Fluid focus

Once in the subsurface, salt beds and diapirs/salt allochthons tend to focus upward escape of basinal fluids derived from compaction of both subsalt and suprasalt sediments, as evidenced by (Warren 2017): (1) localized development of mud mounds and chemosynthetic seeps at depopod edges above diapirs in the Gulf of Mexico and elsewhere; (2) shallow gas anomalies clustered around and above salt diapirs in the North Sea and; (3) localized salinity anomalies around salt diapirs, offshore Louisiana and with large pock-marks above diapir margins in West Africa. Likewise, in the eastern Mediterranean region, gas chimneys in the Tertiary overburden are common above regions of thinned Messinian Salt, as in the vicinity of the Latakia Ridge.

 

Whenever a salt weld or overburden touchdown occurs, fluids can migrate (leak) vertically across the level of a now flow-thinned or no-longer-present salt level. Such touchdowns or salt welds can be in basin positions located well away from the diapir edge and are a significant focusing features in the formation of many larger base-metal and sedimentary copper traps, as well as many depopod-hosted siliciclastic oil and gas reservoirs (see Warren, 2017 and Warren 2016;Chapters 15 and 16).

 

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