Folding of angular unconformable sequences and effects on early folds, Tabberabbera district, eastern Victoria, Australia

Abstract

The Tabberabbera district of the southeast Lachlan Fold Belt has a good example of a complex fold pattern produced by folding of angular unconformable sequences. Ordovician quartz flysch (Hotham Group) contains subhorizontal, upright, tight, easterly trending F 1 folds of Early to Middle Silurian age. These have been reoriented by a locally intense Middle Devonian deformation that has formed an upright isoclinal syncline (Mitchell syncline) in the unconformably overlying Emsian clastic sequence (Wentworth Group). Many of the F 1 folds in the Hotham Group immediately west of the Mitchell syncline have steep northwest trending axial surfaces and are steeply plunging. East of the syncline F 1 folds are upright, with shallow plunges, and gradually become inclined to recumbent as the unconformity is approached. A folded foam-layer analogue matching the geometry of the Mitchell syncline shows that the reorientation of early fold axes and axial surfaces produced by the unconformity-folding event is identical to that predicted by the model.