Silurian to Early Devonian organic‐walled phytoplankton and miospores from Argentina: biostratigraphy and diversity trends

Abstract

The distribution and diversity of marine palynomorphs, such as acritarchs and chlorophytes, and terrestrial palynomorphs, such as miospores, are controlled mainly by palaeoenvironmental and palaeogeographical conditions. Recently, global patterns of organic-walled phytoplankton were illustrated for the Late Silurian to earliest Devonian based on data from different stratigraphic sections and palaeocontinents. Here, we analyze the Silurian and the Early Devonian diversity in the Argentinean Precordillera, Central Andean, and Chacoparanense basins. The evolution of the diversity is evaluated in a well-constrained biostratigraphic framework, bearing in mind local palaeoenvironmental conditions and changes within each basin. Taking into account recently published and unpublished data from well-dated sections, the biodiversity of Silurian phytoplankton seemingly increases upwards, reaching its maximum peak during the Ludlovian. However, palynomorphs are rarely recorded in Wenlockian strata, and the supposed Pridolian layers are not confidently well constrained. The first record of trilete spores in Argentina is Ludlovian, approximately 30 million years after their first appearance in the Late Ordovician. Palynomorph diversity increases in the Early Devonian, with a higher diversity of miospores than that of the marine phytoplankton. We interpret possible discrepancies in biodiversity trends of organic-walled phytoplankton between Argentina and other regions, as related to the quantitatively and qualitatively disparity of data, as well as the lack of rigorous biostratigraphic and palaeoenvironmental assessments of the Argentinean basins.

The palynological record across the Ordovician/Silurian boundary in the Cordillera Oriental, Central Andean Basin, northwestern Argentina

“…The Central Andean Basin had a complex evolutionary history as foreland basin during the early-middle Palaeozoic with an active subduction zone to the west (Astini, 2008;de la Puente and Rubinstein, 2013b;Rubinstein and García Muro, 2013) which was probably inducing unfavorable palaeoenvironmental conditions for the development of land vegetation.…”

“…Interestingly, the Llandovery deposits of the Precordillera Basin and the Central Andean Basin, which are respectively represented by the La Chilca Formation and the Lipeón Formation, had not yielded any trilete spores so far (Rubinstein and García Muro, 2013).…”

Upper Silurian miospores from the Precordillera Basin, Argentina: biostratigraphic, palaeonvironmental and palaeogeographic implications

“…Palynological studies, mainly those concerning marine organic-walled phytoplankton, shed light on the age of this unit, thus allowing the interpretation of an age not older than Ludlow for the base of the Los Espejos Formation in different sections (Rubinstein & García Muro, 2011). These palynomorphs, however, did not confirm the Pridoli and Lochkovian ages for the uppermost part of the Los Espejos Formation (Rubinstein, 2001; Rubinstein & García Muro, 2011, 2013). Therefore, palynological data indicates a Late Silurian age for the formation.…”

“…The incorporation of detailed palynological studies from more sections of the Los Espejos Formation allows us to recognize the presence of miospore assemblages (trilete spores and cryptospores) in almost all of them, from the base to the top, with varying abundances, diversity and quality of preservation (Rubinstein, Le Hérissé & Steemans, 1996; Rubinstein & Brussa, 1999; Rubinstein, García Muro & Steemans, 2010, 2011; Rubinstein & García Muro, 2011, 2013).…”

Preface: Lower Palaeozoic fossils, biostratigraphy and events from western Gondwana

“…Rubinstein and García Muro () provide a preliminary study on diversity trends of organic‐walled phytoplankton from the Precordillera, Central Andean and Chacoparanense basins of Argentina during the Late Silurian and Early Devonian. The authors consider possible discrepancies in the diversity trends of phytoplankton between Argentina and other regions, in relation with biostratigraphical and palaeoenvironmental data.…”