Uppermost Cambrian slope deposits at Highgate Gorge, Vermont: a minor miscorrelation with major consequences for conodont- and trilobite-based chronocorrelation

Uppermost Cambrian and lowest Ordovician slope deposits in Highgate Gorge, northwestern Vermont, yield a succession of conodont faunas (and a few associated trilobite species) similar to that observed in coeval North American carbonate-platform sequences. Decimeter-scale sampling of a 15-m-interval in two sections comprising thin-bedded limestone–shale rhythmites alternating with thick-bedded debris flow conglomerates yielded 60 trilobite specimens and more than 5,000 conodont elements from 48 productive horizons. The new biostratigraphic control does not support earlier claims that the lowest occurrence of Cordylodus proavus in the Gorge Formation and presumably in other slope sequences is significantly older than the base of the C. proavus Zone in platform deposits; rather, it demonstrates the isochronous persistence of this boundary across the North American (Laurentian) shelf margin into Iapetan slope deposits. The common occurrence of the deep, cool-water conodont Eoconodontus alisonae and the agnostoid trilobite Lotagnostus hedini in the Eoconodontus Zone at Highgate Gorge makes it possible to extend the correlation even farther from the Laurentian platform into uppermost Cambrian strata in Kazakhstan and China. This new information greatly strengthens arguments in favor of using this zonal boundary for defining the international boundary between the Cambrian and Ordovician Systems. In earlier studies of Highgate Gorge strata, composite treatment of biostratigraphic data from similar but non-correlative intervals (Zones 2 and 3) in two sections created an illusion of significant stratigraphic overlap of C. proavus with older faunas and direct association of some trilobite species for which overlap has never been established. Composite treatment of data from Zones 2 and 3 under designations such as “main zone’ or “upper zone’ should be discontinued and species that have been reported as occurring together in the “main zone’ should not be assumed (on the basis of that association alone) to have come from the same stratigraphic level.

[1]  B. Chatterton.  Sunwaptan (Upper Cambrian) trilobites of the Cow Head Group, western Newfoundland, Canada , 1991 .

[2]  J. F. Miller.  Conodonts as biostratigraphic tools for redefinition and correlation of the Cambrian–Ordovician Boundary , 1988, Geological Magazine.

[3]  S. V. Dubinina,et al.  Batyrbay Section, South Kazakhstan, U.S.S.R. – potential stratotype for the Cambrian–Ordovician Boundary , 1988, Geological Magazine.

[4]  B. Norford.  Introduction to papers on the Cambrian–Ordovician Boundary , 1988, Geological Magazine.

[5]  J. H. Stitt.  Trilobites of the Upper Cambrian Sunwaptan Stage, Southern Canadian Rocky Mountains, Alberta. , 1988 .

[6]  A. G. Harris,et al.  Off-platform Silurian sequences in the Ambler River quadrangle: A section in Geologic studies in Alaska by the U.S. Geological Survey during 1987 , 1988 .

[7]  B. Pratt,et al.  PALEOSCENE #3. Dual Biostratigraphy: Zones and biofacies , 1986 .

[8]  J. Derby.  Erratum: Great Progress but No Decision by the Cambrian-Ordovician Boundary Committee , 1986 .

[9]  R. Stevens,et al.  Stratigraphy and correlation of the Cambro-Ordovician Cow Head Group, western Newfoundland , 1986 .

[10]  S. Culver,et al.  Petrologic and foraminiferal evidence for active downslope transport in Wilmington Canyon , 1986 .

[11]  D. Stanley.  Mud redeposition and problems of assessing microfossil, isotopic and radiocarbon data in the Mediterranean , 1985 .

[12]  E. Landing.  HIGHGATE GORGE: UPPER CAMBRIAN AND LOWER ORDOVICIAN CONTINENTAL SLOPE DEPOSITION AND , 1983 .

[13]  S. Westrop,et al.  Trilobite biofacies of the Cambrian-Ordovician boundary interval in northern North America , 1983 .

[14]  R. Ludvigsen.  Upper Cambrian and Lower Ordovician trilobite biostratigraphy of the Rabbitkettle Formation, western District of Mackenzie , 1982 .

[15]  P. Bitter,et al.  Upper Cambrian to Lower Ordovician conodont biostratigraphy and biofacies, Rabbitkettle Formation, District of Mackenzie / , 1980 .

[16]  J. Hazel,et al.  Concepts and Methods of Biostratigraphy , 1977 .

[17]  A. Shaw,et al.  Paleontology of northwestern Vermont ; [Part] 16, Trilobites of the Upper Cambrian Gorge Formation(upper Bed 3) , 1968 .

[18]  A. Shaw,et al.  Paleontology of northwestern Vermont; [Part] 15, Trilobites of the Upper Cambrian Gorge Formation (lower part of Bed 3) , 1968 .

[19]  A. Shaw,et al.  Paleontology of northwestern Vermont; 14, Type section of the upper Cambrian Gorge Formation , 1968 .

[20]  A. Shaw,et al.  PALEONTOLOGY OF NORTHWESTERN VERMONT. XV. TRILOBITES OF THE UPPER CAMBRIAN GORGE FORMATION (LOWER PART OF BED 3) , 1968 .

[21]  D. Winston,et al.  LATE CAMBRIAN AND EARLY ORDOVICIAN FAUNAS FROM THE WILBERNS FORMATION OF CENTRAL TEXAS , 1967 .

[22]  F. Rasetti.  Revision of some late Upper Cambrian trilobites from New York, Vermont, and Quebec , 1946 .

[23]  F. Rasetti.  Upper Cambrian trilobites from the Levis conglomerate [Quebec] , 1944 .

[24]  P. Raymond.  Upper Cambrian and Lower Ordovician Trilobita and Ostracoda from Vermont , 1937 .

[25]  C. Schuchert.  Cambrian and Ordovician of northwestern Vermont , 1937 .