THE DELTA ACCRETION CONTROLLED BY ENVIRONMENTAL PARAMETERS CASE STUDY: KALIGARANG DELTA, NORTH SEMARANG, INDONESIA Karina Melias ASTRIANDHITA 1 , WINANTRIS 2 , Budi MULJANA 2 , Purna Sulastya PUTRA 3 , PRAPTISIH 3 1 Master Student of Faculty of Geology, Padjadjaran University, Indonesia, 2 Faculty of Geology, Padjadjaran University, Indonesia 3 Research Center for Geotechnology, Indonesian Institute of Sciences *Corresponding Author: [email protected]Abstract 90 detail samples of Kaligarang Delta; located at the Northern part of Semarang, Central Java, Indonesia; has been collected and identified along the 45 meters length core. The core was analyzed by non-destructive (XRF), destructive (organic content, grain size) techniques to obtain the environment parameters. There are two interval points that indicated the differentiation between Fe and Ca value and grain size. In the first interval 9 meter, the fluctuated values of Fe and Ca indicated by low percentage sand and high clay content. The second interval at 18 meter has occurred the peak of Fe and Ca content in conjunction with high clay content. It indicated that the shoreline shifting to the north in Kaligarang delta is dominated by two environment parameters, there are very fine of grain size and high Fe and Ca contents. In the other words, high sediment supplies have an important role than the influence of wave or wind current. Keywords: Kaligarang Delta; Fe and Ca contents; Grain size; Organic Content 1. INTRODUCTION Kaligarang Delta is situated at the Northern Semarang, Central Java Province, Indonesia. Many researches in Semarang, such as study on land subsidence and mineralogical characteristics of the clay minerals in Semarang City using XRD and SEM-EDX analyses [1,2], abrasion and accretion by satellite image [3] tectonic in Kaligarang [4,5] sea water intrusion in North Semarang [6], erosion [7]. Therefore, there isn’t any publication about environment sediment supplies based in grain size, organic content, and Fe and Ca content. The reason of this location; land subsidence zone happened 4- 6 cm/year. The aim of this paper is to describe the sedimentary records based on grain size, organic content, and Fe and Ca content in Kaligarang, Delta. 2. MATERIALS AND METHODS Core SMRG-2 (-6.57 0 S, 110.24 0 E) was taken from Kaligarang, Semarang. Laboratory work was supported by Indonesian Institute of Sciences. 45 meters length core (n=90) was analyzed by non- destructive (XRF), and destructive (organic content, grain size) techniques. Sediment grain size, organic matter content, and mineralogy were analyzed using remaining sediment corresponding to each sample. Organic content was calculated by loss-on ignition (LOI) method at 550°C using Thermo Gravimetric Analyzer. Grain size was analyzed using Malvern Mastersizer 2000 particle size analyzer, to establish the percentage of clay (0–2 µm), silt (2–20 µm) and sand (20–2000 µm) [8]. Fe and Ca content were analyzed using XRF XL3. Developing additional methods for quickly gathering data from coastal sediments would both encourage the use of coastal systems in paleoclimate analysis, and improve the efficacy of their paleoenvironmental reconstructions. Core Scanning X-Ray Fluorescence (XRF) is a relatively new technique that produces qualitative trace element data [9] The 2nd Join Conference of Utsunomiya University and Universitas Padjadjaran, Nov.24,2017 31
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THE DELTA ACCRETION CONTROLLED BY ENVIRONMENTAL PARAMETERS CASE STUDY: KALIGARANG DELTA, NORTH
90 detail samples of Kaligarang Delta; located at the Northern part of Semarang, Central Java, Indonesia; has been collected and identified along the 45 meters length core. The core was analyzed by non-destructive (XRF), destructive (organic content, grain size) techniques to obtain the environment parameters. There are two interval points that indicated the differentiation between Fe and Ca value and grain size. In the first interval 9 meter, the fluctuated values of Fe and Ca indicated by low percentage sand and high clay content. The second interval at 18 meter has occurred the peak of Fe and Ca content in conjunction with high clay content. It indicated that the shoreline shifting to the north in Kaligarang delta is dominated by two environment parameters, there are very fine of grain size and high Fe and Ca contents. In the other words, high sediment supplies have an important role than the influence of wave or wind current.
Keywords: Kaligarang Delta; Fe and Ca contents; Grain size; Organic Content
1. INTRODUCTIONKaligarang Delta is situated at the Northern Semarang, Central Java Province, Indonesia. Many
researches in Semarang, such as study on land subsidence and mineralogical characteristics of the clay minerals in Semarang City using XRD and SEM-EDX analyses [1,2], abrasion and accretion by satellite image [3] tectonic in Kaligarang [4,5] sea water intrusion in North Semarang [6], erosion [7]. Therefore, there isn’t any publication about environment sediment supplies based in grain size, organic content, and Fe and Ca content. The reason of this location; land subsidence zone happened 4-6 cm/year. The aim of this paper is to describe the sedimentary records based on grain size, organic content, and Fe and Ca content in Kaligarang, Delta.
