Carlos O. Limarino

Eolian permian deposits in west and northwest Argentina

Abstract The sedimentary and stratigraphic characteristics of eolian Permian deposits exposed in Mendoza, La Rioja and San Juan Provinces (west and northwest Argentina) are described in this paper. The eolianites are fine and medium sandstones with large-scale cross-bedding, multiple parallel truncation planes and some asymmetrical ripples. Three genetic types of deposits have been identified: dune facies, eolian sand-sheet facies and mixed fluvial-eolian facies. Fine and medium sandstones with large-scale cross-bedding and multiple parallel truncation planes are here interpreted as dune deposits (mainly crescentic dunes), and unstratified or flat-bedded sandstones as eolian sand-sheet deposits. Mixed fluvial and eolian sequences, composed of sandstones, mudstones and some matrix-supported conglomerates, represent a transitional facies between those formed in eolian and fluvial environments. This considerable deposition of eolian sediments was probably brought about by the existence of an extensive, medium to low-latitude continent and the withdrawal of marine environments. The environments with highest aridity occurred towards the south and west of the region. The eolian circulation pattern was controlled by a long ensialic volcanic arc emerging towards the west of the basin.

Paleoclimatic significance of the lacustrine Carboniferous deposits in Northwest Argentina

Abstract The origin and probable paleoclimatic significance of Carboniferous lacustrine deposits in northwest Argentina are discussed. These rocks are developed extensively throughout northwestern Argentina, but are described in the present paper only from the region of the Sistema del Famatina. Five lithofacies have been identified: (A) laminated siltstones and claystones; (B) thinly interbedded mudstones and sandstones; (C) interlayered mudstones and sandstones with sole structures (flute marks and tool marks); (D) conglomerates and fine sandstones; (E) sandstones and diamictites. These lithofacies are interpreted as lacustrine deposits formed during the final episode of the Carboniferous glaciation. Lithofacies A originated as a suspension-load deposit in the central and intermediate parts of the lake; the presence of dropstones in this lithofacies suggests coeval ice-rafting processes. Underflow currents probably formed lithofacies B, and lacustrine turbidites lithofacies C. Lithofacies D and E were deposited in marginal environments and represent in some cases shoreline bars and small deltas. The age of the lacustrine episode is deduced from paleobotanical information. Both palynological and megafloristic data suggest that these deposits were formed during the middle Carboniferous. A palynological assemblage dominated by Cristatisporites-like spores characterizes these sediments.

BUMBUDENDRON VERSIFORME. A NEW LYCOPHYTE SPECIES FROM THE LATE PALEOZOIC OF ARGENTINA

Abstract Bumbudendron versiforme sp. nov. is described on the basis of imprints from the Agua Colorada Formation, Sierra de Famatina, Argentina. It is characterized by fusiform leaf cushions with a variable length-width ratio in a single stem. Megaspores are found associated with the lycopod remains. Comparisons with other species having infrafoliar bladders are made. The associated microflora suggests a Late Carboniferous age for this lycophyte species.