Middle Devonian microfloras from the Chigua Formation, Precordillera region, northwestern Argentina

Abstract

Rich palynological assemblages have been obtained from the Middle Devonian Chigua Formation (Chinguillos Group, San Juan Province), western Precordillera, Argentina, at two new localities (Del Chaco and Don Agustín creeks). From the palyniferous levels at Del Chaco Creek, there are two assemblages: one is very rich in microplankton (assemblage 1) whereas the other is dominated by spores (assemblage 2). The level obtained from Don Agustín Creek, poorest in overall taxa, is also rich in microplankton (assemblage 3). Compared with coeval microfloras elsewhere, a late Emsian–early Eifelian, and an early Givetian age are proposed for the first and the second assemblages respectively. A third assemblage (assemblage 3) tentatively represents a timespan around the Givetian–Frasnian boundary. The proposed age based on the palynomorphs reinforces previous palaeontological records. Variation in the microplankton diversity, fluctuations in the microplankton/spore ratio and differences in acritarch morphology are used here to interpret changing proximity to palaeoshoreline and so to recognize fluctuations in relative sea level that occurred during the deposition of the Chigua Formation.

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

“…The limited diversity and relatively poor preservation of the phytoplankton of the La Chilca Formation could be interpreted as a result of the stressed post-glacial environment (Paris et al, 2000;Vecoli, 2008). Moreover, the geodynamics of the Silurian basin (Ramos, 2004) and the later Andean orogeny probably affected the fossil preservation (Amenábar, 2009).…”

Middle Devonian herbaceous lycopsid Haplostigma from the Paraná Basin, Brazil: Taxonomy, biostratigraphy and Phytogeography

“…In turn, from the Late (Matsumura et al, 2013;. From the Givetian/Early Frasnian interval to the Famennian, the genus has also been recorded, in Argentina, in the Lólen (Cingolani et al, 2002), Chiguá (Amenábar, 2009), and Punta Negra formations (Frenguelli, 1951;1952;Peralta, 2013); in Bolivia, in the Los Monos and Iquiri formations (Di Pasquo et al, 2013); in Chile, in the El Toco Formation (Moisan et al, 2011); in South Africa, in the Upper Bokkeveld and Lower Witteberg groups (Seward, 1932;Plumstead, 1967); in Antarctica, in the Wilkins Formation (Mildenhall and Schopf, 1980), Beacon Heights Orthoquartzite (Plumstead, 1962), Aztec Siltstone (McLoughlin and Long, 1994), and Dover Sandstone (Schopf, 1968); and in Australia, in the Fiery Range Porphyry (McLoughlin and Long, 1994).…”

“…The age of each Devonian unit was established by several investigators based on different fossil groups (palynomorphs, plants, marine invertebrates, and vertebrates; Table 6). Basically, the dating of Western Gondwana sedimentary deposits has been based mainly on palynomorphs (Daemon et al, 1967;Lange, 1967;Loboziak and Streel, 1995;Loboziak and Melo, 2000;Grahn et al, 2002;2006;2013;Melo and Loboziak, 2003;Grahn, 2005;Rubinstein et al, 2005;Gaugris and Grahn 2006;Di Pasquo, 2007;2013;Di Pasquo et al, 2009;2013;Amenábar, 2009;Mendlowicz Mauller et al, 2009;Breuer and Grahn, 2011), although vertebrate remains were also found in South America (Janvier and Villarroel, 2000;Young et al, 2000;Maisey et al, 2002;Young and Moody, 2002;Burrow et al, 2003) and South Africa (Gess and Coates, 2015). In contrast, in Eastern Gondwana sedimentary deposits vertebrate remains are mainly used for relative datings (Long, 1989;Young, 1993;Young, 1995, Long andTrinajstic, 2010).…”

“…Thus, the chronostratigraphic position of sedimentary deposits as well as their correlations remain relatively speculative or imprecise. The stratigraphic position of the fossil plants and marine invertebrates in the Devonian of Gondwana, together with palynological data, requires further study, except perhaps for data from Argentina, Bolivia and Brazil, where a robust framework has been built over the last ten years (Di Pasquo, 2007;2013;Di Pasquo and Noetinger, 2008; Page 13 of 55 A c c e p t e d M a n u s c r i p t Di Pasquo et al, 2009;2013;Amenábar, 2009;Grahn et al, 2013). Although different fossil groups were used, the main stratigraphic range of occurrence of Haplostigma is well marked within the Eifelian-Givetian interval, as observed by Di Pasquo et al (2013) and Moisan et al (2011) (Fig.…”

“…Western Precordillera (Baldis and Sarudiansky, 1975;Baldis and Peralta, 1999;Amenábar, 2009;Di Pasquo et al, 2009). 3.…”