Archive for April 20th, 2014

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!

Wooster’s Fossils of the Week: A scleractinian coral and its tube-dwelling symbionts (Middle Jurassic of Israel)

April 20th, 2014

MatmorCoral010114aI have a weakness for the beautiful scleractinian corals of the Matmor Formation (Middle Jurassic, Callovian-Oxfordian) of southern Israel. This particular specimen is Microsolena aff. M. sadeki from locality C/W-367 in Hamakhtesh Hagadol, southern Israel. (The “aff.” in the name means “affinities with”. It is a way of saying this looks like a particular species, but we’re not quite sure.) This is a place we’ve now had ten Wooster Team Israel expeditions, the latest of which was last summer. The corals are a prominent part of the very diverse fossil fauna there. Note in the above side view of the specimen the star-shaped corallites (which held individual polyps) each with radiating septa. In the middle of the view you can see a narrow tube covered by coral skeleton. (More on this below.)
MatmorCoral010114bThis is a top view of the coral. It has a generally flat base and an upper surface with extended knobs. Usually this particular species is flat across the top as well as the base, giving it a platter shape as in this previous Fossil of the Week.
MatmorCoral010114cFlip the coral over and we see how it is preserved. The skeleton was originally made of the mineral aragonite, which dissolved after the death and burial of the colony. The resulting void was filled with stable calcite, preserving even fine details of the septa (see below). This delicate preservation, though, is only of the exterior of the skeleton. The interior is coarsely crystalline calcite with no trace of internal coral structures. This preservation, then, is properly called a cast, not true replacement.
MatmorCoral010114tubeThese scleractinian corals had many symbionts (organisms that lived with them). Among them were tube-dwelling worms, probably polychaetes, that spread across the surface. We know this happened while the coral was alive because, as seen above, the septa sometimes grew over the tubes. The tubes themselves are here preserved in three dimensions because they are originally calcitic and did not dissolve after death and burial.

We have much to learn about these gorgeous Jurassic fossil corals of Israel. They are virtually unstudied and offer a great opportunity for comparing them to the global Jurassic coral world.

References:

Martin-Garin, B., Lathuilière, B. and Geister, J. 2012. The shifting biogeography of reef corals during the Oxfordian (Late Jurassic). A climatic control?. Palaeogeography, Palaeoclimatology, Palaeoecology 366: 136-153.

Pandey, D.K., Ahmad, F. and Fürsich, F.T. 2000. Middle Jurassic scleractinian corals from northwestern Jordan. Beringeria 27: 3-29.

Reolid, M., Molina, J.M., Löser, H., Navarro, V. and Ruiz-Ortiz, P.A. 2009. Coral biostromes of the Middle Jurassic from the Subbetic (Betic Cordillera, southern Spain): Facies, coral taxonomy, taphonomy, and palaeoecology. Facies 55: 575-593.

Wilson, M.A., Feldman, H.R., Bowen, J.C., and Avni, Y. 2008. A new equatorial, very shallow marine sclerozoan fauna from the Middle Jurassic (late Callovian) of southern Israel. Palaeogeography, Palaeoclimatology, Palaeoecology 263: 24-29.

Wilson, M.A., Feldman, H.R. and Krivicich, E.B. 2010. Bioerosion in an equatorial Middle Jurassic coral-sponge reef community (Callovian, Matmor Formation, southern Israel). Palaeogeography, Palaeoclimatology, Palaeoecology 289: 93-101.