Rapid Caspian Sea-level change and its impact on Iranian coasts

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Rapid Caspian Sea-level change and its impact on

Iranian coasts

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Rapid Caspian Sea-level change and its impact on

Iranian coasts

Proefschrift

ter verkrijging van de graad van doctor aan de Technische Universiteit Delft,

op gezag van de Rector Magnificus prof. ir. K.C.A.M. Luyben, voorzitter van het College voor Promoties,

in het openbaar te verdedigen

op 4 september 2012 om 10.00 uur

door

Ataollah

ABDOLLAHI KAKROODI

Master of Science in Physical Geography, University of Tehran,

Tehran, Iran

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Dit proefschrift is goedgekeurd door de promotor: Prof. dr. S.B. Kroonenberg Samenstelling promotiecommissie: Rector Magnificus, Prof. dr. S.B. Kroonenberg, Prof. dr. S.M. Luthi Prof. dr. S.A.G. Leroy Prof. dr. P.L. de Boer

Dr. J.E.A. Storms Dr. F.P. Wesselingh Dr. H.A.K Lahijani Prof. dr. ir. M.J.F. Stive

voorzitter

Technische Universiteit Delft, promotor Technische Universiteit Delft

Brunel University, Londen, UK Universiteit Utrecht

Technische Universiteit Delft Naturalis Biodiversity Center, leiden

Iranian National Institute for Oceanography Technische Universiteit Delft, reservelid

ISBN:

Printed in the Netherlands

Cover design by Ataollah A.Kakroodi Picture: Ataollah A.Kakroodi

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Chapter 3: Short and long-term development of the Minakaleh Spit, Southeast Caspian Sea, Iran ... 25

3.3. Holocene sea-level changes ... 29

3.4. Miankaleh spit response during the last cycle ...30

3.5.1. Ground penetrating radar data acquisition and image processing ... 31

3.5.2. Boring and sampling ... 32

3.5.3. Lithofacies ... 33

3.6. Results ... 33

3.6.1. Radar profiles and sedimentary facies ... 33

3.6.2. Lithology and sedimentary facies ... 34

3.6.3. Heavy minerals ... 36

3.7.1. Radar facies interpretation ... 37

3.7.2. Paleogeography of the Miankaleh Spit ... 38

3.8. Conclusions ... 38

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4.2. Geological setting... 44

4.4. Coastal plain development since 1850 ... 46

4.4.1. Gorgan Bay ... 47

4.4.2. Gorgan delta ...48

4.4.3. Hassan Gholi Bay ...48

4.5. Stratigraphy and paleogeography of the Holocene coastal plain ... 51

4.5.1. Outcrops and boreholes ... 52

4.5.2. Sedimentary environment ... 54

4.5.3. Radiometric dating ... 55

4.6.1. Interpretation in terms of sea-level change ... 56

4.6.2. Correlation with data from other Caspian coasts ... 57

Chapter 5: Late Pleistocene and Holocene sea-level change and coastal palaeoenvironment evolution along the Iranian Caspian shore ... 63

5.2. The Caspian Sea ... 64

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5.6. Sedimentary and biofacies record ... 74

5.6.1. Unit 1 (Depth of 27.7-25.7 m) (Late Pleistocene) ... 75

5.6.2. Unit 2 (Depth of 25.7-24 m) (Holocene) ... 77

5.6.3. Unit 3 (Depth of 24-18.75 m) ... 79 5.6.4. Unit 4 (Depth of 18.75-15.7 m) ... 79 5.6.5. Unit 5 (Depth of 15.7-12.10 m) ... 80 5.6.6. Unit 6 (Depth of 12.10-8.50 m) ... 80 5.6.7. Unit 7 (Depth of 8.50-4.95 m) ... 81 5.6.8. Unit 8 (Depth of 4.95-0 m) ... 82 5.6.8.1. (Depth of 4.95-2.5 m)... 82 5.6.8.2. (Depth of 2.5-0 m) ... 83 5.7. Modern lagoon ...84

5.8. Major and minor elements geochemistry and interpretation ... 85

5.9. Stable isotopes ... 88

5.10.1. Late Pleistocene fluctuation ... 91

5.10.2. Holocene sea-level change. ... 92

5.10.3. Comparison to other Caspian sea-level records ... 94

5.10.4. Regional and global correlations ... 96

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Chapter 6 ... 105

Appendix 1: XRD Results. ... 108

Appendix 2: ICP-ES analysis (0.5 g). ... 111

Samenvatting ... 114

Acknowledgments ... 117

Curriculum Vitae ... 119

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Chapter 1

I

NTRODUCTION: THE CASPIAN SEA

1.1. General

The coastal zone is the interface between land and water. It has become a major site for extensive and diverse economic activities and over 50% of the world population now live within 60 km of the coast (UNCED, 1993), which is still on the increase. Recent data obtained from satellite altimetry since 1992 indicate a general rise in Global Mean Sea-level (GMSL) of around 3.1 ±0.4 mm/year. There is worldwide concern for accelerated sea-level rise since the 19th_century.

The Caspian Sea is a closed basin, not connected to the world oceans, with an independent sea-level regime and a sea-sea-level at about 27 m below oceanic sea-level (BOL). The Caspian Sea has experienced much more rapid sea-level changes than the oceans: even in the 20th _{century sea-level}

has fluctuated about three metres, with a maximum rate of sea-level rise in the 1980’s up to 34 cm/year, a hundred times faster than eustatic sea-level rise in the oceans.

This is in the first place a huge environmental problem for people living near the coast. In the Caspian region, 1.6 million people live within 10 km and 3.7 million people live within 50 km from the shoreline of the Caspian Sea (CEP, Caspian Environment Program, 2002). Techniques to predict future sea-level changes are still in their infancy, and the lack of reliable projections makes human activities in the coastal zone and also offshore extremely hazardous. One of the pressing problems is that in spite of decades of hydrological and climatological research, the processes that control Caspian level are still imperfectly understood. On the other hand, rapid Caspian Sea-level change also offers some opportunities. It enables studying with a hundredfold acceleration how coasts react to changing sea-levels: the Caspian Sea presents a real physical model for the impact of oceanic sea-level rise on coasts elsewhere in the world, complementary to laboratory studies and numerical modelling. Moreover, it provides a physical model for sequence stratigraphy, and can give insight in how rapidly biota react to changing sea-level conditions. Past Caspian sea-level changes are recorded in the sedimentary sequences both onshore and offshore, and a thorough analysis of these might provide clues not only to the time scales and causes of sea-level oscillations in the Caspian Sea itself, but also to global patterns of climate change. In the

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present thesis, we focus on the impact of Caspian sea-level change on coastal systems along the Iranian Caspian shores in different time scales. Remote sensing methods and morphological analysis are used to study the impact of the 20th _{century 3-metres sea-level cycle,}

Ground-Penetrating Radar data are used to capture the sedimentary structures of coastal features developed in several centuries of sea-level change, and coring data and laboratory analyses for Late Pleistocene and Holocene time scales. Techniques applied to the core samples include sedimentary facies analysis, magnetic susceptibility, granulometry, 14_{C dating, palaeoecological}

studies (macrofauna, microfauna and pollen), major and minor elements and isotope geochemistry, and mineralogical analyses.

1.2. Sea-level changes

What does sea-level change mean?

There are different ways to define sea-level change, including eustatic sea-level change, relative sea-level change, and water depth change (Fig. 1). Eustatic sea-level is global sea-level which is based on the measurement of the distance between the sea surface and a constant datum, normally the center of the earth. Eustatic sea-level changes can occur both by changes in ocean-water volume, e.g. by storage of ocean-water in ice-caps or their melting, and by thermal expansion or contraction of sea water, and by volume changes of the ocean basins, mostly as a result of tectonics. Relative sea–level means the distance between sea surface and a local datum which can also be measured and referred by a local bench mark in or along the Caspian Sea.

