This ethnographic multiple-case study examines how undergraduate students are socialized into the disciplinary norms, values, and practices of a geoscience course at a Canadian university. Transcending logocentric assumptions about academic discourse, this article advances a broader domain of inquiry----"multimodal academic discourse socialization"----which foregrounds the polysemiotic nature of academic socialization. This approach examines not only linguistic but also a wider range of semiotic resources, including gestural, visual, material, and spatial ones, among others. To understand geoscientists' disciplinary norms, values, and communicative practices, ethnographic data (classroom observations, semi-structured interviews, course-related artefacts) were thematically analysed. Focal students' geoscience poster presentation performances were also analysed using multimodal interaction analysis to scrutinize micro-level instantiations of disciplinary practices. Findings highlight how students were socialized into geoscience 'observations and interpretations' through a recurrent multimodal classroom activity, which was also reflected in micro-level multimodal practices enacted in students' geoscience poster presentations. This study emphasizes that multimodal enactments constitute a crucial dimension of disciplinary practices and values connected with learning to think, view, and represent knowledge as geoscientists.