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Geology

Pleistocene reversal of the Fraser River, British Columbia

Graham D.M. Andrews, James K. Russell, Sarah R. Brown and Randolph J. Enkin

Geology 2012;40;111-114 doi: 10.1130/G32488.1

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Notes

Graham D.M. Andrews1,2*, James K. Russell2, Sarah R. Brown1, and Randolph J. Enkin3 1Earth Research Institute, University of California–Santa Barbara, Santa Barbara, California 93106, USA 2Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada 3Geological Survey of Canada, PO Box 6000, Sidney, British Columbia V8L 4B2, Canada

ABSTRACT The Fraser River in British Columbia, Canada, is the longest non-dammed river on the west merging in the interior plateaus region (Fig. 1), coast of North America and supplies 20 × 106 t/yr of sediment to the Pacifi c Ocean. Abundant which composes ~70% of the area of the Fra- geomorphological evidence indicates that the Fraser River reversed its course to southward ser Basin (Fig. 1 inset) at a mean elevation of fl ow in the recent geological past. Investigation of two volcanic dams at Dog Creek demon- ~1100 m above sea level (asl). It then drains strates northward fl ow of the Fraser until at least 1.06 Ma, before reversal and erosion of the southward through the Fraser Canyon before 270-km-long Fraser Canyon. We propose that the submarine Nitinat Fan off the coast of Brit- entering the sea at Vancouver. ish Columbia records the reversal and sudden input of coarse continental-derived sediment Since the Miocene, evolution of the Fraser ca. 0.76 Ma. This study confi rms reversal of the Fraser River and places a fi rm constraint River has been accompanied by regional and on the maximum age of that reversal. Reversal likely followed stream capture in response to global change, including uplift of the Coast enhanced glaciofl uvial erosion and uplift of the Coast Mountains. Mountains (Farley et al., 2001), multiple glaciations (Jennings et al., 2007), and enhanced

INTRODUCTION 128°W 124°W 120°W Modiﬁ cation of major rivers and their drain- 3000 PEACE

Fraser basin outline 56°N age basins is a poorly understood process asso- RIVER 2000 NECHAKO 56°N Major Fraser River tributary ciated with active tectonics, glaciation, and RIVER 1000 Drainage direction climatically inﬂ uenced erosion (Bishop, 1995). Rocky Mountains 3

Elevation (m asl) Fraser Basin present / past (Ma) Such events strongly infl uence paleogeography, 0 0 50 100 sediment budgets, and provenance. In this paper % area above elevation Quesnel Location mentioned in text InteriorInn plateaus we identify and date a volcanic succession in tet Pleistocene intraplate eri volcanoes central British Columbia, Canada, that records or p laa two episodes of damming of the ancestral Fra- tete 0 km 100 auusu ser River; reconstruction of the paleodrainage s leads us to the inevitable conclusion that the 54°N 54°N Fraser River reversed course from a northward NECNNECHAKOECHAKO N to southward fl ow. RIVER Prince George Several studies have used high-precision FRASERFR RIVER Cariboo Mountains R ages of volcanic dams to date Pleistocene fl u- InteriorInn plateausNazNazkoko AS tet vial systems in North America (e.g., Huscroft et ri Cone or ER p al., 2004; Karlstrom et al., 2007). Here we fi rst la QUESNEL te R RIVER au outline geomorphic evidence for reversal of the IV s Fraser River and then describe the lithostratigra- ER CHILCOTIN Wells C 52°N phy and Ar/Ar geochronology of two prerever- RIVER Fig. 2 OL Grey RIVERUMBIA sal volcanic dams. Although the exact causes of 52°N Coast vovolcanico cac ic 3 field drainage reversal remain unresolved, dating of 13 Dog the succession tightly constrains the maximum Creek 1 age of drainage reversal. Furthermore, we are 9 able to demonstrate geomorphic and sedimen- Mountains 8 tological consequences of reversal in the Fraser Fraser CanyonCanyoCa THOMPSONTHOHO Basin and adjacent Pacifi c Ocean. MPSP ONN RIVER Innterior plateaus Canyon tet 50°N Fraser River rir oro

