Where sedimentology meets structural geology

April 21st, 2014

A seismite? 042114MITZPE RAMON, ISRAEL–“Like a hot dog in a bun.” Late this afternoon, while exploring the Eocene (Lutetian) Horsha Formation near the Nabatean/Roman/Byzantine city of Avdat, Yoav Avni and I ran across these odd features in a limestone layer within the chalks (near N 30.79119°, E 34.75494°). They consist of an elongate core of coarse, bioclastic sediment (the hot dog) in chalky sediments folded around them (the bun). They are all oriented in the same direction.

Another seismite type 042114Some are as big as canoes; others like gravy boats. We suspect that these are seismites — sedimentary sturctures formed by seismic shaking. The chalky, water-saturated sediment would have responded plastically as the slightly denser bioclastic sediments above collected in troughs and then began to descend down into the chalk. This is just an idea. If someone else has seen structures like these, please let us know!

Byzantine Cistern 042114Just below these funny structures is this nice Byzantine cistern filled with water. It is on the edge of a wadi, with about a half-meter step above the wadi base. It has this narrow doorway that leads into an interior cavern, all hand-carved. During a flood, the water reaches a level in the wadi where it begins to decant into the cistern, reducing the amount of sediment that would otherwise fill the cavity quickly. A couple of years ago Yoav organized a team to excavate centuries of silt from this cistern. Now it is full from the winter rains, providing a water hole for the local Bedouin children. It also shows that the Byzantine water storage and conservation techniques of 1500 years ago still work fine today.

A 10K run into the Eocene of the Negev

April 20th, 2014

Horsha view 042014MITZPE RAMON, ISRAEL–Yoav and I had a long hike today into the Eocene succession of rock units in the northern Negev. We wanted to look especially at the Horsha Formation (Eocene, Lutetian) because it has some cool trace fossils and massively large oysters. Along the way there are also interesting features like submarine debris flows, thick chalk deposits, unconformities and faulting.

rainstorm 042014Despite the sunshine in the top image, we started the day with a thunderstorm at our back. It was the first time I’d heard thunder in Israel, and for awhile we contemplated in which rocky crevice we should take cover. (It’s not like we carry raingear with us here.) We did get rained upon, but not seriously.

Yoav and layer 042014Yoav is here looking at a thin limestone unit near the base of the Horsha Formation (at GPS 072; N 30.32537°, E 35.00653°). Note the sharp base and yellowish mineralization of the chalk.

Horsha traces 042014There are fantastic trace fossils in convex hyporelief on the base of this limestone layer.

Trace nummulitids 042014The small disks near this trace are nummulitid foraminifera. They are a major component of this limestone.

Horsha algae 042014There are also many broken bits of calcareous algae.

Giant oysters 042014These giant oysters are common in this unit. Some are bored, which you might be able to see in the specimen on the far left. We will return to this area tomorrow for continued exploration.

Negev Berry shrub large 042014On the long way back to the car we encountered this shrub. I wish I knew the name. Yoav said it was called “Bread of the Monks”, but that has led me nowhere. It may be Ochradenus baccatus, also known as sweet mignonette.

Negev Berry shrub close 042014I’m not one to eat wild plants I don’t know, but Yoav assured me the berries on this shrub were tasty. Indeed. Sweet like blueberries. Worth the risk!

Stratigraphy day at Makhtesh Ramon

April 19th, 2014

Labled cliff 041914MITZPE RAMON, ISRAEL–Usually on Saturdays Yoav Avni and I do something “touristic”, like visit an archaeological site or museum. Since it is the Passover holiday, though, and we are both averse to crowds, we decided to do a little stratigraphy outside Mitzpe Ramon instead. Our challenge from Amihai Sneh was to sort out the lower boundary of the En Yorqe’am Formation (Upper Cretaceous, Cenomanian), so we added another section to our argument.

