Geology of a Continental Slope Oil Seep, Northern Gulf of Mexico

Abstract

ABSTRACT An oil gas seep was documented by replicate sampling with piston corer, abundant high-resolution and sparse multichannel seismic reflection profiling, and chemical and isotopic analyses. The seep occurs on the upper continental slope over a salt ridge interpreted to split and plunge eastward, northeastward, and northward. The relatively shallow diapir over which the seepage occurs is manifested at the surface by a graben in strike section and by a half-graben in dip section. Faulting over the crest is commonly associated with loss of reflected energy or acoustic wipeouts. Most cores taken in wipeouts with prolonged bottom echoes contain oil and gas. The cores also commonly contain secondary carbonate derived from microbial degradation of hydrocarbons. The isotopic lightness of the carbonate and its negative correlation with porosity may be subtle indicators of seepage at sites where oil and gas are not obvious. The seepage demonstrates the existence of source rocks and maturation at this site.