Littoral siliciclastic shallow marine horizontal conformable beds (a heterolithic succession), Middle to Late Miocene, outcropping in northeastern Argentina (Ituzaingó Formation) and overlying transitional confor...Littoral siliciclastic shallow marine horizontal conformable beds (a heterolithic succession), Middle to Late Miocene, outcropping in northeastern Argentina (Ituzaingó Formation) and overlying transitional conformable horizontal regolithic mantle-rock bed derived from them (the Pampean and Post-Pampean Formations), were geochemically analyzed. The focus of this study is placed on the application of geochemical parameter and signature analyses related with the aforementioned geological units, which are of subcontinental extension into South America. The encountered results show an outstandingly similar geochemical behaviour between them. The main conclusion is that regolithic mantle-rock beds were derived from the littoral shallow marine mudstone (silty-argillaceous) beds. This is in oposition to previous aeolian processes proposed early in the 50’s and later. These mudstone beds constitute important sections of the littoral shallow marine sequence beds (outcropping HST parasequence). Such regolitization proposed for the Pampean and Post-Pampean Formations predominantly developed in-situ during the Late Pleistocene and Holocene. The main erosional and mobilized agents were the surface free water (pluvial, fluvial and laminar water sheets) and vadose water. So, the wind flows and/or the immense air flow hurricanes are of insignificant sedimentological influence. Otherwise, there is not a proved appropiate sandy-silty reservoir for a reasonable support of the “aeolian hypothesis”, as well as clear aeolian structures settled in the regolithic mantle-rock bed. In spite of these lines of equality textural-structural evidence, the geochemical values for both major elements and trace elements, demonstrate that the Miocene heterolithic marine succession was the mother rock of the overlying regolithic mantle-rock bed, which was formed as an in-situ mantle-rock bed.展开更多
In Argentina, at Central Andes Eastside, Cumbres Calchaquies, Aconquija Range and Ambato Block constitute a mountain chain that erects about 5,000 masl. Its geological story reveals morphotectonic and magmatic process...In Argentina, at Central Andes Eastside, Cumbres Calchaquies, Aconquija Range and Ambato Block constitute a mountain chain that erects about 5,000 masl. Its geological story reveals morphotectonic and magmatic processes are similar to the Pampean Ranges at which they belong to, giving origin to mineralized areas. Geochemical concentrations of trace metals （Cu, Pb, Zn, Mn, Mo, As） in stream sediments are related to the geology and mineral manifestations of the area. Geochemical high average concentration of Cu, Pb and Mo are observed in all ranges. It highlights the presence of As in Cumbres Calchaquies-Aconquija Range and Zn, Mn in the mountains of Aconquija Range-Ambato Block. It was determined that Cu-Zn-Mn complex is adsorbed or precipitated most frequently by Mn oxides. Complex Pb-Zn, Mn-As, Mo-As and Pb-Mo are absorbed by other agents （clay; oxides of Mn, Fe, AI; organic matter）.展开更多
文摘Littoral siliciclastic shallow marine horizontal conformable beds (a heterolithic succession), Middle to Late Miocene, outcropping in northeastern Argentina (Ituzaingó Formation) and overlying transitional conformable horizontal regolithic mantle-rock bed derived from them (the Pampean and Post-Pampean Formations), were geochemically analyzed. The focus of this study is placed on the application of geochemical parameter and signature analyses related with the aforementioned geological units, which are of subcontinental extension into South America. The encountered results show an outstandingly similar geochemical behaviour between them. The main conclusion is that regolithic mantle-rock beds were derived from the littoral shallow marine mudstone (silty-argillaceous) beds. This is in oposition to previous aeolian processes proposed early in the 50’s and later. These mudstone beds constitute important sections of the littoral shallow marine sequence beds (outcropping HST parasequence). Such regolitization proposed for the Pampean and Post-Pampean Formations predominantly developed in-situ during the Late Pleistocene and Holocene. The main erosional and mobilized agents were the surface free water (pluvial, fluvial and laminar water sheets) and vadose water. So, the wind flows and/or the immense air flow hurricanes are of insignificant sedimentological influence. Otherwise, there is not a proved appropiate sandy-silty reservoir for a reasonable support of the “aeolian hypothesis”, as well as clear aeolian structures settled in the regolithic mantle-rock bed. In spite of these lines of equality textural-structural evidence, the geochemical values for both major elements and trace elements, demonstrate that the Miocene heterolithic marine succession was the mother rock of the overlying regolithic mantle-rock bed, which was formed as an in-situ mantle-rock bed.
文摘In Argentina, at Central Andes Eastside, Cumbres Calchaquies, Aconquija Range and Ambato Block constitute a mountain chain that erects about 5,000 masl. Its geological story reveals morphotectonic and magmatic processes are similar to the Pampean Ranges at which they belong to, giving origin to mineralized areas. Geochemical concentrations of trace metals （Cu, Pb, Zn, Mn, Mo, As） in stream sediments are related to the geology and mineral manifestations of the area. Geochemical high average concentration of Cu, Pb and Mo are observed in all ranges. It highlights the presence of As in Cumbres Calchaquies-Aconquija Range and Zn, Mn in the mountains of Aconquija Range-Ambato Block. It was determined that Cu-Zn-Mn complex is adsorbed or precipitated most frequently by Mn oxides. Complex Pb-Zn, Mn-As, Mo-As and Pb-Mo are absorbed by other agents （clay; oxides of Mn, Fe, AI; organic matter）.
