Eruptive and depositional processes and environments of the Paleocene-Eocene Sejong Formation, Barton Peninsula, King George Island, Antarctica

Abstract

The volcanic sequence in the Barton Peninsula, King George Island, Antarctica, ca. 300-500 m thick, consists of a lower volcaniclastic succession (Sejong Formation, 100-200 m thick) and an upper succession of basaltic-andesite lava flows interlayered with rare welded tuffs. The formation outcrops mainly along the southern coast of the peninsula and is transitionally overlain by the upper succession to the north. Recovered plant fossils indicate deposition of the formation during the Late Paleocene to Eocene. Previous studies have centered on the structures and petrology of the formation, but paid little attention to the eruptive and depositional processes and environments. This study focuses on paleoenvironmental reconstruction of the formation based on sedimentary facies analysis.The Sejong Formation can be grouped into three distinct facies associations (FA): (1) near-vent facies association (FA I), (2) volcanic-apron facies association (FA II), and (3) distal-apron facies association (FA III). FA I, occurring at base of the formation, consists of basaltic agglomerates and tuff breccias that are laterally gradational into massive/jointed ponded basalt lavas through a zone of brecciated basalt. FA II, unconformably overlying FA I, is represented by very thick, tabular beds of andesitic to basaltic, either welded or non-welded, lapilli tuff of pyroclastic-flow origin, rare intervening lava flows, and fluvial red sandstones/siltstones. FA III is a distal equivalent of FA II and, is characterized by channelized mass-flow conglomerates alternating with fluvial red sandstones/siltstones. FA I, showing intimate relationships among basaltic agglomerates, breccias, and vent-filling ponded lavas, suggests activity of Hawaiian or fire-fountaining eruptive centers early during deposition of the Sejong Formation. The overlying facies associations suggest onset of explosive and effusive eruptions of more evolved (intermediate) magmas, resulting in repetitive emplacement of ig