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86-595: This is a brief summary of the geology of Indonesia . Indonesia is located between two major tectonic plates namely, the Australian Plate and the newly-separated Sunda Plate . The tectonics of Indonesia are very complex, as it is a meeting point of several tectonic plates . Indonesia is located between two continental plates: the Sahul Shelf and the Sunda Plate ; and between two oceanic plates:

172-455: A Mohs hardness of 2 to 4, dense limestone can have a crushing strength of up to 180 MPa . For comparison, concrete typically has a crushing strength of about 40 MPa. Although limestones show little variability in mineral composition, they show great diversity in texture. However, most limestone consists of sand-sized grains in a carbonate mud matrix. Because limestones are often of biological origin and are usually composed of sediment that

258-463: A bloom of cyanobacteria or microalgae . However, stable isotope ratios in modern carbonate mud appear to be inconsistent with either of these mechanisms, and abrasion of carbonate grains in high-energy environments has been put forward as a third possibility. Formation of limestone has likely been dominated by biological processes throughout the Phanerozoic , the last 540 million years of

344-692: A heading of 80° (slightly north of due east, at the Amsterdam transform fault to the south western side of Australian plate), 7 cm (2.8 in) per year with heading 120° (southeast) and 6.6 cm (2.6 in) per year near the Macquarie triple junction which is the south eastern side of the Australian plate. The Capricorn plate at the western side of the Australian plate is moving at 1.9 mm (0.075 in) per year ± 0.5 mm (0.020 in) per year with heading 45° (northwest) relative to

430-726: A bend up towards the north-east via the transform faults of the Hunter Fracture Zone to Fiji . The Australian plate interacts at the southern and south-eastern border of the North Fiji Basin with the microplates of the New Hebrides already mentioned, as well as with the Conway Reef plate and the Balmoral Reef plates . To the west of Fiji the Australian plate interacts in the spreading centre of

516-434: A carbonate rock outcrop can be estimated in the field by etching the surface with dilute hydrochloric acid. This etches away the calcite and aragonite, leaving behind any silica or dolomite grains. The latter can be identified by their rhombohedral shape. Crystals of calcite, quartz , dolomite or barite may line small cavities ( vugs ) in the rock. Vugs are a form of secondary porosity, formed in existing limestone by

602-616: A central quartz grain or carbonate mineral fragment. These likely form by direct precipitation of calcium carbonate onto the ooid. Pisoliths are similar to ooids, but they are larger than 2 mm in diameter and tend to be more irregular in shape. Limestone composed mostly of ooids is called an oolite or sometimes an oolitic limestone . Ooids form in high-energy environments, such as the Bahama platform, and oolites typically show crossbedding and other features associated with deposition in strong currents. Oncoliths resemble ooids but show

688-449: A change in environment that increases the solubility of calcite. Dense, massive limestone is sometimes described as "marble". For example, the famous Portoro "marble" of Italy is actually a dense black limestone. True marble is produced by recrystallization of limestone during regional metamorphism that accompanies the mountain building process ( orogeny ). It is distinguished from dense limestone by its coarse crystalline texture and

774-949: A composition reflecting the organisms that produced them and the environment in which they were produced. Low-magnesium calcite skeletal grains are typical of articulate brachiopods , planktonic (free-floating) foraminifera, and coccoliths . High-magnesium calcite skeletal grains are typical of benthic (bottom-dwelling) foraminifera, echinoderms , and coralline algae . Aragonite skeletal grains are typical of molluscs , calcareous green algae , stromatoporoids , corals , and tube worms . The skeletal grains also reflect specific geological periods and environments. For example, coral grains are more common in high-energy environments (characterized by strong currents and turbulence) while bryozoan grains are more common in low-energy environments (characterized by quiet water). Ooids (sometimes called ooliths) are sand-sized grains (less than 2mm in diameter) consisting of one or more layers of calcite or aragonite around

860-412: A considerable fraction of the limestone bed. At depths greater than 1 km (0.62 miles), burial cementation completes the lithification process. Burial cementation does not produce stylolites. When overlying beds are eroded, bringing limestone closer to the surface, the final stage of diagenesis takes place. This produces secondary porosity as some of the cement is dissolved by rainwater infiltrating

