Algal-Bacterial Origin of Micrites in Mud Mounds
Devonian red mud mounds, exposed in Belgium, consist essentially of diverse micrites and carbonate mud. They occur in nodular shales of the Neuville Formation and are confined to a narrow belt along the deeper southern part of the Dinant basin and in the Philippeville massif (Tsien 1983). The Neuville Formation constitutes a facies transition between deeper pelagic shales and limestones of the Matagne Shale, and shallower argillaceous limestones and shales of the Aisemont Formation. Both interfingering and onlapping relationships are present. At their upper and lateral margins, the mounds show several stages of geopetal fillings which are at different angles in sponges and cavities. This suggests that the flanks of the mounds were tilted during deposition. Mounds are flanked at some levels by intertonguing crinoid rudstones and branching coral rudstones, which indicates that current winnowing was important at that time. At other levels mounds are flanked by sponges, Phillipsastrea and Alveolites colonies, and other organisms embedded in the argillaceous shales. The morphology of these organisms differs only slightly from those in the mounds. This indicates that the ecological conditions in the mound and around the mound are very similar. Depositional dips, both in the mounds and in the flanking sediments, at the latest stage of the mound development, are generally more than 10 degrees and range up to 45 degrees.
KeywordsMicrobial Structure Sparry Calcite Algal Filament Reef Debris Early Lithification
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