Taphonomy of fossil whales in diatomaceous sediments of the Neogene Pisco Formation, Peru

The Miocene/Pliocene Pisco Formation in southern Peru contains a rich fossil record of whales and other marine mammals in diatomaceous and tuffaceous sediments. This present work is a description of the taphonomic features of the fossil whales and the characteristics of the associated sediments, and a proposed paleoenvironmental framework to explain the occurrence of the fossil assemblages.; Four study areas were searched for whale skeletons and 484 specimens were documented. Data collected for each fossil occurrence include GPS position, orientation, size, skeletal elements present, degree of articulation and preservation, and relationship between the bones and the associated sediment. Eleven whales were excavated and their taphonomic characteristics were studied in detail. Data on fossil occurrence are used for mapping the fossil distribution and density in several stratigraphic levels.; Fossil whales are abundant in the four study areas. Most whales are fully articulated or partially disarticulated, and only a few are totally disarticulated. Whales with some degree of disarticulation have their bones associated. The bones are well preserved and bear no evidence of abrasion, dissolution, or deterioration owing to transport by water currents, winnowing, or weathering due to long-term exposure. There also is no evidence of invertebrate scavengers on the bones or in the associated sediment. Five whales have their baleen preserved, three of them with the baleen inside the mouth. Shark teeth have been found associated with many whales, but no convincing evidence of shark tooth marks were found on the bones.; The diatomaceous sediments are rich in the diatoms Thalassionema nitztschioides, Chaetoceros resting spores, Paralia sulcata, Delphineis, sp., and Thalassiosira sp. These diatoms record the occurrence of diatom blooms on a shallow shelf near the coast in a regime of upwelling waters. The occurrence of some freshwater diatoms in the sediments suggests the influx of river water entering the basin.; It is suggested in this work that the whales could have died by poisoning due to harmful algal blooms (HABs) that poisoned the food chain. The whales subsequently sank or floated for a time, before sinking, and in some cases have undergone partial disarticulation by detachment of their skulls and mandibles. It is suggested that rates of deposition were high for the whale-bearing diatomaceous sediments, because most of the whales are well articulated, all bones are well preserved, and there is no evidence of bioturbation left by benthic fauna.