Ralph Willard Imlay

Bio: Ralph Willard Imlay is an academic researcher. The author has contributed to research in topics: Cretaceous & Geosyncline. The author has an hindex of 25, co-authored 51 publications receiving 1639 citations.

Correlation of the outcropping Cretaceous formations of the Atlantic and Gulf Coastal Plain and trans-Pecos Texas

Abstract: INTRODUCTION This is Number 9 of a series of correlation charts prepared by the Committee on Stratigraphy of the National Research Council, which will cover the post-Proterozoic sedimentary formations of North America. For general information about the project the reader is referred to the general introduction preceding this paper. The senior author, Lloyd W. Stephenson, is responsible for that part of the chart treating of the Upper Cretaceous series in the Atlantic and Gulf Coastal Plain (exceptions noted below) and the Lower Cretaceous series of the North Atlantic Coastal Plain; with respect to the Upper Cretaceous his presentation is based largely on his personal knowledge of the paleontology and stratigraphy of the area, gained from field and laboratory studies ranging from reconnaissance to detailed; all published information has been considered, and much of it utilized, but it is not practicable to include a complete bibliography. References are given to papers . . .

Correlation of the Cretaceous Formations of the Pacific Coast (united States and Northwestern Mexico)

Abstract: This paper includes a discussion of the historical development of stratigraphic classification of Cretaceous rocks on the Pacific Coast of the United States, a summary of the faunal evidence for correlating the Cretaceous rocks with the European stages, and all the stratigraphic and faunal data available for 61 areas along the Pacific Coast in Washington, Oregon, California, and northwest Mexico. Many of these data, particularly for Washington and Oregon, have not been published previously. The chart includes lists of fossils that are most useful stratigraphically and presents correlations with British Columbia, Japan, and the western interior of the United States. Included are maps that show the general distribution of Cretaceous rocks along the Pacific Coast. Such maps for Oregon and Washington show occurrences that are not shown on any other published maps.

Part IV. Geology of the western part of the Sierra de Parras

Abstract: INTRODUCTION LOCATION AND EXTENT OF AREA The Sierra de Parras lies in southern Coahuila, directly south of the Parras Basin. It begins, on the west, near Puerto La Pena, about 60 miles east of the city of Torreon, and extends east-southeast about 100 miles, as a distinct, rugged topographic unit, finally merging into the ranges of the Sierra Madre Oriental, in the region south of Saltillo. The area mapped extends from Puerto La Pena eastward 26 miles to about 4 miles east of Parras. It comprises about 370 square miles, of which only 260 are mountainous. The width of the mountainous area varies considerably, being 5 miles near La Pena, 12 miles about 10 miles farther east, and 9 miles in the region south of Parras. Its shape is extremely irregular. CONSTRUCTION OF MAP AND SECTIONS Available maps of southern Coahuila are on a scale of 1 to 500,000 and . . .

Cretaceous anoxic events: from continents to oceans

Abstract: Pelagic Cretaceous sediments, deposited in a range of palaeotectonic and palaeogeographic settings, from continents to oceans, are commonly black and bituminous. 3 particular time-envelopes define the major occurrences of such facies: late Barremian-Aptian-Albian, the Cenomanian-Turonian boundary and, to a lesser extent, the Coniacian-Santonian. These intervals define the duration of so-called Oceanic Anoxic Events during which global marine waters were relatively depleted in oxygen, and deposition of organic matter, derived from both terrestrial and planktonic sources, was widespread. Cretaceous OAEs correlate closely with transgressions, and such a correlation exists throughout the stratigraphical column. Flooding of land-masses is thought to have transported much terrestrial plant material seawards; the progressive increase in shelf-sea area is thought to have stimulated production of marine plankton. Bacterial consumption of this organic matter favoured the development of poorly oxygenated mid-to late Cretaceous waters in which many of the characteristic facies of the Period, including glauconitic sandstones and phosphatic chalks, were deposited.

Extinctions of North American Fishes During the past Century

Abstract: Extinctions of 3 genera, 27 species, and 13 subspecies of fishes from North America are documented during the past 100 years. Extinctions are recorded from all areas except northern Canada and Alaska. Regions suffering the greatest loss are the Great Lakes, Great Basin, Rio Grande, Valley of Mexico, and Parras Valley in Mexico. More than one factor contributed to the decline and extinction of 82% of the fishes. Physical habitat alteration was the most frequently cited causal factor (73%). Detrimental effects of introduced species also were cited in 68% of the extinctions. Chemical habitat alteration (including pollution) and hybridization each were cited in 38% of the extinctions, and overharvesting adversely affected 15% of the fishes. This unfortunate and unprecedented rate of loss of the fishery resource is expected to increase as more of the native fauna of North America becomes endangered or threatened.

Structure and Stratigraphy of Forearc Regions

Abstract: Active continental margins and the active flanks of island arcs lie in the forearc regions of arc-trench systems generated by plate consumption. Arc-trench systems are initiated by contractional activation of previously rifted continental margins, by reversal of subduction polarity following arc collisions, and as island arcs within oceanic regions. The varied configurations of shelved, sloped, terraced, and ridged forearcs arise partly from differences in initial geologic setting, but mainly from differences in structural evolution during subduction. In regions where large quantities of sediment are delivered, forearc terranes enlarge during subduction through linked tectonic and sedimentary accretion of deformed ocean-floor sediments and igneous oceanic crust, uplifted rench-floor and trench-slope sediments, and the depositional fills of subsiding forearc basins. Where sediment delivery is small, enlargement is subdued or absent, and shortening of the arc-trench gap may be possible. Trench inner slopes typically are underlain by growing subduction complexes composed of imbricate underthrust packets of ocean-basin, trench-floor, and trench-slope sediments in thrust sheets, isoclines, and melanges. The structure of subduction complexes is governed by the thickness and nature of oceanic layers rafted into the subduction zone, variable thicknesses of trench and slope sediments, and the rate and obliquity of plate convergence. Forearc basins between the magmatic arc and the trench axis include (a) intramassif basins lying within and on basement terranes of the arc massif, (b) residual basins lying on oceanic or transitional crust trapped between the arc massif and the site of initial subduction, (c) accretionary basins lying on accreted elements of the growing subduction complex, (d) constructed basins lying on the arc massif and accreted subduction complex, and (e) a composite of these basins. Strata deposited in forearc basins are typically immature clastic sediments composed of unstable clasts derived from rapid erosion of volcanic mountains or uplands of plutonic and metamorphic rocks within the arc massif. In equatorial regions reef-carbonate associations are also common. Facies patterns of turbidites, shelf sequences, and fluviodeltaic complexes within forearc basins are governed by the elevation of the basin thresholds, the rate of sediment delivery, and the rate of subsidence of the substratum. Petroleum prospects in forearc regions typically are limited by the prevalence of small, obscure structures within the subduction complex, the scarcity of good reservoirs in the forearc basin, the limited occurrence of source beds, and low geothermal gradients except within the arc massif where heat flux is commonly excessive.