Size and style of the Gondwana late Paleozoic ice cover: Insights from U-Pb dating of the Tarija Formation granitic boulders

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Highlights

  • Zircons from boulders from the Pennsylvanian Tarija Fm. (NW Argentina) yield a crystallization age of 2.07 G.a. (Paleoproterozoic).

  • The obtained age restricts the probable source areas to regions located to the SE, in Uruguay, proving a sedimentary transport of, at least, 1500 km.

  • Such transport distance implies the presence of a single and continental scale ice sheet.

Abstract

Two granitic boulders from the Pennsylvanian Tarija Formation were sampled in order to perform laboratory analyses to define their possible provenance. This formation, deposited during the Late Paleozoic ice age (LPIA), represents the climax of glacial-related sedimentation in the Tarija Basin. The boulders were collected from massive diamictite levels in the Cerro Piedras locality, in Eastern Cordillera. Zircons concentrated from these boulders yield Precambrian U-Pb ages. One of the obtained dates has a Concordia Age of 2068.97 ± 6.06 Ma, indicating a crystallization in Paleoproterozoic times.

The obtained ages restrict the candidate source areas to remote regions, located along the cratonic, eastern side of South America. The Rio de la Plata craton is considered the most likely source area. Several granitoids in the Uruguayan portion of the craton (especially in the Piedra Alta Terrane) have radiometric ages between 2.1 and 2.0 G.a., providing a suitable source for the Tarija Formation boulders. The direction and sense of glacial movement indicators described both in the Tarija Basin and in Uruguay support this remote (at least 1500 km) provenance.

The remote provenance of the analyzed boulders implies a sedimentary transport by glacial ice from Uruguayan sources to the northern end of Argentina, proving the occurrence of a continental scale ice sheet. Although the single, continental ice sheet theory has been questioned in the last decades, and alternative models were proposed, direct evidence presented here supports the single ice sheet model.

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)

  • C.J. Spencer et al.

    Strategies towards statistically robust interpretations of in situ U-Pb zircon geochronology

    Geosci. Front.

    (2016)
  • D. Starck et al.

    The northwestern Argentina Tarija Basin Stratigraphy, depositional systems and controlling factors in a glaciated basin

    J. S. Am. Earth Sci.

    (2006)
  • T.H. Torsvik et al.

    Gondwana from top to base in space and time

    Gondwana Res.

    (2013)
  • P. Vermeesch

    IsoplotR: a free and open toolbox for geochronology

    Geosci. Front.

    (2018)
  • J.N.J. Visser

    The palaeogeography of part of southwestern Gondwana during the Permo-Carboniferous glaciation

    Palaeogeogr. Palaeoclimatol. Palaeoecol.

    (1987)
  • I. Wendt et al.

    The statistical distribution of the mean squared weighted deviation

    Chem. Geol. Isot. Geosci.

    (1991)
  • H. Anderson

    Sedimentology and Lithostratigraphy of the Carboniferous Tarija–Chaco Basin, Southern Bolivia: Geodynamic and Paleoclimatic Evolution [unpublished PhD Dissertation]

    (2011)
  • H. Anderson et al.
  • L. Aráoz et al.

    Bioestratigrafía, paleogeografía y paleoecología del Paleozoico de Sierra de Zenta, Cordillera Oriental Argentina

    Ser. Correlación Geol.

    (2016)
  • C.L. Batchelor et al.

    The configuration of Northern Hemisphere ice sheets through the Quaternary

    Nat. Commun.

    (2019)
  • C.E. del Papa et al.

    Sedimentación lacustre glaci-dominada en la Formación Tarija (Carbonífero), sierra de Aguaragüe, noroeste argentino

    Revista de la Asociación Argentina de Sedimentología

    (2001)
  • E. Díaz Martínez

    Síntesis Estratigráfica y Geodinámica del Carbonífero de Bolivia

  • P. Dietrich et al.

    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

    (2019)
  • M. di Pasquo

    Avances sobre palinología, bioestratigrafía y correlación de los Grupos Macharetí y Mandiyutí, Neopaleozoico de la cuenca Tarija, provincia de Salta, Argentina

    Ameghiniana

    (2003)
  • M. di Pasquo

    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.

    (2009)
  • M. di Pasquo et al.

    Interpretación paleoambiental del Grupo Mandiyutí (Carbonífero Superior): evidencias palinológicas, sedimentológicas y tafonómicas

    Ameghiniana

    (1999)
  • M. di Pasquo et al.

    Palinología de la Formación San Telmo (Carbonífero Superior), en la Sierra San Antonio, provincia de Salta, Argentina

    Ameghiniana

    (2001)
  • M. di Pasquo et al.

    Primer registro palinológico del Pennsylvaniano del Norte de la Sierra de Zenta, provincia de Jujuy, Argentina

  • M.M. di Pasquo et al.

    Record of a Pennsylvanian Cisuralian marine transgression, southern Bolivia: a short-lived event in western Gondwana?

    Palaeogeogr. Palaeoclimatol. Palaeoecol.

    (2017)
  • M.M. di Pasquo et al.

    Late Palaeozoic carbonates and glacial deposits in Bolivia and northern Argentina: significant paleoclimatic changes

  • M. di Pasquo

    Palinología, Bioestratigrafía y Correlación de las asociaciones presentes en los Grupos Macharetí y Mandiyutí, Neopaleozoico de la Cuenca Tarija, provincia de Salta, Argentina

    (1999)
  • N. Eyles et al.

    Lithofacies types and vertical profile models; an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences

    Sedimentology

    (1983)
  • N. Eyles et al.

    Hydrocarbon-bearing late Paleozoic glaciated basins of southern and central South America

  • G.E. Gehrels et al.

    Enhanced precision, accuracy, efficiency, and spatial resolution of U-Pb ages by laser ablation–multicollector– inductively coupled plasma–mass spectrometry

    G-cubed

    (2008)
  • P.D. González et al.

    Archaeocyaths from South America: review and a new record

    Geol. J.

    (2013)
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