DATA REPOSITORY:
Figures
Fig. 1: Simplified geological map of the eastern part of the Tandilia System. 1= Sierra de Vigilancía; 2= Sierra del Volcán (revised after Poiré et al. 2003).

Fig. 2: BSE images of six selected zircons of the Sierra de Volcán Diamictite. Spot size is 20 micron. (CL images and the detailed description of the methodology can be found in the data repository, on the homepage of the Laboratório de Geologia Isotópica da Universidade Federal do Rio Grande do Sul and can be acquired contacting F. Chemale Jr. (UFRGS); CL images can be acquired by contacting A. Van Staden). 

Tables:
Table 1: Geochemical results of the four groups of the Sierra del Volcán diamictite. (#= XRF; ¶= INAA; L= lithotype; SH= shale; SAND= sandstone; SILT= siltstone; WCSM= white coarse grained sand matrix of the glacial diamictite; N= chondritic normalized; UCC= upper continental crust after McLennan et al. 2006; LDL= lower detection limit; BFM= Balcarce Formation; PAS= post-Archean shale after Taylor & McLennan 1985). The bottom of the section starts on the left and the top ends on the right hand side of the table. (Detailed analytical description can be found in the data repository)

Table 2: Representative concordant U-Pb age in situ data of detrital zircons from the Sierra del Volcán diamictite. Probability plots can be downloaded from the homepage of the Laboratório de Geologia Isotópica da Universidade Federal do Rio Grande do Sul and can be acquired contacting Dr. F. Chemale Jr. (farid.chemale@ufs.br).

