עבודת גמר )תזה( לתואר Thesis for the degree דוקטור לפילוסופיה Doctor of Philosophy
מוגשת למועצה המדעית של Submitted to the Scientific Council of the Weizmann Institute of Science מכון ויצמן למדע Rehovot, Israel רחובות, ישראל
מאת By יותם אשר Yotam Asscher
תארוך תקופת המעבר ברונזה/ברזל בדרום הלבנט באמצעות C 14
Dating the Bronze to Iron Age Transition in the Southern Levant: A Radiocarbon Study
מנחה: :Advisor פרופ' סטיב ויינר Prof. Steve Weiner ד'ר אליזבטה בוארטו Dr. Elisabetta Boaretto
אלול תשע"ה August 2015 1 Acknowledgements First and foremost, I would like to thank my two supervisors – Prof. Steve Weiner and Dr. Elisabetta Boaretto. I couldn’t have asked for better role models, having both of you as supervisors is the best thing I could have asked for enjoying my research.
Steve – You are a driving force: I am constantly inspired by your vast knowledge, dedication, and tireless drive to initiate new projects. I admire your ability to get excited about any good result and your encouragement when the results aren’t looking so good. You have built an empire for on-site archaeological science that I am privileged to be part of. I’m grateful for your encouragement, support and guidance, all of which helped me develop into an “archaeo- chemist” able to ask archaeological questions and develop the research methods to solve them. Above all, I thank you for giving me opportunity to do MA in archaeology during my PhD, and for having the patience to help me develop my writing skills, which I know must not have been easy. Lastly, I’ll always cherish the moment we learned that Eppendorf is the best container to dissolve phytoliths (Friday morning 14/6/13). Lisa – You taught me everything about 14C, politics in the academic world, and how to work hard and have fun at the same time. This last aspect is very important to me: to have fun while working. Your enthusiasm for understanding the mechanisms of processes has greatly influenced my own research approach, highlighting the importance of uncovering all of the little details in a system in order to maintain the highest quality of research. And of course, there’s your messy desk method which I’ve unwittingly adopted (I think my desk shows it) and since Einstein said messy desks lead people to think more clearly, I’m pretty content with that. Lastly, I admire your courage to come to Midburn and to see the desert in a new perspective: not everyone has the open mind, energy and curiosity to do that! I’ll cherish the many moments in the corridors of Kimmel when we joked about nothing. I would also like to thank Prof Gunnar Lehman, Prof Aren Maeir, Prof Daniel Master and the PhD advisory committee for fruitful discussions and helpful comments. To Genia Mintz and Lior Regev, for their understanding even when I did some pretty crazy things. And to all the Kimmel people for making this research center a special place to come to every day. And of course, to the most important person in my life: my lovely wife Rachel for her support.
2 Title Page Acknowledgements 2 Table of Contents 3 List of abbreviations 4 Abstract (English) 5 Abstract (Hebrew) 6 Chapter 1: Introduction 7 Chapter 2: Methods 15 Chapter 3: Determining the age range of the Bronze to Iron Age transition in the 17 southern coastal Levant Chapter 3.1 – Absolute Dating of the Late Bronze to Iron Age Transition and the 17 Appearance of Philistine Culture in Qubur el-Walaydah, Southern Levant Chapter 3.2 – Radiocarbon Dating Shows an Early Appearance of Philistine 18 Cultural Material in Tell es-Safi/Gath, Philistia Chapter 4: Discussion 19 Chapter 4.1 – The LB|Ir Absolute Transition Dates in Canaan 25 Chapter 4.2 – The LB|Ir Absolute Transition Dates around the Eastern 40 Mediterranean Chapter 4.3 – Broader Implications for Associating the Early Aegean-like Pottery 49 to the Sea Peoples from the 13th century BC Main Conclusions of this Research 50 Chapter 5: Appendix 51 Chapter 5.1 - Radiocarbon Data for Survey of Bayesian Models (Chapter 4) 51 Chapter 5.2 – Towards Dating Phytoliths: a New Method to Extract the Occluded 59 Carbon for Radiocarbon Analysis Chapter 5.3 - A Rapid On-site Method for Micromorphological Block 79 Impregnation and Thin Section Preparation Chapter 5.4 - Towards Identifying Burning Events in Situ: Using Density 98 Separation to Purify Charred Micro-Particles in an Iron Age Pyrotechnological Pit at Qubur el-Walaydah, Israel Publications 117 Bibliography 117
3 List of abbreviations
AMS – Accelerator mass spectrometry FTIR – Fourier transform infrared spectroscopy FWHM – Full width at half maximum pMC – Percent modern carbon BP – Before present BC – Before Common Era Et al. – et al.ii (Latin, and others) LB – Late Bronze Ir – Iron Age RTD – Rehovot AMS RTT/K – Rehovot and Tucson
4 Abstract Archaeological records of the transition from the late Bronze to Iron Age period show a major political change in the Ancient Near East. During this transition in the southern Levant, the dominant political entity of the Egyptians weakened and smaller groups became more dominant, such as the Israelites and the Philistines. The historic date of this transition is mainly based on historical records mentioning the Philistines in relation to Egyptian kings. The current archaeological/historical understanding is that the Philistines arrived after 1200 BC, and settled the region following warfare with the Egyptian kingdom. Radiocarbon dating provides an independent chronological record for this transition. However, the precision of a single measurement is significantly lowered due to wiggles in the calibration curve that form a 200 year long plateau. Our methodology of dating archaeological records before, during and after the transition, using many radiocarbon dates from secure contexts in a clear stratigraphic sequence, makes it possible to achieve high resolution dating. This methodology required us to develop new tools to study stratigraphic relations and new materials for dating to increase the number of radiocarbon dates from secure contexts. This methodology was applied in two Philistine sites: Tell es-Safi/Gath and Qubur el- Walaydah. Radiocarbon dates show the Bronze to Iron transition and the appearance of Philistine pottery began during the 13th century BC (1300-1200 BC), which is before the historical dating. These transition dates in comparison to dates available from other sites in the Southern Levant and the Ancient Near East show that the cultural transition is not contemporaneous between different sites. The inconsistency between the radiocarbon transition dates and the historical dating changes our understanding of the arrival of the Philistines to the southern Levant. The historical implications are that the early material culture that is associated to the Philistine entity should now be associated to the presence of other foreign groups of people in this region mentioned in Egyptian historical texts during the 13th century BC. It also shows that the Philistines became a political entity after foreign groups were already settled in the region. The variability of about 100 years of the Late Bronze to Iron Age transition date has implications regarding the use of relative dating in archaeology. Relative chronology assumes that similar pottery assemblages are dated to the same time, even if found in different regions. This study shows that for high resolution dating, this assumption may be incorrect.
5 תקציר תקופת המעבר בין הבורנזה המאוחרת לברזל מלווה בשינויים פוליטים בכל המזרח התיכון הקרוב. במהלך תקופה זו, ישנה ירידה בהשפעה הפוליטית של האימפריות ועלייה בהשפעה המקומית של קבוצות אתניות חדשות כמו הישראלים והפלישתים. תארוך בתקופה זו מבוסס ברובו על כתבים היסטוריים שמציינים פרעונים מצרים ופלישתים, המתארכים את המעבר בין הבורנזה המאוחרת לברזל לקצת אחרי 1200 לפנה"ס. תארוך אבסולוטי המבוסס על הדעיכה הרדיואקטיבית של פחמן 14 , הוא בעייתי בתקופה זו בגלל הרזולוציה הנמוכה שנובעת מישורת בעקומת הכיול של 200 שנה. מתודולוגיה חדשה של תארוך חומר תרבותי לפני, במהלך ואחרי תקופת המעבר, עם הרבה תאריכים ממקומות לא מופרעים, מאפשרת להשיג רזולוציה גבוהה לזמן המעבר. מתודולוגיה זו עזרה לקבוע את תאריך המעבר בשני אתרים המכילים תרבות פלישתית בישראל: קובור אל- וולדיה ותל צאפי/גת. התאריכים מאתרים אלו מראים שקרמיקה "פלישתית" הופיעה כבר במהלך המאה ה13- לפנה"ס, לפני התארוך ההסטורי של הגעת הפלישתים, וגם שתאריכי המעבר התרבותי בין אתרים שונים שונים ב100- שנה. תוצאות אלו נתמכות בסקר ספרות של תאריכי פחמן 14 מאתרים רלוונטים בכל המזרח התיכון הקרוב. חוסר ההתאמה בין תאריכי פחמן 14 והתארוך ההסטורי משפיעים על הבנת הגעת הפלישתים לאזור המזרח התיכון. אחת ההשלכות היא ששיוך הקרמיקה ה"פלישתית" לפלישתים לא מדוייקת, ושקירמיקה זו צריכה להשתייך לזרים אחרים שהיו באזור בזמן זה. שיוך התרבות החומרית עם הקבוצה האתנית הפלישתית מבוסס על שילוב הממצאים הארכיאולוגים עם מקורות מקראיים, שאמינותם ההסטורית מוטלת בספק. כאשר משייכים את הקרמיקה ה"פלישתית" לזרים באופן כללי )כי הקרמיקה בהחלט לא מקומית(, יש התאמה בין המקורות ההיסטורים לתאריכי פחמן 14, כיון שיש עדויות להגעת זרים לאזור המזרח התיכון בתקופת המאה ה13- לפנה"ס. אחת ההשלכות היא שהפלישתים הפכו ליישות פוליטית דומיננטית לאחר שזרים כבר היו באזור. השלכות ארכיאולוגיות נוספות הם בנוגע לתארוך יחסי, המבוססת על ההנחה שקרמיקה דומה בצורתה וסגנונה צריכה להיות מתוארכת לאותו הזמן. תארוך תקופת המעבר מתארכת את הזמן בו היה מעבר סגנוני בין קרמיקה המשוייכת לברונזה ולברזל. תארוך זה בוצע בין אתרים שונים, והשוני בין האתרים הוא כ100- שנה. תוצאות אלו מראות שההנחה שקרמיקה דומה מבחינת הסגנון מתוארכת לאותו הזמן היא לא מדוייקת בפחות מ100- שנה ויכולה לשמש רק כקוים מנחים בהבנת הזמן של התקופות השונות ולא כשיטת תארוך מדוייקת.
6 Chapter 1: Introduction
The Late Bronze to Iron Age transition at the end of the second millennium BC, involved complex cultural, social and political changes in the eastern Mediterranean region. During and after this transition, dominant political entities in the Ancient Near East, such as the Hittites, Cypriots and Egyptians, weakened and disappeared from the historical and archaeological records (Ward and Joukowsky 1992; Gitin et al. 1998; Killebrew 2005; Yasur-Landau 2010; Cline 2014). The weakening of these political entities resulted in destructions of the major political centers, collapse of the palatial system, and loss of trade routes between key geographic centers, while new and local political entities established themselves. Reasons for the apparent collapse of empires all over the Ancient Near East were sought in historical sources as well as using scientific data. New entities such as the “Sea Peoples” are mentioned in historical sources in Egypt, Anatoilia and Syria, in association with destruction of key city- states (Hitchcock and Maeir 2013; 2014; Maeir et al. 2013). Climatic changes which introduced pressure on the city-state system are noted in historical records of the Amarna letters and reinforced by scientific indicators that show arid conditions during this period (Drake 2012; Langgut et al. 2013; Killbrew and Lehmann 2013).
In the southern Levant, during this period, the weakening of the Egyptian empire is accompanied by the appearance of new political groups such as the Israelites and “Sea Peoples” (Ben-Shlomo et al. 2008; Faust and Lev-Tov 2011; Maeir et al. 2013; Hitchcock and Maeir 2013). The first mention of the Israelites is during a military campaign of Pharaoh Merneptah (late 19th dynasty of the New Kindgom of Egypt). The first mention of the “Sea Peoples” is in warfares between Egypt and the “Sea Peoples”, described in inscriptions and texts from the 19th and the 20th dynasties of the new kingdom of Egypt. One of the main historical sources that describe the “Sea Peoples” are reliefs found in the mortuary temple of Ramesses III from the 20th dynasty of the new kingdom in Egypt (Medinat Habu temple). The inscriptions show Ramesses III battling with the “Sea Peoples” in sea areas and on land. Another important historical source, the Papyrus Harris I, describes how Ramesses defeated the “Sea Peoples” and settled them in the southern Levant (Albright 1932; Alt 1944; Killebrew 2005). In historical texts, the designation “Sea Peoples” encompasses the ethnonyms Lukka,
7 Sherden, Shekelesh, Teresh, Eqwesh, Denyen, Sikil/Tjekker, Weshesh, and Peleset (Killebrew and Lehmann 2013; Yasur-Landau 2010).
During the Late Bronze Age, trade connections between the Aegean world and the Levant introduced imports of Mycenaean pottery to the Southern Levant, especially Late Helladic IIIA2 and Late Helladic IIIB styles (Yasur Landau 2010). During the LB/Ir transition these Mycenaean imports disappeared and Aegean-like pottery produced in Cyprus (D’Agata et al. 2005; Mountjoy 2010) started to appear in small amounts, mostly in the northern sites of Canaan: Dan, Akko, Tel Keisan, Megiddo and Beth Shean (Yasur-Landau 2010; Mazar 2007).
The Late Bronze to Iron Age (LB/Ir) transition in the southern coastal Levant is identified by the appearance of ceramic vessels associated typologically to Aegean-style material culture (Dothan 1982). This new material culture is thought to reflect the appearance of the Philistines, associated with the “Sea Peoples” group Peleset, and hence the region is referred to as Philistia (Albright 1932; Alt 1944; Finkelstein 1995; Dothan 1982; Sandars 1985; Noort 1994; Oren 2000; Yasur-Landau 2010; Dothan and Ben-Shlomo 2013; Maeir et al. 2013). Based on the extensive studies in Ashdod and Tel Miqne-Ekron (located in Philistia), a sequence of the early phases of Philistine material culture was established. The early locally produced Philistine pottery is known as Late Mycenean IIIC:1b and is identified mainly by its characteristic monochrome decoration on bell-shaped bowls, kraters, strainer jugs, feeding bottles and stirrup jars (Dothan and Zukerman 2004; Sherrat 2013). These pottery types also appear in the following phase of Philistine material culture with characteristic bichrome decoration on a white slip background. To distinguish between imported Late Mycenaean IIIC vessels (found in northern sites), and locally-produced Late Mycenaean IIIC style pottery with monochrome and bichrome decorations (found mostly in Philistia), the imported Late Mycenaean IIIC vessels are not labeled specifically while the locally-produced Mycenaean IIIC style (monochrome style) is labeled “Philistine 1” and the Philistine bichrome style is labeled “Philistine 2” (Dothan et al. 2006).
Large amounts of Philistine 1 pottery was found only in Philistia (southern coastal Levant), especially in Ashkelon, Ashdod and Tel Miqne-Ekron. Philistine 1 pottery was also found in
8 smaller numbers in Tell es-Safi/Gath (Maeir and Ehrlich 2001). Sporadic sherds of Philistine 1 were found in Tel Haror, Haruba, Tell Jerishe, Akko, Ras Ibn Hani, Sarepta, Gezer, Beth Shean (Dothan and Zukerman 2004) and Qubur el-Walaydah (Asscher et al. 2015a). In the following phase, Philistine 2 was found abundantly in Philistia, but also in the Upper Galilee (Hazor and Dan), the northern coast and Akko Plain (Dor and Tell Keisan), the Jezreel Valley and its margins (mainly Megiddo and Afula), the Central Hill Country (Shiloh, Bethel, and Tell en-Nasbeh), and in the Negev Desert (Beersheba and Tel Masos) (Gilboa et al. 2006).
The complex material culture situation is reflected in the different terminologies used in relation to the LB/Ir transition. The period following the Late Bronze IIB is called Iron Age IA by Mazar, and Late Bronze Age III by Ussishkin and Finkelstein (Mazar 1997; Finkelstein and Piasetzky 2011). One of the main reasons for the different terminologies is that material culture differs between the southern coastal Levant (Philistia) and the rest of the region (Finkelstein 1995; Bunimovich 1996; Mazar 2007; Killebrew and Lehmann 2013). Another reason for the different terminologies, is that the Egyptian presence in northern Canaan is still found after the arrival of the Philistines in Philistia (Mazar 2007; Master et al. 2011; 2015), and while the arrival of the Philistines marks the transition between the Late Bronze to Iron Age in Philistia, the end of the Egyptian presence marks this transition outside Philistia. Table 1 summarizes the relative chronology of the Aegean-like pottery styles in the Aegean, Cyprus, Syria and Canaan (Killbrew and Lehmann 2013). We note that the LB/Ir transition occurred during the period that follows the LB IIB. We do not know if the transition occurred at the beginning (following Mazar) or at the end (following Finkelstein), therefore, we use the notation LB|Ir for the period that follows the Late Bronze IIB in Canaan (Sharon et al. 2007). In order to understand the chronology of the LB/Ir transition in different sites in Canaan, we determine the absolute time of the beginning and the end of the LB|Ir period separately.
9 Canaan Canaan Aegean-like Pottery (Finkelstein Relative Cyprus Syria (Mazar Aegean Styles and Piasetzky Chronology 1990) 2011) Late Helladic IIIA2 and LC IIB– LH IIIA2– LB LB IIA LB IIA IIIB IIC IIIB Late Bronze Late Helladic IIIB and LH IIIB LC IIC LB LB IIB LB IIB Mycenaean IIIB Late Late
locally LH IIIC Imported produced Early Mycenaea Mycenaean LC IIIA Iron IA Iron IA LB III n IIIC:1b LH IIIC LB|Ir IIIC:1b (Philistine Middle Monochrome)
LH IIIC Proto White-Painted and LC IIIB Iron IB Iron IB Early Iron I Late Sub- Iron Age Philistine Bichrome mycenaean
Historical and Archaeological Chronologies of the LB|Ir period
The chronology of the LB|Ir period in Canaan is mainly based on Egyptian historical records and Egyptian artifacts that can be related to the well-established Egyptian chronology. Table 2 shows the relevant Egyptian chronology and inauguration dates of kings based on radiocarbon dating (Bronk Ramsey et al. 2010). Modeled Modeled Name of King Inauguration Date Inauguration Date Dynasty (Bronk Ramsey et al. Range at 1σ (68%) Range at 2σ (95%) 2010) BC BC Ramesses II 1292-1281 1297-1273 Merenptah 1226-1215 1231-1207 19th Dynasty Amenmessu 1216-1205 1221-1197 Sety II 1213-1201 1218-1194 Saptah 1207-1195 1212-1187
10 Queen Tausret 1201-1189 1206-1181 Sethnakhat 1198-1187 1204-1179 Ramesses III 1196-1185 1202-1176 20th Dynasty Ramesses IV 1165-1154 1171-1145 Ramesses V 1159-1148 1165-1139 Ramesses VI 1155-1144 1161-1135
Regarding the appearance of new political groups such as the Israelites and Philistines, Egyptian historical records mention the Israelites in the Great Karnak Inscription of Merneptah (Kitchen 1982a) and the Philistines (the “Sea Peoples” group Peleset) in the confederation of peoples (Kitchen 1983) at Ramesses III’s mortuary temple, Medinet Habu (Redford 1992). The periods of Merneptah and Ramesses III’s are dated to the end of the 13th and the beginning of the 12th century BC respectively (Shaw 2000; Bronk Ramsey et al. 2010). The Egyptian withdrawal from Canaan is dated by archaeological finds from their last occupation levels, which include scarabs, statues and plaques of Ramesses IV and VI of the 20th dynasty. These are dated historically to the second half of the 12th century BC, namely around 1130 BC (Mazar 1997; Finkelstein and Piasetzsky 2011; Shaw 2000; Bronk Ramsey et al. 2010). Egyptian finds that are directly related to pottery that is associated to the arrival of the Philistines are rare, and the few finds that do, such as the one found in Ashkelon (Master et al. 2011), set a date to the 20th Dynasty (12th century BC). The lack of Egyptian finds associated to Philistine material culture makes it difficult to date the arrival of the Philistines accurately using only material culture (Finkelstein 1995; 1998; Bunimovitz and Faust 2001; Ussishkin 2008).
