Conference:
IGCP 610 Second Plenary Meeting and Field Trip, Baku, Azerbaijzan, 12-20 October 2014.
Authors:
Elmira Aliyeva, Dadash Huseynov, Salomon B. Kroonenberg, A. Baba-Zadeh, Marc de Batist, R. Hoogendoorn, Speranta-Maria Popescu, Jean-Pierre Suc.
Abstract:
High resolution studies on the new core and seismic data from the Kura River delta in the southwest Caspian Sea has provided deep insight into its late Pleistocene – Holocene history, enabling characterizations of short-term climatic variations and an improving of the Caspian Sea level curve. The data display several phases of delta retrogradation during the Caspian Sea highstands, interrupted by erosional phases during lowstands, recognizable in the seismic profiles as prominent reflectors. The first phase is represented by coarse sands with numerous shell fragments encountered at the base of the deepest well A at the subCaspian depth of 34 m. The data obtained allow us to assume that sand deposition took place during the late Pleistocene Caspian lowstand (24–25 14C ky BP) (Sequence 1). Overlying dark reddish-brown sandy shales (interval 3034 m) were deposited during the time interval 18–23.7 ky BP (Atelian regression), which corresponds to the last glacial phase (Lunkkaa et al., 2001; Svitoch, 2013). These sediments are characterized by a lack of, or very rare fresh-brackish water mollusks (Dreissena) in the lowermost portion, and enriched in Fe2O3 and MnO suggesting sedimentation in the continental environment. We assume a deep Caspian Sea regression in the late Pleistocene (1825 ky BP) with the sea level falling to 102 m (Svitoch, 2013). The subsequent warming recorded in the peaks of warm temperature and subtropical palynomorphs was accompanied by a sea-level rise and accumulation of grey shales with abundant mollusk and ostracod shells (core interval 25–30 m). The deep Mangyshlak regression at the beginning of the Holocene is recognized in the core samples as peat deposits or shallow water grey sandy shales with sand laminae and shallow water ostracods (interval 21–25 m) (Sequence 2). Recovered palynomorphs display cool temperature and a peak in halophytes. The sea level was gradually falling from –92 m (12 ky BP) to –96.5 m (9.24 ky BP). The overlying Kura delta’s Holocene sediments consist of a 20 m thick interval of thinly bedded silty clays and laminated dark grey clays. Locally, sand and shell-rich horizons occur. The data have given concise insight into the development of the delta during the last ~10000 years. They show several phases of delta retrogradation during the Caspian Sea highstands, interrupted by erosional phases during lowstands, recognizable in the seismic profiles as prominent reflectors. The first phase is represented by reddened fluvial clays (Sequence 1), possibly affected by soil formation during a lowstand at –90 m absolute depth and dated at 12000 BP. These are overlain by several meters of laminated clays and silts, 14C dated at 9240–5920 BP (Sequence 2). This succession is truncated by a prominent reflector bounding Sequence 3 (modern delta dated at 1400 BP consisting of thin laminated clays). Sequence 3 consists of four progradational and retrogradational phases of a higher order corresponding to: (1) a lowstand at about –48 m absolute depth and correlated with the 11th century Derbent Regression, (2) laminated deltaic clays and silts, passing locally to organic clays with fluvial diatom assemblages, (3) an erosional event, related to a lowstand in the 16th century, (4) The last 200 years deposited succession. The onshore delta consists of progradational sequences of channel-levee sands and floodplain silts and clays deposited during gradual sea-level fall and overlain by clays and silts reflecting the last phase of rapid sea-level rise since 1977. Overall sedimentation rates in the delta determined by 210Pb methods range between 1.5–3.0 cm/year. Data on O and C isotope composition of ostracod shell carbonate as well as Ca/Mg, Sr/Ba ratios therein testify to significant climate and basin salinity changes throughout the Pleistocene-Holocene. They provided us with a unique opportunity to characterize short-term climatic cyclicity, which was the major lake-level control. The applied multi-component demonstrates a strong influence of climatically driven rapid fluctuations of the Caspian Sea level on stratigraphic architecture and faunal assemblages in the Pleistocene – Holocene succession.