Chronology of middle Holocene hunter–gatherers in the Cis-Baikal region of Siberia: Corrections based on examination of the freshwater reservoir effect

Abstract

A dataset of 256 AMS radiocarbon dates on human skeletal remains from middle Holocene cemeteries in the Cis-Baikal region, Siberia, and associated carbon and nitrogen stable isotope values are analyzed for new insights about culture history and processes of culture change. First, based on the typological criteria all dated human burials are assigned to mortuary traditions and typochronological units–Late Mesolithic, Early Neolithic, Late Neolithic and Early Bronze Age. Next, all dates are corrected for the Freshwater Reservoir Effect (FRE) according to the regression equations developed using paired radiocarbon dates on human and terrestrial faunal remains from the same graves and examined for chronological trends using a Bayesian approach. While the entire corrected culture historical sequence is younger by roughly 200–400 years relative to the previous model the shift of the specific period boundaries is not systematic due to the varying proportion of aquatic food in the diets of the relevant groups. Examination of the dataset subdivided into smaller spatio-temporal units provides additional insights. During the Early Neolithic, in the Angara and Southwest Baikal micro-regions there is a chronological trend toward increased reliance on aquatic food. During the Early Bronze Age in the Little Sea micro-region, there appears to be a trend toward increased reliance on the Baikal seal. This shift, however, can also be interpreted as increasing migration over time of new groups from the Upper Lena. The sample from the Early Neolithic Shamanka II cemetery in Southwest Baikal shows two non-abutting phases of use each displaying a trend toward greater consumption of aquatic foods. These findings provide new chronological framework for the study of other cultural changes affecting middle Holocene hunter–gatherers in the region. The results may also allow better correlation with other sequences, cultural and environmental, that are not affected by the FRE.

Introduction

Middle Holocene prehistory of the Cis-Baikal region in East Siberia (Fig. 1) belongs to one of the many cases around the world where examination of materials from mortuary sites has dominated archaeological research. Grave goods and human skeletal remains have been the focus of many studies essentially since the beginning of professional archaeology in the region. Although much has been written about culture history and cultural and biological variation among these groups, many questions regarding the processes of culture change still remain unanswered (e.g., Weber and Bettinger, 2010, Weber et al., 2011). The explicit emphasis on mortuary sites also created an imbalance with regard to dating, both typological and chronometric, as well as the cultural characterization of the different periods and micro-regions. The periods with well-documented cemeteries naturally have been given much attention with many attempts to define them in cultural and chronological terms. In contrast, the periods without cemeteries (e.g., Middle Neolithic and, to a lesser extent, Late Bronze Age) have received much less attention and their cultural characteristics and temporal boundaries remain vague.

Middle Holocene prehistory of Cis-Baikal is also interesting in that it has seen a long debate about its chronology and experienced several fundamental revisions to its culture history (cf. Weber, 1995 for review). To keep the matter brief, the first relatively well-documented model of continuous progression of hunter–gatherer cultures or stages (Khin'–Isakovo–Serovo–Kitoi–Glazkovo–Shivera; Okladnikov, 1950) was criticized by many Siberian scholars and eventually fell apart under the weight of radiocarbon evidence (Konopatskii, 1982, Mamonova and Sulerzhitskii, 1989, Weber, 1995); however, the names of the relevant mortuary traditions are in use to this day without many revisions. According to the new chronological evidence, the Kitoi mortuary tradition is much older than Isakovo and Serovo, which, in turn, appear to be chronologically parallel. The Glazkovo and Shivera traditions, whose typochronological placement was based on the presence of copper and bronze objects, retain their original position at the end of the sequence. A few dates appeared to be quite old, perhaps representing the Late Mesolithic Khin' tradition in the Okladnikov model, but they were either subject to very large measurement errors or their archaeological context was compromised, thus raising doubts about the general archaeological identity of this early mortuary tradition (Weber et al., 2010).

Further reassessments of this initial radiocarbon evidence and the subsequent accumulation of a much larger set of dates by the Baikal Archaeology Project confirmed the main points of the new culture history model but also led to some revisions (Weber, 1995, Weber et al., 2002, Weber et al., 2006, Weber et al., 2010, Weber and Bettinger, 2010: Table 1). The most important of these was the identification of a roughly millennium-long period with no formal cemeteries at all, thus breaking the chronological continuity of Neolithic mortuary traditions (Weber and Bettinger, 2010, Weber et al., 2010):

Following the long-standing Russian school of archaeology, Cis-Baikal's hunter-gatherer culture history is defined on the basis of technological criteria. Thus, changes in the stone industry (i.e., mostly proliferation of the microlithic technique) define the Mesolithic, the bow and arrow, ground stone tools, and ceramics identify the Neolithic, and objects of copper and bronze the Bronze Age. Further divisions within Neolithic are based mainly on the characteristics of the mortuary protocol (see below for more detail) while within the Bronze Age on the appearance of new forms of metal artefacts. Since animal and plant domesticates were introduced into the region only during the Iron Age and historical times, respectively, subsistence of all preceding groups was based on various combinations of game and seal hunting, fishing and gathering.

The work reported in this paper represents the next step in the revisions to the middle Holocene culture history in Cis-Baikal. While the changes may at first appear as less dramatic than those associated with earlier applications of radiocarbon dating in the region, it will become evident later in the paper that they are perhaps even more important. The matter regards corrections based on the identification of a Freshwater Reservoir Effect (FRE) impacting the radiocarbon ages of human skeletal remains on which our understanding of the culture history and process of middle Holocene Cis-Baikal relies to a substantial extent.

While the marine reservoir effect has been known for some time and from many archaeological and environmental settings around the world, the importance and complexity of the FRE has been only recently recognized (e.g., Ascough et al., 2010, Cook et al., 2001, Lillie et al., 2009, Olsen et al., 2010, Higham et al., 2010, Wood et al., 2013). Its presence suspected for some time (e.g., Prokopenko et al., 1999), a FRE has also been confirmed in the aquatic system of Lake Baikal based on the comparison between dates obtained on bones from terrestrial herbivores and the Baikal seal representing the same stratigraphic units at the multilayered archaeological campsite Sagan-Zaba II on Lake Baikal (Nomokonova et al., 2013). Since the diets of middle Holocene foragers in the region included spatially and temporally variable amounts and kinds of aquatic foods (Weber et al., 2011), radiocarbon determinations made on human skeletal remains are likely to overestimate their true age to correspondingly variable degrees. To assess the extent of FRE impact on the radiocarbon age of human osteological remains, paired dating of human and animal terrestrial herbivore skeletal material from the same grave was implemented (Bronk Ramsey et al., 2014, Schulting et al., 2014, Schulting et al., 2015). Separate correction equations were developed for the entire Cis-Baikal region as well as for its constituent micro-regions: the Angara River combined with Southwest Baikal, the Little Sea area and the Upper Lena (Fig. 1).

The primary goal of this paper is a preliminary assessment of the revisions to the regional culture history resulting from the corrections to the ¹⁴C-dates available for middle Holocene hunter–gatherers from Cis–Baikal. An investigation of temporal dietary trends is our secondary goal. After these introductory notes, we present the available set of radiocarbon dates generated for Cis-Baikal and review the principles of typological dating of Cis-Baikal mortuary assemblages. We follow with the introduction of the FRE correction equations used in the paper and explain the methods of analysis. The discussion of the results is divided into two parts. Part one is an assessment of Cis-Baikal middle Holocene culture history as a whole and part two is organized by micro-regions, where more specific chronological patterns are examined. The paper ends with a summary of the findings and a number of conclusions of broader archaeological relevance.