A sedimentologia da "Formação arenitos e argila de Aveiro": cretácico superior, bacia ocidental portuguesa

Abstract

In the upper Cretaceous of the north section of the Western Portuguese Basin, four facies associations have been defined (I, II, III, IV), belonging a tidal flat complex.The association I, was deposited in a subtidal environment, represented by a lagoon separated from the open marine water by a barrier island; it includes central and marginal lagoonal facies and washover deposits.The intertidal environment, association II, is formed by a mud flat subject to oscillations of the water level and periods of subaereal exposures. Three morphological areas have been identified: lower mud flat related to the margin lagoon, middle mud flar and higher mul flat covered by halophites.The association III, was deposited in tidal channels of high sinuosity; according to its characteristics, two types of channels with different positions in the tidal flat can be distinguished: tidal creeks of small dimensions and simple structure, normally associated with tidal bars end tidal inlets oh greater dimensions and complex structure.The association IV belongs to a supratidal environment in witch the main processes were: vegetation colonization and organic matter accumulation in lower level, in transition to the higher mud flat, strong oscillations of water level and long period subaereal exposures in the higher levels where the evaporitic conditions are prevalent.