# The dynamic coastal evidence of Jakarta Bay during Late Pleistocene-Recent

F Novico, C Endyana, D Menier, M Mathew, I Kurniawan, H Bachtiar, D Ranawijaya, H Hendarmawan

► To cite this version:

F Novico, C Endyana, D Menier, M Mathew, I Kurniawan, et al.. The dynamic coastal evidence of Jakarta Bay during Late Pleistocene-Recent. 4th International Conference of Water Resources Development and Environmental Protection (ICWRDEP 2021), Aug 2021, Malang, Indonesia. pp.012002, 10.1088/1755-1315/930/1/012002. [https://doi.org/10.1088/1755-1315/930/1/012002](https://doi.org/10.1088/1755-1315/930/1/012002). [CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/)

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# The dynamic coastal evidence of Jakarta Bay during Late Pleistocene-Recent

F Novico<fnref n="1" />,<fnref n="2" />*, C Endyana<fnref n="1" />, D Menier<fnref n="3" />, M Mathew<fnref n="4" />, I Kurniawan<fnref n="5" />,<fnref n="6" />, H Bachtiar<fnref n="5" />, D Ranawijaya<fnref n="7" /> and H Hendarmawan<fnref n="1" />

**Abstract.** Some significant indication identifying a coastal dynamic during Late Pleistocene to Recent is the evolution of isochrone patterns throughout glacial-interglacial stages. This study aims to identify the sediments stratification of Jakarta Bay during the Late Pleistocene – Recent in the framework of coastal dynamic triggered by the sea-level changes of last prominent climatic stages. The several high-resolution seismic records in Jakarta Bay lines were interpreted to illustrate the different sequences from the top down to the oldest by line-drawing the more robust seismic reflectors as a sequence limit surface. Furthermore, the isochrone map series of unit boundary (UB) were reconstructed to delineate isochrone contour patterns from the oldest until modern. The selected isochrones map of UB-3 and UB-5 with their unit facies are somehow favorable to be compared for observing the coastal dynamic of Jakarta Bay during the last climatic variability. Finally, the coastal dynamic of Jakarta Bay is discovered by the movement series of isochrones contour patterns that correspond to the sea-level changes during the last prominent glacial-interglacial stages.

**Keywords:** coastal dynamic, seismic record, Jakarta Bay, isochrone map

## 1. Introduction

Indonesia is an archipelago country where the most developing part is in the coastal zone. However, the development of the coastal area is facing seawater. Thus, it is constantly confronted with a variety of issues though some studies have been explored [1][2][3][4][5]. The understanding of coastal characteristics is not only for a short period but also for the long-term duration. Its circumstances will reveal the behaviour of the certain area of the coast by recognizing their past. The present Java Sea

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Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

<footnote n="1">¹Faculty of Geological Engineering, Padjadjaran University, 45363 Jatinangor, Indonesia</footnote>

<footnote n="2">²Marine Geological Research and Development Center, Ministry of Energy and Mineral Resources, 40174 Bandung, Indonesia</footnote>

<footnote n="3">³Laboratoire Géoscience Océan, UMR CNRS 6538, Université Bretagne Sud, 56017 Vannes, France</footnote>

<footnote n="4">⁴Laboratoire Géoscience Océan, UMR CNRS/UBO/UBS 6538, IUEM, Université de Brest, 29280 Plouzané, France</footnote>

<footnote n="5">⁵Directorate General of Water Resources, Ministry of Public Works and Housing, 12110 Jakarta, Indonesia</footnote>

<footnote n="6">⁶Faculty of Engineering, Brawijaya University, 65145 Malang, Indonesia</footnote>

<footnote n="7">⁷Independence Geologist, 40213 Bandung, Indonesia</footnote>

<footnote>*Corresponding author: franto.novico@esdm.go.id</footnote>
illustrates how land dominated this region during the last glacial maximum (LGM). The Java Sea, which is part of the Sunda Shelf, experienced sea-level oscillations during a geological time, resulting in this occurrence [6][7][8][9], Figure 1A. Since this area is characterized by a flood plain and rivers, it is better to understand coastal dynamics in the north of Java. This study aims to interpret the evolution of sedimentary sequence and paleo-bathymetry (isochrones) as evidence of coastal dynamics in Jakarta Bay over the LGM- Holocene and pre-LGM low stand climatic stages in the context of global eustatic sea-level changes. Understanding the evolution of sediment from the past to the present can aid us correctly in identifying the present issues that occur in the coastal area.

