Evolution with depth from detrital to authigenic smectites in sediments from AND-2A drill core (McMurdo Sound, Antarctica)

摘要: We have examined the nature and origin of smectites in glaciomarine sediments AND-2A drill core (McMurdo Sound, Antarctica) by means X-ray diffraction (XRD) analyses on clay fraction, field emission scanning electron microscopy (FESEM), (SEM) observations SEM-EDS microanalyses smectite particles. Relying variation throughout it was possible to split sequence into three units. Smectites are either detrital or authigenic. Detrital close montmorillonite-beidellite composition while newly-formed frequently higher Fe-Mg contents intermediate compositions between saponite nontronite field, with lower amounts field. In upper sedimen tary sections (Unit I, Unit II, 36–440 mbsf, 0.7–16.5 Ma) interpreted be predominantly detrital, whereas portion III, 440–1123.20 16.5–20.2 authigenic most common feature. The predominance mica, abundance chlorite, units indicate physical weathering under cold dry climate, a dominant provenance for minerals from Transantarctic Mountains. unit considered mostly they likely result early diagenetic processes, being formed alteration volcanic material (glass, pyroxenes feldspars) and/or through precipitation fluids hydrothermal origin. Our survey attests importance discrimi nating as occurrence ancient sedimentary successions might lead incorrect paleoclimatic interpretations, since can affected thus obliterating climatic signal.