An integrative physical, mineralogical and ichnological approach to characterize underfilled lake-basins

Lakes are particularly sensitive to environmental fluctuations, which arerecorded in their facies and stratigraphy. Ephemeral lakes reveal their sensi-tivity to palaeoenvironmental changes in the overprinting of the sedimentaryfeatures in every single bed. Tetrapod-track taphonomic-modes and ichno-logical taphonomic-pathways can be used as sensitive indicators of environ-mental conditions of the track-bearing beds during deposition andimprinting. The Middle Triassic Cerro de las Cabras succession (CuyanaBasin, Argentina) provides an excellent opportunity to these environmentalindicators in an underfilled palaeolake. A model of ichnological preservationfor underfilled lake systems is proposed and the role of the ichnology recordin the sequence stratigraphy analysis is evaluated, based on the integrationof tetrapod-track modes, taphonomic-pathways of playa-lake ichnofauna,mineralogy and physical data. Soft-ground suites include those dominatedby invertebrate grazing traces and arthropod locomotion traces (Suite 1), andthose overprinted by horizontal-vertical dwelling burrows with tetrapodtracks preserved in taphonomic modes B and C (Suite 2). The firm-groundsuite (Suite 3) comprises tetrapod-tracks with the best preservation styles(modes A and B) along less abundant invertebrate dwelling and feedingtraces as found in Suite 2. Clay mineralogy (dominated by illite with subor-dinate smectite) suggests low plasticity of the layers, in agreement with low-relief deformation structures observed in tetrapod-track taphonomic-modes.The well-preserved track tetrapod features documented in the Cerro de lasCabras succession, together with the absence of pedogenic disturbance, tram-pling obliterating the footprints, and/or evidence of strong disturbance bywind, desiccation and/or precipitation, supports short periods of exposure ofthe imprinted surface particular to this succession. An integrated multiproxyapproach is proposed to evaluate the evolutionary interpretation and identi-fication of autogenic versus allogenic controls in underfilled lake-basin histo-ries. The observed aggradational-trend suggests an equilibrium between ratesof accommodation change and sediment supply, and that the basin-centredid not experience prolonged sediment-starved conditions.Fil: Mancuso, Adriana Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Krapovickas, Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Benavente, Cecilia Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Marsicano, Claudia Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin

A multi‐scale approach to laminated microbial deposits in non‐marine carbonate environments through examples of the Cenozoic, north‐east Iberian Peninsula, Spain

This contribution focusses on stromatolites and oncolites as tools to seek diverse environmental and climate information at different temporal scales. The scales are: (a) Low frequency, dealing with macroscopic and megascopic scales, and (b) high frequency, involving calendar and solar frequency bands. Two depositional environments are used for this purpose: (a) Fluvial and fluvial–lacustrine, which can develop under high to moderate gradients, and in low-gradient conditions, and (b) lacustrine, subject to low-gradient, hydrologically closed lake conditions. Several current and ancient examples in the Iberian Peninsula allow high-frequency and low-frequency analyses. Within the wedge-shaped depositional units that fill the high- to moderate-gradient, stepped fluvial systems, stromatolites form half domes and lenticular bodies, commonly at the wedge front. Oncolites are uncommon. These stromatolites developed in moderate to fast-flowing water in stepped cascades and rapids. Their geometry and extent reflect the topography of the bedrock and later ongoing growth. In low-gradient fluvial and fluvial-(open) lacustrine systems the depositional units are tabular, low-angle wedge-shaped and lenticular and have great spatial facies variability. The dominant oncoid and coated-stem limestones form gently lenticular stacked bodies, developed in wide, low to high-sinuosity channels within wide tufaceous palustrine areas and small lakes. In the Ebro Basin saline carbonate lacustrine systems, stromatolites form thin planar to domed and stratiform bodies and are associated with muddy-grainy laminated carbonates and very rare oncolites, together forming ramp-shaped units that represent the inner fringes of high lake-level deposits. This geometry reflects low-gradient lake surface and shallow water conditions. Textural and structural features allow different ranks of laminae and types of lamination to be distinguished. Texture, together with the d13C and d18O values of consecutive laminae, are useful in distinguishing environmental and climate changes operating over different time spans. Periodicity analysis of lamination can help to discern any temporal significance in the lamination