Indonesian Journal on Geoscience Vol. 1 No. 2 August 2014: 109-119
INDONESIAN JOURNAL ON GEOSCIENCE Geological Agency Ministry of Energy and Mineral Resources
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Depositional Cycles of Muara Wahau Coals, Kutai Basin, East Kalimantan
Komang Anggayana1, Basuki Rahmad2, and Agus Haris Widayat1
1Research Group of Earth Resource Exploration, Faculty of Mining and Petroleum Engineering, ITB Jln. Ganesha No. 10, Bandung 2Study Programme of Geology, Faculty of Mineral Technologies, UPN “Veteran” Yogyakarta Jln. Swk 104 (Lingkar Utara), Condongcatur, Yogyakarta
Corresponding author: [email protected]; [email protected]; [email protected] Manuscript received: April 1, 2014, revised: May 12, 2014, approved: August 19, 2014
Abstract - Fifteen samples were taken ply by ply from a 33 m thick drill core of Muara Wahau coal seams for in- terpretation of depositional environments. Generally, lithotype variation in the bottom part of the coal seams has a lower frequency than in the upper part. Petrographical analysis was performed to determine the maceral composition, groundwater index (GWI), and gelification index (GI). The samples from lower sections show much higher GWI-GI values and lower variation frequency than from the upper section. This characteristic is interpreted as the result of development of mesotrophic to ombrotrophic peats during the deposition of lower to upper parts of the section, re- spectively. During the development of the mesotrophic peat, water was more abundant and relatively stable in budget. However, during the development of ombrotrophic peat, water was less abundant and relatively not stable in budget. The latter is related to the water supply depending only on rain, resulted in the more sensitive water table in the om- brotrophic peat. The unstable water table is thought as the reason of higher variation frequency of lithotype, GWI, GI, as well as maceral composition in the upper part of the core. Unstable water table would lead to moist condition in the uppermost layer of the ombrotrophic peat, favoring fungi to grow. This is confirmed by the higher abundance of sclerotinite maceral in samples from the upper part of the coal core. Keywords: coal seam facies, Muara Wahau, Kutai Basin
Introduction supply and deposited-organic matter preserva- tion. Peat water may originate from groundwater, Muara Wahau coals are part of Early Miocene rain water, and intrusion of sea water. The peat Wahau Formation, Kutai Basin, East Kalimantan, water table is fluctuative and sensitive to season consisting of several thick coal seams. The thick- or climate changes. The hydrological condition ness of each seam is up to 60 m. The coal has in peats determined the vegetation and peat type not been disturbed by exploitation, as the site is accumulated in a basin. located in a very remote area. In the present case, the Muara Wahau coals Peat accumulation is controlled by at least two are interesting to investigate. The thick coal key factors: subsidence rate creating accommoda- seams can provide more detailed indications of tion space and organicIJOG matter (trees) supply rate chemical and physical changes during peatifica- (Taylor et al., 1998). The interplay between the tion. With respect to hydrological condition, two factors in equilibrium state brings through the succession of early development of Muara peat accumulation. The longer equilibrium state Wahau coals will be reconstructed and discussed time is reached, the thicker peat would be accu- in detail. Petrographical analysis was carried out mulated. Another important aspect is the presence to characterize the maceral composition of the of water which takes a role as media of nutrient Muara Wahau coals.
