Tabular beds and sheet-like deposits in deep-water systems have been the subject of
much research attention; they can form high quality hydrocarbon reservoirs, owing
to their excellent lateral continuity and predictable geometry. Additionally, deposit
tabularity is a piece of evidence used to infer flow confinement in ancient systems
and thus to evaluate the suitability of outcrop datasets as reservoir analogues. However,
the quantification of tabularity is rarely attempted and a consistent definition on
how to describe it quantitatively is lacking. For this study, published data from
eighteen well-constrained ancient turbidite systems in outcrop were analysed. A simple
and novel methodology for the quantitative calculation of tabularity along a transect
from log panels and photo panels was devised, based on: a) subdividing beds into two
groups based on their thickness, b) calculating the percentage of beds continuous
across a fixed window (500 m) and c) calculating the rate of thinning for the continuous
beds within the same window. Calculations obtained from multiple locations within
individual systems enable the investigation of proximal to distal, and axial to lateral
changes in tabularity to be captured, and therefore permits the evaluation of tabularity
in three-dimensions. A comparison between tabularity of the considered systems and
their inferred degree of basin confinement shows that in the confined systems >= 90%
of beds are continuous over 500 m compared to <= 40% for the two unconfined systems
studied. In addition, different bed types were compared: hybrid event bed thinning
rates are shown to be up to three times those of classical turbidites. This methodology
provides a new tool to compare tabularity within and between systems quantitatively.
It is hoped that the quantitative determination of tabularity will become a common
workflow when describing ancient turbidite systems. It is suggested that this approach
will enhance the value of outcrop data to inform models capturing the architecture
of systems analogous to subsurface hydrocarbon reservoirs.