946-483: A drop of dilute hydrochloric acid is dropped on it. Dolomite is also soft but reacts only feebly with dilute hydrochloric acid, and it usually weathers to a characteristic dull yellow-brown color due to the presence of ferrous iron. This is released and oxidized as the dolomite weathers. Impurities (such as clay , sand, organic remains, iron oxide , and other materials) will cause limestones to exhibit different colors, especially with weathered surfaces. The makeup of

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1032-637: A few million years, as this is the most stable form of calcium carbonate. Ancient carbonate formations of the Precambrian and Paleozoic contain abundant dolomite, but limestone dominates the carbonate beds of the Mesozoic and Cenozoic . Modern dolomite is quite rare. There is evidence that, while the modern ocean favors precipitation of aragonite, the oceans of the Paleozoic and middle to late Cenozoic favored precipitation of calcite. This may indicate

1118-455: A few thousand years. As rainwater mixes with groundwater, aragonite and high-magnesium calcite are converted to low-calcium calcite. Cementing of thick carbonate deposits by rainwater may commence even before the retreat of the sea, as rainwater can infiltrate over 100 km (60 miles) into sediments beneath the continental shelf. As carbonate sediments are increasingly deeply buried under younger sediments, chemical and mechanical compaction of

1204-490: A high percentage of the mineral dolomite , CaMg(CO 3 ) 2 . Magnesian limestone is an obsolete and poorly-defined term used variously for dolomite, for limestone containing significant dolomite ( dolomitic limestone ), or for any other limestone containing a significant percentage of magnesium . Most limestone was formed in shallow marine environments, such as continental shelves or platforms , though smaller amounts were formed in many other environments. Much dolomite

1290-777: A hundred years for a large-scale earthquake to occur off the coast of Sumatra, it may take roughly 500 years off the coast of western Java. Off the coast of western Java there is potentially a backthrust fault. The existence of the backthrust could increase the height of tsunamis off the coast. There are two megathrust segments, one off of Southeastern Sumatra and the other off of Western Java. These segments contribute to tsunamis that average at 11 m (36 ft) in size but that can reach 34 m (112 ft). The combination of megathrusts and backthrusts are reasons for such massive tsunamis. The tectonics processes in Indonesia formed major structures in Indonesia. The most prominent fault in

1376-435: A limestone sample except in thin section and are less common in ancient limestones, possibly because compaction of carbonate sediments disrupts them. Limeclasts are fragments of existing limestone or partially lithified carbonate sediments. Intraclasts are limeclasts that originate close to where they are deposited in limestone, while extraclasts come from outside the depositional area. Intraclasts include grapestone , which

1462-471: A lower Mg/Ca ratio in the ocean water of those times. This magnesium depletion may be a consequence of more rapid sea floor spreading , which removes magnesium from ocean water. The modern ocean and the ocean of the Mesozoic have been described as "aragonite seas". Most limestone was formed in shallow marine environments, such as continental shelves or platforms . Such environments form only about 5% of

1548-525: A lower diversity of organisms and a greater fraction of silica and clay minerals characteristic of marls . The Green River Formation is an example of a prominent freshwater sedimentary formation containing numerous limestone beds. Freshwater limestone is typically micritic. Fossils of charophyte (stonewort), a form of freshwater green algae, are characteristic of these environments, where the charophytes produce and trap carbonates. Limestones may also form in evaporite depositional environments . Calcite

1634-523: A mechanism for dolomitization, with one 2004 review paper describing it bluntly as "a myth". Ordinary seawater is capable of converting calcite to dolomite, if the seawater is regularly flushed through the rock, as by the ebb and flow of tides (tidal pumping). Once dolomitization begins, it proceeds rapidly, so that there is very little carbonate rock containing mixed calcite and dolomite. Carbonate rock tends to be either almost all calcite/aragonite or almost all dolomite. About 20% to 25% of sedimentary rock

1720-448: A plausible source of mud. Another possibility is direct precipitation from the water. A phenomenon known as whitings occurs in shallow waters, in which white streaks containing dispersed micrite appear on the surface of the water. It is uncertain whether this is freshly precipitated aragonite or simply material stirred up from the bottom, but there is some evidence that whitings are caused by biological precipitation of aragonite as part of

