Archaeological Data

People have always lived along the coast, as a source of food and transportation. This trend continues today, with 100 million people worldwide presently living within 1 m of mean tide level (Houghton et al., 1996). As sea levels rose during the Holocene, inundation of settlements and structures from the late Neolithic onward has provided a wealth of potential information for the sea level researcher. The advantages of archaeological data are clear enough. First, dating, particularly with classical cultures of the Mediterranean, Mes-oamerica, and elsewhere, can be very precise, often to within decades using pottery and other artifacts. Second, the relations between the evidence and mean sea level, most notably structures from ancient ports, can also be drawn fairly precisely. A recent archetypal use of archaeological data for reconstruction of sea level history is the work undertaken in the Severn Estuary of southern Britain, where Neolithic trackways, Bronze Age waterlogged wooden buildings, Roman military ditches, and Medieval dikes in coastal wetlands and nearshore tidal flats provide detailed evidence of transgressive and regressive episodes dating back some 3000 years (Allen, 1987; Allen and Rae, 1987; Allen and Fulford, 1988; Whittle, 1989).

Apart from Spanish colonial-era structures, like remnants of an early 17th-century fort at Parris Island, South Carolina, that lies below MSL today (National Academy of Sciences, 1987), shell and other middens are the major archaeological archive for sea level information for the U.S. Atlantic Coast prior to British settlement. Indeed, much of what has been proposed for the late sea level changes in South Carolina and Georgia (Colquhoun and Brooks, 1986; DePratter and Howard, 1977) has relied on middens and associated artifacts. However, few data on past sea levels have been viewed with more suspicion. The rationale is actually quite reasonable: native peoples, having learned to their travail of the great perishability of shellfish, almost immediately cleaned and consumed their catches at the handiest location, the shoreline. Naturally, the sites preferred were those also close to proven sources of shellfish, like oyster reefs. Over time considerable mounds of shell debris accumulated, creating the midden (see Fairbridge, 1976).

In fact, there are ample grounds for believing that this is generally what happened. Most buried shell middens reported in the literature are often in contact with intertidal sediments like salt or estuarine marsh peats (e.g., Colquhoun and Brooks, 1986) or beach sands and ridges (e.g., Stapor et al., 1991). Thus, middens within a carefully worked-out stratigraphic/geomorphic framework can be considered shoreline markers of a sort, but the debate centers in how close to the former shoreline and how high above the past sea level position. Fairbridge (1976) described criteria for the identification of paleo-Indian campsites in Brazil and suggested that most sites were established at least 1 m above normal high tide to prevent flooding even by exceptional events like storms. However, the top of the midden can rise over time substantially above MSL; Fairbridge (1976), in studies of Brazilian middens, suggests as much as 20 m until finally abandoned. Hence, very large middens, built within the last several thousand years, can only provide sea level elevation minima, since apart from postestablishment erosion or destruction, they are unlikely to have been inundated and buried (cf. Fairbridge, 1976; Fig. 2.5).

As testaments to human interactions with the coast, archaeological data add an appealing dimension to sea level studies that perhaps begs the issue of their suitability in many instances. But, in the best-case scenarios where their relationships to former sea levels can be reliably determined, they can provide a measure of dating control (often down to within a decade) that exceeds most other methods.

TRANSGRESSIVE STAGES GLOBAL SYNTHESIS-OLDER (Fairbridge, I960 PERON

REGRESSIVE STAGES-------Bahama

Emergence

YOUNGER PERON

ABROLHOS ROTTNESTPP┬░"">┬░

Roman or (or

Emergence Emergence Emergence

CANANEIA IPARANAGUAI

brazil-----ALEX ANDRO

SUBMERGENCE

SUBMERGENCE- SUBMERGENCE

northern europe ATLANTIC E A'RLY ^climato-stratisraphy -ff SUBB.OREAL (Blvtt-Sernonder)

YOUNGER PERON

Emergence Emergence Emergence

CANANEIA IPARANAGUAI

brazil-----ALEX ANDRO

SUBMERGENCE

SUBMERGENCE- SUBMERGENCE

northern europe ATLANTIC E A'RLY ^climato-stratisraphy -ff SUBB.OREAL (Blvtt-Sernonder)

7000 Yr. b.P 6000

Figure 2.5 Sea level curve for the Brazilian coast from Fairbridge (1976). Note the inclusion of midden dates in the construction of the curve, which are generally construed as indicating transgressive phases.

7000 Yr. b.P 6000

Figure 2.5 Sea level curve for the Brazilian coast from Fairbridge (1976). Note the inclusion of midden dates in the construction of the curve, which are generally construed as indicating transgressive phases.

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