GEOLOGY OF KARANGSAMBUNG

GEOLOGY REGIONAL

I.1 Geomorphology of Karang Sambung
Region Karangsambung, located on ±19 Km to north from Kebumen Town, with coordinate between 07o30’00” – 07o45’00” LS dan 109o15’00” – 109o30’00”BT. Where, in region Karangsambung can be met various igneous rock types, Sediment and Metamorphic as result of subduction process between Hindia-Australia Oceanic Plate with Eurasia Continent Plate.
Based on physiographic sketchmap of Java by Bemmelen (1970), The area of Karangsambung is part of The South Serayu Mountain in Java.
Karangsambung area of width around 30 x 10 km2 is part of mountain of Serayu Selatan which has experienced innermost erosion, causing that, so laids bare pra-tersier rock. The morphology in this area is structural hilly and this area also is called as mélange complex. Besides that, fluvial morphology also there is in Karangsambung area.
The hills in karangsambung area are Waturanda hill, Sipako hill, Paras mountain, Brujul mountain, Jatibungkus hill, and other. This Location is Called as mélange complex because rocks over there is in disorder. Presentation of mélange in the field is in the form of blocks. And the scale of melange something tens until hundreds of meter, but there are also mélange is forming a mountain circuit.
One of morphology which seems to be in Karangsambung that is Luk Ulo river. This Luk Ulo river is including antecedent river, that is river type cutting principal geology sewer structures of the district, and is including mature stadium. Level of maturity of this river seen from meander and river terrace deposit formed on course far from prime river. Besides the prime river, Karangsambung has other river, that river is Kali Muncar , Kali Cacaban, Kali Mandala, Kali Brengkok and other.

I.2 Stratigraphy of Karangsambung
1. Karangsambung Formation
Litology Characteristic : is consisted of grey clay, containing iron concression, numulithes limestone lenses, polemic conglomerate and laminated quartz sandstone. Grey until black clay shows scaly structures with incision to all directions and almost flatten on the surface. Those structures estimated as the result of slumping depositional mechanism that happen under water level with big volume (subaquatic gravity gliding). The estimation is supported by slumping symptoms that is seen at broken and disorder inset of sandstone.
Numulithes limestone, conglomerate and sandstone that we found in there representing olistolith that besieged in clay.
A fine outcrop is found at the river near Karangsambung Village and Banjarsari. Numulithes limestone, polemic conglomerate and iron concressions is found around field college. Pasanggrahan hills next to college, is big polemic conglomerate olistolith.

Age : middle Eocene until late Eocene that based on plankton foraminifera presence. Globorotalia cerroazulensis and Truncolotarloides topilenses besides Nummulites Javana inside of limestone. Besides that, there is also found Alvegina and Discocyclina sp. As late Eocene age boundaries, based on Hantkenina alabamensis presence inside napal from Karangsambung Formation.
In some place that Karangsambung Formation has related with Melange LUH-ULO complex, both of groundmass are contained of clay and black – gray shale, sometimes difficult to get the differentiation. Especially when the outcrop was moldy. One of criteria that can used to differentiating is studying more accurate “boulder” inside there. In Melange, usually showed systematic cracked pattern, in pairs, responses from force work. In Melange, generally have cleavage structures, while on Karangsambung Formation (olistostrom) untidy directions.
2. Totogan Formation
Lithology Charateristic :
This beds have much same with Karangsambung beds. It is laped over scaly, with brown colour, and sometimes purple squeezing. Frgamen which contain this rock in mudstone, sandstone, fossiliferous limestone, and igneous rock to. That fragman have sub-rounded shapes, with slippery surface (like haved erotion) and size it fragmen between 2 until 20 cm, and more than bigger. To that beds have name muddy breccias. With characteristic like that, this beds also can called Olisostrome.
Age :
Age of this beds is Lower-Oligosen or N.2-N.3 zone, that based from founded the Globoquadrina praedehiscens, Globigeriona binaensis and not yet appearance Globigerinoides.
Stratigraphy Relation with Karangsambung beds :
Stratigraphy relation with Karangsambung beds in bottom of Totogan beds, can be perceived perfectly, but with the existence of spanning time, that is among P.17 until N.2 zone. Possibility have designating an unconformity. But with Waturanda beds this beds has conformity.
Depositional Environment :
Depositional environment from Totogan beds, with have much foraminifera plankton, showed marine condition, deep (100-200 m), with precipitous shoreline and steep sea floor so enabling that rock-fall has happened in that place, and continued with olisostrome formed. The condition like this can be descriptioned as geosinklin with fault structure at its edge. At another place even can be observed the bedding very well, and there are also ownig graded bedding structure, which showed having influence of turbidity current. Switchover from olisosthrome to turbidity is happened repeatedly.
The better outcrops is perceived at Luh-Ulo river bank near Totogan village, and beside Totogan to Pucangan village road. At the river bridge Totogan-Pucangan old road, there are showed good outcrop, which showed restating between muddy-breccias and show the bedding. And both of them showed by the same muddy characteristic, that is scaly structure.

