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Research Paper THEMED ISSUE: Tectonic, Sedimentary, Volcanic, and Fluid Flow Processes along the Queen Charlotte–Fairweather Fault System and Surrounding Continental Margin

GEOSPHERE Late Quaternary sea level, isostatic response, and sediment

GEOSPHERE, v. 17, no. 2 dispersal along the Queen Charlotte fault

1 2,3 1 4 https://doi.org/10.1130/GES02311.1 J. Vaughn Barrie , H. Gary Greene , Kim W. Conway , and Daniel S. Brothers 1Geological Survey of Canada–Pacific, Institute of Ocean Sciences, P.O. Box 6000, Sidney, British Columbia V8L 4B2, Canada 2SeaDoc Tombolo Mapping Laboratory, Orcas Island, Eastsound, Washington 98245, USA 9 figures; 1 table 3Center for Habitat Studies, Moss Landing Marine Laboratories, Moss Landing, California 95039, USA 4Pacific Coastal and Marine Science Center, U.S. Geological Survey, Santa Cruz, California 95060, USA CORRESPONDENCE: [email protected] ABSTRACT Alexander Archipelago are exposed to an extreme wave regime (Thomson, CITATION: Barrie, J.V., Greene, H.G., Conway, K.W., and Brothers, D. S., 2021, Late Quaternary sea level, 1981, 1989). In addition to being an exposed high-wave-energy environment, isostatic response, and sediment dispersal along the The active Pacific margin of the Haida Gwaii and southeast Alaska has the area has also undergone dramatic sea-level fluctuations and is the most Queen Charlotte fault: Geosphere, v. 17, no. 2, p. 375– been subject to vigorous storm activity, dramatic sea-level change, and active seismically active area in Canada. With limited access and the energetic shore- 388, https://doi.org/10.1130/GES02311.1. tectonism since glacial times. Glaciation was minimal along the western shelf line, these shores have been, and are, relatively uninhabited, and some marine margin, except for large ice streams that formed glacial valleys to the shelf areas are not yet charted. Science Editor: Shanaka de Silva break between the major islands of southeast Alaska and Haida Gwaii. Upon Just offshore is the Queen Charlotte–Fairweather fault system, a major

Received 6 July 2020 deglaciation, sediment discharge was extensive, but it terminated quickly due to structural feature that extends from the Explorer triple junction, south of the Revision received 15 September 2020 rapid glacial retreat and sea-level lowering with the development of a glacio-iso- islands, to well into the bight of the Gulf of Alaska (Fig. 1). The transform Accepted 14 December 2020 static forebulge, coupled with eustatic lowering. Glacial sedimentation offshore boundary is split into two primary faults: the northern 300 km section is defined ended soon after 15.0 ka. The shelf became emergent, with sea level lowering by, by the transpressional Fairweather fault, which extends southward from Yaku- Published online 19 January 2021 and possibly greater than, 175 m. The rapid transgression that followed began tat along the western front of the Fairweather Range to Icy Point; the fault then sometime before 12.7 ka off Haida Gwaii and 12.0 ka off southeast Alaska, and steps offshore at Icy Point, takes an ~25° clockwise bend (~340°), and becomes with the extreme wave-dominated environment, the unconsolidated sediment the Queen Charlotte fault. This system represents a major transform boundary that was left on the shelf was effectively removed. Temperate carbonate sands that separates the Pacific plate from the North American plate, similar to the make up the few sediment deposits presently found on the shelf. San Andreas fault system of California (Atwater, 1970; Plafker et al., 1978). The The Queen Charlotte fault, which lies just below the shelf break for most of length of the Queen Charlotte–Fairweather fault system is 1330 km, slightly its length, was extensively gullied during this short period of significant sed- longer than the San Andreas fault, with a reported width of 1–5 km, and ~75% iment discharge, when sediment was transported though the glacial valleys of the length is located offshore (Carlson et al., 1985). Recently, most of the and across the narrow shelf through fluvial and submarine channels and was offshore fault zone from south of Haida Gwaii through southeastern Alaska deposited offshore as sea level dropped. The Queen Charlotte fault became the has been imaged in detail using multibeam echosounder (MBES) data and western terminus of the glacio-isostatic forebulge, with the fault acting as a other geophysical techniques that have documented the fault morphology hinged flap taking up the uplift and collapse along the fault of 70+ m. This may and identified features associated with localized deformation along the fault have resulted in the development of the distinctive fault valley that presently (step-overs), submarine canyons, gullies, and submarine slides adjacent to the acts as a very linear channel pathway for sediment throughout the fault system. fault (Barrie et al., 2013; Brothers et al., 2019; Greene et al., 2019). Based on this high-resolution data, a better understanding of plate tectonics and Quaternary sedimentary processes can be realized for this region of ■■ INTRODUCTION the Pacific Northwest. Because the physiography of this continental margin is shaped by the complex interplay between tectonic and sedimentary processes, The western shores of the Haida Gwaii archipelago (formally the Queen which often alternate between periods dominated by constructional (sediment Charlotte Islands) off the northwestern coast of British Columbia (Canada) and delivery and progradation) or destructional (erosion, slope failure, canyon inci- the Alexander Archipelago of southeast Alaska are distinctly rugged with little sion, retrogression, and fault displacement) geomorphic processes, it is now refuge from the North Pacific Ocean (Fig. 1). George Dawson described this possible to provide an interpretive chronology through the late Quaternary. This paper is published under the terms of the coast from his 1878 expedition as having steep rocky sides with little or no Our objective here is to document how the last glaciation and subsequent CC‑BY-NC license. beach and bold water (Dawson, 1878). Indeed, western Haida Gwaii and the sea-level changes have impacted the present morphology of the central and

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southern Queen Charlotte fault, and in turn, how the Queen Charlotte fault has impacted the sea-level history and Quaternary sedimentary processes along this portion of the Queen Charlotte fault margin, subsequent to the last Icy Point 1800 Depth (m) 30 glaciation. The exceptional preservation of faulted geomorphic features along the plate boundary fault provides an unprecedented opportunity to study the fault behavior over many earthquake cycles in a high-latitude Quaternary glacial marine setting. In addition, knowledge of the late Quaternary Pacific Northwest coastal environment provides insight into the viable pathway for early humans as they colonized the Americas (Lesnek et al., 2018).

