Miocene Dinoflagellate Cyst Biostratigraphy of the Península Valdés, Patagonia, Argentina

Abstract

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 Early Miocene–Late 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 cyst taxa are identified. These bioevents allowed a subdivision of the sedimentary succession into two well-defined stratigraphic sections: Early to Middle Miocene (Burdigalian–Langhian/probably Serravalian, 430/425–330/325 m) based on the HOs of Emmetrocysta urnaformis, Cannosphaeropsis quattrocchiae, Cousteaudinium auybriae, and Cleistosphaeridium ancyreum, and Late Miocene (Tortonian–Messinian, between 175–170 and 80/85 m) based on the HOs of Labyrinthodinium truncatum subsp. truncatum, Operculodinium piaseckii, and Reticulatosphaera actinocoronata. The ranges of these taxa are compared with well-documented information on Neogene dinoflagellate cysts recorded from different sites across the North and South Atlantic Ocean and adjacent seas. In general, the dinoflagellate cyst assemblages, as well as the selected diagnostic taxa, exhibit a clear similarity to those of the Northern Hemisphere. The only exception is Hystrichokolpoma rigaudiae, which is asynchronous, possibly indicating local paleoenvironmental conditions.