The Devonian Slave Point, Beaverhill Lake, and Muskwa Formations of Northeastern British Columbia and Adjacent Areas

BRITISHCOLUMBIA DEPARTMENT OF MINES AND PETROLEUMRESOURCES HON.DONALD L. BROTHERS,Minislcr P. I. MULCAHY,Depury Minisfcr

BULLETIN No. 50

by D. L. GRIFFIN

Printed by A. Surrolr, Printer lo Ole Queen's Mort Excellent Majesty in right of lhe Province of British Columbia. 1965 PREFACE

Since 1947, whenthe firstpetroleum and noturol gar permits in British Columbio were issued, consideroble geological doto relating to both surface ond rub- surface hoveaccumulated, particularly fromthe Peace River Districtof northeastern British Columbia where most of the explorotory activity has been centred. Thes,. data hove increased our knowledge of that portion of the Western Canada Sedimentary Basin lying within this province, not only with reference to Mesozoic strata which hove been the source of most of the oil and gos productionto dote, but also to theDevonian sedimentary sequence which is so prominent in the geology of the Conodion Norlhwest.

The petroleum and natural gos potential of the Devonian has long been recognized byindustry and, olthough full invertigotion of its potential in BritishColumbia has been retarded by lack of o market outlet, sufficient wells hove been drilled '-0dote to prove very significant reserves of gas.

This Bulletin presents on interpretation of a part of the strotigrophic semquence currently under octive explorotion within thegeneral Fort Nelson Area. Moteriol for this study was derivedlargely fromdata, samples, andcore submitted by industry to the Department, olthough some field invertigotion in British Columbia was done by the author.

This study is intended os a contributiontoword o better understanding of o partof the Devonian succession which, by virtueof its depositional history, presents sufficient problems to ensure continuing geologicol research.

J. D. Linehom, Chief, Petroleum and Natural Gar Branch.

April 22, 1964. TABLE OF CONTENTS

PAGE

Summary ...... 7 Introduction ...... 9 Acknowledgments ...... 11 Slave Point Formation ...... 13 Previous Description and Correlation ...... 13 Limits and Distribution in BritishColumbia ...... 14 Lithology in BritishColumbio ...... 18 Main Component of theSlave Point Formotion ...... 20 Subsidiary Components of theSlave Point Formotion ...... 22 Rocks of theFacies Front ...... 22 (i) Dark strmatoporoid-beoring colcilutites with obundont biogenicmaterial ...... 22 (ii) Stromatoporoidbiosporiter ...... 22 (iii) Stromotoporoid biomicrites ...... 22 (iv)Light coloured micrites ond fossiliferous micrites ... 23 Interpretation of the limestones of the facies front ... 23 (v) White andgrey dolomite ...... 24 Limestones Occurring at Some Dirtonce from the Facies Front ...... 26 Lithology in Alberto ...... 27 Beoverhill Lake Formation ...... 29 Previous Description and Correlotion ...... 29 Regional Cross Sections ...... 29 Lithologyand Distribution in NorthernAlberta ...... 31 Lithology and Distribution in Northeastern British Columbia ...... 32 Correlation of the Slave Point ond Beaverhill Lake Formations ...... 35 Deposition of the Slave Point Formotion ...... 40 MurkwaFormation ...... 43 Previous Description and Correlation ...... 43 Distribution ...... 43 Lithology ...... 45 Strotigrophic Relationships ...... 45 GeologicalHistory ...... 47 Gas in theSlave Point Formation of BritishColumbia ...... 49 References ...... 53 AppendixI.--Formation Tops in BritishColumbia Wells ...... 55 Appendix 11.--Core Descriptions ...... 59 Appendix Ill.--Mop Showing Locationof Wells used in Study ...... In pocket Index ...... 83

FIGURES

1 . Index mop showing areas of detailed andgenerol study ...... 9 2 . Table of formations ...... 10

3 F I G U R E S (continued)

PAGE

3. Isopach mop of the Slove Point Formotion in northeastern British Columbia ...... 15 4. Diagrommotic cross section(HIJ) from Clorke Lake area,British Columbia,to AthobascaRiver, Alberta ...... 28 5. Index map showing lines of Section ABC and FG ...... In pocket 6. Mechanical log Section ABC showing theSlave Point, Beaverhill Lake, and Muskwa Formotions ...... In pocket 7. Cross section FG showing the lithology in selected wells from Section ABC ...... In pocket 8. Isopach map of the Beaverhill LakeFormation in northeostern British Columbia ...... 33 9. Diagrommotic sections showing alternative interpretations of the relationship between the Slave Point and Beaverhill Lake Formations ...... 36 IO. Cross section KLM showingthe Slave Point and Beaverhill Lake Formations in thearea south ofClarke Lake ...... 39 11. Mop of northeostern British Columbia and northern Alberta showing distribution of theMuskwa and BeoverhillLake Formations ... 42 12. Map showing distribution and thickness of the Muskwa Formotion in northeasternBritish Columbia ...... 44 13. Map showing Slave Point gas fields in northeastern British Columbia 49 14. Cross section NO, ClarkeLake field ...... 50 15. Cross section PQ, Kotcho Lake field ...... 50 16. Cross section RS, PetitotRiver field ...... 51 17. Appendix 111.--Mop Showing Location of Wells used in Study ..... In pocket

PHOTOGRAPHS

Plate I. Dorkstromatoporoid-bearing calcilutitecontaining minor amounts of biogenic moteriol ...... Following W 11. Darkstrornatoporoid-bearing calcilutite with moderate amounts of encrusting stromatoporoids and brachiopod fragments ...... Following W 111. Darkstromotoporoid-bearing calcilutite with moderate amounts of biogenic material including nodular stromotoporoids ...... Following IV. Darkstromatoporoid-bearing calcilutitecontaining abundant Thomnopora and romose stromotoporoids . . Following W V. Dorkstromatoporoid-beoring calcilutite with obundant laminarand romose stromatoporoids ...... Following W Vi. Part of massive stromatoooroid ...... Following W

4 PHOTOGRAPHS (continued)

PAGE

VII. Limestonefrom the faciesfront. Poorly sorted stromotoporoid biosporite ...... VIII. Limestonefrom the fociesfront. Sortedstromotoporoid biosporite ...... , .. Followit7g 90 IX. Limestone from thefocies front. Stromotoporoid bio- sparrudite ...... Following 90 X. Limestonefrom the faciesfront. Stromotoporoid biomicrudite Following 90 XI. White and grey dolomite--microinclusion texture ...... Following 90 XII. White and grey dolomite--macroinclusion texture ...... Following 90 XIII. White ond grey dolomite--banded texture ...... Following 90 XIV. White and grey dolomite--clotted texture ...... , . . . Following 90 XV. White and grey dolomite--nebulous texture ...... Following 90 XVI. White andgrey dolomite--pseudo-brecciated texture . . . . Following XVII. Photomicrograph of darkstromatoporoid-bearing calcilutite Following 90 XVIII. Photomicrograph of intrasparitefrom HB ImperialUnion Paddy a-49-6 (1) ...... Following 90 XIX. Photomicrograph of calcorenite from HB Imp Union Gutoh a-99-K ...... Following 90 XX. Photomicrogroph of foraminifer0 andbrachiopod biosparite from HB Imp Union Gutah a-99-K ...... Following 90

5 THE DEVONIAN SLAVE POINT, BEAVERHILL LAKE, AND MUSKWA FORMATIONS OF NORTHEASTERN BRITISH COLUMBIA AND ADJACENT AREAS

SUMMARY

The SlavePoint Formotion in BritishColumbia ond Alberta is a stmtiqrophic unit composed of limestonesand subordinate dolomites. It is underlain by o hetero- geneousossembloge of rocks assigned to the Watt Mountain-Sulphur Point osselnbloge in the west and the Fort Vermilion-Watt Mountain ossembloge in the east. In northeasternBritish Columbia the Slave Point Formation changes to shole along o linear front, termed the facies front, which trends approximately north-morth- east. The formotion reaches o thickness of almost 500 feet in northeasternBritish Columbia. Toward the east the formotion thins ond in eastern Alberta it is less thon 10 feet thick. The Slave Point Formation in northeastern British Columbia consists of tlhe following: I. The dark stromotoporoid-bearing calcilutites which form the main lithologicol component of the formotion. These dark colcilutites are very widely distributed in the Slave Point of northeastern British Columbia. II. The subsidiary components, which ore divided os follows: A. Rocks occurring in the vicinity of the facies front. These comprise: The dorkstromatoporoid-bearing colcilutiteswith abundant biogenic material. The stromatoporoid biosparites. The stromotoporoid biomicrites. The light coloured micrites and fossiliferous micrites. The white and grey dolomite.

B. Limestones occurring inthe shelf environment usually at distances greotc:r than 25 miles from the facies front. This division includes intromicrites, intl-aspor- ites,and biosporiter. These rock types occur in oddition to thenormal dark stromatoporoid-bearing colcilutites in areas lying at some distancefrom the facies front. The limestones occurring in the vicinity of the facies front indicate that reefs developed along ports of the front. The strongest evidence indicating reef development is considered to be thegreat abundance of stromotoporoids which occur adja8:ent to parts of the facies front. There is not yet sufficient evidence to determine the full lot- era1 extent of the reef zones. Some ofthe limestonesbordering the facies front hove been altered to dolomite which is frequently composed of o lightcoloured coarsely crystalline and a darker colouredfine to medium crystalline phose.The rock is termedthe white and grey dolomite. The closeassociation between the white andgrey dolomite andthe focies front suggests thatproximity tothe front was on importantfactor inbringing about dolomitization. The white and grey dolomite possesses both vuggy and intercrystolline porosity

7 and it forms the reservoir rock in the Clarke Loke, Kotcho Lake, and Petitot River gas fields. The Slave Point Formation is also dolomitized, but only too moderate extent, in several areas lying at some distance from the facies front. These dolomites are termed the shelf dolomites; at certoin localities they contain accumulations of mturol gas. The Beaverhill LakeFormotion overlies the SlavePoint throughout most of northeastern British Columbia and northern Alberta. In the east theBeaverhiII Lake consists moinly of argillaceous limestones and calcareous sholes. The western sections of the Beaverhill Lake are composed of slightly calcareous to colcoreous sholes associated with subordinate amounts of argillaceous limestone. In eastern Alberto the Beaverhill Lake reoches o maximum thickness of almost 700 feet. The formation thins to o pinch out edge in the northwestern port of the area under consideration. Forthe purposes ofthis study the Beaverhill Lake Formation is divided into two units. The upper is termedthe Upper Beaverhill Lakeand consists ofthe combined Mildred, Moberly, and Christina Members of northeastern Alberto. The lower is termed the Lower Beaverhill Lake and consists of the combined Colmut and Firebag Members of northeastern Alberta. West ofobout longitude 116 degrees west the Beoverhill Lake wos eroded prior to the deposition of the overlying Murkwa. This pre-Murkwa erosion affects mainly the Upper Beaverhill Lake. Stratigraphicevidence strongly suggests thatthe SlavePoint and the Lower Beaverhill Lakeplus the lower partof the Christina ore facies equivalents. The main evidence supporting this conclusion is summarized as follows: 1. The distributionand lithology of the SlovePoint Formation connot be sotis- factorily explained by normal transgressive, regressive, or static deposition or by the assumption thot the formation was eroded prior to the deposition of the Beaverhill LakeFormotion. 2. There is a complementary thinning of the Lower Beaverhill Loke to the west as the Slave Point thickens in this direction. 3. Rapid changes fromthe Slave Point Limestone tocolcareaus shales of the Beoverhill Lakeare especially evident in theore0 south of the Clarke Loke gas field in northeostern British Columbia. The Muskwa Formotion unconformobly overlies the Slove Point and Beoverhill LakeFormations in northeosternBritish Columbio and northwestern Alberta. The unit grades upward into the overlying Fort Simpron Shale. The Muskwa consists mainly of greyish black pyritic sholes which in places are siliceous. The formation is prominent on Gamma Roy Logs because of its relatively high radioactivity. In mostareas theMuskwa is between 50 and 100 feet in thickness. On its northeast margin the formation reaches 150 to 250 feet in thickness, and posses by way of an intertonguing relationship into the Fort Simpson Shale. Toword the northwest the Muskwcl olso thickens ond tends to merge into the Besa River Shale. In the original description the Muskwa was defined os the uppermost member of theHorn River Formation. Because of its stratigraphicrelationships and distinctive lithology, it is proposed here thot the Muskwo be separated from the Horn River and be recognized os an independent formation. Considerable pre-Muskwa erasion took place in the northern port of the ore0 of study in the vicinityof theBritish Columbia-Alberta boundary. In this areathe Muskwa overlies a Slove Point section vorying between 175 and 300 feet in thickness.

8 INTRODUCTION

The Slove Point and Muskwo Formations of Devonian age underlie a maim part of northeastern British Columbia. In the north the Muskwo rests directly upon the Slave Point; in the south the Beoverhill Lake Formation lies between them. This bulletin con- riders the nature of there formations in northeastern British Columbia and relatesthem to equivalent strata to the east in Alberta. The formotions discussed are shown in the Table of Formotions (see Fig. 2). The oFa where theseformations occur ond which is considered in d(:tail is bounded on the north by the British Columbia-Northwest Territories boundary (htitude 60 degrees north), on the east by the Alberta-British Columbia boundary (longitude 120 degrees west), and onthe southwest by the Rocky Mountain Foothills (E Fig. I), The late Middle Devonian (Givetian) deposits of northeostern British Columbia and northern Albert0 consist of carbonates and evaporites in the east and central parts of the ore0 under consideration and moinly shales in the extreme west. The zone of facies change is relotively narrow and is referred to LIS the facies front. The carbonate and evaporitic section comprises four main stratigraphic divisions. At the base is the evaporitic ChinchagoFormation which maybe partlyearly Middle Devonian(Eife1ian) in age. The second division includes the Pine Point-Muskeg- lirie Evaporite complex (=e Fig. 2). This division consists of carbonates in the west ne Point Formation). anhydrite and corbonoter(Muskeg Formotion) in the central area,

AREA OF DETAILEDSTUDY SCALE M'ICI o 50 loo 200 MO M~I~S AREA GENERAL ~~ "

Figure 1 .--Index map showing oreas of detailed and general study. 9 andevaporites (Prairie Evaporites) in the east. The thirddivision includesthe Watt Mountain-SulphurPoint-Fort Vermilion assemblage. It is mode up of carbonatesand minor amounts of shole in the west andevaporites. dolomite, and shales in the east. Theuppermost division is theSlave Point Formation. It consists mainly of limestone and occurs throughout the area east of the facies front. The upperthree stratigraphicdivisions changewestward into a shale unit known CIS the Otter Park Member.In part of northeasternBritish Columbia the Otter Park together with the overlying Muskwa andan underlying limestone and shale unit termed the Evie Member hove been considered to be members of the Horn River Formo- tion (see Gray and Kassube, 1963, p. 473). In this bulletin, however,the Muskwo is separaTd from the Horn River and recognized as an independent formation.

BRITISH COLUMBIA & ALBERTA NORTHERN ALBERTA WEST OF THE 6th MERIDIAN T EAST OF THE 6thMERIDIAN lower part of lower part of Iretoa FortSimpson Fort & Simpson ' CookingLake i 7 \ \ \ \ Moberly \ \ \ \

Watt Mountain- I1Watt Mountain IAWSON BAY EWVt Sulphur Point

Prairie

Muskeg Evaporite8 =- Muskeg I. >

L Figure 2.--Table of formotions, showing tormotions which are discussed in detail (in open lettering) and the related formations of northeastern British Columbia and northern Alberto.

10 The Beaverhill Lake Formation which consists of shales and limestone:; of Mid- dle to Upper Devonian age overlies the Slave Point Formotion in northern Ali3erta and port of northeastern British Columbia. The dark Muskwa Shale overlies the Slwe Point in thenorthern port of northeastern British Columbia and the Beaverhill Lake in the southern part of this region. The Muskwa grades upward into the lighter coloured shales of the Fort Simpson Formation. In northeastern Alberta the Muskwa Formation is obsent and the Fort Simpson rests directly upon the Beaverhill Lake Formation, In theextreme west ofthe area of studythe separate shale units lose their identity and the combined Middle and Upper Devonian sholes, associated in some oreas with overlying Mississippion shales, ore included in the Beso River Formation. In this bulletin special attention is given to the lithology of the Slave Point Formation in northeasternBritish Columbia. Regional correlations of the formation are considered and the concept is developed that the Slave Point and a substanti'Jl part of theBeoverhill Lake Formation are complementary facies. Inthepast authors have tended to restrict their attention either to oreas where the Slave Point is dominant(fo1 example Campbell, 1950 and 1957; Belyeaand Norris, 1962; Gray ond Kassube, 1'?63)or to areos where the Beaverhill Lake is developed os a distinctive unit(for example, Belyea, 1952; Crickmoy, 1957; Corrigy, 1959) and as a consequencethe relationship between the two formotions has not been readily apparent. A major exception to this pattern of treatment was the study by Low (1955)in which he made correlations between the Devonian of the Edmonton oreo, which is the type area for the Beaverhill Lake Formation, and the Devonian of the Great Slave Lake areawhere the Slave Point Formation was originally described.However, 01 thetime of his investigation only a small amount of drilling had been carried out and the dirtonce between individual control points wos too great to ollow the stratigraphic changes to be traced in detail. Thus, while Lowwas able to establish the general correlations there were important stratigraphic relationships which could only be revealed byfurther drilling. This study is concerned mainly with stratigraphy,ond the polaeontolcggy of the formations is considered only in general terms. The founo ofthe Beovehill Lcke Form- ation has been adequatelydescribed in the literclture (see Crickmay, 1957; Corrigy, 1959; ond Norris, 1963). The SlavePoint fauna has notreceived such detailed attention and this is undoubtedly a field which warrants further invertigotion. Although it is somewhat arbitraryto repamte o study ofthe lithology and stratigmphy of a formation from a study of its paloeontology, it is considered that the lithologicol andstrotigrophic informotion is sufficientto enable valid interpretations to be mode of thegeologicol history of theformotions described. Insame ctrses more thanone interpretation of the stratigraphicrelationships of thevarious formotions is possible.Nevertheless, it is felt thatthe conceptsdeveloped provide the rnort satisfactory explanation of the currently available facts. The depths to the top of theMuskwo Formation. Beaverhill LakeFormation, Otter Park Member, Slave Point Formation,and WattMountain-Sulphur Point assembloge in all the British Columbia wells which penetrated these units at January 1, 1963 ore givenin Appendix I. Descriptions of BritishColumbia core are presented in Appendix II. The core descriptions illustrate the lithology of the Slave Point. Beover- hill Lakeand Muskwa Formations. Appendix 111 (inpocket) is a map shcmwing the location of all theBritish Columbia wellsmentioned in thetext and figure captions. ACKNOWLEDGMENTS

The author wishes to acknowledge the generous help given by numerous members ofthe British Columbia Deportmentof Minesand PetroleumReswrces duringthe cwrre of this study. The critical reading of the manuscript by Dr. H. R. Belyeo of the Geological Survey of Canada is much appreciated. The Alberta Oil and Gas Conser- vation bard assisted greatly in providing facilities for the examination of drill cutting mples from Alberta wells. SLAVE POINT FORMATION

PREVIOUS DESCRIPTION AND CORRELATION

The term"Slave Point limestones" was introducedby Cameron (1918, p. 26) for o formation exposed on the north and southshores of the west orm.of Great Slove Loke. A briefdescription accompanied the introduction of the new formationwhich was said to be of Middle Devonian age. Several yeors later Cameron presented o more detailedaccount ofthe Slave Point Formation (Comeron, 1922, pp. 23-24). No type section was designated but rocks of the unit were said to outcrop on the south shore of Great SloveLoke at SulphurPoint and on theBuffalo Rivernear Mellor Rapids. On thenorth shore theformation was reported to show on SlavePoint and on the tops of the hills northof Sulphur Bay. Unfortunotely,the exposures at SlavePoint which it would seem approprioteto accept as thetype section ore poor. Only a few feetof strota ore exposed (Comeron,1917, p. 73) ond ot times these orecovered t'y woter (Douglas, 1959, p. 19). Cameron(1922, pp, 23-24) describesthe Slave Point Limestone as greyto brown, thin bedded, fine tomedium grained, bituminous, and fossiliferous in parts, interbedded in places with limy sholes.He estimatedtheir thickness to be 200 feet. Duringthe yeors following Cameron'sinvestigotions geological wor< in the vicinity of the southshore of Great SlaveLoke fluctuated in response to explorotion activity on theleod-zinc deposits whichoccur in thearea. In the region south and west of Pine Point extensive diamond drilling was carried out by various minilg com- panies. The new data derived from these operations enabled Campbell (1950 ond 1957) to present an interpretation of the complicated stratigraphy of the area. Using subsurface information from the southshore of Great Slave Lokm? in the area west of the Little Buffalo River,Compbell (1950, pp. 89-92) assigned some 371 feetof limestonesand dolomites tothe SlavePoint Formation. Four divisionsof the SlovePoint were recognized. The upper two consisted of limestone; the third was an Il-foot band of darkgreenish grey shale withargillaceous limestoneand dolomite, termed the Amco Shale. The lowermost division wos a unit of very vorioble I ithology including limestones,dolomites, greenish sholy material, and clay-limestone Ihreccio. From 1950 onward, exploratory octivity for oil and gas in the southerrt port of the Northwest Territories, northern Alberta, and northeastern British Columbia steadily increased. The exploratory wells provided new information on the subsurface extension of the Devonian rocks outcropping at Great Slave Lake. Low (1955) used this !noterial as a basis for the recognition of new Middle Devonian formations and for a revision of the stratigraphic limits of theSlove Point Formation. He correlated theupper port of Campbell'sfourth SlavePoint unit,mentioned above,and the Amco Shale with the uppermost formotion of the Elk Point Group (the Watt Mountain Formotion) ond suggested that the name Slave Point Formation shwld refer only to the limestone between the Amco Shale andthe overlying UpperDevonian sholes. He correlated the redefined Slave Point Formation with beds occupying a similar strotigmphic position in the sub- surfaceand gave o detaileddescription of theformotion in the well,Cclifornio Standard Steen River No. 2-22 (2-22-1 17-5W6). A similorinterval in the Steen River well hod previously beentermed the TerritoriesFormotion by Hunt (1954, pp. 2'297-2300). However, Low considered that the nome Slove Point had precedence and thus should be adopted in preferenc,. to the namesuggested by Hunt. Law's concept of the SlavePoint Formation is now generally accepted. Thus Compbell (1957) used theterm in a more restricted sense thanpre-

13 viously (Campbell, 1950) and theSlave Point of Belyeaand Norris (1962) and Gmy ond Kassube (1963) approximates to that suggested by Law. Law (1955, pp. 1945 and 1949) considered thatthe SlavePoint Limestone of northern Alberta thinned toward the east and chonged in its lower part to an anhydritic facies. The latter he termedthe Fort Vermilion Member. Law (op. cit.p. 1949) stated that in central Alberta the Slove Point Formation is represented by about 40 feet of limestone at the base of the Beoverhill Lake Formotion. Several authors have drown attention to the thin limestone unit which lies at the base of the Beaverhill Lake Formation in the McMurray area of northeastern Alberta andCrickmay (1957, p. 10) andCorrigy (1959, p. 23) considered it to be theequi- valentof the SlavePoint Formation. Crickmay (1957, p. 10) recognized a separate unit consisting of 54feet of buff colaured, fine grained, magnesian limestone lying below the Firebag Member in Beor Biltmore No. 1. On the basis of strotigrophic position and lithological choracters he interpreted the unit as the equivalent of the Slove Point Formation. More recently Norris (1963,pp. 22-25) has expressed the view that the thin limestone at the base of the Beoverhill Lake in the McMurray area does not correlate with theSlave Point ofnorthwestern Alberta. He gavethe unit formational status and named it the Livock River Formation.However, it is considered that the interpretotion of the Slave Point given later in this bulletin, provider on explanotion of the IUCCBI- sion in the McMurray areawhich does notnecessitate the use of a new formational name. Drilling in northeastern BritishColumbia during the past ten years has revealed thepresence of considerable reserves of natural gas in theSlave Point Formation and therock unit has therefore assumed newimportance from an economicstandpoint. In thearea north of lotitude 56degrees north in northeastern British Columbia more than 100 wells now provide information on the Slove Point and equivalent strata, making it possible to trace these rocks throughout the subsurface of the region. Belyeo and Norris (1962)hove used therecent wellcontrol to correlate the SlavePoint Formation between the Great SlaveLake area and Kotcho Lake in British Columbia and to demonstrate that the formotion changes to shale west of Kotcho Lake. Gray and Kassube (1963) recently described the stratigraphy of the extensively drilled Clarke Lake area. They 0150 gave an account of thefacies changes occurringin the SlavePoint Formotion which in manyareas providefavourable conditions for the accumulation of natural gas.

LIMITS AND DISTRIBUTION IN BRITISH COLUMBIA

The SlavePoint Formation in northeasternBritish Columbia is o sheet-like body ofrock composed largelyof limestone. It covers some 30,000 square milesand throughout most of this orea varies between 200 feet and 500 feet in thickness (see Fig. 3). Toword the west it parses by way of o shorp facies chonge to shale; in the guth it wedges out againstthe Peace River Arch. To theeost and north the formation extends into adjacent oreas of Alberta and the Northwest Territories. The top of the Slave Point is easily recognized both from mechanical logs and in the drill cutting sampler. Thebase of the formation is much more difficult to estab- Iish. The depths of the top and bottom of the formation in almost a11 wells penetrating the unit in northeasternBritish Columbia ot Jonuary 1, 1963,are listed in Appendix I. In thenorth theMuskwa Shale directlyoverlies theSlave Point Formation (northof dotted line on Fig. 3) and the changefrom the dark, bituminous, radioac-

14 Figure 3.--lsopach map of the Slave Point Formation in northeastern British Columbia. The configuration of the facies front is the simplest that current well control allows.

15 five shales tothe Slave Point Limestone is well shownby both the samples andlogs. Further muth theSlave Point is overlainby calcareous shales of theBeaverhill Lake Formotionand olthoughthe lithological change is not os obrupt as in the case of the Muskwa and Slave Point, it con be recognized without difficulty (see- British Columbia wells on Fig. 6). Two factors make it difficult to establish the lower limit of the Slave Point in northeastern British Columbia. First, the contact with the underlying beds is transition- 01 in mostareas, andsecondly thesebeds orevariable in lithology. Beforediscussing how the lower contact of the Slove Point has been estoblished in the area of study it is first necessary to consider briefly the nature of these underlying beds. Low (1955, pp. 1951-1954) considered that the Slave Point Formation of northern Alberta wos underlain by a natural lithological unitconsisting of limestone, breccia, greenshole, dolomite,and in the vicinity of the Peace River landmass various terrigenous clastics. Hetermed the unit theWatt Mountain Formation, Belyeaand Norris (1962, pp. 10-12), however, workingin the Great SlaveLake are0 recognizeda sequence of fossiliferous limestones ond their dolomitized equivalent os the most prominent lithologicalunit underlying theSlave Point. The limestoneswere termed the SulphurPoint Formation and the dolomites the Presqu'ile Formation. In manyareas in the vicinity of Great SlaveLake the Sulphur Point and Presqu'ile Formations are sep- orated from the Slave Point Formation by CI bond, 1 to 20 feet thick,contoining D vorioble amount of green shole wth o waxy lustre. When traced into the subsurface it is apparent that the Sulphur Point embracer agreater stratigraphic intervol than Low's Watt Mountain Formotion. On the basis of common usage, Belyea and Norris (1962, p. 12) restricted the Watt Mountain Formation torefer only to the uppermostbeds of the originol unit and theyrecognized the full limits of the Sulphur Point Formation in the subsurfoce. As noted above one of the maior difficulties in separating the Slave Point For- mation fromthe underlying beds lies in thevery variable nature of thesebeds. Thus, if the lithological types represented by Low's Wott Mountoin Formation and Belyea and Norris' Sulphur Point and Presqu'ile Formations are listed, it is found that arkosic sand, voricoloured shale and siltstone, anhydrite, cryptocrystalline dolomite, limestone breccia, greenshale with awaxy lustre, stromotoporoidol limestone, aphanitic limestone, argillaceous limestone, and coarsely recrystallized vuggy dolomite ore a11 represented. To add to the difficulty of the situation some of these types are similar to those developed within theSlave Point. However, the variability of the beds providesa solution tothe problem thatthey present. As will becomeapparent from the description which follows,the SlavePoint shows only moderate lithologicalvoriotion and consists for the most portof darkstromotoporoid-bearing limestones. It seems therefore most logi- col to recognize the SlavePoint Formation as onupper fairly homogeneous unit overlying a unit of heterogeneous lithology, the latter being referred to herein as the Wott Mountain-Sulphur Point assemblage. Regional correlations suggest that the upper part of the Watt Mountain-Sulphur Point assemblage of northeastern British Columbia and northwestern Alberta posses eastward into thecombined Fort Vermilion-Watt Mountain assemblage ofnortheastern Alberta. Evidencepresented on pages 35 to 41 bearingon the origin of theSlave Pointand underlying bedssupports this correlationand it is thereforeprovisionally adopted in this publication. As c1 consequence of the correlationof port of the Watt Mountoin-SulphurPoint with theFort Vermilion-WattMountain it is advisableto ex- clude the Fort Vermilion Member from the Slave Point Formation. In this bulletin therefore the tern Slave Point Formation refers only to the Slave Point limestones ond dolo- miter and does not include the Fort Vermilion Anhydrite.

