ABSTRACT William Richard Dickinson was born in Nashville, Tennessee, in 1931 and died in Nuku’alofa, Tonga, in 2015. Through a remarkable combination of intellect, self-confidence, engaging humility, and prodigious output of published work, he influenced and challenged (to date) three generations of sedimentary geologists, igneous petrologists, tectonicists, sandstone petrologists, archaeologists, and other geoscientists. Bill grew up in the California Transverse Ranges before heading to Stanford, where he received his B.S., M.S., and Ph.D. While on the Stanford faculty (1958–1979), Bill used a Guggenheim Fellowship in Fiji, New Zealand, and Australia to understand the great mobility of Pacific plates, including relationships between inclined seismic zones beneath island arcs and magmatism, and he began a lifelong study of Pacific potsherds for archaeological studies. In 1969, Bill convened the watershed Geological Society of America (GSA) Penrose Conference at Asilomar, California, on “The Meaning of the New Global Tectonics for Magmatism, Sedimentation, and Metamorphism in Orogenic Belts.” An onslaught of new ideas and insights illuminated plate-tectonic processes, sandstone petrology as a guide to plate-tectonic settings, and plate-tectonic evolution of sedimentary basins. This naturally led to syntheses of Cordilleran basins and tectonics, and Pacific plate tectonics. His most cited papers involve the relation of sand(stone) composition to plate tectonics. Following his relocation to the University of Arizona in 1979, Bill began using detrital zircon as an additional provenance tool, resulting in new paleogeographic reconstructions of North America’s drainage patterns for the late Paleozoic and early Mesozoic. During Bill’s “retirement,” he received the Penrose Medal, the Sloss Award, the Twenhofel Medal, the Rip Rap Award, and the Stanford Distinguished Alumnus Award. He also became a member of the National Academy of Sciences and served as president of GSA. The cumulative impact of Bill Dickinson’s influence on understanding Earth history and processes has been, and will continue to be, among the greatest in the history of our science. The papers in this volume are an impressive tribute to the depth and breadth of Bill Dickinson’s contributions.

The volcanic basement of the Ecuadorian Western Cordillera (Pallatanga Formation and San Juan unit) is made up of mafic and ultramafic rocks that once formed an oceanic plateau. Radiometric ages from these rocks overlap with a hornblende 40 Ar/ 39 Ar plateau age of 88 ± 1.6 Ma obtained for oceanic plateau basement rocks of the Piñon Formation in coastal Ecuador, and with ca. 92–88 Ma ages reported for oceanic plateau sequences in the Caribbean and western Colombia. These results suggest that the oceanic plateau rocks of the Western Cordillera and flat forearc in Ecuador are derived from the Late Cretaceous Caribbean-Colombia oceanic plateau. Intraoceanic island-arc sequences (Rio Cala Group) overlie the plateau in the Western Cordillera and yield crystallization ages that range between ca. 85 and 72 Ma. The geochemistry and radiometric ages of island-arc lavas from the Rio Cala Group, combined with the age range and geochemistry of their turbiditic, volcaniclastic products, indicate that the arc was initiated by westward subduction beneath the Caribbean Plateau. They are coeval with island-arc rocks of coastal Ecuador (Las Orquideas, San Lorenzo, and Cayo Formations) and Colombia (Ricaurte Arc). These island-arc units may be related to the Late Cretaceous Great Arc of the Caribbean. Paleomagnetic analyses of volcanic rocks of the Piñon and San Lorenzo Formations of the southern external forearc show that they erupted at equatorial or low southern latitudes. The initial collision between South America and the Caribbean-Colombia oceanic plateau caused rock uplift and exhumation (>1 km/m.y.) within the continental margin during the Late Cretaceous (ca. 75–65 Ma). Magmatism associated with the Campanian–early Maastrichtian Rio Cala Arc ceased during the Maastrichtian because the collision event blocked the subduction zone below the oceanic plateau. Paleomagnetic data from basement and sedimentary cover rocks in the coastal forearc reveal 20°–50° of clockwise rotation during the Campanian, which was synchronous with the collision of the oceanic plateau and arc sequence with South America. East-dipping subduction beneath the accreted oceanic plateau formed the latest Maastrichtian to early Paleogene (ca. 60 Ma) Silante volcanic arc, which was deposited in a terrestrial environment. Subsequently, Paleocene to Eocene volcanic rocks of the Macuchi unit were deposited, and these probably represent a continuation of the Silante arc. This submarine volcanism was coeval with the deposition of siliciclastic rocks of the Angamarca Group, which were mainly derived from the emerging Eastern Cordillera.

ABSTRACT The Great Valley forearc basin records Jurassic(?)–Eocene sedimentation along the western margin of North America during eastward subduction of the Farallon plate and development of the Sierra Nevada magmatic arc. The four-dimensional (4-D) basin model of the northern Great Valley forearc presented here was designed to reconstruct its depositional history from Tithonian through Maastrichtian time. Based on >1200 boreholes, the tops of 13 formations produce isopach maps and cross sections that highlight the spatial and temporal variability of sediment accumulation along and across the basin. The model shows the southward migration of depocenters within the basin during the Cretaceous and eastward lapping of basin strata onto Sierra Nevada basement. In addition, the model presents the first basement map of the entire Sacramento subbasin, highlighting its topography at the onset of deposition of the Great Valley Group. Minimum volume estimates for sedimentary basin fill reveal variable periods of flux, with peak sedimentation corresponding to deposition of the Sites Sandstone during Turonian to Coniacian time. Comparison of these results with flux estimates from magmatic source regions shows a slight lag in the timing of peak sedimentation, likely reflecting the residence time from pluton emplacement to erosion. This model provides the foundation for the first three-dimensional subsidence analysis on an ancient forearc basin, which will yield insight into the mechanisms driving development of accommodation along convergent margins.