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Introduction: The Caspian Sea

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As the local bench mark on the land itself can rise or fall as a result of tectonic movements, measured sea–level change is only relative, not absolute. Relative sea-level therefore, deals with local and also eustatic sea-level change. Water depth relates to the distance between sea-surface and the top of sediment of the basin which is independent of above mentioned sea- level changes.

1.3. History of the Caspian Sea

Although the Caspian Sea is a lake indeed and its level can be considered as lake-level changes, it has several aspects in common with the oceans. These include its large size, measuring 1200 km in N-S direction between 48° and 36°N, and over 326 km between 48° and 54°E; the large volume of water around 78,000 km3_{, and a great water depth up to over 1000 m, a large catchment area}

of about 3.5 million km2_{(Fig. 2) and the occurrence of severe storm surges with heights of 10 m.}

It was also once connected to the oceans, lastly as recent as the Pleistocene. As a result its water is still brackish, with a salinity of about 13 g/l, one third of that of the oceans. On the other hand there are virtually no tides (3 cm).

The Caspian Sea resembles the Black Sea and the eastern Mediterranean, both of which are also thought to be oceanic remnants of the Tethys Sea now caught up in continental collision zones (Jackson et al., 2002). Renewed convergence between the Arabian and Eurasian plates in the late Eocene–Oligocene, resulting in uplift of the Caucasus region, initiated the separation of the Black Sea and Caspian Sea Basins (Linda and Rouch, 2006). The Caspian Sea has been a closed basin since the Messinian (Jones and Simmons, 1996; Reynolds et al., 1996).

Since its isolation it has experienced dramatic sea-level changes, ranging from lowstands probably several hundreds of metres below the present one in the Pliocene (Hinds et al., 2004, Kroonenberg et al., 2005; Abdullaev, 2008) to 50 m above oceanic level (AOL) in the Last Glacial (Fig.3). Even in the Holocene the amplitude of sea-level cycles may have reached over 100 metres (Varushchenko et al., 1987, Kroonenberg et al., 1997). However, the reconstruction of former Caspian Sea-levels before the start of the instrumental record in 1850 is very complicated and hotly debated (Fig. 4). Old marine deposits have been found in the study area at elevations of more than 150 m (without considering tectonic uplift) also reported elsewhere along the Iranian coast part (Kazancı et al., 2004).

The last prominent Caspian Sea-level cycle lasted only 66 years in the 20th_{century. Sea-level}

dropped almost 3 metres down to 29 m BOL from 1929 to 1977, a period of 48 years, and rose back to its former sea-level from 1977 to 1995, in a period of just 18 years (Fig. 4).

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Fig. 2. The Caspian Sea and surrounding seas and lakes (a) and its catchment area (b).

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Fig. 4. Caspian Sea curve since 1850. Note the last cycle of Caspian Sea-level between 1929 and 1995. Its

level was relatively stable between 1850 and 1929 (a), and a recent high resolution record from radar altimetry data (b).

1.4. Objectives of this thesis

(1) Understanding the impact of rapid sea-level-changes on recent and past coastal evolution along the Iranian Caspian coast, focussing especially on the south-eastern corner of the Caspian Sea.

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Fig. 5. Maps showing the Caspian Sea in the northern part of Iran (a) study area and field sites (b) and the

southern Iranian Caspian (c).

1.5. Approach

This thesis is based on a multi-disciplinary approach outlined in fig. 6. First, remote sensing data enhanced our knowledge of recent shoreline changes in the last cycle of the Caspian Sea along the southern Caspian Sea coast. Second, most attention went to the eastern part of the Iranian coast which experienced several kilometers seaward and landward migration in the last cycle. Field observation and outcrop gave us some ideas to select suitable areas for boring and detailed studies. By using a mobile drilling machine, nine cores have been taken to study former sea-level

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changes by using different techniques shown in Fig. 6. The cores have been taken both onshore and near shore up to around 30 m deep, ranging in age up to Late Pleistocene.

Fig. 6. Flow diagram of the main steps in this thesis. 1.6. Thesis outline

Chapter 2 focusses on shoreline shifts along the entire Iranian Caspian coast in the 20th _{century as}

a result of the last three-metre sea-level cycle, based on LANDSAT imagery as well as older maps.

Chapter 3 studies the fate of the prominent 60 km long Miankaleh spit in the south-eastern corner of the Caspian Sea during the Late Holocene 2600 BP and Little Ice Age highstands and the intervening lowstand, as well as during the last 20th_{century sea-level cycle, using Ground}

Penetrating Radar data and core analyses.

Chapter 4 shows the result of morphological analysis, coring and dating of the Gomishan area in the west-facing part of the Iranian Caspian coast, especially of the delta of the Gorgan River and

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the Hassan Gholi lagoon, which experienced considerable landward and seaward shifts during the 20th_{century cycle and the Late Holocene.}

Chapter 5 focusses on a long core to study Late Pleistocene to Holocene palaeoenvironments, including vegetation history, and other biota. An updated Caspian Sea-level curve from Late Pleistocene to Holocene is presented in this chapter.

Chapter 6 covers the main conclusions of this thesis.

1.7. References

1. Abdullayev, N., Rley, G., Bowman, A., 2008. Petroleum Geology & Hydrocarbon Potential of Caspian and Black Sea Regions, October 2008, Baku, Azerbaijan.

2. CEP. Caspian Environment Program. National Coastal Profile, I.R. IRAN, 2002.

3. Jackson, J., Priestley, K., Allen, M., Berberian, M., 2002. Active tectonic of the south Caspian basin. Geophys. J. Int. 148, 214– 245.

4. Jones, R.W., Simmons, M.D., 1996. A review of the stratigraphy of Eastern Paratethys (Oligocene-Holocene). Bull. Nat. Hist. Mus. London (Geol.) 52 (1), 25-49.

5. Hinds, D., Aliyev, E., Allen, M.B., Davies, C.E., Kroonenberg, S.B., Simmons, M.D., Vincent, S.J., 2004, Sedimentation in a discharge dominated fluvial–lacustrine system: the Neogene Productive Series of the South Caspian Basin: Marine and Petroleum Geology, v. 21, p. 613-638.

6. Kazanci, N., Gulbabazade, T., Leroy, S.A.G., Ileri, O., 2004. Sedimentology and environmental characteristics at the Guilan-Mazandaran plain, northern Iran; influence of long-and short term Caspian level fluctuations on geomorphology. Journal of Marine Systems 46, 154-168.

7. Kroonenberg, S.B., Rusakov, G.V., Svitoch, A.A., 1997. The wandering of the Volga delta: a response to rapid Caspian sea-level changes. Sediment. Geol. 107, 189-209.

8. Kroonenberg, S.B., Alekseevski, N.I., Aliyeva, E., Allen, M.B., Aybulatov, D.N., Baba-Zadeh, A., Badyukova, E.N., Davies, C.E., Hinds, D.J., Hoogendoorn, R.M., Huseynov, D., Ibrahimov, B., Mamedov, P., Overeem, I, Rusakov, G.V., Suleymanova, S., Svitoch, A.A., Vincent, S.J., 2005. Two deltas, two basins, one river, one sea: The modern Volga delta as an analogue of the Neogene Productive Series, South Caspian Basin. In SEPM memoir on deltaic sedimentation, p. 231-256.

9. Smith-Rouch, L.S., 2006, Oligocene–Miocene Maykop/Diatom Total Petroleum System of the South Caspian Basin Province, Azerbaijan, Iran, and Turkmenistan: U.S. Geological Survey Bulletin 2201-I, 27 p.

