Southern Mountains, Yogyakarta Special Region is a zone that extends from the south-eastern part of Yogyakarta Special Region to the east along the southern coast of East Java. From the hydrogeological map, it is known that the area is an area of scarce groundwater. This study aims to determine the potential for groundwater in these areas. The identification of groundwater potential is carried out using the Groundwater Potentiality Index (GPI) method by referring to 5 determining parameters: lineaments, lithology, drainage, topography, and rainfall. Lineament, drainage, and topography data were obtained from the Indonesia Geospatial Portal and the Digital Elevation Model (DEM) belonging to the Indonesian Geospatial Information Agency. The lithological data is obtained from data from the Geological Survey Centre, Geological Agency, Ministry of Energy, and Mineral Resources in the form of Geological Maps of Remote Sensing Image Interpretation Results. Rainfall data were obtained from reports from the Serayu Opak River Basin Office and the Public Works, Housing, and Energy Department of Mineral Resources Yogyakarta Special Region. The evaluation of parameters reveals that even in the scarce groundwater zones, estimation of area with possible of groundwater can be classified into five classes of groundwater potential index, namely: very low (<56.25), low (56.25-90), medium (90-123.75), high (123.75-157.5), and very high (> 157.5). In the next step of research the validation may be conducted on a high and very high GPI value whether their are really is associated with the presence of springs and wells. If it is correlated, future exploration of groundwater in this area will be focused and successful.
The Rembang area is a well-known prospective region for oil and gas exploration in Northeast Java, Indonesia. In this study, the reservoir characteristics of the Ngrayong Sandstone were investigated based on outcrops in the Rembang area. Petrological, mineralogical, petrophysical and sedimentological facies analyses were conducted. These sandstones are grain-and matrix-supported, and composed of very fine to medium, sub-angular to poorly-rounded, moderately-to very well-sorted sand grains. These sandstones are mainly composed of quartz, orthoclase, plagioclase, and micas with minor amounts of clay minerals, and therefore are predominantly classified as sub-lithic arenite and sub-felds pathicarenite. Petrographic observations and grain size data indicate that these sandstones are texturally quite mature, based on their good -sorting and the occurrence of minor amounts of matrix clays. Common clays in the samples include illite, smectite, kaolinite, and gibbsite. The porosity of the Ngrayong sandstones ranges from 25.97% to 40.21%, and the permeability ranges from 94.6 to 3385 millidarcies. Thus, these sandstones exhibit well to excellent reservoir qualities. Eight lithofacies were identified from five measured stratigraphic sections, and are dominated by foreshore and tide-dominated shoreface facies. The Ngrayong sequence shows a single transgressiveregressive cycle. Cross-bedded sandstone and massive sandstone are identified as the most promising potential reservoir facies based on their characteristics in outcrops, their lateral and vertical distributions, their sedimentological characteristics and their petrophysical properties.
Breccia dominated rocks outcropping in the Tanjung Murau-Tanjung Sekakap area have been deposited in a composite system of alluvial fans and Gilbert-type deltas. The sedimentary facies ranges from boulder-dominated facies at the bottom to gravelstone-sandstone-dominated facies at the top of the succession. Other recognized facies are disorganized boulder-cobblesupported breccia (Bd), crudely stratified cobble-boulder-rich breccia (Bs), crudely stratified cobble-rich gravelstone (Gs-1), disorganized clast-supported gravelstone (Gd), crudely stratified pebble-rich gravelstone (Gs-2), normally-inversely-graded gravelstone (Gn-i), crossbedded gravelstone (Gc), stratified sandstone (Ss), massive sandstone (Sm) and homogenous mudstone (Mh) facies. Alluvial fan association feature discontinuous breccias and gravelstones (facies Bd and Bs), where sheet-floods and debris flows are dominant. The gravelstone dominated facies Gd, Gs-1 and Gs-2 intercalated with facies Gc are associated with the topset-foreset of a Gilbert-type fan-delta. The Gilbert-type topset are represented by facies Gc, Gn-i and Gs-2 as well as facies Ss. The dominance of breccia and gravelstone facies of alluvial fan and Gilbert-type topset-foreset delta facies associations suggest that these sediments were deposited on a steeply sloping continental margin with a rate of deposition similar to the rate of subsidence.
