Establishing a stratigraphic reference section for the Middle Miocene marine deposits of Azerbaijan

Given the semi-isolated nature of the Eastern Paratethys Sea, key markers used in global biostratigraphic schemes are barely recognised. Instead, the biostratigraphic subdivisions of the Paratethyan sedimentary succession is based on faunal response to regional paleoenvironmental changes. While this macrofossil-based biostratigraphy does potentially allow for high-resolution subdivision, the use of macrofossils such as molluscs in the subsurface is hard to apply.

In recent years, significant progress has been made in understanding the Middle Miocene to Recent Paratethys stratigraphy by creating high-resolution, absolute age-dated multiproxy stratigraphic records. In these studies, the focus has predominantly been on marginal, shallow-water environments in which the Paratethys regional stages were originally defined. With this framework now in place, can we apply this knowledge to deep-water, fine-grained sediment successions in the region?

The Gobustan region of Azerbaijan has one of the most continuous outcrop records of Early Cenozoic deep-water sediments in the Eastern Paratethys region. We analysed the classic and widely studied Islamdag section. Contradictory age interpretations have been published by different authors, with some intervals assigned to either the Late Eocene or the Late Miocene. This obvious mismatch highlights the importance of establishing detailed biostratigraphic reference localities in Eastern Paratethys deep-water deposits.

During fieldworks in 2016-2017, we logged 450 m of section at cm-scale, trenching through up to 1 m of weathered material to collect ~ 300 samples. A subset of around 65 samples have been analysed to develop a multidisciplinary biostratigraphic scheme. In the field, we referred back to stratigraphic subdivisions of the Gobustan area in Russian lithostratigraphic works dating from the 1920’s and 1930’s. While these subdivisions and reference levels allow for straightforward correlation between outcrops, their significance on a regional scale remains poorly understood.

Here, we aim to establish a high-resolution, quantitative and multiproxy, age-dated stratigraphic framework for these fine-grained marine sediments. The biostratigraphic dataset is predominantly based on palynology (dinoflagellate cysts, acritarchs, green algae, pollen and spores). Additional insights come from sedimentological observations and microfossils. We will propose a high-resolution age model based on magnetostratigraphy and absolute age-dating techniques such as ⁴⁰Ar/³⁹Ar dating of volcanic ash layers. Using these constraints, we will propose a correlation both to global records and to previously published biostratigraphic records in other regions in the Eastern Paratethys, including the Taman Peninsula (Southern Russia) on the shore of the Black Sea, to highlight the importance of these results in a Paratethys-wide context.