Recent crustal movements on the Labrador Shelf

1970 ◽  
Vol 7 (2) ◽  
pp. 571-575 ◽  
Author(s):  
A. C. Grant
Keyword(s):  
Sedimentary Rocks ◽  
Outer Shelf ◽  
Inner Shelf ◽  
Glacial Erosion ◽  
Precambrian Rocks ◽  
Crustal Movements ◽  
Channel One ◽  
Seaward Side ◽  
Isostatic Adjustment ◽  
Structural Disturbance

Seismic profiler investigations have confirmed that the marginal channel that occurs on the Labrador Shelf separates crystalline Precambrian rocks underlying the inner shelf from sedimentary rocks on the outer shelf. The relief of the channel is thought to be mainly the result of glacial erosion, but there is also evidence of structural disturbance associated with this feature. Most seismic profiler transects show pronounced upwarping of the sedimentary strata underlying the seaward side of the marginal channel. One explanation offered for this upwarping is that it may possibly be due to isostatic adjustment following removal of material by glacial erosion.

Silurian fades beneath East Anglia

1993 ◽  
Vol 130 (5) ◽  
pp. 681-690 ◽  
Author(s):  
N. H. Woodcock ◽  
T. C. Pharaoh
Keyword(s):  
Sedimentary Rocks ◽  
Outer Shelf ◽  
Core Material ◽  
Inner Shelf ◽  
East Anglia ◽  
Regional Setting ◽  
Anoxic Basin ◽  
Acadian Orogeny ◽  
Facies Transition

AbstractCore material from proven or probable Silurian sedimentary rocks beneath East Anglia has been re-examined. Four recognizable facies probably represent an environmental transition from anoxic basin slope or outer shelf through oxygenated outer shelf to storm-dominated inner shelf. This transition could have occurred laterally, from east to west across the Anglian Basin, or in time, from Llandovery (early Silurian) up to Př (late Silurian). Partial biostratigraphical constraints allow either interpretation, but the regional setting favours a marked facies transition through time as the Anglian Basin shallowed prior to the Acadian Orogeny. Reddening of the Silurian is mostly secondary beneath the sub-Triassic unconformity.

Late Precambrian Rocks of Eastern Avalon Peninsula, Newfoundland — A Volcanic Island Complex

1971 ◽  
Vol 8 (8) ◽  
pp. 899-915 ◽  
Author(s):  
C. J. Hughes ◽  
W. D. Brückner
Keyword(s):  
Volcanic Rocks ◽  
Main Group ◽  
Volcanic Island ◽  
Precambrian Rocks ◽  
Crustal Movements ◽  
Late Precambrian ◽  
Isostatic Adjustment ◽  
Avalon Peninsula ◽  
Vertical Crustal Movements

A model of island volcanism is presented in which rocks are referred to (1) a "syn-volcanic" constructional phase represented by rocks of four penecontemporaneous facies—vent, alluvial, marine, and plutonic—whose interrelationships are discussed and (2) a "post-volcanic" destructional phase of erosion and sedimentation accompanied by isostatic adjustment resulting in the spreading of an apron of volcanic sediments around a slowly rising and eroding island core.The late Precambrian rocks of the eastern part of the Avalon Peninsula, southeasternmost Newfoundland, are shown to fit this model rather closely, both petrographically and in their distribution and field relationships. The Harbour Main Group of volcanic rocks, the Conception Group of marine volcanic sediments and tuffs, and the Holyrood Plutonic Series, dated at 574 ± 11 m.y., were all formed during the syn-volcanic constructional phase. Their apparently conflicting age relationships can be reconciled to the view that they are penecontemporaneous facies. The Cabot and Hodgewater Groups of marine and alluvial volcanic sediments were formed during the post-volcanic destructional phase. Apart from vertical crustal movements, only minor diastrophic deformation appears to have occurred during these two phases.This model of volcanic island environment may help in interpreting the geology of several other belts in eastern and central Newfoundland comprising late Precambrian and Paleozoic volcanic rocks and sediments.

