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Found 5 results

  1. Dear members, today I want to talk about how one of the most widely known theories of the geo/palaeontological world was born. I'm referring to the the theory according to which an Asteroid Impact caused the end-Cretaceous extinction. Last weekend I have visited the exact spot where, essentialy, this theory was first developed. It is the K/Pg Boundary in the Bottaccione section in Gubbio, a medieval town that lies on the Appenine Mountains, in the heart of Italy (see the red arrow). A widely distributed rock that makes up these mountains is the pelagic limestone sequence of the Scaglia Rossa Formation. The Bottaccione section has been studied for decades, because it represents a rare case of a complete stratigraphic record across the Upper Cretaceous and lower Palaeogene, marked by an evolutionary succession of planktonic foraminiferal biozones. Cores have been extracted throughout the Bottaccione section: Since the 60's a team of italian and foreign scientist recognized a large contrast between the large and diversified association of Cretaceous foraminifers and an association of just a few "dwarf" species in the lowermost layers of the Paleogene. The gap represented by the 1-cm layer at the K/Pg boundary was difficult to explain with a hiatus, but on the other hand the geochronological scale of the '60s was not accurate enough to determine the time covered by the stratigraphic intervals. In the early 70's, a team led by the (then unknown) Walter Alvarez was exploring the palaeomagnetic properties of the Scaglia Rossa at Gubbio and how they could have been utilised to reconstruct the tectonic history of the Italian Peninsula. It ended up that the two teams joined up forces in a collaborative effort. Alvarez focused on the K/Pg layer trying to define how much time it would represent and asked for the help of his father, the nobel laureate Luis. Usually, the sedimentation rate of terrigenous clay or calcareous plankton was inferred, but not in the case of Gubbio. Luis came up with the idea of studying the extraterrestrial material, in form of cosmic dust particles and micrometeorites, that target the Earth. This material is made up of undifferentiated solar matter and it accumulates on the surface of the earth or on the sea floor with a concentration of parts per million of parts per billion (ppb). A trace element that was relatively easy to measure was Iridium, an element of the platinum group. The team expected two plausible results: 0,1 ppb if the clay layer had been deposited in thousand years or a non-detectable concentration, following a deposition in just a few years due to a brief episode of altered climatic conditions. Instead, an unexpected (and inexplicable) result of 3 ppb (later corrected to 9) was detected. Alvarez and colleagues suspected that something may have gone wrong with the analysis. At this point more samples of the boundary clay had to be analysed, also from other sections of the Scaglia Rossa Formation. The final result confirmed that there was an anomalous concentration of Iridium in the boundary clay layer in the order of 6 ppb (as mean concentration from four sections), thus thirty times more abundant than a background of 0.2 ppb measured in Upper Cretaceous and lower Palaeogene sections of the same formation. In the paper published on Science in june 1980, the authors did not limit themselves to explain the geological context of the K/Pg boundary mass extinction, but they formulated a new hypothesis that the anomalous concentration of iridium was the result of the impact of a 10-km-diameter asteroid, which would cause a global catastrophe by disrupting the world’s ecosystems and consequent mass extinction. Now, it's time for the pictures of the K/Pg section! This is a complete view from the other side of the road. The grey wall at the top is part of a medieval aqueduct You can easily distinguish between the white Cretaceous layers and the pink Paleogene layers. As you can see, not much is left! Since Iridium-enriched clay has been extracted for analysis by countless scientists and curious people, now you can see a large gap. In the past, you could have seen a normal section, like in this case, where Luis and Walter Alvarez posed for a picture: I took much of the information from a paper that outlines the history of research in Gubbio (http://paleoitalia.org/media/u/archives/07_Montanari__Coccioni_2019_BSPI_581.pdf). You can find the original 1980 paper here (https://science.sciencemag.org/content/208/4448/1095). Finally, if you'd like a more divulging report, don't miss the Walter Alvarez best-seller, "T. Rex and the Crater of Doom". Well, I hope I was clear and intriguing enough. Gubbio is an awesome place, for its history, geology, food and much more. You should really pay a visit if you are not far! Thank you for your attention, Fabio
  2. until
    NORTH COAST FOSSIL CLUB APRIL MEETING Our main speaker will be Nathan Smith who is a volunteer in the Vertebrate Paleontology Department at the Cleveland Museum of Natural History. The title of his talk will be "The Mesozoic Extinction". For this month's Collector's Corner you are invited to bring in your Mesozoic/Cretaceous Fossils for showing others and sharing information. The Public is Welcome!!!
  3. KT boundary micro glass

    From the album Invertebrates and plants(& misc.)

    Debris, including micro glass "beads" from melted earth ejected into the air, from the KT boundary burn layer. Garfield county, Montana, Hell Creek formation. Late cretaceous (duh) *i added "misc." to this album because this didn't fit anywhere, and I thought it was really cool and should definitely be included somewhere. **There could even be vaporized dinosaur material as part of the glass and melted debris included. There definitely was plenty of it, but I guess realistically, unless it became evenly spread into the atmosphere and airborne debris, this is too small an amount of ejecta, and by percentage such a minuscule amount of vaporized dino, so sadly there probably isn't any.
  4. https://www.telegraph.co.uk/science/2018/05/24/ancestor-living-birds-survived-asteroid-strike-couldnt-fly/ https://cosmosmagazine.com/palaeontology/asteroid-wiped-out-all-but-six-types-of-bird
  5. Aldebarania arenitea

    Found 8 Aug 2013. An extremely rare starfisht, it was 1 of less than 10 complete specimens ever found at that time. It was found in the sand layer of the Rocky Point member of the PeeDee. This layer contains abundant Flemingostrea subspatulata among other oysters along with Hardouinia mortonis and kellumi echinoids. This starfish was invertebrate fossil of the month in 08/2013.
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