depositional settings and their influence on some coal bed

7/29/2019 DEPOSITIONAL SETTINGS AND THEIR INFLUENCE ON SOME COAL BED

http://slidepdf.com/reader/full/depositional-settings-and-their-influence-on-some-coal-bed 1/50

DEPOSITIONAL SETTINGS AND THEIR

INFLUENCE ON SOME COAL BED

PARAMETERS

BY

ORESAJO BAMIDELE

04/55EA107



PRESENTATION OUTLINE

• Introduction

• Objectives

• Depositional Environment of Coal

• Coal Bed Parameters• Influences of the Depositional

Environment

• Case Study• Conclusion



DEPOSITIONAL SETTINGS AND THEIR INFLUENCE ON SOME COAL BED PARAMETERS

• Introduction

• Objectives

• Depositional Settings of Coal

• Coal Bed Parameters

• Influences of the DepositionalEnvironment

• Case Study

• Conclusion



INTRODUCTION

The parameters of coal beds include its thickness,continuity, roof and floor rock, sulphur and trace element

content and ash (Horne et al; 1978).

These parameters to a greater extent determine the qualityof the coal and its eventual economic significance

Variations in these parameters of coal beds can beattributed to the depositional influences on the peat during

accumulation (Warwick 2005).



DEFINITION OF COAL

A sedimentary rock that burns

Mineralized vegetative material

Altered chemical composition

Formed by increased T and P

Partial decay



INTRODUCTION

Coal Composition

Organic components

Inorganic components

Kentucky Geologic Society, 2006Fig1: Components of coal



FORMATION OF COAL

Coal formation relies on three factors:

Accumulation and preservation of vegetal sediment

Biological degradation and alteration of the vegetal sediment to peat

Geochemical processes that induce chemical coalification of the peat

Kentucky Geologic Society, 2006Fig 2: Coalification process



Source: Brooks/Cole 2002-thompson learning

TYPES OF COAL

Fig 3:Types of coal



Fig 4: Distribution of coal in the world (source: Landis and Weaver, 1993)

WOLRD COAL DISTRIBUTION




• Introduction

• Objectives

• Depositional Environment of Coal



• Case Study

• Conclusion



OBJECTIVES

Depositional Settings of Coal

Parameters of Coal Seams

Influences of the Depositional Settings on Coal Seams

Parameters

To ascertain whether a set of parameter can adequately describe

coal deposits formed in one environmental setting versus another




• Introduction

• Objectives




• Case Study

• Conclusion



DEPOSITIONAL SETTINGS OF COAL

Modern Peat Forming Environments :- Peat is the precursor of coal and accumulates in

mires.

Mires

Ombrogenous

Topogenous




Fig 5: Coal forming environments (Nichols, 2009)




These can be divided into two broad categories:

Paralic environment

Limnic Environment



Paralic environment: refers to coastal or near coastalmarine setting. It comprises of;

Non –deltaic coastal Plain setting

Deltaic Setting



PARALIC SETTINGS

Fig6 :Depositional model for peat forming (coal) environment in a Paralic setting

(modified from Ferm 1976)



NON –DELTAIC COASTAL PLAIN SETTING

Peat accumulates; behind relict barrier terraces, on abandoned estuaries and along

abandoned fluvial channel ridges, and on infilled lagoons

Examples: Appalachian carboniferous barrier Environments

Fig 7: Non deltaic setting



Fig8:Simplified diagram depicting delta

morphology (redrawn after Williamson, 1996).

Areas of peat accumulation are;

Lower delta plain

Transitional delta plain

Upper delta plain

DELTAIC SETTING



Depositional Settings of Coal

Limnic Environment: refers to coals form inland, itcomprises of:

Lake

River setting setting



Peat accumulation occurs in the following areas;

Lakes

Flood plain

abandoned channels of meandering rivers

Ox- bow lakes

PEAT ACCUMULATION IN LIMNIC SETTING



Fig 9:Depositional model of the Wyodak-Anderson coal zone in the Decker

coalfield, Montana. Adapted from Moore (1986)

FLOOD PLAIN EXAMPLE




• Introduction

• Objectives




• Case Study

• Conclusion



COAL BED PARAMETER

The parameters of coal beds includes;

Thickness and lateral extent

Coal character

Coal quality




• Introduction

• Objectives




• Case Study

• Conclusion



THICKNESS AND LATERAL EXTENT

Coal beds have elongate, lenticular, discontinuous, circular or pod-like seamgeometries.

Depositional environment that immediately precede the coal swamp shape the

topography on which the mire develops.

Topography affects most directly variations in coal thickness

Depositional settings that coexist laterally with the peat swamp affect lateral

continuity of the coal forming deposits.

Processes of post depositional environments, such as channel washouts, overbank

dicsharge, channel avulsion causes coal bed discontinuties



INFLUENCES OF THE DEPOSITIONAL ENVIRONMENT

Coal bed thickness and lateral extent

Raised swamps and low-lying swamps in inter-fluvial

environments.

Incursion of river sediments due to floods.

chemical and biological conditions existing in the mire.

Size and pattern of these networks of rivers.



