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Palaeobotanical and sedimentological studies on the Lower Bajocian (Middle Jurassic) flora of Yorkshire

Palaeobotanical and sedimentological studies on the Lower Bajocian (Middle Jurassic) flora of Yorkshire
Christopher Richard Hill

1974

Department of Botany, University of Leeds, Leeds LS2 9JT, UNITED KINGDOM.

ABSTRACT

Results are presented from studies on fossil plant beds of Middle Jurassic (Lower Bajocian) age exposed at Hasty Bank in North East Yorkshire. The abundances of the fossils are described quantitatively and the sedimentology of the beds examined in detail.

The upper part of the main plant bed was deposited by a stream channel, the margins of which supported a dense swamp of Equisetum columnare. There is evidence for a belt of vegetation which grew near to salt water and which was characterised by Hirmerella crucis and Pachypteris papillosa. This probably gave way further inland to a flora characterised by Pterophyllum thomasii, Ptilophyllum hirsutum, Marskea thomasiana and many other species.

During deposition the formerly whole plants became fragmented and their organs detached. Associations between these organs were detected repeatedly in the quantitative data, and when considered together with evidence from cuticular studies partial reconstructions of the plants could be deduced from them. These reconstructions agree with those proposed previously by other workers and add the following new ones which are discussed.

Androstrobus major + Pseudoctenis oleosa (Cycadales)
Alvinia florinii + Pseudoctenis lanei/Paracycas cteis (Cycadales)
Palissya harrisii, female cones + foliage shoots (conifer)
Brachyphyllum crucis + Hirmerella crucis (conifer)

The following new taxa are described.
Mariestopesia blackii (van Cittert) gen.et comb. nov. (Marattiales)
Alvinia florinii gen. et sp. nov. (Cycadales)
Zamites johannae sp. nov. (Bennettitales)
Pterophyllum pruinosum sp. nov. (Bennettitales)
Hirmerella crucis (Kendall) comb. nov. (conifer)
Palissya harrisii sp. nov. (conifer)

Mariestopesia is regarded here as somewhat intermediate in morphology between living Angiopteris and Palaeozoic - Triassic forms such as Asterotheca. The resemblance of Alvinia to the megasporophyll of living Cycas is remarkably close.