An integrative physical, mineralogical and ichnological approach to characterize underfilled lake‐basins

Abstract

Lakes are particularly sensitive to environmental fluctuations, which are recorded in their facies and stratigraphy. Ephemeral lakes reveal their sensitivity to palaeoenvironmental changes in the overprinting of the sedimentary features in every single bed. Tetrapod‐track taphonomic‐modes and ichnological taphonomic‐pathways can be used as sensitive indicators of environmental conditions of the track‐bearing beds during deposition and imprinting. The Middle Triassic Cerro de las Cabras succession (Cuyana Basin, Argentina) provides an excellent opportunity to these environmental indicators in an underfilled palaeolake. A model of ichnological preservation for underfilled lake systems is proposed and the role of the ichnology record in the sequence stratigraphy analysis is evaluated, based on the integration of tetrapod‐track modes, taphonomic‐pathways of playa‐lake ichnofauna, mineralogy and physical data. Soft‐ground suites include those dominated by invertebrate grazing traces and arthropod locomotion traces (Suite 1), and those overprinted by horizontal‐vertical dwelling burrows with tetrapod tracks preserved in taphonomic modes B and C (Suite 2). The firm‐ground suite (Suite 3) comprises tetrapod‐tracks with the best preservation styles (modes A and B) along less abundant invertebrate dwelling and feeding traces as found in Suite 2. Clay mineralogy (dominated by illite with subordinate smectite) suggests low plasticity of the layers, in agreement with low‐relief deformation structures observed in tetrapod‐track taphonomic‐modes. The well‐preserved track tetrapod features documented in the Cerro de las Cabras succession, together with the absence of pedogenic disturbance, trampling obliterating the footprints, and/or evidence of strong disturbance by wind, desiccation and/or precipitation, supports short periods of exposure of the imprinted surface particular to this succession. An integrated multiproxy approach is proposed to evaluate the evolutionary interpretation and identification of autogenic versus allogenic controls in underfilled lake‐basin histories. The observed aggradational‐trend suggests an equilibrium between rates of accommodation change and sediment supply, and that the basin‐centre did not experience prolonged sediment‐starved conditions.

The paleoclimatic context for South American Triassic vertebrate evolution

“…The Carnian Chañares-Los Rastros succession has a multiproxy paleoclimate interpretation based on sedimentology, clay mineralogy assemblages, paleontological content, and C and O stable isotope of lacustrine limestone data from the same strata. These integrative data suggest warmer and more humid condition than before or after, also provide evidence that the Carnian Pluvial Episode interval in western Gondwana was indeed warmer and more humid than before or after (Mancuso et al 2020a(Mancuso et al , 2020b. These data are consistent with inferences from palynofloral assemblages for the two units, both of which suggest a relatively humid climate, but with the Los Rastros implying warmer conditions than in the Chañares Formation (Zavattieri and Batten 1996;Zavattieri and Melchor 1999;Ottone et al, 2005;Perez Loinaze et al, 2018).…”

“…Recent radioisotopic ages for the Chañares and Los Rastros formations, which were previously inferred to be Middle Triassic in age, reveal that they are Carnian in age. The CA-TIMS U-Pb zircon dates spanning the Chañares Formation are 236.1 ± 0.6 Ma and 235.2 ± 0.5 Ma (Marsicano et al, 2016) in the northeastern part of the basin, and the date from the lower Los Rastros Formation in the northwestern part of the basin is 234.5 ± 0.9 Ma (Mancuso et al, 2020a(Mancuso et al, , 2020b. The Chañares tetrapod assemblage (Table 1) includes a high diversity of archosauriforms (e.g., proterochampsids, pseudosuchians, and ornithodirans) and high abundance of non-mammalian synapsids (large dicynodonts and smaller cynodonts) (Rogers et al, 2001;Mancuso et al, 2014;Marsicano et al, 2016;Ezcurra et al, 2017;Mancuso and Irmis 2020;Ordoñez et al, 2020), as well as rare actinopterygian and sarcopterygian fishes remains (Gouiric-Cavalli et al, 2017).…”

“…The vertebrate assemblage comprises fish and tetrapods (Table 1), including the actinoperygian genera Neochallaia, Challaia, Calaichtys (López-Arbarello et al, 2010;Gouiric-Cavalli et al, 2017), the cynodonts Cromptodon, Andescynodon and Rusconiodon (Bonaparte 1969(Bonaparte , 1971Abdala and Ribeiro, 2010), indeterminate eucynodonts, and the kannemeyeriid dicynodont Vinceria andina (Domnanovich and Marsicano 2012). There are also footprints preserved in the Sierra de las Higueras area (Las Peñas sub-basin) assigned to pseudosuchian archosaurs and non-mammalian therapsids Mancuso et al 2020aMancuso et al , 2020b.…”

“…Paleoclimate evidence for the Triassic of Argentina is mostly based on single proxy studies, particularly paleobotanical (micro-and macrofloral) studies (Zavattieri 1990c;Zavattieri and Batten, 1996;Artabe et al, 2007;Brea 1995;Brea et al, 2009), but also includes evidence from fauna, sedimentology, paleosols, and geochemistry (Krapovickas et al, 2013;Gulbranson et al, 2015). Only few recent contributions have attempted a multiproxy approach (Benavente et al 2015(Benavente et al , 2019(Benavente et al , 2020(Benavente et al ,2021Mancuso et al 2020aMancuso et al , 2020b.…”

“…Additional information for the Cerro de las Cabras Formation in the Las Peñas sub-basin comes from sedimentology, mineralogy, and tetrapod track taphonomy. In this area, the unit consists of sandstones, siltstones and mudstones interpreted as sandflat and mudflat subenvironments with ephemeral sheetflood water input (Mancuso et al 2020a(Mancuso et al , 2020b. The clay assemblages from this unit are dominated by smectite and subordinate illite, also pointing to an arid seasonal climate regime (Singer 1980).…”