Hybrid event beds (HEBs) are a type sediment gravity flow deposits that generally comprises a basal clean sandstone (H1) overlain by a muddier and less-permeable sandy facies (H3) emplaced during the same transport event. They are commonly found in association with conventional turbidites in the distal and marginal reaches of many ancient deep-water systems; they are important in both exploration and appraisal because their presence and character is not readily predictable and they compromise reservoir performance. The Cretaceous-Palaeocene Gottero turbidite system of NW of Italy developed on the Ligurian convergent margin, transforming from a passive margin basin floor fan to a trench-slope system. Detailed fieldwork, including collection of >4000 m of graphic logs, has shown that HEBs are abundant in the outer fan portion of the system, where they comprise more than 50% of the event beds. In more proximal sectors HEBs occur interbedded with mid-fan sandstone lobes, and may comprise up to 6% of event beds. They are apparently absent in the inner fan, channelised area. The origin of HEBs in the outer and mid-fan sectors is different and is thought to be controlled by the flow magnitude and the loci of mud entrainment by substrate erosion. The outer fan sector is dominated by thick and tabular mudclast-rich HEBs, generated by highly energetic flows capable of eroding the sea-floor locally, sometimes detaching large pieces of substrate by basal injection, and carrying them over relatively short distances as muddy rafts. A number of genetically-related bed types can be recognised, in which the disaggregation of the muddy particles along longitudinal facies tracts progressively leads to the development of a cohesive linked-debrite character to the H3 division. These bed types exhibit rapid internal lateral facies changes developed mainly along depositional strike. In the mid-fan sector thinner HEBs with highly mixed, clast-poor and disaggregated H3 divisions accumulate in muddy interlobe intervals between amalgamated sandstone lobes, and are thought to have been produced by less energetic flows that underwent early turbulence damping following incorporation of cohesive mud from the substrate. The various HEBs bed types and their stratigraphic and lateral distribution are integrated into a new predictive depositional model in order to characterise the high degree of complexity of the hybrid-prone facies associations inside turbidite fans of this type and setting.
Processes, facies trends and lateral variability of hybrid event beds in sand-rich deep-water systems: the North-Apennine Gottero Sandstone (Northwest Italy) / M. Fonnesu, P. D. Haughton, F. Felletti, M. Patacci, W. D. McCaffrey. ((Intervento presentato al convegno AAPG tenutosi a Denver nel 2015.
|Titolo:||Processes, facies trends and lateral variability of hybrid event beds in sand-rich deep-water systems: the North-Apennine Gottero Sandstone (Northwest Italy)|
|Data di pubblicazione:||2-giu-2015|
|Settore Scientifico Disciplinare:||Settore GEO/02 - Geologia Stratigrafica e Sedimentologica|
|Citazione:||Processes, facies trends and lateral variability of hybrid event beds in sand-rich deep-water systems: the North-Apennine Gottero Sandstone (Northwest Italy) / M. Fonnesu, P. D. Haughton, F. Felletti, M. Patacci, W. D. McCaffrey. ((Intervento presentato al convegno AAPG tenutosi a Denver nel 2015.|
|Appare nelle tipologie:||14 - Intervento a convegno non pubblicato|