Southeastern Archaeology ISSN: 0734-578X (Print) 2168-4723 (Online) Journal homepage: http://www.tandfonline.com/loi/ysea20 Reassessing the chronology of the Mississippian Central Illinois River Valley using Bayesian analysis Gregory D. Wilson, Mallory A. Melton & Amber M. VanDerwarker To cite this article: Gregory D. Wilson, Mallory A. Melton & Amber M. VanDerwarker (2017): Reassessing the chronology of the Mississippian Central Illinois River Valley using Bayesian analysis, Southeastern Archaeology, DOI: 10.1080/0734578X.2017.1377510 To link to this article: http://dx.doi.org/10.1080/0734578X.2017.1377510 View supplementary material Published online: 24 Sep 2017. Submit your article to this journal View related articles View Crossmark data Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ysea20 Download by: [UC Santa Barbara Library] Date: 26 September 2017, At: 14:02 SOUTHEASTERN ARCHAEOLOGY, 2017 https://doi.org/10.1080/0734578X.2017.1377510 Reassessing the chronology of the Mississippian Central Illinois River Valley using Bayesian analysis Gregory D. Wilson , Mallory A. Melton and Amber M. VanDerwarker Department of Anthropology, University of California, Santa Barbara, CA, USA ABSTRACT ARTICLE HISTORY Chronology building has long served as a major focus of archaeological interest in the Central Received 19 September 2016 Illinois River valley (CIRV) of west-central Illinois. Previous methods have relied primarily upon Accepted 6 September 2017 relative dating techniques (e.g., ceramic seriation) as a means of sorting out temporal KEYWORDS relationships between sites. This study represents the first investigation into the utility of Mississippian; Bayesian Bayesian techniques (which consider radiocarbon dates in context with archaeological analysis; ceramics; seriation; information) in the CIRV. We present the results of a detailed ceramic seriation of the region, Illinois data that we use as a priori information in our Bayesian models. We then offer contiguous, overlapping, and sequential models of site occupations in the Mississippian CIRV, review the output and appropriateness of each model, and consider their implications for the pace of sociopolitical change in the region. Issues of temporal control have long been of concern to The Central Illinois River valley Mississippian archaeologists. However, the nuts and The Central Illinois River valley is a 209-km segment of bolts of regional chronologies often go unquestioned the Illinois River running from the modern town of Mer- and unmodified for long periods of time. With edosia in Morgan County, Illinois, northeastward to advances in conceptual approaches to analyzing radio- Hennepin in Putnam County (Figure 1). Within the carbon dates and the introduction of a new generation Midwestern Taxonomic System, the Mississippian of modified accelerator mass spectrometers (AMS) that period occupation of the region is classified as the produce dates with low levels of analytical error, it is Spoon River focus based on a complex of traits including pertinent that archaeologists reevaluate existing time rectangular wall-trench houses, cord-marked shell-tem- and space constructs. In this study, we begin the pro- pered pottery, and bluff-top mortuary mounds (Cole cess of revising the Mississippian period chronology and Deuel 1937:220; Deuel 1935). Archaeologists have for the Central Illinois River valley (CIRV) of west-cen- long observed strong stylistic similarities between tral Illinois. Previous chronological systems for the Spoon River focus pottery and Mississippian assem- region relied primarily on qualitative assessments of blages from the greater Cahokia region to the south. ceramic assemblages and the analysis of a relatively Indeed, Cahokia archaeology often has been used to small number of legacy dates calculated using a conven- inform and supplement an understanding of the culture Downloaded by [UC Santa Barbara Library] at 14:02 26 September 2017 tional radiometric (beta count) dating method. Our history of the Illinois Valley (Conrad and Harn 1972; study advances these efforts by presenting a Bayesian Emerson 1991:230–231; Fowler and Hall 1975; Hall analysis of previously available radiocarbon data in 1966). For example, salvage excavations at the Cahokia combination with a new suite of 24 AMS dates from site’s (11MS2) Powell Mound led to the identification the region. In each of the three resulting models (con- of an early Mississippian period occupation dubbed the tiguous, overlapping, and sequential), radiocarbon dates “pure village site culture” associated with thin polished are quantitatively constrained by a detailed ceramic ser- pottery that contrasted with a later “Bean pot-duck effigy iation from five