Geologic Implications of Aeromagnetic Data for the Eastern Continental Margin of the United States

Taylor, Patrick T.; Zietz, Isidore; Dennis, Leonard S.

doi:10.1190/1.1439970

Cited by 130 publications

(32 citation statements)

References 36 publications

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“…But the magnetic profile across it is far from flat and shows very definite traceable linear anomalies ( Figure 5), e.g., the E anomaly of Rabinowitz (1974), the Blake Spur (BS) anomaly of Taylor et al (1968), and the a anomaly of Drake et al (1963). They are quite consistent in the western Atlantic south of the Kelvin Seamounts.…”

Section: °Wsupporting

confidence: 48%

Site 388: Lower Continental Rise Hills

Benson¹,

Sheridan²

1978

Initial Reports of the Deep Sea Drilling Project

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Section: °Wsupporting

confidence: 48%

Site 388: Lower Continental Rise Hills

Benson¹,

Sheridan²

1978

Initial Reports of the Deep Sea Drilling Project

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“…The structural framework of the target rocks (rocks impacted by the bolide) has been established by numerous regional seismic, gravity, and magnetic surveys ( Fig. 2; Ewing et al, 1937;Woollard et al, 1957;LeVan and Pharr, 1963;Taylor et al, 1968;Sabet, 1973;Johnson, 1977;Hawarth et al, 1980;Lyons et al, 1982;Dysart et al, 1983).…”

Section: Introductionmentioning

confidence: 99%

The Chesapeake Bay bolide impact: a convulsive event in Atlantic Coastal Plain evolution

Poag

1997

Sedimentary Geology

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Until recently, Cenozoic evolution of the Atlantic Coastal Plain has been viewed as a subcyclical continuum of deposition and erosion. Marine transgressions alternated with regressions on a slowly subsiding passive continental margin, their orderly succession modified mainly by isostatic adjustments, occasional Appalachian tectonism, and paleoclimatic change. This passive scenario was dramatically transformed in the late Eocene, however, by a bolide impact on the inner continental shelf. The resultant crater is now buried 400-500 m beneath lower Chesapeake Bay, its surrounding peninsulas, and the continental shelf east of Delmarva Peninsula. This convulsive event, and the giant tsunami it engendered, fundamentally changed the regional geological framework and depositional regime of the Virginia Coastal Plain, and produced the following principal consequences. (1) The impact excavated a roughly circular crater, twice the size of Rhode Island (-6400 km2) and nearly as deep as the Grand Canyon (-1.3 km deep). (2) The excavation truncated all existing ground-water aquifers in the target area by gouging -4300 km3 of rock from the upper lithosphere, including Proterozoic and Paleozoic crystalline basement rocks and Middle Jurassic to upper Eocene sedimentary rocks. (3) Synimpact depositional processes, including ejecta fallback, massive crater-wall failure, water-column collapse, and tsunami backwash, filled the crater with a porous breccia lens, 600-1200 m thick, at a phenomenal rate of -1200 m/hr. The breccia lens replaced the truncated ground-water aquifers with a single 4300 km3 reservoir, characterized by ground water -1.5 times saltier than normal sea water (chlorinities as high as 25,700 mg/l). (4) A structural and topographic low, created by differential subsidence of the compacting breccia, persisted over the crater at least through the Pleistocene. In the depression are preserved postimpact marine lithofacies and biofacies (upper Eocene, lower Oligocene, lower Miocene) not known elsewhere in the Virginia Coastal Plain. (5) Long-term differential compaction and subsidence of the breccia lens spawned extensive fault systems in the postimpact strata. Many of these faults appear to reach the bay floor, and may be potential hazards for motion-sensitive structures in population centers around Chesapeake Bay. Near-surface fracturing and faulting generated by the impact shock may extend as far as 90 km from the crater rim. (6) Having never completely filled with postimpact sediments. the sea-floor depression over the crater appears to have predetermined the location of Chesapeake Bay. (7) As large impact craters are principal sources for some of the world's precious metals, it is reasonable to expect that metal-enriched sills, dikes, and melt sheets are present in the inner basin of the crater.In addition to these specific consequences, the crater and the convulsive event that produced it, have widespread implications for traditional interpretations of certain structural and depositional features of the Atla...

