SOUTHERN TASIKMALAYA ANCIENT SUBMARINE VOLCANO: EVIDENCE OF ERUPTIONS AND THEIR DIVERSITY AS GEOLOGICAL HERITAGE

In the southern Tasikmalaya area West Java Province, Indonesia, there are Tertiary volcanic rocks, with an east-west trending distribution pattern. Physiographically, this area is included in the southern mountain zone of West Java and is generally composed of tuff and polymic breccias with intercalated of lava and limestone which are grouped into the Jampang Formation and Genteng Members Jampang Formation. The existence of these volcanic and sedimentary rocks of Oligocene – Middle Miocene in the area is an indication of submarine volcano. The purpose of this paper is to identify evidence of eruptions and submarine volcano products found in the southern Tasikmalaya area, for further assessment of the geological diversity potential as a geological heritage. The method used are field data collection and quantitative data analysis, namely identification of geological heritage based on "Technical Guidelines for the Assessment of Geological Heritage Resources". The submarine volcano products which found in this area are peperite, and basaltic andesite lava at Karang Tawulan Beach, traces of alteration, and hydrothermal mineralization like Panca Tengah jasper, and Cipatujah volcanogenic massive sulphide. These evidences show that volcanic activities in the southern Tasikmalaya took place continuously from Oligocene to Middle Miocene. From the results of the assessment, the geological diversity in this area has a scientific value of "medium-high".


INTRODUCTION
Tectonic and magmatism activities in Java Island have begun since the Late Cretaceous, caused by the existence of a subduction zone located to the south, in the form of the subduction of the Indo-Australian plate under the Eurasian Plate.The movement resulted in superimposed volcanism over time, and this activity continues to this day.This can be seen from the distribution of volcanic rocks on the Java Island, as in Fig. 1, which was proposed by Soeria-Atmadja et al. (1994).The subduction between Sumatera, Java and Borneo had stopped at 90 million years ago and began to be active again around Sundaland 45 million years ago.Antarctica and Australia separated, and Australia began to move northwards (Hall, 2013).Hall (2009) reconstructed the paleogeographic changes of Southeast Asia, and the results showed that tectonic activity that occurred during the Late Eocene -Miocene triggered submarine volcano activities in the southern part of Java Island.The volcanism activity began about 40 million years ago (Late Eocene), and produced Tertiary-aged volcanic rocks in the south of Java Island, known as the Old Andesite Formation (van Bemmellen, 1949) or the Lower Eocene -Early Miocene aged arc volcanic and magmatic rock groups (Soeria-Atmadja et al., 1994).The existence of these rocks is one of the types of evidence that the southern part of Java Island was once part of the volcanic arc.
The existence of ancient volcanoes in the south of Java Island is not easy to observe on the surface because the shape of the landscape has mostly been lost due to weathering and erosion, as well as disturbances in geological structures.However, the product of volcanism activity, in the form of lava-water-sedimentary interactions such as peperites, hyaloclastite, and pillow lava can be used as a reference for proving that the area was once part of a submarine volcano.
Submarine volcanoes (volcanic seamounts) are the most common forms in the deep oceans, generally associated with major fissures or weak zones in the plates, and have a truncated conical shape due to collaps with varying crater and caldera profiles.Small volcanoes generally have circular to elliptical craters, while those measuring 2 -4 km or more have a complex and irregular shape with several volcanic centers, and ridges radiate due to volcanic fracturing zones (Mitchell, 2001).
In addition to its varying shape and size, the bottom of a submarine volcano is generally circular with a diameter of less than one kilometer to several kilometers, with average slope 20º and maximum approximately 40º, and the shape of the peak is relatively flat.These volcanoes, generally have a single eruptive center, the vent is relatively small, some can also develop into composite volcanoes and come to the surface as volcanic arcs.Variations in shape and size depend on the growth mechanism and geometry of the conduits (Batiza and Vanko, 1983), the process of interaction between magma or lava -water (Wohletz and Sheridan, 1983), and confining (hydrostatic) pressure.
One area that has traces of submarine volcanic eruptions that can be clearly observed is South Tasikmalaya, West Java Province, Indonesia.In the description of rock formations on the Karangnunggal Quadrangle Geological Map (Supriatna et al., 1992) it is stated that, the Tasikmalaya area is composed of volcanic rocks formed by subaqueous and subaerial eruption.The southern part of Tasikmalaya, generally composed by volcanic rocks of Oligocene-Miocene, and carbonaceous sedimentary rocks of Middle Miocene -Late Miocene (Fig. 1).
The purpose of this research is to identify evidence of eruptions and submarine volcanic products found in the South Tasikmalaya area, for further assessment of the potential of geological diversity as a geological heritage.Bemmellen (1949), the southern part of Tasikmalaya is physiographically included in the southern mountainous zone of Western Java.The research area consists of polymic breccia and tuffs with intercalation of lava and limestones members of the Jampang Formation and Genteng Members of the Jampang Formation of the Oligocene -Middle Miocene, as well as calcarenites, calcilutites, and marl of Limestone Members of the Pamutuan Formation of Middle Miocene -Late Miocene (Supriatna et al., 1992).

