Sediment-rich shallow seas

The specification says: Describe the

deposition of clastic material formed in sediment-rich shallow seas, to form conglomerates, sandstones and mudstones.

Conglomerate Coarse grained > 2mm. Very poorly sorted. Rounded clasts. Poor sorting suggests what? Rounded clasts suggests what? Clast size suggests what? Suggest environments of shallow

sea deposition. Inter tidal.

There are other high energy environments that can form conglomerates.

What could the conglomerates contain that would indicate that they are marine?

Marine fossils.

Sandstones. Sandstones are clastic rocks

with medium (sand) sized clasts (1/16th – 2 mm).

What does this tell you about the energy of the environment?

Medium/moderate energy. What does it tell you about the

depth of the water? Shallow/medium depth. So what part of the ocean

would you find sandstones forming?

Inter tidal/just offshore/continental shelf.

Sandstones

There are other medium energy environments that can form sandstones. What could the sandstones contain that would indicate that they are marine?

Marine fossils. As you can see typically

beach sands have ripples. How will these be

preserved in the sandstones?

Cross-laminations.

Mudstone

The constituents of these rocks are varied: "Rock Flour" comes from glacial erosion or abrasion by

running water or wind. New "Clay Minerals" can be produced by chemical

weathering of feldspars and ferromagnesian minerals. Such fine grained sediments settle out only in low energy

environments which exist in: estuaries or in the oceans beneath the wave base.

As the original mud deposit has water squeezed out it changes to a sticky compact clay and then to a hard mudstone or laminated shale.

Distribution of Sediments

As you move from the beach offshore the depth of water increases.

Once below “wave base” then there is much less energy.

Further out again as depth increases the energy decreases.

Therefore the sediments get finer.