1806-449: A radial rather than layered internal structure, indicating that they were formed by algae in a normal marine environment. Peloids are structureless grains of microcrystalline carbonate likely produced by a variety of processes. Many are thought to be fecal pellets produced by marine organisms. Others may be produced by endolithic (boring) algae or other microorganisms or through breakdown of mollusc shells. They are difficult to see in

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1892-460: A single Indo-Australian plate . However, recent studies suggest that the two plates have once again split apart and have been separate plates for at least 3 million years and likely longer. The Australian plate includes the continent of Australia , including Tasmania , as well as portions of New Guinea , New Zealand and the Indian Ocean basin. The continental crust of this plate covers

1978-635: Is about half that of the collision with the Sunda plate, but this would not explain some of the largest and most destructive recent earthquakes and eruptions on the face of the planet. There is oblique convergence of what are now the Pacific and Australian plates at about 11 cm/year (4.3 in/year) near eastern Papua New Guinea. This has resulted in shear complexities, resolved by the formation of multiple microplates and convergence velocity that varies between 2–48 cm/year (0.79–18.90 in/year) where

2064-560: Is also favored on the seaward margin of shelves and platforms, where there is upwelling deep ocean water rich in nutrients that increase organic productivity. Reefs are common here, but when lacking, ooid shoals are found instead. Finer sediments are deposited close to shore. The lack of deep sea limestones is due in part to rapid subduction of oceanic crust, but is more a result of dissolution of calcium carbonate at depth. The solubility of calcium carbonate increases with pressure and even more with higher concentrations of carbon dioxide, which

2150-482: Is an uncommon mineral in limestone, and siderite or other carbonate minerals are rare. However, the calcite in limestone often contains a few percent of magnesium . Calcite in limestone is divided into low-magnesium and high-magnesium calcite, with the dividing line placed at a composition of 4% magnesium. High-magnesium calcite retains the calcite mineral structure, which is distinct from dolomite. Aragonite does not usually contain significant magnesium. Most limestone

2236-402: Is carbonate rock, and most of this is limestone. Limestone is found in sedimentary sequences as old as 2.7 billion years. However, the compositions of carbonate rocks show an uneven distribution in time in the geologic record. About 95% of modern carbonates are composed of high-magnesium calcite and aragonite. The aragonite needles in carbonate mud are converted to low-magnesium calcite within

2322-474: Is clusters of peloids cemented together by organic material or mineral cement. Extraclasts are uncommon, are usually accompanied by other clastic sediments, and indicate deposition in a tectonically active area or as part of a turbidity current . The grains of most limestones are embedded in a matrix of carbonate mud. This is typically the largest fraction of an ancient carbonate rock. Mud consisting of individual crystals less than 5 μm (0.20 mils) in length

2408-416: Is commonly white to gray in color. Limestone that is unusually rich in organic matter can be almost black in color, while traces of iron or manganese can give limestone an off-white to yellow to red color. The density of limestone depends on its porosity, which varies from 0.1% for the densest limestone to 40% for chalk. The density correspondingly ranges from 1.5 to 2.7 g/cm . Although relatively soft, with

2494-420: Is controlled largely by the amount of dissolved carbon dioxide ( CO 2 ) in the water. This is summarized in the reaction: Increases in temperature or decreases in pressure tend to reduce the amount of dissolved CO 2 and precipitate CaCO 3 . Reduction in salinity also reduces the solubility of CaCO 3 , by several orders of magnitude for fresh water versus seawater. Near-surface water of

2580-545: Is converted to low-magnesium calcite. Diagenesis is the likely origin of pisoliths , concentrically layered particles ranging from 1 to 10 mm (0.039 to 0.394 inches) in diameter found in some limestones. Pisoliths superficially resemble ooids but have no nucleus of foreign matter, fit together tightly, and show other signs that they formed after the original deposition of the sediments. Silicification occurs early in diagenesis, at low pH and temperature, and contributes to fossil preservation. Silicification takes place through

2666-503: Is deposited close to where it formed, classification of limestone is usually based on its grain type and mud content. Most grains in limestone are skeletal fragments of marine organisms such as coral or foraminifera . These organisms secrete structures made of aragonite or calcite, and leave these structures behind when they die. Other carbonate grains composing limestones are ooids , peloids , and limeclasts ( intraclasts and extraclasts  [ ca ] ). Skeletal grains have

