Cracoe Limestone Formation
Cracoe Limestone Formation is part of the [[Great Scar Limestone Group
Cracoe Village, after which the formation is named, is situated 5.5 miles north-north-west of Skipton. The formation was previously known as the ‘Marginal Reef Limestones’ (see Arthurton et al., 1988, and references therein).
The formation includes mid and mid–pale grey limestones ranging from organic boundstones to packstones and wackestones with a variable grainsize depending on the bioclastic components. Zones of megabrecciation and neptunian dykes (crinoid- and mudstone-filled) are present within the formation at its partial type section at Swinden Quarry (see below).
A partial type section is at Swinden Quarry (SD 975 611 to 982 619), near Cracoe, North Yorkshire, where a large carbonate bank (‘reef’) of pale grey and very pale grey wackestones is exposed, faulted against ‘pre-reef’ and ‘post-reef’ limestones. Zones of megabrecciation and neptunian dykes are also present in the quarry (Arthurton et al., 1988; see also Mundy, 2000).
Distribution and regional correlation
South of the Middle Craven Fault, occurring in a roughly west–east tract extending 20 km east from Settle (SD 83 63) to Burnsall (SE 01 61). The apron reef has become dislocated into fault-slices along the Craven Fault System. The formation passes northwards into the Cove Limestone and Gordale Limestone members and probably also into the Lower Hawes Limestone (Alston Formation, Yoredale Group).
Lower and upper boundaries
The lower boundary has not been proved, but is likely to comprise reef limestones of the Cracoe Limestone Formation resting upon the bedded, mid to mid–dark grey limestone of the Scaleber Quarry Limestone Member.
The upper boundary is a marked unconformity, with the reef limestones of the Cracoe Limestone Formation overlain by dark grey mudstones of the Bowland Shale Formation. Pre-reef and post-reef limestones are present in the partial type section at Swinden Quarry (see above), but the contacts with the reef limestones of the Cracoe Limestone Formation are faulted.
The total thickness has not been proved, but is in excess of 100 m at the type locality.
Age and biostratigraphical characterisation
?Holkerian to Brigantian. The biota is diverse with biostratigraphically significant ammonoids including Goniatites hudsoni, G. wedberensis, Bollandites castletonensis and G. moorei of B2 age (Arthurton et al., 1988), and foraminifers of P1a age including stellate archaediscids and Howchinia bradyana (Strank in Arthurton et al., 1988).
- Arthurton, R S, Johnson, E W, and Mundy, D J C.1988.Geology of the Country around Settle.Memoir of the British Geological Survey, Sheet 60 (England and Wales).
- Mundy, D J C.2000.Field meeting to the Craven Reef Belt: Settle and Cracoe, Sunday 23rd July 2000. (Calgary: Talisman Energy Inc.)