Browsing by Subject "Faults (Geology)--Texas--Gulf Region"

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Chronostratigraphy, depositional rates, continental margin progradation, and growth-fault dynamics within the tertiary wedge, San Marcos arch, northwest Gulf of Mexico
(1988) Travis, Deborah Sue, 1963-; Galloway, William E.
Sedimentation, growth fault slip, and shelf-margin progradation rates were determined for a transect of Tertiary sediments along the axis of the San Marcos arch in the northwestern Gulf of Mexico basin. This low relief area was the site of shorezone depositional systems throughout most of the Tertiary and has not been affected by salt mobilization or the sedimentological overprint of large delta systems. Consequently, rates calculated in the area represent average rather than extreme values. Detailed correlation of 142 well logs and the utilization of paleontologic data from 17 wells made possible the construction of a chronostratigraphic cross section which divided the Tertiary section into 1 or 2 million year increments. A decompaction computer program, which utilizes published compaction curves and distinguishes between normally pressured shale, underconsolidated overpressured shale, and sandstone, calculated original sediment thickness and sedimentation rates for each of the chronostratigraphic layers. Regional sedimentation rates varied almost two orders of magnitude during the Tertiary. These findings seriously challenge the common assumption of relatively uniform sediment supply over geological time spans. Within individual chronostratigraphic layers, sedimentation rates ranged from 4 cm/1000 yrs in the fluvial and transgressive facies to 130 cm/1000 yrs in the lower Miocene outer shelf and slope facies. Decompaction of the section also allowed the calculation of growth fault slip rates and of the percent increase in accommodation on the downthrown side of the faults relative to their upthrown equivalents. Slip rates during times of maximum movement ranged from 250-600 m/my, agreeing with rates calculated for salt dome growth. Percent increase in accommodation on the downthrown side of the faults ranged from 20-83%. Shelf-margin progradation rates were calculated and ranged from -1.5 mi/my (2.4 km/my) during brief times of temporary retrogradation (Queen City and Yegua Formations) to 17.5 mi/my (28.2 km/my) during the Early Miocene
Heat variations caused by groundwater flow in growth faults of the South Texas Gulf Coast Basin
(1985) Bodner, Daniel Paul; Sharp, John Malcolm, Jr., 1944-
Zones of above average subsurface temperatures have been noted in certain areas of the Gulf Coast basin. Their cause has often been credited to geopressure, which presumably traps heat because of higher porosity and consequently lower thermal conductivity. I determined the temperature distribution in a portion of South Texas by collecting and analyzing over 1600 bottom-hole temperature measurements. The analysis included correcting the temperatures with the Kehle correction scheme, constructing isothermal surfaces by both interpolating and extrapolating the data, and Kriging the result. Temperature profiles were plotted for twelve subregions of the study area. The greatest temperature anomalies are associated with the Tertiary Wilcox growth fault zone, and the simple presence of geopressure is insufficient to account for the temperature anomaly. Numerical modeling indicates that growth faults act as zones for concentrated vertical flow. The upwelling of deep basinal fluids advects heat and causes the high temperatures observed in the growth fault zone. The model, by Smith (1983), is two-dimensional, finite element, steady state, and couples heat and fluid transport. It indicates that the source of these fluids is deep, perhaps over 20,000 feet (6096 m) below the surface. The modeling results also suggest that an unidentified region of high thermal and hydraulic conductivity could exist coastward of the Wilcox faults at a depth of about 15,000-20,000 feet (4572-6096m).