A 3D seismic volume was acquired summer 2000 over the southern end of
Hydrate Ridge (FIR), an anomalously shallow ridge 100 km offshore Newport,
Oregon. The survey followed a succession of scientific expeditions aimed at
studying the gas hydrates present in the shallow subsurface that gave the name to
the ridge. This thesis consists of a seismic sequence analysis of the high-resolution
(125 Hz) 3D survey. Identification of seismic units and interpretation of
depositional sequences observed on the seismic sections is presented. The sequence
analysis is compared with the results from nine sites cored during ODP Leg 204
during summer 2002. The first objective is to document in detail the stratigraphy of
the ridge so that we can compare it with the gas hydrate distribution. The second is
to reconstruct the structural evolution through time of this complex anticline as
inferred from the depositional history. The result is a time series of structural
evolutionary cross-sections as well as a series of paleo-bathymetric maps revealing
the development of and interplay between the structures now buried in the
subsurface of southern HR. The structural evolutionary diagrams show the
existence of three anticlines, interpreted as thrust-related folds. They formed at the
deformation front and controlled the distribution and deformation of the sediments
during the Pleistocene. The current southern HR started its uplift less than 0.5 Ma.
A seismic relict in the form of a double BSR is a witness to the evolution of the gas
hydrate system of HR. It confirms the recent uplift of the ridge and consequent
shallowing of the base of the gas hydrate stability zone (GHSZ). Further detailed
studies of the stratigraphy reveal stratigraphic controls on the fluid flow, which in
turn control the distribution of gas hydrates. Analysis of the amplitude map of the
bottom-simulating reflector (BSR), which is a proxy for the free gas distribution,
shows a relationship between anticlinal features within the older strata (older than
1.6 Ma) and strong amplitude anomalies of the BSR, which confirm previous
observations suggesting a very low permeability for the young slope-basin
sediments and an accumulation of gas within the older sediments underneath. / Graduation date: 2004
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29162 |
| Date | 18 February 2004 |
| Creators | Chevallier, Johanna |
| Contributors | Trehu, Anne M. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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