Early Devonian organic-walled phytoplankton and miospores from the Precordillera Basin of San Juan, Argentina: biostratigraphic and paleobiogeographic implications

Abstract

The palynological assemblages of the Talacasto and Punta Negra formations, from the Argentinean Precordillera, were analysed. Marine phytoplankton is dominant in both stratigraphic units. ?Cymatiosphaera florida, Evittia sommeri, Palacanthus ledanoisii, Riculasphaera fissa, Schizocystia pilosa, Tysanoprobolus polykion and Winwaloeusia distracta are among the most age-significant phytoplankton species of the Talacasto Formation, while Amicosporites sp. cf. A. streelii, Dictyotriletes emsiensis Morphon, Dictyotriletes favosus and ?Knoxisporites riondae prove the most biostratigraphically significant miospore species. A Lochkovian to probably late Pragian age is interpreted based on the marine and terrestrial palynomorphs. The lower part of the Punta Negra Formation contains phytoplankton species such as Cordobesia oriental, Cordobesia uruguayensis, Duvernaysphaera stellata, Navifusa bacilla, Polyedryxium fragosulum and Pterospermella sp. cf. P. pernambucensis as well as the miospores Acinosporites sp. cf. A. lindlarensis and Apiculatasporites microconus, which suggests an early Emsian age. Taxa such as Cordobesia, Schizocystia and Winwaloeusia support affinities of the Argentinean assemblages with Gondwana.

Devonian bryozoans from Argentina: new cosmopolitan components of Southwestern Gondwanan basins

“…Fossils are preserved in gray-bluish sandstones (Blue Sandstone Member of Baldis, 1975). In spite of preliminary early Emsian ages interpreted for these fossiliferous levels (Herrera and Bustos, 2001, p. 369), recent palynological data suggest a late Pragian age (García Muro et al, 2017, 2018).…”

“…Conodonts and graptolites are absent and goniatites are extremely rare as in other closely related Lower–Middle Devonian Malvinokaffric basins, so that biostratigraphic calibrations are based on alternative groups. Thus, a Lochkovian to Emsian age was classically proposed for the Talacasto Formation based on brachiopod and palynological data (Benedetto et al, 1992; Herrera, 1993, 1995a, b; Le Hérissé et al, 1997; Herrera and Bustos, 2001; García-Muro et al, 2014, 2017, 2018). According to brachiopod studies, the basal part of this unit is early (but not earliest) Lochkovian in the entire basin, while its top is diachronous and progressively younger to the north (Racheboeuf and Herrera, 1994; Herrera and Bustos, 2001).…”

“…The uppermost levels at the type section of Talacasto Creek correspond to a distinctive nodule-bearing horizon of ochre color referred as a stratigraphic marker by Keidel (1921) and Astini (1991). The strata overlying this marker horizon were considered early Emsian in age or younger (Herrera and Bustos, 2001), but recent palynological information suggests they might be Pragian (García Muro et al, 2017, 2018).…”

The homalonotid trilobiteBurmeisteriaSalter, 1865 in the Lower Devonian of Argentina: new data in the context of southwestern Gondwana

“…The Lower to Middle Devonian Punta Negra Formation lies above the Talacasto Formation. Because classical biostratigraphically useful fossil groups are unavailable, as in other closely related Lower–Middle Devonian Malvinokaffric basins, biostratigraphic calibrations are based on brachiopod and palynological data (Benedetto et al, 1992; Herrera, 1993, 1995a, b; Le Herissé et al, 1997; Herrera and Bustos, 2001; García-Muro et al, 2014, 2017, 2018). The base of the Talacasto Formation is early (but not the earliest) Lochkovian throughout the entire basin (Fig.…”

“…The uppermost levels of the type section of Talacasto Creek include a distinctive, ochre-colored, nodule-bearing marker horizon identified by Keidel (1921) and Astini (1991). The strata overlying this marker horizon were considered to be early Emsian in age or younger (Herrera and Bustos, 2001), but recent palynological information suggests they might be Pragian (García Muro et al, 2017, 2018).

Figure 1.Map of the studied area in the Central Precordillera of the San Juan Province (Argentina), showing Silurian–Devonian outcrops between San Juan and Jáchal cities and the main fossiliferous localities.

Figure 2.Stratigraphic sections and intervals where Burmeisteria occurs.

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