Abundant Rocks Research Articles

Controlling factors of tight sandstone gas accumulation and enrichment in the slope zone of foreland basins: The Upper Triassic Xujiahe Formation in Western Sichuan Foreland Basin, China

The accumulation and enrichment of hydrocarbon reflect different degrees of hydrocarbon charging, which is important for hydrocarbon exploration. In this study, we discuss the controlling factors of tight sandstone gas accumulation and enrichment of Xujiahe Formation in Jinhua-Zhongtaishan area, the slope zone of the Western Sichuan Foreland Basin, Southwest China, based on the analysis of the characteristics of the area's source rock, reservoir, and fault, combined with the tectonic background. This study shows that the accumulation and enrichment of tight sandstone gas in the slope zone of foreland basins are controlled by different factors. The natural gas derived from Xu1 Member is easily accumulated in Xu2 Member sandstone reservoir by vertical migration. The high quality source rock generated a large number of natural gas, which preferentially charge into the high quality sandstone reservoir and finally accumulate at the structural high position. The accumulation of tight gas is controlled by high quality source rock (source rock coefficient >10), high-quality reservoir (reserve coefficient >110), and favorable structure (high position of the local structure). When tight sandstone gas meets all prerequisites above for hydrocarbon accumulation, high content of total organic carbon (TOC) benefits enrichment of tight sandstone gas. In addition, the type I faults could be in favor of the natural gas from Xu1 Member to migrate to the upper part of Xu2 Member high quality sandstone reservoir, especially when the natural gas is generated by the middle and lower part of Xu1 Member high quality source rock, which could significantly improve the gas accumulation efficiency and promotes the gas enrichment and high production. In that case, the enrichment of tight gas is controlled by organic matter abundance of source rock (TOC >1.1%) and favorable source-reservoir communication conditions (the development of Type I faults). As a result, the areas with high-quality source rock and sandstone reservoir, favorable structure and migration pathway will be potential targets of tight sandstone gas in the slope zone of foreland basin.

Landing Site Selection and Characterization of Tianwen‐1 (Zhurong Rover) on Mars

AbstractThe Chinese Mars rover Zhurong onboard the Tianwen‐1 probe successfully landed on Mars in May 2021. Here, we report our efforts in selecting a landing site for Zhurong within a pre‐identified landing region in southern Utopia Planitia. Using the high‐resolution images collected by a camera onboard the Tianwen‐1 orbiter, the landing region was analyzed in detail in terms of surface slopes, crater densities and rock abundances, which enabled the optimized determination of a landing ellipse (56 × 22 km for the major and minor axes) with minimum hazards and assisted the successful landing of the Zhurong rover. We also characterized the landing site and region after landing. Surface images captured by a camera onboard the Zhurong rover revealed a low rock abundance of approximately 4% at the landing site, similar to the rock measurements from orbital data before landing. Images of the surface features and a hole excavated by the pulsed retrorockets beneath the lander suggested a shallow regolith structure with a surficial layer of dust and sand over a layer of duricrust, and brecciated/fragmented rocks and bedrocks beneath. Crater size‐frequency distribution analysis indicated that the landing region might have experienced multiple episodes of resurfacing.

Capturing the complexity of soil evolution: Heterogeneities in rock cover and chemical weathering in Montana's Rocky Mountains

