Geochemical approach for decoding the paleoenvironmental and depositional evolution of a coastal lacustrine Konservat-Lagerstätte (Early Cretaceous, south-Central Pyrenees)
Gil-Delgado, Alejandro (Universitat Autònoma de Barcelona. Departament de Geologia)
Cruset, David (Geosciences Barcelona)
Oms, O (Universitat Autònoma de Barcelona. Departament de Geologia)
Botero, Edgar (Technische Universitaat Hamburg-Harburg)
Ibáñez-Insa, Jordi (Geosciences Barcelona)
Delclòs Alió, Xavier (Universitat de Barcelona. Departament de Dinàmica de la Terra i de l'Oceà)
Sellés, Albert G (Institut Català de Paleontologia Miquel Crusafont)
Galobart, Àngel (Institut Català de Paleontologia Miquel Crusafont)
Mercedes Martín, Ramon (Universitat Autònoma de Barcelona. Departament de Geologia)

Data:	2023
Resum:	The lithographic limestone of La Pedrera de Meià (LPM) in south-Central Pyrenees (NE Spain) is considered one of the best preserved lacustrine-coastal successions of the Early Cretaceous in Europe, hosting a taxonomically diverse record of Barremian biota. While this Konservat-Lagerstätte has been extensively surveyed for paleontological purposes, little is known about the paleoenvironmental and depositional conditions prevailing during the formation of this fossil lagerstätte deposit. LPM limestone is made up of a homogeneous, dark gray to pale brown, faintly laminated 50 m-thick succession of micrite-rich intervals. To shed light on the environmental conditions of deposition, 303 rock samples were studied using a multiproxy approach based on different techniques including petrography, SEM-EDX, XRD, ICP-MS, XRF, Rare Earth Element distributions and C and O stable isotope geochemistry. The combination of sedimentological and geochemical data reveals a vertical shift of facies from littoral to profundal environments and then returning to littoral conditions. Profundal facies are made up of filament-rich mudstones originated from in situ precipitation of micrite either through biotically mediated or physico-chemical processes in undisturbed low energy settings, under anoxic conditions, characterized by the presence of transported terrestrial and lacustrine organisms that are exquisitely well-preserved. Littoral areas are characterized by the presence of in situ charophytes, smooth ostracods, and miliolid foraminifera that accumulated in mud-rich facies indicating low/moderate-energy, shallow-water, and relatively oxygenated conditions. Stable isotopic data and elemental geochemistry suggest a hydrologically closed to semi-closed lacustrine system with a restricted water circulation encouraging dysoxic to anoxic conditions in profundal sediments. Paleoproductivity proxies suggest a good correlation between catchment-derived siliciclastic discharge to the lake and primary productivity peaks. Furthermore, a decline interrigenous input coupled with a reduction of meteoric water entrance to the lake is interpreted based on elemental proxies derived from paleosalinity and paleoredox analysis. Collectively, the strontium/barium (Sr/Ba) ratios, the sparse presence of miliolid foraminifera, and the isotopic signatures indicate an increase in salinity toward the younger intervals of the lake infilling, although their ultimate causes are unclear (i. e. , increased evaporation, or a combination of reduced meteoric input and sporadic marine inputs might explain our data). The present work shows the importance of performing detailed multiproxy geochemical-sedimentological studies to better constrain the unique paleoenvironmental and paleohydrological conditions associated with the exceptional preservation of fossil biotas in Konservat-Lagerstätte deposits in analogous depositional settings.
Ajuts:	Agencia Estatal de Investigación PGC2018-101575-B-I00 Agència de Gestió d'Ajuts Universitaris i de Recerca 2020/FI-SDUR-00360 Ministerio de Ciencia e Innovación PLEC2021-00793 Generalitat de Catalunya ARQ001SOL-173-2022
Nota:	Altres ajuts: acords transformatius de la UAB
Drets:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original.
Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Matèria:	Fossil lagerstätte ; Lacustrine carbonates ; Stable isotopes ; Multiproxy geochemistry
Publicat a:	Sedimentary geology, Vol. 453 (July 2023) , art. 106440, ISSN 1879-0968

DOI: 10.1016/j.sedgeo.2023.106440

15 p, 9.6 MB

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