Abstract Rittman 2021 Pyroclastic deposits from explosive eruptions are preserved in the offshore sedimentary record of the Southern Ocean surrounding Antarctica. Consequently, marine tephrostratigraphy offers a critical resource of data for volcanological reconstructions including age and recurrence of eruptions, intensity/magnitude, and eruptive dynamics, and for the assessment of the potential volcanic hazards posed by the ash-forming eruption at high southern latitudes volcanoes. During the International Ocean Discovery Program Expedition 374 in the Ross Sea, Antarctica, was found a 20 cm-thick tephra layer intercalated in the marine sediments recovered at Site U1524. We present here a full characterization of this tephra including tephra texture, mineral paragenesis and major- and trace-element composition on individual glass shards. The tephra age was also constrained by the 40Ar-39Ar method on sanidine crystals. 40Ar-39Ar data indicate that a best age estimate of 1.282±0.012 Ma, based on both single-grain total fusion analyses and step-heating experiments on multi-grain aliquots. The tephra is characterized by a very homogeneous rhyolitic composition and a peculiar mineral assemblage, dominated by sanidine, quartz, and minor aenigmatite and arfvedsonite-riebeckite amphiboles. The tephra from Site U1524 compositionally matches with a c. 1.3 Ma, rhyolitic pumice fallout deposit cropping out on the rim of the Chang Peak volcano summit caldera, in the Marie Byrd Land, located c. 1300 km from Site U1524. This contribution offers important volcanological data on the eruptive history of Chang Peak volcano and adds a new tephrochronologic marker for the dating, correlation, and synchronization of marine and continental early Pleistocene records of West Antarctica.