We investigate the relationship between chemical weathering, persistence of soil cover, and topography in two neighboring mountain ranges in the northern Rockies of western Montana, USA. We augment existing tools for measuring chemical weathering with adjustments for both local and landscape-scale contributions from unweathered rock fragments, boulders, and bedrock exposure. Adjusted weathering intensities recognize that quantifying weathering in mountainous systems should account for rock exposure, rather than focusing solely on fine-grained soil mantles. Our study systems' distinct morphologies are shaped by their unique climate histories. The previously glaciated Bitterroot Mountains consist of steep hillslopes with abundant rock cover, while the neighboring unglaciated Sapphire Mountains display convex, soil-mantled hillslopes. Over 380 soil thickness measurements, 118 analyses of soil and rock geochemistry, and digital terrain analysis reveal that patchy soils in the bedrock-rich system are roughly half as thick as those in the continuously-soil-mantled landscape, and ~45% less weathered, despite wetter conditions that would be expected to enhance weathering. These disparities increase when accounting for coarse rock fragments in soils and bedrock cover across the study catchments. The near continuously soil-mantled Sapphire system experiences ~1.5 times greater weathering intensity at a catchment scale compared to the bedrock-rich Bitterroot system. Rock exposure across the mountainous study system increases with increasing slope gradient. However, we find no clear threshold at which soils decrease in abundance or weathering intensity, and soils are surprisingly resilient even at the steepest hillslopes (comprising ~60% of the landscape area at slopes >30°). Our new data quantify soil abundance and chemical weathering intensity at both local and landscape scales. This work highlights how measurements of soil and rock cover need to be incorporated into studies quantifying chemical weathering, as traditional approaches may significantly overestimate and mischaracterize weathering regimes in mountain environments.

A Reference Section Through Fast‐Spread Lower Oceanic Crust, Wadi Gideah, Samail Ophiolite (Sultanate of Oman): Trace Element Systematics and REE Crystallization Temperatures—Implications for Hybrid Crustal Accretion

AbstractOceanic gabbros are the most abundant rocks close to Earth's surface. Here we present new data from a consistent profile through the paleocrust of the Samail Ophiolite (Oman), which is thought to provide the best analog for modern fast‐spreading oceanic crust. Incompatible trace elements of co‐existing plagioclase and clinopyroxene fractionate from the mineral core to rim and up section from layered to foliated to varitextured gabbros. Layered gabbro parental melts correspond to mid‐ocean‐ridge basalts (MORB), and plagioclase Ca# shows a pronounced inverse zonation. Likely, they crystallized in situ from hydrous melts, compositionally buffered by replenishment at equilibrium to MORB and near steady‐state boundary conditions. Further upsection, the compositional variability increases. Foliated gabbro rim and core compositions indicate increased fractionation and disequilibrium to MORB, triggered by open‐system fractional crystallization within a heterogeneous magma plumbing structure, characterized by magma mixing, varying ambient water activities, and boundary conditions. Varitextured gabbros are chemically diverse with parental melts partially more primitive than MORB, suggesting that primitive melts directly reach the axial melt lens (AML). REE‐in‐plagioclase‐clinopyroxene thermometry compared to and supported by anorthite‐in‐plagioclase thermometry reveals a relationship of [°C] = 6.1 ± 0.2 × An + 706 ± 19. Crystallization temperatures of the layered gabbros cover a narrow range of 1216 ± 14°C. Considerable temperature variability of 1077–1231°C is observed further upsection, featuring a thermal minimum within the foliated gabbros. This minimum is assumed to represent a zone where the fractionated descending crystal mushes originating from the AML meet with evolved liquids expelled from deeper crustal levels. Our findings suggest hybrid accretion of fast‐spread crust.

Geochronology, geochemistry and petrology of the oligocene magmatism in SE segment of the UDMB, Iran

Despite diverse geochronological-geochemical studies on Cenozoic igneous rocks from the SE segment of the Urumieh-Dokhtar Magmatic Belt (UDMB) of Iran, the nature of the Oligocene magmatic rocks from the farthermost end of the SE segment- where it is linked to the Makran magmatic belt- has been ignored due to the difficulty of access. In this study, we focus on syn-collisional mafic to felsic igneous rocks of calc-alkaline and high-K calc-alkaline affinities from the SE segment of the Urumieh-Dokhtar Magmatic Belt (UDMB) near Nagisun, south of Bam. The Nagisun rocks have low Sr/Y and La(n)/Yb(n), similar to igneous rocks from typical arcs. Zircon UPb ages show comparable ages for plutonic (~ 34–25 Ma) and volcanic (~34–27 Ma) rocks. The εHf(t) values for zircons from plutonic rocks range from −0.3 to +12.8, whereas the εHf(t) values for the volcanic rocks vary from −2.6 to +13. Modelling of trace elements compositions using Nagisan basaltic samples indicate that an 87:2:11 mixture of the depleted MORB mantle, subducting (trench)-sediments and altered oceanic crust with 5% aggregated fractional melting closely matches the trace-element abundances of the Nagisun basaltic rocks. Indeed, the modelling of Sr and Nd isotopic data emphasizes that the Nagisun magmatic rocks could be products of bulk mixing between a depleted MORB mantle and/or a mixed, fertilized mantle with the Cadomian lower and upper continental crust. Furthermore, our compiled data display that the magmatism in the SE segment of the UDMB changed through time from normal calc-alkaline magmatism to adakitic magmatism at ~20 Ma, after the collision with Arabia began ca 27 Ma.

