Mechelen-Zennegat Archeologisch onderzoek in het kader van het Sigmaplan voor de deelzone Zennegat-Battenbroek

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Late Holocene sediment dynamics in a mediterranean mountain environment.

Past environmental change had a significant impact on ancient civilizations in the Eastern Mediterranean region, and these civilizations in turn changed the landscape through e.g. deforestation, agriculture and the construction of irrigation networks. These environmental changes, natural or anthropogenic, are reflected in the geomorphic system. Forest clearance for instance causes enhanced soil erosion on the hillslopes, which in turn leads to sediment deposition in colluvial and alluvial sediment archives. The study of the spatial and temporal variability in the build-up of these archives can provide additional insight into which past changes have shaped the Eastern Mediterranean like it is today. Moreover, we can learn more about how and when ancient man started to exploit the landscape, and how this affected the rural economy of ancient civilizations through hillslope soil depletion and fine sediment deposition in the river floodplains. In the territory of Sagalassos in SW Turkey, palaeo-environmental research has been going on for almost 20 years. In the years prior to this study the main focus was on studying past environmental change in detail in small-scale basins. This approach allows for the reconstruction of vegetation and climate change, and their impact on the geomorphic system with excellent spatial and temporal resolution. However, it is unsure how this small-scale information can be extrapolated to larger areas, such as the entire territory of Sagalassos. Therefore, this study investigated the 260 km² Büğdüz River catchment, which accounts for about 25% of the territory of Sagalassos. The catchment was a vital agricultural production area during the occupation of Sagalassos, and a sizable concentration of settlements was located in the Büğdüz floodplain during the Imperial period. Moreover, medium-scale river system dynamics in the Eastern Mediterranean are poorly known. Finally, the integration of this work with sediment fingerprinting and palynological research that is still ongoing will yield valuable information about past environmental change and the landscape response in the territory of Sagalassos. An extensive literature study showed that data concerning climate and land use change in the Eastern Mediterranean region are abundant, but also that the dynamics of the geomorphic system are poorly understood, especially at larger than local scales. Many local geo-archaeological studies are in the direct vicinity of an archaeological site, which biases the study results towards human impact. In general, it is shown that the impact of human activity on the landscape system and sediment dynamics started to increase from the mid-Holocene onwards. From that moment climate almost only determined the viability of areas at higher altitude for certain crops, e.g. olive trees. The intensity of sediment dynamics follows rather directly the intensity of human activity in the landscape during the late Holocene. The sediments stored within the Büğdüz River floodplain contain a lot of valuable information for palaeo-environmental reconstruction. The Büğdüz River valley was divided into morphologically homogeneous zones in order to allow for the extrapolation of the coring data collected on 32 valley cross-sections. In general, the build-up of the Büğdüz floodplain consists of two units: a coarse gravel unit at the bottom, on top of which one to three meters of fine overbank deposits were deposited. The Büğdüz River system is marked by three main sediment deposition zones: the upstream reaches of both the Büğdüz and Yayla rivers, the flat middle valley, and the alluvial fan of the Büğdüz River near its outlet in the Burdur graben. The other reaches of the Büğdüz River are mainly axes of sediment transport rather than depositional areas. The stream characteristics are largely determined by stream power on the one hand and sediment supply on the other. The sediment archive study in the Büğdüz River catchment, as well as previous sediment archive research in the territory of Sagalassos yielded a lot of radiocarbon data, which were used to study the temporal aspect of geomorphic activity on a regional scale. The construction of cumulative probability functions, the calculation of sedimentation rates and a Monte Carlo modelling approach provided additional insight into the spatial variation in geomorphic activity. In small scale basins, sediment deposition started during the 1st millennium BCE. In the downstream parts of the rivers, this sedimentation pulse occurred later, during the first few centuries CE, as well as since the Middle Ages. This observation is probably due to buffering effects and time lags within the river systems, as well as to the differring timing of initial human impact throughout the study area. To assess the relative impact of the driving forces on