The Earth, is a funny thing.

The Earth, (which needs only be capitalised when referring to it as a name (as opposed to the earth we stand upon)) is a funny thing. The product of an inconceivable large timescales operating on inconceivably small things, it never ceases to amaze me how much we have not been able to witness - and thus, must draw from observation and the small signs remaining. Not only on the mega (i.e. large) scale, but on the meso (intermediate) and micro (small) scale as well.

For an example, take a look at the Yilgarn Craton - among one of the oldest structure on Earth, at ~3 Ga - 3 giga-annum, or 3 billion years ago. Beside the Yilgarn craton is the Darling Scarp, a major fault running from Shark Bay to Albany, and with a throw possibly exceeding 15,000 metres ('throw' usually refers to the vertical displacement here). It's not considered active though, don't worry too much. This is a huge relief for the city of Perth (and most of populated Western Australia) as any activity on this fault could be a serious problem for a lot of people - which tend to live in cities established at the base of the fault-scarp, in the nice rich sediments which filled the basin after the faulting event (which probably took millions of years to form).

If we take a step back and consider, just for a moment, that it must have taken millions of years for the Perth sedimentary basin (as we know it) to form, and that sits beside a structure that is many millions of years older, and then how many millions of years it took for the Perth Basin as we know it today to deposit, and erode, literally hundreds of metres of sediments from various sea-level rises and falls through eons of time. 

It's pretty amazing.

These layers of deposition and erosion eventually form the hydraulic constraints we know today, such as the Kardinya Shale formation, which forms a hydraulic seal (i.e. inhibits movement of water), and considerably more-permeable layers of sandstones and limestone layers, which now facilitate some of Perths drinkable water (a significant percentage now comes from world-class desalination and recycled water plants).

We can dive even further down this rabbit-hole, by looking at the angle-of-deposition of some of these permeable layers. Everyone is familiar with sand-dunes, to some degree. They have a characteristic angle based on the relative wind speed and direction, but it's generally quite shallow - between 10 and 30 degrees dip. Over geological timescales, these dunes will lithify (i.e. become a rock) known as (in the Perth region, at least) an 'eolinate', from the Greek 'aeolian' - i.e. wind-born processes, where the dune angles become permanently emplaced into the rock structure. 

The wonderful thing about coastal hydrogeology, is that people often assume the world is flat.

No, not like that.

The various layering is often assumed to be flat-lying, and thus relatively easy to explain. You can see how, if we introduce these dipping dune layers, the flat-lying assumption is not quite correct, and complicates the flow of water towards the ocean. The layering of coarse beach sediments atop fine wind-borne layers, occasionally intersecting organic layers where plant-life has come-and-gone, comprises of a remarkably dynamic system - all thanks to inconceivably small particles emplaced over inconceivably long time scales.

Thanks for reading.