Development of the Kura Delta, Azerbaijan; a Record of Holocene Caspian Sea-Level Changes

Home , Derbent, Kura (river), Terek (river)

Marine Geology 222–223 (2005) 359–380 = www.elsevier.com/locate/margeo

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

Robert M. Hoogendoorn a,*, Jelle F. Boels a, Salomon B. Kroonenberg a, Mike D. Simmons b,1, Elmira Aliyeva c, Aliya D. Babazadeh c, Dadash Huseynov c

aDelft University of Technology, Faculty of Civil Engineering and Geosciences, Department of Geotechnology, Section of Applied Geology, Mijnbouwstraat 120, 2628 RX, Delft The Netherlands bCASP, University of Cambridge, Department of Earth Sciences, West Building 181A Huntingdon Road, Cambridge CB3 0DH, United Kingdom cGeological Institute of Azerbaijan, Azerbaijan Academy of Sciences, 29A H. Javid Avenue, Baku 370143, Azerbaijan Accepted 15 June 2005

Abstract

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 m 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 modern 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 m below GSL. TS1 is overlain by several metres of laminated clays and silts, deposited during a Late Holocene forced regression (H1). 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 m 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 modern Kura delta that started at the beginning of the 19th century. D 2005 Elsevier B.V. All rights reserved.

Keywords: Kura River; Caspian Sea; delta progradation; regressive deposits; transgressive surface; marine erosion

* Corresponding author. Tel.: +31 15 278 8192; fax: +31 15 278 1189. E-mail address: [email protected] (R.M. Hoogendoorn). 1 Present address: Neftex Petroleum Consultants Ltd, 80A Milton Park, Abingdon, Oxford, OX14 4RY, UK.

1. Introduction redistribution of delta sediments through wave-action on the northern shore. Beside the fluvial and shallow The interaction between (rapid) sea-level change marine processes, rapid sea-level change has a strong and deltaic systems has mainly been examined in influence on the formation of the Kura delta. The outcrop studies (Burns et al., 1997; Naish and present day subaerial delta covers ~200 km2 of largely Kamp, 1997; Reynolds et al., 1996). The Kura delta undeveloped arid lowland and shoreline swamps. This presents the possibility to study the effects of rapid area is the result of the latest phase of delta develop- sea-level changes on active delta environments in a ment which started at the beginning of the 19th cen- well constrained setting. The Kura delta is located tury (Mikhailov et al., 2003). Major human along the southwestern shore of the Caspian Sea, developments that have affected the delta dynamics Azerbaijan (Fig. 1). According to Galloway’s (1975) in the last 50 yrs have been the building of the classification, it is a fluvial-dominated delta, with Mingechaur Reservoir, ca. 150 km upstream of Kura

Fig. 1. (A) Schematic overview of the Kura delta study area with locations of acquired field data. (B) ASTER satellite image of the Kura delta (24 January 2004), (C) Location map including the bathymetry of the southwestern Caspian Sea (rectangle indicates where the Kura delta is located), major faults, syncline and anticline structures and oil and gas fields of the Lower Kura basin from Inan et al. (1997). Inset shows location of the Kura basin in relation to the Caspian Sea. R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380 361

River mouth, and development of industrial fish and During 3 field campaigns 40 cores, up to 7 m rice ponds in the delta plain. depth, were drilled onshore, and 8 wells drilled to Earlier studies of the Kura delta undertaken by 20 m depth in the offshore. In addition 14 piston Belyayev (1971), focussed on hydrology and delta cores penetrated down to 3.5 m, and 18 sparker growth over the last 200 yrs. These have recently profiles were shot in lines parallel and perpendicular been updated and expanded by Mikhailov et al. to the delta contours offshore, with a total survey (2003). Limited work has been done on the (late) length of 215 km (Fig. 1). The resulting data reveal Holocene development of the Kura delta, as well as that the Holocene delta consists of possibly four on the determination of its depositional environments progradational phases and three erosional phases. and lithofacies. The data on delta growth and the During the Holocene the active delta has switched detailed hydrological data, combined with the work location several times as a result of the sea-level of Rychagov (1997), on the fluctuations of Caspian fluctuations, and fluvial dynamics of the Kura River, sea-level do provide a narrow constraint on the sedi- resulting in the subsequent lateral displacement of mentation models and interpretations of the Kura delta the delta apex over a distance of several tens of lithology. kilometres from the Qizilag˘ac Bay (formerly known

Fig. 2. (A) Part of the map of Europe by Joseph Scheda (1845). At the location of the Kura River mouth (centre of the square) there is no evidence of a subaerial body. To the south of the river mouth, an active delta body can be seen, consistent with the deltaic remains observed in the Landsat TM7 Satellite image (2001) of the Kura delta and the Caspian Sea (B). These deltaic remains south of the modern Kura delta indicate active channel switching of the Kura River. 362 R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380 as Kirov Bay) lying to the south of the present delta (Guliyev and Feizullayev, 1997). A mud volcano is (Fig. 2). There are historical records of the Kura found several kilometres offshore, northeast of the discharging into the Qizilag˘ac Bay, as far back as Kura delta. 2500 yrs BP (Mikhailov et al., 2003), explaining the Ever since the late Pleistocene periodic transgres- presence of remnant deltaic features and spits and sions and regressions of the Caspian Sea changed the barriers in this bay. Furthermore the onshore cores coast-line configuration of the present day Kura basin disclosed the major role of the recent 3 m sea-level lowland. During significant transgressions, this low- fall and rise, during the last 200 yrs, in the devel- land turned into an inland shallow water bay, in which opment of the Kura delta. Whereas fluvial and ancient deltas of the Kura River were formed. The marine processes are the primary forces affecting traces of several deltas can be found in the present the formation and morphology of most major deltas topography of the lowland. Over the period of large- (Galloway, 1975), the Kura delta has formed in scale regressions, the delta of the Kura River pro- response to a combination of fluvial processes and truded into the sea far more to the east of the modern the rapid, high frequency sea-level changes in the delta (Mamedov, 1997). Caspian Sea. 2.2. River system characteristics