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2752-460: Is described as coquinite . Chalk is a soft, earthy, fine-textured limestone composed of the tests of planktonic microorganisms such as foraminifera, while marl is an earthy mixture of carbonates and silicate sediments. Limestone forms when calcite or aragonite precipitate out of water containing dissolved calcium, which can take place through both biological and nonbiological processes. The solubility of calcium carbonate ( CaCO 3 )

2838-617: Is described as micrite . In fresh carbonate mud, micrite is mostly small aragonite needles, which may precipitate directly from seawater, be secreted by algae, or be produced by abrasion of carbonate grains in a high-energy environment. This is converted to calcite within a few million years of deposition. Further recrystallization of micrite produces microspar , with grains from 5 to 15 μm (0.20 to 0.59 mils) in diameter. Limestone often contains larger crystals of calcite, ranging in size from 0.02 to 0.1 mm (0.79 to 3.94 mils), that are described as sparry calcite or sparite . Sparite

2924-462: Is distinguished from micrite by a grain size of over 20 μm (0.79 mils) and because sparite stands out under a hand lens or in thin section as white or transparent crystals. Sparite is distinguished from carbonate grains by its lack of internal structure and its characteristic crystal shapes. Geologists are careful to distinguish between sparite deposited as cement and sparite formed by recrystallization of micrite or carbonate grains. Sparite cement

3010-701: Is not parallel to the biogeographical Wallace line that separates the indigenous fauna of Asia from that of Australasia . The eastern islands of Indonesia lie mainly on the Eurasian plate , but have Australasian-related fauna and flora. Southeasterly lies the Sunda Shelf . To the east of Indonesia there appears to be under the Indian Ocean a deformation zone between the Indian and Australian plates with both earthquake and global satellite navigation system data indicating that India and Australia are not moving on

3096-560: Is one of the first minerals to precipitate in marine evaporites. Most limestone is formed by the activities of living organisms near reefs, but the organisms responsible for reef formation have changed over geologic time. For example, stromatolites are mound-shaped structures in ancient limestones, interpreted as colonies of cyanobacteria that accumulated carbonate sediments, but stromatolites are rare in younger limestones. Organisms precipitate limestone both directly as part of their skeletons, and indirectly by removing carbon dioxide from

3182-473: Is otherwise chemically fairly pure, with clastic sediments (mainly fine-grained quartz and clay minerals ) making up less than 5% to 10% of the composition. Organic matter typically makes up around 0.2% of a limestone and rarely exceeds 1%. Limestone often contains variable amounts of silica in the form of chert or siliceous skeletal fragments (such as sponge spicules, diatoms , or radiolarians ). Fossils are also common in limestone. Limestone

3268-472: Is produced by decaying organic matter settling into the deep ocean that is not removed by photosynthesis in the dark depths. As a result, there is a fairly sharp transition from water saturated with calcium carbonate to water unsaturated with calcium carbonate, the lysocline , which occurs at the calcite compensation depth of 4,000 to 7,000 m (13,000 to 23,000 feet). Below this depth, foraminifera tests and other skeletal particles rapidly dissolve, and

3354-518: Is secondary dolomite, formed by chemical alteration of limestone. Limestone is exposed over large regions of the Earth's surface, and because limestone is slightly soluble in rainwater, these exposures often are eroded to become karst landscapes. Most cave systems are found in limestone bedrock. Limestone has numerous uses: as a chemical feedstock for the production of lime used for cement (an essential component of concrete ), as aggregate for

3440-853: The Alpine Fault . South of New Zealand the boundary becomes a transitional transform-convergent boundary, the Macquarie Fault Zone , where the Australian plate is beginning to subduct under the Pacific plate along the Puysegur Trench . Extending southwest of this trench is the Macquarie Ridge . The southerly side is a divergent boundary with the Antarctic plate called the Southeast Indian Ridge (SEIR). The subducting boundary through Indonesia

3526-592: The Antarctic plate , the African plate and the Indian plate . It is however known from movement studies that this definition of the Australian plate is 20% less accurate than one that assumes independently moving Capricorn , and Macquarie microplates. The northeasterly side is a complex but generally convergent boundary with the Pacific plate . The Pacific plate is subducting under the Australian plate, which forms

