Trilobites from Kilbucho and Wallace’s Cast and the location of the Northern Belt of the Southern Uplands during the late Ordovician

Fifteen trilobite species are recorded from the Kirkcolm Formation in the Northern Belt of the Southern Uplands at Kilbucho and Wallace’s Cast, some 12 km apart along the regional strike. Both faunas are from mudstones which overlie a fossiliferous conglomerate. All of these sediments may have been deposited following episodes of mass flow from the north and the faunas were displaced from shallower water habitats. Thirteen of the trilobite taxa can be recognised below family level and eight of these are identical to or very closely allied to species in the early to mid-Caradoc at Girvan and at Pomeroy, Co. Tyrone to the north of the Southern Uplands Fault. This strong faunal similarity suggests, contrary to some tectonic models, that there may have been no more than a few hundred kilometres of strike-slip displacement (possibly much less) along the Southern Uplands Fault.