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!

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.

 

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!

Wooster’s Fossil of the Week: An echinoid from the Eocene of France

July 7th, 2013

newEchinolampas_ovalis_aboralThe above is a specimen of the echinoid Echinolampas ovalis (Bory de St Vincent, 1824) from the Eocene of Civrac-en-Médoc, France. We are looking at what is called the aboral surface — that part of the organism on the other side of its mouth. (I’m sure by now you recognize the little barnacle boring near the bottom of the skeleton.) Below is the oral view of the same specimen.

newEchinolampas_ovalis_oralEchinoids are a kind of echinoderm with a very long evolutionary history from the Ordovician to today. They include sea urchins, heart urchins and sad dollars, along with a few others. All echinoids are covered in life with numerous spines. These spines almost always fall off after the death of the organism, leaving the smooth test we see here. The tiny circles covering the surfaces of this specimen are spine attachments. In life this would have looked like a spiky ball.

In the center of the oral view is a large hole where the mouth was. The plates surrounding this are called the peristome (around-mouth). At the bottom on the oral view are two holes. The larger is where the anus was located (within the periproct of plates); the smaller is a circular boring, likely from a gastropod predator. Since the periproct is not in the center of the aboral surface, this is what is known as an irregular echinoid.
Echinolampas_ovalis_Eocene_Civrac-en-Médoc_France_CloseUp052013Above is a close-up of the center of the aboral surface. The radiating rows of holes were where tubefeet extended. These soft structures at the end of the water vascular system were used for locomotion, moving bits of food towards the mouth, and even respiration. The very center is a finely-porous plate called the madreporite (the opening for the water vascular system). The four holes around it are genital pores for releasing gametes into the water during reproduction. For a simple, globular organism, the echinoid is amazingly complex.
450px-Bory_Saint-Vincent_1778-1846Echinolampas ovalis was named by a scientist with a complex life story of his own. The dashing Jean Baptiste Bory de Saint-Vincent (1778-1846) was one of a remarkable generation of French zoologists. He began his career as a naturalist, studying the fauna on various French possessions in the Indian Ocean. He returned to France and became a soldier in the Napoleonic Wars, serving in the battles of Ulm (1805) and Austerlitz (1805), and participating in the disastrous French campaign in Spain. He was a Bonapartist to the end, opposing the Bourbon restoration, which resulted in exile from France. After his politics faded, he returned to France in 1820 and resumed his career as a traveling naturalist. He named dozens of living and fossil species of invertebrates after the wars, including our quiet little echinoid in 1824.

References:

Kier, P.M. 1962. Revision of the cassiduloid echinoids. Smithsonian Miscellaneous Collections 144(3), 262 pp.

Roman, J. 1965. Morphologie et evolution des Echinolampas (Echinides, Cassiduloides). Memoires du Museum National d’Histoire Naturelle, Nouvelle Serie, C, 15, 1-341.

Thum, A.B. and Allen, J.C. 1976. Reproductive ecology of the lamp urchin Echinolampas crassa (Bell), 1880 from a subtidal biogenous ripple train. Transactions of the Royal Society of South Africa 42: 23-33.

A visit to the Natural History Museum of Utah

May 29th, 2013

NHMU052913SALT LAKE CITY, UTAH–On the last full day of our Utah trip, we toured the Natural History Museum of Utah in Salt Lake City. It is in a spectacular place against the red rocks of the Wasatch Mountains and looking over the Salt Lake Valley. This museum has only been open since November 2011. Its exhibits are very up-to-date and modern.  (My test for recent accuracy is whether birds are acknowledged as dinosaurs and if Australopithecus sediba is in the human evolution section.) I’d like to just share some images from the museum and encourage anyone in Salt Lake City to visit it.

EoceneLake052913Dr. Judge will be impressed with the attention paid to exhibits on the Green River Formation (Eocene). This tableau is designed to show animals in the water (below) and on the beach (above). Note the stromatolites on the shoreline representing some of the features she and her students have worked on in the Green River Formation.

