CENOZOIC SEDIMENTARY FRAMEWORK OF THE GORDA-JUAN DE FUCA PLATE AND ADJACENT CONTINENTAL MARGIN—A REVIEW
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Summary A transect of four coreholes, drilled by the Glomar Challenger across the Irish continental margin at the Goban Spur, evidences a dynamic palaeoceanographic regime during the late Mesozoic and Cenozoic. Shallow marine waters invaded the rift-stage grabens of the Goban Spur in the early Barremian. Thereafter, the margin subsided rapidly, producing a pelagic depositional regime by late Barremian time. Deep marine conditions were maintained as sea-floor spreading began in the early Albian, and chiefly pelagic deposition continued to the present. Among a series of significant post-rift oceanographic changes, one of the most notable is the familiar fluctuation of oxic and anoxic sea-floor environments during the Cenomanian and Turonian. Another marked change took place during the late Palaeocene, when cooler, oxygen-rich, northern bottom waters reached the Goban Spur as a consequence of rifting and sea-floor spreading between Greenland, Rockall Plateau, and Norway. Later during the Cenozoic, the initial production of Antarctic bottom water, several accelerations of polar icecap growth, and fluctuating eustatic sea-level produced a variety of circulatory shifts on the Goban Spur. A particularly significant sedimentological consequence of these interacting processes was the widespread creation of numerous erosional and non-depositional unconformities.
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The first detailed record of the sedimentary and structural evolution of a transform passive margin was recently obtained during ODP Leg 159 on the west African margin. Four sites (sites 959–962) were drilled into continental crust along the prominent marginal ridge that defines the continental margin. The record documents the deformational regime that existed during the early active transform phase and the response of the margin to later thermal rejuvenation.
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Summary The analysis of tectonic formations made it possible to recreate the paleogeodynamic conditions of the development of the northeastern part of the Sakhalin shelf.The stages of the formation of the Cenozoic sedimentary cover are identified by specific complexes of formations.
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Integration of biostratigraphy and magnetostratigraphy is essential to the development of a worldwide biomagnetochronology. Drilling on the Exmouth Plateau during Ocean Drilling Program Leg 122 recovered an almost complete Cenozoic stratigraphic sequence at Site 762. Sediments at this site contain abundant, diverse, and generally well-preserved calcareous nannofossils. The continuity of the stratigraphic sequence, good preservation of the taxa, and availability of magnetostratigraphic measurements on the same cores offered an opportunity to construct a detailed first-order biomagnetochronology for Cenozoic calcareous nannofossils at Site 762. In the authors study, 104 nannofossil evolutionary first occurrences/last occurrences are correlated with magnetostratigraphy for the first time. The new biomagnetochronologic determinations include 28 dates in the Paleocene, 47 in the Eocene, 14 in the Oligocene, 11 in the Miocene, one in the Pliocene, and three in the Pleistocene. In addition, 71 first/last occurrences are determined for species whose first/last occurrences have previously been reported from other areas. The accurate assessment of the reliability (the synchroneity and/or diachroneity) of magnetically dated first occurrences/last occurrences over a wide latitudinal range depends on a data base consisting of many such age assignments. The large number of new dates reported here, and the complementary information on previously published dates, willmore » add significantly to the refinement of Cenozoic biomagnetochronology.« less
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Abstract Although taxonomically distinct, the Cenozoic pleurotomariids are the bottlenecked remnants of the Mesozoic members of the family in terms of morphology, with only conical forms surviving the end-Cretaceous mass extinction. Here, we propose an updated classification scheme for the Cenozoic representatives of this group, based on data from the entire Cenozoic pleurotomariid fossil record. We consider all conventional as well as several new characters so that this scheme can readily help to distinguish Cenozoic pleurotomariid genera. Following the new classification scheme, a revision of the generic status of Cenozoic species previously assigned to ‘ Pleurotomaria ’ Defrance, 1826 is presented. Only a few Cenozoic pleurotomariid gastropods have been reported from the Indian subcontinent. Here we report four species from the Oligocene of the Kutch Basin and the early Miocene (Burdigalian) of the Dwarka Basin of Gujarat, western India, of which two are described as new: Perotrochus bermotiensis n. sp., Entemnotrochus kathiawarensis n. sp., Entemnotrochus cf. E . bianconii , and Entemnotrochus ? sp. 1. UUID: http://zoobank.org/89b6ff67-2834-477f-862b-67691104aca4
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The continental margin of Morocco represents the conjugate segment to the North American margin south of Nova Scotia. The total sedimentary cover in the continental margin province is considerably thinner off Morocco than it is off the east coast of North America. Further, selected portions of the Morocco continental margin have undergone major tectonics, either exposing or bringing near the surface older elements of the stratigraphic section. Thus, scientific objectives requiring sampling of the earliest drift phase sediments, the oldest oceanic crust, and the basement rocks in the ocean-continental transition zone can be more easily addressed off Morocco than off North America. We have recently compiled a synthesis of marine geological/geophysical data for the offshore regions bordering the continental margin of Morocco. The synthesis was undertaken in order to evaluate future scientific deep-sea drill sites. The final product of the synthesis is a set of maps on Mercator projection for the area 29° to 35°N, 5° to 22°W. The maps include: bathymetry contours, free-air gravity anomaly contours, total intensity magnetic anomalies plotted normal to the ship's tracks, seismic velocity crustal structure, reflection time to basement, blue reflector (upper Jurassic) and red reflector (upper Cretaceous), isopach (in seconds of two-way reflection time) of sea floor to basement, sea floor to blue reflector, sea floor to red reflector, and blue refle tor to red reflector, locations of surface sediment samples, hazards, and tectonics. In addition, seismic crustal sections from the nearshore across the disturbed piercement structure province to the deep ocean floor have been compiled. Our synthesis reveals that the continental margin of Morocco consists of several unique segments. A dominant structural unit is the NNE-SSW-trending zone of salt diapirs and piercement structures observed on the continental shelf and slope. The salt is presumed to be of Late Triassic to Early Jurassic age. A prominent magnetic anomaly which may represent a magnetic edge effect anomaly can be traced along most of the western boundary of the Moroccan diapiric zone. On the conjugate continental margin south of Nova Scotia, a diapir zone is also observed. The seaward edges of the Moroccan and eastern North American diapiric zones match very well in pre-drift reconstructions, thus suggesting that before the separation of the African and North American plates a single evaporite basin existe . The magnetic and seismic data suggest that the seaward boundaries of the piercement fields mark the likely boundary between oceanic and continental basement. The westernmost portion of the synthesis area is characterized by the well-defined Mesozoic sequence of magnetic anomalies from M0 (^cong 108 m.y.B.P.) to M25 (^cong 152 m.y.B.P.). These anomalies are situated on seismically observed oceanic crust formed by sea-floor-spreading processes. Between the seaward edge of the diapiric zone and magnetic anomaly M25 we observe a broad structural arch beneath which our single-channel seismic records in general fail to resolve the underlying basement. This is the region of the Jurassic magnetic quiet zone. End_of_Article - Last_Page 537------------
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Taviani, M., Sabelli, B. & Candini, F. 1990 04 15: A fossil Cenozoic monoplacophoran. Lethaia, Vol. 23, pp. 213–216. Oslo. ISSN 0024–1164. A few shells of Micropilina (Mollusca, Monoplacophora) have been found in middle Pleistocene (Sicilian) epibathyal clays at Archi (Reggio Calabria, southern Italy). The species appears conchologically indistinguishable from the Recent Atlantic taxon Micropilina minuta Warén, 1989. This finding represents the first record of a Cenozoic fossil monoplacophoran.
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