Late Quaternary Glaciation and Postglacial Stratigraphy of the Northern Paciﬁc Margin of Canada

Quaternary Research 51, 113–123 (1999) Article ID qres.1998.2021, available online at http://www.idealibrary.com on

J. Vaughn Barrie and Kim W. Conway Geological Survey of Canada, Paciﬁc Geoscience Centre, P.O. Box 6000, Sidney, British Columbia V8L 4B2, Canada

Received September 23, 1998 Charlotte Islands) is an asymmetric and broad, deep marine Areas of southeastern Alaska and the Queen Charlotte Islands trough. Dixon Entrance displays a rugged seabed topography of the northwestern Pacific coast of North America were consid- that Bornhold and Barrie (1991) interpret to be a result of ered to be ice free during the late Wisconsinan glaciation and scouring by westward-flowing glaciers. Assuming there was a glacial refugia existed. However, a glacier extended from main- large ice mass separating the two areas, then our understanding land North America to the shelfbreak in Dixon Entrance separat- of the timing of deglaciation and sea-level change is critical for ing Alaska and the Queen Charlotte Islands. Glacial retreat to the east began sometime after 15,000 to 16,000 14C yr B.P. and ice had assessing whether early human migration took place between completely left Dixon Entrance by 13,500 to 13,000 14C yr B.P. A these areas. rapid sea-level regression occurred soon after deglaciation began, The Cordilleran Ice Sheet had reached its maximum after 14 14 due to isostatic rebound, with relative sea level falling to approx- 21,000 C yr B.P. but before 15,000 to 16,000 C yr B.P., imately 150 m below present in central Dixon Entrance, decreas- based on evidence from Mary Point in southern Dixon En- ing the size of the inlet by about 30 percent by 12,400 14C yr B.P. trance (Blaise et al., 1990). Evidence from deep sea cores The late Quaternary glacial and postglacial stratigraphic sequence suggests that ice retreat began after 15,600 14C yr B.P. (Blaise is more than 100 m thick overlying older Pleistocene sediments et al., 1990). In southeastern Alaska, adjacent to Dixon En- and Tertiary bedrock. A late Wisconsinan diamicton is overlain by trance, deglaciation probably was rapid, with iceberg calving glaciomarine muds formed between approximately 14,400 and 14 causing glacier termini to retreat to near their modern positions 13,000 C yr B.P. Contemporaneous with the deposition of the 14 glaciomarine muds an extensive outwash deposit formed off the by 13,500 C yr B.P. (McKenzie and Goldthwait, 1971; Mann northern coast of the Queen Charlotte Islands to a present depth and Hamilton, 1995). To the south of Dixon Entrance in Hecate of 150 m. During the sea-level lowstand and subsequent transgres- Strait and Queen Charlotte Sound, ice is estimated to have sion, a reworked sand unit was deposited over much of the seafloor retreated from the shelf between 14,160 and 12,910 14C yr B.P. to depths greater than 450 m. The unit is exposed at the seafloor (Luternauer et al., 1989a; Barrie et al., 1991). In northwestern over much of the region, suggesting that seabed hydrodynamic Hecate Strait at the entrance to Dixon Entrance, a date of 14 energy levels were high after 13,000 C yr B.P. and remain so 13,790 14C yr B.P. was obtained from terrestrial sediments today. found in a core at 31 m water depth suggesting ice-free Key Words: late-Wisconsinan glaciation; deglaciation; Queen conditions (Barrie et al., 1993). Charlotte Islands, Canada; glacial refugium; sea-level change. Relative sea level has been influenced by isostatic crustal depression and rebound, the rise and fall of eustatic sea level, INTRODUCTION and local tectonic crustal adjustments. The amount of change varies dramatically from east to west in response to loading by Several authors have suggested that glacial refugia existed and rebound from the Cordilleran ice sheet (Clague, 1983). along parts of the northwestern coast of North America during Josenhans et al. (1997) give evidence for relative fall of sea the last glaciation, particularly on the Queen Charlotte Islands level of more than 153 m at 12,400 14C yr B.P., with large areas (Fladmark, 1979; Warner et al., 1982; Heusser, 1989), in the adjacent to the Queen Charlotte Islands being subaerially ex- Alexander Archipelago, southeastern Alaska (Heaton et al., posed. As the sea transgressed the shelf east of the Queen 1996), and other areas of the Alaskan coastline (Mann and Charlotte Islands, sea level reached a maximum of 200 m Hamilton, 1995; Elias et al., 1996). This has led to further above present in Kitimat trough on the British Columbia main- speculation that this area could have provided a corridor for land at 10,500 14C yr B.P. (Clague, 1985). Up to 230 m of migration of humans into western North America (Fladmark, marine submergence also occurred in southeastern Alaska be- 1979; Luternauer et al., 1989b; Josenhans et al., 1995). Be- tween 13,000 and 10,000 14C yr B.P. (Mann and Hamilton, tween these two areas (southernmost Alaska and the Queen 1995). Eustatic sea-level rise, coupled with subsidence of a

