Pennsylvanian climate signatures from the South Wales coalfield: evidence from fossil plants

Orme, Joseph William 2013. Pennsylvanian climate signatures from the South Wales coalfield: evidence from fossil plants. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The link between vegetation and climate change during the Pennsylvanian Subperiod is of significant scientific interest, in part due to the similarities between that time and the present day. These are the only two intervals in Earth's history with comparable levels of polar ice, and widespread tropical vegetation. Extensive coal deposits were formed in areas of wetland vegetation dominated by arborescent lycopsids. A change in composition and westwards decline of these coal swamps across Euramerica, began in the Middle Pennsylvanian. The South Wales Coalfield possesses potentially the most complete terrestrial record of the Middle Pennsylvanian Subperiod and thus a unique resource for the study of this time. Initially changes in atmospheric concentration of CO2 were to be assessed via measurement of stomatal index. Considerable experimentation with various techniques for obtaining cuticle revealed this to be impossible, preservation being variable but consistently too poor for the identification of stomata. Therefore petrographic analysis of coal was utilised to investigate environmental change, principally peat hydrology. Samples were collected through 24 seams across the South Wales Coalfield. Optical analysis of macerals, the plant derived microscopic components of coal, was used to develop a new petrographic technique for defining maceral facies from detrended correspondence analysis of maceral composition data. These changes are compared to group level changes in the palynological assemblages of roof shales which revealed a clear change in dominance from lycopsids to ferns. I interpret a transition, initiated earliest in the West of the basin, from waterlogged environments dominated by rheotrophic peat substrates and lycopsid vegetation, to a better drained environment with expanded areas of clastic substrate and fern dominated vegetation. Signals from petrographic and palynological data are similar, but due to taphonomic factors these diverge from that from macroflora, the former indicating an earlier decline in lycopsid vegetation during the Bolsovian substage. The coeval northwards migration of the Variscan front, and influx of coarse clastic sediment, is presented as the principal driver of the interpreted environmental and vegetational change in South Wales. The present study supports the model proposed as a result of the IGCP 469 project that the role of climate change may have increased globally as the coal swamps contracted, a positive feedback loop being established in which the progressive loss of a significant carbon sink contributed to the establishment of conditions less favourable for the dominant forest vegetation and thereby their further decline.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Earth and Environmental Sciences
Subjects:	Q Science > QE Geology Q Science > QK Botany
Date of First Compliant Deposit:	30 March 2016
Last Modified:	19 Mar 2016 23:39
URI:	https://orca.cardiff.ac.uk/id/eprint/59831

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