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Site U13191

Expedition 308 Scientists2

Background and objectives

Geological setting of Brazos-Trinity Basin IV

Brazos-Trinity Basin IV is the southernmost of a chain of five north-south-oriented basins on the continental slope of the Gulf of Mexico (Figs. F1, F2) (Satterfield and Behrens, 1990; Winker, 1996). It is located ~250 km south-southeast of Houston, Texas (USA). It forms part of the Brazos-Trinity Fan, a large latest Pleistocene sediment gravity flow depositional system. These basins are a classic area for study of modern deepwater turbidite systems (Morton and Suter, 1996; Winker, 1996; Beaubouef and Friedmann, 2000; Fraticelli, 2003; Anderson and Fillon, 2004). Early work in these basins established the “fill and spill” model whereby deposition in downslope basins would not occur before all upslope basins were filled (Satterfield and Behrens, 1990; Winker, 1996). Subsequent work elaborated on this conceptual model (e.g., Beaubouef and Pirmez, 1999; Friedmann and Beaubouef, 1999). Badalini et al. (2000) and Fraticelli (2003) proposed a contrasting model wherein deposition was contemporaneous in each of these basins.

More recently, Beaubouef et al. (2003) used high-resolution three-dimensional (3-D) seismic data over Brazos-Trinity Basin IV and further refined the work of Beaubouef and Friedmann (2000). Most recently, Mallarino et al. (in press) used piston coring at the margins of Brazos-Trinity Basin IV to characterize its paleogeographic evolution. They described six sedimentary units (Fig. F3) and used biostatratigraphic analysis to constrain the age of these sediments; Brazos-Trinity Basin IV formed during the stepwise sea level fall between 115 and 15 ka, ending just prior to the meltwater pulse to the Gulf of Mexico at 14 ka.

Seismic surfaces

Prior to drilling, we mapped six reflectors in Brazos-Trinity Basin IV from closely spaced, high-resolution, two-dimensional (2-D) seismic reflection data: the seafloor reflector (SF) and Reflectors R10, R20, R30, R40, R50, and R60 (Figs. F4, F5, F6, F7, F8; Table T1). Time-depth conversions were estimated prior to drilling with the following velocity model.

zbsf = 0.7798735 tbsf + 1.66055 × 10–4 t2bsf, (1)


  • zbsf = depth below sea level in meters and
  • tbsf = two-way traveltime in milliseconds from the seafloor to the horizon of interest.

Equation 1 results from a compilation of regional check shot (velocity) data (C. Winker, Shell International Exploration and Production Company, pers. comm., 2005).

The seismic reflection character of the basin sediments (between Reflector R40 and the seafloor) can be divided into an alternating succession of transparent units and more reflective layered units. We mapped three reflectors (Figs. F5, F6, F7):

  • R30 caps the first layered package.
  • R20 lies within the second layered package.
  • R10 caps a thin layered interval in the final reflective package.

Reflector SF caps a high-amplitude but somewhat chaotic package that becomes more layered in the downdip (southern) direction. The reflective layered seismic facies are interpreted as fan deposits, whereas the chaotic and/or transparent deposits are interpreted as debris flows and/or mass transport complexes (Badalini et al, 2000; Winker and Booth, 2000; Beaubouef et al., 2003). Figure F3 illustrates how our mapped surfaces tie to the sediment packages defined in previous work.

Location of Site U1319

Site U1319 is located in ~1430 m of water on the southern flank of Brazos-Trinity Basin IV (Figs. F4, F5). Two-dimensional seismic data illustrate that Site U1319 holes penetrate the flank of the basin. At this location, basin sediments (seafloor to Reflector R40) are projected to be only 35 m thick (Table T1). Beneath the basin sediments (beneath Reflector R40), parallel reflectors from hemipelagic sediments are present.

Site U1319 drilling objectives

The primary drilling objectives at this site were the following:

  • Establish a reference section to determine the change in rock and fluid properties at this normally pressured location.
  • Determine the age of the stratigraphic section and thus contribute to the derivation of an integrated age model for Brazos-Trinity Basin IV.
  • Determine the lithology and stratigraphic evolution of the margin of this basin to allow lateral correlation with the sections at Sites U1320 and U1321.
  • Sample the subsurface biosphere in this reference location.
  • Conduct a logging-while-drilling (LWD)/measurement-while-drilling (MWD) program in a dedicated LWD/MWD hole.

To achieve these objectives, Hole U1319A was continuously cored to terminal depth (TD) at 157.5 meters below seafloor (mbsf). Advanced piston coring (APC) was used to 114.6 mbsf, followed by extended core barrel (XCB) coring. One advanced piston corer temperature (APCT) tool measurement was taken at the bottom of Core 308-U1319A-5H at ~42.5 mbsf. Special tool deployments in Hole U1319A included one deployment of the temperature/​dual pressure (T2P) probe just above the seafloor and one deployment at 80.5 mbsf. A dedicated second hole (Hole U1319B) was drilled to conduct the LWD/MWD operations to a TD of 180 mbsf. This was done to generate a complete set of logging parameters for correlation with core and wireline logging data from Hole U1319A.

1 Expedition 308 Scientists, 2006. Site U1319. In Flemings, P.B., Behrmann, J.H., John, C.M., and the Expedition 308 Scientists, Proc. IODP, 308: College Station TX (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/​iodp.proc.308.103.2006

2 Expedition 308 Scientists’ addresses.

Publication: 8 July 2006
MS 308-103