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0033-5894/99 114 BARRIE AND CONWAY

FIG. 1. Map of Dixon Entrance showing the location of the sediment cores collected and generalized bathymetry.

FIG. 2. Geophysical survey coverage in Dixon Entrance from three scientiﬁc cruises, including airgun seismics, Huntec DTS sub-bottom proﬁles, and sidescan sonar. GLACIATION AND SEA LEVEL, B.C./ALASKA 115

FIG. 3. Geologic cross section through Dixon Entrance. Location is shown in Figure 1. glacioisostatic forebulge, resulted in sea level reaching the Data were collected during three scientific cruises to address present shoreline on the Queen Charlotte Islands by about 9100 the question of the late-Wisconsinan glacier advance and re- 14C yr B.P. and a maximum of 13 to 15 m above current levels treat within Dixon Entrance and to map the resultant surficial at 8900 14C yr B.P. (Clague et al., 1982; Clague, 1983; Josen- geology of Dixon Entrance. During these field programs, a hans et al., 1995). In southeastern Alaska there was variability gridded network of high-resolution seismic survey lines (air- in sea-level histories, with Heceta Island experiencing trans- gun seismic, Huntec DTS sub-bottom profiles, and sidescan gression contemporaneous with that on the Queen Charlotte sonar) were completed, with a line spacing of 9 km (Fig. 2). In Islands, whereas on Prince of Wales Island (Fig. 1) no trans- addition, 15 piston cores and 14 vibrocores were obtained (Fig. gression has been identified (Mobley, 1988) and the sea 1) throughout the Entrance (Conway and Barrie, 1994). The reached its present level by about 9000 14C yr B.P. (Mann and objective of this paper is to (1) interpret the extent of late Hamilton, 1995). Wisconsinan glaciation of Dixon Entrance, (2) determine the

FIG. 4. Huntec DTS sub-bottom profile showing the typical stratigraphy off the entrance to Clarence Strait. Geologic units are defined in the text. Profile location is shown in Figure 1. 116 BARRIE AND CONWAY

FIG. 5. Huntec DTS sub-bottom profile and stratigraphic interpretation of a section of the outwash facies off the northern Queen Charlotte Islands. Profile location is shown in Figure 1. rate and timing of deglaciation and the sea-level response, and trough. A major pass, however, exists on the north and south (3) characterize the resultant stratigraphy. sides of Learmouth Bank, cut steeply to depths of about 470 m and allowing Dixon Entrance trough to open to the REGIONAL SETTING continental slope. The seafloor of central and southern Dixon Entrance is covered with Quaternary sediments un- Dixon Entrance opens to the Pacific Ocean across a nar- derlain by a Miocene–Pliocene siliciclastic succession (Sko- row continental shelf seaward of the Queen Charlotte Is- nun Formation (Higgs, 1991)) and a late Oligocene to late lands. The shelf abruptly deepens to the west at the shelf- Miocene calcalkaline suite of volcanic rocks (Hickson, break formed by the North American/Pacific Plate 1991). During the late Wisconsinan glaciation, glaciers boundaries along the Queen Charlotte Fault. Three promi- flowed into Dixon Entrance from the British Columbia nent transverse sills exist within the trough, Celestial Reef mainland (Clague, 1991), whereas on the Queen Charlotte north of Dogfish Bank in Hecate Strait, one north of McIn- Islands locally derived mountain and piedmont glaciers de- trye Bay, and the other, Learmouth Bank, north of Langara veloped independent of the Cordilleran Ice Sheet. On the Island (Fig. 1). All three sills form rugged, dissected banks coastal lowlands of Graham Island (Fig. 1), glaciation was less than 100 m deep that partially block the axis of the limited and of short duration (Clague et al., 1982b). GLACIATION AND SEA LEVEL, B.C./ALASKA 117