Low grade metamorphic rocks including slate, phyllite, metasandstone with subordinate schist and quartzite are widely distributed in the East Johor, Peninsular Malaysia. Regionally, this rock unit is extended northward up to northern Terengganu area. The protolith of this rocks unit were deposited in shallow marine depositional environment that subsequently metamorphosed during Carboniferous time. The very thick argillaceous and arenaceous rocks more than 5000 metres were produced by fast rate accommodation spaces due to global sea level rise during Early to Late Carboniferous against with high fine-grained sediment supply. Tectonic setting, basin formation and sedimentation processes were controlled by rifting of Indochina-East Malaya continental block from Gondwanaland during Devonian to Late Carboniferous. This rifting formed basins within a passive margin tectonic setting along the western margin of Indochina-East Malaya continental block.Keywords: Metamorphic rocks, shallow marine, Carboniferous, passive margin
A revision on the Palaeozoic lithostratigraphy of east Johor has been made. The Palaeozoic of east Johor comprises of the Mersing Formation, Murau Formation, Dohol Formation, Linggiu Formation, Sedili Volcanic, Jasin Volcanic and Pengerang Tuff. The pre-Permian Mersing Formation, the oldest known rock unit is entirely made up of metamorphosed sedimentary rock of shallow marine origin. Unconformably overlying this unit is the Murau Formation which developed in a small continental faulted basin. The siliciclastic Dohol Formation containing late Early to early Middle Permian Sumalayang limestone as well as the Late Permian Linggiu Formation are also unconformably overlying the Mersing Formation, as are the volcanic units of Pengerang Tuff, Sedili and Jasin Volcanics. The three volcanic units are thought to be contemporaneous and are closely related to the Early to Middle Permian Dohol Formation and the overlying Late Permian Linggiu Formation. The absence of volcanic clasts in the Murau Formation indicates that the later is a prevolcanic, hence pre-late Early Permian formation. The shallow marine Linggiu Formation and the associated volcanic rocks are the youngest Palaeozoic formation in east Johor.
<p>This study attempts to reconstruct paleogeography of Banyumas Basin in association with magmatic arc evolution and its implication to petroleum potential. Based on the volcanic rocks distribution, their association and relatives age, there are three alignments of a magmatic arc, that are: (1) Oligo-Miocene arc in the south (2) Mio-Pliocene arc in the middle (3) Plio-Pleistocene arc in the north. The consequences of the magmatic arc movement were tectonic setting changing during Oligocene to Pleistocene, as well as their paleogeography. During Oligo-Miocene where magmatic arc existed in the southern part, the Banyumas tectonic setting was a back-arc basin. This tectonic setting was changing to intra-arc basin during Mio-Pliocene and subsequently to fore-arc basin since Plio-Pleistocene until today. Back-arc basin is the most suitable paleogeography to create a depositional environment for potential source rocks. Exploration activity to prove the existence of source rocks during Oligo-Miocene is needed to reveal petroleum potential in Banyumas Basin.<br></p>
The early Middle Miocene Ngrayong Formation, an important reservoir of North East Java Basin, is well exposed in the central anticlinal part of Madura Island. The purpose of current study is to classify the depositional environments of the study area based on the characteristics and geometry of sedimentary facies. In the Madura island, the thicker clastics and deeper carbonates of Ngimbang Formation and Kujung Formation of Late Oligocene-Early Miocene deposited in the northeast-southwest asymmetrical half grabens. After the deposition of Kujung Formation, the basin morphology developed nearly eastwest trending shelf edge and the deposition of Tuban Formation began. The fine grained complex of Tuban Formation was followed by the Ngrayong Sandstones deposition. The depositional model of Ngrayong Formation is being producing of wide variety of depositional environments. Large scale cross-bedded sandstones and bioturbated massive sandstones with thin to medium bedded argillaceous limestone that outcrop in the northern part of the study area are deposited in costal environment. The heterolithic sandstone with planar and trough cross-lamination, fine grained sandstone with interlaminated structure and bioclastic carbonate exposed in the central part of the study area are deposited in upper shallow marine area. Dark grey siltstones and mudstones deposited in lower shallow marine area are well exposed in southern part of the study area. In conclusion, Ngrayong Formation in Madura area is developed in three depositional units which are coastal, upper shallow marine and lower shallow marine.
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