10. Reynolds, A.D., Simmons, M.D., Bowman, M.B.J., Henton, J.,Brayshaw, A.C., Ali-Zade, A.A., Guliyev, I.S., Suleymanova,S.F., Ateava, E.Z., Mamedova, D.N., Koshkarly, R.O., 1996.Implications of outcrop geology for reservoirs in the Neogene Productive Series, Apsheron Peninsula, Azerbaijan. AAPG Bull. 82 (1), 25-49.

11. (UNCED)Development, 3-14 June 1992, Rio de Janeiro, Brazil. United Nations Dept. of Public Information, New York, NY 1993.

12. Varushchenko, S.I., A.N. Varushchenko and R.K. Klige. 1987 Regime change of the Caspian Sea and enclosed water bodies in paleotime. Moscow, Nauka, 240 pp (in Russian).

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Chapter 2 is based on: Kakroodi, A.A., Kroonenberg, S.B. (submitted) Shoreline response to rapid 20th_{century sea-level change along}

the Iranian Caspian Coast. The Journal of Coastal Research.

Chapter 2

S

HORELINE RESPONSE TO RAPID 20

th

CENTURY SEA-LEVEL CHANGE ALONG THE

IRANIAN CASPIAN COAST

Abstract

The Caspian Sea, the largest lake in the world, is characterized by rapid sea-level changes. This provides a real physical model of coastal response to rapid sea-level change in a period of just a few years, which may take a millennium along oceanic coasts. Between 1929 and 1995 Caspian Sea-level experienced the last cycle with a range of ± 3 m. This caused disastrous effects along the coast and destroyed many buildings, roads, farms and other human properties. During the preceding 48 years of sea-level fall large area of the sea bottom emerged, which was then used for the development of residential zones. That had to be abandoned when sea-level rose by almost 3 m in a period of 18 years. We have calculated total shoreline shifts in 22 littoral cells using LANDSAT data, each cell containing 3 transects over a 3 km distance. Both landward and seaward shifts occur during rapid sea-level rise between 1977 and 2001.

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2.1. Introduction

The coastal zone is defined as an interactive environment between two systems, marine and land, interacting (eroding and accreting) in response to external factors, both natural and anthropogenic in origin, and acting on a whole range of time scales (French, 2001). The dominant process along the Caspian Sea coast, however, is strongly related to sea-level change. Based on tide gauge record, Caspian Sea-level was relatively stable between 1850 and 1929 and dropped around 3 m between 1929 and 1977 in a period of 48 years from 25.5 to 29.04 BOL. It rose back suddenly between 1977 and 1995 (Fig. 1). Within the Holocene, Caspian sea-level experienced many cycles, and the latest two major highstands occurred at ca. 2600 cal. yr BP and during the Little Ice Age (Kroonenberg et al., 2007; Kakroodi et al., 2012).

Fig. 1. Sea-level curve since 1850. Source: National Iranian Oil Company, compiled by A. Jafari.

Generally, rapid sea-level fall results in seaward progradation of the coastal zone, enticing people to use the emerging sea bottom for residential and industrial development. Rapid sea-level rise results in passive drowning on gentle-gradient coasts, and backstepping accompanied by erosion on steeper coasts (Kaplin and Selivanov, 1995; Storms and Kroonenberg 2007). The morphology of the eastern Iranian Caspian coast changed completely during the last sea-level cycle between 1929 and 1995 (Kakroodi et al., 2012). Existence of an extensive data base on shoreline changes, as well as of tide-gauge data from the middle of the 19th_{century, makes the Caspian sea an}

excellent “natural laboratory“ for the study of the response of oceanic coasts to future rapid water-level changes of one meter or more ( Kaplin et al., 1995).

The sea-level cycles in this century probably reflect secular variations in precipitation in the Volga drainage basin, which themselves are related to systematic deviations in the jet-system–related circulation patterns (Rodionov, 1994; Arpe and Leroy, 2007). Recent satellite altimetry data such

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Shoreline response to rapid 20th_{century sea-level change}

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as TOPEX, JASON and OSTM show that other lakes near the Caspian Sea basin such as Lake Baikal, Lake Urmia, Lake Baikal and Lake Aral experienced also a highstand in 1995, a minor sea-level rise in 2005 and a sea-sea-level fall in 2011 onwards. This implies that lake sea-levels are influenced by a regional climate (Fig. 2).

Fig. 2. Height variation of Caspian Sea-level and surrounding lakes based on TOPEX, JASON and OSTM

data. All have a highstand in 1995, a minor sea-level rise in 2005 and a minor fall in 2012 like the Caspian Sea.

In the present work, the southern Caspian shoreline has been investigated by using LANDSAT data and field observation. We calculated the total shoreline shift along the Iranian Caspian coast (Fig. 3) during the last phase of sea-level rise between 1977 and 2001.

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2.2. Study area

The study area (Fig. 3) is one of the most populated area along the Caspian coast with a population density of more than 270 persons per km2_{. Statistics show that 1.6 million people live}

within 10 km from the shoreline and 3.7 million people live within 50 km from the shoreline (Pak and Farajzadeh, 2007). Whereas the western and middle parts of the southern Caspian coast are well developed, the eastern and north-eastern coasts are less so. The Iranian Caspian coast has a sub-tropical climate and a rainfall pattern that shows a strong gradient from 1900 mm in Anzali in the western part to around 196 mm in the south-eastern corner of the Caspian Sea (Pak and Farajzadeh, 2007).

Fig. 3. The Caspian Sea and location of the study area (a) and 22 littoral cells along the southern Caspian

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The southern Caspian coast is around 750 km long. Its beach contains mostly sand to sandy gravel and in some parts pebbles and cobbles, depending upon the onshore and offshore slope.

While the south-western and southern Caspian shelves in Iran have steep offshore slopes and corresponding steep coasts, the offshore gradient in the south-eastern Caspian is gentle, which correlates well with the gentle gradient onshore. About 40 million tons of sediment is transported to the coast by 61 rivers, which almost all originate in the northern flank of the Alborz Mountains. Only the Sefid Rud River in the west and the Gorgan Rud River in the east begin their courses from the Zagros and Kopet Dagh Mountains, respectively (Lahijani et al., 2008).

As tides are negligible in the Caspian Sea, waves, marine currents, coastal nearshore morphology and rapid sea-level change are the most important factors that control the coastal morphology (Kakroodi et al., 2012).

2.3. Materials and methods

This study used LANDSAT satellite data from the whole southern Iranian coast (Table 1) in conjunction with field observations to detect the shoreline shifts during the rapid sea-level rise of the Caspian Sea between 1975 and 2001. There are no data available during sea-level fall between 1929 and 1977 except an old map in the eastern part and some aerial photographs in the Sefid Rud delta area. LANDSAT data are available via http://www.landcover.org/data.

Table 1. LANDSAT data ID used in the present study.

MSS TM ETM p176r34_2m19750407 p163r34_5t19870716 p163r034_7t20010730_z40 p176r35_2m19770713 p164r35_4t19880919 p164r035_7t20000718_z39 p178r34_2m19780710 p165r34_4t19890508 p165r034_7t20000725_z39 p179r34_2m19750727 p166r34_4t19890702 p166r034_7t20000630_z39 p179r33_2m19750410 p167r33_5t19870610 p167r033_7t20000605_z39

Topographic maps at the scale of 1/25000 were used for geocoding satellite data. The southern Caspian Sea coast has been subdivided into 22 littoral cells and each cell has three transects (except LC19 with two transects) over a 3 km distance (Fig. 6). Therefore, nearly a full cover of the study area was selected (Fig. 3). Shoreline shifts were extracted in ENVIE 4.5 from band 4 of LANDSAT data and edge enhancement technique (High Pass Filter with an Image Add Back 80 %) was applied (Maiti and Bhattacharya, 2008). In total 5 scenes of MSS, 5 scenes of TM and 5 scenes of ETM of NIR bands have been used (Table 1). The near infrared band of ETM imagery was first selected and corrected by using the 1/25000 topographic map and resampled to the 60 m pixel size. Thus, all LANDSAT data were georeferenced through image-to- image registration with the same pixel size. Root Mean Square Error (RMSE) ranged between 0.05 and 0.1 pixel

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showing 3 m to 6 m error in georeferencing. Finally, the shoreline was digitized manually and three vector layers were made, indicating total shoreline shifts between 1975 and 2001. The final outputs show the total estimation for shoreline change during rapid Caspian Sea-level rise (Fig. 4).

