Under the scanning electron microscope (SEM): The odd world of the iron silicides from the Chiemgau impact meteorite crater strewn field (click to enlarge). Contribution to the mineralogy meeting of the Russian Academy of Sciences in Syktyvkar:

Meteorite impact on a micrometer scale: iron silicide, carbide and CAI minerals from the Chiemgau impact event (Germany)

 Michael A. Rappenglück1, Frank Bauer2, Kord Ernstson3, Michael Hiltl4

1 Institute for Interdisciplinary Studies, Gilching, Germany; mr@infis.org - 2 Oxford Instruments GmbH NanoScience, Wiesbaden, Germany; Frank.bauer@oxinst.com – 3Faculty of Philosophy I, University of Würzburg, Germany; kernstson@ernstson.de – 4 Carl Zeiss Microscopy GmbH, Oberkochen, Germany; mhiltl@online.de 

Shortly after the meeting between the 19th and 22nd May in Syktyvkar the Proceedings volume has been published:

Problems and perspectives of modern mineralogy (Yushkin Memorial Seminar–2014) Proceedings of mineralogical seminar with international participation Syktyvkar, Komi Republic, Russia 19–22 May 2014

The Rappenglück et al. contribution condenses the mineralogical evidence of the iron silicides from the Chiemgau impact crater strewn field that has been compiled with invaluable support by Carl Zeiss Microscopy und Oxford Instruments NanoScience.

We remind of the fact that in the beginning of the research on the Chiemgau impact the group of quite experienced local historians and amateur archeologists had detected the metallic iron silicides and, after having been aware of their relation to crateriform structures, had published the possible meteoritic origin of the matter. Investigations and attempts, respectively, to dismiss all iron silicides as industrial waste product, or at least as terrestrial, followed, and they are still spread rumors as for instance by the Bavarian Geological Survey (Landesamt für Umwelt, LfU) which is commented (in German) elsewhere and may be clicked HERE.

Ultimately it is evident that these local historians who later got together with scientists from geosciences, astronomy, archeology and historical scholarship to establish the Chiemgau Impact Research Team (CIRT), are proved right!

The abstract article from the Proceedings volume may be clicked HERE. The corresponding, much more informative POSTER may be clicked also for download. PLEASE NOTE: Depending on the selected browser the screen quality may appear quite different. As the case may be we suggest to save the file on the computer and to activate it with a pdf reading program. WARNING: The poster pdf has a size of more than 50 megabyte.

In addition to the report on the microtektites from the foothills of the Alps we present here the LPSC abstract paper (click to open the full article):

Tektites are well-known gravel-size natural glasses that according to current knowledge form in the very early process of impact cratering by melting and/or vaporizing of superficial soil and rocks ejected as melt or vapor from the impact crater. On reentry in the atmosphere and cooling, the glass bodies exhibiting characteristic shapes fall to Earth where they form part of the impact ejecta. By definition tektites that are smaller than 1 mm are called microtektites. Although the origin of tektites from impact events is generally accepted the exact mode of formation is not well understood.

In the Chiemgau meteorite crater strewn field impact glasses are found widespread in various formations, and tektite-like bodies of a dense black glass with vesicles have attracted considerable attention (Fig. 1).

Fig. 1. Dense black glass particles from the Chiemgau impact strewn field frequently exhibiting tektite-like shape and twisted form similar to irghizites from the Zhamanshin impact crater. These are NOT the Chiemgau microtektites! – Click to enlarge.

Outside the crater strewn field in the foothills of the Alps at some 1500 m altitude (Fig. 2) a systematic search for impact fallout has revealed not only abundant tiny iron silicide particles (e.g., minerals xifengite and gupeiite) but also microtektites widely distributed in the soils (Fig. 3).

Fig. 2. Location map for the Chiemgau impact meteorite crater strewn field and the sites of the microtektite finds. Google maps. – Click to enlarge.

They show the very typical splash shapes like spheres, teardrops and irregular dumbbells (Fig. 3). They are fully transparent and have a mostly yellowish-brownish-grayish color. Bubble inclusions are frequent.

 Fig. 3. Typically shaped microtektites from the soil in the foothills of the Alps near the Chiemgau impact crater strewn field. Optical microscope images, 100 µm scale bar in each case.

The SEM micrographs in Fig. 4 especially point to the in part very strange surface features and bizarre forms exhibiting micrometer-sized glass filaments and twisted bodies.

