When a Tree Falls… A New Approach to Interpreting … · 2020-03-18 · When a Tree Falls… A...
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When a Tree Falls… A New Approach to Interpreting Archaeological Sites in Northern Alberta Krista Gilliland 1 , Jody Pletz, Petr Kurzybov, Peter Stewart, Rob Kadis, and Terrance Gibson 2 Western Heritage, 46A Riel Drive, St. Albert, Alberta, Canada, T8N 3Z8. 1 [email protected], 2 [email protected] Introduction Many archaeological sites in northern Alberta’s boreal forests are difficult to interpret compared to non-boreal sites because: • artifact assemblages are dominated by lithics that have limited interpretive value • poor organic preservation prevents radiocarbon dating • slow sediment accumulation rates can contribute to poor preservation of occupation layers and/or to mixing of artifacts from different time periods in the same layer • disturbance processes (tree throw, cryoturbation) can redistribute artifacts • incomplete understandings of site formation processes can result in erroneous or incomplete interpretations of archaeological sites Boreal forest region in Alberta 1 . Anatomy of a Profile Increasing Understandings Goal To increase understandings of boreal forest archaeology sites by improving the nature and quality of the data collected during routine historic resources impact assessments (HRIAs). Methods Economical, efficient, and easy Sediment-based approach: • Field descriptions of texture, colour •Portable optically-stimulated luminescence (POSL) 2 **(POSL); Uses an optical signal to measure time since sediment was last exposed to sunlight Study sites from HRIAs conducted in northern Alberta during 2013 and 2014 field seasons New Perspectives Unsolved Mysteries • Identifying possible multiple occupations • Documenting extent of disturbances • Suggesting that some sites are of considerable antiquity • Correlating relative chronologies locally and regionally • Contributing to regional palaeoenvironmental reconstructions • Can we work toward establishing regional chronologies using OSL calibration curves 4 ? • What do OSL signals of boreal forest sediments represent? • How do site formation and disturbance processes in the boreal forest actually work? • How to improve correlations of artifacts with sediments? • Some sites appear to be of considerable antiquity • OSL dating could produce archaeologically meaningful ages • The extent of site disturbance is difficult to detect visually • Possibility of distinguishing multiple occupation periods at a site or group of sites • Archaeological stratigraphies can contribute enormously to past understandings of cultural and environmental dynamics of the region GaPv-14 ST133P 1 10 9 8 7 6 5 4 3 11 2 Loamy sand Loamy sand Loamy sand Loamy sand Coarse sand 0 10 20 30 40 50 Root mat Sandy clay loam 1E+03 1E+04 1E+05 1E+06 1E+07 1 02 03 04 05 06 07 08 09 10 11 0.5 1 1.5 1 02 03 04 05 06 07 08 09 10 11 1E+04 1E+05 1E+06 1E+07 1E+08 1 02 03 04 05 06 07 08 09 10 11 1.25 2 2.75 3.5 1 02 03 04 05 06 07 08 09 10 11 0 0.2 0.4 1 02 03 04 05 06 07 08 09 10 11 IRSL (counts) IRSL depletion OSL (counts) OSL depletion IRSL/OSL 1E +04 1.25 2.0 2.75 0.2 0.4 0.0 0.5 1.0 1.5 1E +03 1E +06 1E +06 1E +05 1E +07 1 2 3 4 5 6 7 8 9 10 11 1E +05 1E +07 1E +08 1E +04 3.5 POSL interpretation Relatively rapid deposition Loamy sand in Samples 9, 8 have higher feldspar content (i.e. IRSL/OSL ratio) than underlying Samples 11, 10; may represent influx of freshly eroded material Pause or change in deposition at about 40 cm BS (i.e. above Sample 8, as seen in no. of counts) Relatively rapid deposition Fluctuations in depletion and IRSL/OSL ratios suggest increased variability in source and/or nature of depositional processes compared with above and below; possible transition period (i.e. from fluvial to aeolian deposition) Gradual deposition (no. of counts in Sample 4 is an order of magnitude larger than that in Sample 1), although possible depositional break (B) before Sample 1 Consistency in depletion and IRSL/OSL ratios suggest similar sediment source and depositional processes, particularly when compared to underlying samples POSL results are consistent with interpretation that Samples 4-1 represent aeolian deposition Fluvial Aeolian B Artifact zone Over 200 lithic flakes recovered from between 5-30 cm BS but no visible stratigraphic breaks- Disturbance? Intact? Coarser sands below 30 cm are interpreted as fluvial/glaciofluvial 3 Field texture and colour are especially important to note for more accurate interpretations Age-with-depth pattern suggests minimal disturbance Distinct sediment source from ~25 cm to surface