The Structure of the South-Western Part of the Sykes Anticline, Bowland, West Yorkshire

Abstract

Summary The Carboniferous succession exposed along the Sykes Anticline includes the upper part of the Viséan Series and the lower part of the Namurian Series. The Viséan succession consists of the upper 350 feet of the Worston Group and the Lower Bowland Shales. The Namurian strata of lower Pendleian (E 1 ) age include the Upper Bowland Shales and the Pendle Grit. The sequence is conformable and very similar to that described by Parkinson (1936) in the adjacent Slaidburn district. The anticline is a concentric fold with relatively competent upper and lower levels separated by an incompetent sandwich of shales. The upper level (Pendle Grit) has the general form of a boxfold with dips of about thirty-five degrees on the limbs, an axial zone about a mile wide and a trend of 045 degrees. The lower level (Worston Group) is tightly folded into en echelon periclines with vertical and overturned strata common, and a mean axial trend of 027 degrees. The difference in tectonic style between upper and lower structural levels is attributed partly to the normal process of concentric folding, with the crumpled limestones indicating a lower limit to this, and partly to the disharmony of the Bowland Shales. Dip, strike and oblique joints are found in several well-defined sets, each set related to the anticlinal structure and approximately normal to the bedding.

Development and flow structures of sand injectites: The Hind Sandstone Member injectite complex, Carboniferous, UK

“…The HSM was firstly overlain by hemipelagic and gravity flow mudstones, forming a thick seal (original thickness of w30 m), but would have undergone relatively rapid loading with the emplacement of the Pendle Grit turbidite fan system (Sims, 1988;Martinsen, 1993;Kane et al, 2009Kane et al, , 2010. The Pendle Grit onlaps the pre-existing structure of the Sykes Anticline in this area (Moseley, 1962;Sims, 1988); this could potentially lead to the development of a differential pressure gradient by disequilibrium compaction of sediment deposited over the anticline (Fig. 11).…”

“…The first phase of movement of the Sykes Anticline and WhitendaleeBrennand Pericline was originally though to pre-date the Pendleian, with the present structure formed by compressional reactivation during the late Variscan (Moseley, 1962;Brandon et al, 1998;Kirby et al, 2000); however Arthurton (1984) and Arthurton et al (1988) suggested that these features were active throughout the Pendleian interval, a view which is supported here (based on the prevalence of syn-sedimentary slumping and deformation throughout the Pendleian interval). Previously, in other systems, a close association between injectite occurrence and tectonism has been noted (Newsom, 1903;Dzulynsky and Radomski, 1956;Winslow, 1983;Thompson et al, 1999).…”

“…Rapid loading associated with deposition of the Pendle Grit, and the discordance of the onlap of the underlying structure (Moseley, 1962;Sims, 1988) are both potentially significant factors in the generation of disequilibrium compaction and overpressure development in the HSM sand bodies. Loading in this way would create the highest pressures on the flanks and at the margins of anticlinal or periclinal features, which corresponds precisely with the distribution of the HSM.…”

The relationship of the Bowland shales to the pendleside limestone in the Clitheroe, Slaidburn and Sykes Anticlines

“…Neither in its lithology nor in its goniatite fauna does this breccia resemble the Ravensholme Limestone with which it is correlated in the Clitheroe Memoir (p. 79). Moseley (1962) described the breccia (employing the name Slaidburn Breccia) in the southwestern part of the Sykes Anticline, but he did not find any goniatites in it and was non-committal as to age.…”

“…The duration of the unconformity is greatest north of Lamb Hill House where the top of the limestone below the P, shales is marked by a massive chert bed which may be at the same horizon (?S,) as the 25 ft chert bed near Sykes Farm in the trough of Bowland (Parkinson 1936;Moseley 1962). …”