C. M. G. McHugh

Biologic and geologic characteristics of cold seeps in Monterey Bay, California

Cold seep communities discovered at three previously unknown sites between 600 and 1000 m in Monterey Bay, California, are dominated by chemoautotrophic bacteria (Beggiatoa sp.) and vesicomyid clams (5 sp.). Other seep-associated fauna included galatheid crabs (Munidopsis sp.), vestimentiferan worms (Lamellibrachia barhami?), solemyid clams (Solemya sp.), columbellid snails (Mitrella permodesta, Amphissa sp.), and pyropeltid limpets (Pyropelta sp.). More than 50 species of regional (i.e. non-seep) benthic fauna were also observed at seeps. Ratios of stable carbon isotopes (δ13C) in clam tissues near ∼ 36‰ indicate sulfur-oxidizing chemosynthetic production, rather than non-seep food sources, as their principal trophic pathway. The “Mt Crushmore” cold seep site is located in a vertically faulted and fractured region of the Pliocene Purisima Formation along the walls of Monterey Canyon (∼ 635 m), where seepage appears to derive from sulfide-rich fluids within the Purisima Formation. The “Clam Field” cold seep site, also in Monterey Canyon (∼ 900 m) is located near outcrops in the hydrocarbon-bearing Monterey Formation. Chemosynthetic communities were also found at an accretionary-like prism on the continental slope near 1000 m depth (Clam Flat site). Fluid flow at the “Clam Flat” site is thought to represent dewatering of accretionary sediments by tectonic compression, or hydrocarbon formation at depth, or both. Sulfide levels in pore waters were low at Mt Crushmore (ca ∼ ∼ 0.2 mM), and high at the two deeper sites (ca 7.011.0 mM). Methane was not detected at the Mt Crushmore site, but ranged from 0.06 to 2.0 mM at the other sites.

Widespread fluid expulsion on a translational continental margin: Mud volcanoes, fault zones, headless canyons, and organic-rich substrate in Monterey Bay, California

Remotely operated vehicle (ROV)-based mapping of tectonic features, zones of anomalous reflectivity, and geomorphic targets in Monterey Bay, California, demonstrates the regional abundance of fluid expulsion along the active transform margin between the Pacific and North American plates. Cold seeps—extant communities characterized by chemosynthetic bivalves, bacterial mats, and rare tubeworms—are the surface manifestations of present-day fluid expulsion of sulfide- and methane-rich fluids, whereas slabs, veins, and chimneys of authigenic carbonate represent regions of either dormant methane-rich fluid expulsion, or areas where the present rate of flow is too low to support chemosynthetic fauna. We have found both active and dormant fluid seepage along fault zones, at the surface expression of mud volcanoes, on organic-rich or permeable substrate, and within headless canyons across a wide range of depths within Monterey Bay. The fluid egress at these sites may be driven by a combination of (1) pore-space reduction caused by rapid sedimentation and/or tectonic compaction related to residual Pacific–North America compression, and (2) increased buoyancy due to a decrease in pore-fluid density related to diagenesis and/or catagenesis at depth. Although provocative, the relationship between topographically driven aquifer discharge and sea-floor fluid expulsion remains speculative for Monterey Bay. The widespread distribution of fluid expulsion features controlled by a variety of conduits in Monterey Bay implies that cold seeps may be common features on translational margins.

Sea-level changes and depositional environments in the İzmit Gulf, eastern Marmara Sea, during the late glacial–Holocene period

Abstract Offshore and onshore stratigraphic studies, together with high-resolution shallow seismic reflection profiling and multibeam bathymetric mapping, were carried out in the western and central part of the Izmit Gulf. These studies indicate that the Izmit Gulf was a lacustrine environment as part of the Marmara ‘Lake’ during the late glaciation and early deglaciation until ∼12 kyr BP, when the Marmara Basin was inundated by the Mediterranean waters. Correlation of 14 C-dated onshore and offshore stratigraphic units in the Western Izmit Gulf indicates that generally coarse late glacial sediments overlie a marked erosional surface formed during the low water level of the Marmara ‘Lake’. These coarse sediments are succeeded by 10.4–7 kyr BP old transgressive, and by late Holocene post-transgression mud units. The bathymetry and sub-bottom Chirp profiles clearly show that the paleoshoreline of the Gulf was located at −85 m, having been controlled by the bedrock sill depth of the Canakkale Strait. Another paleoshoreline observed at −65 m on the northern margin of the Western Izmit and Karamursel basins was probably formed during the Younger Dryas sea-level stillstand. The shelf areas during this time were colonized by bioherms, which were subsequently drowned and disappeared after a further rise of the sea level. The presence of a −65 m marine paleoshoreline in the Karamursel Basin indicates that the sill restricting this basin to the west was much deeper than its present −55 m level and was located further south. The Golcuk Basin, restricted by a −38 m sill to its west, was probably not flooded by marine waters until ∼9 kyr BP.

