Early-Middle Holocene Cultural and Climate Shifts in NW Africa
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Early-Middle Holocene Cultural and Climate Shifts in NW Africa: Paleoenvironmental Reconstruction Using Stable Isotopes of Land Snail Shells. A thesis submitted to the Graduate School of the University of Cincinnati in partial fulfillment of the requirements for the degree of Master of Science Department of Geology McMicken College of Arts and Sciences By: Abigail Padgett B.S. University of Mississippi, 2016 Advisory Committee: Yurena Yanes, Ph.D – Committee Chair Andrew Czaja, Ph.D Aaron Diefendorf, Ph.D Abstract The long–term response of humans to climate/environmental changes can be assessed by studying climate proxy records extracted from well–described, dated, and preserved archaeological sequences. Two Holocene Capsian sites from NE Algeria, document a marked change in subsistence strategies near 8,200 cal yrs BP. To examine the potential relationship between cultural shifts and environmental change, analyses were conducted using the stable oxygen (δ18O) and carbon (δ13C) isotopic composition of archaeological shells of the terrestrial gastropod Helix melanostoma from the early to mid–Holocene (10,500 to 6,500 cal yrs BP). This study provides intra–shell and whole shell isotopic profiles to infer seasonal, as well as average local environmental conditions in NE Algeria. The δ18O and δ13C results illustrate that conditions were notably wetter between ~10,000–8,500 cal yrs BP, coinciding with the African Humid Period (AHP), whereas the environment turned significantly drier at ~8,160-7,300 cal yrs BP, immediately after the 8,200 cal yrs BP climate event. These results suggest that noticeable humidity fluctuations occurred during the Early Holocene in NE Algeria and could have impacted the economy and strategies of prehistoric human groups in the area. ii iii Acknowledgements This research would not have been possible without the guidance and support from the following people: First, I would like to sincerely thank the Department of Geology at the University of Cincinnati and it’s faculty members for giving me the opportunity to study what I love, travel, and meet many great people. I am truly honored to have been apart of such a wonderful community. Biggest thanks to my advisor and role model, Dr. Yurena Yanes. I am so appreciative for Dr. Yanes’ patience, honesty, advice, and financial support over the past two years. Her dedication has pushed me to become a better scientist and overall person. I have truly grown as an individual under her guidance and I am lucky to have her as an advisor and friend. Much appreciation extends out to my committee members, Dr. Andy CzaJa and Dr. Aaron Diefendorf, and my collaborator, Dr. David Lubell, for all the contributions feedback, edits, and questions that encouraged me to think critically. I would also like to acknowledge the Society for Sedimentary Geology for providing funding to this proJect. This work was also possible with the help from the University of Illinois Natural History Survey for providing access to some of the sample material used for this research. Lab members Wesley Parker, Evan New, Nora Soto, and Richard Stephenson made my time in the Yanes Lab a tremendous and supportive experience. I am grateful to have found lifetime friends in each of them. I also express much recognition to Anastasia Fries, Sonia Sanchez, Julianne Fernandez, Tim Paton, Shannon Neale, Zoey Dodson, Jenelle Wallace, and the rest of my fellow graduate students for your kindness, friendship, and willingness to give advice, and discuss research. Finally, I would like to thank my parents, grandparents, and other family members for all your continuous support and love throughout this endeavor. A special thanks to my sister Rachel for our almost daily chats that always made me laugh, even on the worst days. I would like to dedicate this thesis to my father, Joey Padgett and grandmother Barbara Guin– thank you for believing in me and supporting my decision to go into the field of geoscience. I truly could not have made it this far without you all. iv Table of Contents Abstract……………………………………………………………………………….…… ii Acknowledgements…………………………………………………………………….…. iv List of Figures………………………………………………………………………….…. vii List of Tables……………………………………………………………………………....viii 1. Introduction………………………………………………………………………………1 2. Background……………………………………………………………………………… 3 2.1 Capsian Culture…………………………………………………………………. 3 2.2 Present Day Climate & Climate Mechanisms in NE Algeria……………………4 2.3 Holocene Climate History in NW Africa……………………………………….. 7 2.4 Current Vegetation in NE Algeria………………………………………………. 8 3. Methods………………………………………………………………………………….. 9 3.1 Archaeological Context of Kef Zoura D………………………………………... 9 3.2 Archaeological Context of Aïn Misteheyia……………………………………. 