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1999 Sedimentology and stratigraphy of the falher c member, Spirit River formation, northeastern British Columbia
Caddel, Edward Matthew
Caddel, E. M. (1999). Sedimentology and stratigraphy of the falher c member, Spirit River formation, northeastern British Columbia (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/11252 http://hdl.handle.net/1880/25381 master thesis
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THE UNIVERSfTY OF CALGARY
Sedirnentology and Stratigraphy of the Falher C Member.
Spirit River Formation, Northeastern British Columbia.
by
Edward Matthew Caddel
A THESIS
SUBMITTED TO THE FACULTY OF GRADUATE STUDIES
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE
DEGREE OF MASTER OF SCIENCE
DEPARTMENT OF GEOLOGY AND GEOPHYSICS
CALGARY, ALBERTA
OCTOBER, 1999
O E. Matthew Caddel 2000 National Library Bibliotbque nationale of Canada du Canada Acquisitions and Acquisitions et Bibliographic Services services bibliographiques 395 Wellington Street 395. rue Wellington OnawaOf'l KlAW OltawaON KIA ON4 Canada Canada
The author has granted a non- L'auteur a accorde une licence non exclusive licence allowing the exclusive pennettant a la National Library of Canada to Bibliotheque nationale du Canada de reproduce, loan, distribute or sell reproduire, pr6ter7distribuer ou copies of this thesis in microform, vendre des copies de cette these sous paper or electronic formats. la forme de microfiche/film, de reproduction sur papier ou sur format electronique.
The author retains ownership of the L'auteur conserve la propriete du copyright in this thesis. Neither the droit d'auteur qui protege cette these. thesis nor substantial extracts fiom it Ni la these ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent 8tre imprimes reproduced without the author's ou autrement reproduits sans son permission. autorisation. The Falher C stratigraphic unit of the Falher Member, of the Spirit River
Formation, in northeastern British Columbia, is a product of deposition by wave and storm processes along a graveliferous, wave-dominated strandplain. Two parasequences and one sequence comprise the Falher C, forming two mappable shoreline trends that are present in the subsurface. The northern parasequence trend (CO) is an early highstand, sandy shoreface facies association occurring in the subsurface of British Columbia. The southern trend consists of a highstand sandy shoreface facies association (C1 parasequence) and a regressive systems tract stratal sequence (RST; C2 sequence) conglomeratic shoreface. Gravel is introduced to the C2 sequence as bedload from narrow, deeply incised channels during a falling relative sea level. Internal erosional surfaces within C2 are source diastems (SD's) which amalgamate along the basal surface to form a regressive surface of erosion (RSE). Conglomerate with the highest porosity and permeability occurs along the southern edge of the C2 sequence, adjacent to coevally deposited channels.
iii ACKNOWLEDGEMENTS
Funding for this thesis was provided by an NSERC post-graduate industrial scholarship in conjunction with Canadian Hunter Exploration Limited and Ulster Petroleums Limited. The Department of Geology and Geophysics at the University of Calgary provided additional personal funding and support. At Canadian Hunter Exploration Limited. I would like to thank Dave Smith and Ron Grams in particular for their support and discussions regarding the Falher C. I would also like to thank Ray Geuder, Dave Willey, Doug Robertson, Ruth Nixon and the remainder of the Deep Basin Team for their technical and financial support. At Ulster Petroleums Limited, I would like to thank Dr. Tom Moslow in particular, for his supervisory and technical support. I would also like to thank the staff at Ulster Petroleums Limited for financial, technical and computer support. At the University of Calgary, I would especially like to thank Dr. Ian Hutcheon for supervisory support, Lynne Maillet-Frotten for her computer-support miracles, Regina Shedd for research aid, and Fed Krause for technical discussions. I would also like to thank Dr. J.P. Zonnevald, Jon Greggs, Sharron Kaser, John Juigalli, Malcolm Bertram, Maurice Shevalier, Dr. Don Lawton, Henry Bland, Dr. Derald Smith and Rick Meyers for support and/or advice in one form or another. Personally, I would like to thank my wife Christina for her help, patience and understanding while I have been finishing the thesis. I would also like to thank my field-assistants Gordon Quapp and Bart Blakney. I would like to thank my parents and family for their personal support. I would also like to thank my friends (especially Jason, Jen, Lynn, and Curtis) for reminding me that the thesis is not worth stressing too much about. DEDICATION
I would like to dedicate this thesis to my lovely wife Christina Caddel, who has patiently waited for me to finish this thesis. She has been there to remind me not to get too stressed out, while at the same time attempting to maintain my focus on the thesis. Her help with printing and page numbers was greatly appreciated. Thank you, Christina.
2.5.5 Facies 30 .Description ...... 2.5.6 Facies 3 .Interpretation ......
2.6.1 Facies 4 = Overview ...... 2.6.2 Facies 4A .Description ...... 2.6.3 Facies 48 .Description ...... 2.6.4 Facies 4C .Description ...... 2.6.5 Facies 40 .Description ...... 2.6.6 Facies 4 .Interpretation ...... 2.7.1 Facies 5A .Description ...... 2.7.2 Facies 58 .Description ...... 2.7.3 Facies 5 .Interpretation ...... 2.8.1 Facies 6 .Overview ...... 2.8.2 Facies 6A .Description ...... 2.8.3 Facies 6B .Description ...... 2.8.4 Facies 6 .Interpretation ...... 2.9.1 Facies 7 .Description ...... 2.9.2 Facies 7 .Interpretation ...... 3.0 STRATIGRAPHIC FRAMEWORK...... 3.1 Introduction to Sequence Stratigraphy ...... 3.2 Sequence Stratigraphy in the Falher Member ...... 3.3 Outcrop Stratigraphy...... 3 -3.1 Facies Assoc~at~ons...... 3.3.2 Parasequences...... 3.4 Cross Sections ...... 3.4.1 Cross Section ADA'...... 3.4.2 Cross Section 6-B'...... 3.4.3 Cross Section C-C' ...... 3.4.4 Cross Section 0-0'...... 3.5 lsopach and Paleocurrent Maps...... 3.5.1 lsopach Map of C2...... 3.5.2 Net Conglomerate...... 3.5.3 Open Framework Cong1omerate:Sand Matrix Conglomerate.... 3.5.4 Paleocurrent Map ...... 3.6 Ground Penetrating Radar...... 3.7 Stratigraphic Architecture ...... 3.8 Paleogeography...... 4.0 SUBSURFACE STRATIGRAPHIC FRAMEWORK...... 4.1 Subsurface Stratigraphy ...... 4.2 Regional Cross Sections ...... 4.2.1 Regional Cross Section R1...... 4.2.2 Regional Cross Section R2...... 4.2.3 Regional Cross Section R3...... 4.2.4 Regional Cross Section R4...... 4.3 Stratigraphic Architecture...... 4.4 Depos~t~onalHistory ...... 5.0 STRUCTURAL GEOLOGY ...... 5.1 Structural Style of Deformation in the B.C. Foothills...... 5.2 Palinspastic Restoration...... 6.0 DISCUSSION...... 6.1 Sequence Stratigraphy and the Regressive Systems Tract ...... 6.2 Depositional Setting and Modem Analogues for the Falher C ...... 6.3 Channel Incision and Avulsion ...... 6.4 Exploration Concerns ...... 6.4.1 Datum Choice ......
viii 6.4.2 Channel Reservoirs...... 177 6.4.3 Permeability ...... 178 7.0 CONCLUSIONS...... 180 References ...... 183 LIST OF TABLES
Table 1-1 Reserve values for the Spirit River Formation ...... 3 Table 2-1 Table of Facies (part 1) ...... 16 Table 2-2 Table of Facies (part 2) ...... 17 Table 3-1 Paleocurrent Measurements...... 104 Table 6-1 Phanerzoic sea-level cycle orders ...... 155 LIST OF FIGURES
Figure 1-1 Lccation Map ...... Figure 1-2 Table of Formations...... Figure 1-3 Outcrop Study Area ...... Figure 1-4 Subsurface wells for northeastern British Columbia ...... Figure 2-1 Shoreline Terminology ...... Figure 2-2 Facies 1 and 2 in outcrop (FC-23) ...... Figure 2-3 Coal (Facies 1) with pebble indentations (MS-39) ...... Figure 2-4 Plant fragments (Facies 1) (a-91.D/93.P.1) ...... Figure 2-5 Facies 2 in outcrop (FC-18) ...... Figure 2-6 Facies 2 in core (coal well T.21) ...... Figure 2-7 Thin section photomicrographs of Facies 2 (a-41.H/93.P.2) ...... Figure 2-8 Outcrop and hand sample photos of Facies 3A ...... Figure 2-9 Trough cross-bedding in Facies 3A on Mount Spieker ...... Figure 2-10 Thin section photomicrographs of Facies 3A (FC.14) ...... Figure 2-1 1 Thin section photomicrographs of Facies 3 (b.53.A/934.16) ..... Figure 2-12 Facies 3C in outcrop (FC.9) ...... Figure 2-13 Conglomerate toesets in sandstone (FC.6) ...... Figure 2-14 Interbedded conglomerate and sandstone (Facies 3C) ...... Figure 2-15 Wood casts on lower bounding surface of Facies 3C ...... Figure 2-1 6 Zones within gravel beachface...... Figure 2-1 7 Diplocraterion isp . in outcrop from Facies 4A (FC.23) ...... Figure 2-1 8 Hummocky cross-stratif ication in Facies 46 (FC.5) ...... Figure 2-19 Channel deposits (Facies 5) ...... Figure 2-20 Thin section photomicrographs of Facies 6A ...... Figure 2-21 Facies 66 in outcrop ...... Figure 3-1 Correlations of the Falher and Wilrich Members (Cant, 1984)..... xi Figure 3-2 Depositional interpretation for the Falher C (Casas. 1996) ...... Figure 3-3 Bullmoose Mountain photo mosaic ...... Figure 3-4 Core-gamma correlation for exploratory coal well C-15 ...... Figure 3-5 Idealized vertical stacking pattern of facies in outcrop ...... Figure 3-6 Locations of outcrop cross~sections...... Figure 3-7 Cross-section A-A'...... Figure 3-8 Measured sections FC-19 and FC-20 ...... Figure 3-9 Photo mosaic of the Falher C in Meikle Cirque ...... Figure 3-10 Erosional basal surface (RSE) of the C2 PSFA ...... Figure 3-1 1 Cross-section 8-B' ...... Figure 3-12 Core description and gamma log for coal well BP.69a ...... Figure 3- 13 Cross-section C-C' ...... Figure 3- 14 Cross-section D-D'...... Figure 3-15 lsopach map of the C2 PSFA ...... Figure 3- 16 Net conglomerate map for the C2 PSFA ...... Figure 3-17 Open framework:Sandy matrix conglomerate map ...... Figure 3-18 Rose diagrams for wood casts in the C2 PSFA ...... Figure 3-19 Location of the ground penetrating radar survey ...... Figure 3-20 GPR lines 01 , 02, and 04 ...... Figure 3-21 GPR lines 03, 05, and 06 ...... Figure 3-22 Fence diagram for the GPR lines...... Figure 3-23 GPR survey methodology ...... Figure 3-24 Paleogeography of the Falher C in outcrop ...... Figure 3-25 Geometry and stacking pattern of the C1 and C2 PSFA's...... Figure 4-1 Location of cross-sections R1 to R4...... Figure 4-2 Legend for regional cross-sections R1 to R4...... Figu re 4-3 Cross-section R 1......
xii Figure 4-4 Cross-section R2...... Figure 4-5 Cross-section R3...... Figure 4-6 Cross-section R4 ...... Figure 4-7 Shoreline trends for the CO and C1/2 PSFA's...... Figure 4-8 Depositional interpretation for the Falher C (part 1) ...... Figure 4-9 Depositional interpretation for the Falher C (part 2) ...... Figure 5-1 Structural geology at Bullmoose MountainlMount Spieker ...... Figure 5-2 Correlation between exploratory coal wells BP-69a and MS-39... Figure 5-3 C1/C2 trend Bullmoose MountainIMount Spieker ...... Figure 5-4 Balanced cross-section (McMechan. 1994) ...... figure 5-5 Location of structural cross-sections (Jones. 1986) ...... Figure 5-6 Balanced and restored cross-section 6 (Jones. 1986)...... Figure 5-7 Balanced and restored cross-section C (Jones, 1986)...... Figure 5-8 Palinspastically restored shoreline trends for the Falher C ...... Figure 6-1 Formation of erosional surfaces due to lowered sea-level...... Figure 6-2 Stratigraphic architecture of the regressive systems tract ...... Figure 6-3 Stratigraphic architecture of the falling stage systems tract ...... Figure 6-4 Offlapping shoreface deposits in a falling relative sea-level...... Figure 6-5 Deposition of facies associations during falling relative sea-level Figure 6-6 Paleogeography of the Falher C in outcrop ...... Figure 6-7 Deposition of coals paleolandward of strandplain deposits ...... Figure 6-8 Holocene regressive shorelines along the Narayit coast, Mexico. Figure 6-9 Wave-cut terraces along Holocene deltas during sea-level fall .... Figure 6-10 Correlation errors for the Falher C ...... Figure 6-1 1 Marine flooding surface vs . downlap surface as a datum choice
xiii 1.0 INTRODUCTION
1.1 PREAMBLE In the Deep Basin of Alberta and British Columbia (Figure 1-I),the Spirit River Formation is a lithostratigraphic unit comprised of conglomerate, sandstone, siltstone, shale, mudstone and coal, and comprises one of the most prolific gas reservoirs in Western Canada (Masters, 1984). Most of the economically recoverable gas occurs in permeable conglomerates that are bounded above and below by carbonaceous mudstone and coal and bounded laterally by non-permeable sandstone. The two most productive Spirit River Formation producing gas fields in Alberta are the Elmworth and the Wapiti Fields (Table 1-1 ). The Falher Member is part of the Spirit River Formation (Figure 1 - 2), and is informally divided into the Falher A, 6, C, D, E and F. Total marketable reserves for the Falher C in Wapiti and Elmworth amount to 2,897~106m 3 , from an initial volume in place of 4,024~10~rn~(Alberta Energy and Utilities Board, 1 996).
1.2 OBJECTIVES The first objective of this study is to provide an interpretation for the depositional origin of facies in the Falher C stratigraphic unit. The depositional origin and paleogeography of the Falher units have been examined at a regional level by a number of authors (Leckie, 1983; Smith et a/., 1984;Jackson, 1984; Cant, 1984). The conglomerate facies have been interpreted as being deposited in a prograding strandplain or barrier island system that parallels and defines the paleoshoreline. The second objective of the study is to determine predictive geometries and spatial relations of the Falher C conglomerate facies. This objective is primarily applicable to hydrocarbon exploration. In the subsurface, to define an exploration play based on well log and core data, a reliable depositional model is most valuable. By determining the facies geometry of the Falher C
# of Marketable In Place Cumulative pools Reserves Volume Production (106m3) (106m3) (1 06m3) ELMWORTH 74 33,078 46,803 16,962 Wapiti 47 12,749 17,150 7,905
Total 121 - 45,827 63,953 24,867 I
Table 1-1 Reserve values for the Spirit River Formation (from Hayes, 8.J.R. etal., 1994)
5 conglomerates, and by defining their spatial relationships, both laterally and vertically, one can more readily predict, with a limited data set, the occurrence and trend of a potential resenroir. The geometry of the conglomerate facies is also significant from a sedimentologic perspective. Gravel shorelines have rarely been studied in contrast to sandy shorelines, in both recent (Emery, 1955; Bluck, 1967a; Carr, 1969; Orford, 1975; Kirk, 1980; Matthews, 1980; Carter and Orford, 1984; Ogren and Waag, 1986; Williams and Caldwell, 1988; Hart, 1991; Leckie, 1993, 1994) and ancient successions (Clifton, 1973; Leckie and Walker, 1982; Bourgeois and Leithold, 1984; Plint et al., 1986; Plint and Walker, 1987 Bergman and Walker, 1987; Massari and Parea, 1988, 1990; Amott, 1991, 1993; Moslow, 199 1; Hart, 199 1; Hart and Plint, 1993, 1995; Moslow and Schink, 1995; MOS~OW, 1998). Understanding the nature and geometry of the conglomerate facies in the Falher C, will provide a model for enhancing the predictability of conglomerate shoreface reservoirs in the subsurface. A third objective is to develop a sequence stratigraphic framework for the Falher C facies. Sequence stratigraphy has become a very useful tool when studying marine siliciclastic deposits. Recently, a number of authors have attempted applying sequence stratigraphic models to the Falher Member (Arnott, 1993; Cant, 1995; Casas and Walker, 1997; Rouble and Walker, 1997). An accurate sequence stratigraphic framework will provide for greater resolution of facies geometry, reservoir characterization, outcrop to subsurface correlation, and insight to the origin of stratal surfaces. The fourth objective of this study is to determine approximate values of structuraVtectonic displacement of the Falher C in outcrop and position it roughly to its original, depositional location. The Falher C in the subsurface of Alberta and British Columbia has an east-west orientation, but occurs in outcrop to the northwest of this trend. Determining whether its present-day position is due largely to structural events or due to depositional changes in orientation of the shoreline, may be done by palinspastically restoring its location in the study area. 6 The final objective is to apply the outcrop observations to the subsurface, using conventional oil and gas well logs, and to assess the reservoir potential of the Falher C conglomerates from the outcrop belt to the Alberta border. This is done through construction of cross sections and outcrop comparisons as an extension of the Falher C trend into the subsurface of the Foothills and Plains of northeastern British Columbia.
1.3 PREVIOUSWORK There have been a number of studies of the Spirit River Formation and its equivalents, some of which focus directly on the Falher Member. However, very few studies have focused directly on the Falher C and very few have focused on the British Columbia strata in subsurface or in outcrop (Leckie, 1983; Carmichael, 1983). Stott (1968, 1982) did initial outcrop work of the Gates Formation (Spirit River Equivalent) for the Geological Survey of Canada. This outcrop work was largely regional and focused on many formations within the Cretaceous strata. Regional paleogeographic maps were constructed for the lower Cretaceous in northeastern British Columbia. The conglomerates of the Gates Formation were examined on Bullmoose Mountain and identified as "alluvial deposits" and the sandstones as "shallow marine" (Stott, 1968). This interpretation was refined to include the conglomerates and sandstones as "low-lying deltaic facies" as recognized by 'lobes of sediment from coalescing fans" (Stott, 1982). Stott also recognized four major transgressive/regressive cycles during Albian time and included the Moosebar and Gates Formations under the first t ransgressive/regressive cycle (Stott, 1982; Figure 1-2). In northeastern British Columbia, there have been two Ph.D. dissertations focusing on the sedirnentology and stratigraphy of the Spirit River equivalents. Leckie (1983) focused on the Gates Formation for NTS map sheet 93-P. Carmichael (1983), focused on the Gates Formation for NTS map sheet 93-1. Both of these studies were regional in extent and neither focused specifically on the Falher C. These studies overlap in the region of Mount Spieker (Figure 1-1). 7 Leckie (1983) provided a comprehensive examination of the Gates Formation (outcrop equivalent of the Spirit River Formation) including the Falher Member. The paleogeography was examined for each of the Falher Member units from outcrop and applied to the subsurface of British Columbia. It was found that shoreline orientations were largely east-northeast to west-southwest in orientation (Leckie 1983). Provenance work was also done for this study and showed that the origin of the sediment was likely from the Omineca Crystalline Belt and Intermontane Belt. Leckie (1986) reviewed the rates, controls and geometries of the members within the Gates Formation in northeastern British Columbia. Multiple transgressions and regressions were interpreted as fourth- order cycles, deposited as a result of tectonic loading on the Peace River Arch. Carmichael (1983. 1988) examined the Gates Formation south of Leckie's study area. Much of his work involved the non-marine succession of the Falher in the Mount Babcock and Mount Frame areas. In this study, most of the conglomerates in the Falher were identified as braided channel deposits. There have been no other works published for the Falher outcrop. Moslow recently analyzed the Falher D interval in an unpublished work for Canadian Hunter Exploration Ltd. (Moslow, 1991) and in abstracts (Moslow and Schink, 1995; Moslow, 1998). In these works, outcrop was examined at closely spaced intervals on Mount Spieker to determine a detailed facies analysis. Offlapping cycles of prograding shoreface facies associations in a wave- dominated strandplain setting were interpreted from these studies. There have been many publications on the Falher in the subsurface. Initial work focused on the Deep Basin as a gas reservoir. Masters (1979) published the first article on the Deep Basin, its low-porosity and low-permeability gas reservoirs and its up-dip water-gas contact trapping mechanism. In the same year, McLean (1979) published a study that recognized the correlation between the Gates Formation in outcrop and the Falher Member and Notikewin Members in the subsurface of Alberta and British Columbia. 8 This work was followed by AAPG Memoir 38 (Masters, 1984), which contained papers on the paleogeography and deposition of the Falher Member and its equivalent strata. Jackson (1984) examined the Mannville Group across Alberta and into northeastern British Columbia. He recognized the east-west trend of the paleoshorelines in the Falher Member. Smith et a/. (1984) published a paleogeographical study of the Lower Cretaceous strata in the Elmworth region. Both publications recognize transgressive and regressive paleoshoreline limits by identifying facies frcm well logs. Cant (1983) published an article regarding the nature of the trapping mechanism in the Spirit River Formation of the Deep Basin. He recognized that the conglomerates in the Falher Member have porosity up to 15% and permeability up to 1 darcy whereas laterally adjacent sandstones have very low permeability (0.001 to 0.5 millidarcies) (Masters, 1979; Cant, 1983). These low permeability sands, in conjunction with an updip water barrier, are believed to be the trapping mechanism for the gas in the Spirit River Formation. Cant (1984) published an article on the deposition of the Spirit River Formation. He recognized five Falher sequences and two Wilrich sequences (Cant, 1984). Several papers have been published on sequence stratigraphy of the Falher units. Arnott (1993) published one of the first papers focused on sequence stratigraphy in the Falher Member. This study focused on the Falher D in the subsurface of the WapitVElmworth Area in west central Alberta. He identified four depositional intervals within the Falher D and identified the bounding surfaces as either marine flooding surfaces or sequence boundaries. Cant (1995) examined the nature of lower and upper deposits in each of the Falher A and Falher 6 successions and their relation to relative rise and fall of sea level. He also recognizes regional differences in surfaces due to variance in sediment input and subsidence. Rouble and Walker (1997) also examined the Falher A and 6 successions in the subsurface of Alberta. Allostratigraphy was applied and four allomembers were identified between the two units. Similarly, Casas and Walker (1997) 9 published a paper on the Falher C and D successions, based on wok from Casas (1997). Aflostratigraphy was also applied and a total of four shoreface allomembers were identified in the Falher C. The C1 and C2 allomembers were interpreted to have formed from small rises and falls in sea level, followed by erosion from successive allomembers. The C3 prograding shoreface was followed by deposition of another shoreface, C4, and lagoonal deposits and channel incision fill (C5 and C6). This is the only published study that documents the Falher C in respect to changes in relative sea level.
1.4 STUDYAREA The study area is located in northeastern British Columbia. On a regional level, the study area for this thesis includes NTS grids 93-P and 93-1. The subsurface strata in northeastern British Columbia are analyzed at this scale. The outcrop study area lies on the eastern edge of the Hart Ranges in the Rocky Mountains (Figure 1-1). The majority of outcrop data was collected on Bullmoose Mountain and the northern portion of Mount Chamberlain. Outcrop data were also collected on Mount Spieker. Both Bullmoose Mountain and Mount Spieker sit on the first major thrust fault west of the Foothills. Bullmoose Mountain is located at a latitude of 55' 12' N and 121' 29' W and has an elevation of 2040m (6692') (Energy, Mines and Resources Canada, 1989a.b). The location of the outcrop sites is shown in figure 1-1. Figure 1-3 shows the study area in detail. Access to the outcrop study area was via all terrain vehicles and helicopter. The study area was chosen for its outcrop exposure of the Falher C as conglomerate and sandstone. Bedrock geology maps by Kilby and Wrightson (1987a.b) were used to identify the Gates Formation location along the Foothills. Topographic maps were then overlain to determine where Gates Formation exposures occurred above the tree line. Previous work by Leckie (1983) and Carmichael (1983) also helped identify areas of potential Falher C outcrop. The Falher C was then identified on logs from exploratory coal drill holes in the outcrop belt. Some of the coal boreholes were drilled only meters from the ,, ,, Exolora:ory cnaldmh no axe C,5 Exs4ara'kx-y cnalnd wt?h me Topopramu Ime tUOO' duva:aon) -0-0 u 4 Tocqr~Dh~~lne (6000- s(sva?Dn) P~adc'ta'~ Thmr =aJ:
00~r~4 2 'VLOUE'ERS 0m 025 0.5- 0.75
Figure 1-3 Outcrop Study area for Mount Spieker, Bullmoose Mountain and Mount Chamberlain. I as circles. Outlines of the mountians are topographic lines 5500' (I676m) and 6000' (11 the outcrop study area. It occurs in the foothills of British Columbia along the edge 01 exposed at surface on the east sides of Bullmoose Mountain and Mount Spieker (Kilby ar
Mountain and Mount Chamberlain. Measured sections are marked as triangles and coal wells hic lines 5500' (1676m) and 6000' (1 829m). The inset map shows the approximate location of ~fBritish Columbia along the edge of the Rocky Mountain Front Ranges. Bullmoose.thrust is Mountain and Mount Spieker (Kilby and Wrightson, 1987a,b).
11 outcrop. These were calibrated to the Falher C in conventional well logs from northeastern British Columbia or to work by Leckie (1983). The Falher Member was then extrapolated to surface. Each exploratory borehole has continuous core and well logs from TD to surface. Coal borehole locations were marked on a topographic map where the Falher C log signature was near surface (c25m) or where the Falher C signature was absent but where the Falher D or Falher F log signature was present near surface. These locations were then plotted using latitude/longitude co-ordinates and connected on a topographic map as potential Falher C outcrop locations. Helicopter reconnaissance was done to confirm presence and continuity of outcrop exposure. The Falher C was confirmed by comparing well log signatures to observations in outcrop. Successful identification of other strata above and below the Falher C also confirmed the correct stratigraphic position of the outcrop. Helicopter reconnaissance in the study area also proved that there were some locations that did not have Falher C conglomerate or locations that simply were not accessible. Measured sections on Bullmoose Mountain and Mount Spieker (Figure 1-3) are the outcrop locations where Falher C conglomerate was present and described.
