The World Petroleum Basins series provides one more manifestation of the great unifying theory that plate tectonics has provided the science of geology. The concept of grouping descriptions of geology and petroleum systems of similar basins to provide a collection of exploration analogs has been made possible by the development of basin classification schemes built on a plate tectonic framework (Bally and Snelson, 1980). Conversely, particular sedimentary sequences in frontier areas may allow the geologist to infer the basin setting in which deposition took place, allowing for modeling of past tectonic and heat-flow history. Therefore, as Arbenz et al. note in the foreword to each of the volumes in this series, these analogs are designed to provide the explorationist with predictive insights into areas with similar geology. This volume presents examples of the fundamental plate tectonic unit: interior rift basins. Basins discussed in this volume are shown in Figure 1.
Although they are the subject of the last volume in the World Petroleum Basins project, interior rift basins are certainly not least in importance. Rifts represent a portion of an evolutionary sequence of crustal and upper mantle stretching that is responsible for normal faulting resulting from extension, the most commonly occurring structural style (Lowell, 1985). In reaching this conclusion, Lowell included the wide spectrum of extension (and the resulting normal faults) which occurs in oceanic spreading, in passive continental margins (nearly 62,000 mi or 99,750 km), in intraplate rifting (the subject of this volume), and in behind-arc spreading. All of these elements are a part of a sequence that culminates in the formation of ocean basins (Figure 2). Inasmuch as mature extended areas, i.e., passive margins, began with an initial rift phase, one must understand rift mechanisms to unravel a very large portion of the earth's geology. Rift basins occur throughout the geologic record and examples discussed in this volume range from the Paleozoic, through the Mesozoic, and into the Cenozoic (Tertiary).
Figures & Tables
Interior Rift Basins
Not only are rift basins the foundation for much of the geologic history of the earth, but they also are very attractive areas for hydrocarbon accumulations. Klemme stated that this geographic area has provided significant hydrocarbon reserves: "By area, these basins represent slightly over 5% of the world's basins (50% productive). However, high recovery has resulted, as they contain 10% of the world's present reserves (12% of the oil reserves and 4% of the gas reserves)." The rift basins discussed in this volume are only a few of the productive and, more importantly, potentially productive rift basins in the world. The term "rift" was coined by Gregory (1896) for the graben that now bears his name in the Kenyan portion of the East African rift system. The study of geology of rift basins began in the Rhine graben. The discovery of hydrocarbons in rift basins about the turn of the century provided new motivation for understanding these basins. This publication was initiated by the AAPG Publications Committee in 1985 and contributors were invited to write. AAPG designed their "World Petroleum Basins" series and sought to publish the definitive volume on each of several basin types. In this volume, "Interior Rift Basins," a detailed, 3-paper overview was written about the Suez Rift basin as representative of interior rift basins. The key papers were followed by less detailed reviews of three other selected interior basins: Pripyat and Dnieper-Donets Basins; Reconcavo Basin, Brazil; Albuquerque Basin Segment of the Rio Grande Rift.