Joint reports


The Modern Kura delta, Azerbaijan. A possible analogue for the Paleo-Kura Productive Series in the South Caspian Basin


 

  • The executive companies: GIA, University of Aberdeen
  • The year of publication: July 2003
  • Code: TA/AW/03-01
  • Volumes: total 1 


SUMMARY


The Modern Kura delta in Azerbaijan has been studied as a possible analogue for that part of the Productive Series in the South Caspian Basin that is supposed to have been deposited by that same river in its Pliocene delta. During three field campaigns 40 augerings up to 7m depth were made in the onshore delta, and offshore 18 sparker profiles were shot in lines parallel and perpendicular to the delta contours, and 14 piston cores down to 3 m and 8 wells down to 20 m were drilled. Laboratory analysis comprised grain size analysis by sieving and laser methods, light and heavy fraction petrography, chemical analysis of CaCO3 and organic matter, biostratigraphical analysis using ostracod, foraminifera, molluse and diatom countings, and radiometric dating using 210Pb and 14C analysis. 3-D stochastic and 2-D numerical modeling complements the onshore data.


The data have given a concise insight in the development of the delta during the last ~1500 years. They show at least three and possible four phases of delta progradation during highstands of the Caspian Sea, interrupted by erosional phases during lowstands, recognisable in the sparker profiles as prominent reflectors. The first phase is represented by reddened fluvial (?) clays (Regressive Systems Tract, RST1) possibly  affected by soil formation during a lowstands at -80 m absolute depth (Sequence Boundary, SB1). These are overlain by several metres of laminated clays and silts, 14C dated at >1400-900 BP on shelly intervals, and shown by microfauna to have deposited in a shallowing sea (RST2). This succession is truncated by the prominent SB2 reflector, corresponding to a lowstand at about -48m absolute depth and correlated with the 11th century Derbent Regression known from hisrorical and archaeological data. It is overlain by another metres-thick, undated succession of laminated deltaic clays and silts, passing locally to organic clays with fluvial diatom assemblages (RST3). This horizon is also truncated by an erosional event, SB3, probably related to a lowstand in the 16th century. During the Little Ice age highstand the Kura River was diverted southwards to the Qizilagac Bay and the barrier coast at the apex of the modern delta was formed. The last phase RST4 is represented by the formation of the onshore Kura delta since the end of the 18th century and an offshore correlative veneer of clays and silts,dated using 210Pb as having also been deposited during the last 200 years. The onshore delta consists of progradational sequences of channel-levee sands and floodplain silts and clays deposited on top of stage RST3 clays during gradual sea-level fall, overlain by clays and silts reflecting the last phase of rapid sea-level rise since 1977. Along the northern shore of the delta sands are deposited in narrow coastal barriers and beaches. Overall sedimentation rates in the delta determined by various methods range between 1.5-3.0 cm/year. Numerical modelling reproduces a realistic stratigraphy of the onshore delta.


Except for the thin and narrow sand bodies in the channels and barriers of the onshore plain, the whole Kura delta consists of clays and silts with virtually no reservoir capacity. Most of the Kura sand is probably trapped further upstream, where subsidence of the Kura trough is greatest. Kura sands are also found in Khvalyn (Pleistocene) highstand deposits far upstream. The presence of  large amounts of sand in the Productive Series outcrops in Babazanan suggests that downstream transport of sand was more effective in the Pliocene than at present. Therefore, also the offshore Pliocene Kura deposits in the fields at present targeted for exploration are probably more sandy than the present-day Kura delta.