GEOLOGICAL OF THE DILI SHEET

STRATIGRAPHY


Stratigraphic of the dili geological map as below;
Qal ALLUVIUM DEPOSIT; loose sediments, clay to boulder sized, tens of metre thick.

Qs SUAI FORMATION; Weakly consolidated coastal deposits consisting of cobble, sand and silt, contain foraminifera, supposed to be Late Pleistocene – Holocene on the basis of the stratigraphic position and the gentle deformation. Approximately 100 meter thick.

Qpa AINARO FORMATION; Old river deposits forming terraces; consists of polymict conglomerate, sand and clay; weakly consolidated, based on stratigraphic position supposed to be Pleistocene – Holocene in age; approximately 100 meter thick.

Qpb BAUCAU LIMESTONE; Coral reef with alternations of calcarenite; unconformably overlies the Viqueque Formation suggesting Pleistocene – Holocene in age; with shallow marine depositional environment, thickness up to 300 meter.

Tpd DILOR CONGLOMERATE; Cross-bedded conglomerate, sandstone and siltstone; Pliocene in age on the basic of stratigraphical position and foraminifera content (Crespin, 1958, in Audley-Charles, 1968) depositional environment supposed to be shallow marine to delta; thickness up to 300 meter.

Tpv VIQUEQUE FORMATION; Alternating conglomerate, conglomeratic sandstone, sandstone and marl; a lot of foraminifera in marl and sandstone; N12-N22 (Plio-Pleitocene) in age, deposited in shelf to upper slope, 800 meter thick.

Tmb BOBONARO COMPLEX; Chaotic rock with scaly clay matrix and blocks of older rock, possibly Late Miocene in age, contains marine foraminifera.

Tmc CABLACI LIMESTONE; Clastic limestone, generally crustalline, fine to coarse grained; white, light greyand pinkish grey coloured; thickly bedded to generally massive; contain larger foraminifera, Early Miocene in age, with shallow marine depositional environment, thickness up to 600 meter.

Ted DARTOLLU LIMESTONE; Mainly composed of bedded calcarenite, brown coloured, consist of two types, i.e. those contain algae and those contain foraminifera; Late Eosen in age; deposited in shallow marine environment, thickness up to approximately 100 meter.

Kw WAIBUA FORMATION; Mainly composed of radiolarian shale, bedded chert, radiolarire, calcarenite and calsirudite; the radiolarian indicates Early Cretaceous age (Crespin & Belford, in Audley-Charles, 1968), with deep marine depositional environments; thickness 500 meter.

Jw WAILULI FORMATION; The lower part in dominated by sandstone; shale siltstone and limestone caontaining belemnites increase upwards, Early Jurassic – Middle Jurassic in age, represents turbidites in relatively deep marine environment; thickness up to 600 – 800 meter.

TRa AITUTU FORMATION; Mainly composed of calcilutite, with chert nodules in some place; locally calcarenite, shale and thin alterations of marl; generally light grey coloured and well bedded, fossils content Holabia and Monotis (Audley-Charles, 1968); Late Triassic in age, with shallow marine environment, thickness up to hundreds of metres.

Pa AILEU FORMATION; Phylite, schist, amphibolite, slate, metasandstone, sandstone, shale, few volcanics rocks and limestone; metamorphism and deformation weakwn southwards; probably Permian to Late Jurassic in age, on the basis of the fossils content reported by Brunschweiler (1977, in Charlton, 1992), i.e. the Permian Crinoids and the Late Jurassic Buchia belemnopsis; with shallow marine environment; thickness up to hundreds of metres.

Pm MAUBISSE FORMATION; Alternating doleritic lava, volcanic clastic, limestone and shale, the limestone contains crinoid and fussulinid fossils; Globiella foordii (Etheridge) which is typical of Gondwana Land was found (Hasibuan, 1994); Permian in age, with shallow marine environment, thickness up to 500 meter.

Pc CRIBAS FORMATION; Shale, claystone, siltstone, micaceous quartz sandstone; calcilutite dominates upward; Permian foraminifera and pelecypods have been reported previously; with shallow marine depositional environment, thickness 500 meter.

Pat ATHOC FORMATION; Quartz sandstone, black shale, calsilutite and the amygdaloidal basalt pre-dominating the upper part; caontains ammonites of Early Permian age (Audley-Charles, 1968), with shallow marine depositional environment, thickness 600 meter.

pPl LOLOTOI COMPLEX; Doleritic lava, volcanic breccia, tuff, green sandstone, meta-gabbro, metadiorite; generally strongly fractured and sheared; probably pre-Permian in age, thickness to be thousands of metre.

Units of Dili Geological Map, Timor Leste
Figure : Correlation of the Geological Map Units

LITHOTECTONIC SUBDIVISION


The rocks in the Dili sheet can be categorized into three lithotectonic units, i.e.:
  1. Parautochtonous unit which is derived from the Australian passive margin.
  2. Allochtonous unit which is derived from the pre-collisional Banda forearc
  3. Autochtonous unit comprising the rocks deposited in the pot-collisional Banda forearc.

STRUCTURE AND TECTONICS


Timor Island is a collision complex between the Australian continent and the Banda Arc subduction system. The peak of collision occurred during Late Miocene – Pliocene, and is supposed to have resulted in metamorphism particularly on the Aileu Formation which previously probably occupied the most distal part of the Australian passive margin. The collision also resulted in formation of chaotic rocks and formation of fold and faults, particularly thrust faults or overthrust.

During the collision, part of the pre-collisional Banda forearc rocks were overthrusted onto the rocks derived from Australia. Since the collision in Late Miocene – Pliocene the autochtonuos deposits are deposited in the post-collisional Banda forearc.

The collision between Australian Continent and the Banda Island Arc is supposed to be still active up to now resulting in faulting and folding in the Pleistocene and the pre-Pleistocene rocks, and gentle tilting on the younger deposits. In Pleistocene Ainaro Formation, mesoscopic open folds were found.

Tectonic activities during the recent times are shown by seismicity activities, shale diaper intrusions, active mud volcanoes and faults (Rosidi, et al, 1981), and uplifting as well as subsidence (Tjia, 1979; Tjokrosapoetro, 1978).

MINERAL AND ENERGY RESOURCES


The occurences of gold, silver, chromite, bentonite, wollastonite and gypsum has been previously reported. The young rocks of fluvial and coastal deposits, such as Ainaro Formation and Suai Formation are recommendable for further investigations on the occurances of placer deposits, particularly gold. Limestone and marble have been locally mined. 

The occurences of petroleum is indicated by the presence of oilseeps found in relatively old rocks, such as Cribas Formation, Aitutu Formation and Wailuli Formation, as well as in relatively young rocks, for instance in the Viqueque Formation. Some of the Paleozoicum and Mesozoicum rocks containing bituminous shale, such as the Cribas Formation and the Wailuli Formation can be the oil source rocks.

Geological map of the Dili sheet can be downloaded at the following link : 2406-2407 Dili


Reference
S. Bachri and R.L. Situmorang, Geological Map of the Dili Sheet, 1994.
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