Tab. 1: Mineralogical composition and chemical analyses of major and trace elements of Ameghino Formation rocks

• Main Authors: Scasso, R A, Grunenberg, Thomas, Bausch, W M
• Format: Dataset
• Language: English
• Published: PANGAEA 2011
• Subjects: Aluminium oxide; Ameghino; Ameghino Formation; Antarctic Peninsula; Calcite; Calcium oxide; Chlorite; Feldspar; Geological sample; GEOS; Illite; Iron oxide; Fe2O3; Lithology/composition/facies; Magnesium oxide; Manganese oxide; Minerals; Phosphorus oxide; Plagioclase; Potassium oxide; Pyrite; Quartz; Rubidium; Sample code/label; Sample ID; Silicon dioxide; Smectite; Sodium oxide; Strontium; Sulfur; total; Titanium dioxide; Zinc; Zirconium; Antarctic; Antarc*; Polarforschung
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.763364; https://doi.org/10.1594/PANGAEA.763364

As a result of a petrographical, mineralogical and geochemical characterization of the Ameghino Formation mudstones (Upper Jurassic- Lower Cretaceous, Antarctic Peninsula), "epiclastic" radiolaria-rich and mixed (radiolaria-rich + tuff) mudstone types were recognized. Contents of clastic material in the mudstones generally increase with younger paleontological age, but local exceptions to this trend have been found. The anoxic environment of the lower part of the sequence changes to more oxidizing conditions towards the top, in transition to the Hauterivian - Barrêmian conglomerates. Element to element correlations show good agreement with the normal differentiation trends of volcanic (andesite-rhyolite) rocks, suggesting that the overall sequence is mainly volcanic in origin with various grade of reworking. For example, the radiolaria-rich mudstone matrix could have been originated from very fine touffaceous suspensions deposited very slowly after the main fall of the tuffs. However, in the upper part of the sequence, some epiclastic supply is revealed by petrographic evidence and illite crystallinity index. The clay mineral association (illite, chlorite and illite-smectite mixed layers) is mainly of diagenetic origin in the stratigraphically lower sections. Low percentages of expandable layers in the illite-smectite mixed layers, as well as the general mineralogical association, suggest a late mesodiagenetic stage, and together with geological evidence, a relatively deep burial (> 1000 m - probably > 2500 m) and temperatures exceeding 100°C.