Mesozoic stratigraphy and geological history of Papua New Guinea

Abstract

The present-day distribution of Mesozoic rocks in Papua New Guinea is interpreted as having developed as a consequence of a mid-Tertiary continent/island-arc collision between the northeast margin of the Australian continent (Papuan Platform) and a southerly facing Cainozoic island-arc system (Northeast Island Arc Province). The zone of interaction (the Central Orogenic Belt) can itself be divided into an outer zone of strongly folded, faulted and partly metamorphosed eugeosynclinal sediments, volcanics and ophiolitic rocks (New Guinea Mobile Belt) and an inner foreland zone of folded and thrusted miogeosynclinal sediments (Papuan Fold Belt). The Mesozoic geology of Papua New Guinea is a history of sedimentation and volcanism that evolved in two distinct environments. The Mesozoic succession that now occurs along the southern portion of the Central Orogenic Belt and across the Papuan Platform developed on and around the margins of a northern extension of the Australian continent (Fly Association), and the succession that now occupies the northern and eastern portions of the Central Orogenic Belt developed around the margins of a volcanic arc (Sepik Association). The Fly Association is poorly exposed in the Papuan Fold Belt and has been encountered in widely spaced petroleum exploration wells over the Papuan Platform. Thin fluvio-deltaic and marginal marine sediments were deposited over the stable Platform. Over the block-faulted margins of the Platform, thick, shallow-marine, miogeosynclinal sediments were deposited in elongate basins, while thinner clastics, volcanics and minor limestone accumulated over adjacent basement highs. Thicker sequences of volcaniclastic shale, siltstone, and minor sandstone were deposited beyond the continental basement. In the Cretaceous these were, in places, intercalated with volcaniclastic material of the flanking Sepik Association. The eugeosynclinal Sepik Association and associated ophiolite segments are now exposed in the New Guinea Mobile Belt. Sedimentation in the Sepik Association may have begun in the Jurassic but mainly occurred in the Cretaceous. During the Early Cretaceous a volcanic arc developed to the north and east of the Fly Association. The arc is envisaged to have developed as a continental margin volcanic arc separated from the Platform sequence by retro-arc basins and, in places, evolved to form remnant arcs separated from frontal volcanic arcs by interarc/back-arc marginal seas. Evidence of admixing of the Fly and Sepik Associations occurs locally, but generally they are mainly separated by major fault zones or their relationships are concealed by Cainozoic cover.