Studying sediment for clues to the past

A small team of archaeologists and members of Secwepemc communities dig test pits in a hay field next to the Eagle River, east of Sicamous, under the July sun. Everyone is covered in the fine, powdery silt that sticks to their sweat dampened clothes as they dig carefully placed test pits, fill handheld shaker screens lined with 6 mm steel mesh, shake out the sediment, and examine what is left for artifacts and bones. Nearby an archaeologist hand cranks a soil auger, taking a sediment sample of deposits over two meters deep. She pulls the auger up hand over hand, careful to do it in a smooth motion so the loose sand does not run out the bottom of the auger bit. She holds the auger bit over a screen and gives it an expert shake. Rich, dark orange sediment followed by a thin black layer slide out onto the screen mesh.

“I’ve got a paleosol at two point five metres in the bottom of this shovel test!”

Everyone stops what they are doing and crowds around the screen, commenting on how well developed the soil is, and grumbling about how much more work they must do.

An important part of archaeology rarely found in local museums, stratigraphy (the study of sediment layers and soils laid down over time) can tell archaeologists many things about the past: what the landscape and climate looked like thousands of years ago, the relative age of artifacts or other cultural objects, and about the people who lived in this region. It also tells archaeologists how deep to dig.

In some places around Kamloops, archaeologists and Secwepemc community members have found stone tools over ten thousand years old, buried eight meters below the surface. Through careful recording and study of the layers of sediment laid down on top of these artifacts, archaeologists can understand how, over the millennia, sand, silt, and clay carried by lakes, rivers, wind, and landslides have covered up and modified the landscape.

In other places around Kamloops, artifacts of a similar age can be found right on, or right below, the surface. The archaeologists and Secwepemc people who find these artifacts can stand in the same spot as a person who lived thousands of years ago, look out onto the landscape, and wonder what it might have looked like back then.

A paleosol, staining created by acid and chemicals leaching into the sediment below from rotting leaf litter, tells archaeologists that an ancient ground surface covered with plants, shrubs, and trees once existed below the modern landscape; a surface that people might have once have hunted, fished, gathered, danced, and gamed on.

Under the surface of ancient pithouse or ‘Kekuli’ depressions (semi-subterranean dwellings common on the interior plateau, starting around 4500 years ago), archaeologists record a complex ‘layer cake’ of stratigraphy uncovered in an excavation, which archaeologists can sometimes reconstruct into a record of generations of its occupants. Some housepit depressions can have hundreds of layers of “cultural stratigraphy”, telling a vivid and detailed story.

As much information as the study of stratigraphy can offer to archaeologists, Secwepemc communities, and anyone interested in the deep past of what we now call British Columbia, the most valuable archaeological sites are those that are left intact, as the act of excavating and recording the stratigraphy of a site destroys it. The archaeological record is non-renewable and many sites have already been disturbed or destroyed by highways, railways, and housing developments; it behooves everyone to preserve what is left for future generations to study.