims. These data were collected on board the University of Otago RV Munida using a Ferranti Ocean Research Equipment (ORE) Geopulse sub-bottom profiling system (boomer). Analogue recordings of these data have recently been digitised, merged with survey data, and archived in SEG-Y format. This has facilitated further processing and analysis of the dataset. Two of these seismic lines image the bench-like feature on which the chimneys are found. These data will be used to investigate the following questions. (1) What role do coast-perpendicular or coast- parallel structures and lowstand sedimentary features have on fluid migration on the shelf? (2) What is the nature of groundwater flow within the shelf and how is it affected by Pleistocene-to-recent sea level variation? (3) What is the linkage between vent/chimney and canyon development on this passive margin?
B43E-1658
Methane seeps and mud volcanoes in the Western Black Sea: First results of RV Meteor cruise M72-4
Cold seeps are a widespread phenomenon in the Black Sea ranging from seeps in water depths located above the gas hydrate stability zone to mud volcanoes and seeps associated with gas hydrates in deeper water. In May 2007, RV Meteor cruise M72-4 investigated the distribution of cold seeps as well as the pathways of the fluids in the subsurface by a combination of seismic and geo-acoustic methods (sidescan sonar, Chirp subbottom profiling, reflection seismic and refraction experiments). Two areas have been targeted in particular: the Sorokin Trough southeast of the Crimean peninsula and the continental slope of the Dnepr submarine fan further to the West. The Dnepr slope area is characterized by numerous gas emissions situated in water depths of less than 725 metres, while beyond this depth they are almost absent. Raw sidescan images show many individual flares that do not leave a mark on seafloor backscatter intensity, while others coincide with irregular patches of high backscatter intensity. These latter locations are associated with higher gas fluxes, but whether high backscatter is related solely to high gas content is yet unclear. The Sorokin Trough, on the other hand, shows the presence of several mud volcanoes that show a wide range of morphologies ranging from flat mud pies to large cones with or without calderas. Some of the mud volcanoes are aligned, which points to a strong underlying structural control. The source level for all mud volcanoes in the Black Sea is located in the Late Miocene Maikop formation, which is located at a depth of several kilometres in the Sorokin Trough. The dynamics of fluid reservoirs at depth in order to produce mud flow activity with very different rheology at lateral distances of a few kilometres is still under investigation. Several of these mud volcanoes show recent activity through either mud flows or gas flares. The gas flares are surprising as the mud volcanoes lie in water depths of around 2000 metres, i.e. well within the depth of gas hydrate stability. However, this flare activity is intermittent. http://www.ifm- geomar.de/index.php?id=seepmod
B43E-1659
Acoustic detection of gas emissions within the submerged section of the North Anatolian Fault Zone in the Sea of Marmara
The 38 kHz, single beam, echo-sounder SIMRAD EK-60 was operated during the Marnaut cruise (May-June 2007) onboard the RV L'Atalante to detect acoustic anomalies related to the presence of gas bubbles in the water column. In the south Cinarcik Basin, strong acoustic anomalies have been found along N140 normal faults within a 3 km wide swath oriented N100. The swath trend corresponds to the orientation of a buried fault system identified in MCS data (Carton and Singh, 2007). Ground-truthing of these anomalies with Nautile submersible enables the founding of gas seeps and bubbles emissions at seafloor. Acoustic anomalies are apparently weaker on the main fault scarp on the northern side of the Cinarcik Basin. In the Central High and Kumburgaz Basin, no acoustic anomalies were detected along the main fault trace. Instead, a cluster with very strong amplitude anomalies was identified at about 1 km away from the fault, on top of a broad anticline. On the Western High, a cluster of acoustic anomalies characterizes the top of an anticline located near 40°49'N, 28°46.8'E, where shallow gas hydrates have been sampled at unexpected water depth of 660 m, well outside the methane hydrate stability field. In the Tekirdag and Central basins, EK-60 lines were implemented along the fault scarps and the acoustic records indicate the presence of gas seeps at fault escarpments. This new set of data confirms previous results obtained with RV Le Suroit in September 2000 with a 112 kHz side-scan sonar towed 200 m above seafloor. Most active sites identified in 2000 were still active in 2007. We note that the only place where no acoustic anomaly was found on the main fault trace corresponds to the Central High and Kumburgaz Basin area. This segment did not rupture during the last century.