Rock Abundance on the Lunar Mare on Surfaces of Different Age: Implications for Regolith Evolution and Thickness

AbstractThe growth of lunar regolith over time affects surface rock abundance, because larger, less frequent impacts are needed to penetrate thicker regolith developed on older surfaces and excavate rocks. On younger surfaces with thinner regolith, smaller, more frequent impacts are sufficient to excavate rocks. We quantify the correlation between observed rock abundances and age on the lunar surface by comparing Diviner rock abundance data to the surface ages of intercrater parts on the maria. Our observations show the expected negative correlation between age and rock abundance. The commonality of nonzero rock abundance values on ancient surfaces, combined with a simple Monte Carlo model of the rock excavation process, suggest that rocks reexcavated from the regolith volume contribute to the presently observed rock population on the lunar surface. The half‐life of meter‐scale surface rocks most consistent with our observations is 80 ± 20 Myr.

Differential Fluid Activity in a Single Exhumed Continental Subduction Unit from Local P-T-M(H2O) Records of Zoned Amphiboles (North Muya, Eastern Siberia)

The behavior of the continental lithosphere in the Alpine-type subduction zones, which primarily depends on its thickness, thermal regime of subduction and availability of fluids/melts, remains an important issue for both metamorphic petrology and geochemistry as well as for resolving the thermomechanical properties of subduction paleo-interfaces. Rehydrated (amphibole- and zoisite-bearing) eclogites from the Neoproterozoic North Muya high-pressure complex (northern Central Asian Orogenic belt, eastern Siberia) were studied in order to assess their peak burial depths, degree of prograde dehydration, and further retrograde hydration extent within a subducted and exhumed continental unit. Three medium-grained eclogites from different localities of HP complex show similarly dry peak assemblages of pyrope-almandine-grossular garnet (XGrs up to 0.30, XPrp up to 0.25) + Na-rich omphacite (up to 44 mol % of jadeite) + rutile + quartz, which are variably replaced by secondary plagioclase + clinopyroxene ± amphibole symplectitic aggregate. The eclogites were subjected to burial at similar peak depths (up to ~17–21 kbar) but different peak temperatures (within ~600–730 °C) with or without notable heating and re-equilibration due to crustal thickening. Variable degrees of exhumation-induced pervasive rehydration led to growth of individual zoned porphyroblastic barroisite-hornblende amphibole ([B]Na = 0.03–0.45) ± zoisite over the primary eclogitic assemblage or after notable thermally-driven development of symplectitic aggregate after omphacite. Amphibole compositions together with the zoisite presence/absence in different samples reflect continuous rehydration by addition of ~0.5–1.5 wt.% at different exhumation conditions, from nearly peak eclogitic P–T (~17–21 kbar) to granulite- and amphibolite-facies depths within the plagioclase stability field (<14 kbar). This diversity most likely required irregular distribution of internally sourced, low-volume, hydrous metamorphic fluid (i.e., from host felsic rocks or metasediments) acting at different depths of the subduction interface. From the performed PTX calculations, I suggest that nearly isochemical (i.e., without any significant modification of the bulk-rock composition other than incorporation of additional H2O), retrograde hydration by only at lower- to middle-crust conditions did not significantly influence the density and the rheology of the subducted continental slices due to both (1) a limited abundance of dense metabasic rocks, which are commonly more fluid-rich (e.g., due to chlorite or amphibole alteration), and (2) the initially dry nature of mafic and felsic continental rocks. The limited dehydration and rehydration scales exemplified by the North Muya eclogites and therefore low availability of hydrous metamorphic fluids may have accounted for the high buoyancy of the eclogitic crust and explained the absence of contemporaneous suprasubduction magmatism in the regional context at ca. ~630 Ma.

