Analysis of coal facies and parting in The Balikpapan formation, Kutai Basin, East Kalimantan

. The research area is located in RKBM coal mining area in East Kalimantan. One factor that influences the presence of parting in coal is the depositional environment. The existence of coal partings in this open pit area needs to be analyzed to determine the following steps in the exploration and further exploitation processes. The purpose of this study is a geological survey with the aim of knowing the coal facies and its parting characterization. The research was done by surface geological observation and drilling method. The results show that the facies association in this mining associated with delta systems such as channel, back swamp, flood plain, levee, crevasse splay, and inter distributary bay. The open pit area is composed of dominant lithology deposited in the upper delta plain environment. The presence of many and thin partings are often found in coal associated with the back swamp facies and deposited in the upper delta plain environment, which is mainly associated with fluvial systems. The distribution of parting in the study area is interpreted as not widespread because it is associated with back swamps that are affected by flood plains, and sometimes their distribution is cut off by channels.


Introduction
The research area is a coal mining area with an open pit mining model in East Kalimantan (Figure 1).The open pit area has coal seams with parting.The parting found is part of noncoal lithology (impurity), which divides or intercalations in one coal seam.The distribution of partings in the study area is not thoroughly known because a more specific facies analysis has yet to be carried out.The existence of partings in coal, in general, will affect the character of coal quality, where the more partings, the quality of the coal tends to decrease.Coal seams in Kalimantan are often associated with other sedimentary rocks, such as sandstone, claystone, or shale [1].The presence of other sedimentary rocks can occur in layers between the coals (inter burden) or intercalations in the coal seams to form partings.Many factors influence the presence of partings in coal, one of which is the depositional environment.Different depositional environments tend to produce different characteristics and qualities of coal.The characterization of coal quality tends to vary according to the coalfield and coal seam, so coal has a high degree of physical and chemical variability.
Friederich & Leeuwen [2] say that coal mining in Indonesia is the main driver of economic growth in Asia.Even though the level of coal exports is sometimes accompanied by demand uncertainty [2], this mining material is still very much needed as a material for generating electricity in the country.Coal mining really helps the development of this country, because of its contribution to providing energy and income per capita [3] which ultimately supports various types of infrastructure development in Indonesia.Even though global policy does not approve of burning coal, currently coal mining is still very much needed to contribute to state income and the livelihoods of people in Kalimantan.For this reason, coal exploration is still very much needed, while waiting for global policies and hoping that one day this mining material can be used as bulk material (building materials, road asphalt, water retaining materials) or other materials needed along with the development of research and innovation.
Based on the description above, it is necessary to research facies to determine the type of depositional environment and interpretation of the parting character in the study area.It is done to overcome the problem of parting by understanding the character of its existence and the extent to which it affects the decline in coal quality, whether it has a significant effect or not.
The issues raised in this study focused on the presence of parting in the Balikpapan Formation, Kutai Basin, East Kalimantan.This study aimed to determine the facies and depositional environment of the lithology (coal and non-coal) and the characteristics of the coal partings.

Geology of the research area
The research area includes the Kutai area [4].The Kutai Basin is a Tertiary basin located in East Kalimantan.This basin is bounded by two fault lines trending northwest-southeast: the Sangkulirang Fault Zone in the north and the Adang Fault Zone in the south.To the south, it is bounded by the Meratus Mountains; to the west, it is bounded by the Kuching Heights; and to the east, it is bounded by the Makassar Strait.
Based on the Sheet Geological Map of Samarinda Supriatna [5] and research by Satyana [6], the stratigraphy of the Kutai Basin is stratigraphically composed of the Pamaluan, Bebulu, Balang, Balikpapan, and Kampungbaru Formations.In this study, the focus is on the lithology that enters the Balikpapan Formation.
The Balikpapan Formation was deposited in a finger alignment above the Pulubalang Formation.This formation consists of alternating claystone and sandstone with coal and limestone intercalations at the bottom.Drilling data that has been conducted in the Kutai Basin proves that the Balikpapan Formation was deposited in a delta system, from plain delta to delta front.The age of this formation is Middle Miocene -Late Miocene.The Balikpapan Formation consists of alternating quartz sandstones, silt claystone, and shales with marl, limestone, and coal intercalations.The depositional environment is littoral to shallow sea with a thickness of up to 800 meters.

