Wooster Geologist in Ohio!

December 16th, 2009

CAESAR CREEK STATE PARK, OHIO–I’ve definitely extended my field season as far as possible.  (And what a season it has been.)  My last fieldwork at the end of this research leave was in Ohio, about three hours south of Wooster.  I visited Caesar Creek State Park this morning where a large cut through an Upper Ordovician section has been set aside as a fossil preserve of sorts.  It is an emergency spillway for Caesar Creek Lake, which is maintained by the US Army Corps of Engineers.  Many Wooster paleontology field trips have stopped here.  Fossils can be collected, but only with a permit (obtained at the visitor center) and following significant regulations.  The fossils are diverse and abundant, including all the stars of the Ordovician seafloor.

My task was to find, photograph and measure an old trace fossil friend: the boring Petroxestes pera.  This is a slot-shaped excavation in carbonate hard substrates formed by bivalves (probably in this case the modiomorphid Corallidomus).

The boring Petroxestes pera (the name means "purse-shaped rock-grinding") in a hardground at Caesar Creek State Park.

The boring Petroxestes pera (the name means "purse-shaped rock-grinding") in a hardground at Caesar Creek State Park.

These elongated holes are among the first bivalve borings.  Some of my students and I think they may have been formed in clusters, and they also may be oriented relative to each other and their local environment.  In any case, I found plenty.  It was an astonishingly cold morning, though, so I didn’t waste any time on the outcrop!

Yes, this photo is here mainly to show just how tough Wooster Geologists are.  And there are some very nice brachiopods and bryozoans!

Yes, this photo is here mainly to show just how tough Wooster Geologists are. And there are some very nice brachiopods and bryozoans!

Mysterious out-of-place rocks in the Ordovician of Kentucky

December 15th, 2009

MAYSVILLE, KENTUCKY–Our short geological expedition to northern Kentucky today was to look at some odd blocks of limestone that sit suspended in the sediments as if they were dropped in while the sequence was accumulating.

An eroded, bored and encrusted limestone block in the Fairview Formation (Upper Ordovician) of northern Kentucky at the Route 11 outcrop (N38.61243°, W83.75575°).

An eroded, bored and encrusted limestone block in the Fairview Formation (Upper Ordovician) of northern Kentucky at the Route 11 outcrop (N38.61243°, W83.75575°).

These rocks are bored by worms and encrusted by bryozoans on their top and sides, and they often sit at high angles to the surrounding strata.

Bryozoans encrusting a side of the block above. The beautiful pinkish bryozoan on the left is the holdfast of a ptilodictyoid which in life held an erect bifoliate portion of the colony. The field of view here is about 10 cm wide.

Bryozoans encrusting a side of the block above. The beautiful pinkish bryozoan on the left is the holdfast of a ptilodictyoid which in life held an erect bifoliate portion of the colony. The field of view here is about 10 cm wide.

It is difficult to imagine a mechanism which deposited large, lithified limestone blocks in the middle of a shallow carbonate ramp. They are almost certainly related to “seismite” structures in the outcrop (see next post), but how these earthquakes would have transported such rocks is a mystery.  We also do not know how quickly the limestone had been lithified before emplacement.  We do know that the sides of these blocks were exposed on the seafloor long enough to accumulate encrusters and borers.

Plenty yet to discover in these well-studied rocks.  It is a continuing lesson for scientists: the more you see the more questions you have.

Wooster Geologist in Kentucky

December 15th, 2009

MAYSVILLE, KENTUCKY–Today I visited the University of Cincinnati for a meeting of Aaron House’s thesis committee, on which I serve.  (Aaron is a 2004 geology graduate from The College of Wooster.)  It all went very well and soon after Aaron took me and two other geologists on a short field trip to an Upper Ordovician outcrop near the Ohio River town of Maysville.

Outcrop of the upper Fairview Formation (Upper Ordovician) on Kentucky Route 11 near Maysville, Kentucky (N38.61243°, W83.75575°).

Outcrop of the upper Fairview Formation (Upper Ordovician) on Kentucky Route 11 near Maysville, Kentucky (N38.61243°, W83.75575°). A distant Aaron House for scale.

Many Wooster students and alumni will immediately recognize all the elements of a typical roadside outcrop of the Cincinnatian Group in winter: gray rocks matching the gray sky, the muddy ditch at the base, and the thin verge of grass extending to the road.  Alternating limestones, siltstones and shales give the outcrop its jagged appearance.