FIG. 6. Geologic cross section across Dixon Entrance from the northern Queen Charlotte Islands to Clarence Strait in southeastern Alaska. Location is shown in Figure 1.

The Entrance is open to Pacific storm systems. The present it is not possible to differentiate ice-contact from ice-proximal mean tidal range in Dixon Entrance varies from east to west deposits. from 5.0 to 3.5 m resulting in strong bottom currents (Thom- The diamicton in Dixon Entrance varies in thickness be- son, 1981; Crawford and Thomson, 1991; Ballantyne et al., tween a few meters and more than 100 m, with an average of 1996). Guilbault et al. (1997) suggest that these open-water about 30 to 50 m. In most areas the upper reflector has a very conditions have existed since deglacial time, with freshwater rough hummocky expression, a result of iceberg scouring and export in an upper layer and saltwater import in a deep return pitting. When exposed at the seafloor, the diamicton facies has layer. a surface veneer of poorly sorted gravel and exposed boulders, and is completely covered with iceberg scours and pits below EVIDENCE FOR LATE WISCONSINAN GLACIATION 100 m water depth that penetrate up to 7.0 m in depth. Diamict deposition is mostly absent on the tops of Celestial Reef and The extent of glaciation of Dixon Entrance is inferred from Learmouth Bank; only in some small basins in the central a seismostratigraphic-derived facies architecture that reveals evidence of diamicton deposition extending throughout Dixon Dixon Entrance ridge is there a thin diamicton (Figs. 3 and 6). Entrance (Fig. 3) and beyond the geophysical survey, which On the north side of the Queen Charlotte Islands, to a depth of ended near the shelfbreak. The diamicton is defined by its approximately of 150 m, high-resolution seismic records show uniform nonstratified character, with a strong surface reflector a complex cut-and-fill seismic facies consisting of poorly and high internal backscatter in the sub-bottom profiles (Fig. sorted outwash overlying the diamict, although it is difficult to 4). Although these acoustic characteristics are normally asso- resolve the character of the underlying unit using the geophysi- ciated with till, it is difficult to differentiate diamictons acous- cal records (Figs. 5 and 6). In eastern Dixon Entrance, thick tically, regardless of origin (Syvitski et al., 1997). In Dixon sequences of fine Holocene sands with extensive shallow gas Entrance, all attempts to core the diamicton failed due to the prevent the sub-bottom signal from penetrating into the section inability of the core to penetrate it, suggesting that this unit is (Fig. 3), and so the mapping of the underlying diamict is over-consolidated. Regardless, based on the acoustic data alone sporadic. 118 BARRIE AND CONWAY

FIG. 7. Stratigraphy and lithology of three selected Dixon Entrance cores showing the distribution and age of glaciomarine (Unit A) sediments. Cores are located in Figure 1, and the details of the radiocarbon dates are provided in Table 1.