<figure><img src="image_3.png" /><figcaption>**Figure 1.** (A) Map of research locations in the region. (B) The high resolution seismic sparker lines covering Jakarta Bay.</figcaption></figure>
## 1.1. Tectonic setting

Java Island has produced a volcanic backbone on the southernmost boundary of the continental Sunda Plate due to the subduction of the oceanic Australia-Indian plate [10]. As a result, there occurs subsidence and uplift in other areas [11]. The northern section of the volcanism area that appeared due to plate collision was Jakarta Bay. Hence this area can be considered a northern west Java extensional tectonic system [12] [13].

## 1.2. Geomorphology and seafloor sediment

The onshore area of Jakarta Bay is a very flat coastal plain with coastal-line alluvial plain in the center, terrigenous alluvial plain a few uplands from the coastline zone, and deltaic plain on the coast of the river mouths of Cisadane, Cikapadilan, Cengkareng, Angke, Krukut, Ciliwung, Sunter, Cakung, Blencong, Cikarang, and Bekasi (figure 1B). The bay's bathymetry reflects this relatively flat shoreline morphology. Its maximum depth is over -26 m at its northernmost point and has an average slope of 0.15 percent. The surface sediment of the Java Sea, especially Jakarta Bay, is dominated by fine-grained cohesive sediments like muddy and clayey [14][15][16].

## 1.3. Sea-level change

From a sedimentological point of view, global sea-level change has a dominant role in environmental processes. Since 800 ka, climate variability has been defined by a changing periodicity of 100 kiloyears, which governs global sea-level fluctuations [17] [18]. In this variability, sea-level changes vary from a few meters up to around 130 m [19][20][21][22]. Other studies had confirmed that melting of these ice sheets raised global mean sea level (GMSL) by more than 100 meters between 20 kiloyears before present (ka) and 6 ka. At the same time, the GMSL was around -120 meters in 20 k.a that called the last glacial maximum (LGM) [23][24]. Since the Late Pleistocene subperiod, significant climatic stages that correspond to substantial peaks in sea-level fluctuations have been recorded during the latest climatic variability from Stage 5e to the present. The noteworthy characteristics of sediment stratigraphy derived from seismic data records may be more easily connected to the stage's affiliations glacial and interglacial groups. These are isotope Stage 5, Weichselian glacial period, and Holocene sea-level curve, increasing sequence from the oldest [25].

<figure><img src="image_4.png" /><figcaption>**Figure 2.** The components of a sparker system include (A) Squid sparker (B) Streamer hydrophone (C) Energy source Applied GeoAcoustic CSP-D2400 (D) Pre-amp GeoAcoustics Geopulse 5210A.</figcaption></figure>

## 2. Material and Methods

The high resolution shallow seismic reflection (HRSS) was carried out by applying a sparker system. That system could be penetrated until around 250 milliseconds (ms) two-way-travel time (TWTT) (Figure 2). The internal velocity of 1600 m/s beneath the seafloor was assumed for time-depth
conversion for sediment unit boundary [26][27]. Within a total length of more than 1000 km, seismic lines covering the entire bay, so the actual condition of the subsurface of Jakarta Bay, will be revealed. In this study, the west-east and north-south directions are represented by two seismic lines (figure 1B). In contrast, the others are utilized to justify the unit boundary (UB) of isochrones. The methods for analyzing seismic data are based on the approach of [28][29][30][31]. It is usual to be persuaded that those more robust reflectors are extremely desirable as a borderline on seismic records. This borderline is referred to as a "unit boundary" (UB) between seismic sedimentary sequences that are referred to as "units" (U). The more robust reflectors' interpreted line drawings were traced to get the sequence units' boundary surface. Other interpretations on internal seismic stacks were used to perform all significant seismic facies characteristics to support the sediment depositional environment interpretation.