Some of the best Ordovician fossils in the world are found in these sedimentary sequences, and the stratigraphy holds many mysteries despite over a century and a half of intensive study by geologists.  Wooster students have completed dozens of Independent Study theses with these rocks, and there are many more to come.  Aaron House is now pursuing a masters degree by assessing and interpreting the preservation of mollusk fossils in the Cincinnatian.

A full geological circle

July 8th, 2009

View from a room in the St. Barbara Hotel, downtown Tallinn, Estonia.

View from my room in the St. Barbara Hotel, downtown Tallinn, Estonia (N59.431802°, E24.743355°).

The Wooster Geology Estonia team is now safely in Tallinn preparing for our visit to the paleontological collections in the university museum tomorrow. For me a private joy is that our hotel building is made of Ordovician limestone, the very same stone that I studied a month ago in Russia.

Goal!

June 8th, 2009

BABINO, LENINGRAD REGION, RUSSIA–Today we visited an active quarry, which is a different experience from the riverbank exposures and abandoned quarries we have been frequenting.  Quarry mud has a special character — a kind of purified mud, the kind of mud all mud aspires to be.  There are also very large trucks splashing by, giant rock saws whining, cranes lifting large blocks, and small groups of curious workmen who want to see what we are doing there with our hammers that now seem so small.  Active quarries can produce the very best exposures for geologists, especially those interested in the boundaries between rock units as we are.  This quarry at Babino N60.03035°, E32.38613°) is particularly good because they quarry Ordovician limestone by first cutting it vertically, and then lifting the rocks away in sections, revealing smooth surfaces perpendicular to bedding.

Cut surface through Ordovician section, Babino Quarry.

Cut surface through Ordovician section, Babino Quarry.

I want most to see the boundary between the Lower and Middle Ordovician rocks, and look at the trace fossils above and below it.  This boundary — a plane in the rocks which extends across northeastern Russia, Scandinavia, and parts of northern Europe — could not be better displayed than the way we saw it here.  It is an erosional surface which has been cemented into a carbonate hardground and then bored (to some extent that we are debating) and abraded smooth.  Above it is a significant change in the fossil fauna, a change which can be seen around the world.  In no place is this boundary better presented to geologists than here.

Lower/Middle Ordovician boundary in the Babino Quarry.

Lower/Middle Ordovician boundary in the Babino Quarry.

The trace fossils along this boundary are complex and may show both boring and burrowing behavior.  The distinction depends on when the sediments were soft, firm and cemented, and on the varieties of organisms which did the work.

Borings in the Lower/Middle Ordovician boundary at Babino Quarry.

Borings in the Lower/Middle Ordovician boundary at Babino Quarry.

I can’t take these specimens home for further examination.  I’d very much like to make thin-sections (slices of rock shaved down until almost transparent for microscopic analysis) of all the critical intersections, but that will have to wait.  Andrey collected many samples he can cut up and share from his lab in Moscow.

Ordovician Hardgrounds

June 7th, 2009

SASS RIVER, LENINGRAD REGION, RUSSIA–The main geological attractions for me on this expedition are the abundant carbonate hardgrounds in the Lower and Middle Ordovician in this part of the world.  A carbonate hardground is a cemented seafloor.  What were soft sediments on the bottom were cemented with carbonate minerals (calcite in the Ordovician) so that they became a rocky surface several centimeters thick.  The sediment is usually carbonate mud and shells, so the result is essentially a limestone seafloor.  Many invertebrate animals colonize these hard surfaces by wither encrusting them or boring into them.  Those eocrinoids illustrated earlier, for example, often encrusted Early and Middle Ordovician hardgrounds.

Today at the Sass River Carbonate Mound locality (N60.02316°, E32.62471°) we saw numerous hardgrounds bored by a shallow variety of a trace fossil called Trypanites.

Borings in Ordovician hardground fragments.

Borings in Ordovician hardground fragments.

These are the most common borings in hardgrounds.  This particular type of Trypanites is remarkably shallow — often appearing as pits rather than the usual penetrating cylinder.  Another difference between these hardground fossil faunas and those I know best in North America and western Europe.

Urban Dinosaurs

May 27th, 2009

My last geological fieldwork (if we can call it that) in Israel on this trip was to examine the Upper Cretaceous limestones and dolomites exposed in Jerusalem. I far prefer my rocks be found in pristine wilderness areas with only bird songs in the background, but the right rocks, of course, can be anywhere. Sometimes, then, we have to work with traffic zooming by, sirens wailing, blasts of car exhaust, and schoolchildren offering to hammer the rocks for us.