3. Waturanda Formation
In Karangsambung area, primary formation is contained of graywacke sandstone at underside an breccias at topside, is cropped well and formed Paras Mountain and Perahu Mountain syncline rift landform at north of Field College. This formation type is located on Waturanda Mountain, north of Kaligending village. Litology in there is cropped well and is contained of sandstone laminated and breccias. The component of breccias mostly is contained of andesitic igneous rock and sandstone groundmass. Graded bedding or inverse graded bedding showed that this formation is turbidite.
Formation age just can determined directly, based on stratigraphy position to underside and topside unit and is estimated as earlier meocene.

4. Bulukuning Formation (New Formation)

5. Larangan Formation (New Formation)

I.3 Structure of Karangsambung
Sewer structures boudinage and boudin which is elliptical, king sized and can be mapped is finite the small ones and cannot be mapped, besieged in a period of Clay basis grind a real common is met.
Rocks consisted of by material of ocean cake, like basalt is having sewer structures pad ( pillow basalt) with interval chert with red clay and clastic limestone has not mixed with clastic sediments of troughing deposit, like grey black Clay and sandstone greywacke causing forms rock bancuh or chaotic rock. Can slip between also metamorf rock group fasies green schist, like schist phylite, chlorite and amphibolite.
Set of rock with characteristic typical of this, what consisted of freeze rocks mixture, sediment, malihan mangled, with equiamplitude surface of crack gerus(shear surface) what levels off, in tectonic term is recognized [by] as mélange ( French with the meaning mixture).
We recognize existence of two types mélange based on by its(the genesis, be tectonic mélange and mélange sedimentary. First usually is conceived of tectonic mélange while secondly is known as sedimentary mélange, or usually is called as olisthostrome. Both types of this detectable mélange in district Luh-Ulo.
Formation of this tectonic mélange hooked; correlated as interaction product of ingot which convergent followed by infiltration phenomenon of ingot ( subduksi or subduction). Lane subduksi ( subduction zone) mostly consisted of from spur mélange ( mélange wedge).
Olisthostrome is rock bancuh happened as result of sedimentation process predominated by gravity. Olisthostrome is shifting down phenomenon in underwater ( sub aquatic gliding) what entangles a number of sediment earths which has collected before all at peripheral portion of basin. Shifting down kinetic can happened because level of angle of repose influence or because of tectonic kinetic.
Tectonic Melange in this Luh-Ulo district consisted of 2 division, that are :
1. Boulders or boudin which is planted ( floats or besieged) in
2. Why should fundamental
The elliptical boulders so reaching some hundred finite thousands of meters. Has as of spread correction with direction of longest axis which hamper equal to distinguished by crack cupola ( systematic kekar)yang as working compression force response. Equiamplitude surface of crack show area gores-garis ( slicken-slided) as characteristic from grind joint (shear fracture).
Formation of boulder in analogous mélange with sewer structures boudinage. Structural like that can happened after table existence of flow stretch (flow stretching) to tectonic impulse befalling mellower rocks.
On all of them although every set of rock forming this detachable mélange but its(the stratigraphy sequence cannot be arranged normally. Stratigraphy principles has cannot be applied here. Hamper every lithology ridge would be shear. Thereby for this mélange applied stratigraphy status komplek by the name of complex mélange Luh-Ulo.

Boulders
Consisted of boulders that is in character strangers(foreigners in a period of basis, and in character has the same deposition area with a period of basis.