2. Regional setting The Kura River is the largest watercourse in the Southern Caucasus. It originates in the springs located 2.1. Geologic setting 2720 m above sea level on the northeast slopes of Kizil-Giadik (Turkey). It then flows through the ter- The modern Kura delta is located on the border ritory of Georgia and the lower reaches of the river are between the Kura and South Caspian basins (Fig. 1). in Azerbaijan, where it flows through the Kura basin The South Caspian basin is part of an active tectonic into the Caspian Sea. In the Kura basin the Kura River zone in which the Greater and Lesser Caucasus are merges with its major tributary, the Araks River. The being uplifted (Mitchell and Westaway, 1999), while Araks River drains the eastern Lesser Caucasus. the Caspian seafloor subsides at a rate of 2.5 mm According to Mamedov (1997), the Araks- and Kura yr 1 (Inan et al., 1997). The Kura basin is situated in River had their own deltas in the past. The total length the eastern part of the depression between the of the Kura River is 1515 km and the total area of the Greater Caucasus to the North and the Lesser Cau- catchment is 188,000 km2 (including the Araks casus to the South. Middle Jurassic volcanism, River). The catchment occupies the greater part of together with shallow-marine Jurassic and Cretac- the Lesser Caucasus and the south-eastern Greater eous sediments form the base of the succession in Caucasus. the Kura basin, which has been encountered at a The Kura water discharge at the river mouth aver- depth of more than 8000 m in the Saatly ultra aged around 17.1 km3 yr 1 (550 m3 s 1) between deep borehole in the centre of the Kura basin 1938 and 1984 (Bousquet and Frenken, 1997). The (Khain, 1984; Khain and Shardanov, 1952; Levin, sediment (bedload and suspended load) of the Kura 1995). From Miocene times onwards, shallow-mar- River upon entering the delta is predominately clay, ine and deltaic sedimentation has been dominant. silt and fine sand (b200 Am). The annual sediment Major uplift occurred at the end of the Miocene as volume reaching the delta averaged 11.3*106 m3 a result of underplating of the Transcaucasian micro- yr 1 between 1967 and 1976 and from 1977 to continent under the European plate. Folding of the 1986 the sediment volume dropped to 8.8*106 m3 Kura basin sediments, and older units, into NW–SE yr 1 (Aybulatov, 2001; Mikhailov et al., 2003). oriented anticlinal structures took place mainly at the end of the Pliocene, leading to the development of 2.3. The Caspian Sea numerous mud volcanoes, still active today. These mud volcanoes are unique geological features and The Caspian Sea, with surface area of 3.93105 give rise to significant gas, water, and oil seepages km2, is the largest inland water body on earth; R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380 363

(Kosarev and Yablonskaya, 1994), it has virtually no seasonal to centuries. The measured seasonal sea-level tides and its salinity is 13 mg/l. The Caspian basin is change is up to 0.4 m (Cazenave et al., 1997) while divided into approximately equal-sized northern, mid- the maximum measured inter-annual Caspian sea- dle and southern parts. The northern part is a shallow level change in the records has been 0.34 m yr 1. shelf region reaching a maximum depth of about 10 These fluctuations are a result of the interaction m. The middle and southern regions are deeper areas, between differences in river discharge (predominantly separated by an east–west oriented underwater range the Volga River), evaporation, precipitation and water near the Apsheron peninsula. The depth of the south- temperature (Kosarev and Yablonskaya, 1994; Rodio- ern Caspian Sea is approximately 1025 m and the nov, 1994). shelf edge is located 20 to 40 km offshore of the The sea-level curve for the last 160 yrs is accu- present day Kura delta. The sea level of the land- rately known from the gauge at Makhachkala, and locked Caspian basin, presently at approx. 27 m since 1993 from satellite measurements (Fig. 3) below GSL, fluctuates rapidly on several time scales, (Kosarev and Yablonskaya, 1994). From 1930 to

Fig. 3. (A) Estimated Holocene sea-level fluctuations of the Caspian Sea (Rychagov, 1993a,b, 1997) and (B) measured Caspian sea-level fluctuation, 1900–2000 AD (Klige and Myagkov, 1992). 364 R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380

1977, sea level dropped by ~2.7 m, and from 1977 to 1995, it rose at a rate of 15 cm yr 1 (Kaplin and Selivanov, 1995). Numerous transgressions and regressions of the Caspian Sea have also occurred in the more distant past (Ignatov et al., 1993; Svitoch, 1991). The Holocene sea-level history has been reconstructed from a marine terrace section along the Dage- stan coast. Results from these studies show five transgressive phases that have been dated around 8000, 7000, 6000, 3000 and 200 BP (Rychagov, 1993a,b, 1997). The lowest documented sea level is estimated at 50 m below global sea level at the end of the Pleistocene or early Holocene (Mangyshlak regression). The Derbent regression, around 1500 BP, reached a minimum of at least 32 m. The highest level reached by the Caspian Sea during the Holocene is around 22 m, the elevation of the present delta apex.

