IGCP Board; 10th session; Report of the ... - unesdoc - Unesco

Ciencias, volumes 52 (4) and 53 (2). San Luis range, a new outcrop of the Bajo de
Veliz was recorded.
In Argentina, palaeomagnetic data obtained for
the Guandacol Formation (early Carboniferous),
Yalguaraz Formation (Middle Carboniferous),
and Portezuelo del Cenizo Formation (Late
Carboniferous-Triassic) suggest two possible
interpretations for the position of the respective
palaeopoles in the polar wandering curve of
South America. According to the preferred interpretation,
the areas now covered by the Yalguaraz
and Portezuelo del Cenizo rocks belong
to an independent plate (Patagonian plate), which
has been welded to the South American one in
post-Carboniferous time. This interpretation
suggests correlation of the Yalguaraz with the
Taiguati Formation (Moscovian) and the Portezuelo
rocks with those of the Piau'i Formation
of northern Brazil (Pennsylvanian), the lower
portions of the Itararé Subgroup (Stephanian)
and the La Colina Formation (Westphalian-
Stephanian).
In the Chubut area, new fossiliferous beds, including
brachiopods and nautiloids, have been
recorded in Upper Palaeozoic rocks at Estancia
La Casilda. The section contains also a unit of
large in situ lycophyte roots and with Sphenophyllum
showing attached strobili.
The Permian Arroyo Totoral Formation at
Dique Anzulon, La Rioja is a 100 m thick sequence
of fanglomerate deposits passing upwards
to a fluviatile sequence which becomes finer upwards
and contains fossil plants including the
licophyte Brasilodendron.
In the Amambay Department, in eastern Paraguay,
sediments previously assigned to the
Palaeozoic proved to be the Mesozoic instead.
Palaeozoic rocks recorded in Bella Vista Department
are Late Palaeozoic in age and contain
fossil plants, among which large stumps of
petrified ferns belonging to the Marattiales.
The Guandacol Formation of the Huaco area,
western Argentina, was shown to be about
320 m thick and subdivisable into three members,
the lower one with rafted clasts and traces
of Orchesteropus atavus, the middle one
with turbidites and Orchesteropus, and the uppermost,
also of turbidite faciès and with abundant
ripples. The Tupe Formation in the same area
(90 m thick) is a fining upward sequence of sandstones.
In the Sierra de Mas area, the Guandacol
Formation may be divided into three
parts, the middle one of turbidite facies and
containing Orchesteropus.
The Bajo de Veliz Formation yielded the first
fossil spiders in the Gondwana area. Two of the
genera already described, Gondwanarachne Pinto
and Hünicken and Magarachne Hunicken, are
among the largest arthropods so far reported.
On the basis of its insect fauna the Bajo de Veliz
Formation is interpreted as being Late Carboniferous.
At the northern extremity of the
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The Chancani Formation in Cordoba had its age
established as Middle to Late Carboniferous on
a palaeontological basis.
In the Paganzo Basin, a newly found turbiditic
sequence below the Lagares Formation may constitute
a new formation within the Paganzo.
Reworked palynomorphs from an older Palaeozoic
section have been recorded in Carboniferous beds
from the Noroeste Basin, in Argentina.
In the Calingasta-Upsallata area, the newly described
El Raton Formation megaflora contains
pteridosperms indicative of pre-early Permian
age for the unit.
Carboniferous beds from the Tiquina straight
contain an assemblage with Retispora lepidophyta
and Umbellasphaeridium scharicum.
The invertebrate fauna of the Agua del Jagüel and
Las Salinas Formation contains species of the
bryozoans Eliasopora, Fistulamina and Septa topora
in association with Orbiculoidea and Lingula
of biostratigraphic/palaeoecologic importance.
In the Sierras Australes, varve-like rhythmites
were recorded for the first time in the Sauce
Grande Formation.
A Glacial origin for the Carboniferous beds of
the Hoyada Verde Formation was confirmed on
the bases of a newly found boulder pavement.
Sediments of the Tarija Formation correspond to
a series of mud-flows and other mass movement
deposits.
Upper Palaeozoic beds in the Cerro la Chilca,
San Juan, are 900 m thick and bounded by a lower
fault and upper angular unconformity. Finding of
Calamites peruvianus indicates a Middle-Late
Carboniferous age for the beds.
Preliminary palaeomagnetic determinations of
rocks from the Los Monos Formation (Devonian),
from Subandean Bolivia, yielded a palaeopole at
274. 0°Eand 32. 2°S, which is consistent with the
Morel and Irving's (1978) polar wandering curve
for South America.
In the Paraná Basin of Brazil, a regional revision
of facies and the environment of the deposition
of the Itararé Subgroup indicates that the diamictites
and associated sediments of this unit in
Paraná and Santa Catarina may fit into three main
facies: (a) grounded-glacier facies; (b) deformed
sandstone/flowtill facies; and (c) glacial
marine facies.
Palaeobotanical results for the Paraná Basin include
the description of new taxa (Ponsotheca
roesleri, Cyclodendron brasiliensis), revision
of collections and new findings of fossil floras.