IJOG/JGI (Jurnal Geologi Indonesia) - Acredited by LIPI No. 547/AU2/P2MI-LIPI/06/2013, valid 21 June 2013 - 21 June 2016 109 Indonesian Journal on Geoscience, Vol. 1 No. 2 August 2014: 109-119
Geological Settings Methods
The studied area is located in Muara Wahau The study was commenced by collecting rep- Sub-regency, East Kutai Regency, East Kali- resentative samples from the coal field. Drilling mantan, Indonesia (Figure 1). The area is mostly programme, which was conducted, penetrated composed of Early Miocene Wahau Formation Seam 1 and Seam 2 in the coal field (Figure 4). according to Supriatna and Abidin (1995) (Figure The selected coal samples were then taken di- 2). The formation was deposited in Upper Kutai rectly ply-by-ply/ply sampling (Thomas, 2002) Basin (Calvert, 1999). The lower part of the for- from Seam 1 core. The samples were separated mation consists of interbedded coralline and algal based on the lithotype observed along the core, limestones. The upper part of Wahau Formation then they were crushed and split for further labo- comprises interbedded tuff, claystones, quartz ratory analysis. sandstones, sandy claystones, and coal layers. For maceral composition, fifteen samples There are two major coal seams in the area (Fig- were investigated using Zeiss Axio Imager A2m ure 3), showing variation in the thickness from polarized microscope in the Laboratory of Earth 15 to 62 m, with gentle dips that range from 8o Resources Exploration, Faculty of Mining and to 12o. The cropline distribution is controlled by Petroleum Engineering, ITB. During the maceral the presence of syncline in the area. Generally, analysis, five hundred points with a minimum the coals are blackish brown, hard, brittle, dull distance of 0.2 mm between each point were in luster, and contain resin and fossilized wood counted from the polished sections. The maceral in some parts. composition is stated as percent (%-volume).
Telen River
Wahau River Sepinang
Muara Wahau
1o N Sangkulirang KALIMANTAN Tanah Merah Tanjung Bengalun
Sangkinah
Muara Kaman 0o Adara K U T A I B A S I N Tenggarong SAMARINDA
Adara Pulung Makassar Strait
1o S Muara Payang BALIKPAPAN IJOGPenajam N Belimbing East Kalimantan Longikis 0 100 Studied Area Kilometres
o o o 115 E 116o E Tanah Grogot 117 E 118 E
Figure 1. Location map of the studied area.
110 Depositional Cycles of Muara Wahau Coals, Kutai Basin, East Kalimantan (K. Anggayana et al.)
SURFACE VOLCANIC AGE DEPOSITS ROCK FORMATION DESCRIPTION INTRUSION PERIOD
Alluvium: pebble, cobble, sand, mud HOLOCENE and plant remain
PLEISTOCENE
QUATERNARY Metulang Vulcanic: andesite, basalt, lava, tuff, aglomerat breccia and laharic PLIOCENE
LATE
MIDDLE Sintang intrusion: stock and dyke of andesite and diorite Upper Wahau Formation: MIOCENE intercalation of tuff, clastone, quartz EARLY sandstone, clayish sandstone, sandy claystone, and lignite Lower Wahau Formation: interbedded coral and algae limestone OLIGOCENE TERTIARY
Marah Formation: intercalation of marl, claytone, conglomrate, and LATE limestone
EOCENE EARLY
Metaphorphic rock and ultra basic PALEOCENE rock
Figure. 2. Regional stratigraphy of Upper Kutai Basin (Supriatna and Abidin, 1995).
116o 42'E 116o 44'E 116o 46'E 116o 48'E 116o 50'E
N o o 1 16'N 1 16'N
0 1 2 4 Km
GT-02 o o 1 14'N 1 14'N Coal Seam 1 Coal Seam 2 GT-03
B PMB-01-08 o o 1 12'N 1 12'N
A o o 1 10'N 1 10'N
Tomw o o 1 8'N 1 8'N
116o 42'E 116o 44'E 116o 46'E 116o 48'E 116o 50'E LEGEND : IJOGSample location Wahau Fm '' Strike adn deep strata Geological Map of Study Area Coal Cropline Seam A Sintang andesite intrusion Anticline, Syncline Coal Cropline Seam B Lineament River A B 0 Coal Seam 1 0 Coal Seam 2
100 100 m m
Figure 3. Geological map and cropline of Muara Wahau coals (modified from Supriatna and Abidin, 1995).
111 Indonesian Journal on Geoscience, Vol. 1 No. 2 August 2014: 109-119
Depth Natural Gamma Ray Coal Thickness (m) -1 CPS 34 1m:100m Vitrinite (huminite) reflectance measurement was 1.0
2.0
3.0 4.0 also carried out in the Centre of Geological Re- 5.0
6.0 7.0 sources, Geological Agency, Ministry of Energy 8.0
9.0
10.0 11.0 and Mineral Resources. Mean random vitrinite 12.0
13.0 14.0 reflectance measurements were performed on the 15.0 16.0 14.00 17.0 18.0 surface of vitrinite particles under oil immersion. 19.0
20.0 21.0 Fifty points of vitrinite reflectance were taken on 22.0
23.0
24.0 25.0 each sample. The identification and classification 26.0
27.0 28.0 of macerals in this study are based on ICCP Sys- 29.0 Seam -1 30.0
31.0 32.0 tem 1994 (ICCP, 1998, 2001, 2011), Suarez-Ruiz 33.0 34.0 33.30 m 35.0
36.0 and Crelling (2008), and Sykorova et al. (2011).
