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AAPG Bulletin

Abstract

DOI:10.1306/10171212101

Modern internal Previous HitwavesNext Hit and internal tides along oceanic pycnoclines: Challenges and implications for ancient deep-marine baroclinic sands

G. Shanmugam1

1Department of Earth and Environmental Sciences, University of Texas at Arlington, Arlington, Texas 76019; [email protected]

ABSTRACT

Thus far, the subject of deep-marine sands emplaced by baroclinic currents associated with internal Previous HitwavesNext Hit and internal tides as potential reservoirs has remained an alien topic in petroleum exploration. Internal Previous HitwavesNext Hit are gravity Previous HitwavesNext Hit that oscillate along oceanic pycnoclines. Internal tides are internal Previous HitwavesNext Hit with a tidal frequency. Internal solitary Previous HitwavesNext Hit (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 sea-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 Previous HitwavesNext Hit travel in packets. Internal Previous HitwavesNext Hit commonly exhibit (1) higher wave amplitudes (5–50 m [16–164 ft]) than surface Previous HitwavesNext Hit (lt2 m [6.56 ft]), (2) longer wavelengths (0.5–15 km [0.31–9 mi]) than surface Previous HitwavesNext Hit (100 m [328 ft]), (3) longer wave periods (5–50 min) than surface Previous HitwavesNext Hit (9–10 s), and (4) higher wave speeds (0.5–2 m s–1 [1.64–6.56 ft s–1]) than surface Previous HitwavesTop (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 sedimentologic 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 facies 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.

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