Methods
The basis of the Pech de l'Azé IV Layer 8 method is the removal of intact blocks from the site for excavation in the lab. Blocks are removed in plaster jackets with a board placed on one face for support. Prior to removal, three faces of the block are already exposed because of the way the bench we are excavating is configured. However, two additional faces and the underside have to be separated from the adjacent sediments and underlying bedrock through minimal excavation and cutting. Prior to plastering the block, a detailed 3D model is made using structure from motion. After plastering the block and prior to removal, multiple datums are placed on the block and recorded with a total station in the same site grid that was used for the 2000-2003 Pech de l'Azé IV excavations.
Once transported back to the lab, the blocks are placed on their side. A frame is then built around three sides of the block and the space between this frame and the block is filled with expansive foam. As the foam dries, additional datums are placed in the foam. Once the block is stable in the frame, the datums on the block itself are recorded using our EDM software and a Microscribe. Knowing when the datums should read in the Pech IV grid system (see step above) and now knowing what they read in the local grid established by the Microscribe, we are then able to translate the local coordinates from the Microscribe into Pech IV coordinates. Once this translation is verified, we record the new datums lodged in the foam surrounding the block. Then again, once these have been verified, we can begin to remove the plaster jacket from the block.
Next two faces of the block are carefully cleaned (the upper surface and one side section). Much of this cleaning is done with the vacuum system which lifts the sediments and prevents them from smudging the section. When the section is perfectly cleaned, we then photograph it including an additional 3D structure from motion model. Because the exposed section is the section that was hidden at the site, we now have a detailed documentation of the stratigraphy on both sides of the block (in addition to details of the stratigraphy on adjacent blocks). The project geologists then prepare a detailed microstratigraphy of the block which will serve as the guide for excavating it.
Excavation is conducted in 10 cm square surfaces to a depth of 1 cm (excavating in from the side because the block in laying on its side). Sediment is loosened using standard excavation tools and immediately vacuumed into vials. The custom build vacuum system uses a 1.4 mm diameter hose and 50 ml vials. All artifacts are recorded using the standard protocols what we have used at all of our sites. Namely, all bones and stones larger than 2.5 cm are piece provenienced using the Microscribe. Elongated artifacts are recorded with two points to capture their orientation. Thus when a square surface is finished, all of its sediments are in vials (usually 2-3 vials), all of the natural clasts and artifacts from 1.8 mm to 2.5 cm are stored in a bag, and all artifacts larger than 2.5 cm are individually stored in their own bags. Each of these items carries a barcode with tracks its information in the recording system. All vials are immediately placed in cold storage, and artifacts are not washed. All excavation and analysis is conducted while wearing gloves.
At the end of each day, all data coming from the project are merged into a single relational spatial database. This database also contains all of the information from the previous excavations. Thus our finds can be placed in context with the previous finds. We are developing methods for better visualization of these data including extensive use of 3D imagery, extracted orthosections, and augmented reality.
The key to the system, however, is the sediment. The sediments from a vial are then divided and sent to the various specialist on our team for analyses. These analyses include testing for biomarkers, aDNA, pollen analysis, and magnetic susceptibility. We are open to additional analyses of the sediment that may provide insights into the use of fire in Layer 8 but also the paleoenvironmental context.
