usually, which is younger, the pebbles in sand, or the sand surrounding the pebbles? I think it's the pebbles in sand.
That makes sense, since erosion has worn down pebbles to make the sand.
thanks
Determining the relative age between pebbles in sand and the sand surrounding them involves understanding the principles of sedimentary rock formation. Sedimentary rocks, including sandstone, are formed by the accumulation and lithification (compaction and cementation) of sediment particles.
When it comes to pebbles within sand, the pebbles themselves are usually older than the sand surrounding them. This is because pebbles are typically derived from the erosion and weathering of larger rocks over time. As these larger rocks break down into smaller particles, including pebbles, they are transported by various agents like rivers or glaciers and eventually deposited as sediment.
Once deposited, these pebbles become part of the sand bed. Over time, additional layers of sediment accumulate above them, eventually leading to their burial. The layers of sediment above the pebbles compact and harden, forming sandstone. As the sandstone forms, the pebbles within it remain relatively unchanged, making them older than the surrounding sand which was deposited later.
It's important to note that this is a generalization, and there can be exceptions depending on the specific geological context. However, in most cases, when pebbles are found within a sandstone formation, the pebbles themselves are likely older than the sand that surrounds them.