New Insight on Stratigraphy and Lithofacies of Banten Tuff Revealed from Eastern Flank of Rawa Danau Volcanic Complex, Java, Indonesia

Abstract

Rawa Danau Volcanic Complex (RDVC) in the western part of Banten—Western part of Java Island, Indonesia, holds records and histories of past violent volcanic eruption. These past volcanic activities manifested as huge Rawa Danau caldera and massive Banten Tuff pyroclastic deposits that are distributed for more than ten kilometres away from the source and have played an important role in shaping the morphology of Banten. Previous studies suggest that Banten Tuff is composed of various pumiceous pyroclastic deposits presumably formed in Early Pleistocene. The deposits cover vast area of Banten, and their thickness exceeds 200 m. Despite their significance, there are no detailed studies that discuss the stratigraphic and eruption dynamics of the deposits. This paper provides new insight on the eruption dynamics based on fieldwork observation, volcanic stratigraphy, and petrologic interpretation. The study focuses on the eastern flank of RDVC, where the well-preserved stratified outcrops are located. Aligned with previous studies, the deposit can be divided into two major eruption sequences: 1) Lower Banten Tuff (LBT) and 2) Upper Banten Tuff (UBT). LBT is interpreted as lithic-bearing ignimbrite with accompanying surge deposit and considered as a single-phase eruption. Lithic-rich characteristics in this unit suggest that LBT might be related to the caldera-forming mechanism. On the other hand, UBT shows a more dynamic sequence. It is composed of two fallout units followed by an ignimbrite formed by the eruption column collapse. The appearance of banded pumice in UBT with contrasting andesitic and rhyolitic compositions suggests a mafic injection as the eruption trigger. Pumice and ash compositions are mostly in dacitic to rhyolitic range, with several samples in andesitic range. Componentry analysis suggests that all eruptions were magmatic in origin.