Gradual deposition from ~ 25 cm to surface Depositional break between ~15 and 8 cm BS Rapid depositional phases for fluvial sediments Depositional break ~40 cm BS Conclusions • Disturbance does not appear to be responsible for artifact distributions • Distinct break at ~25 cm BS likely corresponds to onset of Holocene aeolian deposition • At least 2 occupation periods likely • Oldest occupation may be considerably older than younger one • May be able to date the site using OSL Oldest artifact- bearing sediments are one order of magnitude older than the youngest sediments Calgary Edmonton Foothills Natural Region Upper Foothills Lower Foothills Canadian Shield Natural Region Kazan Uplands Parkland Natural Region Central Parkland Peace River Parkland Foothills Parkland Grassland Natural Region Mixedgrass Northern Fescue Foothills Fescue Dry Mixedgrass 2005 Natural Regions and Subregions of Alberta 2005 Natural Regions and Subregions of Alberta - Alberta Sustainable Resource Development, Alberta Environment, Alberta Community Development and Agriculture and Agri-Food Canada, June 2005 Boreal Forest Natural Region Athabasca Plain Upper Boreal Highlands Lower Boreal Highlands Peace-Athabasca Delta Northern Mixedwood Dry Mixedwood Central Mixedwood Boreal Subarctic Rocky Mountain Natural Region Montane Alpine Subalpine These conditions are obstacles to effectively interpreting, managing, and protecting the archaeology of past cultures that inhabited the northern Alberta region, an area that is undergoing intensive developmental pressure. Boreal Region Field sampling for POSL- almost as easy as shovel testing! Identifying multiple occupations at sites and correlating relative chronologies across a region References 1. Modified from Government of Alberta. 2005. Natural Regions and Subregions of Alberta. Alberta Sustainable Resource Development, Alberta Environment, Alberta Community Development and Agriculture and Agri-Food Canada, Edmonton. 2. Sanderson, D.C W. and S. Murphy. 2010. Using simple portable OSL measurements and laboratory characterisation to help understand complex and heterogeneous sediment sequences for luminescence dating. Quaternary Geochronology 5(2-3):299-305. 3. Fenton, M.M., E.J. Waters, S.M. Pawley, N. Atkinson, D.J. Utting and K. Mckay. 2013. Surficial Geology of Alberta. In ERCB/AGS Map 601. Scale 1:1,000,000. Energy Resources Conservation Board, Edmonton. 4. E.g. Bateman, M. D., S. Stein, R.A. Ashurst and K. Selby. 2014. Instant luminescence chronologies? High resolution luminescence profiles using a portable luminescence reader. Quaternary Geochronology, http://dx.doi.org/10.1016/j.quageo.2014.12.007. Charles Schweger, Department of Anthropology Palaeoecology Laboratory, University of Alberta Tim Kinnaird, David Sanderson, and Simon Murphy, Scottish Universities Environmental Research Centre Robin Woywitka, Alberta Culture and Tourism Canadian Forest Products and Millar Western Whitecourt Acknowledgements Rapid deposition Distinct sediment source Possible disturbance POSL of this Swan Hills profile in- dicated that both buried soils and the overlying sands likely date to a similar time period, and that the sands overlying the buried soils share a similar source that the un- derlying soils do not. This work has the potential to influence cur- rent and future palaeoenvironmen- tal and archaeological reconstruc- tions in the region. GfPs-18 ST712P Ae 11 10 9 8 7 6 5 4 3 1 2 Depth of artifact recoveries 10 20 30 40 cm BS 0 Stratigraphy Root mat with abundant charcoal Description Clay with frequent rounded cobbles Soil horizon 10YR 3/3 10YR 4/4 10YR 5/4 Bm Decreasing age Silty clay loam with abundant rounded cobbles Clay with few rounded cobbles C Interpretation Formation of soil horizons indicates long-term stability of the soil surface (i.e. minimal disturbance) Parent material is interpreted as possibly glaciofluvial in nature Association of artifacts within sediments that include rounded cobbles suggest either disturbance or that the artifacts were deposited along with reworked sediments Possibility that seasonal or episodic flooding of a river during the early postglacial period resulted in localized redistribution of artifacts in this location Artifact distributions are within sediments that ap- pear to be fluvial or glaciofluvial in nature. Visual observation, soil characteristics, and POSL sug- gest this profile is intact. Future work should focus on investigations of site formation processes and correlating artifact recoveries with their associated sediments.
Transcript of When a Tree Falls… A New Approach to Interpreting … · 2020-03-18 · When a Tree Falls… A...
