alfend rudyawan | Royal Holloway, University of London (original) (raw)

Papers by alfend rudyawan

IOP conference series, Nov 1, 2022

The study aims to determine fracture characteristics such as orientation, fracture attributes, fr... more The study aims to determine fracture characteristics such as orientation, fracture attributes, fracture density distribution, and mineral composition of quartz and feldspar. The study used photogrammetry data to know the distribution and geometry of macro-scale fracture, linear scanline and windows scan data to understand the characteristics of mesoscale fracture attribute, and thin section rocks data from oriented samples to determine petrographic analysis and micro-scale fracture. After analyzing each of these data, analog basement fractured reservoir modeling could be built from integrating the data and modeling parameters based on available fieldwork data. The fault in the research area is represented as a Riedel shear with the orientation direction of NNW-SSE, NE-SW, and ENE-WSW. The fracture density is influenced by its position on the fault and increases in the fault damage zone. The granite type in the study area was divided into three types, namely alkali feldspar granite, syeno granite, and monzogranite. Each granite type has a different response to fractures and shows that the fracture density will increase with the greater quartz and k-feldspar in the fault damage zone. Fracture permeability values are strongly influenced by the geometry of fracture position, fracture aperture, and fracture length. This study produced a new perspective for fractured basement reservoirs, especially for granitic rocks, generally the primary target for basement fracture reservoirs along Sumatra.

Earth, Planets and Space

On September 26, 2019, an Mw 6.5 earthquake occurred 23 km northeast of Ambon City, Indonesia, fo... more On September 26, 2019, an Mw 6.5 earthquake occurred 23 km northeast of Ambon City, Indonesia, followed by numerous aftershock series related to a complex fault network reactivation in the Ambon and Seram region. Using moment tensor inversion, we identify the kinematics of fault reactivation based on the focal mechanism solution of 20 aftershocks with Mw > 3.2 and analyze the earthquake sequence from both focal mechanism solutions and spatiotemporal seismicity. The MTs solution of aftershocks revealed three different characteristics of fault reactivation: (i) a 35 km long N-S oriented main fault characterized by dextral strike-slip (ii) a NE-SW reverse fault segment with a ~ 55° northeastward dip located in southwest Seram, and (iii) two strike-slip segments (NNW-SSE and NNE-SSW trends) and an E-W normal fault in Ambon Island. Analysis of spatiotemporal seismicity with the MTs solution suggests that the Mw 6.5 Ambon aftershock sequences can be described as follows: (i) an Mw 6.5 ...

IOP conference series, Mar 1, 2023

Journal of Asian Earth Sciences, 2017

International Journal of Scientific & Technology Research, 2020

Naturally fractured reservoir (NFR) especially in granitic basement in Sumatra is not a new issue... more Naturally fractured reservoir (NFR) especially in granitic basement in Sumatra is not a new issue for research. Generally in NFR modeling, fracture density of rocks in a damage zone is the most significant factor that influence fracture porosity and fracture permeability. The aim of the study is to determining micro fracture in the granitic rocks and proofing that quartz and k-feldspar minerals has significant influence for fracture density. Area of the study at Muaro Silokek, South Sumatra revealed a very heterogeneous granitic rocks outcrop and have high fracture density. At previous study conclude those area is representative as an analog NFR, especially granitic basement reservoir in Sumatra. The main fault which affect fracture orientation was right lateral strike slip faults with NW – SE orientation represented as riedel shears which is Takung Fault trend. The study was conducted using 12 data of thin section granitic oriented sample for micro fracture analysis. The result of ...

Early Cretaceous origin of the Woyla Arc (Sumatra, 1 Indonesia) on the Australian plate 2 3 Elder... more Early Cretaceous origin of the Woyla Arc (Sumatra, 1 Indonesia) on the Australian plate 2 3 Eldert L. Advokaat*1, Mayke L.M. Bongers1, Alfend Rudyawan2, Marcelle K. BouDagher4 Fadel3, Cor G. Langereis1, Douwe J.J. van Hinsbergen1 5 6 1Department of Earth Sciences, Utrecht University, 3584 CS Utrecht, The Netherlands 7 2Geology Study Program, Institut Teknologi Bandung, Bandung, Jawa Barat 40132, 8 Indonesia 9 3Department of Earth Sciences, University College London, London WC1E 6BT, United 10 Kingdom 11 12 *corresponding author: E.L.Advokaat@uu.nl 13 for: EPSL 14 15

The study area is located in Sirnasari area, Tanjungsari District, Bogor Regency, West Java-Indon... more The study area is located in Sirnasari area, Tanjungsari District, Bogor Regency, West Java-Indonesia and geographically located at coordinates 6 o 36'30"-6 o 39'30" Longitude and 107 o 08'15 "-107 o 10'30" Latitude.