16 The upper port of the Wott Mountoin-Sulphur Point ossembloge is ctorocter- ized by beds of limestone breccia and green shole with a woxy lustre. The lottcr is distinctive ond is readily recognized in drill cutting somples. It will be referred to as the greenwaxy shale. In some sections this shale formsbeds up to 5 feet in thickness. However, wellto well correlations andthe mode of occurrenceof the shalt!suggest thot it doer not occur os o single correlative bed, butrother os a series of shale lenses which probably occupy o zone upto 100 feet in thickness. This zone forms ,mpproxi- mately the upper holf of the Wott Mountain-Sulphur Point assemblage. The green woxy shole also occurs os on interstitialmaterial in thelimestone breccias of theWott Mountain-Sulphur Point and olsa os fragments in the breccias. It is therefore 'lpporent thot the shale forms o subordinote but distinctive constituent of the upper port of the assembloge. This foct has been used in establishing the bore of the Slove Point Formo- tion in northeosternBritish Columbio and in thearea studied the contact between the Slove Point ond the Wott Mountoin-Sulphur Point ossembloge is taken at the fiwt occurrence of the green woxy shale. It is probable thot this horizon is slightly higher than the top of the Wott Mountoin selected by Law (1955) in the Steen River well. Certain difficulties ore encountered in using this criterion for establishing the bose of the Slove Point but similar or greoter difficulties ottend other methods of sep- orating theSlove Point from theunderlying beds.The shalenever mokesup o lorge proportion ofthe WattMountoin-Sulphur Point and this factcoupled with the small size of the overage drill cutting sample results in only small omounts of the distinctive shale being present in the somples; in somecases it is completely absent.Fortunately, if the latter is the case, the well in question con often be sotisfoctorily correlated with adjacentwells inwhich the bore of theSlove Point hos beenestablished from the samples.The upper port of the Watt Mountain-Sulphur Point frequently shows o series of deflections on the Gommo Roy Log and these con be used os o hsis for correlotion between closely spaced wells. The distribution ondthickness of theSlove Point Formation in northeastern British Columbia is shown in Figure 3. Several foctors influence the distribution of the formation. The contours suggest o regionalthickening to the west-northwest. To the south this trend is affected by the Peoce River Arch ogoinst which the formation wedges out. To thewest-northwest the formation posses to shale along o sinuous linewhich trends opproximately north-northeast. The sholes equivalentto the SlovePoint were included in the Otter Pork Member of theHorn River Formation by Gray and Kassube (1963). Wells in the Clarke Lake ore0 close to the facies chonge demonstrate thot the SlovePoint can chonge to shale in a distance of less than 1,000 feet and Gmy et al (1962, p. 176) state thot in the same are0 the focies contact is inclined at on angle of at least 25 degrees to 30 degrees. This sharp focies contact will be referred :o os the facies front of the Slave Point Formation. In some areos there is evidence thot the corbonotes adjocent to the .:, ront ore derived from theproducts of reefgrowth. In many oreas, however, it is difficultto determine the original noture of the carbonates of the facies front and thus the extent of reefdevelopment along the front is notknown. It is forthis reason thot theterm focies front is used in preference to such terms as "reef front" or "barrier reef." Well control mobles the focies front to be troced from the Petitot Ri,rer ore0 in thenorth to the Evie Lakearea at Mile 320 on theAlosko Highway (see Fig. 3). South of this the well control is sparse, but the control which is ovailoble-&idered inconiunction with the small amount ofliteroture on the are0 (=e Gallon:, 1962; Warrenond Stelck, 1962) suggests thatthe focies front trends approximately 11s shown by the coorsely broken line on Figure 3. The detailedconfiguration of the focies front in mony ports of northeastern

17 British Columbia is difficult to establish because of the lock of closely spaced wells. The interpretation presented in Figure 3 is, in general,the simplest that thepresent well control allows. Seismic data and future drilling will enable the front to be mapped more precisely and this information may show the presence of emboymenta and promon- tories which, with the currently available information, can only be the subject of con- jecture. The regional dip on the top of the Slave Point Formation is to the southwest at an average of about 40 feet per mile (Gray et 01, 1962, p. 176). At the facies front in the region between the Petitot River and Clarke Lake the top of the Slave Point varies betweenapproximotely 4,500 ond 5,300 feetbelow sea level. It is highest in the Kotcho Lake area. To the south at its feather edge on the Peace River Arch the formotion is more deeply buried. At the pinch out to the north of Fort St. John, for example, the top of the Slave Point lies ot a depth of 8.000 feet below seo level.

LITHOLOGY IN BRITISH COLUMBIA

The following discussion is based moinly on theexamination of core from 39 wellsin northeasternBritish Columbia. At Jonuary 1, 1963, 90 wellspenetrated the Slave Point Formotion in British Columbio having a total penetration of the formation of 24,324 feet. Of this total, 3,234 feet has been cored. The cored rectionr thus represent about 13 per cent of the Slave Point penetrated at that time. The core was exominedmegascopically and thenrepresentative lithologicol typeswere exomined with a stereoscopicmicroscope at mognificotions between x 7 and x 30. Most of the limestones were etched and observotionr were made on the wet surface. In a few instances exomination of thin sections of the rock contributed supplem- entary information. Samples of drill cuttings do not always provideadequate details of lithology in thelimestone sections because of severalfactors. First, there is a tendencyfor the SlavePoint limestones to be altered during the drilling process too dense chalky corbonate in which the texture of the original rock is obliterated. Secondly, the recrystollization of stromotoporoid material toa dense very finely crystalline calcite makes ital- most impossible to recognize the organic nature of this moterial when it is fragmented. Finally, shale contamination which takes place in uncosed holes, may reduce the limestone content of o sample to such an extent that the vlmple connot be considered to be truly representative of the intervolin question. The drillcutting samples, however, contribute useful information on gross lithology subject to these reservotions. The SlavePoint Formation in BritishColumbia is composed moinly of dark coloured limestones which contain varying amounts of stromatoporoid and other biogenic material. These rocksore aphanitic to microgranulor in texture and os a rule the con- stituentparticles (excluding biogenic material) are unresolved underthe Stereoscopic microscope at x 30 magnification. This may result from thesmall size of the porticles, the homogeneous nature of the particles and matrix or from the obscuring effect of finely disseminated carbonaceous material. These dark coloured limestonesore the main lithologicol componentof the Slave Point in northeostern British Columbia. They ore referred to os the dark stromotoporoid-bearing colcilutites. In addition to the main component there are a number of subsidiory components whichcontribute tothe totallithology of theSlave Point Farmotion in northeastern British Columbia. The subsidiary components are described under the following headings: (a) The limestones and dolomites developed in the vicinity of the facies front and (b) the subsidiary components developed at o considerable distance from the facies fr,mt. Thesystem of limestone classificotion presented by Folk (1959ond 1962) has beenfound useful in describingthe subsidiary components andwhere oppropriote his system of nomencloture has been applied. However,the terms introclast old micrite are used in a slightly broader sense than as defined by Folk. The SlavePoint limestones contain o complete range ofparticle!; between 0.04 millimeter and 0.5 millimeter in diameter and there does not appear to lbe CI naturol division between the smaller particles (pellets of Folk) and the larger (introclosts of Folk). The Slave Point particles will be referred to as intrmlosts, a practice which is in keeping with the descriptive nature of the term emphasized by Folk (196:!, p. 64). It should be noted that such intrmlosts may include ollochems of uncertain o.igin such os faecal pellets and recrystallized biogenic fmgments. Folk (1959, pp. 0 and 17) defines the term micrite in a precise way and gives the term genetic implications. Becouse the methods of investigotion used in this study do not allow the exact meosurement of very small particles the term micrite is used in o broader sense to include rocks which are very fine grained or aphanitic in texture and which oppeor to have been formed by the deposition of lime mud. This is more in keeping with the usoge of Leighton and Pendexter (1962, p. 35). The scale suggested by Folk (1959, p. 19) is used to describe crystol size. The smle is similar to the Wentworth but uses o constant ratio of four between the divisions instead of the moreusual two.It con be summarized as follows:aphanocuystalline, < 0.004 millimeter; very finely crystalline.0.004-0.016 millimeter;finely crystalline, 0.016-0.063 millimeter; medium crystalline, 0.063-0.25 millimeter; coorsely crystalline, 0.25-1 millimeter; very coarsely crystalline, 1-4 millimeters; extremely coarsely crystalline, >4 millimeters. In describingthe colour of therocks the Rock-Colour Chart distributed by the Geologicol Society of America has been followed CIS :lorely as is practical. A considerable diversity of stromatoporoids is present in the Slave Point Form- ation. The descriptive terms of Galloway (1957, pp. 350-360) and his methocl of classification are used in describing these organisms. In the post there has been o tendency to distinguish between "stromatoporoids"ond"Amphipora"; in keeping with modern concepts ofclassification this practice is notfollowed. It should be notedthat the term "ramosestromotoporoids" is used to referto Amphiporoand other members ofthe ldiostromatidae. The terms massive, ramose, and laminar are used os defined Iby Gallo- way (1957, pp. 350-360 and p. 374). The term nodular is used to refer to rtronlatoporoid coenostea of rounded form with 0 moximum dimension of approximately 1.5 t3 6 centimeters. Inthe following description ofthe lithology of theSlave Point Formation in British Columbia, the various rock types ore described in the following order:

I. Mainlithologic01 component ofthe SlavePoint Formation -- thedark stromotoporoid-bearing calcilutites. II. Subsidiary components of theSlave Point Formotion. Two main divisicsns can be recognized in this category: A. Rocks occurring in the vicinity of the facies front. These comprise: (i) The darkrtromotoporoid - bearingcolcilutites with abundant biogenic material. (ii) The stromotoporoidbiosporites. (iii) The stromatoporoid biomicrites. (iv) The light-coloured micrites and fossiliferous micrites. (v) The white and grey dolomite.

19 B. Limestones occurringat some distancefrom the facies front (usually > 25 miles). The rocks of this division are mainly intramicrites, introsparites, and biosporites.

I. TheMain Component of the Slave Point Formation TheDark Stromatoporoid-bearing Colcilutite

The darkstromatoporoid-bearing calcilutites orethe most widelydistributed and characteristic limestones of the SlavePoint Formation in northeastern British Col- umbia. The colourof these rocksvaries from brownish grey to dark brownish grey to darkgrey and appears to be mainly impartedby the presence oforganic material, which, following Carorzi (1560, p. 214), will be referred to os carbonaceous material, The etched surface of these limestoneswhen examined under the stereoscopic micra- scope often has a mat appearance devoid of obvious structure. Carbonaceous material if abundant stands above the etched surface as a fine, black "dust." Stylolitic partingscontaining thin films of darkgrey toblack carbonaceous material occur quite commonly in thedark calcilutites. In same coresmall patches of sparry calcite arepresent. They areirregular in shape andare usually less than 0.5 millimeter ocross but in same instances reoch o width of I millimeter. Their origin is not known but it seems likely thot either they fill smoll cavities which remained after deposition or that they ore derived from micritic material by recrystallization. On the bosir of tests carried out on a number of limestone specimens from different parts of northeastern British Columbia, it is concluded thot the dark calcilutites containonly minor omounts ofargillaceous material. This conclusion is supportedby the features of the Gamma Ray Neutron and Gamma Ray Sonic Logs. The coenostea of massive, nodular,and ramose stromatoporoidsore a most importantconstituent of thedark calcilutites. The tabulatecoral Thamnopora also occurscommonly in thererocks. The quantity of thisbiogenic material varies considerably from placeto place and alw indifferent parts ofa single cored interval. It ranges from less than 10 per cent of the rock up to an estimated 60 to 70 per cent (see Plates I to VI). Themost widespreadtype of calcilutiteprobably contains less thon 10 per cent of biogenic material. The rocks containing abundant biogenic material are best developed in the region of the facies front, olthough they occur os locol developments in otherareas. Rocks containing intermediate amounts of biogenic material also occur os local developments in theSlave Point Formation throughout northeastern British Columbia. The examination of manyspecimens of thedark calcilutite underthe stereoscopic microscope and of a small number of thin sections with the petrological microscope, suggests that these rocks may contain obundontallochems of diverse origin. Handspecimen examinationoften indicates the presence of compacted,vague intraclast-likeor pellet-like structures 0.1 to 0.4 millimeterin diameter. The three thin sections examined indicate thot ollochems 0.06 to 0.25 millimeter in diameter and biogenic fragments0.l to 0.4 millimeter in diameter occur quite abundantly in these rocks, at least in same areas (see Plate XVll). The darkstromatoporoid-bearing calcilutites grade in parts to rocksshowing clearly developedintraclarts, 0.1 to 0.5 millimeterin diameter. The intraclastsare commonlyround, ovoid,triangular, rectangular, or kidney-shaped in cross section andalmost invariablyhove a rounded outline. In somecases the intraclastsare dispersed in whatoppeors to be o micritic matrix, whilst in other cases they are closely compactedand sometimes separatedfrom each other by a thin carbonaceous film. In

20 another mode of occurrencewhich is cot as common as theothers the intracl~~stsare dispersed in o clearly developed matrix of Tarry calcite. The intraclost rocks tend to be slightly lighter in colour than the associated dark calcilutites. In addition to stromotoporoids of various types, otherrecognizable biogenic moteriol is often present in thedork calcilutites ondossocioted introclost rocks. The Slove Point core in the well, BA Shell Kluo b-49-F (94-J-9) provides o good section in thefossiliferous dork calcilutites (see Plotes I, 11, IV, V, and VI andAppendix 11). Massive, nodular, romose, and IomKar stromotoporoids ond Thomnoporo are all repres- entedand in ports of thecore stromatoporoids canbe seen completely surrounding specimens of Thamnopora. Most of the encrusting orgonisms show indications of :stromatoporoid structure; some, on the other hand, are olmost devoid of obvious struc:ture in hand specimen and these may be of algol origin. It should be borne in mind, however, that stromotoporoids, recrystollized to a homogeneous finely crystalline colcite could, in hand specimen, simulate algoe belonging to the family Spongiostromoto. Numerous smoll shell fragments replaced bytranslucentcolcite are also present in theSlave Point core of BA Shell Klua b-49-F (94-J-9). The fragmentsore usually elongatedond range up to 0.2 millimeter in thicknessand 5 millimeters in length. It seems likely that most of these fragments are derived from brachiopods. Although shell fragments ore more obvious in the core from the above mentioned Kluo well than in many othersections of SlovePoint core, carefulexaminotion of the colcilutites will often reveol the presence of small, thin-shelled ovoid bodies 1 to 2 millimetersin diameter and thin shellfragments which rangeup to 5 millime:ters in length. There seems little doubt thot the ovoid bodiesare ostrocodes; thelarger shell fragments, as in the case of the Klua core, ore probably derived from brochiopocs. The dark colcilutites which makeup the main part of the Slave Point Formo- tion opparently originated on 0 broadshelf over which o depositional envircnrnentof low energy prevailed. This concept is supported by the fine grained noture of much of the Slave Point carbonate and by the abundance of carbonoceous material in the sediments. The presence of the lotter and the common occurrence of various types 3f biogenic material in thedork colcilutites suggests thot biological activity played avery important port in the formation of these limestones. The limestones of the Slave Point Formotion are dolomitized in some amas. The most profound recrystallization occurs in o narrowzone bordering the facies front and these dolomites will bediscussed in a later section. At this point, however, it is nec- essory to consider briefly the dolomites which occur in areas owoy from the facie; front. Mort of these dolomitesappear to be derived from the dark calcilutites discussed obave, and because they ore widely distributed over o carbonate shelf they will be referred to os shelf dolomites. Wells in which the Slave Point Formation shows substontial intervals 0: dolomite and which lie at some distance from the facies front ore shown on Figure :3 by a distinctive symbol andore listed in Appendix I. The importance of these wells lies in the fact thot in certoin instances the dolomitized sections contain commerciol accumu- lotionsof noturol gas (zAppendix I). The carbonateshelf dolomites ore ,~ruolly mediumdork grey to darkbrownish grey to dork grey in colour and fineto medium crystallinein texture. Some of theshelf dolomites are similar to the white andgrey dolomites of the facies front (to be discussed below) and these probably hod o compor- able mode oforigin. Vuggy andintercrystalline porosity is present in some sections. The causes of dolomitization in the areas awoy from the facies front ore not fully under- stood ond o spatial pattern of dolomitization has not yet emerged.

21 11. TheSubsidiory Components of the Slove Point Formation

A. Rocks ofthe FaciesFront The rock types belonging to this division occur mainly within 1 to 2 miles of the facies front. The limestones described below provide important information on the environmental conditions which prevailed in the vicinity of the facies front during the deposition of the Slave Point Formation. (i) The darkstromatoporoid-beoring colcilutiteswith abundantbiogenic moterial.--Thisrack type represents o continuation of the dork colcilutites discussed obovento the ore0 of the focies front. The rocks possess most of the chorocters olrwdy described but ore notable in this ore0 for theobundonce of contained stromotoporoid moteriol of a11 types.Small patches of sporry colcite, usuolly less than 1 millimeter across, are more common in the dork calcilutites of the facies front than in the colcilutites occurring at some distance from the front. A good section in these dark calcilutites is seen in the Slave Point core of the well, West Not Imperial Clarke Loke b-78-J (94-J-9)(see Appendix 11). (T The stromatoporoid biosparites.--The stromatoporoid biosparites are well displayed in SlovePaint core from the Evie Loke ore0 ond from certain wells in the Clarke Lakeare0 (see Appendix 11). The limestonesconsist mainlyof stromotoporoid fragments showingvarious degrees of roundingand sorting, ret in o motrix of sparry calcite or more dense, very light brownish grey calcite. Brachiopods, CO~O~S,gasteropods,Thomnoporo, and other fossils which are tw poorly preservedfor identification orepresent in some sections. Examples of these limestones ore shown in Plates VII, VIII, and IX. The stromatoporoid moteriol of the biosparites and biosporrudites is often recrystollized too very finely cryrtolline, dense, brownishgrey to light brownishgrey calcite,which shows littleevidence of organicstructure. In same instancesthis material is difficult to distinguish from the micrites of similar colour which will be discussed below. In drill cutting samples it would be almostimpossible to recognize thot this dense,homogeneous calcite was of organic origin and it would probably bedes- cribed as a micrite or calcite mudstone. Because of its origin ond appearonce the recrystallized stromotoporoid material will be referred to os dense, biogenic calcite. Recrystallization can affect the stromatoporoids of ony of the rock types, but it is mentioned here because it is often associated with onother post-depositionol process which is particularly well displayed by some of thebiosporites. The stromotoporoids of these rocks frequently contoin black corbonoceous material which in some instances is distributed throughthe coenosteo in such awoy that it emphasizes theor- ganic structures.When recrystallizationto dense biogeniccolcite occurs,however, the dark carbornceous material migrates either to certain oreos within the coenosteum or, in the case of small fragments, to the periphery of the fragment. Three factors thus contribute to obscure the original textures of the stromotoporoid biosporites. They orethe recrystollizotion of the biogenic rnoteriol, the redistribution of dork carbonoceous compounds within this material and the tendency for the motrixcolcite to be veryfinely cryrtolline ond dense ratherthan sparry. It appears thot certain post-depositionol processes tend to convert, by recrystallization, the vorious components of the rock too dense calcite, fineto very finely crystalline in texture. (iii) The stromotoporoid biomicrites.--This rock type consists of closely com- pactedstromotoporoid coenostea set in a matrix of dense brownishgrey micrite. The rock normally contains only small omounts of carbonoceour moteriol and the stromoto-

22 poroidsore oftenrecrystallized to brownishgrey, dense, biogeniccalcite. The result is a dense brownish grey rock of uniform appearance (see Plate X) and close exorninotion is necessary to distinguish between the two main components. Small prisms of authigenic quartz ore distributed through some of these rocks. Smll voids and fissures in the rock moy be filled with sparry calcite and in coses where incipient dolomitization is present it is often associated with theseareas of Iporry calcite. Theterms stromatoporoid biomicrite and biomicrudite can be appropriatelyapplied to these rocks. They #>rewell develaped in the SlavePoint core of West Not Imp Clorke Lake d-91-L (94--1-9) ond West Not Imp Clarke Lake c-94-L (94-J-9) (E Appendix 11). (iv) The lightcoloured micrites andfossiliferous micrites.--These rc,cks are brownish greygmaphanitic oppearonce and it seems reasonable to assume that they are true micrites. There are only small amounts of stromatoporoid material in these rocks and most would fall into the fossiliferous micrite (containing 1 to 10 per cent fossils) classification of Folk (1962, p. 76). In partsthey grode intointraclost rocks. The intmclastsore 0.1 to 0.3 millimeter in di- ameterand ore mostly round or ovoid in cross section. In somecases they are closely pocked whilst in others they rest in a matrix of sparry calcite. Small fissures ond cavities filled with sporry calcite, occur quite commonly in the rock. The light coloured micrites and intraclort rocks ore frequently ossociot8:d with thedark stromatoporoid-bearing calcilutites. Variousrelationships between :he two may be observed in the Slove Point core of Texaco NFA N Tsea d-47-C (94-P-12) (see Appendix 11). In some ports of this core the dark rock occurs as thin bands crosing lighter material; in other parts there is interbedding of the two types on o smoll scale. Another mode of occurrence is seen where the light micrite takes the form of turbulent "clots" up to 4 centimeters ocross dispersed in a matrixof the dorklimestone. It is possible that some of the banded structures are of algal origin. Interpretation of the limestones of the facies front.--Rocks in the vicinity of the facies front have been described os reef beds (=e, for exomple. Gray and hssube, 1963, pp. 471-472). It has been pointed out by severol authors (Henson, 1950; Nelson et al, 1962) that thereare numerous local environmentsassociated with oreas ofreef developmentand that each environment gives rise to particular types of deposit. The ossembloge consisting of the reef and ossociated fore reef, bock reef, and interreef beds is referred to os the reef complex (Nelson et 01, 1962, p. 249). It is therefore pertinent to enquire whether any of the rock types of the Slave Point Formation con be clssigned too particular part of a reef complex. The informotion currently available unfortunately does not OIIOWo complete and satisfactory interpretation of the area close to the facies front which is the site of potentialreef development. Manyof therocks in thisarea ore dolomitized and os o resulttheir original nature is obscure. These dolomites will bediscussed below. Also, there is o lack of closely spaced core control in the critical areos. Only tentotive sug- gestionscon bemade therefore regarding the interpretation of the rock types from the vicinity of the facies front. Typical biolithites (Folk, 1959, p. 13) derived from the reef core (Nelson et ol, 1962, p. 249) cannot be recognized with certointy. The stromatoporoid biomicrites, discussed obove, provide the closest approach to this type of lithology. The stromoto- poroidbiorparites provide adequote evidenceof shoal conditions ondvigorous wove activity and could well be clostic deposits associated with a true reef. The light ,:olour- ed micrites and fossiliferous micrites may represent local bock reef or interreef cleposits and it is possible that some of the dork colcilutites represent the reef talus. Perhops the most positive evidence indicating the presence of true reef!; in the

23 area of the facies front is the great abundance of numerous forms of stromatoporoids. As these organisms in all probobility had the ecologic potential to erect rigid Wove resis- tant structures (see Hadding. 1941, pp. 18, 43, and 73), it con be concluded that reefs in the sense of Telson et a1 (1962, p. 242) were present in the area of facies change. However, it should be borne in mind thut biolithites have not been recognized with certainty and thatthere is notyet sufficient information to enable the lateral extent of reefs along the facies front to be determined. It may be thot the facies front is &roc- terized by a continuous zone of reefs or alternatively true reefs may occur only intermittently along the front. (v) The white and grey dolomite.--Many of the limestones in close proximity to the facies front have been altered to dolomite. This occurrence is extremely important from an economic standpoint because the vuggy dolomites of the facies front contain mast of the natural gas 10 far discovered in the Slave Point Formation. In the typical development this dolomite consists of two distinct phases, one being medium grey to medium dark grey in colour and the other very light grey to white in colour. The rock will therefore be termedthe white andgrey dolomite. The two phases areassociated together in o number of different ways and this gives rise to several textural vorieties which can be most conveniently described by coining descriptive names inthe following manner (see Plates XI-XVI): 1. Micznclurion texture(ieePlateXI).--Here small inclurionsof the white dolomite, 1 to 5 millimeters across, are scattered in a matrix of dark dolomite. 2. Macroinclusion texture (E Plate XII).--This is similar to the above except for the size of the inclusions. Here they vary between 5 millimeters and 6 to 7 centimeters ocross. In both the textures the boundary between the inclusions and the matrix is we1 I marked. 3. Banded texture (see Plate Xlll).--ln this case the white andgrey phosesoccur as alternatingbandTwhich vary from a few millimetersto severalcentimeters in thickness. 4. Clotted texture (see PlateXI'/).--Rocks with this texture show irregular "clots" of the whitedolomite, with indistinct margins, suspended in a matrixof the dark dolomite. The inclusions vary from less than 1 centimeter up to 7 to 8 centimeters in width. 5. Nebulous texture (see PloteXV).--Here the white phase occurs as "wisps" and fine irregular bands in the dark phase. 6. Pseudo-brecciated texture (=e Plate XVI).--In this care the dark dolomite appears to be in theform ofirregular "blocks" dispersed in on interstitialmotrix of the light phase; if thedark phaseforms thematrix separating "blocks" of the light coloured dolomite then the reverse relationship is apparent. These terms ore useful for descriptive purposes only and it is not intended to suggest thatthey represent fundamentally different types of dolomite.Various grada- tions between the types can be seen and it is probable thatmany of them have a common mode of origin. The dark phose is normally dominant. Microscopic examination reveals thot it is usually fine to medium crystalline in texture with occosionol gradation into the lower part of the coarsely crystalline size class (0.25-1 millimeter). The medium to coarsely crystalline material often hos dark carbonaceous material between the crystals and this imparts the greyish colour to the rock. The finely crystalline material may also possess intercrystalline carbonaceous moterialbut mare frequentlythe crystals are uniformly pigmented. The light phase consists of coarse to very cwrsely crystalline dolomite. Inter-

24 crystalline carbonaceous material may or may not be present. Many ofthe dolomite crystals which compose the two phases are of the same very light grey colour; the actual colourof the phases is relatedto the crystol sizeand the amount ofcarboloceous material present in the rock. Vugs occurin considerable number in the lightcoloured phase; they range fromabout 1 centimeter acrossup to the fullwidth of the core (mostly 3.5 inches in diameter).Many of the vugs are linedwith rhombohedrons of coarse toextremely coarsely crystalline, light coloured dolomite and some quartz.Sphalerite crystals and a yellow minerol which may be sulphur are present in a few of the vugs. The spmlerite occurs either in a dark metallic form or as a yellowish brown translucent mineral. Cor- bonoceovs material is common betweenthe crystals of thevug lining; it is frequently referredto as gilsonite. In areas veryclose to thefacies front carbonaceous moterial fills some of the fissures andsmall cavitieswithin therock. It is hardand in places contains outhigenic dolomite crystals. Vugs ore not restricted entirely to the light phase, but even when they occur directly in the dark phose they are often lined with crystals of white dolomite, The poor recovery obtained from many cored sections in the white and grey dolomite and the lost circulation which often occurs in these zones is adequate testimony to the fact that the dolomite is extremely vuggy. The textures developed in these dolomites suggest that in ;mostcases they are derived fromthe dark stromatoporoid-bearing calcilutites. A comparisonbetwlsen the dark colcilutite and the white and grey dolomite in the well Imp Junior c-98-C (94-1- 11) (%e Appendix II), for example, indicateran obvious relationship between the two. Here the calcilutite has recrystallized to form the dark phase ofthe dclomite qmd the biogenic material is representedby the light phase of the altered rock. During there- placement of the dark matrix it appears that the carbonaceous material of the (original rack is excluded from the growing dolomite crystals, thus giving rise to the interm:rystol- line carbonaceous material of the secondary dolomite. Partlydolomitized rocks in West Not Imp Clarke Lake d-91-L (94-J.-9)and Imp Junior c-98-C (94-1-1 1) (see descriptions of SlavePoint core from these wells in Appendix II) suggest that stromxporoid fragmentsare altered to dolomitefirst at the periphery and that dolomitization then extendsinwards from the outer rim of dolomite so formed. Same of the biogenic fragments are completely replaced by dolomite, others retain a central care of calcite. The calcite core is apparently susceptible to dution and if it is dissolvedaway c1 cavity is producedwhich may thenbecome c1 vug lined with dolomite and quartz. These conclusions are in general agreement with those presented by Gray and Kassube (1963, p. 477) for the dolomitization of the Slave Point limestones in the Clarke Lake field. They considered that dolomitization occurs first in the ccllcclrenitic material of thereef and that in the early stages thesmaller skeletal fragments are entirely replaced and rims of coarselycrystalline dolomite develop on thelarger fossils. It was pointedout that subsequently solution removes theremaining calcite ondproduces a rock withintercrystalline andvuggy porosity. Inwardgrowth ofdolomite mcly then occur which, in some cases, completely closes the vugs. A point of difference between the concepts relating to dolomitization presented by Gray ond Kossube (1963, p. 477) and those presented here lies in the inierpret- ationof thedark colouredintercrystalline moterial. The formerauthors consicler that theintercrystalline material is probablyan early hydrocarbon residue, whereas in this study it is suggested thatthe intercrystalline matter is derived fromthe carbonaceous materiol of the original rock by a process of redistribution and possible alterotion during dolomitization.

