- Email: [email protected]
Wandering gravel-bed rivers and high-constructive stable channel sandy fluvial systems in the Ross River area, Yukon Territory, Canada
GEOSCIENCE FRONTIERS 2(3) (2011) 277e288
available at www.sciencedirect.com
China University of Geosciences (Beijing)
GEOSCIENCE FRONTIERS journal homepage: www.elsevier.com/locate/gsf
ORIGINAL ARTICLE
Wandering gravel-bed rivers and high-constructive stable channel sandy fluvial systems in the Ross River area, Yukon Territory, Canada Darrel G.F. Long a,*, Grant W. Lowey b a
Department of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada Yukon Geological Survey, Energy, Mines and Resources, Government of Yukon, P.O. Box 2703 (K102), Whitehorse, Yukon Y1A 2C6, Canada b
Received 22 March 2011; accepted 12 May 2011 Available online 24 June 2011
KEYWORDS Anastomosing rivers; Wandering gravel-bed rivers; Fluvial architecture; Cretaceous; Yukon
Abstract Mid-Cretaceous strata within the Tintina Trench, 3 km west of the community of Ross River, contain evidence of deposition in two distinct, alternating, fluvial settings. Coal-bearing, mud-dominated strata are commonly associated with high-constructive sandy channel systems, with extensive overbank, levee and splay deposits. Channels are between 3 and 30 m wide and 0.4e7 m thick. They show repetitive development of side and in-channel bar-forms, as well as up-channel widening of the rivers by selective erosion of associated overbank and levee deposits. Levees extended for several hundred metres away from the channels. In this setting low-angle inclined stratification and epsilon cross stratification may reflect lateral migration of crevasse channels or small streams. The paucity of exposure prevents recognition of the channels as products of multiple channel anastomosed systems or single channel high-constructive systems. Gravel-dominated strata, inter-bedded with, and overlying coal-bearing units, are interpreted as deposits of wandering gravel-bed rivers, with sinuosity approaching 1.4. In most exposures they appear to be dominated by massive and thin planar-bedded granule to small pebble conglomerates, which would traditionally be interpreted as sheet-flood or longitudinal bar deposits of a high-gradient braided stream or alluvial fan. Architectural analysis of exposures in an open-pit shows that the predominance of flat bedding is an artefact of the
* Corresponding author. E-mail address: [email protected] (D.G.F. Long). 1674-9871 ª 2011, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved. Peer-review under responsibility of China University of Geosciences (Beijing). doi:10.1016/j.gsf.2011.05.018
Production and hosting by Elsevier
278
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288 geometry of the roadside exposures. In the pit the conglomerates are dominated by large scale cross stratification on a scale of 1e5.5 m. These appear to have developed as downstream and lateral accretion elements on side-bars and on in-channel bars in water depths of 2e12 m. Stacking of strata on domed 3rd order surfaces suggests development of longitudinal in-channel bar complexes similar to those observed in parts of the modern Rh^ one River system. Mudstone preserved in some of the channels reflects intervals of channel abandonment or avulsion. Minimum channel width is from 70 to 450 m. ª 2011, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.
1. Introduction Chert-bearing clastic strata, located in a fault bounded block within the Tintina Trench, about 2 km west of the community of Ross River (Fig. 1, right), were originally thought to be part of an 800e1100 m thick Paleocene sequence of conglomerate and mudstone, with minor sandstone and coal (Kindle, 1946; Wheeler et al., 1960; Tempelman-Kluit, 1977; Hughes and Long, 1980; Long, 1981; Long et al., 1990). While miospores in this block were found to be very poorly preserved due to thermal degradation, a Paleocene (Tertiary) age was assumed because of the similarity of this strata to clastics in a second block at Lapie River, 7 km west of the Ross River town site where Hopkins (1979) recovered a better preserved assemblage of palynomorphs. These included Alnus, which was taken as suggestive of an Early Eocene or late Middle Eocene age. A stratigraphic gap of about 200 m was estimated between the two sections based on vitrinite reflectance gradients (Hughes and Long, 1980). The subsequent discovery of multiple dinosaur tracks in the Ross River block by Gangloff et al. (2000) indicated that the original age assignment was in error. Paylnological investigation of new samples from this section indicates a Mid Cretaceous age, within the range of middle Albian to possibly Cenomanian (Sweet, 1999; Long et al., 2000), consistent with the subsequent interpretation of the six types of ichnogenera (footprints) identified by Gangloff et al. (2004). In the Yukon, there are numerous terrestrial deposits of Upper Jurassic, Cretaceous and Paleogene age that contain conglomerate and sandstone with abundant chert and chert-like clast (siliceous
mudstones, mylonites). In these basins (Fig. 1, left) conglomeratic units have typically been interpreted as products of deposition from braided streams or alluvial fans (Long, 1986). The presence of distinct lateral accretion sets and large scale cross stratification, revealed by strip mining at Ross River indicates that these models are not viable for the strata at Ross River (Long et al., 2000).
2. Geological setting The Ross River area (Fig. 1) is underlain by rocks of the YukonTanana terrane, an assemblage of polydeformed metamorphic rocks of Palaeozoic age (Mortensen, 1990, 1992, 1996; Colpron et al., 2006). According to Mortensen (1992), these consist mainly of pelitic to quartzo-feldspathic metasedimentary schist and gneiss, with minor marble and mafic to felsic metavolcanic, and metaplutonic rocks. The Yukon-Tanana was juxtaposed with other terranes (i.e., Slide Mountain) by regional scale thrust faulting in the Early Mesozoic, so that it now structurally overlies the ancient continental margin of North America (Mortensen, 1990; Colpron et al., 2006; Colpron and Nelson, 2009). The Yukon-Tanana terrane is unconformably overlain by post-accretionary, Mid- to Late-Cretaceous sedimentary and volcanic rocks (Mortensen, 1996). Both the preand post-accretionary rocks are offset by at least 450 km of dextral movement along the Tintina Fault zone, the displacement of which is thought to have begun in the Late Cretaceous and continued through the Early Paleogene (Roddick, 1967; Long, 1981; Pigage, 1990; Gabrielse et al., 2006). The exact position of the main
Figure 1 Location of the Ross River block (right e medium grey shading) and (left) its relation to other Mesozoic and Cenozoic basins containing chert-bearing conglomerates.
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
279
strand of the Tintina Fault in the area is uncertain. Tempelman-Kluit (1977) placed it about 2 km south-west of the area shown in Fig. 2, while magnetotelluric studies by Ledo et al. (2000) indicate that the main crustal discontinuity may be beneath the modern Pelly River. Ledo et al. (2000) also recognized a second crustal discontinuity further to the west, which appears to coincide with the St Cyr fault. All of these faults could be linked at depth, as Creaser and Spence (2005) and Snyder et al. (2005) indicate that the Tintina fault is a crustal penetrative feature, with brittle faulting on multiple strands in the upper crust over a zone that is w30 km wide. Tempelman-Kluit (1977) provides the most complete coverage of the bedrock geology in the Ross River area. The map by Wheeler et al. (1960) is dated, but provides useful descriptive notes. Hughes and Long (1980) and Long et al. (1990) outline the geology and coal resource potential of the sedimentary rocks in the Ross River area, and a detailed map (1:2000 scale) of the area mined is included in the drilling report by Pigage (1987). The surficial geology is described by Plouffe and Jackson (1995), DukRodkin (1999) and Bond (2001).
3. New observations Strata in the Ross River block include at least 427 m of mudstone, conglomerate and sandstone, with minor coal, best exposed in sections dipping 20e30 to the southeast, adjacent to the Robert Campbell Highway (Figs. 1 and 2). Vertical and lateral relations between facies were examined along the roadside sections, and in the small open-pit coal-mine immediately north of the highway (Fig. 1). The geometry of sand and gravel units were investigated using the technique of architectural analysis, as outlined by Allen (1983), Bridge and Diemer (1983), Miall (1988, 1996) and Bridge (1993). This method is based on the concept that strata can be divided into genetically related packets, which in turn can be related to episodes of geographically and temporally limited depositional processes (Miall, 1978, 1996). See below for further details.
3.1. Mudstones Mudrocks dominate the lower 200 m of the section (Fig. 2): they are predominantly dark grey to dark greenish grey claystones with minor siltstone. Most appear massive, with a pseudo-brecciated appearance, or exhibit faint horizontal stratification. Traces of plant roots are rare below the 200 m level and common between the 200 and 310 m levels (Fig. 2). Black, organic rich mudrocks are developed locally in the lower 200 m of the section, but are more common in association with coals in the 200e310 m interval.
3.2. Coal Coal forms a small but significant part of the sequence. Five seams of bituminous coal were identified in the area prior to mining
Figure 2 Litho-stratigraphy of the Ross River block, based on exposures adjacent to the Robert Campbell Highway, at Whiskey Lake. A Z Elevation above base of section in metres. B Z contacts: solid line Z sharp, dashed line Z transitional, dotted line Z not seen,
cross indicates no exposure. C Z grain size: CL Z claystone, z Z siltstone, vf, f, m, c, vc Z sandstone, G Z granule conglomerate, number Z grain size in cm. D Z Paleoflow vectors (north to top). E Z Sedimentary structures: 1 Z appears massive; 2 Z plane bedded; 3 Z wavy bedded; 4 Z ripple cross-laminated; 5 Z trough cross-stratified; 6 Z planar cross stratified; 7 Z mudstone intraclasts; 8 Z dispersed organic material; 9 Z coal; 10 Z traces of fossil plant roots. Section extends from 61 580 1000 N, 132 320 5600 W (base) to 61 580 0800 N, 132 290 0400 W (top).
280
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
(Hughes and Long, 1980). Open-pit mining of the recessive interval below the upper conglomerate has since exposed two coal seams, from which Nadahini Mining Corporation extracted about 50 000 tonnes of coal (Pigage, 1987; Hunt, 1994). The lower of the two seams is a dull woody coal, 1.7e1.8 m thick, which rests on a 40 cm unit of massive (pseudo-brecciated) organic rich mudstone with abundant fossil plant roots. The upper seam is a dull woody coal, 1.5e1.8 m thick, which rests on an organic rich mudstone, and is locally inter-bedded with wavy and ripple laminated fine to very fine-grained sandstones (Fig. 3A). Further near-surface coal deposits may be preserved along strike to the northeast.