Sampling and analytical techniques
Sampling
Samples were collected at a natural exposure of the diamictite located at S37°51’23.4” and W058°07’37.8”. Here, the succession is approximately 6 m thick. Representative samples for this study were collected of the matrix of the upper quartz-rich bed of the glacial diamictite in the Sierra del Volcán, fine-grained siltstones and three samples of the basal pebbly sandstone for petrographic, geochemical and isotope geochemical analysis. 
Heavy mineral separation
Samples were crushed and screened to less than 1000 µm. Heavy minerals were recovered from this pre-concentrate using bromoform (d=2.89 g/cm3); the heavy mineral population was split into several fractions by electromagnetic separation using a Frantz Isodynamic magnetic separator. Each of the different heavy mineral fractions was randomly embedded into epoxy resin, polished and carbon-coated. Heavy minerals were characterized in terms of shape, size, features, inclusions, etc. and identified by Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-ray Spectrometry (EDX) (specifications see below). 
Framework mineral and heavy mineral studies by SEM
Representative samples were selected for polished thin section preparation and the framework mineral and matrix composition analyzed by SEM. Most of the samples were found to be friable enough to liberate individual framework mineral grains without damaging the surfaces. For mineral grain surface analyses, individual detrital grains were thus carefully dislodged from whole rock samples using minimal mechanical force. Mineral grains were mounted on sample stubs and carbon-coated, prior to being examined on a JEOL JSM-5600 with attached Noran EDS detector housed at the Central Analytical Facility (SPECTRAU) of the Faculty of Science, University of Johannesburg. The acceleration voltage was set at 15 kV, at a working distance of 18 mm and a counting time of 60 s per EDX spot analysis.
X-ray fluorescence (XRF) analyses
XRF powders were prepared by milling to a grain size of < 75 µm in a Cr-steel dish, therefore Cr concentrations are discarded. To prepare pressed powder pellets, 8.0 g of sample powder were mixed with 4 g of binder. The binder pellets were milled in an agate mill and mixed with the weighed sample after which the sample was placed in an aluminium cup and pressed at a pressure of 20 tons in a die set. Glass beads were prepared by fusing sample powder into a borate glass. The bead preparation procedure utilized a flux containing 50 % LiM (lithiummetaborate) and 50 % lithium tetraborate with LiNO3 as oxidant. A Minifuse fusion instrument was used to accomplish fusion. A Panalytical Magix Pro X-ray fluorescence spectrometer, operated at 4 kV, and located at SPECTRAU, was used for analysis. Element concentrations are permanently monitored with internal and external standards. Precision lies for every element below 5%.
INAA (Instrumental Neutron Activation Analysis)
Analyses of trace elements were performed by ACTLABS (Ontario, Canada). Sample powders were dissolved in lithium metaborate flux and the resultant bead rapidly digested in dilute nitric acid. Detection limits are reported in Table 1. INAA precision and accuracy based on replicate analysis of international rock standards are 2-5 % (1s) for most elements and ± 10 % for U, Sr, Nd, and Ni.
Laser Ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS)
	Zircons were handpicked from mineral concentrates of the matrix of the glacial diamictite. Only optically inclusion-free grains were selected for U-Pb laser ablation analysis. Cathodoluminescence (CL) images were used to target the cores and captured with a Centaurus CL detector and a JEOL JSM-5600 at SPECTRAU (University of Johannesburg). Spots for laser ablation analysis were selected as to avoid cracks and inclusions (see Fig. 2 data repository for images, laser ablation target spots with a size of 20 µm, and corresponding ages of zircons in Table 2 data repository). U-Pb dating was carried out using a sensitive high-resolution Laser Ablation Multi-collector Inductively Coupled Mass Spectrometer (LA-MC-ICPMS). Zircon grains were mounted in a 1 inch diameter epoxy section and then polished, and a SEM JEOL JSM 5800 was used for BSE images to compare with CL images and light microscopy. The U-Pb zircon data were acquired by a Laser Ablation Microprobe (New Wave UP -213) coupled to a MC-ICPMS (Neptune of ThermoFinningan) at the Laboratório de Geologia Isotópica da Universidade Federal do Rio Grande do Sul (LGI-UFRGS), Porto Alegre, Brazil. Laser parameters during the analyses are repetition rate of 10 Hz, spot size of 25 µm and energy of 5.0 to 6.0 J/cm2. The configuration of the MC-ICPMS were for its Faraday cups for 206Pb, 208Pb, 232Th, 238U and for 202Hg, 204Hg, 204Pb, 207Pb, with acquisition of 50 cycles of 1.04 seconds. Main gas flow was 15 l/min Ar, auxiliary gas flow 0.8 l/m, while the sample has been carried with 0.8 l/min Ar plus 0.45 l/min He. GJ-1 standard was analyzed every 10 zircons and used for internal correction of the obtained sample ratios and error calculation. For every measured cycle of standard and sample, the raw data have been corrected for blanks. The obtained ratios of 207Pb/206Pb and 206Pb/238U have been corrected for common Pb after Stacey & Kramer (1975) curve and age of the analyzed zircon are estimated. Due to fractionation of 206Pb/238U ratio during the ablation, the obtained ratios are calculated as zero ablation intercepts of least-squares regression line (Koesler & Sylvester 2003). Laser-induced elemental fractional and instrumental mass discrimination were corrected by the reference zircon (GJ-1) (Simon et al. 2004), following the measurement of two GJ-1 analyses to every ten sample zircon spots. The external error is calculated after propagation error of the GJ-1 mean and the individual sample zircon (or spot). Analytical data can be acquired from the web-address of the Universidade Federal do Rio Grande Do Sul (UFRGS) in Porto Alegre (Brazil), where the zircons were analysed. For detailed adjustments of the LA-MC-ICPMS technique developed at Porto Alegre please contact Dr. F. Chemale Jr. (farid.chemale@ufs.br)
Koesler, J. & Sylvester, P. J. 2003 Present trends and the Future of Zircon in Geochronology: Laser Ablation ICPMS. Reviews in Mineralogy and Geochemistry, 53, 243-275.
Poiré, D.G., Spalletti, L.A. & Del Valle, A. 2003. The Cambrian-Ordovician siliciclastic platform of the Balcarce Formation (Tandilia System, Argentina): Facies, trace fossils, paleoenvironments and sucession stratigraphy. Geologica Acta, 1, 41-60.
Simon E. Jackson, S. E., Pearson, N. J., Griffin, W.L. & Belousova, E. A. 2004. The application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U–Pb zircon geochronology. Chemical Geology, 211, 47-69.
Stacey, J.S. & Kramers, J.D. 1975. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth Planetary Science Letters, 26, 207-221.
Taylor, S. R. & McLennan, S. M. 1985. The Continental Crust: its Composition and Evolution. Blackwell Scientific, Oxford, 312pp.