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Relation of Syn-Depositional Faulting with Carbonate Growth using Miocene Carbonate Platforms of Central Luconia Province, Malaysia


Abstract and Figures

Interpretation of two Miocene carbonate platforms in Southeastern part of Central Luconia Province has provided an insight of the structural history of the platforms, relating syn-depositional faulting with the platform evolution and it’s internal architecture. Six horizons have been interpreted on both platforms. These horizons represent four different stages of carbonate growth, starting with build-out phase, followed by build-up and build-in phase. Internal architecture of these platforms ranges from standard layer-cake of carbonate platform with flat top (Platform FY) to sub-circular, steep sided margins that appear tilted and ends-up in pinnacle look-alike before carbonate production stopped (Platform EX). Siliciclastic influxes from Borneo deltas have favoured platform growth by suppling nutrients to the reef at the time of carbonate deposition. It also affected the demise of the platforms by providing extra clastic input that created unfavourable water environment for carbonate growth, and leds to subsidence and collapse of the platforms due to increase of gravity loading from rapid accumulation of sedimentary deposits above the platform. Faults are widespread throughout both platforms. All faults are normal, and seem to govern the overall north-south elongation of platforms in Southeastern part this province. However, individual faults are preferably trending NE-SW with dipping angle of approximately 15°-50°. The platforms were tilted, due to major faulting and increase of overburden from growing carbonate layers. As the platform tilted, lateral environmental facies on the platform changed from reef build-up to quiet lagoonal facies environment. The changes are observed laterally over an approximately 2.5- 3.5km distance.
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Relationship between syn-depositional faulting and carbonate
growth in Central Luconia Province, Malaysia
S.N. Fathiyah JamaludiN*, maNuel Pubellier & david meNier
Geoscience Department, Faculty of Geosciences & Petroleum Engineering,
University Technology Petronas, 31750 Tronoh,Perak, Malaysia
*Email address:
Abstract: Using 3D seismic and well data, detailed seismic interpretation has been conducted on two carbonate Platforms
EX and FY located in the Central Luconia Province, Malaysia. The results provide an insight to understand the relationship
of faulting with syn-depositional carbonate growth. Five geo-seismic units were interpreted from the Late Oligocene
to present day sedimentation in the basin. Structural interpretation of both platforms shows that almost all the faults
in the deeper part of the platforms are normal listric faults that resulted from the nal rifting stage of the South China
Sea. Small-scale, steep normal faults within the carbonate units behave relatively as syn-depositional faults that became
the base and template for the reefs to grow as these faults created conjugate and branching faults systems. Apart from
becoming templates for the reefs to grow, these syn-depositional faulting events had also interrupted the growth of reefs
especially those that were located at the platform margin. Slight movement of the branching faults induced sub-marine
landslide to create reefs collapse. The establishment of relationship between faulting and carbonate growth in Central
Luconia Province might be useful for revisiting mature hydrocarbon reservoirs.
Keywords: Central Luconia Province, South China Sea, seismic interpretation, fault, carbonate
Successful carbonate deposition requires a combination
of several environmental factors such as suitable structural
template, sufcient water depth, salinity and enough nutrient
supply. This was the case in the Central Luconia Province
in offshore Malaysia during the Miocene where extensive
carbonate reefs deposited on tilted horst blocks at the time
when the sea oor remained at a shallow depths for a long
time (period of tectonic stability) (Franke et al., 2014).
Research focusing on the sedimentology of the carbonate
platforms in the Central Luconia Province had begun with
the rst publication by Epting (1980) and Doust (1981).
They had suggested that the development of the carbonate
platforms in the Central Luconia were essentially unaffected
by tectonic deformations, and only governed by eustatic sea
level changes. However, improved seismic imaging in the
Central Luconia’s subsurface shows that faulting and folding
were widespread, throughout Miocene to Pliocene. Thus,
apart from eustatic sea level and nutrient supply, signicant
tectonic activity also played a role in the development of
the carbonate platforms in this area.
To investigate the relationship between the growth of
carbonate platforms and structural effects, two reference
platforms, EX and FY located in the southeastern part of
this province, were studied using 3D seismic volume and
well data. Recognition of the relationship between syn-
depositional faulting and growth history of the carbonate
platforms is the key to increase hydrocarbon production
in this basin. This study aims to establish the relationship
between structural framework within carbonate platforms
and its growth in response to syn-depositional tectonics.
