Size and style of the Gondwana late Paleozoic ice cover: Insights from U-Pb dating of the Tarija Formation granitic boulders
Introduction
Despite its location at moderately low paleolatitudes (less than 40°, Gallo et al. this volume), the Tarija Basin hosts world-class volumes of glacial-related rocks, deposited during the Late Paleozoic Ice Age (LPIA). The Pennsylvanian Tarija Formation seems to represent the climax of glacial conditions: a 500–1000 m blanket of glacial diamictites distributed over more than 20,000 km2. Although its glacial origin was questioned by some investigators (López Gamundi, 1986; Eyles et al., 1995; Sempere, 1995; Díaz Martínez, 1996), later scientific work collected evidence that confirmed ice-related genesis of the deposits (Starck et al., 1993b; Starck 1995; Schulz et al., 1999; del Papa and Martínez, 2001; Starck and Del Papa, 2006; Anderson et al., 2010; Anderson, 2011).
The main Tarija Formation facies corresponds to dark gray, massive, diamictites (Dmm, Eyles et al., 1983), which present a scattered pebble to boulder clasts. Among these boulders, the granitic ones are quite abundant (López Gamundi, 1986; Starck et al., 1993b; del Papa and Martínez, 2001). Although these granitic boulders have often been mentioned in the literature, no provenance studies were carried out on them. The present contribution is a first step in this direction, by radiometric dating boulders from the Argentine portion of the basin. The dated boulders were collected in the Cerro Piedras area, in the Eastern Cordillera region (Fig. 1). This location was selected for sampling due to the presence of boulder-sized granitic clasts in these outcrops (Starck et al., 1993b; Starck and Del Papa, 2006). The obtained ages allow asserting a remote source for these large granitic clasts and support the theory of a unique, continental-scale ice sheet.
The idea of a single continental-scale ice sheet was early proposed by previous researchers working on Gondwana glacial-derived sequences which. This single, continental glacial cover theory had a strong acceptation in the geological community (Scotese et al., 1999; Ziegler et al., 1997; Hyde et al., 1999; Starck et al., 1993b; Starck and Del Papa, 2006) during decades until the present century, when alternative theories have been proposed (Fig. 2), challenging the initial paradigm or “traditional view. These new interpretations depicted the occurrence of several smaller, disconnected, ice centers, dispersed along Gondwana (the “emerging view” of Isbell et al., 2012; Rosa, 2015, among others). In the case of the Tarija Basin, it has been suggested that the sediments were transported to the basin by localized glaciers flowing from highlands located along the Michicola Arch (Limarino et al., 2014; Rosa, 2015), even though, clear stratigraphical evidence indicates that this arch formed during post-Paleozoic times (Starck et al., 1993b; Starck 1995, 2011).
Similar to the Michicola Arch, other “highlands” were proposed as ice spreading centers, without clear stratigraphical support, since most of them are located on basins erosive borders, generated after the late Paleozoic sedimentation. The recorded ice flow directions (mainly glacial striations), moreover, show advance toward the proposed highs, as in the case of the western, erosional border of the Paraná basin (Gesicki et al., 2002).
These paleogeographic inconsistencies, plus the remote provenance demonstrated by the analyses presented here, reinforce the classic, single, continental ice sheet model. Additionally, the radial pattern displayed by the published ice flow indicators is in agreement with this model as well.
Section snippets
Geologic background
The Chaco-Tarija Basin developed over southwestern Gondwana, covering regions of the Bolivia, Argentina and Paraguay territories. This present-day distribution is just a remnant of the original extent, which has been severely affected by the tectonic and erosional processes related to plate reorganization triggered by the Atlantic Ocean opening. As other coeval basins, most of the current borders of the Tarija Basin are characterized by erosional truncation on its units, implying a larger
The Cerro Piedras locality
The Cerro Piedras is an isolated outcrop of Neopaleozoic rocks located in Eastern Cordillera to the east of Abra de Zenta pass, at 4000 m altitude (Fig. 3). This outcrop is detached about 7 km from the main belt of Upper Paleozoic outcrops located to the southwest (Starck, 2008). The locality was visited and mapped by Schlawintweit (1938) and Russo (1948, 1951), working for YPF (the Argentinian national oil company). Although this work remains unpublished, the Cerro Piedras became a classical
Samples and analytical techniques
Two granitic boulders (Fig. 4 D, E) were sampled in the locality of Cerro Piedras in order to perform laboratory analyses that allow recognizing their plausible source area. In this study, geocronological dating is presented, whereas petrographycal and geochemical analyses are in progress and will be released in a future contribution. Both boulders, of about 0.7 m length, were macroscopically classified as pinkish granites. Ongoing studies will confirm or modify this assumption.
