Impact-induced surface hardening of polished quartzite cobbles, Triassic Buntsandstein conglomerates, Northern Spain

by Kord Ernstson & Ferran Claudin (2012)

Shocked quartzite cobbles making up widely spread Triassic Buntsandstein conglomerates in Northern Spain have been reported (Ernstson et al. 1999, 2001) to be related to the Mid-Tertiary large Azuara multiple impact event with the formation of the Azuara impact structure and the Rubielos de la Cérida elongated impact basin (Hradil et al. 2001, Ernstson et al. 2001, 2002, Schüssler et al. 2002, Claudin & Ernstson 2003, Ernstson et al. 2003). The quartzite cobbles (and boulders) are peculiarly and intensively pockmarked and cratered (Figs. 1, 2) and show in general a closely spaced subparallel fracturing (Fig. 3). The cobbles’ characteristics become especially evident when they are found scattered in the field as a result of the conglomerate weathering (Fig. 4).

shocked and polished quartzite cobbles from Molina de Aragón

Fig. 1. Typically pockmarked, cratered and polished (the large boulder) quartzite cobbles and boulders from the Triassic Buntsandstein conglomerates.

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The Mesoarchaean Maniitsoq structure, West Greenland – a possible giant ancient impact structure

In the 1 July 2012 issue of the Earth and Planetary Science Letters journal an article has been published on a suspected 100 km sized impact structure that on verification would document the oldest cosmic collision on Earth so far known.

Adam A. Garde, Iain McDonald, Brendan Dyck, Nynke Keulen: Searching for giant, ancient impact structures on Earth: The Mesoarchaean Maniitsoq structure, West Greenland. – Earth Planet. Sci. Let., vol. 337-338, 197-210.

YDB impact: a new chapter

… or a “Requiem” for the rejection of the hypothesis?

YDB abbreviates Younger Dryas Boundary. The Younger Dryas stadial signifies a sharp onset of a period of cold climatic conditions in Earth’s history lasting roughly 1,000 years  between about 11,000 and 10,000 B.C. at the end of the Pleistocene (the “Ice Age”) and the beginning Holocene.

The causes of this event are controversially disputed, and they are conventionally ascribed to perturbations of  North Atlantic circulation. In 2007, a new hypothesis on a giant meteorite impact Continue reading

Chiemgau impact: a probable doublet meteorite crater in Lake Chiemsee

Kord Ernstson (2012)

Since a few years there is evidence of a doublet meteorite crater at the bottom of Lake Chiemsee (Fig. 3) in the Chiemgau meteorite crater strewn field. The search for a suspected impact into the lake was originally based on reports of fishermen about unusual sharp-edged large stones at the lake bottom that had damaged their fishnets. Such stones are in fact foreign matter in the lake. A general echo sounder campaign, followed by a detailed survey veritably revealed a peculiar structure, likewise a foreign element in the lake (Fig.1), with all evidence of a rimmed doublet crater. The similarity to meteoritic dual craters on Mars that formed synchronously by twin projectiles is striking (Fig. 2).

doublet meteorite crater at the bottom of Lake Chiemsee, Chiemgau impactFig. 1. The proposed meteorite doublet crater at the bottom of Lake Chiemsee from detailed SONAR echo sounder measurements. Meter scale indicates water depth.

comparison of doublet meteorite craters on Mars and in Lake Chiemsee, Chiemgau impactFig. 2. Meteoritic dual craters on Mars (image source NASA) and a counterpart at the bottom of Lake Chiemsee: A remarkable similarity. The more diffuse contours of the Lake Chiemsee craters is not surprising because of the impact into water and a loosely bound and water-saturated sedimentary target below.

More evidence of a meteorite impact into the lake came up with the frequent finds of pumice at the shore of Lake Chiemsee (more can be read HERE) and the observation of very young tsunami deposits uncovered in the environs of the lake (see HERE and HERE).

Lake Chiemsee Bavaria Chiemgau impact Fig. 3. Location map for the Lake Chiemsee in southeast Bavaria hiding the probable meteorite doublet crater.

Unfortunately, because of the deep water the crater is not accessible directly.

 

 

Earthquakes and meteorite craters: Rock liquefaction phenomena and the Chiemgau impact.

The impact of cosmic bodies to produce large impact craters is related with the propagation of seismic waves which may release energies comparable to strongest earthquakes, and even beyond that. It is obvious that similar processes and well-known drastic deformations may result in the ground and at the earth’s surface.

In this context, W. Alvarez and coauthors (Alvarez W., Staley E., O’Connor D., Chan M.A., Synsedimentary deformation in the Jurassic of south-eastern Utah, a case of impact shaking? Geology, 1998, 26, 579-582) went into an interesting question when they related characteristic deformations in exposed older geological layers with a possible meteorite impact in a past geologic epoch thus pointing to the Upheaval Dome impact structure (Utah, USA) and distant rock liquefaction phenomena. Rock liquefaction is an established process during strong earthquakes which can lead to enormous modifications of the earth’s surface and catastrophic damage when the seismic shock affects water-saturated uncemented rocks. For the study of earlier earthquakes in the geologic past (paleoseismicity), observations in older layers may be important, and Alvarez had now pointed to the possibility that fossil sedimentary liquefaction features need not necessarily have originated from earthquakes but may be related with former large impact events. A critical debate, however, submitted that in the special case such a context of the relatively small 6 km-diameter Upheaval Dome impact structure and the geological outcrop some 260 km apart must be questioned.

