Chemosynthetic Biological Communities Research Articles

Topographic control of a dispersing hydrothermal plume

Deep-sea hydrothermal vents represent a major source of heat and chemicals to the oceans and support endemic chemosynthetic biological communities. To fully understand the impact of hydrothermal activity upon the oceans, however, requires investigation of both the physical and the biogeochemical processes which are active in hydrothermal plumes and which serve to determine the net hydrothermal flux to the oceans. We have recently conducted a detailed multidisciplinary study of the lateral dispersion of the hydrothermal plume emitted from the Rainbow vent site near 36°15′N, Mid-Atlantic Ridge. Combining velocity measurements from a lowered ADCP, optical back scatter measurements from a deep-tow CTD and methane measurements from bottle samples we are able, for the first time in the Atlantic, to trace a neutrally buoyant plume for a distance of over 50 km. The path of the plume is seen to be heavily controlled by the local topography with a general northeast movement of water. Both particle and methane concentrations decrease downstream over the length of the observed plume. The dataset provides an excellent opportunity to study the mixing and biogeochemical processes active in a hydrothermal plume and estimate fluxes of biogeochemical constituents.

The effect of fault-bend folding on seismic velocity in the marginal ridge of accretionary prisms

Fluid venting in accretionary prisms, which feeds chemosynthetic biological communities, occurs mostly on the marginal thrust ridge. New seismic data for the marginal ridge of the Cascadia prism show significantly lower velocity than that in the adjacent oceanic basin and place important constraints on the interpretations of why fluid venting occurs mostly on the marginal ridge. We employed a finite-element method to analyze a typical fault-bend folding model to explain the phenomenon. The fault in the model is simulated by contact elements. The elements are characterized not only by finite sliding along a slide line, but also by elastoplastic deformation. We present the results of a stress analysis which show that the marginal ridge is under subhorizontal extension and the frontal thrust is under compression. This state of stress favors the growth of tensile cracks in the marginal ridge, facilitates fluid flow and reduces seismic velocities therein; on the other hand, it may close fluid pathways along the frontal thrust and divert fluid flow to the marginal ridge.

Methane-rich plumes on the Carolina continental rise: Associations with gas hydrates

Seafloor venting of microbial gases occurs at 2167 m water depth over the Blake Ridge diapir-Gas-rich plumes were identified acoustically in the water column up to 320 m above a pockmarked sea floor associated with active chemosynthetic biological communities. Plumes and venting fluids emanate from near a small fault that extends downward toward a dome in the bottom-simulating reflector, indicating that fluid and/or gas migration is associated with gas hydrate bearing sediment below. These plumes might be caused by gas bubbles or buoyant dumps of gas hydrate that float upward from the seafloor. 18 refs., 3 figs.

Fluid flow along a strike-slip fault at the toe of the Oregon accretionary prism: Implications for the geometry of frontal accretion

Research Article| May 01, 1993 Fluid flow along a strike-slip fault at the toe of the Oregon accretionary prism: Implications for the geometry of frontal accretion HAROLD J. TOBIN; HAROLD J. TOBIN 1Department of Earth Sciences and Institute for Marine Sciences, University of California, Santa Cruz, California 95064 Search for other works by this author on: GSW Google Scholar J. CASEY MOORE; J. CASEY MOORE 1Department of Earth Sciences and Institute for Marine Sciences, University of California, Santa Cruz, California 95064 Search for other works by this author on: GSW Google Scholar MARY E. MACKAY; MARY E. MACKAY 2Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii 96822 Search for other works by this author on: GSW Google Scholar DANIEL L. ORANGE; DANIEL L. ORANGE 1Department of Earth Sciences and Institute for Marine Sciences, University of California, Santa Cruz, California 95064 Search for other works by this author on: GSW Google Scholar LAVERNE D. KULM LAVERNE D. KULM 3College of Oceanography, Oregon State University, Corvallis, Oregon 97331 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1993) 105 (5): 569–582. https://doi.org/10.1130/0016-7606(1993)105<0569:FFAASS>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation HAROLD J. TOBIN, J. CASEY MOORE, MARY E. MACKAY, DANIEL L. ORANGE, LAVERNE D. KULM; Fluid flow along a strike-slip fault at the toe of the Oregon accretionary prism: Implications for the geometry of frontal accretion. GSA Bulletin 1993;; 105 (5): 569–582. doi: https://doi.org/10.1130/0016-7606(1993)105<0569:FFAASS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Sediment offscraping and accretion takes place predominantly by landward-vergent thrusting along most of the Oregon accretionary prism north of latitude 44°50'N. This indicates very low basal shear stress, probably due to near-lithostatic fluid pressure on the décollement horizon. Recent multichannel seismic and sidescan sonar studies have demonstrated the existence of an oblique, basement-involved, left-lateral strike-slip fault, termed the Wecoma fault. It cuts abyssal plain sediments and oceanic basement of the subducting plate. Where the Wecoma fault intersects the wedge thrust front at 45°09'N, accretion to the wedge occurs through an anomalous seaward-vergent thrust. Linear, fault-parallel erosional gullies, which trend obliquely across the slope on the seaward flank of the frontal anticline in the accretionary wedge, are interpreted as marking the surface traces of splays of the Wecoma fault. Data collected during six Alvin dives on and around these gullies demonstrate that fluid expulsion from the deforming sediments is preferentially concentrated along the fault traces. Evidence includes the presence of chemosynthetic biological communities, pervasive veining and fracturing of the rock, and extensive carbonate cementation, all forming preferentially within the gullies. This strike-slip fault apparently acts as a high-angle fluid escape conduit, channeling fluids from deep within the wedge to the surface. We propose that this fluid conduit causes the local inversion of thrusting to seaward vergence by allowing the escape of highly overpressured fluids from the incipient décollement horizon. The consequent increase in basal effective normal stress favors the development of a seaward-vergent thrust. The discovery of this strike-slip fault acting as an efficient fluid conduit to the surface of the wedge emphasizes the generally unappreciated importance of strike-slip (and normal) faults in dewatering accretionary prisms. Such dewatering features may significantly influence the development of large-scale structures, and they have broad applicability to other tectonic settings, including collision zones and continental fold-and-thrust belts. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.