1.5 STRATIGRAPHY Figure 1-2 is a Table of Formations for northeastern British Columbia Foothills and subsurface and the Central Alberta Plains. The Spirit River Formation in northeastern British Columbia is divided into three members. These members include the Notikewin, the Falher and the Wilrich. The Alberta Study Group (1954) originally defined the Falher Member. The type locality for the Falher is Imperial Falher No. 1 well in 12-23-77-21W5 (CSPG, 1990). It is chronologically equivalent to the Blairmore Group in south central Alberta or the Grand Rapids Formation in northeastem Alberta. The Falher Member is further divided into several informally defined units that have no true or clear stratigraphic connotation. The subdivisions are provided by the oil and gas industry referring to coarsening upward packages bounded by coals. These subdivisions are annotated Falher A, Falher B, Falher 12 C, Falher D and so on. Because of this informal nature, many authors define these subdivisions differently. Smith eta/. (1984) divided the Falher Member into five units (A-E). Cant (1984) also divided the Falher into five units (A-E) but recognized two more prograding, coarsening-upward packages in the underlying W ilrich Member (A-B) and one in the overlying Notikewin Member. Five units (A- D and F) are defined for the Falher by Leckie (1986) with additional coarsening- upward packages defined as the Notikewin and the Moosebar. For this thesis, I have chosen to use a modified version of Masters (1984), which identifies Falher A through Falher F and skips Falher E. The Falher E equivalent is also known as "the fourth coal" and is a thick (-4m) coastal plain association and coal unit present regionally in northeastem British Columbia that underlies the Falher D (Leckie, 1986). To the north part of the province and study region, the Falher C is comprised of offshore marine shale (Jackson, 1984). In this study, shales are recognized in subsurface core, but are not observed in the outcrop belt. In the central region of the study area, the Falher C is composed dominantly of conglomerates and sandstones. Previous studies have shown that these sandstones and conglomerates are shoreface or bamer bar deposits (Smith el at., 1984; Leckie; 1983). South of these deposits, carbonaceous mudstones and siltstones are present. These organic-rich deposits are part of a coastal-plain depositional system. This pattern of deposits is recognized regionally in all of the Falher units (Smith et a/.,1984; Stott, 1982; Leckie, 1983).
1.6 DATABASE The database for this study includes the following: a) Exploratory Coal Boreholes - In the 1970's and early 1980's' numerous wells were drilled and cored for the purpose of exploring for coal seams in the Foothills and Front Ranges of the northeastern British Columbia Rocky Mountains. These wells were logged and cored from surface to total drilling depth (TD). Logs are available on microfiche for most of these wells. The continuous core that was preserved is stored at the core 13 research facility in Charlie Lake, British Columbia. Core is described for 14 exploratory coal boreholes (Appendix 1). The location of these boreholes in the study area is shown in Figure 1-3. b) Conventional Petroleum Wells - Well logs for the Falher C were examined from 56 subsurface wells in British Columbia. Core descriptions were done for the Falher C in 8 of these wells (Appendix 2). These wells are located east of the outcrop (Figure 1 -4). c) Outcrop Descriptions - Outcrop was described and sampled at 33 locations in the study area (Figure 1-3). For each measured section, a description of the lithology and stratigraphic surfaces were conducted. Each site was measured vertically, starting at an underlying Falher unit (if present). Features such as grain size, sorting, composition, sedimentary structures, thickness of each bed, bedding orientation, types of surfaces, trace fossils present, and paleocurrent indicators were all measured and described. d) Outcrop Gamma Logs - A gamma ray scintillometer was used to synthesize a gamma log signature for measured sections. Measurements were taken at 30cm intervals. These data were then plotted using ~icrosoft~Excel. Although the data were measured in counts per second, the relative response may be compared with gamma ray well log responses. The methodology is detailed in a paper by Slatt et a/. (1992). e) Ground Penetrating Radar - A location was chosen in the study area to run ground penetrating radar. A total of seven lines were run. Reflectors on the collected data show orientations of bedding surfaces. The data are discussed in the results of this thesis. f) Thin Sections - Ten thin sections were cut and used to identify petrographic characteristics from various facies within the Falher "C". Figure 1-4 - Location map of Falher C penetrated wells and core described for this study. The inset map shows the location of the subsurface wells examined. 2.1 FACIES- OVERVIEW A facies is a unit of rock, mappable in three-dimensions, grouped according to recognisable sedimentary characteristics and in part, according to stratigraphic position. Outcrop and core for the study area were examined and 7 facies were described and defined (fables 2-1 and 2-2). Some of the facies are further divided into subfacies for a total of 16 facies units. These subfacies are defined by having subtly different sedimentological characteristics and different paleoenvironmental interpretations. The facies are described and organised according to lithology, grain size, sorting, modality, sedimentary structures, trace fossils, 2nd organic remains. These facies, and the contacts between these facies, may be observed by anyone according to the features described. Deposlional processes may be inferred by the sedimentary characteristics of the facies. The facies in this study have similar stacking patterns, and thus a similar vertical succession of facies may be observed throughout the study region. The vertical and lateral stacking pattern of the facies comprise a facies association. An environment of deposition may then be interpreted from: 1) the position of a facies in any one association, 2) its geometry and 3) the depositional processes inferred from the sedimentary characteristics of each facies.
2.2 SHORELINETERMINOLOGY From the facies present in the study area, and from previous work (Leckie and Walker 1982; Smith et a/., 1984; Moslow and Schink, 1995), the Falher C is interpreted to be a wave-dominated, graveliferous strandplain/delta depositional system. To place the facies in an interpreted depositional environment, shoreline terminology has to be defined. Shoreline terminology in the literature is inconsistent and complex. The shoreline may be defined by a combination of coastal processes (e.g. breaker point), tidal zones (e.g., mean low tide), and
Average Sortingl Sedlmmnlrry Trace Interpreted Cscler Lilhology S'ze Organ' Envlrommt of Thlcknne Modallty Strustuns Foullr Remalnr D. V;~~~~,~~~s Low angle locm Lower Shoreface Flcles 4C Flne to very fine iandatone N/A lOOcm Fine ::t Moderate Iamlnatlons and None to Proximal Underlies 48 -- HCS -- oHahore !! Overllea L Plane prrallel to Moderate to conglomerate. Lower Silty to lower medium 25 cm to ~oderrteto' Dlploc~ter abundant Occurs only F~~4O mdlun to prdY /on $ randrtom lmCm well Iy.; csrbonacmus Washover towards very line mrtdrl: phnt rru~mthr. routhwrrd frmgmentr lrminw limit of conglomerrle 5-10 cm Laterally Mdium interbods of varlrbte randrtom wndrton, and chlckmrr, Interkdkd undrtonr adpolymlctlc 0 cm to 400 rdjrcent lo Fck and 2Wmm Poor cong)onnrm@. NIA conglonnrate cm pdymictlc Sand Nom Facie8 6A, p.bble component boundrd conglomerate rhowr normml abow and Chanml klowby 9rrdin0 Facier 1 low a* planar, trough Only in core, fi-y Medlum to croms kddlng, Incirer Into ~.o*. brm8'b to In fim prrinmd Modrrrk to cur I*.; r undrtom (in core only) rrymmtrbrl NOM Facks 4 and undrtons well c*pto~, ripples; urb.tion ovorlaln by Erosional baul Flckr 2 rurllce -,, Sand rupportd 261tmm; conglomerete; carbonrte, clay to Scouredbau; frrnrgrerriw O' (E2S cm '00' NIA Now chart and ehle clrrtr of durn und potymlctk 1- 'C'; undarlks v~irM.rin metrir Facier 4 .--, . .--, , Sand ru~ed 261tmm; Storm drporltr conglomerate; chart, lgmoum kmk li~to along baul A8 kdr within F.dnOB Paor Unrorld NIA f and motmmorphlc cl~of mrn modium art Now rudlce of Frcler 48 and vrrlabk #In tnrtrlr procemr 4C dlartemr Plr nollhr I@; Only In corc Clay and milt; Tekhichln Dirtd lower Eithmr klow SM. Ohen with Mnrllh rdorwry PI~Mpr8lkt, rhoreflcr to Fr*. cm .on* Mod.nb us lip: E mads or , lim undlayrrr (In core only) ,,,,, llm lrminn layerr ~o#rrl//a trrnsitlonrl abow /w.; oNshore conglomerrtm M/mlnth rr r MFS prk Irp . Table 2-2 Table of Facies (part 2). Sedimentological characteristics and interpreted environments of deposition for Facies 48 to 7 18 wave base zones (e.g., fair-weather wave base). Many of the coastal divisions used in the literature overlap, and thus it is important to define the terminology. As much of the terminology used in the literature is defined from sandy shoreface environments, it is also necessary to define the coastal zones for a graveliferous environment. For this thesis, the terms are defined to explain as simply as possible the boundaries for which the shoreline is divided. Figure 2-1 shows a schematic cross section through an idealized shoreline environment (Reineck and Singh, 1980; Pemberton et al., 1992). Backshore is the zone that lies landward of mean-high tide. The backshore is the region in which washover deposits may occur and is commonly separated from the foreshore by a relatively high point called a berm crest (Carter and Orford, 1981; Bourgeois and Leithold, 1984). The backshore may be horizontal or dipping landward and generally is defined by a physiographic change (e.g. cliff face or dunes) or presence of vegetation (Komar, 1976; Dupre et a/. 1980). Between mean high tide and mean low tide is the foreshore. Some authors call this zone the beach or beachface (Bourgeois and Leithold, 1984). Swash and surf processes are commonly present in the foreshore (Clifton et a/., 1971; Reineck and Singh, 1980; Bourgeois and Leithold, 1984). Waves approach the beach and rush upwards. The swash zone is where waves contact the beach and water percolates down through the sediment. The surf zone is where water from the swash zone returns to the active water through percolation while at the same time water approaches the beach from landward-propagating waves (Dupre et a/., 1980; Bourgeois and Leithold, 1984). The definition of the "shoreface" is ambiguous in the literature. Some authors define this zone as the region between mean low tide and fair-weather wave base (Elliott, 1986; Walker and Plint, 1992; Shipp, 1984) and some define it as the region between mean low tide and (storm-weather) wave base (Reineck and Singh, 1980; Pemberton et a/., 1992). Others define the lower boundary at the point where waves first break (Bourgeois and Leithold, 1984; Kirk, 1980). For
20 this thesis, the upper shoreface is defined as the zone between the mean low tide and the fair-weather wave base and the lower shoreface is the zone between fair-weather wave base and storrn-weather wave base. Below storm-weather wave base is the offshore zone. Interbedded lower shoreface sediments and offshore mudstones define the transition zone (Figure 2-1). The upper shoreface is the region where there is almost constant dissipation of wave energy at the sediment-water interface. Longshore currents, which transport water and sediments parallel to the shoreline, and rip currents, which transport water and sediments offshore, commonly occur wlhin the upper shoreface (Dupre et a/., 1980). Longshore bars may occur within the upper shoreface zone and are separated from the foreshore by a longshore trough (Komar, 1976; Shipp, 1984). The lower shoreface is the region between fair-weather and ston- weather wave bases. This is termed the transition zone by a number of authors (Shipp, 1984; Walker and Plint, 1992; Elliott, 1986). It tends to have a lower- angle slope than the upper shoreface (Bourgeois and Leithold, 1984; Shipp, 1984). The processes that affect it are generally storm-related. Sedimentation is often punctuated with coarse-clastics from geostrophic flows. The distal lower shoreface is interbedded with offshore sediments during periods of less-intense activity along the shoreline. Hummocky cross-stratification is commonly, but not excfusively, found within this zone (Leckie, 1988; Duke et a/., 1991). Dip angles along the shoreface are highly varied. In ancient graveliferous shorefaces of the Falher D and F divisions, the angle of dip in the foreshore is about 0-2O,increasing to 3-5O in the upper shoreface and then flattening out to O- 2" in the lower shoreface (Moslow and Schink, 1991). Modem examples can be highly varied. Because of large pebbles or cobbles, the angle of repose is higher for graveliferous shorelines and may have shoreline dips of 5-12" (Kirk, 1980). Shipp (!984) describes shoreline dips of 2-3" for a barred sandy shoreline. Bourgeois and Leithold describe high angle (4-1 6") dips for the foreshore with a maximum of 25" for cobble-rich beaches. The angle of slope depends on grain 21 size, wave height, and percolation rates (Bourgeois and Leithold, 1984; Kirk, 1980).
2.3.1 FACIES1 - DESCRIPTION Facies 1 is identified both in core and in outcrop as coal or highly carbonaceous mudstone. The coal varies in thickness from about 10cm to more than 200cm in the study area. In outcrop this facies is highly weathered and recessive or it is commonly covered by soil. It is more easily observed in diamond drill hole (DOH) coal core (e-g., C-15, T-21, QWD-7401). The coal is highly friable, reflective and often shows slickensides. Individual plant or wood fragments are indistinguishable within the coal. Coal bounds the Falher C at the top and at the base of the vertical succession. A sharp, erosional contact occurs between the underlying coals and the Falher C sandstones or conglomerates (Figure 2-2). The coals at the top of the succession have gradational to sharp boundaries with the underlying conglomerate (Figure 2-3). The coals are interbedded with carbonaceous mudstone, with which they have gradational boundaries. Mudstone of Facies 1 is highly carbonaceous and commonly contains plant detritus and root traces (Figure 2-4). Planar parallel, very fine sandstone laminae are commonly observed.
2.3.2 FACIES1 - INTERPRETATION Facies 1 is interpreted as being deposited in a coastal plain setting. Specifically, deposition occurred in coastal swamps, bays and 10% energy lagoons. Coals are formed in coastal swamps (Reineck and Singh, 1980). Laminated mudstones infer deposition from suspension in an environment prone to low velocitylminimal current transport. Kalkreuth et a/. (1989) describe the occurrence of Gates Formation coals accumulating landward of a high-energy strandplain, and attribute the thickness of these coals to compaction and subsidence of the clastic detritus. Kalkreuth et a/. (1989) attribute low-ash and low-sulfur content of the Gates coals to a high water table and low input of Figure 2-2 Coal and tnudstone from Facies 1 and silty sandstones from Facies 2, overlain by conglomerate Facies 5A. Hammer is 6Ocm in length. Figure 2-3 Coal (Facies 1) from diamond drill hole coal core MS- 39. This photo shows a bedding plane surface at the base of a coal with molds of pebbles from the immediately underlying conglomerates (arrows). I2 crn
Figure 2-4 Molds of plant fragments preserved on bedding plane surface of a carbonaceous mudstone. This sample is from well a-91 -0193-P-1 at 2473 metres depth. Similar plant fossils are observed in the Falher C in exploratory DDH coal core and on the outcrop. 25 marine water. Similar depositional environments have been interpreted for a number of formations in North America, including the Upper Freeport Formation of West Virginia (Belt and Lyons, 1989), the Rock Springs Formation of Wyoming (Levey, 1985), the Blackhawk Formation of Utah (Kalkreuth and Leckie, 1989) and the Cardium Formation of Western Canada (Kalkreuth and Leckie, 1989). Coals within the Falher Member mark significant, regional stratigraphic event horizons in the Deep Basin. The coal is of varying quality and found in up to six seams (Lamberson and Bustin, 1989) in the study region. Coal from the thickest seam, "the fourth coal", is mined just south of the study area. The "fourth coal" occurs regionally into the subsurface of Alberta and British Columbia and marks the base of the Falher D (Wyman, 1984; Moslow and Schink, 1991). The 'Yourth coalwis located north-south between TWP 63 and 71 and Range 1W6 in the east and the outcrop in British Columbia to the west.
2.4.1 FACIES 2A - DESCRIPTION Very fine to upper fine-grained, commonly silty, sandstones compose Facies 2A. This facies is observed more readily in core (T-21; c-80-H/93-P-2) but may also be observed in outcrop (FC-18; Figure 2-5). In outcrop, interbeds of Facies 2A and 2B are commonly observed. Sedimentary structures observed include current ripples, climbing ripples, plane parallel to low angle bedding and carbonaceous laminae (Figure 2-6). Root traces are also common in this facies. Beds of Facies 2A may vary in thickness from 5cm to about IOOcm, generally about 15cm thick. Facies 2A may contain organic remains, whereas Facies 28 does not. Although it contains a large component of quartz, the sandstone, in thin section (Figure 2-7), appears to be a lithic wacke (Williams eta/.,1982). There is a high component of fine-grained material between the grains within this facies. Most of the grains in thin section are quartz or chert, though feldspar and lithic fragments are also present. Organic detritus commonly occurs between the grains, and may occur as detrital grains also. Root traces are observed in thin sect ion. Figure 2-5 Interbedded sandstone and carbonaceous mudstone of Facies 2 (coastal plain) is observed at site FC-18 (Figure 1-3). Beds at this location are 10-15cm thick. Facies 1 carbonaceous mudstone bounds this facies both above and below. Sandstone and rnudstone show planar laminations. Scale bar is 1Scm. Figure Facies 2k fine-grained cross-ripple laminated sandstone. Carbonaceous laminae (CL) are observed on asymnnetrical ripple (AR) laminae foresets. Root traces (Rt) are observed in Facies 2A. The core is from exploratory coal well T-21 at a de!pth of 262m. Sediment from this core was likely deposited as a crevas~se splay fill. Figure 2-7 Thin section C-16 photo micrographs from well a-41-H193-P-2 at a depth of 2520.70m. A)Plane polarized light (PPL) photo of fine quartzose (Qtz)sandstone with organic remains within the matrix. The bifurcating nature of the organics suggests that it isa root trace (Rt). B)Same as A) except with cross-polarized light (XPL) C)Higher magnification view in PPL of the sand grains and the matrix. The sand grains are dominantly quartz (Qtz), but chert (Cht), metamorphic lithics (M) and feldspar (Fld) grains are observed. Organic fragments (Org) occur as grains also, identified as carbonaceous laminae. Detrital clay minerals (Cly) occur between grains. The sand grains show moderate-well sorting. 0)Same as C) except with cross-polarized light (XPL)
30 2.4.2 FACES2B - DESCRIPTION Unlike Facies 1, these mudstones show little evidence of organic debris. These are often interbedded with Facies 2A or may have a gradational lower contact with Facies 2A. Fine, wavy laminations and thin, lenticular beds are present. Bedding is rarely flat. Soft sediment deformation may be observed as water escape structures in DOH BP-69a. Planolites isp. is recognized and bioturbated beds are present in DDH BP-69a. Well c40-F/93-P-2 shows some bioturbated beds and Planolites isp., Palaeophycus isp. and possibly Helminthopsis isp. in this facies. Individual beds of Facies 28 are generally 5 to 30cm thick. Root traces and ichnofossils are present.
2.4.3 FACIES2 - INTERPRETATION Facies 2 sediments are interpreted to have been deposited as bay fills, levee/overbank or splay deposits. Abundant root traces imply a non-marine to marginal marine environment. Carbonaceous laminae and resedimented organic detritus also infer deposition proximal to a current-generated environment with abundant vegetation (i.e. a salt marsh). Climbing ripples are a product of unidirectional, current-generated flow and rapid sediment fallout. Rapid deposition of sediment is also indicated by de-watering and soft-sediment deformation features in the mudstones. Rare burrow traces and general lack of ichnofossils implies an environment of general anoxia or stressed ecologic conditions. Planolites and Palaeophycus, the only trace fossils present in this facies, show a low diversity in the assemblage of diminutive forms. This is common for a bay-fill environment (Pemberton et a/., 1992). Siderite within Facies 28 may be detrital or diagenetic. It is interpreted to be detrital because grains of detrital siderite occur in the interbedded sandstone. Presence of detrital siderite suggests that deposition may have occurred in a deltaic environment where iron-rich minerals are common (Tucker, 1991). Iron- rich sediments may also occur, diagenetically or detritally, in environments where iron-charged ground water is formed during weathering of mafic igneous rocks 31 (Tucker, 1991). Tilley and Longstaffe (1989) suggest that iron-rich minerals formed early in the paragenetic sequence. Petrographically, the sandstone is composed of fine-grained quartz-rich with some chert, feldspar and lithic grains. Texturally and compositionally, the sandstone is immature. There is an abundant clay matrix between the grains. Rootlets are observed in thin section as bifurcating organic material surrounding the grains (Figure 2-7). This supports the interpretation of a marginal-marine to non-marine environment with subsequent subaerial exposure.
2.5.1 FACES3 -- OVERVIEW Chert pebble conglomerates and chert arenite comprise Facies 3. It is subdivided into four subfacies: 3A, 3B, 3C and 3D (Table 2-1). Facies 3A and 38 are both open framework conglomerate, that differ by their respective grain size modalities: Facies 3A is unimodal, 3B is bimodal to polymodal. Facies 3C and 3D are both sandy-matrix, chert pebble conglomerates that differ by their respective framework: Facies 3C is pebble-supported and Facies 30 is sand- supported. Sedimentary structures are difficult to observe in this facies, largely due to the coarse nature of the pebbles in the conglomerate. In 2Y2" diameter core, the sedimentary structures are on a scale too large to observe. In outcrop, the weathered face of the rock and the lichen cover, often mask any sedimentary structures that may be present in the conglomerate.
2.5.2 FACES3A - DESCRIPT~ON This facies is composed of well sorted, unimodal, open framework conglomerate. The clasts are subrounded to rounded chert pebbles averaging between 2mm to 4mm in diameter with a maximum diameter of 6mm. Facies 3A also includes beds of well sorted, coarse to very coarse grained (1000-2000 microns) chert arenite. The chert arenite shares the same characteristics as the conglomerate, except they fall within the sand range and occur as separate beds. Visible porosity of the conglomerates in Facies 3A is on the order of 520% (Figure 2-8). Figure 2-8 Outcrop (above) and hand sample (below) photos of Facies 3A (foreshore), unimodal, open framework conglomerate. Due to the lack of matrix, the outcrop (above) shows recessive weathering. Note the authigenic (white) cement in the hand sample (below). 33 Facies 3A is very common in outcrop and somewhat common in the subsurface of northeastern British Columbia- Facies 3A occurs towards the top of a vertical profile in a facies association. There are no organic remains or trace fossils observed for Facies 3A. due in part to the coarse grained nature of the rock fabric and high degree of hydrodynamic winnowing at the time of deposition. Although difficult to discern, at some measured sections sedimentary structures are observed. High-angle laminasets, low angle planar bedding and trough cross-bedding are observed at a number of other measured sections in Facies 3A. The orientation of these sedimentary structures may either be dipping in a southerly direction or in a northerly direction. Trough cross-bedding is observed in Facies 3A at measured section FC-2 (Figure 2-9). High-angle laminasets, dipping towards the south, are observed at measured sections FC-13 and FC-15. The beds, in which the high-angle laminasets are present, are commonly horizontal or dipping at a low angle in a north to northeast direction. Thickness of individual beds within this facies is generally less than Im, averaging 0.5m. Facies 3A reaches a maximum thickness in the outcrop of 3.5m at measured section FC-4. Thin sections FC14-12 and C-20 are examples of Facies 3A from outcrop and from the subsurface (Figures 2-1 0 and 2-1 1). These both show similar features within the conglomerate. Thin section C-2 shows pebbles averaging about 4mm in diameter whereas this section FC14-12 shows pebbles averaging about 2.5mm in diameter. Predominantly, chert pebbles comprise the clasts, but quartzose sandstone clasts, metamorphic pebble clasts, and igneous pebble clasts also are present. Pore space is present between the grains, but also as microporous chert (Figure 2-1 1). C-2 shows a higher porosity (- 12%) than FC- 14-12 (-4%). Cement is present between the grains. A drusy quartz cement lines the edges of many of the chert clasts. Kaolinite also is present as a cement in between the grains. The contacts between are generally interpenetrating, but stylolitic contacts are also observed. Figure 2-9 Trough cross-bedding is observed in the upper 0.6m of Facies 3A (upper shoreface) conglomerate at Mount Spieker. Orientation of the troughs is to the east. Planar beds are observed in the Facies 3 conglomerate. Length of the hammer (arrow) is 30crn. View is to the north. Figure 2-10 Thin section micrographs of Facies 3Afrom measured section FC-14. A) (PPL) and B) (XPL) Chert clasts with interpentratingboundaries and sutured contacts. A metamorphic clast is present as well. Kaolinite clay matrix is present between the clasts. C) (PPL) and 0)(XPL) Effective porosity (Por) occurs between the grains (interclast). Fractures within clasts indicate ineffective porosity (Frac). Effective porosity for Facies 3 (shoreface conglomerate) in outcrop varies between about 3 and 15%, averaging about 6%. Kaolinite is present in between clasts. Cht - chert clast; Kaol -kaolinite; Qtz - quartz; M - metamorphic clast
2.5.3 FACIES3B - DESCRIPTION Facies 36 is also an open framework, chert pebble conglomerate, however it is polymodal or bimodal in nature. Facies 36 occurs towards the upper part of conglomerate facies associations. Clast diameter varies between 2 and 32 millimetres, commonly in the 4 to 8 millimetre range. Matrix is absent with the exception of occasional medium to very coarse-grained sand-sized particles. Sedimentary structures are generally rare, but as in Facies 3A, low angle planar to trough cross-bedding is observed. Beds are commonly low angle dipping northerly to horizontal, with thickness varying between lOcm and 50cm. This facies is also observed in core, where several beds of chert pebble, polymodal, open framework conglomerate may occur.