The above image is taken from N 30.62947°, E 34.82085°, about three kilometers northeast of town along the rim of Makhtesh Ramon. (Check those coordinates out on Google Maps. Very cool, especially if you tilt the Earth image to show the cliff edge.) The three critical formations are labelled above with our new concept. The top boundary of the En Yorqe’am with the Zafit Formation is not controversial; it’s the base of the En Yorqe’am that is at issue. Presently it is defined as the top of the cemented carbonates shown just above the “Y” of En Yorqe’am. With this definition the unit is about 20 meters thick — less than half its thickness elsewhere. This has led to some tectonic arguments about uplifts, erosion and unconformities that are not supported by the record in the rocks, other than this anomalously thin section. From our studies of the boundary to the south, we believe we have good evidence to put it here between the massive and bedded limestones as shown. The fossils support this (especially oysters) and the thickness of the En Yorqe’am goes back to an expected 50 meters or so. That’s the argument we’re going to make to Amihai, at least. I will see more of this unit with Amihai further north next week.

H-E contact 041914Here Yoav is standing on what we consider the top of the Hevyon Formation, with the En Yorqe’am behind him.

Yoav cliff 041914Let me emphasize to Gloria and my Mother: that is not me on that precipice! Yoav is here checking the lithology and paleontology of the top Hevyon. It all ended well.

storm 041914We got back just as a massive wind and dust storm swept into town. A front is moving through from north Africa. They say it could rain, but I don’t believe it.

Our camel friends in the Negev

April 18th, 2014

camel head 041814MITZPE RAMON, ISRAEL–It is a problematic relationship between camels and me. My first experience with a camel out here was watching one eat my lunch, bag and all, when I foolishly left it in the shade of the vehicle while I measured a section. My students and I have been dissuaded more than once from visiting a particular outcrop by aggressive, bellowing camels standing their ground and looked very, very big and toothy. I was thus a bit hesitant when Yoav just walked up to this beauty on our way to the center of Makhtesh Gadol. I followed and did just fine within touching distance. This is a female (hence the lack of attitude) and a pregnant one at that. She is part of a small herd owned by a Bedouin family that may or may not have an arrangement to graze animals in this nature reserve. She eased my camel anxieties.

camel bed fossils 041814After our encounter I realized that camels actually play a role in our work. This is one of our most productive fossils sites (“GPS 055”). It is an exposure of a marl in subunit 51 in the Matmor Formation. This is also a camel resting spot. They love the soft sediment, probably as a break from the rocky soil elsewhere. We thus find such dry camel wallows often in our explorations of the Matmor. By stirring up the marl, the camels unearth fossils that would otherwise lay hidden.

Random Echinoderm bits 041814Here is a random assortment of crinoid and echinoid bits found in this camel haven. If we ignore the poop and flies, and avoid the angry males, these camels have done us a scientific favor!

“I know a tree”

April 17th, 2014

Acacia distant 041714MITZPE RAMON, ISRAEL–I met this particular tree in 2003 when searching for a good place to have lunch. Yoav said, “I know a tree”, and then we drove a half-hour to get to it. As you can tell, trees are not particularly common in Makhtesh Gadol. Now this acacia has served as a resting place for a dozen Wooster geology students over the years. Its patchy shade is welcome indeed. Today I had a lonely little lunch of nuts and fruit underneath it, with the magnificent makhtesh walls surrounding me.

Acacia close 041714Acacia trees are critical for wildlife and domesticated animals in this region because they maintain an African metabolic timing, being greenest during the hot, dry Negev summer as a genetic memory of the contemporary wet season in Africa. Animals depend on this bounty, despite the thorns and stinging ants. Acacia is known as “shittim wood” in the Bible, where it is mentioned several times.

Makhtesh Gadol 041714I had the beautiful Makhtesh Gadol to myself today. The Passover holiday is a sort of Spring Break for Israelis, so the roads are miserably crowded, even through the Negev. Once I get here, though, I’m in a closed nature reserve that no one can enter without a permit. I have the only permit now, so this is a place of complete solitude for me until I must return to the highway and civilization.