There was no bathymetry map available but the geological map associated with bathymetry give a general offshore slope which can be measured via: Slope degree = arctan (rise/run).

Fig. 4. Flowchart of the present work stages. 2.4. Results

2.4.1. General coastal aspects

Fig.5 illustrates the different morphology of the southern Iranian coasts in 2001 between the shoreline around 27 m BOL and the contourline of 0 m. Typical morphological features include spit-lagoon, barrier-lagoon and deltaic coasts. Anzali lagoon and the Sefid Rud delta (Fig. 5, LC4

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and LC5) are predominant features in the western part of the Iranian coast. The Sefid Rud delta provides 70٪ of total sediment supply to the Caspian Sea along the Iranian coast (Lahijani et al., 2008). During sea-level fall, the delta is largely a river-dominated delta, during sea-level rise a wave-dominated delta. The Miankaleh spit is around 60 km (LC16, 17) and is separated from the land by the Gorgan bay (LC18, 19, 20). There are no data from Miankaleh available in 1995 but the satellite data from 2001 show the spit was breached and disintegrated into several islands, and the spit lost half of its width (Kakroodi et al., 2012).

Fig. 5. Different coastal types along the southern Caspian coast derived from SRTM. The arrows indicate

2001 shoreline. Note the distance between the 2001 shoreline and counterline of 0 m. LC1: Steep slope; LC4: gentle slope with barrier-lagoon system; LC5: Delta; LC11: Very steep slope; LC20; gentle slope with spit-lagoon; LC22: very low angle coast with barrier-lagoon system.

Another lagoon, Hassan Gholi Bay, was a dominant feature in the study area until 1890, but it fell dry during the major drop in sea-level (Kakroodi et al., 2012). During rapid sea-level rise after 1977 another lagoon formed at a more seaward position than the previous ones (LC22).

Between 1987 and 1995, the Caspian Sea reached the maximum level and its coast experienced much erosion and landward shift.

2.4.2. Total shoreline shift between 1975 and 2001

The 1975 LANDSAT MSS data are almost contemporaneous with the 1977 lowstand. TM and ETM data are contemporaneous to Caspian sea-level rise and the highest record in 1995 (Fig. 1). Table 2 presents the total shoreline shifts on the southern Iranian coast during rapid sea-level rise

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extracted from LANDSAT data. It also contains all littoral cells with at least 3 transects of each littoral cell. Fig. 6 indicates shoreline shift within LC22.

Fig. 6. Shoreline shift within LC 22.

Negative value indicates seaward shift. The first column refers to MSS and TM images taken between 1975 and 1989, the second column refer to the TM and ETM images taken in 1987 and 2001 (Table 2). Table 3 presents general coastal aspects along the southern Iranian Caspian and indicates different coastal types along the southern Caspian coast.

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Table 2. Shoreline shifts extracted from LANDSAT data between 1975 and 2001 along the Iranian coast.

_{Shoreline shift (m/y)} _{Shoreline shift (m/y)}

Tr. No 1975-1987 1987-2000 Sum Tr. No 1975-1987 1987-2000 Sum 1 510 60 570 1 180 255 435 LC1 2 123 285 408 LC2 2 150 120 270 3 270 90 360 3 120 75 195 Mean 446 300 1975-1989 1989-2000 1975-1989 1989-2000 1 87 138 225 1 128 30 158 LC3 2 63 120 183 LC4 2 33 91 124 3 96 138 234 3 -42 105 63 Mean 214 115 1978-1989 1989-2000 1978-1989 1989-2000 1 -225 90 -135 1 87 100 187 LC5 2 -45 -33 -78 LC6 2 138 349 487 3 15 33 48 3 -130 0 -130 Mean -55 181 1 54 47 101 1 75 87 162 LC7 2 47 33 80 LC8 2 75 89 164 3 -15 47 32 3 75 0 75 Mean 71 133.6 1 31 33 64 1 70 61 131 LC9 2 27 37 64 LC10 2 48 31 79 3 -42 21 -21 3 -17 -6 -23 Mean 35.6 62.3 1977-1988 1988-2000 1977-1988 1988-2000 1 − 38 38 1 67 30 97 LC11 2 − 52 52 LC12 2 90 75 165 3 − 40 40 3 45 94 139 Mean 43.3 133.6 1 124 134 258 1 171 84 255 LC13 2 138 91 229 LC14 2 76 135 211 3 200 109 309 3 190 62 252 Mean 265.3 239.3 1975-1987 1987-2001 1975-1987 1987-2001 1 45 60 105 1 -61 -225 -286 LC15 2 -33 90 57 LC16 2 -45 270 225 3 -75 135 60 3 85 156 241 Mean 74 60 1 1080 150 1230 1 90 50 140 LC17 2 765 1260 2025 LC18 2 75 152 227 3 2040 315 2355 3 75 180 255 Mean 1870 207.3 LC19 1 19320 2820 22140 1 210 105 315 2 20690 2590 23280 LC20 2 330 360 690 Mean 22710 3 105 195 300 Mean 435 1 195 750 945 1 3400 644 4044 LC21 2 390 285 675 LC22 2 3700 1760 5460 3 585 240 825 3 4096 1820 5916 Mean 815 5140

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Table 3. Field observation of coastal aspects of littoral cells in 2008. Slope values within littoral cell is

between present shoreline and 7 km offshore for all transects (in degrees).

LC Coastal aspect

LC. 1, 2 Beach-sand, small berm, back shore depression, washover and drowned trees. LC. 3 Beach-pebble, cobble, drowned building and trees.

LC. 4 Beach-sand, strong sand progradation, low transgression.

LC. 5 Beach-sand, strong sand progradation, delta influence, sea ward shift during sea-level rise. LC. 6 Old delta area, strong landward shift, seaward shift, drowned building and protective wall,

shoreline bend.

LC. 7 Beach-sand, strong sand progradation, seaward shift during sea-level rise. LC. 8 Narrow beach-sand, drowned building and tree, steep slope, protective wall. LC. 9 Pebble and cobble coast, erosional coast, 0.22°.

LC. 10, 11, 12 Pebble and cobble coast, deep slope, erosional coast, protective wall, 0.32°. LC. 13, 14, 15 Beach-sand, strong sand progradation, aeolian deposit.

LC. 16 17 Beach-sand, spit-lagoon, strong accretion and erosion, anthropogenic impact, 0.11°. LC. 17 Beach-sand, spit-lagoon extreme erosion, end of spit and trapping sediments. LC. 18 Beach-sand, spit-lagoon, coarse sand, near the narrow channel connected the sea. LC. 19 Lagoon, muddy deposits, maximum transgression drowned road and farms, gentle slope. LC. 20 Lagoon, muddy deposits, anthropogenic impact.

LC. 21 Gentle slope, muddy deposits, strong landward shift, drowned residential zone and protective wall.

LC. 22 Lagoon, passive wave circumstance, muddy deposits, strong landward shift, drowned farms and roads, gentle slope both offshore and onshore, 0.05°.