2.5.4 FACIES3C - DESCRIPTION Facies 3C is a clast supported, polymodal, medium to coarse sand-matrix conglomerate. The pebble clasts are predominantly chert, with occasional quartz and rare lithic clasts. Clast sizes vary between 2mm and 64mm in diameter, averaging within the 4-8mm range (Figure 2-12). Lower medium- to lower coarse-grained sandstones occur as separate beds within this facies. These may also occur laterally gradational to Facies 3C conglomerate (Figure 2-13). The sandstone within this conglomerate is moderately-well to well sorted, and the grains are subrounded to rounded. Along the basal surface of many of the sandstone beds within this facies are chert granules or pebbles. These surfaces may be traced in outcrop as coeval bounding surfaces to laterally adjacent conglomerate beds. Individual beds within this facies vary from 20cm to 200cm for the conglomerate beds and 5cm to 40cm for the sandstone beds. Sedimentary structures are not easily visible on lichen-covered faces of the conglomerates. Conglomerates generally have no discernible sedimentary structures within the individual beds. Bedding in the sandstones is seen as trough or planar (Figure 2- 14). In the sandstones, bedding is commonly dipping towards the south to Figure 2-12 Facies 3C (upper shoreface) from measured section FC-9 - polymodal, sand matrix, clast supported conglomerate. The pebbles show a vague alignment with long axes parallel to bedding planes. Length of hammer is 30cm. Figure 2-1 3 Facies 3C (upper shoreface) at measured section FC-6 showing the lateral transition between sandstone (left) and conglomerate (right) in the same bed. The sandstone occurs north (paleoseaward) of the conglomerate. The transition appears as toesets of the conglomerate. The bounding surfaces of toeset laminae in the sandstone contain pebbles and granules - Figure 2-14 A) lnterbedded sand-matrix, clast-supported conglomerate (cngl) and sandstone (sst). The sandstone at this location shows planar horizontal bedding (PHB). Bedding in the conglomerate shows low angle planar beds (LAPB) dipping to the west. The dashed lines show the contacts between stacked facies associations (Chapter 3). The length of the hammer is 30cm. 6) Trough cross-bedding in the interbedded sandstone of Facies 3C (upper shoreface) at measured section FC-9. The beds dip towards the east at this location. Markings on the Jacob Staff are at lOcm intervals.
44 southwest. Accurate measurements on trough direction or dip direction of beds were difficult due to insufficient three-dimensional exposure and due to the weathered face of the outcrop. The basal surface of Facies 3C, where Facies 3D is absent, is erosional. Some bedding contacts of conglomerate within a vertical succession also show an erosional nature. Commonly, wood casts are observed along these erosional or uneven surfaces at the base of the conglomerate. Thin section C-20 is an example of Facies 3C conglomerate. Pebbles are grain supported within a litharenitic sandstone matrix. Chert is the dominant pebble composition, with rare metamorphic and igneous clasts. The sandstone is composed largely of chert and quartz grains that range in size from upper fine- sand to lower coarse-grained sand. Clays are the dominant pore-filling matrix, filling up nearly all available pore space. Kaolinite is the primary clay matrix, but opaque, likely organic, material also is present between the grains.
2.5.5 FACES3D - DESCRIPTION Facies 3D is commonly observed directly below Facies 3C. This unit tends to be less than 30cm thick where it is preserved. This facies is not present at all locations through the study area. It is recognized as a sand-supported, chert pebble conglomerate. The chert pebbles vary in size between 2mm and 64mm, averaging 4-6mm in diameter. The sand matrix is upper medium- to lower coarse-grained sandstone. Grains in the sand matrix are moderately well sorted and subrounded to rounded. They are composed of chert, lithic and quartz grains. The basal surface of Facies 3D tends to be erosional or uneven. Wood casts are often obsewed at the base of these conglomerates (Figure 2- 15).
2.5.6 FACES3 -- INTERPRETATION Conglomerate deposits of Facies 3 are common in the Falher Member. Previous interpretations indicate that the conglomerate in the Falher Member is the product of deposition in high-energy, wave-dominated, graveliferous Figure 2-1 5 Wood casts on lower bounding surface of conglomerate Facies 3C. Wood casts are oriented north and north-east. Arrows are aligned parallel to the orientation of wood casts. The surface the wood casts occur along is erosional and shows evidence of incision into the underlying strata. 46 strandplains (Leckie and Walker, 1982; Smith et a/., 1984; Moslow and Schink, 1991). Facies 3 is interpreted to be graveliferous strandplain deposits. Facies 3 occurs towards the top of a vertical facies succession. It is overlain by Facies 1 or 2 and underlain by Facies 4. Within Facies 3, sand and pebble clast sorting and modality improve upwards, showing a higher degree of segregation. Wave-worked gravel shows this sorting and segregation pattern (Clifton, 1973). Facies 3A and 38 are composed of open-framework conglomerate and well sorted very coarse sandstone. This sorting is the result of hydrodynamic winnowing, likely wave-swash. Swash processes segregate pebble clasts and sand due to differences in grain size, shape and density (Bluck, 1967a; Clifton, 1973). In Facies 38, a process of winnowing has segregated the sand from the gravel fraction, even though the pebbles have a polymodal clast size distribution. Beachface, or foreshore. gravel can be characterized as well sorted, open-framework with a unimodal grain-size distribution (Bluck, 1967a; Bourgeois and Leithold, 1984). Bluck (1967a) identified four depositional zones within the beachface: the large disc zone, the imbricate zone, infill zone and the outer frame zone (Figure 2-16). Clast size and imbrication define the zones. These zones are not clearly identified in the study area, likely because the size- distribution of the clasts in the Falher C are commonly less than 16mm in diameter, whereas the gravel clasts in Bluck's (1967a) study are up to 115mm in diameter. The two zones closest to the berm crest (the large disc and the imbricate) are open-framework, as are the conglomerates observed in Facies 3A and 38. Also, the presence of highly segregated sandstone and conglomerate beds, and conglomerate beds with different sized pebbles, indicate some possible zonation in the foreshore. This is likely caused by wave swash and backwash processes (Bluck, 1967a; Bourgeois and Leithold, 1984). Sedimentary structures, observed in Facies 3A and 38, are typically southward (landward) dipping, high-angle laminasets. Similar features have been obsewed in progradational gravel beaches (Massari and Parea, 1988). STORM BEACH: SKER POINT
OPEN FRAME le'qched of disk pebbles 6 many s~hericrl rod particles
RESERVOIR of particles potentially capable of rapid seaward movement
OUT ERFRAME Figure 2-16 Zones within a beachface at Sker Point, Wales (Bluck, 1967a). Four zones are identified: large disk zone, imbricate zone, infill zone and outerframe zone. These are not clearly identified in the Falher C, however, the open framework conglomerate (large disk and imbricate zones) is present in Facies 3NB and the sand matrix conglomerate (infill and outer frame zones) is present in Facies 3ClD. Sandstone beds, which may equate to the sand run of the infill zone, often separate the conglomerates in Facies 3A from the conglomerate in Facies 3C. 48 These features are likely the result of gravel deposited on the landward side of a beach berm during periods in which waves topple over the berm crest (Dupre et at., 1980). In the beachface, landward-dipping laminasets are observed more commonly in outcrop than seaward-dipping laminasets. This may be attributed to the high-energy waves, upon intersecting the beachface, push sediment landward. Backwash is not a significant process in the upper beachface because water percolates through the open-framework gravel and returns seaward lower in the vertical succession. Northward dipping laminasets and bedding are also observed in Facies 3. These are deposited on the seaward side of the berm crest and tend to have a lower angle of dip: in many places they appear to be horizontal. These sheet- like, low angle beds are observed in gravel beaches (Massari and Parea, 1988; Carter and Orford, 1984). This is attributed to two possible processes. The first is as low-angle, storm erosional events (Elliott, 1986). Planar surfaces form as beach berms are eroded during storm events. Alternatively, waves that approach the shoreline may also have low amplitudes, but significant swash run up (Massari and Parea, 1988). Facies 3C and Facies 30 are sand-matrix conglomerate and sandstone. In a vertical succession, these occur below Facies 3A/B. Sedimentary structures are difficult to observe. Bedding in the conglomerate is generally planar horizontal to low-angle dipping northerly (paleoseaward). Between bedding planes, the conglomerate lacks sedimentary structures. This low-angle tabular bedding is interpreted to be a result of reworking of gravel within the upper shoreface (Bourgeois and Leithold, 1984; Dupre et a/., 1980). Trough cross-beds and low angle parallel bedding features are observed in the sandstone component of Facies 3CID. These beds tend to dip northerly (paleoseaward) or southeasterly (parallel to paleoshoreline). The sandstone is observed to occur as a lateral facies change with the conglomerates of Facies 3. Similar sandstone features have been interpreted as migrating megaripples (Bourgeois and Leithold, 1984), sand-dominated longshore bars (Massari and 49 Parea, 1988; Shipp, 1984) or sand-dominated troughs adjacent to offshore gravel bars (Leckie and Walker, 1982). The latter interpretation is unlikely because the conglomerate of Facies 3 may be traced laterally from foreshore conglomerate through to upper shoreface conglomerates and then into upper shoreface sandstones. Because of the segregated beds of sandstone and conglomerate within this facies, interpreting the sandstone component as a megaripple within a graveliferous shoreline is unlikely. Therefore, the sandstone component is likely the result of a migrating, sand-dominated, longshore bar. This would concur with observations from Shipp (1984), where gravel and coarse-grained sediment was contained within the longshore trough. Shore-parallel dip orientations within the bedding would be due to longshore migration of the sand-dominated bar. Offshore-oriented dipping beds would simply be the seaward side beds of the bar. Discontinuity of the sandstone beds can be attributed to the longshore bar geometry or as a result of erosion from storm-events and subsequent conglomeratic shoreface deposition. Organic material present within Facies 3 is detrital and occurs as transported fragments from the coastal plain. These fragments are incorporated into Facies 3 as offshore-oriented wood or plant fragments, occurring along the scoured basal surface of the conglomerate deposits. This suggests a high- energy, offshore-directed transport of sediment. Storm-deposits have been known to carry on-shore sediment into basin deposits (Nummedal, 1991; Walker and Plint, 1992). This suggests that many of the surfaces within Facies 3 are storm-punctuated. Facies 3 is comprised dominantly of detrital chert clasts. Chert is a microcystalline form of quartz with individual crystals 1-1Opm in diameter. When lithified, it is a very resilient rock. The abundance of rounded chert, and the compositional matunty of the clasts in Facies 3 suggests that the clasts have been transported and reworked for long periods of time. In addition to that, the source area also must have had an abundance of chert. 50 The sandstone in Facies 3 is less mature compositionally and texturally. Facies 3C shows a moderately sorted matrix, composed largely of chert, but also of monocyrstalline quartz, polycrystalline quartz, and lithic fragments. The mineralogy does not vary significantly from the conglomerates of Facies 3, and thus likely had the same source area. The difference in mineralogy likely occurs due to the breakdown into sand-sized particles of rocks less resilient than chert. Assuming that the source area for the sand fragments in Facies 3 is the same source area as for the conglomerates, then the sand fraction within Facies 3 is reworked less than the open-framework conglomerates. Porosity and perrneabiltty within Facies 3 is significant from a reservoir standpoint. The open-framework conglomerates maintain primary porosity because of the packing of chert under compaction. The chert clasts show concavo-convex, interpenetrating boundaries, which form a strong framework that allows for intergranular or interclast poroslty to be maintained. Chert clasts also minimize the amount of quartz overgrowth cement that can be forrned. Figure 2-1 1 shows quartz overgrowths along the boundaries of the chert clasts. Upon close inspection, the large quartz crystals (100400pm in diameter) are growing upon smaller (<100pm) quartz crystals, which nucleate from the chert crystals. Because there are numerous nucleation points for quartz overgrowths to form upon, large, pore-filling quartz crystals do not typically form. Microporous chert is also present, and adds to the porosity, but likely not the reservoir quality of the Falher C. Another element, common to the pore space within the Falher conglomerates is kaolinite. This is a type of clay mineral, formed authigenically, after the precipitation of quartz overgrowths. It is present both in outcrop and in the subsurface. Kaolinite is significant because it decreases the amount of porosity, but has little affect on the permeability (Tucker, 1991). From a reservoir perspective, kaolinite may block the microporosity from the chert clasts. The kaolinite observed in thin section (Figures 2-10 and 2-1 1) formed after the quartz 51 overgrowth cement, as it is observed central to the pore cavities and lines the outside boundaries of the quartz crystals.
2.6.1 FACJES4 -OVERVIEW Facies 4 is a litharenite or chert arenite, and is subdivided into four subfacies based upon grain size and stratigraphic position.
2.6.2 FACIES4A - DESCRIPTION Facies 4A is a well sorted, lower medium- to lower coarse-grained, litharenite. Rounded to subrounded grains and absence of a clay matrix indicate that Facies 4A is texturally mature. Facies 4A is 2.0-4.0m thick and appears either massively bedded or planar horizontal to planar low angle bedded. Individual beds are 0.5 to 1 .Om thick. Dip orientations of the low-angle bedding are towards the northeast at angles of less than 5". Abundance of burrowing is rare to moderate for Facies 4A. Vertical burrows (Figure 2-17), such as Diplocraterion isp., Arenicolites isp., and possibly Skolithos isp. are observed. Small traces observed are identified as Palaeophycus isp., but due to the weathered nature of the outcrop surface, these traces were difficult to identify conclusively. Macaronichnus isp. and cryptobioturbation are also observed in core towards the top of this facies. Root traces are noted towards the top of the vertical succession. Facies 4A is observed at measured sections FC-23 and FC-29 and described in core from wells c-80-H/93-P-2, a-41-H/93-P-2 and a-68-A/93-1-16 (see Appendix).
2.6.3 FACES48 - DESCRIPTION Fine- to medium-grained, moderately well sorted sandstone comprises Facies 4B. Facies 46 varies in thickness between 40cm and 400cm in outcrop. Individual beds are 2-10cm thick. Coarse sand to granule-sized grains may be observed towards the basal surface of bedding planes. Hummocky cross Figure 2-1 7 A) Diplocraterion at outcrop location FC-23 in Facies 4A. Arrows highlight multiple expressions of Diplocraterion. B) Diplocraterion trace with spreite preserved. Diplocraterion suggests a vertically shifting substrate.
54 stratification (HCS) is observed in this facies (Figure 2-18), as are low angle planar beds. Beds dip at a low angle (c3") towards the north. In a vertical succession, this facies generally underlies the Facies 3 conglomerate. Laterally, Facies 48 can be traced to be coeval deposits with Facies 3C/D conglomerate that are situated in a paleolandward direction. In core, Facies 48 occurs stratigraphically below Facies 4A where Facies 3 is absent.
2.6.4 FACIES4C - DESCRIPTION Very fine- to fine-grained, moderately sorted sandstone comprises Facies 4C. Facies 4C occurs in outcrop and in core as 1Ocm to 100cm thick sandstone, with individual beds 1-1Ocm thick. Medium- to coarse-sandstone grains may occur along bedding plane surfaces. In core, thin interbeds of non-carbonaceous mudstone are present. Sedimentary structures in Facies 4C are typically low angle, wavy laminations and some HCS. Beds, in which the laminae are obsewed, are generally horizontal planar. In core, normal grading from sandstone to siltstone is observed. Fossils and trace fossils are absent in this facies, as is organic material.
2.6.5 FACES4D -- DESCRIPTION Facies 40 is composed of silty, very fine- to lower medium-grained sandstone. It occurs as a 2Scm to 120cm thick sandstone with individual beds 20-50cm thick. Bedding is horizontal planar to low angle planar dipping to the south. Very fine horizontal planar, carbonaceous laminations are observed within the beds. Root traces and plant fragments are obsewed within Facies 40. Grading is not observed in outcrop. Some laminasets tend to have a higher component of medium-grained sand and tend to be better sorted. Vertically, these beds occur overlying Facies 4A or Facies 3. Facies 40 only is found along the southward (paleolandward) limit of Facies 3 conglomerate. Figure 2-1 8 Hummocky cross stratification (HCS) in Facies 48 sandstone at measured section FC-5. Note the concave up laminations at the crest of hummock (arrow). 2.6.6 FACES4 - INTERPRETATION Facies 4 represents components of a shoreface environment of deposition. Facies 4A is interpreted as foreshore to upper shoreface sandstones. Facies 4B are lower shoreface sandstones. Facies 4C are lower shoreface sandstones to transitional offshore. Facies 40 are stonn washover sandstones. Facies 4A is interpreted as foreshore/upper shoreface based on the ichnofossil assemblage and the sedimentary structures present. Diplocratenbn isp. and Arenicolites isp. are vertical burrows in sandstone, inferring deposition in a shifting sandy substrate (Pemberton et al., 1992). Also, Macaronichnus isp. is characteristic of a high-energy foreshore environment (Pemberton, 1997). Cryptobioturbation is formed from meiofauna and has the greatest occurrence along the depositional interface (Bromley, 1990). Low-angle planar bedding and horizontal planar bedding can be formed in environments where: 1) critical flow velocity or upper regime, 2) subcritical flow below the velocity of sediment transport or 3) as low-relief bedforrns at shallow water depths (Reineck and Singh. 1980). In a wave-dominated sandy shoreline, planar laminations may occur in the upper shoreface, often as a result of large- scale, low-relief bedforms (Elliott, 1986). Facies 46 and 4C are lower shoreface sandstones grading to offshore- transition. A finer grain-size, interbedded mudstone and presence of HCS is typical of a wave-dominated sandy shoreface (Elliott. 1986) that is punctuated by storrn events (Walker and Plint, 1992). The relation of hummocky cross- stratification to storm deposition has been made note of by a number of authors (Hunter and Clifton, 1982; Duke, 1985; Duke et al., 1991). Duke (1985) identifies the relation of hummocky cross-stratification with hurricanes and winter storm events. He suggests that hurricanes occurred at higher latitudes in the Cretaceous due to a warmer climate. Standing oscillatory waves, caused by great storms, are believed to for HCS below the fair-weather wave base, where these features do not get easily reworked. Other authors, however, argue that 57 hummocky cross stratification is a normal depositional feature in the shoreface (Leckie, 1988). Leckie and Krystinik (1989) make note of hummocky cross stratification and possible geostrophic currents in the Gates Formation. They interpret an offshore-directed flow as opposed to a shore-normal flow. Constant action of these waves are believed to form the HCS below the fair-weather wave base. Facies 40 is interpreted as washover sandstone. This sandstone facies is preserved only along the southward (paleolandward) limit of the Facies 3 conglomerate. Locally, it is on the order of 1m thick and occurs with a width of about 100m along the southerly limit of Facie 3 conglomerate. Washover fans are produced as sheet flow in the back-barrier during storm events (Elliott, 1986). Horizontal or low-angle laminations occur as sediment is carried over the berrn crest into the back-beach setting. Carbonaceous debris is incorporated from vegetstion that occun locally in the back-beach setting. Fine to medium-grained sandstones may be deposited as washover deposits from a graveliferous shoreface (Carter and Orford, 1981). For a recent graveliferous setting, Carter and Orford (1981) noted a presence of washover gravel in proximity to a dune throat, created by erosional incision of water into the dune by storm environments. Sand deposition occurred distally along depositional strike to the graveliferous fans. Facies 40 is possibly the ancient equivalent to the sand deposition of the graveliferous fans. Conversely, washover sandstone of Facies 40 may not be storm-related. Sand-sized fraction may be transported by high- energy waves over the berm crest. As wave-energy decreases approaching the foreshore, the gravel content will drop out of suspension and traction, whereas the sand-sized fraction will remain in suspension. Waves that topple the bemi crest of the foreshore will have dropped the gravel fraction but still carry the sand fraction into the back-beach. The sand-fraction that is not deposited in the washover setting is returned to the upper shoreface by wave backwash. High- angle bedding, dipping in a paleolandward direction, in Facies 3A suggests that waves frequently overcome the berrn crest and deposition occun on the lee side. 58 It therefore is not inconceivable that the sand fraction is deposited in thin layers behind the gravelifemus component.
2.7.1 FACIES5A - DESCRIPTION Facies 5A (Figure 2-19) is an interbedded sandstone and sand matrix conglomerate. Thickness varies from Om as a pinch out to 9m over 120m lateral distance in the outcrop. The individual interbeds of sandstofie and conglomerate tend to be about 5-30cm thick. Thickness of the sandstone interbeds decrease upward within the unit. The sandstone in this facies is moderately sorted, medium-grained sandstone. Sand content decreases with decreasing thickness of the unit. Pebbles within the conglomerate interbeds vary in diameter from 2mm to 65mm. The pebble size increases with decreasing thickness of the unit. Modality of the conglomerate interbeds improves with decreasing thickness. Clasts within the conglomerate component of Facies 5A are polymictic. Lithologies of the clasts include chert, metamorphic lithics, igneous lithics, sandstone, shale and carbonates. In outcrop, the carbonate clasts figure prominently in Facies 5A. In outcrop, the clasts occur as white or tan colored, fractured, rounded pebbles. On the weathered face, these clasts are absent, leaving instead leached voids where these pebbles once occurred. The matrix is poorly sorted. It contains clay to medium-grained sandstone. Thin section FC19-3 shows the poorly sorted matrix and the variable lithologies.
2.7.2 FACIES5B - DESCRIPTION Facies 58 is one of two subfacies not observed in outcrop, but present in core from petroleum wells in northeastern British Columbia. The thickness of Facies 58 varies between 80cm and 600cm. It is moderately well sorted, normally graded sandstone with grain size ranging from upper medium- to lower fine-grained. A variety of sedimentary structures are observed in this facies. In core, many of the laminations observed are low-angle planar and concave-upwards, Figure 2-19 A) Conglomerate beds near the lateral pinchout of Facies 5A at measured section FC-23. The conglomerate is polymodal and polymictic with a sand matrix. Leached pebbles (arrow) indicate where carbonate clasts once were located. The base is erosional and incises into an underlying coal facies. Length of the hammer is 30cm. B) lnterbedded sandstone and conglomerate of Facies 5A. The beds are 5-10cm thick. Pebbles are 24mm diameter in the conglomerate and the sandstone is medium-coarse grained. Two erosional surfaces are observed in outcrop marking the reactivation of the channel, accounting for the thickness at measured section FC-22.
61 low-angle curved. The low-angle curved laminations are interpreted to be trough cross bedding because the laminations converge towards the basal bounding surface. Asymmetrical ripples are also observed. These would have been deposited in a current with a unidirectional flow. Palaeophycus isp. and cryptobioturbation are observed within this facies. There are no organic remains observed. The basal surface of Facies 5B is erosional. Pebbles of 2-4mm diameter can be found along the basal surface, occasionally with rip-up clasts of underlying facies. In well C-40-W93-P-2, Facies 5B incises into Facies 4. Facies 1 or Facies 2 overlies Facies 58.
2.7.3 FACIES5 - INTERPRETATION Facies 5 is interpreted as a channel deposit. The geometry of Facies 5A in outcrop suggests this interpretation as it reaches a maximum thickness of 9m and pinches out laterally. The upper surface is roughly horizontal, whereas the incision surface is curved. The channel in outcrop has an erosional base, incising into underlying coastal plain sediments and coals. The petrology of the Facies 5A conglomerate suggests a different environment than from the Facies 3 conglomerate. Immature sediments and a wider variety of clast tithologies, including carbonate clasts, suggests less working of the sediment in transport and deposition. Sandstone occurs as continuous planar and lenticular interbeds within the conglomerate. Sediment in the conglomerate may have been transported many 10's of kilometers in an alluvial setting. Bluck (1967b) examined the Upper Old Red Sandstone conglomerates in the Clyde area and identified them as alluvial fans deposits grading to channel deposits. The conglomerate of Facies 5A shares similar characteristics with braided stream and river channel conglomerate. Bluck (1967b) describes the braided channel conglomerate as having a wide variety of features including: sand-matrix to sand-supported conglomerate, cross-bedding, planar bedding, and erosional surfaces. River channel conglomerate is recognized by having 62 interbeds of sandstone and conglomerate, with the conglomerate occurring in lenses or laterally continuous beds. Bed thickness in the Upper Old Red Sandstone can exceed 20m. Facies 58 are also interpreted to be channel deposits. These are found in the subsurface and do not contain conglomerate. Occasional pebble lag layers are found towards the base of the unit. Facies 56 fines upwards. as is commonly characteristic of channel deposits (Shuster and Stiedtmann, 1987; Miall, 1992). The fining upwards can occur as vertical aggradation or lateral migration of sediment within a channel valley.
2.8.1 FACES6 - OVERVIEW Facies 6 occurs as conglomeratic layers less than 80cm thick. Facies 6 conglomerate differs from Facies 3 by a clay component to the matrix. Facies 6 conglomerate may be clast- or matrix-supported.
2.8.2 FACES6A - DESCRIPTION Facies 6A is a matrix-supported to clast-supported conglomerate. Carbonate, chert, sandstone, igneous, and metamorphic clasts are all present. Carbonate clasts tend to be weathered in outcrop. Clast size varies between 2mm and greater than 64mm. The average clast size tends to be about 46mm. The matrix is a poorly sorted muddy sandstone matrix. Grains range in size from very fine to coarse sand and are subangular to rounded. The basal bounding surface is scoured in nature. Thin section FC19-3 shows the relationship of the clasts and the matrix in this unit (Figure 2-20). The clay matrix is opaque in transmitted light. In reflected light (C) it occurs as orange-color fines, suggestive of an iron-oxide component. The lithologies of the clasts are similar to those found in the clast-supported conglomerate of Facies 5A. Carbonate and lithic clasts occur in abundance in Facie 6A. Facies 6A shows a texturally inverted conglomerate, where the clasts are rounded, but the matrix is poorly sorted and has a high clay content. Figure 2-20 Photomicrographs from measured section FC-19 for Facies 6A (transgressive lag). A) Plane polarized light view of Facies 6A. Poorly sorted sandsized grains of quartz (Qtz), chert (Cht) and lithics, surrounded by clay minerals (Cly), compose the matrix. Ctasts are composed of lithics such as metamorphic lithics - Meta) and carbonates (Carb). 6)Same as A) except in cross-polarizedlight. C) Same as A) except in reflected light. D) Cross-polarized view of Facies 6A. Rounded carbonate clasts are present. The carbonate clasts are crystalline and may have fractures (frac).
65 2.8.3 FACIES66 - DESCRIPTION This facies is sand supported to clast supported conglomerate with a poorly sorted sandstone matrix and a polymodal clast distribution (Figure 2-21). There are no noted carbonate clasts in this facies, however, some igneous and metamorphic clasts are present. The clasts in this facies are dominantly chert. The conglomerate is polymodal and chaotically bedded. The matrix varies from a mudstone to a coarse sandstone. The pebble sizes vary between 2mm and greater than 64mm. Larger clasts are somewhat restricted to the basal surface of the unit, showing poor normal grading. Load casts and non-linear flute casts are observed along the basal surface for this facies (Figure 2-21A). The contacts are sharp, both at the upper and basal surfaces of this facies. This facies is commonly interbedded, bounded above and below by Facies 4B/C sandstones.
