Basement Control on Shaping and Infilling of Valleys Incised at the Southern Coast of Brittany, France

Abstract

The shape and infilling of the submerged parts of valleys incised along the southern coast of Brittany (France) have been investigated using very high-resolution seismics and a small number of piston cores. The valley location and morphology are found to be controlled mostly by submarine topography, which is marked by a well-developed fault zone that lies between the modern coast and a prominent basement-cored island and shoal complex located 5-15 km offshore. The faults controlled the shape of the valley networks and the amount of incision along the valley profile. They were probably active until the end of incision, because the valley thalwegs show scarps up to 10 meters high where they are crossed by these faults. The valleys were incised during the Quaternary lowstands of sea level, and most of the fill was emplaced during the last postglacial sea-level rise. The valley fills form a transgressive succession, consisting mainly of fluvial deposits at the base (possibly amalgamated from older sequences) overlain by tide-dominated estuarine deposits and capped by offshore muds. The most prominent internal surfaces are the tidal-and wave-ravinement surfaces. The valley-fill architecture is strongly dependent on the valley morphology (depth of incision, width of the valleys, and extent of estuarine intertidal areas). Estuarine deposits inside narrow and linear valleys are mostly aggrading muds, whereas those inside large and dendritic valleys dominantly comprise sandier, tidal-channel and bar deposits.

The paleo-Etel River incised valley on the Southern Brittany inner shelf (Atlantic coast, France): Preservation of Holocene transgression within the remnant of a middle Pleistocene incision?

“…On the French Atlantic coast, the study of incised valleys preserved in shelf sequences has been mainly based on widely-spaced high resolution Marine Geology 329-331 (2012) [75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92] seismic records, supplemented with sparse shallow cores (Bouysse and Horn, 1968;Pinot, 1974;Vanney, 1977;Allen and Posamentier, 1993;Lericolais et al, 2001;Proust et al, 2001;Féniès and Lericolais, 2005;Chaumillon and Weber, 2006;Menier et al, 2006Menier et al, , 2010Chaumillon et al, 2008). Proposed models consist in 2D qualitative models that present the general sedimentary succession and 2D geometrical relations between each seismic/sedimentary unit.…”

Palaeodrainage systems at the basal unconformity of the Bohemian Cretaceous Basin: roles of inherited fault systems and basement lithology during the onset of basin filling

“…In a map view, downstream broadening is observed where a palaeovalley crosses from pre-Carboniferous basement to a Permo-Carboniferous basin fill, and vice versa. The lower resistance of Late Palaeozoic basin fills to weathering and erosion is interpreted to have produced broader palaeovalleys with lower cross-valley relief, in a similar way to the examples in Menier et al (2006). This uniformity of cross-valley relief is not an artifact of interpolation in areas of low borehole coverage, as shown by the lithology-dependent changes in valley width in the densely drilled Ralsko Palaeovalley.…”

“…Attempting to classify the drainage patterns (Howard 1967) of the bedrock-confined palaeovalleys in a study based on an irregular borehole network is not as meaningful here as in high-resolution studies of Quaternary palaeovalley networks such as that by Menier et al (2006). Many of the Bohemian Cenomanian palaeovalleys would fall into the linear longitudinal network type, with elements of rectangular to trellis networks (e.g., the Cvikov Palaeovalley) where the valleys cross faults oblique to their axes.…”

Sequential development of tidal ravinement surfaces in macro- to hypertidal estuaries with high volcaniclastic input: the Miocene Puerto Madryn Formation (Patagonia, Argentina)

“…Strong currents in some macrotidal or hypertidal settings can erode very deep, eventually cutting the transgressive surface (e.g., Allen and Posamentier 1994). Moreover, they may become the main discontinuities within the valley fill (Menier et al 2006;Chaumillon et al 2010;Tessier et al 2012;Ahokas et al 2014). Estuary models for the regressive part of the Puerto Madryn Formation (Scasso and del Río 1987;del Río et al 2001;Scasso et al 2012) fit into the tide-dominated, open-estuary depositional-coast type of Chaumillon et al (2010) that is typically macrotidal to hypertidal.…”

“…Therefore, well-developed TRSs resulting from energetic tidal currents should be expected in the Puerto Madryn Formation. In modern sedimentstarved estuaries of France, the TRS expands upstream, allowing reworking processes by the TRS to occur all along the estuary, and leading in some places to a complete erosion of underlying units (Menier et al 2006;Chaumillon et al 2010;Tessier et al 2012). In the case of the Bahía Punta Fósil and Cerro Olazábal paleochannels, the TRSs deeply scour into the transgressive filling of the channels.…”