10 3.3 Ecology of Helix melanostoma………………………………………………… 11 3.4 Environmental controls on land snail shell δ18O………………………………. 12 3.5 Environmental controls on land snail shell δ13C………………………………. 14 3.6 Sample Selection………………………………………………………………. 16 3.7 Radiocarbon Dating of Shells…………………………………………………. 16 3.8 Stable Isotope Analysis…………………………………………………………17 4. Results………………………………………………………………………………….. 20 4.1 AMS Radiocarbon Dates…………………………………………………….... 20 v 4.2 Oxygen stable isotope composition of modern shells……………………….. 21 4.2.1 Intra-shell data……………………………………………………..... 21 4.2.2 Whole shell data…………………………………………………….. 22 4.3 Oxygen stable isotope composition of archaeological shells…………………..22 4.3.1 Intra–shell data……………………………………………………… 22 4.3.2 Whole shell data…………………………………………………….. 23 4.4 Carbon stable isotope composition of modern shells………………………..... 24 4.4.1 Intra–shell data……………………………………………………… 24 4.4.2 Whole shell data……………………………………………………. 24 4.5 Carbon stable isotope composition of archaeological shells…………………. 24 4.5.1 Intra–shell data……………………………………………………... 24 4.5.2 Whole shell data……………………………………………………. 25 5. Discussion……………………………………………………………………………... 26 5.1 Environmental significance of δ18O in modern shells……………………….. 26 5.2 Paleoclimatic inferences from δ18O in archaeological shells………………... 28 5.3 Environmental significance of δ13C in modern shells……………………….. 31 5.4 Paleoclimatic inferences from δ13C in archaeological shells………………... 32 5.5 Climate mechanisms explaining observed patterns…………………………..34 5.6 Has Holocene climate change triggered cultural shifts in NE Algeria? ……..35 6. Conclusion…………………………………………………………………………….36 Figures………………………………………………………………………………….. 38 Tables…………………………………………………………………………………… 47 References…………………………………………………………………….………… 52 vi List of Figures Figure 1: Geographical setting of the Maghreb region in NW Africa. ………………… 38 Figure 2: Geographical location of the studied archeological sites in northeast Algeria. Figure courtesy of David Lubell, University of Waterloo. Modified from the original in Lubell et al. (1976). …………………………………………………………………… 39 Figure 3: Present-day climate data for the study area in NE Algeria. From Bowen, (2017); Bowen et al., (2005); www.noaa.gov; and www.IAEA.org. ………40 Figure 4: Box plots of intra-shell Helix melanostoma δ18O and δ13C divided by their respective age. …………………………………………………………………………… 41 Figure 5: Intra-shell δ18O values in Helix melanostoma shells throughout snail lifespan. ………………………………………………………………………………42 Figure 6: Box plots of Helix melanostoma average δ18O and δ13C according to their respective age. ……………………………………………………………………………. 43 Figure 7: Intra-shell δ13C of Helix melanostoma shells throughout snail lifespan. …….. 44 Figure 8: Comparison of δ18O and δ13C of Helix melanostoma from NE Algeria (this study) and Libya from Prendergast et al., (2016). ……………………………………………….. 45 Figure 9: Relationship between intra–shell and whole shell Helix melanostoma δ18O and the documented change is subsistence strategies within the Capsian archaeological records in NE Algeria. ………………………………………………………………………………46 vii List of Tables Table 1: Modern monthly climate data in NE Algeria for the recording period between 1998 and 2006. From Bowen, (2017); Bowen et al., (2005); www.noaa.gov; www.iaea.org……………………………………………………………………………… 47 Table 2: AMS 14C dates of archeological Helix melanostoma shells from Capsian archaeological sites, NE Algeria. ………………………………………………….……… 48 Table 3: Intra-shell oxygen stable isotopes of modern and archaeological Helix melanostoma shells from Capsian archaeological sites, NE Algeria. …………………….. 49 Table 4: Intra-shell carbon stable isotopes of modern and archaeological Helix melanostoma shells from Capsian archaeological sites, NE Algeria. …………………….. 50 Table 5: Whole-shell oxygen and carbon stable isotopes of modern and archaeological… 51 Helix melanostoma shells from NE Algeria. viii ix 1. Introduction Climate is a major contributing factor to human civilization and livelihood. The relationship between climate and humans affects migration and settlement patterns, dietary resource availability, enhances certain cultural practices, and motivates the development of technology (Buckland et al., 1996; deMenocal, 2001; Mayewski et al., 2004). Climatic extremes can lead to environmental thresholds that result in alterations in human subsistence strategies, human migration to more climatically preferred locales, or societal collapse all together (Cullen et al., 2000; deMenocal, 2001; Luzzadder-Beach et al., 2012). One major scientific challenge of the 21st century is to determine how civilization will respond to the rapidly changing global climate. Understanding the rate and consequences of climate change on human populations is therefore critical for better predicting the consequences