These data suggest that ice-proximal, and possibly ice- On the seaward side of the central transverse ridge in the contact, deposition occurred in present water depths of up to Entrance (Fig. 3), the diamicton is very thick (100 m) and 400 m. There is no evidence of stratification within the diam- bifurcates into two units, separated by glaciomarine drift (Fig. icton, further suggesting ice-proximal conditions. At least 3). This is similar to the till tongues identified by King and 350 m of ice is required in western Dixon Entrance, allowing Fader (1986) and King et al. (1987) on the Scotian and mid- for deposition of a diamicton in the present 450-m-deep trough Norwegian shelves that interdigitate with glaciomarine units at from the top of Learmouth Bank and to the shelfbreak. This the shelf-break in response to changes in the position of the contrasts with the limited ice thickness on the lowlands of the grounding line. Boulton (1990) suggests that such stratification northern Queen Charlotte Islands (Clague et al., 1982b; Barrie is the result of a sea-level rise, forcing the grounding line to et al., 1993) and in southeastern Alaska (Mann and Hamilton, retreat; with subsequent stabilization, a second prograding till 1995; Heaton et al., 1996). The glacier filled most of Dixon topset bed will form. Entrance, reaching the northern portion of the Queen Charlotte Islands (Blaise et al., 1990). The thin late Wisconsinan ice POSTGLACIAL STRATIGRAPHY cover on the northern Queen Charlotte Islands coalesced with the Dixon Entrance ice emanating from the British Columbia The postglacial stratigraphy of Dixon Entrance can be di- mainland and was deflected westward (Sutherland-Brown, rectly correlated with that in Queen Charlotte Sound (Luter- 1968). There is, at present, no documented evidence of the nauer, 1989a) and Hecate Strait (Barrie and Bornhold, 1989) to Dixon glacier touching the Alaskan Alexander Archipelago on the south. Glaciomarine mud (Unit A; Luternauer, 1989a) the northern boundary. However, an extensive diamicton ex- overlies the diamicton and contains, in decreasing abundance, tends into Clarence Strait in Alaska (Fig. 6). clay (50%), silt (35%), sand (10%), and ice-rafted gravel (5%). GLACIATION AND SEA LEVEL, B.C./ALASKA 119

TABLE 1 Radiocarbon Dates Obtained from Samples Taken from Cores Recovered in Dixon Entrance and Hecate Strait

Water Sample Radiocarbon Laboratory Lithologic Core depth (m) depth (cm) Dated specimen date number unit

END88B02 319 77 serpulid tube 10,600 Ϯ 90 TO-2251 B2 END90A02 389 108 Chlamys rubida 12,230 Ϯ 110 TO-2252 B2 END90A02 389 30 Nuculana fossa 12,670 Ϯ 100 TO-2253 B2 END90A04 254 253 Y. thraciaeformis* 9890 Ϯ 80 TO-4361 B3 END90A04 254 543 Y. thraciaeformis* 9850 Ϯ 90 TO-2254 B3 END90A07 394 411 shell fragments 3170 Ϯ 70 TO-2256 C END90A07 394 543 twig 10,580 Ϯ 90 TO-2254 B2 TUL91C024 293 527 Nuculana fossa 13,770 Ϯ 100 TO-3489 A TUL91C026 238 348 Nuculana fossa 13,000 Ϯ 100 TO-3491 A TUL91C027 376 244 gastropod 2590 Ϯ 100 TO-4881 C TUL91C028 161 95 Nuculana 12,960 Ϯ 60 CAMS-33805 A TUL91C028 161 163 Nuculana 13,140 Ϯ 60 CAMS-33806 A VEC94A023 37 126 Cassidulina reniforme 14,380 Ϯ 110 TO-4888 A TUL95B012 77 40 Macoma 3260 Ϯ 50 CAMS-33799 C TUL95B012 77 93 Macoma 12,520 Ϯ 70 CAMS-33800 ? TUL95B012 77 185 Mytilus 12,690 Ϯ 60 CAMS-26282 ?

Note. Shell dates are corrected for a 600-yr reservoir effect, based on the 72 shell-wood pair dates of Josenhans et al. (1997) from Queen Charlotte Islands and Hecate Strait. Lithologic units are discussed in the text. TO, Iso Trace Radiocarbon Laboratory, University of Toronto. CAMS, Centre for Accelerator Mass spectrometry, Lawrence Livermore National Laboratory. * Yoldia thraciaeformis.

