Cycle hierarchy of a Neoproterozoic carbonate-siliciclastic shelf: Matjies River Formation of the Kango Group, South Africa
The Matjies River Formation of the Kango Group is characterized by a complex multi-cyclic pattern of deposition. The most common cycles are represented by small-scale, rhythmic limestone/shale intercalations of the order of a few decimetres to a maximum of 25 m. These form part of composite units showing similarities to Yoredale cycles in the Carboniferous of Britain and the Neoproterozoic to early Palaeozoic Grand cycles of North America. The Yoredale-type cycles comprise shoaling-upward successions of limestone, shale sandstone, and conglomerate, which range in thickness between 50 and 200 m. The Grand-type cycles reach a maximum thickness of 300 m, typically consisting of basal limestone-dominated and upper shale-dominated half cycles. Together, these small- and medium-scale cycles form the building blocks of a mega-cycle up to 2300 m thick. The Kango cycle, as it is termed here, consists of a basal unit of Yoredale-type cycles followed by a middle unit of Grand-type cycles and an upper unit of limestone with minor dolomite. The Yoredale- and Grand-type cycles were deposited simultaneously but on landward and seaward parts of the shelf, respectively. Their vertical relationship indicates a major transgression of second-order duration, which was interrupted by third-order marine incursions possibly related to eustatic cycles. Continued subsidence eventually led to drowning of the platform and the onset of deeper water sedimentation with minor carbonates.