Modern internal waves and internal tides along oceanic pycnoclines: Challenges and implications for ancient deep-marine haroclinic sands

摘要

Thus far, the subject of deep-marine sands emplaced by baro clinic currents associated with internal waves and internal tides as potential reservoirs has remained an alien topic in petroleum exploration. Internal waves are gravity waves that oscillate along oceanic pycnoclines. Internal tides are internal waves with a tidal frequency. Internal solitary waves (i.e., solitons), the most common type, are commonly generated near the shelf edge (100-200 m [328-656 ft] in bathymetry) and in the deep ocean over areas of seα-floor irregularities, such as mid-ocean ridges, seamounts, and guyots. Empirical data from 51 locations in the Atlantic, Pacific, Indian, Arctic, and Antarctic oceans reveal that internal solitary waves travel in packets. Internal waves commonly exhibit (1) higher wave amplitudes (5-50 m [16-164 ft]) than surface waves (<2 m [6.56 ft]), (2) longer wave-lengths (0.5-15 km [0.31-9 mi]) than surface waves (100 m [328 ft]), (3) longer wave periods (5-50 min) than surface waves (9-10 s), and (4) higher wave speeds (0.5-2 m s~(-1 [1.64-6.56 ft s~(-1)]) than surface waves (25 cm s~(-1 [10 in. s~(-1]). Maximum speeds of 48 cm s~(-1 (19 in. s~(-1) for baroclinic currents were measured on guyots. However, core-based sedi-mentologic studies of modern sediments emplaced by baroclinic currents on continental slopes, in submarine canyons, and on submarine guyots are lacking. No cogent sedimentologic or seismic criteria exist for distinguishing ancient counterparts. Outcrop-based fades models of these deposits are untenable. Therefore, potential exists for misinterpreting deep-marine baroclinic sands as turbidites, contourites, basin-floor fans, and others. Economic risks associated with such misinterpretations could be real.