EARLY CRETACEOUS TERRESTRIAL ECOSYSTEMS FROM PATAGONIA: THE BAQUERO GROUP, A CASE STUDY

Terrestrial paleobiology during the early Cretaceous represents a major topic for the understanding of life evolution in the southern continents. Some of the best examples in this regard come from the Baqueró Group, a geological unit deposited during the late Barremian-early/middle Aptian time span and composed of three subunits. The lower Tico Fm. is represented by lacustrine fine-grained deposits accumulated over pre-existing depressions. These deposits are locally interrupted by fluvial coarse-grained braided channels of moderate sinuosity. The intermediate Bajo Tigre Fm. comformably succeeds the lower unit. It is composed of volcaniclastics associated with ash falls and mass flows linked to heavy rainy seasons. Shallow lake deposits occur in the upper part. The uppermost Punta del Barco Fm. lies uncomformably on the previous unit. It reflects strong volcanic activity indicated by thick ash falls constantly reworked by the action of braided channels.

The Baquero Group bears probably the richest early Cretaceous flora in the Southern Hemisphere. Depending on the unit, the flora is dominated by conifers, cycads, bennettitaleans, pteridosperms and ferns. Conifers show a high diversity of Podocarpaceae, Araucariaceae and Cheirolepideaceae. Bennettitales are the most important group in the lower part of the section with minor cycads and sporadic findings of Ginkgoales. Dipteridaceae and Gleicheniaceae ferns occur throughout the sequence but more importantly in the upper part as well as pteridosperms including some endemic taxa. The flora also records the oldest angiosperms in Argentina.

Several paleocommunity arrangements have been identified in the Baquero flora, including forest, woodlands, aquatics and “grasslands”. These vegetational types were able to grow in a very seasonable climate constantly affected by volcanic activity, giving the whole flora a unique character during the early Cretaceous in Gondwana.