2.8.4 FACES6 -- INTERPRETATION Facies 6A is interpreted to be a transgressive lag. It occurs as a thin conglomerate deposit, with an erosional base, overlying Facies 5A at the base of the Falher C. Facies 5A is interpreted to be a channel deposit. Facies 6A st~aressimilar lithologic characteristics with Facies 5A, particularly with clast lithology. The erosional surface of Facies 6A can be traced through much of the outcrop where it overlies carbonaceous sediment from the underlying Falher D division. Facies 66 has a slightly different composition. It lacks the carbonate clasts that are found in Facies 6A. It occurs as thin beds, within Facies 46 and 4C. There are a number of possible interpretations for this facies: transgressive lag, forced regression lag, debris flow, geostrophic storm deposits (inundites, tempestites), or tsunami deposits (Einsele, 1991). It is not likely a transgressive lag, because there are no clasts from the immediately underlying facies and not texturally inverted. Facies 6B occurs in the middle of deposits interpreted to be upper and lower shoreface sandstones. The grading observed in these sandstones is continuous except for beds of Facies 6B. This suggests an episodic event, with deposition of material in the lower shoreface, showing no Figure 2-21 -A) Uneven basal surface suggests rapid erosional deposition. by the presence of loading and the unsorted nature of the conglomerate. Facies 6B overlies lower shoreface sandstone. B) Poorly sorted conglomerate with clast sizes ranging from 2 to >64rnm diameter. Sedimentary structures are absent within the Facies 6B debris flow conglomerate.The length of the hammer is 30cm. 67 significant changes in relative sea level. For this reason, it is neither a forced regression nor a transgressive lag. Debris flows form from slumping of material, such as mass wasting of a shoreface slope or from coastal material (Eyles et a/.,1988; Major, 1997). The Facies 66 deposits appear laterally continuous along depositional strike, but wedge out basinward. Had these deposits occurred above fair-weather wave base, it may be suggested that they were extended along strike by longshore drift. These deposits are preserved below fair-weather wave base, and thus have not been reworked or transported over long distances post-depositionally. Because of the lateral continuity along depositional strike of Facies 66, and post- depositional transport is minimal, the process which forms Facies 66 must have affected large areas along the shoreline. Facies 66 occurs repetitively towards the base of stacked facies associations, and thus the process that formed Facies 6B must have occurred regularly over time. Storm deposits and tsunamis, which both have similar depositional characteristics, are produced by large waves resulting in coarse-grained deposition below fair-weather wave base. Recorded deposition of large-wave (tsunami) deposits from Hawaii indicates an inverse grading and marked imbrication (Moore and Moore, 1988). However, the composition of the deposited material and coastline along which the deposits occur would be different for Hawaii than it would have been during Father deposition. There are a number of papers that indicate that mixed pebble and sand storm deposition can occur over distances of greater than 100km (DeCelles, 1987; Snedden et a/., 1988; Morton, 1988). DeCelles (1987) notes alternating sandy conglomerate and hummocky cross-stratified sandstone. Facies 66 is found interbedded with Facies 4B, in which hummocky cross-stratified sandstone is found. Facies 6B may be associated with a debris flow initiated by slope failure due to sediment loading on a steeply angled conglomeratic shoreline (Schwab and Lee, 1988). Schwab et a/. (1996) document mass flow deposits on a Mississippi fan. Debris flows are the dominant flow type with thin turbidites 68 deposited adjacent to the depositional lobes. The initiating event occurred as a slope failure in the source channel. The difference between these debris flow deposits and the Facies 6B conglomerate are that the debris flow deposits documented in the Mississippi Fan are composed dominantly of sandstone and are overlain by hemipelagic mud. These debris flow deposits, however, do contain wood casts and plant fragments, as observed in Facies 6A and along the basal surface of Facies 3C and 30 in some measured sections. Alternatively. Facies 68 is likely associated with a storm-related event which could initiate geostrophic flows through sediment loading and changes current flow (Seilacher and Aigner, 1991 ; Nummedal, 1991 ). Leckie and Walker (1982) suggested that the lowermost. interbedded sandstone and conglomerate of the Falher Member on Mount Spieker are storm-generated deposits. By definition, a storm-generated flow is a tempestite deposit. Facies 68 does not contain the typical sedimentary structures (such as current ripples and graded bedding) associated with classical tempestite deposls in a sandy environment (Seilacher, 1991). Myrow and Southard (1996) suggest that turbidites may have different characteristics if they were formed under denslty-current, wave- induced or geostrophic flows. A "classicalwturbidite would fall under the density- current classification and have shore-perpendicular flutes and grooves and be overlain by current ripples. Turbidites that form as geostrophic currents are associated with storm-initiated debris flow deposits. Non-linear grooves along the basal surface. overlain by HCS, are characteristic of a combined geostrophic- wave influenced flow (Myrow and Southard, 1996) and are also observed in Facies 6B. Thus Facies 6B is a debris flow deposit, initiated during stomevents as a result of slope collapse along the shoreface due to increased sediment loading from feeder channels.
2.9.1 FACIES7 - DESCRIPTION This facies is not observed in outcrop. In core, this facies is characterized by shale, often with thin silty or very-fine sandstone layers. Thickness appears to vary, but in the described cores A is on the order of about 1m thick. Sorting is 69 moderate in the sand layers. Sedimentary structures identified are plane parallel, fine laminations. This facies is commonly burrowed with trace fossils such as: Planolites isp., Teichichnus isp., Rosselia isp., and Helminthopsis isp..
2.9.2 FACIES7 - INTERPRETATION Facies 7 is interpreted to have been deposited in a transitional zone to offshore environment. Shale and siltstone would be a product of deposition of suspended sediment. The fining upward nature of the sandstones are expressions of storm deposits (Leckie and Krystinik, 1989). Current ripples indicate a unidirectional current, likely an offshore directed flow of sediment related to storm deposits. Planar horizontal laminations are from slow deposition of suspended sediment. The fossil assemblage, along with the sedimentological features, also supports a distal lower shoreface to proximal offshore depositional environment (Pemberton et a/., 1992). 3.0 ST RATlGRAPHlC FRAMEWORK
3.1 INTRODUCTIONTO SEQUENCE STRATIGRAPHY Stratigraphy has been an integral part of studying the relationships of rock strata since the early days of geological sciences. Sequence stratigraphy is defined as "the subdivision of sedimentary basin-fills into genetic packages bounded by unconfonnities and their correlative conformities" (Emery and Myers, 1996). The development of sequence stratigraphy as a discipline in the geological sciences is summarised by Emery and Myers (1996). Sequence stratigraphy relates these genetic packages to relative sea level change, although the controls on deposition and preservation may not be eustatic changes in sea level. The key importance in sequence stratigraphy is to recognize significant bounding surfaces. There are a number of surfaces that become bounding surfaces for sequence stratigraphic units. A marine flooding surface (MFS) is a surface that marks a deepening of water over any underlying deposits. A marine expression of a marine flooding surface would show a deeper marine facies overlying a shallower marine facies and may exhibit a transgressive surface of erosion (Van Wagoner et a/., 1990). A maximum flooding surface (MxFS) is a marine flooding surface that marks the most extensive marine transgression (Emery and Myers, 1996). It may be recognized as the surface between a retrograding parasequence and a prograding parasequence. A transgressive surface of erosion (TSE) is an erosional surface marking marine transgression, marked by a coarse lag of sediment derived from wave reworking of older deposits. A regressive surface of marine erosion (RSE) is an erosional surface marking marine regression, often as a marine response to a relative drop in sea level (Walker and Wiseman, 1995; Naish and Kemp, 1997). The RSE is also referred to in the literature as a forced regression (FR; Posamentier et a/., 1990; Emery and Myers, 1996) or as a regressive surface of marine erosion (RSME; Plint, 1991). A ravinement surface (RS) is a surface that marks an incision 71 associated with marine transgression and shoreline retreat. A lowstand surface of erosion (LSE) forms during a relative sea level fall, in which previously submerged deposits become subaerially exposed and channel incision increases. A sequence boundary (SB) is defined as "an unconfonity and its correlative conformity" (Vail et a/. 1977; Van Wagoner et a/., 1990). It is, in theory, a synchronous surface, recognized basin-wide, and perhaps world-wide, as one having chronological significance, separating strata above from strata below (Mitchum, 1977; Van Wagoner et al., 1390). A sequence boundary may or may not show subaerial and submarine erosion.
3.2 SEQUENCESTRATIGRAPHY IN THE FALHERMEMBER Since the mid-1980's, many studies examining the Falher Members, particularly in core, have attempted to apply sequence stratigraphy. Cant (1984) was the first to start applying sequence stratigraphic concepts to the Falher Member. The term event correlation referred to correlations done with approximate time surfaces. He used the term sequence to divide the Falher Member into lettered ("A", "B", "C") divisions, marked by marine transgressions (Figure 3- 1). The Falher A and the Falher B have been examined by a number of authors from a sequence stratigraphic standpoint. Cant (1995) published a paper on the sequence stratigraphy of the Falher A and Falher 6. Rouble and Walker (1997) followed with a paper on the Falher A and 6 divisions, using allostratigraphy. There has also been work published on the sequence stratigraphy of the Falher C, 0,and F divisions. Casas (1997) examined the allostratigraphy of the Falher C and D intervals for the subsurface of Alberta, resulting in a complex stacking of allocycles (Figure 3-2). Amott (1993) examined the Falher D interval from a sequence stratigraphic interpretation. He recognized four depositional intervals with a sequence boundary separating the basal two intervals from the upper two intervals. The Falher D division was also examined by Moslow and Schink (1991), and the Falher C, 0, and F divisions were examined by Moslow (1998). Outcrop work indicated different facies Figure 3-1 Correlations for the Falher Member and the Wilrich Member based on "event correlation" (from Cant, 1984). The coals mark the boundaries of many of the Falher divisions. SOUTH NORTH 0 Lagoon/FloodPlain
SL
TSE C2 TSE C1
Sea Level Drop
( TSE ) / Rs€
Channel Incision
Barrier Retreat Ouring Sea Level Rise SL A t.n Transgressive Mudstones --- C -
I I I I I I I I I I 66 67 68 69 70 7 1 I 72 w73 TOWNSHIPS
Figure 3-2 Depositional interpretation of the Falher C for the subsurface of Alberta. Inferred relative sea level is marked as a curve on the left for each event (modified after Casas. 1996). 74 association stacking patterns for each of the Falher divisions. These facies associations varied in width and height as a response to changes in relative sea level.
3.3 OUTCROPSTRATIGRAPHY The Falher C was identified in the study area as outlined in Chapter 1. Previous work from Leckie (1983) and regional bedrock mapping from Kilby and W rightson (1 987a, b) were used to confirm the stratigraphic position of the Falher C on Bullmoose Mountain and Mount Spieker. The Falher D and the Falher F are exposed as well, allowing easy correlation along the outcrop (Moslow and Schink, 1991; Moslow, 1998). The Falher D lacks continuity on the outcrop, but the Falher F is easily traceable and the upper surface of the Falher F sandstone/conglomerate was used to confirm the vertical position of the Falher C in outcrop. Stratigraphy of the Falher C in outcrop was examined with correlations of measured sections and exploratory boreholes (Figure 1-3). The Falher C has excellent exposure in outcrop (Figure 3-3), allowing for observation of stratigraphic relationships and geometries. These stratigraphic relationships were documented with photo mosaics, which aid in making lateral correlations. Correlations from outcrop were made to core and well logs using synthesized gamma logs for the measured sections. Core and well logs from diamond drill holes (DOH) for coal exploration provided a useful database for the outcrop area (Figure 3-4).
3.3.1 FACESASSOCIATIONS A facies association refers to the predictable, lateral and vertical stacking pattern of facies. Identification of facies associations from outcrop was key to the construction of cross-sections and interpretation of geometries. The Falher C marine facies association in outcrop is bounded above and below by coastal plain facies associations (CPFA). Within the CPFA bounding the Falher C are the contacts with the underlying Falher D and the overlying Falher B intervals. WEST
Figure 3-3 Photo mosaic Mngnorth, showing the continuity dthe Falher C outcrop on the south face of Bulln cover. Measured sections are marked in yellow (Figure 1-3). The location dthe ground penetratin! into Meikle cirque on the northeast side of Bulimoose Mountain- Outcrop is also present on Mount C
!of Bullmoose Mountain. The greyish cdarr of the Falher C is due to a combination of weathering and lichen metrating radar (GPR) survey is also indicated on the photo mosaic. The continuity of the wtaop continues Mount Chamberlain where the photo mosaic was shotfrorn. and lichen continues
DDH C-15
0 GR(cB)~~- - 60 Neutron (CP-S) 600 a - - -. LL
Figure 3-4 A "type section" of Falher C shoreface conglomerate and sandstone from exploratory coal well DDH C-15, using described core to well log response. Gamma ray and neutron logs are available in counts per second. Facies and surfaces are discussed in the text. Parasequence labels are discussed in following chapters. 77 An erosional surface marks the base of the Falher C marine facies associations. Coal and carbonaceous mudstone mark the top of the Falher C marine facies associations. Figure 3-5 shows the vertical stacking pattern of facies observed in the outcrop. The four vertical sections show the changes in the stacking of facies from landward to basinward. The coastal plain facies association (CPFA) occurs landward of the maximum limit of marine transgression (MLMT; Figure 3-5A). Because, in the study area, the Falher D and Falher 6 have coastal plain components, it is impossib!e to determine the precise bounding surfaces in the CPFA for the Falher C. Using coal beds as markers, and tracing them to coals bounding the prograding shor~facefacies association (PSFA), one can get an approximate idea for the bounding surfaces. In the outcrop study area, the CPFA was observed on Mount Chamberlain (Figure 1-3) at measured section FC-18 and in well logs from the exploratory boreholes. The CPFA is composed largely of coal and coastal plain mudstone and sandstone (Facies 1 and 2). Carbonaceous debris, plant fragments and iron staining is commonly observed in the facies of the CPFA. Channel deposits are also observed from well logs for the C PFA. Sharp, erosional basal ravinement surfaces incise into the coastal plain facies. A prograding shoreface facies association (PSFA) characterizes the marine sandstone and conglomerate deposits observed in the Falher C. The stacking pattern of marine shoreface facies changes in a basinward direction from dominantly sandstone to dominantly conglomerate. These changes are shown in Figure 3-5 (B-D). The MLMT is the most landward limit of the PSFA, marking the first expressions of marine sedimentation. There are two laterally extensive surfaces present within the PSFA that are significant from a sequence stratigraphic interpretation (Figure 3-5). The first is the erosional surface identified at the base of the Falher C PSFA, incising into underlying coastal plain facies. A transgressive lag (Facies 6A) locally overlies this surface, and where present contains a similar lithology to the underlying strata. Overlying the
80 transgressive lag, or the erosional surface where the lag is absent, are lower shoreface sandstones of Facies 4. The erosional surface at the base of the PSFA is interpreted as a coeval transgressive surface of marine erosion and marine flooding surface (TSWMFS). The southern limit of the TSWMFS is the MLMT. The MLMT marks the maximum marine transgression for the Falher C, but this surface may not be basin-wide, nor does it represent the maximum marine limit for the Falher Member (Leckie, 1983; Moslow, 1998). Along the MLMT is a "sandy shoreface" (Figure 3-58). The TSE/MFS occurs at the base of the PSFA, with a transgressive lag occurring along this surface. This surface incises into the underlying coastal plain facies association. The sandy shoreface is a coarsening upward succession of sandstone, varying between Om (at the landward pinchout) and 8m thick. HCS is present at the base, with trough cross bedding and low angle bedding occurring towards the top of the succession. Vertical burrows, such as Diplocratenbn isp., are observed towards the top of the succession. Washover sandstone is present at the top of the shoreface succession, as a backshore expression of the conglomeratic, prograding shoreface. Coastal plain facies overlie the PSFA. An example of this vertical succession is observed at measured section FC-23 (Figure 3-7). The second surface of significance is a regressive surface of erosion (RSE; Walker and Wiseman, 1995; Naish and Kemp, 1997). This is an erosional surface, produced from high-energy wave processes and rapid deposition of coarse-grained sediment during a fall in relative sea-level. It is recognized in the PSFA basinward of the "sandy shoreface". Proximal to the "sandy shoreface", it occurs as conglomeratic upper shoreface deposits, erosionally overlying sandy lower shoreface deposits (Figure 3-5C). Further basinward, the RSE is recognized at the base of geostrophic flow deposits occurring within sandy, lower shoreface sediments (Figure 3-5D). These geostrophic flow deposits are the distal expression of geostrophic events, which form scoured surfaces within the conglomeratic shoreface. These scoured surfaces are source diasterns (SD; Swift et a/., 1991). They represent storm-induced shoreface ravinement and 81 shifting strandplain orientation as a result of high magnitude storms and instantaneous rising sea-level, during an overall base level fall (Moslow and Schink, 1991). RSE's and equivalent surfaces have been recognized in the Marshybank Formation of Alberta (Plint, 1991); the Cardium (Hart and Plint, 1 993); and the Viking Formation (Walker and Wiseman, 1 995). The significance of this surface is further discussed in Chapter 6.
3.3.2.PARASEQUENCES There are two parasequences, observable in outcrop, bounded by the surfaces discussed above. The first (CI)is bounded below by the TSE/MFS and above by the RSME. It is composed largely of Facies 4 lower shoreface sandstone. Facies 6A is present at the base in some areas of the outcrop, where it exists as a transgressive lag. Other coarser sandstone beds within the C1 parasequence likely formed as a result of longshore transport of coarse sediment in troughs of migrating 3D bedforms. The C1 is thickest, at 8m, towards the southern (paleolandward) part of the study area and is eroded by the C2 parasequence. As a result, the thickness of the C1 decreases towards the north where it is eroded by the C2,to a point where it is eroded completely. The C2 parasequence is marked at the base by the RSME. The upper bounding surface of C2 is unclear, and occurs within the coastal plain facies of the Falher C. This upper bounding surface is a sequence boundary/surface of subaerial exposure, but it is difficult to distinguish from the overlying Falher B, which occurs as coastal plain sediments in the study area. For this reason, the top of the conglomerate facies was chosen as the top of the marine facies association the C2 parasequence. The C2 parasequence is composed dominantly of upper shorefacefforeshore conglomerate. Lower sandstone shoreface facies (Facies 4) underlie the conglomeratic shoreface facies in the C2 parasequence (Figure 3-50). Facies 6B is a poorly sorted, matrix-supported conglomerate, deposited as a resutt of mass-wasting, that immediately overlies the RSME and on source diastems (Swift et a/., 1991) within the C2 parasequence. 82 A third marine parasequence (CO) occurs below the C1 and C2 parasequences and is not observed as a marine facies in outcrop. The CO occurs basinward of the C1 and C2 in outcrop. The CO is expressed as coastal plain facies underlying the Falher C1 and C2 parasequences and overlying the Falher D marine facies association. The bounding surface between the CO coastal plain facies and the Falher D coastal plain facies cannot be determined due to its transitional nature. Parasequence CO is discussed further in Chapter 4.
3.4 CROSS-SECTIONS Four cross-sections (A-D; Figure 3-6)have been drawn up for the outcrop. Cross-section A-A' runs south (paleolandward) to north (paleoseaward) along the measured sections of the outcrop. Cross-section B-5' also runs south (paleolandward) to north (paleoseaward) using exploratory boreholes. Cross- section C-C' runs northwest to southeast along the paleoshoreline (depositional strike) from Bullmoose Mountain to Mount Spieker. Cross-section D-0' runs east to west, southward of cross-section C-C' using exploratory boreholes. These cross-sections were correlated using observations from outcrop, photo mosaics and exploratory coal core. These cross-sections demonstrate the stratigraphic framework within the Falher C and display lithological and facies changes in the outcrop area.
3.4.1 CROSS-SECTIONA-A' Cross-section A-A' (Figure 3-7) correlates measured sections from the southern part of the Falher C outcmp exposure on Bullmoose Mountain to the northern limit of the Falher C outcrop and parallels depositional dip. Basinward is to the north, whereas landward is to the south. Correlations are based on observations made in the field from the outcrop and photo mosaics. The datum is the top of the shoreface sandstone and conglomerate. The distance between the measured sections is marked at the top of the cross-section. The total
Figure 3-7 Cro! trac ma1
Sedimentary !3rudures plener hxiamd bedding s klwaek planar beddng lawMngleCmis~tiar\ ~M-beddng - z3-E- a-- wyijp. -*-9- M -=
igure 3-7 Cross Section A-A' oriented south to north akmg the measured sections in the study area. The comela ' tract deposits (C2). These are separated by a RSE. The RSE is formed from the amalgamation of the may be equivalent to the Falher D & to the transgressive systems tract deposb (CO)of the Falher C.
Falher B
~rfaces/FaaesAssociations 3 - Regressive Surface of Erosion 5 - Marine Floodi Surface Falher 0 i-TransgtessiveSurfaceofErosm - Source Diastem - SeqoenceBoundary . - :A - Pqrading Shareface Facies Assoaat#n :A - Coastal Plain Facies Association I Parasequences I C2 (Regmsbe Systems Trad) I Cl (HighSMd Systems Tract) I 1 0' Crransgressive system Tract?) I Non-Falher C
-ea. The correlations were made fran observations in the out- and from photo m-cs. The PSFA is mpc lgamation of the basal sufices of source diadems (SD's). The base of the C1 is a TSEIMFS andC2 is boundec ~fthe Falher C,
The PSFA is composed of highstand shoreface deposits (C1 ) and regressive systems S andC2 is bounded at the top by a SB. The channel undertying the Falher C shorefacs
(basinward) North
'sterns horeface . distance the cross-section represents is 1.4km and its location is highlighted on Figure 3-6 and in the insert on Figure 3-7. Parasequence C1 is poorly defined in outcrop, as much of it has been eroded by subsequent parasequences. Even where it exists in outcrop, soil and talus commonly cover it, as the sandstone is more recessive than the conglomerate. The base of parasequence C1 is an MFS, which grades laterally basinward to an MFSTTSE, marked by a transgressive lag. North of measured section FC-15, the basal surface is erosional and is immediately overlain by Facies 6A, interpreted as a transgressive lag. At the southern (paleolandward) end of the cross section, in measured sections FC-22 and FC-23, the C1 parasequence is composed largely of shoreface sandstone (Facies 4). In section FC-23, burrow traces of the Skolithos ichnofacies are observed. The C1 sandstone coarsens upward, and is fine- to medium-grained with a high component of lithic grains. Sandstones observed in the lower portion of measured sections FC-4, FC-5, FC-11, FC-4, and FC-31 are interpreted to be part of the C1 parasequence. At FC-23, the upper 1.3m of sandstone are very fine- to fine-grained washover sandstone (Facies 40). The washover deposits observed here are formed from eroded sandstone from the C2 shoreface, which occurs basinward of measured section FC-23. The washover sandstone overlies a 25cm coal bed. Underlying the Falher C PSFA is a Falher D (or CO?) channel deposit in the southern part of the cross-section at FC-23 and FC-22. This same channel deposit is observed at FC-19 and FC-20 (Figure 3-8). Most of the Falher C deposits in outcrop sit on Falher D coals, carbonaceous rnudstone and sandstone of the Falher D coastal plain facies association (CPFA). Falher D shoreface sandstone underlies the Falher D CPFA (FC-31 and FC-4; Figure 3-7). In outcrop, the Falher D sandstone pinches out laterally to the north (Figure 3-9). Where preserved in outcrop, the sediments overlying the Falher C conglomerates are coals and carbonaceous mudstones of the Falher C CPFA, which grade into the CPFA of the overlying Falher B. Figure 3-8 Measured sections FC-19 and FC-20 (Figure 1-3;3-9) from the north end of Meikle Cirque. Falher C PSFA overlies Falher D channel and CPFA. separated by a TSEIMFS and transgressive lag. SOUTH
Figure 3-9 Photo mosaic facing west of Falher C ex regressive conglomeratic shoreface (C; section FC-19 is a high-angle thrust fauH
est of Falher C exposure in Meikle Cirque, on the north side of Bullmoose Mountain. Falher C packages are highligt ntic shoreface (C2).The orientation of the dinoforrns in heFalher C are due in part to the orientation of the cirque an I-angle thrustfault, shown on Figure 1-3. lackages are highlighted in purple, Falher D in yellow and Falher F in blue. The Falher C prograding shoreface facie! ta tion of the cirq ue and due in part to depositional orientation. The Falher C downcuts into Falher D coastal plain facie
?facefacies association (PSFA) is composed of a highstand sandy shoreface (C1) which is eroded by a 11 plain facies association (CPFA). The Falher D shoreface pinches out to the north. North of measured
NORTH
:PSFA)is composed of a highstand sandy shoreface (C1) which is eroded by a (CPFA). The Falher D shoreface pinches out to the north. North of measured
88 The basal surface (RSE) of parasequence C2 is erosional. This is apparent at measured section FC-5 (Figure 3-10), where 4.5m of shoreface sandstone have been eroded away and overlain by shoreface conglomerate. The C2 parasequence is seen in outcrop as stacked PSFA's. Each PSFA is separated from the successive PSFA by a source diastem (SD), forming clinoforming surfaces that can be observed in outcrop (Figure 3-9). The width of these PSFA's varies between about 100m and 400m, and they are thickest in the upper shoreface and then are condensed in the lower shoreface. This geometry results from successive erosion of facies associations into the lower shoreface of previous facies associations. C2 increases in thickness towards the north as compaction of underlying Falher D and F CPFA's increases the amount of accommodation space for the PSFA. To the north (basinward), the upper surfaces of the facies associations subsequently sit stratigraphically lower than the upper surface of the preceding facies association. Towards the north part of cross-section A-A' (FC-32), the basal surface of the C2 prograding shoreface downlap onto the TSWMFS surface.
