Reservoir Geology and Modelling of Carboniferous

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AES/TG/09-29 Reservoir Geology and Modelling of CarboniferousCoal-bearing marginal Marine and Fluvial Depositsof Eastern Kentucky and Implications forHydrocarbon Exploration and Development

October 2009 Patrick Were

Summary of the steps taken in Petrel to model & interpret facies from well logs


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Title : Reservoir Geology and Modelling of Carboniferous Coal-bearing marginal Marine and Fluvial Deposits of EasternKentucky and Implications for Hydrocarbon Exploration andDevelopment

Author(s) : Patrick Were

Date : October 2009Professor(s) : Dr. Andrea Moscariello and Prof. LuthiSupervisor(s) : Dr. Raik Bachmann and Dr. Michiel DekkerTA Report number : AES/TG/09-29

Postal Address : Section for Petroleum GeosciencesDepartment of Applied Earth SciencesDelft University of TechnologyP.O. Box 5028The Netherlands

Telephone : (31) 15 2781328 (secretary)Telefax : (31) 15 2781189

Copyright 2009 Section forPetroleum Geosciences

All rights reserved.No parts of this publication may be reproduced,Stored in a retrieval system, or transmitted,In any form or by any means, electronic,Mechanical, photocopying, recording, or otherwise,Without the prior written permission of theSection for Petroleum Geosciences


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Table of contents

Abstract (2)

1.General Introduction (3)

1.1

Aims and objectives of the project (4)

2.Regional Geology (7)

2.1. Depositional settings and Facies (12)2.2. The Mississippian Paleogeography (12)

2.3.

The Pennsylvanian Paleogeography (13)

3.Data and Methods (18)

3.1. Data collection and input into Petrel (18)3.1.1. Conversion of borehole data for Petrel (19)

3.1.2. Utility of coal seams (22)3.1.3. Making stratigraphic surfaces (25)3.1.4.

Thickness maps and Facies pie-charts (26)

3.2.

Facies modelling (35)3.2.1.

Introduction (35)

3.2.2. Procedure (35)

4.Results (37)

4.1. Overall delta stratigraphy & architecture in study area (37)

4.1.1. Introduction (37)4.1.2. Analysis of cross-sections (37)4.1.3. Description & Interpretation of stratigraphy (38)

4.1.3.1. The Coastal plain system (39)4.1.3.2. The Magoffin transgression (39)

4.1.3.3. The Fluvial-Deltaic system (40)

4.2. Detailed description & interpretation in Broad bottom (44)4.2.1. Stratigraphy & architecture in Broad bottom (44)

4.2.1.1. The Lower coastal plain system (45)4.2.1.2. The Kendrick transgression (46)


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4.2.1.3. The Upper coastal plain system (46)

4.2.1.4. The Magoffin transgression (46)4.2.1.5. The Fluvial-deltaic system (46)

4.2.2. Description & interpretation of coastal-plain (53)

4.2.2.1. Zone 0 (54)4.2.2.2. Zone 1 (56)4.2.2.3. Zone 2 (58)4.2.2.4. Zone 3 (60)

4.2.2.5. Zone 4 (62)4.2.2.6. Zone 5 (64)

4.2.2.7. Zone 6 (66)4.2.2.8. Zone 7 (68)

4.2.2.9. Zone 8 (70)4.2.2.10. Zone 9 (72)

4.2.2.11. Zone 10 (74)

4.2.2.12. Zone 11 (76)4.2.2.13. Zone 12 (78)

4.2.2.14. Zone 13 (80)

4.2.3. Description & interpretation of fluvial-delta (82)4.2.3.1. Zone 14 (82)

4.2.3.2. Zone 15 (85)4.2.3.3. Zone 16 (87)4.2.3.4. Zone 17 (89)4.2.3.5. Zone 18 (91)

4.2.3.6. Zone 19 (93)4.2.3.7. Zone 20 (95)

4.2.3.8. Zone 21 (97)

5.Discussion (99)

5.1. Evolution of the delta in Broad bottom andIts implications for Reservoir and Petroleum Geology (99)

5.2. Reservoir characteristics (104)

5.2.1. Flow barriers (104)5.2.2. Reservoir communication (105)

6.Conclusions (106)7.Recommendations (109)8.References (111)9.Other relevant literatures (116)


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10. Appendices (124)10.1. Stratigraphic surfaces (125)

10.2. Example of raw data from KGS (148)


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List of Figures

Fig. 1.1.Location map of the study area (6)

Fig. 2.1.Appalachian basin, structures and cross-section (9)

Fig. 2.2.Tectonic loading and unloading (10)

Fig. 2.3.Elements of Foreland deformation (11)Fig. 2.4.Paleogeography of basin in the Late Mississippian (14)

Fig. 2.5.Paleogeography of basin in Middle Pennsylvanian (15)

Fig. 2.6.Stratigraphy of Breathitt Group in Perry and Leslie (16)Fig. 2.7.Stratigraphy of basin in Late Carboniferous period (17)

Fig. 3.1.Counties and quadrangles in study area (19)Fig. 3.2.Location of wells in study area (21)

Fig. 3.3.Generation of sedimentological logs from well data (24)Fig. 3.4.Sedimentological logs flattened on horizon (25)

Fig. 3.5.Generation of stratigraphic surfaces in Petrel (26)

Fig. 3.6.A pack of stratigraphic surfaces in Broad bottom 1 (28)Fig. 3.7.A pack of stratigraphic surfaces in Broad bottom 2 (29)Fig. 3.8.Sedimentological logs in Broad bottom (30)

Fig. 3.9.Cross-section A-B, in the NE-SW direction (31)

Fig. 3.10.Cross-section C-D, in the NW-SE direction (33)

Fig. 4.1.Stratigraphic framework of Pennsylvanian (41)

Fig. 4.2.Strike-section E-F in study area (42)

Fig. 4.3.Dip-section G-H in study area (43)

Fig. 4.4.Colour of legend to diagrams for correlated facies (47)

Fig. 4.5. Dip-section for correlated facies in the NW-SE (48)

Fig. 4.6. Strike-section for correlated facies in the NE-SW (50)

Fig. 4.7. Thickness map of the Breathitt Group in BRDBTTM (52)Fig. 4.8. Colour of legend for the facies pie-charts (53)Fig. 4.9. Composite map of isochore and pie-charts in zone 0 (54)

Fig. 4.10. Composite map of isochore and pie-charts in zone 1 (56)Fig. 4.11.Composite map of isochore and pie-charts in zone 2 (58)

Fig. 4.12. Composite map of isochore and pie-charts in zone 3 (60)Fig. 4.13. Composite map of isochore and pie-charts in zone 4 (62)

Fig. 4.14.Composite map of isochore and pie-charts in zone 5 (64)Fig. 4.15. Composite map of isochore and pie-charts in zone 6 (66)

Fig. 4.16.Composite map of isochore and pie-charts in zone 7 (68)

Fig. 4.17.Composite map of isochore and pie-charts in zone 8 (70)Fig. 4.18.Composite map of isochore and pie-charts in zone 9 (72)

Fig. 4.19.Composite map of isochore and pie-charts in zone10 (74)




Fig. 4.23.Composite map of isochore and pie-charts in zone14 (84)Fig. 4.24.Composite map of isochore and pie-charts in zone15 (86)


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Fig. 4.30.Composite map of isochore and pie-charts in zone21 (98)Fig. 5.1. Vertical log along well BRDBTTM004 (100)


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List of Tables

Table 3.1.Well codes and quadrangles in study area (18)

Table 3.2.Names of Coal seams in study area (23)


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Acknowledgement

This project was a grant from SGS to fund an internship position atHorizon Energy Partners in The Hague, I am indeed grateful for the

technical and financial support that was accorded me for itsimplementation.I would like to thank my external supervisors, Dr. Huw Williams and

Dr. Paul Davies, Reservoir Geology consultants UK, for their guidancein data acquisition and software instructions. The constructive

comments, criticism and support from my referees, especially those ofDr. Raik Bachmann and Dr. Michiel Dekker, is greatly appreciated.

Their time and patience with me is very much appreciated. Dr. AndreaMoscariello, the chief project co-odinator, is greatly thanked for the

energy and time he sacrificed to make the project a success. I would

like to thank all my lecturers and colleagues from the UniversityFaculty of Civil Engineering and Geosciences, TU Delft for their supportand co-operation.


