A problem for the impact hypothesis for the Cretaceous-Tertiary (K-T) mass extinction is the apparent absence of an identifiable impact site. The Manson Impact Structure is a candidate because it is the largest recognized in the U.S.; it is relatively close to the largest and most abundant shocked quartz grains found at the K-T boundary; and its age is indistinguishable from that of the K-T boundary based on paleontological evidence, fission track dates, and preliminary Ar-40/Ar-39 measurements. The region of northwest central Iowa containing the Manson Impact Structure is covered by Quaternary glacial deposits underlain by Phanerozoic sedimentary rocks (mostly flat-lying carbonates) and Proterozoic red clastic, metamorphic, volcanic, and plutonic rocks. In a circular area about 22 miles (35 km) in diameter around Manson, Iowa, this normal sequence is absent or disturbed and near the center of the disturbed area granitic basement rocks have been uplifted some 20,000 ft (6000m). Attention was drawn to Manson initially by the unusual quality of the groundwater there. Within the structure three roughly concentric zones of rock associations have been identified: (1) displaced strata; (2) completely disrupted strata, and igneous and metamorphic rocks. Manson was established as an impact structure based on its circular shape, its central uplift, and the presence of shocked quartz within the granitic central uplift. A gravity survey identified locations of low-density brecciated rocks and high-density uplifted crystalline rocks, but the outer boundary of the structure could not be established. Aeromagnetic and ground magnetic surveys showed locations and depths of shallowly buried crystalline rock and the locations of faults. A refraction seismic survey identified the crystalline central uplift, determined that the average elevation of bedrock is 70 ft (20 m) higher outside the structure than within, and was used to map the bedrock topography within the structure. A connec...

Twenty-two reports presenting results from the investigation samples of the Manson impact structure, a crater site in Iowa that was not discovered until 1992. The reports cover a great deal of ground, including geophysical studies of the crater structure, detailed mineralogical, petrological, and ge

This book provides a general introduction to impact stratigraphy, with emphasis on the recognition of distal impact ejecta in the field, by focusing on the impactoclastic layers of the Umbria-Marche sequence in Central Italy, with an almost perfect stratigraphic record over the last 200 Million years. A general introduction to impact cratering and a discussion of distal ejecta and impact layers around the world is followed by a detailed description of the record of the impact of extraterrestrial bodies in sediments of the Umbria-Marche Apennines. The volume is of interest to a diverse audience in the geological and planetary sciences, ranging from (upper) undergraduate to research level. This book can also be used by students and researchers as a field guide to some of the most important Italian impact layers.

From the reviews: "Astronomy and Astrophysics Abstracts has appeared in semi-annual volumes since 1969 and it has already become one of the fundemental publications in the fields of astronomy, astrophysics and neighbouring sciences. It is the most important English-language abstracting journal in the mentioned branches. ...The abstracts are classified under more than a hundred subject categories, thus permitting a quick survey of the whole extended material. The AAA is a valuable and important publication for all students and scientists working in the fields of astronomy and related sciences. As such it represents a necessary ingredient of any astronomical library all over the world." Space Science Review# "Dividing the whole field plus related subjects into 108 categories, each work is numbered and most are accompanied by brief abstracts. Fairly comprehensive cross-referencing links relevant papers to more than one category, and exhaustive author and subject indices are to be found at the back, making the catalogues easy to use. The series appears to be so complete in its coverage and always less than a year out of date that I shall certainly have to make a little more space on those shelves for future volumes." The Observatory Magazine#

Iowa's rock record is the product of more than three billion years of geological processes. The state endured multiple episodes of continental glaciation during the Pleistocene Ice Age, and the last glacier retreated from Iowa a mere (geologically speaking) twelve thousand years ago. Prior to that, dozens of seas came and went, leaving behind limestone beds with rich fossil records. Lush coal swamps, salty lagoons, briny basins, enormous alluvial plains, ancient rifts, and rugged Precambrian mountain belts all left their mark. In "Iowa's Geological Past, " Wayne Anderson gives us an up-to-date and well-informed account of the state's vast geological history from the Precambrian through the end of the Great Ice Age. Anderson takes us on a journey backward into time to explore Iowa's rock-and-sediment record. In the distant past, prehistoric Iowa was covered with shallow seas; coniferous forests flourished in areas beyond the continental glaciers; and a wide variety of animals existed, including mastodon, mammoth, musk ox, giant beaver, camel, and giant sloth. The presence of humans can be traced back to the Paleo-Indian interval, 9,500 to 7,500 years ago. Iowa in Paleozoic time experienced numerous coastal plain and shallow marine environments. Early in the Precambrian, Iowa was part of ancient mountain belts in which granite and other rocks were formed well below the earth's surface. The hills and valleys of the Hawkeye State are not everlasting when viewed from the perspective of geologic time. Overall, Iowa's geologic column records an extraordinary transformation over more than three billion years. Wayne Anderson's profusely illustrated volume provides a comprehensive and accessible survey of the state's remarkable geological past.