The Bible includes descriptions from the Iron Age and post Iron Age, of the interaction between the new political groups in the southern Levant: the Israelites, who settled in the Judean mountains, and the Philistines, who settled in the geographic area of Philistia in the southern coastal plains, and in the cities Ashkelon, Ashdod, Gaza, Ekron and Gath, i.e. the pentapolis. In their attempt to understand the origins of the Philistines and date their arrival, biblical scholars associate the Philistines with the “Sea Peoples” group called Peleset. The link
11 formulated between Peleset and the Philistines led to the paradigm that the biblical Philistines had been a unified, large foreign identity, which had violently invaded Canaan by land and sea, during the period of Ramesses III (20th dynasty), and settled in the southern coastal plain of the Southern Levant (Philistia). This paradigm is based on an interpretation of Egyptian records, the biblical text, and archaeological finds showing new types of material cultures during this period in the southern coastal plains (Philistia). These new types of material cultures were locally produced, according to provenance studies, yet similar stylistically to Aegean styles (Albright 1932; Alt 1944; Finkelstein 1995; Dothan 1982; Sandars 1985; Noort 1994; Oren 2000; Yasur-Landau 2010; Killebrew and Lehmann 2013; Maeir et al. 2013).
The current chronology of the LB|Ir period, based on archaeological and historical records, is that the Egyptians withdrawal and the Philistine arrival to the southern Levant are dated to the 20th Dynasty (12th century BC).
14C dating of the LB|Ir period
High precision absolute dates from Late Bronze and Iron Age layers can place the transition documented by material culture changes within an absolute time frame. However, the Late Bronze Age to Iron Age transition occurred during a period in which the wiggles in the calibration curve form a plateau of approximately 200 years (Reimer et al. 2013). The effect of this plateau is to produce large calibrated ranges for dates in the 13th -12th century BC. Figure 1 shows calibrated radiocarbon dates from sites in Canaan that contain a sequence of periods before and after the LB|Ir period, based on the local pottery. Details of the radiocarbon date ranges, associated strata, designated periods and references are presented in Table 1 in the appendix.
12
13 Figure 1. Calibrated radiocarbon date ranges, from the Late Bronze, LB|Ir and the Iron Age, based on associated pottery found locally at different sites, arranged from south to north, in Canaan. Vertical bars represent the calibrated time range of individual dates (±1σ), colored according to associated material culture. See Table 1 in the supplementary information for details on the radiocarbon dates, associated strata and references. Sites containing Aegean-like pottery from the LB|Ir (associated with the Philistines) are surrounded by a red rectangle.
The effect of the plateau results in overlaps of calibrated ranges of progressive material culture periods, which in turn makes it very difficult to determine a high resolution absolute time range for the LB/Ir transition. In addition to this intrinsic problem, additional “noise” is introduced by samples from poor contexts, samples that cannot be directly related to the material culture, and poorly measured samples (Boaretto 2009). In order to partially alleviate these difficulties, in this thesis we only consider dates from samples that are derived from secure contexts (not reworked), that are not intrusive or residual, and can be related directly to a well defined cultural assemblage.
Recent radiocarbon based chronological studies use different strategies to improve the precision of the LB/Ir transitions dates for each site. One strategy is to directly radiocarbon date transitional layers, and then use historical considerations to constrain the transition date (Kaniewski et al. 2011). A second strategy is to directly incorporate historical constraints in the Bayesian model, in addition to the radiocarbon dates of different strata (Fantalkin et al. 2015; Finkelstein and Piasetzky 2009). A third strategy is to radiocarbon date stratified layers before, during and after the transition, and then use Bayesian statistics to model the transition range (Asscher, Lehmann, et al. 2015; Asscher, Cabanes, et al. 2015; Toffolo, Arie, et al. 2014; Manning, et al. 2001; Manning 2006-2007). Note that the first two strategies mix chronological inputs (radiocarbon dates and historical data). The third strategy only uses the stratigraphic information and the dates as input, and then compares the results to the historical information. We think that the third strategy is most appropriate as the radiocarbon dates are not influenced by the historical dates, and represent the time of the archaeological layers.
14 A major source of noise in high-resolution dating derives from using 14C dates that are not well associated to a clear archaeological context and are not in primary deposition (Boaretto 2007). Primary deposition for charred remains denotes materials found in their burning location. Primary deposition for bones denotes articulated bone assemblage in burials. Primary depositional contexts of charred remains are usually associated with hearths, cooking installations, etc. A new methodology to identify primary depositional contexts in sediments uses an integrative approach which combines observations of macroscopic features with observations of diagnostic parameters at the microscale (Weiner 2010). These signals help to understanding the link between datable remains and the sediments in which they were deposited (Boaretto 2007; Toffolo et al. 2012; Asscher et al. 2015a). The organic and mineralogical remains that associate the datable remains to the sediments are called a “dating assemblage” (Boaretto 2015). The number of signals that link the sediments to the datable remains will determine the degree of confidence in dating the context. Sediment characterization also helps to assess bioturbation and mixing between contexts to assure the dated material represents the layer in which it was found. These are stringent demands. One of the main problems encountered is that the types of short-lived materials that can be dated at high resolution are for practical purposes, limited to charred seeds and bone collagen. We therefore devoted considerable effort to develop new dateable materials, as well as characterization methods that can be used on-site with a relatively short turnaround time.
An integrative approach is therefore needed to build a high-resolution chronology, which combines sediment characterization with many radiocarbon dates in secure contexts. Methods that were used to verify that radiocarbon dates are in secure contexts by linking the dateable remains to the charring process, are described below.
Chapter 2: Methods
A few general methods used throughout the study are described below, and when other methods are used, they are explained in detail in association with the specific results of each chapter.
15 Fourier Transform Infrared (FTIR) Spectroscopy A few grams of archaeological sediments as well as control samples from the geological surroundings were collected. Part of the sample was homogenized in an agate mortar and approximately 0.2 mg were ground to a fine powder and mixed with ~20 mg of KBr (FTIR- grade). Samples were then pressed into a 7-mm pellet using a manual hydraulic press (Specac). Infrared spectra were obtained on-site and/or in the lab using a Nicolet Is5 spectrometer at 4 cm–1 resolution.
Microscopy A few miligrams of materials were placed on a slide. A few drops of Entellan (Merck) were added and covered with a cover-glass and observed and photographed at 100x, 200× and 400x magnification using a Nikon Eclipse 50iPOL microscope.
Radiocarbon dating Charred materials were characterized using FTIR to determine whether clays dominated the fraction before the removal of carbon contaminants (Rebollo et al. 2008). These samples were either not dated or the charred fraction was purified. Pretreatment of the charred materials to remove all organic contaminants prior to the measurement were performed following the protocol of Yizhaq et al. (2005). The purity of the recovered charred remains was tested again using FTIR to determine if the material remaining contains only clay minerals (in which case they were not dated) (Yizhaq et al. 2005). Samples were oxidized in vacuum with cuprum oxide (CuO) at 900°C, and the sample % carbon was recorded. The sample was then graphitized in the presence of hydrogen and cobalt at 700°C. Radiocarbon determinations were made using an accelerator mass spectrometer (AMS) in Rehovot, Israel (the Dangoor- Reasearch accelerator Mass Spectrometer: a 1.5SDH Pelletron, National Electrostatics Corp). Modeling was carried out using Oxcal 4.2.3 (Bronk Ramsey 1995).
Methods developments During this study, several methodological developments were carried out. The main methodological developments, that are related to sediments characterization and increasing the dateable materials in secure contexts, are:
16 1. Developing a method to extract carbon for 14C dating from siliceous plant phytoliths. 2. Developing a method to prepare thin sections of sediments during the excavation season, to establish micro-stratigraphic relations. 3. Developing a method to associate charred micro-remains to primary depositional dateable remains in contexts for dating.
These methodological developments are described in detail in the appendices.
Chapter 3: Determining the age range of the Bronze to Iron Age transition in the southern Levant
In this study, we will examine the possibility that the changes in material culture before and after the transition in Philistia and outside Philistia, may not have occurred simultaneously. Sites that contain relevant associated material culture of the LB|Ir period, such as the Aegean- like pottery, in an on-going excavation is found in Philistia at Tell es-Safi/Gath and Qubur el- Walaydah. The sites stratigraphy and the stratigraphic relations between dateable contexts was studied using the methods explained above. The dateable contexts and associated material culture allowed constructing an independent 14C chronology of the Late Bronze to Iron transition, in which prior to these studies, high resolution radiocarbon chronologies were not available from Philistia.
Chapter 3.1: Determining the Late Bronze to Iron Age transition in Qubur el-Walaydah, Israel During the excavation season of summer 2011, we conducted a radiocarbon study in the archaeological site of Qubur el-Walaydah, in contexts associated with the LB/Ir transition. The full characterization and results of this study were published in the Journal of Radiocarbon (Asscher et al. 2015a).
17
Chapter 3.2: Determining the Late Bronze to Iron Age transition in Tell es-Safi/Gath, Israel During the excavation seasons of 2012-2014, we conducted a radiocarbon study in the archaeological site of Tell es-Safi/Gath, in contexts associated with the LB/Ir transition. The full characterization and results of this study were published in the Journal of Radiocarbon (Asscher et al. 2015b).
Chapter 4: Discussion
18 Sites that contain radiocarbon dates from secure contexts and in stratigraphic relations will always vary with respect to the quality of the contexts in which the materials were found, and the details of the stratigraphic relations between the contexts. Each site will therefore have its own strengths and weaknesses, and these needs to be taken into consideration when using radiocarbon dates to determine the chronology of the LB/Ir transition. Sites that contain the most detailed stratigraphic information, relevant associated material culture, and secure contexts for radiocarbon dating of the LB/Ir transition are Tel Megiddo, Tell es-Safi/Gath and Qubur el-Walaydah (locations are in Figure 2). Aegean-like pottery from the LB|Ir period is found in Philistia at Tell es-Safi/Gath and Qubur el-Walaydah, while none was found in Tel Megiddo.
19
Figure 2. A map of the southern coastline of Israel. Archaeological sites from the Late Bronze and Iron Age periods are marked. The three radiocarbon dated sites Tel Megiddo, Tell es- Safi/Gath and Qubur el-Walaydah are marked with asterisks.
20 Brief Descriptions of the Relevant Archaeological, Cultural and Radiocarbon Data for Each Site
Note that Qubur el-Walaydah and Tell es-Safi/Gath are located in the core area of Philistia, the southern coastal Levant, whereas Megiddo is located well to the north of this area (Figure 2).
Qubur el-Walaydah Qubur el-Walaydah contains a detailed stratigraphic sequence in the Bronze and Iron Ages (Lehmann et al. 2011). The stratigraphy in area 1 has an accumulation of Late Bronze levels (LB IIB) associated with an Egyptian estate, under layer 1-5C, that contained a single bowl of Philistine 1 pottery (Mycenaean IIIC:1b). The bowl is associated with the LB|Ir period (annotated as LB III in Asscher et al. 2015a). Pits containing Iron Age pottery (Iron I) were cut into the LB|Ir layers. The strengths of Qubur el-Walaydah in relation to dating the transition is the availability of dated contexts from a sequence of well-defined archaeological surfaces, with well-defined associated pottery assemblages. Microarchaeology was used to identify dateable samples from primary contexts (Asscher et al. 2015a). The weakness of this site for transition dating is that levels that were associated directly with the LB|Ir period did not contain datable materials. Only levels above and below the transition could be dated (Asscher et al. 2015a). Twenty radiocarbon dates from 11 secure contexts were included in the Bayesian model following stratigraphic information. A temporal gap in the sequence of dates was introduced to account for missing dates in the LB|Ir. By including the gap the beginning of the LB|Ir is modeled to between 1230–1185 BC at 1σ confidence and the end of the LB|Ir is modeled to between 1140–1095 BC at 1σ confidence (Asscher et al. 2015a).
Tell es-Safi/Gath The transitional strata at Tell es-Safi/Gath were found in two areas (A and F), between Strata A7/A6 and F3/F2 (Maeir 2012). Pottery assemblages in Stratum A7 include Cypriot imports associated to the LB IIB period, while Stratum A6 includes Iron I material culture that is associated to the Iron I period (Asscher et al. 2015b). Stratum F2 includes Mycenaean IIIC:1b
21 pottery, that associates this layer to the LB|Ir period, annotated as early Iron I in Toffolo et al. (2012). The strengths of Tell es-Safi/Gath in relation to dating the transition are that the contexts for dating were in primary deposition, the associated pottery assemblages are well defined, and the stratigraphic relations between the contexts can be determined unrelated to material culture (Asscher et al. 2015b). One weakness of the site is that the dateable materials found in a stratigraphic sequence in area A, were not exposed on a large scale and hence the amounts of locally produced Aegean-like pottery (associated with the LB|Ir) are limited. Another weakness is that sediment layers, in which datable materials were found, were not always defined based on architecture. A key layer in the stratigraphic sequence (A6) however could be unequivocally identified based on high phytolith and charred material concentrations and was clearly overlain by Iron I architecture. Ten radiocarbon dates from secure contexts were analyzed using a Bayesian model that incorporated stratigraphic information from Area A. The modeled transition of the beginning of LB|Ir layers is between 1270–1190 BC at 1σ confidence. When additional information was introduced by adding 7 radiocarbon dates from strata (in area P and area F) that were not physically connected to the original stratigraphic sequence in area A, the Bayesian model placed the beginning of LB|Ir between 1310–1250 BC at 1σ confidence, and the end of the LB|Ir between 1230–1155 BC at 1σ confidence (Asscher et al. 2015b).
Tel Megiddo Tel Megiddo contains a long sequence of occupation including the Bronze and Iron Ages. The site is located in the Jezreel valley, 100km north of the southern coastal Levant and does not have Aegean-like pottery present on a large scale as occurs in Philistia. Transitional strata at Tel Megiddo were found in two areas (H and K), between Strata H13/H12 and K7/K6. Pottery assemblages in Strata H12 and K6 are similar to those found in Lachish VI, and did not contain Philistine material culture (Toffolo et al. 2014). The strengths of Tel Megiddo for transition dating are that a large sequence of dates are available for the periods before, during and after the LB|Ir layers, and contexts for dating were associated to well-defined archaeological contexts such as floors and hearths (the stratigraphy of most of the datable contexts was not based on material culture). The weakness of the site is
22 that contexts for dating were not studied using microarchaeological indicators to confirm that they were all in primary deposition, except in special cases. Another weakness is that datable samples were collected in a specific context, but the associated pottery assemblages were reported for a large area (Toffolo et al. 2014). The Bayesian model that was used to provide the LB/Ir transition dates was based on 78 samples from four different excavation areas that cover 10 stratigraphic phases (Toffolo et al. 2014). Dates from two areas (H and K) were modeled separately and integrated to produce a chronological sequence for the entire site on the assumption that layers containing the same material cultures are contemporaneous (Toffolo et al. 2014).The transition in Area H (between Strata H13/H12) shows the beginning of the LB|Ir period is between 1125–1070 cal B.C., and in Area K (between Strata K7/K6) is between 1185–1135 BC at 1σ confidence level. The entire site model shows the beginning of the LB|Ir is between 1180–1135 BC at 1σ confidence level, and the end of the LB|Ir is between 1100–1060 BC at 1σ confidence level.
Figure 3 shows that the beginning of LB|Ir varies by 50-150 years between these 3 well dated sites, and is clearly not contemporaneous in Tel Megiddo, Qubur el-Walaydah and Tell es- Safi/Gath. Note that even within Megiddo the transition varies between different areas within the same site by more than 50 years. The pottery assemblages in Philistia, that mark the beginning of the LB|Ir and the appearance of the Philistines, are dated earlier than the transition to the Iron Age in Megiddo.
23
Figure 3. Calibrated modeled transition dates of the beginning and end of the LB|Ir period in Qubur El-Walyadah, Tell es-Safi/Gath and Tel Megiddo. Each vertical gradient colored box represents a transition time range at each site, and the colors indicate the periods (as seen in Figure 1). In locations the transitions overlap (area H in Megiddo and area A in Tell es- Safi/Gath), smaller boxes are presented.
24 Chapter 4.1: The LB|Ir Absolute Transition Dates in Canaan
In this section, we evaluate the LB|Ir transition dates in sites that have published radiocarbon dates from stratigraphic locations based on material culture, with few radiocarbon dates, that were not found in clear stratigraphic relations and were not checked using microarchaeology if they were found in secure contexts. The sites examined are Tel Beth Shean, Tel Rehov, Tel Miqne-Ekron, Ashkelon and Tel Lachish (See Figure 2 for locations).
Tel Beth Shean Tel Beth Shean is located in the Jezreel valley, 150km from the southern coastal Levant. Northern Canaan sites do not contain Aegean-like pottery on a large scale as occurs in Philistia. In Tel Beth Shean, a sequence of layers associated with the Late Bronze Age was found, including a governor’s Egyptian building from the end of the Late Bronze Age (Mazar and Carmi 2001). The strengths of the site in relation to dating the transition are that Egyptian finds link the Egyptian chronology to the floating local relative chronology in an absolute time frame. Strength is that the LB short lived charred samples were found in a room associated with fire, and although they were not studied using microarchaeological indicators, it is assumed that the charred samples are in primary deposition. One weakness of the site is that there are no radiocarbon dates for the Iron Age period, and only two contexts are relevant for dating the transition – one context is associated with the Late Bronze and the other to the LB|Ir. Another weakness is that the LB|Ir sample was composed of charred grains found in a bin with no indication of fire in situ. A third weakness is that the stratigraphic relations between samples were based on associated cultural materials, since samples were collected in different areas in the Tel: S and N. We used Bayesian statistics to model the radiocarbon dates reported by (Mazar and Carmi 2001), according to the stratigraphic sequence. Radiocarbon dates from Stratum N-4 (associated with the LB IIB since it contained imported Cypriot White Slip bowls) and Stratum S3a (associated to the last Egyptian phase during the LB|Ir phase) were used to determine the beginning of the LB|Ir. Three dates were obtained from one single assemblage of charred cereal grains in Stratum N-4: RT-2597, RT-2594, RT-2156 (see details in Table 1 in
25 supplementary information). Three dates were obtained from charred linen seeds and grains found in a small bin in Stratum S3a: RT-2325, RT-2596, RT-2323. The average combined dates (N-4: 2950±17 and S3a: 2954±20) are positioned in a Bayesian model according to the stratigraphy based on material culture (Mazar and Carmi 2001), shown in Figure 4. The modeled transition shows the beginning of the LB|Ir in Tel Beth Shean is between 1195-1135 at the 1σ confidence level.