The Central Luconia Province (Figure 1a) is a relatively
broad and stable structural block at present (Zampetti et al.,
2004a) covering an area of 240km x 240km (Vahrenkamp,
2004) in offshore Sarawak and has become the target for
many prolic oil and gas exploration since 1968. It has
undergone Eocene extensional tectonics and subsidence in
the north and compressional tectonics in the south. To date,
more than 200 drowned carbonate platforms ranging in size
from a few km2 to more than 200km2 across have been
seismically mapped (Ali and Abolins, 1999) with 55 elds
proven to contain commercial quantities of hydrocarbon,
particularly gas (Ali, 1995; Pierson et al., 2010).
In the Late Early Miocene, when the tectonic activities
were slowing down, reefs started to flourish where
favourable conditions prevailed. Reefs had become more
prolic throughout the Early Middle Miocene to Late
Middle Miocene. The carbonate reefs were interpreted to
be deposited in the inner neritic environment. Inuence
of prograding clastic materials from the nearby Baram
deltas and increase of sediment load from the NW Borneo
Wedge and major sea level falls had subsequently stopped
the carbonate deposition. Clastic deposits continued to
prograde into the Central Luconia Platform since the Late
Miocene until today, and promoted gravitational tectonics
within this province.
Compared to the other basins in the South China Sea,
there was a delay in carbonate deposition at Central Luconia
(Franke et al., 2014) because the Luconia Block was still
colliding and subsiding beneath Borneo during the Late
Oligocene, whereas the other parts of South China Sea had
Bulletin of the Geological Society of Malaysia, Volume 60, December 2014, pp. 77 – 83
S.N. Fathiyah JamaludiN, maNuel Pubellier & david meNier
Bulletin of the Geological Society of Malaysia, Volume 60, December 2014
settled in their rifting processes. Carbonate deposition in
the Central Luconia took place in the Late Early Miocene
but become more prolic in the Middle to Late Miocene
(Zampetti et al., 2004a,b).
The data which include 3D seismic and well data of
Platforms EX and FY (Figure 1b) were made available
by the Petroleum Management Unit (PMU), Petronas and
Shell Sarawak Berhad. The seismic volume used for this
research is a ltered, scaled and migrated seismic volume.
The inline interval was 25m with crossline interval of
12.5m (grid size = 25m x 12.5m), with 245 inlines and
1124 crosslines for Platform FY, and 272 inlines and 492
crosslines for Platform EX.
Interpretation of seismic data began with creation of
a synthetic seismogram. Moderate to good correlations
between synthetic and seismic data were achieved
through seismic to well tie analysis. Horizons for seismic
interpretations were selected according to the obvious
reectors correlated from the seismic to well tie process.
Since the available wells only penetrate up to the depth
of 2280 m (to the base of carbonate layers), interpretation
on the deeper horizons were only based on the continuity
of the seismic reectors, as observed on several seismic
attributes. Maps for each of the horizons were created and
overlaid with fault surfaces.
The internal geometries of the seismic reections within
Platforms EX and FY were also used to understand and
interpret the environment of deposition for each carbonate
unit. In this study, the geometries of seismic reections were
identied and interpreted for the purpose of understanding
the features seen on each interpreted sequence. Sequence
stratigraphy (i.e.: on-lap, top-lap and down-lap) was not
applied in this study. Three seismic geometries were
identied in Platforms EX and FY (Figure 3).
Horizons and Geo-Seismic Units
Eleven horizons (H1-H11) have been interpreted in this
study, with ve geo-seismic units, labelled as Geo-Seismic
Unit 1 to 5 (Figure 2). These units were interpreted based
on a combination of continuity of amplitude displayed on
seismic data, well data (to the extent of its last penetrated
depth) and gathering of information from the available
literatures. The horizons were interpreted within a geo-
seismic framework and tied to the biostratigraphic markers
that correspond to time intervals from recent to 15.97 Ma
(Early Middle Miocene). Biostratigraphic markers for the
deeper horizons were not available for Platform FY and EX.
Well F6 from nearby platform within the Central Luconia
Province, together with the other deeper wells from Balingan
Province and North Luconia Province were incorporated to
interpret the lithology of the deeper horizons.
Horizons were interpreted from the sea bottom, labelled
as Sea Bottom (SB), followed by Horizon 1 (H1) to Horizon
11 (H11) in the deepest part of the seismic section. Horizon
11 to Horizon 7 have the same seismic pattern, and are
grouped as Geo-Seismic Unit 1 (GSU 1). The top of Horizon
7 to Horizon 5 shows the same seismic characteristics and
are grouped as Geo-Seismic Unit 2 (GSU 2). Geo-Seismic
Unit 3 (GSU 3) consists of the carbonate units interpreted
from Horizon 5 to Horizon 3. Geo-Seismic Unit 4 (GSU
4) is grouped from the top of Horizon 3 to Horizon 2. The
nal interpreted Geo-Seismic Unit 5 (GSU 5) is bounded
between Horizon 2 to the sea bottom (SB). The main internal
geometry within each geo-seismic units interpreted in this
study is shown in Figure 3.
