Genetically Related Incised Valleys and Deltas: Sequence and Modern Analogue Modeling From the Nonmarine Santa Barbara Coalfield, Late Pliocene, Italy

Abstract

The morphodynamics of coeval incised valleys and deltas are relatively well understood in marine-paralic environments, but not in the nonmarine, lacustrine counterparts. Here, we analyze the morphology and depositional and sequence architecture of a small-scale valley to deltaic complex preserved in a late Pliocene intermontane coalfield in the Northern Apennines, Italy. Outcrop exposures are integrated with 160+ well logs in an area of less than 1.5 km 2 . The main goal of this study is to demonstrate that spatially restricted yet fully preserved nonmarine systems are well suited for depositional, sequence, and modern analogue modelling, and deserve more attention in the literature.In this study, outcrop and borehole data are merged into isopach maps, highlighting the sedimentary response to a discrete cycle of lake-level retreat and re-expansion. Falling-stage and lowstand phases were characterized by incision of a meandering valley onto a previous highstand shelf, and by the avulsive progradation of an attached, shelf-edge delta. The supply-dominated character of the depositional system along with the limited wave fetch favored in this phase the preservation of the maximum regressive surface across the entire incised-valley to deltaic transect. The following lake-level re-expansion involved estuarine valley back-filling, and the transition from river-dominated to wave-dominated deltaic deposition. Enhanced wave ravinement and associated shoreline-independent prodelta forestepping promoted the development of a transgressive shelf-break bypass. These results are compared with reference sequence and accommodation models, as well as with two modern Ethiopian lakes undergoing acute forced regression. The similar scale and morphology of modern stranded highstand shelves and shelf-edge deltas provide a parallel for assessing the original topographic gradients and depositional dynamics of the late Pliocene case study. Modern and ancient analogues also shed light on the amplification of climate records in endorheic lakes, on the potentially strong avulsive character of falling-stage deltas, and on the sedimentary response to short-lived lacustrine fluctuations in rapidly subsiding basins.

Shoal‐water deltas in high‐accommodation settings: Insights from the lacustrine Valimi Formation (Gulf of Corinth, Greece)

“…The typical vertical facies organization within EDUs is represented by: open lake (OL) deposits at the base, passing upward to prodelta (PD), delta front (DF), mouth‐bar (MTB), distributary channel (DCH) and delta plain (DP) deposits (Figs B to E, A and 7B). Consequently, EDUs display a vertical coarsening‐up (except for delta plain deposits that comprise mainly fine‐grained sediments) and shallowing‐upward trend, as typically expected for prograding deltas (Barrel, ) and more particularly for lacustrine deltaic successions (Ielpi & Ghinassi, ; Zhao et al ., ). The OL deposits are generally thin and often lacking.…”

Syn‐rift sequence development in a fault‐controlled embayment (Early Permian Irwin River Coal Measures, Northern Perth Basin, Western Australia)

“…Leeder & Gawthorpe, ; Collela, ,; Postma & Cruickshank, ). These footwall‐derived wedges are typically steep, short, and abut major bounding faults where fault offsets and transfer zones can act as conduits for drainage systems entering the basin (Gawthorpe & Collela, ; Gawthorpe et al ., ; Miall, ; Ielpi & Ghinassi, ). A tectonic control on the deposition of fluvial conglomerates of the basal IRCM is hence suggested, where rejuvenation along the nearby, basin‐bounding Darling Fault created the slope break necessary for the inception of gravelly braided channel systems from at least two entry points in the Wongoondy and Woolaga Creek areas on the Irwin Terrace (Fig.…”

“…The enlarged embayment occupying the rift basin margin became the locus of increased wave‐fetch and longshore drift that favoured the onset of wave reworking and diminished tidal energy (e.g. Buatois & Gabriela Mángano, ; Salahuddin & Lambiase, ; Ielpi & Ghinassi, ). Storm‐generated facies in FA9 are interbedded with thin tidal shoals similar to sandflats (FA6) showing hardened basal surfaces colonized by sharp‐walled vertical burrows of Diplocraterion and Skolithos filled with coarse sediment and likely representing a Glossifungites ichnofacies (Figs , B and C).…”

“…These channels are typically associated with overbank environments where they form during flooding of the nearby trunk channel, and are characterized by very low sinuosity, minimal lateral migration, and progressive downstream shoaling and broadening (e.g. Tunbridge, ; Ielpi & Ghinassi, ).…”

Worldwide application of synthem stratigraphy in the 21st century: a bibliographical survey

“…This diversity of term use underlines that synthem stratigraphy has remained a vivid direction of research. Moreover, a mixed stratigraphical approach was employed in some studies (e.g., Ielpi, 2011aIelpi, ,b, 2012aIelpi and Ghinassi, 2014), which fact indicates on compatibility of synthem and sequence studies. Finally, synthem stratigraphy has become efficient for extraterrestrial studies.…”