Mid?Devonian movements in the Northeastern Lachlan Fold Belt

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Abstract
Calculations of the angular discordance between the Upper Devonian Lambie/Catombal Groups and underlying Lower Devonian formations at 130 separate locations in six areas in the northeastern Lachlan Fold Belt show that the unconformity is of a low angle except for one locality, near Limekilnes (100°). Fewer than 3% of the calculated angular discordances exceed 30°, and 73%” are less than 20°. Attempts to discover a mid‐Devonian fold direction from the restored orientation of the Lower Devonian beds, after the Upper Devonian beds have been rotated to horizontal, have been unsuccessful. Scatter of the restored bedding poles, either primary, or introduced by deformation or imprecision inherent in the measurement technique, camouflages any consistent mid‐Devonian fold axis. Although there was demonstrable uplift, tilting, and erosion in the mid‐Devonian, limb dips on any mid‐Devonian folds do not exceed 30°. From consideration of our data, and the interpretation of angular unconformities, we conclude that there is insufficient evidence in the northeastern Lachlan Fold Belt to support an orogenic scheme in which the intense meridional deformation is synchronous with the major mid‐Devonian facies change, and part of a terminal orogeny. Only when the structures above, below and across unconformities have been mapped in some detail, will it be possible to define the nature and extent of any diastrophism that accompanied the formation of the unconformities.