Well Logs Interpretations
Gamma Ray Logs for Well EX-2, EX-3, FY-2 and FY-6
have been used in interpreting the lithology for Platform
EX and FY (Figure 4). Regrettably, Gamma Ray Logs are
Figure 1: (A) Location of Central Luconia
Province in the bigger South China Sea,
highlighting the carbonate Platform EX and
FY used in this research. (B) Top carbonate
map of Platform EX and FY with “No data
zone” labelled in between the two platforms.
“No data zone” represents the area without
seismic data (not provided for this research).
Relationship between syn-depositional faulting and caRbonate gRowth in centRal luconia pRovince, Malaysia
Bulletin of the Geological Society of Malaysia, Volume 60, December 2014
not available from top to bottom of the wells. Most of the
logs and cores are tight within a depth of 1700m to 3300m.
All available wells are exploration wells, thus they only
penetrate to either the top of carbonate or inter-carbonate
section within Geo-Seismic Unit 3 of our interpreted data.
None of these wells penetrate into the deeper Geo-Seismic
Units 2 and 1. The lithological interpretation of Platform
EX based on Well EX-2 and EX-3 was made methods by
Gartner et al. (2004) and Zampetti et al. (2004b). In Platform
EX, some limestone breccias have been observed especially
towards the edge of the platform (Figure 5). Three limestone
breccias intervals with a minimum thickness of 1m were
recognized at the top of core in Well EX-3 (Gartner et al.,
2004). Based on gamma ray logs plotted in Figure 4, gamma
ray values ranging from 50 to 80API are common within
limestone intervals, indicating the existence of shales within
the carbonate intervals (contaminated carbonate). Clean
limestones have gamma ray values of 10-30 API. Lithological
interpretation of Platform FY remains condential within
industrial companies.
Structural Interpretation
Faulting affects the whole area covered by the entire
3D seismic survey for both Platforms EX and FY. Structural
interpretation was mainly based on the observable offset
of seismic reectors in the reectivity data or lineaments
observed in the variance (coherence) volume. A total of
50 faults has been interpreted within Platform EX and FY
(Table 1). These faults are mainly planar in nature within
Geo-Seismic Unit 3 and turn into listric shape in the deeper
seismic units. Most faults died out in the Geo-Seismic
Unit 3 but some continues to displace Geo-Seismic Unit
4. No major faults were observed within Geo-Seismic Unit
5, except for small-scale localised fractures. Observation
of seismic data between Platform EX and FY shows that,
there is potential for normal faulting in the saddle area that
separated these two platforms (no data zone in Figure 2).
All faults are normal faults, generally oriented N-S and
NE-SW which seems to govern the north-south elongation
of platforms in the south eastern part this province.
Fault Classes
Faults have been classied into few classes, based on
the units they displaced. The fault classes are summarized
in Table 1.
Platform EX
Platform EX grew on a few small scale domino system
fault blocks. These faults are interpreted to be related to
the last rifting stage of the South China Sea. Throughout
carbonate growth in Platform EX from Middle to Late
Miocene, small scale normal faults are observed. Some of
them were active during carbonate deposition, promoting
platform collapse especially in the Eastern and Western
Table 1: Faults classes in Platforms EX and FY.
Fault Class Criteria Platform EX Platform FY
ADisplaced all geo-seismic units except Geo-Seismic Unit 5.
Displacement in Geo-Seismic Unit 4 is small compare to the older
units. Associated with conjugate faults in the NE of Platform FY.
Not available for
interpretation 10 faults
BFault(s) that displaced Geo-Seismic Units 1 to 3. 14 faults 15 faults
CFault(s) that do not displace Geo-Seismic Units 3, 4 and 5. The
displacement(s) are only visible in Geo-Seismic Unit1 and 2.
Not available for
interpretation 6 faults
DEarlier fault(s) that only displaced Geo-Seismic Unit 1. Difcult to
image in seismic but might be related with rifting fault. Not available for
interpretation 5 faults
Figure 2: Seismic cross-section of Line
AA’ showing ve geo-seismic units (Geo-
Seismic Units (GSU) 1-5) and saddle area
(no seismic data zone) between Platform EX
and Platform FY. Both platforms have been
directly affected by normal faults.
