Sedimentary Rocks

First, we would have to determine the rock’s age. Did you know there’s two different types of aging? Relative and absolute?

What’s the difference? Well, relative would be like saying, this rock is older than this rock. Or this tree is the oldest relative to those other three trees.

While absolute aging, is saying that rock is 150 millions year old. And that tree is 23 years old. Get the picture?

So, to observe a rock’s history, we would need to determine it’s absolute age first, which can be done somewhat accurately through radiometric dating.

Graded bedding is basically when the sediments are layered by size. 

So, you can see the larger sediments are at the bottom. That’s because they’re heavier so they fell faster that the other sediments. The next largest would fall next and so on, which creates this gradation of sediments. Obviously, that means the finest particles, like silt and clay, are at the top.

(WARNING: SOME ARE TASTIER THAN OTHERS)

silt/clay

fine sand

sand

fine gravel/fine pebbles

gravel/pebbles

boulders

(smallest to the largest)

Three types, with a bunch of types within those types..:

Clastic

conglomerate: well rounded, coarse grained

breccia: clasts more angular

tillite: from glaciers

sandstone: sand sediments, well rounded

siltstone/claystone: mudstone

shale: easy cleaves along bedding

Chemical

limestone: fizzes with acid, precipitate of carbon carbonate

chert: precipitate of silica, diatoms

evaporites: crystals left behind evaporation  (halite)

Organic/Biochemical

limestone

chert

coal: plant/animal remains

gypsum: desert rose

Let’s get back on track. Where were we?

Ah, yes, weathering. They shape our landscape by tearing away at rocks and wearing it down to a sand. One way to do that is with water. A lot of it, and moving really fast. Like in rivers.

River processes are quite extensive. 

First thing to remember is that, rivers are measured by their competence (max size particle it can transport) and their capacity (total volume of sediment that can be transported)

They range from old to young, but it’s fairly easy to tell which is which.

Young rivers have:

rapids

waterfalls

vertical erosion

no flood plain

V-shaped valley

Whilst older rivers have:

meandering streams

horizontal erosion

Mass wasting can also be affected by weathering. A lot of geology is affected by weathering.