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Reservoir Geology and Modelling of Carboniferouscoal-bearing marginal Marine and Fluvial Deposits of

Eastern Kentucky and implications for Hydrocarbon

Exploration and Development

By

Patrick Were


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Abstract

A considerable amount of geological information required for subsurfacereservoir characterization of new and old hydrocarbon fields can be attained byanalyzing critically the stratigraphic framework and facies architecture of analog

outcrops and mature fields with a dense network of wells. This project makes useof the dense network of cored boreholes and outcrops to construct, using Petrel,a detailed conceptual model that illustrates facies architecture and stratigraphicframework of the Breathitt Group in the Central Appalachian Basin of EasternKentucky, with the aim of investigating the pattern of depositional environmentsand how they influenced the vertical and lateral distribution of facies in this part ofthe foreland basin. The model provides excellent guidelines as to the distributionof depositional energies in analogous subsurface coastal-plain and fluvial-deltaicreservoir sequences. The study is primarily based on cored borehole data from12 quadrangles in Eastern Kentucky which was loaded in Petrel to generatevertical sedimentological logs of the subsurface. Based on extensive coal seams

and marine flooding surfaces the logs were correlated to obtain the strike and dipstratigraphic sections of the foreland basin. Stratigraphic surfaces and compositemaps of isochors and facies pie-charts were prepared for use in predicting thelateral and vertical distribution of facies, depositional energies and paleo-environments in each zone. Basic principles of sequence stratigraphy were alsoapplied to explain the evolution of the delta system in the basin.Correlations revealed two broad depositional systems caused by differentialsubsidence during alternating periods of active tectonics and quiescence. Theupper system is predominantly composed of immature sediments derived fromthe thrust-fronts in the southeast and transported toward the northwest by highenergy braided and meandering streams, whilst the lower system is composed of

mature sediments whose deposition was mainly influenced by waves/storms andtides from the sea in the northwest that frequently transgressed the subsidingbasin in periods of tectonic quiescence. Further evidence for tectonic influenceon the distribution of facies is revealed by the presence of a series of smallanticlinal and synclinal structures which may affect the dynamics of fluid flow inthe basin. Facies analysis shows that the fluvial system in Broad bottom offersbetter reservoirs with good vertical and lateral connectivity than those in thecoastal plain system, which are only connected in the lateral direction.Nevertheless, the coastal plain system could provide a good source region forthe generation of hydrocarbons, because it has a high content of organic matterand its great depth of burial in the basin, could offer the kitchen (enough heat

energy) for the generation of hydrocarbons.Isochores and pie-charts provide a quick method of reserve estimates in bothmature and new hydrocarbon fields. The method yields important petrophyicalparameters which can assist reservoir engineers to plan accurate flow simulationmodels required for well spacing, well numbers, well positioning, and enhancedoil recovery (EOR).


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1.0. GENERAL INTRODUCTION

Fluvial channel sandstones and particularly fluvial-deltaic deposits are importanttargets for petroleum exploration.The clastic coal-bearing marginal-marine andfluvial-deltaic deposits in the Central Appalachian Foreland Basin in the Eastern

Kentucky Coal Field, USA, have been studied in an area of twelve 7.5-minutequadrangles to reconstruct a 3D geometry and architecture of a conceptualfacies model based on a sequence stratigraphical framework of the LateCarboniferous formations belonging to the Breathitt Group. Significant effort hasbeen focused upon understanding their sequence-stratigraphic framework orarchitecture and internal sandstone body geometries in order to facilitate theconstruction of appropriate conceptual facies/depositional models. Depositionalfacies are a significant control on the distribution of petrophysical properties inclastic reservoirs, largely influencing the reservoirs capacity to store and producehydrocarbons. As facies are one of the key controls on the distribution ofpetrophysical properties, facies models can be integrated into the reservoir

modeling workflow by using them as a template for capturing the distribution ofthe petrophysical properties needed in fluid flow simulation. Sedimentologicalheterogeneities that affect hydrocarbon production occur at a variety of scalesincluding sub-seismic and less than the typical development well spacing. Lackof data at these relatively detailed scales and the need for uncertainty analysishas led to the application of stochastic methods for capturing faciesheterogeneity in reservoir models. However, to be useful and reliable, the use ofstochastic facies modeling algorithms needs to be driven by appropriateconceptual depositional models, largely derived from studies of outcrop andsubsurface analogues. Analogous systems are also used to provide certain keyparameters such as sandstone body dimensions or shale bed length and to

improve our understanding of modeling approaches and reservoir forecasting.The Late Carboniferous outcrops of clastic coal-bearing, marginal marine andfluvial deposits of eastern Kentucky in the United States of America constituteworld famous stratigraphic successions used by many companies as a directanalogue to understand and solve stratigraphic problems in the subsurface coalmines and coal-bearing hydrocarbon reservoirs. This project applied a multi-stage modeling approach using a variety of different algorithms to address faciesmodeling at different stages. In order to obtain the required conceptual faciesmodel the following working procedure was planned: (1) converting raw boreholedata into a compatible form, appropriate for input into Petrel, (2) conversion ofborehole input data into sedimentological logs, (3) correlation of equivalent

stratigraphic marker horizons between well logs based mainly on regionallyextensive coal seams, (4) conversion of correlated horizons into 3D stratigraphicsurfaces and isochores for each zone, (5) preparation of composite thicknessmaps and facies pie-charts in each zone, and (6) the final step involved themanual preparation of the conceptual facies models in each zone based on welllogs and facies pie-charts along cross-sections vertically cut through thethickness maps, in chosen directions.


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The results of this working strategy were stratigraphic conceptual facies modelschronologically arranged to enable the prediction of vertical and lateraldistribution of facies and depositional environments in the study area. It wasobserved that the Breathitt Group is mainly composed of the following alternatingfacies associations: sandstones (Ss), heterolithics (Ht), conglomerates (Cnglmrt),

shales (sh), coals (cl), limestones (ls), and some unknown facies (Unknwn). Acoastal setting, including environments such as a shallow sea, a series of smalldeltas, tidal flats and estuaries, a coastal plain, fluvial channels, and alluvialplains, is envisaged for the deposition of the coal-bearing strata of the centralAppalachian basin in eastern Kentucky.

1.1. Aims and objectives of the project

In order to carry out earth resources exploration and estimation, it is essentialthat appropriate outcrop analogues are carefully selected in order to accuratelysupplement the sparse subsurface data with outcrop-derived measurements.Equally important is the role of sequence stratigraphy to provide certain key

parameters such as sandstone body dimensions or shale bed length which cantremendously help to improve the understanding of modeling approaches andreservoir forecasting particularly for siliciclastic fluvial-deltaic deposits so as tooptimize hydrocarbon recovery from the subsurface. The criteria suggested forappropriate analogue selection may include tectonic setting, geological age andsubsidence rates. The Late Carboniferous outcrops of clastic coal-bearing,marginal marine and fluvial-deltaic deposits in the Central Appalachian Basin ofeastern Kentucky provides an appropriate analogue equipped with world famousstratigraphic successions used by many companies to understand and solvestratigraphic problems in subsurface coal mines and coal-bearing hydrocarbonreservoirs.

Large man-made road cuts including extensive subsurface and coal mine data,quarry excavations and a large number of cored borehole data make this regiona highly interesting area to characterize and quantify sand body geometries, coaland shale extents and their overall 3D spatial distribution (architecture). To dateno full integration of this data has been accomplished. It is therefore the aim ofthis project to collect and integrate a large diversity of stratigraphical andsedimentological data so as to reconstruct a 3D geometry and architecture basedon a sequence stratigraphical framework of part of the Breathitt Group locatedalong the US Highway 80 between the Towns of Hazard and Prestonsburg ineastern Kentucky (Figure 1.1, location map of study area). This study updatesthe geological model of the Breathitt Group in eastern Kentucky (including the

area covered by the quadrangles of Martin, Harold, Broad bottom, Wayland,McDowell, Pikeville, Kite, Wheelwright, Dorton, Mayking, Jenkins West, andJenkins East; Figure 3.1 and Table 3.1), and aims to gain a more detailedunderstanding of the facies distribution, stratigraphy and erosional events in thispart of the Appalachian foreland basin. More specifically the aims are to: (1)Review, undertake, and update core descriptions, facies depositional model,sand-body architecture and sequence stratigraphy of the Breathitt Group ineastern Kentucky. (2) Investigate the thickness distribution of the stratigraphic


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zones in the Breathitt Group. (3) Construct stratigraphic cross-sections usingborehole and outcrop data in the study area which illustrate the distribution offacies and depositional environments in this part of the Appalachian forelandbasin.The genetic processes, which led to the deposition of peat or coal formation and

the highly variable carboniferous sediments in this part of the foreland basin, arenot yet well understood. Applying the concepts of sequence stratigraphy to thefacies model, however, gives considerable insights.With the help of the current geo-modelling computer software techniques (Petrel)cored borehole data was used to develop deterministic accurate conceptualfacies models for the marginal marine and fluvial sequences and ultimately builda sequence stratigraphic-based deterministic geological model of the study area.The detailed facies models extend across the preserved portion of the forelandbasin in the quadrangle of Broad-bottom (9.7 km long, 7.5 km wide and up to 330m thick), which is comparable in scale to the reservoir systems typically resolvedfrom 3D seismic data in the subsurface.


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Fig. 1.1. Location map of the three major Paleozoic basins (Illinois, Michigan and theAppalachian) in the eastern interior of the USA. The basins are separated by a system ofstructural arches and domes including the Cincinnati arch. The study area (inset) islocated in the Appalachian basin in the eastern part of Kentucky, USA.