According to van
The method used in this research is field data collection, quantitative and qualitative data analysis.Field data collection is carried out by recognizing, observing and describing outcrops in detail, including coordinate data retrieval and photo documentation.Furthermore, quantitative data analysis was carried out related to the  Tourism values criteria are included vulnerability, location achievements, barriers to site utilization, security facilities, supporting facilities, population density, relationship with other values, location status, peculiarities, conditions on the observation of geological elements, interpretative potential, economic level, and close to recreation area.
The last criteria is degradation value.These criteria are included damage to geological elements, adjacent to areas/ activities that have the potential to cause degradation, legal protection, accessibility, and population density.

RESULTS AND DISCUSSION
As result of data collection in three locations in the South Tasikmalaya, West Java Province, Indonesia, submarine volcanic products were found in the form of peperite and andesite basaltic lava Karang Tawulan Beach, hydrothermal alteration and mineralization of Jasper in Panca Tengah, and Cipatujah massive sulfide ore deposits.

Peperite-Hyaloclastite-Basaltic Andesite Lava Karang Tawulan Beach
Peperite is a genetic term applied to heterogeneous rocks formed in situ, where magma is intruded and mingling with unconsolidated or poorly consolidated sediments (White et al., 2000;Skilling et al. 2002;White and Houghton, 2006).Peperites consist of fragments of lava and sediment, characterized by a clastic texture where both components can form a matrix (McPhie et al., 1993).
Peperite has an appearance and unique texture that distinguishes the peperite from other similar volcanic rocks, which are commonly found along the contact between sediment and lava.The peperite outcrop found on Karang Tawulan Beach is in the form of dispersed peperite, fluidal peperite, with juvenile clast in the form of andesite embedded in tuffaceous sandstone matrix and is non-carbonate (Fig. 2a).Juvenile clast has a sub-angular -rounded shape, with sizes from gravel to boulder, with fluidal clast morphology.The morphological forms of the fluidal clast are amoeboid, elongate globule, and globular (Fig. 2b).Tuffaceous sandstone matrix is greenish-brown (likely to have been altered into zeolite), grain size 1/4 -1/2 mm, and there is some fracturing that has been filled by marine sedimentary material and glassy lava.There is no bedded or laminated in the tuffaceous sandstone matrix, but in some places, sediment fluidisation is found that evidenced by the presence of narrow and localized, zones along igneous-sediment contacts (Fig. 2c), which reflects the sediment in an unconsolidated or poor consolidated at the time of fragmentation forming a peperite.
Several clasts were found that showed a quench fragmented structure, consisting of a radial fracture which reflects thermal tensile stress, contraction and cracking of the glass, perlithic cracks, glassy structure, and the presence of rim or cortex formed at the edge of the clast or also called "chilled margin" (Fig. 2d).Quench fragmentation or thermal granulation occurs when magma or lava direct contatc with cold liquid (like water, unconsolidated or poorly consolidated sediments), and when magma and water interact explosively during eruptions of phreatomagmatic (Kokelaar, 1986;Wohletz, 1986;Cas and Wright, 1987).In addition to peperites, on the Karang Tawulan Beach there are also outcrops of basaltic andesite lava (Fig. 3a) which form sheeting joint and columnar joint structures (Fig. 3b).The columnar joint on the lava reflects traces of lavacontraction at the time of cooling, where the joint planes are perpendicular to the cooling planes.There are several lava surfaces encountered vesicular vents, and uneven surfaces (resembling bread crust structure), which are formed due to the interaction between the hot lava surface and seawater during the cooling process (Fig. 3c).
There are fracturing and vesicular vents in lava filled with marine sedimentary material and glassy lava (Fig. 3d), reflecting the fragmentation process between lava and wet sediments.This location is interpreted as the central facies of the ancient submarine volcano.