25 It is evident that the textures of the white and grey dolomite couldresultmain- ly from the mode of occurrence and distribution of the biogenic materiol in the original rock. Thus stromotoporoid fragments of vorious sizes dispersed in a matrix of dark colcilutite could give rise to the microinclusion and macroinclusion textures upon dolomitizotion (com are,for example, the dark calcilutite of Plate IV with the white ondgrey dolomlte"5 of late XII). Lorge angular stromatoporoid fragments with relatively little matrix could produce the pseudo-brecciated texture, and very small biogenic fragments with irregular distribution in a dark matrix might give rise to the nebulous texture upon recrystallization. In some cores the white dolomite alone occurs over intervals of up to 6 or 7 inches. It is notclear howthese intervalsdeveloped but it is likely thatthey result from the replacement of fairly homogeneous sediment or biogenic material. Thus,these bodies of white dolomite might be formed by the replacement of large stromatoporoids or alternativelyby the recrystollization of o homogeneous micrite.It is worthnoting in this connection that the Presqu'ile Dolomite (the dolomitized equivalent of the Sulphur PointLimestone) often containsa much higher percentage of the whitedolomite than theSlove Point Dolomite. There is considerableevidence that theformer is derived from fairly homogeneous lightcoloured micrites andsparites. It is alsopossible that some of the substantial intervals of white dolomite fall into the cotegory of vein dolomite discussed by Gray and Kassube (1963, p. 477). The white and grey dolomites of the Slave Point Formation occur mainly at, or closelyadjacent to, thefacies front. Normally the zone of dolomitizotion is norrow. Inthe Clarke Lakeore0 the zone is approximately 14 miles wide; in theKotcho Lake are0 tongues of dolomite may reach severol miles from the facies front. This association strongly suggests that proximity tothefront is an important factor in determining whether or not dolomitization takes place. A possible explanation of this relationship could lie in the fact that the facies front provided a psxlge for migrating solutions, which played an importantpart in introducing newcompounds or inbringing about solution and redistribution of existing material.

B. Limestones Occurring at Some Distance from the Facies Front

It is now necesxlry to consider briefly the lithologicol types and faunol ossem- blages which occur mainly at distonces greater than 25 to 30 miles from the facies front ond which differ from the stromotoporoid-bearing calcilutites with which they are interbedded. These rocks, olthoughnot 05 obundont os thedark colcilutites, may provide important information on the environmental conditions in oreas distant from the zone of potential reef development. In the orea which lies at some distance from the facies front, well developed intraclost rocks ore morecommon than in the broad zone lying immediately behind the faciesfront. Clearly developedintrosporites and intramicrites, conspicuous over con- siderableintervols, con be discerned in theSiove Point core fromthe wells, HB Imp UnionGutah o-'3°K (94-H-10)and HB Imperio1 Union Paddy a-49-6 (I) (94-H-16) (see Appendix II and Plates XVlil and XIX). Most of the intraclasts in these rocksare bzween 0.1 and 0.5 millimeter in diometer. Theshapes encounteredore similar to those previously described for the introclost rocks (Ee p. 20). The fauna of therocks which lie ot o conriderabledistance fromthe facies front alxl shows points of interest which moy eventuolly prove significant. The vorious elements of lithology and fauno ore well illustrated by the Slove Point core in the well, HB Imp Union Gutah a-99-K (94-H-10). In this well the upper part of the core consists

26 mainly of thedark calcilutites with abundantAmphiporo and subordinate occurrences of other ldiostromatidae and massive stromatoporoids. The central part of the cored interval of the Gutah well is slightly lighter in colour (brownishblack-medium brownish grey) and contains well developedintroclast rocks, some ofwhich contain Calcisphaero (see Plate XIX). Clearly developed biosparites containing forominifera and broken braThiopod shells also occur in the central partof the care. The foraminifera rangeup to 2 millimeters across whilst the shell fragments may reach 5 millimetersin length (see Plate XX). Completebrochiopod volvesoccur sporadically in thisport of thecore. Massive, nodular, ramose, and laminarstromatoporoids and Thomnopora are also present. The lowersection of the Gutah core comprises dark stromotoporoid-bearing calcilutites. Other wells which illustrate various elements of the Slave Point fauna in areas away from the facies front are Imp Fontas d-37-6 (94-1-7) and Texaco NFA Townsoitoi d-44-C (94-1-10). It should be noted that it is difficult to determine the precise location of the facies front in relation to these wells but it is assumed at the present time thot they do not lie in close proximity to the front. In the Fontas well brachiopods are common and gosteropods occursporadically. In bothwells there are numerous occurrences of small cylinders of calcite 2 to 8 millimeters long and approximately 1 millimeter in diameter. These bodies often possess o central canal or cavity and in some instances their endsshow suggestions of rodiol serrations. It is probablethot the bodies ore derived from crinoids or some related organism. It is concludedthat a moderate diversityof sedimentaryenvironmtmts and osscciatedfaunas existed in areas lying at some distancefrom the facies front. The presence of well developed biosparites, introsparites, and other introclast rocks, even thoughthey ore a subordinateelement in the totallithology, suggests local areas of deposition in on environment of moderately high energy.

LITHOLOGY IN ALBERTA

Figure 4 shows a cross section of theSlave Point Formation olong a line thot runs fromthe Fort Nelson ore0 in BritishColumbia to the McMurray area ill eostern Alberta (see Fig. 11). As for eost os approximatelythe 6th Meridian in Albertathe Slave Po5 Formationmaintoins the lithology developed in theeostern port (of northeastern British Columbia. Darker colours are dominant (medium brownish grey-brownish block) and most of thelimestones ore dense in texture. In parts of the area there ore subordinate developments of intraclast rocks. Further eost the Slave Point Formation thins considerobly andeastof Bison Lake it is less than 70 feet in thickness. In the area of northeastern Albert0 shown on Section HIJ (see Fig. 4) theSlave Point limestones are medium brownishgrey tovary light brownx grey in colour. Themost commonly developed rock types ore calcilutites and fine to medium grained intraclast rocks which contain superficial oalites in places.

27 MILE 325 FORT NELSON CHIEFSIKANNI BC.ALTA CRINCRAGA I ALASKA nwr AREA RIVER BOUNDARY RIVER I I I FORTSIMPSON H FORT SIMPSON I I I

WATT MOUNTAIN a SULPHUR POINT I

N PEA CE BISON PEERLBSS WABASCA PEERLBSSm ' BISON618 PEACE BEAR I MERIDIAN RIVERLAKE LAKE AREA RIVER BILTMORE'I ON ATRABASCA R FO RT SIMPSON IRETON SIMPSON I FORT J

UPPER BEAVERHILL LAKEICHRISTINA a MOBERLY a MILDRED) I HA~LIM- rop OF GALMU;T.- LOWERBEAVERHILL LAKE(FIREBAG 8 GALMUTI

Figure 4.--Diogrammatic cross section (HIJ) from Fort Nelson area of northeastern British Columbia to Athabosca River, Alberta, showingthe Slave Point, Beavehill Lake, andMuskwo Farmotionr. Major lithologieal changer in theSlave Paint are shown. Note that toward the west the Lower Beavehill Lake (Firebag and Calmut) is gradually replaced by the Slave Point Limestone. Line of section is shown on Figure 11. BEAVERHILL LAKE FORMATION

PREVIOUS DESCRIPTION AND CORRELATION

The Beaverhill LakeFormation was originolly described in the Edmonton area of central Alberto and the studies of Belyeo (1952) subsequently demonstrated phot the formation con be troced into the McMurray area of northeastern Alberta. Law (1955) did not recognize the Beaverhill Loke os anindependent unit in northern Alberta, but instead considered that it merged into the lower port of his Shale Unit. Both C.ickmay (1957) and Corrigy (1959) discussed theBeaverhill Loke in northernAlberta, their attention being mainly directed to the development of the formotion in the M<:Murroy area. The McMurray succession of the Beoverhill Lake forms a convenient reference section to which other sections of the Beaverhill Lake in northernAlberta andBritish Columbio can be related. The rocks equivalentto the Beoverhill Lake outcroppingot McMurray were originally termed the WaterwaysFormation byWarren (1933, p. 149). However,the subsurface extension of these rocks in the same area is often referred to the Betwerhill Lake Formation and this practice will be adopted in the account which follows. Crickmay (1957, pp. 6-9) using information fromoutcrops in the vicinity of McMurray and subsurface information fromthe well, Bear Biltmore No. 1, divided the Beoverhill Loke Formotion (Waterways Formation of Crickmay) of the locality ilto five members.They were nomed, in oscendingorder, the Firebag, Colmut (also k7own CIS theCalumet), Christina, Moberly, and Mildred Ivwmbers. Carrigy (1959, pp. 23-28) andNorris (1963, pp. 25-39) contributed new information on the Beaverhill Lake of the McMurray ore0 and gove very useful accounts of the stratigraphy ond palaeontology of the formation. The Beaverhill LakeFormotion as divided by Crickmoy (1957, pp. 6-9) consists of three members which ore dominantly argillaceous ond two which consist mainly of limestone. The limestone members alternatewith the argillaceous members.The lowermost member, termed the Firebag, consists of approximotely 170 feet of shules and argillaceous limestones. The overlyingCalmut Member consists of about 102 feetof fine grainedand clastic limestonesgrading in some wells toargillaceous limttstones. The ChristinaMember, which succeeds theCalmut, is made up of about 90 feetof argillaceous limestone and calcc~reousshale. This unit is overlain by the Moberly Mem- ber which comprises some 200 feet of clastic limestones with subordinate argillaceous limestones. The uppermost unit of the Beaverhill Loke Formotion in the McMurray area is termedthe Mildred Member. It consists of approximately 140 feet of argillaceous limestones and CO~CCI~~OUSshales. The faunas of there members are well documented by Crickmay (1953, Carrigy (1959), and Norris (1963).

REGIONAL CROSS SECTIONS

Thecmss sections ABC (Fig. 6, in pocket) ond FG (Fig. 7, in pocket) have been prepared in order to illustrate the changes which take place inthe Beaverhill Lake Formation in northern Alberta and northeostern British Columbia and also to demonstrote the relationship between the Slave Point and Beoverhill Lake Formations. Section ABC is based on Gamma Ray Neutron and Gamma Ray Sorlic Logs whereas Section FG is a lithological section showing selected wells from the mechanical logsection. Section ABC runs from Kotcho Loke mor Fort Nelson tothe Athabasco

29 River near McMurroy (%e Fig. 5). Section FG is entirely within northern Alberta run- ningbetween the wells,lmperiol Long Lake11-10-107-7 W6 andTexoco R.O. Corp Mockoy River6-13-91-18 W4 (see Fig. 5). No mechanical logs wererun on the well used byCrickmay (195/) forthe description of the Beoverhill Lake Members. However, there ore now sufficient wells in the McMurray area to enable the members to be correlated to wells which haveode- quotemechonical lag covemge. On section BC (see Fig. 6), the members hovebeen troced out in the wells in which they show wfficienTy distinctive log features. To the northwestthe log character of each member is gradually lost so thot beyond the well, California Standard Mikkwo 12-23-98-21 W4, it is no longer practical to recognize the separate members. Although Crickmoy's members con only be recognized in the eostern quarter of the area covered by Section ABC, it may be noted thot in the east central port of the section the Beaverhill Lake Formotion tends to fall into two noturol units which bear o direct relationship to the members of the McMurroy oreo. There is on upper unit which consists of on alternating sequence of argillaceous limestones and calcareous shales and a lower unit consisting mainly of calcareous shales with subordinate argilloceous limestones.The upper unit corresponds tothe combined Mildred,Moberly, and Christina Members and the lower unit to the Colmut ond Firebog Members of the Beaverhill Lake Formotion. It is proposed to term the upper unit the Upper Beoverhill Lake unit and the lower unit the Lower Beoverhill Lake unit. The top of the Calmut and its equivalent to the west represents the horizon seporclting these two units. It will be seen from the cross sections (see Figs. 6 ond 7) that over much of the western half of the ore0 of study (west of obouFR16 W5) even this twofold division of the Beaverhill Lake Formation tends to break down and the formation comes to consist of calcoreous sholes with subordinate interbedded orgilloceous limestones. It is thus difficultto recognize the upperand lower units ofthe Beoverhill LakeFormation in this oreo, but the persistence of thin "marker" zones with o high colcoreous content enables the horizon correlative with thetop of theCalmut Member to be followed throughto the well, HB Union lmperiol Poddy #2 (c-74-8/94-H-16), in the eostern port of northeastern British Columbio. The horizon corresponding to the top of the Calmut Member hos been selected os the datum for Section FG and most of Section ABC. In the extreme western port of Section ABC this dotum con no longer be used because of the loss of the Beoverhill Lake Formotion. Thebase of the Slove Point Formotion has therefore been used os the datum for the most westerly five wells of the Section ABC. The selection of o dotum within the Beoverhill Lake enables strotigraphic changes taking place at the top and bottom of the formationto be demonstrated more readilython would be the case if thedatum were ploced either above or below the formotion. Most of the correlation lines shown on Figures 6 and 7 ore based on a compor- ison of mechanical log features, which in turn usually reflect lithologicol changes. In those instances where the correlation between adjacent wells of the section wassome- whattenuous additional well control andother types of logswere used tocorroborate the correlations shown. Some importont lithologicol changes connot be recognized from the mechanical logs. In the case of Section ABC it wos notpossible torecognize the break betweenthe Slave Point Limestone and Fort Vermilion Anhydrite using mechonicol logs alone. The correlotions shown on the section for this horizon ore derived from information kindly provided by Canadian Stratigraphic Service, Ltd. of Calgary, Alberta. Informotion provided by this agency has olso been used os a guide in establishingthe top of the Prairie Evaporites and Muskeg Formation in the wells shown in Figure 6.

30 The lithological sectionof Figure 7 supplements the mechanicallog section and demonstrates the lithological changes which take place in the Beaverhill Lake For- mation. The section wos prepared from drill cutting xlmplesexamined by the writer at the Core Storage Centre of the Alberta Oil ond Gas Conservotion Board, Calgary. The octual direction and form of Section ABC is governed by three main foctors. First, the section is arranged so that its overall orientation is approximately mat right angles to the facies strike of the Beaverhill Lake and Slave Point Formations. Secondly, the section has been kept well to the north of the Peace River Arch 50 that it lies in on area where the influence of this tectonic feature is slight. Thirdly, the individuzl con- trolpoints wereselected to form a zigzag pattern so thatthe line betweenadjacent control points lies ot a low angle to the facies strike, thus keeping the lithalogical dif- ferences between these points to o minimum. A consequence of the zigzag nature of Section ABC is the slight variotion in thickness shown by the Beaverhill LakeFormation especially in theeastern half ofthe section. The Beaverhill Lake thins and eventually passes out over the Peace River Arch. As a result the wells of Section BC (=e Fig. 6) closest to the Peace River Arch(see Fig. 5) show slightly thinner sections of the Beaverhill Lake than those farther to thearth- eost .

LJTHOLOGY AND DISTRIBUTION IN NORTHERN ALBERTA

The Beaverhill LakeFormation is widelydistributed in northern Alberta (Ee Fig. 11). The formation is underlainby theSlave Paint Formation and overlain con- formoblyby the Fort Simpron Formation in the east andunconformably by the IMurkwo Formation in the west. In the subsurface of the central part of northern Alberta a more or less complete succession of the Beoverhill LakeFormation is developed. It variesbetween about 500 and 600 feet in thickness. In the southwest of the area the Beaverhill Lake weclges out on the northern and eastern flanks of the Peace River Arch. In the extreme eastern part of northern Alberta the Beaverhill Lake Formation was subiected to erosionbefore the deposition of the overlying Cretaceous sediments. As a result of recent erosion the Beaverhill Lake is now exposed in a brood area of De- vonian outcrops which parallel the edge of the Precambrian Shield in the northeclst cor- ner of the province. Changes occur in both the thickness and lithology of the Beaverhill Lake Far- motion CIS it is traced across northern Alberta. The changes in the thickness of the formotion can be attributed to two principal causes. First, there ore what are believed to be facies changes in the Lower Beaverhill Lake unit. These are dealt with more fully in the following section.Secondly, there are the effectsof thepre-Murkwo erosion os shown in Figure 6 which demonstrates that as the Beaverhill Lake is traced to the northwest the uppermost beds are successively truncated, indicating that the Beaverhill Lake Formation was erodedbefore the deposition ofthe overlying MuskwoFormatian. At Ohio Bede Creek 10-23-106-20 W6 the Muskwa lies above almost 500feet of Beaverhill Lake; in the Kotcho Lakearea, however, the Muskwa liesdirectly upon thm: Slave Point. The line of pinch out of the Beaverhill Lake is shown in Figure 11. Thot there was depositional thinning of part of the Beaverhill Lake in the area of truncation is possiblebut correlations suggest that it was not o mclior COUP: of the stratigraphic thinning of the Beaverhill Lake. The lithological changes in theBeaverhill Lakeare illustrated bySection FG (E Fig. 7). Inthe east the Upper Beoverhill Lake unit consists mainlyof dense, argillaceous, light grey with subordinate light brownish grey limestones alternating with

31 medium light grey to light grey and minor brownish grey colcoreovs sholes. Toward the west the argillaceous limestones become less common and in the central port of Section FG colcoreous shole is the dominant constituent of the Upper Beoverhill Lake. In thewestern port of Section FG theUpper Beoverhill Lake unit is mode up largely of medium dark grey to dark grey ond brownish grey, slightly colcoreous shales. The darker colour of these rocks is probably due to the foct that they contoin less colcoreous material than the shales to the eost. The Lower Beoverhill Lake unit olso shows o westword chonye from o sequence consisting of argillaceous limestones and colcoreous shales to one consisting lorgely of shole.However, in the east theLower BeoverhillLoke contains o higher proportion of shole than the overlying unit, and in the western oreos the shales of the lower unit ore more colcoreous than those of the Upper Beaverhill Loke.

LITHOLOGY AND DISTRIBUTION IN NORTHEASTERN BRITISH COLUMBIA

The Beoverhill Loke Formotion of northeastern British Columbia varies between zeroand 350 feet in thickness.An iropoch map of the formotion is shown in Figure 8 ond the depths to the top and battom of the formotion in 011 the British Columbio wells whichpenetrated it at Jonuory 1, 1963, ore given in Appendix I. The formationat- tains its greatestthickness in theChinchogo are0 (opproximotely lotitude 57 degrees 30 minutes north, longitude 120 degrees 30 minutes west). To the south of this ore0 the formotion pinches out against the Peace River Arch. Possibly it is represented by oren- aceousand silty deposits in thewells, Imperial Pocific Siphan Creek 1-26-86-16 W6 and Southern Production Atlantic 87-1 (12-33-85-16 W6). To the northwest the formotion thins and is lost completely north of obaut lotitude 59 degrees north in northeastern British Columbio. In northeastern British Columbio the Beoverhill Lake Formation is underlain by theSlove Point Formation and unconformobly overlain bythe Muskwo Formotion. The noture of the contact between the Beoverhill Lake and Slove Point Formations is considered in o loter section (=e pp. 35-38). It is importantfor the purposes ofthe present investigationto interpret the strotigrophic equivalence, in terms of the Alberta section, of the Beoverhill Lake Shole developed in northeasternBritish Columbio. As noted abovethe moximum thickness of the Beoverhill Loke in the subsurface of northeasternBritish Columbio is in the Clrin- chago oreo. The current evidence suggests thot the 300 to 350 feet of Beaverhill Lake present in this area is o local thickening of the Beoverhill Lake Formotion in the Poddy oreo. The SlavePoint is similarlythickened in theChinchoga wells. Thus an inter- prefotion of the succession in the Poddy ore0 gives o good indication of the moximwl development of theBeoverhill LakeFormation in the subsurface ofnortheortern British Columbia. The Beaverhill LakeFormation in the well, HB Union Imperial Paddy No. 2 (c-74-B/94-H-16) is represented bythe upper port of tllc Lower Beoverhill Lake unit ondthe lower part of the Upper Beaverhill Lake unit (see Fig. 6). In terms of the succession otMcMurroy therefole the BcovethillLakc TtlIc Poddy well is equivalent to theupper partof the Fircbag Member,the Colmut Memb-1, and a substnntiol pant of the Christino Member of thot clreo. Tho Beoverhill LokeFormution is cotedin foul wcIIs in t~o~llwosle~nR~ilirh Columbia to give o lohl coredfootogc of 59 feet. Tlw COICI itdicote that thr Btmvcl- hill Lnke Consis15 rntlinly of mcdiuw dotk gley, colco~cousIo t~on-caIco~eoussholcs (rce " Figure 8.--lropach mop of the Beaverhill Lake Formation in northeortern British Columbia.

33 Appendix 11).The shales are pyritic in places with the pyriteoccurring either finely disseminated or as singlecrystals up to 1.5 millimeters ocross. In some parts of the Beaverhill LokeShale small chitinous brachiopodsoccur; chitinousmaterial may olso occur os small fragments generally less thon 1 millimeter in diameter. In places the Beoverhill Loke Shale grades to argillaceous limestone which in some instancescontains poorly preservedbrachiopods. Fragmented biogenic material in the size range 1-2 millimeters may olso be present inthe zones ofargilloceous limestone. Drill cutting vlmples from the wells which penetrate the Beaverhill Lake For- mationin northeosternBritish Columbia indicatethat brownish grey and grey, mainly argillaceous limestones make up a smoll but important part of the formation. Other rock types whichoccur in the drillcutting samples fromthe Beoverhill Lokeare brownish grey colcareous shole and occosional calcareous siltstone. Similarities and differencesbetween the Beaverhill LakeFormation and the associated shole units are os follows: The Beoverhill Lake shales ore similar to those of the Otter Park Member,but Groyand Kassube (1963, p. 483) notedthat in the latter unit limestone beds areabsent or veryrare. In this respect then the Otter Park differs fromthe Beoverhill Lake in which limestone beds ore relatively common. The Beover- hill Loke shales differ from those of theFort Simpson Formotion incontaining higher proportions of calcoreousmaterial and interbedded limestone. The Beoverhill Lakeand Otter Pork show similar mechonical log feoturer and both con be distinguished from the Fort Simpson by their lower radioactivity and the lower readings on the interval transit timelog.

