El Alisal: a new locality with trace fossils of the Puncoviscana Formation (Late Precambrian­Early Cambrian) in Salta Province

ACEIVOLAZA, F.G. AND   TORTELLO, M

The Puncoviscana, Suncho and Las Aguaditas/Negro Peinado formations constitute a thick siliciclastic folded succession that cropout on a strip of about 800 km long and 150 km wide in northern Argentina Jujuy, Salta, Tucumán, Catamarca and La Rioja provinces). Sequences are characterized by very low methamorphic sediments grading into schists, some turbidites, pelagic clays, limestones and rare volcanic rocks. Based on paleoichnological data, these units have been assigned to the Late Precambrian-Early Cambrian (eg. Aceñolaza el al., 1988).  

Some main trace fossils localities are Purmamarca (Jujuy), Campo Quijano, Cuesta Muñano, San Antonio de los Cobres (Salta) and Chuscha (Tucumán). The trace fossils recorded until now are diverse: Asaphoidichnus, cochlichnus, Didymaulichnus, Dimorphichnus, Diplichnites, Glockeria, Gordia, Helmintoida, Helminthopsis, Helminthorhape, Helminthoidichnites, Monomorphichnus, Multipodichnus, Neonereites, Nereites, Oldhamia, Phycodes, Planolites, Protichnites, Protopaleodictyon, Protovirgularia, Scolicia, Squamodictyon, Tasmanadia, Torroavangea, Treptichnus, Beltanelliformis and Sekwia (Aceñolaza and Durand, 1973, 1982, 1984, 1986, 1987; Aceñolaza et al., 1999; Durand, 1992; 1993; 1994; 1996; Durand, and Aceñolaza, 1990; Durand et al., 1993).  

About 45 km west of Salta city, in the inmediate vicinity of "El Alisal" (left side of the Quebrada del Toro, Rosario de Lerma Departament, Salta Province), we have found a new outcrop of the Puncoviscana Formation bearing well preserved trace fossils. The locality is represented by an alternation of greyish bluish slates and fine sandstones of 5 to 15 cm thick falso colored diferentiated). Trace fossils are assigned to Torrowangea, Cochlichnus and some unidentifiable limb marks (indet.). The first ichnogenus appear as single almost straigth to sligthly bended traces, of 0.6 to 1 mm wide, with some irregularly transverse annulation, being preserved mainly as epirelief; while the sencond one is characterized by smooth and regularly meandering traces of 0.4 to 0.8 mm wide preserved as hyporelief.  

In addition, it is also mentioned for the first time the presence of the ichnogenus Torroswangea in the locality of Chorrillos. Here, the trace fossil is included in the "red shales and conglomerate type" of sediments defined by Jezek (1990), interpreted as deposited on a starved basin characterized by hemipelagic sedimentation Jezek, 1990).  

References:  

Aceñolaza, F G. and Durand, FR.1973. Trazas fósiles del basamento cristalino del noroeste argentino. Boletín de la Asociación Geológica de Córdoba, 2: 45-55.

Aceñolaza, F G. and Durand, FR. 1982. El icnogénero Oldhamia (traza fósil) en Argentina, caracteres morfológicos e importancia estrarigráfica en formaciones del Cámbrico Inferior. 5to Cóngreso Geológico Latinoamericano, 1: 705-720.

Aceñolaza, FG. and Durand, FR. 1984. The trace fossil Oldhamia: Its interpretation and occurrence in the Lower Cambrian of Argentina. Neues jahrbuch fur Geologie und Paldontologie Monatshefte, 12: 728-740.

Aceñolaza, F G. and Durand, FR. 1986. Upper Precambrian - Lower Cambrian biota from the northwest ofArgentina. Geological Magazine 123: 367-375.

Aceñolaza, FG. and Durand, FR. 1987. Paleontología del límite Precámbrico-Cámbrico de Argentina. X Congreso Geológico Argentino, 1: 315-320.

Aceñolaza, FG., Miller, H. and Toselli, A.J.,1988. The Puncoviscana Formación (Late Precambrian - Early Cambrian). Sedimentology, tectonometamorphic history and age of the oldest rocks of NW Argentina. In: Bahlburg, H., Breitkreuz, Ch. and Giese, P (eds.), The Southern Central Andes. Lecture Notes in Earth Sciences 17: 25-37.

Aceñolaza, FG.,Aceñolaza, G.F. and Esteban, S.1999. Bioestratigrafia de la Formación Puncoviscana y unidades equivalentes en el NOA. In: González Bonorino, G., Omarini, R. and Viramonte, J. (eds.), Geología del Noroeste Argentino, Relatorio XIV Congreso GeológicoArgentino, 1: 91­114.

Durand, FR. 1992. Avances y problemas en la definición del limite Precámbrico-Cámbrico en el Noroeste Argentino. Serie Correlación Geológica, 9: 127-138.

Durand, FR. 1993. Las icnofacies del basamento metasedimentario en el Noroeste Argentino: Significado cronológico y aspectos paleogeogxáficos. XII Congreso GeológicoArgentino, 2: 260­267.  

Durand, FR. 1994. Síntesis sobre el conocimiento icnológico del basamento Precámbrico-Cámbrico del noroeste argentino. Acta Geológica Leopoldensia,l7: 733-746.  

Durand, F.R. 1996. La transición Precámbrico-Cámbrico en el sur de Sudamérica. In: Baldis, B. and Aceñolaza, F G. (eds.), Early Paleozoic Evolution in Northwest Gondwana. Serie Correlación Geológica,12: 195-206.

Durand, FR. and Aceñolaza, FG.1990. Caracteres biofaunísticos, paleoecológicos y paleogeográficos de la Formación Puncoviscana (Precámbrico Superior - Cámbrico Inferior) del noroeste argentino. In: Aceñolaza, FG., Miller, H. and Toselli, A.J. (eds.), El Ciclo Pampeano en el Noroeste Argentino. Serie Correlación Geológica 4:71-112.

Durand, FR., Lech, R.R. and Tortello, M.F 1993. Nuevas evidencias paleontológicas en el basamento Precámbrico-Cámbrico del noroeste argentino. Acta Geológica Leopoldensia, 17: 691-701. 

Jezek, P. 1990. Análisis sedimentológico de la Formación Puncoviscana entre Tucumán y Salta. In: Aceñolaza, FG., Miller, H. and Toselli, A.J. (eds.), El Ciclo Pampeano en el Noroeste Argentino. Serie Correlación Geológica 4: 9-36.