Development of the Kura delta, Azerbaijan; a record of Holocene Caspian sea-level changes

Late Holocene deposits of the Kura delta indicate an alternating dominance of deltaic and shallow marine environments. These major environment shifts are controlled by the high frequency sea-level changes of the Caspian Sea. The level of the Caspian Sea, now at 27 in below Global Sea Level (GSL), changes at rates of up to a hundred times as fast as global sea level, allowing observation of sedimentary processes on a decadal scale that would take millennia in an oceanic environment. The modem Kura delta is a river-dominated delta with some wave action along its north-eastern flank, and without tidal influence. Morphological and hydrological changes have been monitored for over 150 years, continuing up to the present day using remote sensing imagery. Offshore sparker survey data, onshore and offshore corings, biostratigraphical analysis and radiometric dating enable a reconstruction of the Holocene Kura delta. Four phases of delta progradation alternating with erosional transgressive surfaces have been identified, representing just as many cycles of sea-level fall and rise. The first cycle is represented by lowstand deposits truncated by a transgressive surface (TS1) at ca. 80 in below GSL. TS1 is overlain by several metres of laminated clays and silts, deposited during a Late Holocene forced regression (HI). These deposits are truncated by the prominent reflector (TS2), corresponding to the Derbent lowstand around 1500 yr BP and subsequent transgression. This transgressive surface is overlain by prograding shallowing upwards deposits, H2, in turn truncated by a third transgressive surface (TS3), correlated with a lowstand of ca. 32 in below GSL. The last phase, H3, comprises an onshore progradational unit followed by an aggradational unit with an offshore veneer of clays and silts, corresponding to the formation of the modem Kura delta that started at the beginning of the 19th century.