138-9 Mass Extinction Down Under: New Potential Cretaceous-Paleogene (K-Pg) Boundary Sites from Madagascar and Australia

Session: The Cretaceous-Paleogene (K-Pg) Boundary Interval: From Large-Scale Geological Events to Mass Extinction Mechanisms

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New data from two potential Southern Hemisphere Cretaceous-Paleogene (K-Pg) boundary successions, one in northwestern Madagascar and the other in Western Australia, contribute to our understanding of sedimentological and biotic patterns across this critical interval.

The Malagasy record is particularly significant given the island’s long geological isolation following its separation from Africa in the Jurassic (~165 Ma). This isolation has played a pivotal role in shaping Madagascar’s unique biodiversity. In Madagascar, potential K-Pg boundary sediments are primarily associated with the Maevarano and overlying Betsiboka formations in the Mahajanga Basin, northwestern Madagascar. The Maevarano Formation, dated to the latest Maastrichtian, comprises fluvial to marginal marine sandstones, siltstones, and mudstones, and has yielded a rich assemblage of vertebrate fossils, including non-avian dinosaurs, crocodyliforms, and mammals. However, clear identification of the K-Pg boundary itself within these units remains challenging due to limited biostratigraphic resolution and the paucity of continuous sedimentary records across the boundary. The overlying Betsiboka Formation is thought to be Paleocene in age, but its stratigraphic and temporal relationship to the underlying Maastrichtian deposits is still poorly constrained. Ongoing sedimentological, palynological, and geochemical studies aim to resolve the placement and character of the K-Pg transition in this region. Further aim of this project is to integrate botanical and paleontological approaches to explore extinction and survival patterns, especially among basal angiosperms such as the Winteraceae, represented today on Madagascar by Takhtajania.

In Western Australia, recent fieldwork in the Giralia Range (Carnarvon Basin) has revealed a potential K-Pg boundary succession in a series of badlands exposures. Here, the Late Maastrichtian Miria Marl, characterized by ~1–2 m of calcarenite with abundant phosphatic nodules, transitions into the overlying Paleocene Boongarooda Greensand. These units were deposited in a mid- to outer-shelf environment and contain diverse marine fauna, including foraminifera, ammonites, bivalves, gastropods, and vertebrate remains such as turtles and a pterodactyl. While sedimentological and biostratigraphic studies are ongoing, forthcoming palynological analyses may help refine the completeness and placement of the boundary in both regions.

Paleontological and sedimentological data from these mid-latitude localities complement findings from high-latitude Southern Hemisphere sites such as New Zealand, offering valuable contrasts in extinction and recovery patterns, depositional environments, and biotic turnover across different paleogeographic settings during the end-Cretaceous mass extinction.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8910

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