585_Deinosuchus_hatcheri_052913Utah is extremely rich in Mesozoic vertebrate fossils. Here is an impressive skeleton of Deinosuchus hatcheri from the Cretaceous.

CeratopsianWall052913The dinosaur exhibit is world-class. Here is a wall of ceratopsian dinosaur skulls showing evolutionary relationships.

DinoPelvis1_052913My History of Life students are well trained in sorting out major dinosaur groups by their pelvic bones. They could tell you, for example, if this is an ornithischian or a saurischian dinosaur.

DinoPelvis2_052913And this set is of the other group. Can you see the differences?

dinohead052913It appears this dinosaur had barnacles for eyes!

PaleontologistsBehindGlass052913Here is the classic paleontologists-behind-glass exhibit of a working laboratory. (I wonder why they never put working petrologists on display?)

NHMUview052913The architects knew exactly what they were doing when it came to designing the building to take full advantage of the setting. The Salt Lake Valley is fully visible from every floor.

What a great place to end our little Utah excursion this year. The real Team Utah of Wooster Geology will be back in the state next month.

Wooster’s Fossils of the Week: Mackerel shark teeth from the Eocene of the Atlas Mountains, Morocco

May 26th, 2013

OtodusCombined_585This week we highlight another gift to the Wooster Geology Department from George Chambers (’79). Among the many fossils that arrived in three delightful boxes were these shark teeth. They are from the extinct Mackerel Shark Otodus obliquus Agassiz, 1843. They were collected from the Eocene of the Khouribga Plateau in Morocco.
Otodus obliquus multiple 021313_585These shark teeth are rather common, although they are not often available in such fine preservation as these. What intrigues me is how they are collected and placed on the market. The Khouribga Plateau, west of the Middle Atlas Mountains, has some of the largest phosphate deposits in the world. These phosphorites (phosphate-bearing rocks) are mined in open pits by dynamite. After a blast, local commercial collectors rush in to gather fossils in the rubble before large processing machines arrive to process the ore. That can be a matter of minutes. They find many, many fossils in this phosphatic debris, mostly of reptiles and fish.
mackerelsharkThe lamnoid shark Otodus obliquus, a reconstruction of which is above, was a very large animal with some teeth over 10 centimeters in length. It may have been up to 9 meters long. Otodus obliquus was a “macro-predator”, meaning it was at the top of the food chain with a likely diet of marine mammals, fish, and other sharks. Its remains are found throughout the world in Paleocene and Eocene sediments. The fossil evidence suggests that this shark is an ancestor of the massive Carcharocles (“Megalodon”).

Thank you again, George, for these beautiful fossils!

References:

Agassiz, L. 1843. Recherches Sur Les Poissons Fossiles. Tome III (livr. 15-16). Imprimérie de Petitpierre, Neuchatel, p. 157-390.

Arambourg C. 1952. Les vertébrés fossiles des gisements de phosphates (Maroc-Algérie-Tunisie). Notes et Mémoires du Service Géologique du Maroc (Rabat) 92: 1-372.

MacFadden, B.J., Labs-Hochstein, J., Quitmyer, I. and Jones, D.S. 2004. Incremental growth and diagenesis of skeletal parts of the lamnoid shark Otodus obliquus from the early Eocene (Ypres) of Morocco. Palaeogeography, Palaeoclimatology, Palaeoecology 206: 179- 192.

Wooster’s Fossil of the Week: A pretty little fish from the Eocene of Wyoming

March 31st, 2013

Knightia_eocaena_033013_585Most people have seen this fossil fish type. Geologists, in fact, have probably seen Knightia eocaena Jordan, 1907, thousands of times. It is present in nearly every gift shop that sells fossils, usually as small plaques or glued to refrigerator magnets. It is the state fossil of Wyoming and, by all accounts, the most numerous fossil fish in the world. In fact, it is likely the most common vertebrate fossil ever. It is thus no surprise that Wooster has dozens of specimens, most of them donated by students and alumni.

