OSL Dating of the Tolleston Beach at Indiana Dunes National Lakeshore and Its Implications for Interpreting the Archaeological R
Total Page：16
File Type：pdf, Size：1020Kb
University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Dissertations & Theses in Earth and Atmospheric Earth and Atmospheric Sciences, Department of Sciences 10-2018 OSL Dating of the Tolleston Beach at Indiana Dunes National Lakeshore and its Implications for Interpreting the Archaeological Record Malgorzata Mahoney University of Nebraska-Lincoln, [email protected] Follow this and additional works at: http://digitalcommons.unl.edu/geoscidiss Part of the Earth Sciences Commons Mahoney, Malgorzata, "OSL Dating of the Tolleston Beach at Indiana Dunes National Lakeshore and its Implications for Interpreting the Archaeological Record" (2018). Dissertations & Theses in Earth and Atmospheric Sciences. 111. http://digitalcommons.unl.edu/geoscidiss/111 This Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Dissertations & Theses in Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. OSL Dating of the Tolleston Beach at Indiana Dunes National Lakeshore and its Implications for Interpreting the Archaeological Record by Malgorzata Mahoney A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science Major: Earth and Atmospheric Sciences Under the Supervision of Professors David B. Loope and Paul R. Hanson Lincoln, Nebraska October, 2018 OSL Dating of the Tolleston Beach at Indiana Dunes National Lakeshore and its Implications for Interpreting the Archaeological Record Malgorzata Mahoney, M.S. University of Nebraska, 2018 Advisors: David B. Loope and Paul R. Hanson The puzzling scarcity of archaeological sites on the Tolleston Beach, the most lakeward shoreline complex at Indiana Dunes National Lakeshore, prompted an investigation into the development of these parabolic dunes in an attempt to determine whether the distribution of known archaeological sites is governed by ancient human behaviors, or influenced by its dune setting which can affect site preservation and discoverability. In order to accurately understand patterns of past human occupation, it is important to know the timing and extent of dune reactivation. Specifically, whether it was frequent enough to influence settlement patterns in the past, or if it was extensive enough to disturb archaeological deposits later on. Soil samples collected from shovel test pits and from vibracores on the crests of two compound parabolic dunes were dated using Optically Stimulated Luminescence to refine the chronology of the Tolleston, determine the age of near surface deposits (those accessible to archaeologists using standard field methods), and to evaluate the validity of applying those methods in this environment. An examination of sedimentary structures in the vibracores and the variability within the OSL data demonstrated that, even for the shallowest samples in this study, bioturbation was likely not significant enough to affect the reliability of the OSL ages. The Tolleston dunes were shown to be active around 4 thousand years ago and possibly also around 2 thousand years ago. OSL ages from shovel test pits clustered around the timing of stabilization of the parabolic dunes on the Tolleston, while ages from the deeper vibracore samples represented the earliest stages of their formation. Subsequent dune reactivation appears to have not been substantial enough to place archaeological deposits outside of the reach of standard archaeological methods, essentially validating the use of these methods to inventory cultural resources in this environment. Since the geologic setting does not appear to preclude the archaeologists’ access to potential archaeological resources, the sparse distribution pattern of human occupation on the Tolleston Beach might be better explained by exploring cultural habitation choices of past populations. iv Table of Contents 1. Introduction ……………………………………………………….………………………………………. 1 1.1 Purpose of study ……………….…………………………..…………………………………. 1 1.2 Regional setting ………………………...…………………………………………………….. 4 1.3 Archaeology at Indiana Dunes National Lakeshore ……………………… 11 1.4 Shallow OSL sampling and bioturbation ………..……………………………... 16 2. Methods …………………………..………………………………………………………………………… 20 2.1 Field sampling ……………………………………………………………………………….. 20 2.2 Laboratory preparation ……………………..…………………………………………. 21 2.3 OSL measurement and data processing ……………...………………………… 22 2.4. Dose rate estimation ………………………………………………..…………………… 22 3. Results …………………………………………………………………………………………………..…... 24 3.1. Dune Acres results …………………………………..……………………………………. 24 3.2 Stagecoach results ……………………………………………………………..………….. 31 3.3 West Beach results …………………………………………..