50°N r The 1375-km-long Fraser River of British yon plp 3 n la Columbia discharges 3475 m /s of water and 20 Vancouver atat eaea 6 us × 10 t/yr of sediment (Swain and Holms, 1985) Ca nada Strait of Georgia from the 233,000 km2 Fraser Basin into the Pacific Ocean Vancouver Hope Island Strait of Georgia and the Paciﬁ c Ocean (Fig. 1), USA CANCACANADAA ADAA and sustains the largest alluvial delta on the west USAA coast of North America. Currently, the upper 124°W 120°W Fraser River and its many tributaries drain the Figure 1. Physiography of Fraser Basin showing present-day (white arrows) southward ﬂ ow Coast Mountains and Rocky Mountains before of Fraser River through Fraser Canyon to the Strait of Georgia at Vancouver (British Co- lumbia), and northward (black arrows) paleocurrent directions (Read, 1988; Andrews et al., *E-mail: [email protected]. 2011). Insets show location and hypsometric curve of the basin (asl—above sea level).

© 2012 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. GEOLOGY,Geology, February February 2012; 2012 v. 40; no. 2; p. 111–114; doi:10.1130/G32488.1; 4 ﬁ gures; Data Repository item 2012035. 111 Downloaded from geology.gsapubs.org on January 30, 2012 erosion rates (Shuster et al., 2005; Ehlers et al., deltas separated by the glaciosedimentary Dog 2006). Presumably the origins and history of the Creek Formation (Fig. 2B; Mathews and Rouse, Fraser River were inﬂ uenced by one or more of A 122°W 1986). The dams are asymmetric; subaqueous Chilcotin these processes. 0.812 Ma Paleo-dow lithofacies only occur south of the dam axis. River ±0.0175 N Alkali Creek The lavas are part of the much larger Chilcotin

u EVIDENCE OF DRAINAGE REVERSAL baer 7.2 Ma Group, a basaltic volcanic province that under-

nstream

i Several elements of the geomorphology of ±0.6 al lavas lies much of the Fraser River basin (Mathews, the Fraser Basin are typical of reversed drain- 1989). ages: (1) regional slopes that are not parallel 1.107 Ma The lower portion of this volcanic succes- 1.05101.0588 MaM ±0.050 Dam axes to the channel, (2) barbed drainage patterns, ±0.013 sion was emplaced onto the ancestral Fraser Paleo-upst

(3) bedrock canyons, and (4) elevated terraces HPB delt River valley fl oor at the mouth of the ances- Dog and hanging paleovalleys. These elements are Creek tral Dog Creek tributary (Fig. 2A). Dog Creek described in the following. a was then an ice-free, although recently glaci- 2.79 Ma r The northeastern fl ank of the Coast Moun- ±0.30 eam ated (buried striated surfaces), U-shaped val- tains drains into the Fraser River via the north- ley. The Dog Creek paleovalley is now fi lled Canoe ward-fl owing Chilcotin and eastward-fl owing Creek by an 80-m-thick subaerial lava pile dominated Nechako Rivers (Fig. 1). Northward regional <0.1 MaM by thin (≤5 m thick) pahoehoe and intercalated drainage existed across the southern interior pla- autobreccias. Imbricated stretched vesicles indi- teaus from the Paleocene until at least the Mio- 9.03 Ma cate fl ow along the Dog Creek paleovalley to the cene (Tribe, 2005). Currently, the Fraser River ±0.06 west, into the Fraser River valley. 11.2 Ma fl ows to the south. ±0.4 Mapped vesicle stretching directions diverge A pronounced barbed drainage pattern is within the ancestral Fraser River valley at the formed by the 130° bend of the Fraser River mouth of Dog Creek, indicating north and . (Lay, 1940), where the upper Fraser changes CrC south divergent fl ow of the lava (Fig. 2A), and Bar g Bar Cr from northwestward to southward fl ow north Bii we infer this to be the lava-dam axis. Subaerial FrFraser River of Prince George (Fig. 1) and at the confl uence asa lavas occur northward on the terrace beyond with the Quesnel River (160° bend). Lay (1940) er Alkali Creek (~30 km) where they taper out; used these observations to fi rst propose reversal R stretched vesicles consistently show northward iv of the Fraser River, albeit in the Eocene. eer fl ow. South of Dog Creek, subaerial lavas form a The lower Fraser River is confi ned by the thin (15–20 m), laterally extensive subhorizontal

