THE GENERAL GEOLOGY OF AIR PAPAN AREA, EAST JOHOR, PENINSULAR MALAYSIA: EMPHASIS ON FRACTURE PATTERNS AND ITS STRUTURAL IMPLICATION

East Johor is mainly composed of Palaeozoic rock, which is covered by three formations,
which are Mersing Formation, the oldest formation, followed by Murau Conglomerate
and the youngest Jasin Volcanic at that region. Intense deformation took place in the old
days resulted in a variety of fracture systems. By studying the geological structures in
eastern Johor, paleo-stress can be analysed with the understanding on structural patterns.
Besides, the fracture network of the rocks can be further studied in order to find out its
possibility to be one of the fractured reservoir analogues. This study comprises two
significant parameters: deformation patterns and impacts of fractures. By conducting a
fieldtrip to the study area – Mersing-Endau and having a detail observation at the focal
point – Air Papan, required data, such as fracture system measurement, outcrop
observation and rock sample collection were acquired. The observed area is highly
fractured and composed of two lithologies; they are named as Lapilli Tuff and tuff. The
results of XRD reveals that the Lapilli Tuff and tuff are composed of quartz. Their
origins are most probably related to the volcanism which is associated with the
subduction of Sibumasu underneath the East Malaysia Block (Indochina Blocks) during
the Permo-Triassic. A total of 512 fracture readings were measured to study the paleostress
field. Four fracture sets were identified, which are N-S (F1), NE-SW (F2), E-W
(F3) and WNW-ESE (F4) directions. Most of these fractures are steeply dipping, with
the value more than 70°. Fractures formed in Lapilli Tuff, show a quite consistent
fracture pattern. They have been analysed and possible conjugate fracture set was
interpreted in N-S (F1) and E-W (F3) directions, which possible induced by a NE-SW
compression. Similarly, the Penyu Basin, which is approximately 109km to Northeastern
Air Papan, comprised of E-W trending half grabens in the western part which is
possible to be related to E-W fractures in this region. As an implication, the Air Papan
coastline is possible have structural relationship with Penyu Basin, and could be an
analogue of fractured basement.