Deep-Water Turbidites and Their Equally Important Shallower Water Cousins

Mutti, Emiliano¹, Roberto Tinterri¹, Pierre Muzzi Magalhaes², Gustavo Basta² (1) University of Parma, Parma, Italy (2) Petrobras S.A, Rio de Janeiro, Brazil

Most modern turbidite systems form at depths in excess of a thousand meters and similarly deep-water settings are generally inferred from exposed or buried ancient systems. These systems are characteristically made up of a variety of facies deposited by sediment gravity flows. Sharp-based, graded sandstone beds alternating with generally thinner mudstone units are probably the most typical deposit of such systems.

Growing evidence shows that almost identical deposits are equally common and stratigraphically important in shallower water settings of exposed ancient basin fills. Such sediments, most of which have long been unfortunately mistaken for storm deposits because of the common occurrence of HCS or have been assigned a deeper water turbidite origin, are the most genuine expression of deltaic systems dominated by rivers in flood and therefore by hyperpycnal flows. These sand-rich depositional elements commonly grade basinward into thick, delta-slope, mudstone-dominated successions. The correct recognition of the origin and environment of these deposits, which is crucial for differentiating flood-dominated deltaic systems from basinal turbidite systems, can only be accomplished through careful geological mapping, stratigraphic correlations. and facies analyses in both the surface and subsurface.