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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 47 (1997), Pages 311-315

Hydrate Stability Zone Permanence along Dynamic Louisiana Offshore

Allen Lowrie (1), Michael D. Max (2), Rhett Hamiter (3), Ian Lerche (4), Elchin Bagirov (4)

ABSTRACT

The Louisiana offshore, and northern Gulf of Mexico continental margin in general, is an area of multiple dynamic occurrences of hydrates at different periodicities. There is a complex interrelationship between high sedimentation rates, sea level oscillation, climate, and the tectonics of semiplastic salt and shale. Throughout the Neogene, sea level oscillations at 3rd, 4th, 5th, and 6th order intervals are recorded in offshore deposits. Each depositional cycle influences salt and shale tectonics and growth/thrust faults as well as gravity-driven (large and small) slumping, as in the Mississippi Canyon.

Hydrates develop when gases crystallize with water under appropriate temperature and pressure (P-T) conditions. Changes in the P-T regime influence the hydrate stability zone (HSZ). Global climates influenced the Gulf physical oceanography (e.g., glacial ages increased the vertical extent and shallowness of Antarctic Intermediate Water) and sea level (e.g., glacial advances lowered sea level 125 m during the Quaternary). This, in turn, has changed the inputs to the HSZ coincident with at least 4th order climatic frequencies. Salt and shale tectonics disrupts the sedimentary layers and inverts the hydrate to gas, which may escape to the overlying waters and atmosphere, or stays in the sediments.

Maximum impact of P-T changes on a HSZ would occur during the relatively rapid deglaciation phase. Tectonic-sedimentary dynamics appear during lowstands at 4th order oscillations. Tectonics, in turn, rupture hydrate zones.

The dynamics of the process may be studied by asking questions about the rate of hydrate regrowth after disruption. Controls on hydrate regrowth include migration routes and rates of methane migration from source area, volume of methane reservoirs, restoration of hydrate stability zones, and tectonic fractures and fault "healing" after HSZ disruption.


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