S.N. Fathiyah JamaludiN, maNuel Pubellier & david meNier
Bulletin of the Geological Society of Malaysia, Volume 60, December 2014
Figure 3: Seismic geometry based on seismic reection pattern on
Platform EX and Platform FY.
Figure 4: Lithological interpretation based on core interpretation and gamma ray for Well EX2, EX3, FY2 and FY6.
ank of Platform EX (Gartner et al., 2004; Zampetti et
al., 2004a,b). The majority of the faults are closely spaced,
steeply dipping with dipping angles ranging from 40°-70°
with dominant fault system strikes from 015°-040° and
040°-070° (Figure 6).
Fourteen faults have been interpreted within Platform
EX, and they are concentrated in the eastern and western
margins of the platform. Structure interpretation in Platform
EX is only limited to the carbonate section of Geo-Seismic
Unit 3 reasonably due to the small size of the provided
seismic data, hence all the faults in this platform falls in
Class B Fault. Velocity pull-up effects were taken into
account when doing interpretation as extremely high velocity
had passed through the carbonate build-ups of Platform
EX and resulted in fold-look-a-like structure underneath
the carbonate build-up.
Faulting and fractures within this carbonate platform
had somehow created an outline for the platform as
they showed straight segments where the platform edge
coincides with the faults or are guided by the fracture
systems. Multiple sliding events had been interpreted to
be responsible for submarine landslide in Platform EX.
Zampetti et al. (2004a,b) had classied patchy, chaotic and
hummocky seismic geometry to describe slide deposits on
the eastern and western anks of Platform EX. Slide scars
were represented as sharp discontinuities forming crescent-
shaped embayments associated with seismic chaotic bodies
of slide deposits.
Relationship between syn-depositional faulting and caRbonate gRowth in centRal luconia pRovince, Malaysia
Bulletin of the Geological Society of Malaysia, Volume 60, December 2014
Platform FY
Faulting in Platform FY is relatively more pervasive
compared to faulting in Platform EX. Most of the faults cut
through the carbonate platform. Some of the fault(s) were
initiated earlier before the carbonate started to deposit on this
platform and continued to move slowly during deposition of
carbonate, making a syn-depositional faulting event. Sets of
conjugate faults can be seen at the edge of Platform FY (in
NE of the platform). In the northern part of Platform FY,
the faults are oriented in ENE-SW direction while in the
southern part, the faults are oriented about N-S direction
(Figure 7a). The dip angles of these faults are ranging from
40°-80°. Different fault directions within Platform FY might
be indicative of a localised strike-slip fault in this area with
an approximately N-S oriented basement fault, promoting
E-W extension.
Conjugate faults in Platform FY have similar dips of
approximately 30°-40°, oriented NE-SW and NW-SE. A
detailed inspection within Geo-Seismic Unit 3 carbonate
shown that Fault Class B and C develop various numbers of
conjugate fault systems, crossing each other and developed
X-patterns within the carbonate unit(s). Some of the faults
Figure 5: Wells EX2 and EX3 in Platform EX. (A) The wells location on the surface timeslice. (B) Crossline 1, showing Well EX3
penetrates to the depth of approximately 1960m. (C) Inline 2, showing Well EX2 penetrates to the depth of approximately 2090m. (D) Core
images of limestone breccia in the upper part of Well EX3, consist of grainstone, packstone and wackestone (modied after Gartner et al.,
2004). (E) Core images of argilaceous limestone at the base of Well EX2. Exact depth is unknown. (modied after Warrlich et al., 2010).
(F) Core sample showing dolo-mudstone in core of EX3. Exact depth is unknown (modied after Warrlich et al., 2010). (G) Thin section
from Well EX2 showing foraminifera with platy corals in lime-mudstone. Exact depth is unknown (modied after Gartner et al., 2004).
failed to create conjugate systems and later changed into
distributed branching faults, creating positions of mini
horsts and graben patterns within Geo-Seismic Unit 3 that
become the templates for the reefs to grow. These branching
conjugate normal faults within the carbonate units were
tilted and rotated and provided changes in the environment
of deposition from reef build-up to lagoonal facies. This
is proven by fossil assemblages such as corals, corraline
algae, echinoderms and operculina found in Well FY-6. The
fossil assemblages represent shallow open marine close
to reef slope as the possible environment of deposition in
Platform FY (Figure 8).