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2.0. REGIONAL GEOLOGY

The clastic coal-bearing marginal marine and fluvial deposits of EasternKentucky are part of the Central Appalachian Basin, a typical Foreland Basin thathas subsided episodically under the loads of successive thrust-sheets (Reed et

al., 2005 and Tankard, 1986). It is separated from the Illinois Basin (anintercratonic basin) in the west and the Michigan Basin in the northwest by asystem of arches and domes (Figures 1.1 and 2.1A). The eastern Kentucky coalfield is bounded in the north by a system of basement faults that belongs to theRome Trough, a Precambrian aulocogen, and to the west by the Cincinnati arch(Figure 2.1B). Unlike the Midcontinent cyclothems of Kansas and Michigan thatwere controlled by glacio-eustacy and the Illinois Basin cyclothems that wereintermediate between tectonics and eustatic processes, the Appalachiancyclothems were predominantly controlled by flexural tectonics (Greb et al., 2004and Heckel et al., 1998).The three basins were repeatedly decoupled and yoked together from Cambro-

Ordovician until the Late Carboniferous times, due to episodic upwarping anddownwarping of the arches or forebulge system (Tankard, 1986; Buter et al.,1991).The Appalachian Basin and its stratal deposition patterns is mainly a result ofthree major successive collisional tectonic phases or allocycles, namely: theTaconic, the Acadian and the Alleghenian thrust phases (Greb et al., 2002;Tankard, 1986). The three episodes of tectonism together with preconvergencedeposition gave rise to the current basin geometry including a stratigraphy thatconsists of four major unconformity-bounded sequences in the CentralAppalachian Basin. The Carboniferous structures and sedimentation in theAppalachian and Illinois Basins were intricately linked (Greb et al., 2002).

Episodic thrust sheet loading on the eastern margin of the North American cratonwas inferred to have caused lithospheric flexure beneath the loads, with theconsequent downwarp and subsidence of the lithosphere to form a Forelandbasin, the Central Appalachian Basin, close to the orogene and a forebulge (theCincinnati Arch) along the cratonward edge of the basin. The static tectonic loadof the orogen and the dynamic loading due the viscous drag force of mantlecorner flow are the primary subsidence mechanisms that control accommodationand sedimentation patterns in the foreland basin settings (DeCelles and Giles,1996; Catuneanu, 2004). Tectonic loading alone provides the defining features offoreland systems, i.e. their partitioning into the flexural provinces: foredeep(which is the foreland basin), forebulge (which is the peripheral bulge) and the

back-bulge (Figure 2.3). Along the flexural profile the uplift of the forebulge wasvirtually synchronous with the subsidence of the foredeep. This is caused by therapid lateral displacement of the viscous mantle material as a result oflithospheric downwarp beneath the orogen and the adjacent foredeep(Catuneanu, 2004). Several renewals of this process forced the forebulge tomigrate westward into the Illinois Basin (Dorsch et al., 1994; Tankard, 1986).Basement structures were reactivated by the increased load in the foreland, andthose structures distal to the foreland were reactivated by the forebulge migration


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(Eble and Grandy, 1990). Cyclothemic sedimentation within the transgressive-regressive units of the Appalachian foreland basin could possibly have resultedfrom laterally changing flexural deformation (Greb et al., 2002; VerStraeten andBrett, 2000). The Appalachian basin contains a Carboniferous stratigraphicalsuccession whose depositional systems are attributed to deposition in a Foreland

Basin that fluctuated between underfilled and overfilled conditions with facies thatemphasize the sedimentary response to basin tectonic subsidence andperipheral upwarping (Einsele, 1992 and Tankard, 1986).The Appalachian orogenic belts were obducted across an earlier extensionalpassive-margin whose configuration and miogeoclinal wedge influenced thepatterns of compressional tectonism and the structural levels (Howell and Pluijm,1990). The thickest and most extensive part of the foreland basin, as observedfrom seismic studies in the southern Appalachians, occurs where overthrusting ofthe continental margin is greatest (Tankard, 1986).The passive-margin history was terminated by the Taconic orogeny during theMiddle Ordovician. Taconic orogene was characterized by magmatic arc

convergence and accretion of exotic terranes (Tankard, 1986). The earlyforedeep was about 700-2000 m deep and shale dominated. Transition frompassive to convergent tectonics is marked by the Knox unconformity which wasincised across a migrating forebulge. Tectonic loading of the progressivelythicker crust resulted into shallowing of the foreland basin, emergence of theoverthrust terranes and influx of coarser siliciclastics (Tankard, 1986). TheTaconic orogeny persisted until the Early Silurian, when thick sequences of non-marine sediments were deposited into the basin (Chesnut, 1980 and Tankard,1986).Collision between the eastern North American portion of Laurentia and alandmass or series of terranes beginning in the late Silurian or Early Devonianresulted in the formation of the Acadian orogenic belt and subsidence of theadjacent Appalachian retroarc foreland basin (Haworth et al., 1988; VerStraetenand Brett, 2000; and Filer, 2003). Based on the stratal record in the forelandbasin a model for the Acadian orogeny was proposed that recognized three tofour tectonically active to quiescent tectophases between the Early Devonian andthe Early Mississippian. It was intense during the Middle to Late Devonian andbest developed in the northern Appalachians. The Acadian orogeny wascharacterized by voluminous granitic plutonism although less convergent thanthe earlier Taconic orogeny (Tankard, 1986). During this orogenesis the forelandbasin was dominated by basinwide deposition of organic-rich shales ormudstone, especially in the distal part of the basin and prominent unconformitieswere incised along the upwarped margin of the basin. The Acadian orogeniccycle waned through the Mississippian until it was superseded by thePennsylvanian orogenesis, also called the Alleghenian orogeny.The foreland thrust-belt of the Central Appalachian basin evolved mainly duringthe Pennsylvanian-Permian Alleghenian orogeny. Terrigenous sandstones of theBreathitt Formation in eastern Kentucky reflect derivation from this orogenicsource.


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Fig. 2.1. The Appalachian foreland basin resulted from Paleozoic thrusting and flexure (A) System of archethe Appalachian basin from Illinois and Michigan basin. (B) Major structural elements of the Appalachian bsection of the basin between X and X* and the Rectangle in B is the study area (Redrawn from Tankard, 19


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Fig. 2.2. Flexural response to orogenic loading and unloading. Repeated thrusting(loading) results in foredeep subsidence and forebulge uplift. The reverse occurs duringstages of orogenic quiescence (erosional or extensional unloading) when the foredeepundergoes uplift as a result of isostatic rebound, compensated by the subsidence of theforebulge (Redrawn from Catuneanu, 2004).

The crinoid and ammonoid taxa from the Kendrick Shale are indicative of aMorrowan or early Middle Pennsylvanian age. Progradation of the Pennsylvanianmolasse wedge is thus correlated with the early stages of the Alleghenianorogenesis (Chesnut, 1996). The Pine Mountain thrust plate, bounded to thenortheast and southwest by tear faults, has formed a ramp upward across theincompetent Devonian-Mississippian shales and overthrust the Pennsylvaniansection (Figure 2.1B). Alleghenian tectonism resulted in thrust-sheet loading ofthick, unstretched lithosphere towards the centre of the hinge line. Due to thegreat flexural rigidity of the lithosphere the foreland basin became shallow and

generally filled its depositional base-level by relatively coarse terrigenous clastics(Kusznir et al., 1985 and Tankard, 1986).The responses of the lithosphere to thrust-belt loading were modelled with threelithospheric types in an attempt to account for the rock record (Figure 2.3):elastic, uniform viscoelastic and temperature-dependent viscoelastic. It wassuggested that the temperature-dependent viscosity model most satisfactorilyaccounts for the stratigraphy (Tankard, 1986; Filer, 2003). The initial response ofthe lithosphere to loading is elastic, and results in a downwarped flexural basinadjacent to the orogene and a forebulge along cratonward edge of the basin(Figure 2.2 and stage one in Figure 2.3). However, if the thrust load remainedunchanged for long periods, relaxation of the plate-bending stress would result in

deepening of the basin, as well as uplift of the forebulge and its contractiontoward the load (stage two in Figure 2.3). Each new thrust-sheet advancerepeats the entire process. The net result of long histories of thrusting would bethe migration of the forebulge away from the load, its distance reflecting theeffective elastic thickness. Thus thrust-sheet loading on a thick (strong)lithosphere would produce a wider and shallower basin than on a thin (weak)lithosphere (Catuneanu, 2004; Tankard, 1986).


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Fig. 2.3. Elements of foreland deformation in which basin subsidence and peripheralupwarping are a response to thrust-belt loading. (1) Lithosphere responds elastically toinitial loading. (2) Overthrust load remains in place for a long period of time and thelithosphere adjusts viscoelastically. The basin deepens while the forebulge undergoesaccentuated upwarping and contracts toward load. (3) At renewed loading lithosphereagain responds elastically forcing the forebulge to migrate ahead of the advancing load(Redrawn from Tankard, 1986).


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The vertical movement of basin-margin arches may be relatively small, butepisodic uplift may induce erosion and reworking within the surf zone (arch peaksor crests, including the immediate surrounding steep areas on the flanks). Ineastern Kentucky the western margin of the Appalachian Basin comprises thebroad Cincinnati arch including a smaller Waverly arch (Figure 2.1B). Foreland

deformation also reactivated the old listric normal faults in a strike-slip sense asexhibited by the Kentucky River Fault System, which offsets the Waverly arch.

