The eight field trips in this volume, associated with GSA Connects 2021 held in Portland, Oregon, USA, reflect the rich and varied geological legacy of the Pacific Northwest. The western margin of North America has had a complex subduction and transform history throughout the Phanerozoic, building a collage of terranes. The terrain has been modified by Cenozoic sedimentation, magmatism, and faulting related to Cascadia subduction, passage of the Yellowstone hot spot, and north and westward propagation of the Basin and Range province. The youngest flood basalt province on Earth also inundated the landscape, while the mighty Columbia watershed kept pace with arc construction and funneled epic ice-age floods from the craton to the coast. Additional erosive processes such as landslides continue to shape this dynamic geological wonderland.

ABSTRACT Mapping the distribution of productivity in ancient seas is a fundamental requirement for predicting the lateral variation in source rock quality, one of the main uncertainties for exploration in frontier basins, and is also required in the modeling of the carbon cycle in deep time. To construct a predictive tool designed to address this problem, a multifaceted approach based on paleogeographic mapping integrated with Earth-systems modeling has been devised and applied for a series of 18 time slices from the Early Paleozoic to Recent. Plate Wizard™ reconstructions were used as the basis for global paleogeographic mapping. Detailed paleotectonic and paleoenvironment maps were prepared using a global database of paleoenvironmental and lithofacies data compiled for this project. A novel method relating topography and bathymetry to plate tectonic environments was used in the construction of paleo digital elevation models (DEMs), and these DEMs were coupled with state-of-the-art paleo-Earth systems models (UK Meteorological Office HadCM3 paleoclimate model) run specifically for this project. The database also included climate proxies that were used to test the veracity of modeling results. Both upwelling and storms are major factors in the supply of nutrients to the photic zone, and low light levels are a significant seasonal limit on primary productivity, particularly at high latitudes. Each of these elements of the predictive model was derived from the HadCM3 model output. This approach also provides an understanding of paleogeographic and paleoclimatic geohistory that includes drainage basin evolution.