Detailed seismic interpretation of Platforms EX and
FY in the Central Luconia Province has shown well
dened carbonate build-ups that had been affected by syn-
depositional faulting during their growth. Both Platforms
EX and FY have ve geo-seismic units (1-5). The older
geo-seismic units 1 and 2 are dominated with older listric
normal faults. Their displacements in each of the geo-seismic
units are small (to seismic scale), suggesting that these faults
S.N. Fathiyah JamaludiN, maNuel Pubellier & david meNier
Bulletin of the Geological Society of Malaysia, Volume 60, December 2014
Figure 8: Environmental changes from
lagoon (back reef) to reef at/front, observed
in seismic data of Platform FY. The changes
in environment of deposition were due
to template provided by the branching
conjugate faults system in carbonate units
of Platform FY.
Figure 6: Faulting in Platform EX.
Interpreted faults on the section (cross-section
K-K’) and horizontal (coherence (variance))
slice at time 1515ms. The faults are dipping
40°-70°. Faulting stopped during the nal
stage of carbonate deposition and hardly
affected the clastic layers of Geo-Seismic Unit
4 above the platform. Coherence (variance)
slice shows that the top carbonate (green
contour) is bounded by faults on both anks.
Figure 7: Fault trends in Platform FY. (A)
Faults are dominated by two sets. Set 1:
Oriented in N-S direction (red colour) and Set
2: Oriented in ENE-WSW direction (green
colour). (B) Fault trends as observed in the
cross-sections UU’ and YY’.
Relationship between syn-depositional faulting and caRbonate gRowth in centRal luconia pRovince, Malaysia
Bulletin of the Geological Society of Malaysia, Volume 60, December 2014
formed during or just after the nal rifting stage of the
South China Sea. Some of the older listric faults continue
to move during deposition of Geo-Seismic Unit 3 that is
the main carbonate depositional unit in Platforms EX and
FY. Slight movement within the carbonate depositional unit
had either encouraged the reefs to grow on the topographic
highs such as at the tip of a faulted block, or promoted
sub-marine landslides as what we observed in the anks of
Platform EX. In general, syn-depositional faulting within
carbonate platforms in the Central Luconia Province had
provided templates for the reefs to nd suitable bases for
them to grow during Miocene time. However, at the same
time, syn-depositional faulting during carbonate deposition
had led to reef collapse together with other environmental
factors such as storm and wind directions. In conclusion, the
branching conjugate normal faults and older listric faults in
the carbonate deposits might serve as potential hydrocarbon
traps and migration paths within the carbonate reservoirs
in the Central Luconia Province, which can be useful for
exploration revisits.
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... Preliminary analysis of the sub-platforms within the platform itself has shown different modes of karstification albeit developed adjacently to each other. The syn-depositional faulting movements are both make-or-break for the carbonate development; either fragmenting the carbonates or produce a region with conditions, which fits for rapid carbonate growth (Epting, 1989;Bachtel et al., 2004;Ting et al., 2011;Jamaludin et al., 2014;Steuer et al., 2014). The karstification of carbonate platform can occur in several hypothetical modes whether it is sub-aerially modified or internally dissolved along plane of weaknesses due to syn-depositional faulting and fracturation. ...
... 17 Ma) The first build-up horizon initiated in Burdigalian stage (~17 Ma) during the Middle Miocene Unconformity (MMU) exhibited a patchy reef distribution (Fig. 3). The syn-depositional faulting governs the platform fragmentation (Zampetti et al., 2004a(Zampetti et al., , 2004bTing et al., 2011;Jamaludin et al., 2014;Menier et al., 2014) initially sub-divided the carbonate platform up to four depositional phases denoted by the coalesced patchy isolated reefs on top of an elevated and tilted shelf. The evolution of present day carbonate platforms has been governed by the orientation and tilting degree of the antecedent topography. ...
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The development of the Central Luconia carbonates in offshore Sarawak has been governed by the orientation of the Luconia Platform, syn-depositional features generated by the rifting and oceanographic parameters, such as sea level fluctuations, hydrodynamic, climate changes, salinity, and oxygen levels. The studied carbonate platform is developed over a southern field high of Central Luconia Province. The prevalent high frequency sea level fluctuations during the Miocene (Burdigalian to Serravallian stages) developed an extensive array of karst by rapid sub-aerial exposure and re-submergence of the carbonate platforms. Multi-attribute was applied to the 3D seismic volume of one of the selected carbonate platforms in Central Luconia Province to recognise karstic feature developed within the platforms. Though it is explicit that karstification occurred mainly along fractures and faults, the karst distribution in the Central Luconia carbonates remains to be an enigma due to their heterogeneous nature, which in turn provides a challenge in drilling and exploration. The studied platform exhibits patchy growth distribution during the Burdigalian stage. This growth is deemed as the initial stage of carbonate growth followed by a combination of build-out and backstepping for the second growth stage. A major karstification stage is highlighted on the second stage build-up, which correlates with a major sea level drop and the distinctive collapsed-paleocave topography. Drowning is evident on the final stage of the platform that can be correlated to the final surge of sea level rise in the Serravallian.
