Fine-grained Ejecta Research Articles

Soil liquefaction sites following the February 6, 2023, Kahramanmaraş-Türkiye earthquake sequence

AbstractSeismically induced soil liquefaction was listed as one of the major causes of damage observed in the natural and built environment during the 2023 Türkiye-Kahramanmaraş earthquake sequence. Reconnaissance field investigations were performed to collect perishable data and document the extent of damage immediately after the events. The sites with surface manifestations of seismic soil liquefaction in the form of soil ejecta, excessive foundation and ground deformations were identified and documented. The deformations were mapped, and samples from ejecta were retrieved. The ejecta samples were predominantly classified as sands with varying degrees of fines. Laboratory test results performed on liquefied soil ejecta revealed that the fines-containing liquefied ejecta samples are mostly classified as low plasticity clays (CL). Most of CL soil type ejecta were retrieved from Gölbaşı–Adıyaman region. The liquid limits of these samples varied in between 32 and 38%, their plasticity index values were estimated in the range of 16–23%. Surprisingly, two ejecta samples with plasticity indices higher than 30% were retrieved from Hatay airport, one of which was classified as high plasticity clay (CH). The majority of the fine-grained ejecta samples fall either on “Zone B: Testing Recommended” region of the Seed et al. (Keynote presentation, 26th Annual ASCE Los Angeles Geotechnical Spring Seminar, Long Beach, CA, 2003) susceptibility chart. Moreover, 12 out of 74 samples fall outside the susceptible limits defined by Seed et. These preliminary results suggest that clayey soils can produce liquefied ejecta when subjected to cyclic loading. Detailed site investigation and laboratory testing programs are ongoing to further investigate this rather unexpected response. Until their findings become available, the liquefaction susceptibility of silty-clayey soils’ mixtures is recommended to be assessed conservatively with caution.

Winding down the Chicxulub impact: The transition between impact and normal marine sedimentation near ground zero

The Chicxulub impact led to the formation of a ~ 200-km wide by ~1-km deep crater on México's Yucatán Peninsula. Over a period of hours after the impact the ocean re-entered and covered the impact basin beneath several hundred meters of water. A suite of impactites were deposited across the crater during crater formation, and by the resurge, tsunami and seiche events that followed. International Ocean Discovery Program/International Continental Scientific Drilling Program Expedition 364 drilled into the peak ring of the Chicxulub crater, and recovered ~130 m of impact deposits and a 75-cm thick, fine-grained, carbonate-rich “Transitional Unit”, above which normal marine sedimentation resumed. Here, we describe the results of analyses of the uppermost impact breccia (suevite) and the Transitional Unit, which suggests a gradual waning of energy recorded by this local K-Pg boundary sequence.The dominant depositional motif in the upper suevite and the Transitional Unit is of rapid sedimentation characterized by graded bedding, local cross bedding, and evidence of oscillatory currents. The lower Transitional Unit records the change from deposition of dominantly sand-sized to mainly silt to clay sized material with impact debris that decreases in both grain size and abundance upward. The middle part of the Transitional Unit is interrupted by a 20 cm thick soft sediment slump overlain by graded and oscillatory current cross-laminated beds. The uppermost Transitional Unit is also soft sediment deformed, contains trace fossils, and an increasing abundance of planktic foraminifer and calcareous nannoplankton survivors. The Transitional Unit, as with similar deposits in other marine target impact craters, records the final phases of impact-related sedimentation prior to resumption of normal marine conditions. Petrographic and stable isotopic analyses of carbon from organic matter provide insight into post-impact processes. δ13Corg values are between terrestrial and marine end members with fluctuations of 1–3‰.Timing of deposition of the Transitional Unit is complicated to ascertain. The repetitive normally graded laminae, both below and above the soft sediment deformed interval, record rapid deposition from currents driven by tsunami and seiches, processes that likely operated for weeks to potentially years post-impact due to subsequent continental margin collapse events. Highly siderophile element-enrichment at the top of the unit is likely from fine-grained ejecta that circulated in the atmosphere for several years prior to settling. The Transitional Unit is thus an exquisite record of the final phases of impact-related sedimentation related to one of the most consequential events in Earth history.

Lunar surface processes inferred from cosmogenic radionuclides in Apollo 16 double drive core 68002/68001

Measurements of cosmogenic 10Be, 26Al and 36Cl in Apollo 16 double drive core 68002/68001 are combined with a high resolution digital surface model of the sampling site to investigate the surface processes on the Moon. We find both a significant deficit of solar cosmic ray (SCR)-produced 26Al and a lack of SCR-produced 36Cl in the top 3–5 g/cm2 of the lunar regolith. The topographic model shows the core was taken from just inside a crater with a rim diameter of 25–30 cm. These observations are consistent with regolith removal and displacement by a shallow impact that occurred on the order of 100 kyr ago, or less. Our findings are also compatible with shallow mixing, or gardening, of the lunar regolith to depths of a few cm, a value often found in other lunar cores over the ∼106 yr averaging times of 26Al and 53Mn measurements. More definitive regolith mixing depth estimates are not possible due to the likelihood of disturbance in the top of the core as a result of sampling and/or handling. Our results support the hypothesis that the lunar surface experiences more frequent disturbances by small primary and secondary impacts than has previously been assumed. Additionally, we find no evidence that fine-grained ejecta from the 2.0 Myr old South Ray Crater impact reached this site. If the layer of fine-grained ejecta that reached the sampling site from the South Ray Crater was no more than a few cm thick, this absence can be explained by the erosion that formed the small, relatively recent crater at the coring location.