37.0
38.0 39.0 In order to investigate the hydrological regime 40.0
41.0
42.0 43.0 of the ancient peat, two indices were determined.
44.0
45.0 46.0 Groundwater index (GWI) based on Calder et al. 47.0 47.30 48.0
49.0
50.0 (1991) was used to indicate the ratio of strongly
51.0
52.0 53.0 gelified macerals (humocollinite), as well as the 54.0
55.0
56.0 57.0 mineral matter, to weakly gelified ones (humotel- 58.0
59.0 60.0 linite, humodetrinite). Mineral matter is considered 61.0 62.0 61.30 - 62.30 (1.00) 63.0 64.0 to be related to water carrying detritral material 65.0
66.0 67.0 to the former peat during flood (Crosdale, 1995). 68.0
69.0
70.0
71.0 72.0 Humocollinite + Minerals 73.0 ...... (1) 74.0 GWI = 75.0 Humocollinite + Humodetrinite 76.0
77.0
78.0
79.0
80.0
81.0 82.0 The second indicator used in this study is geli- 83.0
84.0
85.0 86.0 fication index (GI) based on Diessel (1986). GI is 87.0
88.0 89.0 a tool to contrast gelified macerals to nongelified 90.0
91.0
92.0 93.0 ones as the indicator of peat wetness. When the 94.0
95.0 96.0 peat is flooded by water, vitrinite and geloiner- 97.0
98.0 99.0 100.0 tinite tend to form. On the other hand, when the 101.0
102.0
103.0 104.0 water table is lower and the peat surface becomes 105.0
106.0 107.0 dryer or moist, teloinertinite and detroinertinite 108.0
109.0
110.0 111.0 will form in the peat surface due to oxidation 112.0 113.0 61.30 - 62.30 (1.00) 114.0 (Lamberson et al., 1991) 115.0 113.70 116.0
117.0
118.0 119.0 Seam-2 120.0 Huminite + Macrinite 121.0 GWI = ...(2) 122.0 123.0 Fusinite + Semifusinite + Sclerotinite + Inertedotrinite 124.0 15.90 m 125.0
126.0
127.0
128.0 129.0 129.60 GWI and GI have different concepts. GWI 130.0
131.0 132.0 133.0 changes reflect the fluctuation of water table which 134.0
135.0 136.0 could happen in both high and low moor peat 137.0
138.0
139.0 140.0 types. In high moor, the water table would typi- 141.0
142.0
143.0 144.0 cally raise, following the development of rising 145.0 146.0 IJOG147.0 peat surface. GI assumes that gelification process 148.0 146.20 - 148.20 (2.00)
149.0
150.0 151.0 takes place in reduced water where the water table 152.0
153.0 154.0 is static regardless of peat surface development. 155.0
156.0
157.0 158.0 The GWI could be correlated with GI on the 159.0 160.0 development of peat as follows: Figure 4. Coal seam profiles (Seam 1 and Seam 2) from 1. GWI < 0.5 and weak gelification (GI < 1) density log interpretations of Borehole GT-02. reflect lower water table of a marsh (Diessel,