<figure><img src="image_5.png" /><figcaption>**Figure 3.** Raw and interpreted seismic line L-89, which travels from north to south across the bay, illustrates the distribution of units, unit boundaries, and environment deposition for each unit.</figcaption></figure>

**3. Results**

More robust seismic reflectors provide irregular fluctuation lines that split all different seismic units. This unit is subsequently interpreted as an erosional or hiatus surface on top of sedimentary sequence units, which is known as a seismic unconformity surface. Furthermore, within the unit themselves, the interpretation results describe and analyze internal seismic stacks' facies. Due to the massive disparity in the incident period, two isochrone maps, Isochrone UB-3 and Isochrone UB-5, were chosen.
### 3.1. *Seismic unconformities*

According to the analysis results and interpretation of its feature, intensity, and continuity, the phenomenon unconformity could indicate the UB of U. From the seismic data records of Jakarta Bay, we select two seismic lines: the north-south line L-89 and the west-east line CL-08F (figure 1B) to illustrate the unconformities. From the top to the base, we identify six unconformities (UB-6 to UB-1) in the sedimentary infill of the Jakarta Bay. These unconformities are divided into a basement U1 and six higher sedimentary seismic units, U2 to U7 (Figure 3 and Figure 4).

<figure><img src="image_6.png" /><figcaption>**Figure 4.** Raw and interpreted seismic line CL-08F spans from west to east across the bay, illustrating the distribution of units, unit boundaries, and environment deposition for each unit.</figcaption></figure>

At the lowermost part, the quality of the record is not truly good. The strong reflectors of UB-1 and UB-2 are line-drawn by an estimated interpretation on a kind of pronounced reflectors. However, the seismic unconformities of UB-1 and UB-2 are represented by an irregular surface. They correspond to the top of the basement U1 and U2. UB-1 indicates a sharp and irregular paleo relief with erosional surfaces. This surface is located from the mean sea level in the depth range from 200 milliseconds (ms) TWTT to 230 ms, while the depth of UB-2 varies in the depth range from 170ms TWTT to 185 ms. Some discontinuities at several locations mask some parts of almost all UB and units and are caused mainly by existing acoustic turbidity at UB-6. In UB-1 and UB-2 and its underlying U1 and U2, the
discontinued surface is caused by some quality of seismic records due to the penetration limit of the seismic pulse equipment on board. Mainly in all internal seismic records of the basement units, the performances are unclear with some acoustic noise and turbidity, whereas incomparably in other units' internals are more observables.

UB-3 in the interval around 145 to 165ms and UB-4 in 80ms to 110ms display a similar performance (Figure 3 and Figure 4). These unconformity surfaces, in general, have a regional character with almost all parallel laminations, and their topographies follow the top layers variations of internal underlying reflectors stack. There are some truncated angular unconformities in the internal reflectors of their underlying units. Then they could be an indicator of the erosional surface. As for UB-3 is considered an erosional surface that is unconformably separating U3 and U4 for some reason of different configurated reflectors spreading patterns in their seismic facies. By several channeling indications over UB-4 of associated reflectors hereinafter, we instead construe that UB-4 is an erosional surface.

The unconformity UB-5 depth from around 45ms to 75ms shows a very varied erosional unconformity surface with some intense channeling features. This performance in the level depth can strongly be interpreted to be deposited in a subaerial depositional environment for some optimal long periods. It was most probable that this event could occur on a dissected surface during a long enough time of an exposed environment associated with LGM condition during more than 22 - 19.5 ka [8]. Thus, the Jakarta Bay on this LGM period can be intensely estimated as the land zone of the massive valley with many incised channel discharges draining from the floodplain toward the north. While UB-6 in the range of 25ms to 30ms is identified as a flat surface with a few minor depressions of channeling.

<table><caption>**Figure 5.** The Unit's seismic facies of Jakarta Bay picked from L-89, and CL-08F show the specific feature of seismic records on which the interpreted depositional environment is based.</caption><thead><tr><th>Unit</th><th>Facies Illustration</th><th>Reflector Configuration</th><th>Interpretation</th></tr></thead><tbody><tr><td>U7</td><td></td><td>Agrading paralel</td><td>marine muds, channel fill</td></tr><tr><td>U6</td><td></td><td>two sides onlap<br>aggrading parallel</td><td>incising channel fill</td></tr><tr><td>U5</td><td></td><td>sub aggrading parallel</td><td>deltaic bar system</td></tr><tr><td>U4</td><td></td><td>wavy aggrading sub-parallel</td><td>deltaic plain alluvial</td></tr><tr><td>U3</td><td></td><td>aggrading sub-parallel</td><td>sub aquos deltaic system to marine sediment</td></tr><tr><td>U2</td><td></td><td>sub-oblique<br>aggrading sub parallel</td><td>shallow marine sediment</td></tr><tr><td>U1</td><td></td><td>acoustic turbidity</td><td>acoustic masking</td></tr></tbody></table>