2. MATERIALS AND METHODSCore SMRG-2 (-6.570S, 110.240E) was taken from Kaligarang, Semarang. Laboratory work was
supported by Indonesian Institute of Sciences. 45 meters length core (n=90) was analyzed by non-destructive (XRF), and destructive (organic content, grain size) techniques. Sediment grain size, organic matter content, and mineralogy were analyzed using remaining sediment corresponding to each sample. Organic content was calculated by loss-on ignition (LOI) method at 550°C using Thermo Gravimetric Analyzer. Grain size was analyzed using Malvern Mastersizer 2000 particle size analyzer, to establish the percentage of clay (0–2 µm), silt (2–20 µm) and sand (20–2000 µm) [8]. Fe and Ca content were analyzed using XRF XL3. Developing additional methods for quickly gathering data from coastal sediments would both encourage the use of coastal systems in paleoclimate analysis, and improve the efficacy of their paleoenvironmental reconstructions. Core Scanning X-Ray Fluorescence (XRF) is a relatively new technique that produces qualitative trace element data [9]
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3. RESULTS3.1 Geological Setting
Semarang is basically underlain by two different geological units: the sedimentary rocks of the volcanic Damar formation in the South mainly consisting of tuffaceous sandstone and volcanic breccia and alluvial sediments in the North, which basically consist of sand and clay[10]. Figure 1 presented the stratigraphic setting of Kaligarang is dominant of Alluvium (Qa). The Alluvium is deposit of coastal plain, river and lake. Kali Garang is the main river that flows crossing Mount Ungaran’s valleys, along the swiftly current of curved stream line [11].
Fig. 1. Sampling Location (Thaden, et al. 1975)
3.2 Mean Grain Size and Organic Content From the figure 2, the stratigraphy of the core composed of: 0-31 meter core are silt; the darker
means coarse – very coarse; 32 meter until 45 meter, samples interlude by fine sand – medium silt. Organic content (LOI analysis) ranged from 0% to 50%. The biggest organic content value is at the depth of 9 meter which is 51.49%. In depth 9 meter, mean grain size shows high clay content; Sediment grain-size seems to be the main controlling factor for organic content value (yellow line in figure 2). 31 meter – 37 meter organic content has smallest value between 1,45% - 5,48%
3.3 Fe and Ca Content In figure 2 shows percentage (in thousand) of Ca and Fe content. Ca values are samaller than Fe
content. There are two interval points (red line) that indicated the differentiation between Fe and Ca value and grain size. In the first interval 9 meter, the fluctuated value of Fe and Ca indicated by low percentage sand and high clay content. The second interval at 18 meter has occurred the peak of Fe and Ca content in conjunction with high clay content. The biggest Fe content shows 55873,7 ppm (depth 19 meter). The biggest Ca content 18876,08 ppm (depth 19 meter).
4. DISCUSSIONThere are positive correlation between mean grain size and organic content [12]. While substrate
becomes coarser (sand) value of organic content are decreased. This interaction happen caused depositional process moderate to low energy (low tidal) [13] in environment systems, organic matter is a binary mixture of terrestrial and aquatic sources. Understanding temporal changes in origin of sedimentary organic content may help identifying periods of enhanced terrestrial input versus authochthonous alga productivity, which in turn sheds light on paleoenvironmental conditions. Terrestrial environments play a profound role controlling sediment dynamics as material is eroded from the hinterland, transported by rivers, and entrained in littoral currents to shape the coast by
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creating barriers, lagoons, marshes, or deltas. Local tectonic process can influence the interplay of sediment supply by gradual uplift or subsidence, impulsive vertical displacement[14]
Chemical elements may play various roles within an ecosystem. The amount of Ca represents the carbonate fraction which can have an allochthnous as well as authochthonous origin[15] The amount of clastic material in sediment is generally inferred from Fe and reflecting weathering, runoff, erosion within the catchment [16] The calcium ion in seawater is used by shellfish to form an outer shell of calcium carbonate, and accumulates over geological time in marine sediments by forming limestone deposits. The distributions of Ca are mainly controlled by the presence of carbonate shells which are comprised of foraminifera and / or coccoliths [17] Fe typically terrigenous elements which suggests a common and stable of siliciclastic provenance [18] high concentrations of Fe were considered to represent input of terrestrial material. Tectonic subsidence played minor role on accommodation accreation, Two intervals in Ca and Fe content, indicated that the shoreline shifting to the north in Kaligarang delta is dominated by two environment parameters, there are very fine of grain size and high Fe and Ca contents. In the other words, high sediment supplies have an important role. Additional studies of the described sediment-recycling process and its role in Kaligarang delta are required. Importantly, the presence of sediment recycling spatial and temporal in delta, including influence by tidal (open-ocean deltas), needs to be investigated.
Fig. 2. Lithostratigraphy, mean grain size, percentages of organic content and Fe and Ca percentage (ppm)
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5. CONCLUSIONBased on the grain size, organic content and Fe and Ca percentage of the core SMRG-2 collectedfrom Kaligarang Delta, the Northern Semarang. We investigated that shoreline shifting to the north inKaligarang delta. The grain size value has associated with organic content data. Increasing anddecreasing grain size correlate well with changing organic content value. This study demonstrates theapplicability of trace element analysis using XRF core scanning to Kaligarang Delta’s sediments. Thedata shows there’re two interval points that indicated the differentiation between Fe and Ca value andgrain size. The two interval points are in depth 9 meter and 18 meter influenced by high sedimentsupply. Hence, the interplay of tectonic, sea level changes, human and natural induced changes ofsediment budgets presents a challenge when deciphering sedimentary sequences in tectonic activecoastal regions.
6. ACKNOWLEDGEMENTWe acknowledge Indonesian Institute of Sciences; Mr. Eko Yulianto, Director of Research Centre forGeotechnology, for providing access. Mr. Eko Soebowo provided many helpful comments and hispermission to use samples. Thanks also go to Mr Joko, Mr Jaka, and Mrs Eki for their helps inlaboratory works. We thankfully appreciate for any supports from the Department of GeologyPadjadjaran University. We are grateful to two anonymous reviewers and the editor for their criticalreviews and suggestions which helped in the improvement of our manuscript
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