Method
Generally, the research method is qualitative research based on surface outcrop, drill, and laboratory data.This qualitative study was carried out by analyzing lithofacies, facies associations to the depositional environment.It was done to characterize the parting conditions in the open pit area under study.
Geological observation is carried out in the field to determine the lithology and its distribution on the surface.In addition, surface data is searched by shallow drilling tools & materials in the field such as geological hammer, compass, loupe, and ruler meter.In the analysis of lithofacies, facies associations, and depositional environment, data was collected in two ways: by measuring stratigraphy and drilling.The purpose of creating a measured stratigraphic section is to describe the stratigraphic conditions of a line, which have been deliberately selected and measured to represent each open pit.
Facies analysis was performed by comparing the depositional environment model of Horne [7].Data processing and map making are assisted using Q Gis, Surpac, Minescape, and MS software.Excel was used to process mapping data and location plotting.

Facies and depositional environment
The primary data used in the study were taken from the open pit area.Data is collected directly in the field by recording outcrop data (Figure 2) and drilling data.
Data collection in the open pit area was carried out using measured stratigraphy based on outcrop data and continued or correlated with drilling data (Figure 3).Measured stratigraphic data was made in 2 traverses, namely sections 1 and 2. The path was made in the direction as perpendicular to the strike (dip direction) as possible and starting from the oldest rock.Furthermore, data were collected on drilling the DH-D-13A, DH-D-16, and DH-D-03 wells.From the results of the data analysis, several facies and depositional environments are interpreted from the rocks that make up the open pit area.In general, the Balikpapan Formation is composed of rocks deposited in a delta system.Therefore, facies and depositional environment analysis refers to the facies model of coal deposition deposited in a delta environment, according to Horne [7].The DH-D-03 well (Figure 4) comprises various lithologies in the form of sandstone, claystone, carbonaceous claystone, and coal.Some lithologies comprise lithofacies and are interpreted to have formed various facies associations starting from channels, back swamp, crevasse splay, interdistributary bays, and levee.Some of these facies associations characterize the depositional environment of the upper delta plain to the transitional lower delta plain.The DH-D-16 well (Figure 4) is composed of lithological variations in the form of sandstone, claystone, carbonaceous claystone, and coal.Some of these lithologies make up lithofacies and are interpreted to have formed in various facies associations starting from the channel, back swamp, flood plain, inter distributary bay, and levee.Some of these facies associations characterize the depositional environment of the upper delta plain to the transitional lower delta plain.
The DH-D-13A well (Figure 4) comprises lithological variations in sandstone, claystone, carbonaceous claystone, and coal.Some lithologies form lithofacies and are interpreted into various facies associations starting from channels, back swamp, and leave.Some of these facies associations characterize the depositional environment only in the upper delta plain.
On MS 1-2 lines (Figure 4), stratigraphic measurements are carried out by identifying surface or outcrop data.Line 1 is carried out to start the old rock stratigraphy, then continue with line 2, which is shifted in the direction of strike.Generally, this route comprises lithological variations in the form of sandstone, claystone, carbonaceous claystone, and coal.

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Some of these lithologies form lithofacies and are interpreted as various facies associations starting from the channel and back swamp.Some of these facies associations characterize the depositional environment only in the upper delta plain.
The interpretation of the depositional environment is based on drilling and stratigraphic measurements data.This interpretation results several facies associations found as follows.