3.3. Sandstones Sandstones form a minor part of the sequence. All have a speckled (salt-and-pepper) texture due to the abundance of varicoloured resistant lithic clasts. They occur as thin sets (5e50 cm) of flat laminated, wavy and ripple laminated silty fine- and very finegrained sandstones; thin to thick cosets (0.1e7 m) of wavy and ripple laminated fine- to medium-grained sandstones; and minor massive and plane laminated, poorly sorted to moderately poorly sorted medium-grained to granular very coarse-grained sandstones in sets 0.15e1.3 m thick. Ripple laminated medium- to very coarsegrained sandstones are found as thin inter-beds in conglomeratic parts of the sequence. Finer grained sandstones are locally interbedded with siltstones and organic rich mudstones, and may contain local (early) nodular siderite concretions (Fig. 3A). Large-scale bedforms include shallow scour surfaces and channels (Fig. 3A, B, C). Epsilon cross stratification is developed locally (Fig. 3D).
3.4. Conglomerates Conglomerates are conspicuous in the upper part of the sequence. They occur in stacked sequences a few metres to more than 90 m
thick (Fig. 2) and as minor components of small channels in finergrained parts of the section (Fig. 4A). They consist predominantly of thick beds (5e550 cm) of yellow-brown weathering, framework supported, moderately well sorted, small- to large-pebble conglomerate (Fig. 5) that can be classified as mature limonitic sedlithrudite (Fig. 6). Petrographically these closely match Cretaceous strata at Indian River, SW of Dawson (Lowey, 1984; Lowey and Hills, 1988; Long et al., 2000). Clasts are predominantly rounded to subrounded with a maximum observed clast size of 9 cm. Rock fragments form an average of 42% of the framework grains, of these 61% are mudstones (40% silicified and 21% carbonaceous), 13% are igneous (predominantly granitic, with minor silicified volcanics), 18% are cherts (black, grey and green), 4% are carbonates, and 5% are sandstones and siltstones. Cements form about 5% of the rock, most are limonitic, with minor carbonate cement. In the section along the Robert Campbell Highway most of the conglomerates appear to be massive or flat laminated (Fig. 4B). In the coal-pit this is seen to be an illusion as most of the strata are characterized by large scale (1e5.5 m) planar and trough cross stratification (Fig. 4C), with grouped sets occupying broad channels up to 12 m deep (Fig. 4D). An unusual scalloped erosional contact was noted at the base of one conglomeratic unit at the north end of the upper pit (Fig. 4).
4. Sedimentary architecture e methodology In order to reconstruct the architecture of the sand and gravel units it was first necessary to construct photo-mosaics of the exposed faces in the upper and lower pits. As strata in the pits dip uniformly at 23 to the SE a series of 95 overlapping photographs were taken for the 250 35 m outcrop in the upper pit, and w120 photographs of the 230 40 outcrop in the lower pit, with the axis of the camera lens oriented down dip, approximately normal to the face of the outcrop. This was achieved using a tripod and a camera
Figure 3 Fine to medium-grained sandstones and mudstones: A. Massive to wavy bedded fine to very fine-grained sandstone with siderite nodules (in upper coal-pit). B. Shallow inclined cosets of fine to very fine-grained wavy laminated sandstone of levee and splay origin (upper coal-pit). C. Local scour surfaces in fine to very fine-grained flat to wavy laminated sandstones of levee-splay origin (upper coal-pit). D. Well-developed epsilon cross stratification, marked by alternating beds of fine to very fine-grained sandstone and siltstone (below upper coal seam in upper pit).
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
281
Figure 4 Conglomeratic strata: A. Planar cross-stratified lens of small pebble conglomerate in small, 8 m wide channel in the upper coal seam, south end of upper coal-pit. B. Typical exposure of small pebble conglomerate in the upper conglomerate adjacent to the Robert Campbell Highway. C. 5.5 m thick composite planar cross stratified, small to medium pebble conglomerate. Dashed lines indicate set boundaries. D. Large scale channel (12 m) thick, with local organic rich mudstone and planar and trough cross-stratified conglomerate, upper coal-pit. E. Scalloped surface at contact between medium pebble conglomerate and silty mudstone, north end of upper pit.
with a perspective correction (architectural) lens (Wizevich, 1991). The apparatus was moved parallel to the face of the exposure, so that a minimum of 50% horizontal overlap of photographs was achieved. A scale was included in each photograph to allow later calibration. Photographs were scanned at 600 dpi and the residual effects of distortion due to outcrop shape partly removed using a perspective correction tool in the scanning program. Images were matched, trimmed and imported into a graphics program. The scale of individual photographs was corrected in the graphics program and a photo mosaic, with a preliminary overlay showing contact relations created. Duplicate copies of the photographs were used to record field observations and to allow verification of assumed contact relations. Dip directions of all accessible measured surfaces were later corrected for tectonic dip, and plotted on the mosaics, so that arrows directed above the horizontal reflect direction of slopes away from the observer and arrows below the horizontal reflect slopes towards the observer. Finally contact relations between elements were verified, classified and labelled (c.f. Miall, 1985, 1996; Bromley, 1991). Due to safety considerations, detailed dip
measurements could only be made along the northern margin of the lower pit, and the lower 3 m of the upper pit (Figs. 7, 8 and 9).
5. Depositional facies 5.1. Overbank, marsh and swamp deposits Clay-mudstones in the Ross River sequence are here interpreted as the products of deposition in overbank marsh and pond environments. They occur as blanket-like elements (FF of Miall, 1996), typically 1e15 m thick, which can be traced laterally for at least 450 m in strata below surface A (Figs. 7, 8 and 9). Well-developed plane lamination, characteristic of lake deposits was not seen. The grey colour is related to moderate dispersed organic content. The predominance of grey, rather than black mudrocks suggests marsh environments with the water table at or near the surface during part of the year. The brecciated appearance of many of the clay mudstones is due to the presence of numerous closely spaced, intersecting curved fracture surfaces. These slickensides are
282
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
Figure 5 Petrography of conglomerates from the Ross River block, with daughter triangle at top right showing varieties of quartz types (Qm Z monocrystalline; Qp Z polycrystalline; Qcp Z coarse polycrystalline: no strained quartz was seen). Daughter triangles at base indicate types of sedimentary lithic fragments present, showing that most samples are classified as sedlithrudites.
typically associated with a fluctuating water table (Try et al., 1984). In dry periods the soil (a vertisol) shrank and cracked, to swell again in wet periods. Rubbing of adjacent soil crumb and blocks during repeated wetting and drying led to the production of grooved and polished surfaces, now represented by slickensides (Fitzpatrick, 1980; Nadon, 1993). Siltstones are typically associated with wavy and ripple laminated sandstones and are interpreted as distal levee deposits (LV elements). Organic rich mudstones and coals were deposited in marsh and swamp environments, away from the main fluvial channels. Finer-grained sandstones appear to have been deposited as overbank, levee and splay deposits. Splay deposits (CS elements) typically have a wedge shaped architecture, with slopes of 1e1.5 (Fig. 3B). Individual CS elements can be traced for 5e50 m (Figs. 8 and 9), and are from a few decimetres to metres thick at the proximal end. The CS elements below surface A appear to have prograded over floodplain mud and silt. They appear to have supported dense vegetation, as indicated by rare preserved plant roots and local homogenization by rootbioturbation. Stacking of levee-splay sequences in the coal-pits (Figs. 7, 8 and 9) indicates an intimate association with stable stream channels. Local scour surfaces (Fig. 3C) may reflect scouring of levees during flood events. Low-angle inclined stratification (Fig. 3D) and epsilon cross stratification may reflect lateral migration of crevasse channels or small streams in secondary areas of the floodplain.
5.2. Stable channel systems Architectural analysis of lenticular sand bodies in the lower pit indicate that these were deposited in low-gradient, highconstructive stream systems, in which bank stability was probably maintained by dense plant growth (c.f. Smith, 1976; Cairncross et al., 1988; Nanson and Knighton, 1995; Makaske et al., 2002). The 39 m wide channel shown in Fig. 10 may have evolved from a small crevasse channel (like those in Fig. 4A), and progressively widened as flow was diverted from the original channel. The stacking of lateral accretion sets (LA elements) in point bars within the channel shown in Fig. 10 indicates that the rivers had only a limited ability to erode channel walls, and were probably never more than 2.5 m deep at times of bank-full discharge. Set boundaries within LA elements appear to dip at up to 6 into the main channel. If the mud-draped, concave-up elements in the second LA element in this fill represent 3rd order sequences produced by macroform growth during seasonal events, or 10 year floods, then the stacking pattern of 4th order surfaces suggests that the channel may have persisted for at least 400 years (c.f. Miall, 1996), with minor expansion during each 100 year flood. Although the abundance of potential levee facies below surface A suggests that the channels were part of a multi-channelled anastomosed fluvial system, that closely matches the Type 1b organoclastic anabranching river model of Nanson and Knighton (1995). The paucity of channel deposits suggests that these were largely single channel systems, which changed position by avulsion, and progressive stream capture, or that channel systems occupied far less than 6% of the alluvial floodplain.
5.3. Wandering gravel-bed rivers Figure 6 Plot of median (M) versus maximum (C) grain size for conglomeratic strata in the Ross River block. Histogram at base shows relative proportion of conglomerate types.
Thicker conglomerate sequences in the Ross River block are here interpreted as products of deposition by wandering gravel-bed
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
Figure 7
283
Left (northern) side of upper pit. For explanation see Fig. 8.
rivers (Forbes, 1983; Miall, 1996; Roberts et al., 1997; Ham, 2005; Li et al., 2008; Rice et al., 2008; Church and Rice, 2009; Hickin et al., 2009), rather than braided rivers or alluvial fans. The roadside exposures appear to be dominated by massive to flat laminated granule to small pebble conglomerates, which would traditionally be interpreted as sheet-flood or longitudinal bar deposits of a high-gradient braided stream or alluvial fan (Long, 1981). In contrast the open-pit exposures show that the predominance of flat bedding is an artefact of the geometry of the roadside exposures. Architectural analysis of exposures in the upper pit
(Figs. 7 and 8) indicates that the sequence is dominated by large scale cross stratification on a scale of 1e5.5 m. These probably formed as gravelly bedforms (GB) on side-bars and in-channel bars in water depths of 2e12 m. Multiple scour and fill of older deposits has produced distinct channel deposits, some with complex sinusoidal geometry suggestive of deposition on point or side-bars (Fig. 7D). This and the broad scatter of paleocurrents (Figs. 7, 8 and 11), is suggestive of episodic migration of the river channels over the floodplain to produce extensive sheet-like bodies, analogous to those recorded in the floodplain of the
284
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
Figure 8 Architecture of the south end of the upper pit, showing A: the unaltered photo mosaic, B: The mosaic with set boundaries plotted. C: Architectural elements and lithofacies with direction of foreset (0th order) surfaces (thin black lines) indicated by a red arrow. Orientation of 1st to 4th order surfaces (black lines) is indicated by a green pin. Orientation of 5th and 6th order surfaces (red) are indicated by large blue pins. All vector data has been adjusted so that slopes away from the observer point up, and those sloping towards the observer point down. Numbers in square boxes indicate hierarchy of surfaces. D: Grouped paleocurrent data (Roses) plotted for main architectural elements. Colours as for pins. Ø Z Vector mean in degrees; N Z number of observations; L Z vector strength; V Z variance; letters and numbers in brackets indicate the elements included, and distance along the pit face in metres. Small histogram indicates distribution of surface dips, and average dip values after correction for tectonic dip. Letters in circles represents unit boundaries used in text.