112 Depositional Cycles of Muara Wahau Coals, Kutai Basin, East Kalimantan (K. Anggayana et al.)
1986) and ombrotrophic peat type (Calder et Humodetrinite (Figure 6b) shows fragmented al., 1991). materials associated with inertinite, liptinite, or 2. GWI 0.5 - 1 and moderate gelification (GI ~ minerals. Densinite appears as a mixture of fine 1) reflect higher water table of a fen? (Dies- fragments of vitrinite. It is more homogenous than sel, 1986) and mesotrophic peat type (Calder attrinite. Humocollinite (Figure 6c) was found as et al., 1991). homogenous, rounded to oval bodies, and often 3. GWI > 1 and strong gelification (GI > 1) re- isolated one within desmocollinite. flect higher water table of a wet forest swamp Cutinite (Figure 6d) is mainly present as thin (Diessel, 1986) and rheotrophic peat type continuous bands in association with vitrinite (Calder et al., 1991). GI > 1 is characterized maceral. Suberinite (Figure 6d) looks as cell walls by limited influx of clastics. filled by other macerals, typically humocollinite. Resinite (Figure 6e) appears as rounded, oval, and unstructured material. Sporinite (Figure 6e) Result and Discussions is present only in a minor amount. It appears as individual body with distinct cell walls and a Coal Lithotype higher relief. Lithotype classification used in this study is Sclerotinite shows rounded to oval forms and based on Stopes (1919) and Diessel (1965). Coal has high reflectance (Figure 6f). This maceral is from the Seam 1 of the Muara Wahau Formation present in all coal samples. could be classified into three lithotypes, those are Mineralogical analayis shows that the coal banded coal (clarain), dull banded coal (clarain), seam from the Seam 1 contains pyrite which is and dull coal (durain). Coal lithotype profile shows present mostly as fine crystals within the dense cycle changes in the vertical section as presented macerals (Figure 6f). The coal seam profiles in Figure 5. Lithotype variation may indicate changes of vegetation type composing coals (Bustin et al., 1983) or changes in sedimentary Sample Number facies, especially related to water table conditions 0 m during peat depositional process. Facies changes 15 14 in both vertical and lateral trends could control the 13 variation of maceral composition. 12 11 10 9 Coal Petrology 8 10 m 7 Microscopic analysis shows that huminite 6 5 reflectance of the Muara Wahau coals is 0.44 % on the average, suggesting brown coal maceral nomenclature based on ICCP System 4 1994. The coals predominantly consist of huminite macerals, with minor liptinite and 20 m inertinite (Figure 6). Huminite maceral of the 3 coals comprises humotelinite, humodetrinite, densinite, and humocollinite. Liptinite maceral Legend: consists of cutinite, resinite, suberinite, and 2 Dull Coal sporinite. InertiniteIJOG maceral is dominated by Dull Banded Coal fusinite, semifusinite, and sclerotinite. 30 m 1 Banded Coal Humotelinite (Figure 6a) is mostly found as thick layers in association with humodetrinite GT-02, Seam-1 and cutinite, grey to dark in colour, sometimes forming lighter layers. This maceral may Figure 5. Coal lithotype profile of seam 1 from Drillhole originate from the lignin of high plants. GT-02.
113 Indonesian Journal on Geoscience, Vol. 1 No. 2 August 2014: 109-119
0 100 mikron 0 100 mikron
Suberinite Humocollinite
Cutinite Humodetrinite Sclerotinite Sporinite Humotellinite Resinite a a d d
0 100 mikron 0 100 mikron
Sclerotinite Cutinite
Sporinite Fusinite
Humodetrinite
b b e e Resinite
0 100 mikron 0 100 mikron Pyrite
Humodetrinite Sclerotinite
Humocollinite
Humodetrinite Sclerotinite
Humocollinite c c f f
Figure 6. Photomicrographs of macerals in the Muara Wahau coals (Seam 1). a. Sclerotinite associated with huminite; b. Sclerotinite and fusinite associated with humodetrinite; c. Humodetrinite in association with round bodies of sclerotinite and humocollinite; d. Suberinite, sporinite, resinite, and cutinite as individual bodies with distinct cell walls; e. Sporinite, resinite, and cutinite as individual bodies with distinct cell walls; f. Huminite macerals in association with round bodies of sclerotinite and pyrite mineral. a, b, c, and f in reflected light mode, while d and e in fluorescence mode. obtain the mineralogial distribution and variation at 47% and 18%, respectively. Generally, humo- in vertical sequence. detrinite abundance exhibits a decrease in depth, the opposite condition with that of humocollinite. Coal Facies/Coal Deposition In segment 1 (sample 1 - 4), the variation is low, Based on the maceral quantification, the while in segment 2 (sample 5 - 15) the variation Muara Wahau coals consist of higher amount is higher. The higher variation of humodetrinite of huminite (73.4 to 88%), lower proportion of - humocollinite in segment 2 may reflect that the liptinite (0.6%-6.8%), and inertinite (5.8%-18%) groundwater in the ancient peat fluctuated more macerals (Table 1). The abundance of the macer- intensively. IJOGFigure 7b indicates that the abundance of als and minerals along the vertical coal profile are shown in Figures 7a - d. liptinite macerals generally decrease in depth. Figure 7a shows the variation of huminite Sporinite and cutinite only appear in some of seg- macerals along the coal profile. Humotelinite and ment 2 samples. Resinite is consistently present in attrinite amount to about 9% and 8% on the aver- all samples, averaging 1.3%. Alginite is present age, respectively, and exhibit no vertical varia- only in some samples of segment 2. Suberinite tion. Humodetrinite and humocollinite average appears in sample 3 - 15 with varying amounts.