When a Tree Falls…A New Approach to Interpreting Archaeological Sites in Northern Alberta
Krista Gilliland1, Jody Pletz, Petr Kurzybov, Peter Stewart, Rob Kadis, and Terrance Gibson2
Western Heritage, 46A Riel Drive, St. Albert, Alberta, Canada, T8N 3Z8. [email protected], [email protected]
IntroductionMany archaeological sites in northern Alberta’s boreal forests are difficult to interpret compared to non-boreal sites because:
• artifact assemblages are dominated by lithics that have limited interpretive value
• poor organic preservation prevents radiocarbon dating• slow sediment accumulation rates can contribute to poor preservation of occupation layers and/or to mixing of artifacts from different time periods in the same layer
• disturbance processes (tree throw, cryoturbation) can redistribute artifacts
• incomplete understandingsof site formation processescan result in erroneous or incomplete interpretations of archaeological sites
Boreal forest region in Alberta1.
Anatomy of a Profile
Increasing Understandings
GoalTo increase understandings of boreal forest archaeology sites by improving the nature and quality of the data collected during routine historic resources impact assessments (HRIAs).
MethodsEconomical, efficient, and easySediment-based approach:
• Field descriptions of texture, colour•Portable optically-stimulated luminescence (POSL)2
**(POSL); Uses an optical signal to measure time sincesediment was last exposed to sunlight
Study sites from HRIAs conducted in northernAlberta during 2013 and 2014 field seasons
New Perspectives
Unsolved Mysteries
• Identifying possible multiple occupations• Documenting extent of disturbances
• Suggesting that some sitesare of considerable antiquity
• Correlating relative chronologies locally and regionally
• Contributing to regionalpalaeoenvironmental reconstructions • Can we work toward establishing regional chronologies using
OSL calibration curves4?• What do OSL signals of boreal forest sediments represent?• How do site formation and disturbance processes in the boreal forest actually work?
• How to improvecorrelations of artifactswith sediments?
• Some sites appear to be of considerable antiquity• OSL dating could produce archaeologically meaningful ages• The extent of site disturbance is difficult to detect visually• Possibility of distinguishing multiple occupation periods at a site or group of sites
• Archaeological stratigraphies can contribute enormously to past understandings of cultural and environmental dynamics of the region
GaPv-14ST133P
1
10
9
87
6
5
4
3
11
2
Loamy sand
Loamy sand
Loamy sand
Loamy sand
Coarse sand
0
10
20
30
40
50
Root mat
Sandy clay loam
1E+03 1E+04 1E+05 1E+06 1E+07
1
02
03
04
05
06
07
08
09
10
11
0.5 1 1.51
02
03
04
05
06
07
08
09
10
11
1E+04 1E+05 1E+06 1E+07 1E+08
1
02
03
04
05
06
07
08
09
10
11
1.25 2 2.75 3.5
1
02
03
04
05
06
07
08
09
10
11
0 0.2 0.41
02
03
04
05
06
07
08
09
10
11
IRSL(counts)
IRSLdepletion
OSL(counts)
OSLdepletion IRSL/OSL
1E+04 1.25 2.0 2.75 0.2 0.40.00.5 1.0 1.5
1E+03
1E+06
1E+06
1E+05
1E+07
1
2
3
4
5
6
7
8
9
10
11
1E+05
1E+07
1E+08
1E+04 3.5
POSL interpretation
Relatively rapid deposition
Loamy sand in Samples 9, 8 have higherfeldspar content (i.e. IRSL/OSL ratio) than underlying Samples 11, 10; may represent influx of freshlyeroded material
Pause or change in deposition at about 40 cm BS(i.e. above Sample 8, as seen in no. of counts)
Relatively rapid deposition
Fluctuations in depletion and IRSL/OSLratios suggest increased variability in source and/or nature of depositional processes comparedwith above and below; possible transition period (i.e. from fluvial to aeolian deposition)
Gradual deposition (no. of counts in Sample 4 isan order of magnitude larger than that in Sample 1),although possible depositional break (B) before Sample 1
Consistency in depletion and IRSL/OSLratios suggest similar sediment source and depositional processes, particularly whencompared to underlying samples
POSL results are consistent with interpretation thatSamples 4-1 represent aeolian deposition
Fluvial
Aeolian
B
Artif
act
zoneOver 200 lithic flakes
recovered frombetween 5-30 cm BSbut no visible stratigraphic breaks-Disturbance? Intact?
