New insights into the paleoecology of brachiopod-arthropod-microbial assemblages from Upper Triassic cryptic submarine cavitiesLazăr, Iuliana (Avtor) Balica, Constantin (Avtor) Grǎdinaru, Mihaela (Avtor) Sandy, Michael R. (Avtor) Kolar-Jurkovšek, Tea (Avtor) Grǎdinaru, Eugen (Avtor) Ducea, Mihai N. (Avtor) Forel, Marie-Béatrice (Avtor) HalorellaFrutexitesNeptunian dike and sillUpper TriassicRomaniaA unique record of an Upper Triassic brachiopod (Halorella)-arthropod (Halorina microcoprolites)-microbial (Frutexites) assemblage is documented from iron-rich carbonates filling a neptunian dike and sill system developed in Carnian-lower Rhaetian limestone host rock from Leurdeasa Hill in the Apuseni Mountains, Romania. The host rock at Leurdeasa Hill through which the dike and sill cross-cut is dated as early Carnian by the conodont assemblage. The paleoecology of this brachiopod-arthropod-microbial assemblage along with the paleoenvironmental context and genesis of iron-rich carbonates filling the Upper Triassic neptunian dike and sill system is examined through integrated analyses including paleontology, taphonomy, microfacies, mineralogy and stable isotopes of carbon and oxygen, as well as patterns of rare-earth elements. Frutexites microstructures and their possible microbial origin are documented for the first time in an upper Norian-lower Rhaetian neptunian dike and sill. Given the broad paleogeographic distribution of the brachiopod Halorella during the Late Triassic and the scarcity of marine paleoenvironments from where this genus has been reported, we conclude that the proliferation of significant populations of Halorella alongside with arthropods and microbial consortia were restricted to submarine cryptic paleoenvironments characterized by peculiar conditions, namely, warm waters, temporarily rich in nutrients, in dark habitats. Geochemical data show that the red carbonate infills are predominantly seawater-derived with minor terrigenous input, later modified by Fe-Mn oxide formation, organic matter cycling, and diagenesis, and record short-term apparent cyclic shifts between oxic and suboxic conditions in a semi-restricted neptunian dike/sill system likely linked to episodic biotic blooms and variable water exchange.Elsevier20262026-06-03 09:45:36Neznano29682UDK: 56ISSN pri članku: 0031-0182DOI: 10.1016/j.palaeo.2026.113829COBISS_ID: 277885443sl