Abstract
Recent biostratigraphic studies on the western argentine Puna recorded the Middle Ordovician conodont Baltoniodus cf. B. navis (Lindström) for first time, related to key graptolite taxa of the Central Andean Basin. The analyzed material comes from the lower and middle thirds of the turbidite succession exposed at the Huaytiquina section, Salta Province, which was previously assigned to the “Coquena” Formation. The conodont fauna was recovered from the calcareous sandstone beds intercalated in the middle portion of this unit, and it is composed by species of the genera Baltoniodus, Gothodus, Trapezognathus, Drepanoistodus, Drepanodus, and Protopanderodus, among others. The conodont association indicates a middle Dapingian (Dp2) age, linking the conodonts of the Argentine Puna with those from Baltoscandinavia and South China. The conodont productive levels also contain graptolites assignable to Tetragraptus bigsbyi (Hall) and Isograptus sp. They are located overlying strata bearing Azygograptus lapworthi Nicholson and underlying deposits with Xiphograptus lofuensis (Lee). The graptolite associations are indicating a Dapingian age (Dp1-Dp2) for the lower and middle portions of the “Coquena” Formation. The current findings from the western Puna, as well as the record of Azygograptus lapworthi related to the early Dapingian (Dp1) index conodont Baltoniodus triangularis in the Argentine Cordillera Oriental, are suggesting that a high-resolution correlation between both geomorphological regions is possible. This also documents that the Cordillera Oriental as well as the Puna were connected parts of the Central Andean Basin, during the interval from the Lower Ordovician (Floian) to the Middle Ordovician (Dapingian), instead of corresponding to the source and infill sectors of the basin, respectively. Furthermore, the regional and global correlations are discussed, and the potential of the Ordovician successions of the Argentine Puna for future advances on conodont-graptolite high-resolution biostratigraphy is highlighted.
Highlights
Conodonts and graptolites are the most important groups to define global stages and correlations of the Lower Palaeozoic sequences (Cooper et al, 2001; Bergström et al, 2004, 2009; Wang et al, 2005, between others)
The current findings from the western Puna, as well as the record of Azygograptus lapworthi related to the early Dapingian (Dp1) index conodont Baltoniodus triangularis in the Argentine Cordillera Oriental, are suggesting that a high-resolution correlation between both geomorphological regions is possible
B. navis associated with Tetragraptus bigsbyi and Isograptus sp., located in the middle portion of the “Coquena” Formation, at the Huaytiquina section confirm a Middle Ordovician (Dapingian, Dp2) age for the studied levels
Summary
Conodonts and graptolites are the most important groups to define global stages and correlations of the Lower Palaeozoic sequences (Cooper et al, 2001; Bergström et al, 2004, 2009; Wang et al, 2005, between others). Later on, Albanesi and Ortega (2016) summarized a graptolite biostratigraphic framework for the Ordovician System of Argentina, including previously postulated graptolite biozones by diverse authors for the Argentine northwestern Andes They referred the Azygograptus eivionicus Biozone (sensu Brussa et al, 2008) to the Lower Dp1?, based on the records of the nominal taxa in the Huaytiquina area, western Puna (Monteros et al, 1996), and the Muñayoc section, at the Quichagua range, northeastern Puna (Martínez et al, 1999). The aim of this contribution is to describe the first conodont record from the Middle Ordovician deposits of the western Argentine Puna and stratigraphically related graptolites, discussing the biostratigraphic ranges of conodont and graptolite key species, to precise the age of the bearing strata and possible biostratigraphic correlations
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