Three Short Papers on Isostasy

1925 ◽  
Vol 62 (5) ◽  
pp. 227-234 ◽  
Author(s):  
W. B. Wright
Keyword(s):  
Earth’S Crust ◽  
Crustal Movements ◽  
Open Mind ◽  
Isostatic Adjustment ◽  
Earth's Crust ◽  
Lines Of Evidence

The question of the supposed isostatic adjustment of the earth's crust to increase or decrease of load has recently come prominently to the fore in connexion with the Wegener hypothesis and Joly's theory of geological transgression and revolution. The principle itself is fairly well established by several independent lines of evidence, but there is room for clearer thinking as to the mechanism attending its operation. Very varied opinions are for instance held as to therapidity and completeness of the adjustment, and unjustifiable assumptions are made with regard to the displacement of magma beneath depressed areas. It is very necessary to keep an open mind on these questions and to search the available evidence for means of defining the nature of the attendant sub-crustal movements.

CAMBRIAN AND PRECAMBRIAN PETROLEUM AN APPRAISAL

1965 ◽  
Vol 5 (1) ◽  
pp. 7
Author(s):  
Grover E. Murray
Keyword(s):  
United States ◽  
North Africa ◽  
Sedimentary Rocks ◽  
The United States ◽  
Northern Territory ◽  
Early Paleozoic ◽  
Precambrian Rocks ◽  
Late Proterozoic ◽  
Organic Evolution ◽  
Early Phases

Accumulated evidence indicates that (1) the major portion of chemical and organic evolution occurred during the 3-5 x 109 years of the earth's history preceding the Paleozoic; (2) the basic elements constituting petroleum existed in the early phases of the earth's history; (3) unmetamorphosed Precambrian and Cambrian lithic types are similar to younger ones; and (4) the population of the later Precambrian and early Paleozoic seas was relatively rich and varied, though hard skeletal parts are notably absent in the Precambrian rocks and, in all probability, were not widely developed.As petroleum is now generally considered of organic origin and is a widely disseminated and integral part of most sedimentary rocks, unmetamorphosed Precambrian and Cambrian strata should be prospective for petroleum. Discoveries of large reserves of oil in the Cambrian in parts of North Africa, Russia and the United States support this asserted prospectivity. Shows of indigenous gas in the late Proterozoic of the Amadeus Basin, Northern Territory, Australia, indicate that unmetamorphosed Precambrian strata may also yield commercial amounts of hydrocarbons.

scholarly journals Ostracode paleoecology of the Bangor-Pennington transition (Chesterian, Mississippian) in northeastern Alabama

1992 ◽  
Vol 6 ◽  
pp. 226-226
Author(s):  
William Olson ◽  
Chris Dewey
Keyword(s):  
Outer Shelf ◽  
Inner Shelf ◽  
Clay Shale ◽  
Terrigenous Input ◽  
Western Flank ◽  
Palaeoenvironmental Change ◽  
Prime Factors ◽  
Distal Lobe

The Pennington Formation (Chesterian, Mississippian) of northeastern Alabama is a regressive, distal lobe of the Pennington/Lee clastic wedge, located on the western flank of the Appalachians in the Tennessee structural salient. The clastic units of the Pennington include sandstone, siltstone, mudstone, clay shale and coal and are genetically related to the effects of progradation. The presence of limestones and dolostones within the southwestwardly prograding and thinning Pennington is due to the lateral equivalency and interfingering relationships of the Pennington with the upper part of the adjacent Bangor Limestone shelf.A highly diverse ostracode fauna as been collected from outcrops along the Pennington-Bangor transition in northeastern Alabama. The most common assemblage of ostracodes is dominated by kirkbyaceans and includes species of Amphissites, Polytylites, Kirkbyella, Kirkbya and Reviya. Bairdiaceans are noteably absent from this assemblage. The Kirkbyacean Assemblage is only found in middle to outer shelf palaeoenvironments where clastic input is high, but where salinity conditions are thought to have been typically marine. In middle to outer shelf limestone-producing palaeoenvironments, a Bairdiacean Assemblage is dominant, although kirkbyaceans are still present.A Sansabellid Assemblage, consisting of kloedenellaceans such as Sansabella, Geisina, Geffenina, Nufferella and Glyptopleura appears to be produced under rapidly changing nearshore, inner shelf conditions, where terrigenous input was often high and palaeosalinities may have been variable or less than normal marine. The Sansabellid Assemblage contains occasional kirkbyaceans, however bairdiaceans are noteably absent. Intermediate assemblages contain elements of the three main assemblages and reflect the transition from the inner to outer shelf.In summary, the ostracode assemblages of the Pennington-Bangor transition in northeast Alabama provide indicators of palaeoenvironmental change during the southwestward progradation of the Pennington deltaic wedge onto the Bangor Limestone shelf. The prime factors resulting in palaeoecological response appear to have been variations in terrigenous input and palaeosalinity.

