Cambrian-Ordovician boundary in the Taconic Allochthon, eastern New York, and its interregional correlation

摘要: Cambrian–Ordovician boundary interval dendroid graptolites and conodonts occur in continental slope facies the Taconic allochthon. The upper part of Hatch Hill Formation has lowest Ordovician (lowest Tremadocian) nematophorous lower Fauna B-aspect conodont assemblages with Cordylodus caseyi (emend.) Iapetognathus preaengensis. Comparable dendroid-conodont faunas Baltoscandia, northeastern China, western Newfoundland; this suggests that no diachroneity can be demonstrated between occurrences Rhabdinopora flabelliformis a number faunal provinces. A practical correlatable stratotype horizon defined by occurrence assemblage within an is advocated. biostratigraphic far less utility due to strong lithofacies-conodont biofacies linkages, unresolved problems species-level taxonomy cordylodans, possible diachronous first-appearances species. Because areally most extensive sequences are siliciclastic-dominated (Avalonian, Baltoscandian, Gondwanan-Hercynian platforms shale-dominated sequences), local R. provides traditional definition for base System Tremadocian Series regions where rare or recoverable only difficulty. Strata correlative Cambrian–Tremadocian not represented across Laurentia. In region, “Sauk III Subsequence” locally important unconformity it, Tremadocian-equivalent rocks unconformably overlie units as low Proterozoic. earliest featured relatively simple eustatic history characterized “early onlap”; compelling evidence supports fall-rise couplet, “Black Mountain event,” interval. Available stratigraphic information reinterpreted demonstrate initially slow subsequently higher rate continued sea level rise