Pliocene-Pleistocene marine deposits overlying Messinian evaporites off northeast Spain are composed of five distinct seismic facies. These facies are interpreted to represent deposition in five adjacent settings: distal (isolated) basin, basin plain, base of slope,slope, and shelf. Contrary to previous studies, a submarine-fan style of deposition is not evident. Distal-basin deposits are characterized by thin, wavy, parallel beds draping the sea floor. Basin-plain deposits are similar but also have flat-lying beds and some low-relief channels. Base-of-slope deposits are dominated by stacked, overlapping, elongate channel/levee deposits that have concave-upward bases and convex-upward tops. Slope sequences are thick accumulations of overbank deposits laterally interrupted by large upward-climbing canyon fill. The shelf component is composed of overlapping and stacked delta lobes. The composite sediment body is a prograded, upward-shallowing, offlap sequence initiated and controlled by the influx of terrigenous sediment from the Rio Ebro during the Pleistocene. This style of deposition is common in the rock record, and our model may be more appropriate as a modern analogue for some rocks than are conventional shelf-canyon-fan models of margin sedimentation.

Ebro River, Gulf of Valencia, Mediterranean Sea↗

USGS1987

Sedimentary processes on the northwestern Iberian continental margin viewed by long-range side-scan sonar and seismic data

The effects of an eastern boundary current in the North Atlantic have been mapped from about 39° north latitude along the Iberian margin to as far north as 43°30 north latitude at the western margin of Galicia Bank. The geostrophic current has produced sediment drifts that are covered with bedforms. The sediment drifts are difficult to detect on Gloria long-range side-scan sonar data but are easily resolved on seismic-reflection records as anomalously thick accumulations of sediment banked against either buried or outcropping basement highs. The bedforms ornamenting the drift surfaces were subdivided into 1,000-m water-depth intervals, and their dimensions were tabulated. There are few bedforms in water depths less han 2,000 m, but from depths between 2,000 and 4,000 m they are numerous and have a mean wavelength of 695 m. Bedforms from depths greater than 4,000 m have a mean wavelength of 999 m. The different wavelengths from different water depths suggest two distinct and separated boundary flows. The wave heights of all bedforms found in water depths greater than 2,000 m are less than 10 m. In order to investigate the continuity of sediment drifting through geological time, the stratigraphic section drilled at DSDP Site 398 was reinterpreted and, using seismic-reflection profiles, was traced throughout the northern Iberian margin. Together, the lithostratigraphic and seismic data indicate that sediment drifting developed along this margin in the Eocene. The lithofacies of the Eocene section is t e oldest to have numerous layers of sand and silt. An unconformity separates the Eocene section from the latest Miocene-Pliocene section. The unconformity is interpreted to be the result of the initial pulses of Mediterranean outflow that followed the Messinian desiccation events. A second period of sediment drifting commenced during the Pliocene once the Mediterranean basin filled and the flow out of the Strait of Gibraltar resumed.

Journal of Sedimentary Petrology↗

USGS1983

Quantitative microfossil, sedimentologic, and geochemical data on cores V1-80-P3, V1-80-G1, and V1-80-P8 from the continental slope off Northern California

Explore the source record for details and available documents.

Open-File Report↗

USGS1981

Tertiary carbonate-dissolution cycles on the Sierra Leone Rise, eastern equatorial Atlantic Ocean

Most of the Tertiary section on Sierra Leone Rise off northwest Africa consists of chalk, marl, and limestone that show cyclic alterations of clay-rich and clay-poor beds about 20–60 cm thick. On the basis of biostratigraphic accumulation rates, the cycles in Oligocene and Miocene chalk have periods which average about 44,000 years, and those in Eocene siliceous limestone have periods of 4000–27,000 years. Several sections were sampled in detail to further define the cycles in terms of content of CaCO 3 , clay minerals, and relative abundances of calcareous nannofossils. Extending information gained by analyses of Pleistocene cores from the continental margin of northwest Africa to the Tertiary cycles on Sierra Leone Rise, both dilution by noncarbonate material and dissolution of CaCO 3 could have contributed to the observed relative variations in clay and CaCO 3 . However, dissolution of CaCO 3 as the main cause of the carbonate-clay cycles on the Sierra Leone Rise, rather than dilution by clay, is suggested by the large amount of change (several thousand percent) in terrigenous influx required to produce the observed variations in amount of clay and by the marked increase in abundance of dissolution-resistant discoasters relative to more easily dissolved coccoliths in low-carbonate parts of cycles. The main cause of dissolution of CaCO 3 was shoaling of the carbonate compensation depth (CCD) during the early Neogene and climatically induced fluctuations in the thickness of Antarctic Bottom Water.

Marine Geology↗

USGS1979