CHARACTERISATION OF CLAY MINERAL ASSEMBLAGES IN PLIOCENE SEQUENCES FROM THE WESTERN FLANK OF THE SOUTH CASPIAN BASIN



Prof. Dr. Werner  Ehrmann

Dipl. Geol. Elshan Abdullayev




International Cooperation:
Prof. Dr. Chingiz Khalifazade
Azerbaijan State Oil Academy, Baku, Azerbaijan

Project Funding:
State Scholarship Program on Education of Azerbaijani Youth Abroad


Scientific Background:

The South Caspian Basin is a relatively young feature with total sediment thicknesses of 25-30 km. The Miocene-Pliocene section has a thickness of 10-12 km. At present, 99% of the oil and gas fields of Azerbaijan and Turkmenistan are related to the Pliocene sediments of the South Caspian Basin. Large fields with estimated stocks of more than 0,5 x 109 tons, such as Surahany, Neft Dashlari, Shahdeniz, Bahar, Guneshly, Azeri, Chirag and Kapaz in the Azerbaijan Sector of the Caspian Sea and Gotur Tepe in the Turkmen sector are localized in Pliocene sediments.


 
Fig. 1: Outcrop of sediments of the Productive Series (Balakhany Suite VII-VI) in Yasamal Valley near Baku, Azerbaijan.

Scientific Objectives:


We study the fine-grained sediments of the Productive Series (Pliocene) at the western flank of the South Caspian Sea for their clay mineral composition in order to identify and quantify the major clay mineral groups of smectite, illite, chlorite and kaolinite by the X-ray diffraction method (XRD). We are especially interested to learn whether the clay mineral composition varies with stratigraphy and whether it can be used to reconstruct the provenance of the sediments and/or the palaeoclimatic conditions in the hinterland. Our study may also give information on the preservation of clay minerals at greater depth in the oil and gas fields, which may have implications for the reservoir geology. In addition to the clay mineral study we investigate the bulk mineralogy in order to identify the source areas of the sediments.




 
Table: Stratigraphy of the Productive Series at the western flank of the South Caspian Basin (Vincent et al. 2010).

Preliminary Results:

For a first overview, we analysed some samples from the Productive Series in Kirmaky Valley (Kirmaky Alti Suite, Kirmaky Suite, Post Kirmaky Sand Suite, Post Kirmaky Clay Suite, Balakhany Suite X) and in Yasamal Valley (Balakhany Suite VI - IX).

In Kirmaky Valley we could identify the four main clay mineral groups smectite, illite, chlorite and kaolinite in the sediments of the Productive Series. Illite concentrations range from 44% to 64%, smectite concentrations from 5% to 41%, chlorite concentrations from 14% to 29% and kaolinite concentrations from 4% to 9%. The quartz content is strongly fluctuating.

In Yasamal Valley the smectite concentrations fluctuate between 0.5 % and 24 %, with low concentrations in the Balakhany VII Suite and high concentrations in the Balakhany IX Suite and a sample from the Balakhany VI Suite. Illite concentrations range from 48 % to 75 %. Chlorite and kaolinite amounts fluctuate from 16% to 28% and from 6% to 17%, respectively. Quartz occurs in high amounts in the Balakhany IX Suite and the Balakhany VIII Suite. Below the Balakhany VIII Suite quartz contents slowly decrease.

The high contents of quartz and pyroxenes in the analysed samples indicate that the majority of the sediments is derived from the Russian Platform. They have been transported by the Paleo-Volga and may have been augmented by rivers draining the Greater Caucasus (Baturin, 1947; Reynolds et al., 1998). Illite and chlorite are the dominating clay minerals. They are detrital minerals, products of physical weathering processes, and possibly indicate a cool and dry climate of the period.


 


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