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Geology topics

W. R. Normark

Publications and source records attributed to W. R. Normark.

At least 73 records · Page 4Linked to original sources
USGS1984

The Crati Submarine Fan, Ionian Sea

The Crati Fan is located in the tectonically active submerged extension of the Apennines chain and foretrough. The small fan system is growing in a relatively shallow (200 to 450 m), elongate nearshore basin receiving abundant input from the Crati River. The fan is characterized by a short, steep, channelized section (inner or upper fan) and a smooth, slightly bulging distal section (outer or lower fan). The numerous subparallel channels head in the shelf or littoral zone and do not form branching distributary patterns. Sand and mud depositional lobes of the outer fan stretch over more than 60% of fan length. ?? 1984 Springer-Verlag New York Inc.

Geo-Marine Letters↗
USGS1984

Delgada Fan: Preliminary interpretation of channel development

The Delgada Fan, an irregularly shaped turbidite deposit extending more than 350 km offshore from northern California, consists of two large leveed-valley units each fed by a separate complex of coalescing submarine canyons and slope gullies. Although the leveed-valley units head within 25 km of each other, both appear to have developed independently during fan growth. The larger southern leveed-valley system has not developed middle-fan distributary channels and appears to illustrate a period of progressive valley abandonment. Although the lower-fan area is underlain by sandy sediments, little sand has been recovered in piston cores from the leveed-valley unit. ?? 1984 Springer-Verlag New York Inc.

Geo-Marine Letters↗
USGS1984

Monterey Fan: Growth pattern control by basin morphology and changing sea levels

Monterey Fan is the largest modern fan off the California shore. Two main submarine canyon systems feed it via a complex pattern of fan valleys and channels. The northern Ascension Canyon system is relatively inactive during high sea-level periods. In contrast, Monterey Canyon and its tributaries to the south cut across the shelf and remain active during high sea level. Deposition on the upper fan is controlled primarily by the relative activity within these two canyon systems. Deposition over the rest of the fan is controlled by the oceanic crust topography, resulting in an irregular fan shape and periodic major shifts in the locus of deposition. ?? 1984 Springer-Verlag New York Inc.

Geo-Marine Letters↗
USGS1984

Navy Fan, California Borderland: Growth pattern and depositional processes

Navy Fan is a Late Pleistocene sand-rich fan prograding into an irregularly shaped basin in the southern California Borderland. The middle fan, characterized by one active and two abandoned 'distributary' channels and associated lobe deposits, at present onlaps part of the basin slope directly opposite from the upper-fan valley, thus dividing the lower-fan/basin-plain regions into two separate parts of different depths. Fine-scale mesotopographic relief on the fan surface and correlation of individual turbidite beds through nearly 40 cores on the middle and lower fan provide data for evaluating the Late Pleistocene and Holocene depositional processes. ?? 1984 Springer-Verlag New York Inc.

Geo-Marine Letters↗
USGS1984

The Laurentian Fan: Sohm Abyssal Plain

The 0.5- to 2-km thick Quaternary Laurentian Fan is built over Tertiary and Mesozoic sediments that rest on oceanic crust. Two 400-km long fan valleys, with asymmetric levees up to 700-m high, lead to an equally long, sandy, lobate basin plain (northern Sohm Abyssal Plain). The muddy distal Sohm Abyssal Plain is a further 400-km long. The sediment supplied to the fan is glacial in origin, and in part results from seismically triggered slumping on the upper continental slope. Sandy turbidity currents, such as the 1929 Grand Banks earthquake event, probably erode the fan-valley floors; but thick muddy turbidity currents build up the high levees. ?? 1984 Springer-Verlag New York Inc.

Geo-Marine Letters↗
USGS1984

Aftermath of comfan-Comments, not solutions

Comparison of descriptions of fans in this volume demonstrates the major problems in developing general models that incorporate modern fans and ancient turbidite sequences. Attempts to develop a unifying fan model are presently premature. The most pressing need is refined definition of the primary common characteristics of submarine turbidite systems such as fans. ?? 1984 Springer-Verlag New York Inc.

Geo-Marine Letters↗
USGS1982

Diverse basalt types from Loihi seamount, Hawaii

Loihi seamount is the southeasternmost active volcano in the Hawaiian-Emperor volcanic chain. The seamount is considered representative of the early phase of Hawaiian volcanism because of its youth, small size, and location near the melting anomaly. Seventeen dredge stations recovered transitional basalt, alkalic basalt, and basanite, in addition to the expected tholeiitic basalt. Four flows of alkalic basalt contain common small dunite xenoliths. The recovered samples have thin palagonite rinds and almost no manganese on the glassy surfaces; we estimate that the lavas are less than about 4,000 yr old, and many are less than 1,000 yr old. Loihi seamount is apparently in a transitional growth phase between the early eruption of alkalic lavas and the commonly observed (subaerial) tholeiitic eruptive phase, previously thought to dominate Hawaiian volcanism from inception until the postcaldera collapse, alkalic stage.

Hawaii↗
USGS1981

First manned submersible dives on the East Pacific Rise at 21°N (project RITA): general results

A submersible study has been conducted in February–March 1978 at the axis of the East Pacific Rise near 21°N. The expedition CYAMEX, the first submersible program to be conducted on the East Pacific Rise, is part of the French-American-Mexican project RITA (Rivera-Tamayo), a 3-year study devoted to detailed geological and geophysical investigations of the East Pacific Rise Crest. On the basis of the 15 dives made by CYANA in the axial area of the Rise, a morphological and tectonic zonation can be established for this moderately-fast spreading center. A narrow, 0.6 to 1.2 km wide zone of extrusion (zone 1), dominated by young lava flows, is flanked by a highly fissured and faulted zone of extension (zone 2) with a width of 1 to 2 km. Further out, zone 3 is dominated by outward tilted blocks bounded by inward-facing fault scarps. Active or recent faults extend up to 12 km from the axis of extrusion of the East Pacific Rise. This represents the first determination from direct field evidence of the width of active tectonism associated with an accreting plate boundary. Massive sulfide deposits, made principally of zinc, copper and iron, were found close to the axis of the Rise. Other signs of the intense hydrothermal activity included the discovery of benthic fauna of gian size similar to that found at the axis of the Galapagos Rift. We emphasize the cyclic character of the volcanicity. The main characteristics of the geology of this segment of the East Pacific Rise can be explained by the thermal structure at depth below this moderately-fast spreading center. The geological observations are compatible with the existence of a shallow magma reservoir centered at the axis of the Rise with a half-width of the order of 10 km.

Marine Geophysical Research↗