ABSTRACT

Carbonates and siliciclastics rarely mix in many, perhaps most, ancient deposits (Mount, 1984). A notable exception is the homogenization of these two sediment families in the ramp deposits of the Arcadia Formation. All 13 of the subfacies in the 150 to 200 m recovered in each of the three core borings are various mixtures of carbonates, siliciclastics and phosphorites. Only 7-15% of the interval consists of solely carbonates of siliciclastics.

What circumstances produced the homogenized carbonate and siliciclastic deposits within the Arcadia Formation? Carbonate sediment production continued, because the supply of siliciclastic sediments to the ramp was relatively small, transport of siliciclastic sediment was primarily by marine processes rather than by streams, thoroughly mixing in all environments by storms and bioturbation with no interruption of carbonate production. Recent examples of similar homogenization are the shelf and shoreline sands of the U. S. South Atlantic and the tidal deposits of Bay Mont St. Michel in France. Slow deposition is a common denominator of these deposits (long transport of sands).