Archive for May, 2011

Cobbling together a Late Cretaceous story

May 27th, 2011

MITZPE RAMON, ISRAEL–This morning Will and I finished our work with the Zihor/Menuha boundary cobbles. We drove to the southern side of Makhtesh Ramon (pictured above) to see the same units we examined 25 kilometers to the north in Wadi Aqrav yesterday. The scenery was spectacular — and the day so hot that the wind felt like a hair-dryer in the face.

Will standing on the very top of the Zihor Formation where it is overlain by the Menuha chalks. This picture was deliberately posed to give his parents a bit of a thrill.

The Zihor/Menuha cobbles in the southern sections. They look very much like those we studied in Wadi Aqrav. They certainly are more numerous here and easy to measure. Some have borings by bivalves (Gastrochaenolites) and worms (Trypanites). We found no encrusters here, but we did find oyster shell fragments.

A difference between these southern exposures and those to the north is that the Zihor Formation top surface here is very well exposed. We can see that it was probably lithified during the erosion that created the disconformity and the cobble lag. It is undulating and well polished. Note that it is also on the edge of oblivion.

The Zihor/Menuha boundary is very distinctive because of the erosional differences, so faults through it show up well. What kind of fault is this? (It is not a trick of perspective because the fault plane has eroded back a bit.)

This is the kind of shade we had in the field today — when we were lucky! It was 40°C by 1:00 p.m. Will is pressed up against an outcrop of the Menuha Formation, by the way, showing a sequence of carbonate nodules that may help explain the origin of the boundary cobbles.

 

The Ora Formation: A future student project?

May 27th, 2011

MITZPE RAMON, ISRAEL–I’ve always enjoyed seeing the Ora Formation, which is exposed only in Makhtesh Ramon and to the south. It is early Late Turonian in age, so it is part of the Upper Cretaceous and about 90 million years old. It has an astonishing range of depositional units, many of which Will and I saw today on our way to our localities. The Ora Formation has been very well studied by Israeli paleontologists and stratigraphers. Their work can now be expanded with more paleoecological analysis and some of the insights we’ve gained from new ideas about Calcite and Aragonite Sea alternations. Maybe another Wooster Independent Study project or two in the future?

A carbonate hardground in the Ora Formation. The holes were drilled by lithophagid bivalves, producing a trace fossil called Gastrochaenolites. These borings are very densely packed, which is more typical for the Jurassic than the Cretaceous.

A unit composed of almost entirely oyster valves in the Ora Formation. It is above what is called locally the “Vroman Bank”. The shells are like large cornflakes. We didn’t get a chance to look in detail, but I’d love to see what kind of sclerobionts are preserved on these oysters.

Will is sitting in an unusual diapiric structure in the Ora Formation. This is a dissected “mud volcano“, or at least what would have been a mud volcano but for the resistant capping rock. Soupy mud was forced out from underneath the overlying limestones forming an inverted cone in cross-section. The limestones dip into the structure because they were forced down by the accumulating mud. The criss-cross lines in the mud are planes of gypsum that intruded the sediments later. Note the blocks of limestone in the “throat” of the structure — this means the limestones were lithified during the event.

Makhteshim Country: A Future UNESCO Geopark?

May 26th, 2011

Yoav Avni and Will Cary hiking down the wadi that exits Makhtesh Gadol. In the background is the wall of the makhtesh. It is made of diverse Cretaceous units.

MITZPE RAMON–Our colleague Yoav Avni of the Geological Survey of Israel is part of a movement to declare the Negev Desert around the three major makhteshim a Geopark cataloged by the United Nations Educational, Scientific and Cultural Organization (UNESCO). A Geopark is defined by UNESCO as “A territory encompassing one or more sites of scientific importance, not only for geological reasons but also by virtue of its archaeological, ecological or cultural value.” Yoav’s dream is that scientists and the general public from around the world will someday visit the makhteshim to tour the unique geological features with an infrastructure in place much like that of a US National Park. The ecological and cultural heritage of this region will be as important as the geology.

Modified from Google Maps.

I played a small role in this process when I wrote a letter to the Israeli government in 2005 (at Yoav’s request) explaining the geological value of Makhtesh Gadol and opposing further expansion of a sand quarry in the northern part of the makhtesh. This added a seed of international scientific interest to the discussion that continues to grow.

Now when we describe geological phenomena and fossils in the makhteshim, we are thinking about the ways we can explain these things to the public through nature trails, museum exhibits and popular press articles. It is exciting to be on the ground floor of such an endeavor.

There is plenty of opposition to this Geopark, of course. On one side are industries and government officials who want to squeeze every bit of economic usefulness from the land; on the other are extreme preservationists who wish to close off large tracts to all human entry. Somehow Yoav and his colleagues will have to find a way to make the future Geopark economically viable and yet with all the protections necessary to preserve its natural assets. This will be a slow process but maybe I will someday be posting blogs from the Makhteshim Country Geopark.