≤ °N 270-km-long and 1000-m-deep bedrock Fraser sheet extending into Canoe Creek (~15 km), and Canyon between Macalister and Hope (Fig. 1), HighCr. overlain by the Dog Creek Formation; stretched ar

where it is incised into the southern interior pla- Bar Cr. vesicles record southward fl ow of the lavas. 1 teaus and oblique to the Coast Mountains. North 5 The subaerial lavas progressively fed and 010km 222.2 MMa and south of the Fraser Canyon the river mean- 122°W ±0.3 buried a 65-m-thick southward-prograding delta ders within a broad valley. 1.06 Ma lava and delta Terrace outlines of hyaloclastite pillow breccia (Fig. 3A). The Hanging tributaries are associated with a 2.79 Ma lava and delta Basalt flow direction hyaloclastite pillow breccia delta exhibits the prominent terrace along the fl anks of the Fra- Chilcotin Group lavas Selected K/Ar date typical architecture of a volcanic Gilbert-type ser Canyon. The terrace is a ≤4° north-dipping 40 39 delta (Skilling, 2002), with prominent normal- ca. 1.06 Ma volcanic vent New Ar/ Ar date surface, 5–10 km wide, 500 m above the Fraser Present-day Fraser River drainage graded, palagonite-cemented foreset beds of River at Dog Creek (Fig. 2A). We infer this to clast-supported and angular hyaloclastite (pil- be the fl oor of the ancestral Fraser River val- low fragments, glassy pillow rinds, and pillows; ley. The terrace is traceable northward to where B Late Wisconsinan till Fig. 3B). The maximum height of the lava- it merges with the present-day valley between 1.06 Ma volcanic dam impounded lake (65 m) is marked by the passage Quesnel and Prince George (Andrews et al., unconformity Dog Creek Formation - glacial sediments zone between hyaloclastite pillow breccia and Pahoehoe lavas - topset 2011). Paleovalleys hanging 250–750 m above unconformity subaerial lavas (Figs. 2B and 3A; Jones, 1968). Passage zone the present river are typically oriented subparal- The lavas, and hence the dam and delta, were 2.79 Ma lel to the Fraser Canyon, but contain imbricated 20 Hyaloclastite emplaced very rapidly based on: (1) the absence m volcanic sediments indicative of northward fl ow (Rouse pillow breccia dam of intervening erosions surfaces, paleosols, and and Mathews, 1979). Several adjacent paleoval- foresets sediment horizons; and (2) paleomagnetic evi- leys, some of them dated where they are partly Ancestral Fraser River valley floor dence of emplacement during a single period of infi lled by lavas (Fig. 1, black arrows), record Permian phyllite and limestone geomagnetic secular variation, probably ≤1 k.y. northward fl ow across the region in the Miocene (Fig. DR1 in the GSA Data Repository1). and Pliocene (Andrews et al., 2011). Figure 2. A: Geological map of terraces and Following a period of glaciofl uvial erosion lava dams along Fraser Canyon, adapted from Read (1988). K/Ar ages from Mathews and deposition (Dog Creek Formation; Mathews VOLCANIC STRATIGRAPHY (1989), Ar/Ar ages from this study. Inset and Rouse, 1986), a second, upper volcanic suc- Neogene volcanic dams across the ancestral shows positions of dams and their relation- Fraser River valley were fi rst recognized at Dog ships to paleofl ow direction. HPB—hyalo- 1GSA Data Repository item 2012035, paleo- Creek (Fig. 1) by Mathews and Rouse (1986). clastite pillow breccia. B: Graphic log show- magnetic and geochronological data sets, is available ing internal architectures of the 2.79 Ma and online at www.geosociety.org/pubs/ft2012.htm, or on We have mapped in detail and dated the same 1.06 Ma volcanic deltas at of Canoe Creek. request from [email protected] or Documents succession (Fig. 2A); we identify two distinct Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, basaltic lava dams and associated volcaniclastic USA.