Figure 4. Calibrated and modeled dates from Beth Shean. Dates are arranged in a sequence from the LB IIB period (Stratum N-4 averaged dates) to the LB|Ir layers (Stratum S3a averaged dates). The modeled date of the beginning of the LB|Ir is between 1195-1135 BC at 1σ confidence level.
Tel Rehov Tel Rehov is located in northern Canaan, 7km south of the site Tel Beth Shean, in a region which did not contain Aegean-like pottery on a large scale as occurred in Philistia. In Tel Rehov, a sequence of layers associated with the Iron Age were radiocarbon dated (Bruins et al. 2003). The strengths of this site in relation to dating the transition are that a large sequence of short lived samples from the LB|Ir and Iron Age layers, were dated. This provides a date for the end of the LB|Ir. The stratigraphic relations between samples were based on architecture and associated cultural materials in a single area (area D). The weakness of the site is that contexts for dating were not studied using microarchaeological indicators to confirm that they were in
26 primary deposition. A second weakness is that the stratigraphic relations between samples within the same stratigraphic layer were not described in details. Another weakness is that the Late Bronze period was not dated. We used Bayesian statistics to model averaged radiocarbon dates reported by Bruins et al. (2003), following the stratigraphic sequence. The average combined dates of Stratum D-6 lower (samples GrN-26120 and GrN-19034 gave an average of 2897±28, associated with the LB|Ir since the associated material culture was similar to the one found in Tel Beth Shean layer S-3) were positioned below the averaged combined dates from Stratum D-6 upper (samples GrN-26118 and GrN-18826 gave an average of 2928±26). Datable materials were not found in Stratum D-5 (associated to the Iron I). Then, the averaged combined dates from D-4b (samples GrN-21046, Gr-N21057 and GrN-21184 gave an average of 2924±23), D-4a (samples GrN- 26121 and GrN-18825 gave an average of 2885±26), D-3 (samples GrA-16757, GrA- 19033, GrA- 21044, GrA- 21056 and GrA- 21183 gave an average of 2831±19) and D-2 (GrN-26112: 2805±15) were sequenced according to the stratigraphy, spanning a sequence from the LB|Ir to Iron Age IIA. The modeled transition of the end of the LB|Ir in Tel Rehov is between 1110- 1050 at 1σ confidence level (Figure 5), and the model agreement is 92% with no outliers.
27 Figure 5. Calibrated and modeled dates from Tel Rehov (see details of the dates and associated strata in supplementary information). Dates are arranged in a sequence from the LB|Ir (Stratum D-6) to Iron Age IIA (Stratum D-2). Dates are presented with their phase name, age before calibration, precision (in round brackets), and their agreement index (in square brackets). The modeled date of the end of the LB|Ir is between 1110-1050 BC at 1σ confidence level. The model can be refined by introducing a gap to take into account the lack of dates from Stratum D-5 (associated with the early Iron I period). Figure 6 shows the model agreement index for a changing gap span between 0-100 years for level D-5. The range of agreement is between 60-95%, showing the highest agreement for a gap of 0-20 years.
100 2 Agreement 95 index 90 outliers 85 80 1 75 70 65
60 Outliers of Number Model Agreement Index [%] Index Agreement Model 55 0 0 20 40 60 80 100 Gap Time [years]
Figure 6. Plot of the overall model agreement index as a function of increasing gap time of levels D-5 (associated with the early Iron I period) in Rehov. The model agreement index is the highest for a gap of 0-20 years (95% agreement).
Introducing a gap of 20 years did not change significantly the transition date of the end of the LB|Ir in Tel Rehov, which is between 1110-1055 BC at 1σ confidence level.
28 Tel Miqne-Ekron Tel Miqne-Ekron is located within the core area of Philistia in the southern coastal plain. Tel Miqne includes large occupations from the Late Bronze and Iron Ages. The LB|Ir includes sediments associated with the appearance of the Philistines (Stratum VII, Field INE), based on the presence of early Aegean-like pottery (Dothan and Zukerman 2004; Killebrew 2005). The strengths of Tel Miqne in relation to dating the LB/Ir transitions dates are that a sequence of short lived samples from during and after the LB|Ir period (Strata VIIb: RTT-4286, VIb: RTT-4283 and Vb: RTT- 4284) were dated (Sharon, et al. 2007). Strength is that the pottery assemblage of the LB|Ir is well-defined and is used as a relative chronological marker for sites that contain early Aegean-like pottery (Dothan and Zukerman 2004). The weakness of the site is that Iron Age contexts for dating were not studied using microarchaeological indicators to confirm that they were in primary deposition, and Late Bronze contexts were not dated. The Bayesian model presented here is based on 3 radiocarbon dates from a single excavation area (Field INE). The dates were modeled according to stratigraphy that was based on material culture (Figure 7) using OxCal software 4.2.3 (Bronk Ramsey 1995). The modeled transition of the end of the LB|Ir (Stratum VIIb/VIb) is between 1120-1050 at 1σ confidence level. The model contains no outliers and has 81% agreement.
Figure 7. Calibrated and modeled dates from Tel Miqne-Ekron. Dates are arranged in a sequence from the LB|Ir (Stratum VIIb) to Iron Age (Strata VIb and Vb). The modeled date of the end of the LB|Ir period is 1120-1050 cal B.C. at 1σ confidence level.
29
Ashkelon The site of Ashkelon is located within the core area of Philistia in the southern coastal plain. Ashkelon includes large occupations from the Late Bronze and Iron Ages. The LB|Ir period includes sediments associated with the arrival of the Philistines (Phase 20), based on the presence of early Aegean-like pottery (Master et al. 2011). The strengths in the site Ashkelon in relation to dating the transition are that a large sequence of short lived samples was dated before, during and after the LB|Ir period, and Egyptian finds of Ramesses III link the floating relative chronology to the well-established Egyptian chronology (Master et al. 2011). Another advantage is that the pottery assemblage of the LB|Ir period is well-defined and is used as a relative chronological marker for sites that contain Aegean-like pottery. The weakness of the site in relation to this radiocarbon study is that Iron Age sediments underwent flotation, and floating datable materials were collected from archeologically surfaces associated with phases 17-20 in grid 38. Late Bronze sediments contain few datable contexts in situ, with poor stratigraphic association. Late Bronze datable materials were collected by hand picking contexts from phases 23 and 21 in grid 38. Another weakness is that the contexts of the Late Bronze period were studied using microarchaeological indicators to confirm they were in primary deposition, but did not contain full “dating assemblages” (Boaretto 2015), which weakened their association to the sediments. Iron Age materials for dating were not studied using microarchaeological indicators, and were based on flotation of sediments. Figure 8 shows a Bayesian model based on nine contexts that contained short lived samples from a single excavation area (grid 38). The radiocarbon dates were positioned in the Bayesian model according to stratigraphy, that was based on architecture and material culture of Late Bronze and Iron Age contexts. Briefly, radiocarbon dates from phase 23 (RTD 6264 and RTD 6259) are positioned before phase 21 (RTD 6260 and RTD 6258), then phase 20b is positioned (which is associated with the arrival of the Philistines and the LB|Ir period, RTD 7574.1, RTD 7574.2). Then phase 20a is positioned (RTD 7573.1, RTD 7573.2) Then a sequence of radiocarbon dates from phase 19b (RTD 7572.1, RTD 7572.2), phase 19a (RTD 7571.1, RTD 7571.2), phase 18b (RTD 7570.1, RTD 7570.2), phase 18a (RTD 7569.1, RTD 7569.2), and
30 phase 17b (RTD 7568.1, RTD 7568.2), are positioned. The combined average of the dates from phases 18b and 18a did not pass the χ² test, and therefore had to be arithmetically averaged (shown by the large calibrated range). The modeled transition from the phase 21 (Late Bronze period) to phase 20 (the LB|Ir period) in Ashkelon is between 1220-1150 at 1σ confidence level. The model contains two outliers, has 50% agreement.
Figure 8. Calibrated and modeled dates from Ashkelon. Dates are arranged in a sequence from the Late Bronze period (Phase 23 and 21) to early Iron I (Phase 20) to the Late Iron I (Phase 19-17). Dates are presented with their phase number, age before calibration, precision (in round brackets), and their agreement index (in square brackets). The modeled date of the transition between the Late Bronze and LB|Ir period (Strata 21/20) is 1220-1150 BC at 1σ confidence level.
Additional information could be incorporated into the stratigraphic model, based on associated material culture and poor agreement between the radiocarbon dates and the sequence. Phases 23 and 21 are in poor agreement with the model. The associated material culture shows phase
31 23 is Late Bronze I from contexts that are considered good for dating, while phase 21 contains contexts that are fills of pits, that are not the ideal contexts. One of the contexts of the pits (RTD 6259) does not contain any material culture, and the associated period is based on architecture. The second sample (RTD 6260) is a context with mixed material culture of the LB I and LB II, and datable materials could not be associated to a single period. Therefore, these contexts are considered as outliers (agreement of 22%). Phase 23 is considered good contexts. However, the dates of phase 23 show as outliers with agreement of 34% because the dates of phase 21, which are earlier, are positioned later in the sequence, and constrains phase 23 dates in such a way they become outliers. Moreover, there is a gap in the time sequence since phase 22 did not contain datable materials. To use the radiocarbon data for chronological questions, we removed the outliers of the contexts from phase 21, and incorporated a gap between phase 23 and phase 20. The length of the gap could be estimated by simulating a gap in the sequence of the modeled dates. Gaps of different duration were tested using OxCal software 4.2.3. Figure 9 shows that the time gap that best accounts for the lack of dates from phases 22 and 21, representing the Late Bronze II period, is 260 years, which is in high agreement judging from the model agreement index (147%).
150 140 130 120 110 100 90 80 70
Model Areement Index [%] Index Areement Model 60 50 100 150 200 250 300 350 Gap Time [years]
Figure 9. Plot of the overall model agreement index as a function of an increasing gap in time representing the Late Bronze II lack of datable materials. The model agreement index is the highest for 260 years (147%).
32
A Bayesian model of the sequence of dates from Ashkelon, including a gap of 260 years to represent the lack of dates from phases 22 and 21 (Late Bronze II period), is seen in Figure 10. The modeled Late Bronze Age to LB|Ir period transition (between phases 21/20) is between 1185-1150 BC at 1σ confidence level. The modeled LB|Ir period to Iron Age transition (between phases 20/19) is between 1160–1130 BC at 1σ confidence level. The model agreement index is 143% and there are no outliers.
Figure 10. Calibrated and modeled dates from Ashkelon. Dates are arranged in a sequence from the Late Bronze period (Phase 23), to a gap of 260 years (representing phases 22-21), to the early Iron I (Phase 20) to the Iron I (Phase 19-17). Dates are presented with their phase number, age before calibration, precision (in round brackets), and their agreement index (in square brackets). The modeled date of the beginning of the LB|Ir period (phases 21/20) is
33 1185-1150 BC BC at 1σ confidence level. The end of the LB|Ir period is between 1160–1130 BC at 1σ confidence level. The model agreement index is 143% and there are no outliers.
Tel Lachish Tel Lachish is located in the south, on the border with Philistia (Figure 2). Lachish is important for dating the Late Bronze to Iron transition since it contains a major occupation during the Late Bronze Age including a large temple (the Fosse temple), as well as a major occupation of the LB|Ir (layer VI) that ends in the destruction of the city (Ussishkin 2004). The strengths of the site in relation to dating the transition are that a long sequence of short lived samples from before, during and after the LB|Ir, were dated and Egyptian finds link the floating relative material culture chronology to the well-established Egyptian chronology. Another strength is that the pottery assemblage of the LB|Ir is well-defined and is used as a relative chronological marker for sites that do not contain Aegean-like pottery (Finkelstein 1995; Ussishkin 2004). The weakness of the site is that contexts for dating were not studied using microarchaeological indicators to confirm they were in primary deposition (as evidenced by several outliers), and stratigraphic relations between the contexts for dating within the same period were not carefully examined. Another weakness is that the material culture associated with the Iron I period is missing in Lachish, creating an occupational gap. We constructed a Bayesian model based on 11 radiocarbon dates that cover 8 stratigraphic phases from different excavation areas (Carmi and Ussishkin 2004). The model follows the stratigraphy in Carmi and Ussishkin (2004) and we used OxCal software 4.2.3 (Bronk Ramsey 1995). Briefly, the radiocarbon date from Stratum P-4 (associated with the Middle Bronze Age, RT-3149: 3125±55) was positioned before the combined averaged dates of Stratum S3a (associated with Late Bronze Age, RT-3152: 2945±65 and RT-3153: 3125±55) and Stratum S2 (associated with Late Bronze Age, RT-2754: 3945±25). Stratum VIIa and P-1 (associated with the end of the Late Bronze Age, RT-2906: 2955±35 and RT-2913: 3855±40), are positioned before Stratum VIb (associated with the LB|Ir, RT-2912: 2915±25) and Stratum VI (associated with the LB|Ir, RT-2755: 2955±25 and Hel-1417: 2810±100). Then a sequence of radiocarbon dates from Iron Age Strata V (RT-3159: 2755±55), IVb (RT-2908: 2715±40), IVa (Hel-1418: 2650±90) and III (Hel-1419: 2110±80) are positioned. The modeled transition of the beginning
34 of the LB|Ir (Strata VIIa/VIb) in Tel Lachish is between 1215-1120 at the 1σ confidence level (Figure 11), and the model contains 3 outliers and has an 88% agreement.
Figure 11. Calibrated and modeled dates from Tel Lachish in an Outlier Model in Oxcal 4.2.3. Dates are arranged in a sequence from the Middle Bronze Age (Stratum P-4) to the Iron Age (Stratum III). If dates are considered outliers, the probability index ‘P’ shows a 0%. The modeled transition of the beginning of the LB|Ir is between 1215-1120 BC at 1σ confidence level. Additional information could be incorporated into the stratigraphic model, based on associated material culture. Stratum V contains material culture associated with the Iron II period. Stratum VI is a destruction layer associated with the LB|Ir phase. Therefore, there is a gap in occupation between Strata VI-V that is associated with the early Iron Age period. The length of the gap could be estimated by simulating a gap in the sequence of the modeled dates. Gaps of
35 different duration were tested using OxCal software 4.2.3. Figure 12shows that the time gap that best accounts for the lack of dates from the Iron I is 260 years. 120
110
100
90 Agreement Index [%] Index Agreement 80 0 50 100 150 200 250 300 350 Gap Span [years]
Figure 12. Plot of the overall model agreement index as a function of an increasing gap in time representing the Iron I lack of occupation. The model agreement index is the highest for 260 years (116%). A Bayesian model of the sequence of dates from Tel Lachish, after removing outliers (RT- 2754 in S-2, RT-2913 in P-1 and Hel-1419 in III), and including a gap of 260 years to represent the Iron I gap, is shown in Figure 13. The modeled transition of the beginning of the LB|Ir is between 1215–1155 BC at 1σ confidence level. The end of LB|Ir (represented in the model as a gap) is between 1175–1115 BC at 1σ confidence level.
36
Figure 13. Calibrated and modeled dates from Lachish. Dates are arranged in a sequence from the Middle Bronze Age (Stratum P-4) to the Iron Age (Stratum IV). The modeled date of the beginning of the LB|Ir is between 1215-1155 BC at 1σ confidence level. The modeled date of the end of the LB|Ir is between 1175-1115 BC at 1σ confidence level.
Figure 14 compares the transition dates of these 5 additional sites to the transition dates of the well dated sites of Tel es-Safi/Gath, Qubur el Walaydah and Tel Megiddo. The transition dates of Tel Rehov and Tel Beth Shean are consistent with those of Tel Megiddo, supporting the notion that the transition in the north is later than in the south. The transition dates of the three additional sites in the south, Ashkelon, Tel Lachish and Tel Miqne are less conclusive. Ashkelon and Lachish dates are intermediate between the southern and northern sites, and the 3 dates that define the end LB|Ir at Miqne overlap with the northern sites. We emphasize that the degrees of certainty of the transition dates from the 5 additional sites are much less than for Tell es-Safi/Gath, Qubur el Walaydah and Tel Megiddo, however, all the sites LB|Ir transition
37 ranges are between the 13th-11th century BC. We therefore conclude that the LB|Ir in Canaan ranges between the 13th-11th century BC in the whole region. Furthermore, the beginning of the LB|Ir in the northern Canaan sites occurs during the 12th century BC, while in Philistia the beginning of the well dated sites of Qubur al Walaydah and Tell es-Safi/Gath occurs during the 13th century BC. Figure 14 also compares the radiocarbon-based chronology of the LB|Ir period in Canaan to the well-dated Egyptian chronology. The beginning of LB|Ir in the south (Philistia), which includes the appearance of Aegean-like pottery in Tell es-Safi/Gath and Qubur el-Walaydah, occurred during the 19th Dynasty (during the reigns of Rameses II and Merneptah in the 13th Century BC). In the north the transition occurs during the 20th Dynasty (during the reign of Rameses III in the 12th Century BC).
38
39
Figure 14. Calibrated modeled transition dates from Late Bronze, LB|Ir period and the Iron Age in Canaan. Each vertical gradient colored box represents a transition time range at each site, and the colors indicate the periods. The Egyptian Dynastic chronology is shown following Shaw (2000), with horizontal colored boxes representing their reign length. The dotted horizontal line shows the change between the 19-20th Egyptian dynasties.
Much has been written on the chronology of the appearance of the Philistines in south Canaan. A high chronology proposes that the Philistines entered the region before Ramesses III (Mazar 1990; 2007; Albright 1932; Killebrew 2005). A middle chronology proposes that the Philistines entered the region in the decade after Ramesses III inauguration (Mazar 1985; Singer 1985; Stager 1985; Killebrew 2005). A low chronology proposes that the Philistines entered the region after the retreat of the 20th Egyptian Dynasty, during the time of Ramesses IV and VI (Finkelstein 1995; Finkelstein 1998; Finkelstein and Piasetzky 2007). The well dated sites of Qubur el-Walayda and Tell es-Safi/Gath are consistent with the high chronology, whereas Ashkelon, where the certainty of the transition date is less, is consistent with the middle chronology. To understand if the appearance of Aegean-like pottery in the southern coastal Levant during the 19th Dynasty (13th Century BC) is unique to Philistia, we also review 14C dates of the LB|Ir and the appearance of Aegean-like pottery in the Eastern Mediterranean, and in particular in Syria, Cyprus and Greece.
Chapter 4.2: The LB|Ir Absolute Transition Dates around the Eastern Mediterranean
Cyprus Cypriot production of Aegean-like pottery, began and increased steadily in quantity and repertoire during the course of the 13th century (Killebrew and Lehmann 2013;Kling 1989; 1991; Sherratt 1991). This is consistent with the appearance of locally produced Aegean- like pottery (namely locally made Mycenaean IIIC:1b) within the 13th century in the southern Levant (Philistia).