34 CORRELATION OF THE SLAVE POINT AND BEAVERHILL LAKE FORMATIONS

In the past it has usuolly been assumed that the Beaverhill Loke Formation was deposited conformably upon the Slave Point Limestone after deposition of the latter hod terminated. Low (1955, p. 1945) consideredthe contact between the Slave Point For- motion and overlying shales to be in places abrupt but probably conformable. His conclusion wasbased on the study of the Slave Point throughout northern Alberta. Belyea (1952, p. 12) who likewiseconsidered an extensive area noted that there was a sharp contactbetween the units now defined os the Beovehill Lokeand Slave Poht Formo- tions. She did not, however, consider that the contact was disconformable. Crickmay (1957, p. IO) on the other hand states that adisconformit, is present between the Slave Point equivalent ond the Beaverhill Lake in the well, Sear Bilt- more No. 1. Norris (1963, pp. 22-25), however,who examined numerous sections in the vicinity of the Biltmore well does not consider that there is strong evidencl: of0 disconformity at the top of the Slave Point (Norris' Livock River) in the area. In fact he presented evidence which suggests that in the McMurray area the Slave Point (ond overlying beds (the Firebag Member) are genetically related. In the Gypsum Cliffs area on the Peace River, however, Norris (op. cit. pp. 61-65) considered that on unc:onfonity was presentbetween the Slave Point Formation and the overlying Peace Point Member (probably equivalent to the Firebag Member); his strongest evidence for the unc:onformity being the sharp faunaland lithological breakbetween the two units.Howevr'r, Norris was dealingwith a comparatively small areaand the faunal and litholcgiccll changes can be explained by other means. The usual concept of a sharp but conformable contact between the Slave Point and Beaverhill Loke Formations appears to be quite in keeping with the facts when only theeastern sections are considered. Further west, however,both the SlavePoint and Beaverhill LakeFormations undergo changes which suggest thatan alternative interpretation is required to explain the regional stratigraphic relotionships of the two. In the following discussion the term Slave Point refers only to the Slwe Point Limestone; the Fort Vermilion Anhydrite is not included. The reason for this usagehos been mentioned previously (E p. 16) ond will become more apparent os the discussion proceeds. Two moin alternative explanationsfor the observed stmtigrophic relationship between the Slave Point and Beoverhill Loke Formations moy be interpreted from Figures 6 and 7. Either the Beaverhill Lake lies upon the Slave Point as a result of ho

35 ? WEST EAST

UpperBh L

FV-WM Io. Discmiamablerelotlonship between SPand Eh L CLARKE LAKE MCMURRAY

MU- MU- Upper Eh L

Ib. Conformablerelationship between SPond Bh L FV-WN

u .Y".I.o M L . e.sv"M LO.. IP . I*..PO111 F"..". m,, Y.mIIIo.-l." -an "UPUpper Bh L

Low: Eh L SP LS

FV-WM 2. SPand Bh L faciesequivalents

Figure9.--Diogmmmatic sections showing the Slave Point and associated formations between Clarke Loke and McMurray to illustrate the alternative interpretations of the relationship between the Slave Point and Beaverhill LakeFormotions. lo. Disconformable relationship. Ib. Normal conform- ablerelotionship. 2. Facies equivalence.

for, to a considerable extent, by a thickening of the Lower Beaverhill Lake unit. In northern Alberta the Slave Point thins at o rate of less than 1 foot per mile. This is considerably less than the rate of thinning shown by formations in the same area which are known to hove been truncated by erosion. A relatively thin sequence of Slove Point is distributed over a very wide area and it would be reosowble to expect that if erosion occounted for the thinning of the formotion, inliers of Elk Point evaporites would bepresent within theSlave Point sub- crop, This phenomenon has not been observed. There seems little basis for the osrump- tionthat there is an erosionalbreak between the Slave Point and the BeaverhillLoke Formations in the orea under discussion. I. (b) If the BeoverhillLoke wos depositedafter the deposition of the Slave Pointand overlies it conformoblythen a satisfactoryexplanation of the thinningof the Slove Point within the limits imposed by the concept of normal depositional thinning is required. This interpretationprovides threemain alternotives. Eitherthe thin Slave Point section in the east is on attenuated sequence resulting from nearshore deposition, or the thinning of the formation is o consequence of regressive deposition, or as o final alternative the thinning moy be considered to result from transgressive deposition. The first possibility which involves the concept of nearshore deposition is considered unlikely because of the extremely gradual thinning of the formation over a large oreo. The effect of 0 landmass or other positive area on the depositional thickness of a unit is usuolly most morked in the immediote vicinity of the positive area. The Elk Point

36 Group, for example, is fairly uniform in thickness over much of northwestern Alberta as the map of Law (1955, Fig. 7, p. 1946) andthe Elk Pointisopach map ond:;ection of Govett (1961,p. 40) demonstrate. There is, however, a rapidthinning of the Upper Elk Point toward a positive area in the 50 miles between the well, Beor Biltmore No. 1 and McMurraytown. A similarsituation exists in northeasternBritish Columtlio where various units of the Middle Devonian Series maintain their thicknessaver much of the are0 in questionbut thin rapidly againstthe Peace River Arch. The extremelygradual thinning of the Slove Point over a large area therefore does not favour the interpretotion thot it results from deposition against a landmass lying to the east. The second possibility which assumes that the thinning of the Slave Point For- mation is o result of deposition from a regressive sea is similarly difficult to uccept in view of the established facts. If the Slave Point were essentially o regressive deposit it would be reawnoble to expect that there would have been considerable evaporite deposition to the east of the are0 of potential reef development in British Columbicl and the Northwest Territories. This is not the case and in foct one of the distinctive fmtures of the Slave Point Formation as compared with the underlying Elk Point Group, which was largely regressive in the sense of Link (1950), is the foct that it consists mainly of limestone whereas the Elk Point is composed largely of dolomite and anhydrite. It may be argued thot the Fort Vermilion Member is an anhydritic baxll unit of the Slave Point Formation and thus provides evidence for the regression hypothesis. but os pointed out previously there is strong evidence that this member belongs genetically with theWatt Mountain-Sulphur Point assemblage.Even if it were includedwith the Slave Point as o transitional bowl member it would constitute only a subordinate component of the formation. Finolly, there is the possibility thot the Slave Point Formation is a transgressive deposit thinning to the eastbecause of onlap in that direction. This concept might be acceptable if it could be shown that the Slave Point lay upon an erasion surface or that therehod been a period of markedregression in theorea now occupied by he Slave Point prior to the deposition of the formation. Neither of these conditions cart be demonstroted,however, and all the ovoilable evidence indicates that the changefrom the underlying beds to the Slave Point is of a transitional nature, particulorly in the west. The concept thot the Slave Point Formation is o single, simple tronsgressive deposit must therefore be discounted. The obove considerations provide strong evidence against interpreting the Slove Point Formation as having been deposited as a single, complete unit, which WCIS followed bythe deposition of theoverlying argillaceous and caIcareous sediments of the Beaverhill Lake Formation, 2. The SlovePoint Formation maybe interpreted as thefacies equivalent of thelower part of theBeoverhill LakeFormotion. This hypothesisimplies that the Beoverhill Lake shales of the more eostern sections are gradually replaced by the Slave Point faciestoward the west. This offersthe most rotisfoctorysolution of '.he Slave Point-Beaverhill Lake problem. The uniform thickness of 250 to 300feet between the top of the Calmut Member and the bore of the Slave Point Limestone over much of northern Albert0 provider strong evidence for the concept thot the Slave Point and Beaverhill Lake Formations are facies equivalents. Towardthe British Columbia border this intervalthickens to about 400 feet. This maybe attributedto two factors. There is probablya slight regional thickening of the interval toward the west and the differential compaction of Iime'itone and shale would cause thesections with aconsiderable amount of limestone to be thicker than the correlative sections to the east in which shale is dominant.

37 The loterolchange of the Beoverhill Lake sholes to limestones of theSlave PointFormotion is particularlyevident in the oreasouth and southeost of theClorke Lake 90s field in BritishColumbio (see Fig. IO ondisopach mops of Figs. 3 ond 8). It will be seen from the section of Figze IO thot just to the south of the field theupper port of the thick section of Slave Point Limestone is reploced to the south by the shales ofthe Beoverhill LakeFormotion. Further south againthe pattern is repeated, so that the thick sequence of Slove Point in Woodley Imperial Kluo o-27-G (94-J-8) and Pure lmperiolBull b-67-J (94-J-1) is replocedlaterally by on upper section of Beoverhill Loke Shale ond o lower intervol of Slave Point Limestone in Imperial Sikonni Chief No. 1 (b-92-D/94-1-14). The facies interpretotion of the Slove Point-Beoverhill Lake interval provides the most sotisfoctory explanation of the distribution of these limestones and shales. The concept that the Bwverhill Lake Formotion is laterally equivalent to dense stromotoporoid-bearing limestones is, of course, not new. Belyeo(1952, p. 13) demonstroted that the Beoverhill Lake of the Edmonton ore0 contains stromotoporoid limestones and Fong (1960, p. 207) demonstroted the equivolence of the Swon Hills Limestone with partof theBeoverhill LakeFormotion. Furthermore, the concept that the Slave Point itself is laterally equivalent to colcoreous sholes is in keeping with the occepted interpretotion ofthe relationship between the Otter Pork Shale ond the Slave Point Limestone (=e Gray and Korrube, 1963). If the concept of the ttrotigrophic equivalence of the Slave Point and Beaver- hill LokeFormotions be accepted then it is possible to relate the Slave Point of north- easternBritish Columbia tothe correlotive beds of eastern Alberta in same detail. As noted previously (seep. 32) the Beoverhill Lake in the Paddy ore0 is equivalent to the upperport of the Firebag Member, the Colmut Member, ond o substantialport of the Christina Member. As theBeoverhill Loke-Slave Point interval is traced from the Paddy oreo to the Clorke Lake area there is only o slight increase in the thickness of the whole intervol. In thewestern partof the Clarke Lakeoreo, however, the Beoverhill Loke has posedcompletely to the SlavePoint facies. On thickness correlotionstherefore it is reasonable to conclude that the thickest sections of the Slove Point Formation in northeastern British Columbio ore equivalent to the Firebog Member, Colmut Member, and ot least the lower port of the Christina Member of the Beoverhill Lake Formotion. This in- terpretotionallows for o slighttruncation of the Slave Point-Beoverhill Loke intervol between the Paddy wells and the western Clorke Lake oreo. In general terms it con be stoted thot the Slave Point Formotion of northeastern BritishColumbio is equivolent, depending on the locotion, either to 011 or port of the Lower Beoverhill Lake unit plus the basal Upper Beoverhill Lake unit. The actual section of Slove Point present ot ony one locotion depends on the extent to which the Beoverhill Loke has posed to the limestone facies ond also on the amount of pre-Muskwa erosion. These factors are vorioble, but in generolthe erosionol influences ore dominant in the north whereas facies chonge is the main foctor accounting for voriotions in thickness toword the west. Koch (1962, p.621) demonstroted that the founo of the Swan Hills Member belongs to the Allonaria olloni and Eleutherokommo homiltoni zones of the middle Woter- ways Formation (approximatelymiddle Beoverhill Lake). lt con be reosonobly inferred therefore thot the moximum development of the Slove Point Formotion correlotes opproximotely with the Swon Hills Member of the Beoverhill Lake Formotion. Koch (op. cit.) however, did not consider the Slove Point and Beoverhill Lake Formotions to be contem- poroneous deposits. This is no doubt because his study of the Slave Point wos restricted

38 K L GULFST4TES IMP. WESTNAT IMP. BASHELL KLUA 64 SHELLKLUA TRIADSOW0 PAC CLhRKE L. b lBDl5I CLARKELAKE r-8 D b.49.F CREEK o.50ClIIJACKFISH 0 3O.K I WEST NAT IMP CLARK E LAKE II CLARKE d BEL I I I

I"I-',',',' I"I-',',',' #','r','ld,',',', ,',I," DATUM-BASE OF SLAVE POINT

1 DATUM-BASEPOIN7 OF SLAVE

Figure IO.--Cross section KLM in the area south of Clarke Lake to show the relationship between the upper part of the Slow Point Formotion and the Beaverhill Lake Shale. The line of section is shown on Figure 12. to northwestern Alberta,on area in which this formation does nat reoch its full development. Despitetheir correlation there is animportant difference between the Slave PointFormation ond the Swan Hills Limestone. The dimensions ofthe Swan Hills and orsocioted reefs can be expressed in terms of tens of miles and they thus provide a depositional assemblage of reef, fore reef, and bock reef beds of relatively mall areal extent.In the case of theSlave Point and Beaverhill Loke Formations, however,the naturoldeposition01 assemblage is of basin-wideproportions and one is thus dealing with a phenomenon of a comparable nature but developed on a very different scale. It is rather like thecomparison between asingle platform reef such as Butt Reef(see Fairbridge, 1950, p. 345) in the Australian barrier reef complex and the whole compG itselfwhich covers a considerable proportion ofthe eastern continentol shelf of Austrolia betweenthe favourable lotitudes. It is probablythe basin-wide extent of the Slave Point-Beaverhill Lake phenomenon which has tended to obscure its true nature. A corollary to thecorrelation of the Slave Point Formation with part of the Beoverhill Lake Formation is the correlation of the upper part of the Otter Pork Member of the Horn River Formation with the lower portion of the Beoverhill Loke (see Fig. 2). The equivalence of these two units could lead to some confusion in nomen&ure, but it is suggested thotthis con be avoidedby continuing the present practiceof naming the calcareous shales below the Muskwa Formation to the west of the facies front the Otter Pork Member and the corresponding shales to the east of the front the Beoverhill Loke Formation.

DEPOSITION OF THE SLAVE POINT FORMATION

On the basis of the fociesinterpretation itcon be inferredthot Beoverhill Lake sediments gradually spread westward encroaching on the areos of Slave Point sedimentation,slowly replacing them. At some timeduring the Upper Beoverhill Lake the Slove Point must hove been completely engulfed by Beoverhill Loke sediments bringing an end to Slave Point deposition. In view of the apparent mutually exclusive nature of the Beaverhill Lakeand Slave Point sediments, it seems reasonable to enquire why the Beoverhill Loke so successfully terminated the deposition of the Slave Point in the oreos in which it become established. There ore two lines of evidence which moy be pursued in this connection;one deals with the lithologic01 nature of the two formations and the other with the faunos of the formotions. The main and oppclrently most significant difference between the litholcgy of the Slave Point and the Beoverhill Loke Formations lies in the high argillaceous content of the latter and the relatively purecolcoreous composition of theformer. Here then lies on explanation of the sharp termination of Slave Point deposition. The Beaverhill Loke simply represents on influx of terrigenous moterial into on area which hod previously been dominated by evaporitic ond carbonate deposition. In view of this it might be argued that the Beoverhill Loke merely represents o sort of "argillaceous Slave Point," but considerations of the founo of the formotions indicote that this is not the case. The Slave Point founo is dominated by stromataporoids, especiolly toward the west. Other importontelements ofthe founaare tobulotecorols, brachiopods, crinoids (?), andostracodes. Gosteropods, rugose corols,and forominifero are less common members of the founa. These orgoniwns in conjunction with the numerous soft- bodied creatures or "occult benthos" of Beoles (1963, p. 681) must hove formed o complex biota adjusted to conditions in on environment almost free of terrigenous moterial. It is 0110 probable thot the physicochemical environment in which this bioto lived, and

40 in fact was partly responsible forproducing, hadan important influence arb thesedi- mentary processes resulting in theformation of theSlave Paint limestone. In such o balanced complex or fabric of interacting organic and inorgonic elements it is easy to envisage thatif port of the fabric werebroken by the intrusion of same deleterious agency then the whole system might soan break dawn. It is concluded therefore that if same element of the Slave Paint faurm or flora was not viable in the conditions of increased argillaceous Sedimentation ancl probable reduced salinitywhich accompanied the onset ofBeaverhill LakeSedimentation, then the biota and physicochemical environment responsible far the formation of the Slave Point limestone could wan be sufficiently upset to bring about on end to its deposition. In these circumstances of changed sedimentation a new biota would soon become established which was adopted to the mare argillaceous environment of the sea floor. The stramataparaids provide on obvious example of a group of orgoni:,ms which were not well adapted to a muddy environment (see Galloway, 1957, pp. 400-403) and they may well have been stenohaline as are the gdern corals. It is tempting to suggest thereforethat theseorganisms werethe "weak"link in thechain which enabled the Beaverhill Lake sediments to slowly eliminate the Slave Paint biota. In any event it is clear fromthe fossil record that once Beaverhill I.ake conditions of sedimentation were established in parts of northern Alberta and British Calum- bio,a biota differing from that ofthe Slave Paint becomeestablished. Brachiopods formthe main element ofthe preserved fauno of theBeaverhill LakeFormation whilst pelecypodsore an importantsubordinate element (Ee Carrigy, 1959 andNcrris, 1963 far description of megafauna). Ostmcades ore o well representedgroup of microfossils in theformation (see McGill, 1963 andLoranger, 19630, 1963b). Since the Slave Point and BeaverhirLoke Farmations each has its own distinctivefacies fauna,. paloeontological correlation between the two formations is likely to be difficult. The SlavePaint is here interpreted as o limestonedeposited during the wide- spread Beaverhill Laketransgression. The transgressivenature of the deposit explains why it differs markedly from the underlying evaporitic strata which are the deposits of aregressive orstatic sea. This geneticconcept ofthe Slave Point Formation is of assistance in the interpretationand classification of the underlying beds. The Fort Vermilion Anhydrite forexample naturally belongs with the main evaporitic sequence even though it is separated from the latter by the clastic Wott Mountain of ttle eastern sections. It appears that the upper part of the Sulphur Paint Formation, the Wott Maun- tain Formation, and Fort Vermilion Anhydrite were all deposited during orcilhting can- ditions which prevailed prior to the onset of the main transgressive phase.

41 Figure I1.--Mop of northeastern British Columbia ond northern Alberta showing the major features of the distribution of the Murkwa and Beoverhill Lake Formations and the line of Section HIJ. MUSKWA FORMATION

PREVIOUS DESCRIPTION AND CORRELATION

Gray and Kossube (1963, p. 473) introduced the term Muskwo Member ond applied it to o sequence of block bituminous shales which overlie the Slave Pc,int Forma- tion in the vicinity of the Clorke Lake gas field in northeastern British Columbia. They considered the Muskwa to be the uppermostmember of the Horn River Formatim. How- ever, for reosonr which will be discussed below it is suggested that the Muskwo Member should be seporotedfrom the Horn River Formotion and recognized CIS anindependent formotion. Gray and Kossube (op. cit., p. 480) designatedthe intewal between6,510 ond 6,630 feetin the well,Gulf States Fort NelsonNo. 2 (0-95-J/94-J-I0) as the typesection of the Muskwo. The followinglithological description wos given: "The member consists of black bituminous shale with abundant pyrite as isolated c,r clustered medium crystalline cubes, or finely disseminated; theshale is locolly soft, micaceous ond flaky, in ploces hard and siliceous. Its outstonding characteristic is its high rodio- activity on well logs." The MuskwoFormation has previouslyonly been recognized in northeastern BritishColumbia. In theClorke Lakearea Gray and Kossube (1963, p. 483) demonstroted thot the Muskwo lies either between the Fort Simpson and Slave Point Formations or, in areos where the Slave Point hos changed to shale, between the Fort Simpson For- mation and Otter Pork Member. South of Clarke Lake they considered thot the Muskwa Shole merged into port of the Beaverhill Lake Formation.

DISTRIBUTION

The Muskwa Shale can be troced,using Gommo Ray Logs, from the creo of type sectionthrough most of northeasternBritish Columbia ond into northwesternAlberta. The distribution of the formotion in Alberta and British Columbia is shown in Figure 11. In BritishColumbia the Muskwa varies between 50 ond 100 feet in thickness over most of its area of distribution (ee Fig. 12). There ore a few local arens in which it exceeds 100 feet in thickness. To the south the formotionthins and finclly wedges out on the flanks of the Peace River Arch. In the northwest the Muskwo varies consider- ablyin thicknessand the GommaRoy Logs suggest thatthe unit thickens and passes westward, by way of on intertonguing relationship, into the Besa River Shale. It is difficult to recognizethe Murkwo with certainty west of the zone ofvarioble thickness shown in Figure 12. In Alberta theMuskwo Formation canbe recognized in the area bounded on thesouth approximately by Township 84 and on the east by Range 15 west of the5th Meridian. Throughout most of thisarea the formation is between 50 and 100 feet in thickness. To the northeast, however, the formation attains a thickness of between 150 and 250 feet, gradually loses its distinctive character, and finally passes into theFort Simpron Formation. The Gamma Ray Log provides the best means of establishing the top ond base of the Muskwa Formation, The typical GammaRoy cuwe of the formotion gradually moves tohigher voluesfrom the normal shale lineof theoverlying Fort Simpson Formation, until o moximum is reached neor the base of the Muskwo. The cuwe then retorns ropidly to the low values of the Slave Point Limestone, or to intermediote values in meos where the Muskwa is underlain by calcareous shales. The drillcutting ramplesfrom the zones of highradioactivity ofven contain

43 7

Figure 12.--Map showing distribution and thickness of Muskwa Formation in northeastern British Columbia.

44 abundantgreyish black shale. In mast cases, however, the samples do not enablethe precise limits ofthe formation to be established, largely because of shale contamination. As a consequence of the shape of the Gamma Ray curve of the Muskwa it is a stroightfomard matter to pick the bare of the formation. The transitional rloture of the upper part of the curve, however, means that the upper limit must be established on an arbitrary basis. In this study the top of the formation is taken 30 to 40 feet below the pointat which theincreasing radioactivity associated with the Fort Simpson-Muskwo contact first becomes evident. The depths of the top and bore of the Muskw,o Formation in all wells in northeastern British Columbia which penetrated the formation ot January 1, 1963, ore listed in Appendix I. In thenorthwest and northeast of thearea of development of the Muskwa in British Columbia and Alberta the Gamma Ray curve does not show the typiccll form, and zones of high radioactivity alternate with zones of intermediate radioactivity over on interval of lOOto250 feet. It is thus difficult to establish the exact limits of the Muskwa in these areas. This is especially so in thenorthwest where the underlying Otter Pork Member also contains radioactive zones which can easily be confused with the Muskwa.

LITHOLOGY

The MuskwaFormotion hos beencored in the wells West Not Kotcho a-9-F (94-P-3) (see Appendix II) and PanAm et al A-1 Snake Riverc-28-D (94,-0-1). The best of theyored sections lies between the depths 6,636 and 6,656 (7) feet in the former well. The maior part of the cored interval consists of greyish block, non-colcareous to slightly colcareous, moderately pyritic shale which shows brown coloured score marks when scratched. At the base of this cored section the contact betwe8.n the greyish black shale and the brownish grey Slove Point Limestone is preserved. However, this contact is not simple and a short sequence at the bose of the core may belong to the Otter Park Member (see Appendix 11). The Muskwayore of West Not Kotcho a-9-F (94-P-3) shows numeriws zones in which crystals of outhigenic borite are common. Seven such zones were caunted in the cored section; the thickest zones cover an interval of 24 inches. The lithologyof the Muskwa has not been extensively studied in northern Alberta. However, there is no reason to believe that it differs greatly from the unit as developed in northeastern British Columbia.

STRATIGRAPHIC RELATIONSHIPS

The form of the typical Gomma Ray curve of the Muskwa Shale enabler certain suggestions to be made regarding the relationship of the formation to the underlying and overlying beds. The sharp decrease inradioactivity defining the bose of the Muskwa suggests a strotigrophic break between the Muskwa andthe underlying beds. Also, the Gamma Roy curve shows evidence of a transitional contact between the Mwkwo and the overlying Fort Simpson Formation. The abrupt lower contact of the Muskwa Formotion is readily explcined in view ofthe fact that the formotion overlies an erosion wrfoce (=e Fig. 6 and discussion of Beaverhill Lake Formation, p.31). Over most ofnortheastern British Columbia and Alberto the Muskwa overlies the eroded Beoverhill Lake Formation. In the northwest of this area, however, the formationlies upon the eroded Slove Point Formotion. The pinch out of the Beoverhill Lake shown on Figure 11 indicates the line of demarcation between these two areas. In theorea where theSlove Point haspassed to shale the Muskwo unconformobly overlies the Otter Pork Member of the Horn River Fcmrmotion.

45 In the area of study considerable pre-Muskwa erosion occurred north of latitude 58 degrees 30 minutes north in the vicinity of theBritish Columbia-Alberta boundary (see Fig. 1 I). There the Murkwa lies on a Slave Point section varying between 175 and 3iTfeet in thickness.Regional stratigmphic trends suggest that more extensiveerosion occurred further to the west. In the western areas, however, the position of the unconformity cannot as yet be established because of the difficulty of recognizing the Muskwa Shale as an independent unit within the Besa River Shale. At the upper contact of the Muskwo, it is concluded that the transitional nature of the contact, suggested by the GammaRay Logs, results from a gradual change in the sedimentary environment which prevailed during the deposition of the Muskwa and the lower port of the Fort Simpson Formation. The Muskwo thus constitutes a bosal unit of the Fort Simpson Formation and QS such it is appropriate to consider it either as a member of the Fort Simpson Formation or as anindependent formation. It is proposedhere that the unit should be given formational status. This course is thought preferable to maintaining the memberstatus of the Muskwa with transferto the Fort Simpson Formation, because future studiesmay again result in a modified interpretation of the unit and in such circumstances reclassification will be unnecessary if the formational status is adopted.

46 GEOLOGICAL HISTORY

Prior to the deposition of the Slave Point Limestone the area uncler consideration hodbeen subjected tofluctuoting conditions, which resulted in the deposition of orgilloceous sediments andevaporites in the eost andlimestone and dolcmitebreccias together withboth fine and coarse clastic deposits in thewest. These sediments form the Watt Mountain-upper Sulphur Point-Fort Vermilion assemblage. This phase of sedimentation wos followed by CI marked change in environmental conditions md waters of normol solinity spread eastward over oreas in which evaporitic sedimentationhad previously been dominant. This in turn resulted in the eostword migration of the stromoto- poroidbiota which hod previously been restrictedto areas ofreef devehpment in the west. Foro relotively brief period corbonate redimentotion prevailed over o very broad shelf occupying northeasternBritish Columbia, northern Alberto, andthe adjacent part of the Northwest Territories. Regionol tectonic movements probably accompanied by climatic changes (these moy have been more profound thon the former) then brought obout changer in the sedi- mentory pattern which were eventually to lead to the almost complete destruction of the stromaloporoid biota in the area being considered.Prior to this culminoticm, however, ports of northeastern British Columbia and northwestern Alberta were the site of prolific orgonic activity occompanied by corbonote sedimentotion. These processes were especially marked along o linetrending approximately north-northeastthrough northeastern BritishColumbia. To the west of thisline, heretermed the faciesfront, argillaceous sedimentation wos dominant. During this phase of limestone deposition argillaceous sediments 01 the Beover- hill Lake Formotion gradually spread westward, resulting in the replacement of the Slove Point biota with one more suited too muddy environment. Finally, ot som time during the Upper Beoverhill Lake the orgilloceous material covered much of the urea in which limestonesedimentation had previously prevailed thus effectivelybringing an end to Slave Point deposition. In the fino1 stages of the Beaverhill Lake transgression it is possible that argillaceous sediments were deposited over the whole of the orea under consideration, but proof of this has been destroyed by the post-Beoverhill Lake erosion. At the end ofBeoverhill Laketime uplift took placein northeasternBritish Columbia and in the northwestern port of Alberto. The erosion which followed was more severe in the north ond as a result the Slave Point Formation was exposed and subjected to subaerial erosion north of about latitude 58 degrees 30minutes north in Lkitirh Colum- bia. Following this period of erosion submergence again took place and the: dark radioactive sholes of the Muskwo Formation were deposited over an area extencing from iust north of the present Peace River to the Northwest Territories and beyond. The deposition of the Muskwcr markedthe beginning of a newphase of sedimentation in which a thick sequence of orgilloceous deposits (the Fort Simpson Formotion) wos laid down over much of northeastern British Columbia and northwestern Alberta. Post-depositionol changes resulted in the dolomitization of parts sf the Slow PointLimestone and in the accumulation ofnaturol gas in thevuggy sec,mdary rock. Themost extensive dolomitization occurredalong the facies front. The fuciescontact probably provided a passage for migrating fluids which played an important part in the recrystallization process. Some of these migrating fluids were no doubt folced by compaction from the great body of sholes lying to the west of the facies front. The naturol gas which occumuloted in the secondary dolomites was probably derived fmm the Slave Point Limestone itself. The abundance of fossils and carbonaceous moterial in the limestone supports this conclusion.

47 The Slave Point Formation was also dolomitized in areas lying ot some distance from the facies front. In these instances,however, the dolomitization is not as extensive as that associated with the focies front. The cause of dolomitization in areas away from the facies front is not known with any degree of certainty but it may be associated with zones of faulting.

48 GAS IN THE SLAVE POINT FORMATION OF BRITISH COLUMBIA

At the present time there are three fields in northeastern British Colrmbia cop- able of producing gas from the Slow PointFormation. From north to south they are the Petitot River, Kotcho Lake, ond ClarkeLoke fields (see Fig. 13). The reservoirrock in these three fields consists lorgely of the white and greydolomite of the facier front. In additionto thedesignated fields there are numerous other areas in which m:ommerciaI quantities of gas have been obtained from the Slave Point Formation. Most 0: these are associated with the dolomitized rocks of the facies front; some however, are osrociated with dolomitized sections of the Slave Point lying to the east of the facies front. Wells capable of producing gas from the two different geological environments are listed and identified by distinctive symbols in Appendix I. They are a110 shown in the Slave Point isopach map of Figure 3. The estimated gas reserves of the Slave PointFormation at January I, 1963, were approximately two trillion cubic feet.* No Slave Point gashas been pr'3duced because the areas of potential production hove not yet been tied into the provincial pipe- line system. Groy ond Kassube (1963) recently gave o full account of the Clarke Loke gar field The dolomite reservoir at Clarke Lake is of sinuous form, being approximately 1;

1 Figure 13.--Mop showing Slave Point gas fields of northeartern British Cdumbio at January Ist, 1963 and lines of Sections NO, PQ, ond RS.