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surface dipping gently northward at an elevation 0km 250 A TopTopsetset lalavasvavasas of ~730 masl at Dog Creek; this is similar to the Fraser 80 m Cascadia River PasPPassagesagge zzoneone Pacific present-day valley north of the Fraser Canyon Ocean Coa m s DC

t Mountains 50°N (Andrews et al., 2011). Moreover, the presence of argin Foreland b HPHHPBPB foresetsforesets two hyaloclastite pillow breccia deltas indicates 50°N Omin that two deep (60 m and 10 m) lava-impounded N eca belt 1026 888 elt lakes existed to the south of Dog Creek. This is 1027 1301 Nitinat consistent with northward ﬂ ow of the ancestral Fan Columbia Fraser River at 2.79 Ma and 1.06 Ma; the vol- River 45°N

canic deltas are exclusively on the southern side 45°N Ridge Astoria Juan de Fuca Fan (paleo-upstream) of the lava dams. 130°W 120°W CobCCobble-sizedbleb -s- zedze B HPB Timing of Reversal Figure 4. Simplifi ed map of Cascadia margin depicting post–0.76 Ma course of Fraser The early Pleistocene stratigraphy of the Fra- River to Pacifi c Ocean, submarine Nitinat ser River valley and Fraser Canyon is not under- Fan, and Ocean Drilling Program sites. Fra- PPillowoww stood, in part due to a lack of dateable geologi- ser River is the Nitinat Fan’s only source of cal or morphological units. Our data indicate Proterozoic detritus from central Canadian that reversal of the Fraser River occurred after Cordillera (light gray area). DC—Dog Creek. PPillowow 1.06 Ma, and this is supported by the limited additional relative and absolute age constraints discussed here. The Fraser Canyon dissects the source of the ca. 0.76 Ma or younger Nitinat GraGravel-sizedravve -ss zedz HPHHPBPB 15 cm prevolcanic terrace and both volcanic dams, Fan (Underwood et al., 2005; Kiyokawa and such that the river is now 400 m lower at the Yokoyama, 2009). A pronounced detrital mona- Figure 3. A: 2.79 Ma delta composed of hya- confl uence with Dog Creek. Canyon erosion zite age peak identifi es a distinctive ca. 1.8 Ga loclastite pillow breccia (HPB) overlain by lavas; passage zone represents highstand was most likely in response to knickpoint retreat source within the Fraser Basin (Kiyokawa and of impounded lake. B: Basaltic pillows in and change in river gradient when the Fraser Yokoyama, 2009); Paleoproterozoic basement poorly sorted HPB. River reversed course (e.g., Bishop, 1995). The rocks only occur in the Omineca and Foreland bedrock fl oor of the Fraser Canyon is locally belts in the northern and eastern headwaters of overlain by ca. 24 ka glacial sediments (Hunt- the Fraser Basin (Fig. 4; Gabrielse et al., 1991). cession was emplaced onto the remnants of the ley and Broster, 1994) and rare gravel and sand Distal hemipelagic sedimentation began fi rst. Stretched vesicles in the upper lavas sug- deposits that may be as old as ca. 59−74 ka ca. 1.6 Ma before a sudden transition to meter- gest a vent on the western margin of the ances- (Lian and Hicock, 2001); therefore the Fraser thick sand turbidites between 0.76 and 0.46 Ma tral Fraser River valley opposite Dog Creek Canyon was probably extant by ca. 74 ka. (Su et al., 2000; Chamov and Kurnosov, 2001; (Fig. 2A). The vent location is marked by local- Underwood et al., 2005). The ca. 0.76 Ma age ized scoria in fl oat at the head of a narrow gully, Implications corresponds with the continental-scale marine below which