2.5. Discussion

2.5.1. Shoreline shifts during rapid sea-level fall between 1929 and 1977

There are no data available during the rapid sea-level fall between 1929-1977. The only available data are an old map from 1890 covering the eastern part and aerial photographs from 1955 covering the Sefid Rud delta area. According to Kaplin et al. (1995), and Ignatov et al. (1993), the rate of regression during rapid sea-level fall ranged 60–100, 150-200 m/year in the northeast and north-western Caspian Sea, and 700-800 m/year in in Komsomoletz Bay in the north respectively, mainly in lagoonal environments. During seaward shift, roads and various industrial and residential structures were built on the former sea floor (Kaplin et al., 1995).

Based on MSS data from 1977 and an old map from 1890, three islands of the Miankaleh spit were connected by longshore currents during sea-level fall, and the spit extended eastwards at a rate of 40-110 m/year towards east (LC17). The Gorgan delta prograded around 85 m/year and 555-640 m/year in the east of the Gorgan bay along the Iranian mainland (Kakroodi et al., 2012). Between 1955 and 1977, the level of the Caspian Sea dropped around 70 cm and based on aerial photographs from 1955 the Sefid Rud delta prograded around 57 m/year. The real seaward shift

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from 1929 is not clear but if we suppose the barrier complex belonged to 1929 shoreline (Fig. 7), it ranged around 120 m/year.

Fig. 7. The Sefid Rud delta in 1955 during the rapid sea-level fall. It is a river dominated delta with some

wave influence at western part of delta.

2.5.2. Shoreline shifts during rapid Sea-level rise between 1977 and 2001

Unlike sea-level fall, the rapid sea-level rise has been well recorded by LANDSAT data since 1977. Fig. 8 presents total shoreline shifts within LCs during rapid sea-level rise between 1975 and 2001 along the Southern Caspian coast.

Fig. 8. Mean shoreline shift between 1975 and 2001 for each cell between LC1 and LC23. LC19 has only two

transects, others have three transects. See Fig. 1 for location. Both landward and seaward shoreline shifts occurred during rapid sea-level rise.

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2.5.3. Seaward shift during rapid sea-level rise

The seaward shift during sea-level rise occurred in the areas with high sediment supply and also areas influenced by anthropogenic activities. Seaward shifts during rapid sea-level rise have been observed in LC5 (Tr. 1, 2), 6 (Tr. 3), 9 (Tr. 3), 10 (Tr. 3) and 16 (Tr. 1). Progradation in the barrier-lagoon and delta environments between LC5 and LC6 is mainly due to sediment supply of the Sefid Rud delta and nearby rivers (Fig. 9).

Fig. 9. Coastal progradation near the biggest river (Sefid Rud) along the Iranian coast in LC5.

The Farahabad and Miankaleh coasts are strongly interfered by human activities at least over the past 40 years. They show both accretion and erosion simultaneously as a result of the anthropogenic effects. Whereas main accretion of sand occurred in the direction of lateral sediment transport particularly on the perpendicular obstruction of coastal zones like ports, extreme erosion acted on the other side (LC16).

2.5.4. Landward shift during rapid sea-level rise

There is a general increase of landward shift from LC1 to LC23, from the western to the eastern Iranian Caspian coast.

The coast between LC1 and LC3 is characterized by small elongated barrier–lagoon systems and the distance between contour line 0 and present shoreline is short (Fig. 5). The mean rate of landward shift in LC1, LC2 and LC3 ranges from 8.5 to 17.7 m/year. Many trees and some buildings were drowned in these areas (Fig. 10).

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Fig. 10. Rapid landward shift in LC1 as shown by abundant tree stumps within the sea.

The mean landward shift in LC4 indicates a lower rate than the previous cells. It is around 4.6 m/year. The only landward shift in LC5 occurs in Tr. 3 around 2.2 m/year. It seems there is a balance between the rate of landward shift and sediment supply mainly form the Sefid Rud River and nearby rivers. The landward shift is limited to a few meter per year due to high sediment input.

LC6 (Tr.1, 2) is located in a coastal bend in the old Sefid Rud delta area. The mean landward shift is high and reached 16 m/year by erosion of the unconsolidated sediments deposited by Sefid Rud River.

The landward shift is 3.3 m/year in LC7 showing a lower rate than the LC6. Its coast is characterized by sand progradation and high sediment supply as accrued in LC5 but at a lower value.

Erosion along the coast during sea-level rise is particularly visible between LC8 and LC12, due to the steep slope. The distance of the two contourlines in LC11 is short, and LC10 shows the maximum slope along the whole southern Caspian coast (Fig. 5). Many buildings and trees were drowned in these areas, particularly in LC8 (Fig. 11), although the main rate of landward shift is low. The mean landward shifts between LC8 and LC12 range from 1.7 to 6.3 m/year.

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Fig. 11. Drowned buildings and roots in LC8.

From west to east, the amount of cobbles, pebbles and coarse sand decreases while sand increases eastwards. From LC12 eastwards, the coastal plain becomes wider and the coast receives sand via predominant eastward longshore transportation, leading locally to spit-or barrier-lagoon environments (Kakroodi et al., 2012). These areas, from LC13 to LC15, show stronger landward shifts than the previous cells, up to 12 m/year in LC113.

A long spit starts at LC16 to the east and ends in Tr. 4 at LC17. The amount of mean landward shift increases eastwards, reaching 71.2 m/year in LC17. LC18, 19 and 20 are located at the mainland side of Gorgan Bay and experienced extreme landward shift due to growth of the lagoon. While LC18, just opposite the seaward spit, shows lower landward shift (7.9 m/year) than LC17, LC19 shows extreme landward shifts over the whole LCs. A large area emerged during sea-level fall from 1929 to 1977 and many roads and farms have been constructed on the newly emerged sea bottom. During sea-level rise most of them drowned. The mean rate of landward shift at the eastern sides of Gorgan bay was around 865 m/year in LC19 (Tr. 1). LC20 indicates a lower average value than LC19 and reached 16.6 m/year. LC21 is located in the Gorgan delta area and exhibits a different behaviour than the Sefid Rud delta. While the Sefid Rud delta experienced also seaward shift during rapid sea-level rise, the Gorgan delta area experienced high landward shifts and one residential zone (Chopaghli) near the delta totally drowned. The amount of landward shift reached 31 m/year. The west-facing coast in the southern corner of the Caspian

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Sea is also a low angle coast which developed lagoon-barrier systems during rapid sea-level rise. Here a shallow S-N stretching lagoon has been formed and the mean landward shift was 195.8 m/year.

2.6. Conclusions

Multi-temporal LANDSAT images have shown to be a powerful tool to study recent shoreline changes as result of the last sea-level cycle of the Caspian Sea between 1929 and 2001.

While large parts of especially the low-angle coasts emerged during sea-level fall between 1929 and 2001, rapid sea-level rise between 1977 and 1995 led to both landward and seaward shoreline shifts. Maximum landward shifts of up to over 1.7 km/year during sea-level rise have been observed in low angle coasts, mostly in lagoon-barrier environments. Seaward shoreline shifts in spite of 3 meters of sea-level rise occurs especially in delta areas where there is enough sediment supply to compensate the increasing accommodation space. Our data show that, the coastline is influenced everywhere, apart from the onshore and offshore slope, also by other local factors such as sediment supply, wave energy, lateral sedimentation transport and other coastal morphology factors. By including previous results (Kaplin et al., 1995) the ideal two-dimensional coastal profiles such as postulated by Bruun rule and other hypotheses have to develop into three-dimensional models (Storms et al., 2002, Geleynse et al., 2011).

