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Semelhante a Preservation Potential of Submerged Archaeological Sites in Maine
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Preservation Potential of Submerged Archaeological Sites in Maine
- 1. Preservation Potential of Submerged Prehistoric Archaeological Sites on the Maine Shelf Stefan Claesson, Ph.D. Ocean Process Analysis Laboratory Joseph Kelley, Ph.D., & Daniel Belknap, Ph.D. Dept. of Earth Sciences University of Maine, Orono
- 2. Preservation Potential of Submerged Prehistoric Archaeological Sites on the Maine Shelf Stefan Claesson, Ph.D. Ocean Process Analysis Laboratory Joseph Kelley, Ph.D., & Daniel Belknap, Ph.D. Dept. of Earth Sciences University of Maine, Orono “ limited subaerial exposure of the present shelf in the Gulf of Maine…inhibited the development of coastal land forms that typically are high in archeological site potential” (Strite, 1990)
- 3. 0 4 km Bass Harbor Green Islands Georges Bank Nova Scotia Maine
- 4. Sea Level in the Gulf of Maine (Shaw et al., 2002)
- 5. Sea Level in the Gulf of Maine (Shaw et al., 2002)
- 6. Sea Level in the Gulf of Maine
- 7. Lunt biface (Crock et al., 1993) 0 4 km
- 8. Ground stone adze and spear recovered by scallop draggers (Price & Spiess, 2007) 0 2 km Morainal Ridges Basin Opening Opening
- 9. SE NW SE NW Innomar SES-2000 Benthos ROV
- 10. A B A B BH-03
- 16. METERS (Below MLLW) YEARS B.P. (Approx.) -26 -25 11,000
- 17. METERS (Below MLLW) YEARS B.P. (Approx.) -26 -25 -24 11,000 9,000
- 18. METERS (Below MLLW) YEARS B.P. (Approx.) -26 -25 -24 -23 11,000 9,000
- 19. METERS (Below MLLW) YEARS B.P. (Approx.) -26 -25 -24 -23 -22 11,000 9,000 8,000
- 20. METERS (Below MLLW) YEARS B.P. (Approx.) -26 -25 -24 -23 -22 -21 11,000 9,000 8,000
- 21. METERS (Below MLLW) YEARS B.P. (Approx.) -26 -25 -24 -23 -22 -21 -20 11,000 9,000 8,000 7,000
- 22. METERS (Below MLLW) YEARS B.P. (Approx.) -26 -25 -24 -23 -22 -21 -20 -19 11,000 9,000 8,000 7,000
- 23. METERS (Below MLLW) YEARS B.P. (Approx.) -26 -25 -24 -23 -22 -21 -20 -19 -18 11,000 9,000 8,000 7,000
- 24. METERS (Below MLLW) YEARS B.P. (Approx.) -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 11,000 9,000 8,000 7,000
- 25. METERS (Below MLLW) YEARS B.P. (Approx.) -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 11,000 9,000 8,000 7,000
- 26. Archaic Period Slowstands Late Early to Mid
- 27. Highly exposed locations are unlikely to contain undisturbed sites or sedimentary deposits The slow rate of sea-level rise provided time to accumulate Coastal/estuarine in the Gulf of Maine, as well as the erosion of glacial landforms. Sedimentary deposits between15-25 m depth representing formations between 7-11ka may be preserved because of the slow rate of local sea-level rise In Bass Harbor, human occupation occurred in a shoreline setting involving erosion of a moraine and formation of spits and wetlands near a brackish-water basin between 9 ka and 8 ka.
Notas do Editor
- This survey project was sponsored by NOAA’s Office of Ocean Exploration and Research in 2007-2008. The goal of this project was to assess the probability of recovering cultural and ecological data from submerged prehistoric landscapes on the Maine shelf.
- The conventional wisdom of geologists and prehistoric archaeologists has been that underwater sites are unlikely to exist in the Gulf of Maine. It is generally believed that landforms now submerged were not sub-aerial long enough to construct landforms that could support human occupation and preserve archaeological sites. This survey project shows, however, that this assessment is incorrect, and that there is significant potential for preservation and discovery of prehistoric archaeological sites in the region.
- In the 1990s, a number of fishermen reported recovering Archaic Period stone tools and artifacts in their scallop drags and fishing nets, particularly from an area called Blue Hill Bay south of Mt. Desert Island and Acadia National Park. To determine whether these artifacts were associated with ancient landscapes and archaeological sites, or simply isolated finds that may eroded from coastal sites, we focused our research and survey work on where artifacts were found by fishermen near Bass Harbor and the Green Islands.
- Sea level change in the Gulf of Maine has been fairly dramatic over the past 15,000 years and through the Holocene period. Deglaciation occurred on the Maine coast about 15,000 years ago. At this time, isostatic depression of land permitted a marine incursion to a local elevation of about 60 m.
