Empirical magnetic modeling of cretaceous submarine volcanic mounds in South Texas



Journal Title

Journal ISSN

Volume Title


Texas Tech University


Late Cretaceous volcanism occurred in South Texas roughly paralleling the Balcones, Luling, and Charlotte fault trends. The resulting dikes, sills and submarine volcanoes were derived from extremely silica deficient magmas producing olivine basalts and associated rock types. The volcanic domes or mounds underwent alteration and served to create high energy carbonate sedimentation around their periphery. The volcanics were subsequently buried by the Cretaceous, Taylor, and Navarro Groups and later Tertiery sediments. Subsurface volcanic tuff mounds trap hydrocarbons within porous altered tuff, flanking carbonate grainstones and packstones, and when present, Taylor and Navarro age sands.

Detailed, low altitude aeromagnetic surveys respond to and map these volcanic anomalies due to their high contrast in magnetic susceptibility with respect to surrounding sediments. Emperical profile modeling of 11 known volcanic domes revealed characteristic signatures with respect to dome size, depth, and shape. The magnetic crystalline basement complex serves to attenuate suprabasement signals, i.e., volcanic mounds. With a general knowledge of the depth to the magnetic basement, suprabasement volcanic mound depth (distance from sensor) can be estimated.

Elaine and Sutil Fields produce from Cretaceous Age rocks whose trapping mechanisms are related to submarine volcanism. A magnetic survey flown at approximately 800 feet above the surface mapped not only the thickest volcanic mounds, but a thin (20 to 100 feet) interval of volcanic material. In the case of the Sutil Field, this volcanic "talus" served as a precursor to a reservoir quality limestone facies. Elaine field was flown at 600 feet flight line spacing and extremely low altitudes, approximately 400 feet above the surface. Interpretation of the data confirmed a volcanic feature and the aerial extent was mapped using hand-drawn residual techniques. The resulting map correlated with the seismic and subsurface maps although a subtle (1 gamma) "nosing" in the contour developed to the northeast. Sparce subsurface data indicates this area to be a volcanic "talus" slope similar to Sutil Field. The greater production from overlying carbonate grainstones to the northeast of the mound may be related to this talus slope in addition to Paleo-wind direction and currents.



Stratigraphic -- Cretaceous, Geology, Volcanism -- Texas, Magnetic prospecting, Geologic modeling