Miocene dinoflagellate cyst biostratigraphy from the Península Valdés, Patagonia, Argentina

Abstract

The present work documents the stratigraphic distribution of dinoflagellate cysts from the upper part (60-585 m) of the YPF.Ch. PV. es-1 borehole, Península Valdés, Argentina. The assemblages exhibit a relatively moderate to low diversity. Most samples are characterized by frequent to abundant taxa of the order Gonyaulacales, such as Spiniferites/Achomosphaera spp., Reticulatosphaera actinocoronata, Operculodinium centrocarpum, and Melitasphaeridium choanophorum. Furthermore, a continuous succession of Lower Miocene-Upper Miocene diagnostic dinoflagellate cyst events was recorded for the first time from the Península Valdés region. Eight diagnostic events of highest occurrences (HOs) of dinoflagellate taxa are identified. These bioevents allowed a subdivision of the sedimentary succession into two well-defined stratigraphic sections: Lower to Middle Miocene (Burdigalian-Langhian/probably Serravalian, 430/425–330/325 m) based on the HOs of Emmetrocysta urnaformis, Cannosphaeropsis quattrocchiae, Cousteadinium auybriae, and Cleistosphaeridium ancyreum, and Upper Miocene (Tortonian-Messinian, between 175-170 and 80/85m) based on the HOs of Labyrinthodinium truncatum subsp. truncatum, Operculodinium piaseckii, and Reticulatosphaera actinocoronata. The range of these taxa is compared with well-documented information on Neogene dinoflagellate cysts recorded from different sites across the North and South Atlantic Oceans and adjacent seas. In general, the dinoflagellate cyst assemblages, as well as the selected diagnostic taxa, exhibits a clear similarity with those of the Northern Hemisphere. The only exception is Hystrichokolpoma rigaudiae, which is asynchronous, possibly indicating local paleoenvironmental conditions.