Halfway River by Hickin et al. (2009). The face exposed in the upper pit above surface A (a 6th order surface) can be divided into four major packages, separated by 5th order surfaces (B, C, D), which are interpreted as distinct channel systems (CH elements).
CH element A-B (the unit between circled letters A and B in Figs. 7, 8 and 9) is between 2 and 14 m thick, and can be traced across both the upper and lower pit, over a distance of at least 450 m (w/d > 36:1). It appears to consist of stacked sets of
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
Figure 9 contrast.
285
View of lower pit with major surfaces indicated as in Fig. 8. Boundaries in the lower unit (below surface A) are traced in white for
gravelly bedform (GB) elements, separated by 3rd order surfaces with dips typically less than 15 (Fig. 11). The preserved strata appear to represent the preserved core of a composite bar-form (gravel-flat), with a core located about 190 m from the north end of the pit (Fig. 8 right). Draping of beds away from this core mimics radar profiles of elongate in-channel, lateral channel bars
in a wandering segment of the Rh^ one River, near Aoste in France (Roberts et al., 1997). The variance of paleoflow indicators in this unit is slightly above the upper limit considered diagnostic of braided systems by Long and Young (1978). Mean flow direction is within 8 of the mean inclination direction of 2nd and 3rd order surfaces (Figs. 7, 8 and 11), indicating that accretion may have
Figure 10 High-constructive (stable) channel deposit, with stacked epsilon cross stratification. Note minor fluvial distributary channel deposit at base of upper coal seam, and splay deposits at the top of the coal seam (lower pit).
286
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
Figure 11 Vector data for 6th (A) and 5th (B, C, D) order surfaces in the upper pit is shown as back roses; 1st to 4th order surfaces are represented by medium grey roses, and 0th order surfaces (forsets) by light grey roses. Arrows represent vector mean for each set (north to top). Ø Z vector mean in degrees, N Z number of observations, L Z vector strength, V Z variance (Determined using the method of Curray, 1956). Information in brackets indicates surface or interval, and spread of data collection points relative to the scale in Figs. 7 and 8. Small histograms associated with individual roses show distribution of dip corrected inclinations in ten degree intervals and the average dip of the surfaces in degrees.
occurred preferentially at the downstream end of bars. Too few paleocurrent indicators were in any one vertical section to allow direct estimation of channel sinuosity, using the method of Miall (1976). When this method is applied to lateral, rather than vertical sets of cross beds, a sinuosity of 1.08 is suggested. Sinuosity estimates using method 2 of Ghosh (2000) give values well in excess of 2.8, which appears inconsistent with the observed geometry. By using the vector mean direction of subsets of grouped paleocurrent data (6e7 vectors per group) as a proxy for thalweg direction, it is possible to estimate the sinuosity as around 1.46, using method 1 of Ghosh (2000), and 1.24, using the method of Ferguson (1977). These results are consistent with those of Church and Rice (2009) who noted that the sinuosity of wandering reaches of the Fraser River had values between those of
braided and gravelly meandering systems. The scalloped erosional surface of the basal 6th order surface at the base of the element at the north end of the upper pit (Fig. 4E) may be analogous to corrasion furrows produced by longitudinal roll vortices under upper flow regime conditions (Allen, 1965; Massari, 1983). CH element B-C cuts 10 m into the underlying channel complex, and has a width of at least 425 m. The channel has a preserved erosional bank, with a slope of about 26 50 m from the north end of the pit. 4th order surfaces in the channel-fill between the bank and the 120 m mark dip away from the bank at between 6 and 30 , suggesting formation as an attached side-bar (LA element). A core complex, similar to those in the Rh^ one may be preserved 150e200 m from the north end of the pit, but is not as pronounced as in CH element A-B. Too few paleocurrent observations were made
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288 to determine sinuosity, but the 81 divergence of the mean paleocurrent flow from the mean slope of 1st to 3rd order surfaces between the 70 and 130 m markers, as well as the 62 divergence between 130 and 180 m, and the 41 divergence between 180 and 250 m suggests a strong lateral accretion component (Fig. 11). CH element C-D is about 8 m thick. It has an exposed length of only 80 m at the north end of the pit (Fig. 7). The 25 m wide lens of organic rich mudstone, capped with inter-bedded siltstone and minor ripple laminated very fine sandstone may represent fines that accumulated in a channel thalweg following switching of the main channel. The uppermost CH element in the upper pit (D-E) is up to 14 m thick and can be traced laterally for 350 m. As the pit sections are approximately normal to inferred stream flow, this provides a minimum channel belt width. Like the underlying CH elements, this exhibits a complex internal geometry, and includes lenses of organic rich mudstone, which may have accumulated in a partly abandoned channel thalweg, or the downstream end of a chute. The CH element is clearly erosive into elements CH C-D and B-C, with maximum bank slopes locally in excess of 60 . This and the presence of coal-spars in the gravels suggest that the overbank environment was at least partly forested, and that bank stability was significantly enhanced by plant roots (Smith, 1976). Limited paleocurrent and slope observation (Fig. 11) indicate that gravel bedforms migrated at 59 away from the maximum slope of the LA surfaces.
6. Conclusions and speculations Strata in the Ross River block appear to have been deposited within a valley system, which ran approximately parallel to the Tintina Trench during the late Early Cretaceous. Fine-grained (sand and mud-dominated) parts of the system appear to have been deposited on low-gradient floodplains characterized by high-constructive single or multi-channel systems, in part resembling modern anastomosed systems. These are inter-bedded with, and overlain by pebble-dominated intervals, which appear to have been deposited in wandering gravel-bed rivers with sinuosity intermediate between braided and meandering gravel-bed systems. The alternation of these two distinct fluvial styles may indicate changes in slope, but is more likely related to changes in drainage basin size, or sediment flux associated with Milankovich driven increases in rainfall.
Acknowledgements We thank NSERC, Lithoprobe (Snorcle) and the Government of the Yukon for providing support for this research, and Art Sweet of the Geological Survey of Canada for his work on the palynology of the mudstones. Andrew McNeil, Jeremie Caza and Sophie Fortin provided able assistance in the field. Sheila Litalian assisted with point counting. This paper is submitted in celebration of the outstanding contributions to geology of my colleague Professor Xianghua Meng on the advent of his 80th birthday.
References Allen, J.R.L., 1965. A review of the origin and characteristics of recent alluvial sediments. Sedimentology 5, 89e191. Allen, J.R.L., 1983. Studies in fluviatile sedimentation: bars, bar-complexes and sandstone sheets (low-sinuosity braided streams) in the Brownstones (L. Devonian), Welsh borders. Sedimentary Geology 33, 237e293.
287
Bond, J.D., 2001. Quaternary geology and till geochemistry of the Anvil district (parts of 105K/2, 3, 5, 6 and 7) central Yukon territory. Indian and northern affairs Canada, exploration and geological services division, Yukon region. Bulletin 11, 48 pp. Bridge, J.S., 1993. Description and interpretation of fluvial deposits: a critical perspective. Sedimentology 40, 801e810. Bridge, J.S., Diemer, J.A., 1983. Quantitative interpretation of an evolving ancient river system. Sedimentology 30, 599e623. Bromley, M.H., 1991. Variations in fluvial style as revealed by architectural elements, Kayenta formation, Mesa Creek, Colorado, USA: evidence for both ephemeral and perennial fluvial processes. In: Miall, A.D., Tyler, N. (Eds.), Three-dimensional Facies Architecture of Terrigenous Clastic Sediments and Its Implications for Hydrocarbon Discovery and Recovery. SEPM Concepts in Sedimentology and Paleontology, 3, pp. 94e102. Cairncross, B., Stainistreet, I.G., McCarthy, T.S., Ellery, K., Grobicki, T.S.A., 1988. Paleochannels (stone-rolls) in coal seams: modern analogues from fluvial deposits of the Okavango Delta, Botswana, southern Africa. Sedimentary Geology 57, 107e118. Church, M., Rice, S.P., 2009. Form and growth of bars in a wandering gravelbed river. Earth Surface Processes and Landforms 34, 1422e1432. Colpron, M., Nelson, J.L., 2009. A palaeozoic northwest passage: incursion of Caledonian, Baltican and Siberian terrains into eastern Panthalassa, and the early evolution of the North American Cordillera. In: Cawood, P.A., Kroner, A. (Eds.), Earth Accretionary Systems in Space and Time. Geological Society of London, Special Publications, 318, pp. 273e307. Colpron, M., Nelson, J.L., Murphy, D.C., 2006. A tectonostratigraphic framework for the pericratonic terrains of the northern Canadian Cordillera. In: Haggart, J.W., Enkin, R.W.J., Monger, J.W.H. (Eds.), Paleogeography of the North American Cordillera: Evidence for and against Large-scale Displacements. Geological Association of Canada, Special Paper, 46, pp. 1e23. Creaser, B., Spence, G., 2005. Crustal structure across the northern Cordillera, Yukon territory, from seismic wide-angle studies: Omineca belt to intermontane belt. Canadian Journal of Earth Sciences 42, 1187e1203. Curray, J.R., 1956. The analysis of two-dimensional orientation data. Journal of Geology 64, 117e131. Duk-Rodkin, A., 1999. Glacial Limits Map of Yukon. Geological Survey of Canada, Open File Report 3694, Scale 