Results. U/Pb zircon ages
Two samples, called A327 and A328, were taken from each of the collected granitic boulders for U/Pb analysis. Zircons belonged to large prismatic crystal with euhedral and subhedral shapes; all of them showed metamictic zones (Fig. 6), without optic resolution. Metamictization could generate partial lead loss (Mezger and Krogstad, 1997) and, therefore, discordant U/Pb ages.
206Pb/238U, 207Pb/235U and 207Pb/206Pb data of A328 sample are shown in Table 1. Typically, discordant filters vary
Granitic boulders provenance
The obtained Paleoproterozoic ages imply a cratonic source for these large clasts. Although a cratonic provenance has already been ascribed by López Gamundi (1986) for the Tarija Formation, the obtained ages from these boulders allow narrowing the possible source area options.
The cratonic signature of the clasts, together with the ice flow indicators allow disregarding a western supply from the Puna Arch, restricting the source of sediments to areas located to the east or southeast of the
Conclusions
The first U-Pb zircon ages for granitic boulders from the Tarija Formation reported in this work indicate a crystallization age of 2.07 Ga (Paleoproterozoic). Granitic rocks with similar ages in the Rio de la Plata Craton, ca. 1500 km to the southeast of the sampled outcrops, are the most likely source for that boulders. This remote provenance implies a sedimentary transport by glacial ice for the mentioned distance, proving the occurrence of a continental-scale ice sheet.
This single, massive
Author statement
Daniel Starck: Writing - Original draft preparation, Conceptualization, Visualization, Field work, Investigation, Review & Editing. Sofía Bordese: Conceptualization, Methodology, Laboratory analyses and data processing, Visualization, Writing - Review & Editing. Cristina Guibaudo: Conceptualization, Methodology, Laboratory analyses and data processing, Visualization, Writing - Review & Editing. Roberto Hernández: Methodology, Investigation, Review & Editing, Funding acquisition.
Funding
Lateandes S.A. (Grupo GEOMAP/Conicet) provided part of the funds for this work.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors acknowledge the Lateandes technical personnel who participated in the sample processing. Daniel Starck's daughters Micaela and Mora provided assistance during the sampling campaign and took the photographies. The manuscript was improved by the valuable comments of Facundo Fuentes, Alejandro Bande and the reviewers, Cecilia del Papa and Maximiliano Naipauer. Carlos Rapela and Raul Becchio provided some hints on the probable source area of the boulders and on the data treatment. We
References (71)
- et al.
Exhumed subglacial landscape in Uruguay; erosional landforms, depositional environments, and paleo-ice flow in the context of the late Paleozoic Gondwanan glaciation
Sediment. Geol.
(2018) Exhumed erosional landforms of the Late Palaeozoic glaciation in northern Ethiopia: indicators of ice-flow direction, palaeolandscape and regional ice dynamics
Gondwana Res.
(2010)- et al.
Review of the Cambrian Pampean orogeny of Argentina; a displaced orogeny formerly attached to the Saldania Belt of South Africa?
Earth Sci. Rev.
(2018) - et al.
Ice flow direction during late Paleozoic glaciation in western Paraná Basin, Brazil
J. S. Am. Earth Sci.
(2002) - et al.
Glacial paradoxes during the late Paleozoic ice age: evaluating the equilibrium line altitude as a control on glaciation
Gondwana Res.
(2012) - et al.
A paleoclimatic review of southern South America during the late Paleozoic: a record from icehouse to extreme greenhouse conditions
Gondwana Res.
