Shallow-water volcaniclastic deposition in the Early Archean Panorama Formation, Warrawoona Group, eastern Pilbara Block, Western Australia

Abstract

The Panorama Formation of the 3.3–3.5 Ga Warrawoona Group in the eastern Pilbara Block, Western Australia, is a regional unit composed largely of silicified felsic volcaniclastic sandstone and tuff deposited at the close of a major period of early Archean felsic volcanism. It is divided into eight lithofacies: (A) volcaniclastic tuff and tuff-breccia, (B) chert-clast conglomerate, (C) well-bedded tuff and tuff-breccia, (D) cross-stratified volcaniclastic sandstone, (E) laminated and cross-laminated siltstone, (F) banded chert, (G) silicified evaporite, and (H) felsic lava. Wave-formed features occur in lithofacies B, C, D, and E. The eight lithofacies occur in four facies associations: (1) sequences of banded chert with lesser amounts of tuff, representing clastic-starved probable basinal environments, (2) sequences of siltstone with variable amounts of tuff, representing lower shoreface and prodelta environments, (3) sequences of cross-stratified sandstone with one or more other facies, representing upper shoreface, fan-delta front, and braided-stream environments, and (4) sequences of turbiditic and ash-fall tuff, representing subaqueous settings under the direct influence of pyroclastic volcanism. In the North Pole Dome, the Panorama Formation is developed directly over basalt and consists of shoaling-upward sequences, from base to top, of associations 1, 2, and 3, interpreted as sedimentation in prograding fan-delta complexes flanked laterally by shoreface environments. In other areas, associations 3 and 4 are developed over thick sections of felsic lava and breccia of the Duffer Formation. Felsic volcanism controlled sediment composition, sediment size, and the rate of sediment supply to surrounding epiclastic systems. Deposition took place under regionally developed shallow-water to subaerial conditions in which deep-water distal facies were not well developed. Despite the abundance of wave-influenced shallow-water environments, evidence for tides is rare, probably because deposition took place under regionally microtidal marine conditions.