40 A comprehensive radiocarbon study in Cyprus dates the transition between the LC IIC/IIIA periods (Manning et al. 2001), which according to relative chronology is contemporaneous with the beginning of the production of Aegean-like pottery in the southern coastal Levant during the LB|Ir. One weakness of this study is that radiocarbon dates from four different sites in different regions were included in a single Bayesian model, and sequenced based on associated material culture. Associated material culture was not reported and long lived materials (wood) were introduced into the sequence of dates. The transition date of the LC IIC/IIIA periods in Cyprus is between 1215-1190 BC (Manning et al. 2001), which is consistent with the dating of the beginning of Aegean-like pottery (namely the appearance of locally made Mycenaean IIIC:1b) in the southern Levant.
Greece A radiocarbon study in the site Assiros Toumba, northern Greece, dates the transition between the LH IIIB/IIIC periods (Wardle et al. 2014). This transition is contemporaneous with the beginning of production of Aegean-like pottery in the southern coastal Levant and the beginning of the LB|Ir (Yasur-Landau 2010). A long sequence that includes the LB|Ir was dated and modeled according to stratigraphy. The appearance of the Late Helladic IIIC occurs between 1330-1300 BC at 1σ confidence level (Wardle et al. 2014). A weakness of this study in Assiros is that the stylistic definitions of the associated material culture are equivocal, since it is difficult to apply the fine divisions of LH IIIC pottery used in southern Greece to the local products of northern Greece, that contain simply-decorated products of the periphery (Wardle et al. 2014). Radiocarbon studies in Lefkandi, Kalapodi and Corinth were used to determine the end of the LH IIIC early in southern Greece (Toffolo et al. 2013). These studies place the transition between the LH IIIC early/middle to between 1130-1060 BC at 1σ confidence level (Toffolo et al. 2013). The few available chronology studies in Greece, therefore, show that the LB|Ir begins in the 14th Century and ends in the middle of the 11th Century BC.
41 Syria
Gibala-Tell Tweini is a large site in the region of Ugarit that was occupied from the Early Bronze Age to the Iron Age. The site has records of the arrival of the Sea Peoples in the northern Levant (Kaniewski et al. 2011;Singer 1999), which according to relative chronology is contemporaneous with the beginning of production of an Aegean-like pottery in the southern coastal Levant during the LB|Ir. One strength of the study is that a long sequence of short lived samples was dated from before, during and after the destruction level that is associated with the arrival of the Sea Peoples (Kaniewski et al. 2011). Another strength is that the pottery assemblage of the destruction level is well-defined. A weakness is that the level 7C-B, associated with the end of the Late Bronze Age, was not dated. Radiocarbon dates from Gibala-Tell Tweini can be arranged stratigraphically, starting with Phase 7D, associated to the Middle-Late Bronze Age (Phase 7D was only dated by a single date: Beta-281584). Then, the next Phase that contained datable materials was 7A, associated with the Sea Peoples destruction layer (Phase 7A contained the dates: Beta- 281582, Beta-281576, Beta-281572, Beta-281590, Beta-281591 and Beta-281570). Then, Phase 6E, associated with an early Iron Age is found (Phase 6E was only dated by a single date: Poz-25442). We sequenced the radiocarbon dates in a Bayesian model according to the stratigraphy described above, considering the dates from phase 7A have a weighted average of 2958±17 (Kaniewski et al. 2011). Figure 15 shows that the beginning of the LB|Ir is between 1440- 1180 BC at 1σ confidence level. The large span is due to the lack of dates from the 7C-B levels.
42
Figure 15. Calibrated and modeled dates from Gibala-Tell Tweini. Dates are arranged in a sequence from the Middle/Late Bronze Age (Stratum 7D) to the Iron Age (Stratum 6E). Dates are presented with their phase name, lab number, age before calibration, precision (in round brackets), and their agreement index (in square brackets). The modeled date of the beginning of the LB|Ir (Strata 7D/7A) is between 1440-1180 BC at 1σ confidence level.
The model can be refined by introducing a gap to take into account the lack of dates from levels 7C-B (the end of the Late Bronze Age). Figure 16 shows the model agreement index for a changing gap span between 0-300 years for levels 7C-B. The range of agreement is between 83-105%, showing the highest agreement for a gap of 275 years.
43 110
105
100
95
90
85 Model Agreement Index [%] Index Agreement Model
80 0 100 200 300 400 Gap Time [years]
Figure 16. Plot of the overall model agreement index as a function of increasing gap time of levels 7C-B (associated with the end of the Late Bronze Age) in Gibala-Tell Tweini. The model agreement index is the highest for a gap of 275 years (105% agreement).
Figure 17 shows the entire Bayesian sequence of the short-lived sample dates in Gibala- Tell Tweini, with a gap of 275 years that represents the Late Bronze Age period (see supplementary information for the run file). The transition date of the beginning of the LB|Ir (between Phases 7C-B/7A) is between 1220-1160 BC at 1σ confidence level for the gap with the highest agreement. The transition date of the end of the LB|Ir (between Phases 7A/6E), is between 1170-1050 BC at 1σ confidence level.
44
Figure 17. Calibrated and modeled dates from Gibala-Tell Tweini. Dates are arranged in a sequence from the Phase 7D (Middle-Late Bronze Age) to a gap that represents Phase 7C- B (the Late Bronze Age) to phase 7A (represents the Sea Peoples destruction layer) to phase 6E (Iron Age). The modeled transition date of the beginning of the LB|Ir destruction layer is between 1220-1160 BC at 1σ confidence level. The modeled date of the end of the LB|Ir is between 1170-1050 BC at 1σ confidence level.
Figure 18 summarizes the chronology of the LB|Ir period in Cyprus, Greece, Canaan and Syria. Figure 18 shows that the transitions dates can vary between sites by 100-150 years, and are clearly not contemporaneous. Therefore, these results are inconsistent with studies that conclude that the LB/Ir transition is contemporaneous between different regions (Fantalkin et al. 2015; Finkelstein and Piasetzky 2009).
45
46 Figure 18. Calibrated modeled transition dates at 1σ confidence level, from Late Bronze, LB|Ir and the Iron Age in the Ancient Near East including Cyprus, Greece, Canaan and Syria. Each vertical gradient colored box represents a transition time range at each site. Large boxes represent transitions with higher degree of confidence relative to the smaller boxes. The Egyptian Dynastic chronology is shown following Shaw (Shaw 2000), with horizontal colored boxes representing their reign length. The dotted line shows the conventional historical dating of the arrival of the Philistines in the southern Levant, dated to 1175 B.C. (roughly the change between the 19-20th dynasty).
The radiocarbon ranges of the appearance of Aegean-like pottery in the Eastern Mediterranean, including sites in Syria, Cyprus and Greece, show Aegean-like pottery began to appear during the 13th century BC. We now briefly review historical references that mention the Sea Peoples during these periods.
Historical Sources of the Sea Peoples in the Levant
Historical references to the Sea Peoples occur in Egyptian, Ugaritic, Hittite, and other Late
Bronze to early Iron Age sources of the ancient Near East. In the northern Levant, the destruction of Ugarit is associated with the arrival of the Sea Peoples (Killebrew and Lehmann
2013; Singer 1999). Ugaritic texts of communications between Ugarit and Egypt, provide an historical terminus post quem for the destruction of Ugarit, by linking Ammurapi (the last
Ugaritic king) to a vizier of the Egyptian pharaoh Siptah (RS 86. 2230 (Freu 1988; Watson and
Wyatt 1999). These textual references lead Yon (Yon 1992) to conclude that Ugarit was destroyed between 1195 and 1185 BC. The date thus marks the end of the LH IIIB in the northern Levant. This date is in agreement with the radiocarbon study conducted in the site
Gibala-Tell Tweini, located in the kingdom of Ugarit, that 14C dated a destruction layer that is associated with the arrival of the Sea Peoples (Kaniewski et al. 2011).
47 In the southern Levant, the Sea Peoples are particularly well documented in Egyptian historical records (Killebrew and Lehmann 2013; Yasur-Landau 2010). The Sea Peoples are generally referred to as groups of people that fought the Egyptians during the Late Bronze and Iron Ages at sea and on land. In particular, battles occurred on land in the northern frontier during the time of Ramesses II (based on Ramesses II’s Kadesh Inscriptions), and at the western frontier during the time of Merenptah (based on Merenptah’s Karnak Inscription). During the time of
Ramesses III, battles occurred mostly at sea based on the Ramesses III’s mortuary temple. In
Ramesses II’s Kadesh Inscriptions (Kitchen 1979), the Sea Peoples groups Karkiša and Lukka are mentioned as entities that Ramesses II fought against in the land of Lukka and Karkiša, which is located in the region of southwestern Anatolia. The Sherden are referred to as captured troops from different campaigns, that were included in the Egyptian army in the time of Ramesses II (Pg 648 in Killebrew and Lehmann 2013). Merenptah’s Karnak Inscription
(Kitchen 1982a), mentions the Eqwesh, Lukka, Shekelesh, Teresh and Sherden as entities who joined the Libyans in battles with Egypt from the west. At Ramesses III’s mortuary temple,
Medinet Habu (Redford 1992), the entities Weshesh, Shekelesh, Sherden, Teresh, Tjekker,
Denyen and Peleset are mentioned as Sea Peoples groups fighting Ramesses III as a threat to
Egypt from the sea.
This demonstrates that there were multiple interactions between various entities that are associated with the Sea Peoples and the Egyptians. These interactions occurred during the 19th and 20th dynasties, spanning the 13th-12th centuries B.C. (Shaw 2000). The historical records are therefore consistent with the radiocarbon dating of the transition from sites in the Eastern
Mediterranean.
48 Chapter 4.3: Broader Implications for Associating the Early Aegean-like Pottery to the Sea Peoples from the 13th century BC
The radiocarbon chronology of the early Aegean-like pottery showing its appearance in the southern Levant during the 13th century BC, has several implications: 1. Decoupling of the early styles of Aegean-like pottery in the southern Levant from that of the Philistine entity, and assumes the Philistine paradigm is incorrect. 2. The earliest settling of some of the Sea Peoples in the land of Ugarit (northern Levant) occurred after they settled in Philistia (southern Levant). 3. The Philistine 1 pottery is now dated as early as the 13th BC and therefore before Ramesses III and the arrival of the Pleset group. Philistine 2 pottery is now dated to the time of Ramesses III and is associated with the Philistine culture. This supports the hypothesis that the interaction between the local Caananites, the Egyptian administration and the early foreign component of the Sea Peoples formed the Philistine identity (Maeir 2013; Hitchcock and Maeir 2013; Stockhammer 2013). 4. Dating the settling of the Sea Peoples in the region before the formation of the Philistine identity indicates that there was no organized, large scale violent uptake of Philistia by the Philistines during the Egyptian regime. The archaeological record of the several destructions in Ashkelon, Tel Ashdod and Tel Miqne during the LB|Ir that were associated with the Philistine arrival (Barako 2000; Dothan 1971) need to be re- examined (Master et al. 2011). 5. The radiocarbon chronologies presented here show that groups of the Sea Peoples settled for ca. 100 years before the Egyptian withdrawal during Ramesses VI period (end 12th century BC). This support the scenario that the Egyptian rulers segregated the minorities with Sea Peoples material culture in Philistia for almost a century (Mazar 1997). 6. The dating of the “Sea People” migration to the 1310-1250 BC in Tell es-Safi/Gath questions the link between the Late Bronze Collapse and the climatic changes in the ancient Near East, that were dated between 1250-1100 B.C. (Killebrew and Lehmann 2013; Yasur-Landau 2010; Drake 2012; Langgut, et al. 2013; Cline 2014; Kaniewski, et al. 2015).
49 Main Conclusions of this Research
1. High resolution dating, of sub-century, is achieved within a plateau on the radiocarbon calibration curve by dating many materials from secure contexts in a clear stratigraphic sequence before, during and after the LB/Ir transition. 2. The appearance of locally produced Aegean-like pottery, associated with foreigner arriving to the southern Levant, occurs during the 13th century BC, which decouples the association of the early types of foreign pottery from the Philistines. 3. The LB/Ir transition is Canaan, differs between sites by more than 100 years, showing relative chronology can be used as guidelines for dating, and not high resolution dating tool of less than a century, and that the transition is not contemporaneous between sites. 4. Radiocarbon dating the occluded carbon of siliceous phytoliths by dissolving the silica structure shows that phytoliths contain old carbon relative to the plants age. 5. Charred micro-particles, purified from sediments based on their density, can be used as an indicator for in situ burning events in archaeological sediments. 6. Thin sections of sediments, prepared on-site using a new method that is based on epoxy and polishing tools, shows good preliminary results in understanding stratigraphic relations between archaeological features.
50 Appendix
Chapter 5.1: Radiocarbon Data for Survey of Bayesian Models (Chapter 4) Table 1 summarizes available radiocarbon dates of transitional strata in Canaan. Duplicates are marked with RT-xxx.1. This table was used to plot Figure 1 in the introduction, showing dates of the LB IIB period as the Late Bronze Age, LB III as the LB|Ir period, and Iron I as the Iron Age, following the annotation of Finkelstein and Piasetzky (2011).
Associa ted 14C age ±1σ year Site Lab # Stratum Reference ceramic BP phase RTD-6264 LB I 23 3360±45 RTD-6259 LB I 23 3095±25 RTD-6258 LB IIB 21 3360±45 RTD-6260 LB IIB 21 3153±50 RTD-7574.1 LB III 20B 2940±30 RTD-7574.2 LB III 20B 2930±30 RTD-7573.1 LB III 20A 2950±30 RTD-7573.2 LB III 20A 2900±40 Iron I RTD-7572.1 19B 3030±35 early Iron I RTD-7572.2 19B 2955±25 early Iron I RTD-7571.1 19A 2870±35 Tel early This study Ashkelon Iron I RTD-7571.2 19A 2950±30 early Iron I RTD-7570.1 18B 2945±30 early Iron I RTD-7570.2 18B 2825±30 early Iron I RTD-7569.1 18A 2965±25 early Iron I RTD-7569.2 18A 2850±45 early Iron I RTD-7568.1 17B 2925±30 early Iron I RTD-7568.2 17B 2896±25 early Tel Beth RT-2597 LB IIB N4 2985±25 Mazar and Carmi Shean RT-2594 LB IIB N4 2925±25 2001
51 RT-2156 LB IIB N4 2910±50 RT-2325 LB III S3a 2980±40 RT-2596 LB III S3a 2960±25 RT-2323 LB III S3a 2900±45 RTT-5501 LB IIB K/8 2920±40 RTT-5502 LB IIB K/8 2945±40 RTT-5503 LB IIB K/8 2980±40 RTT-5882 LB IIB K/8 2990±55 RTT-5504 LB IIB K/7 2935±40 Toffolo et al. 2014 RTT-5884 LB IIB K/7 2980±50 RTT-5885.2 LB IIB K /7 2835±50 RTK-6771 LB IIB H13 3000±45 RTK-6772 LB IIB H13 3170±40 RTT-5080 LB III K/6 2982±15 RTT-5082 LB III K/6 2970±15 Finkelstein and RTT-5083 LB III K/6 2970±18 Piasetzky 2007 RTT-5081 LB III K/6 2961±21 RTK-6283 LB III H12 2902±19 RTK-6282 LB III H12 2898±28 RTT-5500 LB III M/6 2945±40 RTK-6762 LB III H12 2825±40 Toffolo et al. 2014 Tel RTK-6763 LB III H12 2840±45 Megiddo RTK-6768 LB III H12 2865±40 RTK-6769 LB III H12 2810±45 RTK-6770 LB III H12 2915±40 RTT-4500 LB III K/6 2933±29 RTT-4499 LB III K/6 2892±19 Sharon et al. 2007 RTT-4501 LB III K/6 2775±25 Iron I RTK-6511 H11 3105±65 early Iron I RTK-6409 H11 2871±29 early Iron I RTK-6410 H11 2925±28 early Toffolo et al. 2014 Iron I RTK-6280 H11 2920±31 early Iron I RTK-6281 H11 2886±28 early Iron I RTK-6275 H10 2898±26 early
52 Iron I RTK-6276 H10 2882±26 early Iron I RTK-6277 H10 2871±29 early Iron I RTK-6278 H10 2880±26 early Iron I RTK-6279 H10 2859±29 early Iron I Finkelstein and RTT-5078 K/5 2894±15 early Piasetzky 2007 RTT-4286 LB III VIIb 2907±28 Tell Iron I RTT-4283 VIb 2918±26 Miqne/Ekr early Sharon et al. 2007 on Iron I RTT-4284 Vb 2833±32 early RTD-7201 LB IIB A7 3058±16 RTD-7096 LB IIB A7 3032±30 RTD-6711 LB IIB A7 3029±45 Asscher et al. RTD-7098 LB IIB A7 3023±42 2015b RTD-6710 LB IIB P2 2979±45 RTD-7182 LB IIB P2 3079±16 RTT-6139 LB III F2 3070±45 RTT-6140 LB III F2 2940±45 RTT-6141 LB III F2 2970±45 Toffolo et al. 2012 RTT-6142 LB III F2 3010±45 RTT-6143 LB III F2 3045±45 RTT-6144 LB III F2 2960±55 Iron I RTD-7200 A4 2880±30 Tell es- early Safi/Gath Iron I RTD-5940 A4 2850±55 early Iron I RTD-7095 A6 2968±30 early Iron I RTD-6581 A6 2950±55 early Asscher et al. Iron I 2015b RTD-6580 A6 2930±55 early Iron I RTD-6579 A6 2925±55 early Iron I RTD-6983 A6 2903±32 early Iron I RTT-3928 V 2897±23 early Qubur el RTK-6578 LB IIB 1-7 3055±55 Asscher et al. Walaydah RTK-6709 LB IIB 1-5d 3013±34 2015a
53 RTK-6577 LB IIB 1-5e 3000±55 RTK-6605 LB IIB 1-6 2961±37 RTK-6576 LB IIB 1-5e 2934±37 Iron I RTK-6575 1-4_10 2948±29 early Iron I RTK-6573 1-4_7 2926±35 early Iron I RTK-6572 1-4_4 2924±35 early Iron I RTK-6574 1-4_9 2888±29 early Iron I RTK-6773 1-4_8 2882±45 early Iron I RTK-7121 1-4_2 2915±30 early RT-3152 LB IIB S-3 2945±65 RT-2906 LB IIB VIIa 2955±35 Tel RT-3153 LB IIB S-3 3125±55 Carmi and Lachish RW-2755 LB III VI 2955±25 Ussishkin 2004 RW-2912 LB III VIb 2915±25 Hel-1417 LB III VI 2810±100
Run file of the Ashkelon (Canaan) dates Bayesian model: Plot() { Sequence("Ashkelon sequence") { Boundary("Sequence begins"); R_Combine("Phase 22") { R_Date("RTD 6259", 3309, 45); }; Boundary("boundary 22/21"); R_Combine("Phase 21") { R_Date("RTD 6260", 3153, 49);
54 }; Boundary("boundary 21/20"); R_Combine("Phase 20B") { R_Date("RTD 7574_1", 2939, 29); R_Date("RTD 7574_2", 2927, 27); }; Boundary("boundary 20B/20A"); R_Combine("Phase 20A") { R_Date("RTD 7573_1", 2952, 27); R_Date("RTD 7573_2", 2900, 39); }; Boundary("boundary 20A/19B"); R_Combine("Phase 19B") { R_Date("RTD 7572_1", 3027, 36); R_Date("RTD 7572_2", 2956, 26); }; Boundary("boundary 19B/19A"); R_Combine("Phase 19A") { R_Date("RTD 7571_1", 2872, 36); R_Date("RTD 7571_2", 2952, 31); }; Boundary("phase 19A/18B"); R_Combine("Phase 18B") { R_Date("RTD 7570_1", 2946, 32); R_Date("RTD 7570_2", 2825, 28); };
55 Boundary("phase 18B/18A"); R_Combine("Phase 18A") { R_Date("RTD 7569_1", 2964, 26); R_Date("RTD 7569_2", 2852, 44); }; Boundary("phase 18A/17B"); R_Combine("Phase 17B") { R_Date("RTD 7568_1", 2898, 26); R_Date("RTD 7568_2", 2925, 31); }; Boundary("Sequence ends"); }; };
Run file of Gibala-Tell Tweini (Syria) dates Bayesian model: Plot() { Sequence("Tell Tweini sequence") { Boundary("Sequence begins"); Phase("Phase 7D") { R_Date("Beta-281584", 3190, 40); }; Boundary("7D/7C-B"); Phase("Phase 7C-B") { Label("Phase 7C-B time gap of 200 years."); Interval("Phase 7C-B", 200);
56 }; Boundary("7C-B/7A"); Phase("Phase 7A") { R_Date("Beta-281582", 3000, 40); R_Date("Beta-281576", 2990, 40); R_Date("Beta-281572", 2950, 40); R_Date("Beta-281590", 2950, 40); R_Date("Beta-281591", 2950, 40); R_Date("Beta-281570", 2910, 40); }; Boundary("7A/6E"); Phase("Phase 6E") { R_Date("Poz-25442", 2845, 35); }; Boundary("Sequence ends"); }; };
Run file of Tell Lachish (Canaan) dates Bayesian model: Plot() { Sequence("Tel Lachish") { Boundary("sequence begins"); R_Date("P-4, RT-3149", 3125, 55); R_Combine("S-3, RT-3152 and RT-3153") { R_Date("RT-3152, Stratum S-3", 2945, 65); R_Date("RT-3153, Stratum S-3", 3125, 55);
57 }; R_Date("VIIa, RT-2906", 2955, 35); Boundary("LB to LB/Ir Transition"); R_Date("VIb, RT-2912", 2915, 25); R_Combine("VI, RT-2755 and Hel-1417") { R_Date("RT-2755, Stratum VI", 2955, 25); R_Date("Hel-1417, Stratum VI", 2810, 100); }; Boundary("LB/Ir to Iron Transition"); Label("Iron I gap of 260 years"); Interval("Iron I gap", 260); R_Date("V, RT-3159", 2755, 55); R_Date("IVb, RT-2908", 2715, 40); R_Date("IVa, Hel-1418", 2650, 90); Boundary("sequence ends"); }; };
Run file of Tell Beth Shean (Canaan) dates Bayesian model: Plot() { Sequence("Tel Beth Shean") { Boundary("sequence begins"); R_Combine("N-4") { R_Date("RT-2597", 2985, 25); R_Date("RT-2594", 2925, 25); R_Date("RT-2156", 2910, 50); };
58 Boundary("LB/Ir transition"); R_Combine("S3a") { R_Date("RT-2325", 2980, 40); R_Date("RT-2596", 2960, 25); R_Date("RT-2323", 2900, 45); }; Boundary("sequence ends"); }; };
Chapter 5.2: Towards Dating Phytoliths: a New Method for Extracting and Analyzing the Occluded Carbon Shows Older Radiocarbon Concentrations in Modern and Archaeological Phytoliths
Phytoliths are biogenic opal (silica) bodies produced by many plants. Phytoliths vary in shape and size according to plant species and location within the plant (Piperno 2006). Phytolith-rich sediments are abundant in many archaeological sites, and their concentrations and assemblage compositions provide valuable information on past vegetation (Albert et al. 2006). As many of these phytolith-rich sediments form in layers they are excellent stratigraphic markers that would be invaluable if dated (Albert et al. 2008). So far, major contexts in which phytoliths were found, such as animal enclosures and occasionally surfaces or floors used as agricultural storage (Shahack-Gross et al. 2003), could be dated only if associated charred remains were found in situ, which rarely happens.
