Hydrate-bearing sands in the Terrebonne Basin record the transition from ponded deposition to bypass in the deep-water Gulf of Mexico

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Varona, Gabrielle Marie

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Herein, I show how seismic stratigraphy can be used to describe the transition from ponded deposition to bypass within a gas hydrate system in deep-water Gulf of Mexico. In Walker Ridge Block 313 (WR 313), the Green and Orange sands are gas hydrate bearing sheet sands incised by a paleo channel system within the southwestern lobe of the Terrebonne Basin. I discuss two intervals that characterize the deposition of the sheet sands in conjunction with the channel. The Green interval captures the first appearances of coarse-grained material which I classify as the Green sand. The Orange interval encompasses channelized deposits and corresponding muddy levee deposits and is capped by the Orange sand. Within WR 313, the channel is oriented NW-SE and flowed towards the SE where salt related uplift took place. During the Green interval, salt movement influenced the pattern of deposition upstream and incision downstream. During the Orange interval, the channel aggraded, encountered the sheet deposition of the Orange sand, and then shut off. Well log data from two different wells support my interpretation of the Green and Orange sands as sheet sands due to their thickness patterns ~2000 m away from the channel axis. The WR 225 001 (WR 225-1) well penetrates the Green and Orange deposits upstream and the WR 313 H001 (WR 313-H) well encounters these deposits downstream. The gamma ray and resistivity logs from the WR 225-1 well record two coarsening upward signatures several meters apart which are interpreted as the Green sand (74 meters thick) and the Orange sand (22 meters thick). I correlate these gamma ray signatures with thinner packages of the Green sand (35 meters) and the Orange sand (12 meters) in the WR 313-H well on the downstream end. Due to the thickness of the sands away from the channel and the corresponding seismic character, I interpret that the Green and Orange sands record the last episodes of high energy deposition that interact with a submarine channel system.


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