Baranoff ■■ REGIONAL SETTING Island

Queen Charlotte Fault System Fig. 9

The Queen Charlotte fault is a near-vertical fault zone that is seismically 2013 Alaska active down to ~21 km (Hyndman and Ellis, 1981) with a mainly right-lat- Mw 7.5 eral transform motion of ~50–60 mm/yr (Prims et al., 1997; Rohr et al., 2000). Recently, Brothers et al. (2020) analyzed submarine tectonic geomorphology and suggested that the Queen Charlotte fault itself accommodates the majority Dixon Fig. 7 of relative plate motion (48–55 mm/yr). In contrast to the predominately strike- Entrance slip motion along the central and northern portions of the Queen Charlotte fault zone, plate motion along the southern portion is more oblique, with up to 20° of

B 1949 C

r convergence up to central Haida Gwaii (Hyndman and Hamilton, 1993). Because o Mw 8.1 i

t l Fig. 4

i u

m of the high slip rates along the fault, the Queen Charlotte fault tends to rupture Haida h

frequently in large earthquakes. During the past 100 yr, seven earthquakes of i Gwaii a Fig. 3 Mw 7.0 or greater have occurred along the Queen Charlotte fault (Fig. 1), includ-

H S

t ing the 1949 Mw 8.1 earthquake off northern Haida Gwaii, Canada’s largest e

c a

recorded earthquake (Bostwick, 1984). More recently, a Mw 7.8 thrust event 2012 t

near southern Haida Gwaii in 2012 (Lay et al., 2013) and a Mw 7.5 strike-slip Mw 7.8 Fig. 5 event west of Craig (Fig. 1) suggested there are dramatic differences in plate boundary mechanics due to an increasing component of convergence to the Fig. 2 south (Lay et al., 2013; Hyndman, 2015; Tréhu et al., 2015; Brothers et al., 2020).

Figure 1. Multibeam swath bathymetric image and coastal outline of northwestern Glacial History British Columbia, Canada, and southeastern Alaska, USA, adjacent to the Queen Charlotte fault. Figure shows historical large earthquakes greater the Mw 7.0 and the locations of Figures 2, 3, 4, 5, 7, and 9. In the late Quaternary, a glacier from the massive Cordilleran ice sheet extended westward across northern Hecate Strait and through Dixon Entrance and coalesced with ice from Haida Gwaii, deflecting it westward within Dixon Entrance (Sutherland-Brown, 1968; Barrie and Conway, 1999; Mathewes and south parallel to the coast (Shaw et al., 2019). A minimum ice thickness of Clague, 2017). This coalescence was probably short-lived (Clague, 1989). Ice 400 m is suggested for some shelf areas (Josenhans et al., 1995; Barrie and also moved south down the central trough in Hecate Strait (Barrie and Born- Conway, 1999), and an ~690 m thickness is suggested in the northern Hecate hold, 1989; Shaw et al., 2019) and coalesced with ice flowing through the Strait and Dixon Entrance (Hetherington et al., 2004). Off southeastern Alaska, troughs of Queen Charlotte Sound south of Haida Gwaii to the shelf break ice is considered to have reached the shelf break, particularly down the sea (Luternauer and Murray, 1983; Luternauer et al., 1989; Hicock and Fuller, 1995; valleys such as Chatham Strait, though many areas off the Alexander Archi- Josenhans et al., 1995, 1997). The Hecate Glacier was 20 km wide and flowed pelago (Prince of Wales and Baranof Islands) are considered to never been

glaciated, similar to Haida Gwaii (Kaufman and Manley, 2004; Carrara et al., Josenhans et al., 1995). Eustatic sea-level rise, coupled with subsidence of a 2007; Lesnek et al., 2018, 2020; Brothers et al., 2020). Glaciation reached its glacio-isostatic forebulge (Clague, 1983; Luternauer et al., 1989), resulted in maximum extent sometime after 23.0 ka (Blaise et al., 1990). sea levels rising very rapidly, reaching the present shoreline on Haida Gwaii On Haida Gwaii, small ice caps and piedmont glaciers, up to 500 m thick, by ca. 10.5–9.6 ka (Clague et al., 1982b; Fedje et al., 2005). Sea levels reached developed that were independent of the Cordilleran ice sheet (Clague et al., a plateau at 15–13 m above current levels 8.2–4.8 ka and have been falling up 1982a; Clague, 1983). There may have been ice-free areas on the islands and on until the present (Clague et al., 1982b; Josenhans et al., 1997; Fedje et al., 2005). the coastal lowlands of northern Haida Gwaii where glaciation was minimal and Sea-level fluctuations on the outer coast of the Alexander Archipelago of of short duration (Clague et al., 1982a; Clague, 1989; Mathewes and Clague, 2017). southeast Alaska resemble the pattern at Haida Gwaii to the south, although The limited size and extent of the Queen Charlotte Mountain source areas and the marine dates are few (Shugar et al., 2014). A wave-cut terrace at 165 m water proximity of deep water of the open Pacific Ocean, Dixon Entrance, and Queen depth off the west coast of the Prince of Wales and Baranof Islands (Carlson, Charlotte Sound limited expansion of ice on the Haida Gwaii islands (Clague, 2007) may correspond to the lowstand seen off Haida Gwaii. Baichtal et al. 1981, 1989; Warner et al., 1982; Barrie et al., 1993; Barrie and Conway, 1999). (2017a, 2017b) suggested that a peripheral forebulge developed west of the Based on evidence of low-level cirques along the coast as well as glacial ice front, similar to Haida Gwaii, starting at 16.9 ka, with most of the marine striae, Sutherland-Brown (1968) suggested that ice moved out onto the shelf, areas being deglaciated by 14.5 ka. Terraces mapped from multibeam bathym- off western Haida Gwaii, and formed a small ice shelf. However, Clague (1989) etry can be seen at 165–180 m water depth (Baichtal et al., 2017b). In addition, implied that the ice extent was limited and that some areas of the shelf could pahoehoe (subaerial) lava flows occur at water depths of 160 m offshore have been free of ice during the last glaciation. Further, based on recent data, (Baichtal et al., 2017b). Within the island archipelago, sea level reached the no evidence exists for diamicton deposition, and no identifiable glacial or highest levels of between 65 and 190 m sometime after 13.5 ka (Carlson and deglaciation features exist, such as iceberg scours and boulders, which are Baichtal, 2015; Baichtal et al., 2017a, 2017b). usually common in glaciated areas. It is quite probable, therefore, that the west coast of Haida Gwaii had little to no ice cover during the last glaciation. The glaciation along the Pacific North Coast terminated with rapid climatic ■■ DATA ACQUISITION amelioration, resulting in rapid retreat and melting of the ice. Glaciers had retreated from the lowland areas of Haida Gwaii beginning around 17.0 ka (War- Multibeam swath bathymetry was acquired off the west coast of Haida Gwaii ner et al., 1982), but mountain valleys and cirques probably supported remnant between 2009 and 2010, and in the Dixon Entrance area in 2017 (Barrie et al., ice masses until much later (Clague et al., 1982a; Clague, 1989; Mathewes and 2018) using a hull-mounted, Kongsberg 0.5° × 1.0° EM710™, dual-swath, mul- Clague, 2017). Offshore, glacial retreat began off the western margin some- tisector stabilization, chirp-pulse, high-definition beam-forming system, which time after 17.0 ka and possibly as early as 18.1 ka (Darvill et al., 2018). Ice had operated at a frequency of 70–100 kHz. The surveys were carried out from the largely left the lowlands and offshore region by 14.5–13.0 ka (Barrie and Con- Canadian Coast Guard Ship (CCGS) Vector at a survey speed of 10 knots by the way, 1999; Hetherington et al., 2004). Off southeast Alaska, the initial retreat Canadian Hydrographic Service, in cooperation with the Geological Survey of of marine-terminating ice margins from their maximum extent was driven by Canada. The tracks were positioned so as to insonify 100% of the seafloor with factors acting on the ice-ocean interface, including sea-level rise and ocean 50%–100% overlap. Positioning was accomplished with a broadcast differen- warming, leading to intense ice loss via calving in the early stages of degla- tial global positioning system (GPS), and the multibeam data were corrected ciation (Lesnek et al., 2018, 2020). for sound velocity variations in the stratified water column using sound speed casts. The data were edited for spurious bathymetric and navigational points and subsequently processed using CARIS® software. Similarly, multibeam swath Sea-Level History bathymetry was collected off southeastern Alaska between 2009 and 2018; data acquisition methods were summarized by Brothers et al. (2020). All multibeam Relative sea-level curves developed for specific locations along the Pacific data were gridded at 5 m resolution, exported as ASCII files, and imported into margin differ from each other, reflecting complex glacially induced crustal dis- ArcInfo® software for analysis and image production. Hillshade relief surfaces placement. Using geospatial interpolation combined with site-specific relative were created with a solar azimuth of 315°, solar zenith of 45°, and vertical exag- sea-level data, Hetherington et al. (2003) generated a model of glacially induced geration of 2×. The beam-forming feature of the EM710 multibeam system crustal displacement for 500 yr time intervals between 14.2 and 8.7 ka along reduces the footprint at nadir to around 5 m at 400 m water depth and ~13 m at the northern section of Canada’s Pacific margin. On the eastern side of the 1000 m water depth. Thus, by gridding the data at 5 m, the data are undersam- Haida Gwaii, sea level fell by more than 150 m between ca. 15.0 and 13.0 ka pled above 400 m and oversampled at depths greater than 400 m water depth. (Hetherington et al., 2004; Barrie and Conway, 2002a), with large areas adjacent An initial geophysical and sampling survey was undertaken using the to eastern Haida Gwaii being subaerially exposed (Fedje and Josenhans, 2000; CCGS John P. Tully in 1995, during which 600 km of 500 Joule Huntec DTS™