Recent seismic and multibeam data, combined with information from land, provide the basis for a n... more Recent seismic and multibeam data, combined with information from land, provide the basis for a new interpretation of western Gorontalo Bay. The stratigraphy is divided into three parts. The basement (Unit A) is proposed to be Sundaland continental crust, below a major unconformity interpreted to be either Mid Eocene or Early Miocene in age. Above the unconformity is a sequence up to 6 sec TWT divided into two parts. The lower part (Units B and C) is interpreted as quartz-rich marine sediments, with little volcanic debris, derived from granites and continental basement of western Sulawesi. There is a minor unconformity at the base of the upper part (Units D to F). We suggest Units D and E are carbonates. Unit D has major clinoforms indicating water depths less than 200m. At the top of Unit E are linear bands of pinnacle reefs which step back towards the north. They mark rapid subsidence which began at about 5 Ma and are partly buried by Pliocene–Recent deposits (Unit F) in the basin...

SE Asia consists of multiple continental blocks, volcanic arcs and suture zones representing remn... more SE Asia consists of multiple continental blocks, volcanic arcs and suture zones representing remnants of closing ocean basins. The core of this mainland is called Sundaland, and was formed by accretion of continental and arc fragments during the Paleozoic and Mesozoic. The former positions of these blocks are still uncertain but reconstructions based on tectonostratigraphic, palaeobiogeographic, geological and palaeomagnetic studies indicate the continental terranes separated from the eastern margin of Gondwana. During the mid-Cretaceous, more continental and arc fragments accreted to Sundaland, including the intra-oceanic Woyla Arc now exposed on Sumatra. These continental fragments were derived from Australia, but the former position of the Woyla Arc is unconstrained. Interpretations on the former position of the Woyla Arc fall in two end-member groups. The first group interprets the Woyla Arc to be separated from West Sumatra by a small back-arc basin. This back arc basin opened ...

Located at the boundary of three different countries between Australia, East Timor, and Indonesia... more Located at the boundary of three different countries between Australia, East Timor, and Indonesian province of Nusa Tenggara Timur (West Timor), North West Shelf Australia (NWSA) can be divided into Westralian Superbasin (WASB) consisting of Northern Carnarvon, Offshore Canning, Browse and Bonaparte Basin (sensu Yeates, et al, 1987) and one orogenic belt called TimorBanda Orogeny (Figure 1). The NWSA is a world class gas province having reserve estimation of 2.6 billion bbls of oil and 152 Tcf of gas among 233 hydrocarbon field (Longley, et al, 2003). These resource mostly found in Mesozoic play beneath Cretaceous regional seal within WASB. In comparison with the WASB, exploration activity in the West Timor is still in frontier state with total of five wells both on onshore (Banli-1) with minor oil show and offshore well (Napoleon-1, Manta-1, Mina-1 and Belalang-1) with unsuccessful result (Figure 2). These result indicate that the petroleum system and hydrocarbon prospectivity in W...

Frontiers in Earth Science

Three-dimensional outcrop models, or Digital Surface Models (DSMs), have proved their capacity in... more Three-dimensional outcrop models, or Digital Surface Models (DSMs), have proved their capacity in many geoscience studies. Along with the advantage in the rapid acquisition, DSMs are capable of creating virtual models of fractured outcrops to be interpreted for further analysis. This paper reports the DSM robustness by comparing the result of fracture-lineament measurement using DSMs and discusses the possible causes of error that might occur. The first method applied in this study is the scanline method to collect fracture data directly from outcrops, measuring more than 1,400 fracture data. The second method is applying fully automatic and manual fracture identification by optimizing hill-shaded DSMs. Two well-exposed granite outcrops in Bangka, Indonesia, are designed for the pilot area. Structure-from-Motion (SfM) photogrammetry is utilized to generate the DSMs, where a series of aerial images are captured using Unmanned Aerial Vehicle (UAV). The images are then processed into h...