Figure 10 Theoretical model of fluvial architecture in an area of raised swamps (McCabe, 1984)





Fig11: MIRE TYPE(after McCabe,1984)



COAL CHARACTER

van Krevelen, 1993

Main groups are Vitrinite, Liptinite and inertinite

Fig 12: coal maceral



INFLUENCES OF THE DEPOSITIONAL SETTING

Based on ground water level;

Paralic settings, the maceral type of the seam varies

Maceral type of coals of limnic origin is more uniform



Five components can be used to help demonstrate possible influences

between coal character and various environments , They are:

The presence of SO, from sea water

Changes in the level of the water table level, which influences the risk of

fires in the swamp.

Changes in the Eh of the water.

Changes in the pH of the water, which together with Eh influence the

processes of humitication, gellification and putrefaction.

The amount of clay available, which provides iron for making pyrite.




Fig13:Illustration of possible relationship between environment and coal

character(Ryan 1997)




COAL QUALITY

Chemical and physical properties of a coal that

influence its potential use

Comprises of the Sulphur, ash and Trace element

content



PYRITE CONTENT OF COALS

Iron disulfide(FeS2)

Occurs as marcasite or pyrite

framboidal form produced by sulfur reducing microbial

organism found in marine to brackish water



Influences of the Depositional Environment

Paralic coals contain high sulphur content Introduced by

marine to brackish-water environments In the following ways:

Occasional High tides

Percolation of Sea Water Through Unconsolidated permeable

hanging walls



Influences of the Depositional Environment

Consequently, Coals that accumulated in areas under MarineInfluence such as;

Back- barrier: >2% pyritic Sulpur (High)

Lower delta plain: >2% pyritic Sulphur (High)

Transitional setting lower delta plain: 1 to 2% Pyritic

sulphur(Med.)

Upper Delta plain to Fluvial Environment: <1% Pyritic Sulphur

(Low)



Coal Field Sulfur Content Peat Topography Marine Influence

Porttsville(Bitum.) Low to High Planar to Domed High

Allegheny(Bitum.) Med. to High Planar High

Conemaugh(Bitum) Med. To High Planar Low to High

Llewellyn(Anthrac.) Low to Med. Planar to Domed Local

Pottsville (Anthrac.) Low Planar to Domed None

EXAMPLES IN THE APPALACHIAN BASIN

(Warwick, 2005)

Table 1: Key examples in Appalachian basin



ASH CONTENT

Principal sites for peat accumulation have a dominant control on

the ash content of the resultant coal:

Low ash coals originate from domed mires

High ash coals originate from low-lying mires




• Introduction

• Objectives




• Case Study

• Conclusion



The Fort Union Coal in the Powder River Basin

Fig 13:Powder River Basin: northeast Wyoming and southeast Montana.

STRUCTURAL SETTING



STRUCTURAL SETTING

Asymmetrical structural basin with axis trending northwest and southeast close to the

western margin of the basin..

Beds dip on average 20-25 degrees to the east along the west-central margin of the basin

and average 2-5 degrees to the west along the eastern margin.

The Paleocene Fort Union Formation outcrops along the basin margin and is overlain by the

Eocene Wasatch Formation in the central part of the basin.

The Fort Union Formation is more than 6,000 feet thick in the deepest part of the basin

Covers an area of more than 22,000 square-miles

STRATIGRAPHIC SETTING




Fort Union Formation in the Powder River Basin ranges in thickness from 2,300 to

6,000ft

Fort Union Formation is composed primarily of conglomerate, sandstone, siltstone, and

mudstone, and subordinately of limestone, carbonaceous shale, and coal.

Fort Union Formation is divided into the Tullock Member in the lower part, Lebo

Member in the middle part, and Tongue River Member in the upper part.

Tongue River Member contains the most and thickest coal deposits, and the Lebo

Member contains the least number and thinnest coal beds.

Coal beds in the Tongue River Member are more than 200 ft thick.





Fig 14:STRATIGRAPHY OF THE FORT

UNION FORMATION (Flores 1999)

DEPOSITIONAL ENVIRONMENTS




Depositional environments include fluvial systems consisting of

braided, meandering, and anastomased streams in the basincentre, and alluvial fans at the basin margin

Basin-axis, trunk-tributary, fluvial systems were fed by alluvial

fans that drained surrounding ancestral uplifts.

Coal-forming peat accumulated in low-lying swamps and raised

or domed mires in fluvial floodplains, abandoned fluvialchannels, and inter-channel environments





Fig 15:Depositional model of braided, meandering and anastomsed streams in the

powder River basin adapted from Flores (1986)

INFLUENCE OF DEPOSITIONAL ENVIRONMENTS



Raised swamps and low-lying swamps in inter-fluvial environments.

Incursion of river sediments due to floods.

chemical and biological conditions existing in the mire.

Size and pattern of these networks of rivers.




• Introduction

• Objectives




• Case Study

• Conclusion



Conclusion

Peat mires located close to rivers or within river deltas have the possibility

of periodic flooding and the introduction of large amounts of mineral matter.

Mires along coastlines, while not as easily subjected to river flooding, may

be affected by offshore or coastal storms that wash sediment over offshore

bars and beaches into the mires located behind them.

Those environments that coexist laterally with the peat (coal) swamp, as

well as internal processes within the swamp such as the plant growth, plant

decay, fires and water flow, directly affect lateral continuity of the coal forming

deposits.

Conclusively, Depositional setting has been demonstrated to influence

the ;

Quality

Thickness

lateral extent of coal deposits



THANK YOU

depositional settings and their influence on some coal bed

Documents