But, on a closer look, these things were too big. Diatoms are tiny, a large one being less than a quarter of a millimetre in length or diameter. These particles were a millimetre or larger,of varying lengths.
Here is the previous image enlarged. Sure look like poops. But whose? And why, amid acres of submerged sand ripples, were they deposited in a very limited space? Doesn't make sense.
Stumped. I don't know what they are.