Coarser sands below30 cm are interpretedas fluvial/glaciofluvial3
Field texture andcolour are especiallyimportant to notefor more accurateinterpretations
Age-with-depth pattern suggests minimal disturbance
Distinct sediment source from ~25 cm to surface
Gradual deposition from ~ 25 cm to surface
Depositional break between ~15 and 8 cm BS
Rapid depositional phases for fluvial sediments
Depositional break ~40 cm BS
Conclusions• Disturbance does
not appear to be responsible for artifact distributions
• Distinct break at ~25 cm BS likely corresponds to onset of Holocene aeolian deposition
• At least 2 occupation periods likely
• Oldest occupation may be considerably older than younger one
• May be able to date the site using OSL
Oldest artifact-bearing sediments are one order of magnitude older than the youngest sediments
Calgary
Edmonton
Foothills Natural RegionUpper Foothills
Lower Foothills
Canadian Shield Natural RegionKazan Uplands
Parkland Natural Region
Central Parkland
Peace River Parkland
Foothills Parkland
Grassland Natural Region
Mixedgrass
Northern Fescue
Foothills Fescue
Dry Mixedgrass
2005 Natural Regions and Subregions of Alberta
2005 Natural Regions and Subregions of Alberta - Alberta Sustainable Resource Development, Alberta Environment,
Alberta Community Development and Agriculture and Agri-Food Canada, June 2005
Boreal Forest Natural Region
Athabasca Plain
Upper Boreal Highlands
Lower Boreal Highlands
Peace-Athabasca Delta
Northern Mixedwood
Dry Mixedwood
Central Mixedwood
Boreal Subarctic
Rocky Mountain Natural Region
Montane
Alpine
Subalpine
These conditions are obstacles to effectively interpreting, managing, and protecting the archaeology of past cultures that inhabited the northern Alberta region, an area that is undergoing intensive developmental pressure.
Boreal Region
Field sampling for POSL-almost as easy as shoveltesting!
Identifying multiple occupations at sites and correlating relative chronologies across a region
References1. Modified from Government of Alberta. 2005. Natural Regions and Subregions of Alberta. Alberta Sustainable Resource Development, Alberta Environment, Alberta Community
Development and Agriculture and Agri-Food Canada, Edmonton.2. Sanderson, D.C W. and S. Murphy. 2010. Using simple portable OSL measurements and laboratory characterisation to help understand complex and heterogeneous sediment
sequences for luminescence dating. Quaternary Geochronology 5(2-3):299-305.3. Fenton, M.M., E.J. Waters, S.M. Pawley, N. Atkinson, D.J. Utting and K. Mckay. 2013. Surficial Geology of Alberta. In ERCB/AGS Map 601. Scale 1:1,000,000. Energy
Resources Conservation Board, Edmonton.4. E.g. Bateman, M. D., S. Stein, R.A. Ashurst and K. Selby. 2014. Instant luminescence chronologies? High resolution luminescence profiles using a portable luminescence
reader. Quaternary Geochronology, http://dx.doi.org/10.1016/j.quageo.2014.12.007.
Charles Schweger, Department of Anthropology Palaeoecology Laboratory, University of AlbertaTim Kinnaird, David Sanderson, and Simon Murphy, Scottish Universities Environmental Research CentreRobin Woywitka, Alberta Culture and TourismCanadian Forest Products and Millar Western Whitecourt
Acknowledgements
Rapiddeposition
Distinct sedimentsource
Possible disturbance
POSL of this Swan Hills profile in-dicated that both buried soils and the overlying sands likely date to a similar time period, and that the sands overlying the buried soils share a similar source that the un-derlying soils do not. This work has the potential to influence cur-rent and future palaeoenvironmen-tal and archaeological reconstruc-tions in the region. GfPs-18
ST712P
Ae11
109
876
5
4
3
1
2
Depthof artifactrecoveries
10
20
30
40
cm BS0
Stratigraphy
Root mat withabundant charcoal
Description
Clay with frequentrounded cobbles
Soil horizon
10YR 3/3
10YR 4/4
10YR 5/4
Bm
Decreasingage
Silty clay loam withabundant rounded cobbles
Clay with fewrounded cobbles
C
Interpretation
Formation of soil horizonsindicates long-term stability of the soil surface (i.e. minimaldisturbance)
Parent material is interpretedas possibly glaciofluvial innature
Association of artifacts withinsediments that include roundedcobbles suggest either disturbanceor that the artifacts were depositedalong with reworked sediments
Possibility that seasonal orepisodic flooding of a river duringthe early postglacial period resulted in localized redistributionof artifacts in this location
Artifact distributions are within sediments that ap-pear to be fluvial or glaciofluvial in nature. Visual observation, soil characteristics, and POSL sug-gest this profile is intact. Future work should focus on investigations of site formation processes and correlating artifact recoveries with their associated sediments.
