IPC IX Granada 2004

Talks & Posters...

8) Aspects of Caspian palynology

KEITH RICHARDS (1) and STEPHEN LOWE (2)
(1) KrA Stratigraphic, Deganwy, UK

(2) BP Exploration, Sunbury on Thames, UK

Talk presented at the IPC XI, Granada, Spain July 2004

The Caspian Sea is the world’s largest inland body of water, and is bound geographically by Russia to the

northwest, Kazakhstan to the northeast, Azerbaijan to the west, Iran to the south and Turkmenistan to the east.

Palynologically, the Caspian Sea has only recently been the focus of detailed studies, partly due to the importance

of the offshore area to oil and gas exploration, but equally because the Caspian Sea sediments provide a unique

opportunity for research into the regional vegetation and climatic history. This presentation is based on detailed

palynological studies of Miocene to Recent sediments carried out by the author, on cores from offshore wells,

shallow boreholes and outcrop samples from Azerbaijan.

Structurally, the Caspian Sea is divided into two parts; the shallower North Caspian (maximum depth 788m) and

the deeper South Caspian (maximum depth 1025m). The two regions are separated by a sub-sea ridge, where the

water depth is less than c.200m, which extends eastwards from the Apsheron peninsula. Temperature and salinity

gradients also exist between the northern and southern regions. Surface water temperatures vary from below zero

to around 26° C in the north, compared with 7 to 28° C in the south. Salinity is also lowest in the north due to the

freshwater influx from the Volga. During the summer months, when the Caspian is ice-free, salinities at surface

are very low (1-5 ‰) in the extreme north and increase gradually southwards, becoming relatively stable at around

12 to 14 ‰ (just less than half the normal salinity of ocean waters). Salinity in the Caspian Sea does not increase

greatly in the bottom waters, although there are areas, such as the Kara Bogaz inlet on the eastern coast, where

salinity may be very high. The majority of incoming rivers flow from the northern and western coastlines. Of

these, the Volga is by far the most significant and contributes around 80% of the total fluvial discharge to the

Caspian Sea.

In Azerbaijan, much of the emphasis of palynological studies has been placed on the sediments which make up

the so-called “Productive Series” which are predominantly of Early Pliocene age and contain most of the onshore

and offshore hydrocarbon reserves. The onset of deposition occurred approximately at the end of the Miocene,

when the Caspian Sea became cut off from any open marine connection. This isolation of the Caspian Sea can be

demonstrated palynologically in sediments of Late Miocene (Messinian) age, which show a gradual change from

marine-dominated to non-marine, low salinity palynological assemblages. The associated terrestrial pollen

component typically includes relatively common Artemisia, which indicates a dry climate at this time. The in-situ

dinocyst components present include the “cruciform” types of the Spinferites cruciformis complex, confirming

that these types evolved in the pre-Pleistocene.

The palynological assemblages from the “Productive Series” are usually very rich and contain varying

proportions of extra-regional pollen (e.g. Pinus) and regionally / locally derived pollen components. The

quantitative palynological records can be used to show cyclicity and change in palaeo-vegetation and climate.

The relative proportions of brackish water dinocysts (e.g. Spiniferites cruciformis) and freshwater algae

(e.g. Pediastrum) give an indication of palaeo-salinity and can be used to infer periods of relative highstand and

lowstand within the Caspian Sea. Another feature is the frequent presence of reworked pollen, spores and

dinocysts of Permo-Triassic, Jurassic, Cretaceous and Early Tertiary age.

Sediments of Late Pliocene age in the region include the Akchagyl Beds which are marked palynologically by a

re-appearance of open marine dinocysts, signalling a brief period of open marine connection, probably via the

Black Sea. The Pleistocene succession can be sub-divided palynologically into several glacial and inter-glacial stages,

although these cannot be accurately dated on the basis of palynology alone.