Ordovician and Silurian graptolite assemblages from Cerro del Fuerte, San Juan Province, Argentina

Abstract

A description is given of three transects through the Silurian strata of Cerro del Fuerte, San Juan Province, Argentina. All are in the Precordillera structural belt; the Silurian strata probably have conformable boundaries with the Ordovician and Devonian, and there is a regional angular unconformity at the base of the Carboniferous. The Silurian includes two formations, the La Chilca below and the Los Espejos above. Both formations exhibit a coarsening upwards sequence: the Los Espejos Formation spans the Wenlock, Ludlow and, probably, Piidoli epochs, the first being of relatively fine sediments and the latter two of coarser sediments. The third transect also includes Devonian sediments which seem to represent, albeit incompletely, a third coarsening upwards cycle. The graptolite faunas have been extensively collected and form the basis of the systematic section of the paper. Late Ordovician, Llandovery and Ludlow faunas are described.

Graptolite biostratigraphy of the Lower Silurian (Llandovery) shelf deposits of the Western Iberian Cordillera, Spain

“…Jaeger, 1976). This species, however, comes from Lower to Mid-Llandovery rocks in South America and Africa (Turner, 1960;Jaeger, 1976;Grahn & Paris, 1992;Rickards et al 1996), whereas the Spanish material comes from the Upper Llandovery (mid-Telychian) strata. The Spanish specimens are narrower, and have apertural hoods instead of spines.…”

First record of Lower Silurian conodonts from South America: biostratigraphic and palaeobiogeographic implications of Llandovery conodonts in the Precordillera of Argentina

“…Several sections of this formation, which here consists of a > 100-m-thick succession of siltstones, mudstones, and sandstones (Fig. 4), have recently been described by Benedetto (1995b) and Rickards et al (1996). A few graptolite species in the lowermost exposed part of the La Chilca Formation on Cerro del Fuerto were interpreted by Rickards et al (1996) as representing an interval within the atavus through triangulatus biozones, and to be of upper Rhuddanian to lower Aeronian age.…”

“…4), which are shown at level 1 in figure 2 of Benedetto (1995b) and level 14 in figure 3 of Rickards et al (1996). Comparison with the more completely exposed succession at Cerro La Chilca indicates that these coquinas are approximately 40-50 m above the base of the formation.…”

“…4), have recently been described by Benedetto (1995b) and Rickards et al (1996). A few graptolite species in the lowermost exposed part of the La Chilca Formation on Cerro del Fuerto were interpreted by Rickards et al (1996) as representing an interval within the atavus through triangulatus biozones, and to be of upper Rhuddanian to lower Aeronian age. These graptolitebearing strata are overlain by siltstones and finegrained sandstones with a 5-m-thick interval of shelly fossil coquinas (Benedetto, 1995b).…”

Palynology and palynofacies analysis of a Silurian (Llandovery–Wenlock) marine succession from the Precordillera of western Argentina: Palaeobiogeographical and palaeoenvironmental significance

“…) on the lower and middle part of the stratigraphic unit. Based on graptolites, brachiopods and conodonts, it was dated as Late OrdovicianLlandovery, with its top doubtfully assigned to the Wenlock (e.g., Cuerda, 1965;Kerlleñevich and Cuerda, 1986;Brussa, 1987;Cuerda et al, 1988;Benedetto, 1995;Rickards et al, 1996;Lehnert et al, 1999;Albanesi et al, 2006).…”