... According toKrebs (2011), the late Early Miocene Unconformity (EMU) may be composite of at least three hiatuses which include unconformity and condensed sections, ranging age between 16.5 Ma to 19 Ma.Franke et al. (2013) in their recent paper in 2013 had considered the diachronous age for this unconformity and had termed it as End-Rift Unconformity (ERU), especially in the region of SW sub-basin of South China Sea. Nevertheless, this MMU, EMU or ERU reveals a long-lasting uplift of the highly attenuated continental crust for about[5][6][7][8][9][10] Ma after the initiation of seafloor spreading of SCS. Geo-Seismic Unit 3 is overlain by clastic sediment of Geo-Seismic Units 4 and 5. ...
Miocene carbonates reservoirs in the Central Luconia Province in offshore Sarawak had been serving as prolific hydrocarbon reservoirs since more than 20 years ago. This province is bounded by extensive tectonic regimes both in the northern and southern parts. However, until present, the relationship and impacts of these extensive tectonic events to the growth of Miocene carbonates reefs in Central Luconia Province has not been revealed sufficiently. In this work, two carbonates platforms, designated as Platforms EX and FYwere used for detailed interpretation based on seismic attributes analysis and seismic based structural restoration. Structural restoration techniques allow compensation on the faults’ displacements, removal of recent sediment layers and finally restore the older rock units prior to faults’ motions. Integration of sea level response during seismic interpretation had also provided an accurate result. Eleven horizons were interpreted with five Geo-Seismic-Units to represent the cycles of sedimentation in the Central Luconia Province since the Late Oligocene until present day. 50 faults were marked on both Platforms EX and FY, each of these faults were divided into Faults Classes A-D, depending on the Geo-Seismic-Units they displaced. Faults in Platform EX are mostly closely spaced, steeply dipping and concentrated only within Geo-Seismic Unit 3 which is the real carbonates unit. Faulting in Platform FY are relatively more extensive compared to Platform EX and comprises faults in Classes A-D. Conjugate faults are also common within Platform FY.Three possible tectonic evolutions since the Late Oligocene to Holocene were interpreted to be responsible for the development of carbonates growth in the Central Luconia Province. These stages are corresponding for Pre-Carbonate Stage (Late Oligocene - Early Miocene), Syn-Carbonate Stage (Middle - Late Miocene) and PostCarbonate Stage (Pliocene - Holocene). Rifting of the South China Sea and subduction of Proto-South China Sea are believed to be responsible for the development of faulting during Pre-Carbonate Stage, while movement of the ancient Baram Line is thought to control the parallel striking direction of normal faults during Syn-Carbonate Stage. Finally, subsidence and compaction due to the overburden clastic materials from the prograding deltas in the mainland Borneo is considered as the main reason for the impacts of gravitational tectonics in this area. This work had make it possible to relate the relationship of carbonates deposition in Central Luconia Province to the other basins in the southern part of the South China Sea, Carbonates growth marked delay in subsidence history as well as reflecting the age of subsequent break-up of the South China Sea.
The growth timing of the studied carbonate platform at Central Luconia Province is approximately 4 million years governed by series of third-order sea-level fluctuations and syndepositional tectonics. The prevalent sea-level fluctuations during the Miocene developed a flat-topped limestone interval, capped by a relatively thin dolomitic interval. The first karstification period occurred during the sea-level drop in the Burdigalian stage, over a complex horst and graben setting. The complex surfaces were believed to be predominantly configured by the seafloor expansion of the South China Sea, prior to the carbonate initiation and growth. The second subaerial exposure stage was highlighted as the most prominent karstification period during the Langhian stage, with sporadic distribution of sinkholes, paleocollapse caves, and Uvalas. The third subaerial exposure period is deemed to be a minor karstification stage where a slight fall in the sea level led to buildout and expansion of the carbonate platforms. The final growth horizon is finally drowned during the Serravallian without any further subaerial exposure. A growth timing log is developed based on seismic time slices evidences, sea-level curves, and tectonic information highlighting karstification stages of the carbonate platform.