It is always a good day if there are sclerobionts in it

May 26th, 2011

MITZPE RAMON, ISRAEL–Sclerobionts are organisms that live on or in a hard substrate. Paul Taylor and I coined the term in 2002, so I use it as often as I can. Maybe someday more than six people will know what it means. A project for this year’s Israel field expedition is to revisit a locality where an extensive bed of hiatus concretions, most of them bored or encrusted by sclerobionts, is found between the Zihor and Menuha formations in the Upper Cretaceous. (This layer is pictured above.) Andrew Retzler and Micah Risacher will remember the Wadi Aqrav (Scorpion Wash) sections well from their Independent Study work last year. These hiatus concretions were formed when deep erosion produced a disconformity and a lag of cobbles. We already had a GSA presentation on this topic; now we need more information for a future paper.

Will and I hiked through Wadi Aqrav today to collect more information about these Cretaceous cobbles. We found all our previous study sections and a few more outcrops of the Zihor/Menuha formation boundary. Most important, we were able to collect more sclerobionts and other associated fossils.

One of the bored and encrusted Zihor/Menuha cobbles showing its apparent origin as a burrow-fill.

Eroded borings in the surface of one cobble. These are holes in the rock, but if you stare at them long enough they will suddenly look like bumps!

Three oysters on a cobble surface. Two grew together at the same time and one came later. Can you tell which?

Will found this nice irregular echinoid in the matrix between the cobbles. He also found a couple of shark teeth near it. A one-shekel coin, by the way, is 1.7 centimeters in diameter.

Landscape view of the Wadi Aqrav region. Beautiful desert in the Negev Highlands north of Makhtesh Ramon.

Camel stand-off!

May 26th, 2011

MITZPE RAMON, ISRAEL–It wouldn’t be the Middle East without a camel encounter or two. One year a camel literally ate my lunch when I left it in the shade of the car during a long morning’s work. (He even ate the plastic around the sandwiches.) The local Bedouin care for small camel herds that range throughout the Negev. If you’re near a wadi with a source of vegetation and water, camels are nearby. The version here is the one-humped variety: the dromedary (Camelus dromedarius).

Will and I were walking up a long dirt road around noon when we met the large male camel pictured above. He stared us down, standing almost completely still. We immediately saw why he was so intense: a group of females and young camels was behind it and we were about to walk between him and them. Of course, we had no interest in dying under the hooves of a camel (or whatever they do when they attack), so we moved carefully off the road. After a few minutes he slowly strolled down a wadi and the rest of the group caught up with him, a female at the end keeping her eyes on us until they were out of sight.

Females and young following the male down a wadi.

Crinoid success

May 25th, 2011

Will Cary collecting crinoid pieces at a site we creatively call "GPS 055". In the upper left you can see a triangular exposure of marl where Jeff Bowen did his Independent Study work in 2005.

MITZPE RAMON, ISRAEL–One of our missions on this expedition to Israel is to find more and better examples of a distinctive crinoid in the Middle Jurassic Matmor Formation. Crinoids are stemmed echinoderms with a very long geological history, dating back to the Ordovician (or Cambrian, depending on who you believe). They are still alive today so we know much about their biology. They usually have long stems with a holdfast on one end (attaching it to the substrate) and a calyx on the other containing most of the body. The calyx has feathery arms attached at the top that filter the water to catch fine-grained organic particles and pass them down to a central mouth.

Parts of the Matmor Formation have abundant crinoid fragments, all belonging to at least two types of Apiocrinites (a crinoid genus). Two years ago I collected some beautiful specimens, but still lacked some critical pieces. Today Will and I revisited my earlier localities (thank you, GPS technology) and found beautiful specimens.

Our prize is the holdfast pictured above. This is a mass of skeletal calcite the crinoid used to glue itself to the bottom of a coral. The shallow pits apparently represent additional “roots” it used to brace itself in a cavity under the coral. The stem then horizontally protrudes to the right so that the calyx and feeding arms could eventually reach the open seawater. I’ve never seen a holdfast this elaborate in the Jurassic.

Above are typical other parts of this Jurassic crinoid (imaged with all my hotel room photographic skills). At the top are two calyx side pieces showing the interior (left) and exterior (right). The star-shaped object in the middle is the calyx base, seen from the inside. It is flanked by stem fragments, the one on the far right encrusted by an oyster. At the bottom is a crinoid stem with a branching holdfast of another crinoid attached to it.

Mission accomplished as far as the crinoids go!

Makhtesh Gadol: The Movie

May 24th, 2011

MITZPE RAMON–It will not win awards, but I think you’ll get some of the thrill of driving into Makhtesh Gadol in southern Israel from the northwest. Note the one lane road that goes, alas, two ways.

First field day: Makhtesh Gadol (A large bowl of geological delights)

May 23rd, 2011

MITZPE RAMON, ISRAEL–Today Will Cary, Yoav Avni (our friend from the Geological Survey of Israel) and I worked in the northern end of Makhtesh Gadol (“the large crater”). This geomorphic feature looks a bit like an oblong impact crater, but it is actually a kind of breached anticline known as a makhtesh.