Phytoliths from soils were shown to have occluded organic material that is stable for long periods (Wilding 1967). Archaeological phytoliths were dated (Piperno and Stothert 2003), and the method used includes purifying phytoliths from sediments based on their specific density using heavy liquids, then cleaning the phytoliths by removing soil organic materials and carbonates using oxidizing solutions and acids. The purified phytoliths were then heated to high temperatures with an oxidizing catalyst, and the evolved carbon dioxide was collected,
59 and then reduced to graphite, and finally the graphite was dated (Piperno 2006). Chemical etching and oxidation selectively remove exposed organic materials in phytoliths (Wilding 1967) and partially destroy the silica structure (Jenkins 2009). Moreover, this pretreatment and extraction of carbon dioxide at high temperatures shows differences in radiocarbon concentrations between fractions (Yin et al. 2014) and result in variable results with old dates for modern phytoliths and young dates for archaeological samples (Kelly 1991; Santos et al. 2010; Santos et al. 2012; Sullivan and Parr 2013; Alexandre et al. 2015; Piperno 2015; Reyerson et al. 2015). We therefore opted for a different strategy.
Many biogenic minerals, including biogenic silica of diatoms for example, contain occluded organic molecules and macromolecules embedded within the mineral phase (Kröger et al. 2000). This location provides relative protection against degradation, and is referred to as a “protected niche” (Weiner 2010). Plant phytoliths also contain occluded organic material, including lipids, cellulose, lignin and organic molecules possessing carboxylic acids (Elbaum et al. 2009; Watling et al. 2011). These organic materials are embedded in the silica structure, or are present in internal cavities of varying sizes (Alexandre et al. 2015).
A fraction of the trapped organic matter in diatoms and plant phytoliths was reported to be insoluble (Harrison 1996; Elbaum el al. 2009), provided that the silica is dissolved under mild conditions such as buffered ammonium fluoride. This method was first used to dissolve diatom frustules (Kröger et al. 2002). The strategy used in this study is to purify phytoliths with minimal chemical pretreatment, then extract the insoluble fraction, and measure its radiocarbon concentration.
Materials and Methods Purification of phytoliths Modern samples: common wheat (T.aestivum) was collected from a greenhouse located within the Weizmann Institute of Science, Israel. The plants were subjected to dry ashing adapted from Parr et al. (2001) that shows minimum alteration of the structure (Jenkins 2009; Cabanes and Shahack-Gross 2015). Briefly, the plants were cut into small pieces and were placed in a
60 beaker and sonicated for 20 minutes (Cole-Palmer 8891). The wet materials were then placed on a sieve and washed with distilled water for 10 min. This was repeated 3 times and then the materials were dried overnight at 50ºC in an oven. 35grams of cleaned and dried plant materials were burnt in an oven in air at 500ºC for 4 hours. After cooling, the burnt material was placed in 6 N HCl for 10 minutes to remove the carbonates. Then the phytoliths were washed 3 times with water until pH=7 (checked with pH paper). The materials were dried overnight at 50ºC in an oven. Samples were checked for purity under the microscope and using Fourier transform infrared (FTIR). If cellulose was observed under the microscope (shown by strong birefringence), or the bulk material was not pure opal (based on the FTIR), the sample was not dated. Phytoliths that contained adhering charred organic materials and charred plant materials were removed with tweezers prior to dissolution
Archaeological samples: Phytolith-rich sediments were collected from well dated contexts of the Iron Age period in Tell Beth shemesh, Tell Ernai and Tell es-Safi/Gath, Israel. 1gr of material was placed in 50ml polypropylene tubes. Then 10ml of 2.4gr/ml sodium polytungstate was added, and the solution was vortexed and sonicated (Cole-Parmer 8891) for 20min, followed by centrifugation at 3000rpm for 3min (Lumitron 5702). The supernatant containing the less dense materials (mostly phytoliths and clays) was transferred to a new 50ml polypropylene tube, while the heavy fraction in the pellet (mostly quartz and calcite) was discarded. Then 15ml of distilled water were added to the transferred supernatant, to lower the solution density to 1.6gr/ml. This is followed by vortexing, sonication for 20min, and centrifugation at 3000rpm for 3min. The supernatant containing the less dense materials (now mostly carbonized organic materials) was discarded and the heavy fraction in the pellet (mostly phytoliths and some clays) was washed with water. Washing with water was repeated until the solution pH=7 (checked with pH paper). Then 10ml of 1N HCl was added for 1hr to remove any remaining carbonates, while shaking the tube every ten minutes. The sample was again washed with water until pH=7, then dried in vacuum overnight. The entire procedure was repeated once more, mainly to purify the phytoliths as best as possible from quartz and carbonized materials. The samples were dried in vacuum overnight. Samples were checked for purity under the petrographic microscope and with Fourier transform infrared spectroscopy (FTIR), and in case they were still not pure, the procedure was repeated once again.
61
Dissolution of phytoliths About 50mg of purified phytoliths were placed in a 2ml Eppendorf centrifuge tube. Then 1.5ml of a 3% HF and 3% NH4F solution (Harrison 1996) was added, and samples were kept in suspension by rotation for 3 hrs. After 3hrs, the samples were centrifuged at 3000rpm for 3min, and then the tubes were filled with water. Samples were repeatedly washed with water until pH=7 (checked with pH paper), and were dried in vacuum overnight. Samples were then checked for purity under the microscope and with Fourier transform infra-red (FTIR). If the insoluble fraction did not contain siliceous phytoliths, 1 ml of 0.1N NaOH was added for 1 minute to remove materials soluble under alkaline conditions. The samples were centrifuged at 3000rpm for 3min, and washed in water until pH=7 (checked with pH paper), and were dried in vacuum overnight. Samples were checked for composition under the petrographic microscope and with Fourier transform infrared spectroscopy (FTIR), and in case they still contained phytoliths, the dissolution procedure was repeated.
Fourier Transform Infrared (FTIR) Spectroscopy A few milligrams of phytoliths were homogenized in an agate mortar and approximately 0.2 mg were ground to a fine powder and then mixed with ~10 mg of KBr (FTIR-grade). Samples were then pressed into a 7-mm pellet using a manual hydraulic press (Specac). Infrared spectra were obtained using a Nicolet 380 spectrometer at 4 cm–1 resolution.
Microscopy A few milligrams of dry purified phytoliths were placed on a microscope slide. A few drops of Entellan (Merck) were added and covered with a cover-glass. Phytoliths were observed and photographed at 100x, 200x and 400x magnification using a Nikon Eclipse 50iPOL microscope.
Phytolith Refractive Index Determination Phytolith refractive index (RI) was determined following the protocol of Elbaum et al. (2003). Briefly, about 2 mg of purified phytoliths were placed on a slide, and a liquid with a known
62 refractive index (RI=1.46) was added. The RI of individual phytoliths was measured using the Becke line (Head, 1962). The measurement was performed at 400× magnification using a Nikon Eclipse 50iPOL microscope.
MicroCT A Zeiss X-ray tomographic microscope (MICRO XCT-400) was used to study the 3D structure of individual multi-celled phytoliths. The phytolith was attached to the sharp end of a glass fiber with Superglue and placed in the beam center. 1400 projection images were recorded over 180 degrees with an exposure time of 10 s for each image. The final voxel size was 0.25µm. The volume was reconstructed without additional binning, using a back projection filtered algorithm (Zeiss X Ray Microscopy, Peasanton, California, USA). Once the reconstruction of the volume was complete, 3D image processing and analysis were carried out using Avizo software (FEI, Oregon USA).
Radiocarbon Dating We measured the radiocarbon concentrations in 4 different materials: the phytolith insoluble organic fraction, charred short-lived seed samples, soil organic carbon and cellulose from modern wheat. Charred remains: Pretreatment of short lived charred remains to remove contaminants prior to the measurement was performed following the protocol of Yizhaq (2005). The purity of the recovered charred remains was tested using FTIR to determine if the material remaining contains mainly charred remains. If clay minerals were present, the sample was not dated (Yizhaq et al. 2005). Cellulose was extracted using the method of Gupta and Polach (1985). Some 200 mL of Nanopure water (NANOpure DiamondTM, Barnstead) and 20 mL of 1N HCl were added to 10–20 g of whole dried plant leaves, and stirred on an 80 °C hot plate for 1 hour. Sodium chlorite (Fluka 71388-250g) was gradually added until the plant color changed from yellow to white. Then the samples were centrifuged at 3000rpm for 3min, the supernatant was discarded, and the cellulose was repeatedly washed with Nanopure water until pH=7 (checked with pH paper). The cellulose was dried at 120°C overnight.
63 Soil total carbon radiocarbon concentrations were determined by measuring the different carbon components in organic materials (wood, roots, etc.) and inorganic materials (carbonate rocks). About 20 grams of soil materials were homogenized in a mortar, 5 mg of materials were collected and accurately weighed and then graphitized (see below). Dating this fraction represents the total 14C concentration of the soil, in which the plants grew. Phytolith insoluble organic fraction after dissolution (see details above), about 30mg of material was collected, monitored for purity using FTIR and a microscope, and placed in an ampule prior to graphitization.
Graphitization of the insoluble fraction of dissolved phytoliths, cellulose, soil total carbon and charred remains was carried out by oxidization in vacuum with cuprum oxide (CuO) at 900°C, and the sample % carbon was recorded. The sample was then graphitized in the presence of hydrogen and cobalt at 700°C. Radiocarbon concentrations were determined using an accelerator mass spectrometer (AMS) at the Weizmann Institute, Rehovot, Israel using a 1.5SDH Pelletron, National Electrostatics Corp (D-DREAMS AMS). Modeling was carried out using Oxcal 4.2.3 (Bronk Ramesy 1995).
Results The development and testing of the method was carried out on materials from an Iron-age section at Tel Beth Shemesh, as the phytolith-rich layers are overlain and underlain by layers containing charred short-lived materials (Figure 19).
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Figure 19. A) A map showing the locations of the archaeological sites from which materials were analyzed in this study. Scale bar: 20km. B) A section of Iron Age sediments from Tel Beth Shemesh, showing laminations of phytolith-rich grey sediments and black sediments rich in short-lived charred remains. Layer numbers are marked according to stratigraphy.
The Tel Beth Shemesh layers were analyzed using a microscope and Fourier transform infra- red (FTIR) to determine the mineralogical compositions. Layers 12, 18, 19 and 21 contained charred seeds, calcite in the form of ash, clay minerals and quartz. The sediments in between these layers did not contain seeds and their major components were clays, geogenic calcite and quartz. Layer 23 contains high amounts of amorphous silica in the form of phytoliths and small amounts of quartz and clay. Layer 23 is a mixture of uncharred and charred leaf phytoliths (Figure 21). Layer 24 is rich in micro-charred particles, charred seeds, calcite in the form of ash, quartz and clay minerals. Layer 25 contains grasses phytoliths of unburnt leaves and inflorescence, and is rich in siliceous aggregates that are derived from wood (Weiner 2010). Layer 27 contains charred seeds and mainly clay minerals.
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Figure 21. Purified archaeological phytoliths from Tel Beth Shemesh Layer 23. A) An image of an assemblage of burnt phytoliths in plain polarized light showing different phytolith morphotypes, some of which contain charred carbon apparently trapped within the silica structure. Scale bar: 100µm. B) FTIR spectrum of the purified phytoliths showing that it is entirely composed of amorphous silica, based on the following peaks: a broad peak (1) at 3440cm-1 and a small peak at 1640cm-1 (2) associated to bound water, a major peak (3) at 1100cm-1 associated to Si-O stretching, a broad peak (4) at 800cm-1 associated to Si-O bending, and a sharp peak (5) at 467cm-1 associated to Si-O bending.
We used microCT in order to better understand the possible locations of organic matter occluded inside a multi-cell phytolith from Layer 25 (Figure 22A). Figure 22B is a microCT 3D reconstruction of the same multicell from Beth Shemesh showing an aligned array of silicified hollow tubes, encased in a solid outer wall of silica. Figure 22C shows the digital 2D
66 image of the slice through the phytolith shown in figure 22B. This slice confirms that the tubes are indeed hollow, and have different densities, showing higher densities (larger contrast) for the outer hollow tubes. The CT scan shows the presence of abundant mineral encased cavities, raising the possibility that some of the preserved carbon we are analyzing is from these spaces, in addition to molecules that may be occluded inside the mineral phase. The CT scan also shows that the minerals cavities are not always closed, implying that if indeed organic molecules are present in these cavities, they are susceptible to degradation and contamination (Alexandre et al. 2015).
Figure 22. Unburnt archaeological multi-cell grass phytolith from Layer 25 at Tel Beth Shemesh. A) Microscope image in plain polarized light. Scale:100µm. B) MicroCT 3D reconstruction of the phytolith, showing elongated hollow cylinders connected to an outside silica surface layer. A digital slice shows the location of the cross-section shown in C. Scale:50µm. C) MicroCT 2D cross section through the multicell. Note the presence of voids inside the cylinders (arrows). Scale:50µm.
Radiocarbon Dating Different preparation protocols were tested to find the optimal conditions for purifying phytoliths from sediments and dissolving the silica while minimizing loss of the insoluble
67 organic material. Some protocols for purifying phytoliths examined different acidic conditions for removing inorganic carbonates (protocols 2,3,4,7: see details below), while other protocols for dissolving phytoliths tested the effects of solutions at different pH on the phytolith insoluble fraction, on being able to remove dissolved organic materials from the insoluble fraction (protocols 1,5: see details below), and oxidizing solutions to remove exogenous organic carbon prior to dissolution (protocols 8: see details below). Figure 23 shows 14C dates of the insoluble materials of phytoliths from Layer 23, for eight different preparation protocols, arranged according to age. The protocols included: (1) purifying phytoliths from Layer 23 sediments based on their density prior to any 1N HCl treatment using 2.4 gr/ml sodium polytungstate, and also exposing the insoluble fraction to 0.1N NaOH to remove alkaline soluble materials (RTD_7262). (2) Treating Layer 23 sediments for 3hrs with 1N HCl prior to purifying phytoliths using 2.4 gr/ml sodium polytungstate (RTD_7265). (3) Applying the Acid Base Acid (ABA) pretreatment that is used to pretreat charred remains prior to dating following Yizhaq et al. (2005) on purified phytolith of Layer 23 prior to dissolution (RTD 7417). (4) Sonicating the sediments of Layer 23 in a solution of 1N HCl for 1hr, before purifying the phytoliths using 2.4 gr/ml sodium polytungstate (RTD 7260). (5) Purifying phytoliths from Layer 23 sediments based on their density prior to any HCl treatment using 2.4 gr/ml sodium polytungstate, and then exposing the insoluble fraction to 0.1N HCl to remove acid soluble materials (RTD 7261). (6) Purifying phytoliths following the protocol in Katz et al. (2010) and not applying any other solutions prior to dissolution (RTD 7125). (7) Treating Layer 23 sediments to 1hr of 85% H3PO4 prior to purifying phytoliths using 2.4 gr/ml sodium polytungstate (RTD_7263). (8) Applying 30%
H2O2 oxidizing pretreatment (used to clean phytoliths from exogenous carbon prior to dating) to purified phytoliths from of Layer 23 prior to dissolution (RTD 7126). Protocol 1 is the best protocol based on the fact that the dates obtained from the phytolith insoluble fraction, were most similar to the dates obtained from the associated charred seed remains.