high-resolution boomer seismic-reflection and 120 kHz Simrad side-scan sonar all seismic-reflection survey lines collected from the continental shelf off west- profiles were collected along the narrow continental shelf off western Haida ern Haida Gwaii is that there is little to no Quaternary sediment, only bedrock Gwaii and into Dixon Entrance, which allowed for penetration depths up to (Figs. 2, 3, 4, and 5). Even the inlets that are open to the Pacific Ocean with a 100 m (Barrie and Conway, 1996). In addition, a Benthos™ piston corer was muted or no sill at the entrance are predominantly floored by bedrock. The bed- used to collect seafloor sediment (13 cores) in two inlets in central Haida Gwaii rock geology of the onshore areas adjacent to the shelf and enclosing the inlets and within small nearshore basins off the southern Haida Gwaii archipelago. of Haida Gwaii is a diverse assemblage of Jurassic to Tertiary rocks (Anderson Initial interpretations of the survey data and cores collected in Rennell Sound and Reichenbach, 1991). On northern Haida Gwaii, Masset Formation basalt were reported in Barrie and Conway (1996), while results of findings from other cores and radiocarbon dates from Rennell Sound are presented here. A full investigation of the southern and central parts of the Queen Charlotte transform fault system was undertaken using the CCGS John P. Tully in Sep- tember 2015 and in 2017 along the full length of the Queen Charlotte fault to determine fault geometry and activity. A Knudson™ low-power, 12 element, 3.5 kHz, high-resolution CHIRP seismic-reflection profiling system was used to image the subsurface stratigraphy and to select sampling sites in both years. In 2017, a multichannel seismic-reflection survey collected 250 km of data with a U.S. Geological Survey (USGS) Sig2mille™ 1 kJ, 400–1000 Hz sparker system using a 48 channel, solid-core Geometrics Geoeel™ six-section hydrophone streamer with 16 hydrophones spaced 1.6525 m in the first two sections and 32 hydrophones spaced 3.125 m in the trailing sections (four sections). A large (0.75 m3) IKU grab sampler and a Benthos™ piston corer were used to collect seafloor sediment, and a GSC 4K underwater drop camera Channel system was used to photograph the seafloor. All cores were run through a Geotek™ Multi-Scan Core Logger (MSCL), which measured density, velocity,

and magnetic susceptibility. The cores were split, examined, described, and QCF Channel subsampled at the Geological Survey of Canada (Pacific) laboratory in Sidney, British Columbia. Split cores were run through the Royal Roads University Paleo-shoreline MSCL-XZ to collect high-resolution magnetic susceptibility and image data, 201504-01 including bulk density (by gamma-ray attenuation measurements) and P-wave 201504-03 201504-02 velocities. All shell material identified from visual and multiscan images considered large enough for radiocarbon dating were collected. Interpretation of the seismic-reflection data was undertaken using both the Knudson Post Survey and the Kingdom Suite® software packages. Multibeam bathymetry from the central coast of Haida Gwaii and off Dixon Entrance was presented in Greene et al. (2019), along with interpretation of cores collected within these blocks. All other data collected during these surveys are presented here. In addition, detailed multibeam bathymetry images that are not presented here were published in Brothers et al. (2019, 2020). 201702-65

■■ RESULTS 2000 Depth (m) 50

Morphology of the Central and Southern Queen Charlotte Fault Zone Figure 2. Multibeam swath bathymetry image of the southern continental shelf off Haida Gwaii (Fig. 1) showing the subaerial channels to the paleocoastline at ~175 m water depth. Locations of the nine carbonate cores are shown as black dots, and a seabed photograph The continental shelf off Haida Gwaii north to Dixon Entrance is narrow, adjacent to one of the core sites illustrates the skeletal nature of the carbonate deposits. In extending only 4 km off Cape St. James in the south to 25 km near the Cana- addition, the locations of cores described in Figure 6 are shown (yellow dots). Two volcanic da–U.S. boundary in the north. The striking observation from the MBES and cones with methane vents, just seaward of the Queen Charlotte fault (QCF), are highlighted.

