THE SAARLOUIS SEMI CRATER STRUCTURE: NOTABLE INSIGHT INTO THE SAARLAND (GERMANY) METEORITE IMPACT EVENT ACHIEVED

Kord Ernstson1, Werner Müller2, Andreas Gawlik-Wagner3

1Faculty of Philosophy I, University of Wurzburg, Germany ̈ 266809 Nalbach, Germany , 366763 Dillingen, Germany

Berlin

Köln

München

100 km

Saarlouis

Saarland impact

France

Dillingen

Nalbach

Saarlouis

Wallerfangen

Altforweiler

A 8

A 8

A 6201 km

semi crater

impact field

Nalbach crater

The Nalbach impactite strewn field and crater

Shock metamorphism, melt rocks and glasses in

the Nalbach impactite strewn fieldthin sections, photomicrographs; crossed polarizers (XX) and plane light (II).

Quartzite cobble completely transferred to diaplectic glass; XX and II.

Diaplectic sanidine crystals in diaplectic quartzite glass; XX and II.

Ballen structures in silica; XX and II.

Ballen structures merging in cristobalite and tridymite; XX and II.

Multiple sets of planar fractures (PF) and spots of diaplectic glass in quartz; XX.

Planar deformatiom features (PDF) in quartz; XX.

Strongly kinked mica (XX) and "toasted" quartz (II).

Multiple sets (white) of planar features in mica.

Strong shock meta-morphism as in proof of meteorite impact.

50 µm

50 µm

200 µm

electron images

CFe

Fe, O

C

500 µm

layeredimageLocation map for the Saarland meteorite impact event (to the

left): the Nalbach impactite strewn field established a few years ago and the recently discovered Saarlouis semi impact crater (to

the right).

Impact glasses in the Nalbach strewn field

Impact melt rocks in the Nalbach strewn field

The Saarlouis semi crater

Archeological excavation and find of impactites below foundations of a Romanesque church.

Digital Terrain Model (DGM 1): The 200 m-diameter (rim crest) Nalbach crater.

Ti Mn Fe

Suevite, SEM-EDS: iron-metallic spherules in basaltic-andesitic melt rock clasts.

S KCa

C OMg

Al SiP

mostly anorthite, also orthoclase, Mn-Mg pyroxene, andalusite?

Suevite breccia from the crater rim.

clast size grading and alignmentindicate flow texture

shock PDF in feldspar and quartz

500 µm

native iron spherule with carbon filaments

native iron spherules and andalusite re-crystallization(?)

vesicular iron - meltrock clast

Impact melt rock excavated during gas pipeline burying.

Melt rock matrix with moderately shocked quartz grains (q; and photomicrographs to the right) having obviously survived impact shock melting. Thin section photomicrographs, crossed polarizers.

1 mm

q

q

q

qcut face

1 cm

2 cm

Most larger quartz grains show multiple sets of planar fractures (PF) and fainter planar deformation features (PDF).Thin section

photomicrographs, crossed polarizers; field widths 150 µm.

2 cm

open spallation fissures filled with glass

2 cm

bone splinters in glass2 cm

mmscale

1 cm

1 cm

1 cm

Two quartz grains with open tensile, glass-filled spallation fractures

100 µm

200 µm

100 µm

100 µm

100 µm

100 µm

100 µm

400 µm

150 µm150 µm

fractured quartz grainsalmost pulverized

quartz, glass-filled open fractures

200 µm

1 cm

1 cm

after Google Earth

The Saarlouis semi crater: The rim wall crest (+) is forming a segment of a nearly perfect 2.3 km-diameter circle (to the left).

Geological map; simplified from Geoportal.saarland.de (to the right).

Map of shaded relief of the Digital Terrain Model (DTM) and profiles across the rim wall. For comparison other typical crater profiles are

shown. DTM data from LVGL Saarland.

The Saarland impact event - discussion and conclusions

The Saarlouis semi crater - meteorite impact evidence

-- The strong and widely distributed shock metamorphism, the impact glasses, the impact melt rocks and a suevite polymictic breccia establish a proven meteorite impact event near the German-French frontier. The discovery goes back to field observations and sampling by the coauthors W. M. and A. G.

-- So far two impact craters with diameters of 200 m (Nalbach) and 2.3 km (Saarlouis) and a classically countoured rim wall have been identified. Both are in part eroded to feature rather semi craters.

-- The widely distributed near-surface strongly shocked impactites are considered ejected material or/and restored by fluvial transport.

-- Impactites at 2 m depth excavated together with human bones from below the foundations of a Romanesque church in Nalbach exclude any anthropogenic/industrial products.

-- SEM-EDS analyses of suevite composition and formation remain puzzling and require more detailed studies of the in part igneous impact target not exposed in the investigated area.

-- According to the Lower Terrace sediments at the bottom of the Saarlouis semi crater the age of the impact event is Pleistocene or older.

Reference: Buchner, E. et al. (2011) 74th Ann. Meteoritical Soc. Meeting, Abstract #5048. Schmieder, M. et al. (2011). 74th Ann. Meteoritical Soc. Meeting. Abstract #5059. Ernstson, K. et al. (2013) Meteoritics & Planet. Sci., 48, s1, Abstract #5058. Berger, N. (2014) Diploma thesis, University of Trier. Berger, N. et al. (2015) 46th LPSC, Abstract #1255.