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Figure 23. Calibrated dates of charred seeds and the insoluble fractions of dissolved phytoliths from Tell Beth Shemesh. Dates are arranged in a sequence according to stratigraphy from sample BS27 (oldest) to sample BS12 (youngest). On the left hand side, along with the sample number, data (in round brackets) are provided on the age before calibration, and the precision. The dates obtained using the different protocols described in the text are shown.
After establishing the best protocol for phytolith purification and dissolution, we then proceeded to use this protocol to analyze the Beth Shemesh section in detail. This was followed by analyses of samples from two other sites, and modern plants. Table 3 lists the uncalibrated radiocarbon ages of charred seeds and phytolith insoluble fractions of modern and archaeological phytolith samples. Also noted is the context description, associated charred remains, if the phytoliths were burnt or not, and finally if the sediments contain siliceous aggregates (Schiegl et al. 1994) (components that are associated with wood). The δ13C values range between -20‰ to -31‰, showing all modern and archaeological phytoliths are from C3 plants.
69 AMS Archaeological Field layer Context Botanic 14C age ±1σ RTD# %C δ13C site/Modern ID description description year BP [‰] grey layer, olive pit 7437 78 2890±30 -21.5 BS12 compacted half an 7362 61 2950±30 -22.4 sediments olive pit grey layer, fine sediments 2 barley BS18 7363 64 2890±30 -25.4 and many seeds charred remains black layer, fine sediments BS19 olive pit 7364 88 2920±30 -23.6 and many charred remains 7367.1 grey layer, 2 wheat 2890±25 7367.2 -22.2 fine seeds, 1 71 2900±30 Tell Beit averaged -23.0 sediments barley seed 2894±30 Shemesh BS21 date and many wheat and charred barley 7122 63 2950±30 -21.7 remains seeds
7262.1 2950±30 phytolith-rich 7262.2 -22.8 2970±30 layer, poor in 7262.3 23 -23.1 2980±30 siliceous averaged -23.3 2967±18 aggregates, date BS23 contains phytoliths charred burnt phytoliths, 7586.1 contains 2940±30 7586.2 -23.3 spherulites 43 2910±25 averaged -24.9 2922±20 date
70 7587.1 2960±40 7587.2 -29.7 46 2930±30 averaged -25.3 2941±25 date
7759.1 2965±35 7759.2 -23.9 29 3070±60 averaged -24.5 2992±31 date black layer, 7368.1 2900±35 fine 7368.2 -22.9 olive pit 61 2910±30 sediments averaged -25.5 BS24 2906±23 and many date charred olive 7123 67 2880±30 -25.6 remains fragment 7979.1 2970±20 rich in 7979.2 -22.8 13 2950±25 siliceous averaged -20.1 2962±16 aggregates, date BS25 phytoliths unburnt 7760.1 3015±35 phytoliths, no 7760.2 -22.9 21 3060±45 spherulites averaged -25.1 3032±28 date grey layer, legume fine 7124 66 2900±30 -21.3 fragments sediments BS27 and many charred olive pit 7369 62 2950±30 -25.6 remains grey layer, burnt B. 1484.1 Tell Erani phytoliths, no phytoliths 7980 5.8 3020±25 -26.9 L. 105 siliceous aggregates grey patch, 7982.1 4230±25 fine 7982.2 -23.3 Tell es- 4210±25 16E83B062 sediments phytoliths 7982.3 23 -23.3 Safi/Gath 4230±25 and many averaged -23.0 4223±15 charred date
71 remains, no 6989.1 siliceous 4065±45 6989.2 aggregates, seeds 72 4130±45 N.A. averaged burnt 4098±32 date phytoliths 8144 57 *97.44±0.27 -31.1 whole plant phytoliths 8145 46 *98.57±0.26 N.A. 8167 38 *97.29±0.31 N.A. modern Greenhouse in 8137 41 *99.46±0.27 -29.1 samples of whole plant cellulose Rehovot, Israel 8138 32 *100.10±0.27 N.A. T.aestivum greenhouse 8139 39 *73.27±0.25 -26.5 total soil soil in which carbon 8140 34 *71.80±0.23 N.A. plants grew opal mixed with 7983 51 2820±20 -19.9 charcoal opal mixed with 7984 43 2860±30 -21.3 charcoal Blanks N.A opal mixed with humic 7985 8.5 11790±40 -30 substances opal mixed with humic 7986 14 11800±35 -27 substances
Table 3. Uncalibrated radiocarbon ages of charred seeds and phytolith insoluble fractions of modern and archaeological phytolith samples from 3 sites, as well as blanks. Also noted are field layer ID, context description, botanical identification, sample RT number, % carbon, 14C age ±1σ year BP, and the accelerator (AMS) δ13C. Modern samples are reported as percent modern carbon (marked with *). N.A. is information not available.
Figure 24 shows calibrated radiocarbon dates of the phytolith insoluble fractions and the associated charred seeds listed according to stratigraphy in Beth Shemesh (the same sequence as in Figure 19). The dates of the seeds range over 200 years between 1000-1200 BC at the 1σ confidence level. This large range is due to wiggles in the calibration curve during this period that form a 200 year “plateau” (Reimer et al. 2013). The phytolith insoluble fraction ages from
72 Layer 23 and 25, overlap with the range of this “plateau” at the 1σ confidence level, with one outlier (RTD 7760).
Figure 24. Calibrated ages of phytolith insoluble fractions (red) and charred seeds (grey). The samples are listed according to stratigraphy. Seed ages range between 1000-1200 BC at 1σ confidence level. The phytolith insoluble fractions ages overlap with the age ranges of the seeds, with a single outlier (RTD 7760).
Discussion
We applied Bayesian modeling to the sequence in Beth Shemesh, in order to obtain a high resolution analysis of the phytolith insoluble fraction dates compared to the dates from the
73 seeds. Figure 25 shows two Bayesian models of the stratigraphic sequence: the first is based only on seeds, and the second is based on seeds and the phytolith insoluble fraction. The first model shows that modeled combined dates of seeds in the layers above, in between and below the phytolith-rich layers (Layers 23 and 25) range between 1150-1050 BC at 1σ confidence level, with an agreement of 120% and no outliers. Incorporating the dates of the phytolith insoluble fraction within the sequence of seeds, and maintaining the same stratigraphy, lowers the agreement to 34%, and shows that the combined dates from layer BS24 become outliers (below 60% agreement). The modeled ranges of the sequence that includes the phytolith insoluble fractions are between 1210-1050 BC at 1σ confidence level, which is older by 60 years than the range obtained using charred seeds. Excluding sample RTD_7760 (the outlier) from the sequence does not change significantly the model agreement (showing agreement of 40% and layer BS24 is an outlier). However, the modeled ranges of the sequence are between 1195-1080 BC at 1σ confidence level, which is older by 30-45 years than the range obtained using charred seeds.
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Figure 25. Two models of the sequence of dates from Tell Beth Shemesh. The upper model shows a sequence of the combined dates of seeds according to the stratigraphy, and the bottom model shows seeds (grey) and the phytolith insoluble fraction (red) combined dates, based on the same stratigraphy. The black dotted lines show the age range of modeled seeds at the 1σ confidence level, and the red dotted line shows the lower age range of the modeled seeds that include phytolith insoluble fractions. Dates are presented with their layer number (BSxx), age
75 before calibration and precision (in round brackets), and their agreement index (in square brackets).
In Tell es-Safi/Gath, contexts that contain burnt phytoliths, seeds and pottery from the Early Bronze Age were identified and dated. The uncalibrated dates of the seeds were averaged to 4100±30 BP, which is calibrated to between 2850-2580 BC at 1σ confidence level. The large range of 270 years is due to wiggles in the calibration curve during these periods (Reimer et al. 2013), but the dates are in agreement with the expected period based on the Early Bronze ceramics. The phytolith insoluble fraction uncalibrated dates were averaged to 4225±15 BP, which is calibrated to between 2890-2870 BC at 1σ confidence. These results show that the phytoliths are older by between 20-310 years, due to the large calibrated range of the seeds.
The conclusion is that phytolith insoluble fractions can be dated reproducibly, but the dates obtained are older than the associated seeds in Beth Shemesh and Tell es-Safi/Gath. This shows that for sub-century chronological questions, dating the phytolith insoluble fraction is not suitable. In order to better understand the discrepancies between the dates of charred seeds and the phytolith insoluble fractions, we discuss below the possible carbon sources of the phytolith insoluble fraction.
Carbon sources in the phytolith insoluble fraction
The phytolith purification procedure removes all the clays and their associated organic material. So this should not be a possible source of old carbon. The purification procedure cannot, however, separate silica phytoliths from the siliceous aggregates that are relatively abundant in wood ash (Schiegl et al. 1994). The siliceous aggregates will also dissolve in the acid treatment, and leave an insoluble organic fraction, especially if the wood was burned and the associated organic matter is charred. As this organic matter is derived from wood, which could be much older than the time of burning, known as the old wood effect (Zilhão and d’Errico 1999; Guo et al. 2000), the presence of siliceous aggregates in the sample could account for older dates. In our study, only one sediment sample was rich in siliceous aggregates (Layer BS25 in Beth Shemesh). The date obtained from this sample overlaps well
76 with the dates from associated seeds (RTD 7979), indicating that in this case the siliceous aggregates did not introduce older carbon. This might not be the case in other samples that contain both phytoliths and siliceous aggregates.
It has been well demonstrated that the carbon in plant cellulose is derived entirely from the atmosphere. It has however been demonstrated that the organic matter in phytoliths does contain a fraction of radiocarbon that is older than the atmospheric derived radiocarbon in the same plant, and it was proposed that this old radiocarbon is derived from the soil (Santos et al. 2012). This was shown for the total organic material in phytoliths released by oxidizing intact phytoliths at high temperatures. It is therefore possible that this soil derived organic radiocarbon is not incorporated in the insoluble organic fraction of the phytoliths examined here, but is present in the soluble fraction. If this is the case, then phytoliths that were burned in antiquity that presumably have their entire organic component charred and hence insoluble, should be older than unburnt phytoliths. We found no evidence for this when comparing burnt and unburnt phytoliths from Beth Shemesh. We therefore conclude that the insoluble fraction does incorporate a small amount of soil radiocarbon.
We therefore examined the phytolith insoluble fraction from modern wheat (T. aestivum) that was grown in a controlled environment in a greenhouse. The wheat was not exposed to pesticides or carbon based fertilizers. The soil in which the wheat plants grew was 50% peat soil that contains old organic carbon and 50% volcanic rock. The soil did not contain inorganic carbon minerals (carbonates). Phytoliths were extracted from the modern plant using dry ashing (Parr et al. 2001), which removes the organic materials by combustion in the presence of oxygen. This method was used to remove all organic materials outside the phytoliths and avoids the use of chemical solvents such as strong acids and oxidizing solutions, which may affect the carbon composition. Dry ashing is comparable to situations in the past when phytoliths were burned, such as occurred at Tell es-Safi/Gath and Beth Shemesh (layer BS23).
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The modern T.aestivum cellulose was dated and the radiocarbon concentration is reported as the fraction modern carbon (F14C), which incorporates 13C fractionation and background corrections. The F14C range of the cellulose is 0.995-1.0005 (Table 3), which is comparable with recent reports of modern plants (Hirtella americana harvested in 2013) with values of 0.997-1.005 (Piperno 2015). In contrast, the phytolith insoluble fraction F14C range is 0.9805- 0.9748, which is significantly older than the modern cellulose. The total soil carbon F14C range is 0.7229-0.7277. This experiment demonstrates that wheat does extract “old” carbon presumably from the soil, which is in agreement with previous observations (Kuzyakov and Jones 2006; Jones et al. 2009). Some of the older carbon is in the phytolith insoluble fraction. This is in agreement with previous observations of older carbon found in modern phytoliths (Santos et al. 2010; Yin et al. 2014; Reyerson et al. 2015) and is consistent with our observations that the archaeological phytoliths of Tell es-Safi/Gath and Beth Shemesh are older than expected.
Based on the analyses of archaeological and modern insoluble fraction phytoliths, we do not expect that there is a constant offset to older ages in phytoliths, since it depends on the soil organic composition on which the plants grew. The difference observed in Beth Shemesh is around 60 years, but at Tell es-Safi/Gath the difference is greater (in part influenced by the uncertainty introduced by the calibration curve). We therefore advocate caution when using the insoluble fraction for dating. Applications that do not require high resolution sub-century accuracy could be dating in prehistoric contexts, and indication of the general age of certain strata, especially when cultural material is not found. At Tell Erani, certain layers did not contain indicative pottery and the stratigraphic interpretation showed the layers could be associated to many periods: Early Bronze Age, Late Bronze Age, the Persian period, Byzantine or Islamic periods, which range between 3000 BC until 1000 AD. That is due to the small amount of associated material culture with these contexts. The phytolith insoluble fraction date in Tell Erani (RTD 7980) showed that these strata are from the end of the Late Bronze Age, between 1370-1220 BC at the1σ confidence level. Since datable materials were not found in the context from Tell Erani, dating the phytolith insoluble fraction contributed significantly to identifying the archaeological period.
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Conclusions
We present a new method for extracting and radiocarbon dating the insoluble organic fraction from plant phytoliths. The radiocarbon analyses are reproducible. A controlled study at Tel Beth Shemesh shows that the radiocarbon dates of the insoluble fraction are about 60 years older than the associated charred short-lived seeds. We confirm that the phytolith insoluble fraction contains “old” radiocarbon using both modern wheat phytoliths and archaeological phytoliths from another site. Radiocarbon dating of phytolith insoluble fractions cannot be used for high precision dating, but may have applications in prehistoric sites where the accuracy required is less than a century or more, at younger archaeological sites where both phytolith-rich layers and limited short-lived charred materials are available, or where low resolution radiocarbon dates can help resolve chronological questions especially when indicative cultural materials are not available.
Chapter 5.3: A Rapid On-site Method for Micromorphological Block Impregnation and Thin Section Preparation
On-site science based methodologies allow collecting and analyzing information in various fields including diagnosis of tropical diseases, mining geology, soil analysis, forensic studies, military medicine, entomology, micropaleontology, and microbiological research (Goren 2014). In archaeology, on-site based methodologies include mineralogical and elemental studies using portable devices such as Fourier Transform Infrared and portable X-Ray Fluorescence spectrometers (Weiner 2010; Goren et al. 2011). Portable petrographic microscope allows the in-field mineralogical analysis of ceramics and sediments (Goren 2014) and portable UV spectrophotometers allow mapping phosphates in real time (Rypkema et al. 2007).
Archaeological micromorphology is a soil and sediment analysis technique that contributes to understanding site formation processes. It combines microscopic and macroscopic observations
79 of physical properties of sediments, with the aim of evaluating the depositional origin and integrity of archaeological strata. Furthermore, micromorphology offers opportunities for contextual analysis of archaeological materials since micro-artifacts, waste products, and microscopic faunal and plant remains are observed in their in-situ contexts (Courty et al. 1989; Matthews et al 1997; Goldberg and Macphail 2006; Karkanas and Goldberg 2007; Goldberg and Berna 2010). Micromorphology was first developed to examine soil composition and textures using the petrological microscope by Kubiena (1938, 1953, 1970). Micromorphologic examinations are done using the polarized light microscopic analysis under plane-polarized light (PPL) and cross-polarized light (XPL), which enables the study of the optical properties of minerals which are observed in their in situ interrelationships. Post-depositional alterations, such as bioturbation, soil formation, mineral alteration or mechanism of translocation of sediments can be assessed by thin section examination (Courty et al. 1989; Matthews et al. 1997; Karkanas and Goldberg 2007).
To date, archaeological micromorphology was limited to the laboratory since the preparation process included time consuming steps and heavy lab equipment. Preparation of thin sections involves the following major steps: on-site sampling, slow drying of the sediments (which is time consuming especially in wet climates), impregnating the block samples by polymer resin under vacuum, and then the time for the resin to polymerize (a step that requires tools and a lab that protects against volatile gasses), and lastly, using heavy tools to cut and polish blocks and prepare microscopic thin sections. Another constraint results from the fact that impregnation of blocks usually demands consolidated deposits which are larger than the standard-sized slides. Not only the large sample size slows down the polymerization time, but it involves large amounts of toxic resin that demands ventilation and proper lab care.
Therefore, the main constraints of micromorphology are time-demanding steps in the laboratory, and field sampling of badly sorted and highly unconsolidated sediments. The latter problem may be remedied through sampling in Kubiena boxes or coating with Plaster of Paris. In what follows, we will present a new method that makes it possible to extract blocks of sediments irrespective of the degree of sorting that are ready for grinding and polishing without further laboratory impregnation. We present 4 case studies which tested this field impregnation
80 method. In addition, we will present one case of preparing a thin section on-site following the new field impregnation procedure.
Field impregnation procedure Sediments were marked using a trowel on dry excavation sections to match the size of a thin section slide (76x50 mm), and to a thickness of 2-3 cm. Note that day temperatures in the study area can reach over 30°C which facilitates drying out of excavation surfaces. A highly diluted Epoxy (resin EC-502 with hardener EP-802, acquired from “Polymer Gvulot” company, Kibbutz Gvulot, M. P. Halutza 85525, Israel). The resin was mixed on site with the hardener in a volumetric ratio of 2:1 resin to hardener in a 50ml plastic centrifuge tube and then slowly dripped vertically over the marked sediment block using a 3ml disposable plastic pipette. The depth of resin penetration was usually 1-2cm into the section. The polymer was left to harden overnight (a minimum of 8 hours is required), and the next morning, the consolidated thin block was removed from the section using a trowel. The sample was then shaped using a portable Dremel saw to the size of a glass slide and the damp adhering sediments were left to dry (usually minutes in a Mediterranean climate). A fresh Epoxy mixture was then dripped onto the adhered sediments in order to complete the impregnation of the whole sampled volume. The entire field impregnation procedure thus takes 2 days, producing blocks of slide size and 1-2cm thickness (Figure 26). Thin sections were prepared by polishing of the block surface using a Grinder-Polisher EcoMet 250 (Buehler), gluing the polished surface to a glass slide (76x50 mm, Marienfeld Laboratory Glassware) using EpoThin Epoxy (Buehler), and thinning to 30 µm thickness using a PetroThin Thin Sectioning System (Buehler). The thin sections were studied using a polarizing light microscope (Nikon Labophot2-POL or Nikon Eclipse 50iPOL). The description of the thin sections follows the terminology of Bullock et al. (1985).