Fig. 4. SEM images of microtektite-like glass particles.
Note the tiny, micrometer-sized glass filaments (lower
right) of the particle over it.

Relations

Microtektites are known, e.g., from the North American strewn field (cores from the Deep Sea Drilling Project), from the Australasian tektite strewn field, from the Ivory Coast strewn field and seem to be associated with the Chicxulub KT impact and Late Eocene impacts. A problem with proposed microtektite occurrences may arise from a possible confusion with spherules of an origin other than from impact vapor/melt solidification especially when a direct relation with an impact site is lacking. Even volcanic spherules may show dumbbell and teardrop shapes, while industrially produced microscopic glass spheres (e.g. from fly ash) have in general no teardrop or dumbbell counterparts.  A comprehensive consideration of the various possibilities including volcanic, man-made and even organic matter is given by Glass & Simonson (2013).

In the case of the Chiemgau impact microtektites a confusion with volcanic or man-made glass particles can be excluded with a high degree of probability since the very nearby really existing impact site and the exceptionally typical shape of known microtektites provide the simplest explanation for their origin. Nevertheless, a thorough analysis of their composition and a highly magnifying SEM imagery of their surfaces are in progress. Perhaps, some more insight into the general process of microtektite formation – in this case possibly as an impact vapor plume condensate – can be attained.

Reference

Glass, B. P. and Simonson, B.M. (2013): Distal Impact Ejecta Layers: A Record of Large Impacts in Sedimentary Deposits. – Impact Studies, 400 p., Springer.

A new Thunderhole (Donnerloch) and reactions

Since our contribution (Dec 2, 2011) on the impact-induced rock liquefaction (soil liquefaction) and the Thunderhole phenomenon, quite a few new sinkholes have occurred in the Kienberg region north of Lake Chiemsee. The latest somewhat spectacular cave-in happened two weeks ago. A family of mushroom pickers underway in the forest suddenly stopped at a freshly collapsed hole, 1-2 m in diameter and, as later measured, 8 m deep (Fig. 1). Having had a severe scare they at once informed police and fire department for securing the dangerous place. And this was the way the Thunderhole phenomenon for the first time found its way to the media, and newspapers, sound radio and television reported on this “fantastic story” widely initiating public awareness of this geologic hazard in the region. And now people got informed about large ponds and septic tanks having run dry overnight, about broken front axles when farmers had run with their tractor into a suddenly collapsed Thunderhole, about trees that suddenly began to incline, about beginning soil  subsidence several meters wide immediately besides a road, about a Thunderhole exactly on a crossroad, about big open cavities in the underground that had to be sealed by enormous quantities of cement before a new fire station could be built, and so on.

Fig 1. The new 8 m deep Thunderhole in the Kienberg region. Photo H. Schiebl.

To investigate the newly formed Thunderhole geologically we performed a geophysical survey of complex resistivity measurements (resistivity and induced polarization electrical imaging, Fig. 2), and we found the same geologic scenario we had established earlier when we had applied voluminous excavations and geoelectrics to other Thunderholes: The origin of the Thunderholes is closely related with soil liquefaction accompanied by strongest movements of  sand, gravel and big rock boulders bottom up, and the sinkhole character is a later, secondary effect only. And like with strongest earthquakes the Chiemgau Thunderhole rock liquefaction was initiated by the shock of the gigantic Chiemgau meteorite impact event in the Bronze Age/Celtic era.

Fig 2. The Thunderhole sinkhole and a larger endangered area seen in apparent resistivity and induced polarization pseudosections.

Amazingly (not to say ridiculously enough), the officials of the geological survey of Bavaria (Landesamt für Umwelt, LfU) and the local geologist Dr. Robert Darga from the Siegsdorf museum are completely trivializing the phenomenon declaring the Thunderholes as dead-ice holes and speaking of quite normal sinkholes as having occurred in thousands all over Bavaria. Hence they are absolutely ignoring the detailed geological and geophysical investigations of the phenomenon, while contradicting all serious science and research. To understand this highly nonscientific behavior one must know that the officials of the geological survey and Dr. Darga are fearing the Chiemgau impact event come hell or high water …

THE CHIEMGAU METEORITE IMPACT SIGNATURE OF THE STÖTTHAM ARCHAEOLOGICAL SITE (SOUTHEAST GERMANY)

K. Ernstson, C. Sideris, I. Liritzis, A. Neumair