Are Bed Thickness Statistics From Well Bores Valuable for Assessing Flow Confinement in Turbidite Basins? Experimental Insights From Tertiary Basins of Apennines (Italy)

Abstract

How best to analyse and interpret turbidite thickness statistics represent open questions in both applied and pure sedimentology. A key problem is that thickness data collected in the field or retrieved from boreholes are often incomplete and/or biased toward or against certain thickness classes due to bed geometry, erosion and/or resolution, which largely undermines tackling such questions. However, in situations where turbidity currents are ponded by the seafloor bathymetry, depositing basin-wide event beds with flat geometry with negligible erosion, some of the variables involved can be constrained, making it easier to investigate the primary controls on turbidite thickness statistics.

Here we review the bed thickness statistics of the non-channelized parts of the turbidite infill of four Tertiary basins (i.e. Castagnola Fm., Cengio-Bric la Croce units, Laga Fm. and Cellino Fm.) of Apennines (Italy), which share similar stratigraphic evolution from early ponded deposition to late-stage unconfined deposition. Comparison of thickness class subsets from diverse locations and stratigraphic heights within the studied basin fills are used in this study to show that: i) location, quality of thickness data, use of thicknesses from single vs. multiple sampling locations (i.e. sections measured in the field or well logs) and stratigraphic heterogeneity of the studied succession can significantly affect the empirical distribution of turbidite thickness ii) the low-end tail of empirical thickness frequency distribution most likely reflectsa systematic bias against cm-thick Tcd Bouma sequence turbidites; iii) conversely, thickness statistics of thicker turbidite beds show a coherent relationship with respect tothe transition from ponded to unconfined depositional settings.

Notwithstanding the bias against very thin beds due to data collection constraints, this contribution highlights the role of flow stripping, sediment by-pass and bed geometry in altering the initial thickness distribution of ponded turbidites suggesting borehole data (e.g. thicknesses from core description or microresistivity images) can be used as a proxy fordiscriminating ponded from non-ponded or unconfined turbidites.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018