2.4. Delta morphology

A barrier-breach around 1800 AD marked the onset of the progradation of the present day Kura delta. The morphological development has been described in detail by Mikhailov et al. (2003). Pro- Fig. 4. Monitored shoreline progradation of the modern Kura delta gradation of the shoreline and the delta body have (Aybulatov, 2001; Mikhailov et al., 2003). been continuously monitored. Fig. 4 illustrates the rapid progradation during the last ~180 yrs. The sub- shielded from longshore currents and waves. The aerial modern Kura delta is elongated and slightly northern flank of the delta is composed of a barrier lobate. Deposition is asymmetrical, and the delta lagoon complex. The eastern flank is currently sus- accretes to the south–east (1208) as a result of the ceptible to erosion as no sediment is being transported southward directed current. It measures 40 km from to the delta front by the SE channel. the apex to the tip of the delta, is 55 km at its widest point and has a surface of ~200 km2, making it the third largest delta in the Caspian region (Warren and 3. Delta sediments and stratigraphy Kukosh, 2003). The NW–SE oriented Kura River has three channels oriented northeast (NE), southeast (SE) 3.1. Lithology and south (S). At present the SE channel is not active. The channels have a low sinuosity in the delta plain. Lithological profiles of representative cores are During the latest period of sea-level fall, the main shown in Fig. 5, an overview of all lithofacies is channel flowed in south-easterly direction with a sin- given in Table 1, while all core location are shown gle distributary flowing in north-easterly direction. in Fig. 1. The onshore cores were made using a hand During the latest sea-level rise the SE channel closed auger. This device provides quick and simple method and was partly filled, the southern channel formed at to recover a continuous subsurface sediment sample, 1 this time. Currently, the active main southern channel m length, in unconsolidated sediments ranging in bifurcates into numerous (ca. 20) smaller ones that are grain size from clay to fine sand. Most onshore 10–100 m wide at the delta front. These are situated in cores are 7–8 m deep. The piston cores were obtained the leeward side of the delta, and are consequently offshore using a 3.5 m long, 10 cm wide piston corer R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380 365

Fig. 5. Lithologic profiles of selected cores, note that the vertical scale of well 4 (F) is in meters while the others are in centimetres. profiler, and wells were drilled up to 20 m deep, in 2 relatively poorly sorted, dark reddish brown in colour, m sections. very fine to medium silty/clayey sands, with a uni- A typical onshore core (Fig. 5A, B and C) consists form grain size. The thickness of the massive sand of massive dark grey clays and silty sands at the base. layers varies between 10 cm and 1.3 m. The hetero- These pass up into laminated clays and silty clays lithic sands are brownish and reddish and vary in overlain by layered fine sand, silts and clays. These grain size resulting in fining—or coarsening up deposits are often intercalated with sandy beds, mas- sequences. They are well sorted with a thickness sive and heterolithic sands, which vary in thickness that varies between 10 cm and 0.5 m. The top of the (10–100 cm.) and sorting. The massive sands are cores consist of massive clays and silty clays (homo- 366 R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380

Table 1 Characteristics of the lithofacies of the Kura delta Lithofacies Texture Observed sedimentary characteristics Location Massive clay and silts Silty clay and clay Massive, roots, desiccation cracks Onshore Massive sands Medium to very fine sand Massive, sharp boundaries Onshore Heterolithic sands Medium to very fine sand, Coarsening up or fining up, Onshore silty sand badly sorted Interstratified clays, Fine to very fine sand, Layers and lamination Onshore and offshore silts and sands silt and clay Laminated clays and silts Silt and clay Lamination, mud dominated Onshore and offshore Dark grey clays Clay and medium to very Dark grey colour, well sorted layers, Onshore and offshore fine sand mud dominated Shelly sands Medium to fine sand Shells Offshore Cemented shells Shells fragmented and cemented 100% shells Offshore genous) which are rich with rootlets. The onshore and their colour varies from yellowish brown to olive cores located away from the main channel often lack black. The continuous thickness of the laminated sandy deposits. The cores towards the delta front clays reaches 260 cm. In some cases, in proximal as feature a set of layered fine sand, silts and clays on well as distal cores, thin shelly, sandy deposits can be top of the homogenous massive clays. found. Sometimes complete shells occur within these The offshore piston cores (3.5 m) consist of fine coarser layers and vary in size from 1 mm to 5 cm. sediment (Fig. 5D and E). The distal piston cores are The locations proximal to the delta shoreline generally homogenous and consist primarily of laminated clays. show laminated clays at the bottom of the proximal The colour-laminated clays and silty clays are found piston cores which are overlain by layered clays and with abundant mm- to cm-scaled colour transitions silts. The layered clays and silts are sporadically

Delta plain N Proximal delta front Fluvial Sand (Levee & Channel fill) Mouth Bar Barrier lagoon complex Interdistributary bay Distal delta front Prodelta Kura River

0 10 km

Fig. 6. Depositional environments of the modern Kura delta. R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380 367 intercalated with films of fine sand, the thickness of depositional environments. Fig. 6 illustrates the spa- the sand and silt layers varies from 1 mm to 1 cm. tial distribution of these depositional environments. There are also silty clays containing significant Characteristic surficial sediments of the upper amounts of organic material forming black layers, and lower delta plain include massive silty clays, 5–20 cm thick. sands, and layered sands and clays. These lithofa- The wells feature diverse lithofacies over their 24 m cies are interpreted subaerial deposits formed by thickness (Fig. 5F). Massive mottled clays or yellow- fluvial processes. The mottled clays which have ish brown sandy to silty clays, containing abundant, been observed in the lower portion of the well coarse, red granules have been found at the bottom of cores have also been related to a lower delta plain the wells at a depth of ca. 80 m below GSL. The colour depositional environment. Sandy sediments on the laminated clays and layered clays and silts are inter- subaerial delta surface were only found at the bifur- bedded. Whole as well as fragmented shells occur cation of the northern and southern distributaries, within heterolithic, brown, poorly sorted fine sand to forming a point bar on the inside of the river bend. silt. The thickness of the sandy deposits are up to 0.5 Sandy deposits in the subsurface samples of the m. Though generally these deposits thinner than 10 delta plain are represented by massive and hetero- cm. Shells vary in size from ca. 2 mm to 5 cm. Well lithic sands locally deposited in higher energy envir- recovery is poor (30–70% recovery), therefore, these onments in the vicinity of the distributaries, e.g. well data should be interpreted with caution. channel fills, crevasses, or levees. However, the poor sorting, ranging from fine sands to clays, 3.2. Depositional environments indicate an environment where flow energy is sporadically high enough to deposit such a mixture, but Satellite images, field observations and surficial not continuously high enough to effectively sort the sediments were used to classify the delta into several material.

