Ordovician impact crater at Kärdla, Hiiumaa Island, Estonia

Puura, V.; Suuroja, Kalle

doi:10.1016/0040-1951(92)90161-x

Cited by 55 publications

(60 citation statements)

References 1 publication

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“…Comparing the 2.5 mGal maximum negative anomaly found by Sturkell et al (1998a) and the 3 mGal reported by Puura and Suuroja (1992) in their studies of the Lockne and K‰rdla structures to the anomaly data for similarly sized craters formed on land as presented in Table 4 and Fig. 9 definitely places these marine structures in the lower range.…”

Section: Implications For Gravity Modellingmentioning

confidence: 88%

“…9 definitely places these marine structures in the lower range. The state of preservation of the Lockne and K‰rdla structures is good, as ejecta and resurge deposits are partly preserved outside of the crater and very well preserved within the crater (Lindstrˆm et al 1996;Sturkell et al 1998a;Puura and Suuroja 1992). Therefore the subdued characters of these two gravity anomalies should not be interpreted as a feature that is due to poor preservation.…”

Section: Implications For Gravity Modellingmentioning

confidence: 99%

“…Like those, it is of Caradocian (Middle Ordovician) age (Grahn et al 1996). The target had a 140 m thick sedimentary cover of CambroOrdovician limestone, shale, and sandstone (Puura and Suuroja 1992). The water depth at K‰rdla was probably less Fig.…”

Section: Comparisons To Other Impact Cratersmentioning

confidence: 99%

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Density and magnetic susceptibility of rocks from the Lockne and Tvären marine impact structures

Törnberg

Sturkell

2005

Meteoritics &Amp; Planetary Science

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Abstract-The Lockne and Tv‰ren impact craters in Sweden formed in a marine environment during the Ordovician. The contrast in density between the impact breccias and the surrounding target rock of these two craters is significantly lower than what has been found in craters formed in crystalline targets on land. Another marine-target structure, the Estonian K‰rdla structure, demonstrates intermediate contrast in impact breccia and target rock, which we attribute to the interpreted shallowness of the sea at the K‰rdla impact site. We conclude that the main cause for these low-density contrasts is pore and fracture filling of calcite with subordinate quartz and fluorite. Calcite is the most abundant cement, and its density differs most from that of fractured and brecciated bedrock with a low degree of cementation. Furthermore, from the studied cases, it is concluded that the target rock to impact rock contrast is generally the highest in craters formed on land in crystalline targets and the lowest in craters formed at sea, while craters formed on land in sedimentary targets are intermediate. The low density contrasts should decrease the negative gravity anomalies of marine craters.

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Section: Implications For Gravity Modellingmentioning

confidence: 88%

Section: Implications For Gravity Modellingmentioning

confidence: 99%

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Density and magnetic susceptibility of rocks from the Lockne and Tvären marine impact structures

Törnberg

Sturkell

2005

Meteoritics &Amp; Planetary Science

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“…The volume of material comprising Mount Sharp far exceeds the likely volume of material eroded from the central peak, walls, and rim of Gale. Thus-like filled and buried impact craters on Earth (e.g., Puura and Suuroja 1992;Poag et al 2002;Schieber and Over 2005)-the majority of these materials must be clasts that originated elsewhere (outside the crater) or formed in situ as precipitates from fluids (e.g., water) that came into the crater from elsewhere.…”

Section: Fig 1 Location Of Mahli Hardware Aboard the Mars Science Lamentioning

confidence: 99%

Curiosity’s Mars Hand Lens Imager (MAHLI) Investigation

et al. 2012

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The Mars Science Laboratory (MSL) Mars Hand Lens Imager (MAHLI) investigation will use a 2-megapixel color camera with a focusable macro lens aboard the rover, Curiosity, to investigate the stratigraphy and grain-scale texture, structure, mineralogy, and morphology of geologic materials in northwestern Gale crater. Of particular interest is the stratigraphic record of a ∼5 km thick layered rock sequence exposed on the slopes of Aeolis Mons (also known as Mount Sharp). The instrument consists of three parts, a camera head mounted on the turret at the end of a robotic arm, an electronics and data storage assembly located inside the rover body, and a calibration target mounted on the robotic arm shoulder azimuth actuator housing. MAHLI can acquire in-focus images at working distances from ∼2.1 cm to infinity. At the minimum working distance, image pixel scale is ∼14 µm per pixel and very coarse silt grains can be resolved. At the working distance of the Mars Exploration Rover Microscopic Imager cameras aboard Spirit and Opportunity, MAHLI's resolution is comparable at ∼30 µm per pixel. Onboard capabilities include autofocus, autoexposure, sub-framing, video imaging, Bayer pattern color interpolation, lossy and lossless compression, focus merging of up to 8 focus stack images, white light and longwave ultraviolet (365 nm) illumination of nearby subjects, and 8 gigabytes of non-volatile memory data storage.

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“…Localized rim collapse at very shallow water (Fig. 2b) can cause breaches through the crater rim where water can enter less forcefully (e.g., Kärdla, 4 km; Puura and Suuroja 1992).…”

Section: The Formation and Preservation Of Marine-target Craters On Ementioning

confidence: 99%

Marine‐target craters on Mars? An assessment study

Ormö

Dohm

Ferris

et al. 2004

Meteorit & Planetary Scien

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Marine-target craters on Mars? An assessment studyAbstract-Observations of impact craters on Earth show that a water column at the target strongly influences lithology and morphology of the resultant crater. The degree of influence varies with the target water depth and impactor diameter. Morphological features detectable in satellite imagery include a concentric shape with an inner crater inset within a shallower outer crater, which is cut by gullies excavated by the resurge of water. In this study, we show that if oceans, large seas, and lakes existed on Mars for periods of time, marine-target craters must have formed. We make an assessment of the minimum and maximum amounts of such craters based on published data on water depths, extent, and duration of putative oceans within "contacts 1 and 2," cratering rate during the different oceanic phases, and computer modeling of minimum impactor diameters required to form longlasting craters in the seafloor of the oceans. We also discuss the influence of erosion and sedimentation on the preservation and exposure of the craters.

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Ordovician impact crater at Kärdla, Hiiumaa Island, Estonia

Cited by 55 publications

References 1 publication

Density and magnetic susceptibility of rocks from the Lockne and Tvären marine impact structures

Density and magnetic susceptibility of rocks from the Lockne and Tvären marine impact structures

Curiosity’s Mars Hand Lens Imager (MAHLI) Investigation

Marine‐target craters on Mars? An assessment study

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