Determining the age of Vaughan, a potential source crater for lunar meteorites, using boulder size-frequency distributions

We use Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) images to analyze the boulder distribution around Vaughan crater, a small, fresh crater on the far side of the Moon. Using six similar lunar impact craters of known age for comparison, we determine the approximate age of the crater. Vaughan crater lies in a part of the South Pole-Aitken basin that is compositionally similar to lunar meteorite Dhofar 961, on the basis of Lunar Prospector Gamma Ray Spectrometer data, making Vaughan crater a potential candidate for the source of this meteorite and possibly others paired with it. Boulder distributions reveal that as impact craters age, the boulder population density in their ejecta decreases. This understanding allows us to use size-frequency distributions to compare crater ages on the basis of their boulder population density. We find that Vaughan crater is very young (<25 Ma) owing to its placement within the boulder size-frequency comparison plot and its population of large (>10 m diameter) boulders. Additionally, we compare LROC NAC distributions to thermophysically derived values for rock abundance from the Diviner Lunar Radiometer. We find that our LROC NAC count is consistent with Diviner rock abundance values, which further supports the inference that Vaughan is a very young impact crater and could plausibly be a source of lunar meteorite Dhofar 961.

Depositional Setting and Enrichment Mechanism of Organic Matter of Lower Cretaceous Shale in Ri-Qing-Wei Basin in the Central Sulu Orogenic Belt

A suite of source rock consists of mudstone and shale, with great thickness and continuous deposition was found in the well LK-1 in Lingshan island in Ri-Qing-Wei basin. In order to evaluate the hydrocarbon generation prospects of these source rock and find the mechanism of organic matter enrichment, shale samples were selected from the core for TOC (total organic carbon) and element geochemistry analysis. The results show that organic matter abundance of the source rocks are generally high with average TOC content of 1.26 wt%, suggesting they are good source rocks. The geochemical features show that the sedimentary environment is mostly anoxic brackish water to salt water environment with arid to semiarid climate condition. The enrichment mechanism of organic matter varied with the evolution of the basin, which was divided into three stages according to the sedimentary characteristics. In the initial-middle period of rifting evolution (stage 1 and early stage 2), paleoproductivity is the major factor of OM-enrichment reflecting by high positive correlation between the TOC contents and paleoproductivity proxies. While with the evolution of the rift basin, redox condition and terrigenous clastic input became more and more important until they became the major factor of OM enrichment in the middle stage of rift evolution (stage 2). In the later stage of rift evolution (latest stage 2 and stage 3), besides terrigenous clastic input, the effect of paleoclimate on OM-enrichment increased gradually from a minor factor to a major factor.

Has the impact flux of small and large asteroids varied through time on Mars, the Earth and the Moon?

The impact flux over the last 3 Ga in the inner Solar System is commonly assumed to be constant through time due to insufficient data to warrant a different choice for this range of time. However, asteroid break-up events in the main belt may have been responsible for cratering spikes over the last ∼2 Ga on the Earth-Moon system. Due to its proximity with the main asteroid belt, i.e., the main impactors reservoir, Mars is at the outpost of these events with respect to the other inner planets. We investigate here, from automatic crater identification, the possible variations of the size frequency distributions of impactors from the record of small craters of 521 impact craters larger than 20 km in diameter. We show that 49 craters (out of the 521) correspond to the complete crater population of this size formed over the last 600 Ma. Our results on Mars show that the flux of both small (> 5 m) and large asteroids (> 1 km) are coupled, does not vary between each other over the last 600 Ma. Existing data sets for large craters on the Earth and the Moon are analyzed and compared to our results on Mars. On Earth, we infer the formation location of a set of impact craters thanks to plate tectonic reconstruction and show that a cluster of craters formed during the Ordovician period, about 470 Ma ago, appears to be a preservation bias. On the Moon, the late increase seen in the crater age signal can be due to the uncertain calibration method used to date those impacts (i.e. rock abundance in lunar impact ejecta), and other calibrations are consistent with a constant crater production rate. We conclude to a coupling of the crater production rate between kilometer-size craters (∼100 m asteroids) and down to ∼100 m in diameter (∼5 m asteroids) in the inner Solar System. This is consistent with the traditional model for delivering asteroids to planet-crossing obits: the Yarkovsky effect slowly pushes the large debris from asteroid break-ups towards orbital resonances while smaller debris are grinded through collisional cascades. This suggests that the long-term impact flux of asteroids > 5 m is most likely constant over the last 600 Ma, and that the influence of past asteroid break-ups in the cratering rate for D > 100 m is limited or inexistent.