Fig. 7. Sparker profile 5 (0105) showing the downlap of the modern delta to the NE, and the ddrapeT, comprising several, parallel reflectors in the middle of H2 and clinoform stacking in the southern part of the profile indicating the aggrading phase of H2. 368 R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380

The proximal delta front comprises the southern, Mouth bar deposits occur seaward of the river low angle dipping seafloor, and that part of the lower mouth (South). This facies is characterized in the floodplain that is occasionally submerged. Deposits of sub surface samples by laminated sands, and inter- the proximal delta front environment comprise layered bedded sands and muds (85% sand). clays, silts and fine sands. Depending on the local The beach on the northern flank is a very diverse topography and hydrodynamics of the channels, parts geomorphological unit. The beach contains ripples, of the delta front deposits may contain organic mate- storm berms, and washover channels. The beach pro- rial, representing the marshy freshwater environment, graded seaward and facilitated the enclosure of the representing a transition zone between the delta plain back barrier lagoon. The beach consists of well sorted, and the proximal delta front. The distal delta front is medium grained sand. The shelly sands from the wells the part of the delta comprising a high angle slope are interpreted as lower shoreface deposits as the varying between 0.38 and 0.58. The laminated clays are presence of whole shells indicate an open marine found here. The distal delta front gradually changes environment. into the prodelta where sedimentation rates are low. Between the prograding northern distributaries an 3.3. Sparker data interdistributary bay has formed, ca. 0.5 to 1 m deep, in which clay and silt has been deposited during The shallow subsurface of the offshore Kura has floods. This bay was dry during the last lowstand been mapped using 215 km of sparker shallow acous- (1977) and is currently submerged and overgrown tic profiles arranged in a grid of 18 profiles (Fig. 1). with aquatic vegetation. Data quality is sub optimal due to multiples and back-

Fig. 8. Sparker profile 2 (0102) coast-parallel profile, illustrating the two channel types the most S-SE channel (right-hand side of the figure) is horizontally filled with sediments and incised the underlying strata. The most N-NW channel (left-hand side of the figure) serves as an example for an aggradation channel since it is still visible in the surface topography. R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380 369 ground noise. This relates to the high degree of gas parallel character of these reflectors implies vertical saturation in the shallow subsurface. Nonetheless, the aggradation in a delta plain depositional setting (Figs. quality is sufficient to determine the major elements of 7, 8 and 9). The cores which penetrate these reflectors the offshore delta geometry and its shallow subsur- show layered clays, silty clays and fine sands that are face. Five sparker profiles (Figs. 7–11) show the interpreted as proximal delta front deposits. Typical typical features of the Kura delta. In addition to the palaeo-floodplain deposits are only found at the base present day delta (H3), three prograding deposits PH, in wells 4 and 5. Other subhorizontal reflectors are H1 and H2, were identified. Two transgressive sur- interpreted to represent the mud volcano dynamics. faces, TS1 and TS2 were defined as prominent dis- The clinoform reflectors are sigmoid clinoforms continuity surfaces on the sparker data. Furthermore a and interpreted to the prograding delta front to pro- drape of continuous reflectors is recognisable on all delta deposits of the palaeo Kura River. The cores did profiles and is considered to represent sedimentation not reveal any crossbedding to confirm the observa- of the modern Kura delta. Consequently the base of tion of the sparker data, but did contain laminated and this drape is interpreted as TS3. layered clays and silty clays at the locations and Four main features can be recognized within the depths, similar to the modern distal delta and delta profiles: (1) horizontal/subhorizontal reflectors (delta front sediments (Figs. 7, 9, 10 and 11). plain), (2) clinoform reflectors (delta front, prodelta) The concave-upward reflectors are mainly asso- (3) concave-upward reflectors (distributary channels ciated with the topset deposits of Fig. 8. Two channel and possible incised channel), which are often asso- types can be recognized: (1) Channel type 1 incises ciated with (4) hyperbolic reflectors (levees, barrier). and fills horizontally. The incised channel is asso- The horizontal/subhorizontal reflectors represent ciated with a regressive system as it is filled up the topset facies. The stratigraphic position and the when the sea level rises, (2) Channel type 2 aggrades

Fig. 9. Sparker profile 11 (0111) Overview of the northern offshore part, with the sediment drape of the modern delta extending to the slope of the mud volcano. The data also shows the subhorizontal and clinoform reflectors representing the progradational phase of H2. Furthermore the transgressive surface 2 (TS2) can be correlated to a facies change in well 3, TS1 is correlated to the deeper sandy shelly horizon of well 3, which were dated at ca.1400 BP (Fig. 12). 370 R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380

Fig. 10. Sparker profile 7 (0107) data also shows the subhorizontal and clinoform reflectors representing the progradational phase of H2 and reveals the depth interval at which erosive features occur (between 20 and 25 m), as well as interference of the delta with the slope of the submerged mud volcano. vertically, this channel type is associated with a trans- table assumption to relate the hyperbolic features to gressive phase of delta development. When the regres- levee’s and barriers. sive channel is suffocated, other, smaller, channels develop. These channel features are preserved under a drape of sediment, in a similar way to the processes 4. Laboratory analyses observed in the modern delta. Hyperbolic reflectors are commonly found near 4.1. Radiometric dating the channel type 2 and may therefore be associated with levee deposits, although no core has penetrated 210Pb analysis was used to determine sedimenta- these deposits. A second type of hyperbolic reflec- tion speed for a maximum period of 150 yrs (Lami et tors is shown in Fig. 8, which shows a bump in the al., 2000). 210Pb analysis was used to determine sedi- centre on the figure which is not associated with a mentation speed for a maximum period of 150 yrs. the channel in the subsurface. This feature may be results for 210Pb analyses for pistons 7 and 9 (Fig. 12) associated with a barrier bar, though evidence for give estimated sedimentation rates varying from 1.9 to this is limited. Nevertheless, the core data show the 2.2 cm yr 1. The results of the 210Pb analyses from occurrence of shoreface deposits and the north flank the onshore core 12 were inconclusive. This can be of the modern Kura delta has an active barrier explained by a resetting of the internal clock of the system. Subsequently this is thought to be an accep- 210Pb isotope due to emergence of the sediment, and R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380 371