2.1. Depositional settings and facies

Distribution of the Carboniferous depositional systems in eastern Kentucky waslargely controlled by the foreland basin dynamics (Tankard, 1986). The Middle toUpper Pennsylvanian Breathitt Group (~ 950 m thick) comprises delta plainfacies of siltstone, claystone, sandstone, bituminous coal and rare ironstone andlimestone, deposited in a foreland basin setting (Aitken and Flint (1996). TheBreathitt depositional systems reflect periods of deposition in broad embayments

when the basin was underfilled, and alluvial plain deposition at times when thebasin was overfilled. The foreland basin dynamics is reflected by the regionalpersistence of these depositional systems (Tankard, 1986). The first attempt tostudy the lateral variation of the depositional environments in the coal-bearingrocks in the Appalachian Basin was based on Wellers cyclothem model forcharacterizing vertical depositional sequences of rock types from the WesternInterior Basin, through Illinois, to the Appalachian Plateau. A steady reduction ofmarine strata in an eastward or landward direction and an increase in the numberof coal beds possibly arising by the splitting of a major coal bed was observed(Ferm and Weisenfluh, 1989; Greb and Weisenfluh, 1996; Greb and Popp,1999). These coals tend to occur in zones and are prone to lateral splitting

because of foreland tectonic and sedimentation influences (Eble et al., 1999;Greb et al., 2002; Hower et al., 1989 and Hower et al., 1994).

2.2. The Mississippian paleogeography

During the Mississippian (late Acadian) the Appalachian and Illinois Basins werewidely yoked together and most stratigraphic units were regionally persistent.There was a widespread deposition of shales, implying a decaying orogene andan underfilled foreland basin (Tankard, 1986). Episodic uplift along the archresulted in shoaling and wave-current reworking of the stratigraphic units anddeposition of siliciclastics (such as the Berea and Carter Caves Sandstones

deposited as elongate sand bars or barrier islands) and bioclastic Sladelimestone containing numerous unconformities in the basin. As a result ofprogressive uplift and erosion the western flank of the arch the Slade limestonewas punctuated by merging wedges of unconformities which migrated eastward,overstepping each other toward the arch axis (Tankard, 1986). Uplift and erosionalong the arch and basement zone is also the main reason for the varieddistribution and thickness of the Slade intervals (Tankard, 1986; Greb et al.,2002). This was a time of inactive orogene when the basin was relatively starved


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of terrigenous sediment although the limestones do become argillaceousbasinward (Tankard, 1986).As a result of rejuvenation of the orogenic source terrane the shallow marinelimestone was eventually covered by a westerly prograding sandy mud sheet(the Paragon Formation). The arch was at this time relatively deflated and the

two basins (Appalachian and Illinois) yoked together allowing lateral persistenceand minor thickness variation of the paragon shales, mudstones and sandstones.Deposition of the Carter Caves Sandstones is attributed to tidal channelprocesses based on the observation of its mature composition and channeling,reactivation and emergence-runoff structures. The paleogeography of thissandstone is thus regarded as an area of shoal-water reworking and dissectionby shallow tidal channels, with emergent barrier sand bodies forming in places(Tankard, 1986). The positive relief of the arch formed the major shoreline andeffectively dampened the wave and tidal energy. Marine reworking was very rarewithin the subsiding foreland basin behind this arch.The Mississippian was formed late in the Acadian cycle at the time when the

orogenic quiescence and terrigenous sediment starvation coincided with the upliftof the basin-margin arch system and its migration toward the orogene. Thistectono-stratigraphic history supports a viscoelastic model of the lithosphere(Figure 2.3).

2.3. The Pennsylvanian paleogeography

A regional unconformity occurs between Mississippian and Pennsylvanian strataalong the basin-margin arch system and marks the termination of the Acadiandeformation (Martino and Sanderson, 1993; Tankard, 1986). During the earliestPennsylvanian time widespread erosion took place in association with cratonic

emergence in eastern Kentucky and vicinity causing topography of paleovalleyswith notably large relief. This eroded surface was onlapped by successions of theLee and Breathitt Formations during the Early and Middle Pennsylvanian. Theseformations are mostly comprised of sandstone, mudstone, and coal lithologies. Asouthwest transport direction for riverine systems prevailed in eastern Kentuckyoccasionally being transgressed with an interior sea along the basin axis from thesouthwest during Early Pennsylvanian (Figure 2.4). Quartz-rich sandstone bodiesof the Lee Formation were deposited by braided rivers flowing in the northeast-southwest direction (Martino and Sanderson, 1993; Tankard, 1986). Variousfacies of the Breathitt Formation have been interpreted as deposits of lower deltaplain, strand plain, back-barrier lagoon, estuarine, fluvial channel, and swampy

environments (Martino and Sanderson, 1993; Tankard, 1986). During the MiddlePennsylvanian, clastic wedges from the Appalachian Orogen progradednorthwest across the Pocahontas Basin (Figure 2.5).

Generally, the Breathitt depositional systems reflect two main periods ofsedimentation: (1) broad embayments when the basin was underfilled and (2)alluvial plain deposition at times when the basin was overfilled (Tankard, 1986).


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Accordingly, Tankard divided the Breathitt Group into three main depositionalsystems (Figure 2.6 and 2.7) based on the distribution of facies, coal seams andthe regional persistence of the Kendrick and Magoffin marine zones in theforeland basin:

The Lower Breathitt coastal plain system

The Magoffin transgression and The Upper Breathitt fluvial-deltaic system.

The Magoffin transgression is a marine unit of Middle Pennsylvanian age, with abasal limestone deposition that indicates a rapid transgressive flooding period ofcoal swamps and a regressive top indicating the return of rapid clastic influx intothe basin by fluvial streams (Bennington, 1996; Greb and Chenut, Jr., 1992).

N

Fig. 2.4. Paleogeographic map of the Appalachian basin during the Late Mississippian to

Early Pennsylvanian time, when a southwest transport direction for the riverine systemprevailed in eastern Kentucky, occasionally being transgressed with an interior sea alongthe basin axis from the southwest (redrawn from Martino and Sanderson, 1993).


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N

Fig. 2.5. Paleogeographic map of the Appalachian Foreland Basin during the MiddlePennsylvanian time, when clastic wedges from the Appalachian Orogen prograded NWacross the basin (redrawn from Martino and Sanderson, 1993).


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Hz9

HZD

HDX

HML

FCR

FCL

WHI

AMB

Hz7

Hz8

STONEY FORKTRANSGRESSION

FLUVIAL-DELTAIC SYSTEM

MAGOFFIN TRANSGRESSION

COASTAL PLAIN SYSTEM

KENDRICK TRANSGRESSION

COASTAL PLAIN SYSTEM

Bayhead deltas

Bay-fill sedimentation with coals

Subordinate fluvial and tidal deposits

Bayhead deltas

Fluvial channels, subordinate bay-fill andsplay deposits

200 m

150 m

100 m

50 m

0 m

Fig. 2.6. Composite stratigraphic column for the Breathitt Formation in Perry and Lesliecounties (study by Tankard, 1986). Bay-fill deposition dominated coastal plain system. Incontrast, succeeding fluvial-deltaic system is dominated fluvial sandstones. Arrows pointin direction of decreasing grain size. Redrawn from Tankard, 1986.


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Fig. 2.7. Upper Mississippian and Middle Pennsylvanian stratigraphy of the Appalachian basin in eastern KTankard, 1986.


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3.0. DATA AND METHODS

3.1. Data collection and input into Petrel

Cored borehole data from 12 quadrangles in the counties of Knott, Letcher, Pikeand Floyd in Eastern Kentucky (Figure 3.1 and Table 3.1) were obtained from theKentucky Geological Survey (KGS) website for Databases and Publications(www.uky.edu/KGS). The quadrangles are arranged in such a way that datafrom N55 (the quadrangle Martin) is furthest way from the thrust front in thenorthwest and Q57 (quadrangle Jenkins East) is directly in front of the basalthrust. Table 3.1 lists the names of the quadrangles and codes used for namingthe boreholes in the study area.

Table 3.1. KGS numbers and codes for the quadrangles in the study area. Abbreviations

are used for borehole codes.

In some quadrangles with a massive number of wells the search was narrowedto well records longer than 300 ft or to those wells that cover the stratigraphicinterval of interest, i.e. the Four Corners Formation.


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A multi-stage modeling approach with Petrel was engaged using a variety ofdifferent algorithms to address modeling at different stages. The stages involvedincluded: (1) converting the raw borehole data into a compatible form,appropriate for input into Petrel, (2) conversion of the input data intosedimentological logs, (3) correlation of equivalent surfaces between well logs

based on coal seams, (4) preparation of stratigraphic surfaces and isochores in3D between different zones, (5) preparation of composite thickness maps andfacies pie-charts for each zone, and (6) manual preparation of conceptual faciesmodels in each zone based on well logs and facies pie-charts along cross-sections cut through the thickness maps, in chosen directions.

3.1.1. Conversion of raw borehole data for input into Petrel

For every individual well three types of information (raw data in digital format)were extracted and stored in different Excel files before importation into Petrel.

This information includes: The borehole header

The lithological data and codes

The coal seam data.The data was treated and adapted for input into Petrel to create sedimentologicallogs for subsequent geological analysis and interpretations.

Martin

Harol

dBr

oad

botto

m

W

aylan

d

M

cDowell

Pik

evill

e

Kite Wh

eel

wrigh

tD

orto

n

Mayk

ingJenkin

s

wes

t Jenkin

s

east

KENTUCKY

Study area

Easte

rnKentucky

Coal

Field

F

PK

L

Fig. 3.1. Location map of the counties and quadrangles in the study area. In the rectangleF, K, L and P stands for the county names Floyd, Knott, Letcher and Pike, respectively.