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3612-900: The Ediacaran (South African Kuunga Orogeny ). As a separate plate, the Australian plate came into being on the breakup of Gondwana with final separation from what is now the Antarctic plate and Zealandia starting in the Early Cretaceous between about 132  million years ago and finishing in the Cenomanian at about 96  million years ago . The separation continued with various authors modelling full separation time based on sea levels and/or biological separation. A currently widely used reference model for plate movement has total separation of Tasmania by 60 million years ago although some had argued historically that this

3698-698: The Lau Basin with the Niuafo'ou plate and the clockwise rotating Tonga plate under which the Pacific plate is subducting in the Kermadec-Tonga subduction zone . The back arc spreading in the Lau Basin continues almost due south in the line of interaction between the Australian and Tonga plates to the Kermadec plate and on to New Zealand where direct interaction resumes with the Pacific plate south of

3784-592: The New Hebrides plate . As we go south the convergence rate falls from 17 cm/year (6.7 in/year) north of the Torres Islands to 4 cm/year (1.6 in/year) in the central section of the trench, to rise again to 12 cm/year (4.7 in/year) in the south. Very active spreading then resumes in the North Fiji Basin where the edge of the Australian plate makes a transition in

3870-761: The Pacific and Indian oceans. Tectonic uplift of the region, exacerbated by lowered sea levels during recent glaciation , is hypothesized to have altered the regional climate, especially with respect to monsoons , beginning ~4 million years ago. The stratigraphy of the western part of Indonesia is dominated by Cenozoic age formations, ranging from Paleogene to Quaternary . Minor Mesozoic and Paleozoic formations were found in places. Devonian limestones were found in Telen River, East Kalimantan , as fragments within Paleogene clastic sediments . Eastern Indonesia has generally older stratigraphy compared to

3956-757: The Pacific Plate and the Philippine Sea Plate . The subduction of the Indian Plate beneath the Sunda Plate formed the volcanic arc in western Indonesia, one of the most seismically active areas on the planet with a long history of powerful eruptions and earthquakes. This chain of active volcanoes formed Sumatra , Java , Bali , and the Lesser Sunda Islands , most of which, particularly Java and Bali, emerged within

4042-832: The Solomon Sea plate subducts under the South Bismarck plate and Pacific plate at the New Britain subduction zone . To the south of this there is sea floor spreading between the Australian plate and the Woodlark plate in the Woodlark Basin while the subduction of the oceanic crust of the Australian plate occurs to the south east in the New Hebrides Trench of the Vanuatu subduction zone under

4128-532: The Sunda plate (Sundaland plate, previously classified as part of Eurasian plate ) has a maximum convergence velocity of 7.3 cm (2.9 in) per year ± 0.8 cm (0.31 in) per year at the Java Trench decreasing to 6.0 cm (2.4 in) ± 0.04 cm (0.016 in) per year at the southern Sumatra Trench . The eastern collision with the Pacific plate has increasing displacement rates towards

4214-529: The Taupō Volcanic Zone and such direct interaction continues into the Macquarie Fault Zone to the south of New Zealand. There is up to 9.6 cm (3.8 in) per year motion accommodated with complex rotational components in the collision dynamics between the north eastern Australian plate and the rotating Tonga plate , the long thin Kermadec plate and the south western aspects of the Pacific plate. The Pacific plate east to west convergence rates along

4300-476: The Tonga and Kermadec Trenches , and the parallel Tonga and Kermadec island arcs . It has also uplifted the eastern parts of New Zealand's North Island . The continent of Zealandia , which separated from Australia 85  million years ago and stretches from New Caledonia in the north to New Zealand's subantarctic islands in the south, is now being torn apart along the transform boundary marked by

4386-566: The Australia plate. Limestone Limestone ( calcium carbonate CaCO 3 ) is a type of carbonate sedimentary rock which is the main source of the material lime . It is composed mostly of the minerals calcite and aragonite , which are different crystal forms of CaCO 3 . Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as

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4472-468: The Australian plate that the latest tectonic models suggest is still independent from when it first achieved independent rotation to the then Indo-Australian plate several million years ago, the Macquarie microplate. Data from the 11,800 km (7,300 mi) long Southeast Indian Ridge only became available after about 1985 and this gives a fairly consistent spreading rate between the Antarctic and Australian plates of 6 cm (2.4 in) per year at

