López de Bertodano Formation
| Lopez de Bertodano Formation Stratigraphic range: Maastrichtian to Danian 70 to 65.5 Ma |
|
|---|---|
| Type | Geological formation |
| Unit of | Marambio Group |
| Underlies | Sobral Formation |
| Overlies | Snow Hill Island Formation |
| Lithology | |
| Primary | siltstone, mudstone |
| Other | concretion, sandstone |
| Location | |
| Region | Seymour Island, James Ross Island group |
| Country | Antarctica |
The Lopez de Bertodano Formation is a geological formation in the James Ross archipelago of the Antarctic Peninsula. The strata date from the end of the Late Cretaceous (upper-lower Maastrichtian stage) to the Danian stage of the lower Paleocene, about 70-65.5 million years ago.
Dinosaur remains are among the fossils that have been recovered from the formation and include at least two and probably as much as six lineages of indisputably modern birds: one related to waterfowl, a primitive shorebird or related form, 1-2 species of possible loons, a large and possibly flightless bird belonging to a lineage extinct today as well as a partial skull that might belong to either of the smaller species or represent yet another one. The formation also contains a rich fossil invertebrate fauna, including bivalves, gastropods, and cephalopods (ammonites and nautiloids).
The Cretaceous-Paleogene boundary (K-Pg) outcrops on Seymour Island in the upper levels of the López de Bertodano Formation. A small (but significant) iridium anomaly occurs at the boundary on Seymour Island, as at lower latitudes, thought to be fallout from the Chicxulub impactor in the Gulf of Mexico. Directly above the boundary a layer of disarticulated fish fossils occurs, victims of a disturbed ecosystem immediately following the impact event. Multiple reports have described evidence for climatic changes in Antarctica prior to the mass extinction, but the extent to which these affected marine biodiversity is debated. Based on extensive marine fossil collections from Seymour Island, recent work has confirmed that a single and severe mass extinction event occurred at this time in Antarctica just as at lower latitudes.
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