Now for the first time, a compelling direct evidence for the relation of a large meteorite impact with distinct rock liquefaction features has been established. The recently printed article

Ernstson, K., Mayer W., Neumair, A., and Sudhaus, D. (2011): The sinkhole enigma in the alpine foreland, Southeast Germany: Evidence of impact-induced rock liquefaction processes. – Cent. Eur. J. Geosci., 3(4), 385-397.  DOI: 10.2478/s13533-011-0038-y 

describes the first geologic and geophysical investigations of the so-called “Thunderhole” (in German: Donnerloch) phenomenon in the region of the town of Kienberg north of Lake Chiemsee in Southeast Bavaria (Germany).

soil liquefaction from Chiemgau meteorite impact

Fig. 1. A freshly caved-in and a somewhat older thunderhole near the town of Kienberg north of Lake Chiemsee. Strikingly different from customary and well known sink holes e.g. in karst areas, the thunderholes exhibit a highly energetic rock mass transport from the bottom up before collapse, which is typical for liquefaction processes. 

The authors conclude that the innumerable enigmatic sudden sinkhole cave-ins having happened in living memory originate from late and even today acting processes of an earlier shock-induced underground rock liquefaction known from strong earthquake shocks. The geologically prominent underground structures that have now been uncovered are considered the result of impact shocks in the course of the formation of the Chiemgau meteorite crater strewn field (Chiemgau impact), and a comparison is made with the famous widespread and strong rock liquefaction features in the large region affected by the catastrophic 1811/1812 New Madrid (Missouri) earthquake series.

More detailed information about the geophysical measurements (resistivity and induced polarization (IP) soundings) of the thunderhole structures was given in a presentation at the 2011 Fall Meeting of the American Geophysical Union (AGU) in San Francisco:

Kord Ernstson & Andreas Neumair: Geoelectric Complex Resistivity Measurements of Soil Liquefaction Features in Quaternary Sediments of the Alpine Foreland, Germany. – AGU Fall  Meeting, December 5-9, 2011, NS23A-1555.

The poster may be clicked here.

geophysical evidence induced polarization

Fig. 2. From the geophysical investigation of the impact-induced thunderholes in the Chiemgau impact event. The geoelectrical measurements of induced polarization on a profile across an active depression as a precursor of a future thunderhole reveal perfectly clear the intrusion paths bottom up as a document of impact liquefaction.

 

Rubielos de la Cérida impact basin: New impact breccia dikes in Paleozoic silicate rocks

Breccia dikes (dike breccias) are a prominent feature in impact structures, and they have told us a good many about the processes of impact cratering. Among the yet known roughly 200 terrestrial impact structures, Azuara and Rubielos de la Cérida are providing the probably by far best insight into these fascinating geological configurations concerning abundance, exposure accessibility, and diversity with regard to geometry, dimensions and material (also see breccia/dikeshttp://www.impact-structures.com/spainrubielos-breccia-dikes). Recent extensive construction works (storage reservoir, freeway, railroad) near Lechago, Calamocha (CAL; see Fig. 1, red circle) have yielded quite a few nice geological exposures once more documenting the almost everywhere existing impact signature thus underlining that construction work in the large impact region of the Azuara and Rubielos de la Cérida structures may be a hard undertaking – as was impressively shown when the new Autovía freeway line had to cut through the strongly destroyed Paleozoic of the Iberian Chain in the northern rim zone of the Azuara impact structure between Daroca and Cariñena (click here http://www.impact-structures.com/impact-spain/the-azuara-impact-structure/the-2005-autovia-mudejar-geological-exposures/ “The 2005 Autovía Mudéjar geological exposures”).

Below we show images of some newly exposed impact breccia dikes near Lechago exhibiting their characteristic properties and, for comparison, similar dikes and dike systems from the companion Azuara impact structure (location in Fig. 1).

Focusing here on breccia dikes in Paleozoic silicate rocks bears in mind the frequent claim of some Spanish geologists, especially from the Zaragoza university, that the impact breccia dikes are all karst phenomena. Their confusion of breccia dikes with karst features, however, meets some difficulties in the case of silicate siltstones. Also fault breccias can clearly be excluded since these dikes are filled with allochthonous material as is typical for impact-induced highly energetic injection processes.

location map Azuara Rubielos de la Cérida impact structures Spain

Fig. 1. Location map.

impact breccia dike cutting through Paleozoic siltstones Lechago Rubielos de la Cérida impact

Fig. 2. Thick impact breccia dike cutting through Paleozoic siltstones at the new storage reservoir near Lechago (in the red circle of Fig. 1)

impact breccia dike in Paleozoic siltstones; road to Santuario de la Virgen de Herrera Azuara impact

