GEOLOGY OF THE CARBON CREEK AREA (930/15) By A. Legun INTRODUCTION pattern was predictedby the mcthod of structure contoursintrr:;s:ct- ing topography between two points where the attitude of the E,eo- TheCarbon Creek area is located 30 kilometres west ofthe logic contact is known. W.A.C. Bennett DaminnortheasternBritishColumbia(Fig.22-1). Thickness of formations WLScalculated from air photographs. Fieldwork in 1985 war directed toward compilation of the geology Scaleand adjustments for change in scalewith clcvation wer? of the eaqt halfof the map sheetand intcpraring it with 1084 work in calculated using the centreareas of airphotographs. Furthcrco--cr- the west (Leg"". 1985b). The focus of 19115 work was the Carbon tions were made for slope and abliqueness to strike of ridges kin; Crceksyncline which contains more than 70 million tomes of traversed. Relevant formulas are found in Ragan (19x5, p. 21: ani mineable coal, Previous work in the area includes thatof Matthews Compton ( 1962. p. 84). Stratigraphic thickness data arepresent,:d i I (1947). Hughes (1964). Stottand Gibson (1980). Stott (1083). Table 22-1 Legun (1983, 1984. 1385), Gibson (1985:1.and personnel of Utah MinesLtd,andGulfC;madaResourceslnc (1080~19X3assessment reports). The area incltdesthe CarbonCreek licences of Utah Mines STRUCTURE Ltd. as well as the former licenses of Wcst Carbon Creek (Utah The structure of the map-a)-ea consists essentially of a pair c'f Mines Ltd.) and Whittmhbit (Gulf Canadd Resources Inc.). broad synclines separated by a box-like anticlinal structure tizip. Previous work has not adequately resolved the geology or the 22-3). This fold sequence is boundedby major faults. To the wev th: stratigraphy of the are:i: particularly areas bounding the two major WcstCarbonCreeksynclineis~aultej.againstTriassiclimeston~:ron coa-bearing synclines of Carbon Creek and Wesl Carbon Crcek. the Pardonet thrust. To the easl. Fernie shale on the east limb cf the Figure 22-2 shows the geology based ona 19x3 I:125 000 compila- Carbon Creek synclineis faulted against FortSt. John Group shalcs tion map of NTS 930 by the Geological Survey of Canada (Open on the Carbon thrust. Both major synclines tightento the sokltlm!.t File 925). This can be compared to the first draft of a detailed withsubsidiary folding and laulting. Both are doubly plurging compilation by the writer (Fig. 22-3). forming a canoe shapemodifiell by topography. Resultsof stnlcturid and stratigraphic mapping are bcst discussed in the context ,f a METHOD OF STIJDY compuison of old and new maps iFigs. 22-2 and 22-3). The $:lielit The writer, assistcd alternately by Pat Ilesjardins, Pdul Elkins, changes are as follows: and Hugh Chtistic. spent 32 field days tracing and mapping geo- (1) Extension ofCething Formation coal measures from Carbon logic units on the periphery of the Carbon Creek syncline. Some Creek to the Beattie Peak!, area where they pinch out in a work was also done in West Carbon Creek and outside the map-area series of tight, faulted folds.The synclinal extenrion s to the east to solve spccific problems of mapping and correlation. broader than shown ontne (jeological Survey of Canada ,nap Air photographs were used to plot stations as well as to extrapolate and additional faults art: present. geirlogic contacts hetween traverses. Fieldwork data was integrated (2) More extensive distribu!ionof the Bickford Formation ir the with data from previous maps. In areas of poor exposurc, outcrop area of Mount Monach (The Monach). I Figure 22~1.Location of the West Carbun Creck mapxma. -~ Bntish Columbia Ministry of Energy, Mines and Petrolcum Resources. Gevlugical Fieldwork, 1985, Wpcr 1YXh~l I55 I57 TABLE 22-1. FORMATION THICKNESS DATA (See Fig. 22-3 for locations.) Heattie Monteith Peaks Monach Bickford Cadomin A rea Formation Area Formation Formation Formation Formation Metres Metres Metres Metres Metres Ridgesouth of MountWriglcy ....... - 400 442 148 26X Mount Monach..... .... ..... .. - - 336 210 ~ . .... ....Beattie Peaks ..... .. 564 394 ~ - Mount Rochfort ...... ....... - - 2x9 349 CarbonLake ............ .... 612 284 129 33 I MountMcAllister . ... - 212 122 256 MountGething (Interpretation I) ........ >626 >I19 ~ - Mount Gething (Interpretation 2) ........ X46 90 90 * >I 19 (3) Afault SlNCtUre on thewest limb of theCarbon Crcck The fossil bivalve Buchia is vcry common in some locales and syncline near Mount Rochfort and Mount Cowper. less so in others. It may occur as discrete coquina 'beds' within the (4) A much greater southern extent of Gething coal measures in arenites or as dispersed single shells: the degreeof shell fragmenta- the West Carbon Creek syncline and a vcry different syn- tion varies considerably from one bed to another. The thickness of clinal configuration. the Monach Formation varies more than previously reported (Legun. 