49 *Departmental estimate of established disposable gar. 12 3 4

SULPHUR POINT

Figure 14.--Cross section NO--Clarke Lake field. Line of section is shown in Figure 13. Wells shown in section: (1) West Not et 01 Fort Nelson c-70-1 (94- J-10). (2) West Not et 01 Clarke b-70-1 (94-J-IO). (3) West Not et .I Clarke c-78-1 (94-J-10). (4) Gulf States-Imp Clarke L c-64-1(4) (94-J-IO). (5)West Not Imp Clarke Laked-88-L (94-J-9). (6)West Not Imp Clarke Lake c-8-D (94-J-16). (7) Gulf StatesImp Clarke L b-18-D (94-J-16).

DATUM 4500FT BELOW SEALEVEL

I Figure 15.--Cross sectionPQ--Kotcho Loke field. See Figure 16 forlegend. Wells shown in section: (13) Gulf States Kotcho Lake No. 2 d-79-K(94-1-14). (14)West Not KotchoLoke c-67-K (94-1-14). (15) West Nat Kotcho b-54-K (94-1-14). (16) West Nat KotchoLoke d-39-J (94-1-14).

50 mileswide, more than 20 miles in lengthand reaching 360 feet in thickness (see- Fig. 14). A gas/water contact has beenestablished at 5,230 feetbelow seo lev,?l. Thegos in theClarke Lake andother Slove Point fields is of the sweet, drytype. Carbon di- oxide and nitrogen ore the main secondary constituents of the gas. The discovery well of the Kotcho Lake field is West Not Kotcho I.ake c-67-K (94-1-14). It was completed on February 27. 1959.Three wells capable of production now lie in the field area. However, there are indications that several wells to the north hove penetrated the same producing zone. As in the previous cme the rese.voir consists of the white and grey dolomite, but the form of the reservoir doer not appar to be os simple os that of the Clarke Lake field (see Fig. 15). Although it irposriblt: that a con- rideroble intervol of the white and greyzlomite is developed right ot the facies front, wells which ore interpreted CIS being a short distance to the east of the fro,,tshow the development of thinner sections of dolomite which lie at various depths within the Slove Point Formation. It seems probablethat the producing zone, although well dev&ped ot the focies front, extends eastwards from the front as a series of thinner dolomitic tongues. A maximum of 120 feet of gross pay has been recognized in the field. At the present time the depth of the gas/woter contact has not been established with certS3inty but is believed to lie at approximately 4,660 feet below sea level. The Petitot River field lies close to thenorthern border of the provinceand currently contains three wells capable of producing gos from the Slave Point Formation (see Fig. 16). The discovery well is West NotPetitot Riverd-24-D (94-1'-13) which wascompleted on March 13,1959. It is probablethat the well, PanAm et aI Dilly a-30-K (94-P-12) which lies iwt 2 miles south of the field also produces from the same reservoir. Thegross pay in the field reaches142 feet in thickness andthe gor/water

Figure 16.--Cross section RS--Petitot River field. Line of section is hwnin Figure 13. Wells shown in section: (8) PanAm Philira-65-G (94-0-115). (9) West NotPetitot Riverd-24-D (94-P-13). (IO) West Not Petitot River b-I-D (94-P-13). (11) West Not Petitot b-90-K (94-P-12). (12) PanAm et t~lDilly a-27-K (94-P-12).

51 contact has been established ot 5,167 feet below reo level. Production is from dolomitized rocks ofthe facies front and there is reason tobelieve thot the reservoir is of linear formnot unlike thot of the Clarke Lake field.Potential SlavePoint production also associated with the facies front hos been found 12 miles north of the Petitot field in the Cam Lake oreo and 18 miles south of the field in the Tseo oreo. A smallomount of natural gashas beendiscovered in dolomitized sections of the Slave Point Formation lying to the east of the facies front. As indicated previously the dolomite of these areos is referred to as shelf dolomite. Examples of wells penetrating the shelf dolomite which are capoble of production are HB Imperial Union Paddy 0-49-6 (I) (94-H-16) ond BA Shell Klua Creek a-50-C (I) (94-J-9). There ore some cases in which it is difficult to be certain whether one is dealing with production fromthe focies front dolomite or the shelf dolomite. In these in- stancesthe well is so placed that the dolomitization could be explained satisfactorily by the assumption thot the well lier on on indentation of the facies front and the dolomite in question is ofthe facies front type, or bythe assumption that the well lies to the east of the front and the dolomite is of the shelf type (in Appendix I the designotion of the dolomite type in these wells is followed by o query). This situation will be resolved only by further drilling which will enable the configuration of the facies front to be established with certainty. Duringthe 1961-62 drilling season several wellsdrilled to the south of the Kotcho Lakeoreo encountered varying amounts ofdolomite in theSlave Point Farm- otion, butthey did not obtain commercial quantities of natural gas. As in the case of the potentially productive wells just discussed the location of these wells is such thaf it is difficultto classify them withcertainty as eitherfacies front or shelf dolomite wells.In this study theyore tentativelyclassified in thelatter category (see- Fig. 3 and Appendix I). Assuming thenthot the shelf dolomite is notuncommon and bearingin mind thatcommerciol quantities of gas havealready been obtained fromthis dolomitein severalwells, it is reoronableto conclude that the shelf dolomite offers an important second source of natural gas which will supplement the prolific reservoirs of the focies front. It is apparent,however, that seismicmethods will not be os eosilyadopted to finding theshelf dolomite os theyare to locating the facies front. No doubtother techniques will haveto beused inaddition to theseismic surveys in order tolocate fovourable areas for the development of this potentially productive dolomite.

52 REFERENCES kales, F.W. (1963): "Baldness of bedding surface,"Am. Assoc. Pet. Gc:ol.,- Bull., Val. 47. No. 4.. ,,DO. 681-6236, klvea.,. H.R. (1952): "Notes on the Devonian Svstem of the north-centralDlains of Alberta," Geol. Surv., Canudu, Paper 52-27. klyea, H.R. and Norris, A.W. (1962): "Middle Devonianand older Pal<~eozoic formotions of southern District of Mockenzie and adjacent areas," Geol. Surv., -Canada, Paper 62-15. Cameron, A.E. (1917): "Reconnaissanceon Great Slave Lake, Northwestlerritories," Geol. Surv.,Canoda, Sum. Rept., 1916, pp. 66-76. (1918): "Explomtions in the vicinity of Great SlaveLake," -Geol. Surv., -Canada, Sum. Rept., 1917, Pt. C, pp. 21-28. (1922): "Hay and &Iffalo Rivers, Great Slave Lake, and adjacel?t country," Geol. Surv.,Canada, Sum. Rept., 1921, Pt. B, pp. 1-44. Campbell, N. (1950): "The Middle Devonian in the Pine Point area, N.W.T.," Proc., Geol. Arsoc.Canada, Vol. 3, pp. 87-96. (1957): "Stratigraphyond structure of Pine Point areo, N. W. T., I' in StructuralGeology of Canadian Ore Deposits, Vol. II, 6thmmonweolth Mining and Metallurgical Congress,Canada, pp. 161-174. Carozzi, A.V. (1960): Microscopic sedimentarypetrography, John Wile;{ and Sons, New York. Carrigy, "Geology the McMurroy Formation, Pt. Generol geology -. M.A. (1959): -, of Ill: - -. of the McMurray area," Res. Coun. Alberta, Mem. I. Crickmay, C.H. (1957): "Elucidationof rome Western Canada Devonianformations," published by the author, Imperial Oil Ltd., Calgary. Douglas, R.J.W. (1959): "Great Slaveand Trout River mop-areas, NorthwestTerrit- orier (85 Si and 95A, H)," Geol. Surv.,Canada, Paper 58-11, Fairbridge, R.W. (1950): "Recent and Pleistocenecoral reefs of Austr~~lio,"Jour. -Geol., Vol. 58, No. 4, pp. 330-401. Folk, R.L. (1959): "Practicalpetrographic classifications of limestones," Am. Pet. Geol., Bull., Vol. 43, No. 1, pp. 1-38. (1962): "Spectml subdivision of limestonetypes." Am. Asroc. l'et. Geol., Mem. 1: Classification of carbonate rocts, edited by W.E. .Ham, pp. 62-84. Fong, G. (1960): "Geology of Devonian Beoverhill Lake Formation. Swan Hills area, Alberta, Canada,"Am. Asroc. Pet. Geol., Bull., Vol. 44, No. 2, pp. 195- 209. Gallant, B.T. (1962): "Brief notes on the Lower Palaeozoic rocks of the RDcky Moun- tainsalong the Peace River, B.C.,"Edmonton Geol. SOL., FourthAnnual Field Trip Guide Book, pp. 102-108. Galloway,J.J. (1957): "Structureand classification of theStromotoporoidea," -Bull. Am.Poleont., Vol. 37, No. 164, pp. 345-480. Govett,G.J.S. (1961): "Occurrence andstratigraphy of somegypsum and anhydrite deposits in Alberta," Res. Coun. Alberta, Bull. 7. Groy, F.F., Kossvbe,J.R., andVan deVenter, J.H. (1962): "Devonian $gasexplora- tionin northeasternBritish Columbio: aeoloav. ODerations and t:conomics." ~ -. . Jour.Con. Pet. Tech., Vol. 1, No. 4, pp. 175-lh. Gray, F.F. ond Kassube, J.R. (1963): "Geology andstratigraphy of Clarke Lake gas field, northeastemBritish Columbia," Am. Assoc.Pet. Geol., Bull., Vol. 47, No. 3, pp. 467-483.

53 Hadding, Asrar (1941): "The pre-Quarternarysedimentary rocks of Sweden, VI, reef limestones," Lunds Univ. Arssk., New Ser., Pt. 2, Vol. 37, No. IO. Henson, F.R.S. (1950): "Cretaceous and Tertiary reef formations ond associated sediments in Middle East," Am.Asroc. Pet. Geol., Bull., Vol. 34, No. 2, pp. 215-238. Hunt, C.W. (1954): "Norm01Devonian sequence in southern Mackenzie basin, west- ernCanada," Am. Assoc.Pet. Geol., Bull., Vol. 38, No. 11, pp. 2290- 2301. Koch, N. G. (1962): "Correlation of theDevonion Swon Hills Member, Alberta," Abstract of M. Sc. Thesis, Universityof Alberta, 1959, inAlto. Sac. Pet. -Geol., Jour., Vol. IO, No. 11, p. 621. Law, J. (1955):"Geology of northwesternAlberta and adjacent areas," Am. Assoc. Pet. Geol., Bull., Vol. 39, No. IO, pp.1927-1978. Leighton, M.W. andPendexter, C. (1962):"Carbonate rock types," Am. Assoc. Pet. -Geol.,Mem. 1: Classificationof corbonate rocks, editedby W. E. Ham, pp. 33-61. Link, T.A. (1950):"Theory of transgressive andregressive reef (bioherm) development and origin of oil," Am. Assoc.Pet. Geol., Bull., Vol. 34, No. 2, pp.263- 294. Loranger, D.M. (1963a): "Devonianmicrofauna fram northeasternAlberta, Port I: Ostracodo,Orders Leperditicopido and Paloeocopida," published by the author,Calgary, Alberta. (1963b): "Devonianmicrofauna fromnortheastern Alberta, Part 2: Ostra- coda, Order Podocapida," published by the author, Calgary, Alberta. McGill, P. (1963): "Upperand MiddleDevonian ostracodesfrom the BeaverhillLake Formation, Alberta, Conada," Can. Pet. Geol.,Bull., Vol. 2, No. 1, pp. 1-26. Nelson, H.F.,Brown, C.W.,and Brineman, J.H. (1962): "Skeletallimestone classification," Am. AS50C. Pet. Geol.,Mem. 1: Classificationof corbonate rocks, edited by W. E. Horn, pp. 224-252. Norris, A.W. (1963): "Devonianstratigraphy of northeostern Alberta and northwestern Saskatchewan," Geol. Surv., Canada, Mem.313. Warren, P.S. (1933): "The age ofthe Devonian limestone atMcMurray, Alberta," Can.Field-Naturalist, Vol. 47, No. 8, pp.148-149. Warren, P.S. andStelck, C.R. (1962): "WesternCanadion Givetion,"Alto. Sac. Pet. Geol., Jour., Vol. IO, No. 6, pp.273-291.

54 APPENDIX I

List of British Columbio wells showing the depths ot which the following units werepenetrated: Muskwo, Beaverhill Lake, Otter Park, SlavePaint, WottMountain- Sulphur Point. Depths are given in feet below K.B. except for Sinclair wells where the depths are quoted in feet below ground level. All wells which were available at Janu- ary 1, 1963, and which definitely penetratedone or more ofthe above unitsare included. Wells lying in the west of the area of study in which these units are replaced by the Besa RiverShale and wells to the south which lie beyondthe pinch wtof the units are not included.

ABBREVIATIONS

K.B. Kelly Bushing MU Muskwa 6h.L. Beaverhill Lake OP Otter Pork SP Slave Point WM-SUP Watt Mountain-Sulphur Point

* Inthis column Sh indicatesthat the top of theWatt Mountain-Sulphur Point is pickedon the first occurrence of greenwaxy shale; CI indicates that the pick is basedon the first occurrence of sandstone near the bore of the Slave Paint; C indicatesthat thetop is establishedby correlation with adjacent wells basedon thickness, log cbracters, andgeneral lithology. Number of wells in wtlich tap is established by the various means is as follows: Sh - 30; CI - 6; C - 35. f In this column Fd indicatesa well close tothe facies front in whichthe Slave Point is completely or partlydolomitized. Dd indicatesa well distantfrom the faciesfront inwhich theSlave Point is dolomitized,usually only in part. The dolomite of these wells is referred to in the text as the shelf dolomite.

# In this column G indicates that the well is classified as a well capoble of producing gas from the Slave Point Formation.

** Indicates true vertical depth in the case of an inclined hole.

55 WELL NAMELOCATION AND K.B. M" Bh.L. OP WM-SUP * T.D.

Southern Production Atlantic 87-1 12-33-85-16W6 2317 9780 ? ? 10917 Imperial-Pacific Siphon Creek 1-26-86-16 W6 2415 9900 ? 10145 ? 10913 Tenaco N.F.A. Lo Gorde 7-21-87-15 W6 (2) 2532 9808 9828 10010 ? 10740 Texoco N.F.A. Buick Creek d-98-1 (I) 94-A-I 1 2324 10320 10360 10600 10720 CI 1 I424 Sincloir-Canadian Atlantic #B-8-1 d-43-C 94-A-16 9518 9550 9790 ? 9880 CI 10447 Sinclair Julienne a-50-D (813-2) 94-G-1 3718 I2790 12825 12990 13290CI 13734 Dome et 01 Stonolind-Buckinghorre #I d-95 -H 94-G-7 2825 10200 10260 10330 10680 Sh I0949 Sinclair-Canadion Atlontic XB-3-1a-23-E 94-G-10 11441 1 Islo 1 1620 Dd? 12000 CI 12450 Phillips Minaker a-25-D 94-G-15 2582 9420 9500 9548 Dd? 9950C I I361 Texaco N.F.A. Nig Creek a-79-8 (I) 94-H-4 2984 10678 10710 10930 Dd 11215 c 1 I999 Sincloir Pac Chinchoga 0-34-L (89-1) 94-H-8 3087 8950 9050 94w ? 9725 CI 9858 HB Union Chinchoga 0-96-C 94-H-9 2404 7878 7920 8222 a485 c 8739 HB Imp Union Gutah o-99-K Y4-H-10 2136 7740 7820 7970 8220 Sh 9213 Texaco N.F.A. Beotton River #2 b-27-8 94-H-ll 278 1 9082 9123 9310 9570C I0445 Triad BP Conroy Creek c-100-A 94-ti-I2 2512 9004 9053 9190 9550C 9896 HB Imperial Union Paddy a-49-B (1) 94-ti-16 2371 7490 7549 G7835 Dd 8100 Sh 10034 01 HB-Union-ImperialPaddy #2 c-74-8 94-H-16 2408 7480 a 7558 7837 Dd 8090 Sh 8216 HB-Union-ImperialPoddy c-14-C 94-H-16 2254 7405 7500 7780Dd 8030C 8131 Pure ImperialBigfoot d-27-C 94- 1-4 2129 7910 7975 8014 8390C 8471' Imperial Sikanni Chief #I b-92-D 94-1-4 1920 7540 7608 7750 8090C 9930 Imp Fontas d-37-8 94-1-7 1461 61 50 6255 6330 Dd 6630C 7636 Imperial Kohntoh #I b-29-C 94-1-7 1434 6180 6280 6343 6653 c 8439 Texoco N.F.A. Hoy River #I d-22-B 94-1-9 1272 5308 5400 5490 5750 Sh 7409 Texoco N.F.A. Townroitoi d-44-C 94-1-10 1314 5785 5853 5890 Dd 6190C 6959 Sohio ChE Ekwon 0-55-G 94-1-10 1239 5625 5705 5740 Dd 6050 ? Imp Junior c-98-C 94-1-11 1465 6100 6177 G 6207 Dd? 6500 Sh 6632 Imp Kyklo b-73-F 94-1-11 1381 5885 5950 6272C 7914 Dome et CII Elleh a-14-E 94-1-12 I486 6418 6484 6502 6880 Sh 7296 Mobil W Sahtaneh d-86-1 94-1-12 1622 6315 6408 6650 ? 6750C 8261 Mobil W Sohtaneh c-89-1 94-1-12 1613 6290 6381 6700C 7650 Pacific Utahn b-83-C 94-1-13 1694 6555 6.548 8230 West Not et al Yoyo a-74-H 94-1-13 1895 6493 6562 G 6608 6790 Sinclair Pacific Lichen d-31-A 94-1-14 1595 6040 6095 Dd? 6270 Sh 64 70 Sinclair Pacific Lichen c-41-A 94-1-14 5970 6028 6310 West Not Kotcho Lake d-39-J 94-1-14 201 1 6350 G 6410Fd 66W Sh 841 3 West Not Kotcho b-54-K 94-1-14 2030 6430 G 6490 6630 WELL NAME AND LOCATION K.B. M" Bh.L. OP WM-SUP * T.D.

West Not Kotcho Lake c-67-K 94-1-14 2073 6480 G6570 Fd 6702 (Gulf Stater) Kotcha Lake No. 2 d-79-K 94-1-14 2138 6550 6630 6828 c 7240 Sinclair et 01 Dotcin b-46-G 94-1-15 161 1 5770 5862 5880 Dd 6135 CI 6306 Sincloir et 01 Dotcin 0-54-G 94-1-15 5740 582 7 5960 Texoco N.F.A. Walrus b-864 94-1-16 1753 5700 5775 5805 6120 Sh 6501 Pure Imperio1Bull b-67-J 94-J-1 1970 7343 7420 7440 7890C 8271 Sinclair Poc Klua Ck a-55-L (811-1) 94-J-1 2440 8070 8140 8198 8550C 8614 (Phillips) Tenako No. 1 b-91-L 94-J-2 1830 73 75 7480 7690 Dd? 8000 c 9220 Pure Pacific Tenaka c-94-L 94-J-2 1867 7535 7620 7825 8110 c 8472 Triad et 01 Jockfirh c-13-1 94-J-7 1800 6880 6955 71 35 7365 Sh 7770 Wmdley-Imperial Kluo a-27-G 94-J-8 1608 6764 6840 6858 7300 Sh 7630 Triod Sohio Poc Jockfirh a-30-K 94-J-8 1668 6720 6790 G6980 7190 Sh 743 I B.A. Shell Klua Creek a-50-C (I) 94-J-9 1556 6470 6570 G6770 Dd 7030C 8893 B.A.Shell Klua b-49-F 94-J-9 1383 6260 6310 6320 6775Sh 7972 B.A.-Shell Klua Creek No. 2 a-56-H 94-J-9 1490 6432 6520 6720 6800 C 7400 West Not Imp Clarke Lake b-78-J 94-J-9 1309 6100 ? G 6205 6520 5 Gulf StatesImp Clarke Lc-75-K (3) 94-J-9 1329 6222 6340 6650C 7400

West Not Imp Clarke Lake d-88-L 94-J-9 1 364 6260~~ G6357 Fd 6443 West Nat Imp Clarke Lake d-91-L 94-J-9 1366 6185 G 6290Fd 6550 West Not Imp Clarke Lake c-94-L 94-J-9 1372 6233 G 6355Fd 6700 C 8039 Pacific S Ft. Nelson b-96-B (I) 94-J-IO 1605 64 70 6530 7020 Sh 7477 Apache Pacific Fort Nelron a-91-C 94-J-IO 1609 6575 6640 7130? Sh 7560 Pacific Fort Nelson No. 2 a-19-G 94-J-IO 1619 6504 6550 ? 6580 7050C 7480 Pacific Fort Nelson a-44-G (3) 94-J-IO 1533 6528 662 1 6990 Sh 7595 Pacific Apache Fort Nelson b-76-G 94-J-IO 1516 6350 6420 G 6618Fd 6691 Apache Pacific Fort Nelson d-76-G 94-J-IO 1457 6545 6635 7078 ? 7265 Gulf Stater-Imp Clarke L c-64-1 (4) 94-J-10 1310 6193 6290 6655 Sh 7316 West Nat et (11 Clarke b-70-1 94-J-IO 1309 61 18 G 6205 Fd 6422 West Nat et 01 Fort Nelron c-70-1 94-J-IO 1298 6354 6430 6aa7 c 6950 West Nat et CIIClarke c-78-1 94-J-IO 1295 6054 G 6152Fd 6533 West Nat et 01 Fort Nelson d-38-J 94-J-10 1357 6430 6547 7043C 71 03

West Not et 01 Clarke c-47-J 94-J-IO 1343 6282 6390 G 6510Fd 6750C 6957~~ West Not et aI Clarke a-52-J 94-J-IO I328 6205 6288 G 6315 td Gii Gulf Stater Fort Nelson No. 2 a-55-J 94-J-10 1299 6470 6630 7889 Pure Poc Chever c-5-A 94-J-1 I 1776 7385 7466 7940Sh 8596 West Not et aI €vie Lake b-85-H 94-1-14 1948 6510 G6566 6866C 7720 WELL NAMELOCATION AND K.B. M” 8h.L. OP SP j WM-SUP * T.D.

West Nat et 01 €vie Lake b-89-E 94-J-15 1943 6496 6555 6930 C 8240 West Not et 01 €vie d-14-F 94-J-15 1728 6550 6610 6985 C 7925 West Not Imp Clarke Loke c-8-0 94-J-16 1380 6150** G 6270Fd** 6650** Gulf Stater-Imp Clarke L b-18-0 (5) 94-J-16 1379 6258 6372 6716 C 7405 PanAm et (11 A-I Snake River c-28-0 94-0-1 954 6370 6550 7614 Pan Am East Poplar 0-37-F 94-0-2 1224 6780 ? 6890 8139 Pan Am A-1 Corn Lake a-31-1 94-0-16 I494 6710 6750 7000 Sh 7500 TGT Tooga Loke c-27-K 94-P-2 2103 6180 6248 62 70 6610 Sh 6725 Pocific North Kotcho b-44-C 94-P-3 2160 6505 G6589 Fd 6800 Sh 6835 Pocific North Kotcho d-85-C 94-P-3 2190 6605 66 70 7020 Sh 7500 Pacific North Kotcho c-93-C 94-P-3 2153 6500 6572 6920 Sh 7m Gulf Stater Kathy o-34-E (I) 94-P-3 2228 6890 6980 7125 Fd 71 50 West Not Kotcho 0-94 94-P-3 2191 6585 6656 6820 Sh 6966 Atlontic Pac North Kotcho c-22-F 94-P-3 2147 6500 6556 6900 SH 7023 West Not Kathy b-30-F 94-P-3 2196 6600 G 6670Fd 6785 Atlontic Poc E Kotcho b-19-G 94-P-3 2070 ? 6485 6830 C 7072 % West Not Lesellen b-75-F 94-P-4 1741 6820 6950 7796 Texaco N.F.A. Trea b-68-K 94-P-5 2070 6780 G 6875Fd 71 IO Texoco N.F.A. Judy c-53-D 94-P-6 2206 6525 6tQO ? 6685 7000 Sh 7327 Texoco N.F.A. Thetloondw No. I c-40-G 94-P-6 1945 6270 6353 6700 C 8080 Pan Am A-I Kimeo Loke a-28-H 94-P-9 1733 5430 5515 5720 C n57 Pan Am July 0-65” 94-P-9 1544 5350 5427 5700 C 691 3 Texaco N.F.A. N Trea d-47-C 94-P-12 1574 6 770 6860 7116 Sh 8320 Pan Am et (11 Dilly a-27-K 94-P-12 I677 6550 6586 6868 Sh 71 54 Pan Am et 01 Dilly o-30-K 94-P-12 I724 6705 6740 ? G 6803Fd 6900 West Not Petitot b-90-K 94-P-12 I539 6575 G 6680Fd 6732 West Not Petitot River 0-81-L 94-P-12 1539 6550 6696 Fd 6720 West Nat Petitot River b-I-D 94-P-13 1 534 6460 G 6536Fd 6628 West Not Petitot River d-24-D 944-13 1503 6442 G 6520Fd 6680 Pan Am Corn Lake c-25-L 94-P-13 1496 6490 ? 6518 6780 Sh 7090 APPENDIX II

CORE DESCRPTIONS

The wells ore arranged in alphabetical order. All depthsare quoted in feet. Core recovery is complete, or almost so, unless othemise indicated. Wherethe size of the constituent allochems of limestones is referred to as either fine, medium, or coarse grained, it can be assumed that the allochems in question belong to the arenaceous size class.

BA Shell Klua b-49-F Location:b-49-F/94-J-9 Status: abandoned K.B. 1,383 T.D. 7,972 Completed: March, 1962 SlavePoint core: 6,475-6,585 (Recovery: 97 feet) SlavePoint top: 6,320 Base: 6,775

UPPER INTERVAL: 6,475-6,520. This interval consists of organisms of vurioustypes set in a matrix of dark brownish grey calcilutite. Much of the biogenic material appears to be fragmented. The dark calcilutite is generally unresolved at x 30, but in some instances suggestions of fine to mediumgrained intraclasts can be seen in a micritic motrix. The biogenic material consists of: a. Veryabundant Thamnopora. b. OccasionalAmphiporo. c.Large ramose stromatoporoids. d. Laminarstromatoporoids varying from '2 millimeters to 2 centimeters in thickness. These structures reach the full diameter of the core (3.5 inches); they ore usually flatbut sometimes undulating,and are parollel or slightlyinclined lo the horizon toI. e.Nodular stromatoporoids, 1-3 centimeters across,sometimes withirregular growth forms; usually showing reticulate structure. f. A verylarge, massive stromatoporoidoccurs in theupper 5 feetof the interval. It occupies 22 inches of the core. g. Occasionolsolitary corals. h. Occasionalcrinoid fragments. i. Smallfragments ofbrachiopod shells recrystallized to o light colouredtranslucent calcite. The fragments are usually about 0.2 millimeter in thickness and range up to 5 millimeters in length.

