A Bayesian Re-Assessment of the Earliest Radiocarbon Dates from Tiwanaku, Bolivia

Abstract

ABSTRACT. The development of sociopolitical complexity at Tiwanaku around AD 500 was one of the major episodes of social change in the history of the Lake Titicaca Basin. It was the result of poorly understood processes that took place at a series of ceremonial centers in the preceding centuries. The history of Tiwanaku during this time is especially unclear, because the only radiocarbon dates are from excavations whose details were never completely published. Despite this, there is consensus that Tiwanaku was founded around 300 BC. A re-evaluation of the archaeological context of each of these dates shows many of them to be unreliable. Two Bayesian models from independent excavations agree that Tiwanaku was in fact founded centuries later, most likely around AD 110 (50-170, 1). This has important implications for widely used monolith and ceramic sequences, as well as understanding the rise of Tiwanaku and other archaic states.

Temporal Inflection Points in Decorated Pottery: A Bayesian Refinement of the Late Formative Chronology in the Southern Lake Titicaca Basin, Bolivia

“…Our data suggest we can finally abandon Janusek's (2003:45) proposed Late Formative 1B, a short subphase defined by an absence of decorated pottery (Marsh 2012a:214; Mathews 1992:65; Roddick 2009:170). The KDE plot of Kalasasaya red-rimmed vessels (the gray curve in Figure 7a) shows that these vessels were used throughout Late Formative 1 and 2.…”

“…Our only directly associated date is from Lukurmata's Structure 16 (SMU-2118; Bermann 1994:57, 103), 3 but the site's Bayesian model was able to estimate dates for three depositional events with Qeya sherds, which have medians of cal AD 420 , 440 , and 530 . We excluded dates from Tiwanaku (Hv-18) and Khonkho Wankane (AA-66948) from the models because of ambiguous associations with Qeya sherds (see details in Marsh 2012a:211), although they have similar medians: cal AD 430 and 520, respectively. There are too few reliable dates to build a model for Qeya sherds, so we prefer dating these sherds based on their consistent stratigraphical location, above both Kalasasaya styles and below Tiwanaku Redwares.…”

“…It is time to reevaluate the Late Formative chronology. Ponce Sanginés's and Janusek's phases are defined by many unreliable dates that are statistically indistinguishable and have unclear material associations (Augustyniak 2004:32; Isbell 2004:216–218; Marsh 2012a; Mathews 1992:65). All prior chronologies are based on only two sites and define temporal limits based on impressionistic best fits of rounded probability distributions (Janusek 2003:47, 51; Knobloch 2013).…”

“…Excavated contexts typically have 5% decorated sherds, but some have none at all. Until recently there were only a handful of reliable Late Formative dates from two poorly documented excavations at Tiwanaku (Kidder 1956; Ponce Sanginés 1993; see reassessment in Marsh 2012a). There are also taphonomic complications, because later occupations often disturbed Late Formative contexts (Roddick et al 2014).…”

Dating the Expansion of the Inca Empire: Bayesian Models from Ecuador and Argentina

“…The curves differ by around 20 yr for Inca-period dates, which is a small but relevant difference (Adamska and Michczyński 1996: 38; Ogburn 2012: 223). The Inca Empire is mostly located in the Southern Hemisphere, so SHCal might seem appropriate, but atmospheric mixing near the equator can extend as far south as Lake Titicaca, where IntCal is a better choice (see Finucane et al 2007:581; Marsh 2012: 205–6, 2015: 15–6). Currently, there are insufficient data to identify which curve is most appropriate for the northern and central parts of the Inca Empire.…”