114 Depositional Cycles of Muara Wahau Coals, Kutai Basin, East Kalimantan (K. Anggayana et al.)
Table 1. Maceral Composition of Seam 1 the Muara Wahau Coal
Sample Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Maceral group Maceral subgroup Maceral % Volume of each sample
HUMINITE 83.6 81.4 78.6 82.6 86.6 88.0 80.4 73.4 87.8 83.2 75.0 77.4 86.0 81.4 86.8 Humotelinite 12.6 11.0 10.6 10.0 10.6 12.2 8.6 5.0 12.6 10.0 2.8 6.0 8.6 7.4 7.6 Telocollinite 12.6 11.0 10.6 10.0 10.6 12.2 8.6 5.0 12.6 10.0 2.8 6.0 8.6 7.4 7.6 Humodetrinite 52.2 45.0 51.8 49.0 39.4 52.4 53.4 57.6 48.4 56.2 67.4 64.4 63.6 61.2 64.2 Attrinite 8.6 6.0 6.6 7.6 5.2 8.4 8.8 9.2 6.6 11.4 5.0 3.4 8.8 7.2 13.8 Densinite 43.6 39.0 45.2 41.4 34.2 44.0 44.6 48.4 41.8 44.8 62.4 61.0 54.8 54.0 50.4 Humocollinite 18.8 25.4 16.2 23.6 36.6 23.4 18.4 10.8 26.8 17.0 4.8 7.0 13.8 12.8 15.0 Corpogelinite 18.8 25.4 16.2 23.6 36.6 23.4 18.4 10.8 26.8 17.0 4.8 7.0 13.8 12.8 15.0 LIPTINITE 0.8 0.6 2.0 3.2 1.0 1.6 1.6 4.8 1.8 4.0 6.8 5.6 3.0 2.4 1.4 Sporinite 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.0 0.6 0.2 0.6 0.2 0.2 0.2 Cutinite 0.0 0.0 0.0 0.0 0.2 0.0 0.0 0.8 0.2 0.4 0.4 1.0 0.2 Resinite 0.8 0.6 0.6 1.2 0.8 1.0 0.6 2.4 0.6 2.4 3.4 1.4 1.4 1.6 0.4 Alginite 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.0 0.2 Suberinite 0.0 0.0 1.4 2.0 0.0 0.6 0.8 1.6 1.0 0.6 2.8 2.4 1.4 0.6 0.4
INERTINITE 8.8 12.0 15.0 7.6 6.4 5.8 13.6 18.4 6.4 9.6 11.8 13.6 8.6 12.0 9.4 Fusinite 0.4 0.2 1.2 0.8 0.4 0.0 1.2 1.2 0.4 0.6 0.4 0.6 1.4 0.6 0.0 Semifusinite 0.8 1.8 3.0 2.8 0.8 0.2 2.8 2.6 0.2 1.4 1.6 1.6 0.4 1.2 2.0 Sclerotinite 5.8 7.6 7.4 3.4 3.8 4.8 5.6 9.8 5.6 6.0 7.2 8.8 5.8 7.6 5.2 Inertodetrinite 1.8 2.4 3.4 0.6 1.4 0.8 4.0 4.8 0.2 1.6 2.4 2.6 1.0 2.6 2.2 Macrinite 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.0 0.0 0.0
MINERAL MATTER 6.8 6.0 4.4 6.6 6.0 4.6 4.4 3.4 4.0 3.2 6.4 3.4 2.4 4.2 2.4 Oxide 0.6 4.6 2.0 0.6 0.0 0.0 Pyrite 1.8 0.4 2.0 1.6 3.6 1.6 1.8 1.0 1.2 0.6 2.8 2.4 0.6 1.6 1.2 Clay 4.4 5.6 2.4 0.4 2.0 1.6 1.8 1.0 1.2 0.6 2.8 2.4 0.6 1.6 1.2 TOTAL (%) 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Rv. mean (%) 0.45 0.46 0.45 0.45 0.45 0.43 0.45 0.43 0.43 0.42 0.44 0.45 0.45 0.45 0.44
Resinite may originate from various plants. example, revealed that the marine and brackish Thus, this maceral is not a paleoenvironmental- environments would be more effective for spore indicative in the present case. Suberinite origi- and polen preservation than freshwater environ- nates from cork tissues, plant components which ments. In addition, the preservation of spore and are similar to cuticles deriving cutinite. The su- pollen would be less efficient when exposed to berinite source is easier to be destructed during atmosphere. In the Muara Wahau coal, sporinite coalification, consequently, suberinite is rare and is present only in segment 2 which might not be infrequently found in some coals (Taylor et al., related to a specific environment. The absence 1998). In the Muara Wahau coal, suberinite oc- of sporinite in segment 1 may suggest that dur- curs in almost entire vertical coal seam profiles, ing the development of the segment, there