Supplementary material to comment on “Emergence of Complex Societies after Sea Level Stabilized” by J. W. Day Jr. et al.
Paul A. Washington, Kutztown University, Kutztown, Pennsylvania
Citation:
Washington, P. A. (2007), Comment on “Emergence of complex societies after sea level stabilized” by J. W. Day et al.
Eos Trans. AGU, 88(42), 429.
[Full Article (pdf)]
Day et al. [2007] have made a provocative proposal that complex societies evolved around 6000 BP in response to the increased marine productivity of marginal marine and inner shelf ecosystems following sea level stabilization around 7000 BP. Although the effects of sea level stabilization on societal evolution must have been significant, and the known record of complex societies does indeed begin shortly after sea level stabilized, neither a connection between complex society emergence and increased marine productivity nor the assertion that complex societies emerged at this time are necessarily warranted.
The proposal that marine ecosystems responded to the stabilization of the shoreline following the average 10 meters per 1000 years sea level rise and resultant flooding of the continental shelves during the latest Pleistocene and early Holocene is reasonable, and this increased productivity must have provided a substantial boost to coastal societies. Nevertheless, Day et al.'s [2007] proposal that this stabilization of the shoreline was the impetus for the development of complex societies falls apart when the resource use of the most prominent of these early societies is examined.
The emerging Nile Valley (including deltaic “Lower Egypt”), Mesopotamia (including Ur), the Indus Valley, and the Lower Mississippi Valley societies (the emerging complex societies that left the most robust records of organized construction) were all based on the exploitation of riparian and riverine resources, not on marginal marine or shelf resources as claimed by Day et al. [2007]. To claim that these riparian and riverine environments are extensions of the coastal system is to lump together vastly different ecosystems simply because they responded to a common forcing factor (i.e. sea level rise and stabilization). Specifically, the cultures of the Nile Valley, Mesopotamia, and the Indus Valley were centered around the exploitation and cultivation of riparian grains. The coeval Middle and Late Archaic societies of the Lower Mississippi Valley (of which Poverty Point was a later member) were centered more than 300 kilometers inland and primarily exploited riverine resources (fresh-water fish and mussels) [Strickland, 2003; Saunders et al., 2005].
Exploitation of these resources may, indeed, be related to the stabilization of sea level, as the alluvial response to rising sea level may have created an unstable fluvial and riparian environment. Alluvial aggradation within the lower reaches of the aforementioned river valleys was nearly as dramatic as the sea level rise, as river gradients were reduced and low-stand valleys infilled with coarse alluvium in response to sea level rise. The reduced rate of aggradation and concomitant grain-size reduction of the alluvial sediments following stabilization [Aslan and Autin, 1999] would have been favorable to the development of the grain-centered agriculture that was the basis of the emergent Nile, Mesopotamian, and Indian societies. The stabilization of alluvial systems and the lowering of fluvial gradients also would have made it easier to exploit the riverine fish and shellfish populations. Thus, proposing that sea level stabilization may have contributed to societal development is reasonable, but only as long as not all societal development is directly linked to changes in the marine ecosystem. Any linkage to the increased productivity of the marine ecosystem needs to be society-specific and can only apply to coastal societies, which does not accurately characterize any of the aforementioned river valley societies.
At the same time, the claim that these environments would have been so unstable as to not allow exploitation of riverine and riparian resources on a large, organized scale belies the geomorphic analysis of the lower Mississippi Valley (the most studied of these systems and the one most affected by glacial sediment outwash and meltwater) that indicates river channels were relatively stable throughout the late Pleistocene and early Holocene, with any path alterations occurring abruptly and resulting in subsequent long-term stability (Saucier, 1994; Rittenour et al., 2007). In addition, the presence of bedrock or active tectonic barriers (e.g., Washington, 2001; Washington and Chenoweth, 2005) within these river valleys provided large, semi-stable, riparian and riverine environments even during periods of rapid incision and aggradation in other portions of the valley systems. Thus, it is quite possible that the appropriate environmental conditions existed for river-valley cultures to have developed and flourished during this time.
The assertion that complex societies emerged worldwide around 6000 BP promulgates a standard myth within the anthropology and archaeology communities. Although it is true that the oldest preserved evidence of urbanized societies is around 6000 years old, the reason may simply be the preservation and visibility of societal structures rather than the actual emergence of the societies that constructed these features. As Day et al. [2007] have stated, sea level rise averaged about 1 meter per century (i.e. 1 centimeter per year), with a corresponding coastal migration of 1000 to 20000 times that rate (i.e. 1 to 20 kilometers per century, or 10 to 200 meters per year). Significant sea level rise results in flooding of former shoreline locations by wave-dominated coastal waters, which tends to remove surficial materials and sediments; this process can be expected to have drowned and then destroyed evidence of earlier coastal societies. The temporal correspondence between the oldest significant preserved remains of coastal society (La Venta, Mexico) with sea level stabilization is not surprising, mainly because older remains would have been drowned and mostly or completely destroyed. I would argue that the immediacy of the occupation of the barrier islands at La Venta following sea level stabilization indicates that the society was already developed to a critical level prior to the sea level stabilization and had probably occupied earlier barrier island locations, but that those locations were lost to the continuing sea level rise.
