Abstract-The M alingen structure is an approximately 700 m wide, rimmed, sediment-filled, circular depression in Precambrian crystalline basement approximately 16.2 km from the concentric, marine-target Lockne crater (inner, basement crater diameter approximately 7.5 km, total diameter in sedimentary strata approximately 13.5 km). We present here results from geologic mapping, a 148.8 m deep core drilling from the center of the structure, detailed biostratigraphic dating of the structure's formation and its age correlation with Lockne, chemostratigraphy of the sedimentary infill, and indication for shock metamorphism in quartz from breccias below the crater infill. The drill core reveals, from bottom to the top, approximately 33 m of basement rocks with increased fracturing upward, approximately 10 m of polymict crystalline breccia with shock features, approximately 97 m of slumped Cambrian mudstone, approximately 4.7 m of a normally graded, polymict sedimentary breccia that in its uppermost part grades into sandstone and siltstone (cf. resurge deposits), and approximately 1.6 m of secular sediments. The combined data set shows that the M alingen structure formed in conjunction with the Lockne crater in the same marine setting. The shape and depth of the basement crater and the cored sequence of crystalline breccias with shocked quartz, slumped sediments, and resurge deposits support an impact origin. The stratigraphic and geographic relationship with Lockne suggests the Lockne and M alingen craters to be the first described doublet impact structure by a binary asteroid into a marine-target setting.

The Experimental Projectile Impact Chamber (EPIC) is a specially designed facility for the study of processes related to wet-target (e.g., "marine") impacts. It consists of a 7 m wide, funnel-shaped test bed, and a 20.5 mm caliber compressed N 2 gas gun. The target can be unconsolidated or liquid. The gas gun can launch 20 mm projectiles of various solid materials under ambient atmospheric pressure and at various angles from the horizontal. To test the functionality and quality of obtained results by EPIC, impacts were performed into dry beach sand targets with two different projectile materials; ceramic Al 2 O 3 (max. velocity 290 m s À1 ) and Delrin (max. velocity 410 m s À1 ); 23 shots used a quarterspace setting (19 normal, 4 at 53°from horizontal) and 14 were in a half-space setting (13 normal, 1 at 53°). The experiments were compared with numerical simulations using the iSALE code. Differences were seen between the nondisruptive Al 2 O 3 (ceramic) and the disruptive Delrin (polymer) projectiles in transient crater development. All final crater dimensions, when plotted in scaled form, agree reasonably well with the results of other studies of impacts into granular materials. We also successfully validated numerical models of vertical and oblique impacts in sand against the experimental results, as well as demonstrated that the EPIC quarter-space experiments are a reasonable approximation for half-space experiments. Altogether, the combined evaluation of experiments and numerical simulations support the usefulness of the EPIC in impact cratering studies.

The well-documented, well-preserved, and well-exposed Lockne crater is a reference crater for marine-target impact on Earth. To date, it has been subjected to 11 short core drillings and over 5000 outcrop descriptions, as well as several geophysical surveys. The rich data allows detailed analysis of the cratering and modification processes. A unique feature with Lockne is its pristine ejecta layer. The ejecta differs, however, from the typical text book example of a land target crater in that it, to great extent, is made up of relatively extensive, coherent ejecta flaps resting on a target surface with no structural rim uplift. However, little is known about the marine impact excavation process generating the flaps. Here, we provide a lithological description coupled with an analysis of the rock magnetic properties of the Lockne-9 core through the western, downrange ejecta flap. The 31.04m long drillcore shows ~23m of monomict (mafic) breccia overlying a ~5m thick mixed zone of breccia with fracture fill and matrix derived from Palaeozoic sedimentary target sequence (i.e. Lower Cambrian alum shale and conglomerate). The whole breccia package rests with sharp contact on the fractured, granitic basement. The conspicuous lithological and petrophysical differences between the overlying breccias and the basement suggest the former was transported as ejecta. The rock magnetic properties of the ejecta show a magnetic signal that must have existed before the impact event took place. Thus, during the cratering process the ejecta at the studied location was relocated en masse from the central part of the crater to form an ejecta flap, in contrast to the standard ballistic emplacement of individual particles in an ejecta curtain. Highlights:-Rock-magnetism reveals a high magnetisation zone of pre-impact nature -Petrophysical characterization and description of the Lockne-9 core (central Sweden) -Magnetic signal is dominated by magnetite/titanomagnetite -Comparisons of affected and non-affected samples suggest a quick flap formation Research Highlights INSIGHTS IN THE EJECTION PROCESS OF THE LOCKNE MARINE-TARGET IMPACT CRATER FROM ROCK MAGNETIC PROPERTIES IN THE LOCKNE-9 DRILL Abstract:The well-documented, well-preserved, and well-exposed Lockne crater is a reference crater for marine-target impact on Earth. To date, it has been subjected to 11 short core drillings and over 5000 outcrop descriptions, as well as several geophysical surveys. The rich data allows detailed analysis of the cratering and modification processes.A unique feature with Lockne is its pristine ejecta layer. The ejecta differs, however, from the typical text book example of a land target crater in that it, to great extent, is made up of relatively extensive, coherent ejecta flaps resting on a target surface with no structural rim uplift. However, little is known about the marine impact excavation process generating the flaps. Here, we provide a lithological description coupled with an analysis of the rock magnetic properties of the Lockne-9 c...

Målingen is the 0.7 km wide minor crater associated to the 10 times larger Lockne crater in the unique Lockne–Målingen doublet. The craters formed at 458 Ma by the impact of a binary asteroid related to the well‐known 470 Ma Main Belt breakup event responsible for a large number of Ordovician craters and fossil meteorites. The binary asteroid struck a target sequence including ~500 m of sea water, ~80 m of limestone, ~30 m of dark mud, and a peneplainized Precambrian crystalline basement. Although the Lockne crater has been extensively studied by core drillings and geophysics, little is known about the subsurface morphology of Målingen. We performed magnetic susceptibility and remanence, as well as density, measurements combined with gravity, and magnetic field surveys over the crater and its close vicinity as a base for forward magnetic and gravity modeling. The interior of the crater shows a general magnetic low of 90–100 nT broken by a clustered set of high‐amplitude, short wavelength anomalies caused by bodies of mafic rock in the target below the crater and as allogenic blocks in the crater infill. The gravity shows a general −1.4 mgal anomaly over the crater caused by low‐density breccia infill and fractured crystalline rocks below the crater floor. The modeling also revealed a slightly asymmetrical shape of the crater that together with the irregular ejecta distribution supports an oblique impact from the east, which is consistent with the direction of impact suggested for the Lockne crater.