Facies |
Description |
Process |
FA |
Upper Unit |
Coarse sand with trough cross-stratification (Facies St) |
Medium to coarse sands with trough cross-stratification with set thickness up to 2.5 m; quartz and brownish, deformed mud granules scattered at the base. Grains are poorly- to moderately sorted. |
Migration of 3D bedforms with sinuous crests under lower flow regime. Reworking of mud beds in hydroplastic condition. |
Braided stream channel (FA4) |
Sand with tabular cross-stratification (Facies Sp) |
Brownish, medium sands with tabular cross-stratification. Beds are lenticular, up to 1 m thick, and interbedded with Facies St. |
Migration of 2D bedforms with straight crests under lower flow regime. |
Sand with sigmoidal cross-stratification (Facies Ssg) |
Brownish medium sands with sigmoidal cross-stratification with sets covered by clay laminae, and interbedded with Facies Mml of the FA3.The grains are poorly-sorted, displaying positive asymmetry and kurtosis with leptokurtic distribution. |
Bedform migration under unidirectional and lower flow regime, with rapid deceleration when it reaches a floodplain lake or pound. Clay laminae can also be formed by gradual deposition in this process. |
Massive muds (Facies Mm) |
Whitish to reddish, centimetric beds of massive clay with lenticular geometry, filling curved base of beds. |
Deposition of mud under slack water conditions |
Lower Unit |
Intraformational massive mud clast (Gi) |
Yellowish to reddish, massive laminae of gravels, formed by intraformational mud pebbles and cobbles. |
Reworking of laminated mud beds by energetic flood fluvial process. |
Floodplain (FA3) |
Massive to laminated mud (Facies Mml) |
Reddish-whitish, laminated mud beds of up to 50 cm, interbedded with sigmoidal cross-stratification that, in general, fills channelized bedforms. |
Alternation between traction and mainly gravitational settling from suspension. |
Gravel with incipient, even parallel stratification (Facies Gp) |
Brownish to whitish, channelized beds with gravel of lag deposits from basement rocks and ferruginous sandstone boulders (up to 82 cm). |
High to moderate flows generating scours in talweg portions of channels. Lateral migration produces intense reworking of ferruginized ancient siliciclastics deposits and basement rocks. |
Tide-influenced meandering stream channel(FA2) |
Medium- to coarse-grained sands with trough cross-stratification (Facies St) |
Whitish coarse-sand beds with trough cross-stratification (sets up to 35 cm thick). Scattered quartz pebbles in the base of sets. The grains moderately-sorted. |
Migration of 3D bedforms with sinuous crests in longitudinal bedforms, under high to moderate flow regime. |
Medium-grained sand with tangential cross-stratification (Facies Stg) |
Reddish medium sands forming tabular sets of tabular to tangential planar cross-bedding. They are truncated by sets of facies Sth. |
Migration of 2D bedforms on the channel complex bar, under moderate flow regime. |
Hetherolitic cross-bedding sets with alternating sand and mud laminae (Facies SMi) |
Dark brown to whitish, inclined medium to coarse sand beds alternating with mud laminae. They can be interbedded with Facies Mml. The grains are moderately-to poorly-sorted. The upper portion of the strata is marked by ripple marks. |
Lateral accretion in concave marginal portions with sand and mud deposited during moderate- and low-energy flows, respectively, of large to medium-scale point bars. Small-scale bedforms can also migrate onto these bedforms. |
Wavy-bedded rhythmites (Facies Rw) |
Centimetric to metric yellowish to brownish wavy mud laminae alternated with ripple-bedded fine sand layers that can be interbedded with Facies SMi. |
Alternating periods of mud and sand deposition from suspension and bedload transport, respectively. |
Fine-grained sands with trough cross-stratification (Facies St) |
Reddish, fine to medium sand with trough cross-stratification with sets up 30 cm thick. Bedding planes and foresets are covered by clay laminae. Intraformational granules with rounded to tabular clay granules occur scattered along the bottom set. |
Migration of 3D bedforms with sinuous crest under high to moderate energy and tidal influence, with alternation between traction and suspension processes. Bedform migration during flood tidal current, reworking clay laminae deposited during slack-water conditions. |
Subtidal flat (FA1) |
Fine-grained sand with tabular cross-stratification (Facies Sp) |
Reddish, fine to medium sand beds with thickness varying from 20 to 50 cm, with tabular cross-stratification, and cyclic variations of foreset thickness. Bedding planes and foresets, are locally covered by clay laminae. |
Migration of 2D subaqueous bedforms with straight crests. This process alternates with slack-water conditions forming mud drapes on the foresets. Variations in the foreset thickness are related with neap-spring cycles. |
Fine-grained sand with tangential cross-stratification (Facies Stg) |
Reddish fine to medium sands with tangential to quasi-tabular planar cross-stratification interbedded with Facies Sth. Mud drapes occur in the foresets and bedding planes. |
Migration of 2D bedforms in subtidal conditions, with alternations between traction and suspension processes. |
Sand with climbing ripple cross-lamination (Facies Scc) |
Reddish-pinkish, centimetric, fine to medium sand with subcritical climbing cross-lamination. Locally slight reworking of the top set of the Facies St and Sp. |
Migration of 2D ripples with straight crests, with predominance of traction in detriment of settling from suspension processes. Oscillations of dominant energy flow can be indicated reworking of Facies St and Sp. |
Bioturbated sand (Facies Sb) |
Sand beds with intense bioturbation, interbedded with Facies Sth and St. |
Intense mixture of fine-grained sand sediments by bioturbation. |
Sand with sigmoidal cross-stratification (Facies Ssg) |
Sands with sigmoidal cross-stratification, about 15 cm thick. Reworked mud clasts can also be observed in the foresets. |
Bedform migration with rapid decceleration of the water flow. Dominant current reworks clay laminae deposited during slack water. |
Sand with even parallel stratification (Facies Sh) |
Centimetric to metric, coarse to medium sand with planar stratification, locally bioturbated. |
Plane-bed flow under upper flow regime. After this conditions, some organism can be mixture this sediments. |
Wavy to flaser tidal rhythmites (Facies Hwf) |
Centimetric to metric, yellowish to brownish beds with alternation between massive or laminated sands and mud forming wavy to flaser structures. |
Alternation between traction currents that deposited laminated sands (2-D ripples) and slack-water conditions, with deposition of massive mud, during tidal currents and slack-water, respectively. |
Massive mud (Facies Mm) |
Massive mud beds. |
Deposition of mud under slack-water conditions. |