LOWER INTERVAL: 6,520-6,585. This interval is mode up of stromatoporoid material of various types set in a matrix of dark calcilutite; in ports intramicrites and intrasporites (?) are developed. In the upper half of the interval nodular stromatoporoids ore common and in places they attain a diameter of 5 to 6 centimeters. Massive stromatoporoids olso occur. Parts of the rock contain various types of shell fragments replaced by translucent calcite; in some instances the translucent calcite is seen completely surrounding a central nucleusapparently consisting ofmicrite. Encrustingstromotoporoids surrounding specimens of Thamnopora are present in the upper part of this interval. In the lowerhalf of the intewal(approximately 6,555-6,585) Amphiporo is common; the coenostea are of small size, rarely reaching more than 2.5 Zllimeters in

59 diameter. Nodular ond occasional massive stromatoporoids are also present in the rock. Patches of coarsely crystalline sporry calcite are present in parts of this section of core, most ore less than 1 centimeter ocross. Minor incipient dolomitizotion occurs in places.

HB Imperial Union Paddy 0-49-6 (I) Locotion: a-49-B/94-H-16 Status: Gas wellin SlavePoint Formation K.B. 2,371 T.D. 10,034 Completed:August, 1955 Beoverhill Lokecore: 7,825-7,835 Beoverhill Loke top: 7,549 Base: 7,835

Core consists of mediumdark grey, slightly calcareous tovery calcareous shale. Moderate amounts ofpyrite occur in therock usuolly as crystalsoveraging about 0.5 millimeter across; some, however, reach 2 millimeters in moximum dimension. The corebreoks into blocks which show irregularfracture surfaces. In thelower 18 inches of the interval recovery is very poor and the contact with the Slove Point Lime- stone appears to be lost.

SlavePoint core: 7,835-7.865; 7,950-7,990 SlovePoint top: 7,835 Bore: 8.100

FIRST SLAVE POINT CORE: 7,835-7,885. The upper port (7,835-7,865)of this section consists of brownishgrey to darkbrownish grey calcilutitecontaining very abundant biogenicmaterial. The latter is mostlymedium brownish grey incolour and consists largely of massive, nodular and ramose (including abundant Amphipora) stromatoporoids. Thomnopora olro occurs. Much of thestromotoporoid moteriol is recrystoilized to dense biogenic colcite. Crinoid (?) ossicles reaching up to 6 millimeters in diameterare abundant in some intervals. Brachiopods ore also presentbut they ore only a minorelement in the totalfauno. Carbonaceous material is common in parts of thematrix. In placesthe matrixcalcilutite grades intointramicrites and intrasparites;the former are the most common intmclast rocks represented. The lower part (7,8657,885)of this interval is darker in colour than the inter- voI above and contains less biogenic material. The dominant rock type is dark brownish grey calcilutite. In plocesintramicrites and fine to medium grainedintrasparites with Colcisphaeroore developed. Moderate amounts of stromotoporoidsoccur; they are mainly of the smaller ramose type. Carbonaceous material is common in parts.

SECOND SLAVE POINT CORE: 7,950-7,990. This interval consists mainlyof brownish greyto brownish blackcolcilutite containing moderatelyabundant stromatoporoid material, medium brownish grey in colour. Massive, nodular and ramose stromatoporoids includingAmphipom are present in therock. Brachiopodsoccur occasionallyin the calcilutite. Carbonaceous material is present invarying amwnts throughoutthe interval. In theintervol 7,956-7,957 thelimestones hove been olteredto a uniformly pigmented,dark brownish grey, medium crystallinedolomite. Darkbrownish grey fine to medium crystolline dolomite olro occurs at 7,964 ond 7,969 feet. Incipient dolomitization is evident in other ports of the core. Well developedintrosparites occur in theinterval 7,983-7,990. The intraclasts of these rocks ore irregular in shape and ovoid, rectangular, and triangular forms ore present; they ore rounded in outline. The introclosts vory in diameter between 0.12 and 0.5 millimeter (fine to medium grained). 08litesond superficiol oolitesore present 60 in some of these introsporites. A well developedAmphiporo biosporite oc8:urs in the interval characterized by the presence of introclast rocks.

HB Imp Union Gutoh 0-99-K Locotion: 0-99-K/94-H-10 Stotus: abandoned K.B. 2,136 T.D. 9,213 Completed: March, 1962 SlavePoint core: 8.036-8.164 (Recovery: 112 feet) SlavePoint top: 7,970 Base: 8,220

UPPER INTERVAL: 8,03643,060. This interval consists mainlyof dork bro,.vnish grey to brownish block calcilutites which contoin abundant stromatoporoids (mainly w- E). The colcilutite is quite carbonaceous. There ore subordinateoccurrences of ramose stromotoporoids other thon Amphiporo. Nodular stromotoporoids OIYI occur. The matrix rock, in generol, is unresolved at x 30 of the stereoscopicmicroscope; in ports there ore vogue suggestions of included introclasts. It is of interest to note that in this section the Amphiporo ore consistently of small size, being 1 to 3 millimeters in diometer, whereas stromotoporoids of other genera of the Idiostromotideo present in the rock ore mostly between 4 and 6 millimeters in diometer.

CENTRAL INTERVAL: 8,060-8,140. This centrolsection of theSlave Point core grodes frombrownish blockto mediumbrownish grey incolour. Dorkstromotoporoid- bearing calcilutites moke up most of the section. However, the most notable feoture of the interval is the common occurrence of intraclost rocks. The introclasts belong to the fine ond medium orenoceous size classes. Few of the rocks con be definitely soid to be introsporites ond most would foll into the intrasporite-intromicrite classificatilm. Between 8.081 and 8,083 there is on intromicrite-intrasporite contoining abundant Colcisphoero, most of which are opproximotely 150 microns in diom,ater. The peripheral spines con be seen in some instonces. At 8,102 there is an occurrence of o biosporite containing abundant foraminifera up to 2 millimeters across and broken shell fragments (brachiopods 7) up to 5 millimeters in length. Brachiopods occurrporodicolly in thecentral interval of the Gtrtoh core. Stromotoporoids ore common; massive types reaching the full width of the corm?, nodular forms 3 to 5 centimeters in diometer, large ramoseforms and Amphiporo ore 011 represented. There ore subordinate occurrences of lominorstromatoporoids, some of which reach several centimeters in thickness ond occupy the full width of the core. The tabulate coral Thomnoporo is olso present.

LOWER INTERVAL: 8,140-8,164. The lowerinterval of the Gutohcore consists moinly of the dark stromotoporoid-bearing colcilutite. Various types of stromotoporoids ore present ond massive ond nodulor forms are in evidence; however, Amphiporo appears to be the dominant type. Thomnopora is present in ports. Incipient dolomitization is evident in thelower IO feet of thecore. In parts of this lower interval smo11 dork brown crystals of fluorite are present in the limestone.

HB Union Imperio1 Poddy #2 Locotion: c-74-0/94-H-16 Status: abandoned K.B. 2,408 T.D. 8,216 Completed: Morch, 1958 Beoverhill Lokecore: 7,822-7,837 Beoverhill Loketop: 7,558 hse: 7,837

61 This interval consists of mediumdark grey, colcoreous shale which grades in parts tonon-colcoreous shale. Occasioml brachiopods occur in therock. Minor amounts of pyrite arepresent in theshale. The contactbetween the Bwverhill Lake Shole and the Slave Point Limestone does not oppwr to be preserved in the core.

SlavePoint core: 7,837-7,864; 7,866-8,001 (Recovery: 130 feet) SlavePoint top: 7,837 Bose: 8,090

UPPER INTERVAL: 7,837-7,916. (Note that 2 feetbetween 7,864 and 7,666 were not cored). This intervol consists of o foirly uniform sequence of dork brownish grey to brownish blackcalcilutites. Carbonaceous stylolitic portingsare common. Occasion- ally there ore suggestions of introclasts in the calcilutite but these structures are vogue. Stromatoporoid material is foirly common in the interVal and mossive, nodular and ramose forms including abundant Amphipora ore represented. Abundant crinoid (?) ossicles occur in some zones. Other elements of the fauna include Thomnoporo andoccosionol gasteropods. Thick veins ofcalcite occur over short sections of the core. A small proportion of the colcilutites have been altered to dark brownish grey dolomite, fine to medium crystalline in texture.

LOWER INTERVAL:7,916-8,001, This section of theSlove Point core is mode up of dark brownish grey to brownish block calcilutites similar to those of the overlying interval. The lower section, however, contains subordinate developments of fine to medium grained intrasporites and intramicrites, mainly in the intervol 7,965-8,001. Stromatoporoidsore cammon in ports of thecore and massive, nodular, and ramose types ore present. Occasional brachiopods occur in the colcilutites. Thick veins of very coorsely crystalline to extremely coarsely crystolline colcite are present in o few zones. There ore minor developments of dark brownish grey, fine to medium crystolline dolomite in the section.

HB Union Imp Paddy c-14-C Location: c-14-C/94-H-16 Status: obondoned K.B. 2,254 T.D. 8,131 Completed: March, 1959 SlavePoint core: 7,650-7,901 (Recovery: 33 feet) SlavePoint top: 7,780 Base: 8,030

UPPER INTERVAL: 7,650-7,689. This section of core consists mainlyof dolomite, dark grey to dork brownish grey in colour and medium crystolline in texture. There ore indicotions thot the original limestone contained abundant romose stromotoporoids which were subsequently oltered to a light brownish grey, fine to medium crystalline dolomite which grades in parts to white, cwrse to very coarsely crystolline dolomite. The oltered stromotoporoid moteriol contains central cavities in some instances. The dolomite of this interval is moderately vuggy; as o rule the vugs are smoll andore usually less than 1 centimeter across.They arein some instoncesassociated withaltered biogenic materiol; in other cases theyoccur within irregular patches of white, coarse to very coarsely crystalline dolomite. In ports of the rock intercrystalline porosity is developed. In some sections, which together constitute only a moll port of the total interval, the Slave Point has notbeen dolomitized; these sectionsconsist of darkbrownish grey stromatoporoid-bearing calcilutite.

62 LOWER INTERVAL: 7,889-7,901, This interval is madeup of darkbrownish grey to brownish blackcalcilutites, veryfine grained to dense in texture. Ramose stromatoporoidsare common in the rock. The limestones show slightdolomitization in parts.

Imperial Kahntah #I Locotion: b-29-C/94-I-7 Status: abandoned K.B. 1,434 T.D. 8,439 Completed:August, 1955 SlavePoint core: 6,400-6,420; 6,570-6,600 SlavePoint top: 6,343 Bore: 6,653

FIRST SLAVE POINT CORE: 6,400-6,420. This interval consists of darkbrownish grey to brownish block calcilutites, containing occasional thin shelled brachiopods and Amphipora.Carbonaceous material is veryabundant in partsof the interval, The carbonoceous rock is associated with the less corbonoceous rock in o variety of ways; in many cases the former occurs os a matrix in which inclusions of the less curbonaceous moterial are disseminated.Etching is required before these two slightly different limestone phoses canbe recognized. On thewet, etched rock surface the corbonaceous rock is slightly darker in colour than the less carbonaceous material.

SECOND SLAVE POINT CORE: 6,570-6,600. This lowersection of core is modeup of a fairly uniform sequence of dark brownish grey to brownish black calcilLstites which contoin varying amounts of corbonoceous material. Minor amounts of biogenic moterial occur in the interval. Laminarond nodular stromatoporoids are present and a few restricted zones contain numerousramose stromatoporoids.Fragmented brachiopod (?) shells, usuallynot more than 1 centimeter in length,are abundant in place!;. Some of the limestones show incipient dolomitization.

Imperial Sikonni Chief XI Location: b-92-D/94-I-4 Stotus: abandoned K.B. 1,920 T.D. 9,930 Completed: June, 1955 Beaverhill Lakecore: 7,658-7,678 BeoverhillLake top: 7,608 Base: 7,750

The Beoverhill Lake core of this well consists of a fairly uniform sequence of calcareous,medium grey to mediumdark grey shales. The shale tends to break into blocks, often the full diameter of the core, rather than show the fissile character which can be observed in the overlying non-calcareous Fort Simpson Shale. In some intervals the Beaverhill Lake Shale grades into argillaceolJs limestone whichcontains poarly preservedbrochiopod hells andalso smaller fossil fragments. The latterare approximately 1 to 2 millimetersin maximumdimension. Thezones of argillaceous limestone are only a minor development in the total interval. Fractureplones developed in theBeoverhill LakeShale ore unddloting and show numerous irregularities;they orenot smooth as are those developed in theFort Simmon Shale.

63 Imp Fontas d-37-6 Locotion: d-37-8/94-1-7 Status: abandoned K.B. 1,461 T.D. 7,636 Completed:March, 1962 Slave Point core: 6,3484,466 (1 16 feet cut; 113 feet recovered) Slove Point top: 6,330 Base: 6,630

The SlavePoint in thiscore consists of dorkcoloured colcilutite. Two slightly different types can be recognized: one is dark brownish grey to brownish block in colour and shows obundont carbonaceous moterial on the etched surface of the rock, theother is very slightly lighter in colour and shows little evidence of carbonaceous moterialon the etched surface. The two types ore most eosilydistinguished when the rock specimens are exomined wet, ad the colour relationships described above apply to thewet rock. The lightercoloured rock often occurs os inclusions in thedarker limestone. Thin shelled brachiopods are common in the rock;when they occur in the darker limestone they are often infilled with lighter coloured rock. Fragments of brachiopod shells are also quite common and in some cases they are replaced by translucent calcite. There ore obundont inclusions of smoll cylinders of calcite ronging up to severol millimeters in length, especiolly in theupper port of the core. There bodies we similar to those described from the core of Texaco NFA Townsoitoi d-44-C ond are probably derived from crinoids. The interval 6,394-6,420 is mode up largely of the lighter calcilutite crossed by dividing and anclstomosing veins and stringers of carbonaceous calcilutite. This relationship gives rise to a rock which appears to consist of irregularly shaped bodies, 1 to 8 centimeters in moximum dimension, of the lighter coloured limestone, separated from each other by bands and veins of the carbomceous rock. In otherports of thecore (especially the interval 6,3484,375) irregularly shaped inclusions of light brownishgrey siliceous dolomite are present. These inclusions vary from o fewcentimeters in maximumdimension to the full width of thecore (3.5 inches). They oreusually elongated in formand approximatelyhorizontol. It seems likely that the bodies represent inclusions in the dark colcilutites of a rock type which was particularly prone to silicification and dolomitization. In the lower port of the core the darker calcilutite is dominant ond in the interval 6,446-6,466 stromotoporoids are common. Massive,nodulor, and ramose types arepresent. Thamnopora olso occurs. Incipientdolomitization is evident in ports of this intervol. Stromatoporoidsare not common in this cored section except in the lower 20 feet. However, brachiopods are more common in this core than in many other sections of the Slave Point and gosteropodr are also occasionally present. In these respects this sectiondiffers from what maybe consideredthe "normal" Slove Point development of northeastern British Columbio.

Imp Junior c-98-C Location:c-98-C/94-I-I 1 Stotus: Gas wellin SlavePoint Formation K.B. 1,465 T.D. 6,632 Completed:Morch, 1962 SlavePoint Core: 6,210-6,500 (283 feet cut; 233 feet recovered) SlovePoint top: 6,207 Bore: 6,500

64 UPPER INTERVAL: 6,2104,347. This interval is made up predominanllyof limestone. Stromatoporoids and Thamnoporo are dispersed in a matrix of dark brownish grey tobrownish block colcilutite. There aresubordinate amounts of a brownishgrey to medium brownish grey, dense, aphanitic limestone. Biogenic material make!, up opproximately 14 to 18 per cent of the rock. The light aphanitic limestone reprewnts opproximately 3 to 4 per cent of the cored interval. The dark calcilutite, which is the dominant rock type, is in general unresolved under the stereoscopic microscope at x 30 mognification. In ports of the ccsre there are suggestions that the calcilutite grades into on intromicrite and in some places the rock is modeup ofintraclasts separatedby thin films of carbonaceous material. The dark calcilutite contains moderate to abundant omounts of carbonaceous moterial, The lightercoloured aphonitic limestone (micrite ?) usuolly shows abedded relotionship with the darker rock. Thus intervals of the core up to 1 to 2 feet in thickness consist of interbedded light and dark phases. In other places the light phaseforms continuous zones reaching up to 1 to 2 feet in thickness. The lighter coloured aphanitic limestone contains abundant inclusions of sporry calcite which are frequently elongated parallel to the bedding. In some are05 this limestone grades to on introrparite with allochems in the fine to medium arenaceous size class. Much of the brownish grey ophanitic rock is probably a true micrite. Support for this concept is provided by the fact thot in places it contains inclusion!, of Am hi e.There is a possibility that some of the aphoniticlimestone is in realitya "we+" ded intmclost rock and there is evidence of this origin in places. In some parts of the core there ore small inclusions (fine to cwrse grained) of the lighter brownish grey limestone in the dark calcilutite; this relotionship is frequently seen in the dark colcilutite in zones adjacent to the thicker beds of the light coloured rock. Mosttypes of stromatoporoid materialare present in thecore. 111some parts Amphipora is dominant; in others large ramose forms arethe maintype represented. Nodular stromotoporoids(2 to 6 centimeters across)clre common and massive types reach- ingup to 20 centimeters inlength occur in some zones.Thamnoporo is ,lbundont in certoinintervals. In onesection of thecore stromotoporoids can beseer, encrusting Thamnopora. Occasional solitary corols are present in the dork calcilutite.

LOWERINTERVAL: 6,3474,500. This Section of core consists of thedolomitized equivalent of the overlying limestone.Throughout the rock two distinct pt,ases con be recognized; there is a dork coloured matrix phase and a lighter coloured phwe consisting of inclusions. Parts of the core cleorly demonstrate that the dark matrix phase is the equivalent of the dork colcilutite of the overlying rock and thot the light col,=ured phase represents oltered biogenic material. Intervals of the core up to 4 feet in length may be mode up almost exclusively of the dork phose; cllternotively the two phases occur together over intervols up to 2 to 3 feet in length giving rise to the white and grey dolomite. The dark phose is medium grey to medium dark grey in colour and fsr the most port is made up of fine to medium crystalline dolomite; only rarely do the cr:,staIs reach the coorse grade, ond even then they fall into the lower part of this size class. Interstitial carbonaceous material is present between the crystals of the coarser grodes although it is not inevitably present. The finely crystalline dolomite is uniformly pigmented with dork material; some of the medium crystalline dolomite also shows uniform pigmentation. The light phase of this dolomite (described on poge 24 as the white and grey

65 dolomite) is white to very light grey in colour and in mostcases it is coarse to very coarsely crystalline. As noted above much of this light phase clearly represents altered biogenic moterial, and in many cases the nature of the originol material can be recognized. However,when dolomitization is sufficiently advancedthe originol forms of thebiogenic components become blurred ord to some extentunited, and give rise to such textures os the clotted, nebulous, banded and the macroinclusion (see- text for description of terms). Vuas are freauentlv develooed in the centres of the liaht coloured dolomite in- ~I clusions and they range in size fmm'lee thon 1 centimeter ocrok to the full width of the core (3.5 inches). They orelined with very cwrseto extremely coarselycrystalline dolomitewhich often shows curvedcrystal faces.Dark carbonaceous moterial is frequently presentbetween these crystals. Qvortz crystolsoften form port of thevug lining. Some of the vugs orealmost completelyfilled with large crystalsof calcite. It con be assumed from the amount of white dolomite in this core thot the original limestone ofthe total interval contained approximately 5 to 8 percent biogenic material. It appears tohave been of theusuol type seen in thedark calcilutites, thot is, mainly stromatoporoids ond Thamnopora. Some ofthe rock in thissection of core provides examples of the stages by which biogenic material is altered to the white dolomite. The process can be summarized as follows: 1. Dolomitization starts at periphery of fragment and extends inward. 2. Fragmentmay be completely replaced by dolomite. 3. Alternotively, a soluble core may be left which is dissolved out thus forming a vug. The process is more fully described on page 25 of the text.

Imp Kyklo b-73-F Location: b-73-F/94-I-11 Status: abandoned K.B. 1,381 T.D. 7,914 Completed:March, 1962 SlavePoint core: 5,992-6,133 SlovePoint top: 5,950 Base: 6,272

UPPER INTERVAL: 5,9924,058. Dorkbrownish grey to darkgrey calcilutites, containing abundant Am hi ora coenostea, make up this interval of Slove Point core. Some of the AmPIPhi ora 9F;ereoc 4 mllllmeters"5 in diameter. ldiostromatidoe other thanAm hi porn, nodu orstromotoporoids, ond Thamnoporo ore olso present in the rock but e- eyt ore not as common as Amphiporo. The calcilutite shows little structure at x 30 mognification underthe stereoscopic microscope. In ports,however, there ore suggestions of fineto medium grainedintraclosts dispersed in o micriticmatrix. Minor amounts of brownish grey micrite occur; it is commonly in bands, some reaching up to 7 centimeters in thickness,interbedded with thedarker rock. Carbonaceous stylolitic breoks ore developed in parts of the cored interval.

LOWER INTERVAL: 6,058-6.133. The lowerpart of the SlovePoint core is similar in mony respects to thot described above, but in this lower interval massive and nodular stromatoporoids ore common andoccur in addition to Amphipora. There are also subordinate occurrences of Idiostromatidoe other thon Amphiporo. The matrix rock consists of dark calcilutite which gmdes in parts into o rock showing suggestions of fine to medium grained intmclasts. This interval of core contains little of the brownish grey micrite seen in the upper interval. However, one prominent 5-inch band of this rock type occurs at approximately 6,074 feet. In the lower 20 feet of this interval Amphipora occurs only rorely ond nodulor stromotoporoids ore very common.

Pan Am A-I Cam Loke 0-31-1 Location: 0-31-1/94-0-16 Stotus: Gas weil in Slave Point and Sulphur Point Formations K.B. 7,5001,494T.D. Completed: May, 1960 SlovePoint core: 6,759-6,795 (Recovery: 25 feet); 6,839-6,859(Recovery: IO feet); 6,8856,895 SlavePoint top: 6,750 Base:7,000

All three cores consist lorgely of dorkgrey calcilutite, very fin'? grained to dense in texture,contoining abundantstromatoporoid remoins in places. In portsthe colcilutite grades to a rock which shows vague suggestions of being made up of fine to medium grainedintroclasts. Amphiporaoppeors to be the mostcommon stnnnotoporoid in thesection; other genera of theldiostromotidae ond Thomnopora are also present. Amphiporo is veryabundont in some zones. Occosional mossive stromatoporoids occur. Stylolitic breaks are present in places; theyare usuolly highlyirregular in formond contain occurnulotions of dark carbonaceous material. Veins of colcite cut the rock in some intervals; they are often verticol or inclined at 20 to 30 degrees from the vertical.

Pan Am et a1 Dilly a-27-K Location: 0-27-K/94-P-12 Stotus: abandoned K.B. 1,677 T.D. 7,154 Completed:February, 1961 SlavePoint core: 6,615-6,675 SlavePoint top: 6,586 Base: 6,868

Core consists of dork grey ond subordinate brownish grey to dork brownish grey calcilutite, very fine grained in texture which grades in ports to an intraclast rock. The latter is mode up of fine grained ollochems and may be closed as on intramkrite-intrasporite. Corbonaceous material is abundant in some of the limestones. Strotmatoporoidr are abundont in ports of the core; Amphiporo is the most common type. Ramose stromato- poroidsother than Amphipora, nodular stromotoporoids, and Thomnopora also occur. Stylolitic partings contoining carbonaceous material occur intermittently throughout the cored section.

Pan Am et 01 Dilly 0-30-K Locotion: 0-30-K/94-P-12 Stotus: Gos well in SlavePoint Formotion K.B. 1,724 T.D. 6,900 Completed:January, 1962 Slow Pointcore: 6,822-6,858 (Recovery: 31 feet) SlavePoint top: 6,803 Base: notpenetroted

Core is composed of medium dark grey to dork grey dolomite, fine to medium crystalline in texture. Some sections of thecore contoin inclusions (varying in moximum dimension from 1 to 5 millimeters) of white, medium to coorsely crystalline dolomite. These ports of the core moy be said to exhibit the microinclusion texture of the

67 white and grey dolomite. One 6-centimeter section of the core contains abundant inclusions of dolomitized Amphiporo coenostw. They rongeup to severalcentimeters in lengthond are madeup ofwhite dolomite. The inclusions lie at angles ranging between 45 and 70 degrees from the horizontal; they often show the development of medial covities. Vugs occur in thedolomite of thiscore, but they ore not common.They ore mostly small, reaching o maximum dimension of opproximotely 2 to 3 centimeters. The vugs ore lined in mony coses with white dolomite ond/or quartz crystals and in addition often contain corbanoceous moterial. In some instonces the vugs ore olmost completely infilled with quartz. Pyrite occurs sporadically in this Slave Point core.

Pon Am July 0-65-K Location: a-65-K/94-P-9 Status: abandoned K.B. 1,544 T.D. 6,513 Completed: March, 1961 SlavePoint core: 5,446-5,506 SlavePoint top: 5,427 Base: 5,700

Two mainrock types orerecognizoble in this intervol. The first is o medium brownish grey limestone, dense to aphanitic in texture, which is unresolved at x 30 of thestereoscopic microscope. There is little evidence of carbonaceous material on the etched surface of the rock. The colour and dense texture of this limestone suggest that it is o micrite. In some places limestone of a similar colour is mode up of closely compacted ollochems which ore surrounded by thin films of carbonaceous moterial. The second rock type is dork brownish grey in colour and contoins visible carbonoceous material. In mony places this darkerrock is modeup of fine grained ollochems, medium brownish grey in colour, which are separated from each other by o dork corbonoceous matrix. In theupper two-thirds ofthe cored interval the lighter coloured limestone makes up about 30 to 35 per cent of the rock and occurs os irregular inclusions (often of clot-like form) in thedarker limestone. These inclusionsvary a great deal in size, ranging from several millimeters across up to many centimeters in diameter. In some instances the lighter material occupies the full width of the core (3.5 inches). In the lower third of the cored intervol the lighter rock type becomes domin- ont and mokes up most of the core. In places the micritic rock contains small vein-like inclusions,usually less than 1 centimeter in length, of sporry colcite ond/or carbonoceous material. Biogenic moterial is not common in this Slave Point section. However, occosional ramose, nodulor, and massive stromotoporoids occur in parts of the core.

Phillips Minoker a-25-U Location: 0-25-D/94-G-15 Status: abandoned K.B. 2,582 T.D. 11,361 Completed: July, 1960 SlavePoint core: 9,560-9,603 (Recovery: 27.5 feet) SlavePoint top: 9,548 be: 9,950

The coredintervol consists largelyof dolomite, mediumdork grey to dork grey, mainlyfinely crystolline butgrading in ports to medium crystalline. This dork dolomite is osrocioted with white coarsely crystalline dolomite ond colcite. About IO

68 per cent of the rock consists of the lighter coloured material. The light phose occurs in parts as approximately horizontal bands which reach up to 5 millimeters in thickness. In some instancesthese bands arevery ttlin and less than the width of the core in lateral extent. Some of the light coloured dolomite and calcite occurs as irregularly shaped inclusions up toseverol centimeters in diameter. These inclusions Sometimes contain o central cavity. Veins of white .calcite and dolomite also occur in therock. No preferredoccurrence of the light coloured dolomite os opposed to the similorly coloured colcite was noted. In ports the dolomitized remoins of structures that appear to be kohiporo ore present in therock. The coenostea arerecrystalldzed and consist of verylightgrey medium to coarsely crystalline dolomite. Parts of thecore ore fissile in o planeapproximately horizontal, A residue test carried out on some of the fissile material indicotes that it contoins o considerable quantity of argillaceous and silty moterial. There are indications of brecciation in parts of therock, with blocksof the darker dolomite being separated by thin veins of the light phase. It is possihle that this material is in reality o pseudo-breccia. In plocer the dolomite is vuggy. The vugs rarely reach more than 3 centimeters ocross. They ore lined with coorse to extremely coarsely crystalline dolomitt?. Carbon- aceous moterial and quartz crystals occur in the vugs.

