5:15 PM - 7:15 PM
[HQR05-P14] Paleoenvironmental changes in Central Anatolia over the past 5000 years based on ostracods
During the Holocene, it is known that abrupt climatic changes occurred such as 4.2 ka and 3.2 ka events. These climatic changes may have affected twilight of the empires, but their changes, duration, and local extent remain unclear. In this study, we aimed to reconstruct paleoenvironmental changes in the past 5000 years using sediment cores from Eski Acigol, a crater lake in Central Anatolian, Republic of Turkiye, based on the analysis of ostracod assemblages. Eski Acigol was artificially drained in the 1970s and dryed up. Ostracods are a powerful tool for paleoenvironmental reconstruction because the habitat of each species is restricted by the aquatic conditions.
Core EA2301, which is the subject of this study, was collected at Eski Acigol located in 200 km southeast from Ankara, the capital of the Republic of Türkiye. The cores drilled in four holes were correlated on the basis of lithology to produce one mostly successive sections of 4.8 m long. The core consists of fine-grained clastic material containing carbonate and biogenic silica. The age of the core is estimated to cover the past 6,000 years. In this study, hypothetical age is employed, and range of error is about 500 years. Core sample was cut into 1 cm thick slices. Of them, total 81 samples were used in this study. The samples were washed on a 63 μm sieve, and all ostracod shells were picked up from the dried residue.
Total 4735 individuals of six species were identified from 78 of the 81 samples. Cluster analysis suggested that 78 samples were grouped into 3 biofacies and two subbiofacies. Biofaciess 1 had a low abundance of ostracods and a high proportion of H. salina. Because this species prefers very shallow and warm water environments, biofacies 1 was assumed to represent a warm environment with relatively low lake levels. Biofacies 2 is dominated by L. inopinata and C. meerfeldiana, with a small number of ostracods individuals. Sub-biofacies 2a was characterized by equal numbers of L. inopinata and C. meerfeldiana. The coexistence of L. inopinata, preferring very shallow waters, and C. meerfeldiana, suggesting shallow waters, indicates slightly shallow lake water environment. Sub-biofacies 2b was inferred an environment of very shallow because L. inopinata accounts for more than 85%. Biofacies 3 is dominated by C. meerfeldiana, which has a large population of ostracods and prefers low-salinity, relatively deep water. Sub-biofacies 3a are characterized by high abundance of C. meerfeldiana, suggesting a low-salinity and slightly deeper lake water environment. Sub-biofacies 3b are known as abundance of more than 90% of C. meerfeldiana, suggesting a lower salinity and a deeper lake level environment more than sub-biofacies 3a.
Vertical changes of biofacies and sub-biofacies inferred that a shallowing upward generally occurred through the core, with a short-term fluctuation. This shallow coincides with a decrease in the number of ostracods and an increase in amount of Cl and dolomite concentrations in the sediments. These observations suggest that the salinity of the Eski Acigol increased with a decrease in the water level around 3000 years ago. The absence of large rivers flowing into Eski Acigol indicate that this drop in lake water level may be related to the aridification of the surrounding area. In addition to the long-term paleobathymetric trend, the temporary existence of a very shallow environment characterized by the dominance of H. salina was identified in the core depth of 470 cm (around 5000 years ago). According to the ITRAX analysis, this shallowing is consistent with an increase in K meaning relations to an increase in debris inflow due to aridification. In summary, it is inferred that the climate around Eski Acigol in Central Anatolia has been arid since around 3,000 years ago in the long term, and that the climate was temporarily arid around 5,000 years ago.
Core EA2301, which is the subject of this study, was collected at Eski Acigol located in 200 km southeast from Ankara, the capital of the Republic of Türkiye. The cores drilled in four holes were correlated on the basis of lithology to produce one mostly successive sections of 4.8 m long. The core consists of fine-grained clastic material containing carbonate and biogenic silica. The age of the core is estimated to cover the past 6,000 years. In this study, hypothetical age is employed, and range of error is about 500 years. Core sample was cut into 1 cm thick slices. Of them, total 81 samples were used in this study. The samples were washed on a 63 μm sieve, and all ostracod shells were picked up from the dried residue.
Total 4735 individuals of six species were identified from 78 of the 81 samples. Cluster analysis suggested that 78 samples were grouped into 3 biofacies and two subbiofacies. Biofaciess 1 had a low abundance of ostracods and a high proportion of H. salina. Because this species prefers very shallow and warm water environments, biofacies 1 was assumed to represent a warm environment with relatively low lake levels. Biofacies 2 is dominated by L. inopinata and C. meerfeldiana, with a small number of ostracods individuals. Sub-biofacies 2a was characterized by equal numbers of L. inopinata and C. meerfeldiana. The coexistence of L. inopinata, preferring very shallow waters, and C. meerfeldiana, suggesting shallow waters, indicates slightly shallow lake water environment. Sub-biofacies 2b was inferred an environment of very shallow because L. inopinata accounts for more than 85%. Biofacies 3 is dominated by C. meerfeldiana, which has a large population of ostracods and prefers low-salinity, relatively deep water. Sub-biofacies 3a are characterized by high abundance of C. meerfeldiana, suggesting a low-salinity and slightly deeper lake water environment. Sub-biofacies 3b are known as abundance of more than 90% of C. meerfeldiana, suggesting a lower salinity and a deeper lake level environment more than sub-biofacies 3a.
Vertical changes of biofacies and sub-biofacies inferred that a shallowing upward generally occurred through the core, with a short-term fluctuation. This shallow coincides with a decrease in the number of ostracods and an increase in amount of Cl and dolomite concentrations in the sediments. These observations suggest that the salinity of the Eski Acigol increased with a decrease in the water level around 3000 years ago. The absence of large rivers flowing into Eski Acigol indicate that this drop in lake water level may be related to the aridification of the surrounding area. In addition to the long-term paleobathymetric trend, the temporary existence of a very shallow environment characterized by the dominance of H. salina was identified in the core depth of 470 cm (around 5000 years ago). According to the ITRAX analysis, this shallowing is consistent with an increase in K meaning relations to an increase in debris inflow due to aridification. In summary, it is inferred that the climate around Eski Acigol in Central Anatolia has been arid since around 3,000 years ago in the long term, and that the climate was temporarily arid around 5,000 years ago.