Sedimentology, sequence stratigraphy and paleoclimate implications of the Upper Cretaceous-lower Paleocene of the Haria Formation from Gafsa Basin southern Tunisia

Facies analysis and sequence stratigraphic interpretation of the Upper Cretaceous-lower Paleocene succession cropping out in the Gafsa Basin provide new information on sediment cyclicity and paleoclimatic conditions.Mixed carbonate-siliciclastic deposits of the Haria Formation show six principal facies that were deposited in a shallowmarine environment; these are summarized in a homoclinal ramp model that formed during a humid climate in the Late Cretaceous followed by cooler and dryer climate in the early Paleocene. The mixed (carbonate and siliciclastic) deposits of the Haria Formation and are grouped into six facies associations. Carbonate facies described for the first time in the Haria Formation are considered as a new facies in this formation represented by channel deposits and lumachellic limestones. Four depositional zones are recognized on the Haria ramp: 1) basinal, outer ramp (deep water associations); 2) mid ramp (infratidal to subtidal associations); 3) inner ramp (intertidal to supratidal associations); and 4) lagoon facies associations. The mineralogical assemblages are generally indicative of a hot and humid climate with contrasting seasonal change during the Late Cretaceous and have a predominance of smectite, illite and kaolinite clay minerals associated with calcite, quartz and dolomite. This warm climate then become colder and dryer the early Paleocene and was characterized by a significant increase in kaolinite and illite. Nine stratigraphic units are interpreted as depositional sequences showing retrogradational (lowstand systems tract), aggradational (transgressive systems tract) and progradational (highstand systems tract) packages of facies associations. These depositional sequences were controlled by small-scale relative sea-level cycles. These changes in stacking patterns (cycle thickness, cycle type, and facies proportion) allow for reconstruction of long-term sea level trends.