Aspects of upper Carboniferous nonmarine carbonate sedimentology in central England.
The mid- to late-Westphalian C succession in central and northern England
lacks typical marine bands but include various forms of thin, but widely extensive
carbonates which appear at several stratigraphic levels, commonly overlying coal
seams or interdigitating with the associated overbank and lacustrine mUdstones.
These carbonates include the well known sideritic blackband and clayband
ironstones, the Spirorbis lacustrine and palustrine limestones and dolostones, and
some calcretes. They coexist with red beds which tend to dominate the younger
In this study, the term "blackband-type" ironstones is introduced to include
all of the ironstones that overlie, or lie very close above coal seams, throughout the
Westphalian. Based on petrographic, chemical and sedimentologic considerations,
these ironstones are either suggested to replace original limestones (e.g. the typical
blackband ironstones), or to be formed by reduction of original Fe compounds (e.g.
the earlier Westphalian ironstones). In both cases the Fe is proposed to have
migrated from lateritic sources outside the basin. The facies appear to have
evolved progressively in relation to rates of sedimentation and/or subsidence, and
the increasing development of red beds.
The Spirorbis lacustrine and palustrine limestones and dolostones are
suggested to be initiated by brief marine transgressions following regional episodes
of subsidence. They are biogenic in origin and were accumulated in progressively
deepening lakes, in which high clastic supply may have terminated the carbonateforming
processes. The latest Westphalian palustrine limestones were probably
accumulated in widely extensive shallow wetland areas. The calcretes, on the other
hand, show an increasing trend of maturity towards the late Westphalian.
It is suggested that many of the studied carbonates are genetically related
and are comparable to those of the Dinantian in the Midland Valley of Scotland.
The range of Westphalian carbonate forms may however be attributed to local