were except in the lower part (sample 1 and sample 2). very limited spore/pollen producing plants as This may indicate that during the deposition of the peat was still mesotrophic and dominated sample 1 - 2, trees were firstly not present in the by aquatic plants. peat. After that, the peat was starting to develop Inertinite macerals of the Muara Wahau coals trees, forming ombrogenous peat. mainly consist of sclerotinite maceral. In verti- In Tertiary coals,IJOG sporinite originates gen- cal sequence, sclerotinite is the most abundant erally from pollen of angiospermae. Thus, maceral in the top and bottom parts of the seam the mechanism transport of pollen to the peat (Figure 7c). Sclerotinite was derived from fungi swamp might be dominaned by wind (Esterle dwelling in moist environments. The presence of and Ferm, 1994). The preservation of spore and sclerotinite in all investigated samples suggests pollen is generally/mainly controlled by depo- that moist conditions intermittently occurred dur- sitional environments. Taylor et al. (1998) for ing the development of the peat.
115 Indonesian Journal on Geoscience, Vol. 1 No. 2 August 2014: 109-119 15 14 13 12 10 9 8 7 6 5 4 3 2 1 11 14 Sample No. 12 = Oxides 2.4 % 4.2 % 2.4 % 3.4 % 6.4 % 3.2 % 4.0 % 3.4 % 4.4 % 4.6 % 6.0 % 6.6 % 4.4 % 6.0 % 6.8 % 10 8 0,6 6 2,0 Mineral Matter (%) Mineral Matter 3,6 2,0 = Pyrite = Clay 4 4,4 0,4 0,6 d 2,4 5,6 2,6 3,0 2,6 1,0 2,4 2 2,2 2,6 1,2 0,4 3,0 1,8 2,8 2,4 2,0 1,8 1,8 3,6 1,6 1,6 1,2 1,2 1,0 0,6 0,6 0,4 42 43 46 47 41 45 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 44 15 13 14 49 50 48
20 30 40 50 Deepness (meter) Deepness 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Sample No. 8.8 % 8.6 % 9.6 % 6.4 % 5.8 % 6.4 % 7.6 % 9.4 % 15.0 % 12.0 % 13.6 % % 11.6 18.4 % 13.4 % 12.0 % 16 18 20 4,8 = Macrinite 14 3,4 2,6 12 4,0 2,4 2,6 2,4 10 1,6 = Sclerotinite = Inertodetinite 9,8 2,2 1,0 8 1,8 7,4 0,6 5,6 8,8 0,1 Maceral Group Inertinite (%) Maceral Group 6 1,4 7,6 7,6 0,8 3,4 6,0 1,2 c 5,8 5,2 4 5,8 5,6 3,0 = Fusinite = Semifusinite 3,0 4,8 2,6 2,8 2,8 2 0,4 1,8 1,4 1,2 1,6 1,8 2,0 0,8 1,4 1,2 0,1 1,2 1,2 0,8 0,6 0,6 0,6 0,4 0,6 43 46 47 42 45 41 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 44 15 13 14 49 50 48
20 30 40 50 Deepness (meter) Deepness Wahau coals a. huminite; b. liptinite; c. inertinite; d. minerals. Wahau 9 = Suberinite 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 8 Sample No. 1.4 % 2.4 % 3.0 % 5.6 % 6.8 % 4.0 % 1.8 % 4.8 % 1.6 % 1.6 % 1.0 % 3.2 % 2.0 % 0.6 % 0.8 % 7 6 2,8 5 = Resinite = Alginite = 2,4 4 1,6 0,6 0,2 3 Maceral Group Liptinite (%) Maceral Group 1,4 1,4 1,4 2,0 b 0,6 2,4 3,4 2 2,4 7,4 1,0 0,8 0,6 0,4 1 1,0 = Sporinite = Cutinite 1,6 0,2 1,4 0,4 0,4 0,8 1,2 0,6 0,6 1,0 0,4 0,8 0,8 0,6 0,6 0,2 0,6 0,6 0,2 0,2 0,2 0,2 0,2 0,2 0,2 43 46 47 42 45 41 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 44 16 15 13 14 49 50 48
20 30 40 50 Deepness (meter) Deepness 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Sample No. 100 86.8 % 81.4 % 86.0 % 77.4 % 75.0 % 83.2 % 87.8 % 73.4 % 80.4 % 88.0 % 86.6 % 82.6 % 78.6 % 81.4 % 83.6 % 90 80 15,0 13,8 17,0 26,8 12,8 23,4 23,4 7,0 18,8 4,8 18,4 23,6 70 16,2 25,4 10,8 60 = Desmocollinite = Corpogelinite
