Return to the Ora Formation

July 9th, 2013

8_MudVolcano070913MITZPE RAMON, ISRAEL–The last location Wooster Geologists in Israel visited today was on the southern edge of the Makhtesh Ramon structure (N 30.58209°, E 34.89375°). Here are excellent exposures of the Ora Formation (Upper Cretaceous, Turonian). This curious feature was a challenge to the students to interpret. I also got it wrong in my explanation on the outcrop, so listen up Steph, Lizzie and Oscar! The students are standing in a portion of the outcrop that is mud with suspended blocks of limestone. This is a cross-section of a diapir, or body of sediment that has moved upwards through the rocks that cap it. This was caused by water-saturated sediment being compressed by the sediments above, forcing it upwards through cracks and crevices. What I got wrong was that the flat strata on top of the mud was present when the diapir formed. (I said it came later.) The mud never reached the surface to become a mud volcano. This is why the resistant beds below are bent downwards — the upward force of the mud flow was stopped by the capping rock, thus deflecting the edges of the units below. A complicated story — which is one of the many things that makes the Ora Formation interesting.

9_Oysters070913Also in the Ora Formation at this same site is a half-meter-thick unit composed entirely of oyster shells. Many of the oysters are encrusted with other oysters and, who knows, maybe bryozoans as well. (And no, Paul Taylor, I didn’t see any here yet!)

10_Hardground070913The Ora Formation also has a fabulous carbonate hardground, which was a cemented seafloor surface. We can tell this particular surface was hard rock on the Cretaceous seafloor because of all those little holes. These are the borings of bivalves known as Gastrochaenolites. They could only be made by grinding away at a cemented substrate.

Hardgrounds, oysters, odd diapirs … opportunities for future study! Israeli geologists have done fantastic work with this unit, so there are many collaborations possible here.

Adventures in the Triassic: Exploring the Gevanim Valley in Makhtesh Ramon, southern Israel

July 9th, 2013

2_NordmarkiteStock070913MITZPE RAMON, ISRAEL–The second visit of the day for Wooster’s Team Israel 2013 was to the Gevanim Valley on the south side of the Makhtesh Ramon structure. This is a fascinating place where Cretaceous intrusions formed an uplifted dome exposing Triassic sedimentary rocks. It is a rare place to see abundant Triassic marine fossils. Our first stop was a nordmarkite stock intruded into the Gevanim Formation (Middle Triassic, Anisian). We always dedicate this image to our own Dr. Meagen Pollock who knows what nordmarkite is without having to google it.

3_GevanimRamonalinidSite070913Our first task was to locate the Gevanim Formation and examine the many specimens of the large bivalve Ramonalina ramanensis to look for rare Triassic encrusters. Above is an outcrop of the part of the Gevanim which has large numbers of this dark-colored, shoe-shaped clam.

4_Ramonalina070913Here are two nearly complete specimens of Ramonalina ramanensis. Alas, we found not a single encruster. The rumor that there are microconchids on these shells seems to be false. Science marches on.

5_LizzieSaharonim070913Above the Gevanim Formation is the Saharonim Formation (Middle Triassic, Anisian-Ladinian). Lizzie Reinthal is here standing near the base of it exposed in the western part of the Gevanim Valley. This is a very fossiliferous limestone and marl that is extremely well exposed here.

6_CephalopodsSaharonim070913Nautiloids and ammonoids are very abundant in the Saharonim. In fact, just about every large object in this exposure of the unit is one or the other. The coin in the image above is sitting on an ammonoid (a ceratite). The other fossils are internal molds of nautiloids.

7_SaharonimBrachiopods070913Our goal today, though, was to find terebratulid bachiopods with original calcite still preserved. We found dozens, a few of which are shown above. These are mostly of the genus Coenothyris. These specimens are destined for isotopic analysis in the laboratory of Dr. Pedro Marenco at Bryn Mawr College. Mission accomplished.

