Paleoenvironmental changes recorded in the Santa Marta Formation (Santonian–Campanian, Upper Cretaceous), James Ross Island, Antarctica, inferred from palynofacies analyses

Abstract

The Santa Marta Formation (Santonian–Campanian; James Ross Island, Antarctic Peninsula) is part of one of the most complete sedimentary sequences in the Southern Hemisphere. Paleoenvironmental changes recorded in the formation are reflected in the stratigraphic distribution of sedimentary organic matter in the Lachman Crags and Herbert Sound members. Fifty-three samples from the Lachman Crags section and ten samples from the Herbert Sound section were prepared using standard non-oxidative methods for palynofacies. Analyses were performed using transmitted white light and fluorescence microscopy to identify the groups and subgroups of sedimentary organic matter: non-opaque non-biostructured and biostructured opaque particles, membrane fragments, degraded and non-degraded cuticles, spores, pollen grains, fungal spores, Botryococcus, Palambages, dinoflagellates cysts, amorphous organic matter, pseudoamorphous (product of disintegration of macrophyte tissues) and resins. Three palynofacies associations are distinguished: terrestrial, opaque, and marine palynomorphs. Based on stratigraphically restricted cluster analysis (CONISS), three intervals have been identified: Interval 1, at the base of the Lachman Crags section, conspicuously dominated by the terrestrial palynofacies association. Interval 2, the middle portion of the Lachman Crags section, is marked by alternating terrestrial and opaque palynofacies associations. Interval 3, which coincides with the Herbert Sound section, is distinguished by an abrupt increase in marine elements. The composite section shows progressive transgression, accompanied by a decrease in continental elements, culminating in an open marine environment towards the top of the section.