The Negev wildflower post

April 16th, 2014

A DSC_3602 copyMITZPE RAMON, ISRAEL–Today I worked in the Jurassic of Makhtesh Gadol and the Triassic of Makhtesh Ramon. A highlight was that I was joined by Yael Leshno, an Israeli master’s student on her way to a paleontology career. She was very good at finding crinoid parts in the Matmor Formation. Otherwise it was a dusty, windy, non-photogenic day. Time to post wildflower images!

DSC_3555 copyOf course, I don’t know what most of these flowers are, just that they’re pretty. The Negev had good winter and spring rains, so the wildflowers are abundant. [Update: Lyn Loveless, a biologist at The College of Wooster, tells us, “The first two photos are plants in the Brassicaceae (mustard family), and look a lot like Raphanus, wild radish. The one [below] – well, maybe a mint? Bifid stigma, four anthers.” Thank you very much, Lyn!]

DSC_3600 copyThere must be an interesting pollinator for this plant. James in the comments identified this flower as Echium judaeum. Thanks!

DSC_3595 copyI know I’ve identified this plant before, but the name now escapes me. It tends to be in moister parts of wadis. It might be Broomrape (Cistanche tubulosa), a parasitic plant that taps the roots of other plants.

Erodium cicutariumThis I learned is the Stork’s Bill (Erodium cicutarium). It is native to the Mediterranean and was introduced to North America over 200 years ago (and is now an invasive pest in some places). It has a very impressive way of distributing its seeds, one of which is shown in the center of this image.

DSC_3756 copyThe seeds of the Stork’s Bill are so common this spring that they blow around the desert landscape like snow. Each has a feathery shaft to catch the wind, and then a screw-like device that enables the seed to bury itself in the soil with changing humidity and the action of the wind on the shaft. This Wikipedia page on the plant has images of the seeds. Very r-selected!

DSC_3760 copyWhich brings me to this odd creature. You see here a collection of Stork’s Bill seeds bound together like a sheaf of wheat. In the lower right is the head of a caterpillar-like arthropod seeming to carry it along. When I touched it the head retreated into the seed mass.

DSC_3764 copyWhen I turned it over I observed that it is an agglutinated tube of some kind with sticks on the base and the feathery seeds on the top. It looks like a terrestrial equivalent of a caddisfly tube that is pulled along by the little beast. I’d love to hear if anyone recognizes this animal and its habit! [Update: Laura Sirot, a biologist at Wooster, has identified this as a Bagworm Moth. Todah raba, Laura!}

Return to the Jurassic Paradise of Makhtesh Gadol

April 15th, 2014

Makhtesh Gadol 041514MITZPE RAMON, ISRAEL–This week I’m back in Makhtesh Gadol, that great bowl of Jurassic delights. This is the most extensive exposure of marine Jurassic rocks in southern Israel, and it is highly fossiliferous. This is just a brief report. I’ll summarize the latest finds and ideas later.

Greened 608 041514Today I spent most my time sitting on these low outcrops at a place we affectionately call “GPS 004 C/W-608”. It is the most productive site for crinoids and their associated sclerobionts (organisms that lived on or in their skeletons, before or after death). There was something about the original distribution of these organisms, and then the preservation and landscape erosion, that makes this site so good. Today I was not disappointed.

MatmorCollectView070513Compare this view of the site in July last year with Oscar Mmari, Steph Bosch and Lizzie Reinthal (all Wooster seniors now). The winter and spring rains were a bit higher than normal in this part of the country, so the outcrop today looks positively overgrown! This picture makes me miss having my students along on this trip, but such are research leaves.

Holiday in Mitzpe Ramon

April 14th, 2014

Mitzpe Ramon edge 041414MITZPE RAMON, ISRAEL–Pesach (Passover) begins this evening at sundown, but essentially the holiday has started today as people prepare for this evening’s family seders. The town has gone very quiet as stores have closed and traffic dropped to almost no vehicles moving. I spent the day walking around the periphery of Mitzpe Ramon enjoying the beautiful weather and occasionally making some accidental geological observations. As you can see from above, it doesn’t take long to leave the city and enter The Wilderness.