Modern Applied Science, May 30, 2018

A continuous clastic sedimentary rock outcrop in the Karanggayam Area, Kebumen represents the com... more A continuous clastic sedimentary rock outcrop in the Karanggayam Area, Kebumen represents the complete deep marine fan facies of the Middle Miocene Lower Penosogan Formation. Lithology association and vertical succession were observed from a 63 meters detailed measured section along the Karanggayam River. This study aims to identify and classify the turbidite succession as well as the depositional environment of the formation within the North Serayu Basin, Central Java. From the bottom to top the Lower Penosogan Formation is divided into: A2, B2, C2, D2 and F2 facies which represents basin plain, overbank (levee and distal levee), crevasse splay, channel-fill and frontal splay facies respectively. Changes in the depositional environment are interpreted to be influenced by the dynamic changes in morphology and global climate change caused by underwater volcanic activity as a result of Middle Miocene tectonic activity.

IOP Conference Series: Earth and Environmental Science, Jun 1, 2018

This paper presents new finding from the sedimentary sequences, overlooked by previous researcher... more This paper presents new finding from the sedimentary sequences, overlooked by previous researchers, which provide insights to the sea level changes during the deposition of the Middle to Late Pliocene Kalibiuk Formation. Data were acquired from fieldwork via detailed measured section of each sedimentary sequence from the bottom to the upper part of the formation followed by molluscan fossil association analyses. Lithologically, the Cisaat River stratigraphic section is dominated by greenish grey claystone with some light grey fine-grained sandstone intercalation. Based on about 50 m stratigraphic section, 10 molluscan fossils associations were successfully determined. The sequence from bottom to top are: Corbula – Natica association, Nassa sp. association, Olividae – Turricula association, Pecten – Telina association, Telina – Placuna association, Corbula – Marginella association, Placuna – Natica association, Turritella association, Turritella – Marginella association and Dentalina – Architectonica association. Changes in vertical succession of the molluscan association indicates a development from shallow marine to terrestrial depositional environment before gradually overlain by terrestrial sediments of the Kaliglagah Formation. At least there are 2 deepening - shallowing sea level cycles during the deposition of Kalibiuk Formation observed from this section.

IOP Conference Series: Earth and Environmental Science, Jun 1, 2018

Earth and Planetary Science Letters

Key to understanding the plate kinematic evolution of the Neotethys oceanic domain that existed b... more Key to understanding the plate kinematic evolution of the Neotethys oceanic domain that existed between the Gondwana-derived Indian and Australian continents in the south, and Eurasia in the north, is the reconstruction of oceanic plates that are now entirely lost to subduction. Relics of these oceanic plates exist in the form of ophiolites and island arcs accreted to the orogen that stretches from Tibet and the Himalayas to SE Asia that formed the southern margin of Sundaland. The intra-oceanic Woyla Arc thrusted over western Sundaland-the Eurasian core of SE Asia-in the mid-Cretaceous. The Woyla Arc was previously interpreted to have formed above a west-dipping subduction zone in the Early Cretaceous, synchronous with east-dipping subduction below Sundaland. The oceanic 'Ngalau Plate' between the Woyla Arc and Sundaland was lost to subduction. We present paleomagnetic results from Lower Cretaceous limestones and volcaniclastic rocks of the Woyla Arc, Middle Jurassic radiolarian cherts of the intervening Ngalau Plate, and Upper Jurassic-Lower Cretaceous detrital sediments of the Sundaland margin. Our results suggest that the Woyla Arc was formed around equatorial latitudes and only underwent an eastward longitudinal motion relative to Sundaland. This is consistent with a scenario where the Woyla Arc was formed on the edge of the Australian plate. We propose a reconstruction where the Ngalau Plate formed a triangular oceanic basin between the N-S trending Woyla Arc and the NW-SE trending Sundaland margin to account for the absence of accreted arc rocks in the Himalayas. As consequence of this triangular geometry, accretion of the Woyla Arc to the western Sundaland margin was diachronous, accommodated by a southward migrating triple junction. Continuing convergence of the Australia relative to Eurasia was accommodated by subduction polarity reversal behind the Woyla Arc, possibly recorded by Cretaceous ophiolites in the Indo-Burman Ranges and the Andaman-Nicobar Islands.

