Wooster’s Fossils of the Week: Remanié fossils in the Lower Cretaceous of south-central England

August 22nd, 2014

Faringdon ammonite smThe last two editions were about a bryozoan and borings from the Faringdon Sponge Gravels (Lower Cretaceous, Upper Aptian) of south-central England. This week we have some Jurassic fossils from the same unit. That sounds a bit daft at first — Jurassic fossils in a Cretaceous unit? — until it becomes obvious that these are older fossils reworked into a younger deposit. In this case underlying Jurassic ammonites have been unearthed and tossed around with sediment in Cretaceous high-energy tidal channels. These older fossils in a younger context are called remanié, meaning they have been “rehandled” in a fancy French way.

The above image is an example of remanié in the Faringdon Sponge Gravels. It is a partial internal mold of a Jurassic ammonite. Drilled into it are several holes attributed to Early Cretaceous bivalves and called by the trace fossil name Gastrochaenolites. The ammonite fossil was eroded out of an outcrop of Jurassic rock and then bored while rolling around in what would become the Faringdon Sponge Gravels.
Ammonite frag 2 072014This is another Jurassic ammonite internal mold. The jagged lines are the sutures of the ammonite (remnants of the septal walls). This mold was phosphatized (partially replaced with phosphate) before it was reworked into the Cretaceous gravels. Many remanié fossils are phosphatized because of long exposure on the seafloor.
Ammonite frag 1 072014Finally, this is a fragment of another Jurassic ammonite internal mold in the Faringdon Sponge Gravels. It has an odd shape because it has disarticulated along the sutures. We are looking at the face of one of the septa, or at least where this septum would have been if it hadn’t dissolved. You can see some tiny borings that were made by Cretaceous polychaete worms.

In one of the cobbles in the Faringdon Sponge Gravels I found an identifiable ammonite. It was Prorasenia bowerbanki, which indicated that the cobble was derived from the Lower Kimmeridge Clay or Upper Oxfordian clays. The above ammonites are likely from the same Jurassic sequence. This means these fossils were roughly 45 million years old when they were reworked into the sponge gravels. Today it would be as if Eocene fossils were eroding out of a cliff and being incorporated within a modern sediment. When you think about it, this is a relatively common occurrence.

References:

Murray-Wallace, C V. and Belperio, A.P. 1994. Identification of remanié fossils using amino acid racemisation. Alcheringa 18: 219-227.

Pitt L.J. and Taylor P.D. 1990. Cretaceous Bryozoa from the Faringdon Sponge Gravel (Aptian) of Oxfordshire. Bulletin of the British Museum (Natural History), Geology Series, 46: 61–152.

Wells, M.R., Allison, P.A., Piggott, M.D., Hampson, G.J., Pain, C.C. and Gorman, G.J. 2010. Tidal modeling of an ancient tide-dominated seaway, part 2: the Aptian Lower Greensand Seaway of Northwest Europe. Journal of Sedimentary Research 80: 411-439.

Wilson, M.A. 1986. Coelobites and spatial refuges in a Lower Cretaceous cobble-dwelling hardground fauna. Palaeontology 29: 691-703.

Wooster’s Fossils of the Week: Abundant borings in Early Cretaceous cobbles from south-central England

August 15th, 2014

Faringdon cobble in matrix 071714Last week I described a cyclostome bryozoan on the outside of a quartz cobble from the Faringdon Sponge Gravels (Lower Cretaceous, Upper Aptian) of south-central England near the town of Faringdon. This week I’m featuring a variety of heavily-bored calcareous cobbles from the same unit. One is shown above in its matrix of coarse gravel. The holes are bivalve borings known as Gastrochaenolites. As a reminder, these gravels are very fossiliferous and were deposited in deep channels under considerable tidal current influence (see Wells et al., 2010).

Faringdon cobble 1 071714The large and medium-sized flask-shaped borings are all Gastrochaenolites. In the suite of cobbles described in Wilson (1986), there are three ichnospecies of bivalve borings: G. lapidicus, G. cluniformis and G. turbinatus. It is thus likely, although not necessarily, an indication that at least three bivalve species were boring the soft calcareous claystone to make secure homes for their filter-feeding. The thin, worm-like borings are Maeandropolydora, which were probably made by polychaete “worms”.

Faringdon cobble 3 071714Some of the Gastrochaenolites lapidicus borings have remarkably spherical chambers, a testament to the uniform lithological character of the rock.

