Twelve million years ago the UK was covered by a subtropical conifer dominated forest with seasonal rainfall. The mean annual temperature that this forest grew under was 17 - 18.5°C (more than double the modern mean annual temperature for this part of the UK) and the mean winter temperature would have been over 6°C. I have been researching sediments in the Derbyshire Pennines on-off for 4 years now and we have just published our second paper on the results (the first came out in 2012). These sediments are unusual, firstly they are from a geological time interval that is not common on the UK mainland (the Miocene) and secondly they are preserved in collapsed caves. This gives them considerable complexity: the layers are not nicely horizontal (though the rain can be sometimes...) and relating the sediments from each of the 60 different cave collapses to each other is difficult. In our latest paper (which has been made free to read by the Geological Society until 30/11/15) we report new palaeoenvironmental and palaeoclimate information for the UK and revise the ages of these little known sediments.
The Brassington Formation is the most extensive Miocene sedimentary succession onshore in the UK. Because of its unique position at the margin of NW Europe, the pollen from this lithostratigraphical unit provides evidence on the development of vegetation affected by North Atlantic currents and hypothesized atmospheric circulation changes during the Middle to Late Miocene climate cooling. Palynostratigraphy suggests that the uppermost Kenslow Member of the Brassington Formation is not coeval. Previously, all occurrences of the Kenslow Member were assumed to be contemporary. The oldest pollen assemblage is from the more southern Bees Nest Pit, which represents a subtropical conifer-dominated forest of late Serravallian age (c. 12 Ma). A younger assemblage was observed from the more northern Kenslow Top Pit; this indicates that a subtropical mixed forest was present during the early Tortonian (11.6–9 Ma).