Ichnofabric analysis of shallow to deep marine Carboniferous sediments, from the southern Paleotethys margin, Alborz Basin (northern Iran): approaching autogenic and allogenic environmental controls

Palaeoenvironment, palaeogeography, and palaeoclimatology of the Mississippian carbonate ramp in the Alborz tectonostratigraphic zone: Implications for deciphering the controlling factors on ramp evolution

“…Dunham's (1962) nomenclature and modification by Embry and Klovan (1971) was used for the textural classification of carbonates. The new data presented here were integrated with the results of published studies from several decades (e.g., Bahrammanesh, Angiolini, Antonelli, Aghababalou, & Gaetani, 2011; Bayet‐Goll et al, 2020; Bozorgnia, 1973; Brenckle, Gaetani, Angiolini, & Bahrammanesh, 2009; Falahatgar, Vachard, & Sakha, 2015; Mossadegh, 2000; Sharafi, Rodríguez‐Tovar, Bayet‐Goll, et al, 2021; Vachard, 1996; Zandkarimi et al, 2016, 2019) to achieve a synthesis about the palaeoenvironment, palaeogeography, and palaeoclimate of the Mississippian rocks. As a biostratigraphic framework of Mississippian rocks of Alborz, we used the foraminiferal zonation of Zandkarimi et al (2019).…”

“…However, towards the central and northern Alborz sections, the facies sequences related to the shallow water inner ramp section, such as sand shoal and lagoonal/back barrier facies associations, predominate. Variation in the type of platform system mentioned in several studies on carbonate deposits of Mobarak Formation has been mainly attributed to the significant impact of basement faults such as the Mosha‐Firuzkuh Fault on the deposition process and the type of carbonate platform (Brenckle et al, 2009; Mosaddegh, 2000; Sharafi, Rodríguez‐Tovar, Bayet‐Goll, et al, 2021; Zandkarimi, Vachard, Cózar, et al, 2017, Zandkarimi et al, 2019). According to the results of the studies by Zandkarimi et al (2019) on the Mississippian deposits of Central Alborz, the considerable impact of differential subsidence as a result of the reactivation of inherited basement faults is a key factor in the extension of outer‐slope environments and beds and calciturbidites in the deep facies identified in the studies of Nasiri et al (2020)).…”

“…Trace fossils have been analysed based on criteria such as relative abundance, ichnodiversity, and intensity of bioturbation (Taylor & Goldring, 1993). For palaeoclimate interpretation, we used the ichnological zonation presented by Goldring et al (2004), the results of several recently published papers (Bayet‐Goll et al, 2020; Nasiri, Moussavi‐Harami, Mahboubi, & Mosaddegh, 2019; Sharafi, Rodríguez‐Tovar, Bayet‐Goll, et al, 2021) and the geochemical studies of Mousavi‐Taher et al (2021). Palaeogeography has been constructed by comparison and using the works of Stampfli and Borel (2002), Bagheri and Stampfli (2008), Falahatgar et al (2015), Zandkarimi et al (2016, 2019), and Arefifard (2017).…”

“…Towards the top of the succession, a significant reduction of heterolithic bedsets or muddy beds, the presence of thick, amalgamated beds displaying HCS and coarser grain‐size along with the characteristic ichnologic features, all indicate the high‐energy and progressive sorting linked with continuous and intense wave/current reworking in a high‐energy setting of the proximal middle ramp. The grain‐supported microfacies with greater homogeneity than the previous sequence, peloids, disarticulation/fragmentation, and the erosion of crinoid columnals and brachiopod shells in thick calcareous layers with small amounts of carbonate mud and reduced biological turbulence, most probably suggest multiple reworking by successive hydrodynamic events (Bayet‐Goll et al, 2014, 2018; Palma, López‐Gómez, & Piethé, 2007; Sharafi, Rodríguez‐Tovar, Bayet‐Goll, et al, 2021). Expanded storm deposits in the proximal middle ramp of this sequence, with dominant echinoderm‐bioclastic grainstones and packstones and stormy sedimentary structures, are typical evidence of proximal tempestites.…”

“…Interpretation . Extensive changes in grain size, type of facies, and sedimentary structures observed in a proximity‐distality trend from the base to the top of sequence are evidence of the role of storm currents combined with oscillatory flows on middle ramp settings, above storm‐weather base (Bayet‐Goll, De Carvalho, Moussavi‐Harami, Mahboubi, & Nasiri, 2014; Sharafi, Rodríguez‐Tovar, Janočko, et al, 2021). Rhythmically bioturbated low‐energy facies (F1–F3) and sharp‐based limestones (F4–F6) with evidence of storm structures, such as HCS, suggest the alternation of slow fair‐weather fine‐grained deposition with storm‐emplaced limestones in middle‐ramp environments, between the fair‐weather and SWBs.…”