Evidence of extensive carbonate mounds and sublacustrine channels in shallow waters of Lake Van, eastern Turkey, based on high-resolution chirp subbottom profiler and multibeam echosounder data

Abstract

In Lake Van of eastern Turkey, the fourth largest soda lake in the world, high-resolution subbottom profiles and bathymetric data acquired in 2004 and 2012 revealed several hundreds of topographic mounds in shallow waters (<130 m) off the historical town of Adilcevaz in the northern lake sector. These structures are characterized by strong top reflections of transparent internal character, and are 10–300 m wide and 0.5–20 m high. Consistent with previous work, they are interpreted as carbonate mounds formed by precipitation from CO2-rich groundwater discharge into the highly alkaline lake. Their age remains to be determined but their alignment along faults suggests tectonic control on their growth. Several sublacustrine channel networks were observed on the eastern shelf of the lake, which connects with onshore rivers. The channels are up to 500 m wide and 20 m deep, and plausibly were formed by fluvial processes during the major lake level drop reported to have occurred by 14 ka in earlier publications. Erosion is common on the channel walls flanked by levees. The channels are presently inactive or abandoned. At a water depth of 100 m, they all merge into a single larger channel; this channel has a sinuous course initially trending southwestward and then northwestward at a water depth of 130 m. Numerous closely spaced small channels (~10–200 m wide, 1–10 m deep) are also seen on the eastern lacustrine shelf, interpreted as denditric and parallel channel systems formed during lake level fall terminating at ~14 ka. Bathymetric data provide evidence of numerous sublacustrine canyons on the western slope of the lake’s northern basin, most likely remnants of relict rivers formed during this lowstand.