Fig. 11. Sparker profile 14 (0114) in line with the progradational direction of the modern delta shows a high seafloor gradient (0.58) and also depth-related erosive features. Steep clinoform features of the H2 phase appear at the slope. the resulting contamination by fresh water. In contrast, location of well 3 over the past ~1400 yrs is estimated samples from the lower part of onshore core 13, taken at an average of 1.2 cm yr1. At well 3 the reflective from the dark grey clays, show a constant low 210Pb surface of the sparker data (TS2) is located at a depth value. of c. 10 m. Sample 5(1) is from depth 16–16.3 m. Shells (all Dreissena polymorpha/andrussovi) from Therefore, these datings indicate that TS2 is younger well 3 have been dated using 14C isotopes (Table 2 and than ~1400 yrs BP, and at a sedimentation rate of 1.2 Fig. 12). From every sampled interval, shells were cm yr1 its age is around 875 yrs BP, i.e. the 11th examined to assess the likelihood that they were in century AD. TS2 could therefore correspond to an situ. Next the samples were dated to compare the erosional level related to the sea-level rise of the spread of results. Samples 6(1), 6(2), and 5(1) show Caspian Sea following the Derbent regression. a decreasing age upward suggesting they are in situ. The other samples, 3(1), 4(1), and 5(2) are older than 4.2. Biostratigraphic dating and diatom analysis underlying shells from the other samples, indicating that they may have been deposited after being Biostratigraphic analysis of the shells resulted in reworked. As a result, the sedimentation rate at the the recognition of invasive species (Table 2). The 372 R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380

Fig. 12. Lithologic profiles with summary of all age data (based on 210Pb, 14C, Biostratigraphic and diatom data) and interpreted depositional environment. Note that the vertical scale of well 3 is in meters while the others are in centimetres. In well 3 the datum level of the interpretated TS2 of Fig. 9 is shown. timing of first occurrence of invasive species in the from lowest occurring depth of invasive species are Caspian Sea is well known (Kosarev and Yablons- given in Table 1. Piston cores 7 and 9 show an kaya, 1994), and therefore can be used to date historic average rate of approx. 2.3 cm yr 1. This is in agree- deposits. Mytilaster lineatus invaded the Caspian Sea ment with the results from the 210Pb analysis. around 1920–1930, attached to ships coming from the A total of 10 offshore sediment samples were Black/Azov Sea region. Abra ovata was deliberately analysed for diatom content. Of these, 8 were found introduced in order to raise biological production and to contain diatoms, with 5 containing sufficient num- consequently fish productivity in 1939. The barnacle bers to allow counting and detailed environmental Balanus improvisus was introduced with the opening interpretation. The samples typically contained a pro- of the Volga-Don Canal in 1954. The age estimates portion of inorganic material, including quartz and and subsequent average sedimentation rates derived mica, and diatom recovery from these samples was R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380 373

Table 2 Overview of the 14C analyses and biostratigraphic results (Caspian reservoir age is ca. 290 yr, K. van der Borg personal comment) Site Sample Depth (cm) Material Years BP Cal years Well 3 3#3 1050–1060 Dreissena polymorpha/andrussovi *1844F32 1409–1335 Well 3 3#4 1530–1550 Dreissena polymorpha/andrussovi *2829F33 2674–2539 Well 3 3#5(1) 1600–1630 Dreissena polymorpha/andrussovi fresh 1368F36 947–888 Well 3 3#5(2) 1600–1630 Dreissena polymorpha/andrussovi old *1914F32 1495–1420 Well 3 3#6(1) 1710–1715 Dreissena polymorpha/andrussovi fresh 1414F37 984–918 Well 3 3#6(2) 1710–1715 Dreissena polymorpha/andrussovi old 1443F29 1009–944

Site Depth (cm) Invasive species Years Piston core 7 244–246 Balanus improvisus 1954 AD Piston core 9 109–111 Balanus improvisus 1954 AD Well 2 305–310 Abra ovata 1939 AD Well 3 920–925 Mytilaster lineatus 1920 AD low. Recovery of diatoms tended to be highest in stated in absolute values calculated as h =d +w +z, samples with a high proportion of clay. Table 2 and in which d is the depth of the feature in the well or Fig. 12 show the results of the diatom analysis from piston core, w is the water depth at the top of the well, the piston core samples, and the interpretation of their and z the datum level of the sea in 2001 with respect depositional environment. Although there were lim- to the Kronshtadt gauge in the Baltic (27 m). A ited data the diatom analyses of layered silts and clays schematic overview of the geochronolgy for the Kura from the piston cores indicate that the depositional delta deposits in relation to the Holocene Caspian sea- environment is related to a delta front, confirming the level curve (Rychagov, 1997) is shown in Fig. 13. The sedimentological interpretations of the depositional overall depositional patterns, calculated datum levels settings. and 14C datings combined show 4 phases of deposition, one pre-Holocene and three late Holocene phases. These phases are characterised by different 5. Depositional history stages of deltaic deposition associated with erosive marine surfaces, which are interpreted to represent The unique sea-level situation of the Caspian Sea cessation of the sediment supply and transgression. does not allow a straight forward sequence stratigraphic interpretation of the different deltaic deposits 5.1. Phase 1, pre-Holocene deposits (PH, TS1) using definitions as given by, e.g. Hunt and Tucker (1992) and Plint and Nummendal (2000). Regressive The oldest deposits recovered are the stiff red systems tracts (RST) (Myers and Milton, 1996)do mottled clays at the bottom of the deepest wells 4 describe some features found in the deposits of the and 5, at absolute depths of about 89 and 82 m. Kura delta, for instance the boundaries, which can be The mottling in these deposits indicates incipient soil interpreted as transgressive surfaces (TS). Further- formation in floodplain deposits during a pronounced more it could be argued that the overall (early) Holo- lowstand. Such a lowstand did not occur in the Holo- cene Caspian sea-level shows an overall rising trend. cene (Rychagov, 1997) therefore deposits of phase 1 Nevertheless the lack of clear stacking patterns in the are probably pre-Holocene. The late Pleistocene low- sparker data for the different phases of delta deposi- stand of ca. 50 m below GSL of the Mangyshlak tion and the exceptional rate of change of the Caspian regression (ca. 16 kyr BP) (Mamedov, 1997) corre- sea-level restrains us from using sequence strati- sponds well with the well data when datum levels are graphic terms, although similarities between the compensated for the regional subsidence of 2.5 mm deposits and systems tracts will be mentioned. yr 1 (Inan et al., 1997). In both wells sandy shelly In order to be able to refer certain stratigraphic deposits occur on top of the reddish clays at absolute features to former sea levels, all datum levels are depths between 83 and 76 m which are associated 374 R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380

