Limestone Facies and Diagenesis on Tondo Formation at Kaisabu Village Bau-Bau City Southeast Sulawesi Province

This study aims to determine the limestone facies and diagenesis on Tondo Formation. The method used was petrographic method bypolarizing microscope. Based on the physical characteristics and biota contained, the carbonate rocks on tondo formation (Tmtl) can be grouped into two facies, namely: Wackestone and Packestone. The diagenesis process that occurred in Tondo Formation research area is microbial micritization, cementation and neomorphism which indicate that the Tondo Formation has existed on diagenetic environment of marine phreatic, meteoric phreatic and meteoric vadose.


Int r oduct i on
The research area is a Tondo Form ation (Tm tl) located in one of the areas of Bau-Bau city. Earlier, the researcher describes Tondo Form ation (Tm tl) as a form ation of Early M iocene -M iddle M iocene period. The existence of lim estone lithology in the research area is a unique and attractive geological phenom enon to serve as t he research object in the final w ork. The developm ent of highly sensitive lim estone that affects the geological condition change w ill provide excellent inform ation about the geological history. In the research area is included in Tondo Form ation (Tm tl), a form ation com posed of lithology of reef lim estone and calcarenite. M ixing betw een sedim ent w hich is a destruction of shallow m arine sedim ents that is rich in benthic foram inifera w ith deep sea sedim ents is typical of this form ation.The objective of the study is to determ ine the diagenetic process of lim estone facieson Tondo Form ation (Tm tl) and the type of lim estone faciesbased on t he t hin section analysis of the research area.

Regi onal Geology
Buton area is com posed by rock unit w hich can be grouped into M esozoic and Cenozoic rocks.  (Davidson, 1991).
Tectonic events that occur repeatedly cause the older rocks experience several tim es of structure deform ation, so that the older rocks are com monly encountered w ith the relatively sharp layer slope, w hile the younger rocks have relatively sharp layer slope than the old rocks. According to Sikumbang, N., et al., (1995) the t ectonic event has occurred several tim es starting from Pre-Eocene, w here the t ectonic pattern is difficult to determ ine due to the w hole rock has undergone several folding and faulting. The m ain tectonic movem ent that form s the structure pattern until now is expected to occur in the Eocene-Oligocene period forming the trending im brication structure of Northeast-Southw est. The next tectonic activity occurs betw een the Pliocene-Pleistocene resulting in the fold of Pre-Pliocene rocks. The last tectonic activit y that occurred since Pleistocene and has continued until now resulted in the uplifting of Buton and M una island slow ly, in tim e w ith the form ation of reef lim estoneon W apulaka Form ation that show s the st eps.

Di agenesi s
Diagenesis is t he process t hat occurs after the sedim entation process in a rock including chem ical and physical process, but this change is not caused by changes in tem perature and pressure (m etam orphism ) (Scholle and(Ulm er -Scholle, 2003 in Flugel, 2004).Diagenesis process is affected by several factors such as pressure, tem perature, m ineral stability, equilibrium conditions, rate of w ater influx, tim e and structure control. Three m ain processes in diagenesis are dissolution, cem entation and replacement. Each process is characterized by different appearance depends on w ho interprets the condition of carbonate rocks form ation. Here is the process t hat occur in diagenesis: a. M icrobial Micritization This process occurs in m arine environm ent, w hich is formed by the presence of grains drilling activity by endolithic algae, fungi and bacteria around skeletal later the form ed hole filled w ith fine-grained sedim ents or m icrite envelope cem ent, i.e. m icrite surrounding shell. e, so it w ill produce a shell t hat is com pletely m icrited. This is an im portant process w hich generally occurs in the environm ent of stagnant m arine phreatic zone and active m erine phreatic zone (Longm an, 1980). b. Dissolution The process of dissolution is know n by their unstable m inerals that dissolve and form other stable m inerals at the new environm ent, due to the differences of diagenet ic environm ent. It can occur in vadose zone and freshw ater phreatic (Longm an, 1980). c. Cem entation Cem entation process is the m ain diagenetic process in carbonate sedim ent w hen t he pore w ater phase has been saturated on the cem ent phase and t here are no kinetic factors that m ay im pede the cem ent precipitation. This process requires the large circulation of fresh w at er or sea w ater. Diagenetic environm ent is indicated by the different m ineralogy and cem ent fabricdepending on the com position of pore w ater, speed of carbonate supply and precipitation. d. Neom orphism Neom orphism is the process of replacem ent and recrystallization w hen the change in m ineralogy occurred. For exam ple, the coarsening of crystal size on carbonate m ud or m icrite (aggrading neom orphism ) and replacem ent of aragonite shells and cem ent by calcite (calcitization) (Tucker and W right, 1990). This process m ay occur at the beginning of phreatic freshw ater sedim entation and deep burial; e. Dolomitization Dolomitization is the process of replacem ent of mineral calcite into dolom ite caused by the increase of M g content in carbonate rocks. Factors that accelerate the dolom ite precipitation is the m agnitude of M g/Ca ratio in m inerals, the m agnitude of CO2 content, high tem perature and pH, low sulphate cont ent, low salinit y content as w ell as the effect of organic m aterial. Dolomitization process m ay change into replacem ent by t he precipitation process or in the form of cem entation, w hich m ay occur in the environm ent of mixing zoneand deep burial (M orrow . 1982). f. Com paction According to Tucker and W rigth (1990), the com paction process is divided in 2 types, nam ely: 1) M echanical com paction occurs w hen the loading becom es larger w hich cause cracks in the grains, grains are in contact to each other, porosity reduced. 2) Chem ical com paction occurs w hen the grains are in contact, experience dissolution, w hich produce suture contacts and concavo-convex contacts.
Studying the diagenesis products w hich present in a particular environm ent is the key to predict the tendency to porosity in carbonate rocks. According to Longm an (1980) in Tucker and W right, (1990)

