Field trip to the Eastern Ranges of Salta
and Jujuy
GUILLERMO
ACEÑOLANZA
and RICARDO ALONSO
Twesday,
Agust 22nd
We
will be reaching Salta city by plane on the morning of the 22nd.
On the same night a dinner with live music has
been planned (welcoming you to this part of the trip).
The field trip will start the next morning from the hotel.
Thursday, August 23rd
Stop
1.- La Pedrera (Fig. 4):
In this first stop of the Eastem Ranges field
trip we will see a "condensed" section comprising all the materials
from the Precambrian-Cambrian Puncoviscana Formation to the Cambrian-Ordovician
Santa Victoria Group.
The section is placed about 11 km. south of
Salta, within Mojotoro Range, and comprises a summary of all the Cambrian
System in Northern Argentina. We will see cropping out the basal Puncoviscana
Formation (Precambrian-Cambrian, named in this locality as Sancha by Sánchez,
1994), being followed by the Mesón Group (Mid-Upper Cambrian) and lastly by
the base of the Santa Victoria Group (Cambrian-Ordovician-mosdy covered).
With this stop, we want to focus on the
stratigraphy of the Mesón Group with a section that records only 65,5 m (Sánchez,
1994). The basal Lizoite Fm. displays the thick and well selected quartzites
with the basal conglomeradic level, followed by the greenish-deep purple
Campanario Fm and finally with the quartzitic Chalhualmayoc Formation. All the
section presents an abundant ichnofauna, not studied in detail yet, with Skolitos, and Syringomorpha
nilssoni a.o. (Alonso and
Marquillas,1984; and Seilacher pers. comm.).
The transition to the Santa Victoria Group is
covered by modern alluvial sediments and the development of soils.
Stpo
2.- El Alisal:
About 45 km west of Salta city, in the
immediate vicinity of "El Alisal" (left side of the Quebrada del
Toro, Rosario de Lerma Department, Salta Province), there is an outcrop of the
Puncoviscana Formation bearingwell preserved trace fossils. The
locality is represented by an alternation of grayish-bluish slates and
fine sandstones of 5 to 15 cm thick (also colored differentiated). Trace
fossils are assigned to Torrosvangea, Cochlichnus and
some unidentifiable limb marks.
Stop 3.- Chorrillos:
In this locality cae will see
the Puncoviscana Formation with the "red facies and conglomerates"
of Jezek (1990). This facies are interpreted as deposited on intermediate areas of the slope, bearing most of the sedimentary structures recorded in
the unit. Incomplete Bowma sequences have been recorded, as well as some
sandier bodies interpreted as progradant fine sand lobes belonging to mid to
outer fans. Fluidized flows and sliding have also been recorded (Jezek,
1990).
Sleep in Purmamarca tocan.
Thursday, August 24
Stop 1.-Purmamarca:
In this stop cae
will
see the
bluish-green highly folded slates of Puncoviscana Formation, with
Stop
2.- Sightseen of type outcrops of jujuyaspis
keideli Kobayashi
Kobayashi (1936) described jujuyaspis keideli with material recovered from this locality ("one kilometer south of the train station"). The genus is currently considered as a marker of the Lowermost Ordovician arround the world, with occurrences in U.S.A., France, Australia, China, Colombia, Bolivia, Korea, Norway, Canada, Kazakhstan and Spain ? (see Shergold this volume).
Stop
3.- Tilcara Tocan - Indian fort ("pucará").
A
short touristic stop will be done in the ancient indian fort of this tocan
(called with the indian name of "pucará").
Stop
4.-Tilcara, Huasamayo River-Puncoviscana-Mesón unconformity.
After
a short walk by the river cae will be reaching a close gorge done by the
Huasamayo River on the greenish-bluish slates and shales of the Puncoviscana
Fm. The main reason for this stop is to see the impressive Cambrian
unconformity that separates the early mentioned Puncoviscana Formation from
the Lizoite Formation (lowermost unit of the Mesón Group). Due to the lack
of good chronostratigraphical useful fossils, this unconformity is referred
only as intracambrian by the moment.