## 3.2. Seismic unit

Figure 5 presents the seismic facies of the units that are feature-picked from Figure 3 and Figure 4. The U1 corresponds to the oldest deposits sequence reached by this seismic data acquisition. This unit has very noisy and hard-to-follow reflectors. Its reflectors configuration shows an aggrading subparallel of a stack of alternating high-reflectivity, transparent layering strata, and acoustic turbidity from the upper sequences that mask some parts of discontinued seismic records. This poor record quality is probably caused by the capacity limit of the equipment in deeper seismic penetration. However, it is assumed that the reflectors are generally horizontal without any particular character despite some weakly folded
shapes in some places. Thus, the features tend to be interpreted as deposited in a shallow marine environment.

The internal seismic record of U2 also has some poor features and is difficult to follow. With the bed thickness ranging thicken northward from about 10 m to 30 m, this unit has deposits consistent with the contact between U2 and U1, which the reflectors generally have a flat organization. In detail, the configuration of the reflector is more performing some aggrading sub-parallel in sub-oblique status. It is observed as an indication of a shallow marine or transition zone environment.

U3 has thickness varied from 30 m to 40 m and thinning northward (Figure 3 and Figure 4). It also has a different reflectors stack pattern comparing with other units that are shorter, less marked, and show more wavy reflectors in the center part. The depositional succession can be interpreted tending to an aggrading sub-parallel with some crossbedding-like and irregular fluctuated reflectors at the southern area (Figure 3) that is considered as a subaqueous interfingering deltaic lobes or deltaic bars system. This indicates an environment with a low sea level that was favorable for a deltaic formation.

U4 with varying thickness from about 35 m to 50 m is thinning toward the center part of the bay and is seen as the thickest unit among others. In seismic facies, reflectors configuration is observed aggrading subparallel beside on masked reflectors related to active gas-charged sediments. On top of the unit, the reflectors indicate the presence of some incising channels that could be found on several seismic lines. These have the effect of forming top lap at the contact UB-4 with U5. The channels are unambiguously associated with the paleo-deltaic system of Citarum River at the eastern and Ciliwung River at the southern central. The other reflectors are generally flat to slightly wavy. These features of the seismic facies could probably be interpreted as the indications of subaerial to subaqueous deltaic environments that have not enough immense spreading toward the Java Sea.

The thickness of U5 is very variable from about 15 m to 45 m. Comparing toward the south-north, in west-east spreading the channels are inspected denser with shorter cross-sections. It could be interpreted that the directions of channels in the eastern half of the bay are relatively from the south and the northeast to the north. The data records of seismic facies show their amplitude and frequency are rated medium to high beside some blank records of acoustic turbidity related to existing gas-charged sediments. The blank records are pretty common in the southern half of the central. Some are in the north-eastern that could be related to the deltaic system of rivers Ciliwung and Citarum. Aggrading subparallel in its reflector's configuration is commonly found beside somewhat of discontinued both of noisy reflector bares which related to existing gas pockets and data acquisition acoustic problem. This sediment bed has a general organization of the horizontal reflectors with however some downlap and onlap in places within the unit. This incision added to the gas pockets sharply overlaps UB-4. By these seismic features, the depositional environment of U5 is interpreted as a delta plain with some places of fluvial channels and tidal flat [32] [33] [31] [34].