Likewise, evidence of pre-6000 BP river valley societies is likely to have been obscured by the effects of sea level rise. Aggradation of alluvial systems during the early Holocene was a consequence of sea level rise and was only slightly smaller in magnitude, generally reaching average rates of more than 50 centimeters per century in the lower valleys where most of the early societal remains occur. This rapid aggradation lagged slightly behind sea level rise; alluvial stabilization did not occur until around 6000 BP in the Lower Mississippi Valley [Saucier, 1994; Aslan and Autin, 1999], a full millennium after sea level stabilized. Thus, any structures built significantly before around 6000 BP in the Lower Mississippi Valley floodplain can be expected to have been buried; a mound system the size of Watson Brake (around 5500 BP) [Saunders et al., 2005] would have been completely buried if it had been constructed 6500 BP or earlier, and even the 23 meters high mound A at Poverty Point (around 3800 BP) would have been buried if it had been built in the floodplain before 9000 BP. Although both of these systems are built on valley-bounding terraces that were not buried, similar geomorphic locations that were adjacent to tributary river channels throughout the lower Mississippi Valley even two millennia earlier are nearly all buried beneath several meters of alluvium. Similar aggradation rates occurred in Mesopotamia, the Nile Valley, the Indus Valley, and along the other major river systems where early riparian societies flourished. Thus, it would not be surprising if earlier societies existed in these valleys but the evidence of their existence had been deeply buried by the alluvial aggradation accompanying sea level rise.
Since all evidence of any pre-7000 BP coastal societies is expected to be drowned or destroyed, and all evidence of any pre-6000 BP riparian societies is expected to be deeply buried, only those pre-7000 BP societies that were located in upland environments or upstream of rock or tectonic barriers (i.e. protected from Late Pleistocene incision and subsequent burial) can be expected to have had a chance of being preserved. However, none of the earliest known complex societies existed in such settings, so it is not surprising that we do not have evidence of earlier complex societies in those settings either. Therefore, it is not only possible, but quite likely, that the earliest preserved evidence of complex societies represents the beginning of preservation within a much longer continuum of complex societal sites, with the stabilization of sea level and consequent stabilization of alluvial systems being the key factors for the beginning of preservation.
References
Aslan, A., and W. J. Autin (1999), Evolution of the Holocene Mississippi River floodplain, Ferriday, Louisiana: insights on the origin of fine-grained floodplains, Journal of Sedimentary Research, 69, 800-815.
Day, J. W., Jr., J. D. Gunn, W. J. Folan, A. Yáñez-Arancibia, and B. P. Horton (2007), Emergence of complex societies after sea level stabilized, EOS Trans. AGU, 88(15), 169-171.
Rittenour, T. M., M. D. Blum, and R. J. Goble (2007), Fluvial evolution of the lower Mississippi River valley during the last 100 k.y. glacial cycle: response to glaciation and sea-level change, Geological Society of America Bulletin, 119, 586-608.
Saucier, R. T. (1994), Geomorphology and Quaternary Geologic History of the Lower Mississippi Valley, U.S. Army Corps of Engineers, Waterways Experiment Station, 2 vols.
Saunders, J. W., R. D. Mandel, C. G. Sampson, C. M. Allen, E. T. Allen, D. A. Bush, J. K. Feathers, K. J. Gremillion, C. T. Hallmark, H. E. Jackson, J. K. Johnson, R. Jones, R. T. Saucier, G. L. Stringer, M. F. Vidrine (2005), Watson Brake, a Middle Archaic mound complex in northeast Louisiana, American Antiquity, 70, 631-668.
Strickland, C. L. (2003), The use of fish otoliths and analytical techniques for paleoenvironmental interpretation in Archaic archaeological sites in north Louisiana, M.S. Thesis, University of Louisiana at Monroe, 142p.
Washington, P. A. (2001), Geomorphic evidence for the origins and draining history of Paleolake Monroe, Ouachita River Valley, Louisiana and Arkansas, Gulf Coast Association of Geological Societies Transactions, 51, 367-377.
Washington, P. A., and M. S. Chenoweth (2005), Changing river patterns in northeastern Louisiana during the Holocene - interplay of tectonics and aggradation, Geological Society of America, Abstracts with Programs, 37 (2), 40.
