The Gulf of San Jorge (GSJ) is a semicircular basin, approximately 160 km long and 250 km wide, located in the central part of Patagonia between 45°S and 47°S, lacking any present-day major perennial tributaries. The grain size and bulk and clay mineralogical compositions as well as major and minor elements of 75 surface sediment samples from the GSJ and the adjacent continental shelf were investigated to define the spatial distribution, transport pathways, and potential sources of terrigenous material. To better constrain the origins of GSJ sediments, analyses were also performed on 14 terrestrial, riverine, and marine samples from potential source areas around the gulf and Patagonia. The mineral assemblage of surface sediments in the gulf, dominated by plagioclase, quartz, and clays, is a function of the primary continental volcanic geology of Patagonia. The significant concentration of volcaniclastic particles indicated by mineralogical signatures and scanning electron microscope images of sediments suggests a substantial contribution from rhyolitic volcanism to the modern sedimentation in the gulf. High amounts of smectite are carried into the GSJ by dust transport, whereas inputs of chlorite and illite seem to be associated with continental shelf current transport from southern Patagonia. Finally, our results suggest that 50% of the surface sediment in the GSJ is derived from external/oceanic inputs, 40% from inner gulf shores (i.e., erosion and runoff), and 10% from dust (i.e., aeolian transport).

Desiage, P.-A., J.-C. Montero-Serrano, G. St-Onge, A.C. Crespi-Abril, E. Giarratano, M.N. Gil, and M.J. Haller. 2018. Quantifying sources and transport pathways of surface sediments in the Gulf of San Jorge, central Patagonia (Argentina). Oceanography 31(4)92–103, https://doi.org/10.5670/oceanog.2018.401.

METHODS. Contains the source samples and detailed methodology used for the analyses of grain size, SEM, bulk and clay mineralogy, and elemental geochemistry, as well as the statistical approach.

FIGURE S1. Spatial distribution of the mean grain-size for the surface sediments in (a) the Gulf of San Jorge (GSJ) and (b and c) marine park areas.

FIGURE S2. Spatial distribution of tephra (i.e., volcanic rhyolitic tephra) concentrations in the GSJ.

FIGURE S3. (a) Comparison of measured X-ray diffractogram and calculated best-fit curve obtained from RockJock v11 on a representative sample (BV01). The quartz and rhyolitic tephra (Hekla-4) standard used in the XRD analysis are also shown for comparison. (b–c) Scanning electron microscopy (SEM) images of the 300–63 μm fraction of surface sediment sample BV01. (d) K₂O vs. SiO₂ classification diagram for glass shards from BV01, BV06, and BC11 surface samples. The geochemical composition field of different volcanic provinces of the southern part of the SVZ (Carel et al., 2011, and references therein) and ashes from the 2008 Chaitén eruption (Watt et al., 2009; Ruggieri et al., 2012) are presented for comparison.

FIGURE S4. (a) Weight % Si plotted vs. weight % quartz. (b) Weight % Ca plotted vs. weight % plagioclase. (c) Weight % Al plotted vs. weight % clays. (d) Weight % Fe plotted vs. weight % Fe-bearing + chlorite + clays.

FIGURE S5. (a) Box plot illustrating the smectite (S), illite (I), and chlorite (C) relative concentrations of GSJ sediment samples as yielded by RockJock and oriented mounted methods (<2 μm; MacDiff). (b) Box plot of ratios S+I/C and S/I+C showing the relative clays compositions of GSJ sediment samples as yielded by RockJock and oriented mounted methods (<2 μm).

TABLE S1. Mean grain size and End-member (EM) scores for surface sediments of the Gulf of San Jorge (GSJ).

TABLE S2. Mineral composition of bulk and clay fraction of sediment samples.

TABLE S3. Chemical composition of sediment samples.

TABLE S4. Sources contributing to surface samples.

Table S5. (a) Minerals identified in RockJock v11, (b) consolidated list of minerals, (c) minerals used in SedUnMix, and (d) samples associated to sources in SedUnMix.

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