1: 1,000,000. Ferguson, R.I., 1977. Meander sinuosity and directional variance. Geological Society of America. Bulletin 88, 212e214. Fitzpatrick, E.A., 1980. Soils, Their Formation, Classification and Distribution. Longman Inc., New York, U.S.A. 353pp. Forbes, D.L., 1983. Morphology and sedimentology of a sinuous gravel-bed channel system: lower Babbage river, Yukon coastal plain, Canada. In: Collinson, J.D., Lewin, J. (Eds.), Modern and Ancient Fluvial Systems. International Association of Sedimentologists, Special Publication, 6, pp. 195e206. Gabrielse, H., Murphy, D.C., Mortensen, J.K., 2006. Cretaceous and caenozoic dextral orogen-parallel displacements, magnetism, and paleogeography, north-central Canadian cordillera. In: Haggart, J.W., Enkin, R.W., Monger, J.W.H. (Eds.), Paleogeography of the North American Cordillera: Evidence for and against Large-scale Displacements. Geological Association of Canada, Special Paper, 46, pp. 255e276. Gangloff, R.A., May, K.C., Storer, J.E., 2004. An early late cretaceous dinosaur tracksite in central Yukon territory, Canada. Ichnos 11, 299e309. Gangloff, R.A., Storer, J.E., May, K.C., 2000. Recently discovered dinosaur track sites in the Yukon territory, an example of cross-border cooperation. In: Crossing Borders - Arctic Science 2000, Program and Abstracts. Yukon Science Institute, Whitehorse, pp. 88e89. Ghosh, P., 2000. Estimation of channel sinuosity from paleocurrent data; a method using fractal geometry. Journal of Sedimentary Research 70, 449e455. Ham, D.G., 2005. Morphodynamics and sediment transport in a wandering gravel-bed channel: Fraser River, British Columbia. Ph.D Thesis, University of British Columbia, Vancouver, Canada, 272pp. Hickin, A.S., Kerr, B., Barchyn, T.E., Paulen, R.C., 2009. Using groundpenetrating radar and capacitively coupled resistivity to investigate 3-D fluvial architecture and grain-size distribution of a gravel floodplain in
288
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
northeast British Columbia, Canada. Journal of Sedimentary Research 79, 457e477. Hopkins Jr., W.S., 1979. Palynology report on ten samples from the tertiary of the Tintina trench, near Ross river, Yukon territory, submitted by D.G.F. Long, 1979 (NTS 105F). Geological Survey of Canada Paleontology Report T-03-WSH-1979. Hughes, J.D., Long, D.G.F., 1980. Geology and coal resource potential of early tertiary strata along Tintina trench, Yukon territory. Geological Survey of Canada, Paper 79e32, 21 pp. Hunt, J.A., 1994. Yukon Coal Inventory 1994. Unpublished Report for Energy and Minerals Branch, Economic Development, Yukon Territorial Government. Aurum Geological Consultants Inc., Whitehorse, Yukon. Kindle, E.D., 1946. Geological reconnaissance along the Canol road, from Teslin River to Macmillan Pass, Yukon. Geological Survey of Canada Paper 45-21. Ledo, J., Jones, A.G., Ferguson, I.J., 2000. New SNORCLE magnetotelluric data: preliminary implications. In: Cook, F., Erdmer, P. (Eds.), Slave-northern Cordillera Lithospheric Evolution (SNORCLE) Transect and Cordilleran Tectonics Workshop Meeting (February 25-27), 72. University of Calgary, Lithoprobe Report, pp. 124e127. Li, S.S., Millar, R.G., Islam, S., 2008. Modeling gravel transport and morphology for the Fraser river gravel reach, British Columbia. Geomorphology 95, 206e222. Long, D.G.F., 1981. Dextral strike slip faults in the Canadian cordillera and depositional environments of related fresh-water intermontane coal basins. In: Miall, A.D. (Ed.), Sedimentation and Tectonics in Alluvial Basins. Geological Association of Canada, Special Paper, 23, pp. 153e186. Long, D.G.F., 1986. Coal in the Yukon. In: Morin, J.D. (Ed.), Mineral Deposits of the Northern Cordillera. Canadian Institute of Mining and Metallurgy, Special Paper, 37, pp. 311e318. Long, D.G.F., Hughes, D., Abbot, J.G., 1990. Geology of the Ross river coal deposits. In: Abbot, J.G., Turner, R.J.W. (Eds.), Mineral Deposits of the Northern Canadian Cordillera, Yukon - Northeastern British Columbia. Field Trip 14, 8th IAGOD Symposium Field Trip Guidebook. Geological Survey of Canada Open File, 2169, pp. 215e230. Long, D.G.F., Lowey, G., Sweet, A.R., 2000. Age and setting of dinosaur trackways, Ross river, Yukon territory (NTS 105F/15). In: Emond, D.D., Weston, L.H. (Eds.), Yukon Exploration and Geology 2000. Exploration and Geological Services Division, Yukon Region. Indian and Northern Affairs Canada, pp. 181e198. Long, D.G.F., Young, G.M., 1978. Dispersion of cross stratification as a potential tool in the interpretation of proterozoic arenites. Journal of Sedimentary Petrology 48, 857e862. Lowey, G.W., 1984. The stratigraphy and sedimentology of siliciclastic rocks, west-central Yukon, and their tectonic implications. Unpublished Ph.D. thesis, The University of Calgary, Calgary, Alberta, 329pp. Lowey, G.W., Hills, L.V., 1988. Lithofacies, petrography and environment of deposition, Tantalus formation (Lower Cretaceous), Indian river area, west central Yukon. Bulletin of Canadian Petroleum Geolology 36, 296e310. Makaske, B., Smith, D.G., Berendsen, H.J.K., 2002. Avulsions, channel evolution and floodplain sedimentation rates of the anastomosing upper Columbia river, British Columbia, Canada. Sedimentology 49, 1049e1071. Massari, F., 1983. Tabular cross-bedding in Messinian fluvial channel conglomerates, southern Alps, Italy. In: Collinson, J.D., Lewin, J. (Eds.), Modern and Ancient Fluvial Systems. International Association of Sedimentologists, Special Publication, 6, pp. 287e300. Miall, A.D., 1976. Paleocurrent and paleohydrologic analysis of some vertical profiles through a cretaceous braided stream deposit, Banks island, Arctic Canada. Sedimentology 23, 459e484. Miall, A.D., 1978. Lithofacies types and vertical profile models in braided river deposits: a summary. In: Miall, A.D. (Ed.), Fluvial Sedimentology. Canadian Society of Petroleum Geologists, Memoir, 5, pp. 597e604. Miall, A.D., 1985. Architectural element analysis: a new method of facies analysis applied to fluvial deposits. Earth Science Reviews 22, 261e308.
Miall, A.D., 1988. Facies architecture in clastic sedimentary basins. In: Kleinspehn, K.L., Paola, C. (Eds.), New Perspectives in Basin Analysis. Springer-Verlag, New York, United States, pp. 67e81. Miall, A.D., 1996. The Geology of Fluvial Deposits: Sedimentary Facies, Basin Analysis and Petroleum Geology. Springer-Verlag, Berlin. 582pp. Mortensen, J.K., 1990. Geology and UePb chronology of the Klondike district, west-central Yukon territory. Canadian Journal of Earth Sciences 27, 903e914. Mortensen, J.K., 1992. Pre-mid-mesozoic tectonic evolution of the Yukon Tanana terrane, Yukon and Alaska. Tectonics 11, 836e853. Mortensen, J.K., 1996. Geological Compilation Maps of the Northern Stewart River Map Area, Klondike and Sixty Mile Districts (115N/15, 16; 115O/13, 14 and Parts of 115O/15, 16). Exploration and Geological Services, Yukon, Indian and Northern Affairs Canada, Open File 19961(G) 43pp, scale 1:50,000. Nadon, G.C., 1993. The association of anastomosed fluvial deposits and dinosaur tracks, eggs, and nests: implications for the interpretation of floodplain environments and a possible survival strategy for ornithopods. Palaios 8, 31e44. Nanson, G.C., Knighton, A.D., 1995. Anabranching rivers: their cause, character and classification. Earth Surface Processes and Landforms 21, 217e239. Pigage, L.C., 1987. Geological and Drilling Report, Ross River Coal, N.T.S. 105 F-16, Coal Lease 2986. Unpublished Report and Map Prepared for Curragh Resources Inc. Pigage, L.C., 1990. Field guide to the Anvil PbeZneAg district, Yukon territory, Canada. In: Abbott, J.G., Turner, R.J.W. (Eds.), Mineral Deposits of the Northern Cordillera, YukoneNortheastern B.C., 8th IAGOD Symposium Field Trip Guide Book, Geological Survey of Canada, Open File, 2129, pp. 283e308. Plouffe, A., Jackson Jr., L.E., 1995. Quaternary stratigraphy and till geochemistry in the Tintina trench, near Faro and Ross river, Yukon territory. In: Bobrowsky, P.T., Sibbick, S.J., Newell, J.M., Matysek, P.F. (Eds.), Drift Exploration in the Canadian Cordillera, British Columbia Ministry of Energy, Mines and Petroleum Resources, Paper, 1995e2, pp. 53e66. Rice, S.P., Church, M., Wooldridge, C.L., Hickin, E.J., 2008. Morphology and evolution of bars in a wandering gravel-bed river: lower Fraser river, British Columbia. Sedimentology 56, 709e736. Roberts, M.C., Bravard, J.-P., Jol, H.M., 1997. Radar signatures and structure of an avulsed channel: Rh^one river, Aoste, France. Journal of Quaternary Science 12, 35e42. Roddick, J.A., 1967. Tintina trench. Journal of Geology 53, 23e33. Smith, D.G., 1976. Effect of vegetation on lateral migration of anastomosed channels of a glacial meltwater river. Geological Society of America, Bulletin 87, 857e860. Snyder, D.B., Roberts, B.J., Gordey, S.P., 2005. Contrasting seismic characteristics of three major faults in northwestern Canada. Canadian Journal of Earth Sciences 42, 1223e1237. Sweet, A.R., 1999. Applied research report on 13 samples of late cretaceous and tertiary age from near Ross river, Yukon territory (NTS105F). Geological Survey of Canada, Paleontological Report 9-ARS-1999, 5 pp. Tempelman-Kluit, D.J., 1977. Geology of Quiet Lake (105F) and Finlayson Lake (105G) map areas, Yukon territory. Geological Survey of Canada, Open File Report 486, 7 pp. Try, C.F., Long, D.G.F., Winder, C.G., 1984. Sedimentology of the lower cretaceous Mattagami formation, Moose river basin, James bay lowlands, Ontario, Canada. In: Stott, D.F., Glass, D.J. (Eds.), The Mesozoic of Middle North America. Canadian Society of Petroleum Geologists, Memoir, 9, pp. 345e359. Wheeler, J.O., Green, L.H., Roddick, J.A., 1960. Quiet Lake Map-area, Y.T. Geological Survey of Canada, Map 7e1960. Wizevich, M.C., 1991. Photomosaics of outcrops: useful photographic techniques. In: Miall, A.D., Tyler., N. (Eds.), Three-dimensional Facies Architecture of Terrigenous Clastic Sediments and Its Implications for Hydrocarbon Discovery and Recovery. SEPM, Concepts in Sedimentology and Paleontology, 3, pp. 22e24.