(2014) On the treatment of concordant uranium-lead ages
Geochem. Cosmochim. Acta
(1998)- et al.
The Río de la Plata craton and the assembly of SW Gondwana
Earth Sci. Rev.
(2007) - et al.
Gondwanan palaeogeography and paleoclimatology
J. Afr. Earth Sci.
(1999) - et al.
Plesovice zircon — a new natural reference material for U-Pb and Hf isotopic microanalysis
Chem. Geol.
(2008)
Strategies towards statistically robust interpretations of in situ U-Pb zircon geochronology
Geosci. Front.
The northwestern Argentina Tarija Basin Stratigraphy, depositional systems and controlling factors in a glaciated basin
J. S. Am. Earth Sci.
Gondwana from top to base in space and time
Gondwana Res.
IsoplotR: a free and open toolbox for geochronology
Geosci. Front.
The palaeogeography of part of southwestern Gondwana during the Permo-Carboniferous glaciation
Palaeogeogr. Palaeoclimatol. Palaeoecol.
The statistical distribution of the mean squared weighted deviation
Chem. Geol. Isot. Geosci.
Sedimentology and Lithostratigraphy of the Carboniferous Tarija–Chaco Basin, Southern Bolivia: Geodynamic and Paleoclimatic Evolution [unpublished PhD Dissertation]
Bioestratigrafía, paleogeografía y paleoecología del Paleozoico de Sierra de Zenta, Cordillera Oriental Argentina
Ser. Correlación Geol.
The configuration of Northern Hemisphere ice sheets through the Quaternary
Nat. Commun.
Sedimentación lacustre glaci-dominada en la Formación Tarija (Carbonífero), sierra de Aguaragüe, noroeste argentino
Revista de la Asociación Argentina de Sedimentología
Síntesis Estratigráfica y Geodinámica del Carbonífero de Bolivia
Ice-margin fluctuation sequences and grounding zone wedges: the record of the Late Palaeozoic Ice Age inthe eastern Karoo Basin (Dwyka group, South Africa)
Depositional Record
Avances sobre palinología, bioestratigrafía y correlación de los Grupos Macharetí y Mandiyutí, Neopaleozoico de la cuenca Tarija, provincia de Salta, Argentina
Ameghiniana
Primer registro de megafloras y palinología en estratos de la Formación Tarija (Pennsylvaniano), Arroyo Aguas Blancas, Provincia de Salta, Argentina: descripción de dos especies nuevas
Andean Geol.
Interpretación paleoambiental del Grupo Mandiyutí (Carbonífero Superior): evidencias palinológicas, sedimentológicas y tafonómicas
Ameghiniana
Palinología de la Formación San Telmo (Carbonífero Superior), en la Sierra San Antonio, provincia de Salta, Argentina
Ameghiniana
Primer registro palinológico del Pennsylvaniano del Norte de la Sierra de Zenta, provincia de Jujuy, Argentina
Record of a Pennsylvanian Cisuralian marine transgression, southern Bolivia: a short-lived event in western Gondwana?
Palaeogeogr. Palaeoclimatol. Palaeoecol.
Late Palaeozoic carbonates and glacial deposits in Bolivia and northern Argentina: significant paleoclimatic changes
Palinología, Bioestratigrafía y Correlación de las asociaciones presentes en los Grupos Macharetí y Mandiyutí, Neopaleozoico de la Cuenca Tarija, provincia de Salta, Argentina
Lithofacies types and vertical profile models; an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences
Sedimentology
Hydrocarbon-bearing late Paleozoic glaciated basins of southern and central South America
Enhanced precision, accuracy, efficiency, and spatial resolution of U-Pb ages by laser ablation–multicollector– inductively coupled plasma–mass spectrometry
G-cubed
Archaeocyaths from South America: review and a new record
Geol. J.
Cited by (5)
Sediment dispersal and basin evolution during contrasting tectonic regimes along the western Gondwanan margin in the central Andes
2023, Journal of South American Earth SciencesProvenance of Devonian-Carboniferous sedimentary rocks of the Tarija Basin, southern Bolivia: Implications for the geodynamic evolution of the southwestern margin of Gondwana
2024, Bulletin of the Geological Society of America