Onset of Maikop sedimentation in the Talysh (Azerbaijan): climate or tectonics?
Year: 2013
Type: dissertation
Abstract: The Maikop series are composed of a thick succession of black shales, and are considered the most \nimportant source rock for hydrocarbons in the Caspian basin. The type section of this formation is \nlocated near the city of Maykop in Russia, north of the Greater Caucasus. Corresponding anoxic \nsediments can be traced in a vast area from Austria to China. Deposition of these sediments is linked to \nanoxic conditions that prevailed since the birth of the Paratethys and are related to decreased basin \ncirculation. Due to the lack of (micro) organisms or ash layers, the onset of Maikop deposition has not \nbeen dated accurately so far. The Maikop is presently assumed to be of Oligocene to Miocene age. \nPrecise dating of the start of Maikop sedimentation could aid in understanding the role of tectonics and \nclimate change on the onset of anoxia in the Paratethys basin, as both have affected the region during \nthe Paleogene. The Arabia-Eurasia collision has caused uplift, which could have caused a restriction in \ninteraction with the Tethys Sea further south. Alternatively, basin restriction might have been caused by \na major glacio-eustatic regression, associated with the transition from greenhouse to icehouse climate \naround the Eocene-Oligocene transition (EOT). In the Talysh, the mudstone-dominated sedimentary \nsuccession of the Pirembel formation is over 1.5 kilometers thick. This formation is generally interpreted \nas the lower part of the Maikop series. A multidisciplinary stratigraphic approach is used in this study, \nintegrating magneto- and biostratigraphy of the transition to the Pirembel formation, combined with \nradiometric dating and geochemical analyses of the volcanic formation that underlies the Pirembel \nformation. \nThree sections (AZ14, AZ15 and AZ16) were sampled. Biostratigraphic analyses have aimed at \ndinoflagellates, large benthic foraminifera and nannoplankton. Additionally, samples have been \nanalyzed using magnetostratigraphy, thin sections and x-ray fluorescence. Ten samples were prepared \nfor Ar-Ar dating. All samples were barren for dinoflagellates. Large benthic foraminifera were found in \nthe base of sections AZ14 and AZ15 and interpreted to be of Priabonian age. Nannoplankton analyses \nplace section AZ15 within Mediterranean nannoplankton zones MNP18 and MNP19, which are also \nwithin the Priabonian. Magnetostratigraphic analyses of section AZ14 have not yielded any high quality \nresults due to (at least partly) remagnetization. Magnetostratigraphy places the base of section AZ15 in \nchron C17n.2n. The youngest chron that seems evident is C16n. A sedimentation rate is estimated for \nsection AZ15 of 18 cm/kyr. Using this rate, the base of the section is estimated at 38 Ma, the base of the \nPirembel formation at 37.3 Ma and the top of the section at 35.1 Ma. Deposition of the Pirembel \nformation, taken by some researchers as the onset of the Maikop series consequently started before the \nEOT. If the Pirembel formation truly represents anoxic sediments of the Maikop series, the anoxia is \nmost likely related to a restriction in basin circulation caused by tectonics. Slumps and olistostromes are \nindicative for an active tectonic regime, as well as the presence of around 2 km of volcanics of the \nPeshtasar formation, just below the Pirembel formation. However, around 37.3 Ma, the formation of \nthe first Antarctic ice sheets is reported, which might result in a drop in sea level, leading to basin \nrestriction. A climatic cause can thus not entirely be ruled out. \nVolcanics are trachybasalts and basaltic trachyandesites with trace element signatures characteristic for \narc-lavas, and are interpreted to have formed in an arc setting. This is in contrast with previous \ninterpretations that placed these volcanics within a back-arc setting. Basalts were not affected by \nassimilation and fractional crystallization processes, and are all primary melts. Three groups are evident \nwithin section AZ16, both paleomagnetically and compositionally. These groups probably represent \nthree short, intense episodes of magmatism. The basalts of section AZ14 can be linked to the middle and \nupper group of section AZ16. All basalts have shoshonitic compositions and are possibly linked to slab-breakoff during the Paleocene-Eocene.
Author: Boon, Annique Van Der
Language: English
Subfield: Paleontology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W125584412