Page 81 - Sumatra Geology, Resources and Tectonic Evolution

68 CHAPTER 6

Table 6.4. Volcanic units' in the West Sumatra Permian Plutonic- Volcanic Belt
Formation Unit Area Age Thickness (m) Description Reference
Kluet (uncertain Sibolga Early Permian Poorly sorted volcanic Aspden et al. (1982b)
affinity) wackes in roof-pendants
of the Sibolga Granite
Complex
Panti Volcanic Lubuksikaping Probable Permian Varied greenschist facies Rock et al. (1983)
sheared metavolcanics and
non-foliated
volcaniclastics
Silungkang Lubuksikaping Mid-Late Permian Meta-limestones, porphyritic Rock et al. (1983)
(correlation) metavolcanics, metatuffs,
volcaniclastic sandstones
and hornfelsed tufts
Silungkang Calcareous SE Danau Sakmarian-Wordian Sandy limestone, calcareous Silitonga & Kastowo
Member Singkarak stages of Permian sandstone, and clay shale (1975)
(type area) with a few intercalations of Katili (1969)
agglomeratic tuff and
several flows of augite
andesite and basalt
Volcanic c. 1500 Hornblende andesite, augite
Member andesite, meta-andesite
and meta-dacite with thin
intercalations of tuff,
limestone, shale and
sandstone mixed with
tuffaceous material
Silungkang Calcareous Outliers: ?Roadian- Wordian Hard, fractured, locally Silitonga & Kastowo
(formerly Member Near Tanjung vesicular, dark-grey to (1975): age revised
Kuantan) Gadang green-grey basalt with a by Gafoer et al.
Lubukkarak trachytic texture and (1992a)
composed of felsic and
mafic minerals set in a
microlilic groundmass;
diabase
Tabir S. Tabir Mid Permian 150/450 Conglomerate and tuffaceous Rosidi et al. (1976)
sandstone with
intercalation of pisolitic
andesite tuff
Palepat B. Palepat Artinskian-Wordian 1100 Andesitic > acidic lavas and Rosidi et al. (1976)
stages of Permian tufts; randomly distributed
basalt and rhyolite. Also
siltstone, shale and
limestone
B. Tabir > 800 Volcaniclastic rocks, lithic Simandjuntak et al.
and crystalline tufts and (1991)
andesitic lava, locally
diabasic; local clastic
sediment interbeds
B. Tantan >200 Andesitic-dacitic lavas, tufts, Suwama et al. (1994)
diabase, and volcanic
breccias containing clasts
of andesite and dacite,
intercalated with shale,
siltstone, sandstone,
claystone and limestone;
commonly altered and
metamorphosed
Mengkarang B. Mengkarang Asselian Stage ?500 Acid-basic tuff intercalations Suwarna et al. (1994)
in shallow-marine-
terrestial sediments

Sumatra Fault Zone, but Zwierzijcki (1930a) subsequently attrib- and can be dated palaeontologically. Andesitic-dacitic volcanism
uted these outcrops to the Cretaceous, so that they are currently commenced in the Asselian and peaked in the Artinskian
considered to be part of the Woyla Group. (Fontaine & Gafoer 1989). The Tabir Formation, previously
In the southern outcrop, the predominantly volcanic Palepat believed to be of Jurassic age (Suwarna et al. 2000), but now
Formation (Suwarna et al. 1994) interfingers with the lower known to be Permian, interfingers with, and overlies the Palepat
parts of the terrestrial to shallow marine Mengkarang Formation and the Ngaol formations. The Ngaol Formation (obsolete term)