The coolest location was in the moshav of Beit Zeit, just five minutes from downtown Jerusalem. (A moshav is a type of cooperative agricultural community, although in this case heavily urbanized.) A beautiful trackway of ornithomimosaur dinosaur footprints is exposed on a bedding plane of Lower Cenomanian limestone.

combinedbeitzeit052709

The site is of great importance because thus far these are the only dinosaur tracks known in the entire Middle East. The local community purchased the land and erected a protective roof over the trackways. They had a mural painted showing what the area may have looked like in the Cretaceous, installed a custom-made life-size dinosaur model on the bedding plane, and made the area into an educational park. You can see for yourself what happened later. The surrounding fence was too low, so it became a drug hangout, vandals spray-painted the mural and then broke the dinosaur into bits. (The crater where the dinosaur stood is just visible in the photo.)  This natural wonder was simply too accessible to the public.  There are plans to protect the site more thoroughly, and then reconstruct the displays.

I was able to collect a small piece of the limestone bedding plane for analysis back in Wooster. My hypothesis is that the limestone is a marine hardground which cemented very soon after the dinosaurs waded across it, thereby preserving the prints. A thin-section of the rock may show if it had these early cements.

The rest of our urban geological work was on the streets of Jerusalem. Rocky outcrops are common because the city is built on several steep hills which have been quarried for thousands of years. We were able to correct the geological map in some places because of new exposures, and I gathered several ideas for future projects.

Mizzi hilu ("sweet rock"), a lithographic biomicrite member of the Judea Group (Turonian).

Mizzi hilu ("sweet rock"), a lithographic biomicrite member of the Judea Group (Turonian).

Fieldwork in the Golan Heights

May 25th, 2009

I finally got out into the field today. My Israeli colleagues and I left Jerusalem early in the morning and arrived about noon in the Druze village of Majdal Shams on the slopes of Mount Hermon. It is a lovely place with steep hillsides and extraordinary views over green valleys filled with cherry and apple orchards. (I’ll write another post sometime about the complicated politics here, including a long lunchtime lecture I tolerantly received from a Druze man about all the problems in the world coming from “America and the West”. It may have been a good thing that I didn’t quite understand what he was saying until it was explained to me later!)

Part of Majdal Shams seen from the town center and facing Mount Hermon.

Part of Majdal Shams seen from the town center and facing Mount Hermon.

One of the cultivated valleys near Majdal Shams.

One of the cultivated valleys near Majdal Shams.

Our goal today was to examine three marine Jurassic formations (from bottom to top in the geological fashion): the Zohar (mostly limestone), Kidod (mostly shale), and Beersheva (mostly limestone). I had two primary questions: What indications can we find in these rocks of the water depth when they were deposited? What was the intensity of bioerosion of the corals and sponges in these units? Both questions are part of larger studies placing these rocks in context with the rest of the known Jurassic world. This region was on the equator when these units were formed, so we have an unusual opportunity to study Jurassic equatorial ecological conditions.

As is often the case in paleontology, we found some of the best fossils at the boundaries between formations. The top of the Zohar and bottom of the Kidod have wonderful ammonites, belemnites, bivalves, and brachiopods, some appearing to show patterns of microbioerosion. The top of the Beersheva has massive corals and sponges which are thoroughly bored by bivalves, some of which are still in the crypts they excavated for themselves.

On the left is a very large ammonite we found in the top of the Zohar Formation.  Note the hammer for scale.  On the right is a closer view of a partially silicified coral from the top of the Beersheva with holes drilled in it by bivalves, some of which are still in place.

On the left is a very large ammonite we found in the top of the Zohar Formation. Note the hammer for scale. On the right is a closer view of a partially silicified coral from the top of the Beersheva with holes drilled in it by bivalves, some of which are still in place.

All the indications we could find showed that the limestone units were clearly shallow water deposits. The thick shales of the Kidod were laid down in deeper waters well below wave base. Much more work is required, though, before we can come to any conclusions. This is a reconnaissance trip to sort out potential projects for Wooster Senior Independent Study students and my own research. I now see many opportunities here.

Walls in Jerusalem

May 23rd, 2009

Our faculty colleagues on the Hales Fund trip to China have posted on their blog a wonderful photographic blog essay of their encounter with the Great Wall of China. It gives me an excuse to show some cool walls I’ve encountered lately on this trip. All of these structures are made from one of the limestone varieties of Jerusalem Stone.