Fig. 13. Geochronological representation of the different phases of delta development superimposed on the Holocene Caspian sea-level curve (Rychagov, 1997). Giving close constraint to the interpretation of the (late) Holocene deposits of Kura delta. with shoreface environments, Sparker profile 7 (Fig. water depth of 11.4 m. In the uppermost part of the 10) shows a reflector at this level. The results from unit the ostracod Iliocypris brady was found, indica- Rychagov (1997), show that, after the lowstand, at the tive of fresh-water influence. Together these data Pleistocene–Holocene transition, a transgression indicate a generally falling sea level during deposi- occurred. TS1 reflector is interpreted as a marine tion. Six 14C datings were obtained from the shell-rich erosion surface formed during this transgression. horizons in Well 3, located underneath the boundary Since well recovery is very poor, the TS1 reflector between H1 and TS2, and indicated deposition at ca. only occurs in one profile and no biostratigraphic 1400 BP. Therefore the H1 deposits are thought to be information is available for this phase, the position associated with the forced regression preceding the of these deposits in the overall stratigraphy remains Derbent lowstand of 1500 BP (Rychagov, 1997). inconclusive. Since the Derbent regression did not start before 3500 BP and no other depositional units were found 5.2. Phase 2, late Holocene deposits 1, (H1, TS2) between TS1 and TS2 it is probable that no deposition took place at the study site during the early-Holocene. The second phase consists of sedimentation of the The TS2 is a prominent reflector in the sparker unit underlying the Transgressive Surface indicated by sections, especially NE and E of the present delta. The TS2 in the sparker profiles. The seismic facies within surface is highly irregular in shape between absolute this unit is indistinct. The wells that intersect the TS2 depths of 45 and 60 m, and truncates H1 sediments. continue 10–14 m down into this sedimentary unit. Below that it slopes smoothly down to 75 m, the The bottom of the unit is unknown except for the TS1 deepest level it has been recognised (Fig. 11), and reflector of sparker profile 7. The unit consists mainly parallel to the stratification of the underlying unit. The of layered silty clays, with minor intervals of lami- irregular topography of the reflector indicates either nated clays and silts, and, in Well 3 (Fig. 9), several an erosive origin, or an accumulative origin as over- shell-rich horizons. Microfauna in Well 2 indicate a stepped barriers, or both, but in any case features that decreasing depositional depth (with some fluctua- occur in a coastal to onshore setting. The shell horizon tions). Depositional depth in Well 3 fluctuates recovered in Piston Core 5 at an absolute depth of between 10 and 15 m, in harmony with the actual 47 m can also be related to this phase. This is the R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380 375 deepest appearance of TS2 in the sampled data and sions, especially between 47 and 57 m absolute suggests that this may be a lowstand. On the basis of depth. The reflector is smooth at 37 m depth along 14C datings this lowstand must have taken place the shallow SW part of the delta. The age of the around 1400 yr BP. While a lowstand of 34 m is Transgressive Surface can only be established indir- inferred for the Derbent regression (Rodionov, 1994; ectly, since datings from this unit are not available. The Rychagov, 1997; Varushchenko et al., 1987), our data overlying unit is known to have been deposited from suggests that the lowstand fell, to an estimated depth the start of the 19th century onward following the 200 of 37 to 42 m when it is assumed that the shells BP highstand (Rychagov, 1997) . During the period from Piston Core 5 were deposited at a water depth of preceding this highstand major barrier complexes were 5–10 m. Hence this surface is interpreted to be asso- formed (Storms, 2002). Because at that time the Kura ciated with the Derbent lowstand and the subsequent River did not discharge at its present location, but transgression. much further south, in the QVzVlagˇac¸ bay, the barrier complex at the apex of the present-day delta and 5.3. Phase 3, late Holocene deposits 2 (H2, TS3) subsequently TS3 were formed during the 16th and 17th century (Mikhailov et al., 2003). H2 consists of deltaic deposits between TS2 and TS3 reflectors. In some places only a pocket of this 5.4. Phase 4, modern delta (H3) unit has been preserved between the two reflectors. The succession consists of latterly varying facies that As documented by Mikhailov et al. (2003) the are syndepositional. Proximally, organic-rich silty clay modern delta started to form at the start of the 19th was deposited in a delta front environment. A prograd- century and is closely constrained by data on delta ing deltaic sequence with clinoform-shaped reflectors growth, sea-level change and hydrology. H3 is the can be seen on the distal, more seaward side, shown in uppermost sedimentary unit seen in the sparker pro- profile 5 and 11 (Figs. 7 and 9). Furthermore this phase files and consists of the ddrapeT that covers TS3. The is found at the base of the onshore cores and consists of 210Pb profile at Piston cores 7 and 9 shows that the massive dark grey clays and silty sands, similar to the major part of the drape is less than 200 yrs old, and modern delta plain deposits. The depositional depth therefore it is coeval with the major part of the surfi- indicated by the microfauna in Well 2 first increases cial deposits in the onshore part of the delta. The and, then decreases back to its initial level of 25 m. In onshore sequence represents a complex of sandy, silt Well 3 the depositional depth is uniformly about 15 m. and clayey sediments deposited on top of H2 deposits. Both figures are similar to the present water depth of The onshore data reveal a rapid progradation that was 26.3 and 11.4, respectively. Organic-rich clays at facilitated by the shallow offshore platform and the 38 m absolute depth in Piston core 7 contain fresh sea-level fall, starting around 1933. By 1960, before water diatoms, and have higher vegetal organic com- the sea-level reached the 1977 lowstand, the rapid pounds than organic clays from organic clays in piston progradation was halted as a result of the increasing cores sampled in deeper water. This suggests that also accommodation. Sea-level rise after 1977 led to inun- this unit reflects an overall falling sea level. The dation of the present delta plain and deposition of aggrading stacking patterns of sparker profile 5 (Fig. uniform clayey sediments on top of the previous 7) indicate a transition from regression to transgression progradational wedges, an aggradational process that during this phase, which suits the definition of a continues until today. This sequence is confined to the Regressive Systems Tract. In view of the position of tip of the delta and along the shoreline. the deposits between the two transgressive surfaces the age of phase 3 is probably between the 11th and 16th century AD when