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    Depositional Properties and Paleoclimate of a Middle-Upper Pleistocene Fan Delta Sequence in the Bor Plain, Central Anatolia, Turkey
    (Istanbul Univ, Fac Letters, Dept Geography, 2024) Bayer-Altin, Turkan; Karakas, Zehra Semra; Altin, Bekir Necati; Kayseri-Ozer, Mine Segul
    The Bor Plain, which is located in the Middle Kizilirmak subregion of the Central Anatolia Region, extends 14 km toward the west of Nigde. The fan delta deposition system in the southwest of the Bor Plain was formed on the fault-controlled foothills of Mt. Keciboyduran. The fandelta sequence shows that a paleolake formed during a phase because of the mineralogical content and frequently changing facies. Additionally, clay minerals and herbaceous plants reflecting humid and arid climatic conditions illustrate the lake-level changes. Six changes in the lake level occurred from marine isotope stage (MIS) 7 to (MIS) 5. Three major high stands occurred in the paleolake at the lowest and middle parts of the sequence. The first high stand was a stepwise transgression between similar to 240 and similar to 230 ka., and the second high stand was between similar to 200 and similar to 195 ka. The third high stand was characterized by a short transgression at 182 ka. After this stage, the lake receded significantly at 127 and 105 ka, indicating climatic control over the water level changes. In the transition from the Middle to Late Pleistocene, a revival of volcanic activity in the Leskeri monogenic volcanic mass released volcanic material, affecting sedimentation. Volcanic rocks increase dramatically in the upper section of the fandelta during an interval that coincides with low lake-level fluctuations.
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    Determination of drought intensity in Seyhan and Ceyhan River Basins, Turkey, by hydrological drought analysis
    (Springer Wien, 2020) Altin, Turkan Bayer; Saris, Faize; Altin, Bekir Necati
    This paper studied hydrological drought identified by the Streamflow Drought Index (SDI) at eight river-gauging stations in the Eastern Mediterranean part of Turkey for a roughly 43-year period covering from 1972 to 2014 (4 stations), from 1973 to 2015 (2 stations), and from 1969 to 2011 (2 stations). Results of SDI analyses indicate that the number of drought years was highest during the 3-month October-December period. A considerable part of the drought years was determined to be mild drought. Although moderate drought conditions were observed in all stations, moderate drought conditions were determined especially at Goksu-H in the Seyhan River Basin and Sogutlu and Savrun in the Ceyhan River Basin. Short-term fluctuations of dry and wet conditions are the dominant pattern for most of the stations; however, long-term persistent drought conditions are also prominent, especially at Tacin and Korkun in Seyhan Basin and Goksun in Ceyhan Basin. The starting point for the negative trend in the 12-month series was the years 1996, 1999, and 2000.
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    Development and morphometry of drainage network in volcanic terrain, Central Anatolia, Turkey
    (ELSEVIER SCIENCE BV, 2011) Altin, Turkan Bayer; Altin, Bekir Necati
    This paper presents the results of morphotectonic and morphometric research carried out in order to determine the neotectonic development of the volcanic mountains and a drainage network in SW Cappadocia. The study area extends among the Aksaray, Nigde, and Nevsehir Provinces. The study area comprises Hasandag, Melendiz, Keciboyduran, Golludag Mountains and the adjacent parts of these volcanic mountains. Data collected exclusively from 1:25,000 digitised topographic maps and 10 m-resolution DEMs were used to define parameters related to the longitudinal profile of streams. The study area was divided into 10 volcanic units. Longitudinal profiles of 20 streams and stream orders were analysed to determine a regional tectonic differentiation pattern in these units. The streams in the study area drain into four different tectonic depressions. These depressions are Aksaray plain controlled by the Tuz Golu fault (TCF), Ciftlik plain controlled by the Keciboyduran Melendiz fault (KMF), Misli plain controlled by the Derinkuyu fault (DF), and Bor plain controlled by the Nigde Fault Zone (NFZ). An analysis of morphometric parameters shows that the development of a drainage network is associated with faults and rock resistance. Occurrence of morphometric parameters with different values in units reveals that the volcanic mountains were not uplifted in the same period and were subjected to different morphologic processes. High total order number in the south of Hasandag (unit 3) and Melendiz Mountains (unit 7) indicate that the uplift ratio of the southern part is much greater than that of the northern part. Moreover, development of the drainage network in the south is in a more advanced phase than in the north. Indeed, the drainage network in the north is in the youngest erosional phase of all parts of the study area. The increased stream length-gradient indices (SL), and stream gradients and an analysis of headward erosion show that the streams displaying the longest and highest reach of the erosional phase are all in the southern part of Keciboyduran and Melendiz Mountains. The longitudinal profile (Lp) of the present thalweg of the streams is irregular. The irregular Lp are associated with four different causes. These are geological variations in resistance, tectonics, and volcanic topography and downcutting in response to stream incision. The beginning of the fluvial incision in the northern part is younger than in the south. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.
