Constraining the Timing and Depositional Conditions of the Maikop Formation Within the Kura Basin, Eastern Azerbaijan, Through the Application of Re‐os Geochronology and Chemostratigraphy

Abstract

The Oligocene -Miocene Maikop Formation is the key source rock in the South Caspian and Kura Basins. The Maikop is composed of a thick (up to 3 km) succession of clay-rich mudstones containing up to 15% total organic carbon (TOC). Despite decades of study, the mudstones often lack precise age control -Maikop strata rarely contain diagnostic microfaunal assemblages which can be used for dating, stratigraphic correlation, or constraining the depositional setting. Using rhenium-osmium geochronology, this study adds important numerical age data for the Maikop Formation. Of five sample suites analysed from the Kura Basin, eastern Azerbaijan, one Re-Os data-set produced a significant range in 187 Re/ 188 Os versus 187 Os/ 188 Os space to yield an isochron of 17.2 ± 3.2 Ma (Early Miocene). Other sample suites yielded imprecise Re-Os age constraints as a result of variable initial 187 Os/ 188 Os values and a limited range in 187 Re/ 188 Os versus 187 Os/ 188 Os space. The initial 187

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

“…2). The large sampling interval was not considered to be a problem, as Washburn et al (2019) observed relatively similar Re-Os values over several metres of stratigraphy. The selected samples were polished with silica carbide grit pads to minimize weathering effects and to remove any contamination by metal tools.…”

“…The initial 187 Os/ 188 Os ratios of high TOC samples with (moderately) high HI values near the base of member A (0.70 ± 0.03) and near its top (0.80 ± 0.14 and 0.56 ± 0.13, Washburn et al, 2019) are either higher or lower than that of the contemporaneous global ocean (0.61 ± 0.05 and ~0.72; Peucker-Ehrenbrink and Ravizza, 2020). This indicates that there was limited connectivity between the Eastern Paratethys and the global ocean during deposition of these sediments, and suggests that basin restriction resulted in (slightly) higher organic matter preservation as reflected by the higher HI values.…”

“…2). The nominal Re/Os age determined near the top of member A is 17.2 ± 3.2 Ma (Washburn et al, 2019). The Tarkhanian flooding event, which resulted in the cessation of deposition of the Maikop Group, was recently dated as 14.85 Ma (Palcu et al, 2019b).…”

“…However in onshore Azerbaijan, they are exposed at the surface in the Shamakhy-Gobustan area to the west of Baku (Fig. 1a) where outcropping source rocks have been the subject of detailed studies (TOC, Rock-Eval, organic geochemistry: Saint-Germès, 1998; Katz et al, 2000;Feyzullayev et al, 2001;Guliyev et al, 2001;Saint-Germès et al, 2002;Hudson et al, 2008Hudson et al, , 2016Johnson et al, 2010;Bechtel et al, 2013;2014;Alizadeh et al, 2017;Washburn et al, 2019). A synopsis of these studies suggests there is no consistent pattern in source rock data from the Maikop Group (Sachsenhofer et al, 2018a,b).…”

South Caucasus Palaeogeography and Prospectivity: Elements of Petroleum Systems From the Black Sea to the Caspian

“…To the south of the Greater Caucasus within Azerbaijan, a thick Maikopian sequence with excellent sourcerock properties extends into the Kura Basin (e.g. Washburn et al, 2019). However, as the basin narrows into western Azerbaijan and eastern Georgia the proportion of coarse clastics increases, and although the Maikopian is present within the Adjara-Trialeti Basin in the Tbilisi region, and locally appears to exceed 3000 m in thickness, its source potential is poor.…”