THE SEQUENCE AND CORRELATION OF THE COAL MEASURES OF PEMBROKESHIRE

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Abstract
The intensely folded and faulted strata exposed in long cliff-sections in the two structurally detached coalfields of Pembrokeshire (Little Haven–Amroth and Nolton–Newgale) present complex problems of correlation which are considered in detail. Many fossil bands are newly recorded and, where possible, are placed in measured sequences which are correlated by marine bands and are referred to non-marine lamellibranch zones, with occasional use of floral zones. Incomplete Ammanian successions from the Little Haven–Amroth coalfield are generally similar in thickness to corresponding portions of the succession in the western part of the North Crop of the main basin, but evidence exists for marked southward thickening of the basal measures and for moderate attenuation westwards of both the lenisulcata and modiolaris Zones. A tentative succession is proposed for the Morganian of the coastal cliffs, with some sequences assigned to the tenuis Zone and the Rickets Head strata (formerly regarded as the highest Coal Measures in Pembrokeshire) re-assigned to the phillipsii Zone. The chief examples of ‘slump sheets’ cited by Kuenen are shown to lie near the middle of the basal cyclothem of the Ammanian; it is suggested that seismic shuddering, in conjunction with local slumping, produced these contemporaneous deformation-structures. An anomalous thickness of 1100 feet of barren shale previously assigned to the basal Coal Measures of the western area is considered to be of Lower Palaeozoic age, as is the supposed Farewell Rock of Newgale.