……………………………. 33 3.4 Summary …………………………………………….…………………………………………. 34 4. Discussion …………………………..…………………………………………………………………….. 37 4.1 Dating the Tolleston ……………………...………………………………………………. 37 4.2 OSL and archaeology ………………………………...…………………………………… 46 4.3 Archaeology at Indiana Dunes National Lakeshore ……………………… 50 5. Conclusions and recommendations for future work …….………………….... 53 References cited ………………………………………………………………………………………...… 56 Appendix 1: Archaeological sites on the Tolleston Beach …………………...… 63 Appendix 2: Vibracore photographs ………………………………………………………… 66 Appendix 3: OSL data ………………………………………………………………………………….. 70 1 1. Introduction 1.1 Purpose of Study Stretching along the southern shore of Lake Michigan between Gary and Michigan City, Indiana, Indiana Dunes National Lakeshore (INDU) contains three relict shoreline complexes which preserve a record of fluctuating lake levels in the 14,500-year-long post glacial history of the Lake Michigan basin (Figure 1; Chrzastowski and Thompson 1992, 1994). It also preserves a 10,000-year-long history of human occupation in the area (Bringelson and Sturdevant 2007). While the robust archaeological record on two older shorelines within INDU attests to widespread human occupation in the past, the distribution of archeological sites on the youngest, most lakeward dune system – the Tolleston Beach – is sparse, especially at its westernmost extent which comprises the West Unit of the park. The lack of prehistoric sites could be explained in three possible ways: (1) prehistoric people chose not to occupy this area, or they did, but either (2) the nature of the geologic setting prevents us from reaching the depth necessary to recover that record using standard archaeological methods, or (3) the sites were eroded and thus not preserved. Recognizing the challenges associated with interpreting archeology in coastal sand dune environments (Lovis et al. 2009, 2012a, 2012b), this study addresses the question as to whether the distribution of archaeological sites at the park reflects cultural choices of past populations or the natural constraints of the environment. 2 Recent studies (Argyilan et al. 2014; Kilibarda et al. 2014) have shed light on the geologic history of the Tolleston dune field, its initial formation, stabilization and subsequent episodes of reactivation. But the extent and chronology of this reactivation, and especially its impact on shallow deposits is not well understood. This study uses Optically Stimulated Luminescence (OSL) dating to determine the age of near surface deposits in the older, more landward, part of the Tolleston, where remnants of the oldest human occupation may be preserved. In order to understand patterns of past human occupation, it is important to know the timing and extent of dune reactivation, whether it was frequent enough to influence settlement patterns, or if it was extensive enough to disturb archaeological deposits later on. Even if the episodes of eolian reactivation were localized events, they have the potential to affect both the preservation of archaeological sites and our chances of discovering them. OSL dates obtained in previous studies on the Tolleston come almost exclusively from a depth beyond 1 m below the ground surface in an attempt to avoid dating potentially bioturbated sediments (Argyilan et al. 2014; Kilibarda et al. 2014; G.W. Monaghan, personal communication 2017). However, the purpose of this study is to determine the age of shallow deposits which are accessible to archaeologists using standard archaeological field methods (such as shovel testing) and to determine the validity of applying those methods in this environment. Most samples analyzed in this study were collected from dune crests at the depth of 0.7 m below ground surface. This sampling strategy placed them at a depth that is beyond the soil’s A horizon, which is usually most affected by root growth and other 3 bioturbating agents, but still within the normal range of a standard shovel test. If the sediment found at this depth is heavily bioturbated, then this information can be used in deciding on a better, more suitable survey method in the future. Additional OSL samples were collected from vibracores. They extend the vertical column to almost 3 m depth and provide a comparative context for the shallower samples. They also facilitate an examination of sedimentary structures which can be used to evaluate the extent of bioturbation at different depths. Furthermore, a comparison with ages from deeper samples throughout the park will help archaeologists and geologists explore the question as to whether any significant sediment reactivation has happened since dunes were