1985b). It is thick in the anticlinal area between Mount MINNES GROUP Cowper andMount Monach, reaching 400metres or more; in additionthere is a thicktransition zone from the Beattie Peaks MONTEITH FORMATION Formation.Thickness trends west of the anticlinal structure are The Monteith Formation consists of two lithofacies: uncertain. However. to the eastat Mount McAllister nr Carbon Lake (1)., Clean areniterand auartz arenitesthat are massiveto thc Monach Fornration is much thinner (120 metres): there is vir- crossbedded. tually no underlying transition zone and individual arenite units are (2).. Clean to dirty arenites (quartz arenite to wacke) interbedded thinner. The Monach Formation forms a thick, east-tapering lensin with siltstone and shale. the Carbon Creek area. In the Carbon Creek area lithofacies (1) is dominant in the upper BICKFORD FORMATION half of the Monteith and lithofacies(2) is common in the lower half of the Monteith. Shaly recessive intervalsin the Monteith can be 50 The Bickford Formation is a sequence of interbedded arenites and or more metres thick. The base of :he Montcith is transitional into shales. The arenites includesalt andpepperlithic varieties as well as shales of the Fernie Formation. The Monteith Formation is esti- quartz arenites. The shales include carbonaceous shale, dark grey mated to be 612 metres thick near Carbon Lake. Siltstones, and mudstones. Beds of grit and thin coals are presentin some areas. Sedimentary structures include low-angle crossbedding BEATTIE PEAKS FORMATION in the arenites, herbedding in the shales, symmetric ripples, and The BeattiePeaks Formation is dominated by darkgrey and vertical and U-shaped burrows(Diplocrirerion). Plant debrisas well brown shale with inrerbedsofsiltstone and arenite. Arenifeunits are as root casts occur, These features indicdte depositional environ- fissile and increase in thickness and number toward the top of the ments ranging from marginal marine to marginal continental; mar- Formation. Burrowing is common and bedding surfacesare marked ginal marine is more evident in the east, for example, near Carbon by trace fossils of unknown type. The lower contact of the Heattie Lake. Peaks shale with Monteith quartz arenites is sharp and unconforma- The Bickford Formation shows a weak tendency to coarsen up- ble, easily traced on air photographs. The upper contact with the ward and thick arenites may directly underlie the Cadomin Forma- MonachFormation is gradational.The thickness of the Beattie lion. The contact with the Cadomin Formation is placed with the Peaks is calculated to be 392 metres at Beattie Peaks and 212 metres appearance of successive units of pebbly arenite, an increase in at Mount McAllister. carbonaceouscontent, and the general disappearance of flaggy (low-angle crossbedded) and dark coloured lithic arenites.In some MONACH FORMATION locales, such as the east flank of Mount Rochfort. one or more The Monach Formation is typified by units of flaggy, planar to isolated pebbly arenite units,which may be channel deposits, occur shallow crossbedded arenites, massive arenitc, and lesser quartz belowthis dcfincd contact; perhapsthere is agradational and arenite.The units, whichcan be 10 metresor morethick, are continuouschange in sedimentationbetween Bickford and Ca- separated by much thinner intervals of non-carbonaceous shale. domin deposition. In other areas. for example the Carbon Creek Quartz arenites, which may be gritty, form local marker units. The road,the contact is sharp, and burrowedsiltstone (marine) and Monach Formation forms the top of a coarsening upward sequence quartz arenite are in contact with pebbly arenite full of log casts that begins in shales of the Beattie Peaks Formation. The contact (alluvial channel). between the two formations is arbitrarily placed wh.ere arenitc units The lower contact of theBickford Formation is placedwhere become prominent. Arenite units are thin toward the base of the interbedded arenite and shale pass into thick successive units of formation and dominated by horizontal laminations. Units thicken arenite of the Monach Formation with a loss of carbonaceous con- up section and exhibit shallow-angle planar crossbedding, trough tent. This change can be abrupt or gradual. Where flaggy arenitesof crossbedding.and uncommon hummocky cross-stratification. the Bickford are exposed and shaly recessivc units are covered it is Somearenites show the peculiar feature of grading over a few particularly difficult to distinguish the Monach from the Bickford. decimetres into quartz arenite that forms eithera cap on thc unit or a Carefultracing on air photographs of thelower contact of the lens within it. Bickford suggests