scholarly journals The Recent temperate foraminiferal biofacies of the Gippsland Shelf: an analogue for Neogene environmental analyses in southeastern Australia

2001 ◽  
Vol 20 (2) ◽  
pp. 127-142 ◽  
Author(s):  
Andrew J. Smith ◽  
Stephen J. Gallagher ◽  
Malcolm Wallace ◽  
Guy Holdgate ◽  
Jim Daniels ◽  
...  
Keyword(s):  
Planktonic Foraminifera ◽  
Environmental Studies ◽  
Fine Sand ◽  
Silty Sand ◽  
Outer Shelf ◽  
Ecological Niches ◽  
Inner Shelf ◽  
Foraminiferal Assemblage ◽  
Southeastern Australia ◽  
Marine Lakes

Abstract. This study describes the foraminiferal biofacies of a temperate stenohaline shelf and associated euryhaline marine lakes of Gippsland in southeast Australia. The study incorporates facies analyses and interpretations of three types of foraminiferal distributional data: forms alive at the time of collection, recently dead forms and relict forms. Four principal biofacies types occur: (1) the euryhaline marine Gippsland Lakes silts and sands; (2) inner shelf medium to coarse quartz-rich sands and bioclastic silty sands; (3) medium shelf bryozoan-rich bioclastic silt and silty sand; (4) outer shelf bryozoan- and plankton-rich silts and fine sands.The euryhaline marine Gippsland Lakes silts and sands contain abundant Ammonia beccarii and Eggerella, with minor Quinqueloculina, Elphidium and Discorbinella. The Gippsland inner shelf biofacies (0–50 m depths) consists of medium to coarse quartz-rich sands and bioclastic silty sand. Abundant living, relict and recently dead miliolids occur in the inner shelf with rare planktonic forms. Common planktonic foraminifera, with Cibicides, Parrellina, Elphidium and Lenticulina and relict forms occur in the bryozoan-rich bioclastic silt and silty sand of the Gippsland middle shelf (50–100 m depth). Bryozoan and plankton-rich silts and fine sand occur in the outer shelf to upper slope facies (100–300 m) below swell wave base on the Gippsland Shelf. A diverse fauna with common textulariids, Uvigerina, Bulimina, Anomalinoides and Astrononion and rare relict forms, occurs in this biofacies. Planktonic foraminifera and Uvigerina are most abundant at the shelf break due to local upwelling at the head of the Bass Canyon.Estimates of faunal production rates from live/dead ratios and full assemblage data suggest that the fauna of the Gippsland Shelf has not been significantly reworked by wave and/or bioturbation processes. Most relict foraminifera occur in the inner shelf, with minor relict forms in the middle to outer shelf. This pattern is similar to other shelf regions in Australia, where shelf areas were exposed during Pleistocene lowstand times, principally reworking pre-existing inner to middle shelf faunas. Correspondence analyses of the foraminiferal data yield a clear depth-related distribution of the faunal assemblage data. Most of the modern Gippsland Shelf fauna are cosmopolitan species and nearly a third are (semi-)endemic taxa suitable for regional palaeo-environmental studies. From biostratigraphic studies it is clear that the modern Gippsland foraminiferal assemblage evolved since Early Miocene times, with most elements present by the Late Miocene. Hence, the Recent Gippsland Shelf foraminiferal biofacies distribution is a good analogue for Neogene palaeo-environmental studies in the region. The longer ranging pre-Miocene mixture of epifaunal and infaunal taxa are deeper shelf cosmopolitan forms and are inferred to be more conservative since they evolved in relatively lower stress environments, typifying mesotrophic to eutrophic conditions compared to inner shelf epifaunal forms with ecological niches markedly affected by sea-level and temperature fluctuations in zones of constant wave action, in oligotrophic environments.The foraminiferal and facies analogues of this study on the Gippsland Shelf can be used for palaeo-environmental analyses of the Gippsland and Otway Neogene sedimentary successions. Such improvements will lead ultimately to a better understanding of the evolution of the neritic realm in southeastern Australia, an area facing the evolving Southern Ocean during the Cenozoic.

