Geology of Santa Cruz, Argentina
Exposures of the Santa Cruz formation in the cliffs above the Atlantic are inaccessible. The best fossils come from the beaches between high and low tide levels.
The fossil-bearing beds exposed at sea level dip about 3 degrees on a southward strike so that at low tide (when tide is about 7 meters) the same bedding plane is exposed to a breadth of 500-700 meters to seaward. It is then possible to collect large numbers of fossils of similar geological age; most of the fossils from one locality are analytically indistinguishable from one another in age.