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Lower Ordovician faunas, stratigraphy, and sea-level history of the middle Beekmantown Group, northeastern New York

Ed Landing and Stephen R. Westrop
Lower Ordovician faunas, stratigraphy, and sea-level history of the middle Beekmantown Group, northeastern New York
Journal of Paleontology (September 2006) 80 (5): 958-980


The Lower Ordovician middle Beekmantown Group is a very thin carbonate platform succession on the northern New York Promontory that thickens north into the Ottawa aulacogen near Montreal. The Tribes Hill Formation (Rossodus manitouensis Zone) records the earliest Ordovician (late Skullrockian, late early Tremadocian) eustatic high that submerged Laurentia, and produced the lowest Ordovician sequence along the New York Promontory. These dolostones are succeeded in the Beekmantown, New York, area by late Tulean?-Blackhillsian transgressive systems tract quartz arenites of the lower Fort Cassin Formation (Ward Member). The "Fort Ann Formation" (middle Stairsian, upper Tremadocian) of the southern Lake Champlain lowlands (= Theresa Formation sandstones in the Ottawa graben) is absent at Beekmantown, and moderate Stairsian (late Tremadocian) eustatic rise apparently did not inundate the Beekmantown area after Skullrockian-Stairsian boundary interval offlap. Highstand carbonates of the upper Fort Cassin Formation [Sciota Member = "Spellman Formation" and "Ogdensburg Member" of the "Beauharnois Formation" in the Montreal area; designations abandoned] at Beekmantown yield diverse conodonts seemingly characteristic of the Oepikodus communis-Fahraeusodus marathonensis Zone (new). However, associated trilobites, particularly Carolinites tasmanensis (Etheridge, 1919), show a correlation with the upper Trigonocerca typica (trilobite) Zone of the Utah and the overlying Reutterodus andinus (conodont) Zone. This abrupt early Blackhillsian lithofacies change features the appearance of chitinozoans and conodonts known from marginal successions, and records the Laignet Point highstand (new). This highstand is recognized across Laurentia on the west Newfoundland and southern Midcontinent platforms. It is recorded on the east Laurentian continental slope by lower Oepikodus evae Zone dysoxic black mudstone in the Taconian allochthons. Taxonomic re-evaluations include Ulrichodina Branson and Mehl, 1933, with its genotype species U. abnormalis (Branson and Mehl, 1933) emend., as the senior synonym of Colaptoconus Kennedy, 1994; Eucharodus Kennedy, 1980; and Glyptoconus Kennedy, 1980. Paraserratognathus An in An et al., 1983, emend. is the senior synonym of Wandelia Smith, 1991 and Stultodontus Ji and Barnes, 1994. Tropodus Kennedy, 1980 is the senior synonym of Chionoconus Smith, 1991. The trilobite fauna of the Sciota Member includes species of Isoteloides, Benthamaspis, Acidiphorus and Carolinites, of which I. fisheri is new.

ISSN: 0022-3360
EISSN: 1937-2337
Serial Title: Journal of Paleontology
Serial Volume: 80
Serial Issue: 5
Title: Lower Ordovician faunas, stratigraphy, and sea-level history of the middle Beekmantown Group, northeastern New York
Affiliation: New York State Museum, State Education Department, Albany, NY, United States
Pages: 958-980
Published: 200609
Text Language: English
Publisher: Paleontological Society, Lawrence, KS, United States
References: 110
Accession Number: 2006-079859
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. col., 5 plates, 2 tables, geol. sketch map
N44°25'60" - N45°01'60", W74°01'60" - W73°22'00"
Secondary Affiliation: University of Oklahoma, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, The Paleontological Society. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200645
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