Now, igneous rock can obviously be from the Holocene. But what is the youngest age of a large-scale collection of sedimentary rock? In other words, how long does sand or organic material take before it can be turned into sandstone or limestone?
I assume that there are some evaporites or conglomerates forming as we speak that could count as “large-scale”, but I’m more talking about sandstone and limestone here. But while we’re at it how long does it take for the fastest conglomerate to be naturally cemented into what we’d call a conglomerate form of rock? (I assume orders of magnitude less than for limestone and sandstone, but can it take on the order of years rather than centuries or millennia?)
It’s my understanding that sedimentary rock is continuously being created as sediments flow out to sea and settle on the continental shelf (as well as the oceanic basins).
In other words, it’s somewhat of a continuum. If you were to dig into sedimentary deposits, you would find unconsolidated deposits on the topmost layers, which would be more and more cemented together into rock the deeper you went.
It depends. Much sedimentary rock is itself derived from eroded rock, which is cemented together by clays or other chemically distinct soils that can harden in mere years. For things like limestone and sandstone, you have to decide how hard and dry it has to get before it’s called rock.
I understand that there’s an enormous amount of aggregate being formed in a matter of days throughout urban areas on a regular basis.
Ignoring concrete, I agree with the others that it’s going to depend on your definition of when something becomes a rock. It’s a continuous process going on in numerous places throughout the world.