Cenozoic mass-transport facies and their correlation with relative sea-level change, New Jersey continental margin

Abstract Mass-transport deposits reveal something of the timing, source areas and depositional processes that contributed to the evolution of the New Jersey continental margin. Many of the mass-transport deposits rest upon prominent stratal surfaces and sequence boundaries permitting evaluation of the relationship between mass wasting and eustatic change. Five distinct mass-transport facies representative of intercanyon regions of the slope, canyons and continental rise settings are recognized in the Ocean Drilling Program Leg 150 Sites (902–906). These mass-transport deposits consist predominantly of muddy slumps and debris flows, and to a lesser extent sandy mass flows and gravity-related flows. The styles of soft-sediment deformation, mineralogy, and biostratigraphy of these mass-transport deposits provide new information on the mass-wasting history of the continental margin. At intercanyon sites beneath the continental slope (Sites 902–904), mud with disseminated sand occurs mainly at sequence boundaries and related stratal surfaces in upper Oligocene to upper Miocene sections. In contrast, muddy and sandy debris flows and slumps occur at sequence boundaries, stratal surfaces and within sequences in upper Miocene through Pleistocene sections. The type and preservation of mass-transport facies (10–15% of the total sediment recovered) on the continental slope through time, is associated with changes in sediment progradation during the Miocene, which led to a change in the morphology and gradient of the slope throughout the late Neogene. Mass-wasting facies are best preserved (36% of the total sediment) in the canyon-fill deposits recovered from Site 906. The fill of modern Berkeley Canyon is composed of debris flows, whereas the fill of a buried middle Miocene canyon consists of clast supported slumps, debris flows, and turbidites, which document an early episode of canyon excavation and infilling. Apparently the middle Miocene canyon cutting event occurred very rapidly (∼2.5 Ma) and can be correlated to a prominent glacioeustatic sea-level lowering event (13.5±0.5 Ma). Approximately 30 m of debris flows and slumps accumulated at Site 905 on the continental rise during the middle Miocene. Lithologies and benthic foraminifer assemblages show that this material was derived from the continental slope. Downslope transport was again significant during the early Pleistocene at Site 905 when 215 m of slumps and debris flows accumulated. The lithology and age of the clasts and matrix suggest that these deposits resulted from episodes of canyon excavation deep into the lithified rocks of the adjacent continental slope.

Offshore sedimentary effects of the 12 January 2010 Haiti earthquake

Although the 12 January 2010 Haiti earthquake was one of the deadliest earthquakes in history, it left no clear geological evidence of rupture on land. As a tectonic event, the earthquake was complex; even the faults involved remain unclear. Using geophysical and coring data, we document direct evidence of the sedimentation generated by the catastrophic 12 January 2010 earthquake offshore. These studies document submarine paleoseismology methods that can be used for assessing seismic risk in this and other tectonic settings such as the California San Andreas fault, where deeper buried blind thrusts may exist. Shaking by the 12 January main shock triggered sediment failures and turbidity currents from coastal sources to deep-water sinks. An ~0.05 km 3 turbidite was deposited in the Canal du Sud basin (1750 m water depth) over 50 km 2 . Almost 2 months after the main shock, a 600-m-thick sediment plume was still present in the lowermost water column at this location. The turbidite was time correlated to the 12 January earthquake by the excess 234 Th in the sediments. With a half-life of 24 days, its presence documents an infl ux of terrigenous sediment mixing with marine sources derived from the basin slopes. This turbidite, and older ones observed beneath it, displays complex cross-bedded and fi ning-upward stratigraphy indicative of long waves and seiche oscillations that are consistent with locally reported tsunamis. This 12 January sedimentary record highlights the potential for submarine paleoseismology to unravel the seismic history of continental transform boundaries such as the Enriquillo‐Plantain Garden fault in the Dominican Republic, Haiti, and Jamaica, as well as other tectonic settings where no clear land-based evidence for a rupture exists.

Sedimentary features associated with channel overbank flow: examples from the Monterey Fan

Abstract Overbank flow of turbidity currents sweeping through the entrenched Monterey Fan Channel has generated erosional and depositional features along the channel walls and across the adjacent levees. These features, investigated with side-scan sonar, SeaBeam bathymetry, submersibles, and a towed camera sled include fields of sediment waves, overbank channels, gullied walls and terraces, and slump scars. Overbank flow occurs where the channel path is straight, but is accentuated along sharp outside bends. Along straight channel segments sediment waves trend oblique to the channel and are commonly present on the right-hand (when looking downstream) levee adjacent to the channel. Along curved segments of the channel path, large sediment waves, with crests sub-parallel to the channel and with wavelengths reaching 3 km, are present on the outside levee as far as 15 km from the channel. Commonly, a gully is present on the lee side of the sediment wave, near the mid-point of the wave crest. Gullies are the heads of a tributary system of overbank channels, which feed a larger trunk channel on the fan surface.