The borehole header report from the KGS provided the input data for creatingwell header files in Petrel. The well head for each borehole is composed of aname, the X and Y positions, surface elevation for which the Kelly bushing (KB)position was used and total depth (TD). To convert the borehole log information


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into sedimentological logs four basic logs were created in Petrel and combined toyield the required logs. These preliminary logs include:

Ferm Facies (the litho-log obtained from KGS database)

FaciesCurves (derived from the Ferm Facies logs)

Facies (derived from the Ferm Facies logs)

Coals logs (these are comment logs obtained from the KGS seam reports)Figure 3.3 is an example of a sedimentological log correlation in Petrel usingdata input from four wells in the quadrangle Mayking: MYKNG076, MYKNG061,MYKNG001 and MYKNG065.Altogether 286 wells were imported in Petrel for the total study area coveringabout 1900 square kilometers of which about 73 square kilometers in thenorthwester edge were selected for detailed study.Figure 3.2 is a map of the total study area created in Petrel to display allboreholes and locations of the cross-sections made to determine the lateral andvertical distribution of depositional facies as a result of the paleoflow of fluvial andmarine systems during the Middle and Late Carboniferous. The cross-sections E-

F and G-H trend in the NNE-SSW and NNW-SSE directions, respectively, andrepresent the general distribution of facies in this part of the foreland basin.Cross-sections A-B and C-D (inset Figure 3.2) trend in the NE-SW and NW-SEdirections, respectively and represent in detail the distribution of facies in thequadrangle Broad-bottom during the Pennsylvanian times. Note the cross-sections are zigzag lines that do not consider only those wells falling on thestraight lines as depicted in Figure 3.2, but also consider wells within a range ofabout 500 metres from the line.The well logs along each cross-section were correlated using the extensive coalseams and shale layers as maker horizons, to obtain a chronological stratigraphyin the study area (see Figure 3.3). Most horizons can be correlated throughout

the entire study area. However, a few are observed to pinch out midfield at somelocations. Altogether, 26 horizons were observed in cross-sections E-F and G-H,and only 22 in the cross-sections A-B and C-D in the quadrangle Broad-bottom.


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MRTN HRLD BRDBTTM

WYLND McDWLL PKVLL

KT WHLWRGHT DRTN

MYKNG JNKNSWST JNKNSEST

A

B

C

D

F

H

GE

Fig. 3.2.The study area composed of 12 quadrangles, represented by rectangular blocks.Locations of the studied cored wells are indicated by the small circles. Inset in thequadrangle Broad-bottom, the area selected for detailed study. The lines A-B, C-D, E-F andG-H are locations for geological cross-sections explained further in the text.


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3.1.2. Utility of coal seams

During the periods of Langsettian, Lower Pennsylvanian, to Duckmantian andMiddle Pennsylvanian, paleoclimates in Eastern Kentucky were favorable forpeat doming, allowing numerous low-sulfur coals to accumulate in zones and

prone to lateral splitting because of foreland tectonic and sedimentationinfluences, Greb et al. (2002).The thick regionally extensive coal seams have significance in relation to base-level changes and can be used as genetic stratigraphic sequence boundaries innonmarine and marginal basins (Aitken, 1995). They have, therefore, been auseful guide in correlations within this project. Data for the coal seams has beenused to provide input for well tops in Petrel for correlating the stratigraphicsurfaces between well logs. For wells without coal seams fictious well tops wereinterpreted (based on the similarities of log shapes for the lithofacies in theneighboring sedimentological logs) to facilitate correlations between well logs.However, Aitken (1995) urged that the use of coal seams as genetic stratigraphic

sequence boundaries is contentious for the following reasons: (1) they are notsingle surfaces, (2) they are not necessarily maximum flooding surfaces, and (3)systematic variations in accommodation space are not properly accounted for.Hence, coal seams, although readily identifiable and easily correlatable, do notfulfill the criteria for strict, genetic stratigraphic sequence boundary definition, butrather represent a genetic sequence boundary zone (Aitken, 1995).To obtain a clear view of the stratigraphic trends along a given cross-section adatum horizon was chosen along which other horizons were flattened (Figures3.3 and 3.4, illustrate the correlated well logs before and after flattening on ahorizon, respectively). The criterion for choosing such a surface is that it shouldbe relatively thick and regionally extensive. Hence, a coal seam that is

considered to have been processed during the transgressive period of maximumflooding. Flattening on a horizon makes it practically easy to illustrate thechanges in thickness of all the other zones involved. The Fire Clay Coal seam(FCL B) was considered suitable for this purpose. It is relatively thick andregionally extensive in the Appalachian basin. The Fire Clay Coal bed is one ofthe major coal-producing bed in the States. It has a Flint Clay parting, the FireClay tonstein with a volcanic fall origin (Chenut, 1979). It provides a time-correlative datum throughout the basin (Andrew, Jr. et. al., 1994). To facilitate thedescription and interpretation of stratigraphic features in the foreland basin somekey stratigraphic surfaces (coal seams) similar to the Fire Clay Coal seam, whichproved to be extensive across the basin have been used for the stratigraphic

nomenclature (Table 3.2). By means of the available coal seams in the studyarea the middle Pennsylvanian rocks (the Breathitt Group) have been dividedinto three broad units formally ranked as formations and three marine unitsformally ranked as members, and are, in descending order, the Four cornersFormation, Magoffin Shale Member, Hyden Formation, Kendrick Shale Member,Pikeville Formation, and the Betsie Shale Member. The Formations were furthersubdivided into smaller units, which together with the Shale Members add up to21 units (Table 3.2).


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Table 3.2. Nomenclature scheme used for identifying and correlating key stratigraphic coalseams (surfaces) within this project. The table shows the units and formation namesidentified in the study area

surface unit FormationBRS B

BRS A2 1

PCH B2 0

PCH I1 9

PCH A1 8

HZ7 B1 7

HZD A 1 6

HDX A1 5

Four corners

HML B 1 4 Magoffin Member

HML A1 3

FCR A1 2

FCL B1 1

WHI B1 0

WHI A9

Hyden

AMB B8 Kendrick Member

AMB A7

UE3 B6

UE3 A5

UE2 A 4

UE1 B 3

LEK B2

Pikeville

CLN B1 Betsie Member


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Fig. 3.3. Well logs with correlations based on coal seams before flattening on a horizon.The logs also illustrate the four most important information required for the data input intoPetrel: the FermFacies, the FaciesCurves, the Facies and the Coals, all combined to form acomplete sedimentological log.


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Fig. 3.4. The same well logs as in Figure 3.3, but now with the corelations based on adatum layer (FCL B). The pattern of the stratigraphic units in this case can easily beobserved and predicted between wells.

3.1.3. Making stratigraphic surfaces

Having acquired satisfactory stratigraphic cross-sections in the study area, thenext step was to construct stratigraphic surfaces in Petrel for each horizon, usingwell tops provided by the upper surfaces of the coal seams. The well top FCL Bfor the fire clay coal seam was used as the reference surface upon which thesurfaces immediately below and above were constructed using the calculatorfunction in Petrel. To create succeeding and preceding surfaces above andbelow the FCL B isochore points were calculated and isochore thickness mapsfor each zone were made, and then subtracted from the previous surface.Altogether 25 surfaces were generated in the entire study area and 23 in the


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quadrangle Broad-bottom. This marked the first step towards making conceptualgeological and facies models in the study area.At this stage the study was narrowed to an area of about 73 square kilometers inthe northwestern corner of the study area, in the quadrangle Broad-bottom(Figure 3.2).

HZ8 B

HDX A

FCL B UE1 B

Fig. 3.5. Stratigraphic surfaces in 3D obtained using well tops (top surfaces of the coalseams) as input data. The well top FCL B (Fire Clay B coal seam) was used as thereference surface.

3.1.4. Preparation of composite thickness maps and facies pie-charts

The first step toward facies correlation a composite of thickness maps andlithofacies pie-charts created in Petrel with the aim of facilitating the estimation ofthe percentage of lithofacies, including their lateral and vertical distribution,

connectivity and stacking patterns in each stratigraphic zone. The procedure forcreating pie-charts is explained in detail in the next section. Finally, two specialcross-sections (A-B and C-D) were prepared in Petrel by cutting through thethickness maps in the quadrangle Broad-bottom (Figures 3.6 and 3.7). Twofurther sections (E-F and G-H) were prepared in a similar way to illustrate thegeneral stratigraphic trends in the total study area Well logs along or in closeproximity (~ 500 m) to the intersection planes were also included in the cross-sections to facilitate facies correlations and interpretations between wells. The


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stratigraphic sections thus obtained were used as templates for vertically andlaterally correlating facies in the study area. This was done manually with thehelp of the composite maps for zone thickness and facies pie-charts (Figures 4.6to 4.27) and the preliminary stratigraphic sections correlated in Petrel. Individualfacies available in the area have been assigned different colours (Figure 4.4).

This gave the required conceptual facies models, which can also be used asgeological stratigraphic models, representing the distribution and evolution ofsediments, facies, lithotypes in this part of the Appalachian foreland basin ineastern Kentucky (see Figures 4.5 and 4.6).


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Intersection Plane

A

B

Fig. 3.6. Correlated stratigraphic surfaces in the subsurface of Broad-bottom stacked together and cut thrpreparation for the NE-SW cross-section A-B.


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D

C

Intersection plane

N

Fig. 3.7. Correlated stratigraphic surfaces in the subsurface of Broad-bottom stacked together and cut thrpreparation for the NW-SE cross-section C-D.