B43E-1660 INVITED
The Asphalt Ecosystem of the Gulf of Mexico: Results From the Chapopote III Cruise
The Campeche Knolls region of the southern Gulf of Mexico contains numerous diapiric mounds and ridges that are associated with persistent oil slicks and extensive flows of solidified asphalt. Previous investigations1 have documented chemosynthetic communities, gas hydrates, and bubble streams that rise hundreds of meters into the water column. However, only a few of the potential features had previously been investigated. The team2 selected a series of potential sites based on satellite images of oil slicks and geophysical data. These sites were surveyed during a cruise with the Mexican ship JUSTO SIERRA during 11-24 September 2007. Visual surveys using video and digital images were completed over geophysical anomalies. Multi-corer samples of the sediments were then collected based on the visual data. A narrow beam acoustic profiler was used to search for bubble streams. Preliminary results of this expedition are presented. 1 MacDonald, I. R., et al. (2004). "Asphalt volcanism and chemosynthetic life, Campeche Knolls, Gulf of Mexico." Science 304: 999-1002. 2 Chapopote III cruise participants: J. Adams, L. F. Alvarez, J. Bliss, M. Bowells, F. Deng, E. Escobar, O. Garcia, M. M. L. Garduño, A. Gassner, K. Hunter, B. B. Jimenez, A. Leiva, I. MacDonald, T. Naehr, D. Prouty, V. Samarkin, and J. Wood.
B43E-1661
Biogeochemical Controls on Authigenic Carbonate Formation at the Chapopote "Asphalt Volcano", Bay of Campeche
Unusual hydrocarbon seep features, so-called "asphalt volcanoes" were explored in the Bay of Campeche, southern Gulf of Mexico, in the spring of 2006. Guided by data from satellite imagery that showed evidence for persistent oil seeps in the region, we investigated lava-like flows of solidified asphalt along the rim of a dissected salt dome at a water depth of about 3000 m. Fresh asphalt contains copious thermogenic gas and gas hydrate. Slabs of authigenic carbonate form surface crusts with layers of oil pooled beneath. Sediments are anoxic with H2S concentrations of 8 to 13 mM. Gas hydrate forms layers and mounds in the surface sediments. Alkalinity profiles show values from 29 to 35 mM, indicating oxidation of hydrocarbons by reduction of seawater sulfate. Molecular and isotopic compositions of gas hydrate and sediment headspace indicate moderately mature, thermogenic gas. Oily sediment extracts and asphalt pieces are composed of a degraded mixture of hydrocarbons with a peak at n-C30 and a few resolved C29 to C32 hopanes. Authigenic carbonate crusts from Chapopote are porous, aragonite-cemented mudstones. Peloidal textures are common, as are bivalve shells and at least two generations of aragonite-cemented intraclasts. The carbon isotopic composition of the authigenic aragonite cements varies between -28.6 ‰ and -17.9 ‰ (PDB), indicating a contribution of carbon from non-methane liquid hydrocarbons to the total pool of dissolved CO2. δ18O values of the carbonates range from +3.2 ‰ to +4.5 ‰ (PDB), suggesting aragonite formation under near-equilibrium conditions in the shallow subsurface. Molecular fossils extracted from one carbonate sample contain abundant 13C-depleted archeal lipids, derived from anaerobic methanotrophs, suggesting that organisms mediating the anaerobic oxidation of methane are closely associated with carbonate authigenesis at the Chapopote asphalt seep site.
B43E-1662
The Importance of Chemosynthetic Communities and 'Seep-Hunting' to Deepwater Oil and Gas Exploration
Seafloor surveying techniques have often evolved as the industry's needs have evolved. Oil and gas exploration costs have escalated over the last several years, both as a result of increasing offshore overhead costs as well as the increased demand being met by offshore service-related companies. Consequently, more companies are prospecting using inexpensive techniques that rely on scientific expertise, such as seep-hunting, as a means of identifying reservoirs, and the past few years have seen several large-scale industrial deepwater surveys with locating hydrocarbon seeps as a primary goal. The identification of seeps is also a necessity for many pre-drilling operations, as many potential developers must conform to local regulations protecting chemosynthetic communities (eg MMS NTL 2000-G20 for Gulf of Mexico development). In addition to identifying chemosynthetic communities for permitting issues, as prospecting has moved into deeper water the ability to identify seep-related drilling hazards, such as hardgrounds or shallow gas (and hydrates) has also increased in importance. The specialized field of identifying seeps, and related chemosynthetics, hardgrounds, etc., is rapidly growing, aided by advances in mapping technology, such as multibeam backscatter and interferometry, among others. Today all of the geophysical data can be brought into a common interpretation environment providing multiple perspectives, different data overlays, and/or 3D visualizations. Using these techniques, high resolution multibeam and/or side-scan surveys rapidly cover large swaths of seafloor and identify potential seeps in real- time. These targets can then be examined geochemically with a coring program, potentially working simultaneously with the multibeam program. Modern USBL navigation can position a deepwater core in <10m diameter targets. Much of the geochemistry can be analyzed in near-real time at sea (eg headspace/interstitial gas, trace/minor/major ions in porefluids, etc; only isotopic analyses are restricted to better equipped research vessels). The advantages of integrating these data are considerable, and they can be obtained for a fraction of the cost of exploratory drilling or submersible operations. This presentation intends to outline the recent history of the industry's approach to seep-hunting, its increasing importance to oil prospectivity, and future trends in industrial applications and how this might affect academic study in this field (especially related to the advances in seep-hunting technology and software that are becoming industry-standards).