Abstract
Abstract. A 7.38 m long sediment core was collected from the eastern section of the Rhône prodelta (NW Mediterranean) at 67 m water depth. A multi-proxy study (including sedimentary facies, benthic foraminifera, ostracods, and clay mineralogy) provides a multi-decadal to century-scale record of climate and sea-level changes during the Holocene. The early Holocene is marked by alternative silt and clay layers interpreted as distal tempestites deposited in a context of rising sea level. This interval contains shallow infra-littoral benthic meiofauna (e.g., Pontocythere elongata, Elphidium spp., Quinqueloculina lata) and formed between ca. 20 and 50 m water depth. The middle Holocene (ca. 8.3 to 4.5 ka cal. BP) is characterized, at the core site, by a period of sediment starvation (accumulation rate of ca. 0.01 cm yr−1) resulting from the maximum landward shift of the shoreline and the Rhône outlet(s). From a sequence stratigraphic point of view, this condensed section, about 35 cm thick, can be identified on seismic profiles as a maximum flooding surface that marks the transition between delta retrogradation and delta progradation. The transition between the early Holocene deposits and the middle Holocene condensed section is marked by a gradual change in all proxy records. Following the stabilization of sea level at a global scale, the late Holocene is marked by the establishment of prodeltaic conditions at the core site, as shown by the lithofacies and by the presence of benthic meiofauna typical of the modern Rhône prodelta (e.g., Valvulineria bradyana, Cassidulina carinata, Bulimina marginata). Several periods of increased fluvial discharge are also emphasized by the presence of species commonly found in brackish and shallow-water environments (e.g., Leptocythere spp.). Some of these periods correspond to the multi-decadal to centennial late Holocene humid periods recognized in Europe (i.e., the 2.8 ka event and the Little Ice Age). Two other periods of increased runoffs at ca. 1.3 and 1.1 ka cal. BP are recognized, which are likely to reflect periods of regional climate deterioration that are observed in the Rhône watershed. Conversely, the Migration Period Cooling (ca. 1.4 ka cal. BP) and the Medieval Climate Anomaly (ca. AD 950–1250) correspond locally to periods of increased dryness.
Highlights
Deltas comprise a subaerial delta plain, where river processes dominate; a coarser-grained delta front, where river and basinal processes interact; and a muddy submarine prodelta dominated by oceanic processes (Bhattacharya and Giosan, 2003; Galloway, 1975; Postma, 1995)
We study the evolution of the Rhône prodelta in terms of sedimentary environments, during the last 10.5 kyr, as marked by changes in lithofacies and benthic meiofaunal assemblages and in relation to the Holocene sea-level rise and climate changes
The age of seismic unit U500, which corresponds to the early Holocene transgressive parasequence (Fanget et al, 2014), is poorly constrained in core RHS-KS55 (Figs. 3 and 4)
Summary
Deltas comprise a subaerial delta plain, where river processes dominate; a coarser-grained delta front, where river and basinal processes interact; and a muddy submarine prodelta dominated by oceanic processes (Bhattacharya and Giosan, 2003; Galloway, 1975; Postma, 1995). BP, owing to a deceleration of global sea-level rise (Stanley and Warne, 1994). They constitute key element of the continental margin system as they represent the first sink of sediments delivered by rivers (Trincardi et al, 2004). The Rhône delta is one of the most important of the Mediterranean Sea and has been widely investigated combining seismic, sedimentological, and micropaleontological approaches (e.g., Boyer et al, 2005; Fanget et al, 2013a, b, 2014; Gensous et al, 1993; Labaune et al, 2005)
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