Figure 1
Location of President Head Peninsula, Snow Island. a) Plate tectonic position of the northern Antarctic Peninsula at the present day (adapted from
Birkenmajer 1994); AR: Atlantic Ridge, BS: Bransfield Strait, SSa: South Sandwich Islands, SG: South Georgia Islands, SSh: South Shetland Islands, SO: South Orkneys Islands. b) Geographic map positioning the President Head Peninsula, Snow Island at the South Shetland Islands Archipelago, metadata obtained from the Antarctica Digital Database Mapping Services SCAR https://www.add.scar.org/. c) Geological map of President Head Peninsula, indicating the studied section of the Cerro Negro Formation (adapted from
Israel 2015).
Figure 2
Outcrop photographs. a) General view of the studied area that is mostly covered by regolith. b) Stratigraphic profiling process.
Figure 3
Composite lithostratigraphic profile of the Cerro Negro Formation in the north-central portion of the President Head Peninsula, Snow Island.
Figure 4
Samples macrophotographs showing the different lithofacies. a) Sample M.5, medium to coarse-grained graywacke (Gw) with interbedded planar laminated claystone (Cy) and siltstone (Sl) levels that are crossing by two microfractures (mf) and to the top an overload structure (Ls) is observed lying on the finer sediments. b) Sample M.7, claystone, siltstone and very fine-grained sandstone interspersed with flame structure (Fs) and Ls. c) Sample M.14, fine (fT) and coarse-grained (cT) ash tuff laminae crossed by a volcanic glass vein (vgv). d) Sample M.14, matrix-supported lapilli tuff. e) Sample M.15, massive siltstone. f) Sample M.17, siltstone laminae with interbedded fine and coarse-grained ash tuff, several volcanic glass veins are crossing these. g) Sample M.23, fine to medium-grained ash tuff interbedded with few siltstone fine laminae. h) Sample M.25, matrix-supported lapilli tuff with abundant black organic fragments (Of). i) Sample M.27, clast-supported tuffaceous litharenite.
Figure 5
Petrographic photographs showing some details of the microfacies. a–b) Sample M.3, claystone-siltstone laminae under cross polarized light XPL. c–d) Sample M.5, Medium- to coarse-grained grauwacke with abundant rhyodacite lithic fragments, parallel polarized light PPL and XPL, respectively. e) Sample M.7, claystone-siltstone laminae under XPL. f–h) Sample M.13, tuff under XPL, ash matrix with abundant brown kerogen (f), phenocrystals of < 1 mm of plagioclase in pumice (g) showing vesicles (h). i–j) Sample M.14, lapilli tuff, glass, and ash matrix with phenocrystals of > 3 mm of plagioclase under PPL and XPL, respectively. k–l) Sample M.17, siltstone-tuff laminae under PPL and XPL, respectively. m–n) Sample M.25, lapilli tuff under XPL, matrix compound of ash and clastic fine grains with phenocrystals of quartz, plagioclase and oxides, abundant amorphous (Am) kerogen and structured (St) kerogen, and accretionary lapilli filled with palagonite (Pgte) are observed. o–p) Sample M.27, medium- to coarse-grained tuffaceous litharenite under XPL, poor selected and grain supported matrix with sub-rounded to rounded quartz, plagioclase, lithic fragments in welded ash altered to clay minerals (o), structured kerogen (p) grains are abundant as well as amorphous.
Figure 6
Geochemistry plots a) Total alkali vs. silica (TAS) compositional plot (based on
Irvine & Baragar 1971,
Middlemost 1994). b) Tectonic setting plot, where X = 0.303 − 0.0447SiO2 − 0.972TiO2 + 0.008Al2O3 − 0.267Fe2O3 + 0.208FeO − 3.082MnO + 0.14MgO + 0.195CaO + 0.719Na2O − 0.032K2O + 7.51P2O5 and Y = 43.57 − 0.421SiO2 + 1.988TiO2 − 0.526Al2O3 − 0.551Fe2O3 − 1.61FeO + 2.72MnO + 0.881MgO − 0.907CaO − 0.177Na2O − 1.84K2O + 7.244P2O5 (based on
Bhatia 1983).
Figure 7
Stratigraphical distribution of palynofacies ratio, Principal Component Analysis (palynofacies) (PCA), palynoflora ecological indexes ratio, and paleoenvironmental intervals (Q-mode cluster).
’ 8
PCA Biplot scatter plot for palynofacies and samples from the Cerro Negro Formation. In squares (samples M.1 to M.14), and circles (samples M.15 to M.27).
Figure 9
Spores recovered from the Cerro Negro Formation, President Head Peninsula, Snow Island: a–b) Aequitriradites superspinulosus, M.12, EF (R27/3), b) fluorescence mode, c) Antulsporites baculatus. M.2, EF (Z32/3), d–e) Baculatisporites comaumensis, M.7, EF (W28/1), e) fluorescence mode, f) Biretisporites sp., M.2, EF (F36/3), g) Camarozonosporites insignis, M.14, EF (U29/2), h) Ceratosporites equalis, M.1, EF (U28/2), i) Cibotiumspora jurienensis, M.3, EF (R27/2), j) Cicatricosisporites sp., M.7, EF (G29/3), k) Converrucosisporites sp., M.6, EF (X33/2), l) Cyathidites australis, M.14, EF (B29/1). Scale bar 20 µm. England Finder (EF).
Figure 10
Spores recovered from the Cerro Negro Formation, President Head Peninsula, Snow Island: a) Deltoidospora hallii, M.2, EF (L32/2), b) Densoisporites microrugulatus, M.6, EF (C37/2), c) Foraminisporis asymmetricus, M.1, EF (E33/3), d) F. wonthaggiensis, M.1, EF (X27/2), e) Gleicheniidites senonicus, M.1, EF (T26/4), f) Ischyosporites sp., M.1, EF (B27/1), g) Leiotriletes sp., M.14, EF (O29/2), h-i) Muricingulisporis annulatus, M.5, EF (W32/1), i) fluorescence mode, j) Ornamentifera sp., M.1, EF (H36/1), k) Polycingulatisporites sp., M.2, EF (F25/3), l) Psilatriletes radiatus, M.1, EF (P32/4). Scale bar 20 µm.
Figure 11
Spores, pollen grains, algae, and SOM recovered from the Cerro Negro Formation, President Head Peninsula, Snow Island. Spores: a) Sotasporites elegans, M.14, EF (S41/3), b) S. triangularis, M.2, EF (O32/3), c) Undulatisporites pannuceus, M.14, EF (S29/4). Pollen grains: d) Alisporites bilateralis, M.1, EF (A36/3), e) Araucariacites sp., M.1, EF (T26/2), f) Bisaccate, M.14, EF (N29/2), g) Podocarpidites sp., M.14, EF (O38/1), h) Vitreisporites sp., M.14, EF (Q34/1). Algae: i) Botryococcus sp., M.14, EF (H33/1). SOM: j) AOM, M.15, EF (X33/2), k) Phytoclast translucent, M.15, EF (V36/4), l) Pseudoamorphous, M.15, EF (C37/2). Scale bar 20 µm.
Figure 12
Rarefaction curve with 95% confidence intervals of the palynofloristic species from the Snow Island.
Figure 13
Ternary plot AOM-Phytoclast-Palynomorph based on relative frequency kerogen from Snow Island (Adapted from
Tyson 1993, 1995).
Paleoenvironment of the Cerro Negro Formation (Aptian, Early Cretaceous) of Snow Island, Antarctic Peninsula
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