Abyssal Basin Research Articles

Mesozoic magnetic lineations in the Bering Sea Marginal Basin

A compilation of marine magnetic profiles from the Bering Sea marginal basin has revealed the existence of north-south trending magnetic lineations over the deep abyssal basins. The anomalies in the Aleutian and Bowers basins have maximum peak to peak amplitudes of 350 γ and wavelengths characteristic of sea floor spreading anomalies (25–100 km). These lineations are as much as 600 km long. In contrast, linear trends within the Komandorsky Basin are less distinct and have anomalies with variable amplitudes. The magnetic anomalies along an 850-km profile crossing the Aleutian Basin have been correlated with the M1-M13 (117–132 m.y.) sequence of Larson's (1974) Mesozoic time scale. These anomalies increase in age from east to west and yield a half spreading rate of 5.1 cm/yr. North-south trending anomalies within Bowers Basin exhibit shapes and spacings similar to those from the Aleutian Basin, suggesting that these trends may have been connected at one time. Detailed model studies of the anomalies in the Aleutian Basin yield results which support the hypothesis that the igneous crust in the eastern Bering Sea is trapped oceanic plate which may have been part of the Mesozoic Pacific Basin. The model studies have indicated that (1) normalized magnetization intensities are comparable to those estimated for the Mesozoic Hawaiian Lineations in the Pacific, (2) the approximate phase angle of the observed anomalies (−10°±20°) would allow the magnetic lineations either to be formed at their present location or else to be formed at a more southerly site and then moved to their present location, and (3) the width of transitions between adjacent polarity intervals is relatively large (W ≥ 16 km) and may be related to a redistribution of the remanent magnetization within a deeply buried layer 2. The corrected depth to layer 2 is within 5% of the depth predicted for Mesozoic crust (120 m.y.) on the Sclater (1972) depth versus age curves. Although the north-south trending anomalies in the Aleutian and Bowers basins are interpreted as sea floor spreading anomalies, the origin of the anomaly pattern in the Komandorsky Basin is not understood.

Proposed Model for Cenozoic Sedimentary History of Bering Sea: ABSTRACT

The Bering Sea consists of an abyssal basin and a large continental shelf area. The basin apparently was isolated from the Pacific Ocean by the development of the Aleutian ridge near the end of Cretaceous time; the continental shelf area first became submerged near the middle of the Tertiary Period. It is postulated that the sediment eroded from Alaska and Siberia during Cenozoic time (1) was trapped mainly in subsiding basins on the Bering shelf during the Tertiary, (2) was collected mostly in continental rise and abyssal plain deposits of the deep Bering Sea during the low sea levels of the Quaternary, and (3) was transported generally from the Bering shelf northward through the Bering Straits during periods of high sea levels in Pleistocene and Holocene times. Basin-filling was dominated by continental sedimentation in the early Tertiary and by marine deposition in the later Tertiary. Miocene uplift of the Alaska Range more than doubled the drainage area of the Yukon River and established it as the dominant river source (up to 90%) of the Bering Sea; this greatly increased sedimentation in the submergent basins. Subaerial drainage of this and other major river sediment sources during the glacial stages of the Pleistocene resulted in channeling great amounts of sediment across the shelf to the deep Bering Sea basin and cutting of the largest submarine canyons in the world. Occurrence of the thin Holocene marine deposits near the present Yukon delta, of mainly relict sediments in the northern Bering Sea north of St. Lawrence Island, and of several meters of Holocene sediment in the Chukchi Sea permits speculation that now, as in the past, large volumes of Yukon sediment are flushed from the northern Bering Sea into the Chukchi Sea. End_of_Article - Last_Page 629------------

Abyssal Basin Sedimentation: ABSTRACT

Clastic sands and silts transported and deposited by turbidity currents have created the vast abyssal plains of the ocean basins and have constructed the abyssal cones and natural levee systems of the continental rise. Clastic silts and lutites, largely transported by ocean currents, have created much of the continental rise and the outer ridges which parallel the continental margins. Biogenous sediment, resulting from near-surface productivity, more or less redistributed by currents, has created the rolling abyssal swales of productive mid-oceanic areas and has contributed to the continental rise and marginal trench sediments. Although turbidity currents are responsible for the leveling of the abyssal plains, turbidites constitute less than one-third of the sediments beneath the plains. Horizontal size grading in turbidites away from source areas is detectable but small. Apparently a much more important control on size is imposed by the lower courses of the major rivers. Turbidity currents originate near the mouths of several major rivers at the rate of 50 per century but in many other likely areas none have occurred for thousands of years. End_of_Article - Last_Page 344------------