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The clay fractions of Late Tithonian/Berriasian hemipelagic to pelagic carbonates of the Vocontian Trough are studied using X-ray diffraction. Two sections are investigated in Berrias (Berriasian stratotype) and Angles.

In Berrias, the clay mineral assemblages are dominated by illite, mixed layers and kaolinite in various proportions. Most clay minerals seem to have a detrital origin. Kaolinite inputs are due to both the development of a more humid climate and transgressive conditions. In the upper part of the section (Calpionellid zones C to D2), relatively few variations of clay assemblages result from th rd-order eustatic fluctuations. Lowstand systems tracts are characterized by the abundance of illite relative to kaolinite. The proportions of the latter mineral increase in transgressive systems tracts, reach a maximum close to maximum flooding surfaces and decrease in highstand systems tracts.

The most striking feature occurring in the Berrias section is the fact that kaolinite disappears in the grandis and at the base of the subalpina Ammonite subzones. This reflects arid climatic conditions probably related to a second-order lowstand of sea-level. The control of third-order eustatic fluctuations on the clay mineral sedimentation is overprinted by this climatic factor.

In the Berriasian of Angles, the influence of burial diagenesis on clay assemblages is expressed by the replacement of smectite by chlorite in limestone beds. Despite this diagenetic influence, the variations of the illite percentages can be attributed to third-order eustatic fluctuations. Maximum percentages of illite are recorded near the sequence boundaries. These percentages are higher in lowstand systems tracts than in transgressive systems tracts, and the minimum abundance of illite coincides with maximum flooding surfaces.