Cryptalgal‐metazoan bioherms of early Ordovician age in the St George Group, western Newfoundland
ABSTRACT Bioherms are common in the St George Group, a sequence of shallow‐water carbonate rocks deposited on the western continental shelf of Iapetus Ocean. They range from small heads and metre‐sized mounds to extensive banks and complexes many metres thick and hundreds of metres in lateral extent...
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crwiley:10.1111/j.1365-3091.1982.tb01733.x 2024-09-30T14:38:55+00:00 Cryptalgal‐metazoan bioherms of early Ordovician age in the St George Group, western Newfoundland PRATT, BRIAN R. JAMES, NOEL P. 1982 http://dx.doi.org/10.1111/j.1365-3091.1982.tb01733.x https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-3091.1982.tb01733.x https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3091.1982.tb01733.x en eng Wiley http://onlinelibrary.wiley.com/termsAndConditions#vor Sedimentology volume 29, issue 4, page 543-569 ISSN 0037-0746 1365-3091 journal-article 1982 crwiley https://doi.org/10.1111/j.1365-3091.1982.tb01733.x 2024-09-03T04:25:25Z ABSTRACT Bioherms are common in the St George Group, a sequence of shallow‐water carbonate rocks deposited on the western continental shelf of Iapetus Ocean. They range from small heads and metre‐sized mounds to extensive banks and complexes many metres thick and hundreds of metres in lateral extent. The cores of these bioherms are principally composed of thrombolites (unlaminated, branching, columnar stromatolites), structures quite distinct from laminated stromatolites which are common in intertidal beds. Associated with thrombolites is a diverse fauna of burrowing invertebrates, trilobites, nautiloids, pelmatozoans, brachiopods, gastropods, rostroconchs and archaeoscyphiid sponges. On the basis of framework‐building components, three main bioherm types are distinguished: (1) thrombolite mounds, (2) thrombolite‐ Lichenaria or ‐sponge mounds and (3) thrombolite‐ Lichenaria‐Renalcis reef complexes. The framework of the last is the most complex, with abundant cavities and a demonstrably uneven growth surface of thrombolites, corals and free‐standing Renalcis heads, walls and roofs. Some cavities were active sediment conduits while others were protected, their roofs draped with Renalcis and their walls coated by cryptalgal laminites. These bioherms possess the attributes of shallow‐water ecologic reefs. They span a critical time gap in the development of reefs, the transition period from algal‐dominated bioherms of the Precambrian and Cambrian to the metazoan‐dominated bioherms of the Middle Ordovician and remaining Phanerozoic. Article in Journal/Newspaper Newfoundland Wiley Online Library Sedimentology 29 4 543 569 |
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English |
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ABSTRACT Bioherms are common in the St George Group, a sequence of shallow‐water carbonate rocks deposited on the western continental shelf of Iapetus Ocean. They range from small heads and metre‐sized mounds to extensive banks and complexes many metres thick and hundreds of metres in lateral extent. The cores of these bioherms are principally composed of thrombolites (unlaminated, branching, columnar stromatolites), structures quite distinct from laminated stromatolites which are common in intertidal beds. Associated with thrombolites is a diverse fauna of burrowing invertebrates, trilobites, nautiloids, pelmatozoans, brachiopods, gastropods, rostroconchs and archaeoscyphiid sponges. On the basis of framework‐building components, three main bioherm types are distinguished: (1) thrombolite mounds, (2) thrombolite‐ Lichenaria or ‐sponge mounds and (3) thrombolite‐ Lichenaria‐Renalcis reef complexes. The framework of the last is the most complex, with abundant cavities and a demonstrably uneven growth surface of thrombolites, corals and free‐standing Renalcis heads, walls and roofs. Some cavities were active sediment conduits while others were protected, their roofs draped with Renalcis and their walls coated by cryptalgal laminites. These bioherms possess the attributes of shallow‐water ecologic reefs. They span a critical time gap in the development of reefs, the transition period from algal‐dominated bioherms of the Precambrian and Cambrian to the metazoan‐dominated bioherms of the Middle Ordovician and remaining Phanerozoic. |
format |
Article in Journal/Newspaper |
author |
PRATT, BRIAN R. JAMES, NOEL P. |
spellingShingle |
PRATT, BRIAN R. JAMES, NOEL P. Cryptalgal‐metazoan bioherms of early Ordovician age in the St George Group, western Newfoundland |
author_facet |
PRATT, BRIAN R. JAMES, NOEL P. |
author_sort |
PRATT, BRIAN R. |
title |
Cryptalgal‐metazoan bioherms of early Ordovician age in the St George Group, western Newfoundland |
title_short |
Cryptalgal‐metazoan bioherms of early Ordovician age in the St George Group, western Newfoundland |
title_full |
Cryptalgal‐metazoan bioherms of early Ordovician age in the St George Group, western Newfoundland |
title_fullStr |
Cryptalgal‐metazoan bioherms of early Ordovician age in the St George Group, western Newfoundland |
title_full_unstemmed |
Cryptalgal‐metazoan bioherms of early Ordovician age in the St George Group, western Newfoundland |
title_sort |
cryptalgal‐metazoan bioherms of early ordovician age in the st george group, western newfoundland |
publisher |
Wiley |
publishDate |
1982 |
url |
http://dx.doi.org/10.1111/j.1365-3091.1982.tb01733.x https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-3091.1982.tb01733.x https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3091.1982.tb01733.x |
genre |
Newfoundland |
genre_facet |
Newfoundland |
op_source |
Sedimentology volume 29, issue 4, page 543-569 ISSN 0037-0746 1365-3091 |
op_rights |
http://onlinelibrary.wiley.com/termsAndConditions#vor |
op_doi |
https://doi.org/10.1111/j.1365-3091.1982.tb01733.x |
container_title |
Sedimentology |
container_volume |
29 |
container_issue |
4 |
container_start_page |
543 |
op_container_end_page |
569 |
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1811641505511636992 |