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“…Pitman et al (1968) suggested that the magnetic properties of rocks of the Cretaceous quiet zone may have changed owing to diagenetic processes, a scenario that can easily be extended to include the Jurassic Quiet Zone. Indeed, the process of hydrothermal alteration of source basalts has been implied by several authors as a possible cause for the Jurassic Quiet Zone (Vogt et al, 1971;Taylor et al, 1968). Houtz and Ewing (1976) recorded a thickening of low velocity layer 2A crustal rocks associated with the Jurassic Quiet Zone and presumed there might be some connection to the change in magnetic properties therein.…”

Section: The Jurassic Quiet Zonementioning

confidence: 99%

Paleomagnetic and Rock Magnetic Properties of Jurassic Quiet Zone Basalts, Hole 801C . . .

Wallick¹,

Steiner²

1992

Proceedings of the Ocean Drilling Program

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The paleomagnetic and rock magnetic properties of 51 Jurassic basalts from Ocean Drilling Program (ODP) Hole 801C have been examined. Magnetic properties vary with lithologic composition; alkalic rocks and hydrothermally-altered tholeiites are much weaker in intensity and generally contain higher coercivity magnetic components than the older and less-altered tholeiites at the base of the hole. For the entire column, the Jurassic basalts have an average initial natural remanent magnetization (NRM) intensity of approximately 1.24 A/m and average median destructive fields (MDF) of 8.31 mT. These values and the mean Koenigsberger ratio of 1.7 are very similar to results obtained for Jurassic basalts from the Atlantic (DSDP Leg 76). The similarities suggest that the basalts of both sites and their remanence characteristics are representative of Jurassic oceanic crust.The most profound discovery in these samples was the presence of 5 inclination zones, each showing consistent positive (or negative) polarity opposite the overlying and underlying polarity bands. We interpret these to represent a record of change in polarity of the EarüYs magnetic field and, because of the large number over such a short interval (60 m) of crust, we assert that the rapid change in polarity during the Jurassic is the probable reason behind the origin of the Jurassic Quiet Zone. INTRODUCTIONSeveral attempts have been made in the past to reach Jurassic oceanic crust within the region referred to as the Jurassic Quiet Zone in order to examine the magnetic character of samples of that age. Sites 198 (25.8°N, 154.6°E) and 199 (13.5°N, 156.2°E) were terminated due to drilling complications (Heezen, MacGregor, et al., 1973) while nearby Site 585 (13.5°'N, 156.8°E) was stopped in a thickerthan-expected sequence of Lower Cretaceous turbidites (Shipboard Scientific Party, 1985a). Most disappointing was the recovery of a thick sequence of Cretaceous intrusive and extrusive rocks from Hole 462A (17°14.5'N, 165°1.9'E) in the Nauru basin, a site that lies beyond a magnetic anomaly correlated with chron M26, thus indicating a Late Jurassic age (Shipboard Scientific Party, 1981). Further drilling of Hole 462A on Leg 89 yielded similar results (Shipboard Scientific Party, 1985b). Even on the present leg, both Site 800 (21°55.4'N, 152°19.4'E) and Site 802 (12°5.8'N, 153°12.6'E) were terminated in Cretaceous volcanic rocks . The third site, Site 801 (18°38.6'N, 156°21.6'E), however, reached its intended target and finally laid to rest any doubts that the magnetic smooth zone in this region did hold, at least in part, remnants of the Middle and Late Jurassic Pacific plate.While remote sensing studies of variations of the geomagnetic field will continue to play a major role in our understanding of crustal movements and development, they can play only a partial role in our understanding of the origins of the Jurassic Quiet Zone. Only analyses of samples collected directly from the Jurassic Quiet Zone can provide answers to the questions concerning the ...

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Geologic Implications of Aeromagnetic Data for the Eastern Continental Margin of the United States

Cited by 130 publications

References 36 publications

Site 388: Lower Continental Rise Hills

Site 388: Lower Continental Rise Hills

The Chesapeake Bay bolide impact: a convulsive event in Atlantic Coastal Plain evolution

Paleomagnetic and Rock Magnetic Properties of Jurassic Quiet Zone Basalts, Hole 801C . . .

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