River Hodder

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Author(s):

C N Waters (BGS)

MAP TO GO HERE
Map extract from DigMap50k showing the location of Collyholme Wood and the distribution of Pendleside Limestone Formation limestones (in turquoise) and limestone boulder beds (purple), with underlying Hodder Mudstone Formation to NW and overlying Bowland Shale Formation present to SE.

River Hodder, Collyholme Wood, Lancashire [SD 719 576][edit]

The River Hodder section at Collyholme Wood shows good exposures in the Pendleside Limestone Formation, for which this locality is a reference section, and lower part of the Bowland Shale Formation (Arthurton et al., 1988)[1].

BOWLAND SHALE FORMATION[edit]

Much of the lower (Brigantian) part of the Bowland Shales Formation sequence is exposed [SD 7205 5743 to 7255 57221 in the banks of the River Hodder, east of Collyholme Wood.

An exposure [SD 7233 5722] of mudstone contains a few thin beds of partly laminated limestone ranging from calcisiltite to medium calcarenite, and bearing groove- and prod-casts. Poorly-laminated, fine calcarenite beds are typically sharp-based and the top of the limestone grades to mudstones. There are also limestone bullions up to 1 m across and 0.25 m thick, and 0.25 m of mudstone conglomerate with limestone clasts up to 3 cm across. Interbedded limestones continue into the highest parts of the section where they are locally slumped (Arthurton et al., 1988, p. 68). The sequence here contains Neoglyphioceras subcirculare indicative of P2b age.

20 m lower in the sequence a P2a fauna including Sudeticeras crenistriatum is recorded at an exposure [SD 7224 5723] where there are beds of calcisiltite and calcarenite (Arthurton et al., 1988, p. 68).

20 m lower in the sequence, towards the base of the formation, there are P1d mudstones and ‘striped beds’, resting on laminated calcareous mudstones containing 0.35 m of mudstone conglomerate with pale and dark limestone clasts up to 10 cm. Beneath this, there are two thin beds of fine-grained, siliceous sandstone totalling 16 cm are present [SD 7210 5740], with groove-casts trending N45oW (Arthurton et al., 1988, p. 68).

PENDLESIDE LIMESTONE FORMATION[edit]

Comprises a 21 m thick succession, with lower beds of planar bedded lime mudstone/wackestone interbedded with upward fining calcarenites and occasional mudstones, overlain sharply by interbedded massive and upward fining calcarenites and limestone breccias [SD 719 576]. The breccias include chaotic, upward fining and reverse graded units (Gawthorpe, 1986 p197)[2] LINK TO SECTION. Bedded limestones intercalated in the lower part of the limestone conglomerate subdivision are exposed in the River Hodder [SD 7185 5773 to 7192 5752]; the limestones are mostly cherty, intensely bioturbated, medium-dark grey, fine calcarenite packstones. The upper part of the limestone conglomerate, exposed farther downstream [SD 7191 5761 to 7204 5743] is largely dolomitized and includes much dark limestone debris in clasts up to 16 cm where unaltered. Towards the top of the formation, interbedded calcirudite and calcarenite packstone-grainstone with subordinate beds and lenses of mudstone are present. Angular clasts of pale calcilutite of reef facies are set in a dark, partly dolomitic matrix including crinoid, shell and coral debris. LINK TO LOCALITY IMAGE. The highest beds are slump-folded (Arthurton et al., 1988 p61). [1]

Pendleside Limestone Formation in the River Hodder, Collyholme Wood. Limestone conglomerate near top of formation comprises angular clasts of pale calcilutite of reef facies set in a dark, partly dolomitic matrix including crinoid, shell and coral debris. View vertical on river bed. P223853.

References[edit]

  1. 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).
  2. GAWTHORPE, R. 1986. Sedimentation during carbonate ramp-to-slope evolution in a tectonically active area: Bowland Basin (Dinantian), N. England. Sedimentology, Vol. 33, 185-206.