Fl |
Laminated mudstone |
Grey colored, fine-grained mudstone, with fine (mm-thick) lamination, in up to 5-dm-thick tabular or lenticular beds. |
Recurrence of mud cracks. Occasional presence of fossils (palynomorphs, ostracod, clam shrimps, fish and dinosaurs) and evaporite (gypsum pseudomorphs). |
Mud deposition by decantation in standing waters without effect of bottom currents or wave orbitals. Common subaerial exposure. |
Fm |
Massive mudstone |
Red colored massive mudstones with scattered grains of fine sand in lenticular beds of variable thicknesses (centimeters up to 1-m-scale). |
Common bioturbation, sometimes as up to 10-cm-long vertical/oblique tubes with preserved meniscus (spreiten) (Taenidium barretti). Recurrence of up to 20-cm-deep mud cracks. |
Mud deposition by decantation in standing waters without effect of bottom currents or wave orbitals, accompanied by wind-blown sand grains. Common subaerial exposure. |
H |
Heterolithic |
Dm-thick tabular beds of interlaminated fine-grained sandstones and mudstones, with small-scale ripple cross-lamination in the sandstone lenses and variable proportions of sand/mud: 2:1 (flaser), 1:1 (wavy) and 1:2 (linsen). |
Common desiccation cracks in the mudstone laminae. Common bioturbation characterized by 5-cm-long vertical and/or oblique tubes with meniscus (Taenidium barretti). Recurrence of wavy bedding, locally with soft-sediment deformation features. |
Alternation of flow and decantation in subaqueous conditions. Highly variable moisture and water table oscillation with prolonged periods of dryness and subaerial exposition. |
P |
Paleosol |
Light red to purple colored, fine- to medium-grained, structureless sandstones organized in meter-thick tabular beds with carbonate spots, concretions and nodules, as well as mottling zones and/or stained horizons with occasional presence of manganese oxide-hydroxide veins or layers. Common presence of vertical/oblique tubes with meniscus (Taenidium barretti), 2- to 6-cm-long root marks, and recurrence of rhizoliths associated with precipitation of calcium carbonates. |
Occasional relicts of the original stratification, with lateral variation of depth and intensity of obliteration. |
Obliteration of primary structures due to pedogenesis, under reducing and hydromorphic conditions, as indicated by the color purple, presence of layers rich in manganese oxide-hydroxide and abundant bioturbation. |
Sd |
Sandstone with deformational structures |
Red colored, fine- to medium-grained, silicified sandstones organized in tabular beds (dm- to m-thick) with cm- to dm-scale disharmonious folds, fluid escape pillars, and punctual irregular injected sand dikes. |
Subordinated presence of structures indicating brittle deformation, such as small-scale normal and reverse faults, and drag folds. Up to 3-m-scale pyroclasts locally associated with trough cross-bedded and deformed sandstones. |
Soft-sediment deformation by liquefaction and fluidization, including sand dikes injection. Reddening of sediments affected by high temperature bombs and lapilli. |
Sp |
Planar cross-bedded sandstone |
Light red colored, fine to medium-grained sandstones, marked by grain size segregation and pin stripe lamination; occasional lenses of sand inversely graded and ripple cross-lamination. Up to 15-m-thick tabular and lens-shaped sets with planar cross-stratification. |
Well-sorted, rounded, and non-cemented quartz grains, with rare vestiges of partially or completely weathered feldspar. Cm- to dm-scale pyroclast bodies disrupting stratification. |
Migration of large transverse dunes due to wind action under high sedimentation rate, probably with enormous sediment supply. An alternative hypothesis is migration of very large sinuous-crested eolian dunes, whose trough pattern of cross strata is not observable in the outcrop scale. |
Sl |
Parallel-laminated sandstone |
Fine- to medium-grained parallel-laminated sandstones with two-fold grain size segregation, arranged in 0.5- to 2-m-thick horizontal to low angle (less than 5°) strata. |
Rounded calcium carbonate clasts (granule- and pebble-sized) common at the base of sets. |
Protodunes migration across deflation sand flats under high ratio of wind velocity/sedimentary supply. |
Sr |
Climbing ripple cross-laminated sandstone |
Fine- to medium-grained sandstones organized in cm-thick lenticular beds with climbing ripple cross-lamination. |
Common bioturbation characterized by vertical and/or oblique tubes with meniscus (spreiten) of variable thickness (0.5- to 5-cm-thick) (Taenidium barretti). |
Migration of subaqueous ripples in lower flow regime. |
St1
|
Medium- to coarse-grained, trough cross-bedded sandstone |
Medium- to coarse-grained sandstones, moderately to poorly selected, frequently containing granules and pebbles. Lenticular to channelized beds (0.1- to 1.5-m-thick), commonly exhibiting erosive base and sharp top organized in dm-scale finning-upward sets with trough cross-stratification. |
Rounded mud (rip-up) and calcium carbonate intraclasts (granules and pebbles) common at base of sets. |
Migration of three-dimensional subaqueous dunes by the action of unidirectional currents under lower flow regime, with intraclasts from erosion and reworking of other facies. |
St2
|
Meter-scale trough cross-bedded sandstone |
Cream to red colored, fine- to medium-grained sandstones. Foresets marked by grain size segregation with differential cementation (pin stripe lamination) and inversely graded thin lenses. Lens-shaped sets (1- to 10-m-thick) with trough cross-stratification. |
Small-scale deformation features (e.g. disharmonious folds and fluid escape structures) at the base of some foresets. Cm- to dm-thick mottled sandstones, with relict of the original stratification and occasionally preserved root traces on the top of sets. Sub-rounded caliche granules and pebbles at foresets and at base of sets. |
Migration of large sinuous-crested eolian dunes (barchans and/or barchanoid chains), sometimes with sand liquefaction at the base of foresets due to gravitational instability. |