The relationship between movement on the Highland Boundary Fault and deposition of the Lower Old Red Sandstone in the Midland Valley Basin of Scotland is controversial. Most models favour mid-Silurian to early Devonian sinistral movement on the Highland Boundary Fault and development of a transtensional Midland Valley Basin. To constrain Highland Boundary Fault movement during the late Silurian, we examine the basal Lower Old Red Sandstone alluvial succession exposed adjacent to the Highland Boundary Fault. A lack of synsedimentary fault movement indicators, coupled with an increase in stratal thickness across the fault, indicates that the Highland Boundary Fault was not active during Lower Old Red Sandstone sedimentation. A transtensional basin model cannot be sustained.

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