- After this period, crustal rebound led to a rapid relative sea level fall to -60 m, 12,000 years ago. Coincidentally, this is also about the time that Paleoindians appear in the region. Following this local ‘lowstand’, which is very different from the global lowstand of -130 m, sea level rose rapidly again to around -20 m 11,500 years ago before stabilizing. Large landmasses of the continental shelf were sub-aerial at this time, including all of Georges Bank.
- Between 11-7,000 years ago, sea level slows its rate of rise to less than 5 m. It is this ‘slowstand’ period that our study focused on. The oldest intact coastal archaeological sites preserved on land are ca. 4,500 years old. After this point in time, there is ample evidence for coastal settlement and marine adaptation, but prior to this we know nothing about coastal habitation, mostly because it is now underwater. Our survey examined potential areas and conditions for archaeological preservation, but more broadly, the study was interested in answering questions such as, did prehistoric people occupy coastal areas and islands during the ‘slowstand’ period, and if so, how did they adapt to the coastal/marine environment?
- We began our survey by collecting very high-resolution multibeam and seismic data over areas of artifact recovery. The Green Islands was our initial target, where two Early Archaic Period biface blades were found by two different fishermen in the 1980s-90s. The Green Islands form the edge of a shelf valley, or relatively deep gorge, which is carved into bedrock. The gorge is up to 80 m below the surrounding area. This low elevation area would have been one of the first coastal areas on the Maine Shelf inundated by the sea. However, this particular area is part of a Rocky Zone with a highly eroded surface, and we believe that this type of landscape is not conducive to in situ or archaeological site preservation.
- Consequently, we focused our survey on another area on the southern coast of Mt. Desert Island at the mouth of Bass Harbor. Here, in about 20 m of water, Archaic-period artifacts were recovered by a scallop dragger in the 1990s. Multibeam survey of this area revealed 2 parallel ridges with boulder-littered surfaces on their west faces, and more fine-grained sediment surfaces to the east of distinct scarps. North of, and between the ridges, is a shallow basin with a maximum depth of 27 m containing many small depressions or pockmarks. The basin is encircled by breaks-in-slope at about 24 m, with an opening in the northeast, and another opening in the west that connects to deeper water.
- In addition to multibeam sonar, 18 km of chirp, seismic reflection profiles were collected with an Innomar SES2000. The sub-bottom sonar record revealed that the base of the ridges are part of a massive acoustic unit, interpreted as glacial till, or the remnants of a glacial moraine. In-between the ridges, in the basins, is highly stratified glacial marine mud. We ground-truthed these seafloor features using a Rossfelder vibracorer, which was able to extract sediment cores to a depth of nearly 4 m. The vibracores confirm that the spits and scarps that accumulated over the ridges contain intact, Holocene-period deposits.
- The chirp sub-bottom profiler was able to resolve very fine sediment layers within the ridges, which traditional sub-bottom technologies are unlikely to detect. This information was critical in selecting targets to vibracore. We found that the buried sand and gravel layers in the ridges corresponded precisely with the litho-logical changes in the sub-bottom profiles at depths of 1 and 2 m.
- In these cores, the very bottom layers were compacted with an abundance of articulated oysters, clams and gastropods. Several of these shells were in life position, in pristine condition, and showed no signs of transport. These bottom-most shells were also radiocarbon dated to ca. 9,100 BP, signifying clear evidence of the presence of an estuarine system.
- In the cores, we also documented two very organic-rich peat beds. In the upper bed we had perfectly preserved eelgrass that dated ca. 8,000 BP. In a deeper bed, we found plant remains, within which we were able to identify numerous fresh and brackish-water diatoms, suggesting the presence of a nearby freshwater environment.
- The data from the cores, complemented by diatom and pollen analysis, suggests that Bass Harbor was initially a freshwater basin situated in a tundra-like environment.
- However, as sea level rose and infiltrated the basin, it transitioned to an estuarine and barrier beach system, which would have been conducive to human settlement at that time.
- Finally, around 8,000 years ago the moraines slowly began to submerge, making the area increasingly uninhabitable.
- This animation of relative sea level rise over the existing bathymetry shows more precisely how the landscape transformed from a freshwater to marine environment over a period of approx. 4,000 years. The rising ocean reached the basin around 10,000 BP, and by 9,000 BP it was an intertidal system. At this same time, waves from the northwest began to erode glacial till, washing sand and gravel over the crest of the glacial moraines. Longshore currents then began to form spits along the ridges. By 7,000 BP, these coastal features were mostly submerged.
- This animation of relative sea level rise over the existing bathymetry shows more precisely how the landscape transformed from a freshwater to marine environment over a period of approx. 4,000 years. The rising ocean reached the basin around 10,000 BP, and by 9,000 BP it was an intertidal system. At this same time, waves from the northwest began to erode glacial till, washing sand and gravel over the crest of the glacial moraines. Longshore currents then began to form spits along the ridges. By 7,000 BP, these coastal features were mostly submerged.