4558-496: The Earth's history. Limestone may have been deposited by microorganisms in the Precambrian , prior to 540 million years ago, but inorganic processes were probably more important and likely took place in an ocean more highly oversaturated in calcium carbonate than the modern ocean. Diagenesis is the process in which sediments are compacted and turned into solid rock . During diagenesis of carbonate sediments, significant chemical and textural changes take place. For example, aragonite

4644-620: The Mount Barren Group on the southern margin of the Yilgarn Craton and zircon provenance analysis support the hypothesis that collisions between the Pilbara – Yilgarn and Yilgarn – Gawler Cratons assembled a proto-Australian continent approximately 1,696  million years ago (Dawson et al. 2002). Australia and East Antarctica were merged with Gondwana between 570 and 530  million years ago starting in

4730-653: The Southeast Indian Ridge between the Australian plate and the proposed Capricorn plate . It is known that the Eastern Pilbara Craton within present day Western Australia , contains some of the oldest surface rocks on earth being pristine crust up to 3.8 billion years ago. Accordingly, the Pilbara Craton continues to be studied for clues as to the commencement and subsequent course of plate tectonics . Depositional age of

4816-430: The accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life. About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. The remaining carbonate rock is mostly dolomite , a closely related rock, which contains

4902-434: The base of roads, as white pigment or filler in products such as toothpaste or paint, as a soil conditioner , and as a popular decorative addition to rock gardens . Limestone formations contain about 30% of the world's petroleum reservoirs . Limestone is composed mostly of the minerals calcite and aragonite , which are different crystal forms of calcium carbonate ( CaCO 3 ). Dolomite , CaMg(CO 3 ) 2 ,

4988-657: The beds. This may include the formation of vugs , which are crystal-lined cavities within the limestone. Diagenesis may include conversion of limestone to dolomite by magnesium-rich fluids. There is considerable evidence of replacement of limestone by dolomite, including sharp replacement boundaries that cut across bedding. The process of dolomitization remains an area of active research, but possible mechanisms include exposure to concentrated brines in hot environments ( evaporative reflux ) or exposure to diluted seawater in delta or estuary environments ( Dorag dolomitization ). However, Dorag dolomitization has fallen into disfavor as

5074-466: The depositional fabric of carbonate rocks. Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles, based on criteria such as whether the grains were originally in mutual contact, and therefore self-supporting, or whether the rock is characterized by the presence of frame builders and algal mats. Unlike the Folk scheme, Dunham deals with the original porosity of

5160-469: The deposits are highly porous, so that they have a spongelike texture, they are typically described as tufa . Secondary calcite deposited by supersaturated meteoric waters ( groundwater ) in caves is also sometimes described as travertine. This produces speleothems , such as stalagmites and stalactites . Coquina is a poorly consolidated limestone composed of abraded pieces of coral , shells , or other fossil debris. When better consolidated, it

5246-406: The earth's oceans are oversaturated with CaCO 3 by a factor of more than six. The failure of CaCO 3 to rapidly precipitate out of these waters is likely due to interference by dissolved magnesium ions with nucleation of calcite crystals, the necessary first step in precipitation. Precipitation of aragonite may be suppressed by the presence of naturally occurring organic phosphates in

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5332-399: The first refers to the grains and the second to the cement. For example, a limestone consisting mainly of ooids, with a crystalline matrix, would be termed an oosparite. It is helpful to have a petrographic microscope when using the Folk scheme, because it is easier to determine the components present in each sample. Robert J. Dunham published his system for limestone in 1962. It focuses on

5418-572: The formation of distinctive minerals from the silica and clay present in the original limestone. Two major classification schemes, the Folk and Dunham, are used for identifying the types of carbonate rocks collectively known as limestone. Robert L. Folk developed a classification system that places primary emphasis on the detailed composition of grains and interstitial material in carbonate rocks . Based on composition, there are three main components: allochems (grains), matrix (mostly micrite), and cement (sparite). The Folk system uses two-part names;