Modern Applied Science

A detailed stratigraphy description and measurements of the sedimentary facies within the Halang ... more A detailed stratigraphy description and measurements of the sedimentary facies within the Halang Formation has been carried out to provide a thorough assessment of the architectural facies and depositional environment. The study area is located along the Tajum River in the District of Gumelar, Banyumas, Central Java-Indonesia where most of the Halang Formation is preserved in a good condition. Three cycles of facies association from basin plain, in channel to channel overbank deposits were able to be determined from the formation which indicate very active changes of sub-depositional environment that related to transgressive response influenced by the local tectonic during sedimentation takes place.

Jurnal Geologi dan Sumberdaya Mineral

The Tertiary stratigraphy of Situbondo was constructed by a series of volcanoclastic-carbonate tu... more The Tertiary stratigraphy of Situbondo was constructed by a series of volcanoclastic-carbonate turbidite facies of Menuran Formation with Pacalan limestone Member, and Leprak Formation. These formations formed a regional east-west trending circular anticlinorium. The Tertiary formations were covered by Quaternary volcano-clastic Ringgit Formation and subsequent younger Bagor volcanic products. The oldest Tertiary rock units are the Late Miocene-Pliocene Menuran Formation, with Pacalan Limestone Member. Formation is mainly composed of foram-rich marls and calcareous, sometimes tuffaceous sandstones, with conglomerate intercalations. Sedimentation of this formation is interpreted as to be a mixing, from proximal to distal turbidite, involving volcaniclastic and carbonate sources, in a bathyal open marine environment. The Early Pliocene Leprak Formation overlies conformably the Menuran Formation, which consists of alternating calcareous sandstones and tuff sandstones deposited in a ba...

IOP conference series, Nov 1, 2022

The study aims to determine fracture characteristics such as orientation, fracture attributes, fr... more The study aims to determine fracture characteristics such as orientation, fracture attributes, fracture density distribution, and mineral composition of quartz and feldspar. The study used photogrammetry data to know the distribution and geometry of macro-scale fracture, linear scanline and windows scan data to understand the characteristics of mesoscale fracture attribute, and thin section rocks data from oriented samples to determine petrographic analysis and micro-scale fracture. After analyzing each of these data, analog basement fractured reservoir modeling could be built from integrating the data and modeling parameters based on available fieldwork data. The fault in the research area is represented as a Riedel shear with the orientation direction of NNW-SSE, NE-SW, and ENE-WSW. The fracture density is influenced by its position on the fault and increases in the fault damage zone. The granite type in the study area was divided into three types, namely alkali feldspar granite, syeno granite, and monzogranite. Each granite type has a different response to fractures and shows that the fracture density will increase with the greater quartz and k-feldspar in the fault damage zone. Fracture permeability values are strongly influenced by the geometry of fracture position, fracture aperture, and fracture length. This study produced a new perspective for fractured basement reservoirs, especially for granitic rocks, generally the primary target for basement fracture reservoirs along Sumatra.

Earth, Planets and Space

On September 26, 2019, an Mw 6.5 earthquake occurred 23 km northeast of Ambon City, Indonesia, fo... more On September 26, 2019, an Mw 6.5 earthquake occurred 23 km northeast of Ambon City, Indonesia, followed by numerous aftershock series related to a complex fault network reactivation in the Ambon and Seram region. Using moment tensor inversion, we identify the kinematics of fault reactivation based on the focal mechanism solution of 20 aftershocks with Mw > 3.2 and analyze the earthquake sequence from both focal mechanism solutions and spatiotemporal seismicity. The MTs solution of aftershocks revealed three different characteristics of fault reactivation: (i) a 35 km long N-S oriented main fault characterized by dextral strike-slip (ii) a NE-SW reverse fault segment with a ~ 55° northeastward dip located in southwest Seram, and (iii) two strike-slip segments (NNW-SSE and NNE-SSW trends) and an E-W normal fault in Ambon Island. Analysis of spatiotemporal seismicity with the MTs solution suggests that the Mw 6.5 Ambon aftershock sequences can be described as follows: (i) an Mw 6.5 ...