Stratigraphie sequentielle du Dinantien type (Belgique) et correlation avec le Nord de la France (Boulonnais, Avesnois)

2001 ◽  
Vol 172 (4) ◽  
pp. 411-426 ◽  
Author(s):  
Luc Hance ◽  
Eddy Poty ◽  
Francois-Xavier Devuyst
Keyword(s):  
Early Phase ◽  
Outer Shelf ◽  
Large Area ◽  
Third Order ◽  
Inner Shelf ◽  
Southern England ◽  
The North ◽  
Western Germany ◽  
Local Tectonics ◽  
Homoclinal Ramp

Abstract The relative influences of local tectonics and global eustasy in the architecture of the sedimentary units of the Namur-Dinant Basin (southern Belgium) are determined. Nine third-order sequences are recognised. During the Lower Tournaisian (Hastarian and lower Ivorian) a homoclinal ramp extended from southern Belgium through southern England (Mendips) and into southern Ireland. From the upper Ivorian to the lower Visean rapid facies changes occurred due to progradation and increasing prominence of Waulsortian mudmounds. Progradation gradually produced a situation in which inner shelf facies covered the Namur (NSA), Condroz (CSA) and southern Avesnes (ASA) sedimentation areas, whereas outer shelf facies were restricted to the Dinant sedimentation area (DSA). During the middle and late Visean a broad shelf was established from western Germany to southern Ireland. Because the shelf built up mainly by aggradation, parasequences can be followed over a large area. An early phase of Variscan shortening is perceptible during the Livian. The stratigraphic gap between the first Namurian sediments (E2 Goniatite Zone) and the underlying Visean varies from place to place, but is more important in the north.

scholarly journals Influence of cross-shelf water transport on nutrients and phytoplankton in the East China Sea: a model study

2010 ◽  
Vol 7 (4) ◽  
pp. 1405-1437
Author(s):  
L. Zhao ◽  
X. Guo
Keyword(s):  
Surface Layer ◽  
Primary Production ◽  
Chlorophyll A ◽  
East China Sea ◽  
Changjiang Estuary ◽  
Shelf Break ◽  
Outer Shelf ◽  
East China ◽  
The East China Sea ◽  
Inner Shelf

Abstract. A three dimensional coupled biophysical model was used to examine the supply of oceanic nutrients to the shelf of the East China Sea (ECS) and its role in primary production over the shelf. The model consisted of two modules: the hydrodynamic module was based on a nested model with a horizontal resolution of 1/18 degree, whereas the biological module was a low trophic level ecosystem model including two types of phytoplankton, three elements of nutrients, and biogenic organic material. Model results suggested that seasonal variation in chlorophyll-a had a strong regional dependence over the shelf of the ECS. The area with high chlorophyll-a appears firstly at the outer shelf in winter, and gradually migrates toward the inner shelf (offshore region of Changjiang estuary) from spring to summer. Vertically, chlorophyll-a was generally homogenous from the coastal zone to the inner shelf. In the middle and outer shelves, high chlorophyll-a appeared in the surface in spring but moved to the subsurface from summer to early autumn. The annual averaged onshore flux across the shelf break was estimated to be 1.53 Sv for volume, 9.4 kmol s−1 for DIN, 0.7 kmol s−1 for DIP, and 18.2 kmol s−1 for silicate, which are supplied mainly from the northeast of Taiwan and southwest of Kyushu. From calculations that artificially increased the concentration of nutrients in the Kuroshio water, the additional oceanic nutrients were distributed in the bottom layer from the shelf break to the region offshore of Changjiang estuary from spring to summer, and appeared in the surface layer from autumn to winter. The contribution of oceanic nutrients to primary production over the shelf was found not only in the surface layer (mainly at the outer shelf and shelf break in winter and in the region offshore of Changjiang estuary in summer) but also in the subsurface layer over the shelf from spring to autumn.

