Page 51 - Sumatra Geology, Resources and Tectonic Evolution

38 CHAPTER 4

lavas and tufts interbedded with siltstones and crystalline (Vachard 1989a, b). The fauna has affinities with the fauna of
limestones, which they considered to be a volcanic member of the Lower Permian of China and Central Europe (Fontaine &
the Barisan Formation. It is also equivalent to the volcanic unit Gafoer 1989). Fusulinids indicate that the plant beds are of
forming lower part of the Silungkang Formation, described Upper Asselian age, possibly extending into the Sakmarian (Fon-
above. The interbedded limestones are sometimes fossiliferous, taine & Gafoer 1989, footnote on p. 55).
and fragmental brachiopods and crinoids occur in the tufts. The
foraminifer Fusulina sp. was identified from limestones in Bukit Pendopo (Fig. 4.10). Limestone cropping out in Bukit
the Sungai Tabir. A rich brachiopod fauna and the fusulinids Pendopo in the core of a faulted anticline on the Lahat Quadrangle
Veerbeekina and Sumatrina described by Meyer (1920) and Sheet (Gafoer et al. 1986b) has yielded abundant Permian fossils
Tobler (1923) from the Sugai Selajau indicates a Lower Permian including fusulinids, small foraminifera and algae. The fusulinids
age (Fontaine & Gafoer 1989). include Arminina asiatica, Cancellina praeneoschwagerinoides
and Neoschwagerina simplex. These fossils indicate an Early
Ngaol Formation (Fig. 4.5). The Ngaol Formation, defined Murghabian age for this limestone outcrop (Tien 1989).
by Rosidi et al. (1976) in the southeastern part of the Painan
Quadrangle Sheet, includes a Limestone Member with Fusuli-
nella, Sumatrina and Siphoneae (Tobler 1922). High-grade meta- Pemali Group (?Carboniferous-Early Permian) (Fig. 4.10)
morphic gneiss, schist and marble cropping out in the same area
were also inappropriately included in this unit (Rosidi et al. As mentioned above, rocks of Carboniferous-Permian age on the
1976). Fontaine & Gafoer (1989) report that limestones in the islands of Bangka and Billiton have been termed the Pemali
Sungai Tabir downstream of Ngaol village are rich in Middle Group. The Pemali Group in the Taboali District on the southern
Permian fossils, while upstream the rocks are of Jurassic age, tip of Billiton includes 'pebbly mudstones', identical to those of
and recommend that the recognition of the Ngaol Formation as a the Bohorok and Mentulu formations of mainland Sumatra.
separate unit should be abandoned. Again, the Permian rocks in Permian fusulinids were found at Air Durin on the island of
this unit may be regarded as part of the Silungkang Formation.
Bangka by De Roever, in limestones forming part of the Pemali
Group (De Neve & De Roever 1947; De Roever 1951; Ko
Mengkarang Formation (Fig. 4.5). The Mengkarang Formation, 1986). Early Permian fusulinids have also been found offshore
famous internationally for its 'Jambi Flora', was defined by the north coast of the adjacent island of Billiton (Belitung)
Suwarna et al. (1994) from outcrops in the Mengkarang River
(van Overeem 1960; Strimple & Yancey 1976). Other Permian
and adjacent river sections to the SW of Bangko. In earlier descrip- fossils recorded from Billiton include the ammonoid Agathiceras
tions this formation was divided into the Air Kuning, Salamuku sundaicum of latest Artinskian or earliest Kungurian age, found as
and Karing Beds (Zwierzijcki 1935), but these terms are now float in a tin placer (Archbold 1983). Archbold (1983) relates
considered to be obsolete (Fontaine & Gafoer 1989). Rock types this form, and also a Permian nautiloid Neorthoceras to the
in the Mengkarang Formation include conglomerate, sandstone, Permian Bitauni fauna of Timor (Charlton et al. 2002). Strimple
siltstone, claystone, sometimes carbonaceous, limestone and thin & Yancey (1976) report the occurrence of the crinoid Moscovi-
coals. The sandstones are poorly sorted and clasts in conglomer- crinus from Selumar of probable Early Permian, Sakmarian age
ates and sandstones include volcanics, quartzite and vein quartz (Archbold 1983), and undescribed plant fragments of general
(Simandjuntak et al. 1991). Outcrops in the banks of the Batang Permian age have been ascribed to the Cathaysian floral province
Tembesi at Pulau Bayer are composed of sandstone and polymict (van Overeem 1960).
conglomerates with wood fragments and with a siliceous cement.
The sandstones are folded into an anticline on an east-west axis,
overturned towards the north. Thin intervening shales have not
Tempilang Sandstone (Mid-Late Triassic) (Fig. 4.10)
developed a slaty cleavage. These outcrops show imbrication of
thin sandstone beds, indicating westward-directed thrust move-
ments, prior to the folding. On the opposite side of the river, The Middle to Upper Triassic Tempilang Sandstone crops out
vertically bedded grey limestones show algae, bryozoa and gaster- extensively in Bangka Island (Ko 1986). A limestone intercalated
opods weathering out on the surface. Numerous fossil localities in with sandstones and shales in the Lumut Tin Mine yielded
the Mengkarang Formation which have yielded algae, fusulinid Entrochus, Encrinus, Montlivaltia molukkana and Perodinella
foraminifera, brachiopods, gastropods, crinoids and corals are which were attributed a Norian age (De Neve & De Roever
indicated on maps by Fontaine & Gafoer (1989, Figs. 13 & 14). 1947). The characteristic Late Triassic thin-shelled bivalve
The 'Jambi Flora' was originally described by Zwierzijcki Daonella has been reported from the island of Lingga to the
(1935), Jongmans (1937) and Marks (1956). The flora and fauna north of Bangka (Bothe 1925b).
have more recently been reviewed by Asama et al. (1975),
Vozenin-Serra (1989) and Fontaine & Gafoer (1989). Asama
et al. (1975) concluded that the flora, which is rich in lycophytes, Conclusions
pteridophytes, pteridosperms, cordaites, and gymnosperms, is
composed entirely of Euramerican and north Cathaysian species As presently defined (Cameron et al. 1980; McCourt et al. 1993),
and includes no Gondwanan species. It is older than the typical the Peusangan Group includes units of both Permian and Triassic
Cathaysian Gigantopteris flora and may represent an earlier age. Permian rocks occur throughout the island of Sumatra from
stage in its development (Asama 1976, 1984). Vozenin-Serra Aceh in the north to Bukit Pendopo in the south as well as in
(1989) reported the occurrence of Cordaites and coniferous Bangka and Billiton. Triassic rocks are known only from the
wood fragments collected by Fontaine. These wood fragments northern part of the main island of Sumatra, to the north of the
do not show annual rings, which is taken to indicate that they equator, but also occur extensively in Bangka and Billiton
grew in a tropical or semi-tropical environment. After reviewing (Fig. 4.10). The palaeontological evidence for the age of the
the flora, Vozenin-Serra (1989) concluded that it corresponds Permo-Triassic units in Sumatra as determined by Fontaine &
with the oldest horizon of the Cathaysian flora of northern China Gafoer (1989) is illustrated in Figure 4.11.
and represents the southernmost record of this flora. The only possible representative of the Lower Permian in north-
The plant-bearing horizons containing the Jambi Flora are inter- ern Sumatra is the Pangururan Bryozoan Bed whose age, on
bedded with limestones containing fusulinids, tabulate and the basis of its fauna, has not been definitively established. In
rugose corals, brachiopods and a rich tropical algal microflora southern Sumatra on the other hand Lower Permian rocks