CONICET | Buscador de Institutos y Recursos Humanos

Abstract: Integrated biostratigraphical study of La Horqueta section (Aptian-Albian boundary), Cardiel lake, Patagonia, Argentina. La Horqueta at Cardiel lake is a classical section in Santa Cruz province where marine invertebrates include ammonites of the Aptian-Albian transition. New collections at this site yielded palynological remains from several horizons in both Río Mayer Formation (latest Aptian) and Piedra Clavada Formation (earliest Albian). Marine dinoflagellate cysts are found in the lower part of the section; they agree with an Aptian to earliest Albian age suggested by ammonites. Statistical counts of six palynological groups show the dominance of the conifer family Cheirolepidiaceae in the Río Mayer Formation coinciding with the presence of dinoflagellate cysts and the gradual increase of pteridophitic spores and saccate pollen, mainly of the family Podocarpaceae in the upper Piedra Clavada Formation. Angiosperm pollen is present throughout the section although it is more significant in the upper Piedra Clavada Formation where several new types have their first appearance (tricolpate, tricolporoidate and other types). Most palynological taxa are found across the whole section and many are known to occur in other units cropping out in this area, as the Baqueró Group (Early Aptian) or Kachaike Formation (Mid-Late Albian). Only few selected and probably significant species have been found to be of a possible biostratigraphic value and their distribution along the section is shown in a chart.La Horqueta at Cardiel lake is a classical section in Santa Cruz province where marine invertebrates include ammonites of the Aptian-Albian transition. New collections at this site yielded palynological remains from several horizons in both Río Mayer Formation (latest Aptian) and Piedra Clavada Formation (earliest Albian). Marine dinoflagellate cysts are found in the lower part of the section; they agree with an Aptian to earliest Albian age suggested by ammonites. Statistical counts of six palynological groups show the dominance of the conifer family Cheirolepidiaceae in the Río Mayer Formation coinciding with the presence of dinoflagellate cysts and the gradual increase of pteridophitic spores and saccate pollen, mainly of the family Podocarpaceae in the upper Piedra Clavada Formation. Angiosperm pollen is present throughout the section although it is more significant in the upper Piedra Clavada Formation where several new types have their first appearance (tricolpate, tricolporoidate and other types). Most palynological taxa are found across the whole section and many are known to occur in other units cropping out in this area, as the Baqueró Group (Early Aptian) or Kachaike Formation (Mid-Late Albian). Only few selected and probably significant species have been found to be of a possible biostratigraphic value and their distribution along the section is shown in a chart. Resumen: El perfil La Horqueta en el lago Cardiel, provincia de Santa Cruz, es una localidad clásica donde se hallan invertebrados marinos -inclusive amonites- de la transición Aptiano-Albiano. Nuevas colecciones en este perfil brindaron restos palinológicos en varios horizontes que abarcan las formaciones Río Mayer (Aptiano Tardío) y Piedra Clavada (Albiano Temprano). Dinoquistes marinos se hallan en la parte inferior del perfil; ellos sugieren una edad aptiana tardía a albiana temprana, coincidiendo con los datos proporcionados por los amonites. Conteos estadísticos de seis grupos palinológicos confirman la dominancia de la familia de coníferas Cheirolepidiaceae en la Formación Río Mayer, en coincidencia con la presencia de dinoquistes, y un gradual incremento de esporas pteridofíticas y polen vesiculado, principalmente de la familia Podocarpaceae, en la secci ón superior del perfil correspondiente a la Formación Piedra Clavada. Toda la sección presenta polen de angiospermas, siendo más significativa su presencia en la Formación Piedra Clavada, donde nuevos tipos hacen su aparición (tricolpados, tricolporoides y otros). La mayor parte de los taxones ocurren en otros afloramientos de esta región, como en el Grupo Baqueró (Aptiano Temprano) o la Formación Kachaike (Albiano medio-tardío). Solo se hallaron algunas especies que pueden tener valor bioestratigráfico regional y su distribución a lo largo del perfil se sintetiza en una cuadro.