3.4.2 CROSS-SECTIONB-B' Cross-section B-6' is oriented southwest to northeast along the west part of Bullmoose Mountain through five exploratory boreholes (Figure 3-1 I),along a line roughly perpendicular to paleoshoreline. The well name is located above each of the logs, and distances between wells are shown. The datum is the C2 top because it depicts the stratigraphic relations of the two observed Falher C parasequences most accurately. Depths for the "BP" wells are in meters and for the "C" wells in feet. Gamma ray logs are used in each of the wells and are in GAP1 units. Density logs are the other log suite shown for these wells. The exploratory boreholes with "BP" prefix have a coal bulk density log, which is a form of a long-spaced density log. The units are standard density units (SDU) which show relative density (Hulatt, pers. comm.. 1999). Calibration for the logs in the study gives a value of 3.25 gm/cm3 for 0 SDU and about 1.33 gm/cm3 for 6000 SDU with a non-linear correlation. Exploratory boreholes with the "Cnprefix Figure 3-10 Erosional surface at the base of the C2 PSFA, which cuts into sandstone of the C1 parasequence. This surface is a regressive surface of erosion (RSE). The erosional relief along the lower surface is 4.5m. Note how the surface cuts through bedding in the underlying C1 sandstone. The pick is 60an in length. Fgure 3-11 Cross Section B-B'. South to north cross shorehoe is unconformaw overlain by tt north cross section through exploratory coal wells. The fades were calibrated to axe description fix welk BP-6! ~erlainby the C2 regressive shoreface. ion for wells BP-69a and C-15. The C1 highstand
91 display relative neutron emission in counts per second (CPS). This relative neutron measurement is correlatable to coal bulk density. Coals have a low bulk density between 1.2 and 1.8 gm/cm3 whereas sandstone and conglomerate have bulk densities of about 2.3 gm/cm3 (Schlumberger, 1989). Neutron logs reflect the relative amount of hydrogen atoms within a unit of rock. Because hydrogen is more abundant in water and gas, and these accumulate in pore spaces, then the neutron log reflects porosity. Because shale and coal have lower porosities, the neutron log is deflected to the left. Wells BP-69a and C-15 both have core preserved and described (Figures 3-3 and 3-12). The well logs were compared with the core description for a lithological interpretation. As in cross-section B-8', there are two interpreted parasequences: C1 and C2. The C1 parasequence is recognized in well BP-69a (Figure 3-12) with a composition of sandstone and conglomerate. A thin bed (40cm) of carbonaceous mudstone deposited in a lagoon environment is observed in the C1 PSFA in this core. The lower bounding surface of the C1 is a TSE/MFS surface. Overlying C1 sandstones/conglornerates is a bed of conglomerate with a sharp, erosional base. This conglomerate is interpreted to be the landward edge of the shoreface conglomerate of parasequence C2. The C2 is separated from the C1 by an RSME surface. To the southwest in well BP-70, both parasequences are thinner and are bounded above and below by coastal plain mudstones. These are recognized as having higher gamma ray values and are interspersed with coals recognized by the sharp shift to the left on the density logs. In BP-70 washover sandstone is deposited coevally with the conglomeratic PSFA of C2. This would be comparable to the washover deposits observed at measured section FC-23 (cross-section A-A'; Figure 3-7). To the northeast (basinward), the C2 parasequence thickens, and is interpreted to be incising into the C1 parasequence. The C1 parasequence is comparably thinner. A transgressive lag (1-2mthick) occurs at the base of the C1, and is reflected in well logs by a low gamma response at the base of the w .-d F 5 Lithology c 8 Gram S~ze DDH BP-69a
Shale
1 rn 1- z 101 r 2 707 , me. - ..... <...-..-.m-..-K.u ,------..----.-.---.-....-. 1- 2 .-- . .. - 104 , --- ' - 903------1m- --- 1 ---- - TOT------1 100- --
133-
.*.-...... , ...-...... -, LL .....-..-. -.. -4 -..-.--,-....-. -.-....( -.-....,*.-...... *.-...... Figure 3-12 Core description and well log for exploratory coal well BP-69a. The C2 PSFA shows multiple beds of sandstone. 93 Falher C (Figures 3-3 and 3-12). Lower shoreface sandstone overlies the lag, which is reflected as an increase in gamma response. The RSE that separates the C1 from the C2 cuts into the lower shoreface sandstone and is overlain by geostrophic-flow conglomerate (Facies 6A). The C2 parasequence has the same stratigraphic geometries observed in outcrop. The offlapping/clinoforming source diastems are shown on the cross-section. The source diastems can be interpreted by a shift in gamma ray radiation as shown in well BP-71 (Figure 3- 11). Falher D and F may be observed as the 'cleaning" upward gamma response, underlying the Falher C TSE/MFS. Falher B is a spiky log signature interpreted as coastal plain rnudstone and is difficult to distinguish from the Falher C coastal plain succession.
3.4.3 CROSS-SECTIONC-C' Cross-section C-C' (Figure 3-13) is located along the north part of Mount Chamberlain oriented from the northwest to the southeast through five exploratory boreholes (Figure 3-6). Depths for well C-25 are in feet whereas the remaining wells are in meters. The top of the Falher D shoreface is the datum for this cross-section, as it is difficult to interpret the top of the Falher C or the top of the Falher D succession due to the vertical coastal plain amalgamation of facies. There is no core available for these wells and thus the facies interpretations are based on the gamma logs. The intervals on logs characterized by high gamma, and "spiky" character ara interpreted to be coastal plain, carbonaceous mudstones. Falher D shoreface sandstones/conglomerates are recognized by the "blockier" appearance and low gamma response. Coals, marked in black, are interpreted from associated neutron-density logs, not included in this cross-section. There are three channels within the Falher C succession in cross-section C-C'. An increasing gamma response is interpreted as a fining upward lithology associated with channels. These channels are narrow and about 10m thick. The width of the channel valleys is less than 400m. North BP-10
Figure 3-13 Northwest to southeast cross section through the coastal plain fac are interpreted from well logs by an increasing gamma respon suggest individual narrow channels, shifting position through avul cannot be determined from coastal plain log response.
94
C' BP-2A i GR aGAP1, z 0 l Southeast 0.46km ' 0.90 km
'50 BP-5 - GR tWI,
C
----- :. ,I shoreface
-
-
-
-s>
> 3
zoastal plain facies of the Falher C. Coal is marked in black. Channel deposits gamma response upward and are marked in grey. These channel deposits ion through avulsion rather than migration. Individual Falher C parasequences nse.
95 A channel is observed in outcrop of the Falher D (Facies 5; Figure 3-10). It is composed of a conglomerate with a mixed, mudstone and sandstone matrix. The high gamma response implies a high component of shale or mudstone. This may be deceiving if the channel fill is a mixed mud-sand matrix-supported conglomerate and the pebble content decreases upwards. In other words, although the log response might suggest a fine-grained sediment fill, it is possible, based on outcrop observations, that the channel fill is conglomeratic. It is believed that incision by these channels, observed in the boreholes on Mount Chamberlain (Cross-section C-C'; Figure 3-13), was contemporaneous with the C2 conglomerate shoreface facies. These channels are at different stratigraphic levels and they occur between the coal marker beds that bound the PSFA. There is no indication of lateral migration of these channels, as interchannel well logs display numerous coal layers. The channels observed in well logs do not cut through the preserved Falher C conglomeratic shoreface in outcrop, which also suggests contemporaneous deposition.
3.4.4 CROSS-SECTIOND-D' Cross-section D-0' is oriented northwest to southeast from west Bullmoose Mountain to Mount Chamberlain, utilizing exploratory boreholes and measured sections (Figure 3-14). This cross-section is oriented parallel to depositional strike along the southern limit of marine facies. This section displays the thickest occurrence of the C1 parasequence where it is overlain by the conglomerate of parasequence C2. The "BPnwell depths are in meters and have a gamma-bulk density suite of downhole logs. The "C"wells are in feet and have a gamma-neutron suite of logs. Described core from BP-69a, and outcrop observations from measured section FC-02 were used for facies calibration to gamma logs. The C1 parasequence is shoreface sandstone overlying coastal plain facies. The C1 sandstone has a lower gamma response than the underlying mudstones. The surface that separates the C1 parasequence from the underlying coastal plain is an MFS, which is coeval with a TSE further basinward. Datum: Top of Falher D sandstone/conglomerate
Figure 3-1 4 Cmss-section D-D'. Nolthwest-southeast cross-section along ti st cross-section along the paleohndward edge. The C1 PSFA is in green and the C2 PSFA is in orange. The CF is in orange. The CPFA is in grey. Measured sectbn FC-02 is located on Mwnt Spiek~.
97 In well BP-69a, The C1 is a conglomerate interbedded with sandstone and carbonaceous mudstone beds. In this cross section, the C1 parasequence is thickest at Mount Spieker (FC-02; Figure 3-14), where a coal caps the C1 parasequence. This coal may be similar to the one observed on Bullmoose Mountain at site FC-23 (cross-section A-A'; Figure 3-7). The C2 parasequence is conglomeratic at FC-02 and BP-69a. In both locales, the basal surface of the C2 is an erosional surface (RSE). At FC-02, the C2 parasequence erodes into a coal. In wells BP-70, C-29 and BP-32, the C2 parasequence is identified by a deflection of the gamma log. It is unclear whether the C2 parasequence is conglomeratic in these wells or if it is composed of washover sandstones as observed at FC-23 (cross-section A-A'; Figure 3-7). Well BP-8 consists entirely of coastal plain deposits. This facies change occurs within 350 m of the well BP-14a, and marks the maximum transgressive limit of the Father C (C1 and C2) marine facies. Cross-section D-0' shows along-strike continuity of the southem-limit of marine facies. It demonstrates that there is a sandy shoreface laterally separating coastal plain facies from the conglomerates of parasequence C2. This HST sandy-shoreface existed sometime prior to incision and deposition of the C2 conglomerate shoreface. The presence of the coal at FC-02 suggests that the time period was long enough for coastal swamps to deposit peat prior to C2 shoreface incision.
3.5.1 ~SOPACHMAP OF C2 Figure 3-15 shows a total thickness isopach map for the C2 parasequence. An isopach map for the C1 parasequence was not constructed because it is not present everywhere and may be covered or partially covered in many measured sections. The paleolandward limit of the C2 PSFA is marked by the Om contour line. The thickness of the C2 increases to the northeast to a maximum of 15.lm of
Figure 3-15 lsopach of the total thickness of the C2 PSFA in the Bullmoose Mountain area. The paleolandward limit is oriented north-west to south-east along depositional strike. The C2 thickens from Om to over 6m along a 300m wide fringe adjacent to the paleolandward limit. The C2 is thickens to the central part of the study area and thins to the north.
99 measured thickness. From that point, it decreases in thickness north to 6.9m at measured section FC-19. The 3m contour line along the paleolandward edge closely approximates the location of washover sandstone deposited contemporaneously with the C2. The washover sandstone observed in outcrop and in core is 1-3m thick (1.Sm at measured section FC-23). Shoreface conglomerate begins to appear between the 3m and 6m contours, where erosion and incision occur along the RSE. The 6m contour line extends in a northeast trend along the measured sections between Bullmoose Mountain and Mount Chamberlain (Figure 3-15). This is because of erosion and weathering of the upper surface of some of the measured sections on the order of <1 .Om. North of the 6m contour line, the RSE becomes more horizontal and the thickness of the conglomerate is more consistent. The variation in the thickness of the C2 PSFA is a result of stacked shoreface sequences. The shoreface sequences are thicker in some locations due to the shifts in shoreline orientation, which are caused by changes in accommodation space in front of the shoreline. The thickest C2 PSFA occurs in outcrop where the underlying Falher D shoreface sandstone is absent (Figure 3- 9). More accommodation space may occur in this location in the outcrop due to differential compaction of coastal plain facies that underlie the Falher C. The C2 PSFA trend is laterally continuous along strike. In outcrop, the C2 PSFA may also be observed at Mount Spieker, which occurs 8km to the southeast along depositional strike (Figure 3-6). The width of the C2 PSFA along depositional strike is varied. In the Bullmoose MountainIMount Chamberlain area, the width of the C2 PSFA is 1.5km-2.5km. widening to the southeast. The width varies due to the shifting orientation of the shoreline and the stacked shoreface FA'S. The C2 PSFA is widest in proximity to a depositional point source and thinner away from a depositional point source.
3.5.2NET CONGLOMERATE Net conglomerate of the C2 PSFA was mapped and contoured (Figure 3- 16). The conglomerate mapped was the shoreface conglomerate from Facies 3
Figure 3-16 lsopach map of the net conglomerate for the C2 PSFA in the Bullmoose Mountain area. Conglomerate thickens to the northeast. The conglomerate remains less than 3m thick to the east. Conglomerate thickness is directly related to accommodation space available during deposition, which resulted in shifting orientations of the depositional shoreline.
101 for the C2 PSFA. The paleolandward limit of the C2 conglomerate is marked by the Om contour, which trends northwest to southeast. The thickness of the C2 conglomerate increases to greater than 3m within 100-200m of the paleolandward limit of the C2 conglomerate. Between the Om and 3m contours marks the initial appearance of shoreface conglomerate and the initial appearance of the RSE. The Om contour separates the C1 sandy shoreface from the C2 conglomeratic shoreface. The thickness of the C2 conglomerate increases to the northeast to 12.4m at measured section FC-7, and thins again to the north to 5.6m at measured section FC-19. The variation in thickness is related to the shifting shoreline orientation and changes in accommodation space due to differential compaction of underlying coastal plain facies. The net conglomerate map shows a similar relation to the isopach map of the C2 parasequence. The amount of C2 conglomerate increases with increasing overall thickness of the C2 parasequence.
3.5.3 OPENFRAMEWORK CONGLOMERATE:~ANDMATRIX CONGLOMERATE RATIO MAP The posted values for this map were taken from observations of the measured sections, and displays the Facies 3NB conglomerates compared to the amount of Facies 3CID conglomerates (Figure 3-1 7) for the C2 PSFA. The limits of open framework conglomerate and of sandy matrix conglomerate are marked on the map and approximate the paleolandward limit of the C2 PSFA. Throughout most of the outcrop area, the ratio is less than 1.O, which means there is more sandy matrix conglomerate (upper shoreface) than open framework (foreshore) conglomerate, which is to be expected in a shoreface environment. In other words, the swash zone, which is responsible for winnowing of the sand component of the conglomerate, represents only 1m-4m in a total of 8m-12m vertical shoreface succession. In the area where the ratio is less than 1.0, the open framework conglomerate varies in thickness from 1.5m to 3.5m, with the sandy matrix conglomerate varying in thickness from 2.0m to 7.5m. The contours parallel the trends observed in the total thickness and conglomerate thickness isopach maps for the C2 interval. The smallest ratio occurs at
103 measured section FC-20 at 0.18. Where the C2 PSFA is the thickest is where the ratios are the smallest, and is a reflection of thicker upper shoreface sandstone. Values greater than 1.0 indicate measured sections where open framework conglomerate is thicker than sandy matrix conglomerate. Figure 3-17 highlights in dark gray where there is a ratio of 2.0 or greater, where there is twice as much or more open framework conglomerate than sandy matrix conglomerate. This is located where the net conglomerate thickness is 6m or less (Figure 3-16). The highlighted area also occurs adjacent to the projected location of a channel mouth. The channels observed in the exploratory boreholes (Cross section C-C'; Figure 3-13) of the Falher C CPFA on Mount Chamberlain are shown on Figure 3-17. On the northwest side of the projected channel mouth, the open framework:sandy matrix ratio is less than 0.5. The open framework conglomerate accumulated more on the southeast side of the channel. This segregation of sandy matrix may be due to transport of sand-sized grains to the northwest by longshore currents. It may also indicate that the morphology of the beach during time of deposition allowed for greater winnowing of the conglomerate on the southeast side of the channel mouth.
3.5.4PALEQCURRENT DATA Paleocurrent measurements were taken where possible from measured sections in outcrop. Measurements were taken of orientations of wood casts and groove casts along the basal surface of SD's and laterally adjacent debris flow conglomerate (Facies 6) in the Bullmoose area during the 1998 field season. There were five sites at which wood casts were preserved and recorded. These are described in Table 3-1. The locations of these observations are shown on Figure 3-18. Outcrop observation of lateral facies changes and mapping the location and orientation of the backedge conglomerate-sandstone contact indicates that the paleoshoreline is oriented to NW-SE. The major orientation of wood and Stn I DESCRIPTION # of Major Minor Measure- Orientation Orientation :#iI ments I 31 1 South end of Meikle Cirque 31 N (0s) E-W I 1 1 SN / Immediately south of Stn 15 15 N (-S) ENE- I WSW I I 1SS i Further SW of Stn 15 63 NE (-SW) 1 NW-SE ' 14 / Station 14 - north Bullmoose 39 NE (-SW) 1 NW-SE I Saddle i 1 27 1 West of Saddle NE (-SW) E-W I I 1 I NW (-SE)
Table 3-1 Paleocurrent measurements from wood casts along erosional surfaces within the C2 parasequence.
106 groove casts is, in general, perpendicular to this paleoshoreline. The minor orientation of the wood casts parallels the inferred orientation of the shoreline. These data suggest that these wood casts were carried offshore by a (strong) unidirectional current. Preservation of the wood casts and groove casts along the basal surfaces of SD's does indicate that these features were not wave reworked. If these had been wave reworked, the long axes of the wood casts should be aligned parallel to the shoreline or perpendicular to dominant wave direction. Preservation would have occurred as a result of rapid sedimentation following incision and transport of the wood casts. The east-west secondary orientation (medium gray; Figure 3-18) could have resulted from two possible processes. The first possibility is that the long axes of the wood casts would have aligned perpendicular to the dominant flow orientation. Studies on clast orientation during rapid flows indicate that small proportions of elongate clasts are oriented perpendicular rather than parallel to the dominant flow direction (Major, 1998). The other possible process that could have caused the secondary wood cast alignment is reworking by longshore currents. Longshore currents could result in the reworking of wood casts to align parallel to the paleoshoreline. Although longshore currents likely played a role in the geometry of the conglomerate shoreface and conglomerate transport, it is unlikely that longshore currents affected the alignment of wood casts at the base of the SD's. The wood casts and groove casts suggest that no wave reworking had taken place along this surface and the sand matrix conglomerate directly overlying these SD's show no observable bedding or reworking.
3.6 GROUNDPENETRATING RADAR Ground penetrating radar (GPR) is the process and the associated results of a geophysical survey that measures the energy reflections of transmitted. 10 to 1000 MHz frequency, electromagnetic (EM) waves to measure features within a substance (i-e. rock). For a detailed explanation of GPR theory and methodology see Davis and Annan (1989), Annan and Cosway (1992) and Jol, 107 (1993). The principle behind ground penetrating radar is similar to that of seismic or sonar reflection techniques. EM waves are transmitted into the substance with a transmitter antenna. The EM waves propagate though the substance and are reflected with a change in electrical properties and are received at surface with a receiver antenna. The primary properties which affect the propagation of an EM wave in the subsurface are electrical conductivity and dielectric constant (Jol, 1993). Electrical conductivity is the ability of a substance to conduct an electrical current. The dielectric constant is a measure of relative permittivity which is the substance's ability to store an electrical charge when an electrical field is applied (Jol, 1993). A ground penetrating radar survey was run on the south face of Bullmoose
Mountain (Figure 3-19). The location was chosen because it was close to 2 laterally continuous exposed outcrop face at measured sections FC-14 and FC- 15 and because Falher C conglomerate was exposed directly at surface in this location. The outcrop is exposed, in part, by an access road built to maintain repeater stations. The bedding in the outcrop dips in the same orientation as the slope of the surface. Line lengths and orientations were chosen for having the least amount of vegetation and soil cover, to avoid impedance of the radar signal. Six lines were run (Figure 3-19) in crossing orientations. Lines 01, 02. and 04 were run west to east (Figure 3-20), lines 05 and 06 were oriented south to north and line 03 was run southwest to northeast (Figure 3-21). With these lines, a fence diagram was constructed for correlation between lines (Figure 3-22). The survey was performed as a reflection survey using a Sensors & Software pulseEkko IV system, operated with an IBM PC 486 laptop (Figure 3- 23). The number of stacks selected was 128 with a total time window of 1000ns. Lines 01, 02, 03 and 05 were run with a 400V transmitter. Lines 04 and 06 were run with a 1000V transmitter due to equipment failure with the 400V transmitter. 1OOMhz antennae were used at a 1m spacing intervals. Spacing was measured using a 30m measuring tape. Topographic measurements were surveyed using a theodolite and reflector. Because the outcrop dips in the same orientation as Figure 3-19 Location of GPR lines. The lines were run on the south face of Bullmoose Mountain along outcrop exposed at surface. The lighter areas are exposed Falher C and darker areas are vegetation cover. The outcrop here forms a dip-slope, where the bedding surfaces dip at the same angle as the surface slope of the mountain. Lines 05 and 06 were run south-north, lines 01,02 and 04 were run west-east and line 03 was run southwest to northeast. Lines 01,02 and 03 run along an access road. In o LINE 01 1 WEST 3 EAST 0
Figure 3-20 GPR lines 01, 02 and 04. These lines are oriented west-east. blue line is the basal reflector, separating Falher C sandstones ' between the C1 and C2 parasequences. The greenline is a be where it is interpreted to change lithology from conglomerate to
EAST WEST
a
0 -t! LINE 04
~rientedwest-east. Paleoiandward direction is interpreted to be oriented WNW-ESE. Reflections are bedding su ilher C sandstones from underlying Falher D mudstone and coal. The red line is a strong, roughly horizontal refle le green line is a bedding plane. traceable in outcrop at the surface. It dips towards the northeast. In line 04. the Irn conglomerate to sandstone. Yellow lines trace other apparent refledors.
rC1 LINE 02 0 01 C 3 EAST
EAST I
3E. Reflections are bedding surfaces and lithology changes. The I strong, roughly horizontal reflector, interpreted to be the contact Is the northeast. In line 04, the green line is dashed to the east,
SOU LlNE 05 NORTH Distance (m)
LlNE 03 Distance (m) SOUTHW
Figure 3-21 GPR lines 03,05and 06. Lines 05 and 06 are oriented south-north. Lil interpreted to be WNW-ESE. Reflections on the GPR data are bedding plane that is dipping to the northeast. A strong dipping direction (about 5 (blue line) and the CllC2 contact (red line) generally parallel one an01 interpreted to be erosional. Many of the reflectors in the data are diffio content. The yellow lines are traces of reflectors that may represent beddl
C7 N 0 0 0* SOUTH a aa LINE 06 a NORTH NORTH E c .-E A 2 Distance (m 1
ave7. 5z '2.c u-:3.0-= - s--4.0 G--5.0 -z "2- - S 0 .7.0 2~ 0 tl
0 c z J i NORTHEAST 4 5 . 54 . . -.-55 60 70 75 --. -- -.- - - .p=.-.- --- . --- - 4- -- - - .7 _ - Reflector traces - Bedding surface , CZCl contact (RSE) -Base of C2 (MFS)
th-north. Line 03 is oriented southwest to northeast. Paleoshoreline orientation is are bedding surfaces and lithology changes. The green line represents a bedding tion (about So)is seen along the reflector the green line follows. The basal reflector llel one another. These show undulation in the dip direction. Both surfaces are 3ta are difficult to follow, likely because of lateral variations in lithology and pebble resent bedding surfaces, lithology changes or changes in groundwater.
. -: -< ...... - ' . . :.; ..., . .r.,--.;.,:.. :.-:-----... % 1 > ; -.--, ., - ' >. .. - ;.; ,-,-... ;.; :::;:;::<: .-::-.>* ... .:- ...... -.. ,. . :-. . .. :...... - .- ..- -..,., ...... :.:+. - .,,. ;--. - - ...... - ,-, ... ,..-- ...... -:.. -7'. ,,- -:--4 .:-,.; ->.,- : . I -_*- .. .::.:. .7, . - -- .-.- ? .. . .-. , -,- .. . -. . . -. - -..- . -- - ...... - .. *...... -, ...... , . - -...... - ,:;..., --- .- -.- ....-.. ... - - ...... ;.. , \, ...... ': ::' ::' :,;: :;.; :.;< .; -,.:; ;;;: - ,-:: ' : . - .. -. - ._ ....- .\::;- :..- . 1; : - . . - .* .__I>..... -. .-.-,... - .. -... z . -:- . : ,.,. ;...... _ . _ - ...... -. . -.I..-, ...... - -. . : . a. '- * -. -- . - X.,*-.r .', -.-.. -. --
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.. . - ...... *-*.-. - . - I .- + .....:...... -I -1 ;- A <-, ..-. ,; ,; . .,.:--<. -...... -: .>. :>,, $!::::?, ;;-:.- :*;:.':;;.;-:.;<: ;+ ?; ::::.- -:::-.-- .: , .: --.. :: ...... :...... - .... --. . -.; - ... -L-...> --;;-;;;;;;-:-;ji:;::-;..;,;:; -....-. , . ,. --=--. , . ,. . , ,..- -,': -..'-.'.' . - . -I- - & .._..._.._....--...... , .- -...... - I- (. - -. . ,:... -: -.....- .. ,- ...... a. :-..:...... :---..>. :.> :>- ..:< >: ; :'*.; -. t..;,- :";;:~3;.:.;-?.- ...... ; 7 ...... >-. ....-. ..-=-'r --.-d_.:-.:. il... -...... - -.-.....-:- - ._-. . -.,_-..-.. . -, ...." .... -...... -.. ,
Figure ;-23A) The GPR survey was operated with an IBM PC 486 laptop and Sensors 8 Software console. The equipment was mounted on the front of an An/. B) The survey was run as a reflection survey with spacing between the transmitter and receiver at 1 metre intervals. 100 MHz antenna were used. the slope, the topographic measurements are negligible (~30crn after removing mean slope angle). The results of the surveys were plotted using Sensors & Softwares pulseEKKO IV plotting software. A constant gain multiplier value of 300 was used. A velocity of 0.1 lOm/ns was chosen. This value was initially estimated using values from Annan and Cosway (1992) by comparing values for dry sand (0.1 5m/ns), wet sand (0.06m/ns), limestone (0.12m/ns) and shales (0.09rn/ns). The distance to the deepest reflector (-10m) is comparable to the thickness of the outcrop closest to the GPR location. Reflections shown on the results are from changes in the dielectric properties of the reflecting material. This may be due to a lithology change, or presence of water or air along a bedding surface or fracture. There are a number of published examples, from both ancient and modem sediments, of bedding surfaces being delimited by GPR data. Smith and Jol (1997) used GPR to analyse a modem Gilbert-type delta from Peyto Lake, Banff National Park. Topset, foreset and bottomset beds were identified from reflections on the survey results. Meyers et a/. (1996) describe identification of erosional scarps, caused by earthquake events, along a modem barrier in Washington State. USA. Presence of magnetite along these erosional surfaces produces strong reflectors on the GPR results. Dipping foreset beds are identified as well and compared to Vibracore data. Bedding has been interpreted and identified on GPR results from ancient examples also. Stephens (1994) discusses an example from the Kayenta Formation in Colorado, USA. In this study, a grid-survey was performed along a cliff edge to compare results from the GPR data. A complex series of channel deposits were distinguished on radar data. Most of the reflectors were traceable over several hundred metres and correlated to bedding surfaces or changes in lithology. McMechan et a/.(1 994) describe another example from the Ferron sandstone in Utah, where radar results were used as a 3-0 model for reservoir changes. The reflections were identified in this study as bedding contacts from an ancient tidal channel. 114 As with these previous studies, the reflections in this study are interpreted to be bedding surfaces or lithology changes. Three reflectors were traced out on all the lines. The strong reflector at the base of each line is interpreted to be the contact between C1 shoreface sandstone and underlying CPFA mudstones. This line is marked as a blue line on the GPR results. This reflector occurs between 150 and 200ns. Mudstones, shales and clays have a much higher attenuation (1-300dB/m) than lithified rock (0.01 -1dB/m), and thus disperse a radar signal (Annan and Cosway, 1992). About 10-40ns above the basal reflector is marked a red line. This line is interpreted to be the contact between the C2 sandstone/conglomerate and the C1 sandstone. This surface is interpreted to be a marine flooding surface. The reflector is strong and roughly parallels the basal reflector. The reflectors above the red line dip towards the north and east (lines 04 and 05; Figures 3-20 and 3-21). These reflectors are believed to be toesets of upper shoreface conglomerate grading to lower shoreface sandstone. The reflectors above the red line are difficult to trace. The green line on the GPR results is a bedding plane, which is observed at surface at the 6m distance mark on line 05. This reflector is traceable on nearly all the lines and shows a dip towards the NNE. It may correlate to a diastem between facies associations and would concur with observations from the outcrop. Lines 05 and 06 (Figure 3-21) show prominently dipping reflectors, at about 5" to 8", in a northerly direction. This dip orientation is less prominent in an easterly direction (Figure 3-22) and many of the reflectors in lines 01, 02 and 04 are roughly horizontal or show a dip in either direction. Lateral changes in pebble content and lithology show up as discontinuous reflectors that are difficult to distinguish from laterally continuous bedd~ngplanes.
