POSSIBLE TRIASSIC-JURASSIC BOUNDARY SECTIONS, HARTFORD BASIN, EASTERN NORTH AMERICA

Examination of long-known outcrops plus two new cores in the Hartford basin allow a comparison between probable Triassic-Jurassic boundary sections of the latter basin with those better known from the Newark basin.

Gray, well-bedded strata of the uppermost New Haven Fm. beneath the Talcott basalt at two exposures (Cinque Quarry, and Silver Ridge) and in two cores (Silver Ridge) contain abundant conifer wood, shoots, and cones. That pollen consisting only of Corollina has been identified at the Cinque Quarry (1,2) strongly suggests that these strata are of Early Jurassic age. The sequence of facies in the uppermost New Haven is extremely similar to those seen in the northern Newark basin where the Triassic-Jurassic boundary may be cut out by a tectonostratigraphic sequence (TS III-IV) hiatus (2).

Two candidate sections in the northern Hartford basin (where the Talcott is lacking) are the Clathropteris locality in Holyoke (3) and the Rt. 91S cut in Northampton (4). The former section looks remarkably like the complete boundary section at Exeter in the southwestern Newark basin (2), where the TS III-IV boundary is a correlative conformity. In both cases there is a claystone with a "fern spike" dominated by Granulatisporites infirmus and Converrucosisporites cameronii (3,4), both produced by the dipteraceous fern Clathropteris meniscoides (3); and in both cases Triassic taxa are absent. Either both represent the Triassic-Jurassic boundary or they represent only a distinctive habitat of Clathropteris that in Exeter is by "chance" at the Triassic-Jurassic boundary, although Clathropteris habitats themselves may be a signal of events broadly around the Triassic-Jurassic boundary, such as a "super greenhouse" effect. The Rt. 91 section contains the lowest limestone of the Shuttle Meadow Fm. and an underlying thin red and purple mudstone sequence. The latter superficially resembles the red Grist Mills section (2). At Exeter and Grist Mills a modest Ir anomaly has been found (5) and clearly examining these Hartford basin sections for a comparable geochemical tracer is the next priority.

1) Heilman, JJ. 1987. Jour. Sci. Ed. 25:8. 2) Olsen, et. al. 2002. G.S.A. Spec. Pap. 356:505. 3) Cornet, B, Traverse, A. 1975. Geosci. Man 11:1. 4) Fowell, SJ. 1994, Ph.D thesis, Columbia Univ., NY, 154 p. 50 Olsen, et. al. 2002. Science 296:1305.