Interdistributary bay-crevasse splay
This environment is characterized by thick coal seams, low sulfur content.Characterized by extensive swamp development.The transitional lower delta plain coal seams tend to be thick.The interdistributary bay facies is characterized by massive claystone, dark gray in color; while the crevasse splay is characterized by layered, coarsening upward sandstones dominated by quartz and feldspar minerals and carbonaceous claystone with coal intercalations.

Channels
This facies association is characterized by sedimentary rocks, dominated by sandstones formed from moderate to very coarse fractional sediments and even gravel.Substantial river flow velocity (bedload) strongly influences these rocks' formation.The characteristics of the channel facies formed in the upper delta plain in the study area have a dominant lithological composition of medium-coarse sandstone to gravel and massive sedimentary structures to cross-bedding.The nature of the sandstones in the study area fining upward, starting from the coarse grain size, which erodes the precipitated layers that were formed earlier.

Backswamp
Thick enough coal with many thin but abundant claystone and carbonaceous claystone fractions characterizes this facies association.The back swamp facies in the study area is interpreted to be formed from the overflow of floods that pass through natural levees in the form of silt and peat deposits.An impurity layer in claystone can occur due to the transport of flood material from the river.

Levee
This facies association is characterized by fine fraction sedimentary rocks ranging from fine sandstone, siltstone to thick claystone.Some of these facies form a normal or fining upward gradation structure.It shows high depositional energy at the beginning, followed by the deposition of a suspension of clay-sized grains as a result of stagnant water that exceeds the river's body (overbank of a river body).In the study area, some plant remains were also found; this indicates that the rock is a natural embankment (levee) in river deposits (upper delta plain).
In some parts, the facies feature in the study area contains iron oxide (undergoes oxidation), which makes the rock very compact.It is due to the condition of the embankment, which continues to experience repeated flooding and drying.

Floodplain
This facies association in the study area is characterized by thick claystone, siltstone, and carbonaceous siltstone to very fine sandstone.Facies associations are interpreted as part of the overbank deposits of a river body.It shows that material deposition in the area has calm energy.The facies association, dominated by fine-sized material, is often interpreted as floodplain sediments.The content of plant residues in the facies strengthens this assumption.
The flood plains that form in the river environment are caused by the lack of capacity of the river body to accommodate the flowing water discharge.Therefore, the material that should be transported through the river is blown away.It causes fine particles to be transported in suspension and deposited on the floodplains.This facies association is deposited in low energy and calm water.However, sandy material can also be deposited on floodplains on either side of the river body and formed as a result of river flood overflow.
Based on the various facies associations interpreted in the study area, the rocks that make up the study area are interpreted to have been deposited in the delta system (associated with the Ancient/Old Mahakam Delta).It is supported by the existence of research locations and interpretations of the depositional environment in the study area, which was deposited in the upper delta plain environment to the transitional lower delta plain and is associated with the Balikpapan Formation.
Based on stratigraphic measurements, interpretation of facies, and depositional environment and their correlation, the depositional environment in the studied area is dominated by rocks deposited in the upper delta plain.It is interpreted that the open pit area studied is mainly deposited in the upper delta plain environment (Figure 4), which is characterized by facies associations dominated by the influence of river systems in the upper delta channels such as back swamp, channel, levee, and flood plain.Coal seams that may represent the upper delta plain are usually thinner and more discontinuous [7].
The channel facies formed in the studied area has grains that tend to be coarse sand to even gravel.In addition, there are quite a lot of traces of roots or tree fossils in the field.It indicates that the channel is formed at the top of a delta system because there is much vegetation.The upper delta plain environment is also characterized by a back swamp forming quite thick coal but lots of thin silt-clay particles.In addition, plant remains were also found in the levee facies indicating that the rock is a natural embankment in river sediments in the upper delta plain.Another factor that supports the depositional environment is that many floodplain facies are a collection of rocks formed from overbank deposits in a river body.
Based on the stratigraphic correlation, it can be interpreted that the RKBM area is composed of rocks deposited in a progradation system of a delta (Mahakam Delta).It can be seen from the sequence of depositional environments where from the bottom, it was deposited in a deeper environment (transitional lower delta plain), and progressively upwards (towards younger rocks), it was deposited into a shallower environment.Another term for this process is the occurrence of shallowing (progradation) so that initially, the environment is deep into a shallower environment.Zamani et al. said that lower delta plain coal is usually characterized by lateral continuity and substantial thickness [8].