133o 30’ W 133o 10’ W 133o 40’ W 0 4 km

201504-23 N B

30’

53 201504-25 A Sag Pond 201504-27 201504-26 Sediment Seal Transport Inlet Divide

’ D Rennell Sound 0

53 Sediment 201102-31

Sag Pond Pockmark Field C Transport 0 2000 m Divide TUL95B-05 201102-34 1600 Depth (m) 275 201504-15

) A B

Submarine -280 m

( -290

s r

Slide h -300

e t

t -310

e p

-320 e Sag Pond M

-330 D 201504-21 0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000 2,200 2,400 C DistanceMeters (m) D Sag Pond N 400

00’

)

(

’

Submarine 0

Dune Field o 460 53 0 500 m 0 6 km 1600 Depth (m) 100 Figure 4. Multibeam swath bathymetry image of the Queen Charlotte fault off Figure 3. Multibeam swath bathymetry image of the Queen Charlotte fault off central Haida north-central Haida Gwaii (Fig.1) illustrating the sediment transport pattern within Gwaii (Fig. 1) illustrating the sediment transport pattern within the fault valley, including the fault valley and bathymetric high point of the fault where the seafloor is signifi- submarine dune field at one of the escape points along the fault, and the location of the cantly disturbed by gas. Profiles are denoted across the disturbed seafloor, showing strike-slip right-step offsets (sag ponds) along the fault. In addition, the channel system the fault valley and a 3.5 kHz CHIRP profile of the same disturbed seafloor adjacent from Rennell Sound to the fault is shown (red line). Locations of cores collected are shown, to the northern extreme of the right-step basin (sag pond). An extensive pockmark and those highlighted in the text are identified. field is visible on both sides of the fault.

132o 20’ W 132o 00’ W

Queen Charlotte Fault

’

52 Tasu Channel

Figure 5. Multibeam swath bathymetry image of Tasu Inlet off central Haida Gwaii (Fig. 1) showing the subaerial channel exiting the inlet and submarine

Sea Level Lowstand channel that crosses from the lowstand

T paleocoastline at ~175 m water depth

s to the Queen Charlotte fault. Notice the

N parallel fault (Tasu fault) within the inlet.

’

1900 Depth (m) 60

predominates (Hickson, 1991), and in the south, plutonic Jurassic and Tertiary of seafloor faulting is more difficult (e.g., Fig. 2; Brothers et al., 2020). A 4 km volcanic rocks occur (Anderson and Reichenbach, 1991). Sparse mobile coarse transpressional step-over wraps around the eastern flank of a seamount (Rohr, sediment occurs in the small depressions formed by the rough igneous bedrock 2015) and then immediately takes a 3 km transtensional step that extends south offshore (Fig. 2). The pattern of exposed bedrock is characteristic of all areas almost to the southern end of Haida Gwaii (Brothers et al., 2020). Just offshore, of the shelf surveyed, except the shelf off Dixon Entrance and within protected two distinctive cones occur (Fig. 2), both of which have significant plumes fjords and inlets, where mixed deposition predominates. extending 500 m up into the water column. These plumes have been identified Tréhu et al. (2015) and Brothers et al. (2020) broadly divided the Queen on three surveys in 2011, 2015, and 2017 with little change. Samples collected Charlotte fault into three sections based on predicted magnitude of oblique from the small craters at the top of the cones consist of carbonate crusts near convergence, crustal-scale seismic-reflection profiles, and the MBES data. the multiple vents and large boulders, primarily vesicular basalts. Radiocarbon For the central and southern sections of the fault, the Queen Charlotte fault is dates from shells taken from the carbonate crust fragments (201702–65; Fig. 2) located below the shelf break in water depths of between 500 and 2200 m. The varied between 23,080 and 21,880 14C yr B.P. (25.0 ka). slope above the fault is dominated by small canyons and gullies that mostly The multibeam sonar bathymetry data revealed evidence of a fault valley terminate at the fault (Harris et al., 2014). South of 53°8′N, talus fans have with small depressions on the upper slope primarily within the central section formed at the mouths of the largest canyons in a trough that occurs between of the fault (Figs. 3 and 4). The depressions form where strike-slip right-step the Queen Charlotte terrace and the fault zone (Harris et al., 2014; Hyndman, offsets have realigned the fault due to oblique convergence (Barrie et al., 2013). 2015; Brothers et al., 2020). North of this, the canyons and gullies enter the The en echelon right-step offsets or pull-aparts result in subsiding basins northward-shallowing fault valley from both sides, returning to a gentler slope (grabens) up to 700 m in length (Fig. 3). Multibeam mapping completed in with displaced gullies and canyons crossing the fault north of 54°N. 2017 (Barrie et al., 2018) revealed a larger basin (sag pond), 1.0 km in width Based on the MBES data, the boundary between the central and southern and 4.0 km in length, with a right-step of 1.0 km (Fig. 3). This shift of the fault sections happens at 53°5′N, where the Queen Charlotte fault bends to the east. occurs 14 km south of the predicted epicenter of the 1949 Mw 8.1 earthquake. South of this, the linear fault extends parallel to the Haida Gwaii coastline along Just north of the epicenter (25 km), the Queen Charlotte fault steps to the right the upper slope just below the shelf break less than 10–15 km off southern (30 m) within another basin, and beyond its northern terminus, it is bounded Haida Gwaii. South of ~52°23′N, the deformation is distributed, and mapping by a very rough seafloor surrounded with numerous pockmarks (Fig. 4). The

rough surface is a result of significant gas expulsion along and immediately 201504–02 were collected just seaward of the fault. The upper unit in both adjacent to the Queen Charlotte fault, based on the seismic-reflection data. cores is olive-gray silty fine bioturbated sand (62 cm in core 201504–01 and The disturbed area occurs at a high point (300 m water depth) along the cen- 172 cm in core 201504–02), which overlies olive-gray laminated silt (Fig. 6). A tral portion of the fault and extends for 10 km with a disturbed zone width of radiocarbon date within the lower unit of core 2 is 15,981 k.y. B.P. (Table 1). 1.4 km adjacent to the fault on either side (Fig. 4). Like the previous two cores, core 201504–03, on the landward side of the fault