This mud is consistently ﬁner than samples from the glacioma- Charlotte Sound. Only in the trough that extends south out of rine mud (Unit A) to the south. Four C14 dates within this unit Clarence Strait in Alaska is there any appreciable accumulation (13,770 14C yr B.P. in Core TUL91C024, 13,000 14C yr B.P. in of Unit C muds (Fig. 4). Core END90A07 is typical of Unit C; Core TUL91C026, and 13,140 to 12,960 14C yr B.P. in Core the bioturbated and laminated mud consists primarily of silt TUL91028; Fig. 7 and Table 1) suggest that glaciomarine mud with lesser amounts of clay and generally less than 10% sand units were deposited in the same time frame as on the shelf to (Fig. 8). Overlying the outwash of southern Dixon Entrance are the south. Off the northern shores of the Queen Charlotte thin modern reworked sands (Fig. 5), except where Hecate Islands a thick (15–40 m) and extensive apron of outwash Strait meets Dixon Entrance. Here a thick Holocene sand unit sediments (Fig. 5), similar in age to Unit A, extends to the has been deposited as the result of erosion of the eastern Queen present depth of 150 m (Fig. 6). The distribution of this facies Charlotte Islands (Barrie and Conway, 1996). Elsewhere in coincides with the maximum predicted sea-level lowstand for Dixon Entrance, late Wisconsinan till or Unit B2 crops out at the region (Josenhans et al., 1997). the seabed. Unit B2 often forms the top of the stratigraphic

The overlying Unit B and, in particular, Unit B2 (Luternauer, sequence, even to depths of 450 m or more (Core END90A01; 1989a) is present in all cores and is consistently thicker in Fig. 1). section and has a higher sand content (Ͼ50%; Fig. 8) than seen in Hecate Strait and Queen Charlotte Sound. This sand unit DEGLACIATION OF DIXON ENTRANCE ranges in thickness between 0.5 to more than 20 m. The thickest sections are found proximal to the banks, especially A core obtained on Dogﬁsh Bank in northern Hecate Strait Learmouth Bank (Fig. 3, 4, and 8). Four C14-dated samples (Fig. 9) contains cold-water foraminifera (Cassidulina reni- within this unit range between 12,670 and 10,580 14C yr B.P. forme) in ice-proximal laminated ﬁne-grained sediments that (Table 1), consistent with ages from other areas. date to 14,380 14C yr B.P. (Core VEC94A23; Table 1), indi-

An isolated lobe of early Holocene mud (Unit B3; Luter- cating that glaciomarine conditions existed as early as 14,400 nauer, 1989a) is found in west-central Dixon Entrance at ca. 14C yr B.P. in central Dixon Entrance. Radiocarbon ages from 250 m water depth. Here, the laminated mud contains a greater the glaciomarine sediments overlying the diamict suggest that concentration of sand (10 to 20%) than examples to the south, open-water conditions existed in western Dixon Entrance be- as seen in Core END90A04 (Fig. 8). fore 13,800 14C yr B.P. and in the eastern portions before Unit C (Holocene Mud) in Dixon Entrance is absent in many 13,100 14C yr B.P. Clague (1985) suggests a minimum age for areas and does not have the consistent sedimentology or dis- deglaciation of the Prince Rupert area (Fig. 1) of 12,700 14Cyr tribution found in the troughs of Hecate Strait and Queen B.P., at the eastern end of Dixon Entrance. Dixon Entrance, 120 BARRIE AND CONWAY

FIG. 8. Stratigraphy and lithology of ﬁve selected Dixon Entrance cores showing the postglacial chronology. Core locations are shown in Figure 1. Details of the radiocarbon dates are provided in Table 1.

