Calcareous dinoflagellate cysts from the Tithonian - Valanginian Vaca Muerta Formation in the southern Mendoza area of the Neuquén Basin, Argentina

IVANOVA, D.K.; KIETZMANN, D.A.

Malargüe

Simposio; VI Simposio Argentino del Jurásico; 2016

Universidad de Buenos Aires

The Late Jurassic ? Early Cretaceous marine sedimentsof the Andean region show an excellent record of different calcareousmicrofossils (e.g., ostracoda,foraminifera, nanoplankton, saccocomids, calpionellids and calcareousdinoflagellate cysts). Detailed micropaleontological studies of Vaca MuertaFormation (Early Tithonian ? Early Valanginian) in the southern Mendoza NeuquénBasin from three sections are conducted with the aim of establishing a majorpresence of microfossil representatives from different microfossil groups. Theanalysis of thin sections from the outcrops: Arroyo Loncoche, Río Seco delAltar and Tres Esquinas section reveals a relatively rich micropaleontologicalassemblage of calcareous dinoflagellate cysts, as well as levels with poor preservedcalpionellids and benthic foraminifera. Particularly, calcareous dinoflagellatecysts include 25 known species (with 4 subspecies): Cadosina parvula, C. minuta, C. fusca fusca, C. fusca cieszynica,Crustocadosina semiradiata semiradiata, C. semiradiata olzae, Colomisphaeralapidosa, C. nagyi, C. carpathica, C. tenuis, C. fortis, C. lucida, C.heliosphaera, C. conferta, C. radiata, C. vogleri, Stomiosphaera moluccana, S. wanneri,S. acuelata, Committosphaera pulla, C. sublapidosa, Parastomiosphaera malmica,Carpistomiosphaera tithonica, C. valanginiana, Stomiosphaerina proxima. The calcareous dinoflagellate cysts constitute one ofthe most common calcareous microfossil groups widely distributed in the pelagicsediments in the Tethyan realm during Late Jurassic ? Early Cretaceous time,and have significant stratigraphic importance. Some specieswith biostratigraphic value of the Tethyanregion have been identified also in theAndean region: 1) Parastomiosphaeramalmica, Colomisphaera nagyi and Committosphaerapulla are known only from lower Tithonian.2) Colomisphaera tenuis, Colomisphaera fortis and Stomiosphaerina proxima are importantmarkers for uppermost Tithonian ? Berriasian (although their FO should bereviewed in detail in Argentina). 3) Colomisphaeraconferta appears in the uppermost part of upper Berriasian. 4) Carpistomiosphaera valanginiana and Colomisphaera vogleri are markers forthe lower Valanginian. More detailed studies of these groups will allow theircorrelation with Tethyan biozones, and contribute to improve biostratigraphicschemes in the Neuquén Basin.