the lavas are well exposed. Flow Our hypothesis can be tested and improved isotope stage 16 glacial event (Jennings et al., of lava diverged about a second dam axis and in several ways. Cosmogenic exposure dating 2007). The implications are that the Fraser River formed thin subaerial lavas to the north and a and 4He/3He thermochronometry (e.g., Schil- had to (1) drain the central and eastern Canadian thin (10 m) subaerial lava-fed hyaloclastite pil- dgen et al., 2010) within the Fraser Canyon Cordillera (Fig. 1), and (2) fl ow to the Pacifi c low breccia delta to the south (Fig. 2). would provide an independent date of the can- Ocean by 0.76–0.46 Ma. This demands reversal yon incision event. We also expect that drainage between 1.06 and ca. 0.76 Ma. 40AR/39AR GEOCHRONOLOGY reversal, independent of canyon incision, should River incision rates can be estimated by mea- New 40Ar/39Ar whole-rock and existing K/Ar be recorded in the downstream and/or marine suring the difference in elevation between two whole-rock ages for basalts in the Fraser Can- sedimentary records. Sudden or rapid initiation dated terraces (e.g., Karlstrom et al., 2007). yon are shown in Figure 2A (for descriptions of a major river draining a sediment-rich conti- The provisional, minimum incision rate at of analytical methodology and samples, see the nental interior would be expected to manifest as Dog Creek between 2.79 Ma and 74 ka was Data Repository). A sample of lava from the a large, contemporaneous, terrigenous sedimen- ~150 m/m.y.; if reversal and canyon incision base of the fi rst dam in Dog Creek yields an tary fan at the mouth of a submarine canyon. occurred at 0.76 Ma, the minimum incision rate age of 2.79 ± 0.3 Ma (Fig. DR2). Lava within This idea has hitherto not been explored with was ~200 m/ m.y. To the best of our knowledge the second dam was sampled on both sides of regard to the Fraser River. these are the fi rst long-term incision rate esti- the Fraser Canyon and yielded ages of 1.107 The Fraser River supplies the large submarine mates for the Fraser River and are comparable ± 0.050 Ma (Fig. DR3) and 1.058 ± 0.013 Ma Nitinat Fan, an ~15,000 km2 sedimentary fan to long-term incision rates in the eastern Grand (Fig. DR4), with a weighted mean of 1.06 fi lling the Cascadia Basin of the Pacifi c Ocean Canyon (Karlstrom et al., 2007) and rivers in the ± 0.15 Ma (Fig. DR5). All errors are 2σ (95% off the coast of Vancouver Island (Fig. 4; Car- Cascade forearc (Stock et al., 2005). confi dence). son, 1973). It is a ≤2.7-km-thick turbidite fan Without reversal of the Fraser River, the deposited on the younger than 8 Ma Juan de 1000 km2 Fraser Delta and Vancouver would not DISCUSSION Fuca abyssal plain (Flueh et al., 1998; Under- exist; instead the area would have been drained wood et al., 2005), where the Strait of Juan de by a multitude of small montane rivers, simi- Paleogeography of the Fraser River Fuca empties westward across the Cascadia lar to the drainage elsewhere along the Coast Our reconstruction of the ancestral Fraser margin through several submarine canyons. Mountains. The Fraser River would instead River valley from mapping of terraces and over- Sediment provenance studies of the turbi- fl ow elsewhere, perhaps across the low drain- lying lavas reveals a ≤10-km-wide, low-relief dite layers indicate that the Fraser River is the age divides (≤50 m) into the adjacent Peace-

