title: The Neogene development of the Zagros Foreland Basin in the Lurestan-Arc, Iran. A new integrated model using geochemistry, clay mineralogy and micropalaeontology
Creators: name: Dietzel, Christian Artur Friedrich
Publisher: name: Universität Tübingen
Year: 2025
Subjects: subject: Mineralogie , Ton , Mikropaläontologie , Geochemie , Zagrosgebirge , Neogen
subject: 550
subject: clay
subject: mineralogy
subject: micropaleontology
subject: Neogene
subject: geochemistry
subject: Zagros

description: The Mesopotamian Foreland Basin represents an important sedimentary archive for the Neogene evolution of the Zagros Mountain Belt and the adjacent Arabian Shield. In this dissertation a combined sedimentary profile from the Zarrinabad and Changuleh syncline anticline structures was analysed using whole rock geochemistry, clay mineralogy and micropalaeontological data of 84 samples and compared to previously published data of soluble salt geochemistry and magnetic susceptibility from Böhme et al. (2021). The combined profile has previously been dated by magnetostratigraphy and encompasses Sediments from the Serravallian (12.6 Ma) to the earliest Pleistocene (2.4 Ma) (Homke et al., 2004). It comprises the uppermost parts of the evaporative Gachsaran Formation, fluvial sediments of the lower Aghajari Member, alluvio-fluvial-aeolian sediments of the Lahbari Member and alluvial conglomerates of the Bakthiary Formation. Increased transformation of illite and chlorite to smectite by chemical weathering indicates a change from arid to semi-arid climate conditions from the Serravallian towards the mid Tortonian. Geochemical analysis of the sediments using whole rock XRF data also demonstrates a significant provenance shift during the early-mid Tortonian. An increase in mafic and ultramafic elements such as Mg, Cr and Ni as well as radiolarians indicates enhanced uplift and erosion of ophiolites, mafic magmatites as well as radiolarites from the Imbricate Zagros zone. The additional magnesium availability gives then rise to the formation of palygorskite in soils along the floodplain. A reduction in chemical weathering and a transition towards arid climate conditions is indicated in clay mineralogy in the early Messinian. Clay mineralogy and geochemistry are reflective of significant change at the onset of the hyper-arid Lahbari Member at 5.6 Ma. A strong increase in soluble salts is encompassed by an increase in palygorskite, which is not coupled to local magnesium availability as demonstrated in the Lower Aghajari Member. The Lahbari Member is interpreted to comprise fine-grained distal alluvial fans in a bajada environment originating from older Gachsaran and Aghajari sediments of the uplifting along the Zagros Mountain Front Flexure due to tectonic basin convergence. These fine-grained alluvial fans are interbedded with thick silts with aeolian contribution which are geochemically indicated to have largely been recycled from the local alluvial material. Additional atmospheric nitrate and chloride, which is distributed throughout these silts was likely sourced externally from atmospheric deposition during a penecontemporaneous hyper-arid period (NADX). Clay mineralogy indicates an increase in humidity towards arid conditions the upper part of the Lahbari Member in the Zanclean. The Lahbari Member is superseded by coarse grained conglomerates of the Bakthyari Formation at 2.5 Ma reflecting the deepening of erosion into older well consolidated strata of the neighboring uplifting Anaran Anticline. Several samples througout the profile contained small charophyte gyrogonites of Chara vulgaris, Chara globularis, Nitellopsis obtusa and Chara sp. giving information on freshwater availibility on the floodplain such as in temporary ponds after seasonal flooding. Furthermore, XRD analysis revealed the presence of the zeolite mineral erionite in many samples throughout the whole sedimentary profile, which can form from weathering of volcanic glass in alkaline conditions.