“The Carpentry” in Makhtesh Ramon: Unexpected columnar jointing

July 9th, 2013

1_JointedSandstone070913MITZPE RAMON, ISRAEL–At first glance this rocky outcrop in the middle of Makhtesh Ramon appears to be a typical columnar-jointed basalt. We’ve seen this many times on our blog (for example here and here). However, these rocks are entirely a quartzose sandstone. They have the typical polygonal joints of a cooled lava flow, but the rock is an unmetamorphosed sedimentary unit. This remarkable site is known as “the carpentry” (Haminsara) in the park.

How did these joints form? It is not from the sandstone melting and then cooling, like you’ll see in some places on Wikipedia. (And some people think this is basalt, which is a good reason for more interpretive signs in this place.) Likely it was a hydrothermal process by which superheated water from nearby intrusions warmed up the sandstone until it expanded a bit, and then it cracked along these joints during cooling. The sandstone was never heated to temperatures that would turn it into quartzite, much less liquid. Columnar-jointed sandstone is rare but not unique, as you can see here and here.

This was the first stop for the Wooster Geologists in Israel today as we explored parts of Makhtesh Ramon to follow up on various small projects.

A day of geological exploration in the Negev: the En Yorqeam Formation (Upper Cretaceous) at Makhtesh Ramon

July 8th, 2013

12_EnYorqeamView070813MITZPE RAMON, ISRAEL–Our final stop on our geological tour today was close to our temporary home: on the northern rim of Makhtesh Ramon (N 30.62831°, E 34.81759). Exposed here is the En Yorqeam Formation (Upper Cretaceous, Cenomanian), seen above as the less resistant marly unit between two resistant limestones. I did my first presentation on Israeli geology with bored and encrusted oysters from the En Yorqeam, which were also the subjects of a Fossil of the Week post.

We visited this outcrop today because there are some stratigraphic questions about its thickness and distribution. Its rich fossil fauna has also not been described in detail. This would be an ideal Independent Study project someday, especially with one large outcrop so close to our headquarters.

13_Echinoids070813Echinoids are the stars of the fossil fauna in the En Yorqeam. In just ten minutes we picked up over a dozen well preserved specimens. The large ones at the top are Heterodiadema lybicum. I don’t know the identity of the two in the bottom row. I bet some sharp student, though, can come up with the names quickly!

A day of geological exploration in the Negev: Matred Formation fossils and bonus petroglyphs

July 8th, 2013

8_OscarSilicifiedRingMatred070813MITZPE RAMON, ISRAEL–Our third stop in our geological journey today was 19 km north of Mitzpe Ramon (N 30.76084°, E 34.72020°) at another outcrop of the Matred Formation (Middle Eocene). We again had silicification, but no corals this time, The silica replaced the original limestone in a very strange way, producing these dark rings. Since silica is harder than limestone, the surrounding unreplaced limestone erodes faster, leaving the silicified rings in relief. They look anthropogenic, but they’re entirely natural. Again, mysteries abound.

9_SilicifiedBivalvesMatred070813In this close view of the silicified limestone are numerous bivalve shells that were replaced with silica just like the matrix. They appear to be a random distribution of shells with no preferred orientation.

10_SilicifiedFossil070813There are two fossils here replaced with silica. We’ll let the readers guess what they are.

11_Petroglyph070813These curious rings of black rock on the top of a hill attracted local peoples. Over the centuries (no one knows exactly how many or when) they carved numerous petroglyphs through the patina on the rock surfaces. We will also entertain guesses as to what is represented here!

A day of geological exploration in the Negev: Silicified corals in the Matred Formation (Eocene)

July 8th, 2013

MatredFormationView070813MITZPE RAMON, ISRAEL–Our next stop on this day of exploration was 32 km southeast of Mitzpe Ramon at outcrops of the Matred Formation (Middle Eocene). The location is N 30.36899°, E 34.98655°. Look at those coordinates on Google Maps and you’ll see that they are from the peak of that black mountain on the right of the above view. The black color is from the weathering of thoroughly-silicified (infused with silica) coral-rich limestones. Ordinarily paleontologists tend to stay away from such preservation because the matrix as well as the fossils are coarse, hard chert. These fossils, though, are important because they give strong clues about the depositional environment of the sediments. In this case, in situ coral reefs mean shallow water.

