New Evidence of Impact Origin of Smerdyachee Lake (Russia, Moscow Region)

NEW EVIDENCE OF IMPACT ORIGIN OF SMERDYACHEELAKE (RUSSIA, MOSCOW REGION)

Ivan I. Amelin1, Viacheslav K Gusiakov1,Dallas H Abbott2,Alexei К. Kiselev3, Dee L Breger2,4, Patrick McCafferty5

1 Institute of Computational Mathematics and Mathematical Geophysics, Novosibirsk, Russia,

2 Lamont -Doherty Earth Observatory, Palisades, New York, United States, 3 Minin University, Nizhny Novgorod, Russia, 4 Micrographic Arts, Saratoga Springs New York, United States,5 Queens University Belfast, Northern Ireland, United Kingdom

The heartland of Russia has many enigmatic deep lakes. Shallow lakes have a more obvious origin, perhaps as kettle lakes, oxbow lakes or subsidence features. Deep lakes, particularly round lakes with partial or complete rims are more problematic. Traditionally, round or nearly round lakes with rims are candidates for Holocene age impact structures. The problem is that there are too many such lakes in a relatively small area - Russia has a minimum of 15 deep, round lakes with diameters between 0.2 and 3 km. Even with a possibly increased impact rate during the Holocene, these deep lakes would represent the entire budget of Holocene impacts concentrated in only one region of the Earth.

One proposed impact lake is Smerdyachee near the town of Roshal in the Moscow region. This lake is perfectly round with a raised rim. It is situated on a Holocene fluvioglacial terrace between the Polya and Voimega rivers (Klyazma, Oka, Volga basin) (fig. 1).

Figure 1. Smerdyachee location map. Red circles: major cities. Green circles: lake-filled crater candidates. Black spot left of S in Smerdyachie: location of Ni-rich material on Smerdyachie rim. Smerdyachie is part of a field of deep, circular lakes of possible related origin.

It has a diameter of about 350 meters and a maximum depth of 38 m. Several Russian scientific groups previously explored this lake [1-3]. Because Smerdyachee is not a big impact crater, where the maximum shock pressure during the impact is enough to create obvious impact features, e.g. shatter cones or shocked minerals, it is not included in the Earth impact database [3]. Expeditions of the Holocene Impact Working Group (HIWG) to Smerdyachee in 2013 and 2014 collected some new data that further suggest an impact origin.

The HIWG expeditions found that the lake had a raised rim that was highest SE of the lake. Because of wild fires in 2010, the soil was deeply trenched around the lake. The trenches exposed many fragments of basement limestone. The overlying material consists of unconsolidated sand and silt-sized, quartz-rich sediments. We found clasts of brachiopod, crinoid and gastropod-bearing Carboniferous carbonate rock up to 32 cm in diameter on the SE rim of Smerdyachee. These clasts are present over about 1/3 of the total circumference of the lake. There are no limestone fragments in soil exposed more than about 200 meters from the edge of the lake. If Smerdyachee is a Holocene-age impact crater, this excavation of deeper horizons is expected. The maximum depth of excavation in an impact crater of 300-350 m diameter is nearly100 m. Local geological data verify this hypothesis: the basement at Smerdyachee is at ~40 meters depth. It consists of Carboniferous age carbonate rock with fossils of brachiopods, crinoids and gastropods.

The HIWG expeditions found many recently fallen trees along the rim. Unlike the dark organic rich soil at the surface, the soil in the root balls of the fallen trees was white and contained limestone fragments. Because the soil was exposed on a vertical surface, it was not susceptible to contamination from atmospheric deposition. We used an Nb super-magnet to sample this soil. Magnetic material from the soil in the root ball of a fallen tree on the SE rim contains Fe-rich particles and spherules with visible Ni in an energy-dispersive X-ray microanalysis (EDS). This fact is not enough to prove impact origin because there is a small probability we could find cosmic particles anywhere on the Earth's surface. We must first know the typical concentration of cosmic particles near Smerdyachee. If our samples have a significantly larger concentration of Ni-rich particles this would strongly suggest an impact origin.

In May 2014, a HIWG expedition made panned concentrates of the sediment on the rim. To the NW, the concentrated sediment has a negative magnetic susceptibility (-0.07 to -0.03 cgs units), consistent with a higher concentration of pulverized limestone. To the SE, the sediment has a positive magnetic susceptibility (0.06 to 0.35 cgs units). The areas of positive magnetic susceptibility lie on the SE two-thirds of the rim of the lake (fig.2).

Figure. 2. Location of investigated samples on the Smerdyachee lake rim. Red dots are fossil locations. Other dots are locations of measurements of magnetic susceptibility. The white dot has the highest value of magnetic susceptibility. Dark blue dots have negative values of magnetic susceptibility.

The highest susceptibility value is from the sample taken closest to the lake shoreline on the SE rim (fig. 2). This spatial distribution of susceptibility could mean that there is a higher concentration of iron-rich material on the SE side of the lake. To test this hypothesis, we plan to remove the calcium carbonate from our previously measured samples and then to remeasure their magnetic susceptibility. We will then examine the material with the highest magnetic susceptibility for possible impactor fragments.

This work was supported by RFBR grant 12-07-00564a and a special expedition grant of Siberian Branch of Russian Academy of Science.

References

1. Badjukov D. D., Brandstätter F., Ivanova M. A., Korochantsev A. V., Kurat G., Lorents C. A., Nazarov M. A., and Ntaflos T. The Smerdyachee Lake: A Possible Impact Crater near Moscow, Russia, in Proceedings Lunar and Planetary Science Conference, Houston, TX, 2003, LPI, p. 1566.

2. Kashkarov L. L., Badjukov D. D., Ivliev A. I., Kalinina G. V. and Nazarov M. A. The Smerdyacheye Lake: New Evidence for Impact Origin and Formation Age, in Proceedings Lunar and Planetary Science Conference, Houston, TX, 2005, Volume 36, LPI, p. 1822.

3. Engalychev S. Yu. Impact crater in the eastern part of Moscow region in Vestnik Sankt-Peterburgskogo universiteta. Ser. 7, 2009, V. 2. p.3-11. (in Russian)

4. Spray, J. G., 2013, Earth Impact Database: Frederickton, NB, Canada, University of New Brunswick.