Triassic-Jurassic Rifting by W. Manspeizer Summary
Extensive field studies on the African and North American plates during this past decade have yielded a wealth of new data and ideas about rift basins and the origin of passive margins. New surface and subsurface basins have been identified; fossils abound in strata that only recently were considered barren; oil exploration is being actively pursued in continental strata of the Richmond-Taylorsville, Sanford and Newark basins, Late Triassic marine strata have been identified in Georges Bank off the coast of Massachusetts, and the roles of wrench tectonics, successor basins and listric normal faults have challenged the classical view that these are simple extensional basins. This two part work brings together representative examples of these studies. It is not intended as an exhaustive synthesis of the subject, but rather a vehicle to present new data, new ideas and alternative views. Some of the papers present regional summaries, others attempt to relate local features to regional questions, while others describe modern rift basins as possible analogs of early Mesozoic basins. Geologic data from the Atlantic passive margins record that continental rifting of central Pangaea occurred during the latest Triassic-earliest Jurassic (Liassic), and that sea-floor spreading probably began no later than the Middle Jurassic. The primary subject of this book focuses on the Triassic-Jurassic rifting events that led to the breakup of Pangaea and the opening of the central Atlantic Ocean. Whereas other treatises have focused on the origin of the passive margins, inferred primarily from geophysical data of the offshore basins, this volume primarily and uniquely focuses on land-based field studies of the onshore synrift basins. Offshore studies of synrift basins are also included and add substantially to our understanding of the breakup. However, the onshore data base, while complementary, is different, thus providing researchers with a different insight to the questions at hand. The book is organized into four sections. Section I, Pangaean Plate in Time and Space, first locates Pangaea in space and then places the Triassic basins within an historical context on the Alleghanian-Variscan Orogens. Section 2, the offshore and onshore basins of the North American and African Plates, comprises about 70% of all papers in this book, and includes papers on structural geology, petrology, paleontology, sedimentation, organic geochemistry, vulcanism and mineral resources. Section 3, Related Mesozoic Atlantic Rift Basins, includes papers on Iberia, Western Europe, the Benue Trough and Brazil. The final section of the book, Analogs, includes the rift basins of East Africa, the Red Sea, the Gulf of Elat (Aqaba), the Dead Sea and the Rio Grande. The book is richly illustrated throughout with figures, photographs, tables and fold-out maps, including nine in full colour.