Jasper Cimedang River, Panca Tengah
In Cimedang River, Panca Tengah found traces of hydrothermal alteration in the form of jasper minerals.Jaspers found in Panca Tengah area are generally brown, red, yellow, and black, with one or more color combinations (Fig. 4a), are not translucent (opaque), solid, and hardness ranging from 6.5 -7 Mohs scale.In some jasper boulders, are several parts that show quite varied color combinations (some even to 5 colors).This is probably caused by the presence of impurities in jasper, which are derived from the composition of lava and peperite-forming marine sediments, and hydrothermal solutions.Jasper in the most common area among gemstone lovers as "Panca Warna" which means five colors.
Jasper in the Cimedang River is found associated with peperite-hyaloclastite (Fig. 5).This indicates that the formation of jasper is associated with the subaqueous setting.In this area there is also quartz mineralization that fills the fracturing (cavity filling) in the peperite to form a vuggy and saccharoidal structure (Fig. 5b).

Cipatujah Massive Sulphide Ore Deposits
Volcanogenic Massive Sulphide (VMS) deposits are important sources of copper (Cu), zinc (Zn), tin (Pb), gold (Au), and silver (Ag).These deposits formed near sites of circulating hydrothermal fluids driven by magmatic heat are quenched through mixing with bottom waters or pore waters in near-seafloor lithologies (Shank III and Radolph, 2012).In other words, VMS is a massive sulfide deposit that forms in the submarine volcanoes environment, both in the convergent zone and the divergent zone (midocean ridge and continental rift) (Fig. 6).
The forming of VMS deposits rich in sulfide ores is generally caused by the presence of seawater as a good catalyst because it has a certain chemical composition, infiltrated through fracturing on the ocean floor due to the increasing hydrostatic pressure.Magmatic fluid that has been mixed with seawater then heated by a heat   source (it can be magma) at temperatures from 400 °C -650 °C.The mixing reaction between the two fluids causes high levels of sulfides and sulfates.The hot fluid slowly rises to the surface due to temperature differences and then radiates to the surface and forms VMS deposits.Massive sulfide lenses vary in shape and size, resembling petals and sheets, generally stratiform and lenses (Fig. 7).Massive ores in VMS deposits consist of > 40 % sulphide, usually pyrite, pyrrhotite, chalcopyrite, sphalerite, galena, non-sulfide gangue minerals such as quartz, barite, anhydrite, iron oxide, chlorite, sericite, and talk.The ore composition is dominated by Pb-Zn-, Cu-Zn-, or Pb-Cu-Zn-, and some deposits are zoned vertically and laterally (Shank III and Radolph, 2012).In the modern ocean, VMS is very similar to sulphur tongues called black smokers.From the description above, an assessment of the potential for geological diversity as a geological heritage was carried out, based on the Technical Guidelines for the Assessment of Geological Heritage Resources (Bidang Geosains Pusat Survei Geologi, 2017).The results of the assessment of the four elements mentioned above can be seen in Table 2, Table 3, Table 4, and Table 5 obtained the total value for the Karang Tawulan Beach peperite is 316.25%, the Panca Tengah jasper is 281.25%, and the Cipatujah VMS Hill is 302.5%.Based on this percentage value, geological diversity in the research area has a scientific assessment of "medium -high".

CONCLUSIONS
In the Southern Tasikmalaya area, West Java Province, Indonesia, traces of submarine volcanoes like peperite and basaltic andesite lava Karang Tawulan Beach, hydrothermal alteration and mineralization such jasper Panca Tengah, and massive sulfide ore deposits of Cipatujah was found.This is one of the evidence that in the past, the southern part of Java Island, especially South Tasikmalaya was part of the volcanic arc, which developed into an island arc.From some geological diversity found in the research area, a quantitative assessment of the potential of geological diversity as a geological heritage was carried out, and the calculation results showed a medium -high scientific value.This means that the areas have evidence or scientific record of an event on earth that has occurred or is currently occurring.In addition, it can be used for research and educational tourism, so that it can be proposed as a geological heritage (Geoheritage).

Figure 3 .
Figure 3. (a) Lava outcrops and peperite on Karang Tawulan Beach; (b) Columnar joint structure on the lava; (c) Vesicular structute in the lava, which are formed due to the interaction between the hot lava surface and seawater; (d) the surface of the columnar joint, where the joint planes are filled with marine sedimentary material and glassy lava.

Figure 7 .
Figure 7. (a) Massive sulfide ore deposits in the Cipatujah area that have been mined by the local community; (b) mineralization of chalcopyrite, pyrite, bornite, and anhydrite; (c) Chalcedony minerals are blackish gray.
supporting facilities, population density, relationship with other values, location status, peculiarities, conditions on the observation of geological elements, educational information potential, and geological diversity.

Table 2 .
Scores for various criteria used for the assessment of geological heritage sites based on scientific values.

Table 3 .
Scores for various criteria used for the assessment of geological heritage sites based on educational values.

Table 4 .
Scores for various criteria used for the assessment of geological heritage sites based on tourism values.

Table 5 .
Scores for various criteria used for the assessment of geological heritage sites based on the values of the risk of degradation.