Knightia lived in freshwater lakes throughout western North America during the Eocene. It is closely related to herring and sardines, and almost certainly had similar life habits. We know that it lived in large schools, and we suspect it had a diet of phytoplankton and insect larvae. It was low on the ecological food chain, just like its modern cousins, and so was an important food source for all sorts of larger fish, reptiles, birds and mammals.
MeagensFish585We tend to see most often beautifully preserved, complete Knightia specimens like the one at the top of the page. This is because if a fossil is very common, collectors can afford to keep only the best specimens. It is fun, though, to see what the average Knightia looks like in the fossil record. Above is a specimen collected by our petrologist Meagen Pollock from an outcrop in Wyoming. Note that the fish are contorted and often overlapping — specimens that are usually discarded by collectors. This slab shows better that these fossils occur in vast, complicated, messy death assemblages, probably because of volcanic ash falls or quick changes in lake chemistry.
Knightia_BW_TamuraThis is a digital reconstruction of Knightia (© N. Tamura). Note the deeply forked tail and flattened top of the head.

Dsjordan_wikipediaKnightia was named in 1907 by the accomplished and very problematic David Starr Jordan (1851-1931). Jordan was a well known fish expert, having been inspired by the iconic ichthyologist Louis Agassiz himself. He taught at several colleges and universities, eventually serving as president of Indiana University (at 34, the youngest university president at the time) and as the first president of Stanford University. He was a very successful university president, especially in the first years of Stanford.

But, but … David Starr Jordan was also a eugenicist, believing in compulsory sterilization of the “unfit”. On the bright side (if there is one here), he opposed war because it tended to kill the most fit members of society. Jordan also shockingly covered up the apparent murder of Jane Stanford, co-founder of the university, in 1905. Jordan does not look good at all in that story, most of which was sorted out only about ten years ago. Who would have guessed that a murder mystery could lurk in the taxonomic history of these pretty little fish?

References:

Grande, L. 1982. A revision of the fossil genus Knightia, with a description of a new genus from the Green River Formation (Teleostei, Clupeidae). American Museum Novitates 2731: 1-22.

Jordan, D.S. 1907. The fossil fishes of California; with supplementary notes on other species of extinct fishes. Bulletin, Department of Geology, University of California 5:136.

Wooster’s Fossil of the Week: A giant oyster (Eocene of Texas)

May 6th, 2012

It’s no ordinary oyster, of course, because it comes from Texas. It certainly is the largest oyster I’ve ever seen. Wooster received it as part of a large donation in 2010. (You can see students studying it in this previous blog entry.)

All we know is that it came from Texas (a notoriously big place) and the Eocene Series. It appears to be the extinct oyster Crassostrea gigantissima (Finch, 1824). Curiously, this is the first fossil species described from the Paleogene of North America (see Howe, 1937). It is worth quoting the entire description:

Fossils. This extensive formation is chiefly composed of a large species of ostrea, which I believe has not yet been described. A specimen of it may be seen in the Philadelphia museum; it is twelve inches long and two and three-quarters wide, and each valve from half to two and a quarter inches thick — Major Ware says they occur larger; on account of their great size I propose to call them Ostrea Gigantissima. The shells appear but slightly changed by their residence in the earth, and are in many parts used for burning into lime. (Finch, 1824, p. 40)

This is what it took to name a new species in 1824! Since then, of course, we have a detailed set of rules for naming animal taxa detailed in the International Code of Zoological Nomenclature. The Lawrence (1991) reference below is an example of what we often have to do in order to bring old names like “Ostrea Gigantissima” up to, well, Code.

The interior of the attaching valve of Crassostrea gigantissima.

The top surface of our giant oyster is riddled with these small holes. They are produced by the boring sponge Entobia, which is the next Fossil of the Week.

References:

Finch, J. 1824. Geological essay on the Tertiary Formations in America. The American Journal of Science and Arts 7: 31-42.

Howe, H.V. 1937. Large oysters from the Gulf Coast Tertiary. Journal of Paleontology 11: 355-366.

Lawrence, D.R. 1991. The neotype of Crassostrea gigantissima (Finch, 1824). Journal of Paleontology 65: 342-343.

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