Southwest corner of the retaining wall for the Temple Mount.  The massive lower blocks were carved and emplaced during the reign of King Herod the Great (37 - 4 BCE).

Southeast corner of the retaining wall for the Temple Mount. The massive lower blocks were carved and emplaced during the reign of King Herod the Great (37 - 4 BCE).

Golden Gate (Bab el-Rahma) in the eastern city wall.  Jewish tradition is that the Messiah will pass through this gate into Jerusalem.  Possibly for that reason the Muslim rulers in the 7th Century closed it up and placed a graveyard in fron of it.

Golden Gate (Bab el-Rahma) in the eastern city wall, another construction during Herod the Great's reign. Jewish tradition is that the Messiah will pass through this gate into Jerusalem. Possibly for that reason the Muslim rulers in the 7th Century closed it up and placed a graveyard in front of it.

Middle of the north city wall.  This is the side of the walled city most vulnerable to invaders, so the height of the wall was enhanced by quarrying out the limestone beneath it.  The door leads into one of many subsurface quarries underneath this part of the Old City.

Middle of the north city wall. This is the side of the walled city most vulnerable to invaders, so the height of the wall was enhanced by quarrying out the limestone beneath it. The door leads into one of many subsurface quarries underneath this part of the Old City.

The stones atop Jaffa Gate on the western side of the city walls shows bullet and shell scarring from the 1948 War of Independence.  Jordanian troops held the Old City and the Israelis were desperate to relieve the Jewish Quarter inside.

The stones atop Jaffa Gate on the western side of the city walls show bullet and shell scarring from the 1948 War of Independence. Jordanian troops held the Old City and the Israelis were desperate to relieve the Jewish Quarter inside.

A bit of limestone wall exposed in the Chapel of Adam inside the Church of the Holy Sepulchre.  Christian tradition is that this is the burial place of Adam, which was supposed to be directly below the crucifixion site of Golgotha.  The crack you see in the rock was believed by early Christians to have been formed during the earthquake upon the death of Jesus.  Archaeologists suggest that it was a pre-existing crack in an old quarry.  What I found interesting was that someone has placed a strain meter across the crack!  Any movement of the rock here will not be good news for the Church of the Holy Sepulchre.

A bit of limestone wall exposed in the Chapel of Adam inside the Church of the Holy Sepulchre. Christian tradition is that this is the burial place of Adam, which was supposed to be directly below the crucifixion site of Golgotha. The crack you see in the rock was believed by early Christians to have been formed during the earthquake upon the death of Jesus. Archaeologists suggest that it was a pre-existing crack in an old quarry. What I found interesting was that someone has placed a strain meter across the crack! Any movement of the rock here will not be good news for the Church of the Holy Sepulchre.

The "broad wall" is a remnant of an 8th Century BCE fortification built by King Hezekiah to expand the size of Jerusalem.  It was uncovered while Israeli engineers were clearing the debris in the Jewish Quarter after it was liberated in 1967.

The "broad wall" is a remnant of an 8th Century BCE fortification built by King Hezekiah to expand the size of Jerusalem. It was uncovered while Israeli engineers were clearing the debris in the Jewish Quarter after it was liberated in 1967.

Jerusalem Stone

May 22nd, 2009

Jerusalem is indeed the “city of gold” when the sun rises or sets on it. The slanting rays give the beautiful stonework on the facings of its buildings a golden glow. Since the British captured the city in World War I, it has been the law that all buildings must be faced with Jerusalem Stone, which is a mix of Late Cretaceous limestones and dolomites quarried in this part of the Judean Hills.

City wall near the Jaffa Gate lit by the setting sun.

City wall near the Jaffa Gate lit by the setting sun.

The most beautiful and durable of the stone types is called meleke. It is a Turonian (Late Cretaceous) biomicrite with numerous stylolites (jagged lines showing internal pressure dissolution), some trace fossils, and occasionally numerous molds of fossil mollusks.

Close-up of the meleke variety of Jerusalem Stone.

Close-up of the meleke variety of Jerusalem Stone. Finger is on a small stylolite.

The local stone can be easily seen in outcrops on the north side of the Old City where the walls were built directly atop old quarry sides. The present quarries are now mostly in the West Bank and are very busy supplying stone for new construction throughout Jerusalem.

New construction in western Jerusalem using Jerusalem Stone.

New construction in western Jerusalem using Jerusalem Stone.

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