Glaciomarine sequence stratigraphy in the Mississippian Río Blanco Basin, Argentina, southwestern Gondwana. Basin analysis and palaeoclimatic implications for the Late Paleozoic Ice Age during the Tournaisian.

Abstract

The Late Paleozoic Ice Age (LPIA) has been well recorded in the uppermost Mississippian–Pennsylvanian of Gondwana. Nevertheless, little is known about the temporal and geographic dynamics, particularly during the early Mississippian. We report on exceptional Tournaisian glaciomarine stratigraphic sections from central Argentina (Río Blanco Basin). Encompassing c. 1400 m, these successions contain conspicuous glacigenic strata with age constraints provided by palaeontological data and U/Pb detrital zircon age spectra. A variety of marine, glaciomarine and fan-deltaic environments indicate relative sea-level variations mainly associated with tectonism and repetitive cycles of glacial activity. Provenance analysis indicates a source from the Sierras Pampeanas basement located to the east. Fifteen sequences were grouped into three depositional models: (1) Transgressive Systems Tracts (TST) to Highstand Systems Tracts (HST) sequences unaffected by glacial ice; (2) Lowstand Systems Tracts (LST) to TST and then to HST with glacial influence; and (3) non-glacial Falling-Stage Systems Tracts (FSST) to TST and HST. The glacial evidence indicates that the oldest Mississippian glacial stage of the LPIA in southwestern Gondwana is constrained to the middle Tournaisian. In contrast with previous descriptions of Gondwanan coeval glacial records, our sequence analysis confirms complex hierarchical climate variability, rather than a single episode of ice advance and retreat.Supplementary material: Detailed stratigraphic sections, palaeocurrents and compositional analysis and U/Pb detrital Zr methodology and data are available at: https://doi.org/10.6084/m9.figshare.c.5011424

Effects of Uplift on Carboniferous Exhumation and Mountain Glaciations in Pericratonic Areas of SW Gondwana, Central Argentina

“…This is because rock uplift forces (which were controlled in the landscape modeling) play an important role in these computations. The occurrence of middle Mississippian alluvial conglomerates overlying earlier Mississippian marine strata (see Ezpeleta et al, 2020;Milana & Di Pasquo, 2019), strengthen our hypothesis. However, like for Model 1, it requires a suitable geodynamic mechanism to explain remarkable mountain building across the pericratonic distal foreland.…”

“…Model 2 (i.e., Carboniferous mountain building and exhumation), in contrast, allows reproducing a simpler thermal history (Figure 3) with realistic paleoelevation, but also matches well with the preserved stratigraphic and erosional history. In the few outcrops where such history is preserved (e.g., Precordillera), marine lower‐middle Devonian strata unconformably underlay marine lower Mississippian rocks (Ezpeleta et al., 2020). This suggests a late Devonian erosional stage (associated with some of the deformational processes stated above, or another one), was followed by basin subsidence under sea level in the Mississippian.…”

“…The formation of the mountains, where Carboniferous paleovalleys were embedded, was interpreted in term of orogenic processes along the SW margin of Gondwana during middle Devonian (Isbell et al., 2012, see Table 1), and related to collision of continental terranes, deformation that has been more recently (and alternately) associated with flat subduction (debate out of the scope of this contribution, see discussions in Alasino et al., 2012; Heredia et al., 2016, 2018; Willner et al., 2005, 2011). However, the formation of mountain glacier paleovalleys postdate these orogenic events by > 60 myr (see Ezpeleta et al., 2020; Isbell et al., 2012) while most of the paleocurrent indicators and glacial records support a significant ice activity toward the east of the Gondwana margin, toward the pericratonic areas (in the Argentine Sierras Pampeanas, e.g., Ezpeleta et al., 2020; Valdez Buso et al., 2021). Alternatively, the mountain glacial landscape evolution has been associated with a rifting phase (Astini et al., 2011), but no Mississippian structures have been described to date along the inner SW Gondwana margin.…”

Porongodendron minitensis gen. nov. sp. nov. a new lycopsid from the Mississippian of Argentina with adaptations to tundra-like conditions

“…The stratigraphic record surveyed in this contribution corresponds to the Mississippian filling of the Río Blanco Basin (Scalabrini Ortiz 1972), a high paleolatitude southern basin (>60° according to Isaacson et al 2008) that forms part of a series of Late Paleozoic basins developed in southwestern Gondwana linked to the functioning of an active tectonic margin (Limarino and Spalletti 2006). In addition, these Mississippian units contain many glacial features which, together with the paleogeographical position of the basin, and further evidence from other coeval regions of southwestern Gondwana, suggest a cold wet climate during this interval (Iannuzzi and Rösler 2000;Caputo et al 2008;Isaacson et al 2008;Prestianni et al 2015;Ezpeleta et al 2020).…”

The Late Palaeozoic Ice Age unconformity in southern Namibia viewed as a patchwork mosaic

“…Indeed, basins with thick glaciomarine sequences (e.g. the Rio Bianco Basin, Argentina: 1.4 km thick) favour rather nuanced interpretations for earlier phases of the LPIA, with climate phases hierarchically organised with glacial advance, retreat and non-glacial intervals (Ezpeleta et al, 2020).…”