Wackes are commonly produced by turbidity currents, though we cannot be sure without seeing graded bedding.
Wackes are commonly produced by turbidity currents, though we cannot be sure without seeing graded bedding.
Mainly medium sand (to coarse sand in the case of L327a).
Yellow-brown iron stained quartz, cemented by the same yellow brown oxide. A few larger quartz grains up to 5 mm long. Grains are angular to sub-rounded, and poorly sorted.
Fizzing with acid, indicating that there is a carbonate cement.
Angular to sub-angular grains of quartz, displaying undulose extinction.
Most have thin brown rims of iron oxide.
A few grains of feldspar.
Minor carbonate cement (sparite).
Deposited in an aqueous environment, since it is not clean enough to be aeolian.
Iron staining
Hematite (Fe2O3) → red (blood-red, cherry-red, brown-red) iron-staining
Limonite (FeO(OH)•nH2O) → yellow or brown iron-staining
The yellow colour of this rock is probably produced by limonite.
Cretaceous
Carston, Lower Greensand
Hunstanton
Mainly medium sand (to coarse sand in the case of L327a).
Yellow-brown iron stained quartz, cemented by the same yellow brown oxide. A few larger quartz grains up to 5 mm long. Grains are angular to sub-rounded, and poorly sorted.
Fizzing with acid, indicating that there is a carbonate cement.
Angular to sub-angular grains of quartz, displaying undulose extinction.
Most have thin brown rims of iron oxide.
A few grains of feldspar.
Minor carbonate cement (sparite).
Deposited in an aqueous environment, since it is not clean enough to be aeolian.
Iron staining
Hematite (Fe2O3) → red (blood-red, cherry-red, brown-red) iron-staining
Limonite (FeO(OH)•nH2O) → yellow or brown iron-staining
The yellow colour of this rock is probably produced by limonite.
Fine laminations can be seen when the thin-section is held up to the light.
Moderately well rounded quartz grains with thin rims of hematite, and overgrowths of quartz in optical continuity with the original grain.
Occasional grains of very fine quartzite, microcline, plagioclase, mica and decomposed fine-grained igneous rocks.
Siliceous cement and the secondary quartz overgrowths hold this rock together.
The grains are finer as a whole in L326b, and less well rounded.
Probably deposited in an aeolian environment, since it almost entirely comprises well sorted and well rounded quartz grains.
Fine laminations can be seen when the thin-section is held up to the light.
Moderately well rounded quartz grains with thin rims of hematite, and overgrowths of quartz in optical continuity with the original grain.
Occasional grains of very fine quartzite, microcline, plagioclase, mica and decomposed fine-grained igneous rocks.
Siliceous cement and the secondary quartz overgrowths hold this rock together.
The grains are finer as a whole in L326b, and less well rounded.
Probably deposited in an aeolian environment, since it almost entirely comprises well sorted and well rounded quartz grains.
Quartz grains, sub-angular to sub-rounded, occasionally rounded, displaying undulose extinction.
Lithic fragments including flint and quartzite.
Some grains of feldspar.
Rare small green clasts.
Grain supported.
Cemented by a sparry calcite cement. The cement crystals are large, each enclosing a number of sedimentary grains.
Deposited in an aqueous environment; grains are not rounded enough to have been deposited in an aeolian environment.
The rare green clasts are made up of a cryptocrystalline material, which may be a type of amphibole called glauconite, and some rather decomposed rhyolite or andesite.
Quartz grains, sub-angular to sub-rounded, occasionally rounded, displaying undulose extinction.
Lithic fragments including flint and quartzite.
Some grains of feldspar.
Rare small green clasts.
Grain supported.
Cemented by a sparry calcite cement. The cement crystals are large, each enclosing a number of sedimentary grains.
Deposited in an aqueous environment; grains are not rounded enough to have been deposited in an aeolian environment.
The rare green clasts are made up of a cryptocrystalline material, which may be a type of amphibole called glauconite, and some rather decomposed rhyolite or andesite.
Quartz (~65%)
- Includes fresh quartz grains with undulose extinction, quartzite grains with internal sutures, and quartz vein material. Some quartz grains have opaque rims.
Feldspar (~35%)
- Mainly microcline, some plagioclase. Some microperthite texture and decomposition to clays.
All grains are moderately rounded and fairly well sorted. The rock is well compacted. A thin film of cement mainly hematite and clay coats the grains.
This rock contains too much feldspar, and the grains are not sufficiently well rounded nor well sorted to have been deposited in an aeolian environment. The sediments were deposited in an aqueous environment.
sandstone
feldspathic arenite
Quartz (~65%)
- Includes fresh quartz grains with undulose extinction, quartzite grains with internal sutures, and quartz vein material. Some quartz grains have opaque rims.