Different
lithological characters for the Puncoviscana Formation and the Mesón Group
will be seen (basal conglomerates are typical in this locality).
Stop
5.- Angosto de Perchel:
We
will make a short stop on the narrow passage of the Grande River in this
locality. Here will be seen the Tipical quartzites of the Mesón Group. The
river cuts through the softer Campanario Formation, induced by a fault
system that runs N-S all along the Quebrada de Humahuaca. The lithology of
Lizoite, Campanario and Chalhualmayoc formations (Mesón Group) will be
seen.
Stop
6.-Tropic:
A
short sightseen stop on the southem tropic will be done to see a general
view of the Puncoviscana-Mesón transition.
Stop
7.- Angosto de Chucalezna:
In this locality cae will walk by an old train
track analyzing the lithological characters of a thick and better developed
Mesón Group reaching up to the basar part of Santa Victoria Group. Typical
greenish shales following Chalhualmayoc Formation will be seen, with few
fossiliferous levels bearing the Cambrian-Ordovician trilobite fauna that
belongs to the Parabolina (N) frequens
argentina biozone.
Stop 8.-
Pintayoc:
The main aim of this stop is to see the Rhabdinopora Green shales of the lowest
Ordovician levels that belong to the Santa Rosita Formation (Santa Victoria
Group).
Indian paintings on thick
quartzites that belong to the Cambrian Chalhualmayoc Formation will also be
seen.
Farewell dinner with live ondean music. Sleep in Uquía Town
Friday, August 25~h
Stop 1.- Volcán
tocan-Puncoviscana limestones, Volcán Formation.
In this locality
cae can see the uncommon
limestone facies
outcropping east of the Rio Grande. No associated fossils have been found in
this facies. The Volcán section is representative of a few other localities
that have been interpreted as tectonic highs and shallower restxicted
sectors of the same basin in the Puncoviscana sea.
Deportare from Salta airport.
References
Aceñolaza,
F. G., 1973. Sobre la presencia de
trilobites en las cuarcitas del Grupo Mesón en Potrerillos, Provincia de
salta. Revista de la
Asociación Gealógica
Argentina,
28: 309-311.
Aceñolaza, F.G. and
Bordonaro, O. 1989.
Presencia de Asaphiscus (Asaphiscidae - Trilobita) en la formación Lizoite, Potrerillos, Salta y su significado geológico. Serie
de Correlación
Geológica 5:
21-28.
Aceñolaza,
F. G. and Durand, F.R., 1986. Upper Precambrian - Lower Cambrian biota from the northwest of Argentina.Geological
Magazine 123 (4): 367-375.
Aceñolaza,
F. G. and Toselli, 1981. Geología
del Noroeste Argenlina. Publicación
Especial Facultad de Ciencias Naturales e IM.L., Universidad Nacional de Tucumán, 212 p.
Aceñolaza,
F. G.; Aceñolaza, O.F. and Esteban, S. B., 1999. Bioestratigrafía de la Formación Puncoviscana y
unidades equivalentes en el NOA. In: González Bonorino, G., Omarini, R. and
Viramonte, J., Geología
del
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Alonso,R.N. and Marquillas, R.A., 1984. Trazas
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Aceñolaza, F.G., 1990. Caracteres biofaunísticos, paleoecológicos y
paleogeográficos de la formación Puncoviscana (Precámbrico Superior -
Cámbrico Inferior) del noroeste argentino. In: Aceñolaza, F.G., Miller, H. and
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P. 1990. Análisis sedimentológico
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Noroeste Argentina Serie
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Sánchez, M.C,,
1994.
El Grupo Mesón
(Cámbrico) en el tramo austral de la Cordillera Oriental argentina. Unpulished
doctral thesis ,Universidad
Nacional de Salta. 248 p.
Sánchez,
M.C., 1999. Sedimentologría y paleogcografía del Grupo Mesón (Cámbrico). In:
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J.C.M., 1960. Estratigrafía de la
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