Recent volcanic resurfacing of Venusian craters

Abstract Ejecta from impact craters on Venus are a major source of fine-grained materials across the planet, and crater spatial distribution has been studied as a guide to the relative age and resurfacing rates of large regions. Of particular interest is the potential intersection of distal crater deposits and tesserae, highly deformed landforms that may be the oldest materials on Venus. The composition of tesserae is unknown, but is key to understanding whether water played a role in crustal differentiation. Thus, tesserae are ideal sites for future landed missions to identify possible felsic materials, but the short lifespan of surface landers means that efforts must be made to avoid contaminating surface materials from craters. Here we develop a method to detect distal crater ejecta on tessera terrain across Venus using NASA Magellan radar data. Our results show that fine-grained ejecta are unevenly distributed in the tesserae with respect to nearby craters. Many tesserae within a few hundred kilometers of plains craters do not have evidence for thick (>5–10 cm) mantling material, indicating that eolian or mass-wasting processes have moved the debris off the highland ridge slopes. At Sudenitsa Tesserae, within the young Beta-Atla-Themis region, we observe a radar signature of mantling debris, but there is no apparent source crater to which this material can be traced. We infer that the source crater has been resurfaced by volcanic activity within the past 80 m.y., and suggest that similar fine-grained ejecta deposits may have built up over time in other tesserae across Venus.

Impact-driven planetary desiccation: The origin of the dry Venus

The fate of surface water on Venus is one of the most important outstanding problems in comparative planetology. Although Venus should have had a large amount of surface water (like the Earth) during its formation, the current water content on the Venusian surface is only 1 part in 100 000 of that of the mass of Earth's oceans. Here a new concept is proposed to explain water removal on a steam-covered proto Venus, referred to as “impact-driven planetary desiccation”. Since a steam atmosphere is photochemically unstable, water vapor dissociates into hydrogen and oxygen. Then, hydrogen escapes easily into space through hydrodynamic escape driven by strong extreme ultraviolet radiation from the young Sun. The focus is on the intense impact bombardment during the terminal stage of planetary accretion as generators of a significant amount of reducing agent. The fine-grained ejecta remove the residual oxygen, the counter part of escaped hydrogen, via the oxidation of iron-bearing rocks in a hot atmosphere. Thus, hypervelocity impacts cause net desiccation of the planetary surface. I constructed a stochastic cratering model using a Monte Carlo approach to investigate the cumulative mass of nonoxidized, ejected rocks due to the intense impact bombardment. The ejecta mass after each impact was calculated using the π-group scaling laws and a modified Maxwell's Z model. The effect of projectile penetration into the ground on the ejecta mass was also included. Next, an upper limit on the total amount of removed water was calculated using the stoichiometric limit of the oxidation of basaltic rocks, taking into account the effect of fast H2 escape. It is shown that a thick steam atmosphere with a mass equivalent to that of the terrestrial oceans would be removed. The cumulative mass of rocky ejecta released into the atmosphere reaches 1 wt% of the host planet, which is 10 000 times of the current mass of the Earth's atmosphere. These results strongly suggest that chemical reactions between such large amounts of ejecta and planetary atmospheres are among the key factors required to understand atmospheric mass and its composition, not only in the Solar System but also in extrasolar systems.

Generation and emplacement of fine-grained ejecta in planetary impacts

We report here on a survey of distal fine-grained ejecta deposits on the Moon, Mars, and Venus. On all three planets, fine-grained ejecta form circular haloes that extend beyond the continuous ejecta and other types of distal deposits such as run-out lobes or ramparts. Using Earth-based radar images, we find that lunar fine-grained ejecta haloes represent meters-thick deposits with abrupt margins, and are depleted in rocks ⩾1 cm in diameter. Martian haloes show low nighttime thermal IR temperatures and thermal inertia, indicating the presence of fine particles estimated to range from ∼10 μm to 10 mm. Using the large sample sizes afforded by global datasets for Venus and Mars, and a complete nearside radar map for the Moon, we establish statistically robust scaling relationships between crater radius R and fine-grained ejecta run-out r * for all three planets. On the Moon, r * ∼ R −0.18 for craters 5–640 km in diameter. For Venus, radar-dark haloes are larger than those on the Moon, but scale as r * ∼ R −0.49, consistent with ejecta entrainment in Venus’ dense atmosphere. On Mars, fine-ejecta haloes are larger than lunar haloes for a given crater size, indicating entrainment of ejecta by the atmosphere or vaporized subsurface volatiles, but scale as R −0.13, similar to the ballistic lunar scaling. Ejecta suspension in vortices generated by passage of the ejecta curtain is predicted to result in ejecta run-out that scales with crater size as R 1/2, and the wind speeds so generated may be insufficient to transport particles at the larger end of the calculated range. The observed scaling and morphology of the low-temperature haloes leads us rather to favor winds generated by early-stage vapor plume expansion as the emplacement mechanism for low-temperature halo materials.