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PKV007 PKV010 Bb029 011 028 010 012 020 005 004 076 073 072 HRLD033 Bb023 015 024

Fig.3.8. Detailed log cross-section linking all wells in the quadrangle Broad bottom and a few others from


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SSW

Fig. 3.9. Detailed cross-section A-B (see Figure 3.1 for location)


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SSW

Fig. 3.9. continued.


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NW

Fig. 3.10. Detailed cross-section C-D (see Figure 3.1 for location


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NW SE

Fig. 3.10. continued


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3.2. Facies modelling

3.2.1. Introduction

To acquire a better knowledge and understanding of the stratigraphic frameworkand facies distribution and architecture of the Breathitt Group of formations ineastern Kentucky, a detailed study was carried out in a single quadrangle (Broadbottom) northeast of the study area. This part of the field was chosen because ithas a relatively sufficient number of wells (17) evenly distributed and coveringalmost the entire stratigraphic intervals of the Breathitt Group, including the FourCorners Formation, the Magoffin Member, the Hyden Formation, the KendrickMember, the Pikeville Formation and the Betsie Member. The Four cornersformation has been eroded in most of the southern parts of the study area, butstill exists in areas further from the thrust-front. In the quadrangle Broad bottomthere exist a few wells that avail data about the Four Corners Formation. In this

study thickness maps and lithofacies pie-charts have been used to construct thebasin stratigraphy.Thickness variations in a given zone can be due to a variety of stratigraphic andstructural causes including tectonics, subsidence and differential compactionduring and after deposition. Therefore, thickness maps are a valuable guide forstructural and stratigraphic interpretation.

3.2.2. The procedure

The lithological information obtained from the cored wells in the area was usedas input data into Petrel. A zigzag cross-section connecting all existing wells in

the quadrangle Broad-bottom, as well as two from the neighboring quadrangleHarold, was constructed in Petrel (Figure 3.8). Next the stratigraphic surfaceswere correlated based on the extensive coal seams and marine flooding surfacesin the area dividing the basin into genetic stratigraphic units. Thickness maps(Isochores) were generated in Petrel for the zones between successive surfaces.The isochore maps thus derived are representative of time equivalentdepositional zones or sequences within the Breathitt stratigraphic interval. Pie-charts were created in each isochore or zone displaying the percentage volumeof each lithofacies along those wells that have log information on the entirethickness interval of each zone.The procedure for creating pie-charts in Petrel can be summarized as follows:

Open a new 2D window. Select the polygon for the area Broad bottom anddisplay the thickness map for any desired stratigraphic interval by selecting itfrom the list of isochores in the lower part of the input pane. Insert the wells thatactually have data in this interval. Using the general log correlation cross-sectionfor the area Broad bottom, those wells that wholly penetrate the selected intervalcan be selected. In the upper part of the input pane right click attributes andselect the option insert new attributes. Under new attributes select and click theoption continuous, which then leads one to the attribute operations. Select


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zone to level 1, facies, %, SSTV, in that order and eventually run the settings.Under facies choose either a single facies at a time from the list of 14 lithofaciescoded for this project or select all of them at once to save time for several runs.Petrel will draw a pie-chart for each borehole showing the proportions of eachlithofacies logged along the well bore in that stratigraphic interval. This procedure

is repeated for all zones.For each stratigraphic zone pie-charts and isochore maps were used to criticallyanalyse the thickness, and lateral distributions of each facies, including faciesassociations and proportions, and grain-size trends, with the aim of derivingquantitative and qualitative information about the vertical and lateral distributionof depositional energies and environments in the unit. This information is crucialat the initial stage of any scheme for geological reservoir modelling. The faciesvolumes, obtained from the pie-charts, and their patterns identified in each wellwere then used to predict or interpolate the facies vertical and lateral distribution(and hence the depositional environments) between wells. Thus, pie-chartsprovided a statistical database for the quantity of each facies in a given zone.

To facilitate the task of facies description and interpretation process a compositeof contoured isochore map and pie-charts were generated in each zone (seeFigures 4.6 to 4.27). The subsequent architectural and sequence stratigraphicalanalysis was based on cross-sections A-B and C-D.The main elements of these cross-sections include: (1) the vertical stackingpatterns of the sedimentary bodies (lithofacies) along each well that partially orwholly penetrate the mapped interval of the Breathitt Group in the area of Broadbottom, (2) the stratal surfaces (in principal these are the coal seams), (3) thestratigraphic units or zones composed of various facies associations andbounded above and below by the stratal surfaces. Each lithofacies was given aspecific colour and the bounding surfaces are named according to theNomenclature scheme adopted from Chesnut (1996) (Table 3.2). Stratigraphiccorrelation sections A-B was oriented parallel to the strike of the basin structuresand axis and section C-D was oriented parallel to the dip direction of thedeposited facies in the basin (Figures 3.2, 3.9, 3.10, 4.4 and 4.5).A simple lithofacies subdivision scheme was used in the cross-sections,consisting of only seven different types which, nevertheless, highlight the mainlithological heterogeneity in the formations (Figure 4.4). They include: (1)Conglomerates (Cngl 12), (2) Sandstones (Ss 10), (3) Heterolithics (Ht 8), (4)Shale (Sh 6), (5) Coal (Co 2), (6) Limestone (Ls 13), and (8) Unknown (Un 0).The numbers attached to the facies abbreviation are litho-codes used by theKGS database centre.


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4.0. RESULTS

4.1. Overall stratigraphy in the entire study area

4.1.1. Introduction

A reliable geological sequence stratigraphic framework and facies architectureare necessary in order to investigate coal and other hydrocarbon resources inany exploration basin and the central Appalachian basin of Eastern Kentucky, inparticular, so as to understand the depositional mechanisms (tectonics, eustatic,subsidence, paleoclimates, etc) that were involved in controlling the distributionof the deposited facies in the basin. It is also necessary to develop a usablestratigraphic framework that accurately reflects the present knowledge of thecoal-bearing strata. Two cross-sections, E-F and G-H, were constructed acrossthe study area (based on stratigraphic surfaces generated by in Petrel throughthe sedimentologic logs that were obtained from 286 cored boreholes in the areaof twelve quadrangles in Eastern Kentucky) in order to examine the stratigraphic

and structural framework of the coal-bearing rocks in the basin (Figures 3.2, 4.1,4.2, and 4.3). The SSE-NNW cross-section is oriented parallel to the dip directionof the stratal units, whereas the SSW-NNE cross-section is oriented parallel tothe strike direction (Figure 4.2 and 4.3). Table 3.2 is a modified version of thenomenclature scheme used by Chesnut (1996) to describe the geologicalstratigraphic framework for the coal-bearing rocks of the Central AppalachianBasin (Figure 4.1).

4.1.2. Analysis of cross-sections (E-F and G-H)

Generally, the two cross-sections reveal a regional characteristic thickness trend

in the stratigraphic strata of the Breathitt Group in the study area. The stratamainly tend to thin laterally across the basin from the thrust-front in the southeasttoward the basin margin in the northwest (Figure 4.2 and 4.3), demonstrating thegeometry of a typical foreland basin.The strike cross-section E-F (Figure 4.2) is thicker in the SSW direction (~ 1200ft) near the basin axis and thinner in the NNE (~ 800 ft), the plunge direction.Furthermore, the strike-section reveals a significant proportion of a broad domal(anticlinal) structure in the foreland basin onto which all the mapped strata aresuperimposed. The section also shows a series of small folds around the peakregion of the domal structure in the SSW and a broad synclinal structure midfield.These tectonic distortions however tend to wane out toward the NNE direction.

The trending axes for all these structures are oriented in the NNW-SSE direction.

Similarly, the dip cross-section G-H (Figure 4.2) is thicker in the SSE (~ 1320 ft)near the thrust-front and thinner in the NNW (~ 740 ft) toward the basin margin.Unlike the strike-section the small folds are uniformly spread onto the entire flankof the large domal structure in the field with a tendency to increase the frequencyand amplitude toward the basin margin (forebulge) and waning out in thedirection of the thrust-front. These structures have their axes trending in the


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NNE-SSW direction. Also to be observed in this section is the degree of stratalinclination, which decreases down the stratigraphic column. Thus the strata in theFour Corners Formation are inclined most and those in the Pikeville Formationleast. Both sections show that the major transgressive marine units are relativelythicker than other strata in the basin. This implies they are zones of major

tectonic subsidence and sea level rise which out balanced the rate of sedimentdeposition.The Breathitt Group is observed to contain many strata that are aerally extensiveacross the basin, indicating basin- or larger-scale control over their deposition.This may be explained by two mechanisms: (1) tectonics was of a basin-scaleand (2) eustatic controls were of great extent. Tectonic mechanisms can be usedto explain the transgressive-regressive cycles observed in the strata, as thrust-block emplacement caused these foreland basin-scale features.

Pennsylvanian glaciation in the Southern Hemisphere and its consequent glacio-eustatic control over coastal sedimentation of the Central Appalachian Basin has

been suggested (Chesnut, 1996; Aitken and Flint, 1996). A coastal setting,including environments such as a shallow sea, a series of small deltas, tidal flatsand estuaries, a coastal plain, fluvial channels and alluvial plains, is envisagedfor the deposition of the coal-bearing rocks of the Central Appalachian Basin(Chesnut, 1996). Sea-level changes on the order of several tens of metres wouldhave had drastic effects on Pennsylvanian coastal settings and transgressions,whether of eustatic or tectonic origin and would have extended inland for severalhundreds of kilometers in such lowland settings (Aitken and Flint, 1996).