Relationship between the Aspy and Bras d'Or "terranes" in the northeastern Cape Breton Highlands, Nova Scotia

1993 ◽  
Vol 30 (9) ◽  
pp. 1773-1781 ◽  
Author(s):  
Shoufa Lin
Keyword(s):  
Shear Zone ◽  
Sedimentary Rocks ◽  
The West ◽  
Precambrian Rocks ◽  
Late Precambrian ◽  
Cape Breton ◽  
Basal Conglomerate ◽  
Back Arc ◽  
Eastern Highlands ◽  
Basin System

According to previous interpretations, the Eastern Highlands shear zone separates Ordovician–Silurian volcano-sedimentary rocks to the west (Cheticamp Lake Gneiss of the Aspy "terrane") from late Precambrian sedimentary rocks and dioritic – tonalitic plutons and Early Ordovician granite to the east (Bras d'Or "terrane"). New mapping discovered a basal conglomerate of the Cheticamp Lake Gneiss that rests on deformed diorite of the Bras d'Or "terrane" and contains clasts similar or identical to rocks of the Bras d'Or "terrane." The late Precambrian rocks of the Bras d'Or "terrane" are also overlain by a volcano-sedimentary sequence of Silurian age (Clyburn Brook formation). These observations suggest that rocks of the Aspy "terrane" lie unconformably on those of the Bras d'Or "terrane." The Eastern Highlands shear zone is therefore not a terrane boundary. The Ordovician–Silurian rocks of the Aspy "terrane" are interpreted to have formed in an arc–back-arc basin system. The back-arc basin is interpreted to have formed by rifting in the Bras d'Or "terrane" and the Eastern Highlands shear zone to have been related to the closure of the basin.

scholarly journals Streaming flow of an Antarctic Peninsula palaeo-ice stream, both by basal sliding and deformation of substrate

2011 ◽  
Vol 57 (204) ◽  
pp. 596-608 ◽  
Author(s):  
Benedict T.I. Reinardy ◽  
Robert D. Larter ◽  
Claus-Dieter Hillenbrand ◽  
Tavi Murray ◽  
John F. Hiemstra ◽  
...  
Keyword(s):  
Flow Velocity ◽  
Antarctic Peninsula ◽  
Outer Shelf ◽  
Inner Shelf ◽  
Ice Flow ◽  
Transparent Layer ◽  
Basal Sliding ◽  
Fast Ice ◽  
Fast Flow ◽  
Streaming Flow

AbstractAcoustic sub-bottom profiler surveys on the northeast Antarctic Peninsula shelf indicate that parts of the seabed are underlain by an acoustically transparent layer that is thin on the inner shelf and becomes thicker and more extensive towards the outer shelf. Sedimentological and geophysical data are combined to construct a bed model where streaming ice flow, by both deformation and basal sliding, took place within cross-shelf troughs. The model suggests only limited deformation contributed to fast flow on the inner shelf, i.e. in the onset zone of ice streaming, where the bed was predominantly underlain by a stiff till. Thus, fast ice flow in this area might have been by basal sliding, with deformation confined to discontinuous patches of soft till <40 cm thick. Towards the middle and outer shelf, extensive, thick sequences of soft till suggest a change in the dominant subglacial process towards widespread deformation. This downstream change from basal sliding to subglacial deformation is manifest in the transition from stiff-till dominance to soft-till dominance, while a downstream increase in ice flow velocity is evident from the complex geomorphic imprint on the inner shelf evolving to the more restricted set of bedforms on the outer shelf.

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