Sediment Transport Pattern 201504-03 201504-02 201504-01 201504-26 0 Void Void Sediment moving off the shelf onto the upper slope is trapped within the fault valley for the greater part of the 1200 km of the offshore portion of the Queen 20 Charlotte fault system. As a result, there are few outlets past the fault valley further down the slope. For example, off central Haida Gwaii, there are only four

primary outlets that cross the fault, usually at one of the step-over basins. Small 40 fans have developed downslope of each these outlets (Figs. 3 and 4). Where

the surface trace of the fault reaches 600 m water depth, there is a sediment e

transport divide, with sediments south of this moving south down the fault val- 60 i

ley and sediments north of this moving in the opposite direction (Fig. 3). This 13,090 yr. u pattern is repeated again in the area of the highly disturbed gas expulsion area, BP T at the shallowest point of the fault (300 m water depth) off Haida Gwaii (Fig. 4). 80 Submarine channels mapped from the coast of Haida Gwaii to the shelf break and into the canyon system often align with these sediment transfer

100 silt Lithology clay f.sand c.sand m.sand outlets out of the fault valley. For example, at the narrow entrance of Tasu f.gravel Inlet off southern Haida Gwaii, a channel imaged in the MBES bathymetry silt

Lithology clay f.sand c.sand m.sand f.gravel can be seen crossing the narrow shelf until it reaches the Queen Charlotte 120 fault (Fig. 5). A dominant feature of the continental shelf off western Haida

Gwaii is the occurrence of channels (10–25 m deep) seaward of all the major Core Depth (cm) Depth Core inlets (Barrie and Conway, 1996), with the Rennell Sound channel being the 140 largest (Fig. 3). These channels are cut into bedrock and are characteristic of Bioturbation fluvial channels in dimension and shape (widths of 300–800 m), but they are Shell presently devoid of any sediment other than a thin layer of mobile sand. Our 160 Gravel interpretation is that all these channels represent sea-level lowstand fluvial Lamination channels discharging glacial meltwater to the shelf break across a narrow and Sand Clast 180 relatively flat coastal plain. On the very narrow continental shelf off southern Haida Gwaii, a coastal plain is evident in MBES bathymetry, with channels

that bifurcate and drain both into Hecate Strait to the east and into the Pacific 200 Ocean, directly into a submarine canyon system (Fig. 2). Here, the sea-level lowstand is evident by the wave-cut terrace along Hecate Strait that continues around the southern end of the Haida Gwaii archipelago to the Pacific margin, 220 where the lowstand terrace forms the shelf break. This base of the wave-cut 15,981 yr. BP lowstand terrace is at ~175 m water depth. silt

Lithology clay f.sand

240 c.sand m.sand f.gravel silt

Lithology clay f.sand c.sand m.sand f.gravel Core Sedimentology Figure 6. Schematic diagrams of representative cores adjacent to the Queen Charlotte fault. Cores 201504–01, 201504–02, and 201504–03 were collected on both sides of the At the southern extreme of the fault zone, just south of Haida Gwaii, fault at its southern extreme (Fig. 2), and core 201504–26 was collected adjacent to the three cores were collected adjacent to the fault (Fig. 2). Cores 201504–01 and fault off north-central Haida Gwaii (Fig. 3). Lithology: f—fine, m—medium, c—coarse.

(Fig. 6), contains the same two units with a radiocarbon date of 13,090 k.y. B.P. TABLE 1. RADIOCARBON AGES O SAPLES RO AREA (Table 1) in the laminated silt unit. Below this, a 23 cm gravel unit is under- AROND HAIDA GWAII DISCSSED IN TET lain by a gray mud with highly disturbed laminations to the base of the core. Core Water Sample Dated 14C age Calibrated Lab no. Over the central portion of the fault zone, some 12 cores were collected. depth depth specimen yr B.P. age CAS m cm cal. yr B.P. Greene et al. (20189) described seven cores off central Haida Gwaii near Cart- wright Canyon, including five cores collected within a 6-km-long and 3-km-wide TL95B05 152 31 Wood 11,290 60 11,241 33927 rift ridge submarine slide (Fig. 3). Cores collected near the fault are dominated TL95B05 152 116 Wood 11,820 60 11,780 33928 TL95B05 152 226 Wood 12,380 60 12,639 33929 by dense sand and mud units that may have been compacted by seismic shak- TL95B05 152 244 Coperella 12,360 60 12,606 33796 ing throughout the late Pleistocene and early Holocene (Greene et al., 2019). TL95B05 152 440 Wood 12,340 60 12,564 26280 One core just beyond the slide (core 201504–21; Fig. 3) consists of a thin fine 201504‑02 1770 232 Shell 14,095 35 15,981 167530 sand unit with an erosional lower boundary that overlies dark-gray laminated 201504‑03 1665 71 Shell 12,005 30 13,090 167531 clay with minor gravel (Fig. 6). This lower unit is interpreted to be glaciom- 201504‑23 476 15 Shell 13,460 35 15,052 167541 arine. The ages of the sediments from all these cores range from 50,377 k.y. 201504‑38 165 340 Shell 3580 20 2976 167544 201504‑39 174 276 Shell 6500 25 6627 167545 B.P. to 15,034 k.y. B.P. Greene et al. (2019) suggested, based on these dates, 201504‑39 174 386 Shell 10,955 25 11,815 167546 that sediments younger than 15.0 ka are rare due to significant sedimentation 201504‑39 174 412 Shell 10,710 25 11,315 167547 shutdown after this early stage of deglaciation. Two cores collected within 201504‑41 137 33 Shell 3825 20 3293 167548 the fault in 2011 showed similar results (Barrie et al., 2013). Core 201102–32 201504‑41 137 129 Shell 7680 20 7741 167549 and core 201504–15, both located within the right-step basin (sag pond), have 201504‑41 137 146 Shell 10,690 25 11,286 167550 turbidites with ages of 24,698 k.y. B.P. in 201504–15 (Greene et al., 2019) and 201504‑42 211 149 Shell 10,730 25 11,348 167551 201504‑42 211 171 Shell 11,015 25 11,929 167552 42,000 k.y. B.P. in 201102–32 (Barrie et al., 2013). Further north along the fault 201504‑42 211 225 Shell 11,505 30 12,629 167553 14 valley, core 201102–31 has dates of 14,700 and 14,000 C yr B.P. (16.0 and 201504‑42 211 286 Shell 11,975 30 13,054 167554 15.3 ka) in sandy gravels (Barrie et al., 2013). 201504‑42 211 361 Shell 12,560 30 13,608 167555 Within the 4-km-long right-step basin off northern Haida Gwaii, four cores 201702‑65 802 1 Shell 23,080 60 25,701 200414 (201504–23, 201504–25, 201504–26, and 201504–27) were collected on either 201702‑65 802 16 Shell 21,880 60 24,324 200415 side of the fault (Fig. 4). These cores consist of repetitive interbedded sand Note: Radiocarbon dating was undertaken at the Keck Carbon Cycle Accelerator and muds interpreted to be turbidites (e.g., 201504–26; Fig. 6). The cores were ass Spectrometry acility at the niversity of California, Irvine. Calendar ages were converted from raw 14C ages using the arine13 calibration curve of Reimer barren of dateable material, except in core 2015004–23 (Fig. 6), where a date et al. 2013. This calibration was accomplished with the program OCal version of 15,052 k.y. B.P. (Table 1) was obtained at 15 cm. Further north, off Dixon 4.2.3 Bronk Ramsey, 2009. Entrance, three cores (201504–28, 201504–29, and 201504–30) were collected near the fault and were described by Greene et al. (2019). No dateable material was found within these cores. base of the coarse unit, there is an erosional boundary, below which there is a North of Dixon Entrance, five cores were collected 12 km off northern Dall dark-gray mud with some laminations and occasional shell material to 390 cm. Island near Craig, Alaska, on the shelf inshore of the fault. Here, large expo- The Holocene muds have radiocarbon dates ranging from 7741 k.y. B.P. to sures of granite basement rock crop out on the seafloor and appear to have 2976 k.y. B.P. (four dates; Table 1). The underlying coarse gravel and sand unit been differentially eroded along fractures and faults well exhibited in the MBES found in cores 39, 41, and 42 all date narrowly to between 11,929 k.y. B.P. and bathymetry (Fig. 7). Cores 2015004–38 and 2015004–40 are entirely olive-col- 11,286 k.y. B.P. (five dates; Table 1). The lower mud unit in core 2015004–42 ored bioturbated Holocene muds with occasional shells. Core 2015004–39, has three dates progressively getting older down core from 12,629 k.y. B.P. to collected in 174 m water depth, has 385 cm of Holocene mud that overlies 13,608 k.y. B.P. (Table 1). a 28 cm laminated stiff gray mud and finally a 38 cm sandy gravel unit with Inshore, four cores were collected in two inlets along the west coast of shells and rounded clasts up to 3 cm (Fig. 7). Another core (2015004–41) in Haida Gwaii, and nine cores were collected along the inner shelf at the extreme shallower water (137 m water depth) has an olive-colored bioturbated mud southern end of the archipelago in 1995. Cores collected along the inner shelf that overlies a coarse sandy gravel unit. An erosional boundary occurs at the of southern Haida Gwaii consist of thin deposits of carbonate sand. Wass et base of the gravel unit (153 cm), and below this boundary, there is a dark-gray al. (1970) first identified bryozoan carbonate sands in the Great Australian mud with distorted laminations to the base of the core at 370 cm (Fig. 7). The Bight, and later research identified the extensive southern Australian calcar- fifth core (2015004–42) was taken 15 km south of cores 38–41, along a north- eous skeletal sediment deposits as a “shaved shelf,” a relict shelf with active south–trending gully at 211 m water depth. An olive-colored bioturbated sandy winnowing (James et al., 1994, 2001). Similar relict shelf carbonate sands are mud is again underlain by a coarse sand unit with shells at 132–172 cm. At the found in southern Queen Charlotte Sound north of Vancouver Island (Nelson

