Archive for June 29th, 2011

A little something for igneous petrologists

June 29th, 2011

Like a lonely little onion in a petunia patch, a boulder of red granite sits on the cobblestone beach off Soeginina Cliff, western Saaremaa, Estonia.

KURESSAARE, ESTONIA–Hard-rock geologists sometimes complain that I flood this blog with too many sedimentary rocks and fossils (and just wait until I get to the Estonian wildflowers!). There are actually quite a few igneous and metamorphic rocks on Estonia — just like there are in Ohio — in the Pleistocene glacial till. They show up well on the beaches here in contrast to the sedimentary rocks around them.

A closer view of the above rock, just to show it really is granite.

Granite in action! A granitic vein through some unfortunate rock.

Saaremaa Silurian stromatolites studied

June 29th, 2011

KURESSAARE, ESTONIA–Our fieldwork today at the Soeginina Cliff locality ended with an examination of a sequence of stromatolites near the top of the exposed Ludlow section. Stromatolites are layers of sediment accumulated by photosynthetic cyanobacteria. They are the earliest fossils known, some 3.5 billion years old, and these structures are still being formed today. Bacteria were present at the beginning and no doubt will be the only surviving life at the end.

In the image above, the stromatolitic portion of the outcrop begins at Nick’s upraised arm and goes almost to the top of the exposure. It is a complicated story because they seem to be sitting on an erosional surface cut into the dolomite underneath. There are also patches of what appears to be gravel under some of the stromatolite domes. A dolomitic sand fills the spaces between the stromatolite heads. Stromatolites can tell us a lot about the paleoenvironment of this area during the Silurian.

Closer view of the stromatolites at Soeginina Cliff.

Top view of the Soeginina stromatolites showing the fine layering produced by cyanobacteria. (Note the clever use for scale of a Euro with the map of Estonia on it. You can easily pick out the island of Saaremaa!)

I don’t usually come across stromatolites in my work. The last time I saw a few was with Matthew James on a great field trip to British Columbia. Part of the joy of supervising student research is that I must learn alongside them!

Thriving in the shingle: the story of Sea Kale

June 29th, 2011

KURESSAARE, ESTONIA–A very common perennial plant at the foot of the cliffs we are studying in Estonia is Sea Kale (Crambe maritima Linnaeus). It is beautiful with large, thick leaves and central stalks with bursts of white flowers, each with a purplish throat and yellow pistil. Turns out there is a bit of geological context and history of this edible plant in Western Europe.

Sea kale lives in a place where few other plants can survive. Shingle and cobblestone beaches have very little soil and are usually saturated at depth with brackish water from rain mixed with seawater. If the cobbles are mostly calcareous, as they are on Saaremaa, nutrient levels are low. Sea kale does well in this place because it is halophytic (tolerant of higher salinity than most terrestrial plants) and can collect enough nutrients because it has so few competitors. Its seeds float and so the plant can disperse via coastal sea currents. It is pollinated by numerous species of flies, beetles and bees, so it has no dependence on a particular pollen vector.

Sea kale was a popular vegetable in Europe during the 19th Century and before, but it fell out of favor as more easily cultivated plants became marketable. The new geological angle on sea kale is its ability to grow nutritious tissues in salty water. As freshwater resources become more scarce, biologists are looking at more ways to cultivate sea kale in marginal marine environments, and geologists are helping identify and preserve limestone shingle and cobble beaches for its continued growth. One of those places is Vilsandi National Park in western Saaremaa where we’ve been working this week.