Discussion of ‘Palaeocurrent direction and velocity in the Great/Main Limestone on the Alston and Askrigg blocks of northern England’: Proceedings , Vol.52, part 4, pp. 353–359, 1999

Abstract

C. T. Scrutton writes: I read with interest R. A. Fairbairn’s excellent article on the determination of the current directions dominant during the deposition of the Great Limestone in Northern England. The corals that he mentions, which occur in abundance at certain levels within the limestone, could provide some additional information on the conditions prevailing at the time. The solitary rugosans, principally Dibunophyllum bipartitum , lived as straight to slightly curved coralla, more or less upright in the sediment and corresponding to type Evii and particularly Fvii coralla as illustrated in my recent paper (Scrutton 1998, fig. 14). Three factors would have determined their stability, the extent to which they sank down into the soft lime-mud substrate with increasing growth and weight, the consistency of that substrate, and the degree of sediment build-up around them. During life in an environment below fair-weather wave base, conditions were probably reasonably calm with only light current activity. Persistent stronger currents would have resulted in asymmetrical scour around the coral-sediment interface, producing more strongly horn-shaped coralla (Scrutton 1998, fig.14). However, very few specimens are now found in position of growth. Fairbairn (1999, p. 354) reported that many specimens are found prone and aligned on bedding planes, with their long axes at right angles to the prevailing current direction. This disorientation, as he notes, was most likely due to the effects of intermittent storms scouring the supporting sediment and inducing toppling, with subsequent current activity resulting in the alignment of the prone coralla. In addition, it ...