Rapid subsidence and sedimentation from oblique slip near a bend on the North Anatolian transform fault in the Marmara Sea, Turkey

Several basins are developing near bends on strands of the North Anatolian transform fault in northwest Turkey. Oblique slip on these faults, rather than strain partitioning, accounts for trans- tension and subsidence. These basins are asymmetric, and tilt and subside most rapidly at their narrow ends near the bends. The turbidite surface marking the floor of the Cinarcik Basin (eastern Marmara Sea) was mostly abandoned at a sudden drop in sedi- mentation, which was likely coincident with the 14 ka lake-sea transition, and is now a warped reference surface from which we can measure strain and sedimentation. Subsidence and tilt are rap- id, but do not require late Quaternary changes in regime. They are linked to transcurrent motion by slip parallel to an oblique bend on the North Anatolian fault and suggest tsunamogenic ver- tical motion in large Marmara Sea earthquakes.

Evidence for widespread creep on the flanks of the Sea of Marmara transform basin from marine geophysical data

“Wave” fi elds have long been recognized in marine sediments on the fl anks of basins and oceans in both tectonically active and inactive environments. The origin of “waves” (hereafter called undulations) is controversial; competing models ascribe them to depositional processes, gravity-driven downslope creep or collapse, and/or tectonic shortening. Here we analyze pervasive undulation fi elds identifi ed in swath bathymetry and new high-resolution multichannel seismic (MCS) refl ection data from the Sea of Marmara, Turkey. Although they exhibit some of the classical features of sediment waves, the following distinctive characteristics exclude a purely depositional origin: (1) parallelism between the crests of the undulations and bathymetric contours over a wide range of orientations, (2) steep fl anks of the undulations (up to ~40°), and (3) increases in undulations amplitude with depth. We argue that the undulations are folds formed by gravity-driven downslope creep that have been augmented by depositional processes. These creep folds develop over long time periods (≥0.5 m.y.) and stand in contrast to geologically instantaneous collapse. Stratigraphic growth on the upslope limbs indicates that deposition contributes to the formation and upslope migration of the folds. The temporal and spatial evolution of the creep folds is clearly related to rapid tilting in this tectonically active transform basin.

Exploring submarine earthquake geology in the Marmara Sea

The disastrous 1999 earthquakes in Turkey have spurred the international community to study the geometry and behavior of the North Anatolian Fault (NAF) beneath the Marmara Sea. While the area is considered mature for a large earthquake, the detailed fault geometry below the Marmara Sea is uncertain, and this prevents a realistic assessment of seismic hazards in the highly-populated region close to Istanbul. Two geological/geophysical surveys were recently conducted in the Marmara Sea: the first in November 2000 with the R/V Odin Finder, and the second in June 2001 with the R/V CNR-Urania. Both were sponsored and organized by the Institute of Marine Geology of the Italian National Research Council (CNR), in cooperation with the Turkish Council for Scientific and Technical Research (TUBITAK) and the Lamont-Doherty Earth Observatory of Columbia University Multi-beam bathymetry, multi-channel seismic reflection profiling, magnetometry high-resolution CHIRP sub-bottom profiling, and bottom imaging were carried out with a remotely operated vehicle (ROV). Over 60 gravity and piston cores were collected.

Contemporary sedimentary processes in the Monterey Canyon-fan system

Abstract A study of the Monterey Canyon and fan was conducted to investigate contemporary sedimentary activity using a camera sled, Alvin dives and Sea-Beam bathymetry. Physical characteristics and plan view morphology of the walls, terraces, thalweg floor and levees of the Monterey Canyon and fan, as well as the gullied and non-gullied regions of the adjacent continental slope have been studied. The canyon floor and fan valley thalweg channel from 2900 to 3500 m exhibited properties indicative of moderate to low energy conditions (weak currents, smoothed sea-bed, deposits of disintegrated kelp, bioturbated mud substrate, fecal pellets, absence of scour). Chemosynthetic communities consisting of clams and a pogonophoran, were found in the fan valley from 3000 to 3600 m. Local areas of rockfalls and slumps from the canyon and fan valley walls were not fresh (sedimented, abundantly colonized by benthic biota). Terraces and levee crests were mud-draped and bedrock exposures on canyon walls were encrusted by benthic organisms. Freshest disturbances were found in gullies on the adjacent continental slope where bedrock was scoured clean of sediment and loose debris. A major submarine slide detached from escarpments on the lower slope, and extends across the fan. The slide surface was mud-draped, hummocky, and contained bedforms with wavelengths up to 150 m and up to 10 m relief. The survey was conducted shortly before the Loma Prieta earthquake (October 17, 1989) that caused substantial ground motion in on-shore regions of Monterey Bay. Any substantial sub-sea disturbances generated by the ensuing earthquake should be discernable from the pre-earthquake state by comparison with the deep-sea photographs and observations.