Sedimentary environments and geochemistry of Upper Eocene and Lower Oligocene rocks in the northeastern Caucasus

The Paratethys area extends from Central Europe to the borders of the Caspian Sea in Central Asia and hosts a significant number of petroleum provinces, many of which have been charged by Eocene to Miocene source rocks of supra‐regional significance. These include highly oil‐prone Middle Eocene marls and limestones in the Eastern Paratethys (Kuma Formation and equivalents) which are several tens of metres thick. Estimates of the source potential index (SPI) indicate that the Kuma Formation in the northern Caucasus and the Rioni Basin (Georgia) may generate 1 to 2 tons of hydrocarbons per square metre (tHC/m2). This implies that the Kuma Formation may also be an important and additional source rock in the eastern Black Sea. Oligocene and Lower Miocene pelitic rocks (Maikop Group and equivalents) are considered to be the most important source rocks in the Paratethys. Vertical variations in source potential record different stages of basin isolation that reached a maximum during the Early Oligocene (NP23) Solenovian Event. However major variations exist between different sub‐basins in the Central and the Eastern Paratethys. In the Central Paratethys, the highest quality source rocks occur in the Carpathian Basin where the Menilite Formation, several hundreds of metres thick, can generate up to 10 tHC/m2. Locally the Menilite Formation is about 1500 m thick and continues into the Lower Miocene. In these settings, the Menilite Formation can generate approximately 70 tHC/m2. In the Alpine Foreland Basin (Schöneck and Eggerding Formations) and the Pannonian Basin (Tard Clay Formation), oil‐prone source rocks are restricted to the Lower Oligocene. In the Eastern Paratethys, the best source rock intervals of the Maikop Group are typically associated with the Early Oligocene Solenovian Event. By contrast, with the exception of the Kura Basin in Azerbaijan, the potential of Upper Oligocene and Lower Miocene rocks is often limited. In total, the Maikop Group may generate up to 2 tHC/m2 in the North Caucasus area and 4 tHC/m2 in the Rioni Basin. A particular source rock facies is found in the Western Black Sea where diatomaceous rocks with good oil potential accumulated in the Kaliakra Canyon during Early Miocene time. This facies may generate up to 8 tHC/m2, but is probably limited to shelf‐break canyons. Middle and Upper Miocene rocks are the main source for oil and thermogenic gas in the Pannonian Basin System, and also contributed to thermogenic hydrocarbons in the Moesian Platform and the South Caspian Basin. In addition, Upper Oligocene and Miocene rocks are the source for microbial gas in several basins including the Alpine and Carpathian foredeeps.

Section: North Caucasusmentioning

confidence: 95%

Paratethyan Petroleum Source Rocks: An Overview

Sachsenhofer

Popov

Ćorić

et al. 2018

“…Therefore, this interval is attributed to the Lower Maikop Formation (sensu Weber, 1935). The early Solenovian Event itself (early NP23), often characterized by carbonate-rich sediments (Polbian or Ostracoda Bed; Gavrilov et al, 2017;Sachsenhofer et al, 2017Sachsenhofer et al, , 2018a, is not exposed but may occur several tens of metres below the base of the section. The exposed sediments have varying and partly high TOC contents, but very low HI values (≤90 mgHC/gTOC; Table 2); in the case of sample IDF-07, this is despite the high alginite content (82 vol.%).…”

Section: Maikop Group (Islamdag Section)mentioning

confidence: 99%

New Geochemical Insights Into Cenozoic Source Rocks in Azerbaijan: Implications for Petroleum Systems in the South Caspian Region

