Papers by Riza Rahardiawan
Journal of Asian earth sciences. X, Jun 1, 2024
The northeastern Sunda Strait is a narrow strait separating Java and Sumatra islands. Currently, ... more The northeastern Sunda Strait is a narrow strait separating Java and Sumatra islands. Currently, it forms a seaway between the Java Sea and the Indian Ocean. The geological setting of the region is extremely dynamic, but how the Plio-Pleistocene interplay between sea level oscillations, magmatism, and tectonics, which lead to the current setting, has not been completely understood. We analysed an important set of legacy shallow seismic data from this area to decipher these intricate relationships. Our results indicate that the tectonic extension partly dismantled the Indonesian arc since the Middle Miocene. However, volcanic products formed a barrier between the Sunda Shelf and the Indian Ocean during the Late Pliocene to the Middle Pleistocene. Marine flooding started during the Middle Pleistocene but bypassed the barrier by flooding the NW edge of Java Island. During the Late Pleistocene, high amplitudes and longer periods of the glacial-interglacial cycles ultimately connected the Java Sea with the Indian Ocean. Still, it was only during the Holocene that important erosion made this seaway efficient in transporting seawater between the two reservoirs.
BULLETIN OF THE MARINE GEOLOGY, 2018
This paper reports copper, zinc, lead, cadmium, and chromium records of Jakarta Bay sediment sinc... more This paper reports copper, zinc, lead, cadmium, and chromium records of Jakarta Bay sediment since 600 AD and reonstruct environmental changes since that time. Jakarta Bay This study uses samples from a 150 cm long gravity core (TJ-17, 106.902488°E, 5.99381°S) that was acquired from the eastern part of Jakarta Bay in 2010 onboard RV Geomarin I by the Marine Geological Institute. Heavy metal content in Jakarta Bay sediments is used to track environmental changes onland from this site. Heavy metal concentration was analyzed using atomic absorption spectrometry on bulk samples that were taken in 5 cm interval. The results yield background level of Cu at 16 ppm, Zn at 75 ppm, Pb at 20 ppm, Cd at 0.01 – 0.15 ppm, and at Cr 80 ppm. Vertical record of heavy metals show two stages of environmental changes in the region: from 600 AD to 1600 AD and 1800 AD onward. These changes are interpeted as related to land use changes caused by human activity in the West Java region.
BULLETIN OF THE MARINE GEOLOGY
The offshore sedimentary basin of North Central Java is a marine basin located in the northern pa... more The offshore sedimentary basin of North Central Java is a marine basin located in the northern part of North Serayu Basin. This basin was formed through the uplift of the southern part of Central Java (Bumiayu) caused by the movement of a pair of horizontal faults. Studies of sub-basin delineation and basement configuration are rarely carried out in this basin. Therefore, the gravity method referring to subsurface-density variations was carried out to obtain this information. This research aims to delineate sedimentary basins and interpret the geological subsurface based on gravity data using spectral analysis, highpass and lowpass filters, also 2D gravity modeling. An average estimation depth to the basement in the study area of about 2.22 km was determined using spectral analysis. Qualitative analysis shows the basement-high pattern, sub-basin, and structure lineament patterns. The 2D model shows three layers consisting of the upper sedimentary layer of Tertiary-Neogene and the mi...
BULLETIN OF THE MARINE GEOLOGY, 2016
South Makassar Strait is located between Kalimantan and Sulawesi Islands that is an important oce... more South Makassar Strait is located between Kalimantan and Sulawesi Islands that is an important oceanographic pathway connecting between the Pacific and Indian oceans. This area is a part of sedimentary basin that has specific seabed morphology and sediment characteristics, including foraminifera as a component of sediments. The purpose of this study is to determine community structure of benthic foraminifera related to sediment characteristics. This study used 20 top core sediment samples from water depth between 200 and 1500 m. There are identified 38 species of benthic foraminifera and some of them are characterized the study area: Anomalinoides colligerus, Lenticulina suborbicularis, Planulina wuellerstorfi, , and Pseudonodosaria discrete. The diversity index is categorized as moderate values (1.0=H'= 3) and the average of evenness values is about 0.79. The dominance values are less than 0.5 indicate that there is no dominant species in the study area. In relation to sediment ...
