--> Patterns of Bed Thickness and Grain-Size Distribution in Classical Turbidite Systems

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Patterns of Bed Thickness and Grain-Size Distribution in Classical Turbidite Systems

Abstract

This study aims to evaluate the role of bed thickness and grain-size distributions in characterizing deep-marine turbidite systems. The purpose is to develop a methodology, based on a statistical approach, which can be used to evaluate the depositional sub-environment of turbidite deposits or to point out basin-wide differences between depositional systems (e.g. confined or unconfined deposits). Starting from the collection of thickness and grain-size data from turbidite beds, this method can also be used when point data (boreholes) or limited outcrops are available. Field data were collected from classical, extensively-studied deep-marine systems, with well-understood stratigraphic architecture: the Marnoso-Arenacea system, in Italy, and the Grés d'Annot system, in France. Fieldwork involved extensive logging of turbidite successions, gathering of bed thickness data, and in-situ grain-size measurements using visual comparator and hand-lens. Laboratory analysis consists of detailed grain-size analysis conducted in representative thin sections of sandstone samples collected during fieldwork and statistical processing of collected datasets. Statistical analysis is focusing on fitting of frequency distributions, quantitative recognition of non-random facies clustering, and detailed analysis for the presence of asymmetric cycles in vertical grain-size trends. Results for selected proximal and distal sections indicate the presence of different mixed distribution models (mainly of lognormal type) for each section type, which may be related to flow characteristics and grain size range. Facies clustering analysis based on Hurst statistics and Monte Carlo simulation is also being implemented, revealing a non-periodic long-term pattern of clustering of low and high bed thickness values. Different grain-size trends were also detected in sandstone beds correlated across different parts of deep-marine systems. Current study is focusing on investigating the potential association of the above observations with particular depositional processes along the proximal or distal parts of the studied deep-marine deposits. Successful use of bed thickness statistics and grain-size trends for the classification of deep-marine architectural elements can provide a potentially powerful tool to assist the subsurface characterization of turbidite systems, which is crucial to improve planning of hydrocarbon exploration and oilfield development.