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Résumé

Late Cenomanian rudist-rich facies studied in Central Tunisia, along a North-South transect, starting from Jebel Kebar and reaching Jebel Berda through Jebel Meloussi, show varied compositions and are organised into varied morphologies. In Jebel el Kebar, according to [1], the Gattar Member (upper part of the Late Cenomanian Zebbag Formation) is formed of a "bioconstructed unit" containing Durania arnaudi (Choffat) and Durania arnaudi var. intermedia (Choffat).

Our recent observations show that the Gattar Member is composed of three units exhib1ting varied geometries and compositions. From the base to the top, these units are:

- Bedded carbonates rich in fragmented rudists, organised into wackestones-packstones cycles.

- Massively bedded and lensoid lithosomes [2], [3] rich in joined and entire rudists represented by

Durania arnaudi (1]. - Well thin-bedded carbonates, onlapping the convexed top of the lensoid rudit-rich carbonates containing floating rudist debris. ' To the South, in Jebel Meloussi, rudist-rich units, metric in thickness and showing joined entire rudists (to be determined) occur below the Gattar Member (within the C unit of the Zebbag Formation [4], (5)). More to the South, in Jebel Berda, rudist-rich carbonates also occur below the Gattar Member (probably in the "D" carbonatic unit [5]. This rudist-rich unit contains scarce rudists