Reciprocal Changes In Foreset To Bottomset Facies In A Gilbert-Type Delta: Response To Short-Term Changes In Base Level

Abstract

Results of a detailed sedimentological study of the mid-Pleistocene Gilbert-type Ilias delta at the southern coast of the Corinth Rift, Greece, are reported. The study indicates that the development of a turbidite-dominated facies assemblage (TFA) of delta foreset deposits is associated with an oblique delta-brink geometry, which signifies a deficit of delta-front accommodation due to the falling or stable base level. A debrite-dominated assemblage (DFA) of foreset deposits forms when the base level is rising and the delta-brink geometry becomes sigmoidal, signifying an increase in delta-front accommodation. The comparison of coeval foreset and toeset to bottomset deposits in the delta indicates a reverse pattern of reciprocal changes in facies assemblages, with the foreset TFA deposits corresponding to delta-foot DFA deposits, and with the foreset DFA deposits corresponding to delta-foot TFA deposits. This reciprocal alternation of TFA and DFA facies assemblages is attributed to changes in the delta-front accommodation driven by short-term base-level changes, with a degree of ''noise'' in the facies record due to the system autogenic variability and regional climatic fluctuations. The study sheds a new light on the changing pattern of subaqueous sediment dispersal in Gilbert-type deltaic systems in response to base-level changes. It also indicates a new possibility for the recognition of a hidden record of such changes in other similar ancient deltas on the basis of their detailed facies analysis.

An Early Permian, paleopolar, postglacial, river-dominated deltaic succession in the Mackellar–Fairchild formations at Turnabout Ridge, Central Transantarctic Mountains, Antarctica

“…We found no evidence at Turnabout Ridge for Gilbert-type deltas with steeply inclined foresets (e.g. Winsemann et al, 2007;Gobo et al, 2014) and no evidence for shallow lacustrine shorelines. Our results differ from Miller and Isbell (2010) in that the trace-fossil assemblages and ichnocoenoses at Turnabout Ridge are not consistent with those expected for a freshwater-lacustrine system (Hasiotis et al, , 2013.…”

Ice‐marginal forced regressive deltas in glacial lake basins: geomorphology, facies variability and large‐scale depositional architecture

“…The studied forced regressive ice-marginal deltas have many characteristics in common with other (glacigenic) Gilbert-type and shoal-water deltas, including the stairstepped fan, tongue-shape or lobate geomorphology (Posamentier & Morris 2000;Ritchie et al 2004a, b;Olariu & Bhattacharya 2006;Villiers et al 2013), the large-scale depositional architecture (Dunne & Hempton 1984;Postma 1995 (Clemmensen & Houmark-Nielsen 1981;Dunne & Hempton 1984;Nemec 1990;Lønne 1995;Massari 1996;Sohn et al 1997;Nemec et al 1999;Lønne & Nemec 2004;Fabbricatore et al 2014;Gobo et al 2014Gobo et al , 2015Ventra et al 2015;Dietrich et al 2016;Carvalho & Vesely 2017;Massari 2017). Although the meltwater-source areas are likely to have yielded a significant fraction of silt and mud from glacial erosion the coarse-grained foresets are nearly devoid of silt and mud.…”

“…Alluvialplain aggradation and delta-front progradation commonly accompany normal regression, whereas fluvial incision and sediment bypass occur during forced regression (Posamentier & Morris 2000; Ritchie et al 2004a, b;Strong & Paola 2008;Catuneanu et al 2011), leading to a rapid basinward stepping of delta lobes (Fig. A possible genetic link between the delta-front morphodynamic responses to baselevel changes and the delta-slope sedimentation processes may help in the recognition of a hidden record of base-level change if the topset-foreset transition zone is eroded (Gobo et al 2014(Gobo et al , 2015. A possible genetic link between the delta-front morphodynamic responses to baselevel changes and the delta-slope sedimentation processes may help in the recognition of a hidden record of base-level change if the topset-foreset transition zone is eroded (Gobo et al 2014(Gobo et al , 2015.…”

Miocene sea-level changes in northernmost Anatolia: Sedimentary record of eustasy and tectonism at the peri-Pontide fringe of Eastern Paratethys

“…The planar parallel-stratified and cross-stratified beds represent, respectively, longitudinal (Nemec and Postma, 1993) and transverse or oblique mid-channel bars (Miall, 1985(Miall, , 1996 stacked upon one another in shallow (30-50 cm) stream channels.The laterally discontinuous, coarse-gravel linings of the bedset erosional bases are channel-floor lag deposits (Nemec and Postma, 1993;Miall, 1996). The erosional, oblique contact of the foreset with the topset indicates delta progradation with a stable or falling deltabrink trajectory (sensuHelland-Hansen and Martinsen, 1996), which is consistent with the hyperpycnite-dominated facies of the delta foreset (Gobo et al, 2014).…”