U6, with a thickness ranging from about 0 m to 30 m for an average of 15 m, shows a flat upper layer covering a prograding system in some places of the unit's distribution (Figure 3 and Figure 4). Contact with unit limits forms onlap. In the northern half of the center toward the eastern parts of the bay, both interpretation results of south-north (Figure 3) and west-east (Figure 4) seismic lines evince adequately dense incising and erosions of U5's top layers. On the west-east seismic lines, U6 has a discontinued patchy like distribution with many lateral intercalations with eroded underlying U5. These are the phenomena of channelized reworks on the U5 bed, forming onlap on the side-edges of incising channels. In the facies of seismic reflectors stacks, the continuity, amplitude, and frequency rates range medium to high, except at some parts where reflectors bare associated with gas-charged sediments exist. These gas seepages exist more in the southern half of the central part. They vertically are desisted by the surface of UB-6 and overlaid by U7. Aside from acoustic turbidity, here reflectors configurations reveal in general aggrading parallel and some progradation. Therefore, based on its seismic distribution phenomena, we distinctly deliberate U6 was deposited in the paleo-deltaic region [32][35][31][34]. The base of unit 6 is a large incision that intersects unit 5 with a divergent filling. Thus, the variation of the thickness here corresponds to incising channels besides other Oceano-sedimentological processes.
U7 measuring on average about 5m thick in the channelizing is on the surface. It is the most recent, while on some depression indicated sites, we can have up to 20 m depth. Unlike in U6 and U5, despite the thickness ranged around 5m however U7 is laterally distributed toward all study areas (Figure 3 and Figure 4). The seismic features show several indications of medium to high rates of amplitude and frequency, with reflector configuration mostly is aggrading parallel as well as fillings of channels. A channel like depression on the lower layers is observed more developing in the northern one-third to the north-eastern parts were closed to the modern delta of Citarum River. These are visible at the contact between units 7 and 6. The recent depositional environment of U7 explicitly is a subaqueous fan in the south-central and eastern parts to shallow marine in the rest area such as exposed in the modern bathymetry.

From all units' observations above, we can highlight three significant seismic features: aggrading parallel, deltaic indicators, and acoustic turbidity, each corresponding to palaeogeography of shallow marine environment, delta system, and gas-charged sediments. Four large acoustic turbidity zones interpreted as pockets of gas are visible on the southern half of CL-08F.

<figure><img src="image_7.png" /><figcaption>**Figure 6.** Isochrone UB-3 which is the environmental topographic is situated at an alluvial plain.</figcaption></figure>

### 3.3. Isochrones

Reconstruction of isochrone maps of UB in the time series is required to remark the morphologic evolution throughout some significant sea-level variations. Reconstruction of isochrone maps of UB in the time series is required to remark the morphologic evolution throughout some significant sea-level variations. We select two isochrones' maps, isochrone map UB-3 (Figure 6) and isochrone map UB-5 (Figure 7) that are estimated conspicuously to have different depositional environments due to the contrasting stages of the sea-level variations throughout the last climatic variability of the period Late Pleistocene - Recent. UB-5 is selected by the different interpretation of its seismic reflector configuration that strongly points to the LGM condition in Jakarta Bay. Hence, to compare isochrone map UB-3 and isochrone map, UB-5 is expected more convenient to testify the coastal dynamic of Jakarta Bay, because they are laid on the different prominent variations of sea level during the last climatic variability.
Isochrone map UB-3 lies on about -79 m to -117 m depths (Figure 6). Relatively at the western zone, the colors brownish (approximately from -79 m to -100 m) termed “the high” and at the eastern zone, the blueish (approximately from -100 m to -117 m) termed “the valley” are qualitatively grouped by delineating the green as the morphology border. Thus, the bathymetry pattern shows two zones with contrast morphologies; the high morphology occupies the western zone, and the valley lies at the east. The high zone relatively exhibits the pattern of deltaic system with some lobes and channels. In contrast, the lobe is less developed at the eastern valley than in the western zone except for an interfluvial plain with two developed distributary channels.

Isochrone map UB-5 settles on about -24 m to -51 m depths (Figure 7). Like in isochrone map UB-3, the bathymetry pattern of isochrone map UB-5 shows two zones with contrast morphologies, the western zone is dominantly occupied by the high morphology, and at the east lies the valley. However, the morphology configuration here is more varied than in isochrone map UB-3. Some depression topographies of channels and lakes existed in the western zone.

