Shifting sites and shifting sands: a record of prehistoric human/landscape interactions from Porcupine Strand, Labrador

Smith, Jennifer Suzanne (2005) Shifting sites and shifting sands: a record of prehistoric human/landscape interactions from Porcupine Strand, Labrador. Masters thesis, Memorial University of Newfoundland.

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Abstract

Porcupine Strand, on the central coast of Labrador, has experienced dramatic landscape changes since deglaciation: sea level has fallen over 110m; the former nearshore seabed now lies exposed, forming the coastal lowlands; powerful glacier-fed braided rivers flowed across the northern lowlands, carrying sand and gravel to the sea; with sea-level change, the coastline configuration has evolved from a large indented embayment to a relatively straight shoreline. Although most of this landscape change occurred quite rapidly during the two or three millennia following deglaciation, considerable change must have been witnessed by humans since they first occupied the Strand over 7200 ¹⁴C BP. Perhaps the most notable of these were changes in sea level and related coastline displacement, climate variability and its impact on landscape processes (e.g., coastal erosion, sand dune activity), and vegetation change. Because prehistoric cultures relied heavily on marine resources and located their habitation sites close to the active shoreline, the position of ancient shorelines is critical in planning archaeological surveys and interpreting site function in the context of local environment and landscape. -- The primary objectives of this research are: (1) to refine postglacial relative sea-level history using new radiocarbon-dated geological and archaeological samples; (2) to reconstruct palaeoshoreline elevation and configuration for selected time slices using relative sea-level records, topography and mapped raised marine features; and (3) to interpret the local landscape context of archaeological sites preserved in sand dunes and on raised beaches. -- Two 1:50,000 scale surficial geology maps (13H114 E and Wand 13I/3 W) were prepared from aerial photograph interpretation and limited field mapping as baseline data for the study. Glaciofluvial sand and gravel, deposited in front of the retreating Laurentide Ice Sheet, constitute a large proportion of the surficial sediment in the map area. Coastal exposures, extending tens of kilometres along the Strand, reveal thick deposits of glaciomarine mud and sand overlying rare occurrences of till and bedrock. Glaciomarine sediments were deposited by glacier-fed meltwater streams onto the glacioisostatically depressed coastal lowlands, forming Hjulström type deltas. Raised shorelines were identified up to 116 m above present sea level. Fossiliferous mud and sand underlie much of the coastal lowlands, and in places is obscured by bog. Organic samples (4 shell, 2 driftwood) from raised marine sediments were collected for radiocarbon dating. They range in age from 30 to 8820 ¹⁴C BP. Aeolian deflation of emerged glaciomarine sand has resulted in the development of dune systems discontinuously along the entire Strand. Radiocarbon dates on buried soils (n=10) and peaty horizons (n=2) in the dunes range between 40 and 3000 ¹⁴C BP and indicate periodic cycles of stabilization and reactivation. Coastal hills and upland surfaces consist mostly of exposed or concealed bedrock having only minor till cover. -- Holocene marine limit elevation declines from 116 m in the south to 98 m above sea level (asl) in the north. The establishment of marine limit is estimated to be between 9000 and 8000 ¹⁴C BP based on a marine shell date in the south and a previously published age on the isolation of a freshwater basin to the north, respectively. Initial emergence was rapid in the south at 6.4 m/century until 7000 ¹⁴C BP, when relative sea level dropped below the modem shoreline. No data are available to reconstruct the submerged interval of sea-level history. Farther north, initial emergence was slightly slower at 4.6 m/century until 6000-7000 ¹⁴C BP. After this time the relative sea-level record is poorly constrained and may represent either continued slow emergence to present or emergence followed by submergence. This latter scenario is supported by the apparent absence of raised marine deposits in the age range 30 to 6750 ¹⁴C BP and evidence for recent coastal submergence (e.g. coastal cliff recession). -- Many archaeological sites are located on raised beaches. All prehistoric groups are represented by sites within 15 m of sea level. No obvious pattern is identified between site age and elevation; however this may be explained by the small change in the relative sea level position over the last 6000 to 7000 ¹⁴C BP. If sites older than 7000 ¹⁴C BP are present, they should occur on shorelines higher than 15 m asl. The position and configuration of these shorelines are reconstructed using the refined sea-level history and available topographic data for the Strand. These shorelines tend to be highly embayed in contrast to the relatively straight shorelines of the last 7000 ¹⁴C BP or so. These reconstructed coastal landscapes should help refine search strategies for older archaeological site on the Strand. -- The oldest radiocarbon-dated soil suggests that sand dune development has primarily occurred over the last 3000 ¹⁴C BP. Buried soils and peat horizons overlie strongly indurated marine and glaciomarine sediments. These sediments are the likely source of the aeolian sand. Twelve radiocarbon-dated buried soils and peat indicate eight periods of dune re-vegetation and stabilization in the last 500 ¹⁴C BP, which were likely due to changing local conditions (e.g., aridity, forest fires, and human activity). -- Over half of the archaeological sites recorded on the Strand are exposed in sand dunes through deflation. As a result, much of the artifact evidence and related cultural features (e.g., fire hearths) are reworked onto the bottoms of blowouts and have lost their stratigraphic context. Archaeological sites were located in four blowouts which also contain dated soil horizons. Generally, there is weak correspondence between the interpreted age of the cultural material and the radiocarbon-dated soil horizons exposed in blowout walls. This is thought to reflect the locally variable and complex dune stratigraphy. Caution is therefore advised in using dated soil horizons in sand dunes to define cultural history of local archaeological sites along the Strand.

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