the geomorphic system, namely climate variations and land use change, the WATEM/SEDEM model was applied on the 10 km² Gravgaz catchment. The sediment archives in the Gravgaz valley bottom had been studied in detail by Six (2004) and allowed for the reconstruction of the temporal pattern of sediment deposition. The modelling approach indicated that climate did not play an important role in determining the main trends in valley sedimentation in the Gravgaz catchment. The impact of the initial human disturbance through deforestation was much more important because it triggered severe hillslope erosion. After the initial disturbance the landscape remained erosion-prone from a vegetation point of view, but soil depletion on the shallow limestone hillslopes caused erosion rates and hence valley sedimentation to slow down significantly. The archaeological consequences of this geomorphic-oriented research are threefold. First, it was shown that early disturbance of a sensitive landscape led to the loss of fertile soil on the hillslopes before the peak in human activity during the Roman period. This early soil erosion caused fertile sediment to be accumulated on the valley floors, which allowed intensive agriculture to be practiced on easily accessible terrain. Second, the lack of fertile soil in the valleys caused settlements only to be located in or near the valley bottoms from the Roman period onwards. Third, the deposition of several meters of alluvium in the river valleys may have buried possible evidence of earlier occupation. This may distort our view of where people lived before Roman Times.Dankwoord I Abstract III Samenvatting V Vulgariserende samenvatting VII List of acronyms IX General introductory remarks XI Table of contents XIII List of figures XVII List of tables XXI Part I: Introduction 1 Chapter 1: Introduction 3 1.1 Background: Holocene sediment dynamics research 3 1.2 Bakground: geo-archaeological research in the territory of Sagalassos 6 1.3 Research objectives 8 1.4 Thesis outline 9 Chapter 2: Holocene environmental change and its impact on sediment dynamics in the Eastern Mediterranean 13 2.1 Introduction 13 2.2 Methods 15 2.2.1 Study area 15 2.2.2 Data sources 17 2.3 Holocene environmental change 24 2.3.1 Eastern Mediterranean Holocene palaeo-climate 24 2.3.2 Climatic caused vegetation and anthropogenic land use history 29 2.4 Sediment dynamics and environmental change in the Eastern Mediterranean landscape 34 2.4.1 Colluvial sediment archives 36 2.4.2 Alluvial sediments 37 2.4.3 Fluvial-marine sediment sequences 42 2.5 Discussion 44 2.5.1 Methodological constraints 44 2.5.2 Interactions between climate, vegetation and man 46 2.5.3 Novel approaches: quantification and geomorphic modelling 47 2.5.4 Nature of sediment dynamics during the Holocene 48 2.6 Conclusions 50 Chapter 3: Study area 53 3.1 Introduction 53 3.2 General tectonic and lithostratigraphic setting 54 3.3 Geological map BÃ¼Ä düz catchment 57 3.4 Settlement history 59 3.5 Land cover history 62 3.6 Climate 64 Part II: The sedimentary record 65 Chapter 4: Sediment characteristics and storage in the BÃ¼Ä düz River floodplain 67 4.1 Introduction 67 4.2 Study area: BÃ¼Ä düz River catchment 70 4.3 Methods 72 4.3.1 Field data collection and stratigraphy 72 4.3.2 Geomorphic zonation 73 4.3.3 Floodplain area estimation 76 4.3.4 Sediment storage quantification 76 4.4 Results and discussion 77 4.4.1 Coring density 77 4.4.2 Geomorphic zonation 80 4.4.3 Alluvial stratigraphy 87 4.4.4 Sediment storage quantification 99 4.4.5 Bedload transport capacity BÃ¼Ä düz River system 105 4.4.6 Tectonic influence on the BÃ¼Ä düz River system 108 4.5 Conclusions 109 Chapter 5: Sensitivity of the Eastern Mediterranean geomorphic system towards environmental change during the Late Holocene: a chronological perspective 113 5.1 Introduction 113 5.2 Methods 116 5.3 Results 123 5.3.1 Cumulative probability distribution analysis 123 5.3.2 Temporal analysis of sediment accumulation at Gravgaz and Bereket 125 5.3.3 Mean sedimentation rate analysis 126 5.4 Discussion 127 5.5 Conclusions 132 Part III: Linking process with record: modelling geomorphic processes at the landscape scale 135 Chapter 6: Modelling of Late Holocene landscape change in a small Mediterranean mountain catchment 137 6.1 Introduction 137 6.2 Study area 139 6.3 Methods 140 6.3.1 Sediment archive data 140 6.3.2 Model description 141 6.3.3 Model adaptation 142 6.3.4 Model input parameters 144 6.3.5 Model calibration 147 6.3.6 Model scenarios 148 6.4 Results 149 6.5 Discussion 151 6.6 Conclusions 162 Part IV: General discussion: human impact on the environment 165 Chapter 7: General discussion and conclusions 167 7.1 Geomorphic activity in the territory of Sagalassos versus the Eastern Mediterranean 167 7.2 Archive dependency: temporal variability between small scale and large scale 171 7.3 Driving factors of the geomorphic system over a Holocene time scale 173 Appendices 179 Appendix 4.1 181 Appendix 4.2 193 Appendix 4.3 195 Appendix 4.4 197 Appendix 6.1 199 References 209nrpages: 235status: publishe