Lithologic, geomorphic, and climatic controls on sand generation from volcanic rocks in the Sierra Nevada de Santa Marta massif (NE Colombia)

Tectonics, climate, and lithology are the three main factors controlling the generation and transfer of sediments as well as their textural and compositional signatures. In this paper, we investigate the generation of sands from volcanic rocks in nine drainages with mixed lithological assemblage in a high-relief – subtropical climate setting (Sierra Nevada de Santa Marta, NE Colombia). The integration of geomorphological analysis with sand petrography, and bulk-rock and clay geochemistry allows us to constrain the dynamics regulating the generation of sediments derived from felsic and mafic-intermediate volcanic basement rocks in relation to plutonic and metamorphic lithologies. The petrographic composition of modern fluvial sands from the area is extremely variable (litho-feldspatho-quartzose, feldspatho-quartzose, and quartzose-feldspatho-lithic), but it reveals a strong dilution of (especially mafic) volcanic compositional signals, and a consequent overrepresentation of plutonic and metamorphic lithologies. Traditional chemical weathering indices fail to represent the extent of chemical alteration, but instead seem to favour preservation of provenance signals. Chemical weathering primarily affects feldspars and the ferromagnesian groundmass of mafic volcanic rock fragments. Enrichment of ferromagnesian elements in the clay fraction supports the notion that mafic volcanic rock fragments are unstable relative to plutonic and metamorphic rocks. Drainage features (particularly river network and relief) control the abundance of volcanic lithic fragments and the rates and extent of chemical weathering. A linear log-ratio model permits us to quantify sediment generation from volcanic rocks in this mixed-lithology setting. The results indicate that even in the case where volcanic grains are practically absent in the sand fraction, there could still be up to 20% of volcanic rocks in the drainage basin, and in the case that 50% of the sand grains are volcanic, around 75% of drained lithologies are expected to be volcanic. Our results demonstrate that the contribution of volcanic detritus to modern sands systematically underrepresents the areal proportion of volcanics rocks in mixed source areas. Post-depositional diagenetic modifications are likely to alter and/or dissolve volcanic lithic fragments, making accurate reconstruction of sediment provenance even more difficult. Sediment-generation models based on a range of mixed lithologies in various tectonic and climatic settings will be needed to improve estimates of the abundance of volcanic rocks in drainage basins of ancient sediment routing systems.

Re-Evaluating Influence of Rocks on Microwave Thermal Emission of Lunar Regolith Using CE-2 MRM Data

The influence of rocks on the microwave thermal emission (MTE) of the lunar regolith has not been fully studied with the four-channel microwave radiometer (MRM) data onboard Chang’e-1/2 satellites. To highlight the influence of the rocks on the MTE of the regolith, the Hertzsprung basin located near the lunar equator in highland regions is selected as the study area. The comparison between the brightness temperature (TB) maps derived from the Chang’e-2 MRM data and rock abundance (RA) map derived from the Diviner data postulates three special issues about the correlation between the MTE features and the regolith with rocks. Then, aimed to interpret the issues, two new layered regolith models and the corresponding radiative transfer models are constructed. The main results are as follows. First, the observation and the simulation both verify that the regolith with rocks will provide a cold TB anomaly at night and at low frequencies at daytime, but result in a hot anomaly at high-frequency at daytime. Moreover, the temperature profiles of the regolith with surface and hidden rocks are evaluated with the theoretical model. Second, the simulation results verify the existence of the hidden rocks in the lunar regolith assumed when studying the TB performances of the Hertzsprung basin. Third, the rock distribution revealed by the TB maps shows a different view compared to that estimated by the Diviner data in space and values, and the change of the TB with frequencies postulates a new view about the variation of the RA with depth. This study hints that the MRM data probably provide a new way to quantitatively estimate the RA values of the lunar regolith, and the results will be meaningful to improve understanding of the evolution of the impact craters.

