By Abdi Suprayitno

Coal Geology

Chapter 1

Origin, age and occurrence of coal

Coal is a complex solid object, consisting of various elements representing many chemical components, most of them are derived from the remains of plants, consisting of various fibers which consists of multiple cells. By Thiessen (1947)

Coal is a solid object is composed by carbonaceous macerals. This definition include all the coal from various degrees of coal (coal rank) that begins from peat, lignite, sub-bituminous coal, bituminous coal, semi-anthracite, anthracite and meta-anthracite. By Spackman (1958)

Coal is a combustible sedimentary rock, formed by the remains of plants in varying levels of preservation, followed by the process of compacting and buried in the shallow basins. As soon as the barrier layer down constantly, the buried remain plant is influenced by temperature and pressure process. By The International Hand Book of Coal Petrography (1963)

Coal is a combustible sedimentary rock, derived from plants (mainly contain of carbon, hydrogen, and oxygen), brown to black, since depositional exposed to chemical and physical processes result the enrichment of carbon content. Wolf (1984)

Coal is sediment, organoclastic in nature, composed of lithified plant remains, which has distinction as combustible material. By Thomas (2002)

What Is Coal ?

Geotectonic PositionPaleotopografiGeographical PositionClimateFlora / PlantsDecompositionBasin SubsidenceGeological TimePost-Depositional ProcessOrganics Changing

Coal Forming Factors

Geotectonic PositionClimateBasin geometrySediment supplyAccommodation spaceFlora type

Coal Forming Factors

PaleotopografiBasin geometry Swampy area are formed

Geographical PositionClimateGroundwater surface Sea water abration

Coal Forming Factors

ClimatePlants growing

Tropical wet climate can build bright coalNeither in the pole earth

FloraSpecify the kind of flora/plants

DecompositionDetermine bacteria decompose the plants

Coal Forming Factors

Basin SubsidenceSubsidence and plant accumulation are in balance,

produce thick coalIf Subsidence < accumulation : plant will

decompose with airId Subsidence > accumulation : thin coal, plants

are not grown up well

Geological TimeProduce good coal, if buried with thick sedimentExcept coal is intruded by intrusions, high rank

coal

Coal Forming Factors

Post-Depositional ProcessEffect the quality of coal, such as structure,

intrusion, erotion

Organic ChangingBiochemistry Geochemistry

Coal Forming Factors

Biochemical ProcessPresent aerobe and anaerobe bacteria

Plants (cellulose) Glucose Gas and Water

Peatification

Aerobe bac.

Water

Aerobe bac.

Air

Peat

Anaerobe bac.

Deeper

Biochemical Process Vitrinisation Fusinitisation

Peatification

Peat characteristic :Brown to black> 75 % water content< 60 % carbon contentShown the origin plantsCan cut by a knifePorous like sponge

Peatification

Geochemical Process (physicochemical stage)Peat Lignite Bituminous AnthracitePressure + temperature + timePeat accumulation (coal 1 ft) :

Lignite : 160 yearsBituminous : 260 yearsAnthracite : 490 years

Temperature :200 deg C : > 10 million years150 deg C : > 50 million years100 deg C : > 200 million years50 – 60 deg C : Never be formed

Coalification

Coalification

Coal Rank control factors :Original coal rankIntrusion and structurePressureTemperatureDisturbing type and its period

Coalification

Autochthonous Coal (In situ)Seat earth presentRoot is perpendicular with

beds or seamClean coal (low ash)Steady swampWide spread coalHomogenous thicknessPresent fine grained

quartz sandstoneGood forming macerals

Allochthonous Coal (Drift)No seat earthNo perpendicular rootVary quality and thicknessDeltaic formationSharp contact with above

sedimentMarine environmentPresent Coal ballsSpotting coal spreadingHigh ashPresent macerals and

minerals

Depositional Basin

• Continental• Fluvial• Desert• Lacustrine • Glacial

• Marginal-marine / shoreline• beach / barrier island• estuarine / lagoonal• tidal flat

• Marine• neritic• oceanic

Depositional environment

Coal Depositional Basins

Lacustrine system

It can be formed by fault, rifting; landslide; crater explosion then collapse; fluvial activity.

Insitu and drift coal

River

Continental environment

Fluvial Flood Basin

River environment

Fluvial Flood Basin

River environment

Deltaic systemRiver enter the oceanSediment supply rapid than distribution to

basinInsitu and drift coal

Lagoonal and barrier island systemConsist of sandy barrier island; the lagoon;

channel crossed the barrier to the open seaInsitu and drift coal

Marginal-Marine / Shoreline environment

Deltaic System

Marginal-Marine / Shoreline environment

Regressive marine

Marine Environment

Coal Depositional Basins

TPI (Tissue Preservation Indices) & GI (Gelification)

TPI indicates where the peat was decomposed

GI indicates wetter condition

TPI – GI Vs Depositional Environment

Most of coal is formed in coastal area (Diessel, 1984)

Coal Environment

Refer to Horne (1978) in coastal area :

Back Barrier : thin coal, spread along the strike, layering, high S.

Lower delta plain : thin coal, vary in S content , along the channel, splitting

Transitional lower delta plain : thick coal, low S, splitting, washout

Upper delta plain - fluvial : thick coal, low S, pod shaped, splitting

Coal Environment

First period Lower Carbon to PermianNorth America and Europe

Second PeriodLower Cretaceous to TertiaryCoal

Third Period QuaternaryPeat

Coalification Period

PaleogeneOmbilin (West

Sumatera)Bayah (West java)Pasir (East

Kalimantan)Sebuku (South

Kalimantan)Melawai (West

Kalimantan)

NeogeneWarukin and Dohor

(South Kalimantan)Pamaluan,

Pulaubalang, Balikpapan dan Kampung Baru (East Kalimantan)

Coal Formation in Indonesia