Summary of site:
The importance of the Tullyhona stream section lies in its exposure of 2 contacts between 3 of the major Carboniferous formations in the south west of Northern Ireland. The lowest, the Benbulben Shale Formation and its contact with the Glencar Limestone Formation, is clearly exposed in the stream banks. The beds are inclines at low angles to the south and a gradual transition from dark grey mudstones and shales of the Benbulben Formation to the shaley limestones of the Glencar by an increase in carbonate content is ideally displayed. At the top of the stream the strongly bedded Glencar rocks are abruptly terminated by the base of a pure carbonate mud mound, the Knockmore Member that marks the base of the Dartry Limestone Formation. The section is not complicated by faulting and the transitions between the formations show no break in sedimentation.
These rocks were deposited in an equatorial basin around 338 million years ago. The dark, shaley muds of the Benbulben Formation represent deep water sediments probably remote from the nearest shoreline. At the onset of Glencar times even the supply of fine mud to the basin was reduced and more organic lime sediments appeared in the shallowing water until the sea bed was sufficiently shallow to be colonised by the poorly understood organisms responsible for the mud mounds that mark the beginning of the Dartry Limestone Formation. The fluctuating depth of the basin was controlled by movement along active faults.
There are no immediate threats to this section which is one of the best showing the transitions between these important Carboniferous formations. Its entire length is within the Florence Court Forest which is a National Forest Park.