An In-Flight Recalibration for Chang’E-1 and E-2 Microwave Radiometer Datasets Based on Highland Thermophysical Models

The Chang’E-1 and E-2 (CE-1 and CE-2) orbital sounders provided high-resolution global maps of lunar microwave brightness temperatures (TBs) at wavelengths of 0.8, 1.55, 3.85, and 10 cm covering approximately two years of data over the 2007–2010 time frame. The four-channel microwave radiometers (MRMs) effectively sampled the upper ~2 m of the lunar regolith and are diagnostic of thermal and electrical properties, including mineralogy, rock abundance, and, potentially, interior heat flow. Early comparisons of colocated data between the two instruments revealed ~10–20 K offsets between the CE-1 and CE-2 measurements that required in- flight recalibration efforts. These have included comparisons with model predictions at Apollo sites as well as adjustments of the cold sky horn reference temperatures to include contamination from lunar surface emissions. This article proposes an in- flight recalibration methodology that focuses on correction of the preflight transfer coefficients that determine the relative importance of component losses along the radiometer hardware paths connecting the antennas to the detectors. It is shown that for each channel, a single parameter, representing the ratio of the cold sky and main antenna transfer coefficients, can be constrained by knowledge of the stable regolith physical temperatures below the diurnal-varying layer and is sufficient to establish values for the complete set of hardware transfer coefficients. The in- flight comparisons proposed for recalibration are based on backside highland models of regolith thermal properties. Potential remaining offsets of the recalibrated MRM data are evaluated in terms of parameter uncertainties of our chosen nominal thermal model.

Calculation and controlled factors of hydrocarbon expulsion efficiency using corrected pyrolysis parameters: A Songliao case study

In recent years, rock pyrolysis parameters combined with a mass balance method have been used to calculate the hydrocarbon expulsion efficiency. However, due to the experimental procedure of rock pyrolysis, the residual hydrocarbon amount (S1) is underestimated, and the hydrocarbon-generation potential of kerogen (S2) is overestimated, so that the hydrocarbon expulsion efficiency calculated from the pyrolysis parameters before correction is higher than the actual value. In this paper, the pyrolysis parameters were corrected by performing pyrolysis before and after the extraction of source rocks, and the hydrocarbon expulsion efficiency of the mudstone of the Qing 1 member of the Ha14 well in Songliao basin was calculated using the chemical kinetics method. The hydrocarbon expulsion efficiencies before and after the correction were considerably different, the hydrocarbon expulsion efficiency of the Ha14 well after correction was 17.5% lower than that before correction. The study show that the higher the abundance and maturity of source rock are, the higher the hydrocarbon expulsion efficiency is; the oil-type organic matter has a higher hydrocarbon-expulsion efficiency than the gas-type organic matter; the interbedded sand and mud type source-reservoir configuration relationship is beneficial to hydrocarbon expulsion; the underwater diversion channel phase has the highest hydrocarbon expulsion efficiency.