and Bornhold, 1983) and adjacent to eastern Haida Gwaii (Carey et al., 1995). The western Haida Gwaii deposits (cores 95–26–35; Fig. 2), however, contain a greater percentage of very fine carbonate sand. The carbonate fraction of 201504-39 201504-41 0

the sediments is entirely of skeletal origin, primarily barnacles, bryozoans, 200 Depth (m) 30 P

and assorted bivalves and gastropods, and averages 80%–85% of the total y

40 3 sediment content (Fig. 2). The average thickness of the carbonate deposit 9

, is 1–5 m, and it has been interpreted to be underlain by lacustrine deposits 60 3 (Josenhans and Zevenhuizen, 1996). Temperate carbonate deposits normally 80

100 . occur in areas where sediment input is low, the seafloor is primarily bedrock 201504-38 r

or gravel, hydrodynamic energy is high at the seabed, and ample nutrients 120 4

201504-39 7

xxx 7 are available (Nelson and Bornhold, 1983; Nelson et al., 1988; Scoffin, 1988; 140 Carey et al., 1995). There is extensive exposure of a rough bedrock surface, 11,286 160 yr. BP and vertical mixing occurs off the southern cape of Haida Gwaii (Crawford et

180 )

al., 1995), providing both the substrate and nutrient-rich water required for m

c 200 (

carbonate production.

h t

201504-40 220 P p

Sedimentation within the fjords of western Haida Gwaii, which are con- e

y D 240

strained by a bedrock sill at the entrance, such as Tasu Inlet (Fig. 5), is composed 7 e

2 r

o 260 ,

of fine-grained, organic-rich, bottom sediments, i.e., typical sedimentation for 6

201504-41 C Canadian fjords (Syvitski et al., 1987). The seaward entrances to these fjords 280

are usually very narrow and shallow, and, consequently, Pacific wave energy 300 does not penetrate to any appreciable degree. Inlets that are oriented such that 320 they are not open to the Pacific oceanic conditions, such as Seal Inlet (Fig. 3), Bioturbation 340 also contain fine-grained Holocene sediments overlying bedrock. Shell

360 P

Within the largest inlet, Rennell Sound, seismic-reflection data show Gravel

Lamination silt

380 clay stratified sand overlying a coarse-grained unit with a complex cut-and-fill 5 f.sand c.sand m.sand f.gravel xxx 1 Sponge Spicules 8

stratigraphy normally associated with drowned fluvial sediments (Barrie and 400 1 Lithology

