Abstract
The Cenozoic succession in the Lower Kura Basin includes largely uniform, often carbonate-free mudstones. Because age dating of these sediments has proved difficult, the stratigraphy of the Cenozoic succession and the distribution of organic-rich strata are poorly known. A better understanding of the Cenozoic succession is not only important for petroleum-systems-analysis, but also for the understanding of the Cenozoic evolution of the Caucasus region. Therefore, bulk geochemical data (carbonate, TOC, sulphur, Rock-Eval) of 885 samples and biostratigraphic data were collected along seven outcrop profiles. This enabled the establishment of a continuous stratigraphic record from the Middle Eocene to the Late Miocene (Pontian). The study results show that potential source rocks are present in three stratigraphic units: the Middle Koun (Middle Eocene), Maikop Group (Oligo-Miocene) and Diatom Formation (Upper Miocene). The Middle Koun is about 100 m thick near the Caspian Sea and contains highly oil-prone sediments (2–24 wt% TOC; HI 300–577 mgHC/gTOC), which may generate 1.5 tHC/m2. The Maikop Group contains on average 1.8 wt% TOC, but is often gas-prone. Highly oil prone layers (2–5 wt% TOC; HI 300–450 mgHC/gTOC) are rare. Nevertheless, the Upper Maikop Formation may generate ∼2 tHC/m2. The Diatom Formation contains paper shales with high TOC contents (3–22 wt%) and HI values (350–770 mgHC/gTOC). The paper shale unit is more than 60 m thick near the Caspian Sea and can generate 3.8 tHC/m2. Previously it was thought that the Maikop Group had the highest petroleum potential, whilst Upper Miocene and Middle Eocene source intervals were overlooked. The Middle Eocene to Lower Oligocene succession in the Kura Basin is largely carbonate-free. In contrast, coeval successions elsewhere in the Caucasus region contain sediments with varying, but often high carbonate contents. Differences in carbonate content imply greater water depth during deposition in the Kura Basin.
| Originalsprache | Englisch |
|---|---|
| Aufsatznummer | 106148 |
| Seitenumfang | 25 |
| Fachzeitschrift | Marine and petroleum geology |
| Jahrgang | 150.2023 |
| Ausgabenummer | April |
| Frühes Online-Datum | 31 Jan. 2023 |
| DOIs | |
| Publikationsstatus | Veröffentlicht - Apr. 2023 |
Bibliographische Notiz
Funding Information:Field work was supported by BP Caspian Ltd .
Funding Information:
Tmax data (<435 °C) show that the organic matter in all studied sections is thermally immature. This is also supported by the Production Index (PI), which is generally below 0.1 (e.g. Peters, 1986). Higher PI values are probably artefacts due to very low S2 values. Relatively high PI values in Maikopian sediments with low Tmax values (average 422 °C) in the Siyaki section (Fig. 11; Table 2) might reflect the presence of migrated hydrocarbons. This interpretation is supported by the presence of oil-stained sandstone in nearby sections (including Jangi; Weber, 1935). Tmax and PI data for the Siyaki and Jangi North sections are plotted versus stratigraphic position in Fig. 11. The plot shows that despite the interval being almost 2000 m thick, there is no systematic increase in either parameter. This is also true when the Tmax (average 416 °C) and PI data (average 0.09) of the Akchagylian samples from the Lokbatan section, overlying the Productive Series, are included. This shows that maturity gradients are low and reflect a low (palaeo-)geothermal gradient. This finding is in agreement with present day geothermal gradients of about 23 °C/km in the region (Abdullayev et al., 2022) and modelling results of Inan et al. (1997), who postulated low palaeo-heat flow in the Lower Kura Basin.Field work was supported by BP Caspian Ltd.The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Vusala Aghayeva reports financial support was provided by BP Caspian Ltd.The authors thank Keith Richards and Tom Hoyle (CASP) for kindly providing palynofacies data from the Yashma section. Graham Blackbourn generously provided paleogeographic maps presented in Fig. 15. We also thank the journal reviewers, Sergey Popov and Nazim Abdullayev, as well as the editor, Brian Katz, for their positive criticism, which helped to improve the paper considerably. Finally, we also thank BP Caspian Ltd for supporting field work in 2021.
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