TURBIDITES DEPOSITIONAL SYSTEMS OF THE LOWER HALANG FORMATION, STRATAL ARCHITECTURE OF SLOPE TO BASIN FLOOR SUCCESSION

TURBIDITES DEPOSITIONAL SYSTEMS OF THE LOWER HALANG
FORMATION, STRATAL ARCHITECTURE OF SLOPE TO BASIN FLOOR
SUCCESSION
M. Ma’ruf Mukti1, 4 , Cipi Armandita2, Hade Bakda Maulin3 and Makoto Ito4
1) Puslit Geoteknologi – LIPI, Jl. Sangkuriang Bandung 40135, telp: 022-2503654 fax: 022-
2504593, email: maruf.mukti@gmail.com; 2) BPMIGAS, Jakarta;
3) Paradigm Geophysical Indonesia, Jakarta; 4) Dept. of Earth Sciences, Chiba University, Japan
ABSTRACT
A sedimentological study in the western part of North Serayu Basin has been
conducted and concentrates on the lowermost, 350 m thick mud/sand-rich depositional
system of the Middle–Late Miocene Halang Formation. On the basis of field mapping,
observation of centimeter-scale lithofacies features and laboratory works, lithofacies
were identified and grouped into four lithofacies associations. These lithofacies
associations include: channel and overbank deposits, sheet-package sandstones,
sediment waves and/or distal overbank deposits, and hemipelagic deposits. Several
ash tuff beds and hemipelagic deposits intervals were used as datums for clarifying
spatial and temporal variations of the four lithofacies associations in seven measured
sections along the trough axis over 22 km. Overall, the succession shows downslope
direction to the east-southeast, with sand percentage range from 50%–25%. Features
observed in the channel-fills suggest the high-sinuosity patterns. Sheet-package
sandstones are interpreted to represent both frontal-splay and crevasse-splay deposits
in relation to channel-sheet package and overbank deposits, respectively. Some of the
geometry of fine-grained intervals exhibit wave-like geometry and interpreted to
represent sediment-waves on a distal overbank environment. Six stages of depositional
units have been mapped and their general pattern of the stages shows landward and
basinward movement of the Halang turbidite systems. The direction of paleotransport
from west-northwest to the east-southeast can be explained by the existence of a paleohigh to the west of research area that supply the sediment source to the lower
Halang Formation. The development of calcareous and volcanic deposition within lower
Halang Formation possibly indicates the development of proto-Ciremai and carbonates
equivalent to Parigi Formation in the Arjawinangun High to the northwest of research
area.