MatredCoral070813This is what the silicified corals look like in this part of the Matred Formation. We are looking down on the top of a colony. The holes represent the original corallites. Material like this cannot be identified to more than the family or genus, but we see enough to know that they are corals.

NummulitesMatred070813In this piece the bean-shaped fossils are large benthic foraminiferans that still retain their original calcareous skeletons. The matrix around them has been silicified. This type of preservation remains a mystery, especially when in the same unit we see the same fossils have been silicified and the matrix is not. More geological puzzles!

WadiView070813This wadi near the site is so beautiful I wanted to include an image. This would be a fun place to work, although maybe the spring would be more hospitable!

A day of geological exploration in the Negev: the Hazeva Formation (Lower Miocene)

July 8th, 2013

1_NachalParanFault070813MITZPE RAMON, ISRAEL–It is a tradition with the Wooster Israel expeditions to spend one day with our colleague Yoav Avni geologically explore areas beyond those associated with our present research topics. This is the way we plant seeds for future research endeavors — and Senior Independent Study projects. Today we went to four sites, which I will present in brief vignettes.

Our first stop of the day was in Nachal Paran at N 30.32329°, E 34.96388° about 35 km southeast of Mitzpe Ramon. The image of above is from our outcrop looking up at the faulted boundary of a large graben in which the valley is formed. Preserved within this down-dropped structure is a thick section of the Lower Miocene Hazeva Formation.

2_HazevaFormation070813Most of the Hazeva consists of reddish sandstones and conglomerates deposited by a very large river system that was flowing from the Arabian Peninsula into the Mediterranean. There have been a variety of African-derived mammal fossils in this unit, including elephants and giraffes. The unit of interest for us today is the gray rock at the base of the above image. It is a thin limestone unit no more than one meter thick. Its top has a scalloped pattern that may be due to ancient karstic weathering when the river deposited muds and gravels upon it. It appears to be a lake deposit formed just before the river moved into the region.

3_HazevaCloser070813Team Israel 2013 is here looking at a cross-section of the lacustrine (lake-formed) limestone and the sediments beneath it. One of the issues is how do we know that the limestone was formed in a lake. The best clue is the occurrence of tiny high-spired gastropods throughout the matrix. Another would be the presence of trace fossils that may represent the horizontal trails of snails and/or freshwater arthropods like isopods or insects. There is a pervasive pattern of vertical tubes that remains mysterious. Are they trace fossils or some sort of diagenetic phenomenon? A further question is why this lake was there in the first place considering that it sits in a section almost entirely formed of typical terrestrial siliciclastic sediments. Does it represent a brief climate change? A tectonically-induced change in the local hydrogeology? Plenty of questions here for future geological researchers.

Goodbye, Makhtesh Gadol (for now)

July 7th, 2013

GoodbyeMakhteshGadol070713MITZPE RAMON, ISRAEL–Today Team Israel 2013 had its last visit to Makhtesh Gadol, marking the end of Lizzie Reinthal’s and Steph Bosch’s fieldwork. We collected our last specimens from the Matmor Formation, which is exposed only in the center of this magnificent structure. The students above are looking down into the northern part of the makhtesh from the viewpoint at Mount Avnon.

MakhteshGadol070713This is a view from the same spot looking south along the western wall of the makhtesh. You can see a bit of the curvy, narrow road below that we used to enter and exit the makhtesh. This road was built by the British during World War II when they thought there might be oil underneath this breached anticline.

MG_BronzeAgeStructure070713This ring of stones is the remnant of a Bronze Age livestock pen, along with a probable small shelter for the shepherd in the lower left. This features are found throughout Makhtesh Gadol, usually up on the flanks of the walls or the Matmor Hills. I happened to come across this one in today’s walkabout.

LastCollecting070713Finally, here are students collecting at our last site — the southernmost exposure of the echinoderm-rich subunit we’ve found to be so productive. This morning we found … wait for it … two more bryozoans! This is usually not big news in most of the places I’ve worked, but it sure is here. They are again runner-types, but not Stomatopora. Much more to report on these after we get back home with them.

