Laterally accreted deposits in low efficiency turbidites associated with a structurally-induced topography (oligocene molare group, tertiary piedmont basin, nw italy)

The origin of laterally accreted deposits in ancient deep marine successions is often controversial. Indeed, not always do these features imply the occurrence of meanders or high-sinuosity turbidite channels, but they can be generated by other causes, such as sediment-gravity-flow dynamics controlled by the morphology of tectonically confined mini-basins. This work discusses laterally accreted deposits composed of sharp-based, normally graded beds in a very small tectonically controlled mini-basin. These beds, characterized by a well-defined asymmetrical crosscurrent facies tract, form well-developed lateral-accretion surfaces dipping in directions ranging between W and SW, and perpendicular to the paleocurrents directed towards the N. For this reason, these deposits have always been interpreted as point bars related to meandering channels. A new detailed stratigraphic framework and facies analysis have led to an alternative interpretation, namely that these deposits record lateral deflections of small volume, longitudinally segregated turbidite dense flows against a structurally controlled morphological high. This interpretation is also supported by a comparison to other tectonically controlled turbidite systems that are characterized by higher degrees of efficiency but show similar laterally accreted deposits and cross-current facies tracts

Modelling parametric uncertainty in large-scale stratigraphic simulations

Abstract We combine forward stratigraphic models with a suite of uncertainty quantification and stochastic model calibration algorithms for the characterization of sedimentary successions in large scale systems. The analysis focuses on the information value provided by a probabilistic approach in the modelling of large-scale sedimentary basins. Stratigraphic forward models (SFMs) require a large number of input parameters usually affected by uncertainty. Thus, model calibration requires considerable time both in terms of human and computational resources, an issue currently limiting the applications of SFMs. Our work tackles this issue through the combination of sensitivity analysis, model reduction techniques and machine learning-based optimization algorithms. We first employ a two-step parameter screening procedure to identify relevant parameters and their assumed probability distributions. After selecting a restricted set of important parameters these are calibrated against available information, i.e., the depth of interpreted stratigraphic surfaces. Because of the large costs associated with SFM simulations, probability distributions of model parameters and outputs are obtained through a data driven reduced complexity model. Our study demonstrates the numerical approaches by considering a portion of the Porcupine Basin, Ireland. Results of the analysis are postprocessed to assess (i) the uncertainty and practical identifiability of model parameters given a set of observations, (ii) spatial distribution of lithologies. We analyse here the occurrences of sand bodies pinching against the continental slope, these systems likely resulting from gravity driven processes in deep sea environment

Holocene paleo-hydrographic and landscape evolution of the Pisa coastal plain (Tuscany, Italy) integrating remote sensing and high-resolution stratigraphic data

The Pisa coastal plain is a portion of the wider Arno strand plain (NW Tuscany) characterized by outcropping juxtaposed beach ridges originated from the shoreline progradation over the last 3000 yrs (Pranzini, 2001). The plain is crossed by the Arno river, that ows through the city of Pisa, and it is bounded by the Serchio river northward (Fig.1). Its “shallow” subsurface records the late-Quaternary cyclic alternation of continental and nearshore deposits (T-R cycles) related to glacis-eustatic sea-level uctuations (Aguzzi et al., 2007; Amorosi et al., 2009). A good konwledge of the stratigraphic framework together with the existence of an abundant stratigraphic database, make this area suitable for high-resolution stratigraphic subsurface reconstructions. Based on the development and testing of an integrated remote sensing-stratigraphic approach, a cross-disciplinary depositional architecture reconstruction (still in progress) of the last 6000-5000 yrs, with particular emphasis on the palaeo-hydrographic evolution, is presented here with the aim to provide new insight into the mechanism of Mediterranean delta plain development. Several sinuous paleo-traces were identied on aerial and multispectral satellite images (Fig. 2). The paleo-traces are attributable to the two main rivers owing in the plain (Arno and Serchio) and occur at dierent depths along the stratigraphic sections (Fig. 3). The data-crossing allows the “calibration” of some paleo-traces from the city of Pisa westward (Fig.4). During the last 5000 yrs BP the paleo-hydrographic network and its related paleo-environments document a two-fold sedimentary evolution (Sarti et al., 2015). The rst phase, characterized by the development of wide deltaic marshlands crossed by shallow channels and lying the antecedent lagoon, started at the beginning of the Eneolithic age (ca. 5000 cal yr BP) and lasted up to the Bronze age (ca. 3800 yr cal BP). Then, an alluvial plain was established in the Pisa city area, passing seawards to a sandy strand plain. The present delta plain began to develop under the inuence of a uvial network whose branches were mainly oriented E-W (Arno River) and N-S (Serchio River). Specically, two sub-stages can be distinguished: i) a phase of intense fuvial activity with deeply-incised channels and poorly drained oodplain conditions, lasting up to the Etruscan period (2500-2200 cal yr BP), and ii) the onset of awell-drained alluvial plain, at the transition with the Roman age (ca. 2000 yr cal BP) and still in evolution, characterized by more stable and less numerous uvial channels. The use of an integrated remote sensing-stratigraphic approach in this study gives good results and it could be exported in similar context although further analyses are required