Faringdon cobble 5 071714Occasionally bivalve shells are found still preserved in their crypts, along with nestling brachiopods. Some shell bits are visible in the borings above.

FaringdonCobble 585 071714Some of the cobbles are so heavily bored that they fall apart quickly on removal from the matrix. On the Cretaceous seafloor this intensity of boring must have reduced many cobbles to bits before burial — a classic example of bioerosion.

Diagram 071714What is very cool about these Faringdon cobbles is that the borings often overlapped inside, creating a network of tunnels and small cavities that hosted dozens of bryozoan, foraminiferan, sponge, annelid worm, and brachiopod species. This is a diagram from Wilson (1986) showing the combination of external encrusters in a high energy, abrasive world, and coelobites (cavity dwellers) in the protected enclosures. A diverse community can be found on each cobble, inside and out. In a future post I will describe some of these coelobite fossils.

References:

Pitt L.J. and Taylor P.D. 1990. Cretaceous Bryozoa from the Faringdon Sponge Gravel (Aptian) of Oxfordshire. Bulletin of the British Museum (Natural History), Geology Series, 46: 61–152.

Wells, M.R., Allison, P.A., Piggott, M.D., Hampson, G.J., Pain, C.C. and Gorman, G.J. 2010. Tidal modeling of an ancient tide-dominated seaway, part 2: the Aptian Lower Greensand Seaway of Northwest Europe. Journal of Sedimentary Research 80: 411-439.

Wilson, M.A. 1986. Coelobites and spatial refuges in a Lower Cretaceous cobble-dwelling hardground fauna. Palaeontology 29: 691-703.

Wooster’s Fossil of the Week: An Early Cretaceous cobble-dwelling bryozoan

August 8th, 2014

Faringdon quartz 071714One of my formative experiences as a young paleontologist was working in the Faringdon Sponge Gravels (Lower Cretaceous, Upper Aptian) of south-central England while on my first research leave in 1985. (I was just a kid!) These gravels are extraordinarily fossiliferous with sponges, brachiopods, corals, vertebrate bones, and a variety of cobbles, both calcareous and siliceous. These coarse sediments were deposited in narrow channels dominated by tidal currents with significant energy reworking and sorting the fossil and rock debris. Above is a cobble of very hard vein quartz from the Sponge Gravels. On the left end you see an encrusting bryozoan with an unusual morphology.
LhwydThe fossils of the Faringdon Sponge Gravels have been studied for a very long time. The first formal notice of them is a museum catalogue compiled by Edward Lhwyd (image above) and published in 1699. Lhwyd (1660-1709) was a Welsh natural philosopher better known by his Latinized name Eduardus Luidus. He had an unfortunate childhood being the illegitimate son of what has been reported as a “dissolute and impractical” (and poor) father. Still, he was better off than most and had schooling all the way up to Oxford (but he could not afford to graduate). In 1684 he became an assistant to Robert Plot, the Keeper of the Ashmolean Museum in Oxford. He became a great scientific traveler and collector, specializing in plants and fossils and (eventually) ancient languages of Britain. In 1691 he was appointed Keeper at the Ashmolean. His book detailing fossils of Britain (Lithophylacii Britannici Ichnographia) was published with financial assistant from his good friend Isaac Newton.
Corynella in Lhwyd plate 18This is plate 18 from Lhwyd (1699). The fossil in the upper right is the sponge Corynella from the Faringdon Sponge Gravels.

Lhwyd’s views on the origin of fossils are with describing. This is a summary from Edmonds (1973, p. 307-308):

He suggested a sequence in which mists and vapours over the sea were impregnated with the ‘seed’ of marine animals. These were raised and carried for considerable distances before they descended over land in rain and fog. The ‘invisible animacula’ then penetrated deep into the earth and there germinated; and in this way complete replicas of sea organisms, or sometimes only parts of individuals, were reproduced in stone. Lhwyd also suggests that fossil plants known to him only as resembling leaves of ferns and mosses which have minute ‘seed’, were formed in the same manner. He claimed that this theory explained a number of features about fossils in a satisfactory manner: the presence in England of nautiluses and exotic shells which were no longer found in neighbouring seas; the absence of birds and viviparous animals not found by Lhwyd as fossils; the varying and often quite large size of the forms, not usual in present oceans; and the variation in preservation from perfect replica to vague representation, which was thought to represent degeneration with time.

