At Home in the Herms

If you want to make a bunch of Pavilion scientists excited, just mention “the herms”. I just did my second submersible flight through the herms and it was spectacular! Let me give you a little background, so that you can understand why the flight was such a treat:

A bioherm is a mound constructed by biological organisms. A classic example is a patch reef: a decimeter to meter scale mound that is built by corals, sponges, and other reef animals. You may not think of a mound of organisms as being very sturdy, but just as your body is capable of making hard bones, other organisms such as corals also make hard skeletons. When those skeletons start to pile up, you get a bioherm – a biological mound!

So, what in the world does this have to do with microbialites. Remember that microbialites are “organosedimentary structures”, meaning they are built up of minerals that are influenced by organisms. “Whoa!” I hear you cry, “Does that mean that a microbialite is a bioherm? Well, a single microbialite is not usually defined as a bioherm, but if you pile up enough microbialites, you do end up with a mound that is constructed by organisms! By that definition there are some places in Pavilion Lake where we observe large piles of microbialites that can be defined of bioherms.

Thinking about microbialite bioherms is something that some of us geologists do quite frequently. Long before the organisms that build coral reefs evolved, big bioherms and reef structures still existed. Rather than being built by corals, sponges, or even shells, the ancient bioherms and reefs were built out of microbialites! Can you imagine SCUBA diving or piloting a submersible around ancient microbialite bioherms and reefs! Boy, I wish I had a time machine. Since I don’t have a time machine, I do the next best thing. Can you guess what that is? Yup, I come here and study the microbialites in Pavilion Lake. The details we learn about the microbialites in Pavilion Lake will help us to understand the fossil record of ancient microbialite reefs. That will help us to understand how life evolved on early Earth! Crazy cool stuff!

Ok, back to the Pavilion Lake herms. Here is where we are going to get really confusing! The “herms” are not actually bioherms, hence the lack of the “bio”. The herms are an area of sediment mounds at the southern end of the central basin of the lake. Now I know you are screaming, “but if they aren’t bioherms, which are so cool, why are you crazy scientists so excited about them!” It turns out that even though the herms are just sediment mounds, they are covered by some of the most interesting microbialites in the lake. There are a lot of different microbialite morphologies crammed into a very small space. If you start at the bottom of any given herm, you can often see several distinct morphotypes just by looking up two meters of slope. Likewise, if you move around a herm several meters, you often can see changes in morphotype or surface texture. Those are rapid changes! I’m sure you are asking yourself why the microbialites would be changing that rapidly, and that is one of our big research questions this year! It may be that the mounds are a place of significant environmental variability. In other words, there may be interesting water flow patterns, light conditions, variations in sedimentation, etc. that are unique to the herms. Any of these variables may be influencing the morphology of the microbialites! In short, the herms are a really complicated place, and if you haven’t figured it out yet, the scientists as Pavilion Lake love to study really complicated and interested places!

-Bekah