Zusammenfassung
Die Horn-Plateau-Formation ist ein mitteldevonisches Kalkriff, etwa 0,6 km breit und 120 m mächtig, das in den Interior Plains 180 km westlich von Yellowknife, Northwest Territories, aufgeschlossen ist. Die vorliegende Arbeit beruht auf einer Untersuchung von Proben aus Aufschlüssen und aus 5 Bohrungen im Riff und seiner Umgebung.
Korallen sind die wichtigsten der Gerüstbildner, und Krinoiden-Reste die Hauptbestandteile der Sedimente. Drei Makrofazies werden in diesem Krustenriff erkannt: 1. der Riffkern, ein Bereich, worin riffbildende Korallen besonders häufig waren; 2. eine Riffebene charakterisiert durch Sedimente von Sand-Korngröße; und 3. eine Riffflanke mit Sedimenten von Kies-Korngröße. Über dem Kern und der Flanke war das Wasser stark bewegt, während ruhigeres Wasser die Riffebene bedeckte. Eine Unterteilung der Makrofazies ergab 11 Mikrofazies unterschiedlicher Struktur und Zusammensetzung.
Abstract
The Horn Plateau Formation is a Middle Devonian limestone reef approximately 0.4 miles in diameter and 400 feet thick which crops out on the Interior Plains about 110 miles west of Yellowknife, Northwest Territories. The study is based upon examination of material collected from the outcrop and 5 core-holes drilled on and near the reef.
Corals are the most important framebuilders present and crinoid ossicles contribute most to the sediment volume. Three macrofacies of this coral patch reef are recognized: 1) organic reef, an area where framebuilders grew profusely, 2) reef flat, an area characterized by sand sized sediments, and 3) reef flank, an area of predominantly gravel sized sediments. Strongly agitated water conditions prevailed over the organic reef and reef flank macrofacies whereas moderately agitated water covered the reef flat. Subdivision of the macrofacies has produced 11 microfacies of distinctive texture-composition combination.
Résumé
Le Horn Plateau est un récif calcaire du Dévonien moyen d'un diamètre de 0.4 mille et d'une épaisseur de 400 pieds environ. Il affleure dans les Plaines environ à 110 milles à l'Ouest de Yellowknife (Territoires du Nord-Ouest). L'étude est basée sur l'examen d'échantillons d'affleurements et de cinq forages effectués dans et près du récif.
Les coraux sont les plus importants organismes constructeurs et les entroques forment la majeure partie du volume sédimentaire. Trois macrofaciès ont été reconnus dans le récif de plateforme: 1) récif organique, domaine riche en organismes constructeurs, 2) replat récifal, domaine caractérisé par des sables, et 3) flanc du récif, domaine à débris grossiers. Le récif organique et le flanc du récif se trouvaient dans des eaux très agitées tandis que des eaux modérément agitées couvraient le replat récifal. Les macrofaciès ont été subdivisés en 11 microfaciès présentant des combinaisons texture-composition distinctes.
Краткое содержание
В Interior Plains, 180 км на запад от Yellowknife, и сследовали формацию плато Horn, представляющ ую собой среднедевон ский известковый риф в 0,6 км ширины и 120 м мощнос тью. Отобрали пробы не только из обнажений, но и из 5-ти буровых скв ажин рифа и его окрест ностей. Основную часть осадо чных пород образуют остат ки Crinoiden, а тело — кораллы. О тмечают 3 макрофация: 1) Ядро рифа, т. е. район, гд е отмечается обилие рифообразующих кораллов; 2) поверхност ь рифа, где отложены пе счанистые седименты, и 3) склоны рифа с отложением гра вия. Над ядром и склона ми имел место, вероятно, сильн ый волноход, в то время, ка к поверхность рифа по крывали спокойные воды. Эти макрофации подразде лены на 11 микрофациев р азличной структуры и состава.
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Vopni, L.K., Lerbekmo, J.F. Sedimentology and ecology of the horn plateau formation: A middle devonian coral reef, Northwest Territories, Canada. Geol Rundsch 61, 626–646 (1972). https://doi.org/10.1007/BF01896338
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DOI: https://doi.org/10.1007/BF01896338