Page 100 - Sumatra Geology, Resources and Tectonic Evolution

TERTIARY STRATIGRAPHY 87

I I I
~P 94 ~ 96 ~ 98 ~
~ ANDAMAN
"~ SEA
GULF
................................................... .... ~ ..... / / /
/
-6 ~ oF
.
Banda [ NORTH .... :':/
SUMATRA 9
"X BASIN
MALAY~"
N
-- 4~ NA, TUN A"
\ ISLAND'S

N
N "~ NA TUNA
_2 ~ \ / SEX ,
\
\ 0
\
,~ N i A~
\ ISLANDS
/
_0 o BATU
\ ISLAND LINGGA
ISLANDS
\
M'B 1 L 1 N ~
, 0 < B'A\S IN >= ,

.
.
.
.
~\ s IBERU~T
L._
_ 2 ~ INDIAN
OCEAN
),N t~
M EN TA ~W-#~
%\ ~" ISLANDS
"5
k__.
Sumatran Tertiary basins outlins ~, 4,,
N
_4 ~
N O
Sundaland continental crust
\~, a,
Volcanoes N
A
N
\
Sumatran Fault System
"~ ENGG2
\
_ 6 ~ ~. \
Subduction zone
\
0 100 200 300 400 500km
94 = 96 ~ 98 ~ 1 00 ~ 1 02 ~ \
I I I I I
Fig. 7.1. Structural sketch map of Sumatra showing the Tertiary backarc, forearc and intra-arc basins and localities mentioned in the text.
applied in modified form to the forearc basins, and is only appli- In the earliest stages of sedimentation on Sumatra, Tertiary
cable in the most general way to the forearc islands. The strati- shallow-water continental margin sediments were deposited
graphic relations between this scheme and the most commonly directly on the eroded surface of the Sundaland pre-Tertiary base-
recognized formations in Sumatra are shown in Figures 7.6-7.8. ment. Deposition followed a period of erosion considered to
extend from the latest Cretaceous into the early Tertiary. In the
backarc area these deposits, which include the Tampur and
Pre-Rift stage (Eocene) Meucampli formations (Fig. 7.2), are restricted to the North
Sumatra Basin. In South Sumatra, Eocene Nummulitic limestones
Sediments of the Pre-Rift stage are relatively poorly represented occur on the margins of the Bengkulu Basin (Gafoer &
in Sumatra, but are more common elsewhere in Sundaland. Purbo-Hadiwidjoyo 1986). In Central Sumatra, no formations
Platform limestones that have been dated as Eocene occur uncon- are known from this stage, but their former presence is docu-
formable on pre-Tertiary basement in Java, Sulawesi and Borneo. mented by reworked clasts of Nummulitic limestones in Early
A comprehensive report on these limestones is presented in Tertiary conglomerates and melanges of the outer arc islands
Wilson (2002). The units characteristically are distributed along (van Bemmelen 1949; Budhitrisna & Andi Mangga 1990;
the margin of the Sundaland pre-Tertiary basement and they Samuel et al. 1997).
clearly predate the subsequent formation of horst and graben The Tampur Limestone of North Sumatra is described by
structures. van Bemmelen (1949), Cameron et al. (1980, 1982a),