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    Drainage morphometry and its influence on landforms in volcanic terrain, Central Anatolia, Turkey
    (ELSEVIER SCIENCE BV, 2011) Altin, Turkan Bayer; Altin, Bekir Necati; Efe, R; Ozturk, M
    An evaluation of morphometric parameters was made to study drainage morphometry and its influence on landform processes, flood and erosion characteristic in subbasins which are located in volcanic terrain between Nigde and Aksaray Province SW Cappadocia, Central Anatolia. The study area was divided into 28 subbasins. The high flood potentiality exists on the high volcanic cones, dom, dissected foot of mountains and the high parts of plateaus covering the 13 subbasins, and are associated with high slope, shape of subbasins, impermeable geology and sparce vegetation. The moderate flood potentiality exists on the plateaus covering the 9 subbasins and is associated with high drainage density, high stream frequency, high bifurcation ratio and high slope conditions; although these subbasins have long narrow shapes. The low flood potentiality exists on plains covering 5 subbasins and is associated with low slopes and its long narrow shape. Analysis of drainage morphometry helps to understand interrelationships between landforms and flood potentiality for planning and management in basins. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of The 2nd International Geography Symposium-Mediterranean Environment
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    Evaluation of Drainage in the Upper Catchment of the Yesilirmak River Basin Along the Alm us Fault, Northern Turkey
    (Istanbul Univ, Fac Letters, Dept Geography, 2020) Altin, Turkan Bayer; Altin, Bekir Necati
    The Yesilirmak River Basin is located in the North Anatolian Fault Zone (NAFZ) which is one of the fault zones with intense seismic activity in Turkey. The Almus Fault is a segment of the North Anatolian Fault (NAF). This study aims to reveal the effect of the Almus Fault on the drainage development and morphotectonic evolution of the upper catchment of the Yesilirmak River Basin and the relative tectonic activity of the fault. Morphometric indices such as, stream length gradient index (SL), mountain front sinuosity (Smf) and fan entrenchment (E) indicate that the downward of the sub-basins is tectonically more active than the upward which is ascribed to the tectonic activities along the Almus Fault. The Smf value is 1.4 at the west and decreases to 1.1 at the mouth of the sub-basins on the east. This indicates that the tectonic activity along the Almus fault in the study area increases from west to east and the uplift rate in the northern part is higher than the southern part of the study area. Development of the drainage network started during Pliocene due to differential uplift and a humid climate then developed under tectonic forcing during Quaternary.
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    Evolution of Drought Climatology and Variability in the Central Anatolia Region, Turkey, for the Period 1970-2020
    (Springer Basel Ag, 2023) Bayer-Altin, Turkan; Turkes, Murat; Altin, Bekir Necati
    In this study, drought climatology and drought variability in the continental semi-arid and dry sub-humid Central Anatolia Region were analyzed using the annual and seasonal precipitation totals, Aridity Index (AI) and Standardized Precipitation Index (SPI), along with the long-term trends in their time-series. Trends in precipitation totals, 12-month SPI and annual AI series were statistically determined by applying the Mann-Kendall rank correlation test (M-K test) and its sequential analysis. The climatological probability of drought and wet events was evaluated according to different classes in the region. Annual AI values indicate that dry sub-humid climate was dominant from the mid-1990s to mid-2000s, and then semi-arid conditions were dominant from the mid-2000s to recent years. The climatological probability of monthly SPI values being severely dry is dominant mostly in the semi-arid and dry sub-humid central, south and east districts of the region. According to the M-K test, statistically significant decreasing trends were determined for annual total precipitation and the 12-month SPI series in Keskin, Pinarbasi, Sariz, urgup and Aksehir. Nonsignificant and statistically significant decreasing trends in spring precipitation were determined at approximately 67% of the stations and at Ilgaz, Kulu, Eskisehir, Keskin, Zara, urgup and Sariz stations, respectively. With respect to the desertification in the Central Anatolia Region, the most vulnerable subregions for desertification processes are the Konya subregion and the Upper Kizilirmak subregion, mainly characterized by semi-arid and dry sub-humid environmental conditions.
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    The Holocene terraces of the desiccated Bor Lake and Neolithic occupation in Bor Plain, Central Anatolia, Turkey
    (Springer, 2021) Altin, Turkan Bayer; Kayseri-Ozer, Mine Sezgul; Altin, Bekir Necati
    The lacustrine sediments and geomorphological data from the Bor Plain situated at elevations between 1050 and 1100 m in southern Central Anatolia provide record between 9800 and 6700 yr cal BP of climate changes and events. The main aim of this study is to determine the relationship between the location of Neolithic sites and the deposition and recession phases of the lake during Holocene. The geomorphological history of the Bor Plain and palynological results allows us to reconstruct the relationship between the Holocene environment and reconstruction of Neolithic settlements within a spatially well-defined lacustrine landscape of similar to 600 km(2). A 75 +/- 13 ka aged terrace, consisting almost entirely of calcite and situated about 76 m above the plain floor, indicates that the plain was covered with a paleolake in the transition from MIS 5 to MIS 4. Considering the low total organic carbon and the high CaCO3 clay values, we conclude that the lake slowly receded in 9867 +/- 39 cal BP. However, the presence of aquatic herbaceous forms such as Nymphaceae and Cyperaceae indicates an increase in the water level of the lake during 6776 +/- 35 cal BP, after which it transitioned to a dried lake. Thus, the progression and recession phases of the lake became the determining factor in the site selection of Neolithic settlements on mounds by which are found the plain floor at elevations between 1090 and 1100 m in this period on the Bor Plain.