available at www.sciencedirect.com
China University of Geosciences (Beijing)
GEOSCIENCE FRONTIERS journal homepage: www.elsevier.com/locate/gsf
ORIGINAL ARTICLE
Wandering gravel-bed rivers and high-constructive stable channel sandy fluvial systems in the Ross River area, Yukon Territory, Canada Darrel G.F. Long a,*, Grant W. Lowey b a
Department of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada Yukon Geological Survey, Energy, Mines and Resources, Government of Yukon, P.O. Box 2703 (K102), Whitehorse, Yukon Y1A 2C6, Canada b
Received 22 March 2011; accepted 12 May 2011 Available online 24 June 2011
KEYWORDS Anastomosing rivers; Wandering gravel-bed rivers; Fluvial architecture; Cretaceous; Yukon
Abstract Mid-Cretaceous strata within the Tintina Trench, 3 km west of the community of Ross River, contain evidence of deposition in two distinct, alternating, fluvial settings. Coal-bearing, mud-dominated strata are commonly associated with high-constructive sandy channel systems, with extensive overbank, levee and splay deposits. Channels are between 3 and 30 m wide and 0.4e7 m thick. They show repetitive development of side and in-channel bar-forms, as well as up-channel widening of the rivers by selective erosion of associated overbank and levee deposits. Levees extended for several hundred metres away from the channels. In this setting low-angle inclined stratification and epsilon cross stratification may reflect lateral migration of crevasse channels or small streams. The paucity of exposure prevents recognition of the channels as products of multiple channel anastomosed systems or single channel high-constructive systems. Gravel-dominated strata, inter-bedded with, and overlying coal-bearing units, are interpreted as deposits of wandering gravel-bed rivers, with sinuosity approaching 1.4. In most exposures they appear to be dominated by massive and thin planar-bedded granule to small pebble conglomerates, which would traditionally be interpreted as sheet-flood or longitudinal bar deposits of a high-gradient braided stream or alluvial fan. Architectural analysis of exposures in an open-pit shows that the predominance of flat bedding is an artefact of the
* Corresponding author. E-mail address: [email protected] (D.G.F. Long). 1674-9871 ª 2011, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved. Peer-review under responsibility of China University of Geosciences (Beijing). doi:10.1016/j.gsf.2011.05.018
Production and hosting by Elsevier
278
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288 geometry of the roadside exposures. In the pit the conglomerates are dominated by large scale cross stratification on a scale of 1e5.5 m. These appear to have developed as downstream and lateral accretion elements on side-bars and on in-channel bars in water depths of 2e12 m. Stacking of strata on domed 3rd order surfaces suggests development of longitudinal in-channel bar complexes similar to those observed in parts of the modern Rh^ one River system. Mudstone preserved in some of the channels reflects intervals of channel abandonment or avulsion. Minimum channel width is from 70 to 450 m. ª 2011, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.
1. Introduction Chert-bearing clastic strata, located in a fault bounded block within the Tintina Trench, about 2 km west of the community of Ross River (Fig. 1, right), were originally thought to be part of an 800e1100 m thick Paleocene sequence of conglomerate and mudstone, with minor sandstone and coal (Kindle, 1946; Wheeler et al., 1960; Tempelman-Kluit, 1977; Hughes and Long, 1980; Long, 1981; Long et al., 1990). While miospores in this block were found to be very poorly preserved due to thermal degradation, a Paleocene (Tertiary) age was assumed because of the similarity of this strata to clastics in a second block at Lapie River, 7 km west of the Ross River town site where Hopkins (1979) recovered a better preserved assemblage of palynomorphs. These included Alnus, which was taken as suggestive of an Early Eocene or late Middle Eocene age. A stratigraphic gap of about 200 m was estimated between the two sections based on vitrinite reflectance gradients (Hughes and Long, 1980). The subsequent discovery of multiple dinosaur tracks in the Ross River block by Gangloff et al. (2000) indicated that the original age assignment was in error. Paylnological investigation of new samples from this section indicates a Mid Cretaceous age, within the range of middle Albian to possibly Cenomanian (Sweet, 1999; Long et al., 2000), consistent with the subsequent interpretation of the six types of ichnogenera (footprints) identified by Gangloff et al. (2004). In the Yukon, there are numerous terrestrial deposits of Upper Jurassic, Cretaceous and Paleogene age that contain conglomerate and sandstone with abundant chert and chert-like clast (siliceous
mudstones, mylonites). In these basins (Fig. 1, left) conglomeratic units have typically been interpreted as products of deposition from braided streams or alluvial fans (Long, 1986). The presence of distinct lateral accretion sets and large scale cross stratification, revealed by strip mining at Ross River indicates that these models are not viable for the strata at Ross River (Long et al., 2000).
2. Geological setting The Ross River area (Fig. 1) is underlain by rocks of the YukonTanana terrane, an assemblage of polydeformed metamorphic rocks of Palaeozoic age (Mortensen, 1990, 1992, 1996; Colpron et al., 2006). According to Mortensen (1992), these consist mainly of pelitic to quartzo-feldspathic metasedimentary schist and gneiss, with minor marble and mafic to felsic metavolcanic, and metaplutonic rocks. The Yukon-Tanana was juxtaposed with other terranes (i.e., Slide Mountain) by regional scale thrust faulting in the Early Mesozoic, so that it now structurally overlies the ancient continental margin of North America (Mortensen, 1990; Colpron et al., 2006; Colpron and Nelson, 2009). The Yukon-Tanana terrane is unconformably overlain by post-accretionary, Mid- to Late-Cretaceous sedimentary and volcanic rocks (Mortensen, 1996). Both the preand post-accretionary rocks are offset by at least 450 km of dextral movement along the Tintina Fault zone, the displacement of which is thought to have begun in the Late Cretaceous and continued through the Early Paleogene (Roddick, 1967; Long, 1981; Pigage, 1990; Gabrielse et al., 2006). The exact position of the main
Figure 1 Location of the Ross River block (right e medium grey shading) and (left) its relation to other Mesozoic and Cenozoic basins containing chert-bearing conglomerates.
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
279
strand of the Tintina Fault in the area is uncertain. Tempelman-Kluit (1977) placed it about 2 km south-west of the area shown in Fig. 2, while magnetotelluric studies by Ledo et al. (2000) indicate that the main crustal discontinuity may be beneath the modern Pelly River. Ledo et al. (2000) also recognized a second crustal discontinuity further to the west, which appears to coincide with the St Cyr fault. All of these faults could be linked at depth, as Creaser and Spence (2005) and Snyder et al. (2005) indicate that the Tintina fault is a crustal penetrative feature, with brittle faulting on multiple strands in the upper crust over a zone that is w30 km wide. Tempelman-Kluit (1977) provides the most complete coverage of the bedrock geology in the Ross River area. The map by Wheeler et al. (1960) is dated, but provides useful descriptive notes. Hughes and Long (1980) and Long et al. (1990) outline the geology and coal resource potential of the sedimentary rocks in the Ross River area, and a detailed map (1:2000 scale) of the area mined is included in the drilling report by Pigage (1987). The surficial geology is described by Plouffe and Jackson (1995), DukRodkin (1999) and Bond (2001).
3. New observations Strata in the Ross River block include at least 427 m of mudstone, conglomerate and sandstone, with minor coal, best exposed in sections dipping 20e30 to the southeast, adjacent to the Robert Campbell Highway (Figs. 1 and 2). Vertical and lateral relations between facies were examined along the roadside sections, and in the small open-pit coal-mine immediately north of the highway (Fig. 1). The geometry of sand and gravel units were investigated using the technique of architectural analysis, as outlined by Allen (1983), Bridge and Diemer (1983), Miall (1988, 1996) and Bridge (1993). This method is based on the concept that strata can be divided into genetically related packets, which in turn can be related to episodes of geographically and temporally limited depositional processes (Miall, 1978, 1996). See below for further details.
3.1. Mudstones Mudrocks dominate the lower 200 m of the section (Fig. 2): they are predominantly dark grey to dark greenish grey claystones with minor siltstone. Most appear massive, with a pseudo-brecciated appearance, or exhibit faint horizontal stratification. Traces of plant roots are rare below the 200 m level and common between the 200 and 310 m levels (Fig. 2). Black, organic rich mudrocks are developed locally in the lower 200 m of the section, but are more common in association with coals in the 200e310 m interval.
3.2. Coal Coal forms a small but significant part of the sequence. Five seams of bituminous coal were identified in the area prior to mining
Figure 2 Litho-stratigraphy of the Ross River block, based on exposures adjacent to the Robert Campbell Highway, at Whiskey Lake. A Z Elevation above base of section in metres. B Z contacts: solid line Z sharp, dashed line Z transitional, dotted line Z not seen,
cross indicates no exposure. C Z grain size: CL Z claystone, z Z siltstone, vf, f, m, c, vc Z sandstone, G Z granule conglomerate, number Z grain size in cm. D Z Paleoflow vectors (north to top). E Z Sedimentary structures: 1 Z appears massive; 2 Z plane bedded; 3 Z wavy bedded; 4 Z ripple cross-laminated; 5 Z trough cross-stratified; 6 Z planar cross stratified; 7 Z mudstone intraclasts; 8 Z dispersed organic material; 9 Z coal; 10 Z traces of fossil plant roots. Section extends from 61 580 1000 N, 132 320 5600 W (base) to 61 580 0800 N, 132 290 0400 W (top).
280
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
(Hughes and Long, 1980). Open-pit mining of the recessive interval below the upper conglomerate has since exposed two coal seams, from which Nadahini Mining Corporation extracted about 50 000 tonnes of coal (Pigage, 1987; Hunt, 1994). The lower of the two seams is a dull woody coal, 1.7e1.8 m thick, which rests on a 40 cm unit of massive (pseudo-brecciated) organic rich mudstone with abundant fossil plant roots. The upper seam is a dull woody coal, 1.5e1.8 m thick, which rests on an organic rich mudstone, and is locally inter-bedded with wavy and ripple laminated fine to very fine-grained sandstones (Fig. 3A). Further near-surface coal deposits may be preserved along strike to the northeast.