3.7 STRATIGRAPHICARCHITECTURE The Falher C outcrop at Bullmoose Mountain and Mount Spieker displays the paleoiandward limit of marine transgression and subsequent deposition. Two parasequences may be observed in outcrop for the Falher C. The C1 parasequence is the result of the deposition of a "sandy" shoreface. The lower 115 bounding surface of the C1 parasequence is a coeval TSWMFS and the upper bounding surface is an erosional RSE. The C1 parasequence is thickest towards the southern limit of marine facies. The C2 parasequence is a regressive, incised, conglomeratic shoreface. The basal surface of the C2 parasequence is an RSE. It is formed as the result of wave ravinement during shoreface deposition of coarse-clastic sediment likely in association with severe storms. The RSE is a diachronous surface, composed of a multitude of shoreface erosional events. Each of these erosional surfaces are diastems representing very little time hiatus. Channel avulsion also, often occurs as a result of severe storms. With a shift in channel mouth depocenter, the strandplain orientation is altered. As relative sea level drops, shoreface incision continues, forming the diachronous erosional basal surface of the C2 parasequence.
3.8 PALEOGEOGRAPHY Figure 3-24 shows a paleogeographic map for the study area. In the southern part of the study area. coastal plain facies (shown in green) are found. The coastal plain facies of the Falher C are difficult to distinguish from the coastal plain facies of the Falher 6 or the Falher D (Cross-section C; Figure 3-15). The boundaries between these are typically picked from coal beds (Cant, 1984). Narrow, deep, relatively straight channels incise into the coastal plain facies and feed sediment to the shoreline (Figure 3-13). These channels do not show evidence of lateral migration. The C1 parasequence is shown in pink on Figure 3-24. The southern limit of the C1 parasequence marks the maximum transgressive limit of the marine facies in the study area. The C1 parasequence is a sandy shoreface, and occurs as a 0-400m wide sandstone body separating coastal plain facies from the conglomeratic regressive shoreline of parasequence C2. The C1 parasequence is interpreted to be a highstand shoreface, representing the deposition that occurred between relative sea level rise and relative sea level fall. 1-- I/ J /I -3= """
Figure 3-24 Paleogeography of the Falher C in the ,Bullmoose I geography of the Falher C in the Bullmoose MountainIMount Spieker Region
117 The C2 parasequence incises into the C1 parasequence. The C2 parasequence is composed of regressive conglomeratic strandplain deposits. Changes in strandplain orientations are shown in different colors on Figure 3-24. Each of the boundaries between the strandplains are reflected in the subsurface by source diastems in the C2 shoreface. To the north, lower shoreface (yellow) and offshore marine facies (blue) are shown in their predicted locations. Complete facies associations of lower shoreface or offshore facies are not observed in outcrop. Figure 3-25 shows a schematic 3-D block diagram for the Falher C in outcrop. Dip orientation is shown along the long axis of the block diagram and strike orientation is shown along the short axis. The C1 parasequence overlies and incises into the Falher D coastal plain, and dips towards the north-northeast. There may be a coal layer presented at the top of the C1 parasequence to the south (FC-23 - Figure 3-7; FC-02 - Figure 3-14). The TSEfMFS at the base of the C1 is marked in blue. The C2 parasequence is shown incising into the C1 parasequence. The basal RSME is shown in red. Each of the clinoforrning black lines represent a process diastem. These process diastems dip in a north-northeasterly direction. as observed from outcrop and from GPR. The GPR data also show uneven surfaces along strike. reflected in Figure 3-25 along the short axis. The changing strandplain orientations are also shown in Figure 3-25. Towards the north, the C2 parasequence incises more deeply into underlying strata. Incision is greatest in the outcrop where the Falher D shoreface is absent, and a thicker C2 is deposited as a result of an increase in accommodation space due to differential compaction of the underlying Falher D and Falher F CPFA's. North of the outcrop area, the C2 thins and grades into distal marine sediments and the C2 overlies the CO parasequence, observed in the subsurface of northeastern British Columbia. South
Figure 3-25 Schematic diagram showing the geometry and stacking pattern of the 4 TSWMFS surface at the base of the C1 parasequence is marked in blue. are marked in different colours for the C2 parasequence. Which each st parasequence incises the greatest where the underlying Falher D shorefa(
North
-. ~ . -~
attern of the C1 and C2 parasequences and the related facies associations. The erosive arked in blue. The C2 has a RSE at the base marked in red. Different shoreline orientations Nhich each shift in shoreline orientation, there is greater incision and downlapping. The C2 her D shoreface is absent.
4.0 SUBSURFACE STRATIGRAPHIC FRAMEWORK
4.1 SUBSURFACESTRATIGRAPHY Well logs, from the subsurface of British Columbia, were examined from 40 conventional subsurface wells. Falher C core was examined for 8 of these wells (Figure 4-1 ). With data from these wells, 4 cross-sections were constructed (Figures 4-1 to 4-6). These cross-sections were constructed to identify the Falher C interval and to attempt to correlate the regional trend of the Falher C shoreface from the outcrop belt into the subsurface. On each of the cross- sections, a number of facies were interpreted from log character. The facies marked include coastal plain, foreshorelupper shoreface, lower shoreface/offshore, and channel. Surfaces were then picked based on the breaks between the inferred environments of deposition. Surfaces with a sequence stratigraphic significance were then identified and labeled on the diagram. In the subsurface, there is no ideal datum, as very few surfaces can be considered horizontally deposited and synchronicity is questionable along most surfaces, for any great distance. The datum chosen for the cross-sections was the TSWMFS (at the base of the C1) towards the south and the RSE at the base of the C2 to the north, which closely approximates the MFS. This surface was easy to pick based on the interpreted lithologies and reflected the stratigraphic relationships observed in the Falher C. This datum changes where C1 becomes absent. Surfaces are interpreted on well logs, for both exploratory boreholes and wells, from correlated core descriptions. Descriptions of the core were compared and calibrated to gamma ray and sonic well log signatures. These calibrated log responses were then used to make subsurface well log correlations. Gamma- sonic suites of logs were used for correlation. Gamma ray logs were used because, when calibrated with core, they may be used to interpret lithology. The gamma ray tool measures natural radioactivity from gamma rays emitted by radioactive elements in a formation (Schlumberger,
121 1989). These are then calibrated to American Petroleum Institute (API) units. Abundant in shales, potassium, with an atomic weight of 40 (K~'), is the most common radioactive element found in the earth. Other radioactive elements that may be measured are uranium and thorium. Shale content is reflected on the gamma ray log by having a higher API than formations lacking shale. In the Falher, shales have an avsrage of 120 API, whereas sandstones average 45 API. Sonic logs measure the travel time of a sound wave through a medium. The sonic tool measures interval transit time, measured in microseconds per foot (vs/ft), which is the time required for a sound wave to travel 1ft wlhin the formation (Schlumberger, 1989). Travel time varies for different lithotogies. Coals have a gamma ray response averaging about 50 API and a sonic travel time of about 400 pslft. Other lithologies in the Falher C average about 200 vs/ft. Two key surfaces were identified on the regional cross-sections. At the base of the cross-sections is a TSE/MFS surface. This surface is a diachronous surface that will be discussed later. The second surface is an RSE that closely parallels an MFS. This is the surface chosen as the datum on the cross-sections where identifiable. The key surfaces separate two sequence stratigraphic "packages". The oldest package (CO) occurs towards the north. It contains a lowstand wedge and a prograding shoreface. The basal surface is a TSEIMFS and to the north, it is a sequence boundary (SB), separating the Falher C from the underlying Falher D. The upper surface is an MFS or an RSE where the MFS is eroded away. The second "packagen contains the C1 and C2 parasequences identified from outcrop. This is a regressive deposit following maximum transgression and deposited during a fall in sea level. The basal surface is a TSEIMFS (where the C1 exists) and an RSE (where the C2 exists). The break between the C1 and C2 is shown on the regional cross-sections, where identifiable. 4.2 REGIONALCROSS-SECTIONS Four cross-sections (R 144; Figures 4-3 to 4-6) show the stratigraphic relations of the Falher C in the subsurface of British Columbia. Stratal surfaces were correlated based on well log signatures and their calibration to described core. The following four facies were identified from log signatures and patterns were used to identify them on the cross-sections: coastal plain facies, shoreface, offshore and channel (Figure 4-2). Coastal plain facies were identified as having a variable gamma-log signature and a 'spiky" sonic signature. Extremely low sonic velocity inflections in the sonic log infer the presence of coal. Shoreface consists of sandstone or conglomerate and it is identified as having a low, blocky gamma signature and a blocky" sonic log. No attempt was made at discerning sandstone from conglomerate in the subsurface conventional wells, because the differences between these two lithologies are not discernible on logs. The offshore and offshore-transition facies have a moderate to high gamma value and a blocky sonic signature. The channel facies have low gamma, with increasing values upward and a blocky to variable sonic pattern. The interpreted channels often have a sharp change in log signature at the base and are laterally discontinuous with proximal wells. The Falher C interval was identified by use of scout tickets, regional marker horizons and comparison of well logs. The thick 4'"oal directly underlies the Falher D. By identifying and correlating the 4" Coal, the Falher D could be identified and thus the Falher C. These cross-sections were constructed to identify the trend of the Falher C shoreface from outcrop on Bullmoose Mountain and C4ouat Spieker to the subsurface of British Columbia. They were also constructed to identify significant differences in the character of the Falher C in the subsurface compared to the outcrop. The stratigraphic framework of the Falher C was also examined in light of existing models from previous work (i.e. Casas, 1996). &LJ-&La :ft*f*S .L"LL&+ L~,",",",",~ Coastal Plain Facies - variable gamma and ..L"~~.LJ .&+.L+++AC&LJ.4 U~piky"sonic log
Shoreface sandstone and conglomerate - low gamma value often decreasing upward; blocky sonic log
------Offshore to offshore transition -,- - -,sandstone and conglomerate - moderate-high gamma value; blocky sonic log
.*. ...a . --.. . - . - . Channel Facies - low gamma, often increasing upward; laterally discontinuous with proximal wells, sharp change in log signature at base of facies
I Cored interval with described core (see Appendix)
Figure 4-2 - Legend for cross sections R1 to R4 (Figures 4-3 to 4-6) 4.2.1 REGIONALCROSS-SECTION R1 Regional cross-section R1 (Figure 4-3) is oriented south to north, over 50.5 km, in NTS blocks 93-1-16 and 93-P-1. Core from R1 was described for wells b-53-N93-1-16 and a-68-A.193-1-16 (Appendix). Facies and surfaces were identified and correlated. The datum chosen is a regressive surface erosion (RSE) within the Falher C. This datum closely parallels the MFS that it erodes through, and is identified as offshore facies overlying shoreface facies. This datum was chosen because it reflects the stratigraphic relationships within the Father C and it is easily identified on logs. This RSE also serves to separate an older, northerly parasequence (CO) from the younger, southerly parasequence (C2) observed in outcrop. This surface has a component of erosion due to incision of the shoreface facies within the younger parasequence. The lower parasequence (CO) occurs towards the northerly part of the section in NTS 93-P-1. A unit at the base of the Falher C is identified by a lower gamma response, interpreted to be sandstone or conglomerate. This basal unit is interpreted to be a wedge of sediment, likely deposited as sediment-bypass during a lowstand (LSW) and possibly subsequently reworked during transgression. Overlying the basal LSW unit is a marine shoreface facies association. To the north, the marine shoreface succession is composed of offshore facies, grading into coarser-grained shoreface facies to the south. The lower parasequence (GO) thins in NTS 93-1-16, and is observed in well a-68- A/93-1-16 as a basal package of sediment 1m thick. The lower bounding surface is a transgressive erosional surface marking a marine flooding event. The channel in well b-53-A&-1-16 may be time-equivalent to the CO or the C1 parasequence. It is difficult to tell, because it is the only well in proximity with a channel. In core, this channel consists entirely of open-framework, clast- supported conglomerate (see appendix). If this conglomerate was likely initially deposited within the shoreface of the CO parasequence, it may have also been subsequently re-worked into the C1 and C2 parasequences and may not be present in vast quantities in the CO parasequence. This would suggest that CO Figure 4-
Figure 4-3 Regional Cross Section R1 - Swth to north cross section in NTS grids 93-1-16 and 93- RSWSB between the CO and the Falher 8. south of that the datum is the RSE betwaer
GR M .-* Sonic
16 and 93-P-1. The datum in cross-section is bariable and chosen to approximate a horizontal plane: to the nortl iE between the C1 and C2 parasequences and to the south the datum is the TSElMFS between the CO and C1 p
1 93-P-1 Sonic
FS between the CO and C1 p&sequence.
126 channels may have sourced the conglomerate observed in the C2 shoreface. If it was deposited with the C1 parasequence, then the conglomerate is preserved in the channel valley. From an exploration standpoint, this conglomerate may be deposited at some distance away from these channels. If it is time-equivalent to the C1 sequence, then it suggests that there is a channel mouth present in proximity to this well. Because the channel is conglomeratic, there may be reservoir conglomerate in proximity to the channel mouth. Since the nearby wells are composed dominantly of sandstone, and not of conglomerate (Appendix), the channel is likely time-equivalent to the CO parasequence. The C1 parasequence is the most southerly shoreface, and the same as observed in outcrop (see R4; Figure 4-6), marking the maximum transgression during Falher time. The C1 parasequence is a highstand shoreface in outcrop. In the subsurface, the basal surface marks the maximum marine transgression of the Falher. The C2 shoreface is an incised shoreface prograding to the north. The C2 shoreface wedges out towards the south part of NTS 93-P-1, likely as a result of rapid marine regression, and is capped by coal and carbonaceous mudstones, deposited following the relatively rapid marine regression over the Falher deposits.
4.2.2 REGIONALCROSS-SECTION R2 Regional cross-section R2 (Figure 4-4) is oriented south to north in NTS grids 93-1-1 5 and 93-P-2 (Figure 4-1). To the south, the wells are located in the Grizzly gas field. Core from R1 was described for wells b-53-Af93-1-16 and a- 68-A193-1-16 (Appendix). The datum chosen is the regressive surface of erosion (RSE) to the north and the TSWMFS to the south. A similar stratigraphic relationship is observed in cross-section R2 as in R1. Towards the south, the C1lC2 parasequence is observed. This parasequence thins and eventually wedges out to the north (basinward). Also to the north, the facies change from a marine sandstonelconglomerate to marine mudstone is interpreted from the gamma-log signatures. A coarse sand unit is observed underlying the C2 marine mudstone in wells c-27-1193-1-15 to c-94-
GR M Sonic
Figure 44 Regional Cross Section 2
6.2 krn
Section 2 (R2) - South to north cmss section tnrough NTS grids 93-1-15 and 93-P-2 -
128 B/93-P-2. This coarse unit is interpreted to be a transgressive lag. formed during transgression and deposited prior to the C1 sandy shoreface. It is 1-3m thick and occurs in about a 25km wide (north-south) band. North of well c-94-B/93-P-2, a shoreface trend is observed below the MFS surface underlying the C2 marine mudstone. This shoreface is equivalent to the CO parasequence from cross-section R1, and is interpreted to be a prograding shoreface facies association (PSFA). The CO is capped in cross-section R2 by a carbonaceous mudstone. A core through well c-80-W93-P-2 (Appendix) shows the coarsening upward shoreface succession. Macaronichnus isp. is observed towards the upper part of the shoreface succession in this well. Marine mudstone caps the carbonaceous mudstone. A coarse wedge of sediment is observed towards the base of the CO parasequence. This is interpreted as a lowstand wedge/transgressive lag, formed during low relative sea-level and subsequent rise of sea-level.
4.2.3 REGIONALCROSS-SECTION R3 Regional cross-section R3 (Figure 4-5) is a west-east cross-section through NTS grids 93-P-3 to 93-P-1 (Figure 4-1 ). This cross-section extends roughly 85km, from the Falher C outcrop belt east to the Alberta-B.C. border. Core, in two wells along this cross-section, has been described. Well c-40-F/93- P-2 (Appendix) has a cored interval of two stacked channel FA'S. Welt a-41- H/93-P-2 (Appendix) is cored through part of the Falher C and the Falher D. The Falher C interval is composed largely of marine mudstone. The datum for cross- section R3 is the same surface used on the other regional cross-sections. R3 runs roughly parallel to the axis of the shoreface trend observed in the CO parasequence. The basal surface of the CO is an MFS or TSWMFS. At the base of the CO is 0 to 3m of coane sediment, reflected by a lower gamma value. This basal coarse sediment is interpreted to be a low-stand wedge/transgressive lag. It likely formed during low relative sea level and during the initial rise in sea level. This coane package of sediment is not present along the entire length of the cross-section, which suggests a "wedge" or "fan" that is laterally 11.5 krn
Datum: RSE in Fafher C
I I Figure 4-5 Regional cross-s
3.4 km a414 1 93P-2 6.2 lan d-33-E 1.93~-t 2.0 km
GR M
Sonic
-....
...
Regional cross-section R3 oriented west to east from NTS grids 93-P-3 to 93-P-t .
130 discontinuous. Overlying this coarse unit are marine mudstones inferred by a higher gamma value and lack of a ''spiky'' sonic log signature. The coarse sediment at the base of the CO is also observed in core in well a-41-Hl93-P-2. This grades vertically into nearshore marine sandstone. This pattern can be traced east to west from the A1bertdB.C. border to well c-40-Fl93-P-2, at which point there is no evidence of marine mudstone. In the c-40-Fl93-P-2 well, there are two stacked channel facies associations observable in core (Appendix). The lower channel is overlain by carbonaceous mudstone, and is interpreted to be the top of the CO parasequence. The upper channel is interpreted to be part of the C1/C2 parasequence. The lower parasequence is absent to the west in this cross-section. The upper parasequence (C1/C2) is not oriented west-east along the same trend as the CO parasequence. To the west and in the outcrop belt, the C1lC2 is composed completely of coastal plain sediment. In well C-40-Fl93-P-2, the C2 is composed of a channel overlain by coastal plain facies. East of this channel, marine sediment is present, and the C2 from coarse marine sediment (low gamma value) to marine mudstone between wells d-46-Gl93-P-2 and b-48- Hl93-P-2. The marine sediment "wedges outwtowards the east and is absent at well c-40-Fl93-P-1.
4.2.4 REGIONALCROSS-SECTION R4 Regional Cross-section R4 (Figure 4-6) is oriented northwest to southeast along the maximum transgressive limit of the Falher C. To the northwest, wells c-93-U93-P-3 and a-86-W93-P-3 are located in closest proximity and to the east of the outcrop. Cross-section R4 extends to the southeast to the Alberta-B.C. border over a distance of 118km. Wells a-68-Af93-1-16 and b-53-AI93-1-16 are wells with described core in the Falher C in this cross-section. The datum chosen for this cross-section is the base of the C1/C2. Because this section parallels the maximum transgressive limit, the datum is a TSWMFS marking the maximum transgression over the Falher D, except where this surface is removed by the RSE at the base of the C2. The RSE bounding the C1/C2 parasequences
Figure 4-6 Regional Cm
Figure 4-6 Regional Cross Sedon ~4- northwest to southeast aoss sectbt~akng the southem limit of I limit of marine transgression in the Falher C.
Sonic 4
--.
132 is difficult to identify because the C2 and C1 are lithologically similar (i.e. sandstone on sandstone or conglomerate on sandstone) and therefore difficult to distinguish on gamma logs. The CO parasequence is only present as a marine deposit towards the northwest in the plane of the cross-section where the CO paleostrandline trend intersects the C1/C2 paleostrandline trend. At this point, the CO facies have gamma values suggestive of sandstone. The basal bounding surface of the CO parasequence is a TSWMFS, overlying the Falher D. The C1/C2 parasequence overlies the CO parasequence in the northwest and immediately overlies Falher D along the remainder of the section. Marine sandstone/conglomerate facies of the C1lC2 vary between 3 and 25m in thickness along cross-section R4. The C2 parasequence is typically 10-15m thick. The C2 parasequence is present in most wells in cross-section R4, and overlies the C1 where present, or the Falher D where the C1 is absent. This stratigraphic relationship is observed in outcrop where the C1 is incised completely by the C2 parasequence (cross-section A; Figure 3-9). The C1 parasequence occurs closest to the maximum transgressive limit. In outcrop the C1 is composed of marine shoreface sandstone, interpreted to be a highstand shoreface. It is bounded above by an RSE, at the base of the C2 parasequence. From observations in the outcrop, the highest quality reservoir conglomerate occurs in the C2 parasequence along the maximum transgressive limit of the C1. The conglomerate channel FA in well b-53-A.193-1-16 (see Appendix) is discussed with cross-section R1 (Figure 4-3). Channel incision into underlying strata makes it difficult to determine whether it is time equivalent to the CO or C1 parasequence. Also complicating correlation of the channel FA in a CPFA is its composition of conglomerate in contrast to the shoreface in the C1/C2 parasequence which is sandstone (see core descriptions in Appendix). 4.3 STRATIGRAPHICARCHITECTURE The regional subsurface cross-sections display a subtly more complex relationship than observed in outcrop. There are two shoreface trends traceable in the subsurface of the study area in British Columbia (Figure 4-7). The northern trend is the CO parasequence. The CO parasequence is not observed in outcrop, as it occurs about 5-10 km northeast of the outcrop. The southern shoreline trend is correlatable to the outcrop, and consists of the C1 and C2 parasequences. This trend marks the maximum transgressive limit of the Falher C. The C1 parasequence is the highstand shoreface, which is followed by incision of the C2 parasequence. The C2 parasequence is a regressive shoreface deposited during a fall in relative sea level. In outcrop, the C2 parasequence is composed of a prograding conglomeratic shoreface facies association, and is the principal reservoir quality rock for hydrocarbon exploration. The C1 parasequence in outcrop is composed of sandstone. In the subsurface, the C1 appears, based on described core and well log signatures, to also be composed of sandstone. The C2, based on core and well log signatures, appears to be conglomerate in some locations and sandstone in others. This is likely a function of proximity to channels, which provide joint sources of the conglomerate. The CO parasequence appears to be composed of sandstone only where observed in the subsurface.
4.4 DEPGSITIONALHISTORY Figures 4-8 and 4-9 show the interpreted depositional history for the Falher C in northeastern British Columbia. The Falher C was deposited during a rise and subsequent fall in sea level. It is comprised of two parasequences. The first parasequence was deposited during a hiatus in the rise of sea level. The second parasequence followed the rise in sea level and was deposited during the subsequent relative fall in sea level. During the first depositional stage (Stage 1; Figure 4-8) a wedge of coarse sediment was deposited towards the nolthwest. It formed either during low Figure 4-7 Mapped trends of the CO shoreface parasequence and the C112 shoreface parasequences. Reservoir quality conglomerate is located towards the maximum transgressive limit of the C112 parasequence.