Foreign boulders ( exotic blocks)
a. Rock ofiolit, what consisted of basalt, gabro and some base ultra rocks. Basalt with forms typical of integer gives impression is having sewer structures pad. Generally laid bare hardly nearby group of sedimentary rock consisted of by red clay with inset baturijang ( chert). The relation of both types of this very tightly rock because precipitated at the time of the same with formation of basalt lava. Both showing properties existence of strong disintegration influence. Group of this sedimentary rock precipitated at deep sea to ocean floor ( sediment pelagosbiogen). Gabro and rock malihan is more dominantly laid bare in north. Serpentine generally Nampak is solidy breciassed causing its(the outcrop seen as boulders with form of angle and slips in a period of the same rock basis also is grind powerfully. Serpentine is changes rock from peridotite.

b. Metamorf Rock consisted of by phyllite, mica . schist and amphibole schist and rock malihan is containing glaucophane mineral.

Sedimentary rock boulders ( native blocks)
This rock comes from deposition basin which nearby troughing. Generally is consisted of sandstone greywacke. Greywacke can be considered to be result of deposit in a basin which its(the state is decline swiftly. This greywacke boulders swiftly. This greywacke boulders initially is layers which in the form of inset in Clay that is then is separated or cut to pieces at the time of taking place it hammering between ocean cakes with continent cake. Tightly association with deposit clastic estimable black Clay of its(the sedimentary process as turbid current deposit. This clastic sediment boulders called as also as native blocks, to differentiate it from exotic blocks.

Why Should Fundamental
Consisted of clay sliced strong ( pervasively sheared) shows areas splits directional ( cleavage). In field is this basic sewer structures gives the gleaming form if broken. Why should this basis is smooth clastic deposit in peripatetic troughing always makes balance to infiltration process of ingot.
In petrography seems to be a period of this basis has experienced phenomenon changes which is weak that is with silicate minerals appearance and chlorite.
Life " complex mélange Luh-Ulo" which show the time at the time of the happening of phenomenon subduction between ingots Hindia-Australia with Sunda ingot is determined based on consisting in fossil in a period of black shale basis. This life member life would " minimum" subduction, while involving boulders life in it will give life " maximum" foraminifera plankton which showing Upper Kapur until Paleocene. While from boulder which consisted of crystallized limestone and chert to give life middle kapur
Thereby complex life mélange interpreted as Upper Kapur until Paleocene.
Beside based on fossil, determination of life " complex mélange Luh-Ulo" this also is done based on rock component malihan which there is in mélange. With method potassium-argon taken away from by rugged mica . mineral and mica . schist got life 117 million years ( Kapu Awal). And 85 million years is gotten by the way of rubidium-strontium from phyllite rock. By using scar method splits ( fission track) to zircon mineral from quartz porphyry rock is gotten [by] approximately 65 million years ( Final Lime until Paleocene).

Slump
Slump is a form of mass wasting event that occurs when loosely consolidated materials or rock layers move a short distance down a slope. The landmass and the surface it slumps upon is called a failure surface. When the movement occurs in soil, there is often a distinctive rotational movement to the mass, that cuts vertically through bedding planes (landslides take place along a bedding plane or fault). This rotational movement moves along a curved slip surface of regolith (the failure surface) which overlies bedrock. This results in internal deformation of the moving mass consisting chiefly of overturned folds called "sheath folds." The surface of the mass often remains relatively undisturbed, especially at the top. However, hummocky ridges may form near the toe of the slump . The cut which forms as the landmass breaks away from the slope is called the "scarp" and is often cliff-like and concave. Cracks at the head scarp drain water, killing trees. Power lines, fences, roads, houses, and other manmade structures are frequently damaged if in the path of a slump. Slumps frequently form due to removal of a slope base, either from natural or manmade processes. Stream or wave erosion, as well as road contstruction are common instigators for slumping. It is the removal of the slope's physical support which provokes this mass wasting event. Earthquakes also trigger massive slumps, such as the fatal slumps of Turnagain Heights Subdivision in Anchorage, Alaska. This particular slump was initiated by a magnitude 8.4 earthquake that resulted in liquifaction of the soil. Around 75 houses were destroyed by the Turnagain Slump.
The speed of slump varies widely, ranging from meters per second, to meters per year. Sudden slumps usually occur after earthquakes or heavy continuing rains. The rain provides lubrication for the material to slide, and increases the self-mass of the material. Both factors increase the rate of slumping. Slumps may also occur underwater along the margins of continents and islands. These submarine slumps can generate disastrous tsunamis. The underwater terrain which encompasses the Hawaiian Islands gains its unusual hummocky topography from the many slumps that have taken place for millions of years.

Karangsambung
Earth crust is formed by three kinds of rocks, there are : igneous rocks, sedimentary rocks and metamorphic rocks. Three kinds of that rock could be found in Karangsambung. Those rocks can be slaty form from ancient seafloor being base Java Island.