Lithofacies and volcano-sedimentary evolution of the Paleocene—Eocene Sejong Formation, Barton Peninsula, King George Island, Antarctica

Abstract

The Paleocene—Eocene volcanic succession (ca. 500 m thick) in the Barton Peninsula, King George Island, Antarctica has been regarded as a stratiform complex formed in an island-arc setting. However, responsible eruptive and depositional processes and environments have been poorly constrained. This study conveys a detailed facies analysis and field mapping and attempts to reconstruct the volcano-sedimentary evolution. Three distinct facies associations are identified from the lower part (Sejong Formation) of the Barton volcanic succession. At the base of the succession, Facies Association (FA) I occurs as semi-circular patches in map view, forming distinctive edifice of massive or vertically jointed basalts along with fringing piles of basaltic flows, agglomerates and tuff breccias. FA 1 is thus interpreted as spatter-cinder cones formed by Hawaiian fire-fountaining to Strombolian eruptions, probably at peripheral parasitic vents. The overlying, either conformably or unconformably, FA II is represented by very thick, tabular beds of andesitic to basaltic, either welded or non-welded, lapilli tuffs and tuff breccias, and rare intervening lava flows. The repetitive emplacement of ignimbrite sheets and attendant lava flows suggests onset of explosive and effusive eruptions of more evolved (intermediate) magmas from the main central vent and consequent build-up of a large-scale stratovolcano. FA III, consisting mainly of fluvial red sandstones/siltstones locally with channelized mass-flow conglomerates, occurs in fault contact with FA I or intercalated with FA II deposits. It most likely represents intermittent floodplains in low lands extending from lower slopes of the stratovolcano of FA II during inter-eruptive periods. Identification of spatter-cinder cone complexes (FA I) and the proper designation of the overlying pyroclastic-flow deposits (FA II) in this study provide a crucial basis in genetic understanding of the Barton volcanic succession in relation with