Megaspores and a Palynomorph from the Lower Potomac Group in Virginia

Abstract

A plant microfossil assemblage comprising seven species of megaspores; <i>Verrutriletes carbunculus</i> (Dijkstra) Potonié, <i>Echitriletes</i> cf. <i>E. lanatus</i> (Dijkstra) Potonié, <i>Erlansonisporites erlansonii</i> (Miner) Potonié, <i>Thylakosporites retiarius</i> (Hughes) Potonié, <i>Arcellites disciformis</i> (Miner) Ellis and Tschudy, <i>Arcellites</i> cf. <i>A. pyriformis</i> (Dijkstra) Potter, and <i>Paxillitriletes</i> species Hall and Nicolson; two species of the microspore <i>Crybelosporites</i> Dettmann, <i>C. striatus</i> (Cookson and Dettmann) Dettmann adherent to specimens of <i>Arcellites disciformis</i>, and <i>Crybelosporites</i> species adherent to specimens of <i>Echitriletes</i> cf. <i>E. lanatus</i>; and the palynomorph <i>Dictyothylakos pesslerae</i> Horst; is recorded from the Patuxent Formation, Potomac Group, Lower Cretaceous (Barremian-Aptian) in Virginia, USA. A preliminary analysis of the enclosing matrix for microspores and pollen has related the collection site closely to lowermost Zone I of the Potomac Group as described by Hickey and Doyle (1977). The megaspore assemblage supported by acceptance of the oldest possible date derived from the microspore and pollen analysis suggests correlation with the Barremian-Aptian horizons in the English Wealden, Lower Cretaceous, and specifically with the “Arcellites Flora” of Hughes. Megafossils comprising two seed cones belonging to the Pinaceae, <i>Pityostrobus hueberi</i> Robison and Miller and <i>Pityostrobus virginiana</i> Robison and Miller have been reported from the site. A fruit or cupule of <i>Caytonia</i> has been found along with numerous seeds, fern fragments, coniferous woods, and cycadopsid cuticles. This array of megafossils is not described or illustrated herein. A backswamp area of sedimentation and type of habitat is suggested on the basis of the lithofacies and generalized composition of the flora. The writer fully agrees with Tschudy (1976) as to the importance of searching for megaspores in continental Mesozoic rocks to aid in correlating and subdividing the deposits more effectively.