sequentially occupied sites in the culture” with thicker and more coarsely made pottery region. We present the results of these models and (Kelly 1933; Titterington 1938). Griffin (1941), Griffin then assess the suitability of each as a chronological (1949), Griffin (1952) later reclassified these as the Old system for the region. Village and Trappist foci. Old Village pottery was CONTACT Gregory D. Wilson [email protected] Supplemental data for this article can be accessed at https://doi.org/10.1080/0734578X.2017.1377510 © Southeastern Archaeological Conference 2017 2 G. D. WILSON ET AL. Figure 1. Map of the CIRV with study sites labeled. observed as being present at Cahokia, the Lower and a provisional Marbletown complex (AD 1300–1400). Central Illinois River valleys, the Aztalan site (47JE1) The Mississippian occupation of the LaMoine River in southern Wisconsin, the Cambria focus in the Missis- area was divided into the Gillette phase (AD 1050– sippi River valley, and the Mill Creek aspect of northwes- 1150), a combined Orendorf and Larson horizon (AD tern Iowa (Griffin 1949:48). Moreover, the subsequent 1150–1300), the Crabtree phase (AD 1300–1375), and Trappist ceramic complex was described as closely the Crable phase (AD 1375–1450). related to that of the Spoon River focus. Esarey and Conrad (1998) later revised Conrad’s sys- Downloaded by [UC Santa Barbara Library] at 14:02 26 September 2017 In a 1972 paper, Conrad and Harn further subdivided tem by calibrating the existing radiocarbon dates (Stuiver the Mississippian occupation of the CIRV into three and Reimer 1993) and constructing a four-phase sequential phases (Eveland, Larson, and Crable) based sequence for the entire region consisting of the Eveland on the qualitative analysis of ceramic assemblages from (AD 1100–1200), Orendorf (AD 1200–1250), Larson the Cooper (11F5), Crable (11F249), Dickson Mounds (AD 1250–1300), and Crable/Bold Counselor (AD (11F10), Eveland (11F353), Larson (11F3), and Sleeth 1300–1425) phases. They defined phase boundaries by (11F48) sites. The subsequent generation of a suite of comparing calibrated intercepts, and they attempted to radiocarbon dates from the region (Bender et al. 1975) integrate the various broadly defined ceramic series in allowed Conrad (1991) to revise further the existing the region. There was also an explicit attempt to synchro- chronology. Conrad created taxonomic distinctions nize the Early Mississippian Eveland phase with the Stir- between the northern (Spoon River) and southern ling phase from the greater Cahokia region, as both (LaMoine River) portions of the valley. For the Spoon phases share strong ceramic stylistic characteristics River area, he devised a three-phase sequence consisting (Conrad 1991:124–130). of the Eveland (AD 1050–1150), Orendorf (AD 1150– This long history of chronological research has 1250), and Larson phases (AD 1250–1300), followed by allowed archaeologists to identify a series of important SOUTHEASTERN ARCHAEOLOGY 3 historical developments in the region. The transition to a document the rapidly changing political, social, and Mississippian way of life appears to have begun in the economic relationships in the region. In this study, we eleventh century. This was directly associated with the present an examination of the Mississippian period political consolidation of the Cahokia polity located 77 occupation of the CIRV that relates temporal trends in river km to the south (see Conrad [1989]; Conrad ceramic design to radiocarbon dates. While such an [1991]; Harn [1991]). Bioarchaeological research has approach is not new to the region, earlier chronological revealed little evidence of intergroup violence in the systems relied primarily on qualitative assessments of region during this era (Hatch 2015). This lack of violence ceramic assemblages and the analysis of a relatively is an important observation in that the preceding Term- small number of legacy dates calculated using conven- inal Late Woodland period was characterized by a tional radiometric dating methods. Our new models decrease in interregional exchange networks and intensi- integrate and supplement these systems using Bayesian fied intergroup hostilities (Milner 1999:122). This era of analysis and prior information (e.g., ceramic seriation) relative peace ended by the beginning of the thirteenth to constrain quantitatively the probability distributions century as warfare engulfed large portions of the Mid- of calibrated radiocarbon dates from Mississippian west and Midsouth (Dye and King 2007:162; Emerson settlements in the CIRV. 2007:135–137; Krus 2016; Milner et al. 1991; Steadman As an initial step in the current analysis, Wilson con- 2008; VanDerwarker and Wilson 2016).