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Figure 26. A cross section of polished impregnated sediments. The original surface (bottom of block) after polishing the surface, shows Epoxy penetration depth ranges between 1-2cm. White arrows point to areas that were not impregnated fully.
Some advantages of this procedure are avoidance of using large quantities of resin, and extracting blocks that are the right thickness and size for thin section preparation, i.e., there is no need for lengthy laboratory impregnation of sediment volumes that are much larger than those required for production of thin sections, and no need to use slab saws after impregnation in order to reduce impregnated blocks to slide sizes. In addition, the field impregnation allows extraction of highly unconsolidated (sandy) and badly sorted sediments, as all elements are consolidated before block extraction from the excavation section.
Location of Study We tested the effectiveness of the field impregnation method in 4 different sites in Israel. One sample was extracted and prepared from each of the following sites: Qubur el-Walaydah, Tell es-Safi/Gath, Megiddo and Ashkelon. Figure 27 shows the locations of these sites on a soils map, showing that the sites are located in areas with different soils, which will affect the composition of the sediments in the site and the impregnation effectiveness. Table 4 outlines the bedrock and surface soils in the vicinity of these sites.
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Figure 27. A soil map of Israel. Archaeological sites from this study are marked, showing Qubur el-Walaydah, Tell es-Safi/Gath, Megiddo and Ashkelon.
83 In order to evaluate the suitability of the field impregnation for preparation of high quality micromorphological thin sections, we focused on studying the mineralogical composition, grain size distribution, porosity and microstructure which seem to be the most important parameters that influence Epoxy penetration depth, consolidation and polish grade.
Results
Figure 28 shows flatbed scans of the thin sections that were produced from the different sites. These large scale images show that the field impregnated blocks retained the stratigraphic relationships between layers. The overall slide thickness is quite uniform indicating that impregnation successfully consolidated all types of minerals and grain sizes.
84 85 Figure 28. Scans of thin sections that were impregnated in the field. A) Sample QW111D106_229. Loess sediments including clay-rich and spherulite-rich laminations (adapted from Asscher et al. 2015a) from square D106, area 1 at Qubur el- Walaydah. White arrows point to locations of interfingering clay-rich and spherulites-rich laminations. Scale is 1cm. B) Sample P15AE083. Stratified phytolith rich layers in a clay-rich deposit from square AE, area P at Tell es-Safi/Gath. The phytolith accumulation show several depositional events including three distinguished layers of phytoliths (shown by white arrows). Scale is 1cm. C) Sample QH5L198LB011. A deposit of high temperature activity remains, including organic charred remains, ash and phytoliths from square H5, area Q at Megiddo. A large charcoal piece marks the ash surface. Scale is 1cm. D) Sample ASH1590. A deposit of stratified surfaces, including a thick grey sandy surface, rich in organic charred remains and pottery from square 74, grid 51 at Ashkelon. White arrow points to a pure layer of sand. Scale is 1cm.
Figure 29 shows features at the micro-scale from the four thin sections. Delicate remains were found intact, including dung spherulites, phytoliths, coccoliths, and charcoal. The sediments contain hard and soft materials and all have been rather uniformly ground indicating high quality impregnation. Large grains of sand (quartz) sometimes appear shattered; a normal phenomenon attributed to grinding. A few quartz grains dislocated out of the samples due to differences in hardness; a common phenomenon that partly relates to quality of impregnation but also to speed of grinding. A feature that formed from fast resin consolidation was identified in only one sample where ‘Epoxy nodules’ were found in cracks and voids (figure 29C within charcoal). This could be an effect of poor penetration, but it was rare.
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87 Figure 29. Images of features in thin sections that were impregnated in the field. A) Sample QW111D106_229. Spherulite accumulation in Qubur el-Walaydah. White arrows point to the spherulite accumulation. Image taken in cross polarized mode at X200 magnification. Scale is 100µm (adapted from Asscher et al. 2015a). B) Sample P15AE083. A sequence of phytolith rich layers, showing sediments accumulated in between two distinguished layers of phytoliths. A fragment of pottery is found on the bottom phytolith layer. Image taken in cross polarized light with grey background to see the laminations of the phytoliths at X20 magnification. White arrows point to the phytolith layer. Scale is 1000µm. C) Sample QH5L198LB011. A large charcoal piece found on an ash surface in Megiddo. The charcoal piece contains a structure that resembles Epoxy resin nodules. Image taken in plain polarized mode at X100 magnification. Scale bar is 100µm. D) Sample ASH1590. Quartz grains in a sand-rich sediments in Ashkelon. The grains are broken by the polishing. Arrows point to locations where quartz grains became disconnected from the carrying glass. Image taken in cross polarized mode at X100 magnification. Scale bar is 100µm.
Table 4 summarizes the main finds in each context regarding the bedrock and sediments, mineralogy, grain sizes and porosity.
Bedrock Sample and Grain Sizes and Site and surface Porosity context Mineralogy soils
Upper - The main Upper - Dominant QH5L198LB011 minerals are clays, voids are vesicles Stratified Chalk and calcite and quartz. and channels, and sediments in Megiddo alluvial The fine fraction is irregular vughs that Level Q-6, grumusols silty clay with a constitute between associated to the coarse fraction 5-15% of the thin early Iron IIA composed of sand- section area. Some 88
occupation. size quartz grains of the voids are and pebbles of interconnected. carbonate rock
fragments arranged Lower - Most voids in an open are irregular vughs porphyric related that are between 15- distribution. 25% of the thin Lower – The main section area. The minerals are calcite, voids are largely quartz and clays. interconnected. This layer is rich in
wood ash, charred organic material, and phytoliths. Multicellular phytoliths are present. The fine fraction is silt-sized quartz with a coarse fraction of sand- size quartz and calcite grains arranged in an open porphyric related distribution.
Clay-rich layers - Clay-rich and QW111D106_229 The minerals are Loess sediments - Stratified Qubur el- clays, calcite and The voids are mostly sediments in a Loess Walaydah quartz. The coarse vesicles, channels deep sounding in fraction is well and some planes that Stratum DS_1-5, sorted subangular constitute between
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associated to the silt-sized quartz 10-20% of the slide Late Bronze Age arranged in a single area. Few irregular occupation. spaced porphyric vughs are present, Layers of around related distribution, connected over vast 3 mm thick and the fine fraction areas, in the clay- alternate between is dense silty clay. rich and loess layers.
clay-rich and Loess layers – The loess. The loess- minerals are quartz, rich layer contains calcite and clays. dung spherulites. The coarse fraction is silt-sized quartz in a porphyric related distribution, and the fine fraction is composed of micritic calcite and some silty clay.
Upper and Lower Upper and Lower parts of the slide - parts of the slide - P15AE083 The minerals are The voids are mostly A phytolith-rich clays, calcite and Chalk, vesicles and surface is found in quartz. The fine Calcrete channels that the center of the fraction is silty clay (Nari), constitute between Tell es- slide. It was with a coarse Brown 5-15% of the area. Safi/Gath identified in a fraction of well Rendzina, Phytolith-rich layer room associated to sorted subangular and alluvial – The voids are Stratum P2 Late sand-sized quartz grumusols. mostly vughs and Bronze/Iron I arranged in a single some planes that occupation. spaced porphyric constitute between distribution. The 10-20% of the area. clay-rich layers
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above and below The voids are the phytolith-rich connected especially layer are rich in in the phytolith-rich charred organic layer. materials and pottery fragments and seem as they are the result of the degradation of mud bricks. The sample also contains micritic calcite with scattered pinwheel pattern of coccoliths, and large carbonate rocks.
Phytolith rich layer – The minerals are opal, clays and quartz. Three episodes of phytolith depositions of 1mm thick were identified. In between the phytoliths deposition, sediments containing silty
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clays and quartz sand were found.
Upper - The
sediments contain Upper – The voids quartz (silt and are channels and sand), clays and some vesicles that calcite. The fine constitute between fraction is silty clay 15-20% of the area. ASH1590 and silt-sized Grey Layer – The quartz. The coarse Stratified voids are mostly fraction is sand sediments that vughs with some quartz grains include clay-rich vesicles that sediments arranged in a Nile sand, constitute between overlying a thick closed-single consolidated 15-20% of the. The grey layer that spaced porphyric aeolianites voids are somewhat includes pottery distribution. Ashkelon (Kurkar), connected in the fragments and Grey Layer - The Beachrock, ashy layer. burnt remains, sediments contain and Hamra Lower – The sand associated to the quartz (silt and soils layer contains Iron Age period. sand), clays and packing voids in a Overlying the calcite. The fine course monic clay-rich fraction is silty distribution. The sediments is a quartz and calcitic voids are vughs that pure sand layer. ash. The coarse are not connected, fraction is sandy that constitute quartz grains between 15-20% of arranged in a single the. space porphyric distribution.
Lower - The
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sediments contain quartz, clays and calcite. The closed porphyric sandy quartz is a sand layer, with pottery fragments and charred remains.
Discussion
Here we present a field impregnation procedure for preparing micromorphology blocks. Blocks from contexts containing different archaeological features were collected at the sites Qubur el-Walaydah, Tell es-Safi/Gath, Megiddo and Ashkelon. The results are discussed in relation to the ability to impregnate sediments with different mineralogy, grain sizes and porosity, while retaining delicate micro- stratigraphic features.
Results show that impregnation is achieved in the field and is slightly influenced by different mineralogical composition. Clays, calcite and quartz were all found in the different contexts, but in different proportions. Calcitic rich layers such as the ash layers in Ashkelon and Megiddo and quartz rich layers such as in Ashkelon and Qubur-el-Walaydah were fully impregnated in the field. Clay rich layers in Tell es- Safi/Gath were also impregnated in the field, but several parts had to be impregnated with more Epoxy prior to gluing the sample to a slide, due to poor initial penetration.
The different grain sizes showed that impregnation is achieved in fine silty sediments (such as in Qubur el-Walaydah), fine clay sediments (such as in the upper and lower layers in the slide of Tell es-Safi/Gath and Megiddo upper layer) and coarse sandy sediments (such as in Ashkelon).
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Voids were between 5-20% of the area for all contexts. Penetration depth was deeper (more than 1 cm) for the sample from Ashkelon (sand-rich sediments with 15-20% voids in volume and type of voids of packing that are highly interconnected). Voids interconnectivity in clay sediments (such as the context in Tell es-Safi/Gath) were low compared with the interconnectivity in the silty and ashy sediments. Clay-rich sediments were not fully consolidated, and contained areas with “lumps” of Epoxy that could not penetrate deeper (the areas which are not consolidated were re- consolidated by fresh Epoxy when detected).
In relation to the ability to retain delicate features, the four thin sections show that micro-stratigraphy, delicate organic structures and mineral structural information is well represented despite lack of prolonged oven drying and vacuum impregnation. Notably, this may work well for archaeological occupation deposits but less so in well-developed clay-rich soils.
Evidence for burning can be identified from charred plants and bones, and the presence of calcitic wood ash in samples QH5L198LB011 from Megiddo, and ASH1590 from Ashkelon. Indication for compaction of organic remains are observed in sample P15AE083 from Tell es-Safi/Gath and sample QW111D106_229 from Qubur el-Walaydah. The phytolith layer in Tell es-Safi/Gath is a result of sequential deposition of organic remains that underwent degradation in which only the inorganic component remained. The layer contains interfingering between sediments and three distinguishable phytolith laminations. Clearly, microstructure in all 4 samples is well preserved despite rapid field impregnation. Mineralogy does not seem to influence the quality of field impregnation in the cases presented here, yet, clay-rich and organic- rich sediments may not be rapidly impregnated.
Depth of resin impregnation in the field is critical for production of high quality thin sections. Consolidated samples of sediments with penetration of less than 1cm were difficult to polish prior to glass mounting and usually included holes due to the topography of the sediment sample. Moreover, they tend to warp on the carrying glass during the gluing process which causes the sample to be lost in places (example is seen in sample ASH1590). A thickness of 1-2 cm is ideal. This is similar to the
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thickness of pre-cut blocks produced following slab sawing. Obtaining 1-2 cm thick samples in the field is possible as shown above.
We have shown here that production of well-impregnated blocks of sediments can be achieved on site in a matter of 2 days, with a success rate of 70-80% (about one out of five samples would break after impregnation). The next step is to prepare thin sections on site.
On-Site Thin Section Preparation To develop further the idea of on-site impregnation and preparation, an attempt to grind and polish slides on-site was made during excavations in the prehistoric site of Boker Tachtit. The site is located on a river bed (Nahal Zin), contains two depositional units: a fluvial gravel accumulation overlying fine-grained alluvial sediments. A block sample of the contact between the two units was extracted using the field impregnation procedure outlined above. Pre-mounting polishing was done, with constant wetting using a manual water sprayer, by a belt sander (Makita 9404 model) at the lowest speed possible (the model has a variable speed control dial with a speed that ranges between 690-1440 feet/min) using sand papers that vary in grit between 40-320 (Figure 30). A glass was glued to the polished section using the same mixture of Epoxy as was used for the field impregnation. The Epoxy hardened overnight, and the other side was cut with a Dremel saw to save a piece of the consolidated block. The mounted thinned block was then ground by hand using the belt sander to a thickness of roughly 100µm (based on the interference colors of quartz grains). The sample was then polished by hand using waterproof silicon carbide paper of grit 320 (Klingspor). The overall preparation time was 3 days, with a working time of between 3-4 hours, and a half of the block was kept for archiving. The thin section prepared on-site during the excavation season was as good as a thin section prepared from the same contact a year earlier using the common laboratory procedure (Aldeias, personal communication, 2014).
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Figure 30. The process of thin section preparation on site. Two main steps are (A) the dripping of Epoxy on to the sediments in the section. (B) Polishing the block on a polishing tool after the Epoxy is hardened.
Figure 31 shows the thin section prepared on-site in Boker Tachtit. The contact between the fine-grained sediment and the gravel is clearly visible, and microscopic biogenic minerals such as micro-fossils and coccoliths were identified in the fine- grained sediments.
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Figure 31. Images of features in Sample BT-203bis thin section prepared in the field. A) A scan of the section, showing the gravel contact with the loess sediment. Scale: 1cm. B) Image of micro-fossils in plain polarized mode (PPL) at X100 magnification. Scale: 100µm. C) Image taken of a coccoliths (marked with arrow) in cross polarized mode (XPL) at X200 magnification. Scale: 100µm.
Thin section preparation on-site enables obtaining information on micro-stratigraphic properties during excavation. This may be important for determining excavation strategies during the excavation season, as well as many other fields, including, stratigraphy, material identification, micromorphology, phytolith analysis, radiocarbon and other dating techniques, charred botanical remains, pollen, and bone remains. The new rapid impregnation method also dramatically reduces the time between field sampling and the availability of results, and also the cost of materials (lower volumes of resin) and need/cost of specialized lab instruments such as vacuum
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chambers and slab saws. Lastly, because of reduced volumes of resin this field procedure also reduces environmental pollution and health hazards.
Conclusion A rapid micromorphological sample preparation method was developed which enables the preparation of thin sections on-site within about 3 days. Well preserved micro-stratigraphy of sediments, delicate features and mineral identification was demonstrated, showing that this method is a powerful tool to solve preliminary geoarchaeological and stratigraphic questions and identify micro-archaeological features during the excavation season. This method can be extended to other applications in geology, sedimentology, soil sciences, mining research, etc.
Chapter 5.4: Towards Identifying Burning Events in Situ: Using Density Separation to Purify Charred Micro-Particles from an Iron Age Pit at Qubur el-Walaydah, Israel
Macroscopic-sized fragment of charcoal (macro-charcoal) in natural sediments and soils enables the reconstruction of past environmental processes like fires, natural vegetation changes and pedological processes, especially if the fragments are still in their primary context (Carcaillet et al. 2006; Willis and van Andel 2004; Wang et al. 2005; Hajdas et al. 2007). In archaeology, macro-charred plant remains shed light on past landscapes, food habits and also provide carbon for radiocarbon dating (Miller 1989; Liedgren et al. 2007; Eckmeier at al. 2009; Caracuta et al. 2012; 2014). While the origin of macro-charcoal can be determined based on morphology and anatomy (anthracology), charred micro-particles (< 1mm) usually do not retain morphological features and are too small to identify their origin. The material available is also usually too small for radiocarbon dating. Micro-charcoal is commonly used as a visual marker for burning events based on the black color they impart to the sediment (Bird and Cali 1998; Lindskoug 2012; Nelle 2013). 98
Abundant charred micro-particles in sediments form black lenses, which are often used as stratigraphic markers (Di Pasquale et al. 2010; Asscher et al. 2015a). It is important to verify that the charred micro-particles are in primary depositional contexts when using them as stratigraphic markers. Charred micro-particles in secondary deposition caused by anthropogenic activities or bioturbation that mix sediments will affect the stratigraphic understanding of the site.
In this study, we purify charred micro-particles from archaeological sediments using density separation, and study their association to dating assemblages in primary deposition. The location of the study is an archaeological Iron Age pit in Qubur el- Walaydah (Locus 11.015), southern Levant. For more information on this Bronze and Iron Age site, see Lehmann (2011). The sequence of sediments includes inter- fingering between black lenses and the local loess sediments to form 10 stratigraphic layers within the pit (Figure 32). These layers are associated with Iron Age pyrotechnological activities dated to the 12-11th centuries BC (Asscher et al. 2015a).
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Figure 32. The location of area of study in Qubur el-Walaydah, adapted from Asscher et al. (2015a). A) A schematic map of the southern Levant, showing the site location and its coordinates B) Planar view of the site. The white rectangle is the location of the Iron Age pit (locus 11.015) in square C102, area 1. Squares are 5 x 5 meters. C) The western section of the pit. Black lenses are shown within the local loess sediments. Black circles represent the locations of seeds and grey circles represent the locations of the samples in this study, identified by sample numbers in black. Scale bar is 20cm.
Materials and Methods Charred micro-particles purification Sediment samples were homogenized and 2g were placed in a 50ml polystyrene centrifuge tube. Then 10ml of sodium polytungstate (1.7 g/mL density) were added and vortexed, followed by sonication for 20 min (Cole-Parmer). This density was found to be the most suitable density cut-off to separate organic materials in
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sediments from the heavier minerals (Cerli et al. 2012). Samples were centrifuged at 3000 rpm for 3 min. The supernatant contained mainly the less dense materials (organic and inorganic), and the pellet contained the dense heavy fraction (mostly sediment minerals). The supernatant was transferred to another tube and the pellet was discarded. Then water was added to the supernatant to obtain a volume of 50ml in order to dilute the sodium polytungstate. The process of washing was repeated between 3-5 times to remove all the polytungstate and then the tube was left under vacuum overnight. The dry material was labeled as “micro-particles”. Then, 200mg of the less dense materials were placed in a 15ml polystyrene tube. 2ml of 1N HCl were added for 1 hour to dissolve carbonates. The sample was washed by adding water until a volume of 15ml, then the tube was centrifuged and the supernatant was discarded. The process of washing was repeated between 3-5 times until pH=6 was obtained, using pH paper. Then, 10ml of 0.1N NaOH were added for 1 hour to dissolve degraded organic materials. The supernatant was collected and transferred to a new 15ml tube. 2ml of 1N HCl were added to the supernatant to allow the precipitation of the alkali soluble materials. After 10min, the solution was centrifuged at 3000rpm for 3min. The supernatant was removed and water was added until the level reached 15ml. Then the tube was centrifuged and the water was discarded. The tube was left under vacuum overnight, and the dry material was labeled as “soluble micro-particles”.
