Maastrichtian-Danian Northpatagonian rocky shore, Argentina

Abstract

The Atlantic Maastrichtian-Danian (K/P) transgression over northern-central extra-Andean Patagonia (Argentina) covered both Mesozoic sedimentary basins and the Northpatagonian Massif (NPM). The flooding of the NPM resulted in a regional unconformity/nonconformity (70.000 km2) between the pre-Cretaceous basement (Jurassic Chon Aike Silicic Large Igneous Province and igneous-metamorphic Paleozoic basement) and the K/P marine transgressive record, constituting the widest known ancient rocky shore of South America (Northpatagonian rocky shore). The transgressive stratigraphic record over the basement is mainly composed of isolated carbonate bioclastic deposits up to 40 m thick with predomination of bivalves, echinoderms, bryozoan, coralline red algae, and foraminifera skeletal remains; we interpreted these bioclastic near-shore deposits as rocky shore associations. The hard substrate, irregular seacoast and low accommodation space over the NPM provided a preferential ecological niche for encrusting biota (i.e., Oyster reefs) during the K/P epicontinental flooding. The colonization of “engineer ecosystems” organisms over thousands of square kilometers probably enhanced the coastal biodiversity. The K/P Northpatagonian rocky shore favored the conformation of a short-lived, transgressive, cool-water carbonate factory in the south-eastern extreme of South America.