A high-resolution, two-dimensional seismic survey covering 7500 km 2 provides an unprecedented view of the evolution of a Miocene-Pliocene carbonate platform in the East Natuna-Sarawak Sea, Indonesia. The Segitiga Platform (1400 km 2) contains Terumbu Formation carbonate strata as much as 1800 m thick that were deposited in platform interior, reef and shoal margin, and slope to basin environments. The Segitiga Platform was subdivided into 12 seismic sequences that demonstrate a history of (1) initial isolation, (2) progradation and coalescence, (3) backstepping and shrinkage, and (4) terminal drowning. Interpretations of seismic facies maps for each sequence were used to help illustrate platform history. These seismic fades maps indicate that the Segitiga Platform originated as three smaller platforms on extensional fault-block highs. Deep intraplatform seaways separated these smaller platforms. Progradation of shallow-water carbonates filled the seaways during a phase of coalescence and the three platforms were amalgamated to form a merged composite platform (1400 km2; middle-upper Miocene). A rapid relative rise in sea level at the end of Miocene time caused a major backstepping of the carbonate margins (and a concomitant drowning of the adjacent Natuna field carbonate platform to the east) resulting in a platform of greatly reduced size (600 km 2) during the lower Pliocene. Rapid subsidence, combined with an eustatic rise at the end of the early Pliocene, caused terminal drowning of the Segitiga Platform. The platform was buried by younger siliciclastics of the Muda Formation. Eustatic sea level change controlled the timing of sequence-boundary formation, but structural movements modified internal sequence character and fades distribution. Faulting created topography that acted as templates for the initiation of carbonate platform deposition and provided pedestals for the localization of backstepped platforms. Cessation of faulting may have instigated progradation of the platform resulting from the deceleration of accommodation-space production. Regional subsidence may have controlled the location and extent of platform backstepping. Geographic variability in sequence stacking of coeval platform margins is observed over relatively short distances. Progradation is most strongly developed on the leeward side of the platform, but increased accommodation resulting from the rapid local subsidence or changing oceanographic currents also influenced the direction and magnitude of progradation.
The Mega Platform is a 30- × 50-km-large and 1.2-km-thick middle Miocene carbonate platform located in the Luconia Province, offshore Sarawak, Borneo. The platform originated in the late early to early middle Miocene on a regional fault-bounded structural high, first aggraded and then backstepped during a series of third-order sea level fluctuations during the middle Miocene (TB2.3-2.6). The Jintan Platform termination with an area of 8 × 12 km is one of the prominent backsteps toward the top of the Mega Platform. Three-dimensional (3-D) seismic indicates that growth on Jintan ceased relatively early with continued carbonate aggradation in adjacent smaller terminations (M1, M1-East). Spectacular reservoir architecture and diagenesis are revealed by the seismic. Several transgressive, aggradational, and progradational cycles are overprinted by repeated karst events. Dissolution features and bank-margin collapse are aligned to a deep-seated regional fault system, which periodically became reactivated during carbonate growth. A large triangular-shaped graben formed during one of the faulting periods but subsequently healed by a prograding reefmargin sequences. Two alternative scenarios are presented to explain the ultimate demise of the platform. The first proposes drowning resulting from a combination of subsidence and eustatic sea level rise. The second evokes a much-later drowning, which was preceded by a long period of exposure resulting from a second-order sea level fall and an initial decrease in subsidence caused by the onset of tectonism in Borneo during the late Miocene. In any case, following a hiatus of about 5 m.y., the platform was finally buried by deep-marine siliciclastics that prograded into the basin from the large delta systems of northwest Borneo. Recognition of growth architecture, faulting, and karstification is a key to exploiting the hydrocarbon reservoirs of the Mega Platform. A 30-m-thick low-porosity and -permeability layer shields the gas trapped in Jintan from the underlying aquifer. Penetrated by only one well, the extent of the layer and areas of breaching caused by faulting and karstification are identified on seismic. Interpretation of the seismic is critical to assessing whether and how the underlying aquifer is felt during reservoir depletion and whether there is pressure communication between adjacent reservoirs connected via the aquifer. Cores and logs from three wells provide ground truthing of reservoir architecture, karst features, and faulting derived from the interpretation of reflection and inversion seismic. The interpretation is then imported into static and dynamic 3-D models to constrain reservoir properties, predict dynamic behavior, and guide optimum field development.