IOP conference series, Mar 1, 2023

Journal of Asian Earth Sciences, 2017

International Journal of Scientific & Technology Research, 2020

Naturally fractured reservoir (NFR) especially in granitic basement in Sumatra is not a new issue... more Naturally fractured reservoir (NFR) especially in granitic basement in Sumatra is not a new issue for research. Generally in NFR modeling, fracture density of rocks in a damage zone is the most significant factor that influence fracture porosity and fracture permeability. The aim of the study is to determining micro fracture in the granitic rocks and proofing that quartz and k-feldspar minerals has significant influence for fracture density. Area of the study at Muaro Silokek, South Sumatra revealed a very heterogeneous granitic rocks outcrop and have high fracture density. At previous study conclude those area is representative as an analog NFR, especially granitic basement reservoir in Sumatra. The main fault which affect fracture orientation was right lateral strike slip faults with NW – SE orientation represented as riedel shears which is Takung Fault trend. The study was conducted using 12 data of thin section granitic oriented sample for micro fracture analysis. The result of ...

Early Cretaceous origin of the Woyla Arc (Sumatra, 1 Indonesia) on the Australian plate 2 3 Elder... more Early Cretaceous origin of the Woyla Arc (Sumatra, 1 Indonesia) on the Australian plate 2 3 Eldert L. Advokaat*1, Mayke L.M. Bongers1, Alfend Rudyawan2, Marcelle K. BouDagher4 Fadel3, Cor G. Langereis1, Douwe J.J. van Hinsbergen1 5 6 1Department of Earth Sciences, Utrecht University, 3584 CS Utrecht, The Netherlands 7 2Geology Study Program, Institut Teknologi Bandung, Bandung, Jawa Barat 40132, 8 Indonesia 9 3Department of Earth Sciences, University College London, London WC1E 6BT, United 10 Kingdom 11 12 *corresponding author: E.L.Advokaat@uu.nl 13 for: EPSL 14 15

The study area is located in Sirnasari area, Tanjungsari District, Bogor Regency, West Java-Indon... more The study area is located in Sirnasari area, Tanjungsari District, Bogor Regency, West Java-Indonesia and geographically located at coordinates 6 o 36'30"-6 o 39'30" Longitude and 107 o 08'15 "-107 o 10'30" Latitude.

Recent seismic and multibeam data, combined with information from land, provide the basis for a n... more Recent seismic and multibeam data, combined with information from land, provide the basis for a new interpretation of western Gorontalo Bay. The stratigraphy is divided into three parts. The basement (Unit A) is proposed to be Sundaland continental crust, below a major unconformity interpreted to be either Mid Eocene or Early Miocene in age. Above the unconformity is a sequence up to 6 sec TWT divided into two parts. The lower part (Units B and C) is interpreted as quartz-rich marine sediments, with little volcanic debris, derived from granites and continental basement of western Sulawesi. There is a minor unconformity at the base of the upper part (Units D to F). We suggest Units D and E are carbonates. Unit D has major clinoforms indicating water depths less than 200m. At the top of Unit E are linear bands of pinnacle reefs which step back towards the north. They mark rapid subsidence which began at about 5 Ma and are partly buried by Pliocene–Recent deposits (Unit F) in the basin...

SE Asia consists of multiple continental blocks, volcanic arcs and suture zones representing remn... more SE Asia consists of multiple continental blocks, volcanic arcs and suture zones representing remnants of closing ocean basins. The core of this mainland is called Sundaland, and was formed by accretion of continental and arc fragments during the Paleozoic and Mesozoic. The former positions of these blocks are still uncertain but reconstructions based on tectonostratigraphic, palaeobiogeographic, geological and palaeomagnetic studies indicate the continental terranes separated from the eastern margin of Gondwana. During the mid-Cretaceous, more continental and arc fragments accreted to Sundaland, including the intra-oceanic Woyla Arc now exposed on Sumatra. These continental fragments were derived from Australia, but the former position of the Woyla Arc is unconstrained. Interpretations on the former position of the Woyla Arc fall in two end-member groups. The first group interprets the Woyla Arc to be separated from West Sumatra by a small back-arc basin. This back arc basin opened ...