Pure POC Cheves c-5-A Location:c-5-A/94-J-I 1 Status: abandoned K.B. 1,776 T.D. 8,596 Completed:February, 1962 SlavePoint core: 7,466-7,524; 7,624-7,682 (Recovery: 55 feet) SlavePoint top: 7,466Base: 7,940

FIRST SLAVE POINT CORE: 7,466-7,524. This interval consists of brownish block calcilutite with abundontAmphiporo, 2 to 4 millimeters in diameter.Other typesof stromotoporoids are also present but in lesser amounts. The matrix rock is unresolved at x 30 under the stereoscopic microscope. The colcilutite varies from extremely corbonaceous to moderatelycarbonaceous, except in the lower 12 to 15 feet of the interval where it is only slightly carbonaceous. Occosionol corbonoceous porting occur in the rock.Colcite veining is evident in placer. The limestone hwrminor dolomitization in Some intervals. The rock of the lower 15 feet (7,509-7,524) ofthe intervol differ!; romewhot from that above. It contains less carbonaceous moterial and in places the rcak is composed of fine to medium grained introclosts which ore usually mergedtogett8er to produce o rock of fairly uniform texture; in somecases, however, rporry calcile fills the interstitial spaces.Sparry colcite ohoccurs as smalldiscrete patches. Tbis materiol oftenfills small spaces parallelto thebedding; in other casd no obvious patternof distribution can be recognized. A distinctive fissile fracture, approximately horizontal, is evident in this interval; it does not appear to be related to any obvious slructures or constituentsof the rock. Amphiporaoccurs in moderate amounts in these limestones, The fissile chorocter also occurs in other parts of the core but it is not os pronounced as in the lower 15 feet of the interval.

SECOND SLAVE POINT CORE:7,624-7,682. The calcilutiteof this SlavePoint core is brownish grey to brownish black in colour and in general is unresolved at x 30

69 magnification. There is less evidence of carbonaceous material in the rock than in the care ofthe upper core.Occasional carbonaceous stylolitic breaks occur.Minor fine to medium grainedintmsparites, brownish grey in colour,are present in thissection. However, they rarely reach a stage of clear development. Ramose stromatoporoidsin- cluding Amphipora occur sporadically. Thamnopom is also present in places. Inclusions of parry calcite occur occasionally in the rock. They toke the form eitherof elongated inclusions, usually approximately parallel to the bedding, which reach up to 1 centimeter ormore in lengthand are usually less than 1 millimeterin thickness, or the sparry calcite may occur os irregular patches usually less than 2 to 3 millimeters in maximum dimension. The former type of inclusion is often associated with rocks showing intraclost structure. Some of thelimestones possess the fissile character noted between 7,509 and 7,524 feet in the upper core.

Sohio CBE Ekwon a-55-G Location: a-55-G/94-1-10 Status: Gas well in theMississippian K.B. 1,239 T.D. 6,050 Completed:February, 1962 SlavePoint core: 5,831-5,865 Slove Point top: 5,740 Bare: not penetrated

The core consists of dork brownish grey to dark grey calcilutite; the total interval contains moderate omounts of biogenic materiol. In the upper 10 feet Amphipom is common; thecoenostea oreusually 2 to 3 millimetersin diameter. At approximately 22.5 feet from the top of the core a IO-inch zone contains abundant ramose stromatoporoids (including Amphipora).Nodular stromatoporoids and Thamno ora also occur in this zone. There are sporadic occurrencesof Amphipora and* nodu or stramatoporoids throughoutthe rest of thecore. The colcilutite is carbonaceous to o varyingextent, and numerous carbonaceous, stylolitic breaks are present in the core. Calcite veining occurs throughout much of the rock.

Texaco NFA Nig Creek 0-79-8 (1) Location: a-79-B/94-H-4 Status: Gas well in the Triassic K.B. 2,9&1 T.D. 11,999 Completed:February, 1954 SlavePoint core: 11,110-11,130 (Recovery: 14feet); 11,135-1 1,150 (Recovery: 12 feet) SlovePoint top: 10,930 Base: 11,215

FIRST SLAVE POINT CORE: 11,11C-11,130. Darkgrey to greyish blackcalcilutites make up the major part.of this interval. The colcilutite is dense to aphanitic in texture. Abundant ramose stromotoporoids including Amphipom are present in the rock. Nodular stromatoporoidsand Thamnopora also occur.Occasional brachiopods ore present in parts of the interval. In the upper 5 feet of this cored section the limestones are portially altered to dark grey, fineto medium crystallinedolomite. It is moinly the matrix rockthat is offected by dolomitization; the biogenic material remains unaltered.

SECOND SLAVE POINT CORE: 11.135-11.150. This interval is composed of dark grey to greyish block calcilutites, uniformly dense in texture. Amphipora occurs spor-

70 adically in the calcilutite. In parts ofthe rock smoll, oftenelongated in'dusions of sporry calcite ore present. They vary from 1 millimeter to 5 millimeters in length. In the upper part of the core very small tubelike structures occur. They ronge up to 2 millimetersin length and are obout 0.1 millimeterin width. The structures show numerous closely spaced cross partitions arronged ot right angles to the main oxis.

Texaco NFA N Tsea d-47-C Location: d-47-C/94-P-12 Status: obandoned K.B. 1,924 T.D. 8,320 Completed:February, 1962 SlavePoint core: 6,875-7,116 (Recovery: 236 feet) SlovePoint top: 6,860 Base: 7,l I6

UPPER INTERVAL: 6,875-7,081. The core of this interval provides o goodsection in rocks that appear in part to be true micrites. The micrites ore medium brownish grey to brownish grey in colour and are aphanitic in texture. In placer they contain ostra- code tests (oppmximotely 0.5 millimeter in maximum dimension). In other pxts of the rock small, round, thick-wolled structures occur, 100-150 microns in diameterwhich have a core of clear calcite. In general the micrite contains few of the larger biogenic fragments,but occosionol stromatoporoid coenosteo ore present. The lightcoloured micrites make up 50 to 60 per cent of this cored interval. The micrite is associated with a dork brownish grey to dark grey, carbonaceous calcilutite, which is only poorly resolved under high power of the stereoscolaic microscope (x 30). There ore occasional suggestions of sparry calcite in the rock md thus it moy grode in parts to o sprite. This darker rock occurs most abundantly in the upper quarter (approxinu tely 6,875-6,925) of the interval under discussion. The dark calcilutite contains more of the larger biogenic constituenls than the lighter coloured micrites. Large ramose stromatoporoids are present. Massivt: stromatoporoids,nodular stromotoporoids, and Am hi or0also occur. Thamnoporo is seen in places and brachiopodshells are occasionaly encountered. The lighter coloured micrite and" the dark calcilutite are commonly interbedded on o smoll scole; frequently stringers ond clots of the lighter coloured materiol pass into thedark material. In some instancesthere ore inclusions of thedork matwialin the light material. The light or dork rock type may occur over intervals of up to several feet to the exclusion of the other type. On the other hand the two rock types may be intermixed over intervals of up to several feet. In places the light coloured rock OCCUIS os turbulent "clots" in o motrix of the dork calcilutite. These "clots" reach 4 to 5 centimeters across. Whereconsiderable intervals are madeup of thelighter material it is often crossed, approximotely horizontally, by thin veins of darker carbonaceous mcterial. In places these veins are highly irregulor and appear to cross the bedding. Incipientdolomitization occurs in placesand is seenmost frequently in the dork rock type. Dolomitization in this cored intervol is only of minor importmce.

LOWER INTERVAL: 7,081-7,116. At 7,081 alimestone breccio occurs which consists of rounded fragments of brownish grey micrite, 1 millimeter to 3 centimeters ocross, set in o motrix of very light grey, dense, argilloceous limestone. When the breccia is etchedthe light grey motrix material stonds abovethe included limestone frogments, presumably because the etching process removes the colcium carbonate from the matrix

71 and leaves o thin CNSt ofunaffected argillaceous moterial on the rock. Below the brecciated zone, in the intervol 7,082-7,086, this distinctivevery light greylime- stone occurs as irregular inclusions, up to severalcentimeters across, in the surrounding brownish grey limestones. The lowermostsection, 7,086- 7,116, of this SlovePoint core consists of brownish grey and medium brownish grey micrites which ore interbedded with increasing amounts of dork brownish grey and dark grey calcilutites towords the base of the intervol. There rocks are almost devoid of the larger biogenic (stromotoporoid) material.

Texaco NFA Townsoitoi d-44-C Location: d-U-C/94-1-10 Status: abandoned K.B. 1,314 T.D. 6,959 Completed: March, 1962 Slove Pointcore: 5,903-5,923.5 (The interval 5,923.5-5,952 was alsocored but no recovery wos obtained.) SlavePoint top: 5,890 Base: 6,190

The core consists of dork brownish grey to brownish block colcilutite contoining moderate to obundunt amounts of biogenic material. The rock is very carbonaceous in parts. The biogenicmateriol consists moinly of nodularstromotoporoids and ramose stnmotoporoids including Amphipora. In the upper IO feet of the corethere are num- erousoccurrences of small cylindrical structures which may be derived from crinoids. These structures reach o maximum dimension of about 8 millimeters; they often show a centrol conol or cavity. Small shell fragments, usuolly less than 5 millimeters in length, are olso distributed rporodicolly through the rock; they are replaced in many cases by whitishtranslucent calcite. The limestones show minor incipientdolomitization in places. Most of the calcilutites of this section ore unresolved at x 30 under the stereoscopic microscope. However, there are indications that in ploces the calcilutite grodes to a rock made up of fine to medium groined allochems of irregulor shape which are either closely compacted or associoted in o micritic matrix.

Texoco NFA Tsea b-68-K Location: b-68-K/94-P-5 Status: Gos well in SlovePoint Formotion K.B. 2,070 T.D. 7,110 Completed: March, 1961 SlovePoint core: 6,8766,900 (Recovery: 22.4 feet) SlovePoint top: 6,875 Base: notpenetrated

This core consists of the white and grey dolomite. The dork phose is medium dark grey in colour and varies from fine to medium crystalline in texture. The medium crystalline grades often show intercrystalline carbonoceous material. The finely crystol- linedolomite is mostly uniformlypigmented and discrete particles of corbonoceous mattercannot be seen. In some ports ofthe corea very finely disseminated yellow minerol (sulphur 7) occurs interstitially in the medium crystalline dolomite. The white dolomite of this core is cwrse to very coarsely crystalline. It occurs in lesseramounts thonthe dork dolomiteand gives rise tothe bonded, clotted, and microinclusion textures. In the first, thin bands of the white dolomite 2 to 3 millimeters ocross, often with o medial cavity, cross the dork phose ot a slight angle to the hori- zontol, but in rore cases they are inclined ot 30 degrees from the horizontal. In parts

72 . the bonds show onundulating form.Thicker bands reaching up to 1 centimeter across arepresent in parts. In the clotted texture seen in this core "clots" of white dolomite with vague outlines and varying from 0.5 to 8 centimeters across are distributed in the dark dolomite. The microinclusiontexture is illustrated in Plate XI. Small inclusions of the white dolomite, usually less than 5 millimeters across are disseminated in a matrix of the dark dolomite. Vugs are common in this core. They vary from 0.5 centimeter acres!, to the full width of the core (3.5 inches). The vugs are lined with cwrse to very coarsely crystal- linewhite dolomite together with quartzcrystals. Dark carbonaceous malerial often occurs in the vugs. Many of the vugs are elongated in form; others hove a rcNunded outline.

Texaco NFA Walrus b-86-L Location: b-86-L/94-1-16 Status: Gos well in theMississippian K.B. 1,753 T.D. 6,501 Completed: Morch. 1962 Beaverhill Lakecore: 5,779-5.788.5 (Recovery: 8.5 feet) BeoverhillLake top: 5,775 Ease: 5,805

The interval consists of medium grey to medium dark grey, non-calcareous to verycalcareous shale. The shale tends to breok into blocksrather than thin plates. Moderate amounts of very finely disseminated pyrite occur in ports; 5 feet from the top of the core a 2-inch zone contains abundant pyrite; it occurs in aggregates with crystals up to 1.5 millimeters across. In some places the rock contains verysmall lrogments of brownish blackchitinous material. These range up toapproximately 1 millimeterin length. Dark grey to dark brownish grey argillaceous limestone occurs in ihe interval 5,785-5,786. The limestonecontoins much broken and fragmented biogenicmaterial. It also containslarger, more complete,but poorly preservedbrachiopod shells. Inter- bedded with the limestone is a medium dark grey, non-colcareous shale contoining small chitinous brachiopod valves.

TGT Tooga Lake c-27-K Locotion: c-27-K/94-P-2 Status: abandoned K.B. 2,103 T.D. 6,725Completed: February, 1961 SlavePoint core: 6,319-6,504 SlavePoint top: 6,270 Ease: 6,610

UPPER INTERVAL: 6,319-6,429. This intervalof SlavePoint core consists of brownish grey to dark brownish grey calcilutite, very fine grained to dense in tex-ure. Cor- bonaceous material is moderatelyobundont in the rock; some of it occurs in stylolitic partings. In placesthe calcilutites grade intorock which shows suggestiolsof intrasporite texture. Biogenicmateriol occurs abundantlyin some sections of the core, It consists mainlyof small Am hi ora (approximately 2 to 3 millimeters in diameter) but olso in- cludesother ramose-+orms and nodular and massive stromatoporoids. Thumnopora is abundant over the interval 6,404-6,429; it alsa occurs sporadically in other parts of the core. Occasionally brachiopod shells occur in the core; in somecases they (Ire replaced by light coloured translucent calcite.

73 LOWER INTERVAL: 6,429-6,504. The rockof this interval consists of brownishgrey to dark brownish grey stromotoporoid-bearing colcilutite, which grades in several places intofairly well developed fine tomedium grainedintrosparites. The lightercoloured rock (brownishgrey) is dominant in thelower 35 to40 feet. There are suggestions in parts of the core of intromicrites. The intraclasts of the latter tend to be angular in outline and to merge into the matrix. It should be noted, however, that the intraclast rocks form only a minor element in the total lithology. Carbonaceous material occurs inonly moderoteamounts. Biogenic material is common in some intervols. Amphipora and nodular stromatoporoids occur over restricted intervals usually about 1 to 2 feet in thickness ond containing mainly either one type or theother. Idiostromatidae, other than Amphipora, and Thamnopora 01% occurin the rock.

West Not et al Clorke b-70-1 Location: b-70-1/94-J-10 Status: Gas well in Slave PointFormation K.B. 1,309 T.D. 6,422 Completed:Januory, 1961 SlavePoint core: 6,260-6,284 (Recovery: 21.5 feet) SlavePoint top: 6,205 Base: notpenetrated The cored interval consists of vuggy white and grey dolomite. The main types of texture represented are the clotted, bonded, and macroinclusion. In some sections of the core white coarsely crystalline dolomite is very abundant; in one 7-inch section it maker up 75 per cent of the rock. The vugs in the rock mnge in size from less than 1 centimeter across up to the full width of the core (3.5 inches). Black carbonaceous material occurs in the vugs and also in fissures in therock. In placesthe curbonoceous materialcontoins disseminated crystals of dolomite which fall into the fine size class. Thin, irregular inclusions and interbeds of dark grey carbonaceous shale occur in places. Some ofthe shale is slightly calcareous, in otherplaces it shows a greasy lustre.

West Nat et aI Clarke c-78-1 Locotion:c-78-1/94-J-10 Status: Gas wellin SlavePoint Formation K.B. 1,295 T.D. 6,533 Completed:February, 1960 SlavePoint core: 6.183-6,199 (Recovery: 1 foot) SlavePoint top: 6,152 Base: notpenetroted

The recoveryfor this intervol is very poor; only 1 footof rock representsthe coredsection. The recoveredmaterial consists of roundedfragments of the white and grey dolomite. The texture of the rock is difficult to ascertain because of the fragmen- tary condition, but the clotted texture can be recognized in places. Some areos of the dark phase of the rock oppeor to be argillaceous. The dolomite contains vugs in parts. The very poor recovery from this interval suggests that the original rock was extremely vuggy. West Nat et al Clarke c-47-J Locotion: c-47-J/94-J-10 Status: Gas wellin SlavePoint Formation K.B. 1,343 T.D. 6,957Completed: January, 1957 SlavePoint core: 6,550-6,572 (Recovery: 16 feet) SlavePoint top: 6,510 he: 6,750

74 The recoveredmaterial consists largely of white andgrey dolomie which is moderately vuggy. Over the total interval the light coloured phase is abundantond it makesup 60 to 65 per cent of the recovered material. Some intervals, reaching up to 7 inches in thicknessconsist almost entirely of white dolomite. The followi81g textures of the white and grey dolomite were observed: banded, clotted, and pseudo-lxecciated. In the latter blocks of the dork dolomite occur in a matrix of the lighter phase and the reverse relationship is 01% developed. In places the darker coloured dolomite is cut by veins of white, coarse to very cwrsely crystalline dolomite. Carboncrceous material occurs both between the crystals of thedark phase of white and grey dolomite and also in the vugs. Pyrite occurs in ports of the rack.

West Not et a1 Evie d-14-F Locotion: d-14-F/94-J-15 Status: abondoned K.B. 1,728 T.D. 7,925 Completed:December, 1961 Slave Point core: 6,902-6,960 Slave Point top: 6,610 Base: 6,985

This Wove Point core is composed mainly of biosparruditer. The rock grades in ports to a biosporite with ollochems in the arenaceous size class. Stromatoporoids con- StitUtethe mainbiogenic component; much of themoteriol is fragmentedtmd thus its formconnot berecognized. However, ramose stromotoporoids are well represented and in oddition many of the fragments are probobly derived from nodulclr and massive forms. Over substantial intervals of the core this biogenic moteriol is distributed in ,, ,, matrix of sparry colcite, which gmdes in parts to dense, finely crystalline calcite. Much of thestromatoporoid moterial has undergone recrystalliraticsn to dense biogeniccalcite, light brownishgrey incolour. Accompanying the recrystallization process there has been o redistribution of the corbonoceovs moterial with o tendency for it to become aggregated in certoin oreas of the fragments or to be extruded almost completely from the biogenic materiol. Inthe lower half of this SlavePoint core medium brownishgrey limestones occur which possess a more uniform texture than the biasparrudites. There is much fine carbonaceous banding in these rocks; usuolly it is approximately horizontal. Microscopic examination reveolr that the rocks ore composed in part of closely compacted biogenic material, which posses into 0 rock made up of fine to coarse grained ollochemr (intm- clastsor fossilfragments). Interstitial sporry calcite may fill the spaces betweenthe allochemsbut in some arms theyare merged together to form alimestone of micritic oppearonce.

West Not et 01 Evie Lake b-89-E Locotion: b-89-E/94-J-15 Status: abandoned K.B. 1,943 T.D. 8,240 Completed: September, 1960 SlavePoint core: 6,634-6,679;6,730-6.780; 6,840-6,890(Recovery: 45 feet) SlavePoint top: 6,555 Bose: 6,930

FIRST SLAVE POINT CORE: 6,634-6,679. The upper 35 feetof this core is mode up largely of fragmentedstromatoporoids. Over most of the interval the biogenic materiol is closely compacted with amatrix consisting of sporry colciteor more rarelyfinely crystollineto aphonitic calcite. In some intervals the biogenic componerltsare dis-

75 persed in a matrix of dark gray colcilutite. The lower IO feet of the core consists mainly of darkgrey calcilutite which contoins relotively small omounts of biogenic material. The dork grey calcilutite thusforms a rock in its own right and also occurs os the matrix in rocks composed largely of stromotoporoid fragments. The calcilutite contains abundant carbonaceous material which imparts the dark colour. The stromatoporoid materialin thecore is mainlyin d fragmented condition and most of it appears to be derived from lorge romose types (coenosteo 0.5 to 1 centimeter indiameter), but in oddition fragments of small romose and nodular stromatoporoids ore present. Thomnoporo and occosional large brachiopods reaching 3 centimeters ocross also occur.

SECOND SLAVE POINT CORE: 6,730-6,780. The dominant lithologicol typerepre- sented in this core is thestromotoporoid biosparite. The biogenic fragments varyin size from the fine arenaceous size grade up to diameters in excess of 2 centimeters. The larger fragments in some cases are recrystallized to brownish grey dense biogenic calcite with theaccompanying redistribution of contained corbonaceous material. The fine to medium grained biosparites ore often dork grey in colour ond close examination is necessary to establish the fact that the rock is a biosparite. A certain amount of size sorting of the biogenic material is evident and biosparites with fragments in the fine to medium arenaceous size grader occur in places os beds from 6 inchesto 1 foat in thickness. Other sections ofthe core consist of more poorly sorted biosparrudites. In placer indications of bedding con be seen in the fine to cwrse grained biosparites; in the observed coses it is approximately horizontal. Stromotoporoidsore the most common organic structurespreserved in thecore and it appears that amongst these forms the lorge romose types are dominant. However, much of the material is fragmented and its original nature is difficult to establish. Mos- sivestromotoporoids occuroccasionally; Amphipora wos not recognized with certainty but this fon may occur as recrystallized fragments. Brachiopods occur in partsof the core and gasteropods ore occasionally encountered. Thamnopora is another member of the founol assemblage. The colour of the rocks of this cored section varies between dark grey and light to medium brownish grey. The amount of corbonaceous material present in the rock and theway it is distributedbetween the biogenic fragmentsand the matrixore the main foctors which influence the colour of the rock. In some parts of the lower section of this core limestones that appear to be true micrites are developed. They ore light brownish grey in colour and they contoin vorying omounts of biogenic material.

THIRD SLAVE POINT CORE: 6,840-6,890. The third SlavePoint core continues the pattern seen in the second core. The lower core consists mainly of stromotoporoid biosporites,the fragments of which range in sizefrom very fine to coarse grained and up into therudaceous size class, thelatter embracing the lorge stromatoporoid frogments. Much of the stromotoporoid moterial is fragmented but lorge ramose types together with nodular forms which reach a maximum dimension of 2 to3 centimeters can be recognized. There are occosional mossive stromatoporoids, many centimeters in moximum dimension, and laminar types are also present. As in the case of the preceding core the way in which the corbonoceous moterial is distributed is o most important factor in determining the colour of the rock. In the lower 5 feet and also over restricted intervols in other parts of the core

76 auniform, light brownishgrey, aphanitic limestoneoccurs. Some of thism,Jteriol may be dense biogenic calcite derived from the recrystallizotion of algal or stnmatoporoid material. Again, parts of it may be o true micrite and there is evidence in ploces that the rock wos originally an intrasparite which hos subsequentlyundergone recrystallization toform a dense aphanitic limestone.Veins of carbonaceous matericl cross this light coloured rock in the lower 5 feet of the core.

West Not Imp Clarke Lake c-8-D Location: c-8-D/5'4-J-16 Status: Gos well in SlavePoint Formation K.B. 1,380T.D. 6,650* Completed: December, 1959 SlavePoint core: 6,307-6,330* (Recovery: 14 feet); 6,343-6,366* (Recovery: 6 feet); 6,436-6,468* (Recovery: 3 feet) SlavePoint top: 6,270* Ease: notpenetrated

FIRST SLAVE POINT CORE: 6,307-6,330. The recoveryfor this interval is 14 feet. The core consists of white and grey dolomite showing the clotted, macroincltnion, nebulous andpseudo-brecciated textures.Veins ofwhite dolomite usually a3out 2 to 3 millimeters in width cross thecore in ploces. The rock is vuggy. Some of the vugs attain a width of3 to 4 centimeters. Carbonaceous moterial is often present in the vugs. Occasional carbonaceousbreaks (stylolites ?) aredeveloped in therock. Some sections of the core, up to 12 centimeters in length, consist of cwrsely to very cwrsely crystalline dolomite with abundant carbonaceous material between the cryst(,ls. A foot of core at the bore of the interval consists of brownish grey, fine to medium crystalline dolomite showingthe microinciusiontexture. The inclusionsare distributed in such a woythat they give rise toturbulent structures within therock. This lowersection of brownish dolomite appears to be argillaceous.

SECOND SLAVE POINT CORE: 6,343-6,366. Only 6feet of core wm recovered from this interval. The upper 2 feet consist ofcarbnaceous, dolomitic, nrgillaceous moterial, greyish black in colour. Vugs orepresent in the tuck and they contain carbonaceous material. The lower 4 feet of the core is made up of vuggy white and grey dolomite. There ore indicationsof brecciation in thisdolomite. Darkcmbonaceous moterial ond small omounts of sphalerite occur in fissures in the rock.

THIRD SLAVE POINT CORE: 6,436-6,468. Only 3 feetof rock was recoveredover this interval. Most ofthe recovered material consists of greyish block, carbonaceous shale. The rock shows thedevelopment of irregular partings which exhibit a "greasy" surface. Brown coloured scoremorks areproduced when the shale is scrotched with o steel needle. Alsopresent in the recovered material is an &inch section of the white and greydolomite showingpseudo-brecciated texture. The dolomitecontains argillaceous inclusions and is pyritic in parts. The evidence suggests that these threeSiove Point cores come from on area very close to the focies front. The vuggy nature of the rock indicated by the poor recovery, and the presence of abundant orgillaceous ond carbonaceous matttriol support this interpretation.

*Inclined hole, figures quoted ore true vertical depths

77 West Not Imp Clarke Lake b-78-J Locotion:b-78-Jb4-J-9 Status: Gas well in SlavePoint Formotion K.B. 1,309 T.D. 6,520 Completed:March, 1961 Slave Point core: 6,205-6,243; 6,2714,331; 6,4354,491 Slave Point top: 6,205 Base: cat penetrated

The following remorks refer to all three cored sections, except as indicated.

The limestone of these cores contains abundant stromotoporoidmaterial both in a fragmented ond a more complete form. The upper two intervols contain a higher proportion of biogenic material than the lower interval. Most of the stromotoporoid material is derived from massive, nodulor, laminor, and large ramose types; Amphipora occurs only in relatively subordinate amounts. There is a considerable diversity of size and shape amongst the stromatoporoid fragments; some oreobviously derived from ramose types,others ore more ongulor in outline and these vary from 1 to 2 centimeters in maximum dimension.Other, more complete stromatoporoid coenostea, are much larger. The rtromatoporaid material is mainly medium brownish grey in colour; it grades to light brownishgrey in ports. The stromatoporoidfrogments ore frequently oltered to very finely crystolline calcite (dense biogenic calcite). The matrix in whichthis biogenic moteriol is dispersed consists of o dork brownishgrey to darkgrey calcilutite. Underthe microscope this rock is seen to pars in ports to an introclost rock, in which the introclasts ore in the fine to mediumaren- aceous size clou ond ore set in o matrix of corbonoceous, micritic calcite or more rarely sporry calcite. In the upper part of the lowermost core (6,4356,491) clearly developed biosparites occur in subordinateamounts. They consist of stromotoporoidcoenostea, both large ramose ond nodulor types, compacted together in a sparry colcite matrix. In the lower port of the some core (6,4354,491) there are intervols which are relatively free of stromotoporoid materiol and dark grey and dork brownish grey colours areprominent. The rock oppeors to be a Mlcilutite-biosparite-intrasparite assemblage in which the allochems of the sparites are in the fine to medium orenaceous size clors.

West Not Imp Clarke Lake d-91-L Locotion: d-91-L/94-J-9 Status: Gas wellin SlovePoint Formation K.B. 1,366T.D. 6,550 Completed:March, 1960 SlovePoint core: 6,2914,303; 6,4564,499 SlavePoint top: 6,290 Base: notpenetratea

FIRST SLAVE POINT CORE: 6,2914,303. This core consists to a largeextent of stromatoporoidmoteriol. Massive stromotoporoids, large ramose stromotoporoids Am hi- I4 pora,ond fragments of these typesare 011 present. Much of thebiogenic materlol IS ~ystalliredto brownish grey dense biogenic calcite. In parts of the core the organic moteriol is closely compocted ond in =me oreos minor interstitial sporry calcite is present; in other parts of the core the biogenic components ore dispersed in a brownish grey micriticmatrix which alsocontains fine to coarse, ongulorollochems and ortrocode shells. Carbonaceous moteriol is present and it is often restricted to a fissure pattern

78 which crosses the recrystollized stromatoporoid moteriol; in a smaller number of instonces it surrounds the outer border of the biogenic fmgments. The larger stromotoporoids tend to show oreas in which the carbonaceous moteriol is oggregoted, and other oreas which are relatively free of this materiol. In summary, it can be said thot the core consists moinly of closely compacted stromatoporoid materiol together with stromotoporoid biomicrites.