EGU General Assembly Conference Abstracts, Apr 1, 2017
JURNAL GEOLOGI KELAUTAN, 2016
Morfologi dasar laut di daerah penelitian agak curam dan bergelombang, terdapat pada kedalaman la... more Morfologi dasar laut di daerah penelitian agak curam dan bergelombang, terdapat pada kedalaman laut antara 50 sampai 2000 meter. Pembentukan morfologi dasar laut ini sangat dipengaruhi oleh adanya gejala sesar-sesar aktif. Dari interpretasi runtunan seismik terlihat jelas adanya struktur- struktur geologi berupa sesar dan pelipatan. Adanya bentuk struktur bunga (flower structure) menunjukkan bahwa gejala tektonik aktif dari sesar Palu- Koro, Kolaka, Matano, Lawanopo masih berlangsung sampai sekarang. Keberadaan sesar-sesar aktif ini perlu diwaspadai karena dapat menimbulkan gempa diseluruh Teluk Bone. Kata kunci: sesar aktif, struktur bunga, sesar Palu-Koro Morphology of study area shows a steep and a slighty wavy seabed with the depths between 50 to 2000 meters. The formation of this morphology is strongly influenced by the presence of active faults. Seismic sequence interpretation shows the geological structures such as faults and folds. The present of the flower structure suggest...
ABSTRAK Morfologi dasar laut di daerah penelitian agak curam dan bergelombang, terdapat pada keda... more ABSTRAK Morfologi dasar laut di daerah penelitian agak curam dan bergelombang, terdapat pada kedalaman laut antara 50 sampai 2000 meter. Pembentukan morfologi dasar laut ini sangat dipengaruhi oleh adanya gejala sesar-sesar aktif. Dari interpretasi runtunan seismik terlihat jelas adanya struktur-struktur geologi berupa sesar dan pelipatan. Adanya bentuk struktur bunga (flower structure) menunjukkan bahwa gejala tektonik aktif dari sesar Palu-Koro, Kolaka, Matano, Lawanopo masih berlangsung sampai sekarang. Keberadaan sesar-sesar aktif ini perlu diwaspadai karena dapat menimbulkan gempa diseluruh Teluk Bone. Kata kunci: sesar aktif, struktur bunga, sesar Palu-Koro ABSTRACT Morphology of study area shows a steep and a slighty wavy seabed with the depths between 50 to 2000 meters. The formation of this morphology is strongly influenced by the presence of active faults. Seismic sequence interpretation shows the geological structures such as faults and folds. The present of the flower st...
JURNAL GEOLOGI KELAUTAN, 2016
Sedimen dasar laut di daerah perairan Madura dan sekitarnya umumnya mengandung kandungan gas yang... more Sedimen dasar laut di daerah perairan Madura dan sekitarnya umumnya mengandung kandungan gas yang dampaknya terhadap sifat fisik sedimen dasar laut sangatlah signifikan. Hal ini kaitannya dengan rencana peletakan pondasi bangunan infrastruktur di Perairan Selat Madura dan sekitarnya. Berdasarkan hasil yang diperoleh dari pemboran dimulai dari kedalaman 1 hingga 20 m dibawah permukaan dasar laut mengandung gas biogenik.. dengan kandungan metana berkisar 50 hingga 60 ppm sedangkan kandungan propana dan isobutana kurang dari 0,2 ppm. Kedalaman lebih dari 20 m dibawah permukaan dasar laut hingga 60 m adalah gas termogenik. Konsentrasi maksimum gas termogenik berupa propana, isobutana dan etana pada kedalaman 52.85 m berkisar dari 0,1 hingga 8,453 ppm. Dari kedua tipe gas ini tahap pembentukan diagenesanya berbeda akibat pengaruh temperatur yang berbeda, sehingga mempengaruhi stabilitas sifat fisik dan keteknikan sedimennyapun berbeda pula. Untuk itu dalam perencanaan pembangunan infrast...
BULLETIN OF THE MARINE GEOLOGY, 2016
Karimata Strait is a part of Sunda Shelf connected South China Sea with Malacca Strait, Indian Oc... more Karimata Strait is a part of Sunda Shelf connected South China Sea with Malacca Strait, Indian Ocean and Java Sea. This shelf was a large Sunda Land that has been detected by many evidences as records of various paleo-environments. The purpose of this study is to recognize the characteristic community of ostracoda related to the environmental history of this shelf. Three selected cores sediments represented east (A), middle (B) and west (C) parts of Karimata Strait were used for Ostracoda based on standard method on micropaleontology. Additional method was applied of SEM-EDX analysis to abnormal specimens. The result shows that there are 43 species of ostracoda belonging to 34 genera identified in the study area. The highest number of ostracoda is found in Core B, in the middle part of the strait, and the lowest value belongs to the Core A that close to the land of Kalimantan. Several genera of Ostracoda were documented in all cores: Actinocythereis, Cytherella, Cytherelloidea, Keij...
