Where did the sediments come from that forms the aquifier?

Answer 1

What is usually meant by an aquifer is a given formation that contains potable water. There are many aquifers in the world. A formation could be made from almost any kind of sediment that is both porous and permeable. In other words, as long as the sediment contains spaces that allows it to hold water, and those spaces are connected together which allows the water to flow.

As to where the sediments come from, there are various possible sources. Sediment is the pieces and fragments broken from other rocks. These other rocks can be igneous (volcanic), metamorphic or even other sediments. Sedimentary rocks can even be laid down by chemical processes.

A sediment's orginal composition depends almost entirely on what minerals the parent rock contains. As a sediment is buried it is compressed, de-watered and heated. The fragments may become cemented together and turned to rock. This process is known as diagenesis. Some of the original mineral are lost as they are turned to clay during this process. In order for a rock to be an effective aquifer however, the clay content should be low, as too much clay will lead to the blocking of the passages between the pores.

Quartz, the mineral that makes up common sand, is resistant to chemical alteration, so sandstone is a common (but by no means the only) aquifer rock.