Deformation patterns of upper Quaternary strata and their relation to active tectonics, Po Basin, Italy

Abstract

Despite increased application of subsurface datasets below the limits of seismic resolution, reconstructing near-surface deformation of shallow key stratigraphic markers beneath modern alluvial and coastal plains through sediment core analysis has received little attention. Highly resolved stratigraphy of Upper Pleistocene to Holocene (Marine Isotope Stage 5e to Marine Isotope Stage 1) alluvial, deltaic and coastal depositional systems across the southern Po Plain, down to 150 m depth, provides an unambiguous documentation on the deformation of previously flat-lying strata that goes back in time beyond the limits of morphological, historical and palaeoseismic records. Five prominent key horizons, accurately selected on the basis of their sedimentological characteristics and typified for their fossil content, were used as highly effective stratigraphic markers (M1 to M5) that can be tracked for tens of kilometres across the basin. A facies-controlled approach tied to a robust chronology (102 radiocarbon dates) reveals considerable deformation of laterally extensive nearshore (M1), continental (M2 and M3) and lagoon (M4 and M5) marker beds originally deposited in a horizontal position (M1, M4 and M5). The areas where antiformal geometries are best observed are remarkably coincident with the axes of buried ramp anticlines, across which new seismic images reveal substantially warped stratal geometries of Lower Pleistocene strata. The striking spatial coincidence of fold crests with the epicentres of historic and instrumental seismicity suggests that deformation of marker beds M1 to M5 might reflect, in part at least, syntectonically generated relief and, thus, active tectonism. Precise identification and lateral tracing of chronologically constrained stratigraphic markers in the 14 C time window through combined sedimentological and palaeoecological data may delineate late Quaternary subsurface stratigraphic architecture at an unprecedented level of detail, outlining cryptic stratal geometries at the sub-seismic scale. This approach is highly reproducible in tectonically active Quaternary depositional systems and can help to assess patterns of active deformation in the subsurface of modern alluvial and coastal plains worldwide.

Probabilistic Assessment of Slip Rates and Their Variability Over Time of Offshore Buried Thrusts: A Case Study in the Northern Adriatic Sea

“…Inland, recent or ongoing tectonic activity and fault reactivation in individual seismic events can be studied by analyzing geologic exposures (Bresciani and Perotti, 2014;Livio et al, 2014;Amorosi et al, 2016Amorosi et al, , 2020Zuffetti and Bersezio, 2020), or by detecting river drainage anomalies (Burrato et al, 2003), or by inspecting GPS and remote-sensing data (Serpelloni et al, 2012;Pezzo et al, 2013Pezzo et al, , 2020Nespoli et al, 2016Nespoli et al, , 2017. Instead, the just mentioned approaches cannot be used in the marine environment, especially where the Pleistocene sedimentation rate exceeds the tectonic signal leading to a completely undisturbed and almost flat bathymetry.…”

A Long-Term Record of Quaternary Facies Patterns and Palaeonvironmental Trends from the Po Plain (NE Italy) as Revealed by Bio-Sedimentary Data

“…Four fossiliferous statigraphic units composed of swamp/lagoon to bay sediments are identified via meiofauna analyses at~201-177 m; 147-135 m; 92-76 m and 15-0 m core depth (Units 1-4 in Figure 3). Published chronological data and stratigraphic correlations across the study area constrain the two youngest units (Units 3, 4) to the last 125-130 kyrs, whereas Units 1 and 2 can be attributed to the Middle Pleistocene in a general way only [29,37]. These units are sandwiched between sedimentary successions tens of m thick, almost deprived of body fossils and formed by a variety of coarse-grained (fluvial channel) to fine-grained (overbank) alluvial facies associations, locally interrupted by swampy deposits containing at most hypohaline ostracods (mainly P. ex gr.…”

“…The lack of absolute ages and biostratigraphic markers hampers any confident chronological (MISs) attribution to Units 1-2 as well as any reliable physical correlations with other cores recovering pre-MIS 5e sediments in the Po Plain, especially in inland areas affected by Quaternary tectonic deformations (e.g., [37,43]). However, sedimentological evidence (i.e., the presence of shallow-marine facies in a relatively inland position) suggests the prominent interglacials MIS 11 and MIS 9 (Figure 4), both exceeding the present sea level [24], as the best candidates for Units 1 and 2, respectively.…”

“…To the best of our knowledge, facies-based stratigraphic analyses of Mediterranean successions encompassing hundreds of thousands of years are few and mostly located in the N Adriatic area-NE Italy (Po Plain and Venice Lagoon-Figure 1; [30][31][32][33][34]), where a relatively thick Quaternary record occurs due to favourable tectonic conditions. In particular, the southern portion of the Po coastal plain (Figure 1) represents a suitable candidate for long-term palaeoenvironmental studies, because: (i) it belongs to a rapidly subsiding basin (Po Basin: up to 2.5 mm/yr over the last 1.43 Myr; [35]), that hosts a stratigraphically expanded Quaternary succession [36,37], and (ii) a set of 200 m long continuous cores has been recovered during the drilling campaign promoted by the Geological Survey of Regione Emilia-Romagna, contributing to the Geological Map of Italy at 1:50,000 scale (CARG Project).…”

Compositional, micromorphological and geotechnical characterization of Holocene Tiber floodplain deposits (Rome, Italy) and sequence stratigraphic implications

“…This is of great value for sequence‐stratigraphic studies but has the inevitable downside of overlooking facies variability at the mesoscale and microscale. In this regard, palaeosol micromorphology deserves closer attention as it provides indications with respect to the duration of non‐deposition and the degree of soil development (McCarthy & Plint, 1998), and thereby can be employed to recognize major and minor stratigraphic markers (for example, sequence boundaries, maximum flooding surfaces, parasequence boundaries, transgressive and non‐marine flooding surfaces; Blum & Price, 1998; Blum & Törnqvist, 2000; Diessel, 2007; Srivastava et al ., 2010; Jerrett et al ., 2011; Milli et al ., 2016; Srivastava et al ., 2018; Zuffetti et al ., 2018; Amorosi et al ., 2021). Although the use of petrographic procedures to characterize compositional variations within chronostratigraphic units and across stratigraphic unconformities has been applied in sand provenance studies (e.g.…”