Sub-Bottom Profiling (SBP) records and results of geochemical analysis of 12 surficial sediment c... more Sub-Bottom Profiling (SBP) records and results of geochemical analysis of 12 surficial sediment cores from various water depths collected from the offshore Waropen Basin-Papua are presented. Presence of gas is clearly observed on sub-bottom profiler records. Shallow gas was identified through acoustic response due to gas accumulation and gas escape on sub-bottom profiles. Acoustic evidences of gas accumulations within near surface geology consist of high amplitude reflections and associated acoustic blanking, gas plumes and morphological features like pockmarks. Total organic carbon analysis of 12 surface sediment cores varies between 0.5% to 1.3% which indicate that the sediments have an abundance of organic matters. Gas chromatographic analysis of hydrocarbon composition detected only methane, a biogenic origin of shallow gas. Acoustic and geochemical evidence in the Waropen Basin indicates extensive shallow gas accumulations in the Late Quaternary sediments, some trapped within t...
JURNAL GEOLOGI KELAUTAN, 2016
Pelabuhan Cirebon dan rencana pelabuhan Astanajapura di bagian utara Jawa Barat, saat ini sedang ... more Pelabuhan Cirebon dan rencana pelabuhan Astanajapura di bagian utara Jawa Barat, saat ini sedang mengalami ancaman akan pendangkalan, hal ini ditunjukkan oleh tingginya aktifitas pengerukkan oleh PT. Pelindo yang dilakukan setiap 6 bulan sekali. Untuk mengevaluasi masalah pendangkalan tersebut, penulis melakukan telaah menggunakan metoda geologi dan geofisika yang difokuskan pada penafsiran seismik pantul dan pemboran inti. Hasil penafsiran seismik pantul dangkal memperlihatkan adanya pola progradasi yang saling menindih. Hal ini ditafsirkan bahwa proses sedimentasi di daerah ini berjalan sangat aktif hingga sekarang. Sedangkan keberadaan pola reflektor sejajar dan sigmoid kombinasi dengan pola syngled dan divergent di bagian bawahnya, menunjukkan bahwa sedimen merupakan endapan delta di dekat pantai. Dari hasil pemboran inti, dijumpai sedimen fraksi halus setebal 20,00 meter, dari atas ke bawah tersusun atas lempung lanauan, lempung dan pasir lepas. The Cirebon and the planned Asta...
JURNAL GEOLOGI KELAUTAN, 2016
Makalah ini membahas tentang sebaran dan kandungan unsur tanah jarang, di Perairan dan pantai Kua... more Makalah ini membahas tentang sebaran dan kandungan unsur tanah jarang, di Perairan dan pantai Kuala Kampar baik dalam sedimen permukaan maupun di bawah permukaan. Untuk mengetahui dan memahami sebaran unsur tanah jarang di daerah selidikan, empat puluh lima contoh sedimen telah dilakukan analisis unsur tanah jarang. Berdasarkan analisis REE, maka unsur tanah jarang di Perairan Kuala Kampar dan sekitarnya terdiri dari Thantalum (Ta), Neobium (Nb), Zirkonium (Zr) Ytrium (Y) Zirkonium ditemukan dalam seluruh contoh yang dilakukan analisa kimia.. Dalam percontoh sedimen permukaan dasar laut sebaran zirkonium mempunyai kandungan antara 2,8 ppm -130 ppm. Sedangkan dibawah permukaan sedimen dasar laut berdasarkan data bor zirkonium ditemukan dengan kandungan antara 20,1 ppm - 75 ppm. Ytrium ditemukan pada seluruh contoh yang dianalisis kimia. Pada sedimen permukaan dasar laut sebaran ytrium mempunyai kandungan antara 4,1 ppm -39,3 ppm. Sedangkan dibawah permukaan sedimen dasar laut dari da...
Knowledge on physical properties of seafloor sediments is essential in planning offshore construc... more Knowledge on physical properties of seafloor sediments is essential in planning offshore construction, in particular oil and gas construction. Changes in the physical properties of sediments such as faults and fractures, as well as the presence of gas within seafloor sediments can be detected as a decrease in acoustic wave velocity due to reduction in sediment shear strength. Normalization of Cimanuk River in early 1980s has resulted in higher sediment influx and increasing rate of compaction that change the physical properties of the sediment. Analysis of amplitude and wave velocity using software SonarWiz 5 on the records obtained from sounding equipment: Sub-Bottom Profiler type ODEC Strata Box and Bathy 1500, show significant change in wave speed that is caused by shallow gas seepage associated with fractures in the Polygonal Fault System (PFS ). This fault system formed as a result of diagenetic processes of fine grain sediment and reduction of the sediment shear strength due t...
