Browsing by Author "Sumita, Mari"

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Seismic Stratigraphy of Lake Van, Eastern Turkey
(Pergamon-elsevier Science Ltd, 2014) Cukur, Deniz; Krastel, Sebastian; Schmincke, Hans-Ulrich; Sumita, Mari; Cagatay, M. Namik; Meydan, Aysegul Feray; Stockhecke, Mona
More than 1500 km of multi-channel seismic reflection profiles combined with ICDP (International Continental Scientific Drilling Program) drilling data, provide important insights into the stratigraphic evolution of Lake Van, eastern Turkey. Three major basins (Tatvan, Northern and the Deveboynu basins) comprise the main lake basin and are separated by morphological highs (Ahlat ridge and Northern ridge). Moreover, NE SW faults, parallel to the general tectonic lineament of the area, dominate the entire basin and are in charge of creating graben and half-graben structures. Well-developed prograding deltaic sequences on top of the basement were recognized by seismic stratigraphy analysis. Most likely, they formed during the initial flooding of Lake Van similar to 600 ka. The Tatvan basin sediments are dominated by mass-flow deposits of various origins alternating with undisturbed lacustrine sediments including distinct tephra layers. Faulting along the Tatvan basin margins may have triggered margin-wide slope failures. Ahlat ridge started to form between ca 340 ka-290 ka. Since then, Ahlat ridge was sheltered from major mass-flows due to its elevation. Hence, slow lacustrine sedimentation has prevailed throughout lake history on Ahlat ridge, which was the location of the main drill site during the ICDP. Several lake level fluctuations are evident on the eastern slope area but the deep basins were permanently covered by water. A significant lake-level low stand (ca 600 ka BP) was found at similar to 610 m below present lake level. The setting of the lake changed at about 30 ka. Tectonic activity appears to have waned significantly as the mass-transport deposition decreased across the Tatvan basin while normal undisturbed lacustrine sedimentation prevailed. A different setting is found in the Northern basin from ca 90 ka to Present, especially due to the strong influx of mostly volcaniclastic turbidites causing sedimentation rates to be about 3.5 times higher (drill Site 1), than at Site 2 (Ahlat ridge). (C) 2014 Elsevier Ltd. All rights reserved.
Structural Characteristics of the Lake Van Basin, Eastern Turkey, From High-Resolution Seismic Reflection Profiles and Multibeam Echosounder Data: Geologic and Tectonic Implications
(Springer, 2017) Cukur, Deniz; Krastel, Sebastian; Tomonaga, Yama; Schmincke, Hans-Ulrich; Sumita, Mari; Meydan, Aysegul Feray; Horozal, Senay
The structural evolution of Lake Van Basin, eastern Turkey, was reconstructed based on seismic reflection profiles through the sedimentary fill as well as from newly acquired multibeam echosounder data. The major sub-basins (Tatvan Basin and Northern Basin) of Lake Van, bound by NE-trending faults with normal components, formed during the past similar to 600 ka probably due to extensional tectonics resulting from lithospheric thinning and mantle upwelling related to the westward escape of Anatolia. Rapid extension and subsidence during early lake formation led to the opening of the two sub-basins. Two major, still active volcanoes (Nemrut and Suphan) grew close to the lake basins approximately synchronously, their explosive deposits making up > 20 % of the drilled upper 220 m of the ca. 550-m-thick sedimentary fill. During basin development, extension and subsidence alternated with compressional periods, particularly between similar to 340 and 290 ka and sometime before similar to 14 ka, when normal fault movements reversed and gentle anticlines formed as a result of inversion. The similar to 14 ka event was accompanied by widespread uplift and erosion along the northeastern margin of the lake, and substantial erosion took place on the crests of the folds. A series of closely spaced eruptions of Suphan volcano occurred synchronously suggesting a causal relationship. Compression is still prevalent inside and around Lake Van as evidenced by recent faults offsetting the lake floor and by recent devastating earthquakes along their onshore continuations. New, high-resolution bathymetry data from Lake Van reveal the morphology of the Northern Ridge and provide strong evidence for ongoing transpression on a dextral strike-slip fault as documented by the occurrence of several pop-up structures along the ridge.