--> ABSTRACT: Development from a Homoclinal Ramp to an Isolated, Tectonically Unstable Carbonate Platform: Lower Cambrian of Southwest Sardinia, by Thilo Bechstadt, Maria Boni, Thomas Schledding, and Matthias Selg; #91038 (2010)

Datapages, Inc.Print this page

Development from a Homoclinal Ramp to an Isolated, Tectonically Unstable Carbonate Platform: Lower Cambrian of Southwest Sardinia

Thilo Bechstadt, Maria Boni, Thomas Schledding, Matthias Selg

In the Lower Cambrian of southwest Sardinia, a carbonate platform developed, showing clearly different stages of evolution: (1) a homoclinal ramp containing algal-archaeocyathan mounds (consisting mainly of Epiphyton and Renalcis boundstone) in the west, clastic tidal flats in the east; (2) an ooid-pellet barrier ramp with ooid-shoals, prograding toward the west. The back-shoal area contains some algal (Girvanella)-archaeocyathan biostromes, but mainly peloidal mudstones and increasingly tidal deposits (clastic and carbonates) toward the east as well as at the top of the sequence; (3) an isolated platform, aggraded to sea level and rimmed by local slope deposits; (4) a drowned isolated platform, consisting of peloidal mudstones to wackestones in inner parts, remnants of e evated margins with higher energy facies in outer parts, and (5) breakdown of the platform in the Middle Cambrian, marked by the onset of nodular limestones covered by clastics.

Deposition of stratabound lead, zinc, and barium deposits was favored either by the platform facies itself (some barite deposits) or by showing a distinct relation with the prominent tensional tectonics, i.e., they occur within matrix and cemented breccias (debris flows, internal breccias) or as massive sulfides, deposited in restricted, small-scale basins.

The strong effects of tensional tectonics (slumping, debris flows, internal breccias, neptunian dykes) indicate a thinning of the continental crust, either within a passive continental margin setting or, alternatively, within a backarc setting, the volcanic arc being much farther to the west (possibly in Spain or southern France).

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.