Mitzpe Ramon archaeology 041414This is a small archaeological site on the western end of town. I don’t know much about it, other than it is likely Iron Age. Israeli archaeology students often map it for practice.

Western Makhtesh Ramon 041414A view of the western end of Makhtesh Ramon because … why not?

Mitzpe Ramon Camel 041414This feature is called The Camel for obvious reasons. It perches on the edge of the makhtesh and has long served as a beacon for a route in and out of the makhtesh. An observation platform has been built on it as a “saddle”. The units here are the En Yorqe’am at the base and the camel itself made of the dolomitic Zafit Formation.

Mitzpe Ramon En Yorqe'am 041414I took advantage of the quiet to visit a housing development and check out the problematic muddy dolomitic unit near the base of the En Yorqe’am.

Ibex 041414Finally, I met this young, friendly Nubian ibex (Capra nubiana), one of hundreds that calmly wander the streets here. He was happily eating bread slices that had been thrown out in preparation for Pesach.

 

Wooster’s Fossil of the Week: An unusual scleractinian coral from the Upper Cretaceous of Israel

April 13th, 2014

Aspidiscus 041114aOriginally this was going to be a mystery fossil for a crowd-sourced identification while I’m here in Israel doing fieldwork, but through the wonders of the internet I finally found a match for the strange fossil above: it is the scleractinian coral Aspidiscus König, 1825 (Family Latomeandridae) Yoav Avni and I found several specimens in the lower third of the En Yorqe’am Formation (Upper Cretaceous, Cenomanian) in the Negev of southern Israel. I had never seen anything like it before.

The view above is of the upper surface of this discoidal fossil. There are several short and seemingly random ridges, which I learned later are called monticules in this genus. Each monticule has a series of septa, or thin vertical partitions. This was a compound coral, meaning it had multiple polyps on its surface, presumably each sitting on a monticule.
Aspidiscus 041114bThis is a reverse view of the En Yorqe’am variety of Aspidiscus. The pits appear to be molds of a gastropod on which the young coral must have recruited. It then grew centripetally, making a fine series of growth lines across a soft sediment.
Aspidiscus cristatus diagramThis diagram from Pandey et al. (2011) is a diagram of Aspidiscus cristatus found in the Cenomanian of Sinai, not too far from here. (This species is also found in Algeria, Tunisia, Spain, Greece, and Afghanistan — all in the Cenomanian.) Note that the center of A. cristatus has two large crossing monticules and the Israeli specimen does not. This is why I’m keeping it in open nomenclature — it doesn’t appear to be the same species. A. cristatus is found in the middle to early late Cenomanian; the En Yorqe’am specimen seems so far to be only in the early Cenomanian. This may mean the Israeli version is an older species. Both clearly liked living in marly shallow marine sediments.
Aspidiscus symbiontsHere’s the bonus: look at the round holes in the upper surfaces of these two specimens. These are caused by symbionts of some kind that lived within the growing coral. You can see best in the specimen on the right how the coral grew around the symbionts, producing a kind of tube. Nice.

Sorry for the lower quality of images this week. I’m photographing the fossils as best I can with a bedside lamp, a tiny tripod, and a shirt for background.

References:

Avnimelech, M. 1947. A new species of Aspidiscus from the Middle Cretaceous of Sinai and remarks on this genus in general. Eclogae geologicae Helvetiae 40: 294-298.

Gill, G.A. and Lafuste, J.G. 1987. Structure, repartition et signification paleogeographique d’Aspidiscus, hexacoralliaire cenomanien de la Tethys. Bulletin de la Societe Geologique de France 3: 921-934.

Pandey, D.K., Fürsich, F.T., Gameil, M. and Ayoub-Hannaa, W.S. 2011. Aspidiscus cristatus (Lamarck) from the Cenomanian sediments of Wadi Quseib, east Sinai, Egypt. Journal of the Paleontological Society of India 56: 29-37.