The origin of seismic reflections in slope deposits of a Miocene carbonate platform, offshore Sarawak, was studied using cores, well-log data, and twodimensional seismic. This isolated carbonate platform has slope angles ranging from 2 to 25°. Our interpretation of the seismic data is that the asymmetric and high-rising platform (250-300 m relief) has different stratigraphic character for the southern and northern flanks. The southern slope was characterized by bypass or erosion throughout the aggrading phase of platform development. It was subsequently buried by shale with downbending, onlapping beds that indicate terrigenous sediment transport from the south. An alternative is folding during tectonic deformation. On the northern flank, the shale already started to pile up during platform aggradation. Phases of erosional or bypass conditions were short and alternated with two phases formed when platform debris interfingered with surrounding shale. Shale intercalations can be recognized seismically by negative reflections that quickly lose amplitude away from the platform. Although the overall shape of the platform is probably related to an older structural pattern of the Luconia Province, the asymmetry of the platform architecture and the distribution of sediments are most likely the results of paleowinds.
The morphology of Carbonate platforms may be influenced by tectonic activity and eustatic variations. 3D seismic data and satellite imagery are used in order to investigate the morphological similarities between present-day carbonates platforms, East of Borneo Island and Miocene carbonate platforms of the South China Sea. The morphological similarities exhibit platform fragmentation, that could be caused by subtle faulting, sufficient to drown reef rims; platform contraction, which is a result of back-stepping of the reef margin during a relative sea level rise and polygonal patterns in internal lagoons, described as mesh reefs in modern platforms and possibly interpreted as karst in Miocene platforms. Vertical movements may trigger the formation of new geomorphological conditions that modify the distribution of coral growth with respect to the new hydrodynamic conditions in space and time. These movements (uplift and tilting) reduce and localize the space necessary for the coral ecosystem, explaining the contraction leading to drowning of parts of and, ultimately, the whole platform.
Seismic reflection data imaging conjugate crustal sections at the South China Sea margins result in a conceptual model for rift-evolution at conjugate magma-poor margins in time and space. The wide Early Cenozoic South China Sea rift preserves the initial rift architecture at the distal margins. Most distinct are regular undulations in the crust-mantle boundary. Individual rift basins are bounded to crustal blocks by listric normal faults on either side. Moho uplifts are distinct beneath major rift basins, while the Moho is downbended beneath crustal blocks, with a wavelength of undulations in the crust-mantle boundary that approximately equals the thickness of the continental crust. Most of the basin-bounding faults sole out within the middle crust. At the distal margins, detachment faults are located at a mid-crustal level where a weak zone decouples crust and mantle lithosphere during rifting. The lower crust in contrast is interpreted as being strong. Only in the region within about 50 km from the Continent-Ocean Transition (COT) we suggest that normal faults reach the mantle, enabling potentially a coupling between the crust and the mantle. Here, at the proximal margins detachment fault dip either seaward or landward. This may indicate the presence of exhumed mantle bordering the continental margins. Post-rift shallow-water platform carbonates indicate a delay in subsidence during rifting in the South China Sea. We propose that this is an inherent process in highly-extended continental margins and a common origin may be the influx of warm asthenospheric material into initially cool sub-lithospheric mantle. On a crustal-scale largely symmetric process predominate in the initial rifting stage. At the future COT either of the rift basin bounding faults subsequently penetrates the entire crust, resulting in asymmetry at this location. However, asymmetric deformation which is controlled by large scale detachment faulting is confined to narrow areas and does not result in a margin-wide simple-shear model. Rather considerable along-margin variations are suggested resulting in alternating “upper and lower plate” margins.
3-D seismic reflection data and a variance cube are used to determine the architecture and investigate the triggering processes of submarine landslides affecting the flanks of a Miocene carbonate platform in the Luconia Province, Malaysia. The slide masses exhibit, in time-slice displays, chaotic, patchy seismic patterns, in otherwise smooth reflections. They lie basinward of the slide scar, tend to widen in the transport direction, and end in indistinct lobes. Slide scars appear as crescent-shaped embayments in otherwise straight or oval platform-edge contours. However, slide scars show planar morphology where they coincide with a fault zone. In vertical sections, the basal surfaces of the slides are steep concave slope segments (slide scar) that rapidly flatten where they dip under the slide masses. Slide masses appear as zones of discontinuous wavy reflections that wedge out in both upslope and downslope directions, extend for 1.5 km into the basin, and have a maximum thickness of 130 m. The slide deposit on the western flank is the result of at least two individual sliding events. Two seismically chaotic bodies are separated by a smooth reflection interpreted as an intercalation of hemipelagic mud between carbonate-rich slide masses. Syndepositional faulting affects the geometry of the platform and the platform margins, particularly at the time of slope failure. We suggest that the slides were generated by the interplay of steep-slope progradation and faulting accompanied by seismic shocks.