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The AAPG/Datapages Combined Publications Database

CSPG Special Publications


Sedimentology of Gravels and Conglomerates — Memoir 10, 1984
Pages 399-411
Ancient Submarine Slope-Fan Systems

Clast Size and Bed Thickness Trends in Resedimented Conglomerates: Example From a Devonian Fan-Delta Succession, Southwest Poland

Szczepan J. Porebski


The Upper Devonian-lower Tournaisian Swiebodzice succession (ca. 4000 m thick) is interpreted as a submerged fan-delta complex of resedimented conglomerates, sandstone turbidites and fossiliferous mudstones. The mud-poor, dominantly clast-supported conglomerates are divided into five main facies, including: inversely graded beds (IG), inverse-to-normally graded beds (ING), normally graded beds (NG), normally-graded-stratified beds (GS), and ungraded beds (UG). All of these bed types show a positive relationship between bed thickness (BTh) and maximum clast size (MCS). The five MCS distributions are interrelated in having the same coefficient of variation. The same sort of an intrinsic relationship links the BTh distributions. The variability in MCS is larger than in BTh. There is a general rapid decrease in mean MCS associated with a less rapid decrease in mean BTh, and an increase in occurrence of sandstone cappings, in the order: IG-UG-ING-NG-GS. This order possibly indicates maturing flow if MCS is a measure of transport distance. A comparison between sections suggests a downfan decline in the amount of IG and UG beds and an increase in the proportion of NG and GS beds, and of sandstone cappings within conglomerate bodies. This is accompanied by a tendency for the BTh/MCS gradient and BTh/MCS ratio to increase basinwards. These trends are interpreted in terms of a distally decreasing slope and concentration of clast dispersion.

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