SEDIMENTARY PHASE OF SUMBA ISLAND (INDONESIA)

SEDIMENTARY PHASE OF SUMBA ISLAND (INDONESIA)
C.I. Abdullah a, E. Suparka a, V. Isnaniawardhani b
a Program Studi Teknik Geologi, Institut Teknologi Bandung, Jalan Ganesha 10 Bandung
b Teknik Geologi, Universitas Padjadjaran, Jalan Raya Bandung-Sumedang Km. 21
Jatinangor, Sumedang
ABSTRACT
The island of Sumba, presently located in the southern row of islands of the Eastern
Nusa Tenggara province of Eastern Indonesia, has a unique position, being part of the
Sunda – Banda magmatic arc and subduction system. It represents a continental
crustal fragment located at the boundary between the Sunda oceanic subduction
system and the Australian are continent collision system, separating the Savu Basin
from the Lombok Basin. New data on sedimentary rocks collected from Sumba are
presented in this paper, including biostratigraphy supported by lithostratigraphy and
geodynamic.
The stratigraphy of Sumba is composed of slightly to unmetamorphosed sediments of
Mesozoic age, unconformably overlain by considerably less deformed Tertiary and
Quaternary deposits.
Three distinct calc – alkaline magmatic episodes are recorded during Cretaceous –
Paleogene are : the Santonian – Campanian episode (86-77 Ma), the Maastrictian –
Thannetian episode (71-56 Ma), the Lutetian – Rupelian episode (42 – 31 Ma).
The island is distinguished into four sedimentary phase; they are : (i) The Late
Cretaceous to Paleocene stage (96 to 54 Ma) represented by marine turbidites
accompanied by the Santonian-Campanian (86-77 Ma) and the Maastrichtian-
Thanetian (71-56 Ma) magmatic episodes respectively; (ii) The Paleogene stage (66.5
to 25.2 Ma) represented by neritic sedimentation accompanied by Lutetian-Rupelian
magmatic episode (42-31 Ma); (iii) The Neogene stage (25.2 to 1.65 Ma) is
characterized by rapid sedimentation in a deep sea environment; (iv) The Quaternary
stage (beginning 1 Ma) was marked by the uplift of terraces.
The relatively simple tectonics of Sumba suggests that the island has never been
subjected to intense deformation. This implies that from Late Cretaceous-Neogene
time Sumba has never been involved in the collision between the Indian – Australian
and Asiatic plates, except during a minor compressive episode in the Paleogene.
Keywords : Sumba, Mesozoic, Paleogene, Neogene, Quartenary, biostratigraphy,
foraminifers, nannoplankton, geochronology, magmatic episode