This paper was translated in 1975-76 partly as an exercise in learning geological aspects of the Italian language and partly in preparation for several months of field work and study with the authors of the paper. The translation was examined and substantially improved by my Italian teacher, Mrs. Mary West of Sunnyvale, California, and by the authors. However, I take full responsibility for any possible misinterpretations and poorly organized or poorly worded portions.This paper is a very significant one in the field of sedimentology and represents a major breakthrough in the environmental interpretation and subdivision of turbidite facies. It has had great impact on many aspects of geology, including field mapping, petroleum exploration, lithostratigraphy, biostratigraphy, studies of modern and ancient deep-sea fans, slopes and basin plains, and most of all on facies analyses of deep-sea sedimentary rocks. The need for an English translation had been expressed to me by many colleagues, both in the U.S. and abroad, and I hope that republication of the paper in English will extend its usefulness to more individuals involved in diverse geologic studies.The original paper had an English abstract, and this is not reproduced here. Some aspects of general turbidite facies problems have been published subsequently by the authors and associates; some of these publications are listed in an annotated bibliography at the end of the translation.
The vertical and lateral stratigraphic relations of facies and facies associations, palaeocurrent directions, and geometry and internal organization of associated thick‐bedded and coarse‐grained bodies of sandstone provide the framework for distinguishing five thin‐bedded turbidite facies in the Eocene Hecho Group, south‐central Pyrenees, Spain. Each facies is characterized by a number of primary features which are palaeoenvironmental indicators by themselves. These features and their palaeoenvironmental significance are summarized below.
The impressive regularity and lateral persistence of bedding and depositional structures, combined with the association of thin hemipelagic intercalations are typical characteristics of the basin plain thin‐bedded turbidites. Lateral variations in bed thickness, internal structures, grain size, sand: shale ratio, and amounts of hemipelagic intercalations are present in these sediments, but take place so gradually that they cannot generally be recognized at the scale of even very large exposures. The basin plain facies has a remarkable character of uniformity over great distances and considerable stratigraphic thicknesses.
Thickening‐upward and/or symmetric cycles with individual thicknesses ranging from a few metres to a few tens of metres are typical of lobe‐fringe thin‐bedded turbidites. The sediments that comprise the cycles contain small but recognizable variations in bed thickness and sand: shale ratio. The diagnostic cyclic pattern can be detected in relatively small exposures. It should be noted that in absence of coarse‐grained and thick‐bedded sandstone of the depositional lobes the above cyclic pattern is diagnostic of fan‐fringe areas.
An extremely irregular bedding pattern with lensing, wedding, and amalgamation of individual beds over very short distances, sharp rippled tops of many beds, and internal depositional structures indicative of mainly tractional processes without substantial fallout, are typical and exclusive characteristics of channelmouth thin‐bedded turbidites.
Bundles of interbedded thin‐bedded sandstone and mudstone as thick as a few metres that are separated in vertical sequences by mudstone units of roughly similar or greater thickness are typical of interchannel thin‐bedded turbidites. The most diagnostic feature of this depositional environment is the presence of beds of sandstone filling broad shallow channels as probable crevasse‐splays.
Thin, thoroughly rippled sandstone beds with marked divergence of the bedding attitude characterize the channel‐margin facies. The divergence or expansion in thickness, is consistently toward the channel axis. Small and shallow channels filled with thin‐bedded deposits, interpreted here as crevasses cut into channel edges or levees during period of severe overbanking are also characteristic.
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