Pincent's Kiln

[SU 651 720]

Introduction

This small, disused quarry on the north-east side of Theale, Berkshire, is now in the grounds of a hypermarket but some exposure has been retained (Figure 7.17)a and (Figure 7.18). It is one of the few sites where plant macrofossils can be collected from sandy and muddy sediment low in the Reading Formation of southern England. The site is of especial interest as it shows the relationship between the plant-bearing levels and the unconformity with the underlying Chalk.

There has been little published work on the palaeobotany of this site. Plant fossils were mentioned by Collinson et al. (1985) and a list of species was published by Crane and Goldring (1991), who also placed the plant-bearing levels in a stratigraphical context.

Description

Stratigraphy

The geology of the site has been described by Whitaker (1872), Blake (1903), Crane and Goldring (1991), and Daley (in Daley and Balson, 1999, p. 78). Approximately 4.5 m of Palaeogene deposits overlie Chalk (Figure 7.17) and (Figure 7.18), the contact being a planar unconformity with extensive burrowing (Figure 7.17)b and (Figure 7.19). The basal 1 m of the Palaeogene strata here consists of glauconitic sands and pebbles of the Upnor Formation, which are interpreted as shallow marine. The Chalk is extensively burrowed by Glyphichnus Bromley and Goldring (1992), a probable crustacean burrow. The overlying Reading Formation (Figure 7.17) and (Figure 7.18) is mainly medium to coarse sands with some mudstone lenses. These upper beds cut down into the Upnor Formation and were deposited by a prograding fluvial system.

Palaeobotany

The Reading Formation here has yielded a range of plant fossils (Crane and Goldring, 1991), including the leaves Lauraceaephyllum stenolobatus Koch and Platanus schimperi (Heer) Saporta and Marion. An important but as yet undescribed fruit and seed flora occurs in sandy scours and fills. Crane and Goldring mention the fruit Leguminosites gardneri Chandler (= Leguminocarpon gardneri (Chandler) Herendeen and Crane, 1992) and seeds of Vitis sp. and an undetermined menispermacean. Collinson et al. (1985) described the lycophyte megaspores Mineriporites mirabilis (Miner) Potonié and Erlansonisporites sp. (Figure 7.20) from the sandy unit.

Interpretation

Pincent's Kiln is one of the very few places where plant macrofossils have been found at low levels in the Palaeocene–Eocene transition beds of southern Britain. Although collecting anything more than small specimens is now difficult, it is the only place where the plant-yielding horizons can still be seen in their stratigraphical context with the underlying Upnor Formation and Chalk. The sediments containing the fruits, seeds and megaspores are sandy scours and fills. It therefore complements the Cold Ash site, which has yielded a more diverse assemblage from silty-clay channel fills, and thus helps in the overall interpretation of the Palaeocene–Eocene transition vegetation of southern England.

The lycophyte megaspores Erlansonisporites (Figure 7.20) from here have been found to show iridescence comparable to that of precious opal (Hemsley et al., 1994 and references quoted therein). This has led to the establishment of a model of self-assembly in biological systems (Hemsley et al., 1994), currently being investigated experimentally (Hemsley et al., 1998, 2000).

Conclusions

Pincent's Kiln is the best available site for showing the stratigraphical context of the Reading Formation plant-bearing levels low in the sequence, and thus helps in the reconstruction of the vegetational habitats of southern Britain, about 54 Ma ago.

References