Located at the boundary of three different countries between Australia, East Timor, and Indonesia... more Located at the boundary of three different countries between Australia, East Timor, and Indonesian province of Nusa Tenggara Timur (West Timor), North West Shelf Australia (NWSA) can be divided into Westralian Superbasin (WASB) consisting of Northern Carnarvon, Offshore Canning, Browse and Bonaparte Basin (sensu Yeates, et al, 1987) and one orogenic belt called TimorBanda Orogeny (Figure 1). The NWSA is a world class gas province having reserve estimation of 2.6 billion bbls of oil and 152 Tcf of gas among 233 hydrocarbon field (Longley, et al, 2003). These resource mostly found in Mesozoic play beneath Cretaceous regional seal within WASB. In comparison with the WASB, exploration activity in the West Timor is still in frontier state with total of five wells both on onshore (Banli-1) with minor oil show and offshore well (Napoleon-1, Manta-1, Mina-1 and Belalang-1) with unsuccessful result (Figure 2). These result indicate that the petroleum system and hydrocarbon prospectivity in W...

Frontiers in Earth Science

Three-dimensional outcrop models, or Digital Surface Models (DSMs), have proved their capacity in... more Three-dimensional outcrop models, or Digital Surface Models (DSMs), have proved their capacity in many geoscience studies. Along with the advantage in the rapid acquisition, DSMs are capable of creating virtual models of fractured outcrops to be interpreted for further analysis. This paper reports the DSM robustness by comparing the result of fracture-lineament measurement using DSMs and discusses the possible causes of error that might occur. The first method applied in this study is the scanline method to collect fracture data directly from outcrops, measuring more than 1,400 fracture data. The second method is applying fully automatic and manual fracture identification by optimizing hill-shaded DSMs. Two well-exposed granite outcrops in Bangka, Indonesia, are designed for the pilot area. Structure-from-Motion (SfM) photogrammetry is utilized to generate the DSMs, where a series of aerial images are captured using Unmanned Aerial Vehicle (UAV). The images are then processed into h...

Modern Applied Science, May 30, 2018

A continuous clastic sedimentary rock outcrop in the Karanggayam Area, Kebumen represents the com... more A continuous clastic sedimentary rock outcrop in the Karanggayam Area, Kebumen represents the complete deep marine fan facies of the Middle Miocene Lower Penosogan Formation. Lithology association and vertical succession were observed from a 63 meters detailed measured section along the Karanggayam River. This study aims to identify and classify the turbidite succession as well as the depositional environment of the formation within the North Serayu Basin, Central Java. From the bottom to top the Lower Penosogan Formation is divided into: A2, B2, C2, D2 and F2 facies which represents basin plain, overbank (levee and distal levee), crevasse splay, channel-fill and frontal splay facies respectively. Changes in the depositional environment are interpreted to be influenced by the dynamic changes in morphology and global climate change caused by underwater volcanic activity as a result of Middle Miocene tectonic activity.

IOP Conference Series: Earth and Environmental Science, Jun 1, 2018

This paper presents new finding from the sedimentary sequences, overlooked by previous researcher... more This paper presents new finding from the sedimentary sequences, overlooked by previous researchers, which provide insights to the sea level changes during the deposition of the Middle to Late Pliocene Kalibiuk Formation. Data were acquired from fieldwork via detailed measured section of each sedimentary sequence from the bottom to the upper part of the formation followed by molluscan fossil association analyses. Lithologically, the Cisaat River stratigraphic section is dominated by greenish grey claystone with some light grey fine-grained sandstone intercalation. Based on about 50 m stratigraphic section, 10 molluscan fossils associations were successfully determined. The sequence from bottom to top are: Corbula – Natica association, Nassa sp. association, Olividae – Turricula association, Pecten – Telina association, Telina – Placuna association, Corbula – Marginella association, Placuna – Natica association, Turritella association, Turritella – Marginella association and Dentalina – Architectonica association. Changes in vertical succession of the molluscan association indicates a development from shallow marine to terrestrial depositional environment before gradually overlain by terrestrial sediments of the Kaliglagah Formation. At least there are 2 deepening - shallowing sea level cycles during the deposition of Kalibiuk Formation observed from this section.