several alternating stages of rapid 6. Discussion regression and rapid transgression occurred (Rycha- gov, 1997). The history of the Kura delta can be traced back The TS3 reflector truncates the H2 unit with an only for a relative small time interval in this study. The irregular topography with ridges, benches and depres- present position of the delta corresponds with the axis 376 R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380 of the rapidly subsiding Kura basin (Khain and Shar- The important role of Caspian sea-level has been danov, 1952) and it is also situated at the head of a described. Since all Caspian deltas, such as the Volga, prominent submarine valley, suggesting a period of Ural and Terek deltas are subjected to the same rapid deep incision in its early history. The bulge shape of base level change, it is essential to establish if simila- the submarine delta suggests a cumulated thickness of rities occur in the development of the Kura and other at least 50 m. All these facts suggest that its history Caspian deltas. The Volga delta is the most studied must go back much further than can be retrieved from Caspian delta system; it is also a fluvial dominated our data. With respect to the available data, the historic delta affected by the rapid Caspian sea-level fluctua- and newly collected data form only a part, although the tions. However, studies show that fluvial processes network of core and sparker data compliment one and sea-level fluctuations are not the only primary another and clearly characterize the Kura delta. controls over the Volga delta development. A funda- For a better understanding of the significance of mental control on delta morphology and stratigraphy the development of the late Holocene Kura delta it is is the low gradient (Aybulatov, 2001; Kroonenberg et useful to compare it to other deltas, as many sedimen- al., 1997, in press; Overeem et al., 2003). The Ural tological investigations of modern fluvial-dominated River also enters the shallow northern Caspian Sea, deltas have concentrated on the Mississippi delta therefore delta morphology is similarly controlled by (Coleman et al., 1998; Fisk, 1961; Frazier, 1967; the low gradient of the basement over which the delta Gould, 1970; Roberts, 1997), it is logical to use it progrades. The Terek delta, in contrast, is largely as a reference point. A number of similarities exist reworked by wave action resulting in a highly destruc- between the Mississippi and the Kura deltas. (1) All tive delta environment (Mikhailov, 1997). So despite sediment is concentrated in a single channel with a the major influence of the Caspian sea-level on these limited number of outlets. (2) Both deltas build out on deltas, they all evolved differently. The general shelf their own unconsolidated sediments. (3) Present day edge setting bathymetry of the Kura delta (Fig. 1), and delta fronts are being (partly) redistributed by waves. the minor influence of waves, make the Kura delta (4) Different phases of delta development can be more comparable with other delta settings. It is there- recognized. However, some differences in the fore the better suited as a natural laboratory to test sequence of events leading to the above mentioned conceptual models of sea-level change in deltas. analogues are also recognized. Primarily, a scale dif- The early Pliocene Productive Series in Azerbaijan ference, both spatial and temporal is evident. The consist of fluvial deltaic sediments deposited in the Mississippi delta is bigger in all aspects, water and isolated South Caspian Basin by several large river sediment discharge, delta surface and delta volume systems, which were also subjected to an unstable sea- and has been at its current location for at least 2000 level regime (Hinds et al., 2004; Reynolds et al., yrs (Coleman et al., 1998), whereas the current Kura 1996). Many offshore and onshore hydrocarbon delta has switched at least 4 times during the same occurrences are in this unit (Aliyeva, 1988; Bagirov period. Secondly, the Mississippi delta started to and Lerche, 1998). The Productive Series in the develop after a major avulsion has occurred (To¨rnq- southwest of the South Caspian Basin has volcano- vist et al., 1996). Avulsions are caused by decrease of genic heavy mineral assemblage, indicating prove- the river gradient as a result of several processes that nance form the Kura River, which rains Jurassic and interact, such as subsidence, rise of floodplain lake Cenozoic volcanic deposits in the Lesser Caucasus levels or relative sea-level rise (Overeem et al., 2003). (Pashaly, 1964). Despite similarities with regards to The sequence of events in the Kura delta seems to be depositional setting of the early Pliocene Productive different: progradation starts as a result of sea-level Series, this study shows that any comparison between fall and the subsequent sea-level rise causes aggrada- the Kura delta and the Productive Series is difficult tion and eventually a switch of the delta lobe. Despite because of the differences in lithology. Except for the the differences the Kura delta could be described as a thin and narrow sand bodies in the channels and bbaby birdfootQ (Fig. 1) delta based on the similar barriers of the onshore plain, the whole late Holocene morphological development patterns as seen in the Kura delta consists of clays and silts, while the Pro- Mississippi delta. ductive Series is characterized by the presence of large R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380 377 amounts of sand (Reynolds et al., 1996). Several coastal barriers are found. Its stratigraphy reflects both reasons can be put forward for the absence of sand rapid Caspian sea-level change, and variations in in the present delta. The Kura River occupies the axis sediment output of the Kura River. Reconstruction of a very rapidly subsiding basin. The strongest sub- of the detailed stratigraphy is made difficult by the sidence in the past has occurred not close to the coast, limited resolution of the sparker data, and low recov- but ca. 100 km inland near Kurdamir (Inan et al., ery from the well samples. However the detailed 1997). Here part of the sand may be trapped before historical data, the reconstructed Caspian sea-level it reaches the coast. curve, the knowledge of the onshore cross-section and the offshore core data provide the possibility to reconstruct a stratigraphic framework for the cyclic 7. Conclusions late Holocene deposits that underlie the modern Kura delta. Depositional geometries, key surfaces, and stra- The modern Kura delta is a single-channel, river- tal patterns based on sparker data are used to define dominated delta, with some wave influence at its the architecture of the late Holocene depositional northern edge. Its main offshore Holocene sediment cycles and their relation to Caspian sea-level change. body is at least 20 m thick and consists of clays and The interpretation of the late Holocene Kura delta silts, with rare sandy shell horizons. On the surface of development can be summarised in seven stages (Fig. the onshore delta plain channel-levee sands and sandy 14A and B).