Study area is located in South Banda Basin near the triple junction between Eurasian, Pacific and... more Study area is located in South Banda Basin near the triple junction between Eurasian, Pacific and Indo-Australian Plates. This area is part of back-arc thrusting zone that evolved to compensate convergence between Australia Continent and Banda Arc. Based on seismic section in this area, geological structure analysis is characterized into three distinctive zones. There are Thrust Zone (TZ), Proto Thrust Zone (PTZ) and Normal Fault Zone (NFZ). TZ is defined by distribution of numerous of thrust fault, PTZ contains a blind zone or folds instead of thrust fault, and NFZ defined by distribution of numerous normal fault in the upper portion of seismic section. PTZ identified at several seismic section along the bending zone of oceanic crust. The appearances of bending zone will be easily understood by comprehend the driving mechanism of Australia Continent to the Northeast. The bending zone also related to geometry and tectonic stress of collision. Based on this mechanism it was clearly u...
JURNAL GEOLOGI KELAUTAN, 2016
Hasil kegiatan penelitian geologi kelautan Lembar Peta 0421menghasilkan data seismik dan pemeruma... more Hasil kegiatan penelitian geologi kelautan Lembar Peta 0421menghasilkan data seismik dan pemeruman sepanjang lebih kurang 963,73 kilometer. Dari peta batimetri ditemukan beberapa kelurusan dengan arah hampir baratlaut-tenggara dan diduga merupakan sesar. Hasil penafsiran data menunjukkan bahwa stratigrafi rekaman seismik, daerah penelitian secara garis besar dapat dibagi menjadi 4 (empat) unit yaitu unit 1; unit 2; unit 3, dan unit 4. Jika dikaitkan dengan geologi regional daerah penelitian, unit 1 diduga dapat disebandingkan dengan Formasi Peunasu berumur Miosen, unit 2 diduga dapat disebandingkan dengan Formasi Seurula & Formasi Julurayeu berumur Pliosen, unit 3 diduga dapat disebandingkan dengan endapan volkanik Toba berumur Plistosen, dan unit 4 diduga dapat disebandingkan dengan aluvial berumur Holosen. Pembagian unit tersebut berdasarkan pada adanya bidang tidakselarasan (onlap), dan pepat erosi (erosional truncation). Kata kunci : lembar peta 0421, unit seismik, ketidakselara...
Journal of Oceanography, Oct 31, 2014
Sedimen dasar laut dapat mendeskripsikan kondisi geologi yang terjadi di masa lampau hingga masa ... more Sedimen dasar laut dapat mendeskripsikan kondisi geologi yang terjadi di masa lampau hingga masa kini. Penelitian ini bertujuan untuk mengetahui kondisi lapisan-lapisan sedimen dasar laut Perairan Utara Jawa (Lembar Peta 1310) berdasarkan profil penampang seismik Sub Bottom Profile. Pengambilan data lapangan dilakukan pada bulan September 2013 menggunakan kapal Geomarin I milik Pusat Penelitian dan Pengembangan Geologi Kelautan, Kementerian Energi dan Sumber Daya Mineral,analisa sedimen dilkukan pada bulan November, 2013 di Laboratorium Geologi P3GL, Cirebon. Metode penelitian yang digunakan bersifat deskriptif denganmateri yang diteliti berupa data pemeruman dasar laut, sampel sedimen dasar dan data rekaman seismik Sub Bottom Profile. Hasil interpretasi menunjukansedimen dasar pada daerah penelitian dkelompokan dalam 4 lapisan pengendapan yang terdiri dari Unit 1 adalah lapisan terluar sedimen berumur resen dengan fraksi butir halus. Unit 2 merupakan bidang batas sekuen erosional truncation yang mengidentifikasikan terjadinya erosi.Unit 3 adalah lapisan sedimen yang sebagian telah terkikis karna berbatasan dengan bidang erosi dan basemen akustik.Unit 4 adalah lapisan akustik basemen yang telah mengalami deformasi.Berdasarkan hasil analisa sampel sedimen dasar pada daerah penelitian berupa lempung dan lanau pasiran.
Continental transform boundaries tend to develop on former subduction zones. Pre-existing accreti... more Continental transform boundaries tend to develop on former subduction zones. Pre-existing accretion and collision structures may play key roles in continental transforms. Oblique accretion and strain partitioning in subduction systems may exhibit key structures that transition into a transcurrent regime. Here we examine a portion of the northwestern Sunda Arc, the type example of strain partitioning in oblique convergence. It developed the largest displacement in the 2004 megathrust rupture, one of the largest known. Data of unprecedented resolution on seismicity, structure and morphology offer new opportunities to study oblique subduction tectonics. This work uses selected MCS data from the KH-10-05 cruise by R/V Huhako Maru and a wide assortment of published data to focus on the Sunda arc offshore northern Sumatra. A 3-zone upper plate model fits well most of the arc. A narrow frontal zone of active accretion is marked by the trench slope. Landward is a wider zone of older more co...
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Papers by Riza Rahardiawan