Syn-eruption vegetation dynamics, paleosurfaces and structural controls on lava field vegetation: An example from the Palaeogene Staffa Formation, Mull Lava Field, Scotland

Jolley, D., Bell, B., Williamson, I. and Prince, I. (2009) Syn-eruption vegetation dynamics, paleosurfaces and structural controls on lava field vegetation: An example from the Palaeogene Staffa Formation, Mull Lava Field, Scotland. Review of Palaeobotany and Palynology, 153(1-2), pp. 19-33. (doi:10.1016/j.revpalbo.2008.06.003)

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Abstract

Lavas and sedimentary rocks of the Palaeogene Staffa Formation are exposed in the south-west of the Island of Mull in the Inner Hebrides, Scotland. Here, we present the results of an extensive programme of analysis of palynofloras from intravolcanic sedimentary rocks across this, the oldest part of the Mull Lava Field. This analysis has been allied to field and aerial photograph mapping, which have provided evidence that the earliest flows and sediments of the Staffa Formation were emplaced into two NW–SE trending fault controlled valleys. This extensional structural regime was also utilised by the NW–SE trending Mull dyke swarm. Early syn-depositional movement on graben margin faults is indicated by anomalously thick alluvial sediments, and ponded lava flows on the downthrown sides. Sedimentary and palynofacies data indicate an overall southeasterly drainage direction for the Staffa Formation paleo-valley system, the palynofloras reflecting this in increased dominance of mire vegetation communities, in the wetter, lower reaches of the catchment. The palynofloras are subdivided into four ecological groupings. Mid to late succession communities dominate the two youngest depositional sequences of the lava field, reflecting the filling of the valley structures, and the development of an increasingly stable environment. The youngest surface includes the renowned Ardtun Leaf Beds, which are shown to be atypical of much of the Staffa Formation flora, being located on a graben margin alluvial fan. This youngest surface also provides evidence for the subsequent inversion of the original graben structure across the south of the area, while active eruption continued in the north. Inversion is attributed to the emplacement of the oldest members of the nearby Mull Central Complex, and heralds the eruption of the trap-forming Plateau Group lavas.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Bell, Dr Brian
Authors: Jolley, D., Bell, B., Williamson, I., and Prince, I.
Subjects:Q Science > QE Geology
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Review of Palaeobotany and Palynology
ISSN:0034-6667
Published Online:24 June 2008

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