Conway, 1996). Channels leading out of the inlet can be seen on both the 420 11,315 yr. BP seismic-reflection data and regional bathymetry (Fig. 3). In core TUL95B-05, silt collected in a water depth of 152 m, a bioturbated, muddy-sand unit with 201504-42 Lithology clay f.sand c.sand m.sand f.gravel organic and shell material overlies well-sorted, massive fine sand with a sharp erosional contact between units (Barrie and Conway, 1996). Four radiocarbon Figure 7. Multibeam swath bathymetry image off northern Dall Island in south- dates (Table 1) taken from wood and one shell within this upper unit indicate a eastern Alaska (Fig. 1) on the shelf inshore of the Queen Charlotte fault indicating rapid sedimentation rate between 12,380 and 11,290 C14 yr B.P. (5.5–6.0 cm/yr). the locations of the five cores collected. Schematic diagrams of cores 201504–39 No dateable material was collected in the massive sand unit. Below this, there and 201504–41 are shown. Lithology: f—fine, m—medium, c—coarse. are interbedded silt and sand units with minor gravel and wood fragments. Wood fragments selected from the base of this unit at 4.40 m suggest an age of 12,340 C14 yr B.P. (12.6 ka; Table 1). The lowermost unit in this core is a black Conway, 1999; Hetherington and Barrie, 2004). This is thought to have been a massive sand unit that grades into fine gravel that is devoid of any marine consequence of a migrating glacial forebulge with a very thick (2500 m) ice load indicators or dateable fragments. This is interpreted to be an alluvial facies. on the mainland of British Columbia (Clague, 1983) and a limited ice load on Haida Gwaii and in Hecate Strait (Clague, 1989; Barrie et al., 1991, 1993), during a period of eustatic sea-level lowering. Within the largest inlet on western ■■ DISCUSSION Haida Gwaii, Rennell Sound, sea-level lowstand occurred just prior to 12.6 ka accompanied by significant deposition. The rapid submergence of this site fits Late Quaternary Sea-Level Change closely with the sea-level curves for eastern Haida Gwaii (Barrie and Conway, 1999, 2002b; Fedje and Josenhans, 2000; Hetherington et al., 2004; Hether- Emergence of the continental shelf off western Haida Gwaii by greater ington and Barrie, 2004; Shugar et al., 2014). Isostatic uplift (70+ m) resulted than 150 m at the beginning of the Holocene has been postulated (Barrie and in a relative sea-level drop of at least 152 m (Hetherington and Barrie, 2004).

Cores collected north of Dixon Entrance off southeast Alaska suggest a 135o W 130o W sea-level lowering by greater than 175 m between 11.3 ka and 12.0 ka. In cores 201504–41 and 201504–42, below the erosional boundary that underlies the coarse sand unit, there are dark-gray muds that progressively get older to the Chatham Strait base of the cores. The implication is that these cores were collected near the sea-level lowstand at ca. 12.0 ka and after a steady regression were quickly

drowned by a transgressing sea. This would suggest a possible sea-level o

56 lowering by up to 175 m just inshore of the fault, which occurred just after the Alexander lowstand off Haida Gwaii. As proposed by Baichtal et al. (2017a, 2017b), the Archipelago development of a forebulge that resulted in a maximum sea-level lowering of ~175 m would suggest persistent ice to the east within the mainland until Cordova Clarence ca. 11.5 ka. Upon collapse of the forebulge, and coupled with eustatic sea- Bay Strait level rise, sea levels reached a maximum transgression on the outer islands between 11.5 and 10.6 ka (Carlson and Baichtal, 2015; Baichtal et al., 2017a, Learmonth

o Bank Dixon Entrance 2017b). Baichtal et al. (2017b) presented a proposed sea-level curve for the

54 region that complements the findings presented here. Haida Gwaii Hecate Strait Postglacial Chronology of the Queen Charlotte Fault Zone Margin

During the glacial maximum, ice exited Dixon Entrance (Barrie and Con- way, 1999), reaching the shelf edge in the vicinity of the Mukluk Fan (Dobson

N rough et al., 1998; Shaw et al., 2019). Evidence described by Lyles et al. (2017) and o T Lesnek et al. (2020) shows that topography exerted a strong control on ice 52 movement in Dixon Entrance. A major ice stream flowed northward along Moresby Icebergs Queen Clarence Strait, and farther west, a second stream flowed norward up Cor- Charlotte dova Bay and Tievak Strait (Fig. 8). Ice that remained in Dixon Entrance and Sound approached the Pacific Ocean was likely steered by local topography, and in particular, Learmonth Bank (Fig. 8). Grounded ice moved to either side Vancouver Island because Learmonth Bank is shallower than 50 m and the channels to the north and south are over 400 m deep. The southern channel past Learmonth Figure 8. Local last glacial maximum illustrating the northward flow away from Bank is less than 10 km in width, with the mountainous shores of Haida Gwaii Dixon Entrance and diversion around Learmonth Bank, the glacial flow of ice out of Queen Charlotte Sound and development of an ice shelf, and the flow forming the southern boundary, whereas the channel to the north is deep and of icebergs into the Pacific Ocean around Haida Gwaii and off the Alexander over 22 km in width, suggesting most of the ice went to the north-northwest. Archipelago. Ice limits were based on the findings of this paper and those of Evidence from core data just south of Dixon Entrance, along the Queen Char- Carrara et al. (2007) and Shaw et al. (2019). lotte fault on the upper slope, where the southern channel past Learmonth Bank leads, suggests virtually no glacial sedimentation and sediment ages from radiocarbon dating generally older than 15.0 ka (mostly between 50.4 Deglaciation began after 17.0 ka and before 15.6 ka, based on the oldest and 15.0 ka; Greene et al., 2019). Conversely, cores collected in 2017 just north dates in Dixon Entrance and Hecate Strait (Barrie and Conway, 1999). Evidence of Dixon Entrance are rich in glaciomarine sediments down the continental from Haida Gwaii shows that ice still existed in the western mountain range at slope of southern Alaska (Barrie et al., 2018). To the south, ice moved out 14.5 ka and possibly persisted longer (Mathewes and Clague, 2017; Shaw et al., of Queen Charlotte Sound and became a floating ice shelf that moved out 2019). At this same time, sea level began to drop rapidly, reaching a lowstand of Moresby Trough south of Haida Gwaii (Shaw et al., 2019). West of Haida at ca. 12.7 ka off Haida Gwaii and 12.0 ka off southeast Alaska. Outwash from Gwaii, little to no ice extended onto the narrow shelf. Consequently, Haida Haida Gwaii was transported across the short subaerial shelf by several chan- Gwaii acted as an ice shadow to glacial sediment transport to the Pacific, nel systems to the shelf break. Sediment discharge continued until ca. 10.0 ka limiting deposition to the continental shelf and upper slope to the west of and abruptly terminated once most of the ice had melted out of the western the islands (Greene et al., 2019). Haida Gwaii mountain chain. In addition, rapid sea-level rise quickly resulted

