Late Miocene to Pliocene Tsunami Deposits in Tegal Buleud, South Sukabumi, West Java, Indonesia

Yan Rizal,Nur Rochim,Mika R Puspaningrum,Jahdi Zaim,Aswan Aswan,Wahyu D Santoso

doi:10.5539/mas.v13n12p80

Abstract

Java is a volcanic island arc formed by the northwards subduction of the Eurasian and Australian Plates. Due to this active subduction, Java has been frequently shocked by earthquakes, which might induce tsunami events. However, there are hardly any ancient geological records of tsunami events in the area. This study aims to determine the presence and to identify sedimentary characters of tsunami deposit in Tegal Buleud, South Sukabumi, West Java. In the study area, there were 4 tsunami layers which were found as thin intercalation within the claystone layer of the Bentang Formation. Those paleotsunami deposits characterized by the occurrence of irregular/disturbed structure such as siltstone rip up, clay clasts, and flame structure occur in normal graded bedding sandstone layer. The grain-size distributions show bimodal and multimodal patterns, with mixing of marine microfossils from inner and middle neritic. The planktonic foraminiferal assemblage indicates that the age of the sediment comparable to N19 (equivalent to Late Miocene - Early Pliocene, at about 5.33 &ndash; 3.6 Ma), suggested that these paleotsunami layers were deposited due to the Mio-Pliocene tectonic activity. All the paleotsunami deposits found in Study area are the first and oldest tsunami deposit recorded in Java even in Indonesia. With the discovery of the previously unexplored Late Miocene to Pliocene tsunami deposits found in the study area, the result of this study can be used as a reference for the identification of the Tertiary tsunami deposits present in other parts of Indonesia.

Highlights

The Indonesian Archipelago is located in a very active tectonic zone, at the boundary of three large plates of the world and nine other small plates that collide each other and form complex meeting paths of plates (Bird, 2003)
With the discovery of the previously unexplored Late Miocene to Pliocene tsunami deposits found in the study area, the result of this study can be used as a reference for the identification of the Tertiary tsunami deposits present in other parts of Indonesia
The lithological units studied in Tegal Buleud consist of claystones that belongs to Late Miocene to Pliocene of Upper Bentang Formation

Summary

Introduction

The Indonesian Archipelago is located in a very active tectonic zone, at the boundary of three large plates of the world and nine other small plates that collide each other and form complex meeting paths of plates (Bird, 2003). The tectonic structure of the western part of Indonesia, or known as the Sunda Arc including Java Island, is formed by the collision between the moving northward Indo-Australian plate and the relatively idle Eurasian plate (Hamilton, 1979 and Hall, 1998). Sources of the earthquakes in Java that has been clearly identified are the active subduction zone at the south of the island (Figure 1). West Java is one of the regions that exemplify high tectonic activity, including earthquakes. Java tectonics is dominated by subduction to the north of the Australian Plate under the Eurasian Plate with an approximate movement of 6 cm/year with near normal direction to the trough, 100-200 km below the island of Java. Volcanic and sedimentary activities that have taken place since the Late Cretaceous produced a series of lithological formations in West Java. The outcrop of the shallow marine Bentang Formation in particular, is well-exposed in Tegal Buleud (Figure 1)

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