Palaeohydrodynamics and computer simulation of turbidites in the Marnoso-Arenacea, Northern Apennines, Italy

Abstract

Observation of turbidite features including areal development and thickness of Bouma units, grainsize and grading are used to define the flow parameters of a turbidity current. Observations have been made on four beds in the Marnoso-Arenacea formation in the Northern Apennines, Italy. This allows the estimation of turbidity current depth, volume, velocity, deceleration and density variation. A computer simulation of sediment deposition at a single locality from a turbidity current flow has been developed. The latter enables theoretical units derived from experimental and theoretical studies to be compared with field observations. Studies of a large turbidite, the 'Contessa bed' show that it was introduced into a long, narrow basin from a southeasterly source and continued to flow northwestwards before turning on itself with the consequent reversing of structures. It is postulated the reversal was due to the collision of the turbidity current against an intra-basin fault scarp. This reversed the current before it had reached the full length of the basin. Syndepositional mudflows have been discovered in three beds, occurring at the Bouma 'C' and 'D' interface. They are related to sediment highs, fan-fringe positions and inherent instabilities in the sediment. After liquefaction, movement and freezing the mudflows were succeeded by normal Bouma ‘D’ sedimentation.