5504-429: The geologic record are called bioherms . Many are rich in fossils, but most lack any connected organic framework like that seen in modern reefs. The fossil remains are present as separate fragments embedded in ample mud matrix. Much of the sedimentation shows indications of occurring in the intertidal or supratidal zones, suggesting sediments rapidly fill available accommodation space in the shelf or platform. Deposition

5590-421: The last 2–3 million years. The Pacific and Sahul plate movements controlled the tectonics of the eastern portion of Indonesia. Subduction occurs along Southeastern Sumatra and West Java. Sumatra is more active in recent years despite being in the same subduction margin. The reason for the lack of frequent seismic activity over West Java is a problem of time frame and not of tectonic activity. While it may only take

5676-402: The middle of India and Australia landmasses, with Australia as the point of reference, presently Australia is moving northward at 3 cm (1.2 in) per year with respect to India consistent with a zone of deformation between the two plates as commented upon earlier. This zone of deformation may actually presently involve some of India. The northwards collision of the Australian plate with

5762-405: The north from a low of less than 0.2 cm (0.079 in) per year at the southern end of the Macquarie Fault Zone , where there is the major plate triple junction with the Pacific and Antarctic plates . Due to vector complexities at the north eastern end of this collision, which includes several spreading centres, it is perhaps simplest to state that the average displacement rate to the north

5848-556: The northern part of West Papua to East Sulawesi for about 2000 km. The various formations in the Indonesian Archipelago and New Guinea 's Torres Strait form geologic choke points to shipping and aqueous transport , particularly at depths below 100m (where said aqueous transport is largely closed); such routes, whether closed or still extant, collectively comprise the Indonesian Seaway between

5934-410: The ocean basins, but limestone is rarely preserved in continental slope and deep sea environments. The best environments for deposition are warm waters, which have both a high organic productivity and increased saturation of calcium carbonate due to lower concentrations of dissolved carbon dioxide. Modern limestone deposits are almost always in areas with very little silica-rich sedimentation, reflected in

6020-426: The reaction: Fossils are often preserved in exquisite detail as chert. Cementing takes place rapidly in carbonate sediments, typically within less than a million years of deposition. Some cementing occurs while the sediments are still under water, forming hardgrounds . Cementing accelerates after the retreat of the sea from the depositional environment, as rainwater infiltrates the sediment beds, often within just

6106-482: The relative purity of most limestones. Reef organisms are destroyed by muddy, brackish river water, and carbonate grains are ground down by much harder silicate grains. Unlike clastic sedimentary rock, limestone is produced almost entirely from sediments originating at or near the place of deposition. Limestone formations tend to show abrupt changes in thickness. Large moundlike features in a limestone formation are interpreted as ancient reefs , which when they appear in

6192-460: The rock. The Dunham scheme is more useful for hand samples because it is based on texture, not the grains in the sample. A revised classification was proposed by Wright (1992). It adds some diagenetic patterns to the classification scheme. Travertine is a term applied to calcium carbonate deposits formed in freshwater environments, particularly waterfalls , cascades and hot springs . Such deposits are typically massive, dense, and banded. When

6278-407: The same vectors northward and have started a process of again separating. This zone is along the northern Ninety East Ridge which implies this area presently is weaker tectonically than the area where originally the Indian and Australian plates merged which is believed to have been further to the north west. There is also deformation in an approximately 1,200 km (750 mi) zone north of

6364-479: The sediments increases. Chemical compaction takes place by pressure solution of the sediments. This process dissolves minerals from points of contact between grains and redeposits it in pore space, reducing the porosity of the limestone from an initial high value of 40% to 80% to less than 10%. Pressure solution produces distinctive stylolites , irregular surfaces within the limestone at which silica-rich sediments accumulate. These may reflect dissolution and loss of

6450-662: The sediments of the ocean floor abruptly transition from carbonate ooze rich in foraminifera and coccolith remains ( Globigerina ooze) to silicic mud lacking carbonates. In rare cases, turbidites or other silica-rich sediments bury and preserve benthic (deep ocean) carbonate deposits. Ancient benthic limestones are microcrystalline and are identified by their tectonic setting. Fossils typically are foraminifera and coccoliths. No pre-Jurassic benthic limestones are known, probably because carbonate-shelled plankton had not yet evolved. Limestones also form in freshwater environments. These limestones are not unlike marine limestone, but have

