Abstract
Facies analysis and stratigraphy of the Ipixuna Formation (Late Cretaceous-?Early Tertiary), eastern Cameta Sub-basin, revealed a variety of depositional environments including tidal-influenced (?) fluvial channel, flood plain/mud plug, tidal flat, bay fill, tidal channel and tidal delta. These deposits are better justified applying a wave-dominated estuarine model. The marine influence is attested by the nature of the sedimentary structures attributed to tidal processes (i.e., reactivation surfaces, foresets with bi-directional azimuths, mud couplets), as well as by the ichnological assemblage consisting of Diplocraterion, Planolites, Thalassinoides, Teichichinus, Taenidium,Skolithos. Chondrites ? e Cylindrichnus. In addition to these features, estuarine nature is revealed by the upward gradation from fluvial to tidal-influenced deposits. The stratigraphic analysis led to distinguish two stratigraphic units (A1 and A2) bounded by regionally correlatable discontinuity surfaces (SD1 and SD2). The question remains whether these are completely unrelated sequences or if they record low amplitude sequences formed within a compound estuarine system due to high frequency relative sea level fluctuations. A better characterization of these stratigraphic units is important for the kaolin exploration, as the high quality kaolin is confined to unit A1, while the semi-flint is related to unit A2.
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