IOP Conference Series: Earth and Environmental Science, Jun 1, 2018

Earth and Planetary Science Letters

Key to understanding the plate kinematic evolution of the Neotethys oceanic domain that existed b... more Key to understanding the plate kinematic evolution of the Neotethys oceanic domain that existed between the Gondwana-derived Indian and Australian continents in the south, and Eurasia in the north, is the reconstruction of oceanic plates that are now entirely lost to subduction. Relics of these oceanic plates exist in the form of ophiolites and island arcs accreted to the orogen that stretches from Tibet and the Himalayas to SE Asia that formed the southern margin of Sundaland. The intra-oceanic Woyla Arc thrusted over western Sundaland-the Eurasian core of SE Asia-in the mid-Cretaceous. The Woyla Arc was previously interpreted to have formed above a west-dipping subduction zone in the Early Cretaceous, synchronous with east-dipping subduction below Sundaland. The oceanic 'Ngalau Plate' between the Woyla Arc and Sundaland was lost to subduction. We present paleomagnetic results from Lower Cretaceous limestones and volcaniclastic rocks of the Woyla Arc, Middle Jurassic radiolarian cherts of the intervening Ngalau Plate, and Upper Jurassic-Lower Cretaceous detrital sediments of the Sundaland margin. Our results suggest that the Woyla Arc was formed around equatorial latitudes and only underwent an eastward longitudinal motion relative to Sundaland. This is consistent with a scenario where the Woyla Arc was formed on the edge of the Australian plate. We propose a reconstruction where the Ngalau Plate formed a triangular oceanic basin between the N-S trending Woyla Arc and the NW-SE trending Sundaland margin to account for the absence of accreted arc rocks in the Himalayas. As consequence of this triangular geometry, accretion of the Woyla Arc to the western Sundaland margin was diachronous, accommodated by a southward migrating triple junction. Continuing convergence of the Australia relative to Eurasia was accommodated by subduction polarity reversal behind the Woyla Arc, possibly recorded by Cretaceous ophiolites in the Indo-Burman Ranges and the Andaman-Nicobar Islands.

Modern Applied Science

A detailed stratigraphy description and measurements of the sedimentary facies within the Halang ... more A detailed stratigraphy description and measurements of the sedimentary facies within the Halang Formation has been carried out to provide a thorough assessment of the architectural facies and depositional environment. The study area is located along the Tajum River in the District of Gumelar, Banyumas, Central Java-Indonesia where most of the Halang Formation is preserved in a good condition. Three cycles of facies association from basin plain, in channel to channel overbank deposits were able to be determined from the formation which indicate very active changes of sub-depositional environment that related to transgressive response influenced by the local tectonic during sedimentation takes place.

Jurnal Geologi dan Sumberdaya Mineral

The Tertiary stratigraphy of Situbondo was constructed by a series of volcanoclastic-carbonate tu... more The Tertiary stratigraphy of Situbondo was constructed by a series of volcanoclastic-carbonate turbidite facies of Menuran Formation with Pacalan limestone Member, and Leprak Formation. These formations formed a regional east-west trending circular anticlinorium. The Tertiary formations were covered by Quaternary volcano-clastic Ringgit Formation and subsequent younger Bagor volcanic products. The oldest Tertiary rock units are the Late Miocene-Pliocene Menuran Formation, with Pacalan Limestone Member. Formation is mainly composed of foram-rich marls and calcareous, sometimes tuffaceous sandstones, with conglomerate intercalations. Sedimentation of this formation is interpreted as to be a mixing, from proximal to distal turbidite, involving volcaniclastic and carbonate sources, in a bathyal open marine environment. The Early Pliocene Leprak Formation overlies conformably the Menuran Formation, which consists of alternating calcareous sandstones and tuff sandstones deposited in a ba...