What is most interesting about these ideas is that they have no reference to Noah’s Flood or other divine interventions.

In 1708, Lhwyd was elected a Fellow of the Royal Society in 1708. He didn’t enjoy this privilege long for he died of pleurisy the next year at age 49.
Reptoclausa hagenowi Cretaceous England 071714Now back to the bryozoan on the Faringdon cobble. It is the cyclostome Reptoclausa hagenowi (Sharpe, 1854). It has an odd form of irregularly radiating ridges of feeding zooids (autozooids) separated from each other by structural zooids (kenozooids). I like to think (although I have no evidence) that this morphology was resistant to abrasion in the rough-and-tumble life of living on a cobble in a high-energy channel. There are few other encrusters on the outer surfaces of the Faringdon cobbles.

The next two Fossils of the Week will also be from the fascinating Faringdon Sponge Gravels.

References:

Edmonds, J.M. 1973. Lhwyd, Edward, p. 307-308. In: Gillespie, C.C. (ed.). Dictionary of Scientific Biography, 8. Charles Scribner’s Sons, New York, 620 pp.

Lhwyd, E. 1699. Lithophylacii Britannici Ichnographia. London, 139 pages.

Meyer, C.J.A. 1864. I. Notes on Brachiopoda from the Pebble-bed of the Lower Greensand of Surrey; with Descriptions of the New Species, and Remarks on the Correlation of the Greensand Beds of Kent, Surrey, and Berks, and of the Farringdon Sponge-gravel and the Tourtia of Belgium. Geological Magazine 1(06): 249-257.

Pitt L.J. and Taylor P.D. 1990. Cretaceous Bryozoa from the Faringdon Sponge Gravel (Aptian) of Oxfordshire. Bulletin of the British Museum (Natural History), Geology Series, 46: 61–152.

Wells, M.R., Allison, P.A., Piggott, M.D., Hampson, G.J., Pain, C.C. and Gorman, G.J. 2010. Tidal modeling of an ancient tide-dominated seaway, part 2: the Aptian Lower Greensand Seaway of Northwest Europe. Journal of Sedimentary Research 80: 411-439.

Wilson, M.A. 1986. Coelobites and spatial refuges in a Lower Cretaceous cobble-dwelling hardground fauna. Palaeontology 29: 691-703.

Wooster’s Fossil of the Week: A fragment of an asteroid (the sea star kind) from the Upper Cretaceous of Israel

June 8th, 2014

zichor asteroid aboral 585This is not an important fossil — there is not enough preserved to put a name on it beyond Family Goniasteridae Forbes, 1841 (thanks, Dan Blake) — but it was a fun one to find. It also photographs well. This is a ray fragment of an asteroid (from the group commonly known as the sea stars or starfish) I picked up from the top meter of the Zichor Formation (Coniacian, Upper Cretaceous) in southern Israel (Locality C/W-051) on my field trip there in April 2014. We are looking at the aboral (or top) surface; below is the oral view.
zichor asteroid oral surface 585In this oral perspective you can see a group of tiny, jumbled plates running down the center. This is the ambulacrum, which in life had a row of tube feet extending out for locomotion and grasping prey.
asteroid 2004Above is a sea star held by my son Ted on Long Island, The Bahamas, back in 2004. You can see a bit of resemblance between this modern species and the Cretaceous fossil, mainly the  large knobby ossicles running down the periphery of the rays.

The asteroids have a poor fossil record, at least when compared to other echinoderms like crinoids and echinoids. It appears that all post-Paleozoic asteroids derive from a single ancestral group that squeaked through the Permian extinctions (Gale, 2013). There is a significant debate about the evolution of the asteroids (see Blake and Mah, 2014, for the latest). Unfortunately our little critter is not going to help much in its resolution.

Recently it has been discovered that some living asteroids have microlenses in their ossicles to provide a kind of all-surface photoreception ability. Gorzelak et al. (2014) have found evidence that some Cretaceous asteroids had similar photoreceptors. Maybe our fossil goniasterid fragment could yield this kind of secret property with closer examination.

References:

Blake, D.B. and Mah, C.L. 2014. Comments on “The phylogeny of post-Palaeozoic Asteroidea (Neoasteroidea, Echinodermata)” by AS Gale and perspectives on the systematics of the Asteroidea. Zootaxa 3779: 177-194.

