Five surface sections and one subsurface section of Late Cretaceous--early Tertiary sedimentary rocks were studied in the Punta Arenas-Strait of Magellan area, southern Chile. The rocks range in age from middle Maestrichtian to early Eocene and consist of the following formations from base to top: Santa Ana Beds, Rio Blanco, Carrera, Chorrillo Chico, San Jorge, and Agua Fresca (eastern Brunswick Peninsula area); and Fuentes, Rocallosa, Chorrillo Chico, San Jorge, and Agua Fresca (Seno Skyring area). The Cretaceous-Tertiary boundary is in the Chorrillo Chico Formation which covers the entire area.

The rocks studied are varieties of graywacke, siltstone, and argillite. Heavy-mineral studies indicate a varied source area including silicic plutons, metamorphic and gneissic rocks, and some volcanic terrane.

Lithologic, paleoecologic, and geochemical data show that the transition from middle Maestrichtian to early Eocene was gradual. Generally, the depth of water in which the stratigraphic units were deposited decreased continually through time.

Geochemical element analyses were made in an attempt to correlate the pre-Chorrillo Chico units in the Seno Skyring and Brunswick Peninsula areas. The study was limited and the results were not decisive. However, evidence was found to support correlation of the middle Rocallosa Formation with the Carrera Formation. The results obtained warrant further geochemical studies to aid correlation in the area.

All evidence collected indicates that, before deposition of the Chorrillo Chico Formation, the Late Cretaceous basin in this area was bisected by a northeast-southwest-trending topographic ridge. Because of the presence of this ridge, the sedimentation histories in the northwestern and southeastern parts of the area differ, and units deposited on either side of the ridge are difficult to correlate.