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RuMert

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Hi all!

I was finally able to visit the Volga site thanks to a water level/ good weather window. The journey was mostly a success, I got a better understanding of the site, used new means of transportation and examined more of the shoreline. Among the finds were two dozens of marine reptile verts and bone fragments and LOTS of ammonites and other mollusks. Unfortunately the river level was not low enough, 1m higher than during my 1st trip, 0,5m lower than in the 2nd. But it was at least possible to walk the shore. There's still a lot more to do, but now I have a pretty clear idea how to maximize the hunt results for the next trip.

The report will be picture-heavy and divided into several blocks I'll be adding in the next few days. Let's start with the scenery.

IMG20201009115441.jpg

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That bacon looks a little raw! Thank you for the tour. I collect insects in addition to fossils so it was very exciting for me to see species I only see in academia!

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3 hours ago, RuMert said:

it was promptly consumed

How did it taste? :default_rofl:

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It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt

 

-Mark Twain

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Geologic setting

I was wrong when I said the site had been created by the Kuybyshev reservoir. The site existed previously while the reservoir moved the opposite bank eastward and accelerated erosion. The shore is productive for at least 40 km, with its most famous part being the Gorodishchi section (2km long).

This section was discovered by the expedition of P. Pallas (1801) and since then has been constantly in the field of view of researchers. Papers containing a description of this section number in dozens. The first description was given by R. Murchison (Murchison, Verneuil, Keyserling, 1845). A.P. Pavlov (1884, 1886) noted the presence of deposits which are currently related to the Kimmeridgian and the Lower Volgian. A.N. Rozanov (1919) described the Volgian part of the section. N.P. Mikhailov (1962) subdivided the Upper Kimmeridgian into zones and showed the presence of all the three zones of the Lower Volgian substage. Soon, he and P.A. Gerasimov (Gerasimov, Mikhailov, 1966) proposed the Gorodishchi section as the lectostratotype of the Volgian stage of the Jurassic.

 

A view of the section itself

ol.jpg

 

From below. We also see a thick light-gray layer at the bottom of the colorful pack of black and yellow layers. The former is the Kimmeridgian clay while the latter - Volgian shales, sandstones and marls. These two layers and stages dominate the landscape for dozens of kilometres.IMG20201012170734.jpg

 

see how many distinct layers are present making the slope look like a layered cake

IMG20201012162359.jpg

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What is Volgian?

 

Since the separation of the Upper Jurassic into the Kimmeridgian and Portlandian stages in 1849, the latter produced quite a discussion around its place in the geologic timescale. Three local units were used: Portlandian for the Anglo-Paris Basin, Tithonian for the Tethys and the Pacific region, and the Volgian for the East European Platform. Russian geologists used all of them with an emphasis on the Volgian stage. The main reason behind isolating the Volgian is substantially different conditions and ammonite zones. I don't think you hear often about such genera as Ilowaiskya, Zaraiskites, Pavlovia, Virgatites and Craspedites, while in the Volgian they define the stratigraphy. There were hardly any political reasons for supporting a separate stage, as many Soviet paleontologists advocated the use of Tithonian. In 1996 the Volgian Stage was deemed obsolete and removed from the Geologic Time Scale in favor of the Tithonian according to the guidelines of the Interdepartmental Stratigraphic Committee of the Russian Federation (ISC RF). Many prominent scientists still support the Volgian stage though. Some papers you could read on the subject are here and here. As to me, I prefer the Volgian as I was born on the Volga after all:D

And if you still wonder, the Volgian stage is named precisely after sites such as the one I describe here.

 

Here's a very approximate map of the shore. The Volgian and the Kimmeridgian intersect and are present everywhere, the related fossils showing up in most unusual locations. All I can say the Kimmeridgian is more pronounced in the north, so the majority of the surface-collected fossils will be from this stage with little Volgian ones, while more to the south - the other way round. There are still Volgian patches in the north and Kimmeridgian ones in the south, while in some locations they are mixed 50/50. 

IMG20201011102538.jpg

 

Does it look like the Jurassic Coast? In part. It's definitely a "sea" with a long fossiliferous shore relating to the Jurassic, with ammonites and ichthyosaur verts, where you surface-collect everything (it's just more efficient and safe). The differences are as follows: 

1. a bit later geologic stage, nothing older than Callovian, mostly Kimmeridgian and later;

2. the foreshore is much narrower, sometimes unpassable;

3. no empty big rocks, boulders with fossils are found in parts of the shore

4. softer matrix;

5. almost no concretions to crack, they do not form around fossils overlapping them;

6. looks like not so rich finds: I didn't see so many associated verts/ribs/scales as they frequently demonstrate in Britain;

7. No tides obviously, but there can be algal bloom:)

 
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In local Kimmeridgian fossils are squished and pyritised in clay

IMG20201010140143.jpg

 

They are later washed out and accumulated by waves in "pyrite pockets"

IMG20201010114039.jpg

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sometimes forming small "pyrite beaches", surrounded by clay

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Typical Kimmeridgian fossils: a crushed pyritised ammo, a blackened belemnite, a partly squished bivalve and a pyritised aptichus

IMG20201011114246.jpg

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A typical Volgian beach is made up of small pebbles and looks beautiful

IMG20201012162511.jpg

 

There could be bits of shale present

IMG20201012105925.jpg

 

As well as big boulders full of fossils

IMG20201012132026.jpg

 

with impressive ammo imprints and so on

IMG20201012105102.jpg

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IMG20201012130842.jpg

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It's really great to be able to see the various forms of preservation on these fossils. It helps you appreciate the well preserved ones which are on the market all the more.

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Greetings from the Lake of Constance. Roger

http://www.steinkern.de/

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