2.7. References

1. Arpe, K., Leroy, S.A.G., 2007. The Caspian Sea-level forced by the atmospheric circulation, 964 as observed and modelled. Quaternary International 173 (174), 144-152.

2. French, P.W., Coastal defence: processes, problem, and solution. 2001. Routledge, London, UK, 366p.

3. Geleynse, N, Storms, JEA, Walstra, DJR, Jagers, HRA & Stive, MJF (2011). Controls on river delta formation; insights from numerical modelling. Earth and Planetary Science Letters, 302(1-2), 217-226. (TUD).

4. Ignatov, E.I., Kaplin, P.A., Lukyanova, S.A., Solovyova, G.D., 1993. Influence of the recent transgression of the Caspian Sea on its coastal dynamics. J. Coastal Res. 9 (1), 104-111.

5. Kakroodi, A.A., Kroonenberg, S.B., Hoogendoorn, R.M., Mohammadkhani, H., Yamani, M., Ghassemi, M.R., Lahijani, H.A.K., 2011. Rapid Holocene sea-level changes along the Iranian Caspian coast. Quaternary International 263, 93-103.

6. Kaplin, P.A., Selivanov, A.O., 1995. Recent coastal evolution of the Caspian Sea as a natural model for coastal response to the possible acceleration of global sea-level rise. Marine Geology 124, 171-178.

7. Kroonenberg, S.B., Abdurakhmanov, G.M., Badyukova, E.N., van der Borg, K., Kalashnikov, A., Kasimov, N.S., Rychagov, G.I., Svitoch, A.A., Vonhof, H.B., Wesselingh, F.P., 2007. Solar-forced 2600 BP and Little Ice Age highstands of the Caspian Sea. Quaternary International 173-174, 137-143.

8. Lahijani, H., Tavakoli, V., Amini A., 2008, River Mouth Configuration in South Caspian Coast, Iran, Environmental Sciences, vol. 5, no. 2, pp. 65-86.

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9. Maiti, S., Bhattacharya, A.K., 2008. Shoreline change analysis and its application to prediction: A remote sensing and statistics based approach. Marine Geology 04265.

10. Pak, A., Frajzadeh, M., 2007. Iran’s Integrated Coastal Management plan: Persian Gulf, Oman Sea, and southern Caspian Sea coastlines. Ocean & Coastal Management 50, 754–773.

11. Rodionov, S.N., 1994. Global and Regional Climate Interaction: The Caspian Sea Experience. Water Science and Technology Library, vol. 11. Kluwer Academic Press, Baton Rouge, 241pp.

12. Storms, J.E.A., Kroonenberg, S.B., 2007. The Impact of Rapid Sea-level Changes on Recent Azerbaijan Beach Ridges. Journal of Coastal Research 23(2), 521-527.

13. Storms, J.E.A., G.J. Weltje, J.J. van Dijke, C.R. Geel & S.B. Kroonenberg 2002. Process-response modelling of wave-dominated coastal systems: simulating evolution and stratigraphy on geological timescales. J. Sed. Research 72, 226-239.

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Chapter 3 is based on: Kakroodi, A.A., Kroonenberg, S.B (submitted). Short and long-term development of the Miankaleh spit, Southeast Caspian Sea, Iran. The Journal of Coastal Research.

Chapter 3

S

HORT AND LONG-TERM DEVELOPMENT

OF THE MIANKALEH SPIT, SOUTHEAST

CASPIAN SEA, IRAN

Abstract

The development of the 60 km long Miankaleh Spit in the south-eastern corner of the Caspian Sea has been studied in two different time scales.

At the start of the 20th_{century 3-m sea-level cycle the spit already existed, but it emerged}

prominently during the lowstand in the late 1970-ies, and drowned and fell apart into several islands during the following highstand that culminated in 1995.

The analysis of GPR data, core data and sedimentological analyses (grain size, biofacies, carbonate content, heavy mineral and magnetic susceptibility) show that the Miankaleh spit and the Gorgan Bay did not yet exist during the well-known 2600-2300 cal. yr BP highstand, and at that time waves and longshore currents deposited barrier systems along the mainland coast. During the lowstand, deltas from rivers draining the eastern Alborz Mountains extended much more westwards than at present. Only during the last major highstand in the Little Ice Age the present-day Miankaleh Spit was formed by eastwards progradation caused by strong longshore currents.

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3.1. Introduction

Rapid sea-level changes in the Caspian Sea offer an excellent opportunity to study coastal evolution on human time scale (Kaplin et al., 1995; Kroonenberg et al., 1997; Hoogendoorn et al., 2005; Leroy et al., 2007; Kakroodi et al., 2012). Sandy beach and lagoon-barrier systems started to develop along Caspian coasts when sea-level rose around 10,500 cal. yr BP, after a deep early-Holocene lowstand. These coastal systems advanced landward until another lowstand of around 7700 cal. yr BP (Kakroodi et al., chapter 5). Coastal morphology reacted rapidly to subsequent fluctuations of the Caspian Sea. Previous Holocene highstands reached levels up to around 22 below oceanic level (BOL), well above the present level around 27 BOL (Kakroodi et al., 2012). Southern Caspian coasts can be generally subdivided into erosional and accretionary coasts. In the south-eastern part of the Caspian Sea the predominant feature is the Miankaleh Spit with a large lagoon behind it, the Gorgan Bay. Both the spit and the Gorgan bay morphology are strongly controlled by rapid sea-level changes (Kakroodi et al., 2012). During rapid sea-level fall in the last sea-level cycle between 1929 and 1995 (Fig. 1), the Miankaleh Spit grew eastward and increased both in length and width until the 1977 lowstand, while Gorgan Bay decreased in size considerably. During the subsequent 3-metres sea-level rise from 1977 to 1995, Miankaleh Spit was severely eroded and decreased in size, and was breached into several parts while Gorgan Bay behind the spit increased considerably.

Fig. 1. Caspian Sea curve from 1850 to 2000 based on tide gauge (a) and recent altimetry record of Caspian

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Short and Long-term development of the Miankaleh Spit

27

A second lagoon, in the N-S oriented part of the south-eastern corner of the Caspian Sea, the Hassan Gholi Bay in the northern part of the delta of the Gorgan River, fell dry during the last sea-level fall, and completely emerged (Kakroodi et al., 2012), whereas the Gorgan delta itself prograded rapidly at the rate of 85 m/year. During the 18 years of rapid sea-level rise between 1977 and 1995, a new shallow lagoon formed at a more seaward position than the old one, while the Gorgan delta partly drowned and retrograded at a rate of around 140 m/year (Kakroodi et al., 2012). What would be the reaction of the spit in longer time scales, as Caspian sea-level experienced many cycles in the Holocene? (Kakroodi et al., 2012). Is there any evidence of past higher amplitude sea-level changes in the stratigraphy of the spit? Identifying major events within the spit may provide valuable information about its long term response to sea-level change. We will examine these questions by using ground penetrating radar (GPR) and sediment cores.

3.2. Study area

The study area (Fig. 2) is located in the south-eastern part of the Iranian Caspian coast.

This coastal area includes spits, barrier-lagoons and deltaic environments. Generally, during rapid sea-level rise, the barrier-lagoon systems shift landward and their sizes depend upon the offshore and onshore slopes. During rapid sea-level fall lagoons dry out if there is no river inflow to feed them and if the coastal climate is arid or semi-arid. This is particularly the case along the south-eastern Caspian coast. Monthly precipitation decreases rapidly from west to east along the Iranian Caspian coast, from around 100 to 25 mm, averaged over Jan 1951 to Jan 2004 (Fig. 3a). A wind-rose of 10 years derived from Amirabad Buoy weather data indicates most wind coming from N-W to S-W which steers the predominant longshore current direction (Fig. 3b).

