Geology topics

G.C. Kineke

Publications and source records attributed to G.C. Kineke.

4 recordsLinked to original sources

USGS2005

Influence of the Atchafalaya River on recent evolution of the chenier-plain inner continental shelf, northern Gulf of Mexico

This study examines the influence of the Atchafalaya River, a major distributary of the Mississippi River, on stratigraphic evolution of the inner continental shelf in the northern Gulf of Mexico. Sedimentary, geochemical, and shallow acoustic data are used to identify the western limit of the distal Atchafalaya subaqueous delta, and to estimate the proportion of the Atchafalaya River's sediment load that accumulates on the inner shelf seaward of Louisiana's chenier-plain coast. The results demonstrate a link between sedimentary facies distribution on the inner shelf and patterns of shoreline accretion and retreat on the chenier plain. Mudflat progradation on the eastern chenier-plain coast corresponds to the location of deltaic mud accumulation on the inner shelf. On the central chenier-plain shelf, west of the subaqueous delta, relict sediment is exposed that was originally deposited between ???1200 and 600 years BP during activity of the Lafourche lobe of the Mississippi Delta complex. Mass-balance calculations indicate that the eastern chenier-plain inner shelf and coastal zone form a sink for 7??2% of the sediment load carried by the Atchafalaya River. ?? 2004 Elsevier Ltd. All rights reserved.

Continental Shelf Research↗

USGS2000

Observations of storm and river flood-driven sediment transport on the northern California continental shelf

In the winter of 1996-1997, three bottom-boundary layer tripods were placed in an alongshelf array on the northern California continental shelf off Eureka, CA in 60-65-m water depth. During the observation period, multiple storms and river discharge events occurred, as well as the largest flood on record since 1964. Suspended-sediment concentration at all three sites fluctuated in response to both wave resuspension and advection of river-derived sediments. However, considerable spatial differences in low-frequency currents and suspended-sediment concentration were observed at the three sites. Sediment flux vectors calculated during periods of high suspended-sediment concentration suggest a convergence of sediment flux coincident with the center of recent flood deposits. Suspended-sediment concentrations observed at the two northern tripod sites following the large flood reached magnitudes typical of fluid mud (> 10 g/l) in a thin near-bed layer. The net sediment flux during the single three-day event was two orders of magnitude larger than any other event during the winter, and accounted for seven times the flux observed over an entire year (1995-1996). A conceptual model for the advection of sediment to the mid shelf is proposed in which river plume sediments are trapped on the inner shelf either due to a weak front or the rapid input of sediment from a confined plume, and form a thin layer of fluid mud. The fluid mud subsequently is transported seaward due to gravitational forcing. The measured sediment concentration and velocity profiles on the shelf provide strong evidence to support this conclusion. (C) 2000 Elsevier Science Ltd.

Continental Shelf Research↗

USGS1996

Observations of sediment transport on the Amazon subaqueous delta

A 19-day time series of fluid, flow, and suspended-sediment characteristics in the benthic boundary layer is analyzed to identify major sedimentary processes active over the prodelta region of the Amazon subaqueous delta. Measurements were made by the benthic tripod GEOPROBE placed on the seabed in 65 m depth near the base of the deltaic foreset beds from 11 February to 3 March 1990, during the time of rising water and maximum sediment discharge of the Amazon River; and the observations included: hourly measurements of velocity and suspended-sediment concentration at four levels above the seabed; waves and tides; and seabed elevation. Results of the first 14-day period of the time series record indicate that sediment resuspension occurred as a result of tidal currents (91% of the time) and surface gravity waves (46% of the time). Observations of suspended sediment indicated that particle flux in this region is 0.4–2% of the flux measured on the adjacent topset deposits and is directed to the north and landward relative to the Brazilian coast (268°T). Fortnightly variability is strong, with particle fluxes during spring tides five times greater than during neap tides. On the 15th day of the data record, a rapid sedimentation event was documented in which 44 cm of sediment was deposited at the study site over a 14-h period. Evaluation of various mechanisms of mass sediment movement suggests that this event represents downslope migration of fluid muds from the upper foreset beds that were set in motion by boundary shear stresses generated by waves and currents. This transport mechanism appears to occur episodically and may represent a major source of sediment to the lower foreset-bottomset region of the subaqueous delta.

Continental Shelf Research↗

USGS1995

Measurements in the bottom boundary layer on the Amazon subaqueous delta

An instrumented bottom tripod (GEOPROBE) recorded flow and suspended sediment data in the bottom boundary layer above the lower foresets of the Amazon subaqueous delta in 65 m mean water depth in February, 1990. After about two weeks of operation the apparent seafloor at the tripod site rapidly elevated over a 14-hour period by about 44 cm. This sudden change, which was detected by an acoustic altimeter and which caused the loss of signals from the lowermost GEOPROBE current and optical sensors, is though to have been caused by the incursion of a dense bottom layer of fluid mud that migrated downslope from shallower sections of the foresets. The fluid-mud migration across the outer part of the foresets, if a repetitive and occasional process in this region, could be a major mechanism for episodic seaward growth of the delta. Current velocity profiles are used to estimate shear velocities, u*, and roughness lengths, zo, during the first two weeks of measurements. -from Authors

Marine Geology↗