Gale, A.S. 2011. The phylogeny of post-Paleozoic Asteroidea (Neoasteroidea, Echinodermata). Special Papers in Palaeontology 38, 112 pp.

Gale, A.S. 2013. Phylogeny of the Asteroidea, p. 3-14. In: Lawrence, J.M. (ed.), Starfish: Biology and Ecology of the Asteroidea. The Johns Hopkins University Press, Baltimore.

Gorzelak, P., Salamon, M.A., Lach, R., Loba, M. and Ferré, B. 2014. Microlens arrays in the complex visual system of Cretaceous echinoderms. Nature Communications 5, Article 3576, doi:10.1038/ncomms4576.

Loriol, P. de. 1908. Note sur quelques stellérides du Santonien d’Abou-Roach. Bulletin de l’Institut égyptien 2: 169-184.

Mah, C.L. and Blake, D.B. 2012. Global diversity and phylogeny of the Asteroidea (Echinodermata). PLOS ONE 7(4), e35644.

Wooster’s Fossil of the Week: A helpful echinoid from the Upper Cretaceous of Israel

April 27th, 2014

Echinoids a 042214These beaten-up fossils have served me well in the field this month. They are the regular echinoid Heterodiadema lybicum (Agassiz & Desor, 1846). They are common in the Cenomanian throughout northern Africa and the Middle East. These particular specimens, the other sides of which are shown below, are from the En Yorqe’am Formation we’ve been studying here on the rim of Makhtesh Ramon, southern Israel. When I find them in abundance I know I’m in the top half of that formation. They’ve previously been featured indirectly as a Fossil of the Week for the bites they made into the shells of oysters, producing the trace fossil Gnathichnus.
Echinoids b 042214The species Heterodiadema lybicum was named by Pierre Jean Édouard Desor (1811-1882) in 1846. We’ll meet him in a later entry. The genus Heterodiadema was erected in 1862 by Gustave Honoré Cotteau (1818-1894), who is pictured below. There is not much at all about Cotteau in the English literature, but with Google Translate I was able to sort out a bit of his story from the French. He was one of those glorious amateurs who make such important contributions to the science of paleontology. (I like the new term “citizen scientists” for this group, although I emphasize I’m a citizen too!) Cotteau was a judge in Auxerre, Burgundy, France. In his spare time he had a passion for living and fossil echinoids, eventually amassing a collection of over 500 species. He was also, as you might guess, a volunteer curator of the city museum in Auxerre. In 1889 he was President of the Société zoologique de France, a highly prestigious position. He was an important force in the early understanding of echinoderms.
Cotteau GustaveAgain, these specimen photos were taken under “field conditions” in Israel with a cleaner’s cloth for a background. As you read this, though, I am with luck back in my cozy home in Wooster.

References:

Agassiz, L. and Desor, P.J.E. 1846. Catalogue raisonné des familles, des genres, et des espèces de la classe des échinodermes. Annales des Sciences Naturelles, Troisième Série, Zoologie 6: 305-374.

Geys, J.F. 1980. Heterodiadema libycum (Agassiz & Desor, 1846), a hemicidaroid echinoid from the Campanian of Belgium.  Anales de la Societe geologique du Nord 99: 449-451.

Smith, A.B., Simmons, M.D. and Racey, A. 1990. Cenomanian echinoids, larger foraminifera and calcareous algae from the Natih Formation, central Oman Mountains. Cretaceous Research 11: 29-69.

Among citizen scientists in southern Israel

April 24th, 2014

Zichor M2 M3 042414MITZPE RAMON, ISRAEL–Today Yoav Avni and I drove south to meet an enthusiastic group of naturalists in Arava of the Jordan Rift Valley. The group is led by Dr. Hanan Ginat and consisted of a micropaleontologist and three amateur collectors who have all added considerably to scientific knowledge. We did fieldwork together in the magnificent Menuha Formation (Upper Cretaceous). The outcrop above is the boundary between a middle unit of the Menuha (“M-2″) and the upper chalks (“M-3″) in Wadi Zichor.

Gidon and fossils 042414Here is Gidon and a fraction of his collection, which is mostly from the local Cretaceous. There were fossil types here I’ve never seen before. Like all good citizen scientists, he knows how to collect and observe with location and stratigraphic control, and he has learned an immense amount about fossils and the organisms they represent.

