Carbonate Internal Breccias: A Source of Mass Flows at Early Geosynclinal Platform Margins in Greece
Hans Füchtbauer, Detlev K. Richter, 1983. "Carbonate Internal Breccias: A Source of Mass Flows at Early Geosynclinal Platform Margins in Greece", The Shelfbreak: Critical Interface on Continental Margins, Daniel Jean Stanley, George T. Moore
Download citation file:
Internal breccias caused by dilation of slightly lithified limestones have been investigated in the Triassic and Jurassic of the island of Hydra (Greece). They occur between shelf platform and rift basin of the early Tethys and are in general composed of monomictic and closely fitted angular clasts of platform carbonates. The matrix consists frequently of reddish deep-water limestones with thin-shelled molluscs (filaments) and radiolarians; it was sucked-in from above as a result of dilation during brecciation. The vertical succession includes about 20–30 m beginning with (a) fractured and fissured shallow-marine limestones grading upward into (b) internal breccias and (c) mass flows (characterized by a low degree of fitting and considerable roundness). Internal breccias imply a very small lateral displacement; they provide an important source for mass flows near shelf-to-slope breaks. Repeated brecciation is typical. The breccias are most frequently composed of shallow-water limestones, but are overlain by basin sediments. This indicates that the brecciation was connected with tectonic downwarping. We suggest that these breccias were produced by large migrating flexures, and that such flexures are a tectonic alternative or substitute for faults.
In the Triassic and lower Jurassic limestones of the island of Hydra, five major breccia horizons are recognized. They correlate well with major tectonic phases in the early geosynclinal history of the northern and eastern Alps, in which internal breccias were found as well. This coincidence emphasizes the significance of such breccias in the evolution of geosynclines.
Figures & Tables
The shelfbreak is that point where the first major change in gradient occurs on the outermost edge of the continental shelf. Although this environment delimits the boundary between two principal and well-defined provinces, the continental shelf and slope - and thus is of the first order of importance on continental margins - it has received surprisingly little specific attention in either modern oceans or in the rock record. This volume, the first compendium dedicated specifically to the shelfbreak, was derived from an SEPM Research Symposium convened at the joint Annual Meeting of SEPM and AAPG on June 2, 1981. The material is organized in a manner to illustrate examples of the shelfbreak in both modern oceans and the rock record.