then, would have been ice-free by 13,500 to 13,000 14C yr B.P. northern Hecate Strait that dates to 14,380 14C yr B.P. (Core and possibly much earlier, with bergs calving from ice at the VEC94A23; Table 1) is at a present water depth of 37 m British Columbia mainland until 13,000 14C yr B.P. This is (Fig. 9). Consequently, relative sea level was above 30 m consistent with the timing of deglaciation of southeastern but not higher than present sea level, as there is no record of Alaska (Mann and Hamilton, 1995). At the time that evidence submergence of the eastern coast of Graham Island at this for ice rafting ends in eastern most Dixon Entrance, coarse time (Clague et al., 1982a). Just 9 km south of this site, three higher-energy sediment was deposited in western Dixon En- cores were collected that contain terrestrial sediments rep- trance. This suggests that seabed hydrodynamics had increased resenting a tundra environment (Barrie et al., 1993) at 14 signiﬁcantly by 12,700 C yr B.P. 13,790 14C yr B.P. (TUL91C34; Fig. 1). This means that ice had left the region and sea level fell signiﬁcantly in as little SEA-LEVEL RESPONSE as 590 years (using a 600-yr reservoir correction). Another A regression on the continental shelf occurred soon after core taken from a nearshore sand deposit in 77 m of water deglaciation. The core in marine sediments obtained in in northeastern Hecate Strait at its junction with Dixon GLACIATION AND SEA LEVEL, B.C./ALASKA 121

FIG. 9. Stratigraphy and lithology of two cores from Hecate Strait. Core VEC94A023 contains ice-proximal sediments with abundant cold water foraminifera (Cassidula reniforme) and core TUL95A012 contains nearshore sediments deposited during lowered sea level. Cores are located in Figure 1 and the details of the radiocarbon dates are provided in Table 1.

Entrance (Fig. 9) dates to between 12,520 and 12,690 14Cyr bridge, resulting in the Entrance becoming an eastward- B.P. (Core TUL95B12; Table 1). Rapid regression on the shallowing inlet open to the Pacific (Fig. 1). Based on continental shelf therefore occurred between ca. 14,400 and foraminiferal species from Dixon Entrance, Guilbault et al. 14 12,400 C yr B.P., contemporary with deglaciation, due to (1997) argue for open marine conditions and vigorous cir- rapid isostatic rebound (Fig. 10). The emergence would culation shortly after 13,000 14C yr B.P. when water tem- have been greater toward the west consistent with a migrat- peratures changed from glacial to transitional. The flow ing glacioisostatic forebuldge (Clague, 1983). Relative sea- would have been enhanced during the glacial forebulge level lowering in eastern Dixon Entrance was approximately stage by more vigorous tidal mixing in the shallower water 80 m and 150 m in central Dixon Entrance. Relative sea and by greater freshwater discharge from retreating glaciers. level reached a maximum low stand after 13,000 14C yr B.P. The open water circulation of Dixon Entrance prevented (Barrie et al., 1993) and remained low until approximately 14 intense downwelling of lower-salinity water, colder surface 12,400 C yr B.P., after which transgression occurred (Jo- senhans et al., 1997). waters, and associated blocking of deep-water intrusions During this period of lowered sea level, currents on the that prevailed during this period in Hecate Strait and Queen seabed of Dixon Entrance were energetic enough to move Charlotte Sound (Patterson, 1993; Guilbault et al., 1997). sediment and winnow out fines to present depths of 450 m. Abundant outwash from the Queen Charlotte Islands and The possible reduction in size of the Entrance and its emergent bank areas (Sutherland-Brown, 1968) was avail- complete restriction toward the east may have resulted in able for reworking by the transgressing sea. These factors even stronger tidal currents than exist today. Hecate Strait would have contributed to the development of the thick B2 would have been cut off from Dixon Entrance by a land Unit over much of Dixon Entrance. 122 BARRIE AND CONWAY

toward the central and western extremes of the Entrance. Whereas there still was no land bridge connecting southeastern Alaska to the Queen Charlotte Islands or mainland British Columbia, open-water reaches were considerably shorter (ca. 20 km long). Temperatures had changed from glacial to transitional at or shortly after 13,000 14C yr B.P., and reached present levels shortly after 10,000 14C yr B.P. (Guilbault et al., 1997).