Holocene environmental change and its impact on sediment dynamics in the Eastern Mediterranean

Investigators have studied past environmental change in the Eastern Mediterranean region from a number of perspectives. While climate reconstructions and palynological research have focused on forces that drive the geomorphologic system, many researchers have attempted to use sediment archive studies to identify periods of change in sediment dynamics. Due to the large variability in environmental parameters and the variety of landscapes present in the Eastern Mediterranean region, research has focused on sediment archives ranging from small colluvial sites to deltas of large rivers on the Mediterranean coast. As the cultural record for the region is extremely rich, the main goal of palaeo-environmental research in the Eastern Mediterranean has been to identify the relative importance of human impact on the landscape. Nevertheless, sediment archives have significant limitations: chronological control for many palaeo-environmental records is highly uncertain, and rates of landscape change are oftentimes difficult to assess. Most palaeo-environmental research has been conducted on or near archeological sites, where direct human impact may obscure the indirect impact on sediment dynamics through land-use changes. Quantification and modeling of sediment dynamics in the Eastern Mediterranean environment offer one solution. When erosion and sediment transport rate analyses are incorporated, periods of relatively important change can be identified. Using multiple approaches the relative importance of the main driving forces, climate and land use, become distinguishable. Since field-based data from the actual sediment archives remain vital, an overview of numerous studies in the Eastern Mediterranean is provided in order to draw a general picture for different time periods and the relative scale of regional landscape development during the Holocene. A comparison of sediment dynamics with the record of driving forces indicates that while climate was the main driver of the geomorphic system during the early Holocene, at some point human impact became widespread and began to dictate sediment dynamics to a large extent. From the Byzantine Period onward soil properties seem to play an increasingly important role, as the hillslope soil reservoir in the Eastern Mediterranean was progressively depleted during the late Holocene.status: publishe

Mechelen-Zennegat. Archeologisch onderzoek in het kader van het Sigmaplan voor de deelzone Zennegat-Battenbroek

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Towards a quantification of agricultural carrying capacity in the past: the application of a soil erosion model to estimate crop productivity

Humans have impacted their environment throughout history, especially since the introduction of widespread agriculture and the associated forest logging activities, thereby creating anthropogenic landscapes in which environmental processes are no longer in equilibrium. Under certain conditions, this has led to a drastic reduction in carrying capacity with negative feedback to the sustainability of society. Soil erosion and the resulting reduced agricultural productivity has been pushed forward as one of the contributing factors responsible for the collapse of ancient societies. Yet, quantitative data supporting these hypothesis is still lacking. Furthermore, more attention was recently given to the resilience of ancient societies against soil erosion and its negative consequences, challenging the ideas of collapse. In order to tackle these questions, local site-specific information on land use and soil erosion needs to be upscaled to entire regions or territories. A modeling approach can help to achieve this. The territory around the ancient city of Sagalassos (Taurus Mountains, SW Turkey) was selected to quantify crop productivity through space and time. In order to simulate erosion, the spatially distributed soil erosion & sediment delivery model WaTEM/SEDEM was used. Results show how land cover variations and the depletion of soil reservoir have a larger influence on the central valley sedimentation rates in comparison to climatic variability. The general amount and spatial pattern of net erosion was well reproduced by the model, although it failed to capture the more detailed field work derived sedimentary chronologies. The soil erosion model offers the opportunity to get information on soil depths in both space and time, which can be used as input for the crop productivity model. The model results from the Gravgaz catchment show how deforestation and agriculture led to the depletion of the existing soil reservoir while creating agricultural potential in the central valley’s through the accumulated sediments. Although preliminary results show that soil thickness on its own isn’t a strong predictor for crop yields, future work will include soil thickness at least as one of the factors controlling crop productivity. Promising soil properties – crop yield relations can be found in literature, but they still need to be verified for the territory of Sagalassos. Hence, present day crop yield data need to be collected to form a basis for model validation. Furthermore, soil properties of ancient soils will have changed throughout time. Therefore, the model will have to include the dynamic properties of soils over time.status: publishe

A sediment fingerprinting approach to understand the geomorphic coupling in an eastern Mediterranean mountainous river catchment

