The Paleocene-Eocene volcanic succession in the Barton Peninsula, King George Island, Antarctica: lithofacies, eruption styles and depositional processes

Abstract

1. IntroductionThe volcanic succession in the Barton Peninsula, King George Island, Antarctica, has been regarded as a stratiform complex formed in an island-arc setting. It consists of a lower volcaniclastic succession (Sejong Formation, 100–200 m thick) and an upper succession (ca. 200-–300 m thick) of basaltic-andesite lava flows interlayered with rare welded tuffs (Tokarski 1988, Birkenmajer 1998, Lee et al. 2002). Recovered plant fossils indicate deposition of the formation during the Late Paleocene to Eocene (Chun et al. 1994). Previous studies have centered on the structures, petrology and geochemistry of the volcanic rocks, but paid little attention to the responsible, eruptive and depositional processes and environments (Yoo et al. 2001). This study focuses on the Sejong Formation and attempts to reconstruct volcano-sedimentary evolution based on detailed facies analysis and field mapping. A revision on the stratigraphy is proposed; the basaltic rocks that have been attributed as late-stage intrusion (dikes or plugs) are reassessed as lava/agglutinate complexes at the base of the Sejong Formation and are designated as Chottae Member.2. Lithofacies and Facies AssociationsBased on composition, texture (coherent vs clastic) and grain size, nine lithofacies are identified in the Sejong Formation: basaltic lava (lithofacies BL), basaltic agglutinate (BA), basaltic tuff breccia (BTB), basaltic lapilli tuff (BLT), andesitic lava (AL), andesitic tuff breccia (ATB), andesitic lapilli tuff (ALT), reworked conglomerate (C), and sandstone/siltstone couplets (S/Z). These volcanic rocks can be grouped into three facies associations based on the constituent facies, facies sequences, and their field relationships. Each facies association records formation in distinct eruptive and/or depositional environments: (1) spatter/cinder cones (Facies Association (FA) I), (2) volcaniclastic apron (FA II), and (3) distal apron to floodplain (FA III).2.1. F