Examination of a number of ancient turbidite basins in the Alpine geosynclinal chains of the circum- Mediterranean region supports the assumption that many of the sediments therein were deposited in deep-sea fan environments. Sand—body geometry and vertical sequence analysis provide criteria for detecting associations of inner, middle, and outer fan facies in these turbidite sequences.
Examples of these three main facies associations are reported from selected Tertiary geosynclinal tur- bidites occurring in the northern Apennines (Ranzano Sandstone and Bobbio Formation) and on the island of Rhodes, Aegean Sea (Messanagros Sandstone). The proposed depositional model based on these studies is not unlike models of certain deltaic systems and emphasizes progradational, aggradational, and recessional events of turbidite sedimentation in complexes of ancient deep-sea fans.
Middle fan deposits commonly show thinning and (or) fining upward cycles developed within channel-fill sequences. Such cycles are readily comparable to those of abandoned fluvial channels that are also filled with similar sequences in delta-plain environments. In both cases, channel and interchannel areas indicate prevalent vertical accretion. Active deltaic outbuilding is expressed typically by stream-mouth bars whose progradational character is shown by the occurrence of thickening and (or) coarsening upward cycles. Detailed inspection of several northern Apennine turbidite formations has shown that sandstone bodies, closely exhibiting such a progradational pattern, are extremely widespread. These turbidite sediments are here interpreted as outer fan deposits, and are thought to be responsible for deep-sea fan growth in most ancient basins.
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Modern and Ancient Geosynclinal Sedimentation
The Kay Conference was held in Madison, Wisconsin, November 1972. This symposium volume contains the texts of papers presented at Madison. It is organized in a topical manner, and in most areas of discussion, modern analogues and ancient examples together provide a comparative basis for evaluating sedimentary models for geosynclines. In the 1970s students of both modern and ancient sediments have compiled an immense body of knowledge relevant to the geosynclinals concept. Moreover, the new theory of plate tectonics has required a complete reassessment of the geosynclines as well as orogenesis. The purpose of this volume is to evaluate by comparison of modern and ancient sediments a number of depositional models applicable to the great variety of strata seen in orogenic belts also called geosynclinal.