Kathryn D. Sullivan
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Ph. D. Thesis
(PDF -聽 40.25 Mb)
The ocean-continent boundary in the Newfoundland Basin is defined on the basis of seismic reflection and magnetic data as the seaward boundary of the continental margin magnetic smooth zone. The boundary is diachronous, being coincident with the J-anomaly (115 Ma) between the Southeast Newfoundland Ridge and the Newfoundland Seamounts and being of younger, but uncertain age north of the seamounts. These data are combined with recently-published data to define a pre-drift fit for Iberia-North America that is without gaps and continental overlaps.Active seafloor spreading began in the southern Newfoundland Basin at J-anomaly time (115 Ma); rifting began much earlier, perhaps in Triassic time (concomitant with the opening of the main Atlantic basin to the south). Changes in magnetic anomaly trends document two pole shifts prior to anomaly 31/32: At about 102 Ma the spreading axis shifted from the 015o J-anomaly trend to 055o, and spreading occurred simultaneously in the Newfoundland Basin and the Bay of Biscay about a pole located northeast of Paris; at about 80 Ma (anomaly 34) the spreading shifted to the Cenozoic geometry evident in the pattern of magnetic anomalies 34 through 1.
The Southeast Newfoundland Ridge formed on oceanic crust along the southeastern extension of the Newfoundland Fracture Zone. Two processes were involved: migration of a leaky transform fault along the trend from 102-80 Ma and differential vertical movements in post-Middle Cretaceous time. The Newfoundland Seamounts represent volcanic activation of two structural trends, the seaward prolongation of a major continental structure (evident gravimetrically) and the fracture zones formed during the Biscay-Newfoundland Basin spreading phase. Late-stage trachytic volcanics on Scruncheon Seamount (40Ar/39Ar age = 97.7 + 1.5 Ma) and the formation of a shallow-water limestone cap on Shredder Seamount (Early-Middle Cretaceous fauna) indicate that seamount volcanism had largely ceased by mid-Cretaceous time.
Three acoustic stratigraphic sedimentary units are defined on the basis of seismic reflection profiles and sonobuoy data. These correlate well with the units defined by Horizons b and A in the Northwest Atlantic and with the sedimentary sequence drilled on the Iberian and Biscay margins by the Deep Sea Drilling Project. The distribution and character of the Newfoundland Basin units document the uplift of the southern Grand Banks and Southeast Newfoundland Ridge in Early cretaceous time and the onset of active bottom currents (turbidity and/or contour currents) in the Late Cretaceous or Early Tertiary.
Magnetic surveying and modelling in the southern Newfoundland Basin confirm the existence of magnetic lineations in oceanic crust of Late Cretaceous (Cretaceous Normal Polarity Interval) age that appear to be due to field reversals. It is shown here that chemical alteration or tectonic rotation of crustal blocks could account for the observed lineations without field reversals.
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Pages: 306
Supervisor: Charlotte Keen