Makhtesh Gadol from Google Maps.

We are interested in the Matmor Formation, a series of Middle Jurassic marls and limestones in the center of the structure. Our special interest is a fossiliferous unit in the Matmor Formation that is found throughout the exposure. It is very rich in crinoids, echinoids, corals and sponges, with a few brachiopods, ammonites and bivalves as well. We want to understand the distribution of this unit and its fossils.

Yoav Avni and Will Cary marching through the Matmor Formation.

If we saw this formation in only two dimensions, as in a typical roadcut, it would be easy to interpret. However, we have it exposed in 3-D because it is heavily dissected by small wadis. More data this way, and far more complications. We learned today that there are distinct facies (rock types characterized by fossils and/or sediments indicating a particular depositional environment) found in very close relationships. The rock units are patchy and the fossils patchy within the lithological patchiness. The number of variables used to predict fossil occurrences is now very large!

All these facies are laterally equivalent in a very small space.

One of the many scleractinian corals in the Matmor Formation. These corals were originally aragonitic and are now replaced by calcite. The replacement process was unusually fine-grained here.

Our base of geological operations: Mitzpe Ramon, Israel

May 22nd, 2011

We have written many times about the geology of southern Israel in our blog posts over the past two years, and there is plenty more to come this week. We haven’t discussed the little town we stay in during our expeditions. So I’m starting with an image of Will Cary overlooking the Makhtesh Ramon for the geological context, but it is the community behind him that interests us today.

Mitzpe Ramon was established on the northern edge of the makhtesh in 1951 as a way station and workers’ village on the road to the southern city of Eilat. It has a magnificent perspective on the makhtesh, and thus the Hebrew name means “Ramon view”. The first permanent residents came in the 1960s as refugees from northern Africa and central Europe. Later immigrants came primarily from the United States and Russia.

Map of southern Israel and its neighbors (from Google) with Mitzpe Ramon pinned in the center.

This mix of heritages gives this little town a unique community unlike any other in Israel. Large numbers of Black Hebrew Israelites left the United States in the 1960s and 1970s to settle in Israel. This group believes, essentially, that they are a “lost tribe” of Israel, some maintaining they are the only true Israelites remaining. You can imagine the controversies they stirred in Israel with such claims, so many began to settle in the more distant Negev development towns where they would be out of the mainstream of Israeli national life. Now a generation later they are full Israeli citizens and integrated enough into Israeli society to serve in the military and hold political offices. The Black Hebrew Israelites in Mitzpe Ramon wear knitted kippot (head coverings) and a colorful style of dress that looks to me right out of 1970 Harlem. They speak English among themselves (and to us), and they’ve established American jazz clubs in this little desert town.

An elevated view of Mitzpe Ramon I took in September 2009.

Walking through the neighborhoods of Mitzpe Ramon you see a complex mix of cultures, from old Russian men sitting on benches with suit jackets and tightly buttoned shirts (regardless of the temperature) through fresh-faced (and always well-armed) soldiers the age of my students to African-American-Israeli children singing in the playgrounds in Hebrew while their parents converse in English. Above it all a bright blue desert sky, and below some of the most fascinating rocks in the world.

A neighborhood block in Mitzpe Ramon.

Wooster’s Fossil of the Week: Encrusting craniid brachiopods (Upper Ordovician of southeastern Indiana)

May 22nd, 2011

The two irregular patches above are brachiopods known as Petrocrania scabiosa encrusting the ventral valve of yet another brachiopod (Rafinesquina). That species name “scabiosa” is evocative if not a little unpleasant — it is also the root of the English “scab”.

Petrocrania scabiosa is in a group of brachiopods we used to call “inarticulates” because their two valves are not articulated by a hinge as they are in most brachiopods. Instead they are held together by a complex set of muscles. Now we place these brachiopods in the Class Craniforma, an ancient group which originated in the Cambrian and is still alive today.

Petrocrania scabiosa was a filter-feeder like all other brachiopods, extracting nutrients from the seawater with a fleshy lophophore. The Wooster specimens are part of our large set of encrusting fossils (a type of sclerobiont) in our hard substrate collection. They have irregular shells that are circular in outline when they grew alone, and angular when they grew against each other.

Some craniid brachiopods were so thin that their shells repeated the features of the substrate underneath them, a phenomenon known as xenomorphism (“foreign-form”).

Petrocrania scabiosa brachiopods (circular) on a Rafinesquina brachiopod, along with a trepostome bryozoan that encrusted some brachiopods and grew around others. The P. scabiosa on the far left shows xenomorphic features. Specimen borrowed from the University of Cincinnati paleontology collections.

A 2007 College of Wooster paleontology field trip to the Upper Ordovician locality near Richmond, Indiana, where these specimens were found. Students are in the traditional paleontological poses.

« Prev - Next »