Table 1
Summary of the main facies features observed in the Priabonian deposits of the Guzargues basin, and interpretations in terms of depositional processes.
Facies code. Facies name | Lithology | Sedimentary structures | Depositional processes |
---|---|---|---|
Gu. Poorly sorted, massive, channel-shaped conglomerates (Fig. 7A) | Poorly sorted, massive, locally normally graded conglomerates. Highly heterometric, sub-rounded to well-rounded clasts (pebbles to small boulders), mainly composed of local Mesozoic (Upper Jurassic to Lower Cretaceous) carbonates. |
Well-defined basal erosional surfaces with gutter/scour structures. Channels displaying few clast imbrications, 50 cm up to 3 m in depth, 3 to 5 m in width. |
Channel-lag deposits under subaerial flashy braided-stream flows (Barrier et al., 2010) |
Gt. Weakly sorted, cross-bedded, stratified conglomerates with coarse-grained sand lenses (Fig. 7B) | Clast-supported, stratified conglomerates. Weakly sorted, heterometric, subrounded clasts (granules to small boulders of Mesozoic carbonates). Occurrence of poorly sorted lenses of coarse-grained sand matrix surrounding individual pebbles. |
Fining upward infill. Trough cross-bedding. |
Minor channel fills (Miall, 1978). Transverse- or diagonal-bar deposits under subaerial perennial braided-stream flows (Barrier et al., 2010). |
Gm. Matrix-rich, normally gradded, stratified conglomerates (Fig. 7C) | Matrix-rich, normally graded, stratified conglomerates. Poorly sorted, subangular to subrounded clasts (granules to cobbles) made of local Mesozoic carbonates, common siliceous (quartz) clasts (originated from Cévennes and/or Montagne Noire Paleozoic peripheral units) and ginger (Aptian?) sandstones. |
Some beds with horizontal alignment of clasts. Few clast imbrications into horizontal foreset strata. “Gradual” basal surfaces. |
Longitudinal-bar deposits under subaerial competent and perennial braided-stream flows (Barrier et al., 2010) |
Sst. Moderately sorted, medium- to coarse-grained, cross-stratified sandstones with lenses of subrounded gravels and pebbles (Fig. 7C) | Moderately sorted, medium- to coarse-grained sandstones. Layers (and lenses) of well-sorted subrounded clasts (granules to pebbels) composed of Mesozoic carbonates, some Lutetian mudstones and common Bartonian oncoliths as fragments or complete specimens. |
Fining-up trend. Cross-stratification with grading foresets. Well-defined internal erosional surfaces. |
Bar deposits under subaerial sheet flows or stream flows. |
Sp. Medium- to coarse-grained, cross-bedded sandstones (Fig. 7E) | Weakly sorted, medium- to coarse-grained sandstones which can contain scattered granules at the base. | Cross-stratification. Internal erosional surfaces. Few small scour structures. |
Megaripple deposits under subaerial sheet flows or stream flows. |
Sr. Massive, pedoturbated, well-sorted, fine-grained sandstones (Fig. 7D) | Massive, well-sorted, fine-grained sandstones. | Pedoturbation (root sleeves, destructuration of primary sedimentary structures by root growth). Locally few asymmetrical ripples at the top. |
Ripple deposits under subaerial sheet flows or stream flows. |
Fm. Massive, silty claystones with planar siltstone to fine-grained sandstone layers (Fig. 7D) | Reddish to yellowish (also purplish red in some horizons of plastic texture), massive, silty claystones with few thin (millimetric to centimetric) layers of well-sorted siltstones and very fine-grained sandstones. | Fining-up grading in siltstone to fine-grained sandstone layers. | Deposits from suspension fallout in a floodplain. Overbank or waning flood deposits (siltstones and very fine-grained sandstones). |
P. Pedogenetic carbonate nodules (Fig. 7F) | Indurated, cm to dm carbonate nodules, often scattered within plastic claystones, sometimes coalescent to form continuous carbonate horizons. | Vertical root casts. | Soil (Miall, 1978) or temporary vegetalized surface. |
Gm, Gt, Sp, Sr, Fm and P are abbreviations from the facies code provided by Miall (1978).
Gu and Sst are abbreviations defined by Barrier et al. (2010).
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