Facies Analysis from the Langhian to Serravallian Turbidite Deposits of the Marnoso-Arenacea Formation (Northern Apennines, Italy)
This work discusses the sedimentology and facies analysis of the Miocene foredeep turbidites of the Marnoso-arenacea Formation. The high-resolution stratigraphy of this interval has allowed to identify five bed types and relative facies tracts considered important to understand the interaction between flow efficiency and basin physiography. These beds are: Type 1 beds-Thick to very thick beds (0.5-4m) that pass downcurrent into thin and fine-grained beds. From base to top, the basal sandstone unit consists of: a) a continuous massive to crude laminated unit; b) a slurry unit characterized by a silty sandstone, with liquefaction structures and mudstone clasts; c) an upper unit constituted by thin laminated fine-sandy siltstone. Type 2 beds-Very thick beds (1.5-4m) characterized by: a) a basal unit consisting of medium-to coarse-grained massive sandstone; b) an intermediate unit with a highly deformed unit, often with contorted sandstone and thin mudstone beds such as in a slump; c) fine-grained laminasets. These beds pass downcurrent into thin and fine-grained beds. Type 3 beds-Thick to very thick beds (>>1m) capped by a thick mudstone unit which usually increase in thickness downcurrent. They are composed of: a) a basal massive division with medium-grained sandstone; b) a laminaset of fine-grained sandstone; c) a clear alternation of laminated and liquefied thin fine-grained units. Type 4 beds-These beds (>1m) are normally graded and fine-grained beds that become progressively finer and thinner downcurrent. Type 5 beds-Thin to very thin (< 10cm) fine-grained beds characterized by combined flow structures such as biconvex-rounded ripples. Type 1 beds are interpreted as being related to the progressive mud erosion occurring upcurrent, they tend to increase in structural controlled stratigraphic units. Type 2 beds are found at the base of structural controlled stratigraphic units and are interpreted as important elements indicating tectonic uplift. Type 3 are contained-reflected beds deposited by combined turbulent flow modified by ponding processes; while type 5 thin beds are deposited by dilute turbulent flows able to flow over topographic highs. Type 4 beds, by contrast, are related to waning and depletive turbulent flows. In conclusion, the knowledge of vertical and lateral distribution of these beds is particularly useful to understand the basin physiographic, represented by subtle topographic highs and depocenters created by thrust-propagation folds.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009