Abstract
Karst terrains that develop in bodies of rock salt (taken as mainly of halite, NaCl) are special not only for developing in one of the most soluble of all rocks, but also for developing in one of the weakest rocks. Salt is so weak that many surface-piercing salt diapirs extrude slow fountains of salt that that gravity spread downslope over deserts on land and over sea floors. Salt fountains in the deserts of Iran are usually so dry that they flow at only a few cm/yr but the few rain storms a decade so soak and weaken them that they surge at dm/day for a few days. We illustrate the only case where the rates at which different parts of one of the many tens of subaerial salt karst terrains in Iran flows downslope constrains the rates at which its subaerial salt karst terrains form. Normal seawater is only 10% saturated in NaCl. It should therefore be sufficiently aggressive to erode karst terrains into exposures of salt on the thousands of known submarine salt extrusions that have flowed or are still flowing over the floors of hundreds of submarine basins worldwide. However, we know of no attempt to constrain the processes that form submarine salt karst terrains on any of these of submarine salt extrusions. As on land, many potential submarine karst terrains are cloaked by clastic and pelagic sediments that are often hundreds of m thick. Nevertheless, detailed geophysical and bathymetric surveys have already mapped likely submarine salt karst terrains in at least the Gulf of Mexico, and the Red Sea. New images of these two areas are offered as clear evidence of submarine salt dissolution due to sinking or rising aggressive fluids. We suggest that repeated 3D surveys of distinctive features (± fixed seismic reflectors) of such terrains could measure any downslope salt flow and thus offer an exceptional opportunity to constrain the rates at which submarine salt karst terrains develop. Such rates are of interest to all salt tectonicians and the many earth scientists seeking hydrocarbons associated with salt bodies.
Highlights
Thousands of salt diapirs surface on sea floors and extrude submarine sheets of salts of various ages that have gravity spread downslope in hundreds of basins worldwide in the past or are still doing so at present [1]
We suggest that repeated 3D surveys of distinctive features (± fixed seismic reflectors) of such terrains could measure any downslope salt flow and offer an exceptional opportunity to constrain the rates at which submarine salt karst
We suggest considering submarine karst terrains developed in salt dissolved by upwelling fluids as a special category of submarine salt karst terrains
Summary
Thousands of salt diapirs surface on sea floors and extrude submarine sheets of salts of various ages that have gravity spread downslope in hundreds of basins worldwide in the past or are still doing so at present [1]. Assuming a lack of permanent moorings in the area, each of these could consist of a wave glider on the surface communicating to an array of 35 seafloor transponders or beacons Wave gliders hold their precisely known positions and measure the position of the seafloor transponders with sufficient precision to register relative lateral and vertical displacements of the seafloor beacons of 1.5 cm/year. This work opens by outlining an analysis of a subaerial karts terrain on a salt extrusion in Iran to illustrate its potential for constraining rates of salt flow and dissolution. It presents new images as evidence for submarine slat dissolution and discusses the likely differences between subaerial and submarines salt karst terrains It ends by advocating constraining the rates at which submarine salt extrusions flow and dissolve from above or below. Such rates should be of interest to all salt tectonicians and geologists seeking hydrocarbons offshore
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