What is Biogenous sediment?

What is Biogenous Sediment? (In Plain English)

Ever wonder what happens to all the shells and tiny critters that live in the ocean after they, well, don’t anymore? A lot of it ends up as biogenous sediment – basically, the underwater graveyard of marine life! Think of it as the ocean’s way of recycling. This stuff, also called biogenic sediment, is made up of the hard parts of dead marine plants and animals that pile up on the seafloor. We’re talking shells, bones, even the microscopic skeletons of single-celled organisms.

So, what’s this “sediment” actually made of? The main ingredients are calcium carbonate (CaCO3) and silica (SiO2). Calcium carbonate is what makes up the mineral calcite, and silica is often found as opal, which is like a hydrated version of silica.

How does it all come together? Simple: sea creatures like algae and protozoans pull these compounds straight out of the water to build their shells and skeletons. When they kick the bucket, their remains sink down, down, down, slowly but surely creating layers of biogenous sediment. Over time, it builds up like snow in winter.

Now, let’s break down the different types of this marine “snow.”

First, we have the big stuff – macroscopic remains. These are the things you can actually see, like shells, teeth, and bones. But honestly, you don’t find huge piles of this stuff lying around, except in places like coral reefs.

Way more common is the microscopic variety. Imagine the tiniest shells imaginable, from even tinier organisms. When these little guys die and their shells accumulate, they form this fine-grained, almost mushy layer. And when at least 30% of a sediment layer is made up of this microscopic biogenous material, we call it a biogenous ooze. Sounds kinda gross, right? But it’s super important!

There are two main kinds of ooze:

• Calcareous Ooze: This is the calcium carbonate superstar. It’s made from the shells of things like foraminifera and coccolithophores. These calcite-loving organisms thrive in warm waters that are just packed with calcium carbonate.
• Siliceous Ooze: This one’s all about the silica. It comes from the shells of diatoms (a type of algae) and radiolarians (a type of protozoan). You’ll find this ooze hanging out in cooler, nutrient-rich waters, where silica doesn’t dissolve as quickly.

Okay, so why should you care about underwater graveyards? Well, biogenous sediments are like time capsules. They can tell us a lot about what the Earth was like way back when. For example, if we see a change in the types of plankton remains on the seafloor, that can tell us the seawater temperature changed. Seriously cool, right? Scientists can even figure out past climate history by analyzing oxygen in these sediments.

Where you find these sediments depends on a few things:

• Productivity: If there’s a lot of life in the surface waters, you’re more likely to get a build-up of sediment. Makes sense, right?
• Destruction: Sometimes, those skeletal remains dissolve before they can even become sediment. Calcium carbonate, for example, dissolves more easily in deep, cold water.
• Dilution: If there are other types of sediment around, like clay, it can “dilute” the biogenous sediment.
• Water Depth: How deep you are plays a big role in how well carbonate is preserved. There’s something called the carbonate compensation depth (CCD), and below that, calcium carbonate just dissolves.

You’ll often find calcareous oozes chilling on the deep Atlantic seafloor, while siliceous oozes prefer the Pacific.

And get this: diatoms, those little guys that make up siliceous ooze, are actually useful! Their remains, called diatomaceous earth, are used in all sorts of things, from filtering agents to toothpaste abrasives. Who knew dead algae could be so handy?

So, there you have it! Biogenous sediment: it’s more than just underwater “stuff.” It’s a window into the past, a resource for the present, and a key part of the ocean’s ongoing story. It’s a complex world down there, governed by all sorts of biological, chemical, and physical processes. Next time you’re at the beach, take a moment to think about all the tiny creatures whose remains might one day become part of this fascinating sediment.