3.3. Sandstones Sandstones form a minor part of the sequence. All have a speckled (salt-and-pepper) texture due to the abundance of varicoloured resistant lithic clasts. They occur as thin sets (5e50 cm) of flat laminated, wavy and ripple laminated silty fine- and very finegrained sandstones; thin to thick cosets (0.1e7 m) of wavy and ripple laminated fine- to medium-grained sandstones; and minor massive and plane laminated, poorly sorted to moderately poorly sorted medium-grained to granular very coarse-grained sandstones in sets 0.15e1.3 m thick. Ripple laminated medium- to very coarsegrained sandstones are found as thin inter-beds in conglomeratic parts of the sequence. Finer grained sandstones are locally interbedded with siltstones and organic rich mudstones, and may contain local (early) nodular siderite concretions (Fig. 3A). Large-scale bedforms include shallow scour surfaces and channels (Fig. 3A, B, C). Epsilon cross stratification is developed locally (Fig. 3D).
3.4. Conglomerates Conglomerates are conspicuous in the upper part of the sequence. They occur in stacked sequences a few metres to more than 90 m
thick (Fig. 2) and as minor components of small channels in finergrained parts of the section (Fig. 4A). They consist predominantly of thick beds (5e550 cm) of yellow-brown weathering, framework supported, moderately well sorted, small- to large-pebble conglomerate (Fig. 5) that can be classified as mature limonitic sedlithrudite (Fig. 6). Petrographically these closely match Cretaceous strata at Indian River, SW of Dawson (Lowey, 1984; Lowey and Hills, 1988; Long et al., 2000). Clasts are predominantly rounded to subrounded with a maximum observed clast size of 9 cm. Rock fragments form an average of 42% of the framework grains, of these 61% are mudstones (40% silicified and 21% carbonaceous), 13% are igneous (predominantly granitic, with minor silicified volcanics), 18% are cherts (black, grey and green), 4% are carbonates, and 5% are sandstones and siltstones. Cements form about 5% of the rock, most are limonitic, with minor carbonate cement. In the section along the Robert Campbell Highway most of the conglomerates appear to be massive or flat laminated (Fig. 4B). In the coal-pit this is seen to be an illusion as most of the strata are characterized by large scale (1e5.5 m) planar and trough cross stratification (Fig. 4C), with grouped sets occupying broad channels up to 12 m deep (Fig. 4D). An unusual scalloped erosional contact was noted at the base of one conglomeratic unit at the north end of the upper pit (Fig. 4).
4. Sedimentary architecture e methodology In order to reconstruct the architecture of the sand and gravel units it was first necessary to construct photo-mosaics of the exposed faces in the upper and lower pits. As strata in the pits dip uniformly at 23 to the SE a series of 95 overlapping photographs were taken for the 250 35 m outcrop in the upper pit, and w120 photographs of the 230 40 outcrop in the lower pit, with the axis of the camera lens oriented down dip, approximately normal to the face of the outcrop. This was achieved using a tripod and a camera
Figure 3 Fine to medium-grained sandstones and mudstones: A. Massive to wavy bedded fine to very fine-grained sandstone with siderite nodules (in upper coal-pit). B. Shallow inclined cosets of fine to very fine-grained wavy laminated sandstone of levee and splay origin (upper coal-pit). C. Local scour surfaces in fine to very fine-grained flat to wavy laminated sandstones of levee-splay origin (upper coal-pit). D. Well-developed epsilon cross stratification, marked by alternating beds of fine to very fine-grained sandstone and siltstone (below upper coal seam in upper pit).
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
281
Figure 4 Conglomeratic strata: A. Planar cross-stratified lens of small pebble conglomerate in small, 8 m wide channel in the upper coal seam, south end of upper coal-pit. B. Typical exposure of small pebble conglomerate in the upper conglomerate adjacent to the Robert Campbell Highway. C. 5.5 m thick composite planar cross stratified, small to medium pebble conglomerate. Dashed lines indicate set boundaries. D. Large scale channel (12 m) thick, with local organic rich mudstone and planar and trough cross-stratified conglomerate, upper coal-pit. E. Scalloped surface at contact between medium pebble conglomerate and silty mudstone, north end of upper pit.
with a perspective correction (architectural) lens (Wizevich, 1991). The apparatus was moved parallel to the face of the exposure, so that a minimum of 50% horizontal overlap of photographs was achieved. A scale was included in each photograph to allow later calibration. Photographs were scanned at 600 dpi and the residual effects of distortion due to outcrop shape partly removed using a perspective correction tool in the scanning program. Images were matched, trimmed and imported into a graphics program. The scale of individual photographs was corrected in the graphics program and a photo mosaic, with a preliminary overlay showing contact relations created. Duplicate copies of the photographs were used to record field observations and to allow verification of assumed contact relations. Dip directions of all accessible measured surfaces were later corrected for tectonic dip, and plotted on the mosaics, so that arrows directed above the horizontal reflect direction of slopes away from the observer and arrows below the horizontal reflect slopes towards the observer. Finally contact relations between elements were verified, classified and labelled (c.f. Miall, 1985, 1996; Bromley, 1991). Due to safety considerations, detailed dip
measurements could only be made along the northern margin of the lower pit, and the lower 3 m of the upper pit (Figs. 7, 8 and 9).
5. Depositional facies 5.1. Overbank, marsh and swamp deposits Clay-mudstones in the Ross River sequence are here interpreted as the products of deposition in overbank marsh and pond environments. They occur as blanket-like elements (FF of Miall, 1996), typically 1e15 m thick, which can be traced laterally for at least 450 m in strata below surface A (Figs. 7, 8 and 9). Well-developed plane lamination, characteristic of lake deposits was not seen. The grey colour is related to moderate dispersed organic content. The predominance of grey, rather than black mudrocks suggests marsh environments with the water table at or near the surface during part of the year. The brecciated appearance of many of the clay mudstones is due to the presence of numerous closely spaced, intersecting curved fracture surfaces. These slickensides are
282
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
Figure 5 Petrography of conglomerates from the Ross River block, with daughter triangle at top right showing varieties of quartz types (Qm Z monocrystalline; Qp Z polycrystalline; Qcp Z coarse polycrystalline: no strained quartz was seen). Daughter triangles at base indicate types of sedimentary lithic fragments present, showing that most samples are classified as sedlithrudites.
typically associated with a fluctuating water table (Try et al., 1984). In dry periods the soil (a vertisol) shrank and cracked, to swell again in wet periods. Rubbing of adjacent soil crumb and blocks during repeated wetting and drying led to the production of grooved and polished surfaces, now represented by slickensides (Fitzpatrick, 1980; Nadon, 1993). Siltstones are typically associated with wavy and ripple laminated sandstones and are interpreted as distal levee deposits (LV elements). Organic rich mudstones and coals were deposited in marsh and swamp environments, away from the main fluvial channels. Finer-grained sandstones appear to have been deposited as overbank, levee and splay deposits. Splay deposits (CS elements) typically have a wedge shaped architecture, with slopes of 1e1.5 (Fig. 3B). Individual CS elements can be traced for 5e50 m (Figs. 8 and 9), and are from a few decimetres to metres thick at the proximal end. The CS elements below surface A appear to have prograded over floodplain mud and silt. They appear to have supported dense vegetation, as indicated by rare preserved plant roots and local homogenization by rootbioturbation. Stacking of levee-splay sequences in the coal-pits (Figs. 7, 8 and 9) indicates an intimate association with stable stream channels. Local scour surfaces (Fig. 3C) may reflect scouring of levees during flood events. Low-angle inclined stratification (Fig. 3D) and epsilon cross stratification may reflect lateral migration of crevasse channels or small streams in secondary areas of the floodplain.
5.2. Stable channel systems Architectural analysis of lenticular sand bodies in the lower pit indicate that these were deposited in low-gradient, highconstructive stream systems, in which bank stability was probably maintained by dense plant growth (c.f. Smith, 1976; Cairncross et al., 1988; Nanson and Knighton, 1995; Makaske et al., 2002). The 39 m wide channel shown in Fig. 10 may have evolved from a small crevasse channel (like those in Fig. 4A), and progressively widened as flow was diverted from the original channel. The stacking of lateral accretion sets (LA elements) in point bars within the channel shown in Fig. 10 indicates that the rivers had only a limited ability to erode channel walls, and were probably never more than 2.5 m deep at times of bank-full discharge. Set boundaries within LA elements appear to dip at up to 6 into the main channel. If the mud-draped, concave-up elements in the second LA element in this fill represent 3rd order sequences produced by macroform growth during seasonal events, or 10 year floods, then the stacking pattern of 4th order surfaces suggests that the channel may have persisted for at least 400 years (c.f. Miall, 1996), with minor expansion during each 100 year flood. Although the abundance of potential levee facies below surface A suggests that the channels were part of a multi-channelled anastomosed fluvial system, that closely matches the Type 1b organoclastic anabranching river model of Nanson and Knighton (1995). The paucity of channel deposits suggests that these were largely single channel systems, which changed position by avulsion, and progressive stream capture, or that channel systems occupied far less than 6% of the alluvial floodplain.
5.3. Wandering gravel-bed rivers Figure 6 Plot of median (M) versus maximum (C) grain size for conglomeratic strata in the Ross River block. Histogram at base shows relative proportion of conglomerate types.
Thicker conglomerate sequences in the Ross River block are here interpreted as products of deposition by wandering gravel-bed
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
Figure 7
283
Left (northern) side of upper pit. For explanation see Fig. 8.
rivers (Forbes, 1983; Miall, 1996; Roberts et al., 1997; Ham, 2005; Li et al., 2008; Rice et al., 2008; Church and Rice, 2009; Hickin et al., 2009), rather than braided rivers or alluvial fans. The roadside exposures appear to be dominated by massive to flat laminated granule to small pebble conglomerates, which would traditionally be interpreted as sheet-flood or longitudinal bar deposits of a high-gradient braided stream or alluvial fan (Long, 1981). In contrast the open-pit exposures show that the predominance of flat bedding is an artefact of the geometry of the roadside exposures. Architectural analysis of exposures in the upper pit
(Figs. 7 and 8) indicates that the sequence is dominated by large scale cross stratification on a scale of 1e5.5 m. These probably formed as gravelly bedforms (GB) on side-bars and in-channel bars in water depths of 2e12 m. Multiple scour and fill of older deposits has produced distinct channel deposits, some with complex sinusoidal geometry suggestive of deposition on point or side-bars (Fig. 7D). This and the broad scatter of paleocurrents (Figs. 7, 8 and 11), is suggestive of episodic migration of the river channels over the floodplain to produce extensive sheet-like bodies, analogous to those recorded in the floodplain of the
284
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
Figure 8 Architecture of the south end of the upper pit, showing A: the unaltered photo mosaic, B: The mosaic with set boundaries plotted. C: Architectural elements and lithofacies with direction of foreset (0th order) surfaces (thin black lines) indicated by a red arrow. Orientation of 1st to 4th order surfaces (black lines) is indicated by a green pin. Orientation of 5th and 6th order surfaces (red) are indicated by large blue pins. All vector data has been adjusted so that slopes away from the observer point up, and those sloping towards the observer point down. Numbers in square boxes indicate hierarchy of surfaces. D: Grouped paleocurrent data (Roses) plotted for main architectural elements. Colours as for pins. Ø Z Vector mean in degrees; N Z number of observations; L Z vector strength; V Z variance; letters and numbers in brackets indicate the elements included, and distance along the pit face in metres. Small histogram indicates distribution of surface dips, and average dip values after correction for tectonic dip. Letters in circles represents unit boundaries used in text.
