Gas hydrate disturbance fabrics of southern Hydrate Ridge sediments (ODP Leg 204): Relationship with texture and physical properties |
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| Authors: | Elena Piñero Eulàlia Gràcia Francisca Martínez-Ruiz Juan Cruz Larrasoaña Alexis Vizcaino Gemma Ercilla |
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| Institution: | (1) Unitat de Tecnologia Marina (CSIC), Centre Mediterrani d’Investigacions Marines i Ambientals, Pg. Marítim de la Barceloneta 37-49, 08003 Barcelona, Spain;(2) Instituto Andaluz de Ciencias de la Tierra (CSIC/Universidad de Granada) Facultad de Ciencias, Campus Fuentenueva, 18002 Granada, Spain;(3) Laboratori de Paleomagnetisme, Institut de Ciències de la Terra “Jaume Almera” (CSIC)/Universitat de Barcelona, c/ Lluís Solé i Sabarís s/n, 08028 Barcelona, Spain;(4) Institut de Ciències del Mar (CSIC), Centre Mediterrani d’Investigacions Marines i Ambientals, Pg. Marítim de la Barceloneta 37-49, 08003 Barcelona, Spain |
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| Abstract: | Soupy and mousse-like fabrics are disturbance sedimentary features that result from the dissociation of gas hydrate, a process
that releases water. During the core retrieval process, soupy and mousse-like fabrics are produced in the gas hydrate-bearing
sediments due to changes in pressure and temperature conditions. Therefore, the identification of soupy and mousse-like fabrics
can be used as a proxy for the presence of gas hydrate in addition to other evidence, such as pore water freshening or anomalously
cool temperature. We present here grain-size results, mineralogical composition and magnetic susceptibility data of soupy
and mousse-like samples from the southern Hydrate Ridge (Cascadia accretionary complex) acquired during Leg 204 of the Ocean
Drilling Program. In order to study the relationship between sedimentary texture and the presence of gas hydrates, we have
compared these results with the main textural and compositional data available from the same area. Most of the disturbed analyzed
samples from the summit and the western flank of southern Hydrate Ridge show a mean grain size coarser than the average mean
grain size of the hemipelagic samples from the same area. The depositional features of the sediments are not recognised due
to disturbance. However, their granulometric statistical parameters and distribution curves, and magnetic susceptibility logs
indicate that they correspond to a turbidite facies. These results suggest that gas hydrates in the southern Hydrate Ridge
could form preferentially in coarser grain-size layers that could act as conduits feeding gas from below the BSR. Two samples
from the uppermost metres near the seafloor at the summit of the southern Hydrate Ridge show a finer mean grain-size value
than the average of hemipelagic samples. They were located where the highest amount of gas hydrates was detected, suggesting
that in this area the availability of methane gas was high enough to generate gas hydrates, even within low-permeability layers.
The mineralogical composition of the soupy and mousse-like sediments does not show any specific characteristic with respect
to the other samples from the southern Hydrate Ridge. |
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