Climate-driven dinoflagellate cyst stratigraphy of the Oligocene-lower Miocene turbidite succession of the Lower Congo Basin (offshore NW Angola).

Biostratigraphic studies of cuttings from wells located in the Lower Congo Basin, offshore northwestern Angola, document with unprecedented wealth of data the organic-walled dinoflagellate cyst (dinocyst) assemblages of the Malembo Formation. The identification of a series of dinocyst events (highest and lowest occurrences, influxes and acmes) recurring in the same stratigraphic position in different wells and cross-calibrated by calcareous nannofossil data, provides a tool for age control and correlation of the Oligocene and lower Miocene in the equatorial and South Atlantic region. Proceeding downwards in the stratigraphy of the examined succession, the lowest occurrence of Pyxidinopsis pastilliformis , detected within the CN3 nannofossil Zone, approximates the Langhian-Burdigalian boundary, whereas the lowest occurrences of Sumatradinuim druggii and Sumatradinium hispidum occur at the base of the CN2 nannofossil Zone in the Burdigalian. The lowest occurrences of Sumatradinium soucouyantiae and Barssidinium taxandrianum fall within the Zone of acme of Hystrichokolpoma rigaudiae at the Burdigalian-Aquitanian transition, and immediately above the acmes of Cribroperidinium tenuitabulatum and Systematophora - Cleistosphaeridium group that are supposed to reflect climate cooling pulse Mi-1a. The presence of Chiropteridium spp. and Membranophoridium aspinatum is limited to the upper part of the Chattian. An influx of Tuberculodinium vancampoae , possibly related to a warmer interlude during a period of overall climate cooling, occurs in proximity of the Chattian-Rupelian boundary. The nearly synchronous highest occurrences of Gerdiocysta conopeum , Eocladopyxis peniculata and Heterosphaeridium sp. provide a robust infra-Rupelian biohorizon. Further down in the Rupelian, the influxes of Pentadinium laticinctutm and Distatodinium paradoxum are interpreted as responses to cooling pulses. The lowest occurrence of G. conopeum , detected in the basal part of the NP23 nannofossil Zone, corresponds to the global first appearance of this excellent Rupelian marker. Genera Deflandrea and Wetzeliella are noticeably missing in the studied material just as they lack in some coeval dinocyst assemblages reported in the literature from low paleolatitude Atlantic sections. The recorded alternation of influxes and acmes of Gonyaulacoid dinocyst taxa indicative of cooler and warmer water conditions was probably climate-driven, i.e. paced by cooling pulses and relatively warmer interludes characterizing the climate evolution during the Oligocene and early Miocene. Indeed, the lack of acmes of Peridinioid cysts suggests that climate, rather than constantly elevated nutrient levels ensured by the Congo River discharge, was the discriminant factor triggering the observed blooms of Gonyaulacoid cyst-forming taxa. The delivery of large volumes of sands into deepwater settings via gravity-driven fluxes was favored by sea-level drops and is ultimately associated with pulses of climate cooling and Antarctic ice-sheet growth, finally reflected by the composition of the dinocyst assemblages. In addition to paleoecological factors, hydraulic fractionation resulting from sedimentary processes that transported palynomorphs down the slope as part of turbidite fluxes, contributed to shape the palynological assemblages observed in this study. • Ditch cuttings from 20 wells offshore Angola were investigated for biostratigraphy. • Palynoflora and calcareous nannoflora abound in the Oligocene-Miocene Malembo Fm. • A recurrent series of dinocyst events provides a tool for age control and correlation. • Dinocyst acmes were supposedly paced by climate cooling pulses and warmer interludes. • Hydraulic fractionation induced by turbidite fluxes shaped palynological assemblages. [ABSTRACT FROM AUTHOR]