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Mackenzie or Columbia River systems (Fig. 1). Chamov, N.P., and Kurnosov, V.B., 2001, Epigen- Mathews, W.H., 1989, Neogene Chilcotin basalts in Our results underline the youthful character of esis of sediments in the Cascadia accretionary south-central British Columbia: Geology, ages, prism, western continental margin of United and geomorphic history: Canadian Journal of the landscape of southwestern British Columbia States: Lithology and Mineral Resources, v. 36, Earth Sciences, v. 26, p. 969–982, doi:10.1139/ and its dramatic geomorphic transformation in p. 445–459, doi:0024–4902/01/3605–0445. e89-078. response to contemporaneous uplift and glacio- Ehlers, T.A., Farley, K.A., Rusmore, M.E., and Mathews, W.H., and Rouse, G.E., 1986, An early fl uvial erosion of the Coast Mountains in the Woodsworth, G.E., 2006, Apatite (U-Th)/He Pleistocene proglacial succession in south- past 2 m.y. (Farley et al., 2001; Shuster et al., signal of large-magnitude accelerated glacial central British Columbia: Canadian Journal of erosion, southwest British Columbia: Geology, Earth Sciences, v. 23, p. 1796–1803, doi:10.1139/ 2005; Ehlers et al., 2006). Hitherto the timing v. 34, p. 765–768, doi:10.1130/G22507.1. e86-165. of the reversal of the Fraser River, incision of Farley, K.A., Rusmore, M.E., and Bogue, S.W., Read, P.B., 1988, Tertiary stratigraphy and indus- the Fraser Canyon, and formation of the Nitinat 2001, Post–10 Ma uplift and exhumation of the trial minerals, Fraser River: Lytton to Gang Fan had not been linked to the uplift and gla- northern Coast Mountains, British Columbia: Ranch, southwestern British Columbia: British Geology, v. 29, p. 99–102, doi:10.1130/0091- Columbia EMPR Open File Report 1988–29, ciofl uvial evolution proposed for the southern 7613(2001)029<0099:PMUAEO>2.0.CO;2. scale 1:50,000. Canadian Cordillera. Flueh, E.R., Fisher, M.A., Bialas, J., Childs, J.R., Rouse, G.E., and Mathews, W.H., 1979, Tertiary We propose, tentatively, that post–2 Ma uplift Klae schen, D., Kukowski, N., Parsons, T., geology and palynology of the Quesnel area, of the Coast Mountains, combined with glacio- Scholl, D.W., ten Brink, U., Tréhu, A.M., and British Columbia: Bulletin of Canadian Petro- Vidal, N., 1998, New seismic images of the leum Geology, v. 27, p. 418–445. fl uvial erosion ca. 0.76 Ma, encouraged bedrock Cascadia subduction zone from cruise SO108— Schildgen, T.F., Balco, G., and Shuster, D.L., 2010, incision throughout southern British Columbia, ORWELL: Tectono physics, v. 293, p. 69–84, Canyon incision and knickpoint propagation leading to capture of the upper ancestral Fra- doi:10.1016/S0040-1951(98)00091-2. recorded by apatite 4He/3He thermochronome- ser River by a south-fl owing stream within the Gabrielse, H., Monger, J.W.H., Wheeler, J.O., and try: Earth and Planetary Science Letters, v. 293, Coast Mountains. Further studies are required to Yorath, C.J., 1991, Part A. Morphogeological p. 377–387, doi:10.1016/j.epsl.2010.03.009. belts, tectonic assemblages, and terranes, in Shuster, D.L., Ehlers, T.A., Rusmore, M.E., and understand the process of reversal (e.g., stream Gabrielse, H., and Yorath, C.J., eds., Geology Farley, K.A., 2005, Rapid glacial erosion at capture) and how it was triggered. of the Cordilleran orogen in Canada: Geo- 1.8 Ma revealed by 4He/ 3He thermochronom- logical Survey of Canada Geology of Canada, etry: Science, v. 310, p. 1668–1670, doi:10.1126/ CONCLUSIONS no. 4, p. 15–28. science.1118519. Huntley, D.H., and Broster, B.E., 1994, Glacial Lake Skilling, I.P., 2002, Basaltic pahoehoe lava-fed