Abstract
The Arlington Archosaur Site between Dallas and Fort Worth, Texas, USA, is known as a rich fossiliferous section. The age of these rocks is generally considered to be mid-Cenomanian, but conflicting evidence suggests they may be as young as the Late Cenomanian–Early Turonian. To address the issue, a palynological study was designed and conducted based on close sampling of the four lithofacies associations, labelled A to D, in ascending order. The study was quantitative and focused on palynological associations to determine the palaeoenvironment, palaeoclimate, biostratigraphy and age of the exposure. The rich palynological assemblages comprise spores from seedless plants, gymnosperms, angiosperms, fungi, freshwater algae, acritarchs and dinoflagellate cysts. Bryophyte spores were abundant mainly in Facies A and B, with Zlivisporis cenomanianus taking over the habitat of bryophytes in Facies D. Lycophytes abundant in the alluvial and coastal plains are considered to have been transported. Conifer pollen represent the predominant group of gymnosperms, mainly transported into the section. Freshwater algal remains include Schizophacus laevigatus/Ovoidites parvus, Schizosporis reticulatus, Botryococcus sp. and Pediastrum sp. The overall terrestrial vegetation represented in the palynological assemblages indicates tropical to subtropical palaeoclimatic conditions. In addition, the assemblage richness and abundance peaks of dinoflagellate cysts are interpreted as an increased marine influence and possible flooding surfaces. The results support the alternation of marine incursions within deltaic and floodplain sequences related to short term climate oscillations that affected the vegetation on the upland and lowland drainage areas. Key palynological markers point to an early Late Cenomanian age whereas the Cyclonephelium compactum–membraniphorum (Ccm morphological plexus) presence signals the incursion of boreal waters during the Plenus Cold Event of the Ocean Anoxic Event 2 reaching the southern coast of Appalachia.
Published Version
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