SECOND SLAVE POINT CORE: 6,456-6,499. The coredsection consists ofan upper limestone intervol (6,456-6,461). a central section of limestones and dolomitm?s (6,461- 6,487), ond o lower intervol consisting of limestone (6,487-6,495). The upperand lower limestone sections aresimilar to those described for the first Slove Point core. The limestone of the upper intervol is dark grey in colour whilst thot of the lower intervol is brownish grey in colour. Both sections contain considerable omounts of stromotoporoid moteriol (massive, lorge ramose types, andAmphiporo ore represented). The biogenic materiol is either closely compacted or dispersed in o matrix of dorkgrey or brownish grey micrite. Recrystallization has produced o rock of dense uniform texture. The limestone shows incipient dolomitizotion. The centralintervol (6,461-6,487) consists of anolternoting series oflime- stones and dolomites. The I imestones ore mostly dark grey in colour and appear to consist largely of fragments of biogenic moteriol. Some of the dolomites of the central intewol ore of the white and grey type (=e page24) and show microinclusion,macroinclusion, and nebulous textLNres.They oppeor to be derived from stromotoporoid-bearing calcilutites which carried moderote to abundant omounts of biogenic moterial--the lotter giving rise to the light phase and the dork colcilutite to the dark phase of the dolomites. These dolomites ore vugsgy in ports; the vugs vary from less than I centimeter in maximum dimension up to 3 to 4 centimeters. Limestones showing partialdolomitizotion are present in thesection and in these rocksthe biogenic fmgmentsare altered to white coarsely crystallinedolomite whilstthe matrix limestone shows disseminatedcrystals of dolomitein the medium to cwrse size grades.

West Not Imp Clorke Loke c-94-L Locotion: c-94-L/94-J-9 Status: Gos well in SlavePoint Formation K.B. 1,372 T.D. 8,039Completed: Februory, 1959 SlavePoint core: 6,355-6,383 (Recovery: 17.5 feet); 6,401-6,565 .(Recovery: 141.6 feet) SlovePoint top: 6,355 Base: 6,700

FIRST SLAVE POINT CORE: 6,355-6,383. The core consists moinlyof white and grey dolomite. The clotted, nebulous, ond microinclusion textures (%e pages 24 and 25) oredeveloped. Some intervals consist of mediumgrey, medium crystollinc: dolomite, Small vugs oredeveloped throughout the cored section. They are lined with coarse to very cwrsely crystolline dolomite and vary from a few millimeters to several #centimeters in maximum dimension. Quartz crystalsand carbonaceous materioloccur in the vugs. Intet.crystolline porosity is developed in addition to the vuggy porosity.

SECOND SLAVE POINT CORE: 6,401-6,565. This coredintervol con readily be divided into two parts: on upper port (6,401-6,513) consisting of dolomite and a lower part 16,513-6,565) consisting moinly of limestone.

79 The dolomite section (6,401-6,513)consists for the most port of the white ond greydolomite although some sections of thecore, reaching up to 15 centimeters in length, ore made up of white coarsely crystalline dolomite. The following textures can be recognized in thewhite andgrey dolomite: microinclusion, mocroinclusion, nebulous, clotted, and pseudo-brecciated. For the interval as o whole the white dolomite makes up obout 35 per cent of the core and the darker, usually matrix-forming dolomite, represents about 65 per cent of the core. The darker dolomite is medium light grey to medium grey in colou~. andmedium tocoarsely crystalline in texture;the medium crystolline typesore the most common. lntercrystolline carbonaceous moterial occurs in thismedium ond coarsely crystalline dolomite. The light coloured phose of the white and grey dolomite in the core is coorse to very coarsely crystalline in texture. Vugs ore common in this phase and they ronge from less than 1 centimeter across up to several centimeters in diameter. They ore lined with very coarse crystals of dolomite; quartz crystals olso occur in the vugs. Carbon- aceous material is frequently present between the crystals of the vug lining. Inaddition to thevuggy porosityintercrystalline porosity is developed in places between the crystals of the dark phase of the white ond grey dolomite. As noted above the section 6,513-6,565 of this core consists largely of limestones. There form CI complex group of carbonates which are difficult to interpret because of the poor condition of the core and the tendency for original textures to be lost by recrystallization. Medium brownish grey to brownish grey intrasparites (possibly biosparites)occur which show fine to coarse grained allochems. They oppeor to grade in parts to a rock with little evidence of allochems and thesemay be "welded" intromicrites or possibly true micrites. In other parts of the core brownish grey biomicrites are developed. The vogue forms of large biogenic fragments can be seen embedded in the biomicrites and some of the micrites (?). There is evidence that o considerable number of massive stromotoporoids occur in the core which in somecases have sporry calcite infilling cavities in thestructure; large ramose forms are olso present. Some intervals of the core probably consistedalmost entirely of large ramose stromatoporoids set in a matrixof sparry calcite. In o fewinstances this rocktype is clearly developed (%e Plote IX) but more often recrystollization of the stromatoporoids to dense biogenic calcite andan apparent deformation (compression) of the rock hove obscured its original nature. Incipient dolomitization occurs in ports of the limestone section. The dolomite crystals are either disseminated more or less evenly through the rock or isolated in small patches. The secondary dolomite is medium andcoorsely crystalline intexture. In some of the more clearly developedbiogenic rocksthe dolomitization is restrictedto matrixmaterial lying between the biogenic fragments. Authigenicquartz prisms occur commonly in some of the micrites (?) and biomicrites of this limestone interval.

West Nat Kotcho a-9-F Location: 0-9-F/94-P-3 Status: obandoned K.B. 2,191 T.D. 6,966 Completed:March, 1961 Muskwocore: 6,636-6,656 (Recovery: 20 feet) Muskwatop: 6,585 Base: 6,656

80 The Muskwo Formation of this core consists of greyish block, nor-colcoreous to slightly calcoreous shale, which shows brown coloured scoremorks whenscrotched with o steel needle. The rock is moderately pyritic in ports. In the lower 2 feet of the core chitinous brochiopodsore very common. Authigenic barite occurs in theshale; it is normally restricted to narrow zones which may reach a thickness of 2.5 inches. Seven of these zones are present in the cored intervol. At the bose of this core the dark shales lie above the Slave Poinl Limestone. A short unbroken section of core 2.5 feet from the bose of this interval shows a contact between 0.15 inch of shaleand 1.5 inches of biomicrite containing crinoid fragments ond stromatoporoid moteriol. The contact is shorp, unduloting ond approxirnotely hori- zontol. Below this thin limestone the lithology passes bock to shale and at the bose of the cored shole intervol another short unbroken section of core appears to represent the contoct with theSlove Point Formotion. In this case o shorp contact is pleservedbe- tween 0.25 inch of shale and l inch of Slave Point Limestone. The above description indicates thot the contact between the Slav,: Point and overlying shales is not o simple, shorp contoctbetween o limestone unit ,md o shale unit. However, it should be borne in mind thot in o well such os the present one, situ- oted close to the facies front, the Slove Point may in foct be overlain by o thin section of the Otter Park Shale which in turn would be overlain by the Muskwo Formation. This could readily account for the minor interbedding of limestone ond shale observed near the contact.

SlovePoint core: 6,656-6,693 (Recovery: 33 feet) SlovePoint top: 6,656 Ease: 6,820

The Upper 15 feet of this interval is modeup lorgely of fragmentcld stromatoporoids. The fragments range in maximum dimension from olmost 2 inches ocrctss(diameter of core) down to particles which fall into the orenoceous size class. The fmgments are either compacted together or disseminated in o matrix of calcilutite which oppeors to be argillaceous in places. Some parts of thesection consist mainly ofcalcilutite. The limestone of this upper intervol varies from brownish grey to light brownish grey in colour. Much of the stromatoporoid moteriol in the rock is recrystallized to dertse biogenic colcite. The biogenic rocks of theupper 15 feet grade down in the lower port of the core to brownish grey to dark brownish grey limestones. denre in texture, in whish moderate omomts of strornatoporoid material ore present. These rocks contoin firNely disseminated corbonoceous material in places.

81 INDEX

Alberta 9, 11, 27, 29-31, 37, 38, 40, 41, 43, 115, 47 Alberta Oil and Gos Con- servation Boord 12, 31 Alberta wells 12 algae- 21, 23 Allanaria olloni- zone 38. allochems 19,20, 59, 65, 67, 68, 72,75, 78, 80 A m co Shale Amco 13 Amphiporo 27, 19, 59-63, 79 65-74, 78. 76, argillaceous material 20 A thob asc o River Athobasco 29 attenuated sequence 36 Austrolionborrier reef complex 40 b arite, outhigenicbarite, 45, 81 BA Shell Klua b-49-F 21, 59 BA Shell Klua Creeka-50-C (I) 52 btt Reef 40 Bear Biltmore #I 14,29, 35, 37 Beaverhill Lake Formation 9, 11, 14,16, 43, 45 core 32 care descriptions 60-63, 73 correlotion 35-40 formation tops 55-58 lithology ond distribution, NorthernAlberta 3 1 -32 Northeostern B.C. 32-34 maximum development in B.C. 32 prev ious descriptionprevious 29 regional sections 29-31 Beaverhill Laketransgression 41, 47 Belyea, H. R. 12 Bero River Formation 11, 43, 46 biogenic material 19. 26. 59, 60, 62, 63, 65, 66,68, 70, 72-76, 78, 79 in dark calcilutites 20, 21 recrystollizotionof 22 biolithiter 24 23, biomicrite 80, 81 biomicrudite 23 biosporites 20, 22, 27,78, 61, 76, 75, 80 biosporruditer 22,75, 76 biota47 41, 40, Bison Lake 27 bituminous shales 43 brachiopods 21, 22,27, 34, 40,41, 60-64, 70, 71, 73, 76 colcilutites 27, 59-74, 76,78, 79, 81 Colcisphoera 27,60, 61 calcite 66, 67, 69, 75

83 California Standard Mikkwa 12-23-98-21W4 30

Colifornia~~ ~ Standard Steen River No. 2-22 13 Colmut Member 29, 30, 32, 37, 38 Cam Lake area 52 Canadian Stratigraphic Service 30 carbonaceous material 20-22, 24, 25, 47, 60, 63-81 carbonate deposition 40 carbonate sedimentation 47 Chinchaga area 32 Chinchaga Formation 9 chitinous brachiopods 81 chitinous material 34, 73 Christina Member 29,30, 32, 38 Clorke Lake area 14,17, 18, 22, 26, 38 Clarke Lake gas field 25, 38, 43, 49, 51 climatic changes 47 conformable contact 35, 36 corals 22, 41, 59, 65 rugose 40 tabulate 40 core descriptions BA Shell Klua b-49-F 59 HB Imperial Union Paddy 0-49-6 (1) 60 HBImp Union Gutah a-99-K 61 HB Union Imperial Paddy x2 61 HB Union Imp Paddy c-14-C 62 Imperial Kahntah x1 63 Imperial Sikanni Chief #I 63 Imp Fontas d-37-8 64 Imp Junior c-98-C 64 Imp Kyklo b-73-F 66 . Pan Am A-I Corn Lake 0-31-1 67 Pan Am et a1 Dilly a-27-K 67 Pan Am et a1 Dilly a-30-K 67 Pan Am July a-65-K 68 Phillips Minaker a-25-D 68 Pure Poc Cheves c-5-A 69 Sohio C & E Ekwan a-55-G 70 Texaco NFA Nig Creek a-79-B (I) 70 Texaco NFA N Tsea d-47-C 71 Texaco NFA Townsoitoi d-44-C 72 Texaco NFA Tsea b-68-K 72 Texaco NFA Walrus b-86-L 73 TGT Tooga Lake c-27-K 73 West Nat et 01 Clarke b-70-1 74 West Not et a1 Clarke c-78-1 74 West Not et a1 Clarke c-47-J 74 West Not et al €vie d-14-F 75 West Not et 01 Evie Lake b-89-E 75 West Nat Imp Clarke Lake c-8-D 77 West Not Imp Clarke Lake b-78-J 78

84 core descriptions (continued) West Not Imp Clarke Lake d-91-L 78 West Nat Imp Clarke Loke c-94-L 79 West Not Kotcho 0-9-F 80 core examinotion 18 correlative facies 35 Cretaceous sediments 31 crinoids 27, 40, 59, 60, 62, 64, 72,81 crystal size 19 dark stromatoporoid-bearing calcilvtites 18-22, 27 dense biogenic calcite 22, 75-78, 80, 81 depositional assemblage 40 depositional environment, SlavePoint Formation 21, 27 depositional thinning 31, 36 Devonian outcrops 31 disconformity 35 discovery wells 51-~ dolomites 21, 24,51, 52, 60, 62, 64, 65, 67-70, 77, 79 colour of 24. 25 textures of 24; 26, 72, 73 dolomite, vuggy 25, 62, 66, 68, 69, 73-75, 77,79, 80 white 26,74, 75, 77, 80 white and grey 19,21, 24-26, 49, 51, 65,66, 68,72-75, 77, 79, 80 dolomitization 23, 25,26, 47, 48, 52, 63, 66, 69 incipient 60, 61, 63, 64,71, 72. 79. 80 drill cutting samples 12,18, 22, 31, 34, 43 drilling season, 1961-62 52 Edmonton mea 11, 29,38 Eifelion 9 Eleutherokommo homiltoni zone 39 Elk Point Group 13, 36,37 Evie Loke area 17, 22 Evie Member IO erosion 31,35, 36, 38, 46, 47 erosion surface 37.45 evoporite deposition 37; 40, 47 focies changes 31, 38 focies equivalent 37, 38 facies founa 41 facies front 9,17, 20, 22, 24, 26, 47,48, 49-52, 77. 81 interpretation of limestones 23 reef development 23, 24 rocks of 22 facies strike 31 faulting 48

85 fauna.Beaverhill Lake Formation 11... 29. 41 SlavePoint Formation 11,19-22, 26, 27, 40, 41 Firebag Member 14,29, 30, 32, 35, 38 fluorite 61 foraminifera 27, 40, 61 Fort St. John 18 Fort Simpson Formation 11, 31, 34, 43, 45-47, 63 Fort Vermilion Member IO, 14,16, 30, 35,37, 41 Gamma Ray Logs 17, 43, 45, 46 Gamma Ray Neutron Logs 20, 29 Gamma Roy Sonic Logs 20, 29 gas fields 49-52 90s production 49 gas reserves 49 90s type 51 gos/woter contact 51,52 gasteropods 22,27, 62, 64, 76 gilsonite 25 Givetian 9 Greot Slave Loke 11, 13,14, 16 Qreen woxy shale 17 gross pay 51 Gulf Stotes Fort Nelson No. 2 43 Gypsum Cliffs area 35 HB Imp Union Gutah a-99-K 26, 27, 61 HB Imperial Union Paddy 0-49-B (I) 26, 52, 60 HB Union Imperial Poddy #2 30, 32, 61 HB Union Imp Paddy c-14-C 62 Horn River Formation IO, 17, 40, 43,45 ldiostromotidoe 19,27, 61, 66, 67,74 . Imp Fontos d-37-B 27, 61 Imp Junior c-98-C 25, 64 Imp Kyklo b-73-F 66 Imperial Kohntah #1 63 Imperial Long Loke 11-IO-107-7W6 30 Imperial Pacific SiphonCreek 1-26-86-16W6 32 lmperiol Sikonni Chief #I 38, 63 inliers 36 intmclasts 19,20, 23, 26,59, 61, 62, 65-67, 69, 74,75, 78 intraclast rocks 26,27, 60, 61, 65, 67,74, 78 intraclost-like structures 20 intromicrites 20,26, 59-62, 65,74, 80 intrasparites 20, 26,27, 59-62, 65, 70, 74,77, 80 Kotcho Lake ore0 14,18, 31,52 Kotcho Loke gas field 51 limestone breccia 16,17, 47, 71 limestone clossificotion 19

86 Livock River Formation 14. 35 Lower Beaverhill Loke unit 30; 32, 35, 36, 38 marker zones 30 McMurray area 14,29, 30, 35 micrite 19,23, 26, 65,66, 68, 71, 72, 76, 77, 79, 80 micrites,fossiliferous 23 micritic matrix 59, 66, 78 microfossils 41 Mildred Member 29, 30 Mississippian 11 Moberly Member 29, 30 Muskeg Formation 9, 30 Muskwo Formation 9-11, 14, 31,32, 40, 47, 81 core 45 core descriptions 80-81 distribution 43-45 formation tops 55-58 lithology 45 log characteristics 43 previous description 43 stratigraphic relationships 45, 46 natural gas 14, 21, 24,47, 49-52 nomenclature, Otter Pork and Beoverhill Loke 40 Northwest Territories 13, 47 Ohio Bede Creek 10-23-106-20 W6 31 oslites 60 ostracodes 21,40, 41, 71, 78 Otter Park Member IO, 11,17, 34, 38,40, 43, 45, 81 member tops 55-58 Paddy area 32, 38 paloeontology 11 paloeontological correlation 41 Pan Am A-1 Cam Loke 0-31-1 67 Pan Am et 01 A-I hoke River c-28-D 45 Pan Am et CII Dilly a-27-K 67 Pan Am et aI Dilly a-30-K 51, 67 Pan Am July a-65-K 68 Peace Point Member 35.. Peoce River 35. 47 Peace River Arch 14;16-18, 31, 37, 43 pelecypods 41 pellets 19, 20 Petitot River are0 17, 18 Petitot River gas field 49, 51 Phillips Minaker a-25-D 68 physicochemical environment 40, 41 Pine Point Formation 9

87 platform reef 40 porosity 21, 25, 62, 79, 80 Prairie Evaporites 9, 30 Precambrian Shield 31 pre-Muskwa erosion 31, 38, 46 Presqu'ile Formation 16, 26 positive area 36, 37 producing zone 51 Pure Imperial Bull b-67-J 38 Pure Pac Cheves c-5-A 69 pyrite 34,43, 60, 62, 68, 73, 75, 77, 81 quartz, authigenic 23, 80 quartz crystals 66, 68, 69, 73, 79, 80 mdiooctivi ty 34, 43, 45 reef complex 23, 24, 40 reef development 47 reef growth 17 reefs, dimensions of 40 regional dip 18 regression 37 regressive deposition 36, 37, 41 reservoir 49, 51,52 reservoir rock 49 rock colour 19 sedimentary processes 41 seismic methods 52 Shale Unit of Law 29 shelf dolomites 21, 52 potential production 52 shell fragments 21,59, 61, 72 SlavePoint Formation 9-11, 29-32, 43, 45-47, 49-52 core 18 core descriptions 59-81 correlation 35-40 deposition 40-41 distribution in B.C. 14-18 formation tops 55-58 lithology in Alberta 27 lithology in B.C. 18-27 maximum development 38 previous description 13,14 Sohio C & E Ekwan a-55-G 70 Southern Production Atlantic 87- 1 32 sparry calcite 20, 22, 60, 65, 68-71, 75,78, 80 sphalerite 25, 77 Spongiostromota 21 stratigraphic thinning 31, 35, 36 stromotoporoid biomicrites 19,22, 23, 79 stromotoporoid biosparites 19, 22, 23,76 88 . stromatoporoidlimestones 38 stromotoporoids 18-24, 26, 27, 40, 41, 59-81 various types various 19 styloliticpartings 20, 62, 67, 73 SulphurPointFormation 16, 26, 41 superficial oiilites 27, 60 Swan Hills Member 38, 40 table of formations 10 tectonic movements 47 terrigen ou s material 40 material terrigenous T erritories FormationTerritories 13 Texaco NFA Nig Creek 0-79-6 (1) 70 Texaco NFA N Tseo d-47-C 23, 71 Texaco NFA Townsoitoid-44-C 27, 72 Texaco NFA Tsea b-68-K 72 Texaco NFA Walrus b-86-L 73 Texaco R.O. Corp. Mockay R iver 6-13-91-18River W4 30 TGT Tooga Lake c-27-K 73 Thamnopora 20-22, 27. 59-62, 64-67, 70, 71, 73, 74, 76 thin sections 20 transgressive deposition 36, 37, 41 transitionalcontact 45, 46 Tsea area 52 typesection, MuskwaFormation 43 S lave Point FormationPointSlave 13 unconformity 35, 45, 46 Upper BeaverhillLake unit 30, 32, 38, 47 Upper Devonian 11, 13 vuggy porosity 47 W aterw ay s Formation 29, 38 Waterways Formation29, WattMountain Formation 13, 16, 17, 41 Watt Mountain-Sulphur Point assemblage 10, 11, 16, 17, 37, 47 assemblage tops 55-58 well control, SlavePoint Formation 18 Wentworth scale 19 West Not et 01 Clarke b-70-1 74 West Not et 01 Clarke c-78-1 74 West Not et a1 Clarkec-47-J 74 West Not et 01 Evie d-14-F 75 West Not et a1 EvieLake b-89-E 75 West Not Imp ClorkeLake c-8-D 77 West Not Imp Clarke Lake b-78-J 22, 78 West Not Imp Clarke Loke d-91-L23, 25, 78 West Not Imp Clarke Lake c-94-L 23, 79 West KotchoNot a-9-F 45, 80

89 West Not KotchoLake c-67-K 51 West NotPetitot River d-24-D 51 Woodley Imperio1 Kluo o-27-G 38

. Plate I. Dark stromatoporoid-bearing colcilvtite with only minor omounts of biogenic material. x 2/3. From the well, BA Shell Klua b-49-F (94-J-9) at 6,524 feet. Photogroph of cut and etched core xrmple.*

Plate II. Dark stromatoporoid-beoring colcilutite with moderate amounts of encrusting stromatoporoidr andbrachiopod fragments. x 4/5. From BA Shell Klva b-49-F (94-J-9) at 6,520 feet. Photograph of cut and etched core sample.

*The coin used CIS a scale in Plates I to XX is 1 .9 centimeters in diameter. Plate I.

. Plate II. Plate 111. Dark stromotoporoid-bearing calcilutitewith moderate amounts of biogenic materiol (Am hi ora mort common type)showing welldeveloped nodular stromoto- poroidr. xemthe well, ImpFontaa d-37-B (94-1-7) at 6,459 feet. Photograph of cut and etched core sample.

Plate IV. Darkstromotoporoid-bearing calcilutite containing abundant Thomnopora ond ramose rtrmotoporoids. Noturol size. From the well, BA Shell Kluo b-49-F (94-J-9) at 6,512 feet. Photograph of cut and etched core sample. Plate Ill.

Plate IV. Plote V. Dark stromotoporoid-bearing calcilutitewith abundant laminarand ramose stromatoporoids. x4/5. From the well, BA ShellKlua b-49-F (94-J-9) at 6,507 feet. Photograph of cut and etched core mmple.

Plate VI. Port of massive rtromotoporoid from the well, BA Shell Kluo b-49-F (94-J-9) at 6,478 feet. x 3/5. This specimenoccupies CI continuous22-inch section of the core. Photograph of cut and etched surface of core xlmple. Plate V

Plate VI Plate VII. Limestone from the faciesfront. Pwrly sorted stromatoporoid biosporite from West Not et 01 Evie Lake b-89-E (94-J-15) ot 6,777 feet.Notural size. Rock consists mainly of poorly sorted stromatoporoid frogmentr partly recrystallized to dense biogeniccalcite, set in a matrixof sparry colciteand dense calcite.Note large brochiopod shell atleft. Dark carbnoceousmaterial occurring in fissures in the recrystallized stromotoporoid fragments con be seen ut lower left of photograph. Photo- graph of cut and etched core sample.

Plate VIII. Limestonefrom the faciesfront. Sorted stromotoporoid biorparite from West Not et aI Evie Lake b-89-E (94-J-15) at 6,861feet. Notural size. Mortof the stromotoporoid fragments haveundergone recrystallizationto dense biogeniccalcite. Dark rings of carbonaceous moterial surround mony of the frogmentr. The darkbond which crosses the lower halfof the specimen contoinsbiogenic fragments which are smaller thon those in other ports of the rock. Photograph of cut and etched core sample.

Plate IX. Limestone fromthe facies front. Stromatoporoidbiosparrudite from West Not Imp Clarke Lakec-94-L (94-J-9) ot 6,523 feet. x 4/5. Roundedfragments of ramose stromotoporoids are set in a matrix of sparry calcite. Photograph of cut and etched core sample.

Plate X. Limestone fromthe facies front. Stromatoporoid biomicrudite from West Nat Imp ClarkeLake c-94-L (94-J-9) at 6,539 feet.Approximately natural size. Ramose and nodvlor stromatoporoids are closely pocked in a micritic motrix. Photograph of cut and etched core sample.

Plate XI. The white andgrey dolomite--microinclusiontexture. x 5/6. From Texaco NFA Tsea b-68-K (94-P-5) at 6,881 feet. Photograph of cut core surface.

Plate XII. The white andgrey dolomite--macrainclurion texture.x 3/4. From West Nat Imp Clarke Laked-91-L (94-J-9) at 6,463 feet. Photograph of cut coresurface. Plate XI I. Plate XIII. The white and grey dolomite--bonded texture. Approximately natural size. Details of location and depth not available ot time of publication. Photograph of core sample.

Plate XIV. The whiteand grey dolomite-right ride of photograph shows the clotted texture.Approximately natural size. From West Not Imp Clarke Loke c-94-L (94-J-9) at 6,480 feet. Photograph of cut core surface. Plate Xlll

Plate XIV.

i Plote XV. The whiteand grey dolomite-left side of photograph shows thenebulous texture. Natural size. FromWest Not Imp Clarke Loke c-94-L (94-J-9) ot 6,472 feet. Photograph of cut core surfoce.

Plate XVI. The white and greydolomite--pseudo-brecciated texture. x 5/6. From West Not Imp Clarke Lake c-94-L (94-J-9) ot 6,467feet. Photograph of cut core surface. Plate XV.

Plate XVI Plate XVII. Darkrtromatoparoid-bearing colciluiite from Pure POC Cheves c-5-A (94- J-ll) at 7,507 feet.Thin section in transmittedunpolarized light. x 15. Amphipora coenorteum atright of photograph; cross section of ortrocode at lowercentre. Note presence of dark bodies 0.06 to 0.2 millimeter in diameter.

Plate XVIII. lntrasporite from HB Imperio1 Union Paddy a-49-6 (1) (94-H-16) at 7,986 feet. Thin section in transmittedunpolarized light. x 11.5. Irregularly shaped intraclasts, mainly 0.1 to 0.5 millimeter in diameter are set in 01 matrix of sparry calcite. O6Iiter and ruoerficial o5lites ore olx) common in the rack.

Plate XIX. Colcorenite showing cross sections of ostracodes andCalcisphaera from HB Imp UnionGutah a-99-K(94-H-10) at 8,081 feet. x 13. Photograph ofetched surface. The peripheral spines of several specimens of Colcisphaero can be seen in the lower left-hand quarter of the photograph.

Plate XX. Foraminiferaand brachiopod biosparite from HE Imp UnionGutoh a-99-K (94-H-10) ot 8,102 feet. Thin section in transmittedunpolarized light. x 8.5. Photo- graph showscross section of several foraminiferaand numerous brachiopodshell fragments. The matrix material is sporry calcite. Plate XVII. Plate XVIII.

Plate XIX. Plate xx.