Karst palaeoenvironments: a reconstruction with particular reference to the Morecambe Bay area

Abstract

At least four phases of karst development can be recognised in the Morecambe Bay area of northwest England : an intra-Carboniferous phase resulting from intermittent subaerial erosion associated with temporary falls in the level of the Lower Carboniferous sea; a Permo-Carboniferous phase probably characterised by streams from adjacent areas of impermeable rock sinking at the limestone boundary and forming swallet-type cave systems; an ?01igo-Miocene phase of interstratal karstification; and a Late Quaternary phase of karst development. The caves of the Late Quaternary phase contain deposits of Late and Post-glacial age, although palaeomagnetic evidence suggests that certain of the deposits may be somewhat older. Thus, the bulk of these caves may be of at least last interglacial age.
It is possible to reconstruct the former pattern of drainage through the now-abandoned caves and to show that the caves probably date from more than one phase of hydro- logical development. Nevertheless, the results of earlier attempts to date former episodes of hydrological development by matching the altitudes of caves with those of former base levels in the area are shown to be invalid.
A semi-quantitative picture of the palaeohydrology of certain karst drainage systems in the area is provided using evidence obtained from bedform flow-features and hydraulically-transported deposits in the caves. By means of sedimentological analysis, it is also possible to reconstruct the hydraulic conditions under which former flows occurred.
The surface topography of the>area, previously regarded as largely a response to episodes of planation associated with falling sea levels, is studied. No evidence, neither of a morphological nor of a sedimentological nature, is found to support the idea of marine planation. Finally, some of the characteristic surface karst features of the area are described, including large-scale closed depressions, cemented screes, and features regarded by earlier workers as poljes.

Citation

(1981). Karst palaeoenvironments: a reconstruction with particular reference to the Morecambe Bay area