CONCLUSIONS

An extensive glacier emanating from the British Columbia mainland and Clarence Strait of southeastern Alaska, joined by local ice from the northern Queen Charlotte Islands, moved across Dixon Entrance to the shelfbreak, reaching a maximum extent sometime after 21,000 14C yr B.P. Deglaciation of the area ended between 13,500 and 13,000 14C yr B.P. with the complete retreat of the late-Wisconsinan glacier and disappear- ance of icebergs from the Entrance. During deglaciation, until ca. 12,400 14C yr B.P., sea level was lowered by up to 150 m in central Dixon Entrance, resulting in the development of an extensive coastal plain and a reduced waterway. Dixon En- trance at this time was open to the Pacific storms and was macrotidal, resulting in the erosion of pre-existing glacial sediments and deposition of a thick sand unit to modern depths FIG. 10. Generalized sea-level curve of the northern Pacific margin of of more than 450 m. This unit still forms the seabed over much Canada. of Dixon Entrance today implying that hydrodynamic energy levels have remained high since the transgression. Holocene IMPLICATIONS FOR REFUGIA sedimentation has been negligible except for a restricted area at AND HUMAN MIGRATION the southern entrance to Clarence Strait of southeastern Alaska and the northeastern corner of the Queen Charlotte Islands. Archeological evidence exists for human occupation on the 14 Queen Charlotte Islands by 9300 C yr B.P. (Hobler, 1978; ACKNOWLEDGMENTS Josenhans et al., 1997) and on Prince of Wales Island in 14 southeast Alaska at 9700 C yr B.P. (Heaton et al., 1996). We thank the Captains and crews of CFAV Endeavour and CSS John P. Evidence for humans earlier than these dates is likely drowned Tully for their support in the collection of the data in Dixon Entrance and the and in most cases has been destroyed by a rapidly transgressing participants of cruises PGC90-03, PGC91-06, and PGC95-04. R. Franklin sea that rose at an average rate of 5 cm/yr (Josenhans et al., produced the graphics and early versions were improved by A. T. Hewitt and 1997). Prehistoric occupation in the Pacific Northwest may R. G. Currie. Critical revision of J. Clague and G. Thackray improved and enhanced the manuscript significantly. This is Geological Survey of Canada have been largely limited to the resource-rich coastal zone and Publication 1997151. along rivers that supported major fish runs. The late Wiscon- sinan coastline was constantly changing, and humans depen- REFERENCES dant on the coastal zone would have moved in response to these changes. Any remaining evidence of human activities at Ballantyne, V. A., Foreman, M. G. G., Crawford, W. R., and Jacques, R. this time will only be found in estuarine environments that (1996). Three-dimensional model simulations for the north coast of British have survived the early Holocene marine transgression and lie Columbia. Continental Shelf Research 13, 1655–1682. up to 100 m below present sea level. Barrie, J. V., and Bornhold, B. D. (1989). Surficial geology of Hecate Strait, Adjacent to Dixon Entrance, favorable climatic conditions British Columbia continental shelf. Canadian Journal of Earth Sciences 26, 1241–1254. for human occupation existed from 13,000 14C yr B.P. or Barrie, J. V., and Conway, K. W. (1996). Evolution of a nearshore and coastal earlier, although it would have been a much-cooler climate macrotidal sand transport system, Queen Charlotte Islands, Canada. In than today consistent with a treeless tundra environment “Geology of Siliciclastic Shelf Seas” (M. DeBatist and J. Jacobs, Eds.) pp. (Mathewes, 1989; Barrie et al., 1993; Mann and Hamilton, 233–248. Geological Society Special Publication No. 117, London. 1995). Sea level was as much as 150 m lower at this time Barrie, J. V., Bornhold, B. D., Conway, K. W., and Luternauer, J. L. (1991). GLACIATION AND SEA LEVEL, B.C./ALASKA 123

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