Lower Cretaceous Provenance and Sedimentary Deposition in the Eastern Carpathians: Inferences for the Evolution of the Subducted Oceanic Domain and its European Passive Continental Margin

Abstract

Reconstructing orogenic systems made up dominantly by sediments accreted in trenches is challenging because of the incomplete lithological record of the subducted oceanic domain and its attached passive continental margin thrusted by collisional processes. In this respect, the remarkable ~600 km long continuity of sediments exposed in the Eastern Carpathian thin‐skinned thrust and fold belt and the availability of quantitative reconstructions for adjacent continental units provide excellent conditions for a paleogeographical study by provenance and sedimentological techniques constraining sediment routing and depositional systems. These sediments were deposited in the Ceahlău‐Severin branch of the Alpine Tethys Ocean and over its European passive continental margin. We report sedimentological, paleomagnetic, petrographic, and detrital zircon U‐Pb data of Lower Cretaceous sediments from several thin‐skinned tectonic units presumably deposited in the Moldavides domain of the Eastern Carpathians. Sedimentological observations in the innermost studied unit demonstrate that deposition took place in a deepwater basin floor sheets to sandy turbidite system. Detrital zircon age data demonstrate sourcing from internal Carpathian basement units. The sediment routing changes in more external units, where black shales basin floor sheets to sandy mud turbidites were sourced from an external, European continental area. Although some degree of mixing between sources located on both margins of the ocean occurred, constraining a relatively narrow width of the deep oceanic basin, these results demonstrate that the internal‐most studied unit was deposited near an Early Cretaceous accretionary wedge, located on the opposite internal side relative to the passive continental margin domain of other Moldavides units.

Provenance of Oligocene lithic and quartz arenites of the East Carpathians: Understanding sediment routing systems on compressional basin margins

“…One age cluster that peaks at 290-330 Ma can be associated, based on zircon U/ Th ratios (Figure 11b), with two possible sources: a magmatic (U/Th < 5) and a metamorphic (U/Th > 5), (Hoskin & Schaltegger, 2003). This characteristic is also found in rocks from the Ceahlău (Roban et al, 2022), Teleajen, Audia and Tarcău nappes (Roban et al, 2020), suggesting a mix between magmatic and metamorphic sources derived from the Dacia and the Danubian units (Figure 6b). Another shared a peak at 72 Ma (Late Cretaceous, Campanian stage) is attributed to subduction magmatism associated with the nearby closure of the Neotethys (Gallhofer et al, 2015).…”

“…A less pronounced peak at 325-340 Ma can be correlated with the Variscan orogeny, coinciding with a period of regional metamorphism (Ducea et al, 2018) although most zircons of that age are magmatic (Figure 6a,b). The Albian deposits covering the front of the Getic Nappe (Bucegi Conglomerates; Săndulescu, 1984) and the ones within the Teleajen-Audia nappes (Figure 6a,b) show similar age distribution profiles and U/Th pattern to those of the Dacia mega-unit (Roban et al, 2020(Roban et al, , 2022Stoica et al, 2016).…”

“…The exposed basement in the Ukrainian Shield contains zircons that yield mainly Proterozoic and Neo-archean ages (c. 1500, 2000and 2700Ma, Bibikova et al, 2013Shumlyanskyy et al, 2012Shumlyanskyy et al, , 2015. This signature is also recognizable in the western Neo-proterozoic sedimentary cover of the East European Craton (Francovschi et al, 2021;Roban et al, 2020;Żelaźniewicz et al, 2020).…”

“…These characteristics and the presence of green clasts (e.g. Roban et al, 2020) place F G R E 1 2 (a) reconstruction during Oligocene illustrating the possible drainage routes associated with the depositional systems Fusaru and Kliwa, as well as the turbidites morphology in the Moldavides Basin, based on the integration of the current study results and the previous comprehensive studies: litho-stratigraphical (Kovác et al, 2017;Popov et al, 2004;Salata & Uchman, 2019;Saulea et al, 1969) tectono-stratigraphical (Barrier et al, 2018;Van Hinsbergen et al, 2020-grey lines framework) and thermochronological (Fügenschuh & Schmid, 2005;Kounov & Schmid, 2012;Merten et al, 2010;Necea et al, 2021;Sanders et al, 1999). The turbidites system configuration has been interpreted based on sedimentological and palaeocurrents measurements acquired during this study and completed with those of (Contescu et al, 1966;Jipa, 1966); (b) Sketch showing the basin configuration during Oligocene-Miocene times, illustrating the advancing of the Carpathian indenter over the subducting plate.…”

“…During the Cretaceous–Quaternary interval, the exhumation advanced to the east; (b) Geological cross section through the East Carpathians after (Merten et al, 2010). The thrust faults bounding the nappes are coloured according to their timing, which correlates with the exhumation intervals displayed in a; (c) Simplified tectono‐stratigraphical chart of the East Carpathians illustrating the depositional and structural relationships of the east‐vergent nappes, and depositional environments, modified after Săndulescu, Kräutner, et al (1981); Săndulescu, Ștefănescu, et al (1981); 1:50,000 and 1:200,000 geological maps published by the Geological Institute of Romania, and Merten et al (2010); Mațenco (2017); Roban et al (2020). Post‐tectonic sedimentation overlying nappes are not displayed.…”