Pillow basalts for Dr. Pollock

June 4th, 2013

PillowsCastle060413CATANIA, SICILY, ITALY–These are Dr. Meagen Pollock’s favorite kind of rocks: pillow basalts. Above we have a spectacular example of pillow basalts exposed in cross section below a castle ruin in Aci Castello a few kilometers north of Catania. The pillows (more are shown below) are in the middle of this natural outcrop carved by the sea.

Pillow basalts are formed when basaltic lava is erupted underwater. The surface of the flow quickly cools and begins to solidify as the interior fills with lava. The result is a flattened spheroid of basalt with chilled margins. The castle, by the way, was built in 1076 by conquering Normans.

Megapillow060413The light was not great for this shot, but you should be able to make out in the lower right a large body of basalt with columnar joints radiating from the center. This is, I was told, a “megapillow’ of basalt from a large flow.

PillowWall060413Here we have a closer view of the pillows in the wall shown above. On several of these pillows you can just make out a fine-grained chilled margin.

PillowBed060413This is a view of the wave-eroded platform below the castle showing the pillows form the top. I left the roasting Europeans in the frame for scale. Note that while these pillows appear with almost circular outlines in cross-section, they are actually serpentine in shape.

These pillow lavas were formed with the beginning of volcanic activity roughly 600,000 years ago that led to the present Mount Etna complex. They show the submarine phase of eruption before the eruptive center was uplifted above sea level. They are the most spectacular pillows I’ve ever seen.

Exploring Mount Etna

June 3rd, 2013

MountEtna060313_585CATANIA, SICILY, ITALY–The International Bryozoology Association conference field trip began with a day on the magnificent compound basaltic stratovolcano that virtually defines the eastern half of Sicily: Mount Etna. We did not get to climb all the way to the top — that would have been a bit of an expedition — but we hiked around its diverse southern flank. The view above is looking toward the summit in the back left, a parasitic cone from an 18th Century eruption in the middleground, and in the bottom right is a trekkers cabin built (of course) almost entirely of vesicular basalt.

SmokingEtna060313Here is a closer view of the summit. The white smoke on the right is from active fumaroles near the top. Etna is one of the most active volcanoes in the world. Last month, in fact, it was erupting so much that a visit like ours today would not have been allowed. I ticked off a geological bucket list item: standing on an active volcano’s slopes. It is not close to the activity Dr. Pollock and her students have witnessed in Iceland over the years, but exciting for this paleontologist!

Sicily lies at the boundary between the African and European tectonic plates, producing an extremely complex geological situation that is still debated. We know, at least, that Mount Etna’s ancestors began erupting underwater about 600,000 years ago, and the axis of eruptive activity has slowly moved to the northwest. We are essentially looking at a series of successive volcanoes intersecting and overlapping previous versions.

Parco dell' Etna 060313This is the entrance we used into the national Parco dell’etna on the south side of the volcano. Note the perfect weather and the delightful contrast between the jet-black rock and greenery. There was less and less vegetation as we moved upslope.

ParasiticConeOutside060313This is the outside of a parasitic cone on the flank of the volcano. Through it emerged a lateral flow of lava.

ParasiticConeInside060313This is the inside of the same cone as above. The rest of it collapsed after the lava completely exited.

LavaTube060313The entrance to a lava tube. The lava flowed through its own hardened crust, leaving behind this rocky tunnel that looks very much like the ancient lava tube we visit on our Mojave Desert field trip. This particular one dates back to the 18th Century. Technically we’re looking through a window to the floor of the lava tube itself.

TreeLavaFossils060313Who says you can’t see fossils on an active volcano? These are basalt external molds of tree trunks formed when a flow of lava engulfed a forest. These are in the Parco dell’etna headquarters.

ParkOfficers060313When we visited the Parco dell’etna headquarters, we heard a brief presentation in the chapel of the abandoned monastery they occupy. The president of the park then addressed us. Can you tell which of the five people above is the president? (Hint: She’s wearing a scarf.) They are excited to announce that Mount Etna is now a UNESCO World Heritage site.

mineralpickingEtna060313Our last geological activity on Mount Etna for this week was a visit to the top rim of an eroded parasitic cone to find tiny little euhedral crystals of the mineral pyroxene (or, rather, a mineral from the pyroxene group). Here you see paleontologists in a very familiar pose but doing something distinctly unpaleontological.

NicosiaWines060313We ended the day at the very modern Nicosia winery where they grow the grapes in the rich volcanic soil on the slopes of Mount Etna. It was very interesting to see the industrial production of various types of wines, but I’m afraid the wine tasting was wasted on me.

We will visit Mount Etna once again when the full conference starts next week. I’ll have more images from a different part of the volcano. Tomorrow’s field trip is going to be along the seashore, so there will be some very different images.