IJOG50 50,4 44,8 43,6 44,0 44,0 54,8 40 54,0 41,8 61,0 62,4 45,2 39,0 41,4 44,6 48,4 30 Maceral Group Huminite (%) Maceral Group = Telocollinite = = Densinite 20 a 8,6 8,4 6,6 11,4 13,8 5,2 7,6 6,6 6,0 8,8 8,8 7,2 10 9,2 3,4 12,2 12,6 12,6 5,0 10,6 10,0 10,6 11,0 10,0 8,6 8,6 7,6 7,4 6,0 5,0 2,8 43 46 47 42 45 41 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 44 16 14 15 13 49 50 48
20 30 40 50 Deepness (meter) Deepness Figure 7. Comparison of maceral distribution in vertical section the Seam-1, Muara
116 Depositional Cycles of Muara Wahau Coals, Kutai Basin, East Kalimantan (K. Anggayana et al.)
Maceral variation and distribution in vertical hydrological regime was influenced by both section of the coal profile, as mentioned above groundwater and rain water. Such condition clearly reveal that the peat developed under would lead to the relatively more stable water the mesotrophic to ombrotrophic conditions. table. Segmen 2 represents the development of Mesotrophic peat was mainly developed in the ombrotrophic peat type. The hydrological segment 1 of the coal profile indicated by the regime in the ombrotrophic peat relied only presence of aquatic plants. On the other hand, on rain water. This condition would promote the ombrotrophic peat might occur during the less stable water table, as rain water is very deposition of segment 2 dominated by trees with sensitive to season and climate changes. Water less water influence. table fluctuation might occur faster resulting Figure 8 shows the vertical variation of GWI, in a more frequent moist condition in the peat GI, humocollinite, inertinite, sclerotinite, and surface. This could allow fungi to grow. Thus, mineral matter profiles. Segment 1 (sample 1 - 4) consequently the coal in segment 2 contains shows lower fluctuation profiles, while segment 2 relatively more sclerotinite. (sample 5 - 15) indicates high fluctuation profiles. In order to investigate the relation between the The change of the fluctuation pattern in the vertical above parameters, some correlation plots were coal profiles matches with that of coal lithotype. made. Some of the plots are shown in Figure 9, Segmen 1 represents the development of while the complete coefficients of determination the mesotrophic peat type. In the peat, the are listed in Table 2. The parameters are
Groundwater Index (GWI) Gelification Index (GI) Gelovitrinite Inertinite Sclerotinite Mineral Matter 30 10 10 10 10 Ombrotrophic Mesotrophic Low Tide High Tide 25 15 15 15 15 15 15 15 15 15 14 14 14 14 14 20 13 12 13 13 13 13 12 20 20 11 12 20 12 20 12 Segment 1110 11 10 10 10 11 10 11 2 9 8 9 9 8 9 8 8 9 25 8 7 25 7 6 25 6 7 25 6 7 25 7 6 6 5 5 5 5 5 30 30 30 30 30 Depth (m) Depth (m) Depth (m) Depth (m) Depth (m) 4 Depth (m) 4 4 4 4 35 35 35 35 35 Segment 1 3 3 3 3 3 40 40 40 40 40 2 2 2 2 2 45 45 45 45 45 1 1 1 1 1 50 50 50 50 50 0.1 0.5 1.0 1.0 5.0 10.0 20.0 0 5 10 15 20 25 30 35 40 0 5 10 15 20 0 2 4 6 8 10 0 2 4 6 8 10 Gelification Index (GI) % Gelovitrinite % Inertinite Sclerotinite Mineral Matter