Seeing the archaeological site of Shivta through a geologist’s eyes

April 12th, 2014

01 Yoav Shivta 041214MITZPE RAMON, ISRAEL–The tradition we’ve built over the years on our Israel expeditions is to travel to interesting places on Saturdays to take a break from work. Yes, it appears geologists never really stop geologizing, but then that’s not really “work”, is it? Today Yoav, part of his family and I went to the Nabatean-Byzantine city of Shivta to explore the ruins and ponder the role of geology in the development of the settlement. You can find Shivta on the map at N 30.88185°, E 34.62878°. This site was studied by several archaeologists over the years, but I’m most impressed by the visit of T.E. Lawrence here in 1914. (Yes, that Lawrence.)

The questions: Why did this city develop here off the main routes? Did climate change force the abandonment of this city along with many other Negev settlements? Obviously we’re just poking around with these, but Yoav has some really good observations.

02 Shivta drainage 041214Obtaining enough water in this very dry place would have been the first problem to solve. The area has a limestone bedrock that the inhabitants could cut and carve to make many channels to direct storm rainwater into cisterns for storage and use during the dry seasons. Here we see a channel cut directly into the bedrock floor of the city plaza. At the top of the image are rock slabs covering the channel. They would have extended for the whole length to reduce evaporation.

03 Shivta cistern 041214That drainage channel, and many others, leads to this large cistern in the center of the town. It is mostly filled with sediment now. During its use it was many meters deep and had plastered walls to reduce leakage. Archaeologists have calculated that enough water could be stored in this cistern and many others through the city to support the population. This is with present rainfall amounts (about 10 cm a year). These cisterns could be easily built because about a meter below the hard limestone is a soft sandstone that can be excavated quickly.

04 Shivta quarry 041214The building stones for Shivta were obtained in the city itself and a few dozen meters away. Here is one of the ancient quarries. The limestone can be split vertically and horizontal slabs removed for use. You thus only have to cut the stone in two dimensions rather than three.

05 Southern church Shivta 041214This is the beautiful Southern Church. It has a classic Byzantine design. The interiors were made with soft Eocene limestones that could be easily smoothed and carved, while the rougher limestones were used for support out of sight. Some fragments of facing marbles, imported from Italy, can be seen in the alcoves.

06 Stones southern church 041214The stone above is fine-grained Eocene limestone suitable for carving. The stone in the background is coarser limestone. This is a portion of the Southern Church.

07 Shivta rock ceiling 041214Wood is a rare material, so the roofs were made of stone slabs laid across stone arches. Yes, you can imagine the earthquake danger!

08 Northern Church 041214The larger Northern Church is in the background here. Note the thick, sloping walls, especially on the left side.

09 Northern church buttress 041214In this closer view of the walls (and the Avni family dog, Anicha — great outdoor dog!), we see that the bulk of them are made of the rough limestones, and they were constructed to buttress the failing original walls, a smooth portion of which can be seen in the top right. These buttresses were made after earthquakes destabilized the finished walls.

10 Shivta earthquake damage 041214Yoav is pointing here to further earthquake damage to the buttresses themselves. The Shivta people lived through several earthquakes and continued to reinforce their structures.

11 Shivta garden 1 041214To the north of the city is this spectacular garden. It is an experimental plot to see if economic plants like olives, carob and pomegranates can be grown with just the local water trapped in basins in the Byzantine manner. The experiment ended years ago and the plants are doing great.

12 Shivta garden 2 041214This is a carob tree (Ceratonia siliqua), which is an important source of food and medicine throughout the Mediterranean region. Clearly it does well under these circumstances.

13 Shivta garden 3 041214These are olive trees, with a field of wildflowers beneath. With present rainfall amounts enough water can be trapped for agricultural and domestic use in Shivta. The hypothesis that some sort of desertification event (a common idea) ended these desert settlements is difficult to support when the dry conditions of today can still support the original community. It was likely economics and politics that spelled the end of Shivta, not climate change. We also see how critical the local geology was to the early inhabitants of this isolated city. They chose the location well for the agricultural and economic conditions of the time.

 

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