in an erosive transgression of the narrow shelf with extreme oceanic energy that this occurred in response to a warm, relatively thin lithosphere, com- that continues to the present day. Consequently, sediment delivery from the bined with the tectonic influence of the decoupled Pacific and North American west coast of Haida Gwaii was very short, starting at ca. 14.5 ka and ending plates along the Queen Charlotte fault. They further suggested that the Queen just after 12.7 ka. Most of this delivery would have been earlier than 12.7 ka, Charlotte fault acted as a hinged flap, taking up the isostatic forebulge uplift as the western Haida Gwaii mountains initially deglaciated. and collapse along the fault (Fig. 9). The apparent near-vertical and singular During deglaciation, icebergs and ice would have moved out of Dixon knife-edge character of the Queen Charlotte fault north of 52°23′N supports Entrance, mostly to the northwest and north, as sea-level lowering and the this possible interpretation. However, there is no conclusive evidence that subaerial Learmonth Bank would have restricted ice exiting to the southwest can be taken from the detailed morphology to further support this hypothesis. (Fig. 8). At the same time, icebergs were transporting sediment south of Haida Assuming that the fault did take up to 70+ m of motion for the period of Gwaii onto the continental slope out from Queen Charlotte Sound (Fig. 8; Barrie 15.0–13.0 ka, there would have likely been greater earthquake activity. Evidence and Bornhold, 1989; Shaw et al., 2019). Ice sediment transport north and south of enhanced volcanic frequency during this same time interval is apparent off of Haida Gwaii would have ended by 14.0 ka (Barrie and Conway, 1999; Shaw southeast Alaska, adjacent to the Queen Charlotte fault (Praetorius et al., 2016). et al., 2019), as ice retreated into the mainland fjords. At present, little to no The increased earthquake and volcanic activity would then have resulted in sediment derived from Haida Gwaii and the Alexander Archipelago reaches increased development of submarine failures and turbidites adjacent to the the narrow shelf and upper slope to the Queen Charlotte fault. Reworked sedi- fault, but there is little evidence of this within the cores collected along the ment does move along the fault from the bathymetric highs and exits the fault fault. However, as suggested by Greene et al. (2019), sediments younger than valley at the few eroded exit points (Figs. 3 and 4), usually associated with the 15.0 ka are rare due to significant sedimentation shutdown after this early step-over basins or sag ponds. Deep-water submarine dunes (>1000 m water stage of deglaciation, and consequently little evidence would be obtained depth) occur where the sediments exit the fault valley system onto the lower from core data. slope (Barrie et al., 2013). A distinctive fault valley occurs along most of the fault (Fig. 9) north of the southern convergence zone, following the upper continental slope until it reaches the slope break at 55°54′N. Though the fault valley occurs parallel to ■■ LATE QUATERNARY RESPONSE OF THE QUEEN CHARLOTTE FAULT the slope, it has a very distinctive V-shaped valley character, usually 100–300 m wide with side slopes averaging 25–75 m in height. The 70+ m of drop and rise Shoreline tilt during the development and collapse of the forebulge across of the North American plate adjacent to the Pacific plate during the develop- Haida Gwaii reached 2.1 m km–1, and Hetherington and Barrie (2004) suggested ment and collapse of the glacio-isostatic forebulge over 2000 yr could have

A A’

D 230

10’ 250 ( Isostatic

o m Adjustment

) 56 QCF 270 Figure 9. Multibeam swath bathymetry Distance 500 1500 1500 2000 2500 m image of the northern Queen Charlotte fault (QCF) off southeastern Alaska (Fig. 1) illustrating the morphology of the fault valley and sediment dispersal onto the continental slope through channels below the fault. Schematic profile A-A′ across the fault illustrates the characteristic shape of the fault

N valley that may have developed during

00’ deglacial isostatic adjustment.

o 200 56 2400 Depth (m) A’ 0 1.25 2.5 5 7.5 10 A

Kilometers Submarine Failure 135o 40’ W 135o 30’ W

Columbia continental shelf, Canada: Quaternary International, v. 20, p. 123–129, https://doi resulted in the development of this unique geomorphic character of the Queen .org/10.1016/1040-6182(93)90041-D. Charlotte fault. The subsequent 500 m of strike-slip movement and erosion Barrie, J.V., Conway, K.W., and Harris, P.T., 2013, The Queen Charlotte fault, British Columbia: within the valley by sediment transport processes certainly would have modi- Seafloor anatomy of a transform fault and its influence on sediment processes: Geo-Marine Letters, v. 33, p. 311–318, https://doi.org/10.1007/s00367-013-0333-3. fied the feature, but these processes may not fully explain the consistent fault Barrie, J.V., Greene, H.G., Brothers, D., Conway, K.W., Enkin, R.J., Conrad, J.E., Lauer, R.M., McGann, valley character that is a primary feature of the present Queen Charlotte fault. M., Neelands, P.J., and East, A., 2018, The Queen Charlotte–Fairweather Fault Zone—A Sub- marine Transform Fault, Offshore British Columbia and Southeastern Alaska; Cruise Report of 2017003PGC CCGS Vector and 2017004PGC CCGS John P. Tully: Geological Survey of Canada Open-File Report 8398, 159 p. ACKNOWLEDGMENTS Blaise, B., Clague, J.J., and Mathewes, R.W., 1990, Time of maximum late Wisconsin glaciation, The collection of multibeam bathymetry was undertaken by the Canadian Hydrographic Service west coast of Canada: Quaternary Research, v. 34, p. 282–295, https://doi .org/10 .1016 /0033 (Department of Fisheries and Oceans) in cooperation with the Geological Survey of Canada in -5894(90)90041-I. Canadian waters, and by the U.S. Geological Survey Coastal and Marine Geology Program and Bostwick, T.K., 1984, A Re-examination of the 1949 Queen Charlotte Earthquake [M.Sc. thesis]: the Alaska Department of Fish and Game in U.S. waters. The officers and crew of the CCGS John P. Vancouver, B.C., Canada, University of British Columbia, 115 p. Tully are acknowledged for able seamanship during collection of the geophysical and sediment Bronk Ramsey, C., 2009, Bayesian analysis of radiocarbon dates: Radiocarbon, v. 51, p. 337–360, sample data in poorly charted waters. Peter Neelands, Robert Kung, Greg Middleton, and Bob https://doi.org/10.1017/S0033822200033865. Murphy are thanked for invaluable assistance at sea and in the laboratory. We thank Royal Roads Brothers, D.S., Andrews, B.D., Walton, M., Greene, G., Barrie, V., Miller, N.C., ten Brink, U., Haeus- University for the use of the Geotek split-core multisensor core logger. sler, P.J., Kluesner, J.W., and Conrad, J.E., 2019, Slope failure and mass transport processes along the Queen Charlotte fault: Southeastern Alaska, in Lintern, D.G., et al., eds., Subaque- ous Mass Movements: Geological Society [London] Special Publication 477, p. 69–83, https:// doi.org/10.1144/SP477.30. 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