Applying Geoarchaeological Methods on an Iron Age site: Part two of a two-part study discussing Archaeological Prospection for Ytings, Gotland Jessica Coleman Master thesis, 30 hp Archaeology Masters Programme / Masters Thesis Spring term 2017 Abstract: Geoarchaeology has had a long history within archaeology around the world, but not so much so in Gotlandic archaeology. This study is aimed at drawing attention to this by using magnetic susceptibility (MS) and phosphate (P) analysis of an Iron Age site at Ytings, Gotland. This is where a small silver hoard was discovered in 1888, and in 2009 a geophysical survey was done, via metal detector, and concluded with the theory of there being a workshop in the southern field and a farmstead in the north (ArkeoDok, 2011). The first part of this study discussed predictive modeling and whether or not the information available at the time would be enough to generate a reliable model (Coleman, 2016). The first study concluded with not being able to do so since the only discrete data available was from the metal detecting survey, which when used alone is not the most reliable instrument for archaeological prospection (Coleman, 2016). This led to this current study, which is the second part of a two-part study of Ytings. This study is aimed at using geoarchaeological methods for archaeological prospection to illustrate the benefits and need for these types of studies on Gotland, by comparing the MS and P results with the 2015 excavation report. 2 1. Introduction………………………………………………………..………………..6 • Defining Geoarchaeology and archaeological prospection and their role in archaeology. • Continuation of previous discussion about predictive modeling on Gotland. 2.Purpose and Research Questions…………………………………………….……..7 • To provide context to the 2015 excavation and how it compares to the metal detecting survey from 2009. • Theoretical prospective • Present a hypothesis as to where possible archaeological sites may be located. o How to interpret the finds from metal detecting surveys? o What explanations could account for the concentration of metal finds in the South from the 2009 metal detecting survey? o Are there any areas that exhibit archaeological potential and what areas can be delimitated from the search? 3. Advantages of Archaeological Prospection…….….…....….….….……...…..…...8 • Archaeological excavation and budget • Example Case studies: o “Unveiling the prehistoric landscape at Stonehenge through multi-receiver EMI” o “Soil chemical analysis as an interpretive tool for ancient human activities in Piedras Negras, Guatemala” o “A review of geophysical archaeological prospection in Sweden” 4. Review of Predictive Modeling and Background of Gotland……..…………… 14 • Predictive Modeling within archaeology • Case Studies: o Gustaf Svedjemo: “Predictive Model for Iron Age Settlements on Gotland, 200 – 600 AD.” o Gustaf Svedjemo and Erland Jungert: “Examples of Historical Maps in GIS and Databases” o Dan Carlsson: “The Ancient Cultivation of Arable Land” • Archaeological sites and Features of Ytings • Gotland’s Geology and Landscape • Iron Age Gotland • What Next: Phosphate analysis and Magnetic Susceptibility 5. Archaeological Prospection and Excavation at Ytings………………………… 32 • Sampling Strategy and Collection • 2015 Excavation Report 3 6. Results…………………………………………………………………………… 38 • Lab work • Magnetic Susceptibility • Phosphate Analysis • Munsell Color 7. Discussion……………………………………………………...……………..…… 55 • Magnetic Susceptibility and Phosphate results • Results and Discussion 8. Conclusion……………………………..…….……...………………………….…. 59 9. Bibliography…………………………………………………………………….… 60 4 Table of Figures: FIGURE 1: FEATURES AND FINDS REGISTERED WITH RIKSANTIKVARIEÄMBETET 22 FIGURE 2: A CLOSER LOOK AT THE REGISTERED SITES FROM THE STUDY AREA. 22 FIGURE 3: METAL DETECTING MAP FROM 2009. 23 FIGURE 4: BEDROCK OF GOTLAND. 25 FIGURE 5: THE DIP IN THE STRATUM OF THE BEDROCK. 25 FIGURE 6: A GIS MAP OF THE SOIL IN THE AREA. 26 FIGURE 7: THIS IS A GIS MAP OF PRESENT DAY WETLANDS 27 FIGURE 8: YTINGS REFERENCE SAMPLING AREAS 31 FIGURE 9: SAMPLING AREAS. 33 FIGURE 10: 2015 EXCAVATION PLAN. 36 FIGURE 11: UPDATED METAL DETECTING MAP. 37 FIGURE 12: GRAPH: SUM OF MS DATA BY AREA. 41 FIGURE 13: GRAPH: SUM OF MSLF AND MSQ BY AREA. 42 FIGURE 14: GRAPH: SUM OF MSLF AND MSQ IN ’GRID’ BY ROW. 42 FIGURE 15: GIS MAP OF MSQ. 44 FIGURE 16: GIS MAP OF MSLF DATA WITHIN THE 'GRID'. 45 FIGURE 17: MSLF IN RELATION TO THE 2015 EXCAVATION 46 FIGURE 18: GRAPH: SUM OF P DATA BY AREA. 48 FIGURE 19: GRAPH: SUM OF CITP AND PQ DATA BY AREA. 48 FIGURE 20: GRAPH: SUM OF CITP AND PQ IN ’GRID’ BY ROW. 49 FIGURE 21: GIS MAO OF PQ DATA BY AREA 50 FIGURE 22: GIS MAP OF CITP DATA IN GRID 51 FIGURE 23: GIS MAP OF CITP IN RELATION TO THE 2015 EXCAVATION 52 FIGURE 24: GRAPH: MUNSELL HUE BY AREA 54 FIGURE 25: GIS MAP WITH THE HIGHEST CITP AND MSLF RESULTS 56 FIGURE 26: GIS MAP 2015 EXCAVATION MAP WITH CITP AND MSLF DATA . 