137 relative sea level as a low stand wedge, or during the rise in relative sea level as a transgressive lag. In the first case, sediments were deposited basinward as sediment bypass during a low sea level. This is typical of a lowstand wedge in a shelf-break environment, where sediment bypasses the shelf and is deposited along a slope. Because the Falher Member was deposited in an interior seaway, there is no shelf-break and thus the term lowstand wedge is inappropriate. This doesn't mean it couldn't have been deposited during a low relative sea level. Rather, if it is a low-relative sea level deposit, it is simply the deposition of sediment in a basinward location. However, the basal surface of the Falher C in the CO parasequence appears erosional and sharp in core, and a similar basal surface is observed in outcrop. In outcrop, this surface is a TSWMFS, which formed during a rise in sea level, where marine sediments transgressed over (typically) non-marine sediments. This surface likely was not highly erosional, but probably transported sediment basinward, as sea level rose. This sediment accumulated basinward as a coarse-sediment wedge. As transgression would have occurred along the entire shoreline, the wedge produced would be thin (less than 3 meters thick) and traceable laterally over long distances. The sediment wedge is observed in the regional cross-sections. The coarse sediment wedge occurs as a 15-25 km wide body (R1 and R2; Figures 4-3 and 4-4) traceable over 10's of km's (R3; Figure 4-5). The next stage in the evolution of the Falher C stratal architecture was the deposition of a prograding shoreface (Stage 2; Figure 4-8). This shoreface was a progradational shoreface FA, because it is observed as coarsening-upwards in core (Appendix) and cleaning-up in well logs. If it were a transgressive shoreface, it should consist of a normally graded package of sediment, as distal marine sediment transgresses over proximal marine sediment. This is not the case. This shoreface parasequence is 15-30km wide (R1 and R2; Figures 4-3 and 4-4) and is traceable roughly west-east in NTS grids 93-PI to 93-P-3 (R3; Figure 4-5). 138 Following Stage 2 was another rise in relative sea level (Stage 3; Figure 4- 8). A TSWMFS surface formed as the result of marine transgression with eroded sediment forming a transgressive lag. This transgressive lag is observable in outcrop (FC 19 and 20; Figure 3-8)and in subsurface well logs (R1 and R2; Figures 4-3 and 4-4). This lag is 0 to 0.8 m thick in the outcrop and 1-2 m thick in the subsurface. The transgressive lag (Facies 6A) was recognized in outcrop as having an erosional base and a lithology matching the underlying strata. The TSE/MFS is a diachronous surface. Basinward, it is an MFS, whereas landward it is a TSWMFS (Figure 4-8). The transgressive lag basinward overlies the MFS, but is time equivalent to the TSWMFS landward. This transgressive lag was deposited after the CO parasequence, but prior to the C1 sandy shoreface. It is included in the C1/C2 parasequence. Stage 4 marked the maximum marine transgression for the Falher C and subsequent deposition of the C1 highstand sandy shoreface (Figure 4-9). This sandy, highstand shoreface is observed in outcrop (Cross-sections A and D; Figures 3-7 and 3-14) and in the subsurface (b-53-A/93-1-16; Appendix), and is preserved in the outcrop as a 0.2-2.0 km wide, linear sandstone body between the coastal plain facies and the C2 conglomeratic facies. The C2 parasequence is also observed overlying and basinward the C1 parasequence in the subsurface. The C1 parasequence is observed only as a sandy shoreface, with some conglomeratic beds, as opposed to a conglomeratic shoreface. This means that it is less likely to be of reservoir-quality. Stage 5 occurred during a falling relative sea level (Figure 4-9), and represented an episode of shoreline incision. The RSE is a product of base-level lowering and shoreline translation basinward. Internal erosional surfaces formed as a result of severe storms, which eroded underlying shoreface facies. Subsequent deposition occurred slightly stratigraphically lower and slightly basinward. As sea level fell, so did the level of incision along this basal surface. Incision was the greatest where the shoreface is the steepest. Basinward, where marine mudstone was deposited, there was very little incision. Thus, basinward, 139 the RSE surface is roughly equivalent to the MFS formed during marine flooding. The RSE surface is diachronous, incising deeper with each successive episode of regressive shoreface deposition. The internal erosional surfaces within the regressive shorefaces are a source diastems (SD). The SO'S represent more proximal marine sediments being deposited erosionally over more distal sediments. At the outcrop scale (10-IOOm's), the amount of erosion and the hiatus represented by those surfaces is minimal. Deposition and erosion is autogenically controlled. At the subsurface scale (0.1 - 1Okrn's) these surfaces begin to represent significant time differences. Stage 6 (Figure 4-9) finished as the coastal plain prograded over the entire marine sequence. As sea level dropped, the coastal plain facies shifted basinward. Coals commonly formed, and are traceable over 10's of km's and are typically used to identify the Falher Divisions (Cant 1984). These coals dispiay a distinctive densitykonic log response and can be traced in the regional cross- sections (Rl; Figure 4-3). 5.0 STRUCTURAL GEOLOGY
5.1 STRUCTURALSTYLE OF DEFORMATIONIN THE B.C. FOOTHILLS The Rocky Mountains are defined as having Palaeozoic or older rocks exposed at surface (JonesJ986 and McMechan, 1987). The Bullmoose- Chamberlain study area occurs along the westernmost flank of the Rocky Mountain foothills, east of the Front Ranges of the Rocky Mountains. Bullmoose Mountain and Mount Spieker are categorised as part the British Columbia Foothills, as they are defined by complex folding, "blind thrustsn and Mesozoic rock exposed at surface. Thrust faults and folding characterise the Foothills of northeastern British Columbia, with the folding often reflected by chevron folds and box-folds (Thompson, 1979). Often, the thrust faults are "blind thrusts", which are thrusts that are not exposed at surface. Rather, these thrusts are responsible for folding in the overlying strata (Thompson, 1981). Bullmoose Mountain and Mount Spieker both have a thrust fault along the respective eastern flanks of each mountain (Figure 5-1). A number of folds are also observed at surface (Figure 5-1). The location of the faults and folds are from Kilby and Wrightson (1987a and 1987b). The thrust fault at the north end of Bullmoose Mountain is exposed at surface dipping at a high angle (>85"). Fracture measurements (Figure 5-1) largely parallel the orientation of the thrust faults. The thrust fault, termed Nuisance Thrust (McMechan, 1994), splays at surface north of Bullmoose. The second, more northerly thrust fault is Bullmoose Thrust (McMechan, 1994). These are the only major faults at surface that affect the structural position of the Falher C. The displacement along the thrust is minimal. This is exemplified by the fact that the Falher C is observed at Mount Spieker at measured sections FC-01 and FC-02 west of the thrust (Figure 5-1). Exploratory borehole MS-39 east of the thrust contains the Falher C as a conglomerate overlying the C1 parasequence. The map distance between these points is 3km. Figure 5-2 compares Leckie's (1982) description of well MS-39 to exploratory borehole BP- Bullmoose Thrust
ra, Gacralcq coa4M MU roan,
=-,, Exyorslq coal n1 mtr cae 'cpgraarr are (5% eevarar) SC-. - -o=ra~rc we 16000 emator)
Fccs larbcre syrc~mt -*=, ' s -- m '- 'm 0- 025 05m 01s i
f \ \ r T 1. : i h5 1 \ \ i \ k ). 7-% - \ Figure 5-1. Location of folds and faults in the BullmooseISpieker area from k McMechan (1 994). Measurements from o
;and faults in the Bullmoosel~iekerarea from Kilby and Wrightson, (1987) and - McMechan (1994). Measurements from outcrop are also displayed.
Bullmoose Mtn. Mount Spieker BP-69a MS-39
FALHER C
GATES
TSBMFS
-.------.---..-----em-.------.----. GATES --ae-.--.----.
uccbct-tft amcn~~~~~~ OC ~Cnmrncn-, =&& VA I~>~~u%AJsz gure 5-2 Exploratory coal wells BP69a and MS-39. The description for well MS-39 is from Leckie (1982). Both wells show interbeds of conglomerate and sandstone. These are interpreted to be proximal to the maximum paleolandward limit of the C2 parasequence. 143 69a. Well BP-69a contains the C1/C2 (parasequence break) on Bullmoose Mountain (see Figure 5-3). A similar sequence is observed in well MS-39. Facies Associations in both wells are characterized by interbeds of conglomerate and sandstone, and are interpreted as C11C2 shoreface proximal to the maximum transgressive limit. Figure 5-3 shows the projected trend of the C1lC2 on Mount Spieker. The C1lC2 trend occurs just south of exploratory boreholes BP-69a and MS 39 and measured sections FC-01 and FC-02. After projecting the trend on either side of the fault, the amount of lateral separation on the thrust fault is less than 1km. Most of the shortening that occurs in the structural deformation of the B.C. Foothills occurs in the form of folds, that form in the hanging walls of underlying "blind thrusts" below the surface (Thompson, 1981). Many of the folds are expossd at surface and shown on Figure 5-1. Two versions of geological maps have been published for the study area in recent years. Kilby and Wrightson (1987a,b) published 1:50,000 scale maps showing the structural geology and mapped formations for NTS grids 93-P-3 and 93-P4. McMechan (1994) published a 1:250,000 scale map for NTS grid 93-P, showing similar structures for the Bullmoose Mountain area.
5.2 PALINSPASTICRESTORATION Initially, one of the goals of this study was to palinspastically restore the structurally displaced strata observed in the outcrop on Mount Spieker and Bullmoose Mountain. Simply stated, this means to pull back all the deformation due to folding and faulting and place the outcrop to the location it would have been at prior to uplift. To perfonn a palinspastic restoration properly, a large data set must be collected, balanced cross sections must be made (Dahlstrom ,I969), and computer-aided calculations must be made to properly "pull backnthe strata. To get an accurate picture of the structural deformation in an area, the data that must be collected and analysed include extensive regional field measurement, air photos, well logs and seismic lines. This work would have cost more time and Figure 5-3 C1/C2 trend on ~ullmwseMountain and Mount Spieker. The 1 along the thust fault is less than Ikm. TI are from Kilby and Wrightson (1 987a.b) i
n lose Mountain and Mount Spieker. The projected displacement along the thust fault is less than 1km. The location of the faults are from Kilby and Wrightson (1987a,b) and McMechan (1994).
145 money than the project was funded for to acquire the resources and precisely analyse the data. Two studies produced balanced structural cross sections that are within 10km of Bullmoose Mountain. The most recent is a balanced cross section to accompany the geological map for NTS grid 93-P (McMechan, 1994; Figure 54). This section runs southwest to northeast, perpendicular to the major faults, and occurs about 1Okm northwest of Bullmoose Mountain. This section shows very little deformation for the lower Cretaceous strata, with only five faults intersecting the lower Cretaceous and only one (Bullmoose Thrust) exposed at surface. A detachment fault occurs at the base of the Triassic and extends to about 30km northeast of Bullmoose Mountain (Figure 5-4). Lateral separation and the displacement along this fault appears minimal, with most of the shortening in this section accounted for by short, high angle, splay thrusts in Triassic strata. The other study was done by Jones (1986) in conjunction with Canadian Hunter Exploration Ltd. to examine the regional structure of the British Columbia Foothills. This study involved detailed fieldwork and the construction of several balanced cross sections though the British Columbia Foothills into the Front Ranges of the Rocky Mountains (Figures 5-5 to 5-7). These sections are used in this study because of their proximity to the outcrop and the fact they intersect the Falher C trend. There is no vertical exaggeration on these balanced cross sections. Like McMechan (1994), the cross sections show very little deformation of lower Cretaceous strata. Blind thrusts are responsible for most of the deformation in this region and most occur in Triassic or older strata. These cross sections account for most of the shortening occurring along en-echelon stacked thrust faults. These thrusts occur in Triassic and Paleozoic strata, and thus that is where the greatest amount of displacement occurs (Jones, 1986). The inferred structural style of deformation differs somewhat in these sections. McMechan (1994) shows numerous thrusts, splaying from one another, whereas Jones (1986) indicates an en echelon style of deformation in the Paleozoic strata. However, the Gates Formation does not seem to have the Sea level t 0
Figure 5
,approx. location of Bullmoose Mountain
Figure 54 Balanced cross-section from McMechan (1994). This section is oriented southwest to northei same line as section C from Jones (1986; see Figures 54;58). I
; oriented southwest to northeast, north of ~ullrnooseMountain along the I. st, north of Bullmoose Mountain along the
Figure 5-5 Location of structural cross-sections B and C from Jones (1986) and present- day trends of the CO and C112 parasequence sets. The balanced cross- sections and palinspastically restored sections are shown in Figures 5-6 and 5-7. 148 same complex structure as stratigraphically lower units like the Jurassic or Triassic formations. The difference between the restored locations for either would be less than two kilometers. McMechan (1987) and Jones (1986) both comment on the lack of triangle zones within the Foothills of British Columbia, unlike the Foothills of Alberta. Although the two balanced cross sections (Figures 5-4 and 5-7) are slightly different, deformation is minimal for Lower Cretaceous strata. Restoring these cross sections would likely result in very little difference in displacement for the Lower Cretaceous strata. Jones (1986) also performed patinspastic restorations for the balanced cross sections in his study (Figures 56 and 5-7). The two cross sections included for this study intersect the Falher C trend and are in closest proximity to the Falher C in outcrop. Structural cross section B (Figure 5-6; Jones 1986) is oriented southwest to northeast, perpendicular to the major thrust faults. The style of deformation shown in the balanced cross section depicts en-echelon stacking of faults in the Paleozoic strata. The palinspastically restored cross section was done using computer modeling. The locations of the CO and the C1/2 parasequence trends are indicated on both the balanced cross section and the palinspastically restored cross section. These were done by tracing out the locations of the parasequence trends interpreted from the regional cross sections (R1-R4). The positions of the restored locations were simply determined by using a piece of string to measure the location from the pin line on the balanced sections and then extended to the equivalent location on the palinspastically restored section. The measurement is not precise, but the error in measurement is less than 1km for every 1Okm of restored distance. Using this method, the CO parasequence set is displaced up to 0.2 * 0.02km. The C1/2 parasequence is displaced about 4.1 km. Structural cross section C (Figure 5-7) also has a balanced cross section and a palinspastically restored section. The style of deformation is similar in this cross section and in structural cross section B. The positions of the Falher C trends are also displayed on these cross sections. Because the trends overlap in Figure 5-6 S@~dud 8 from Jo~ The section is oriented southwest to tion B from Jones (1986). Balanced croasaection is above, palinspastically restored is bekw. ed southwest to northeast, southeast of Mount Spieker. (Figure 5-5)
Pin I in8
above, palinspastically restwed is below. :er. (Figure 5-5)
- WE: kr~muow an usnu rut a, mc urncm~tm~ms-scmiaIS runt~~o ~mu~ rn w w ~OOCLrttrrr rm Llaln o rllr mlmow. It w rn ~CMIUL strlrlmaz -.nu m tv?cm QI
Figure 5-7 Structural aoss-sedon C 1 The section is oriented sou
rn I~CI. C-~J e E. 8-194 OR CT r ~ng.-R.u roJrcrt8 6 a P 81W A 8 b Cur Suuu D-374
IS-section C from Jones (1986). Balanced cross+ecth is above, palnspclstically restormd is belaw. oriented southwest to northeast, north of Bullmoose Mountain (Figure 5-5). a E. %t~*8-t94 Oa cr u &tar a-19-14 Qlrv CT u O~utrc-nr raJrcno 6 a 4 Suwr~r-l0-A 8r br 0-3-4 + pin line
;ection is above, palinspestically restored is below. se Mountain (Figure 5-5).
151 this cross section, the amount of displacement of the CO parasequence is approximately the same as that of the C112 parasequence. After determining the restored position for the C trends, the displacement was calculated to be 10.9km, with an error of +I- 1.l km. The maximum amount of shortening along this cross section is 39km of Triassic strata (Jones, 1986). The restored trends are shown on Figure 5-8. Restoring the trend for the CO parasequence set shows that it has a restored orientation that is almost due east-west. The C1/C2 parasequence shows an orientation roughly east-west at the Alberta-B.C. border, but it curves at this point towards the northwest into the outcrop belt. The values calculated for crustal shortening in the Bullmoose Mountain area are reasonable, if not overestimated. McMechan (1 987) published a study describing the structural geology and palinspastic restoration of the Mount Selwyn area (NTS 93-0-1 1 to 93-0-14)northwest of Bullmoose Mountain. Liu et a/.(1996) calculated the amount of displacement in the Grand Cache area of the central Alberta Foothills to the southeast of Bullmoose Mountain. In the central Alberta Foothills, the dominant style of structural deforrnation occurs in triangle zones. Simply stated, triangle zones are the style of deforrnation whereby displacement occurs vertically as a result of a series of opposite-facing faults forming triangular shapes. The maximum amount of displacement caused by shortening in the Cretaceous strata in the central Alberta Foothills is 2.7km (Liu et a/., 1996). This is significantly smaller than the amount calculated for the Bullmoose Mountain area. The style of deforrnation is significantly different for northeastern British Columbia. Most of the displacement occurs in blind thrusts and en-echelon stacking in northeastern British Columbia (Thompson, 1981; Jones. 1986; McMechan, 1987). McMechan (1 987) calculated the amount of shortening in Upper Triassic to Upper Cretaceous strata in the Foothills proximal to Mount Selwyn at 14km maximum. This value is closer to the value of 10.9km calculated for Bullmoose Mountain. Because the structural styles of deforrnation for Bullmoose Mountain are more closely related to the Mount Selwyn area than
I53 for the central Alberta Foothills, the value of 10.9km is reasonable. The balanced cross section by McMechan (1994; Figure 5-3)shows some oppositely verging thrust faults, similar to those in triangle zones. Most of the shortening in the cross section by McMechan (1994) occurs vertically along minor splay thrusts (Figure 5-3). This suggests, by comparison to the study by Liu et a/. (1996). that the values for shortening calculated from the study by Jones (1986) may be overestimated. Whether the values for displacement are overestimated or not, there remains a curvature to the trend of the Falher C. The CO parasequence set maintains an east-west orientation. The C1/2 parasequence set curves from an east-west orientation to a northwest-southeast orientation towards ihe outcrop belt. This inferred paleostrandline orientation is therefore likely due to the shape of the depositional basin. From this study, it is recognized that the C112 parasequence set represents the maximum transgressive limit of the Falher C and it was deposited prior to and during a significant drop in relative sea level. Sediments were derived from as far as 25 to 150 km to the southwest, from a source terrain believed to be the Ominica Crystalline Belt (Leckie, 1986b). Uplift was occurring during this time in the Ominica Belt (Stott, 1984; Cant and Stockmal, 1989). The inferred curvature in the depositional basin, based on restoration of the Falher C paleostrandline trends, can be attributed to a high sediment input from the southwest during deposition of the tectonically influenced clastic wedge. 6.0 DISCUSSION
6.1 SEQUENCESTRATIGRAPHY AND THE REGRESSIVESYSTEMS TRACT Sequence stratigraphy was first introduced by the Exxon Research Group in 1977 as "seismic stratigraphy" (Payton, 1977). The original concept of seismic stratigraphy was based entirely on 3* order eustatic sea-level changes in basins with a shelf-slope break (Vail et a/., 1977). Since then, seismic stratigraphy, which soon became known as sequence stratigraphy, became incredibly popular among stratigraphers. With the explosion in popularity came refinements in the sequence stratigraphic model, accompanied by a plethora of terminology, much of which is contradictory including some terms which have multiple definlions. It is not necessary in this thesis to discuss all of the terminology and refinements made to sequence stratigraphy. For detailed summaries on sequence stratigraphy, one can refer to Van Wagoner et a/., 1990; Emery and Myers, 1996; Posamentier et a/.,1993; or Van Wagoner, 1995. The term "sequence" is one of the sequence stratigraphic terms that has been used variably (Carter, 1998). The original Exxon definition was based on 3rdorder eustatic changes in sea level. A 'sequencen by this definition would be "several 10's to 1000's of feet thick, ranging from several 100's to 10,000's of square miles in extent and deposited during an interval of 10' to >lo6 years" (Van Wagoner eta/.,1990). Sequences, defined on true eustatic changes in sea level, can be shown in Quaternary sediments at 5m.6" and 7thorder (Table 6-1) as a result of glacio-eustatic changes. Carter (1998) defines any sequence based on true eustatic changes in sea level as being encompassed by a global sea-level model (GSM). Because true eustatic changes are difficult to determine in ancient sedimentary sequences, most sequence stratigraphic correlations fall into the sequence stratigraphic model (SSM; Carter, 1998). This is the recognition of sequences based on surfaces formed by changes in relative sea level. Relative sea level is the sea level position relative to preserved sediments in response to
156 eustatic sea level changes, sediment supply and tectonism. The definition of a sequence boundary in this model has been a heated debate among the geo- scientific community for years. The classical Exxon model defines the sequence boundary as "an unconformity and its correlative conformity which is laterally continuous, wide spread surface covering at least an entire basin and seems to occur synchronously in many basins around the world (Van Wagoner et a/., 1990; c.f. Vail et a/., 1977; c.f. Vail and Todd, 1981; c.f. Vail et a/., 1984; c.f. Haq et al., 1988). By this definition, sequences can only occur world-wide. Galloway (1989) proposed that the sequence boundary be located along the maximum flooding surface to mark sequences between high points in sea level. Carter (1998) sites a number of examples of defining a sequence at high-order sea level changes, based on stratigraphic architecture and surfaces recognized. The SSM is defined as a single cycle of sea level change (Carter, 1998). The original Exxon model defined three systems tracts: lowstand systems tract (LST) deposited during the falling relative sea level and during low relative sea level; transgressive systems tract (TST) deposited during a rise in relative sea level; and highstand systems tract (HST) deposited during high relative sea level and the initial stages of falling sea level (Van Wagoner et a/., 1990). In recent years, a fourth systems tract (the Falling Stage Systems Tract or the Regressive Systems Tract) has been proposed by a number of authors to encompass strata deposited during relative sea level fall (Plint and Nummedal, unpublished papec Hunt and Tucker, 1992, 1995; Hart and Long, 1996; Naish and Kamp; 1997). The Exxon model did not account for a systems tract for a falling relative sea level because it was theorized that pervasive subaerial erosion occurred during this time and sediments were not deposited as separate entities. It has also been suggested that sediments deposited during a falling sea level were not easily identifiable at the resolution of seismic data (Plint and Nummedal, unpublished paper). Sedimentation that was progradational and offlapping was included in the highstand systems tract and strata deposited as a result of subaerial erosion were included in the lowstand systems tract (Plint and 157 Nummedal, unpublished paper ; Carter, 1998). It was later recognized that strata may be deposited on the upper slope and abandoned during sea level falls and these sediment bodies were termed 'stranded parasequences" (Hunt and Tucker, 1992), "shelf perched depositsn (Van Wagoner et a/., 1990) or "forced regressive deposits" (Posamentier et a/.. 1992). The placement of the sequence boundary within these 'stranded parasequencesnis dependent on whether these sediment bodies are included among the highstand systems tract or the lowstand systems tract in the Exxon model of sequence stratigraphy. For this reason, a number of authors have proposed the creation of a new systems tract to account for deposition of sediments during the fall in sea level (Plint and Nummedal, unpublished paper; Hunt and Tucker, 1992, 1995; Hart and Long, 1996; Naish and Kamp; 1997). Because the Exxon group did not originally give a definition of a systems tract to accompany falling sea level, and because there has been no official definition since, there is a plethora of semantics that relate to surfaces and sedimentary packages formed during falling sea level. Most of the proposed systems tracts identify an erosional surface, or in some cases, multiple erosional surfaces, at the base of the systems tract. This surface was termed forced regression by Plint (1991). The identification of a forced regression surface (or its equivalent) has been key to the interpretation of deposition during a relative sea level fall in many studies (Bergman and Walker, 1987; Posarnentier et al., 1990; Plint, 1991; Ainsworth, 1994; Walker and Wiseman, 1995; Hart and Long, 1996). The equivalent of a forced regression has also been called a basal surface of forced regression (BSFR; Hunt and Tucker, 1992), regressive surface of erosion (RSE; Naish and Kemp, 1997; Walker and Wiseman, 1995), and regressive surface of marine erosion (RSME; Plint and Nummedal, unpublished paper). This erosional surface forms during sea level fall, but not as a result of subaerial exposure and subsequent sea level rise, but rather as a result of high- energy wave oscillation during sea-level fall. Figure 6-1 (Plint, 1991) demonstrates the formation of this erosional surface. As sea level falls, the fair- LOWSTAN3 EROSION EXTENDS 10's OF Km SEAWARD CIf THE SHCGELlNE -- -
Yofly mudby soc flow -C__L- t-*= 1-- I- 6' ..-.A::: 2::* Sard moved only durcclg sforws SmrQtane ~rtracmsrjwed a = ? Eorq rubmarrrc I1in1'1ca9ion
' 4- 9--= - '- J - ze 9 - - - - D .- nd nrqhstorddurmQ vtse - . 1 I-" shleafim- t - --: ,/ ,- -2 -g -- - _, - - . . - .. Marme floodng sdrtace .-..-. I- z . C-- c- - t #-, -.f -: --
Figure 6-1 During highstand conditions, fair weather wavebase (FWWB) occurs above the sea floor. As sea level drops, the FWWB also drops and erodes the underlying sediment. Pebbles often occur along this surface as a result of deposition following erosion. From Plint (1991 ). 159 weather wave base (FWWB) drops. As a result, sediment that was not being reworked by waves under fair weather conditions is eroded and transported down the depositional slope. Sediments deposited within fair-weather wave base overlie this surface and form deposits, which are presewed as "stranded parasequencesw. The upper bounding surface is the surface of subaerial exposure that follows with sea-level fall (Plint and Nummedal, unpublished paper) The proposed systems tract for falling relative sea level has been termed forced regressive systems tract (FRST; Hunt and Tucker, 1995; Naish and Kemp, 1997), forced regressive wedge systems tract (FRWST; Hunt and Tucker, 1992), falling stage systems tract (FSST; Hart and Long, 1996; Plint and Nurnmedal, unpublished paper), and regressive systems tract (RST; Naish and Kemp, 1997). The FRST, FSST and RST are all variations on the same principle. The RST refers to progradational sediment packages deposited during a fall in sea level where the basal unit is gradational with underlying sediment (Naish and Kemp, 1997). This is opposed to the FRST (or FRWST), which is identified as having an erosional base and characterized by down-stepping progradational geometry (Figure 6-2; Hunt and Tucker, 1992; Naish and Kemp, 1997). The definition of a falling stage systems tract is similar. Plint and Nurnmedal (unpublished paper) propose that the FSST be defined as the package of sediment, deposited during relative sea level fall, bounded at the base by an erosional surface and bounded at the top by a subaerial surface of erosion. The FSST lies above the HST and below the LST (Figure 6-3). Plint and Nummedal also comment on the presence of "high-order" parasequences, each with an erosional basal surface, which compose the FSST (Figure 6-4). I disagree with Naish and Kemp (1997) that two separate systems tracts should be recognized for a fall in relative sea level. Systems tracts were defined to categorize packages of sediment with respect to (relative) sea level position. Separating systems tracts for falling sea level based on a "gradationaln surface as opposed to an erosional surface leads to confusion. Erosion takes place to Low
SB 1 SBZ
Key adace8 -TSE superposed on SB 1 Sequence 1 . HST shordne , . , . , . SB cormlatrvo conformtry 12 9qumeI.RSTsharslns ---- Transgmsslva sttrface 1 3 Sq-a 1 LST shorecne - - - - HSTiRST bounday RSE (4' !hc,ume2.TSTJlordna -.-.-.- . DLS .S Sequence 2. HST &Whm
'6 -8 2 - FRST shWhtW ,I Soquome 2.LST dKnrllne
Figure 6-2 Sequence stratigraphic architecture of systems tracts according to Naish and Kemp (1997). A regressive systems tract (RST) is represented by strata deposited during a falling relative sea level that has a non- erosional basal contact. The forced regressive systems tract (FRST) is deposited during a falling sea level and has an erosional basal surface. Sequence boundaries (SB) occur at the break between a RSTIFRST a and the LST. Q) 0 -a a $5 .E sg . za w^ 22m==E a* -w+ = t gk.2 LCa uo", 2 2 03zn : .G Q] .c 2s c L 8.~80 m.S cU yp~a mar 8 .C 8 m +: -gt '"3Q]cn@Ern= nu0 Q) E 8Z.z Ec-3our a*Q)S! .-cm"'0, ,L 2 g uucn-m 0 0 QZ rn m m- &&-5 cn ur u, PQ) E E e-g --EQ) a3 Sf05 - 0 0 ESsm a Em C 0 0)- Cd a*E 0 c = 0 -2 ==Jam-= g-,gE! .o+Etj z a-0 a st5:g m Q-- '=as+>- 2 Qv,z Z'gQ Q)r E228 Q)Q+ 3 3
163 some extent along most surfaces of deposition, leaving a hiatus, however slight, along bedding contacts (Ager, 1993). If there is deposition during sea level fall that shows little or no erosion (RST) and deposition during sea level fall showing significant erosion (FRST), what separates the two besides recognizing an erosional surface? It could also be possible that the rate of relative sea level fall could change, so that in the same systems tract gradational contacts could be present in one location and erosional surfaces could be present in another location. Rather than separate these deposits into two systems tracts, they should be included into one. Plint and Nummedal (unpublishedpaperj, and Hunt and Tucker (1992, 1995) do not account for the possibility of sediments. deposited during relative sea level fall, that have non-erosional bases as observed by Naish and Kemp (1997). For example, Figure 6-4 shows "regressive mudstonesn overlying non-erosional and erosional surfaces in this model. I propose that one systems tract should be named that includes both scenarios. Regressive systems tract (RST) is the best terminology for this. Parasequences, when observed at the scale of core, or outcrop, that were deposited during a fall in relative sea level, may be confused with sediments from a highstand (or even lowstand) systems tracts. An example from the Canterbury plains (Leckie, 1994) is a recent example of transgressive and regressive deposits occurring along the same coastline during a period of highstand. By calling the systems tract a FSST, one implies an eustatic change in sea level. By calling the systems tract an RST, one implies the stratigraphic nature of regressing shoreface deposits. Also, the term regressive in the RST matches the term transgressive in TST. The term "forcedn in FRST or FRWST implies that sedimentation is occurring counter to the natural cycle of sedimentation. A relative sea level curve, by definition has to have a sea-level fall, if it has a sea- level rise. This is a naturally occurring segment of the sea-level cycle. The key difference between regressive deposits in a RST versus a HST is the stacking pattern. Regressive parasequences in an RST occur adjacent to and slightly 164 stratigraphically lower than the previous parasequence. Parasequences in a HST occur offlapping one another, either horizontally, or climbing upwards. The author also disagrees with Plint and Nummedal (unpublished paper) in that the lowstand systems tract overlies the FSST (or RST) (Figure 6-3). If sea level is falling to produce sediments in the FSST, then sediments deposited during low relative sea-level (LST), should be positioned adjacent to (with the upper surface stratigraphically lower) the FSST. The diagram by Naish and Kemp (1 997) illustrates this (Figure 6-2). Plint and Nummedal (unpublished paper) indicate that the FSST is composed of several higher order parasequences, each with an erosional base, formed as a result of high-order rises and falls in sea level (Figure 64). This suggests that the FSST is a higher-order sequence unto itself. The multiple erosional bases comprise the stratigraphically lowest, regionally traceable surface (RSME). The author disagrees with the explanation by Plint and Nurnmedal (unpublished paper) that these "higher-order parasequencesware caused by rises and falls in relative sea level. In this thesis, similar observations were made in outcrop for parasequence C2 (Figures 3-7 and 3-9). Stacked facies associations (FAs) occur as offlapping packages of sediment that sit slightly stratigraphically lower than the previous FA. At the base of each of the FAs is an erosional surface. This surface is equivalent to the erosional surfaces discussed by Plint and Nummedal (unpublished paper). Sedimentological evidence (such as hummocky cross stratification and wood casts along the basal surface) indicates that these deposits are storm related. Figure 6-5 shows a conceptual model of the formation of the FAs in parasequence C2. Sea level continuously is dropping as deposition is occurring. In Figure 6-5a, deposition of FA2 begins at time 0 (to). Sea level is falling while shoreface sediments are deposited and prograding. At 11 (Figure 6-5b), a storm event erodes the shoreface. During this interval, wave base drops to storm weather wave base. Scoured sediment from the shoreface is then deposited at the toe of the shoreface in storm-initiated, geostrophic flow deposits. After the m (0 'sanu!)uo3 a3ejaJoqs jo uo!)epe~60Jdpue alunsaJ suo!)!puo3 ~aqlea~~!ej (3 .MOM 3!qdo~~soa6e se pal!sodap r pue sluaupas aDejaJoqs aql uo~jpapoJa aJe sluaupag ~oo~eas a10 01 aseq aAeM aql do~psIuaAa w~ols(g -1aAal eas an!)e(aJ 6u!llej pue suo!ypuo3 JaqleaM ~!q6uunp aaejaJoqs 3!)e~awol6uo3lo uo!lepe~ljo~dsnonu!)uo3 (y 166 storm subsides, fair weather conditions resume and progradation of the shoreline continues (Figure 6-5c). The upper surface of the shoreface sediments in FA3 occurs at sea level for tl. Relative sea level continues to fall to t2, where the cycle is repeated. Coastal plain deposits overlie the FAs and are deposited during sea level fall.
