Shallow-Water Stromatactis Mud-Mounds on a Middle Ordovician Foreland Basin Platform, Western Newfoundland
- C. L. V. Monty,
- D. W. J. Bosence,
- P. H. Bridges and
- B. R. Pratt
Published Online: 14 APR 2009
Copyright © 1995 The International Association of Sedimentologists
Carbonate Mud-Mounds: Their Origin and Evolution
How to Cite
Stenzel, S. R. and James, N. P. (1995) Shallow-Water Stromatactis Mud-Mounds on a Middle Ordovician Foreland Basin Platform, Western Newfoundland, in Carbonate Mud-Mounds: Their Origin and Evolution (eds C. L. V. Monty, D. W. J. Bosence, P. H. Bridges and B. R. Pratt), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304114.ch4
- Published Online: 14 APR 2009
- Published Print: 17 JUL 1995
Print ISBN: 9780865429338
Online ISBN: 9781444304114
- shallow water;
- phases of foreland basin evolution;
- Synsedimentary fractures;
- numerous, narrow (several millimetres wide) fractures;
- Table Point Formation- organo-sedimentary buildups
Isolated, stromatactis-bearing mud-mounds occur at the top of the Middle Ordovician Table Point Formation, a platformal carbonate deposited on the flank of the Taconian foreland basin in western Newfoundland. In situ mounds crop out at two places and resedimented mud-mound clasts in younger foreland basin conglomerates indicate similar buildups formed in other areas. Mound dimensions are unknown; the best exposed is at least 150 m wide and 35 m thick.
Basal sediments of one well-exposed mound were deposited in shallow subtidal and tidal flat environments. The top 30 m of this mound are massive, mottled limestones with stromatactis. Similar massive limestones also occur at the top of the second in situ mound and make up the resedimented clasts. They are mostly mud-supported, fossiliferous and peloidal limestone pervaded by a fine fenestral fabric. Predominant skeletal components are pelmatozoan fragments and leperditiid and other ostracodes; trilobites, gastropods, cephalopods, brachiopods and sclerosponges (Lapidipanis) are also present. Lithistid sponges are conspicuous but not abundant. Girvanella is abundant, occurring as oncolites, discontinuous mats and nodules of entwined filaments, but does not form an interconnected framework. Halysis, Nuia and an unnamed dasycladacean alga are also present. These sediments are interpreted to have accumulated in a restricted, shallow subtidal environment.
Stromatactis cavities partly filled with marine internal sediment and cement pervade the massive mud-mound limestone. Sheet-like stromatactis originated as extensional fractures caused by faulting. Other associated marine sediment-filled sheet cracks and marine sediment- and cement-filled high-angle fractures also record episodic displacements. Possible vadose cement fabrics in some stromatactis suggest subaerial exposure.
Both in situ mounds are overlain by deep water sediments (Table Cove and Black Cove formations). Those sediments record collapse of the foreland basin carbonate platform and indicate that mound growth ceased in response to tectonic drowning of the platform. This Table Point lithofacies was controlled by peculiar hydrodynamic conditions dictated by synsedimentary faulting across the foreland basin platform.