In turbidity current mechanics, ponding is the ability of topography to fully trap flow, thereby producing a flat topped suspension spreading over the whole basin. Conversely, spilling occurs when turbidity currents are able to partially run up the bounding topography so that part of their suspension cloud is subject to flow stripping. Among the many sedimentary signatures, thick, basin-wide mud caps have been since long recognized as a proxy for inferring flow ponding in confined basins. However, whether ponding or flow stripping dominate mostly depends on physical structure of incoming turbidity currents (i.e. density stratification, thickness, flow duration and discharge rate etc.) and height of bounding topography which may be time-variant due to changes in sedimentary input and basin topography. Examples of ponded turbidite systems are present in different geodynamic contexts (e.g. salt-withdrawal mini-basins of passive margins, structurally confined basins of rifted margins and foreland basin systems) both on outcrop and in the subsurface where they can constitute prolific target in hydrocarbon exploration. Fostered by the need of oil industry for hard data to be used in stochastic modeling, geoscience statistics have previously been applied to assess ponding in turbidites from statistical distribution of bed and facies thickness datasets either from outcrop or well log. This study focuses on the sheet-like turbidite systems of the Castagnola Basin (Early Miocene), which were deposited in a small, structurally-confined depocentre of the Tertiary Piedmont Basin (Ligurian Alps, Northern Italy). Based on event bed thickness and facies statistics on a base-to-top sedimentary section logged in the field in great detail and estimation of basin size, this study aims at portraying the response of depositional architecture to progressive infilling and subsequent widening of the Castagnola Basin (from few km2 to few tens Km2). Data analysis shows an upward increase in net/gross, sandstone bed frequency and ratio of sandstone bed to mud cap thickness, along with an overall decrease in mud caps thickness. Yet, sandstone bed/mud cap thickness shows distinctive statistical distributions for different thickness classes which possibly relate to interplay of turbidity current physical structure and basin size. Collectively, these results suggest switching of the Castagnola turbidite systems from a ponded- to a spill-dominated depositional setting in which stripping of the finer-grained fraction of turbidity currents becomes progressively more efficient as the host basin is filled up. Further development of this research may contribute to evolutionary models of fill and spill mini-basin and provide a wealth of quantitative data useful in stochastic and forward modeling of ponded turbidite systems.
|Titolo:||Assessing turbidite depositional architecture and ponding through bed and facies statistics: an example from the Castagnola mini-basin (Early Miocene, NW Italy)|
MARINI, MATTIA (Primo)
|Data di pubblicazione:||6-mar-2014|
|Settore Scientifico Disciplinare:||Settore GEO/02 - Geologia Stratigrafica e Sedimentologica|
|Citazione:||Assessing turbidite depositional architecture and ponding through bed and facies statistics: an example from the Castagnola mini-basin (Early Miocene, NW Italy) / M. Marini, M. Patacci, F. Felletti, S. Southern, W.D. McCaffrey. ((Intervento presentato al convegno Reducing Subsurface Uncertainty & Risk through Field-based Studies tenutosi a London nel 2014.|
|Appare nelle tipologie:||14 - Intervento a convegno non pubblicato|