The principal mountain belts surrounding the South Caspian Basin are the eastern part of the Greater Caucasus, the Talesh, Alborz and Kopet Dagh (Jackson et al., 2002). Around 130 rivers flow from these mountains to the Caspian Sea (Rodionov, 1994) and transport clastic sediments to the coast. In Iran, the most important sediment suppliers are the Sefidrud and Gorgan Rivers which have formed prominent deltas. The Tajan River and Neka River are the most important rivers in the western part of the study area and Qareh Su River and Gorgan River in the eastern part (Fig. 2a). The sediments are eventually distributed along the shoreline by waves and longshore currents. In the southern Caspian the current is mostly from west to east (Lahijani et al., 2009; Kakroodi et al., 2012).

The coastal plain consists of Quaternary deposits mainly of from fluvial, eolian and marine origin. There is also another source of sediments is produced directly from mud volcanos that are found at the north-eastern Iranian coast (Kakroodi et al., 2012).

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Fig. 2. The Caspian Sea with the studied area (a). Part of Miankaleh spit (Ashoradeh) with profile of GPR

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Fig. 3. Averaged monthly precipitation over Jan 1951 to Jan 2004 along the southern Caspian Sea plotted

through website: http://www.esrl.noaa.gov (a) and rose diagram derived from Amirabad port Buoy over 10 years (b).

3.3. Holocene sea-level changes

The first Holocene Caspian curve was published by Rychagov (1977, 1997) and later revised by Hoogendoorn et al. (2005), Kroonenberg et al. (2007), Kakroodi et al. (2012), on the basis of data from Dagestan and the Volga delta in Russia, the Kura delta in Azerbaijan, and the Golestan area in Iran. Rapid sea-level rise occurred in early Holocene between 10,500 and 7700 cal. yr BP (Kakroodi et al., chapter 5), followed by a deep regression. From 3200 cal. yr BP onward at least five Holocene sea-level cycles have been identified in the very shallow south-eastern Caspian basin (Kakroodi et al., chapter 5). A highstand of at least 22 m BOL was reached around 2600 cal. yr BP, continuing to around 2300 cal. yr BP (Kroonenberg et al., 2007; Kakroodi et al., 2012) (Fig. 4).

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Fig. 4. The Bagho outcrop dated at 2400 cal. yr BP. See Fig. 2a for location.

Sea-level fell after that until the Derbent lowstand at 32 m or even 48 m BOL around 1500 cal. yr BP reported in different absolute levels (Hoogendoorn, et al., 2005; Kakroodi et al., chapter 5). The subsequent highstand at ca. 24 m BOL was probably synchronous with the Little Ice Age (Kroonenberg et al., 2007; Kakroodi et al., 2012). After 1929 sea-level fell until the lowstand in 1977 at 29 BOL, but it rose back rapidly up to 1995 as a result of increased Volga river discharge. Caspian Sea-level during this last cycle correlates well with lake levels elsewhere in the Caspian region (Kakroodi et al., 2012). The present sea-level is around 27 BOL, with a falling trend from 2011 onwards as a result of a European Russia drought in 2010 (Arpe et al., 2012). Seasonal variations in Volga influx give rise to annual variations in water level of 30-40 cm.

3.4. Miankaleh spit response during the last cycle

An old map from a 1890 highstand shows that the Miankaleh spit consisted of several islands (Fig. 2, 5). When sea-level fell from 1929 to 1977, the spit broadened and the islands were connected by lateral sediment transport and change in base level. The only remaining open channel was almost blocked by the growth of spit in 1977 and the Gorgan bay was nearly totally separated from the sea (Fig. 5).

Between 1977 and 1987, the sea-level rose up to 1 m and the spit size decreased towards east. A narrow connection formed between Gorgan Bay and the Caspian Sea. Finally the Caspian Sea

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reached a highstand in 1995 and the spit was split in several parts and one island (Ashoradeh Island) totally separated from the Miankaleh spit.

Fig. 5. Miankaleh Spit during the last cycle of the Caspian Sea. See the text for details.

3.5. Materials and methods

3.5.1. Ground penetrating radar data acquisition and image processing

About 1 km of two-dimensional Ground Penetrating Radar (GPR) has been surveyed parallel to the Miankaleh Spit using a RAMAC/GPR system. An unshielded transmitter and receiver antenna with a mean frequency of 100 MHz has been used according to the target object. Different types of processing have been carried out on the GPR reflection data including DC shift, static correction, gain function, band pass filtering and running average filter. The depth scale was based on

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average near surface velocity which was determined from common midpoint measurements. The measured subsurface wave velocity is around 0.049 m/ns.

The water table is around 2 m based on the well data in the studied area. In order to identify the radar facies, relevant bounding surfaces and their interpretation, we used the principles outlined by Neal (2004). Due to high noise influenced by power cables at the surface, we ignored using the data which surveyed across to the spit.

3.5.2. Boring and sampling

Two cores up to 12.2 m at around 26 BOL were taken at two sites at the end of spit that was preserved at least during the last cycle of the Caspian Sea (Fig. 2b). The plastic tubes used for sampling were 5.5 cm in diameter; samples were taken at 60 cm interval (Fig. 6).

Fig. 6. Core sample between 9.6 and 9 m depth.

The cores were split lengthwise and photographed to examine the depositional facies. One half of each core was stored at the National Iranian Institute for Oceanography, while the other half was used for analyses. Most details focus on the longer core, spit 2. The samples at average of 35 g were collected based on the sedimentary facies from the two cores. Samples were first dried in an oven at 55 °C, weighed and powdered for determining of carbonate content (2 g) using the Bernard method and for further analyses. Sub-samples (150) were extracted and washed with hydrogen peroxide solution (35%) for fully removing organic matter. Finally they were sieved through sieves (with Mesh No 10, 30, 60, 100, and 230) to determine Caspian Sea biota. Dry sub-samples of 25 g were sieved and shaken for 30 min by Mesh No 500, 250, 125, 63 µm and < 63 µm. Twenty eight samples were taken for heavy mineral analysis according to the standard procedure in the Geological Survey of Iran.

Volume Magnetic Susceptibility (VMS) was determined in the cores by passing the core through coil using a MS2C core logging Scanner from Bartington. The diameter of the susceptibility meter loop was 10 cm and the progression step was 2 cm. The sensitivity of the meter was about 2x10-6 SI. The values of VMS were normalized by considering the maximum value (3.75 SI) as 1.

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3.5.3. Lithofacies

The lithofacies are based on grain size, biofacies (general biota), carbonate, colour, sedimentary structures, magnetic susceptibility and GPR identification in the upper parts. Biofacies was identified under binocular microscope by using several references mostly by Birshtein and Romanova (1968).

3.6. Results

3.6.1. Radar profiles and sedimentary facies

According to the geometry, continuity and termination of the reflections and interval and terminology of Neal (2004), at least four radar facies have been identified by radar reflection (Fig. 7). The major boundary occurs around at 2 m, indicating a change between brown sand at the top and gray fine sand at the bottom.

Fig. 7. GPR profile on the Miankaleh Spit (Ashoradeh). For location see Fig. 2b.

A parallel structure is visible throughout of radar facies A while the radar facies B shows a convex structure indicating high angle of radar reflection at sides. The radar facies C indicates a discontinuous structure particularly in the middle part. The radar facies D is less continuous and indicates a waved-shaped structure but a continuous reflection at the base. Boundary E shows high attenuation and no internal structure is visible.