Parting Characterization
The discussion of parting character in this study relates to facies, depositional environment and later has implications for coal quality.The detrital nature and composition of the many particulates and the high ash content in the coal seams can indicate an active tectonic presence, resulting in high accommodation space during peat growth [8].
The existence of partings in the research area will undoubtedly affect the decline in coal quality, but what is of concern in this study is the extent to which the resulting reduction in coal quality.Concerning the mining process, the extent to which this decline in quality can be tolerated, and what the mining and exploration strategy will be in the future.
In the research area, parting is often found in coal associated with the back swamp facies and deposited in the upper delta plain environment, which is associated with many river systems.Thin -very thin partings and quite a lot of them will be complicated to separate during the coal-getting process so that the partings are carried along during the hauling process.
The many partings are interpreted due to the influence of the swamp environment (coal formation environment) in the study area near and associated with the dominant river meandering system (Figure 5).In this environment, there will also tend to be many flood plains; the product of the overflow of floods that passes through the levees is generally in the form of silt-clay deposits.It will tend to form a layer of clay-siltstone inserted into the coal when it begins to form due to the transport of flood material from the river.
Based on the interpretation of the character of the parting above, the existence of parting in the RKBM area is most likely only in certain areas and does not spread widely.It is so because the back swamp area affected by the main river floods is most likely only in the flood overflow area, not far away because channels sometimes cut it off, so it is suggested that mining or further exploration can be directed in the direction of the strike to find out how far the parting boundary is developing.
The type of parting needs to be identified, as well as the boundaries of the parting.The depositional environment can influence parting conditions.High energy environments with marine influences can give rise to the dominance of organic components of higher plants [9].As for the coal environment in delta areas such as in the research area, parting conditions can occur due to the influence of terrestrial material inserted between organic components.Currently our country needs a lot of energy, one of which can be met by coal.Responding to the need for coal which is driving economic needs [2], of course current exploration and exploitation activities need to be intensified.Exploration that prioritizes the study of the depositional environment and coal parting is still relevant and important to understand the required coal quality.This is useful for understanding the presence of coal parting in open pits and its influence on coal quality.

Conclusion
Based on the results of the analysis and discussion, it can be concluded that the facies associations in the studied field consist of various facies associated with delta systems such as channel, back swamp, flood plain, levee, crevasse splay, and inter distributary bay.The RKBM open pit area comprises dominant lithology deposited in the upper delta plain environment.
The parting character in the study area shows an association with the depositional environment where the presence of many and thin partings is often found in coal associated with the back swamp facies and deposited in the upper delta plain environment, which is mainly associated with river systems (fluvial).The distribution of parting in the RKBM is interpreted as not wide-spread because it is associated with back swamps that are affected by flood plains, and sometimes their distribution is cut off by channels.

Fig. 1 .
Fig. 1.Location of the research area in the RKBM mining area, in East Kalimantan.

Fig. 2 .
Fig. 2.An example of parted coal outcrop is in an open pit area.

Fig. 3 .
Fig. 3. Measurable stratigraphic collection locations in the open pit area.

Fig. 4 .
Fig. 4. The correlation and stratigraphy of rocks make up the RKBM open pit area predominantly deposited in the upper delta plain environment.

Fig. 5 .
Fig. 5. Illustration of the depositional environment in stratigraphic measurements of the open pit area (shown in red box), the presence of partings widely associated with back swamp and floodplain facies (modification from [7]).