Fig. 3. For comparison: impact breccia dike in Paleozoic siltstones; road to Santuario de la Virgen de Herrera (1 in Fig. 1). Azuara impact structure.

two thick impact breccia dikes cutting Paleozoic siltstones, Autovía Mudéjar Azuara impact structure

Fig. 4. For comparison: thick impact breccia dikes cutting roughly perpendicular through the bedding of the Paleozoic siltstones. Autovía Mudéjar in course of construction; near Cariñena (2 in Fig. 1). Azuara impact structure.

system of impact breccia dikes Paleozoic siltstones Lechago storage reservoir Rubielos de la Cérida impact

Fig. 5. Large system of impact breccia dikes in Paleozoic siltstones at the new storage reservoir near Lechago. Note that the dominant set of dikes is cutting sharply across the bedding (see Fig. 6). In the top: Unfolded post-impact Tertiary sediments.

system of Rubielos de la Cérida impact breccia dikes in Paleozoic siltstones storage reservoir Lechago.

Fig. 6. Segment of the wall in Fig. 5.

System of impact breccia dikes cutting Paleozoic silicate rocks. Autovía Mudéjar Azuara impact

Fig. 7. For comparison: System of impact breccia dikes cutting sharply through Paleozoic silicate rocks. Autovía Mudéjar in course of construction; near Cariñena (2 in Fig. 2). Azuara impact structure.

Regmaglypts on clasts from the Puerto Mínguez ejecta, Azuara multiple impact event (Spain)

comparable regmaglypts on meteorites and impact-affected limestone clasts Tabor meteorite and Rubielos de la Cérida impact

Fig. 1. Amazingly similar: Regmaglypts on the surface of the Tabor meteorite and on a limestone clast from the Puerto Mínguez impact ejecta.

Among the various deformation features exhibited by the carbonate clasts in the Puerto Mínguez ejecta deposit (striae, nail prints, grooves, rotated fractures, irregular fractures with complex bifurcations, mirror polish, etc), regmaglypted clast surfaces are a prominent feature (Fig. 1). For the first time described by K. Ernstson (2004), they establish clear evidences of an aerial transport of quite a few clasts of the ejecta.

 

regmaglypts on the surface of an iron meteorite ablation feature

Source: Cascadia Meteorite Laboratory, Portland State University

Fig. 2. A Gibeon meteorite exhibiting distinct regmaglypts.

Regmaglypts (or thumbprints) are reliefs commonly reported for the surface of some meteorites (Figs. 1, 2). The depressions originate from dynamic air pressure [continue …] and from selective erosion by material melting (ablation) off the surface of the meteorite on its passage through the atmosphere. The relief may show polygonal, spherical, rounded or elliptical shape, and a pattern like fingers over wet clay is frequent.

We suggest the ablation features observed in the ejecta have originated from a similar process that is carbonate melting and ablation off the surface on the passage of the ejecta clasts through the heated impact explosion cloud.

Of course, the depressions on the Puerto Mínguez clasts in a way remind of lapiés (karren) features on surfaces of exposed limestones. Lapiés consist of shallow, straight grooves or runnels incised into the limestone by solution. Because of the striae and polish regularly coating the regmaglypted surfaces, and because the regmaglyptic clasts are embedded as individuals in the ejecta matrix (Fig. 3), an in situ formation as lapiés can clearly be excluded.

regmaglypts on a limestone boulder embedded in the Puerto Mínguez impact ejecta

Fig. 3. The regmaglypted individual embedded in the Puerto Mínguez impact ejecta is incompatible with an in situ dissolution (“lapiés” formation).

Alternatively, the “lapiés” depressions existed already before the impact and survived rock fracturing, excavation, and emplacement of the ejecta. This can be excluded because many clasts are regmaglypted all around (Fig. 4), and the frequently observed sharp-edged ridges of the regmaglypts (Fig. 4) would not have survived the excavation and ejection process.

regmaglypts on all sides of a limestone boulder Puerto Mínguez impact ejecta

Fig. 4. Front and rear of a regmaglypted limestone clast from the Puerto Mínguez ejecta. The regmaglypts all around and the sharp ridges exclude a “lapiés” formation before excavation and ejection.

In a few cases, the ablation by obvious carbonate melting of the clasts has eaten deeply into the clast (Fig. 5) reminding of similar distinct ablation features of some meteorites (Fig. 6).

regmaglypted limestone clast Puerto Mínguez ejecta, deep-reaching ablation features

Fig. 5. A regmaglypted limestone clast from the Puerto Mínguez ejecta exhibits prominent ablation reaching deeply inside into the limestone clast. For comparison see the meteoritic ablation features in Fig. 6.

 Derrick Peak, Antarctica, meteorite deep-reaching ablation features

Fig. 6. The Derrick Peak, Antarctica, meteorite. Image courtesy of NASA.

An extended article on the Puerto Mínguez regmaglypted ejecta including many images can be read here.

Impact-affected limestone clasts with regmaglypts have been reported also from the Chiemgau impact. An article may be clicked.