There are two main types of rocks: here.
One group is the result of this low sedimentation.
, The counting of all of the organisms through the water coloumn and they deposit at the bottom of the ooceans at the bottom of this basin.
So we have limestone, they have a pink-reddish color here. 00:00:19
Then we have marlstone this grey/light grey interval, which has more silt and softer material.
, And then we have another group of rocks which resulted from a faster deposition.
It's the washing over from shallow parts of the basin and the reworking transport of .
sandgranes shells of other organisms, and these are the turbidites.
And it's this thin layer here. 00:00:55
So we have the normal sedimentation, slow, sedimentation, limestones and marlstones, and the more rapid sedimentation of the turbidites.
So the alternation of limestone/ marlstone is cyclic in Zumaia.
And we see cycles limestone marlstone limestone marlstone.
These cycles are orbitally controlled because of the orbit of the Earth.
Around the Sun.
, So this movement affects the climate on Earth and also the deposition of the sediments at the bottom of the ocean.
Each limestone/marlstone cycle was deposited within 20,000 years.
, So this is an excellent age control through time. 00:01:42
This is very rare in the geological record and the good thing about Zumaia is: we can count years.
20,000 years everytime.
We see these couplets .
Limestone/marlstone couplets. 00:01:56
This is a very good age control.