c. M i cr obi al M i cr i t i zat i on
Petrographic observation at station 3 is a m icrobial micritization. M icrite is a matrix that is usually dark in color. On the lim estone, it is present as very fine grain. Micrite has a grain size of less than 4 m icrom eters. In t he electron m icroscopy study, it show s that micrite is not hom ogeneous and show s a rough to fine size w ith the boundaries betw een crystals -planar, curved, jagged or irregular shape. M icrite m ay suffer from alteration and m ay be replaced by a rough m ozaicm icrospar (Tucker, 1991). (Figure 3)

d. M i cr obi al M i cr i t i zat i on
This diagenesis product show s the type of m icrobial micritizationformed on petrographic incision. This process occurs in m arine environm ent, w hich is formed by the presence of grain drilling activity by endolithic algae, fungi and bacteria around skeletal. Then t he hole form ed is filled w ith finegrained sedim ents or m icrite envelope cem ent w hich is the m icrite surrounding the shell. Such produce a shell that is com pletely m icrited. According to Longm an 1980, in Tucker andW right 1990, it is an im portant process that generally occurs in an environm ent of stagnant m arine phreatic zone and active m arinephreatic zone. (Figure 4) e. Neom or phi sm From the results of the petrographic incision observation w hat is produced by this process is aggrading neom orphism w hich is m icrite recrystallization into crystals the large-sized crystal is called m icrospar. The crystals form ed have a m ore turbid microspar appearance because these crystals com e from m icrit recrystallization of carbonate m ud. Tucker and W right (1990) state that neom orphism occurred in diagenetic environm ent of m eteoric phreatic and m eteoric vadose. Neom orphism is the process of replacem ent and recrystallization w hen t he change in m ineralogy occurred. For exam ple, the coarsening of crystal size on carbonate m ud or m icrite (aggrading neom orphism ) and replacem ent of aragonite shells and cem ent by calcite (calcitization) (Tucker, 1990). (Figure 5).
Based on the observations on diagenesis product both from field observations at the outcrop and the petrographic incision analysis it can be interpreted t hat the diagenetic environm ent   b. W ackest one Faci es This facies found in Calcarenite Unit exists in the research area are scattered in the East to the w est part of Kaisabu area. In this facies, the rock outcrop is in grayish fresh color and generally m assive and there are pores in it. The com ponents are in the form of carbonate m inerals such as calcite and dolomite. Based on the field observation and the results of petrographic analysis of the rock sam ples, in the outline it is seen as dom inated by W ackestonefacies. The facies in this zone has t he characteristics that contains an abundance of coral, dom inant red algae and there are algae fraction along w ith other fossil fraction that cannot be identified.Based on the result s of petrographic analysis of W ackestonefacies sam ple, it has the characteristics of very fine grain size and has associations w ith larger clastic fragm ents but not dom inant. Fig. 6. Scheme diageneis environmental changes that occurred in the study area (Tucker and W right, 1990) (Petrographic Analysis cross nicol w ith magnifications 10x )

Conclusi ons
Based on the analysis w hich has been conducted, the author concludes that: 1. The diagenetic process that occur in the research area of Tondo Formation is microbial m icritization, cem entation and neom orphism w hich indicate that the Tondo Form ation has existed on diagenetic environm ent of m arine phreatic, m eteoric phreatic and m eteoric vadose. 2. Lim estone research area is com posed by t w o facies associations, nam ely algae faciesforamineferapackestone and algae facies foraminefera w ackestone.