To understand the response of a river to anthropogenic disturbance, knowledge of the links between erosion, sediment deposition, and sediment export is crucial. Therefore, starting from field observations and connectivity proxies, a sediment fingerprinting approach using geochemical tracers was used to elucidate the subrecent sediment dynamics in the 264-km2 Büğdüz River catchment in SW Turkey. A topography-based connectivity index was used as a proxy for hillslope–channel coupling and stream power estimations as a proxy for the within-channel connectivity. Quantitative provenance information provides a link between potential sediment sources and the derived sediment currently stored within the fluvial system. Provenance signals from both contemporary river bed sediments (n = 144) and subrecent floodplain deposits (n=28) provide more insight into the coupling of the hillslopes to the river channel and the coupling within the river channel itself. Furthermore, comparing the provenance signal with the areal extent of potential sediment sources upstream in the form of enrichment ratios sheds light upon the variation of the erodibility of the sources and the connectivity within the catchment. Results indicate that the valley gradient exerts an important control on the spatial variability of geomorphic coupling in the Büğdüz catchment. Furthermore, different sediment sources (lithologies) show distinct sediment production rates. In addition to the observed spatial variability, coupling relations are characterized by an important seasonal variation, indicated by variable contributions of local and more distant sediment sources.status: publishe

Late-Holocene human impact on fluvial systems in a Mediterranean mountain ecosystem

Within the territory of Sagalassos, a classical city in the Western Taurus Mountains (SW Turkey), detailed sedimentological and palynological analyses in small catchments have revealed a strong local impact of human-induced land use changes on the physical environment during the so-called Bey¸sehir Occupation (BO) Phase. In order to test whether larger geomorphic systems respond similarly to human impacts in this mountain environment, we aim to reconstruct the late-Holocene floodplain sediment dynamics of the Bü˘gdüz River catchment (264 km2). In total, 32 percussion drill corings, sampled every 10 cm, were made so far in the floodplain of the Bü˘gdüz River and a first approximation of sediment texture was made. From seven sub-samples, sufficient amounts of organic matter could be retrieved to be radiocarbon dated by AMS. First results revealed two distinct sediment deposition phases: first, up to 5m of mainly coarse sediments alternating with thin silty layers were deposited. This phase was still active around Cal. 890-780 BC. Next, up to 2.5 m of mostly silty sediment was deposited, the majority after Cal. AD 900-1000. No exact data on the transition from the first to the second phase are available, however. The average floodplain sedimentation rates, 1.59 ± 0.13 mm a−1 for the first and 1.46 ± 0.13 mm a−1 for the second phase, do not differ much. Towards the periphery of the floodplain, alluvial and colluvial deposits most likely interfinger, resulting in a considerably higher sedimentation rate since Cal. 780-410 BC (i.e. 2.20 mm a−1). Compared to smaller catchments, where the higher sedimentation rates during the BO Phase decline sharply afterwards, the sedimentation rates in the Bü˘gdüz River system remain rather stable, illustrating the greater buffering capacity of larger fluvial systems in response to important human-induced land use changes since classical times. Nevertheless, these land-use changes have brought about changes in main sediment texture deposited (i.e. transition from gravels to silt) and river morphology (transition from a braided to a single-thread channel).status: publishe

Geomorphologic coupling and decoupling in a Mediterranean mountain catchment under changing environmental conditions as evidenced by sediment fingerprinting

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Unravelling changing sediment sources in a Mediterranean mountain catchment: a Bayesian fingerprinting approach

To determine the provenance of Holocene floodplain deposits of the Bügdüz catchment in southwest Turkey a Bayesian fingerprinting approach was used. An important requirement for any provenance study is that the potential sediment sources show sufficient spatial and compositional heterogeneity. The spatial distribution of potential sources, in this case the various lithologies present within the catchment, was mapped using field observations and ASTER and Quickbird satellite images. To distinguish the source lithologies a set of geochemical tracers was identified with the use of a Linear Discriminant Analysis. This optimum fingerprint was then used in the mixing model to determine the sediment provenance. The Bayesian mixing model uses Markov chain Monte Carlo random walks to determine the most probable source composition and mixing proportions. The uncertainty associated with the input data can be incorporated into the model through the prior probability distributions. The spread of the posterior probability distributions represents the uncertainty associated with the mixing proportion calculation. The main contrasts in provenance of the floodplain deposits reflect the spatial distribution of potential sediment sources throughout the catchment. There are, however, also important temporal variations in sediment provenance and lateral differences due to the nature of floodplain build-up. The observed spatial and temporal variability of sediment provenance gives a first indication that hill slope-channel and within-channel coupling relations are not uniform through the catchment and that different locations showed a distinct response to disturbances.status: publishe