Fourier Transform Infrared (FTIR) Spectroscopy A few grams of sediments rich in micro-particles were collected from the Iron Age pit, as well as control samples from the geological surroundings. Part of the sample was homogenized in an agate mortar and approximately 0.2 mg were ground to a fine powder and mixed with ~20 mg of KBr (FTIR-grade). Samples were then pressed into a 7-mm pellet using a manual hydraulic press (Specac). Infrared spectra were obtained on-site and/or in the lab using a Nicolet Is5 spectrometer at 4 cm–1 resolution.
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Thermal Gravimetric Analysis A few miligrams of micro-particles extracted from archaeological sediments and control samples were accurately weighed (between 2-4 grs) and placed in an alumina crucible. Samples were then heated to 800°C in a ramp of 20°C/min in a TGA SDT Q600 instrument. The weight loss and the weight loss change were recorded continuously as a function of temperature using a TA Universal Analysis 2000 v4.5A.
Microscopy A few miligrams of charred dry micro-particles were placed on a slide. A few drops of Entellan (Merck) were added and covered with a cover-glass and observed and photographed at 100x, 200× and 400x magnification using a Nikon Eclipse 50iPOL microscope. A particle volume distribution of micro-particles was carried out following (Igathinathane et al. 2008). The images were uploaded into the software ImageJ edition 1.48v, and continuous black areas were counted as a single particle and the area of the particle was normalized to the image scale. A histogram was made in the software SigmaPlot v11.0, with the threshold for a particle being a minimum of 150µm3, and the amount of bins (each bin contains the number of occurrences for a specific volume range) to cover the entire data is 20.
Charred micro-particle concentrations Charred micro-particle concentrations were determined following an adaptation of the protocol for phytolith counting of Katz et al. (2010). Briefly, duplicates of sediment samples (N=12) were homogenized and 20-30 mg (accurately weighed) were placed in a 0.5ml Eppendorf tube. Then 50 µL of 6N HCl were added to dissolve the carbonates. After carbonate dissolution, 450µL of sodium polytungstate (1.7 g/mL density) were added and then vortexed, followed by sonication for 20 min (Cole- Parmer). Samples were then centrifuged at 5000 rpm for 5 min. The supernatant was transferred to another tube, vortexed, and 50 µL of the solution were placed on a slide and covered with a cover-glass. Charred micro-particles were counted at 200× magnification using a Nikon Eclipse 50iPOL microscope following the method described in Katz et al. (2010). 102
Radiocarbon Dating Charred micro-particles were purified from well dated sediments in an Iron Age pyrotechnological pit. The charred micro-particles (N=8 samples) were characterized using FTIR to determine whether the clays dominated the fraction before the removal of carbon contaminants (Rebollo et al. 2008). Pretreatment of the charred micro- particles to remove all contaminants prior to the measurement were performed following the protocol of Yizhaq et al. (2005). The purity of the recovered charred remains were tested again using FTIR to determine if the material remaining contains only clay minerals (in which case they were not dated) (Yizhaq et al. 2005). Samples were oxidized in vacuum with cuprum oxide (CuO) at 900°C, and the sample % carbon was recorded. The sample was then graphitized in the presence of hydrogen and cobalt at 700°C. Radiocarbon determinations were made using an accelerator mass spectrometer (AMS) in Rehovot, Israel (the Dangoor-Reasearch accelerator Mass Spectrometer: a 1.5SDH Pelletron, National Electrostatics Corp). Modeling was carried out using Oxcal 4.2.3 (Bronk Ramsey 1995).
Results Figure 33 shows images of charred micro-particles purified from archaeological and geological sediments. The micro-particles from archaeological sediments do not transmit light (Figure 33B). A small number of particles that transmit light, and are light brown, was also observed. The micro-particles of geological sediments were richer in geogenic minerals, organic materials that retain the shape of organic tissues and organic materials that do not transmit light, namely black charred remains.
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Figure 33. Images of slides containing micro-particles from geological and archaeological sediments. A) Representative geological micro-particles (sample QC3). Organic brown tissues and minerals are seen. The inset shows the crossed polarized image, showing the minerals birefringence. Scale bar is 100 microns. B) Representative archaeological micro-particles (sample 310 in Figure 32). A large distribution of sizes of black charred materials is seen. Brown particles that transmit light and do not look completely charred are marked with yellow arrows. Scale bar is 100µm.
Figure 34 shows a volume distribution histogram of micro-particles from a black lens and geological controls (the samples in Figure 33). The volume was calculated using imageJ software (see details in Methods). Micro-particle volumes from geological controls ranged in sizes between 300-140,000µm3 (well below the 1mm3, which is a convenient size for recognizing morphologies of wood types). Micro-particle volumes from black lenses range between 150-24,000µm3, with the majority of the particles below 10,000 µm3. Micro-particles from archaeological sediments in between the black lenses had a similar volume distribution to the black lenses, with fewer particles. This indicates that burnt contexts contain larger amounts of small particles relative to the controls.
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Figure 34. A representative histogram of the micro-particle volume distribution in black lenses and geological controls. Micro-particles from black lenses are mostly below 10,000µm2 and are more abundant, compared with micro-particles from geological controls. Note the volume range for geological controls is higher since it contains larger particles.
FTIR was used to characterize the fractions containing micro-particles from geological control sediments and archaeological samples. Figure 35 shows that micro- particles purified from geological controls contain mostly clays, based on the major peak position at 1032cm-1 (1). Micro-particles from archaeological sediments contain peaks which are characteristic of charred materials, positioned at 1583cm-1 (2) and 1387cm-1 (3) (Guo and Bustin 1998; Trompowsky et al. 2005; Benites et al. 2005), 105
and clays that were exposed to heat, based on the shift of the main peak of clays from 1032cm-1 to 1038cm-1 (1’) and the lack of the structural water peaks at locations 521cm-1 (4) 3620 cm-1 and 3697 cm-1 (5) (Berna et al. 2007; Eliyahu-Behar et al. 2012). The presence of charred remains associated to clays that were exposed to heat indicates that the micro-particles from archaeological sediments were burnt in situ.
Figure 35. FTIR spectra of micro-particles purified from archaeological sediments (red) and geological control sediments (black). Micro-particles of geological control sediments contain peaks of clays: 1032cm-1 (1), 521cm-1(4), 3620 cm-1 and 3697 cm-1 (5). Micro-particles of archaeological sediments contain peaks of carbonized materials: 1583cm-1 (2) and 1387cm-1(3), and clays that were exposed to elevated temperatures: 1038cm-1(1’).
The ratio of inorganic to organic components in archaeological and geological micro- particles was quantified using Thermal Gravimetric Analysis and Differential Scanning Calorimetry (TGA-DSC), which allows associating weight loss with a specific temperature range in an oxidation environment. Figure 36 is an example of TGA-DSC curves of micro-particles from a black lens heated to between 25-800°C; showing weight loss at three temperature ranges: between 25-80°C (about 10%), 300- 400°C (about 30%) and 450-550°C (about 25%). The temperature range between 25- 80°C is associated with loss of bound water, the range between 300-400°C is associated to uncharred organic materials and the range between 470-550°C is 106
associated with thermally resistant organic materials such as charred remains (Leifeld 2007). We focus on the range of 300-550°C to characterize the charred and uncharred organic materials in micro-particles from sediments.
Figure 36. Thermal Gravimetric Analysis and Differential Scanning Calorimetry curve of micro-particles from a black lens at Qubur el-Walaydah. The weight loss between 25-800°C shows 10% of the weight is lost between 25-80°C, around 30% is lost around 380°C and 25% is lost around 480°C. The range between 300-550°C is associated to oxidation of organic materials.
Figure 37 shows weight loss % of charred (470-550°C) and uncharred (300-400°C) of micro-particles from archaeological and geological sediments. Micro-particles from geological controls (QC1 and QC3) contains between 80-90% inorganic content and 10-20% organic content that is associated with uncharred remains. Micro-particles from black lenses contained 45-65% inorganic content (mostly clays), and organic content of between 35-55% by weight. Micro-particles from sediments in between the black lenses contained 80-85% inorganic content (mostly clays), and organic content of between 15-20% by weight. Black lenses contain higher amounts of charred micro-particles compared with the geological controls and the sediments in between the black lenses, which is consistent with the visual observations (Figure 32).
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60
50
40
30 Charred % 20 Uncharred %
Organiccontent [%] 10
0 333 328 324 326 323 317 313 310 QC1 QC3 Sample ID
Figure 37. Weight loss of micro-particles purified from archaeological and geological sediments in the range of 470-550°C (charred, marked in red) and 300-400°C (uncharred, marked in blue). The uncharred content in all the samples varies between 5-15%. The black lenses (marked with stars) contain higher quantities of charred remains, which increase their total organic component in the sediments to between 40- 50%.
Figure 38 shows concentrations of charred particles in 1 gram of sediment for black lenses, sediments in between the black lenses, a hearth in the vicinity of the pit (square B104) and geological controls (see details in Methods). Black lenses and the hearth show concentrations of above 60,000 charred particles per gram sediments, which is significantly higher than sediments in between the black lenses and geological controls, which show less than 20,000 particles per gram. These results are in agreement with the thermal analysis showing that micro-particles in black lenses contain larger portions of charred remains.
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120000
100000
80000
particles -
60000
40000
# of charred of # micro 20000
0
Sample ID
Figure 38. Charred micro-particle concentrations of archaeological sediments and geological controls. Concentrations in black lenses (samples 310,323,324 and 333) are similar to the concentration inside a hearth in the vicinity of the pit (square B104).
Thermal and structural characterization of micro-particles that are lighter than a density of 1.7gr/ml show that contexts of in situ burning contain higher concentrations of charred materials compared with surrounding sediments, which have low concentrations of charred micro-particles.
Radiocarbon dating
Table 5 shows uncalibrated radiocarbon ages of organic materials from the Iron Age pit sediments: micro-particles, “soluble micro-particles”, seeds and materials soluble in alkaline conditions from the sediments. Radiocarbon ages of micro-particles from the sequence of sediments are in the range of the expected periods according to previous dates (Asscher et al. 2015a). Radiocarbon age of control geological sample (QC1) shows modern age. Ages of the soluble materials of micro-particles and 109
sediments are not in the range of expected ages, showing transportation of dissolved carbon from different sources.
Lab # 14C age ±1σ Sample Sample type C% (RTD-) year BP QC1 micro-particles 6982 15 104 PMC 310 barley seeds 7121* 61 2915±30 micro-particles 6987 61 2890±45
soluble sediment materials 7439 24 2945±32 313 micro-particles 6927 31 2940±50 soluble micro-particles 6928 46 2970±50 317 barley seeds 6573* 59 2925±35 micro-particles 6940 30 2855±50 soluble micro-particles 6941 38 2945±50 323 micro-particles 6930 51 2940±50 soluble micro-particles 6931 57 2900±50 soluble sediment materials 7440 69 3032±28 326 micro-particles 6929 48 2985±50 soluble micro-particles 6942 46 2855±50
soluble sediment materials 7442 8 3109±55 barley seeds 6574* 56 2890±30 micro-particles 6934 31 2950±50 324 soluble micro-particles 6935 56 2910±50 soluble sediment materials 7441 61 2906±32 micro-particles 6932 25 2920±50 328 soluble micro-particles 6933 41 3000±50 barley seeds 6575* 76 2950±30 micro-particles 6936 46 2930±50 333 soluble micro-particles 6937 51 2825±50 soluble sediment materials 7443 5 2965±59
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Table 5. Radiocarbon ages of samples collected from the Iron Age pit at Qubur el Walaydah and geological controls. Samples are arranged according to stratigraphy. Sample type, lab number and % carbon are listed. Barley seeds radiocarbon dates from layers in which micro-particles were sampled are marked (*). See details in Asscher et al. (2015a). Geological organic sample (QC1) shows 104 PMC, which is equivalent to modern day.
Figure 39 shows uncalibrated ages of different fractions from each layer. There is a large overlap between seeds and the micro-particles ages that are found in black lenses and sediments in between the black lenses. The alkaline soluble micro-particles and soluble sediment materials do not overlap in a systematic way, showing older or younger ages that are significantly different.
Figure 39. Uncalibrated ages at 1σ confidence level of four fractions from an Iron Age pit at Qubur el-Walaydah: seeds, micro-particles, alkaline soluble micro-particles materials and alkaline soluble materials of the sediments. The samples are ordered according to the stratigraphy shown in Figure 30.
The calibrated dates of the micro-particles range between 1000-1215 BC, at 1σ of confidence level. The large range of calibrated age (of 200 years) is due to wiggles in the radiocarbon calibration curve (that forms a ‘plateau’) which produces a wide range of possible dates for a single measurement.
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Discussion
Material characterization (thermal and structural) show that micro-particles that are lighter than density 1.7gr/ml and range in sizes below 1mm3 contain charred materials associated with heat altered clays in archaeological sediments, while in geological controls are mostly inorganic minerals. Charred micro-particles concentrations show that black lenses, which are in situ burnt contexts, contain higher concentrations relative to the sediments in between the black lenses.
Asscher et al. (2015a) reported Bayesian modeled dates of the short lived samples of the Iron Age pit. The different layers range between 1040-1160 BC at 1σ of confidence level (Asscher et al. 2015a). Figure 40 shows modeled dates of the charred micro-particles, sequenced according to their stratigraphic locations. The model agreement index is 119%, with no outliers, and the modeled dates range between 1040-1210 BC at 1σ of confidence level. All dates were modeled using IntCal13 calibration curve (Reimer et al. 2013) in Oxcal software 4.2.3 (Bronk Ramsey 1995).
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Figure 40. Calibrated and modeled dates of a sequence of micro-particles of an Iron Age Pit in Qubur el-Walaydah. The age range of the pit (1040-1160 BC) is marked by two black lines at 1σ confidence, based on the seeds age range that is shown at the bottom of the figure (see details at Asscher et al. 2015a). Micro-particles age range is marked by grey lines, showing a range of 1040-1210BC at 1σ confidence. Dates are presented with their sample ID number, location of sample, age before calibration, precision (in round brackets), and their model agreement index (in square brackets).
There is a large overlap in ages between the charred micro-particles and the ages of the seeds from the Iron Age pit. However, the charred micro-particles range is older by 50 years, which shows that charred micro-particles could not be used to date the pit accurately, but could associate the charred micro-particles to the general activity of
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the pit. The sediments in between the black lenses do not contain burning events in situ (see details in Asscher et al. 2015a). However, the low concentrations of charred micro-particles that are present in these sediments contain similar 14C concentrations as the pit and are associated with clays that were exposed to heat. This leads to the conclusion that these charred micro-particles in the sediments in between the black lenses transported there by mixing between the black lenses and the surrounding sediments.
Another source of evidence for mixing comes from thin sections examined under the microscope of micromorphological blocks. Figure 41 shows a slide of sample 324, in which a thin layer of charred micro-particles is found. FTIR analysis shows aragonite is present in layer 324 (Asscher et al. 2015a), ascribed to high temperature activities (Toffolo and Boaretto 2014). Sediments above and below the charred layer do not show characteristics associated with high temperatures on the macro scale. A single channel rich in voids and small charred pieces (tens of microns) is noted above the thin layer of charred remains. The channel is probably associated with roots or worm activities (bioturbation); however, the amount of micro charred remains found in the channel is small and reflects an event of bioturbation of no more than 1-2cm. This evidence shows bioturbation is one of the ways in which micro-particles from the black lenses are translocated to the sediments in between the black lenses.
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Figure 41. Thin Section of a micromorphology block from the location of sample 324. A) A scan of the slide, showing a black layer rich in charred remains. White rectangle shows the location of a channel with filled in charred remains, in sediments above the black layer. Scale: 1cm. B) Higher magnification of the charred remains in the black layer, showing the particle size variations. Charred remains size range between 10-500µm based on visual inspections. Scale is 1000µm. C) An image of a channel, filled with charred remains. White arrows show area of compaction at the edges of the channel. Scale is 1000µm.
Micro-particles from archaeological sediments contain organic materials that could in principle be used for dating. Charred micro-particles are, however, not a good material for dating to solve sub-century chronological questions. This is mainly because the charred organic material is not identified and could introduce the old wood effect (Zilhão and d’Errico 1999; Guo et al. 2000), and the presence of clays in the charred micro-particles (as seen by the low %C in the dated samples, and the presence of inorganic content that is up to 50% in black lenses) will introduce carbon
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that is bound to clays, which prevents them from being suitable for high resolution dating (Yizhaq et al. 2005). Charred micro-particles can also easily be translocated from one layer to another by bioturbation. Charred micro-particles could be used to solve chronological questions in prehistory, where the resolution of sub-century is not required, and the dates could provide a general understanding of the period of occupation, especially if other datable materials are not found.
Concentrations of charred micro-particles show higher concentrations in burning events found in situ, and lower concentrations in the surrounding sediments. This could be used to track paleo-surfaces and stratigraphic features that do not include architecture or cooking installations (such as hearths). Concentrations of charred micro-particles could be used to assess mixing of sediments in large stratigraphic units, that together with micromorphology (that provides information on mixing in the micro scale) will provide a better understanding of depositional processes in the site.
Heat related components such as ash, heated clays, aragonite, phosphates and burnt phytoliths, establish a dating assemblage, which increases the confidence that datable charred remains (such as seeds and wood) are in primary deposition (Boaretto 2015). We demonstrate that the fraction that is lighter than 1.7 gr/ml concentrates charred micro-particles that are associated with this dating assemblage. Concentrations were significantly higher in the black lenses, linking further the sediments to an in situ burning event. Associating charred micro-particles to the dating assemblages, adds a component that increases the confidence in identifying burning events in situ, while providing information on the possible mixing with the surrounding sediments.
Conclusions We show that micro-particles that were purified using density separation help in our understanding of stratigraphic relations and mixing of sediments in an Iron Age pit at Qubur el-Walaydah, Israel. Radiocarbon dating, structural and thermal analysis show that charred micro-particles are present in higher concentrations in in situ burning events. This could be used to identify burnt surfaces, stratigraphic features and assess mixing between sediments. 116
Publications
Published The dating project in Qubur el-Walaydah was published in the journal Radiocarbon,57(1) p77-97. The dating project in Tell es-Safi/Gath was published in the journal Radiocarbon 57(5) in press.
Will be submitted within 2 months We have an advanced draft of a synthesis paper on the chronology of this transition in the Ancient Near East incorporating existing radiocarbon studies (as discussed above in the discussion chapter 4) to establish a broader chronology for the LB/Ir transition. The phytoliths dating project has produced a reliable set of data and the chapter in this thesis is written in the form of a methodological paper. This will be submitted for publication.
Will be published The Ashkelon project, although more complicated than Qubur and Safi because it contains radiocarbon dates that were not linked to the sediments in which they were found, is producing good information on the period of the LB/Ir transition. This will be published in the near future.
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