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Michael E. Field

Publications and source records attributed to Michael E. Field.

44 records · Page 3Linked to original sources
USGS1981

Sand waves on an epicontinental shelf: Northern Bering Sea

Sand waves and current ripples occupy the crests and flanks of a series of large linear sand ridges (20 km × 5 km × 10 m high) lying in an open-marine setting in the northern Bering Sea. The sand wave area, which lies west of Seward Peninsula and southeast of Bering Strait, is exposed to the strong continuous flow of coastal water northward toward Bering Strait. A hierarchy of three sizes of superimposed bedforms, all facing northward, was observed in successive cruises in 1976 and 1977. Large sand waves (height 2 m; spacing 200 m) have smaller sand waves (height 1 m; spacing 20 m) lying at a small oblique angle on their stoss slopes. The smaller sand waves in turn have linguoid ripples on their stoss slopes. Repeated studies of the sand wave fields were made both years with high-resolution seismic-reflection profiles, side-scan sonographs, underwater photographs, current-meter stations, vibracores, and suspended-sediment samplers. Comparison of seismic and side-scan data collected along profile lines run both years showed changes in sand wave shape that indicate significant bedload transport within the year. Gouge marks made in sediment by keels of floating ice also showed significantly different patterns each year, further documenting modification to the bottom by sediment transport. During calm sea conditions in 1977, underwater video and camera observations showed formation and active migration of linguoid and straight-crested current ripples. Current speeds 1 m above the bottom were between 20 and 30 cm/s. Maximum current velocities and sand wave migration apparently occur when strong southwesterly winds enhance the steady northerly flow of coastal water. Many cross-stratified sand bodies in the geologic record are interpreted as having formed in a tidal- or storm-dominated setting. This study provides an example of formation and migration of large bedforms by the interaction of storms with strong uniform coastal currents in an open-marine setting.

Marine Geology↗
USGS1981

Thermogenic hydrocarbons in unconsolidated sediment of Eel river basin, offshore northern California

Thermally produced hydrocarbons were recovered from unconsolidated sediment ponded within a bathymetric depression on the surface of a shale diapir in the offshore Eel River Basin of northern California. Evidence that the hydrocarbons are thermogenic consists of the following: (1) very high concentrations of hydrocarbon gases, particularly ethane through butanes (C 2 -C 4 ); (2) methane having a carbon isotopic composition (relative to the PDB standard) of −43 and −44 per mil; (3) presence of gasoline-range (C 5+ ) hydrocarbons; and (4) presence of a complex mixture of heavy hydrocarbons (C 15+ ) with n-alkanes having a petroleumlike distribution. This mixture of gaseous and liquid hydrocarbons likely originated deep within the basin and migrated to the surface through fractures and faults developed during the emplacement of the diapir. The presence of thermogenic hydrocarbons in unconsolidated surface sediment indicates that conditions for petroleum generation have existed within this offshore basin.

California↗
USGS1980

Modern sedimentary facies of the open Pacific coast and Pleistocene analogs from Montery Bay, California

Depositional processes and sedimentary structures of wave-dominated Pacific coastal environments vary systematically with water depth. The depth-limited open-coast facies identifiable by their sedimentary structures are the inner shelf, barred or nonbarred nearshore, beach, and coastal dune facies. These facies are most commonly preserved in shallowing-upward progradational sequences. The vertical sequence of sedimentary structures preserved in marine terrace deposits in the northern Monterey Bay region is very similar to that predicted on the basis of the modern facies. Few marine sediments deposited during the marine transgression that accompanied rising sea level were preserved. Most of the the marine and eolian sediments form a progradational sequence deposited mainly during intervals of falling sea level. In contrast, the sediments that form the adjacent fluvial terraces were deposited mainly during periods of rising sea level and became entrenched during the subsequent lowering of sea level. In combination, these fluvial, marine, and eolian deposits provide a record of a complete eustatic cycle. The recognition of the role of changing sea level in controlling patterns of coastal sedimentation and landform development during the Quaternary allows the development of a generalized model for Quaternary sedimentation along a wave-dominated coastline. The application of this model has aided in the interpretation of older Pleistocene sediments in the region (e.g. the Aromas Sand). It also has resulted in the recognition of at least eleven glacio-eustatic cycles preserved in the stratigraphic record of the Monterey Bay area during the Quaternary.

California↗
USGS1979

Location and hydrocarbon content of a gravity core from the offshore Eel River basin, northern California

The core was collected from ponded sediment near the crest of a diapir-like feature on the Eel Plateau. The measured hydrocarbons are likely to have been derived from deep in the Neogene sedimentary section of the Eel River Basin. Their presence at the surface may indicate migration along fractures in or bordering the diapiric feature and seepage into unconsolidated sediments that are ponded locally within structural and bathymetric depressions. The extent of low molecular weight hydrocarbons at or near the-surface elsewhere in the basin is unknown, but the information based on hydrocarbon composition obtained at this site indicates the possibility that thermogenically-derived hydrocarbons have formed and accumulated in the sedimentary rocks of the offshore Eel River Basin.

California↗