Generally the Breathitt Group in the study area is mainly composed of alternatinglitho-facies of coals, shales, heterolithics, conglomerates and sandstones. Adetailed explanation of facies and their distribution in the Breathitt fluvial-deltaicstrata in eastern Kentucky will be given in section 4.2 for the quadrangle Broad-bottom. The following is a brief description and interpretation of the stratigraphyin the entire study area.

4.1.3. General description and interpretation of the stratigraphy in studyarea.

Similar to the results of previous studies (e.g. Tankard, 1986), the stratigraphy ofthe Breathitt Group in the study area may be broadly divided into three zones(FC, H, and Pk) separated by two major marine transgressive zones, Magoffinand Kendrick (Figures 4.2 and 4.3). The uppermost zone (FC) is a fluvial-deltaic

group of formations known as the Four corners formations. The middle zone (H)is a coastal plain system of formations known as the Hyden formations. It isseparated from the uppermost and the preceding zones by the Magoffin andKendrick transgressive systems, respectively. The lowermost zone (Pk) is alsobelongs to the coastal plain system.


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4.1.3.1. The Coastal Plain System (H and Pk)

The lower coastal plain system (Pk) occupies the stratigraphic interval betweenthe Kendrick and the Betsie transgression systems. Bay-fill and bayhead deltafacies, and locally incised channels are present but less abundant than in the

Hyden system of formations. Subordinate fluvial sandstones comprise about 10-20% of this succession and form thin, isolated bodies interspersed intransgressive deposits composed predominantly of heterolithic lithofacies. Coalsare thick and regionally extensive.

The upper coastal plain depositional system (H) occupies the stratigraphicinterval between the Amburgy (AMB) and the Haddix (HDX) coal zones,sandwiched between two major transgressive sequences: the Kendrick Shalemember at the bottom and the Magoffin Shale member at the top. The depositedlithofacies in this interval include sandstones and conglomerates, shales,heterolithics, and coals. These facies were predominantly deposited in various

environments including Lower Delta Plain, Strand Plain, Back Barrier Lagoon,Estuarine Channel, and Swamp. Stratigraphic relationships show overall thinningtoward the basin margin, the Cincinnati-Waverly arch complex.Bay-fill and bayhead delta facies, locally incised by channels are predominant.The coals are thick and regionally persistent. The preceding major transgressiveinterval, the Kendrick Shale, is similar in all aspects to the Magoffin ShaleMember.

4.1.3.2. The Magoffin transgression

Magoffin transgression is a record of marine flooding in the foreland basin as it

subsided beneath the loads of the advancing thrust-sheet complex in thesoutheast. In the study area the Magoffin exhibits foreland basin geometry (i.e.asymmetric prism) and is sandwiched between the stratigraphic surfaces HDX(at the top) and HML B (at the bottom). It is about 300 ft thick in the southeast (inthe area of the quadrangle Mayking) and about 75 ft in the northeast, in thequadrangle Broad-bottom (Figure 4.1). It is dominated by heterolithics and shalefacies with minor sandstones in the middle and top zones. It has an overallupward coarsening trend in grain size. Three major facies tracts can be observedalong well BRDBTTM024 in the Magoffin zone: a basal transgressive intervalwith shale and heterolithic facies, a bay-margin progradation interval withsandstone facies, and an upper marine interval with shale facies. Magoffin

sedimentation terminates with peat swamp accumulation and in some sectionserosion (e.g. along well BRDBTTM015) by fluvial channels and incised valley fills(e.g. conglomerates along well BRDBTTM004).Magoffin is a regionally persistent marginal marine interval that demonstrates amajor tectonic control that caused overdeepening of the foreland basin. The richinvertebrate fauna in this zone records an early Atakon age (Tankard, 1986).Deposition of the Magoffin during the Atokan was contemporaneous withoverthrusting in the Ouachita orogenic belt, indicating that basin subsidence and


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transgression resulted from overthrust loading. Furthermore this rapid responseof the lithosphere to overthrust loading implies an initial elastic behaviour(Tankard, 1986). Similar rock types, paleoenvironmental settings, and faunacharacterize the Kendrick and Magoffin paralic systems (Chesnut, 1996 andTankard, 1986)

4.1.3.3. The fluvial-deltaic system (FC)

The Upper fluvial-deltaic system (identified as FC in Figures 4.2 and 4.3) is themain theme of this thesis and will be described and interpreted in detail in thenext section using thickness maps and cross-sections. The transition from thetransgressive system (Magoffin) to the Breathitt fluvial-deltaic system (the FourCorners Formations) is very abrupt, as observed from the presence of basalconglomerates and sandstones bodies in the lower sequences (Figure 4.5 and4.6). This marks the entry of major rivers into the foreland basin. It is about 660 ft

in the southeast and about 500 ft in the northwest (Figure 4.3). It is characterizedby a framework of multistory channel sandstone bodies that coalesce along striketo form relatively continuous sandstone units measuring several kilometers inwidth (see Figure 4.5a). Channel fill sandstones usually comprise more than 70% of the entire stratigraphic column. Braided and coarse-grained meanderingstream deposits are very common in this system with subordinate amounts ofpaleovalley fills. Subordinate facies include heterolithics (which are possiblyoverbank mudstones) and coals, as well as shales which may possibly belong tothe interdistributary bay and crevasse splay lithologies. Overall the fluvial systemconsists of progradational lowstand deposits.The rapid change from the transgressive marine sedimentation in the Magoffin

zone to sand-dominated alluvial plain deposition was probably due the tectonicreactivation of the source terrane in the southeast by orogenic uplift. Coarseclastics were shed from the orogene faster than the subsiding foreland basincould accommodate it, resulting in an overfilled basin (Tankard, 1986). The mostimportant result for this study is the observation of the positive and negativestructural elements (anticlines and synclines) in the basin, which may havesignificantly influenced the drainage pattern in the Four Corners Formation.The fluvial-deltaic system terminates with an extensive coal unit and a regionalmarine deposition, the Stoney Fork Shale Member.


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Fig. 4.1. A stratigraphic framework of Pennsylvanian rocks in the Central Appalachian Basin, redrawn fro


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1200

2400

MagoffinShaleMember

KendrickShaleMember

BetsieShaleMember

FC

H

Pk

SSW

Vert

icalelevation

in

ft.a.s.l.

Fig. 4.2. Strike section (E-F) of the Breathitt Group in the study area in Eastern Kentucky. It was constructeintersection plane through 22 stratal surfaces (see Figure 3.2 for location). FC stands for Four Corners groHyden group of Formation, and Pk stands for the Pikeville group of Formations.


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700

1440

MagoffinS

haleM

Kendrick

Shale

BetsieShale

FC

H

Pk

NNW

Fig. 4.3. Dip section (G-H) of the Breathitt Group in the study area in Eastern Kentucky. It illustrates the ov(i.e. thickening toward the thrust-front). See further explanation in the text.


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4.2. Description and Interpretation of the Stratigraphy,architecture and facies distribution in the quadrangleBroad bottom

4.2.1. Overall stratigraphy and architecture in Broad bottom

The work reported in this section forms a small part of the total study areacovering about 73 square kilometers, with a stratigraphic control provided by 17wells, which have been used to define and map 21 units/zones. The result offacies analysis of each individual zone along the two cross-sections, A-B orientedin the NE-SW and C-D oriented in the NW-SE directions, gave rise to the generalstratigraphy illustrated in Figures 4.5 and 4.6. These cross-sections demonstratethat each statal unit is characterized by: (1) a facies association with a verticalthickness in the order of tens of metres, (2) a lateral extent of several hundredsof metres to a few kilometres, and (3) a length of several kilometres. The

stratigraphy is mainly dominated by seven lithofacies: sandstones (Ss),heterolithics (Ht), conglomerates (Cnglmrt), shales (sh), coals (cl), limestones(ls), and some unknown lithofacies (Unknwn) which in this project has beeninterpreted to be sandstone. The conglomerate and most sandstone lithofaciesbelong to fluvial-channels and incised valley fills. Other depositionalenvironments include mouth-bars, estuaries, prodeltas, distributary andInterdistributary facies deposits. The heterolithic and shale lithofacies mainlyrepresent sea transgressional facies and depositional facies that flanked thefluvial channel banks and are therefore composed of a mixed assortment ofaccumulated fine-grained sediments. They may therefore occur as channel-lobetransition or frontal splay deposits. Limestone is most likely to have precipitated

from a marine environment while coals are a result of peat generation in swampyand marshy environments. Both limestone and coals could be indicators ofmaximum marine flooding surfaces.

Broadly the stratigraphy in Broad bottom may be divided into five parts, similar tothose observed in the stratigraphy for the total study area (Figures 4.2 and 4.3).In a descending order these zones/units may include:(1) Units 21 to 15 (the fluvial-deltaic system)(2) Unit 14 (the Magoffin transgressive system)(3) Units 13 to 7 (the upper coastal plain system)(4) Unit 6 (the Kendrick transgressive system

(5) Units 5 to 0 (the lower coastal plain system.

