Palynostratigraphical analysis of the late Maastrichtian – early Danian in the Gaviotín Formation, Punta del Este Basin, Uruguay

Abstract

Palynological analysis were carried out for the uppermost Cretaceous – lowermost Palaeogene in the Gaviotín well, which was drilled in the marginal area of the offshore Punta del Este Basin (Uruguay). The studied interval (from 1582 to 1884 m) corresponds to the lower and middle parts of the Gaviotín Formation and the upper part of the underlying Mercedes Formation. The samples provided assemblages dominated by fairly well preserved organic walled dinoflagellate cysts. A total of 117 taxa were identified, several of them are recorded for the first time in the basin. The purpose of this study is to typify the uppermost Cretaceous – lowermost Palaeocene marine sediments of the Punta del Este Basin, which are part of the Gaviotín Formation, focused on their stratigraphical and palynological characteristics. According to the lithology, well logs and microfossil content, three intervals were recognized. The upper part of Mercedes Formation was deposited in a deltaic environment. The lower part of the Gaviotín Formation represents a shallow marine environment. The analysis of the middle part of the Gaviotín Formation (i.e. the upper part of the interval here studied) also reflects shallow marine conditions. Abrupt lithological changes around 1700 m depth, along with a sonic shift probably corresponding to a paraconformity and some biostratigraphical events allowed us to suggest that the K/Pg transition might be close to this depth. These assemblages bear several species that characterize the upper Maastrichtian – Danian interval in many sites from low, middle and high latitudes studied with high sampled resolution. These records demonstrate that the dinoflagellate provincialism suggested more than four decades ago for the Campanian cannot be recognized for successions younger than Maastrichtian. Our results permit the definition of a biostratigraphy that will assist drilling and hydrocarbon exploration in this and other mid-latitude Southwestern Atlantic basins.