- This animation of relative sea level rise over the existing bathymetry shows more precisely how the landscape transformed from a freshwater to marine environment over a period of approx. 4,000 years. The rising ocean reached the basin around 10,000 BP, and by 9,000 BP it was an intertidal system. At this same time, waves from the northwest began to erode glacial till, washing sand and gravel over the crest of the glacial moraines. Longshore currents then began to form spits along the ridges. By 7,000 BP, these coastal features were mostly submerged.
- This animation of relative sea level rise over the existing bathymetry shows more precisely how the landscape transformed from a freshwater to marine environment over a period of approx. 4,000 years. The rising ocean reached the basin around 10,000 BP, and by 9,000 BP it was an intertidal system. At this same time, waves from the northwest began to erode glacial till, washing sand and gravel over the crest of the glacial moraines. Longshore currents then began to form spits along the ridges. By 7,000 BP, these coastal features were mostly submerged.
- This animation of relative sea level rise over the existing bathymetry shows more precisely how the landscape transformed from a freshwater to marine environment over a period of approx. 4,000 years. The rising ocean reached the basin around 10,000 BP, and by 9,000 BP it was an intertidal system. At this same time, waves from the northwest began to erode glacial till, washing sand and gravel over the crest of the glacial moraines. Longshore currents then began to form spits along the ridges. By 7,000 BP, these coastal features were mostly submerged.
- This animation of relative sea level rise over the existing bathymetry shows more precisely how the landscape transformed from a freshwater to marine environment over a period of approx. 4,000 years. The rising ocean reached the basin around 10,000 BP, and by 9,000 BP it was an intertidal system. At this same time, waves from the northwest began to erode glacial till, washing sand and gravel over the crest of the glacial moraines. Longshore currents then began to form spits along the ridges. By 7,000 BP, these coastal features were mostly submerged.
- This animation of relative sea level rise over the existing bathymetry shows more precisely how the landscape transformed from a freshwater to marine environment over a period of approx. 4,000 years. The rising ocean reached the basin around 10,000 BP, and by 9,000 BP it was an intertidal system. At this same time, waves from the northwest began to erode glacial till, washing sand and gravel over the crest of the glacial moraines. Longshore currents then began to form spits along the ridges. By 7,000 BP, these coastal features were mostly submerged.
- This animation of relative sea level rise over the existing bathymetry shows more precisely how the landscape transformed from a freshwater to marine environment over a period of approx. 4,000 years. The rising ocean reached the basin around 10,000 BP, and by 9,000 BP it was an intertidal system. At this same time, waves from the northwest began to erode glacial till, washing sand and gravel over the crest of the glacial moraines. Longshore currents then began to form spits along the ridges. By 7,000 BP, these coastal features were mostly submerged.
- This animation of relative sea level rise over the existing bathymetry shows more precisely how the landscape transformed from a freshwater to marine environment over a period of approx. 4,000 years. The rising ocean reached the basin around 10,000 BP, and by 9,000 BP it was an intertidal system. At this same time, waves from the northwest began to erode glacial till, washing sand and gravel over the crest of the glacial moraines. Longshore currents then began to form spits along the ridges. By 7,000 BP, these coastal features were mostly submerged.
- This animation of relative sea level rise over the existing bathymetry shows more precisely how the landscape transformed from a freshwater to marine environment over a period of approx. 4,000 years. The rising ocean reached the basin around 10,000 BP, and by 9,000 BP it was an intertidal system. At this same time, waves from the northwest began to erode glacial till, washing sand and gravel over the crest of the glacial moraines. Longshore currents then began to form spits along the ridges. By 7,000 BP, these coastal features were mostly submerged.
- The early slowstand period on the Maine shelf was likely conducive to coastal settlement. What is unclear, is if the Late Archaic slowstand was a continuation of earlier cultural traditions and maritime subsistence, or something very different. There is evidence of inland fishing and hunting in the Early and Middle Archaic periods, but no evidence of coastal adaptation, and this is something that will remain unknown until a submerged site from this period is located, excavated and studied. This study focused primarily on establishing preservation potential, and given the preservation potential and presence of artifacts in Bass Harbor, this is a very promising area for locating such an archaeological site.
- What is known is that: In rocky zones such as the Green Islands, the presence of isolated finds are possible, but the presence of intact archaeological sites are unlikely. Preservation potential can be narrowed to areas on the Maine shelf to water depths between 15 and 25 m. This represents the early slowstand period between 11-7,000 years ago. There was ample time during this initial slowstand period for estuarine systems to form – areas that would have been suitable for human habitation. Therefore, human occupation at the Bass Harbor site, in a beach/estuarine setting, was possible 10-8,000 years ago.
- Continued research in submerged prehistoric archaeology is critical toward discovering an underwater archaeological site on the Maine shelf. Such a discovery can inform us not only about the early cultural origins and coastal adaptations of Native Americans in the Gulf of Maine, but also will inform us about early Holocene climate and the impact of future sea level rise on coastal environments. For questions about this research project please contact Stefan Claesson.