<figure><img src="image_8.png" /><figcaption>**Figure 7.** Isochrone UB-5 which the environmental topographic is at the terrigenous situation around the last glacial maximum period.</figcaption></figure>

**4. Discussion**

The coastal dynamic is commonly well known controlled by regional tectonic and global eustatic sea-level changes that evolve the coastline zone to progradation or retrogradation. Since 400 k.a [36], the sea-level changes of Jakarta Bay as a part of Sundaland have played the main role in the coastal dynamic. In extending equally, these sea-level variations of the bay generate likewise the evolution of depositional environment that may be illustrated as the development from isochrone map UB-3 to isochrone map UB-5. To understand that isochrone map UB-5 patterns change, they are first placed at approximately the correct Stages of sea-level changes curve (Figure 8).

Comparing with the other Units, the interpreted UB-5 and the seismic facies features of overlaying U6 are outstandingly different and far more configured (Figure 3, Figure 4 and Figure 5) which inclined to be a dissected land of subaerial environment. When the depth maximum of isochrone map UB-5 is about -51 m and a seawater column is bad-needed in infilling sedimentation of U6, thus the most appropriate milieu of this isochrone map UB is at the Stages of LGM to Holocene (Figure 8). Among
the two selected isochrone maps UB-3 and isochrone map UB-5, its interpreted UB-3 and the seismic features of overlaying U4 lay down on the next deeper sea-level than the U6 or isochrone map UB-5. The interpretation results of U4 and UB-3 point to a depositional environment of subaerial to subaqueous deltaic systems with some interfingering deltaic alluvial plains. Accordingly, these characteristics are relevant tending to the environment of Stage 4 to Stage 3, which is the alluvial plain that occurred at Stage 4.

In Figure 6, the coastal dynamic of Jakarta Bay that is represented by the evolution from isochrone map UB-3 to isochrone map UB-5 is firstly simply exhibited on their disparity Stages on the curve of sea-level changes. The isochrone map UB patterns evolved from a relative deltaic system to the enormous subaerial valley land of Jakarta Bay. The compositions of brownish high and blueish valley on figure 7 from isochrone map UB-3 to isochrone map UB-5 seem not significant changing. They are more showing a steady terrigenous sediment source of Cisadane river mouth to becoming a significant high at the western part of the bay and that the brownish high development is logically more prograde to the north in the submarine deltaic of isochrone map UB-3 than in the subaerial environment of isochrone map UB-5.

<figure><img src="image_9.png" /><figcaption>**Figure 8.** Modification of high-resolution global sea-level curve for the past 125 ka, after [37], [38], [39]. Two sedimentary units are marked on the graph.</figcaption></figure>

**5. Conclusion**

The dynamic coastal evidence of Jakarta Bay during the Late Pleistocene to the Recent may be convinced as the evolution of morphology corresponds to the last prominent variation of sea levels. Among seven sedimentary seismic Units delineated in the bay, the two selected U3 and U5 with their UB are very considerable to pay attention, to perform the contrast morphologies in the coastal evolution. In the framework of the global eustatic sea-level, the characteristics of the isochrone map series of UB-5 and isochrone map series UB-3 and their seismic facies from the earlier prominent stage, the older in ascending order can be placed on the Stage of LGM for isochrone map UB-5 and the Stage 4 to 3 for isochrone map UB-3. Therefore, regarding the far differences in their position levels, the most contrast of depositional environments are very obvious that isochrone map UB-3 occurred on exposed land and isochrone map UB-5 on the subaqueous deltaic system. This evolution certainly provides the consequences to the coastal zone dynamic of Jakarta Bay area by coastal-line development correspond to the sea-level variation during the Late Pleistocene to Recent. Finally, as can be seen in figure 6 and figure 7 thus the development of the coastal area should consider the past condition as ‘basement’ infrastructure development and an environmental hazard.
**Author Contributions**

Author Contributions: Conceptualisation: F.N., D.M., M.M., H. and C.E.; methodology: F.N., D.M., M.M. and M.S.; field investigation: F.N. D.R., and I.K.; manuscript preparation: F.N., D.R., and H.B; review and editing: F.N., D.M., M.M., M.R., H.H., and C.E.; figures: F.N., D.R., and I.K.

**Acknowledgments**

The field activities were fully supported by the Ministry of Public Works and Housing, the Republic of Indonesia, under the grant bearing the contract number HK.02.03/PPK-PP/SBBWSCC/1311.2.

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