Winny home 042414We had tea in Winny’s desert house. The interior (and exterior) is dominated by delightful fossils (and many other objects). It is a classic desert-dweller’s home. The micropaleontologist Sarit is in the foreground. (I have only phonetic first names. I’ll collect last names later!)

Stratodus Winny 042414Winny collected this four-meter long Cretaceous fish named Stratodus. She must now be the world’s expert on its complex anatomy. It is just a taste of her other fossils, including a bryozoan-encrusted ammonite from the Ora Formation (Turonian) she freely and eagerly gave me for research.

Field party 042414The field party is here assembled to study a site where they helped find and excavate an Elasmosaurus plesiosaur — the first in Israel.

Menuha view 042414A view of the Menuha Formation in the Arava. This is an extraordinary outcrop, and you can tell by the minimal vegetation that this is the driest part of the Negev.

I very much enjoyed my time with this fun and dedicated crew. They reminded me so much of the naturalists I grew up with in my own desert home of Barstow, California. I made many connections here that will benefit future research programs and Independent Study projects for Wooster students. It was inspiring to see what joy these people have in pursuing their scientific passions, like all other citizen scientists I work with.

This was my last day of fieldwork on this expedition. Tomorrow the long trip home begins!

Wooster Geologist in Jerusalem and the Judean Mountains

April 23rd, 2014

GSI buildings 042314MITZPE RAMON, ISRAEL–Very early this morning (5:05 am) Yoav and I boarded a bus in Mitzpe Ramon for a journey north to Jerusalem. After a change of buses in Beersheva, we arrived in Jerusalem 3.5 hours later. (This is Yoav’s commute to his office!) I was scheduled to give a morning talk at the Geological Survey of Israel‘s headquarters in a crowded haredi (ultraorthodox)  neighborhood. It is always a moment to leave the noisy streets and pass through a gate onto the campus of the Survey, shown above. This is an old British military base from the 1940s, and it shows the wear.

GSI parking 042314The parking here is incredible. The cars are closely imbricated. Drivers who blocked other cars leave their phone numbers on their windshields so they can be summoned to move. Some just leave their keys inside for others to shift them out of the way. Here’s an advantage of taking the bus! The Survey will have a new campus elsewhere in the city in about four years.

Talk chairs 042314Geologist and good friend Amihai Sneh is here setting up chairs for the talk in the conference/tearoom.

Talk set up 042314Here’s my lecture set-up ready to go. The talk went well enough, and my geological colleagues had a lot of good comments and ideas afterwards. As with any presentation, I was most pleased to have it over!

Yoav IS 042314After the talk and lunch, Yoav, Amihai and Eitan Sass (a well-known Israeli geologist and former advisor of Yoav) planned a fieldtrip to further explore Cenomanian units in an attempt to solve some correlation dilemmas. This is the same project we have been working on with the En Yorqe’am Formation to the south. We actually used Yoav’s equivalent of an Independent Study thesis he completed over 25 years ago in Jerusalem. It looks like a master’s thesis. A critical fence diagram from the work is shown above. It was very useful in our explorations.

Yoav Bet Meir Newe DanielYoav is here examining an exposure of the Bet Meir Formation in the Newe Daniel settlement in the southern West Bank. We examined it in several places, noting changes in the amount of dolomitization and fossil content. It was best exposed here because of recent construction.

Nodules Bet MeirDr. Sass has studied these nodules in the Bet Meir Formation and concluded they are after anhydrite nodules. In fact, some still have anhydrite entombed within later quartz replacement. This chalky sediment was likely influenced by flows of dense brines from nearby shallow evaporitic basins.

Newe Daniel 042314Did I mention we were in the West Bank? This was very interesting, and an unexpected visit for me. These settlements are entirely normal once you’re on the inside, but the various layers of security measures on the outside are impressive. I learned a lot about the history of this particular place from my colleagues. Complex, to say the least.

Herodium 042314History moment. From a tower in Newe Daniel you can see a curious conical mountain called the Herodium. It is far too steep to be natural. It was constructed by Herod the Great as a palace and his tomb. The recent discovery of the actual burial site is a dramatic story.

Jerusalem surrender monumentBonus history moment: On the walk from the bus station to the Survey headquarters, Yoav and I passed this monument to the surrender of Jerusalem to British troops on December 9, 1917. This too is a good story. It happened on this spot. Check out the famous image below from that day.

Ottoman_surrender_of_Jerusalem_restored

 

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.

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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