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Sediment petrography, mineralogy and geochemistry of the Miocene Islam Dağ Section (Eastern Azerbaijan): Implications for the evolution of sediment provenance, palaeo‐environment and (post‐)depositional alteration patterns
Author(s) -
Baldermann Andre,
Abdullayev Elshan,
Taghiyeva Yelena,
Alasgarov Alasgar,
JavadZada Zohrab
Publication year - 2020
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/sed.12638
Subject(s) - geology , sedimentary depositional environment , provenance , petrography , siliciclastic , geochemistry , sedimentary rock , facies , detritus , weathering , late miocene , paleontology , structural basin
The reconstruction of regional long‐term patterns recorded in marine sedimentary successions of the Eastern Paratethys is important in understanding the role of Cenozoic climate change and orogenic activity on the depositional environment and sedimentation dynamics in Western Asia. In this study, the environmental conditions in the early to middle Miocene (Islam Dağ section) in eastern Azerbaijan are elucidated using petrographic–mineralogical relations, detrital indicators, weathering indices and δ 13 C and δ 18 O signatures of organic‐rich (total organic carbon: ca 3 to 6 wt. %) argillites. Sedimentary facies and chemical proxies (Na/K, K/Al, Si/Al, Ti/Al ratios, chemical index of alteration values) indicate arid conditions, reduced weathering rates in the hinterland and sediment deposition in an euhaline and poorly oxygenated deep‐water basin during the early Miocene, followed by a shift to humid conditions, higher weathering rates and an oxygenated water column in the mid‐early Miocene. Long‐term aridification and deposition of gypsiferous and calcareous argillites under generally more oxygenated, euhaline to polyhaline conditions in a lacustrine or restricted shelf setting until the middle Miocene is evidenced by gradual changes in element ratios and the chemical index of alteration. Discriminant function analysis suggests the Russian Platform, drained by the Palaeo‐Volga and Palaeo‐Don river systems, to be the source area for the siliciclastic input throughout the Miocene, although a minor contribution of volcanogenic detritus and mafic components from the Greater Caucasus is possible. The C–S–Fe associations and increasing Fe/Al ratios towards the middle Miocene support the concept of continuous influx of detrital Fe and total organic carbon. The formation of ferruginous smectite from alteration of volcanic ash layers could have affected the preservation of total organic carbon and therefore the sedimentary C and Fe budget in the Eastern Paratethys basins. Palaeo‐climatic reconstructions based on δ 13 C (−34·5 to +1·7‰ Vienna Pee Dee Belemnite) and δ 18 O (−34·7 to −4·8‰ Vienna Pee Dee Belemnite) records of authigenic carbonates should be made with great caution, as the pristine marine signatures may be affected by the oxidation of organic matter and meteoric diagenesis.