Halfway River by Hickin et al. (2009). The face exposed in the upper pit above surface A (a 6th order surface) can be divided into four major packages, separated by 5th order surfaces (B, C, D), which are interpreted as distinct channel systems (CH elements).
CH element A-B (the unit between circled letters A and B in Figs. 7, 8 and 9) is between 2 and 14 m thick, and can be traced across both the upper and lower pit, over a distance of at least 450 m (w/d > 36:1). It appears to consist of stacked sets of
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
Figure 9 contrast.
285
View of lower pit with major surfaces indicated as in Fig. 8. Boundaries in the lower unit (below surface A) are traced in white for
gravelly bedform (GB) elements, separated by 3rd order surfaces with dips typically less than 15 (Fig. 11). The preserved strata appear to represent the preserved core of a composite bar-form (gravel-flat), with a core located about 190 m from the north end of the pit (Fig. 8 right). Draping of beds away from this core mimics radar profiles of elongate in-channel, lateral channel bars
in a wandering segment of the Rh^ one River, near Aoste in France (Roberts et al., 1997). The variance of paleoflow indicators in this unit is slightly above the upper limit considered diagnostic of braided systems by Long and Young (1978). Mean flow direction is within 8 of the mean inclination direction of 2nd and 3rd order surfaces (Figs. 7, 8 and 11), indicating that accretion may have
Figure 10 High-constructive (stable) channel deposit, with stacked epsilon cross stratification. Note minor fluvial distributary channel deposit at base of upper coal seam, and splay deposits at the top of the coal seam (lower pit).
286
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
Figure 11 Vector data for 6th (A) and 5th (B, C, D) order surfaces in the upper pit is shown as back roses; 1st to 4th order surfaces are represented by medium grey roses, and 0th order surfaces (forsets) by light grey roses. Arrows represent vector mean for each set (north to top). Ø Z vector mean in degrees, N Z number of observations, L Z vector strength, V Z variance (Determined using the method of Curray, 1956). Information in brackets indicates surface or interval, and spread of data collection points relative to the scale in Figs. 7 and 8. Small histograms associated with individual roses show distribution of dip corrected inclinations in ten degree intervals and the average dip of the surfaces in degrees.
occurred preferentially at the downstream end of bars. Too few paleocurrent indicators were in any one vertical section to allow direct estimation of channel sinuosity, using the method of Miall (1976). When this method is applied to lateral, rather than vertical sets of cross beds, a sinuosity of 1.08 is suggested. Sinuosity estimates using method 2 of Ghosh (2000) give values well in excess of 2.8, which appears inconsistent with the observed geometry. By using the vector mean direction of subsets of grouped paleocurrent data (6e7 vectors per group) as a proxy for thalweg direction, it is possible to estimate the sinuosity as around 1.46, using method 1 of Ghosh (2000), and 1.24, using the method of Ferguson (1977). These results are consistent with those of Church and Rice (2009) who noted that the sinuosity of wandering reaches of the Fraser River had values between those of
braided and gravelly meandering systems. The scalloped erosional surface of the basal 6th order surface at the base of the element at the north end of the upper pit (Fig. 4E) may be analogous to corrasion furrows produced by longitudinal roll vortices under upper flow regime conditions (Allen, 1965; Massari, 1983). CH element B-C cuts 10 m into the underlying channel complex, and has a width of at least 425 m. The channel has a preserved erosional bank, with a slope of about 26 50 m from the north end of the pit. 4th order surfaces in the channel-fill between the bank and the 120 m mark dip away from the bank at between 6 and 30 , suggesting formation as an attached side-bar (LA element). A core complex, similar to those in the Rh^ one may be preserved 150e200 m from the north end of the pit, but is not as pronounced as in CH element A-B. Too few paleocurrent observations were made
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288 to determine sinuosity, but the 81 divergence of the mean paleocurrent flow from the mean slope of 1st to 3rd order surfaces between the 70 and 130 m markers, as well as the 62 divergence between 130 and 180 m, and the 41 divergence between 180 and 250 m suggests a strong lateral accretion component (Fig. 11). CH element C-D is about 8 m thick. It has an exposed length of only 80 m at the north end of the pit (Fig. 7). The 25 m wide lens of organic rich mudstone, capped with inter-bedded siltstone and minor ripple laminated very fine sandstone may represent fines that accumulated in a channel thalweg following switching of the main channel. The uppermost CH element in the upper pit (D-E) is up to 14 m thick and can be traced laterally for 350 m. As the pit sections are approximately normal to inferred stream flow, this provides a minimum channel belt width. Like the underlying CH elements, this exhibits a complex internal geometry, and includes lenses of organic rich mudstone, which may have accumulated in a partly abandoned channel thalweg, or the downstream end of a chute. The CH element is clearly erosive into elements CH C-D and B-C, with maximum bank slopes locally in excess of 60 . This and the presence of coal-spars in the gravels suggest that the overbank environment was at least partly forested, and that bank stability was significantly enhanced by plant roots (Smith, 1976). Limited paleocurrent and slope observation (Fig. 11) indicate that gravel bedforms migrated at 59 away from the maximum slope of the LA surfaces.
6. Conclusions and speculations Strata in the Ross River block appear to have been deposited within a valley system, which ran approximately parallel to the Tintina Trench during the late Early Cretaceous. Fine-grained (sand and mud-dominated) parts of the system appear to have been deposited on low-gradient floodplains characterized by high-constructive single or multi-channel systems, in part resembling modern anastomosed systems. These are inter-bedded with, and overlain by pebble-dominated intervals, which appear to have been deposited in wandering gravel-bed rivers with sinuosity intermediate between braided and meandering gravel-bed systems. The alternation of these two distinct fluvial styles may indicate changes in slope, but is more likely related to changes in drainage basin size, or sediment flux associated with Milankovich driven increases in rainfall.
Acknowledgements We thank NSERC, Lithoprobe (Snorcle) and the Government of the Yukon for providing support for this research, and Art Sweet of the Geological Survey of Canada for his work on the palynology of the mudstones. Andrew McNeil, Jeremie Caza and Sophie Fortin provided able assistance in the field. Sheila Litalian assisted with point counting. This paper is submitted in celebration of the outstanding contributions to geology of my colleague Professor Xianghua Meng on the advent of his 80th birthday.
References Allen, J.R.L., 1965. A review of the origin and characteristics of recent alluvial sediments. Sedimentology 5, 89e191. Allen, J.R.L., 1983. Studies in fluviatile sedimentation: bars, bar-complexes and sandstone sheets (low-sinuosity braided streams) in the Brownstones (L. Devonian), Welsh borders. Sedimentary Geology 33, 237e293.
287
Bond, J.D., 2001. Quaternary geology and till geochemistry of the Anvil district (parts of 105K/2, 3, 5, 6 and 7) central Yukon territory. Indian and northern affairs Canada, exploration and geological services division, Yukon region. Bulletin 11, 48 pp. Bridge, J.S., 1993. Description and interpretation of fluvial deposits: a critical perspective. Sedimentology 40, 801e810. Bridge, J.S., Diemer, J.A., 1983. Quantitative interpretation of an evolving ancient river system. Sedimentology 30, 599e623. Bromley, M.H., 1991. Variations in fluvial style as revealed by architectural elements, Kayenta formation, Mesa Creek, Colorado, USA: evidence for both ephemeral and perennial fluvial processes. In: Miall, A.D., Tyler, N. (Eds.), Three-dimensional Facies Architecture of Terrigenous Clastic Sediments and Its Implications for Hydrocarbon Discovery and Recovery. SEPM Concepts in Sedimentology and Paleontology, 3, pp. 94e102. Cairncross, B., Stainistreet, I.G., McCarthy, T.S., Ellery, K., Grobicki, T.S.A., 1988. Paleochannels (stone-rolls) in coal seams: modern analogues from fluvial deposits of the Okavango Delta, Botswana, southern Africa. Sedimentary Geology 57, 107e118. Church, M., Rice, S.P., 2009. Form and growth of bars in a wandering gravelbed river. Earth Surface Processes and Landforms 34, 1422e1432. Colpron, M., Nelson, J.L., 2009. A palaeozoic northwest passage: incursion of Caledonian, Baltican and Siberian terrains into eastern Panthalassa, and the early evolution of the North American Cordillera. In: Cawood, P.A., Kroner, A. (Eds.), Earth Accretionary Systems in Space and Time. Geological Society of London, Special Publications, 318, pp. 273e307. Colpron, M., Nelson, J.L., Murphy, D.C., 2006. A tectonostratigraphic framework for the pericratonic terrains of the northern Canadian Cordillera. In: Haggart, J.W., Enkin, R.W.J., Monger, J.W.H. (Eds.), Paleogeography of the North American Cordillera: Evidence for and against Large-scale Displacements. Geological Association of Canada, Special Paper, 46, pp. 1e23. Creaser, B., Spence, G., 2005. Crustal structure across the northern Cordillera, Yukon territory, from seismic wide-angle studies: Omineca belt to intermontane belt. Canadian Journal of Earth Sciences 42, 1187e1203. Curray, J.R., 1956. The analysis of two-dimensional orientation data. Journal of Geology 64, 117e131. Duk-Rodkin, A., 1999. Glacial Limits Map of Yukon. Geological Survey of Canada, Open File Report 3694, Scale 1: 