minor depositional cycles. Of 53 observed bedding planes within or bounding the formation, 11 represent cycle boundaries. Three of these are regionally important inception horizons, which have guided much of the bedding-related speleogenesis in this part of the succession. Selected examples from one area are noted; many other examples occur west and east of Leck Fell/Kingsdale. Inception of Caves: Table 1. Relative elevations (metres above Ordnance Datum) and vertical difference between four major inception horizons in five cave systems in the western Yorkshire Dales, England (see also Figure 1). Close similarities of some elevations were formerly assumed to relate to surface “erosion levels”. Inter-horizon differences vary across the outcrop, and are not corrected for geological dip or the effects of faulting

doi:10.4324/9780203483855-238

Chapter

minor depositional cycles. Of 53 observed bedding planes within or bounding the formation, 11 represent cycle boundaries. Three of these are regionally important inception horizons, which have guided much of the bedding-related speleogenesis in this part of the succession. Selected examples from one area are noted; many other examples occur west and east of Leck Fell/Kingsdale. Inception of Caves: Table 1. Relative elevations (metres above Ordnance Datum) and vertical difference between four major inception horizons in five cave systems in the western Yorkshire Dales, England (see also Figure 1). Close similarities of some elevations were formerly assumed to relate to surface “erosion levels”. Inter-horizon differences vary across the outcrop, and are not corrected for geological dip or the effects of faulting

Chapter

minor depositional cycles. Of 53 observed bedding planes within or bounding the formation, 11 represent cycle boundaries. Three of these are regionally important inception horizons, which have guided much of the bedding-related speleogenesis in this part of the succession. Selected examples from one area are noted; many other examples occur west and east of Leck Fell/Kingsdale. Inception of Caves: Table 1. Relative elevations (metres above Ordnance Datum) and vertical difference between four major inception horizons in five cave systems in the western Yorkshire Dales, England (see also Figure 1). Close similarities of some elevations were formerly assumed to relate to surface “erosion levels”. Inter-horizon differences vary across the outcrop, and are not corrected for geological dip or the effects of faulting

ABSTRACT

Some inception horizons represent discontinuities between contrasting lithologies and hence have virtually zero thickness. For example, the boundary between the Porcellanous Bed (finegrained, hypersaline limestone), and underlying sparite in the western Yorkshire Dales, England (Figure 1; Table 1) guides cave passage elevations regardless of topographical level. The speleogenetic efficiency of this boundary probably reflects what is missing rather than what remains and it is hypothesized that dissolution has removed late-cycle evaporites that are absent from the idealized cyclic successions. Among many lesser springs, the presence of two major resurgences (Leck Beck Head and Keld Head) at this horizon but at different elevations provides compelling evidence for the role of inception horizons. Farther east, major risings at Black Keld and Malham Cove, also at different elevations, are guided by the Cove/Kilnsey limestones boundary, an inception horizon that corresponds to the Mid-Holkerian Break (Table 1). Thin beds of atypical lithology, such as clay partings or coal seams, also occur in the western Dales (Figure 1; Table 1). A good example is the Notts Pot coal seam, rich in pyrite that provides a source of sulfuric acid. Similar conditions are found at contacts between thicker “clay” beds (terrigenous shales, seatearths, and volcanic tuffs) and carbonate beds. The Mid-Asbian Break (Figure 1; Table 1) is marked locally by a 2 m thick pyrite-rich shale that infills depressions in the highly uneven paleokarstic surface below. Argillaceous intervals are also implicated in guiding early speleogenesis in some evaporitic successions.