Palynological contributions to the chronology and stratigraphy of the Hartford basin in Connecticut and Massachusetts

Abstract

Recent discoveries of palynoflorules at numerous localities in the Newark Group basins of the eastern United States provide new evidence for correlation of deposits in these basins. Floras from the Shuttle Meadow and Portland Formations of the Newark Group rocks in the Hartford Basin of Connecticut and Massachusetts indicate that the Triassic‐Jurassic boundary is located within the rocks of this basin: a shift of Corollina from more than 90% C. meyeriana to more than 90% C. torosus occurs somewhere between the Shuttle Meadow and Portland Formations and generally indicates a Rhaeto‐Liassic age. In the Shuttle Meadow Formation, the overall shape of the palynoflora (particularly the presence of Convolutispora klukiforma), associated fish, paleomagnetic data, and radiometric dates, as well as megafossil evidence of Brachyphyllum scotii and Clathropteris menis‐coides, support a basal Liassic age for this formation. Reptilean evidence in older strata of the Hartford Basin suggests that the Triassic‐Jurassic boundary may lie just below the Shuttle Meadow Formation. In addition the Portland Formation contains a palynomorph association clearly favoring early to middle Liassic age. Comparisons are made on the basis of studies of recently discovered Newark Group palynoflorules of early Liassic age from Virginia and of Carnian‐Norian age from New Jersey. Paleobotanical and geological evidence is summarized, showing that the predominantly Corollina (Hirmerella) palynofloras of the Hartford Basin were associated with a warm, seasonally wet and dry climate, and casting doubt on the idea that Corollina‐producing plants composed a swamp association within the original basin. Twenty‐seven genera and 42 species are described, as are 1 spore and 1 pollen type of uncertain taxonomic position. Eight new species are described: Camerosporites reductiverrucatus n. sp., Corollina murphyi n. sp., Cycadopites andrewsii n. sp., Cycadopites durhamensis n. sp., Cycadopites west‐fieldicus n. sp., Dictyophyllidites paramuensteri n. sp., Foveosporites agawa mensis n. sp., Verrucosisporites cheneyi n. sp. Six new combinations are proposed: Araucariacites punctatus (Nilsson) comb. nov., Callialasporites segmentatus (Balme) comb. nov., Corollina itunensis (Pocock) comb. nov., Corollina simplex (Danzé‐Corsin & Laveine) comb. nov., Cycadopites reticulatus (Nilsson) comb, nov., Granulatisporites infirmus (Balme) comb. nov. The genera Circulina and Corollina are formally emended, as are the species Corollina torosus (Reissinger) Klaus and Circulina simplex Malyavkina.