Middle Devonian microfloras and megafloras from western Argentina and southern Bolivia: their importance in the palaeobiogeographical and palaeoclimatic evolution of western Gondwana

Abstract

The study of microfloras and megafloras from western Argentina and southern Bolivia presented here extends our knowledge of the biodiversity and succession of floristic events during the Middle Devonian, and hence improves the current biostratigraphy. Among floral remains, species attributable to ‘Haplostigma’ are mostly recorded from the same Grandispora pseudoreticulata and other palynomorph-bearing sections at Balapuca (southern Bolivia) and Del Chaco and La Cortadera creeks in the Precordillera of Argentina. The northernmost record of Grandispora pseudoreticulata is recorded from a third palynoassemblage from the Pando x-1 corehole of northern Bolivia. A great similarity among all these assemblages (notably abundant Grandispora pseudoreticulata) suggests the identification of terrestrial connections, or at least proximity, of these local areas and other regions in South America during the Givetian. Comparison with other contemporary Gondwanan palynofloras shows cosmopolitan species (e.g. Geminospora lemurata, Samarisporites triangulatus, Archaeozonotriletes variabilis, Chelinospora concinna) along with some others with more restricted distribution (e.g. Grandispora pseudoreticulata, Leiotriletes balapucensis, Acinosporites ledundae). This pattern defines an Afro-South American Subrealm, which most likely results from the effects of palaeolatitude and, in a lesser way, local palaeoenvironmental conditions. On the other hand, such a level of cosmopolitanism supports previous palaeogeographical reconstructions where a narrow Rheic Ocean was developed between Euramerica and the northern parts of Africa and South America.

Lycopsids from the Upper Devonian of northern Chile with remarks on the geographical distribution of the morphogenus Haplostigma Seward

“…with spine-like appendages and no true leaves. This has been done for Devonian material from all over Gondwana (Plumstead 1967;McLoughlin and Long 1994;Gutiérrez 1996;Gutiérrez and Archangelsky 1997;Cingolani et al 2002;Di Pasquo et al 2009). …”

“…50°S (Fig. 4), although it should be noted that the identity of this latter species has been questioned (see review in Di Pasquo et al 2009). Most species have rather restricted distribution, except H. irregularis which is absent in southwestern Gondwana but is known from eastern Brazil to southern Australia (Kräusel 1960;Plumstead 1962;Grindley et al 1980;Anderson and Anderson 1985).…”

“…Berry et al 2000;Cingolani et al 2002;Edwards et al 2001a, b;Gerrienne et al 2001;Di Pasquo et al 2009). However, occurrences of Devonian plants in Chile have not yet been documented in detail.…”

“…The genus is widespread in the Middle to Upper Devonian of middle to higher palaeolatitudes in Gondwana and is frequently found in coarsegrained sandstones (Edwards 1990;Di Pasquo et al 2009). …”

“…Haplostigma furquei is the most common species and is restricted to the Middle to Upper Devonian of western Argentina, Bolivia and Chile(Fig. 4;Di Pasquo et al 2009). Haplostigma irregularis is known from western Brazil, South Africa and Antarctica.…”