del- We mapped and dated a pair of volcanic dams Camelsfoot: A Late Wisconsinan advance tas: Large-scale characteristics, clast genera- rapidly emplaced into the ancestral Fraser River stage proglacial lake in the Fraser River valley, tion, emplacement processes and environmental valley. Our results confi rm reversal of the Fra- Gang Ranch area, British Columbia: Canadian discrimination, in Smellie, J.L., and Chapman, ser River to a southward drainage and erosion of Journal of Earth Sciences, v. 31, p. 798–807, M.G., eds., Volcano-ice interaction on Earth and the Fraser Canyon since 1.06 Ma. The subma- doi:10.1139/e94-073. Mars: Geological Society of London Special Huscroft, C.A., Ward, B.C., Barendregt, R.W., Jack- Publication 202, p. 91–113. rine Nitinat Fan most likely formed in response son, L.E., and Opdyke, N.D., 2004, Pleistocene Stock, J.D., Montgomery, D.R., Collins, B.D., Diet- to the reversal and the sudden increase in ter- volcanic damming of Yukon River and the rich, W.E., and Sklar, L., 2005, Field measure- rigenous sediment supply; based on its internal maximum age of the Reid Glaciation, west- ments of incision rates following bedrock ex- stratigraphy we suggest that reversal occurred central Yukon: Canadian Journal of Earth Sci- posure: Implications for process controls on the ences, v. 41, p. 151–164, doi:10.1139/e03-098. long profi les of valleys cut by rivers and debris ca. 0.76 Ma. Uplift and glaciations in the Pleisto- Jennings, C.E., Aber, J.S., Balco, G., Barendregt, R., fl ows: Geological Society of America Bulletin, cene likely increased erosion rates signifi cantly, Bierman, P.R., Rovey, C.W., Roy, M., Thorleif- v. 117, p. 174–194, doi:10.1130/B25560.1. encouraging a drainage modifi cation process that son, L.H., and Mason, J.A., 2007, Glaciations: Su, X., Baumann, K.H., and Thiede, J., 2000, Calcar- led to capture and reversal of the Fraser River. Mid-Quaternary in North America, in Elias, eous nannofossils from Leg 168: Biochronol- S.A., ed., Encyclopedia of Quaternary science, ogy and diagenesis, in Fisher, A., et al., eds., Volume 2: Amsterdam, Elsevier, p. 1044–1051. Proceedings of the Ocean Drilling Program, ACKNOWLEDGMENTS Jones, J.G., 1968, Intraglacial volcanoes of the Scientifi c results, Volume 168: College Station, We thank the Hancock family and the Dog Creek Laugarvatn region, south-west Iceland: Geologi- Texas, Ocean Drilling Program, p. 39–49. and Canoe Creek First Nations for their hospitality. cal Society of London Quarterly Journal, v. 124, Swain, L.G., and Holms, G.B., 1985, Ambient wa- Janet Garbites and Brian Jicha provided the Ar/Ar p. 197–211, doi:10.1144/gsjgs.124.1.0197. ter quality assessment and objectives for the analyses. Comments from Bert Struik, Bob Ander- Karlstrom, K.E., Crow, R.S., Peters, L., McIntosh, Fraser River sub-basin from Kanaka Creek to son, Dave Huntley, Lisel Currie, Dorothy Merritts, W., Raucci, J., Crossey, L.J., Umhoefer, P., and the mouth: British Columbia Ministry of Envi- and reviews by John Smellie, Ryan Crow, and two Dunbar, N., 2007, 40Ar/39Ar and fi eld studies of ronment Water Management Branch Resource anonymous reviewers greatly improved the manu- Quaternary basalts in Grand Canyon and model Quality Section Overview Report, 226 p., script. Funding provided by the Geological Survey of for carving Grand Canyon: Quantifying the in- http://www.env.gov.bc.ca/wat/wq/objectives/ Canada’s Targeted Geoscience Initiative 3 Program. teraction of river incision and normal faulting fraserkanaka/fraserkanaka.html. 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Printed in USA

114 GEOLOGY, February 2012