IDEAN   23403
INSTITUTO DE ESTUDIOS ANDINOS "DON PABLO GROEBER"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Ichnology of an intertidal paleosurface: the record of tidal water fluctuations, paleotopography, microbial mat variability and trace fossil distribution in the Lower Cretaceous of Patagonia, Argentina.
Autor/es:
PAZOS P.J.; FERNANDEZ D.E, ; COMERIO M.; OTTONE G.
Lugar:
St Johns
Reunión:
Congreso; III International Congress on Ichnology; 2012
Institución organizadora:
Memorial University
Resumen:
Tidal flats are complex environments influenced by tidal fluctuations, fluvial discharge, and climate; the interplay of such factors affect the time of subaerial exposure, microbial mat development, and preservation of trace fossils in recent and ancient settings. Microtopography related to the lateral migration of a tidal channel permitted to analyse trace fossils with physical and biologically induced sedimentary structures. In the depressed areas, tidal ebb ripples are well preserved. These contain delicate xiphosuran trackways developed before the water level drop recorded on the ripple crests. In the ripple troughs, exquisite meandering and looping trace fossils are preserved. The preservation is enhanced by microbial mats that favoured undermat minners, but precluded vertical borrowers. Water table fluctuations are documented in flat-topped ripples, with longitudinal markers of water level positions that vary laterally indicating inclined paleotopography. The shallow paleotopographic areas show almost complete erosion of ripples and development of epistratal mats where slippery conditions are documented by vertebrate tracks, tentatively assigned to dinosaurs. The examination and comparison of the microbial mats under SEM, permits to conclude that these were unaltered where the invertebrate trace fossils are recorded, but there they were bended and remobilized in the rim of the slippery tracks, confirming an epistratal nature of the biofilm but also the unrecovery of the mat without conclusive evidence of mat exposure.  Laterally moving in the direction of the shallowest area, only deformation on the sedimentary induced structures are recognized but organized in a perpendicular pattern of deformation documenting complex water circulation during tidal ebb.  Absence of ebb ripples, presence of marine palynomorphs such as algae and dinoflagelates suggest that the trace fossils were produced during the tidal flood while reduction of the water level related to the paleotopography took place, without any evidence of fluvial interaction on the tidal flat during the ebb part of the tidal cycle.