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Boy meets microbialite

Posted on June 30th, 2010 by Tyler Mackey

Today was my first research dive of the 2010 PLRP season, starting a project on microbialite morphology. I am a geology graduate student from UC-Davis and, while I’m not a true microbiologist, my thesis work is focused on the potential signatures that their communities can leave in the rock record.

Side view of the MOUS showing vertically oriented growth structures (note lasers are 10cm apart)

Growth processes in the Pavilion Lake microbialites may give insight into the significance of ancient microbial carbonates. I’m particularly excited to join the PLRP crew because of the wide range of microbialite morphologies that are present here. In the course of the next two weeks, I will be diving on one particularly large microbialite, affectionately dubbed the MOUS (microbialite of unusual size). The carbonate structure is apparently templating a boulder from a rockslide. While today was mostly an exploratory dive to photograph and survey the structure, I will mostly be investigating the relationship among light regime, microbialite morphology, and invertebrate grazers.

Above the MOUS with blocks of microbialite

Locating the MOUS underwater was our first task of the day. We dropped down near its recorded location and then followed the lake bottom down along a landmark rockslide until we reached 85 feet. From previous dive records, we knew that the top of the structure was at 87 feet, so we swam parallel to shore until we intersected it. The visibility in Pavilion Lake is great (particularly as I’ve done most of my training off of Northern CA) so it was pretty easy to spot.

Sediment deposit with surrounding growth on the top of the MOUS

While my dive buddy, Mike Delaney, worked putting in a temporary transect line to help us more reliably locate the structure (particularly during night dives), I photographed some of the major regions. Large blocks have spalled off the side of the structure throughout its growth, forming an incipient conglomerate of sorts at its base. I’d love to see this in the rock record!

Mike Delaney installing temporary transect line

One of the aspects of modern analogues that really fascinates me is time-averaging. What we see here on the surface of the lake is a geological instant, and over time the current growth surface will be incorporated into the microbialite subsurface. What would this look like? Outside of this project, one of my broader research questions is determining what sort of paeleoenvironmental record might be left in a microbialite, and how that signature is altered with preservation, or lack thereof.

I’m excited to learn more about the interactions between these microbialite structures and their surrounding environment as the field season progresses. There is always room for the unexpected in fieldwork, and I look forward to seeing what future dives will uncover in the lives of these microbial communities.

-Tyler

Editor’s note: Tyler’s boyish good looks have earned him the affectionate nickname “Boy” among the science team – resulting in the title of the blog entry.