Detecting human-knapped flint with marine high-resolution reflection seismics: A preliminary study of new possibilities for subsea mapping of submerged Stone Age sites

Abstract

Seismic high-resolution Chirp profiles from the welldocumented submerged Stone Age settlement Atlit-Yam, located off Israel's Carmel coast, display systematic disturbances within the water column not related to sea-floor cavitation, vegetation, fish shoals, gas or salinity/temperature differences, where flint debitage from the Stone Age site had been verified archaeologically. A preliminary series of controlled experiments, using identical acquisition parameters, strongly indicate that human-knapped flint debitage lying on the sea floor, or embedded within its sediments, produces similar significant responses in the water column. Flint pieces cracked naturally by thermal or geological processes appear not to do so. Laboratory experiments, finite element modelling and controlled experiments conducted in open water on the response to broad-spectrum acoustic signals point to an excited resonance response within humanknapped flint even for sediment embedded debitage, with acoustic signals within the 2-20 kHz interval. The disturbances observed in the water column on the seismic profiles recorded at Atlit-Yam are, therefore, based on these results, interpreted as resonance from human-knapped flint debitage covered by up to 1.5 m of sand. Such a principle, if substantiated by further research, should facilitate efficient and precise mapping of submerged Stone Age sites.

Acoustic Mapping of Submerged Stone Age Sites—A HALD Approach

“…The role of sound in relation to the knapping process is of course interesting, but its further implications are also potentially useful. Given that, when excited by tapping, detached lithics can produce what appear to be single tones or rather narrow frequency intervals, they may also resonate when excited by an acoustic signal within the relevant frequency intervals and, as a consequence, produce a measurable acoustic response, as already documented in the Bang & Olufsen Sound Laboratory by Hugo Rasmussen in 1982 (Figures 2 and 3) [41]. These results were later independently replicated in the Wellbore Acoustic Lab at Texas A&M University in two experiments undertaken in 2018.…”

“…It was the first known submerged Stone Age site to which this method was applied (in 2015). Within the surveyed part of the settlement, the recordings showed a strong correlation between the areas with knapped flint and preserved structures and the 'haystacks' (Figure 9) [41] observed in the water phase-a very specific noise-related phenomenon, apparently caused by the knapped lithics. An important aspect of these findings is that acoustic responses that were positionally stable over time were obtained from areas where the cultural deposits were covered by up to 2 m of medium-sized sand (Figure 9).…”

“…After the samples were placed on the seafloor clear acoustic responses were obtained from the positions where the knapped samples were placed but only from these positions, also when these pieces were embedded in sediment in plastic buckets. The naturally cracked pieces produced no detectable responses (Figure 7) [41,54]. Acoustic response features from knapped lithics generally distinguish themselves from gas bubbles in the water phase by not stretching all the way from the seafloor to the water surface.…”

“…Opposite the mobile responses from fish or fish shoals the lithic response features are stabile over time with regard to position. That such features, repeating themselves at numerous passages of the test samples at three different test locations in shallow water (2.0-7.5 m) [41,54], should be the result of 'processing artefacts', too short recording windows, etc. is so unlikely that it can be excluded.…”

“…Therefore, the development of a methodology that can map submerged Stone Age sites directly and efficiently, including buried sites, will represent a significant contribution to underwater archaeology. A major opportunity in this respect is the response to acoustic excitation obtainable from the knapped lithics that are the hallmark of the Stone Age, but not from naturally cracked lithic pieces [41,42]. This paper presents an innovative and cost-effective acoustic Human-Altered Lithic Detection (HALD) approach to mapping submerged Stone Age sites, which is currently under development.…”