Feldspar (~35%)
- Mainly microcline, some plagioclase. Some microperthite texture and decomposition to clays.
All grains are moderately rounded and fairly well sorted. The rock is well compacted. A thin film of cement mainly hematite and clay coats the grains.
This rock contains too much feldspar, and the grains are not sufficiently well rounded nor well sorted to have been deposited in an aeolian environment. The sediments were deposited in an aqueous environment.
sandstone
feldspathic arenite
This rock was deposited in a moderate energy, aqueous environment. The grains are not well rounded enough to be aeolian sediments.
sandstone
arenite
This rock was deposited in a moderate energy, aqueous environment. The grains are not well rounded enough to be aeolian sediments.
sandstone
arenite
Rounded clasts of very dark red brown amorphous silica (chert) and polycrystalline quartz.
Matrix of quartz grains (typically 0.25 mm) and fine-grained carbonate cement (sparite). Dark red-brown iron staining.
Iron staining
Hematite (Fe2O3) → red (blood-red, cherry-red, brown-red) iron-staining
Limonite (FeO(OH)•nH2O) → yellow or brown iron-staining
The red-brown colour of this rock is probably produced by hematite.
Rounded clasts of very dark red brown amorphous silica (chert) and polycrystalline quartz.
Matrix of quartz grains (typically 0.25 mm) and fine-grained carbonate cement (sparite). Dark red-brown iron staining.
Iron staining
Hematite (Fe2O3) → red (blood-red, cherry-red, brown-red) iron-staining
Limonite (FeO(OH)•nH2O) → yellow or brown iron-staining
The red-brown colour of this rock is probably produced by hematite.
Very poorly sorted.Angular to sub-angular clasts up to 30 mm long. Randomly orientated.
Clasts mainly pale grey, some white, some red.
Red-brown colour of the fine-grained matrix indicates iron staining.
Matrix and some clasts fizz with acid, indicating that they are made of carbonate. This is a limestone.
Iron-staining
Hematite (Fe2O3) → red (blood-red, cherry-red, brown-red) iron-staining
Limonite (FeO(OH)•nH2O) → yellow or brown iron-staining
The red-brown colour of this rock is probably produced by hematite.
Permian
Brockram, Cumbria
Very poorly sorted.Angular to sub-angular clasts up to 30 mm long. Randomly orientated.
Clasts mainly pale grey, some white, some red.
Red-brown colour of the fine-grained matrix indicates iron staining.
Matrix and some clasts fizz with acid, indicating that they are made of carbonate. This is a limestone.
Iron-staining
Hematite (Fe2O3) → red (blood-red, cherry-red, brown-red) iron-staining
Limonite (FeO(OH)•nH2O) → yellow or brown iron-staining
The red-brown colour of this rock is probably produced by hematite.
Six vials containing unlithified terrigenous sediments of different grain sizes. These are:
| grain size (mm) | grain size (phi) | |
| Very coarse sand | 1-2 | -1-0 |
| Coarse sand | 0.5-1 | 0-1 |
| Medium sand | 0.25-0.5 | 1-2 |
| Fine sand | 0.125-0.25 | 2-3 |
| Very fine sand | 0.063-0.125 | 3-4 |
| Mud | <0.063 | >4 |
Six vials containing unlithified terrigenous sediments of different grain sizes. These are:
| grain size (mm) | grain size (phi) | |
| Very coarse sand | 1-2 | -1-0 |
| Coarse sand | 0.5-1 | 0-1 |
| Medium sand | 0.25-0.5 | 1-2 |
| Fine sand | 0.125-0.25 | 2-3 |
| Very fine sand | 0.063-0.125 | 3-4 |
| Mud | <0.063 | >4 |
Fine-grained, blue-green, sedimentary texture.
Slaty cleavage.
Some patches of lighter and finer-grained material.
Slaty cleavage due to the alignment of chlorite and muscovite.
Cross-cut by the blobs of the fine-grained material. These are orange-brown in thin-section. Could be water-lain ash, ripped-up to form clasts.
Very fine-grained, brown matrix, probably volcanic ash.
Carbonate, quartz and opaque clasts slightly larger than the matrix.
Fine-grained, blue-green, sedimentary texture.
Slaty cleavage.
Some patches of lighter and finer-grained material.
Slaty cleavage due to the alignment of chlorite and muscovite.
Cross-cut by the blobs of the fine-grained material. These are orange-brown in thin-section. Could be water-lain ash, ripped-up to form clasts.
Very fine-grained, brown matrix, probably volcanic ash.
Carbonate, quartz and opaque clasts slightly larger than the matrix.