Abstract Apaleoseep system consisting of hundreds of sand injectites and authigenic carbonate structures crops out in the Panoche and Tumey Hills, central California. This paleoseep system developed on the western margin of the Great Valley forearc basin and is contained within the uppermost, early Paleocene part of the dominantly siliciclastic Moreno Formation. It is 20 km (12 mi) long and is distributed over more than 700 m (2296 ft) of stratigraphic section. Injectites appear in the lower 600 m (1968 ft), thinning upward from 3 m (9.8 ft) to less than 1 cm (0.4 in.), and cooccur with the paleoseep carbonate structures in the uppermost 200 m (660 ft) of section. The paleoseep slab, mound, and concretionary carbonates are 13 C depleted (to −46‰ Vienna Peedee belemnite) and commonly contain pipelike structures and the remains of chemosynthetic macroinvertebrates, including tube worms and lucinid bivalves. Their diverse morphologies likely reflect different rates and styles of fluid flow, but most show a similar paragenesis beginning with biologic colonization and pervasive micrite authigenesis and concluding with sparite precipitation in vugs and conduits. The close stratigraphic and compositional associations of paleoseep carbonate structures with injectites suggest that they were contemporaneous, and that injectites controlled the location of the seeps. Variations in abundance, morphology, and geochemistry of the authigenic carbonates, fossils, and injectites across the outcrop area indicate considerable variability in seep venting rates locally, regionally, and throughout the nearly 2-Ma duration of the seep system. Thus, the Panoche and Tumey Hills locality offers a four-dimensional view of the nature and evolution of a large, injectite- driven, cold seep in a forearc setting.

Abstract The contributions of the La Plata Museum to the geology of Argentina began following the exploratory trips of its founder, F.P. Moreno, in the 1870s. The geological expeditions of the La Plata Museum started in the 1880s and covered the Andean region, although they were focused in the Patagonian Andes. They became more important from 1893 when they were related to explorations aimed at fixing the boundary between Argentina and Chile. Within 10 years the geographical and geological bases of large and almost unknown regions were established. R. Hauthal studied the area between the Last Hope Inlet and Lake Belgrano, defining its stratigraphy and publishing the first geological map of the Cordilleran region between c. 49° 30′ and 52° S. The geology between Lake Buenos Aires and the Rio Negro (41–47° S) was established by Santiago Roth. The stratigraphic succession, facies and structural changes through the Argentine–Chilean Cordillera at the latitude of Lake Nahuel Huapi and Lake Lacar were studied by L. Wehrli, while studies at the latitude of Neuquén and Mendoza (36–39° S) were carried out by C. Burckhardt. Mesozoic and Cenozoic fossils were studied either in the Museum or abroad. Supplementary material: Map of southern South America (Argentina and Chile) showing the distribution of towns in 1870 is available at https://doi.org/10.6084/m9.figshare.c.3283385.v1