Sedimentology and Paleontology of the Early Ordovician Through Early Silurian Shallow Water Carbonates of the Mingan Islands National Park and Anticosti Island, Québec PDF Download

Author: André Desrochers
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 114

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Author: D.A.T. Harper
Publisher: Geological Society of London
ISBN: 1862393737
Category : Science
Languages : en
Pages : 485

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The Early Palaeozoic was a critical interval in the evolution of marine life on our planet. Through a window of some 120 million years, the Cambrian Explosion, Great Ordovician Biodiversification Event, End Ordovician Extinction and the subsequent Silurian Recovery established a steep trajectory of increasing marine biodiversity that started in the Late Proterozoic and continued into the Devonian. Biogeography is a key property of virtually all organisms; their distributional ranges, mapped out on a mosaic of changing palaeogeography, have played important roles in modulating the diversity and evolution of marine life. This Memoir first introduces the content, some of the concepts involved in describing and interpreting palaeobiogeography, and the changing Early Palaeozoic geography is illustrated through a series of time slices. The subsequent 26 chapters, compiled by some 130 authors from over 20 countries, describe and analyse distributional and in many cases diversity data for all the major biotic groups plotted on current palaeogeographic maps. Nearly a quarter of a century after the publication of the ‘Green Book’ (Geological Society, London, Memoir12, edited by McKerrow and Scotese), improved stratigraphic and taxonomic data together with more accurate, digitized palaeogeographic maps, have confirmed the central role of palaeobiogeography in understanding the evolution of Early Palaeozoic ecosystems and their biotas.

Author:
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 642

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Author: Patricia Brennan-Alpert
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 172

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Author: Geoscience Information Society
Publisher:
ISBN:
Category : Earth sciences
Languages : en
Pages : 444

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Author: Susan L. Duffield
Publisher: National Library of Canada
ISBN: 9780315109421
Category :
Languages : en
Pages :

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Author: Andre Desrochers
Publisher:
ISBN:
Category :
Languages : en
Pages :

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An undeformed sequence of Lower and Middle Ordovician shallow-water carbonates is exposed on the Mingan Islands located along the Quebec North Shore of the Gulf of St. Lawrence. This sequence comprises dolostones of the Romaine Formation and limestones of the Mingan Formation. The late Canadian to earliest Whiterockian Romaine Formation is subdivided into three formal members: Sauvage Member, Sainte-Genevieve Member and Grande Ile Member. The Chazyan Mingan Formation is subdivided into four formal members: Corbeau Member, Perroquet Member, Fantome Member and Grande Pointe Member. -- The Romaine Formation represents a shallowing-upward sequence comprising a thin basal assemblage of trangressive sandstones, a middle assemblage of subtidal carbonates and an upper assemblage of cyclic peritidal carbonates. Romaine sediments were pervasively dolomitized in shallow subsurface environments (possibly in mixing zones) before the end of post-Romaine karst erosion. -- The Mingan Formation is a complex environmental mosaic of peritidal and subtidal limestones with a basal trangressive sandstone overlain by tidal flat siliciclastics. Sedimentation changed abruptly with deposition of peritidal and subtidal limestones prior to a period of subaerial exposure resulting in the formation of a karst surface with substantial relief. Resubmergence of this irregular rocky coastline with scattered beachrocks, resulted in a complex facies mosiac with sand shoals forming in underlying paleokarst depressions as tidal deltas 1-10 km wide. -- Three superimposed calcarenite cycles are present in the Mingan sand shoal complex. These sand shoals were periodically exposed and subject to karstification in response to minor fluctuations in sea level. The amount of sea level fall was minor and deeper inter-shoal areas were not affected by subaerial exposure but were sites of more restricted deposition. -- Mingan reef limestones are of three types: biostromes, bioherms which grew in tranquil settings, and bioherm complexes which grew under more turbulent conditions. Reef organisms include lithistid sponges, bryozoans, tabulate corals and solenoporacean algae which occur in a variety of different biotic assemblages. These builders are in part inherited from older bioherms and in part newly involved taxa. Mingan bioherms are typically small mound-shaped structures composed of abundant skeletons and rich in lime mud. Stromatoporoids are conspicuously absent as builders in the Mingan bioherms in contrast to the classic Chazy reefs of Vermont and New York. -- Three different types of paleokarst surfaces are present in the Mingan sequence: 1) an extensive karst plain, represented by the post-Romaine unconformity; 2) an irregular karst, represented by the intra-Mingan paleokarst and 3) local karst surfaces capping calcarenite cycles. -- Alteration of the Mingan limestones resulted from three distinct phases of diagenesis: marine, near-surface and deep burial; near-surface is the most important, especially beneath subaerial exposure surfaces. Vadose cement is not present in spite of extensive evidence of subaerial exposure. Crystal debris, similar to "vadose silt" and formed by the internal erosion of contemporaneous phreatic cements, was subsequently deposited as geopetal internal sediment.

Author: Pascale Daoust
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Anticosti Island, located in Eastern Canada, displays one of the most complete, best exposed, and most fossiliferous carbonate successions spanning the Ordovician-Silurian (O/S) Boundary in the World. This study develops a new high-resolution framework for the post End-Ordovician extinction strata ( ̃260 m thick) exposed in coastal outcrops and recovered from a continuous drill core (La Loutre #1), both located in the western part of the island. In total, eight facies, all associated with a storm-dominated carbonate system, were recognized and organized into a multi-order depositional cycles. A new high resolution isotopic curve with more than 300 data points from well-preserved bulk micrite samples covers the late Hirnantian to Early Aeronian time interval and corresponds to the upper Ellis Bay, Becscie, Merrimack and lower Gun River formations. Two distinct positive carbon isotope excursions are present in the late Hirnantian part of the Ellis Bay Formation (+5?) and in the lower Aeronian part of the Gun River Formation (+2?). These positive isotopic carbon excursions provide a distinctive chemostratigraphic signature for regional and global correlations with other O/S sections. Like the Quaternary ?18O marine signal, our ?18O record is largely coupled with multi-order cyclic facies changes. This study demonstrates the importance of glacio-eustasy following the End-Ordovician glacial maxima as one of the primary factors controlling the stratigraphic architecture of paleotropical neritic carbonates during the Early Silurian.

Author: Susan I. Duffield
Publisher:
ISBN:
Category : Acritarchs
Languages : en
Pages : 676

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Author: David R. Budge
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 34

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