[First Hit]![]() |
---|
Click to view presentation in PDF format.
Search and Discovery Article #50091 (2008)
Posted October 24, 2008
*Adapted from oral presentation at AAPG Annual Convention, San Antonio, Texas, April 20-23, 2008.
1 Marine Science, Texas A&M University at Galveston, Galveston, TX. ([email protected])
2 Oceanography, Texas A&M University, Galveston, TX
Sediment transport from river mouths via hyperpycnal flow is a well documented process for
high gradient
rivers worldwide. However, many important hydrocarbon-bearing deltaic systems were derived from
lower
gradient
systems where hyperpycnal flow is not normally attributed. The Brazos River provides a modern
example of such a low-
gradient
river. We had the unique opportunity to sample the mouth and proximal shelf of the
Brazos River during the flooding of July 2007. Using a CTD equipped with a turbidity sensor, water column
profiles were taken on an along-shelf transect from the river mouth 10 km northeast in the direction of the plume
transport and an across shelf transect from the river mouth 8 km offshore to the seaward edge of the plume. In
addition, bottom-water samples and shallow gravity cores were collected to determine the thickness of the flood
deposit, suspended sediment concentration, pore-water salinity, and grain-size distribution. We found both a high
turbidity hypopycnal plume as well as a high turbidity bottom layer, with low turbidity in the middle of the
water column. Brazos River mud is characteristically red, while marine sediment is olive-grey. Preliminary result
reveal a distinctively red, porous storm layer, composed of up to 30% sand that extended 5 km from the river
mouth. The presence of sand within the storm layer and the high turbidity bottom layer suggest hyperpycnal flow
existed during the flood. If this is the case, hyperpycnal flow may be a regular occurrence on the Brazos River
and may be more common within low-
gradient
river systems than previously believed, providing an additional
mechanism for transporting both sand and mud across the inner shelf.
They normally are asociated with:
Brazos River is:
Brazos River provides an ideal natural laboratory to investigate:
Kineke, G.C., K.J. Woolfe, S.A. Kuehl, J.D. Milliman, T.M. Dellapenna, and R.G. Purdon, 2000, Sediment export from the Sepik River, Papua New Guinea; evidence for a divergent sediment plume: Continental Shelf Research, v. 20/16, p. 2239-2266.
Mulder, T., and J.P.M. Syvitski, 1995, Turbidity currents generated at river mouths during exceptional discharges to the world oceans: Journal of Geology, v. 103/3, p. 285-299.
Parsons, J.D., C.T. Friedrichs, P.A. Traykovski, D. Mohrig, J. Imran, et al., 2007, The mechanics of marine sediment gravity flows: Continental Margin Sedimentation; from Sediment Transport to Sequence Stratigraphy, Special Publication International Association of Sedimentologists, v. 37, p. 275-337.
Rodriguez, A.B., M.D. Hamilton, and J.B. Anderson, 2000, Facies and evolution of the modern Brazos Delta, Texas; wave versus flood influence: Journal of Sedimentary Research, v. 70/2, p. 283-295.
Appreciation is expressed to Carmen Fraticelli, Damian O’Grady, and ExxonMobil Upstream Research Company.