6536-638: The south starts subducting under the Pacific plate at a rate of 3.6 cm/year (1.4 in/year) at the Puysegur Trench , which ends in the south as a long series of transform faults between the two plates called the Macquarie Ridge Complex, commencing with the McDougall Fault Zone and ending with the Macquarie Fault Zone. The south western portion of the zone has the Pacific plate interacting with an area of

6622-522: The subduction systems with the Kermadec plate, which are perhaps simpler to state, are among the fastest on Earth, being 8 cm (3.1 in) per year in the north and 4.5 cm (1.8 in) per year in the south. At the central Alpine Fault in New Zealand the subduction component of the Pacific plate moving westward is about 3.9 cm (1.5 in) per year. The Australian plate then to

6708-533: The water by photosynthesis and thereby decreasing the solubility of calcium carbonate. Limestone shows the same range of sedimentary structures found in other sedimentary rocks. However, finer structures, such as lamination , are often destroyed by the burrowing activities of organisms ( bioturbation ). Fine lamination is characteristic of limestone formed in playa lakes , which lack the burrowing organisms. Limestones also show distinctive features such as geopetal structures , which form when curved shells settle to

6794-553: The water. Although ooids likely form through purely inorganic processes, the bulk of CaCO 3 precipitation in the oceans is the result of biological activity. Much of this takes place on carbonate platforms . The origin of carbonate mud, and the processes by which it is converted to micrite, continue to be a subject of research. Modern carbonate mud is composed mostly of aragonite needles around 5 μm (0.20 mils) in length. Needles of this shape and composition are produced by calcareous algae such as Penicillus , making this

6880-583: The west across Makassar Strait , and ends in the Mangkalihat Peninsula in Borneo. The fault is named after the capital city of Central Sulawesi, Palu , on the west coast of Sulawesi and the Koro River, which is formed by the fault zone. Sorong fault is a significant left lateral fault in the eastern part of Indonesia, named after Sorong City . It has east-west orientation and extends from

6966-548: The west of Indonesia is the Semangko Fault or the Great Sumatran Fault, a dextral strike-slip fault along Sumatra Island (about 1,900 km). The formation of this fault zone is related to the subduction zone in the west of Sumatra. Palu-Koro fault is another major structural feature formed in the central part of Indonesia. This fault runs across the central part of Sulawesi Island and extends offshore to

7052-542: The western part. The stratigraphy ranges from Permian to Tertiary . Ichthyosaur fossils were found in the mud volcanoes in Kai Island , indicating Mesozoic deposition in the sub-surface (Charlton, 1992). Mesozoic macrofossils were studied in Misool Island by Fauzie Hasibuan (1996). Australian Plate The Australian plate later fused with the adjacent Indian plate beneath the Indian Ocean to form

7138-749: The whole of Australia, the Gulf of Carpentaria , southern New Guinea , the Arafura Sea , the Coral Sea . The continental crust also includes northwestern New Zealand , New Caledonia and Fiji . The oceanic crust includes the southeast Indian Ocean , the Tasman Sea , and the Timor Sea . The Australian plate is bordered (clockwise) by the Eurasian plate , the Philippine plate , the Pacific plate ,

7224-451: The work involved in determining these plate vectors involves assurance that the points of reference are representative of the plates they are on, as distortion will be likely in areas of tectonic activity. Further assumptions such as there are only 8 plates were made in earlier modelling when as many as 52 may exist, with independent movement, although fair accuracy for larger plate movement can be obtained if only 25 are modelled. In terms of

7310-440: Was as recent as 45 million years ago. The Australian plate, which Australia is on, is moving faster than other plates. The Australian plate is moving about 6.9 cm (2.7 inches) a year in a northward direction and with a small clockwise rotation. The Global Positioning System must be updated due to the movement, as some locations move faster. Technically movement is a vector and requires to be related to something. Much of

7396-416: Was likely deposited in pore space between grains, suggesting a high-energy depositional environment that removed carbonate mud. Recrystallized sparite is not diagnostic of depositional environment. Limestone outcrops are recognized in the field by their softness (calcite and aragonite both have a Mohs hardness of less than 4, well below common silicate minerals) and because limestone bubbles vigorously when

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