The depositional differences of confined and unconfined turbidite sheet systems

The depositional architecture between unconfined and confined turbidite sheet systems are increasingly recognized, but the major differences are not summarized. This paper aims to summarize the major differences based on the well-studied published systems with known degree of confinement and depositional architectures. The unconfined and confined turbidite sheet systems differ greatly in four aspects: sedimentary facies, stacking patterns of individual beds, facies associations and onlap styles. The sedimentary facies in confined systems are mainly thick beds, occasionally with grain size breaks, overlain by thick mud caps; whereas beds in unconfined turbidite systems present less mud proportion. The stacking patterns in confined systems in mainly vertically stacked, whereas compensationally stacked in strike direction, and progradationally or retrogradationally stacked in dip direction. One facies association have only been identified in confined systems and four facies associations are found in unconfined systems. The vertical log of unconfined turbidite sheet systems presenting a transition of facies association, whereas no transitions in confined systems. The depositional architecture of turbidite sheet systems is controlled by both sediment supply and basin relief. The establishment between degree of confinement and various parameters in this study can be applied in the petroleum industry.