1,000,000. Ferguson, R.I., 1977. Meander sinuosity and directional variance. Geological Society of America. Bulletin 88, 212e214. Fitzpatrick, E.A., 1980. Soils, Their Formation, Classification and Distribution. Longman Inc., New York, U.S.A. 353pp. Forbes, D.L., 1983. Morphology and sedimentology of a sinuous gravel-bed channel system: lower Babbage river, Yukon coastal plain, Canada. In: Collinson, J.D., Lewin, J. (Eds.), Modern and Ancient Fluvial Systems. International Association of Sedimentologists, Special Publication, 6, pp. 195e206. Gabrielse, H., Murphy, D.C., Mortensen, J.K., 2006. Cretaceous and caenozoic dextral orogen-parallel displacements, magnetism, and paleogeography, north-central Canadian cordillera. In: Haggart, J.W., Enkin, R.W., Monger, J.W.H. (Eds.), Paleogeography of the North American Cordillera: Evidence for and against Large-scale Displacements. Geological Association of Canada, Special Paper, 46, pp. 255e276. Gangloff, R.A., May, K.C., Storer, J.E., 2004. An early late cretaceous dinosaur tracksite in central Yukon territory, Canada. Ichnos 11, 299e309. Gangloff, R.A., Storer, J.E., May, K.C., 2000. Recently discovered dinosaur track sites in the Yukon territory, an example of cross-border cooperation. In: Crossing Borders - Arctic Science 2000, Program and Abstracts. Yukon Science Institute, Whitehorse, pp. 88e89. Ghosh, P., 2000. Estimation of channel sinuosity from paleocurrent data; a method using fractal geometry. Journal of Sedimentary Research 70, 449e455. Ham, D.G., 2005. Morphodynamics and sediment transport in a wandering gravel-bed channel: Fraser River, British Columbia. Ph.D Thesis, University of British Columbia, Vancouver, Canada, 272pp. Hickin, A.S., Kerr, B., Barchyn, T.E., Paulen, R.C., 2009. Using groundpenetrating radar and capacitively coupled resistivity to investigate 3-D fluvial architecture and grain-size distribution of a gravel floodplain in
288
D.G.F. Long, G.W. Lowey / Geoscience Frontiers 2(3) (2011) 277e288
northeast British Columbia, Canada. Journal of Sedimentary Research 79, 457e477. Hopkins Jr., W.S., 1979. Palynology report on ten samples from the tertiary of the Tintina trench, near Ross river, Yukon territory, submitted by D.G.F. Long, 1979 (NTS 105F). Geological Survey of Canada Paleontology Report T-03-WSH-1979. Hughes, J.D., Long, D.G.F., 1980. Geology and coal resource potential of early tertiary strata along Tintina trench, Yukon territory. Geological Survey of Canada, Paper 79e32, 21 pp. Hunt, J.A., 1994. Yukon Coal Inventory 1994. Unpublished Report for Energy and Minerals Branch, Economic Development, Yukon Territorial Government. Aurum Geological Consultants Inc., Whitehorse, Yukon. Kindle, E.D., 1946. Geological reconnaissance along the Canol road, from Teslin River to Macmillan Pass, Yukon. Geological Survey of Canada Paper 45-21. Ledo, J., Jones, A.G., Ferguson, I.J., 2000. New SNORCLE magnetotelluric data: preliminary implications. In: Cook, F., Erdmer, P. (Eds.), Slave-northern Cordillera Lithospheric Evolution (SNORCLE) Transect and Cordilleran Tectonics Workshop Meeting (February 25-27), 72. University of Calgary, Lithoprobe Report, pp. 124e127. Li, S.S., Millar, R.G., Islam, S., 2008. Modeling gravel transport and morphology for the Fraser river gravel reach, British Columbia. Geomorphology 95, 206e222. Long, D.G.F., 1981. Dextral strike slip faults in the Canadian cordillera and depositional environments of related fresh-water intermontane coal basins. In: Miall, A.D. (Ed.), Sedimentation and Tectonics in Alluvial Basins. Geological Association of Canada, Special Paper, 23, pp. 153e186. Long, D.G.F., 1986. Coal in the Yukon. In: Morin, J.D. (Ed.), Mineral Deposits of the Northern Cordillera. Canadian Institute of Mining and Metallurgy, Special Paper, 37, pp. 311e318. Long, D.G.F., Hughes, D., Abbot, J.G., 1990. Geology of the Ross river coal deposits. In: Abbot, J.G., Turner, R.J.W. (Eds.), Mineral Deposits of the Northern Canadian Cordillera, Yukon - Northeastern British Columbia. Field Trip 14, 8th IAGOD Symposium Field Trip Guidebook. Geological Survey of Canada Open File, 2169, pp. 215e230. Long, D.G.F., Lowey, G., Sweet, A.R., 2000. Age and setting of dinosaur trackways, Ross river, Yukon territory (NTS 105F/15). In: Emond, D.D., Weston, L.H. (Eds.), Yukon Exploration and Geology 2000. Exploration and Geological Services Division, Yukon Region. Indian and Northern Affairs Canada, pp. 181e198. Long, D.G.F., Young, G.M., 1978. Dispersion of cross stratification as a potential tool in the interpretation of proterozoic arenites. Journal of Sedimentary Petrology 48, 857e862. Lowey, G.W., 1984. The stratigraphy and sedimentology of siliciclastic rocks, west-central Yukon, and their tectonic implications. Unpublished Ph.D. thesis, The University of Calgary, Calgary, Alberta, 329pp. Lowey, G.W., Hills, L.V., 1988. Lithofacies, petrography and environment of deposition, Tantalus formation (Lower Cretaceous), Indian river area, west central Yukon. Bulletin of Canadian Petroleum Geolology 36, 296e310. Makaske, B., Smith, D.G., Berendsen, H.J.K., 2002. Avulsions, channel evolution and floodplain sedimentation rates of the anastomosing upper Columbia river, British Columbia, Canada. Sedimentology 49, 1049e1071. Massari, F., 1983. Tabular cross-bedding in Messinian fluvial channel conglomerates, southern Alps, Italy. In: Collinson, J.D., Lewin, J. (Eds.), Modern and Ancient Fluvial Systems. International Association of Sedimentologists, Special Publication, 6, pp. 287e300. Miall, A.D., 1976. Paleocurrent and paleohydrologic analysis of some vertical profiles through a cretaceous braided stream deposit, Banks island, Arctic Canada. Sedimentology 23, 459e484. Miall, A.D., 1978. Lithofacies types and vertical profile models in braided river deposits: a summary. In: Miall, A.D. (Ed.), Fluvial Sedimentology. Canadian Society of Petroleum Geologists, Memoir, 5, pp. 597e604. Miall, A.D., 1985. Architectural element analysis: a new method of facies analysis applied to fluvial deposits. Earth Science Reviews 22, 261e308.
Miall, A.D., 1988. Facies architecture in clastic sedimentary basins. In: Kleinspehn, K.L., Paola, C. (Eds.), New Perspectives in Basin Analysis. Springer-Verlag, New York, United States, pp. 67e81. Miall, A.D., 1996. The Geology of Fluvial Deposits: Sedimentary Facies, Basin Analysis and Petroleum Geology. Springer-Verlag, Berlin. 582pp. Mortensen, J.K., 1990. Geology and UePb chronology of the Klondike district, west-central Yukon territory. Canadian Journal of Earth Sciences 27, 903e914. Mortensen, J.K., 1992. Pre-mid-mesozoic tectonic evolution of the Yukon Tanana terrane, Yukon and Alaska. Tectonics 11, 836e853. Mortensen, J.K., 1996. Geological Compilation Maps of the Northern Stewart River Map Area, Klondike and Sixty Mile Districts (115N/15, 16; 115O/13, 14 and Parts of 115O/15, 16). Exploration and Geological Services, Yukon, Indian and Northern Affairs Canada, Open File 19961(G) 43pp, scale 1:50,000. Nadon, G.C., 1993. The association of anastomosed fluvial deposits and dinosaur tracks, eggs, and nests: implications for the interpretation of floodplain environments and a possible survival strategy for ornithopods. Palaios 8, 31e44. Nanson, G.C., Knighton, A.D., 1995. Anabranching rivers: their cause, character and classification. Earth Surface Processes and Landforms 21, 217e239. Pigage, L.C., 1987. Geological and Drilling Report, Ross River Coal, N.T.S. 105 F-16, Coal Lease 2986. Unpublished Report and Map Prepared for Curragh Resources Inc. Pigage, L.C., 1990. Field guide to the Anvil PbeZneAg district, Yukon territory, Canada. In: Abbott, J.G., Turner, R.J.W. (Eds.), Mineral Deposits of the Northern Cordillera, YukoneNortheastern B.C., 8th IAGOD Symposium Field Trip Guide Book, Geological Survey of Canada, Open File, 2129, pp. 283e308. Plouffe, A., Jackson Jr., L.E., 1995. Quaternary stratigraphy and till geochemistry in the Tintina trench, near Faro and Ross river, Yukon territory. In: Bobrowsky, P.T., Sibbick, S.J., Newell, J.M., Matysek, P.F. (Eds.), Drift Exploration in the Canadian Cordillera, British Columbia Ministry of Energy, Mines and Petroleum Resources, Paper, 1995e2, pp. 53e66. Rice, S.P., Church, M., Wooldridge, C.L., Hickin, E.J., 2008. Morphology and evolution of bars in a wandering gravel-bed river: lower Fraser river, British Columbia. Sedimentology 56, 709e736. Roberts, M.C., Bravard, J.-P., Jol, H.M., 1997. Radar signatures and structure of an avulsed channel: Rh^one river, Aoste, France. Journal of Quaternary Science 12, 35e42. Roddick, J.A., 1967. Tintina trench. Journal of Geology 53, 23e33. Smith, D.G., 1976. Effect of vegetation on lateral migration of anastomosed channels of a glacial meltwater river. Geological Society of America, Bulletin 87, 857e860. Snyder, D.B., Roberts, B.J., Gordey, S.P., 2005. Contrasting seismic characteristics of three major faults in northwestern Canada. Canadian Journal of Earth Sciences 42, 1223e1237. Sweet, A.R., 1999. Applied research report on 13 samples of late cretaceous and tertiary age from near Ross river, Yukon territory (NTS105F). Geological Survey of Canada, Paleontological Report 9-ARS-1999, 5 pp. Tempelman-Kluit, D.J., 1977. Geology of Quiet Lake (105F) and Finlayson Lake (105G) map areas, Yukon territory. Geological Survey of Canada, Open File Report 486, 7 pp. Try, C.F., Long, D.G.F., Winder, C.G., 1984. Sedimentology of the lower cretaceous Mattagami formation, Moose river basin, James bay lowlands, Ontario, Canada. In: Stott, D.F., Glass, D.J. (Eds.), The Mesozoic of Middle North America. Canadian Society of Petroleum Geologists, Memoir, 9, pp. 345e359. Wheeler, J.O., Green, L.H., Roddick, J.A., 1960. Quiet Lake Map-area, Y.T. Geological Survey of Canada, Map 7e1960. Wizevich, M.C., 1991. Photomosaics of outcrops: useful photographic techniques. In: Miall, A.D., Tyler., N. (Eds.), Three-dimensional Facies Architecture of Terrigenous Clastic Sediments and Its Implications for Hydrocarbon Discovery and Recovery. SEPM, Concepts in Sedimentology and Paleontology, 3, pp. 22e24.