57 5 1. Introduction Archaeology has come a long way from its humble beginnings into a comprehensive science that utilizes multiple concepts and methods from other sciences in order to better understand past societies. This continued growth of archaeology and it's mergence with other disciplines enables archaeologists to capture a clearer image of the past than was available before. One example of this amalgamation is geoarchaeology. Geoarchaeology is defined as a multi-proxy approach that implements the methods and concepts of earth science into archaeological research (Butzer, 1982; Rapp and Hill, 1998; Ghilardi and Desruelles, 2009). Geoarchaeological methods and concepts have been applied with an increasing frequency since the 1970's, with efforts to distinguish itself as a separate discipline that uses geoscience methods for when evaluating archaeological records (Rapp and Hill, 1998). This created the problem of geoarchaeology not being clearly defined since it encompasses other disciplines such as: sedimentology, pedology, stratigraphy, geophysics, remote sensing, etc., mentioning other popular disciplines that overlap and sometimes considered to be synonymous with geoarchaeology such as; geochemistry, environmental archaeology, archaeopedology, etc. these disciplines overlap with other fields of science (i.e. geology, pedology, chemistry) (Ghilardi and Desruelles, 2009). This study reviews a geophysical method measuring magnetic susceptibility and a geochemical method of phosphate analysis on soil samples to use for archaeological prospection. Archaeological prospection is a predictive method that can use multiple types of data collected to hopefully find and/or provide context to archaeological sites (Neubauer, 2004). Two concerns archaeologists have today is the growing threat of destruction that urban expansion presents and the accelerated growth of erosion (natural or anthropogenic) have upon archaeological sites (Neubauer, 2004). These threats to archaeological sites creates the demand for quick, accurate, and non- destructive survey methods that can identify, therefore protect and preserve to be able to study those areas of historical interest. This is where archaeological prospection and geoarchaeology come in. The first part of this study started as an attempt to raise awareness about the potential that geoarchaeology has with hopes to reverse its slow progression in Swedish archaeology, especially when compared to other areas in the world (Coleman, 2016). 6 This idea led to predictive modeling as a means for archaeological prospection. The first part of this study covered predictive modeling in detail, analyzing various methods and data needed for the modeling process (Coleman, 2016). The conclusion of that study is what created the need for a second part or continuation, because at the time there was not enough appropriate data which then affected the ability to create a model for the Iron Age site at Yitngs, Gotland. The primary data source was from a metal detecting survey done in 2009, this led to the hypothesis that there might be a farmstead (boplats) in the north field and a workshop in the south (ArkeoDok, 2011). Hoping to confirm this hypothesis an excavation was done in 2015, yielding no evidence to support this theory (Arendus, 2015). The first study discussed that the use of a metal detector and how alone, it collects a biased set of finds that may have led the archaeologists to misinterpret the finds and that the data was not enough to ‘predict’ or assume where archaeological sites could be located (Coleman, 2016). The significance of these two studies is that there are very few geoarchaeological studies on Gotland, hopefully making this a stepping stone for further research. This study discusses magnetic susceptibility and phosphate analysis as potential methods to collect information of (about?) an area and their accuracy for archaeological prospection. Then compare those results to the metal detecting survey and the resulting excavation report that has since occurred at Ytings. 2. Purpose and research questions: Other than addressing the need and benefits of exercising geoarchaeological/geophysical methods in Sweden, and advocating for other studies such as this. The goal of this study is to further illustrate how the magnetic susceptibility and phosphate analysis from the soil samples collected at Ytings provides useful contextual information and apply this to the 2015 archaeological excavation. Lastly to demonstrate how singular element analysis is not a recommended approach for prospecting archaeological sites.