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3.6.2. Lithology and sedimentary facies

Five lithological units (Fig. 8) have been identified and the lithology information is listed at table 1. The grain size of two cores is shown in Fig. 9. The fractions 125 µm and 63 µm predominate. It shows upward coarsening and the amount of the 125 µm fraction increases within the brown sand facies above 2 of core. Whereas there is strong correlation between depth and grain size for the two fractions clayey silt (63 µm) and medium sand (125 µm), the very fine sand does not show a strong correlation.

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Table 1. Lithological information.

Depth cm Sedimentary facies Biofacies Environment

0-210 Brown to reddish medium sand mostly 125 µm, abundant heavy minerals, well sorted and roundness, homogenous.

Abundant shell fragments, assemblage of Caspian Sea fauna, gastropods, bivalves and ostracods.

Spit or barrier, high energy environment.

210-630 Gray fine sand, silty sand mostly 65 µm, more laminated gray silty fine sand with shell concentrations downwards.

Abundant Caspian Sea fauna, mostly bivalves, ostracods, foraminifers.

Upper shoreface deposits.

630-850 Alternation of silty sand and clayey silt, wood at 6.8 m.

Caspian Sea fauna and charophytes. Lagoon.

850-1170 Alternation of brown clayey silt and olive to gray silty clay.

Charophytes, bivalves, foraminifers, ostracods, insect remains.

Lagoonal and delta deposit. 1170-1220 Olive to gray clayey silt. Diatoms with ostracods

and foraminifers.

Relative deeper part.

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3.6.3. Heavy minerals

Heavy mineral concentrations increase from bottom to top, with the highest concentrations in uppermost units 5, 4 and 2 (Fig. 10). This is also the coarsest sediment in the core, suggesting that heavy minerals are concentrated by surf in a beach environment in unit 4 and 5. Here the heavy mineral-rich layers show an association in which pyroxenes, magnetite and biotite are dominant, with additional high percentages of iron oxides (limonite).

There is an additional heavy-mineral-rich peak in Unit 2 between 9.2 and 11 meters depth, which is less sandy, and which shows a different mineral assemblage, characterized mainly by high percentages of amphiboles (Table 2).

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Table 2. Selected heavy mineral abundances.

Depth m Heavy mineral %

Magnetite Limonite Pyroxene

Group

Amphibole Group Biotite Zircon

0.5 39.46 0.05 14 7 0.01 14.5 0.01 1.2 43.37 0.01 12 6 0.01 22 0.01 1.4 40.12 0.01 9 6 0.3 24.11 0.01 1.8 35.82 1 9 3 0.3 19.01 0.15 2.4 29.42 3 6 0.3 0.3 19.01 0.15 3.2 22.27 0.01 4 2 0.2 14 0.01 3.8 27.585 0.025 5 2.5 2.5 15.02 0.01 4.2 19.82 2 0.25 2.5 2.5 10.03 0.01 4.4 15.875 0.025 0.01 1.5 0.15 9.01 0.01 4.6 12.415 0.025 0.15 1.5 0.01 9.02 0.01 4.8 10.615 0.025 2.5 0.25 0.01 5.025 0.01 5 0.305 0.025 0.01 0.25 0 0 0.01 5.4 6.665 0.025 0.3 3 0.01 3 0 5.6 0.315 0.025 0.01 0.01 0 0.25 0 6.1 6.685 0.025 0.01 0.3 0.01 6.01 0 6.5 5.325 0.025 0.01 2.5 0.01 2.51 0.01 6.7 5.555 0.025 0.01 5 0.25 0.25 0 7.4 0.27 0.01 0 0.25 0 0.01 0 7.8 5.345 0.025 0 2.5 0.25 2.51 0.01 8 0.27 0.01 0 0.01 0 0.25 0 8.4 0.115 0.025 0.01 0.02 0 0.01 0.01 9.2 3.046 0.01 2.25 0 0.01 0.236 0.01 9.4 34.46 0.025 5.5 0 27.525 0.3 0.225 10.3 25.68 0.025 2.75 0.01 22 0.3 0.225 10.8 28.71 0.025 0.3 0.01 27.535 0.3 0.225 11.3 0.12 0.01 0 0.01 0.01 0.02 0.01 12 0.12 0.01 0.01 0 0 0.02 0.01 12.2 0.37 0.025 0.25 0.025 0 0.01 0.01 3.7. Discussion

3.7.1. Radar facies interpretation

Although there is no major change of radar reflection but the top radar facies around 2 m depth (Radar facies A and B) might result from high and lowstand probably during the Little Ica Age and change in base level with strong lateral sediment transportation during lowstand from 1929 to 1977 in the last cycle. Since a lower part deposits (Unit 4) reflects an upper shore facies deposits identified both by a biofacies, sedimentology structure and radar reflection (Radar facies D), this might indicate the major highstand of 2600-2300 cal. yr BP event.

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3.7.2. Paleogeography of the Miankaleh Spit

The core Spit 2, apart from fluvial facies in unit 2, shows a typical coarsening-upwards sequence, starting with deeper water sediments at the bottom, and showing progressive shallowing. However, in this case the situation is different, as the core is from a spit that has grown eastwards as a result of longshore currents. We can speculate about the sequence of events using data from the nearby coast and the coring. Along the southern shore of the Gorgan Bay near the town of Bagho, a profile was studied and sampled from an extensive barrier deposit on the mainland, dated at 2400 cal. yr BP (see Kakroodi et al., 2012 for details) a prominent highstand that has been recognized also elsewhere in the Caspian (Karpychev, 2001, Kroonenberg et al., 2007). Barriers at such a sheltered site are unexpected, as the Miankaleh spit prevents waves from reaching that part of the coast. The presence of that barrier at Bagho suggests that during the 2400 cal. yr BP highstand the present Miankaleh spit did not yet exist. The present-day spit shows at its western end a number of aborted spits or hooks with a more south-eastern orientation, which, when extended to the shore, are in line with the Bagho barrier system.

Several data from our core corroborate that view. The brownish deltaic deposits at 9.2-11 m depth in the core show a heavy mineral assemblage dominated by amphibole, a mineral abundant in the rivers such as Gorgan and Qareh Su Rivers that drain the eastern part of the Alborz Mountains. However, the heavy minerals of the sands in the upper portion of the spit are dominated by pyroxenes and magnetite, suggesting they have been transported eastwards by longshore currents from rivers situated further westwards and draining volcanic areas such as the Damavand volcano (Lahijani and Tavakoli, 2012).

This suggests that (1) the amphibole-rich deltaic deposits represent rivers that extended much more seawards than at present, which might be indicative of a lowstand, and (2) the spit itself was formed during the prominent last highstand known from the Caspian Sea in the Little Ice Age, as evidenced by heavy minerals and GPR profile. This development resembles those in the Agrakhan spit along the Terek delta (Karpychev, 2001) and the Turali barrier system in Dagestan (Kroonenberg et al., 2000, 2007). Moreover, also in those systems we see a deviation in the orientation of the Little Ice age barrier system with respect to those from the previous 2600-2300 cal. yr BP highstand.

3.8. Conclusions

The development of the Miankaleh spit has been studied in two different time scales. At the start of the 20th_{century 3-m sea-level cycle the spit already existed, but it emerged prominently during}

Rapid Caspian Sea-level change and its impact on Iranian coasts

Rapid Caspian Sea-level change and its impact on

Iranian coasts

Rapid Caspian Sea-level change and its impact on

Iranian coasts

ABDOLLAHI KAKROODI

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Contents

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Chapter 1

I

NTRODUCTION: THE CASPIAN SEA

Chapter 2

S

HORELINE RESPONSE TO RAPID 20

th

CENTURY SEA-LEVEL CHANGE ALONG THE

IRANIAN CASPIAN COAST

Chapter 3

S

HORT AND LONG-TERM DEVELOPMENT

OF THE MIANKALEH SPIT, SOUTHEAST

CASPIAN SEA, IRAN