A Wooster Geologist in Sicily

June 2nd, 2013

MountEtna060213CATANIA, SICILY, ITALY–This summer Wooster’s Team Italy consists of only me. Maybe in the future I’ll take students here for Independent Study projects depending on what I find. I’ve just arrived in the city of Catania on the eastern coast of Sicily. Above is a view of the gorgeous Mount Etna from the plane as we landed. This volcano dominates the city, both structurally and historically. More on that later. Twenty-three hours of travel through four airports has tuckered me out. Luckily we have an early dinner at 8:00 p.m.

I’m here for the 17th meeting of the International Bryozoology Association. It starts with a glorious field trip around the island. I plan to report daily as long as there is a wirleless connection.

The joy of thin-sections

December 30th, 2009

A beautiful view of a modern hardground in thin-section.  The platy orange, pinkish and brown grains are the mineral biotite (a mica), the gray and white angular grains are quartz, and the tan irregular grains are recrystallized shells and cements.  Sampled dredged from about 650 meters in the Strait of Messina between the Italian mainland and Sicily.  Collected by Agostina Vertino.

A beautiful view of a modern hardground in thin-section with cross-polarized light. The platy pinkish and brown grains are the minerals muscovite and biotite (micas), the gray and white angular grains are quartz, and the tan irregular grains are recrystallized shells and cements. Sample dredged from about 650 meters in the Strait of Messina between the Italian mainland and Sicily. Collected by Agostina Vertino.

WOOSTER, OHIO–Bitterly cold Ohio days are perfect for geological lab work, especially with thin-sections under a warm microscope accompanied by a music-filled iPod. The next best thing to fieldwork. A thin-section is a slice of polished rock glued to a microscope slide and then ground down to a standard thickness of 30 microns so that light easily passes through it. Minerals, fossils and other internal features become visible in a thin-section which would otherwise go unnoticed in the hand sample. We use polarized light to reveal optical properties of the crystals for identification and analysis. Often a thin-section in cross-polarized light shows an astonishing array of colors, fabrics and textures.

What is most fun is to take a drab rock and find the microscopic treasures within through thin-sectioning. For example, this is the rock I worked with today:

A hardground sample from the Strait of Messina (the same rock as seen in the thin-section above).  This sample was dredged from the deep-sea and is encrusted by the coral Desmophyllum dianthus and tiny tubeworms.  Collected by Agostina Vertino.

A hardground (cemented seafloor) sample from the Strait of Messina (the same rock as seen in the thin-section above). This sample was dredged from the deep-sea and is encrusted by the coral Desmophyllum dianthus and tiny tubeworms. Collected by Agostina Vertino.

A sample of the same hardground as above with the organic material removed.  On the right is a closer view of the sand-sized grains making up the rock.  Notice that even in this view you can tell that the grains are poorly cemented to each other -- the rock is very crumbly.

A sample of the same hardground as above with the organic material removed. On the right is a closer view of the sand-sized grains making up the rock. Notice that even in this view you can tell that the grains are poorly cemented to each other.

An Italian colleague (Agostina Vertino of the Dipartimento Scienze Geologiche – Università Catania) and I are examining these unusual hardgrounds from deep in the underwater canyon at the bottom of the Strait of Messina. This is a very energetic system (the currents are fast), so the grain size is surprisingly coarse for a deep-water deposit. The composition of the sediment is highly variable, ranging from feldspars and micas to shell fragments and microscopic skeletons of foraminiferans. Our first question is the simplest: How are these sediments cemented? The thin-sections show us.

Carbonate rock fragments in the Strait of Messina hardground showing a thin fringe of calcareous cement (probably aragonite) precipitated on their edges.  The cement is formed when these crystalline fringes intersect and hold the grains together.

Carbonate rock fragments in the Strait of Messina hardground showing a thin fringe of calcareous crystals (probably aragonite) precipitated on their edges. The cement is formed when these crystalline fringes intersect and hold the grains together.

As you would expect, a rock so lightly cemented crumbles easily, and it has a very high porosity and permeability. It is remarkable that such an unstable substrate serves so well as an attachment surface for encrusting organisms such as corals, tubeworms, bryozoans and sponges.

The dark areas in this thin-section view (as in the others) are open spaces.  This particular hardground is highly porous and permeable.

The black areas in this thin-section view (as in the others) are open spaces. This particular hardground is highly porous and permeable. Note the bright fringing cements on the grains.

The porosity and permeability of this sediment is undoubtedly a key to its cementation. Fluids could move quickly and in considerable volume through this deposit, gradually precipitating the tiny, tiny calcareous crystals on the exposed grain surfaces. It is also possible that dissolving aragonite shells in the sediment supplied the necessary carbonate for the cement. There is much work ahead to figure that one out.

We will post more portraits of our geological laboratory studies this winter as we simultaneously prepare for next summer’s fieldwork. This is the life!

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