Figure 8. Vertical variation of GWI, GI, humocollinite, inertinite, sclerotinite, and minerals.
16 y= 9.986x+4.589 14 R2 =0.371 12
10
8 IJOG6 4 Gelification Index (GI)
2
0 0 0.2 0.4 0.6 0.8 1 Groundwater Index (GWI)
Figure 9. GWI versus GI correlation.
117 Indonesian Journal on Geoscience, Vol. 1 No. 2 August 2014: 109-119
Table 2. Correlation of GWI, GI, Macerals, and Minerals
No Parameter Correlation Coefficient of determination (R2) 1 GWI vs. GI + 0,37 2 GWI vs. humocollinite + 0,96 3 GWI vs. inertinite - 0,29 4 GWI vs. sclerotinite - 0,39 5 GWI vs. minerals + 0,24 6 GI vs. humocollinite + 0,49 7 GI vs. inertinite - 0,89 8 GI vs. sclerotinite - 0,62 9 GI vs. minerals + 0,02 10 Humocollinite vs. minerals + 0,13 typically positively correlated. GWI is positively variation in depositional cycles. The variation correlated with GI, as both indices are sensitive of lithotype and maceral composition reveals to groundwater influence. Both indices are also two segments showing different patterns along positively correlated with mineral and some the vertical profile. Segmen 1 (lower part of the macerals which are well preserved in a wet coal profile) shows depositional cycles related condition under water table. Several parameters to relatively stable water table, as interpreted by show negative correlation as shown by inertinite the less frequent changes of sclerotinite, GWI, and sclerotinite vs. GWI and GI. These macerals and GI. Segmen 2 (upper part of the coal profile) developed under a moist condition, in parts where shows depositional cycles related to less stable sometimes covered by water. water table, as it shows more frequent changes A strong negative correlation occurs in of the latter parameters. Based on the relatively parameters GI vs. inertinite. It is normal, as the low GWI, GI, and the absence of correlation two parameters require opposite depositional between the two parameters and mineral matter environments. Gelification can only occur content, the Muara Wahau coal is interpreted to below water table (reduction) condition, while be deposited in mesotrophic peat (segment 1) inertinite could only be derived in moist or which subsequently developed to ombrotrophic oxidation condition. The correlation between GI peat (segmen 2). and mineral matter is very weak. It is confirmed that the mineral might be epigenetic, rather than related to groundwater flow in the peat. Acknowledgment This also confirms that the peat development was not initiated by eutrophic peat type, but it was directly commenced by mesotrophic The authors are most grateful for permission of and then ombrotrophic peats. Eutrophic peat data publication from PT. Bhakti Persada Energi. generally depends on groundwater flow for Supports from Physics Laboratory of Centre of nutrient supply. Coal which was deposited in Geological Resources (PSDG) for petrographi- such peatland should haveIJOG well correlation with cal analysis are gratefully acknowledged. mineral matter content.
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118 Depositional Cycles of Muara Wahau Coals, Kutai Basin, East Kalimantan (K. Anggayana et al.)
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