Depositonal environments modern delta (H3) Depth (m) 3 D 1860 D' A 1907 1929 1946 2001 A` 2 Delta plain Mouth Bar P. D. 1 Proximal delta front H2 (Paleo delta) Caspian 0 Sea level Fluvial Sand 1 (Levee & Channel fill) 1977 2 Caspian 3 Sea level 4 A 5 0 5 km Coverage by onshore cores (A) Coverage by offshore core- and sparker data B Data gap Breached Barrier Modern aggrading Downlap of Modern Kura delta ~-27m

? ~-32m Modern prograding TS3 delta H2 H2 N Environment Stage TS2 ~-48m Delta Plain D H3 1.5 ky TS2 Delta Front H1 Well3 D' Barrier TS3 TS1 A ~-80m Delta Plain PH Well2 H2 TS1SB1 ??? A' Delta Front H1 PH Major Accoustic Reflector

Fig. 14. (A), interpretation of the main (D-AV) onshore core section through the Kura delta. Vertical dashed lines approximate the Caspian sea- level and the delta front location at the time indicated. The delta front moves along stream constructing a progradational delta sequence during the relatively stable sea level (1800–1933) and during the sea-level fall (1933–1977). The major sea-level rise (1977–present day) can be recognized as an overlap on top of the progradational sequence near the delta front. The aggradational sequence is confined to the tip of the delta and along the southern shoreline. (B) Schematic summary of the Kura delta development, in order to illustrate all phases/stages of delta deposition and marine erosion. 378 R.M. Hoogendoorn et al. / Marine Geology 222–223 (2005) 359–380

7.1. Stage 1 (PH) when the Kura River was diverted southwards to the Qzlag˘ac¸ Bay. Pre-Holocene fluvial sedimentation (probably top of a lowstand deposits) identified by reddish soil in 7.7. Stage 7 (H3; modern delta) the delta plain sediments recovered from deep well data associated with the Mangyshlak regression based Deltaic sedimentation resumed at the present-day on depositional depth. position from the start of the 19th century onwards, depositing a series of prograding sandy to clayey 7.2. Stage 2 (TS1) bodies in the present delta plain, and a veneer of clayey and silty sediments offshore on top of the PH was followed by formation of a Transgressive last erosional discontinuity (TS3). The last 1929– Surface after the Mangyshlak lowstand, with no sedi- 2000 sea-level cycle is expressed onshore by progra- ment transported to this location by the Kura River. dation during base level fall, and aggradation due to flooding of the delta plain during sea-level rise in 7.3. Stage 3 (H1) most recent times. This single sea-level cycle can be distinguished in the cross section of Fig. 14A. Reactivation of sediment supply resulting in pro- The Kura delta evolution shows cyclic behaviour; a gradational deltaic deposition of a shallowing- progradational delta body is formed during 3 regres- upwards sequence of clays, silts and shell horizons sions at or near the present location while during deposited during the Derbent regression (before 1500 transgression the delta body probably shifts to the BP), depositional depths at the start of the regression Qzlag˘ac Bay. The resulting erosional phases at the were comparable to the present-day and estimated at a present location are good markers for the Caspian Sea maximum 42 m below GSL at the end of this stage lowstand. Therefore it can be concluded that the major (forced regressive deposits). control of the Kura delta is the rapid sea-level change of the Caspian Sea as well as the Kura River 7.4. Stage 4 (TS2) dynamics.

The absence of sediment supply and transgression, following the Derbent lowstand (maximal, ca. 42 m Acknowledgements absolute depth, 1500 yr BP), resulted in a period of marine erosion. Identified in the sparker profiles as Shell, BP, and ConocoPhilips are thanked for spon- Transgressive Surface 2 (TS2). soring this project. Part of this research was co-funded by the DUT-DIOC WATER 1.6 project. This paper is 7.5. Stage 5 (H2) part of the PhD thesis of R.M. Hoogendoorn. 210Pb analyses were carried out by ing. W. Boer associated Renewed deltaic progradation with clayey and silty with the NIOZ (Dutch Institute for Sea Research). Dr. sediments on top of the TS2 erosional discontinuity. K. van der Borg of the Utrecht University (UU) per- Sparker data shows that the prograding system gra- formed the 14C AMS analysis. Dr. A. Mitlehner, dual changes into an aggrading system, becoming micropalaeontologist from Millennia Limited, UK car- more fluvial and organic near the top of the sequence. ried out diatom analysis. Frank Wesselingh of Natur- alis determined the shell samples. K. Scholte of the 7.6. Stage 6 (TS3) Delft University of Technology (DUT) processed satellite images and assisted in the field. Furthermore A next phase of no sediment supply and trans- we would like to thank P.J. Kloosterman (y), R. Von- gression resulting in an erosive surface, possibly hof, the KMGRU, CASP and GIA for their coopera- related to a 16th century lowstand and following tion and support. B. Ibrahimov is specially thanked for transgression ending in the highstand of 200 BP. his assistance in the field. Colleagues at DUT, G.J This stage probably related to the 17th–19th century, Weltje and J, Noad helped substantially with their R.M. 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