6.2 DEPOSITIONALSETTING AND MODERNANALOGUES FORTHE FALHERC Depositionally, the Falher divisions, including the Falher C, have been interpreted as strandplain or barrier island depositional systems, with preserved beach berms, along a wave to storm dominated shoreline (Smith et a/., 1984; Cant, 1984; Leckie and Walker, 1982; Casas and Walker, 1997; Rouble and Walker, 1997). Evidence from this study, observed in outcrop and in core, generally concurs with this interpretation (see Chapter 2 facies interpretations). The geometry and paleogeographic interpretation of the outcrop facies suggest shoreface sandstone and conglomerate were deposited episodically by waves and longshore currents during phases of coastal progradation (Figure 6-6). The shoreface facies occur laterally adjacent to and are overlain by carbonaceous siltstones/shales deposited in near-shore swamps, bays and lagoons (Figure 6-7; Kalkreuth and Leckie, 1989). There are many modem examples of attached barrier island and strandplain depositional systems and wave dominated barrier islands (Curray et a. 1969; McCubbin, 1981; Davis, 1994; Dingler and Clifton, 1994; FitzGerald et a/., 1994). Most of these examples are sand-dominated coastlines. Clifton et a/. (1971 ) described the depositional features in a wave-dominated, non-barred, sandy shoreface. The facies and the bedforrn geometries along bedding plane surfaces observed reflect the geometries observed in the Falher C in outcrop and from GPR data collected for this study (see Chapter 3). The processes active on wave-dominated shorefaces are inferred to be the same processes that occur along a wave-dominated strandplain or on a wave-dominated barrier island. Curray et a/. (1969) discuss the depositional history of a Holocene progradational (regressive) strandplain at Nayarit, Mexico. This serves as a Figure 6-6 Paleogeography of the Falher C in the Bullmoose Mountail leography of the Falher C in the Bullmoose MountainlMount Spieker Region
Figure 6-7 Depositional setting for coastal plain coals paleolandward of strandplain deposits in the Gates Formation. Width of the strandplain varies in proximity to channel mouths. From Kalkreuth and Leckie (1 989). 169 recent analogue for the deposition of the Falher C. The strandplain deposits from Nayarit, Mexico were deposited during Holocene, glacio-eustatic, marine transgression and then followed by progradation (regression). From observation of cored wells in the Nayarit strandplain, transgressive shoreface deposits are preserved and overlain by regressive shoreface deposits (Curray et a/., 1969). Regressive shoreface deposits comprise the rnajonty of the Nayarit strandplain. Multiple sets of shore-parallel beach ridges occur as relatively straight, linear bodies. Each beach ridge set reflects a period of shoreface/shoreline progradation (Figure 6-8). Sediment source (fluvial) and climatic changes affect the geometry and morphology of each of these paleoshorelines. Curray et a/. (1969) showed that the shoreface geometries are strongly affected by channel avulsion. Climatic changes also have an effect on the depositional geometries preserved along a strandplain, as wind and current changes affect the longshore transport of sediment. The width of the strandplain deposits along the coastline of Nayarit is a function of proximity to channel mouths (point sources of sediment) and the direction and sediment transport capaccty of longshore currents. Changes in frequency of shoreline progradation occur on the order of 500 to 1500 years (Curray et al, 1969), equivalent to >7morder cycles (Table 6- 1)- Ground Penetrating Radar (GPR) data and outcrop observations of the Falher C indicate linear, subparallel, but variable in preserved width, conglomeratic shoreface deposits. As in the recent example by Cunay et a/. (1969), the ancient sediments preserved in the Falher C appear to vary in width and geometry. Using the study by Curray et a/. (1969), the shoreface geometries in the Falher C are likely influenced by proximity to a channel mouth and by longshore currents. Evidence for longshore transport is difficult to ascertain in the outcrop. Very few, clearly defined paleocurrents were measured within the weathered, conglomeratic outcrop. Most of the paleocurrents observed occur along the basal surface of the source diastems (SD's) and are oriented to the north (Figure 3-18). A second paleocurrent orientation is noted on these rose
171 diagrams to the northwest-southeast. This may be a product of longshore current transport. However, it may also be a product of statistical long-axis alignment of clasts in a flow-perpendicular orientation.
6.3 CHANNEL~NCISION AND AVULSION A paleogeographic reconstruction (Figure 6-6) for the study area indicates the presence of Falher C channels directly south of the coeval shoreface deposits. The width of the shoreface deposits on Bullmoose Mountain is approximately 2km- The channels in the southern part of the study area do not indicate a sinuous or meandering drainage pattern. Rather, the channels are narrow, linear and deep and separated by coastal plain facies. The absence of wide channel valleys suggests channel incision and channel avulsion as opposed to channel meandering and sediment deposition at point bars. The channels in the study area are believed to have been the point source of gravel for the shoreface conglomerate. The gravels were likely sourced up to 100km away in the Ominica belt, which at the time of Falher deposition was undergoing erosion following tectonic uplift (Leckie, 1986; Cant and Stockmal, 1989). Chert pebbles are believed to have been sourced from the Paleozoic and Triassic strata up to 25km away (Leckie, 1986). In well logs, based on gamma response, these channels appear to have a sharp basal contact with coarse sandstone to conglomerate fining upward into fine sandstone and mudstone. The bulk of the fill in these channels appears to be mudstone or sandstone. This is significant because these channels were infilled with fine-grained sediment after channel abandonment during highstand and subsequent falling sea-level. Channels would have been filled with gravel during rising sea-level and highstand. As relative sea level rises, channel incision is minimal proximal to the coastline. Channels aggrade within their valleys adjacent to the coastline during sea level rise. Channel valleys compensate for a rising sea level, or during highstand, through aggradation of bedload sediment within the channels. The suspended sediment load transported to the shoreline during this time will be predominantly sand-sized grains. For this reason, the transgressive and 172 highstand shoreface sediments are sand-dominated. During relative sea-level fall, the channels begin to incise to compensate for the lowering base level. Channels incise into former bedload deposits. This sediment is "flushed" with increasing fluid velocity due to increased channel gradient with lowering relative sea level. Thus the gravel fraction. which was previously being deposited within the channels, is transported to the shoreface during the relative fall in sea level. The gravel, sand and mud transported to the shoreface are then winnowed by wave processes and transported along the shoreline by longshore currents. The channels do not laterally migrate; rather, they avulse during the fall in relative sea level. Hart and Long (1996) describe similar deposition in recent sand- dominated Canadian deltas (Figure 6-9). During highstand, progradational shoreface sediments are deposited. In this study (Hart and Long, 1996), deposition occurs immediately following deglaciation. In the case of the Falher divisions, relative sea level is influenced by tectonism to the southwest and by sediment input to the shoreline in addition to any eustatic sea level changes. With the Holocene deposits, relative sea level begins to fall as glacial rebound occurs (Hart and Long, 1996). Channels feeding the coastline begin to incise to compensate for the lowering of sea level. The channels maintain a narrow width and linear orientation. Coarsest sediment occurs proximal to the channel mouths, fining both laterally along shore and downslope of the channel 'point source (Hart and Long, 1996). Wave processes form terraces during sea level fall. These wave-cut terraces emulate the appearance of strandplain sediments. The process of deposition of the wave-cut terraces may be similar to the formation of FAs in the Falher C (Figure 6-5). Sediment eroded during the formation of the wave-cut terraces in the Holocene deltas is bypassed to the toe of the depositional slope as sediment gravity flows. Because the Falher is deposited in an intracratonic seaway, there is no shelf-slope break. Thus, in the Falher, eroded sediment is deposited at the base of the shoreface (Figure 6-5). Lowstand deposition of Holocene deltas form lowstand shoreface deposits. The - 2. Relative sea-level fall
Figure 6-9 Hart and Long (1996) observations from Holocene Canadian deltas formed as a result of relative sea level fall. During sea level fall, channel incision forms narrow, straight channels feeding sediment to the shoreline. Waves form 'Yerraces" as sea level falls. These wave-cut terraces emulate the appearance of strandplain deposits. The shoreface sediments are widest in proximity to the channel mouth. 174 equivalent deposits in the Falher would occur north of and overlie the C1/C2 parasequence and mark the onset of the Falher B deposition.
6.4.1 DATUMCHOICE The regressive, falling stage, conglomeratic shoreface model for the Falher C may apply to other Falher Members. One of the most common practices in stratal correlations is to pick a datum that is flat, horizontal and synchronous. Unfortunately, very few surfaces exist that match these criteria. One of the common surfaces used for correlations in the Falher Member is the coal that overlies the shoreface facies. This is a poor choice of a datum because, if the shoreface facies associations are downstepping from a regressive systems tract, then the surface is not flat, horizontal nor synchronous. Using this datum y:cu!d resu!? in the appearance of a highstand shoreface deposited during stillstand in relative sea level (Figure 6-1Ob). Another surface that is commonly chosen for a datum is the maximum flooding surface at the base of the Falher divisions. Both Plint and Nummedal (unpublishedpaper) and Carter et a/. (1998) discuss the MFS as a datum. Carter et at. (1998) state that the MFS is likely a flat surface, but is often picked as the downlap surface (DLS) as opposed to the MFS. The DLS and MFS are separated by condensed lower shoreface sediment and result in two orientations (Figure 6-1 1). In the Falher C, the MFS at the base of the shoreface succession is a diachronous, erosional, sloping surface. It too would make for a poor choice in a datum. The result of using this surface would suggest the possibility of stacked, climbing FA'S deposited during a highstand with increasing accommodation space (Figure 6- 1Oc). There is no ideal datum for the Falher. One solution is to use either of the common surfaces and orient the datum at a sloping angle as opposed to a horizontal surface. The other solution is to use the RSE surface if it is present and recognizable in core and well logs. In the Falher C, the RSE approximates M-' Coastal plain (coal) deposits as datum
C2 appears to be depos~ted~n static sea level dunng HST
C2 and CO may mistakenly be correlated
Figure 6-1 0 Common correlation errors for Falher divisions. A) Stratigraphic architecture observed for the Falher C from outcrop B) The same architecture using the coastal plain sediments as a datum. The C2 shoreface appears to offlap as if deposited in a stillstand HST. C) The same architecture using the MFSITSE as a datum. The C2 shoreface appears to climb stratigraphically as if deposited in a HST with a rising sea level or increasing accommodation space. A. Aggradation of clinoform toes 25 km J I
0. Current scour of clinoform toes
Figure 6-11 Datum choices for the marine flooding surface (MFS) versus the downlap surface (DLS) from Carter et a/. (1998). A) True position of the MFS. Presence of condensed sediment at the toe of the shoreface sediment creates an apparent DLS. Strata are truly climbing, but would appear to be horizontal if the apparent DLS is used. B) In regressive shoreface sediments, where the DLS is a scoured surface, the DLS may scour through the MFS. Condensed sediments have been scoured away. 177 the horizontal better than the other common surfaces, as it parallels the MFS following the CO parasequence set. If this datum choice is applied to the Falher C or the other Falher divisions, it is important to recognize the RSE. This surface will be a sharp, erosional surface with shallower water sediments directly overlying deeper water sediments. This difference may be subtle. Source diastems (SD's) may emulate the RSE, and at some point they are coeval surfaces (Figure 6-5). If multiple erosional surfaces are identifiable in core, or well log, then it is likely that the shoreface is represented as a regressive systems tract. A conglomeratic deposit or pebbly bed may occur directly overlying the erosional surface (Facies 68). This bed is a geostrophic flow deposit, formed at the toe of a shoreface as a result of storm-initiated erosion, which created the SD's. This debris flow contains wood casts incorporated from coastal plain deposits and transported basinward. Gutter casts are also identifiable at the base of the conglomeratic deposits, and form as a result of wave-related erosion during sea level fall (Plint, 1991 ; Myrow and Southard, 1996). These beds are laterally discontinuous, grading to thin granule layers basinward. The thickness of these beds varies between O.lm to 2.0m, and is a function of: a) the amount of sediment eroded and subsequently deposited, b) the amount of deposited sediment that is reworked, and c) the depth of fair-weather wave base. The RSE surface may erode into LST, TST, or HST sediments. On Bullmoose Mountain, outcrop evidence indicates that the Falher C erodes through the HSf and TST sediments of the C1 parasequence set. This may or may not occur in other Falher divisions. This would be a function of the rate of relative sea level fall and the amount of accommodation space for sediment.
6.4.2 CHANNELRESERVOIRS Shoreface conglomerates represent significant gas reservoirs in the Deep Basin (Moslow, 1998). An alternative reservoir play may occur in channel deposits. Well b-53-a/93-1-16 contains a conglomeratic channel deposit. The channel sediments presewed in this well represent coarse bedload sediment 178 deposited during the transgressive systems tract. The conglomerate may be preserved in this channel, as opposed to having been "flushed our due to channel avulsion. This type of deposit may represent additional reservoir plays in the subsurface.
Permeability is a concem in hydrocarbon exploration within the Falher Members (Moslow and Schink, 1991). Permeability barriers within the Falher C are a significant concem. Falher C reservoirs occur in small "podsn along the primary trend of the shoreface, creating small, but prolific, gas pools (Moslow, pers. comm.). There are a number of factors that could influence the geometry and size of these pools and the permeabiltty wlhin. Recognition of unimodal chert pebble conglomerate as the highest reservoir qualw lithology indicates that depositional factors play a significant role in geometry and distribution of hydrocarbon pools (Cant and Ethier, 1984). Depositionally, the conglomerate strandplain is the widest and highest quality in proximity to the channel source. Laterally along strike, the trend of the conglomerate reservoir is less wide and increasingly sandy (Curray et a/., 1969; Hart and Long, 1996). Sand and mud- filled channels also behave as a permeability barrier. These channels incise through the conglomeratic shoreface during lowstand and are later filled during the following transgression. Facies association boundaries are resolvable on GPR data. This suggests that the erosional surface of the SDs has some property change across it to register as a change in dielectric constant. Although shoreface conglomerate and sandstones are stacked upon one another along these surfaces, fine-grained sediment deposited during erosion may also drape this surface. The fine-grained sediment can also serve as a permeability barriedretardant. Several stacked FAs over the width of about a kilometer may produce a significant permeability difference across a reservoir. Finally, clay minerals and diagenetic cements may also decrease the permeability in a Falher reservoir (Cant and Ethier, 1984; Tilley and Longstaffe, 1989). 179 7.0 CONCLUSIONS The Falher C division of the Falher Member is a product of deposition by wave and storm processes along a graveliferous, wave-dominated strandplain. Sedimentological features such as hummocky cross-stratification and erosional facies association boundaries support this interpretation. Coastal plain sediment overlying the Falher C also indicates deposition was from an attached barrier or strandplain system. Two mappable shoreline trends are present in the subsurface. The northern trend is a highstand, sandy shoreface. The southern trend consists of a highstand sandy shoreface and a regressive conglomeratic shoreface. The two trends converge north of the outcrop on the Bullmoose Mountain study area. Falher C channels are linear, narrow and deeply incised channels. During transgression and highstand, these channels transported primarily sand to the shoreline. During falling relative sea level, channel incision results in the transport of gravel to the shoreline in addition to sand and mud. Gravel is transported along shore by longshore currents and waves. Strandplain deposits are widest and reservoir quality conglomerate is most prominent in proximity to channel mouths. Three parasequences comprise the Falher C, which together represent one depositional sequence of lowstand to highstand to lowstand. The CO parasequence occurs in the subsurface of British Columbia. At the base of the CO is a wedge of sediment formed during lowstand and subsequent transgression. It is composed largely of sediment eroded off of the exposed shoreface and sediment eroded during transgression. Following this, a hiatus in depositional transgression occurred, forming sandy highstand shoreface deposits. Transgression then resumed, forming the initial deposits of the C1 parasequence. At the base of the C1 is a transgressive lag, formed as a result of eroded sediments from the shoreline during marine transgression. The southerly limit of the C1 parasequence represents the maximum limit of marine transgression. A C1 sandy shoreface formed during highstand along this 180 southerly limit. The C2 parasequence is a conglomeratic shoreface of about 2-4 km width. Sequence stratigraphic analysis of the Falher C indicates that the conglomerate shoreface sediment was deposited during a falling relative sea level. Deposition during a falling relative sea level occurs in the regressive systems tract (RST; Hunt and Tucker, 1992, 1995; Walker and Wiseman, 1995; Naish and Kemp, 1997). The base of this systems tract is recognized in the Falher C as an erosional surface with significant topography. This regressive surface of erosion (RSE) is a diachronous surface, composed of the erosional basal surface of multiple stacked, down-stepping, facies associations (FAs). The source diastems (SDs) formed during stormevents as relative sea level was dropping. Conformable coastal plain deposits that mark the top of the Falher C overlie the C2 parasequence. Outcrop of the Falher C is located in the Foothills of northeastern British Columbia. Exposure of the Falher C occurred during the Late Cretaceous and Early Cenozoic during the Laramide orogeny (McMechan. 1987; Cant and Stockmal, 1989). Structural displacement of the Falher C is a result of shortening due to faulting and folding within the Foothills belt. Most of the shortening in the Foothills of northeastern British Columbia occurs due to folds and "blind thrustsn (Thompson, 1981). 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CORE DESCRIPTIONS
CONVENTIONAL SUBSURFACE WELLS crlrrrr Icy-
. .- - -- ~~ -- *A>. urn CUSTK: CORE LOGGING FORM Well Location - b43-A/Q3-1'16 + Jrl &d-9 Well Stillus - f- - c Hmc-t~&U CUSflC CORE LOGGING FORM Well Localion - d-sc-~/as-I-lb &A. Welt Status - FmlSW8LUnit- ~r CUSTlC CORE LOGGiNG FORM well ~-(ia, - m-66-4/13-1-1( 4- 44-a- we11status - ~aru~b.tUnil - punc m-f.e& r CUSnC CORE LOGGING FORM well ~ocation- a- 91-019 3-f'-1 M,,C .&aC &e&Lrri Well Status - Ff8tSt.t WH- FMM
CUSfK: CORE LOGGING FORM we11Location - ~-W-H/*~-P-t C-k& k3&dhad Well Status - F--unit- FLM c CLASnC CORE LOGGING FORM Well Loation - b-ug'H/43-@- fid, dd A,&- Well Status - FmlSM.lMl- feu#% Nmme - f 9' .=/& Feld - 0- - /6 /?6 CUSfK: CORE LOGGING FORM Well Loution - r-SV-P?/riS/ CLASnC CORE LOGGING FORM wen oati ion - ~-@-dk>-~-Z 6"- Ls-r [ W~IIS~~IW- w- ~..&n 8'~ N--LdG& &c/ APPENDIX 2
CORE DESCRIPTIONS
EXPLORATORY COAL BOREHOLES NATURE Of CONTACT - PurpCor*rc --- GRIIIOHI- - ti-
SE~NtAnY'IEXNFIES I STRUCTURES BURROW TRACES Ur: r ~l(lYt.C~ rr = IYL.-- -- csc = -c-m-'- mi tAr1 -....ricsl*.r STRATAL SURFACES = YrkCL.Qlyk.ba r I-sdmw.ltrak = r ---Srr(.crJ- = r ---(tlor---1 t Ydnm-lrCa STRATAL UNnS =- =- m-1- = -srrrrar- I 1"m.".hs-7nd = --
LEGEND FOR CORE DESCWPnONS CLASflC CORE LOGGING FORM Well Locatton: & p. 6~-A well Status: ~rnl~tra~Unit: p4--wrrt ~~~:f-. W Field:
OESc-
cA~S4d
-w rue - /4!dL.4 dd, Xxi'e ------k -ah-& li -4 -- -d k-4id*'= ------I ------OD------x --- e------4 -*- & - a&*-
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