We still have five more working days in Israel. One will be devoted to finishing Oscar’s fieldwork, one to finishing smaller projects in the Makhtesh Ramon area, one to exploration of geological sites Yoav has chosen for us, one for a trip to Jerusalem and the headquarters of the Geological Survey of Israel, and a final day to make sure we’ve done all we came to do.

Geoarchaeology in Timna Valley

July 6th, 2013

StephChalcolithicMine070613MITZPE RAMON, ISRAEL–Wooster senior Steph Bosch is a double major in archaeology and geology. Rather than do a joint Independent Study project, she is actually doing two theses, which will no doubt be challenging this coming academic year, but she is more than a match for the task. Because of her interest in ancient mining, after our trip to Eilat we stopped by Timna Valley to look at some of the oldest mines in the world. Here she is inside a Chalcolithic copper mine at least 6000 years old. It was carved into the relatively soft Cambrian sandstone with stone tools, the marks of some of which can still be seen on the walls. (Elyssa Belding Krivicich will remember sitting in that same place for a photograph back in the day!) I am amazed we could crawl through a warren of these ancient mines, but then the surrounding mountains are riddled with hundreds that are well protected.

TimnaMushroom070613The landscape is fascinating, especially for geologists. The Cambrian sandstone is colorful and easily eroded, producing hoodoos like these as remnants on an intrusive igneous rock substrate.

TimnaArches070613That soft sandstone also weathers into natural arches, two of which you should be able to find in this view of the western wall of the valley.

TimnaSmeltingCamp070613During the 14th through the 12th centuries BCE, the Egyptians had an elaborate and extensive mining and production system at Timna. Here are the remains of a smelting camp where ore was processed to make ingots of copper. In this area is the smelter, a shrine, and a work building that had several rooms, each for a particular industrial purpose.

TimnaSmelter070613The smelter is easy to find because it is still to this day surrounded by fragments of black, glassy slag, a byproduct of the process.

OreCopperTimna070613The copper ore itself is easily seen as green-blue veins in the nearly white sandstone. The sandstone is very porous (it apparently represents the cross-bedded deposits of ancient braided streams) and is easily penetrated by hot waters generated by magmatic activity below. It appears to me to be the copper silicate mineral Chrysocolla.

Timna was a great place to look at the intersection of geology and archaeology.

Bryozoans finally make an appearance in the Jurassic of southern Israel

July 5th, 2013

MatmorCollecting070513MITZPE RAMON, ISRAEL–The concentrated effort of all four Wooster Geologists in Israel finally paid off in fossil bryozoans today. Steph Bosch (center) is studying the bryozoans of the Matmor Formation (Middle Jurassic) in Makhtesh Gadol for her Independent Study project. We have bryozoan specimens collected on earlier expeditions to the Matmor, but on this trip have been stymied in our efforts to add to the meager collection. Bryozoans are rare in these equatorial sediments, even though the diversity of other fossils here is very high. We want to describe this fauna for the first time and place it in its environmental and evolutionary context.

This afternoon we visited a site at the far northeastern end of the makhtesh where we knew lots of crinoids were preserved. (The locality is creatively known as “GPS 004”; N 30.94916°, E 35.01110°.) Our working hypothesis is that bryozoans preferred the same conditions as echinoderms in the Matmor Sea. The strategy worked: we found two runner-type bryozoans on crinoid columns. They are the stomatoporid-type of uniserial runner, giving us at least two different species of bryozoan now from the Matmor. Undoubtedly there are more such specimens on the many crinoid ossicles we collected to wash and examine later in the Wooster lab. They are far too small to photograph here in my hotel room!

Steph, appropriately, found the first specimen. Oscar Mmari (on the left) found the second just as we were leaving. Lizzie Reinthal (on the right) is actually working on crinoid taphonomy, so she was very pleased by all the specimens we collected today.

MatmorCollectingView070513A wider view of our collecting site in the Matmor Formation, with the northeastern wall of Makhtesh Gadol in the background.

It feels good to now have all three Wooster seniors with materials they’ve collected for their Independent Study projects. A nice way to end our first week of work in Israel!

« Prev - Next »