Considering all the units together, the overall thickness trend that was observedin the general stratigraphy (i.e. stratal thinning toward the NW or NE, Figures 4.2and 4.3) still holds true for the stratigraphy in Broad-bottom. However, this maynot be true for some sections (units 0 through 6) in the lower parts of thestratigraphy. This may be partly due to the differences in the magnitudes of thedepositional controls (including tectonism, differential subsidence, and eustasy)


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along the stratigraphic column. The upper parts, for instance, were deposited atthe time of the Atokan orogenic activity, causing a significant inclination to thedeposited stratas in the southeast. The inverse relationship between thethicknesses of some neighbouring stratigraphic units has also been observed.Nevertheless the overall stratigraphic thickness map for the Breathitt Group in

Broad-bottom clearly demonstrates the thickness trend (Figure 4.7). Althoughless obvious, the general tendency for the units to plunge in the NE and dip in theNW can still be observed in Broad bottom. However, one of the series ofanticlines and synclines that were observed in the general stratigraphy for theentire study area is now exaggerated in the dip-section (Figure 4.5). Thesynclinal structure (asymmetrical in shape) tends to increase its curvature(straining power) with depth through the fluvial system until the Magoffintransgression when its curvature begins to relax with depth, through the Kendricktransgression until the Betsie transgression when its small anticlinal lobe to theNW of the axis totally disappears. At the top of the fluvial system the structurehas one anticlinal lobe to the NW of its axis (along wells BRDBTTM023 and 015),

but begins to develop its second and broader lobe on the SE (along wellsBRDBTTM024, 005, and 004) with increasing depth. However, at greater depths,in unit 2, for instance, when the NW lobe is almost completely attenuated, that onthe SE side of the axis can still be observed, although very much diminished inshape. The strike section also exhibits a small anticlinal structure (along wellsBRDBTTM029, 011, and 028) which is much less in magnitude than thoseobserved in the dip-section.The age of the correlated part of the Breathitt Group has been estimated bebetween 306 Ma (top of unit 21) and 315 Ma (top of unit 0), based on theassumption by Greb et al. (2002) that the individual coal-clastic cycles haddurations of approximately 400 ka. Further, the coal-clastic cycles are assumedto be eustatically controlled fourth-order sequences, grouped into sequence setsto form third-order sequences (Aitken and Howell, 1996 ; Miall, 1991).Generally the following observations were made: (1) Stratal thickness increasesin the SE direction toward the axis of the foreland basin, (2) the intensity offolding (tectonism) attenuates with depth, (3) the proportion of marine (shales)and heterolithic lithofacies increases with depth, (4) conglomerates are mostlyobserved in the upper coastal plain and the lower fluvial system, deposited at thebase but sometimes in the middle of the stratal units, and (5) the proportion ofsandstone lithofacies decreases with depth.

4.2.1.1. The Lower coastal plain system

Generally, the lower coastal plain system (units 5, 4, 3, 2, 1 and 0) has a very lowproportion of sandstone facies and is predominantly composed of shales andheterolithics. In some locations, however, e.g. in unit 5 along well BRDBTTM004,conglomerate facies may be observed. These are likely to be a result of forcedregressions deposited by the oscillating sea-level, at sea level fall. The depositedsediments of this system, like the rest of the coastal system, are retrogradationaland generally tend to coarsen upwards.


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4.2.1.2. The Kendrick transgression

The Kendrick transgression (unit 6), like the Magoffin, thickens toward the basinaxis, with the grain-size of its sediments coarsening upwards. It is predominantlycomposed of heterolithics and shales, with some minor sandstone facies in themiddle and upper tracts.

4.2.1.3. The Upper coastal plain system

In the upper coastal plain system (units 13 to 6), the pairs of units 14+13, 12+11,and 10+9 are inversely related in their thickness. The last two units (8 and 7) inthis system, however, exhibit the true foreland basin geometry, i.e. they tend tothicken toward the thrust-front. This system has an equal proportion ofsandstones and heterolithics plus shales. The strike cross section shows a largenumber of sandstone bodies and conglomerates laterally stacked together butseparated by thin shales between units. The proportion of sandstones tends toincrease towards the NE (strike section, Figure 4.6).

4.2.1.4. The Magoffin transgressionUnit 14, the Magoffin transgression, as before shows a thickness pattern typicalof the foreland basin geometry, i.e. thickening in the directions toward the thrust-front load or basin axis. It shows a tendency for its grain size to coarsen upward.It is predominantly composed of marine facies (shales) and heterolithics.

4.2.1.5. The Fluvial-deltaic system

In the fluvial-deltaic system (units 21 to 14) the unit pairs 21 and 20, 17and 16,are inversely related in thickness, while the rest (units 19, 18 and 15) showconstant thickness along the dip-section (Figure 4.5). The system shows anoverall tendency for its grain size to thin upward and its deposits are mostly

composed of sandstone and conglomerates (> 75 %), with the rest being shalesand heterolithics lithofacies.


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Fig. 4.4. A Colour legend to Figures 4.5 and 4.6


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Fig. 4.5. (a) A schematic dip-section, illustrating the sequence stratigraphic framework and Depositional Sthe upper part of the Breathitt Group (units 11 to 21). Correlations were done in Petrel based on the extensobserved in the sedimentological logs. The logs were constructed in Petrel using cored borehole data alothe quadrangle Broad bottom (see Fig.3.2 for location). The numbers and codes at the top are identities fothose on the sides are the names of major coal seams used for correlations and sequence stratigraphic abdepositional processes. See Table 3.2 for nomenclature of the coal seams.


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Fig. 4.5. (b)Sequence stratigraphic framework and Depositional System Tracts for facies in the lower part to 10) along the same cross-section as in (a). The diagram is as well a conceptual facies model showing t

distribution of facies in the Breathitt group of Formations between the stratigraphic surfaces BRS B and LSystem Tract, TST = Transgressive System Tract, HST = Highstand System Tract, and FSST = Falling StagSequence Boundary, FS = Flooding Surface. The approximate age of deposition is also indicated on the ridirection of fining of the sediment grain-size. See Figure 3.2 and Table 3.2, respectively, for the location ofof the coal seams.


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Fig. 4.6. (a) A schematic strike-section showing the sequence stratigraphic framework and Depositional Sthe upper part of the Breathitt Group (units 11 through 21). Correlations were done based on the extensiveshales observable in the sedimentological logs, constructed from cored borehole data along cross-sectiobottom, see Fig.3.2 for location. The numbers at the top are names for the reference wells used in correlatdefinition of the sequence stratigraphic abbreviations to the right and Table 3.2 for the names of the coal s


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Fig. 4.6. (b) Lower part of the stratigraphic section A-B (units 1 through 10), for the lower part of the Breath


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Fig. 4.7. Thickness map of the Breathitt Group (21 units) in the quadrangle Broad-bottom.Thickness is given in ft and indicated by the colour legend and the contours. In themidfield thickness is influenced by the synclinal structure oriented NE-SW. The mapshows a general progradation of the delta from the SE (thickest part) toward the NW(thinnest part of the basin).


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4.2.2. Description and Interpretation of coastal plain facies

The rest of this chapter will try to describe and interpret facies in eachstratigraphic unit/zone mapped in the quadrangle Broad-bottom. The zones are

numerically arranged from bottom to the top (1 to 21). The descriptions andinterpretations attached to these units are based on the general characteristicfeatures observed in terms of unit thickness, and distribution of facies ordepositional energy as illustrated by the composite maps of isochors andlithofacies pie-charts. The maps together with the two stratigraphic cross-sections (Figures 4.5 and 4.6) form the basis for the descriptions andinterpretations. In general five dominating lithofacies associations are observedin the area of Broad bottom. They include sandstones, heterolithics, shales,conglomerates, and coals. Other lithologies present however, in minor quantitiesinclude ironstone and limestones. As a rule in geology descriptions andinterpretations of the stratigraphic units are done starting from the bottom (0) to

the top (21) of the stratigraphic units.Thickness maps for each unit have been drawn equipped with lithofacies pie-charts at locations of cored boreholes that wholly or almost wholly penetrate theinterval. Such composite maps give a general idea about sediment transportdirections (paleoflow directions) including the distribution of the depositionalenergies and facies in each stratigraphic unit. The principles of sequencestratigraphy, where appropriate, have been applied to interpret the environmentsof deposition and facies associations in the zones. Figure 4.8 shows the colourlegend used for the nomenclature of the facies quantified in the pie-charts.

Fig. 4.8. A Colour legend for the pie-charts in Figures 4.9 to 4.30


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4.2.2.1. Zone 0 (BLR B CLN B)

B

C

D

A

Fig. 4.9. A composite of stratigraphic thickness map and lithofacies pie-charts used for thedescription and interpretation of facies and environments of deposition in zone 0, betweensurfaces BLR B and CLN B. Note that the map is contoured in ft.


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Zone description

The unit bounded below and above by the stratigraphic surfaces BLR B and CLNB, respectively (see Figures 10.1 and 10.2 in the Appendix). The unit shows thegeometry of a foreland basin, i.e. thickest (110 ft.) in the southwest (the direction

of the thrust-front) and thinnest the northwest and northeast, to a minimum ofabout 55 ft in some locations. Facies distribution as observed from the pie-chartsin the unit shows a steady decline in depositional energy toward the northeast.Facies present in a decreasing order of magnitude include shales, heterolithicsand sandstones, sandwiched in thin coals at the bottom and top of the unit.There is a tendency for the proportion of sandstone and heterolithi

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