Aghayeva

Sachsenhofer

Baak³

et al. 2021

The Maikop Group and the Diatom Formation constitute the two main source rocks in the South Caspian Basin and onshore Azerbaijan where large‐scale oil production began more than 150 years ago. However, the stratigraphic distribution of the source rocks and the vertical variation of source‐rock parameters are still poorly understood. The aim of the present paper is therefore to investigate in high resolution the source‐rock distribution in the Perekishkyul and Islamdag outcrop sections, located 25 km NW of Baku, which provide nearly complete middle Eocene and lower Oligocene to upper Miocene successions. Bulk geochemical parameters of 376 samples together with maceral, biomarker and isotope data were analysed. In addition, new Re/Os data provide independent age dating for the base of the Upper Maikop Formation (30.0 ± 1.0 Ma) and the paper shale within the Diatom Formation (7.2 ± 2.6 Ma). The presence of steradienes in high concentrations demonstrates the thermal immaturity of the studied successions, limiting the application of some biomarker ratios. Intervals with high TOC contents and containing kerogen Type II occur near the top of the middle Eocene succession. However, because of the low net thickness, these sediments are not considered to constitute significant hydrocarbon (HC) source rocks. The Maikop Group in the Islamdag section is 364 m thick and represents lower Oligocene (upper Solenovian) to middle Miocene (Kozakhurian) levels. Samples are characterized by moderately high TOC contents (∼1.8 wt.%) but low hydrogen index (HI) values (average ∼120 mgHC/gTOC) despite a dominance of aquatic organic matter (diatoms, methanotrophic archaea and sulphate‐reducing bacteria). Rhenium‐osmium chronology suggests low sedimentation rates (∼25 m/Ma), which may have had a negative impact on organic matter preservation. Terrigenous organic matter occurs in variable but typically low amounts. If mature, the Maikop Group sediments at Islamdag could generate about 2.5 tHC/m2. The Diatom Formation includes a 60 m thick paper shale interval with high TOC contents (average 4.35 wt.%) of kerogen Type II‐I (HI up to 770 mgHC/gTOC). The source potential is higher (∼3 tHC/m2) than that of the Maikop Group. The organic matter is dominated by algal material including diatoms. High TOC/S ratios suggest deposition under reduced salinity conditions. Strictly anoxic conditions are indicated by the presence of biomarkers for archaea involved in methane cycling. For oil‐source correlations and a better understanding of the petroleum system, it will be necessary to distinguish oil generated by the Maikop Group from that generated by the Diatom Formation. This study shows that these oils can be distinguished based on the distribution of specific biomarkers e.g. C30 steranes, C25 highly branched isoprenoids (HBIs), and the C25 isoprenoid pentamethylicosane (PMI).

“…Fig. 10 shows nannofossil stratigraphy for the Eocene-Oligocene transition at the Chirkey section previously studied by Gavrilov et al (2017) and the Miatly section (locations in Fig. 1).…”

Section: The Eocene -Oligocene Boundary Interval Biostratigraphymentioning

confidence: 99%

“…At the Chirkey section (Gavrilov et al, 2017), the Khadum Formation includes similar OM-rich lithofacies but they are intercalated with thick intervals of mudstones with low organic content resulting in an increase in the total thickness of the formation. In the Miatly section by contrast, a more condensed section of the Khadum Formation is present with a generally higher content of organic carbon.…”

Section: Organic Materialsmentioning

confidence: 99%

Stratigraphy, Sedimentology and Geochemistry of the Oligocene – Lower Miocene Maikop Group in Dagestan, Ne Caucasus

Gavrilov

Nedumov

Shchepetova

et al. 2021

Samples of Maikop Group sediments from the Sulak section were analysed for their contents of Mo, S, Fe, Mn, V, Ni and other elements. A stagnation coefficient (Mo/Mn x 100) was calculated and was interpreted as a measure of the intensity of anoxia in the Maikop palaeobasin. Anoxic conditions are interpreted to have reached a maximum in the Rupelian and Aquitanian during deposition of the Khadum and Riki Formations respectively. However, geochemical conditions were unstable and the oxygen concentration in the bottom waters varied widely over time. Thus, the Zuramakent Formation at the top of the Maikop Group was largely deposited in normally oxygenated conditions.