Hyperfine Structure of Regolith Unveiled by Chang’E-5 Lunar Regolith Penetrating Radar

This work presents the results of the Lunar Regolith Penetrating Radar (LRPR), installed at the bottom of the Chang’E-5 (CE-5) lander, which is the first antenna-array radar deployed for the investigation of an extraterrestrial body. Radar imaging results unveiled a hyperfine structure for the top 2.5-m-thick lunar regolith with an unprecedented high resolution of 5 cm. The interpretation of the results permitted to state that subsurface regolith is dominated by fine grains with abundant rock fragments. The radar imaging results were also used to drive the drilling process until a fragment jammed the core inlet at about 100-cm underground. Laboratory measurements of the samples returned at Earth allow to estimate the real part of relative permittivity and the loss tangent, which are 3.04 ± 0.02 and 0.014 ± 0.002, respectively.

Peculiarities of performance of experimental filtering works in sites subsoil operated by single water intakes

The article discusses the methods used in the field experimental filtration work, which allow you to gain knowledge about the filtration properties and water abundance of rocks. The features of the experimental filtration work in the subsoil areas operated by single water intakes are shown. It is noted that these are small water bodies, both in terms of the number of water wells and the amount of actual water withdrawal. The article proposes to use short-term single pumpings as a field research method in the above-mentioned areas, according to the results of which it is possible to substantiate the amount of required water withdrawal and determine the calculated values of the water conductivity coefficient. As an example, the results of pumping are considered, obtained during the implementation of experimental filtration work at three single water intakes located within the Latitude Ob region. The results of the experimental filtration work served as the source material for calculating the reserves of fresh groundwater. Fresh groundwater reserves were calculated and approved for each site in the amount of 499 m3/day for category B.

Rock Size‐Frequency Distributions at the InSight Landing Site, Mars

AbstractRocks around the InSight lander were measured in lander orthoimages of the near field (&lt;10 m), in panoramas of the far field (&lt;40 m), and in a high‐resolution orbital image around the lander (1 km2). The cumulative fractional area versus diameter size‐frequency distributions for four areas in the near field fall on exponential model curves used for estimating hazards for landing spacecraft. The rock abundance varies in the near field from 0.6% for the sand and pebble‐rich area to the east within Homestead hollow to ∼3–5% for the progressively rockier areas to the south, north, and west. The rock abundance of the entire near field is just over 3%, which falls between that at the Phoenix (2%) and Spirit (5%) landing sites. Rocks in the far field (&lt;40 m) that could be identified in both the surface panorama and a high‐resolution orbital image fall on the same exponential model curve as the average near‐field rocks. Rocks measured in a high‐resolution orbital image (27.5 cm/pixel) within ∼500 m of the lander that includes several rocky ejecta craters fall on 4–5% exponential model curves, similar to the northern and western near‐field areas. As a result, the rock abundances observed from orbit fall on the same exponential model rock abundance curves as those viewed from the surface. These rock abundance measurements around the lander are consistent with thermal imaging estimates over larger pixel areas as well as expectations from fragmentation theory of an impacted Amazonian/Hesperian lava flow.

Geochemistry and Organic Petrology of Middle Permian Source Rocks in Taibei Sag, Turpan-Hami Basin, China: Implication for Organic Matter Enrichment.

The Taodonggou group of Middle Permian is an important source rock in Taibei sag of Turpan-Hami basin. Due to its deep burial, drilling has only been revealed in recent years. Based on organic petrology and organic geochemistry experiments, this paper studies the organic petrology, organic geochemistry, sedimentary environment, and hydrocarbon generation potential of source rocks in Taibei sag, Turpan-Hami basin, and reveals the influence of the sedimentary environment on the organic matter abundance of source rocks. The results are as follows: (1) The organic matter of the Middle Permian source rocks in Taibei sag of Turpan-Hami basin is mainly sapropelite and exinite. The vitrinite is mainly vitrodetrinite, and the exinite is mainly lamalginiite. (2) The total organic carbon content value is 0.55–6.08 wt %, and the average value is 2.58 wt %. The PG value ranges from 0.78 mg HC/g to 30.86 mg HC/g, and the average value is 4.88 mg HC/g. Chloroform asphalt “A” is 0.046–0.8767 wt %, and the average value is 0.285 wt %. The types of organic matter are mainly III and II–III, and the Ro value is 0.628–1.49 wt % (average = 0.988 wt %). The Tmax distribution is 329–465 °C. The average temperature is 434.7 °C, which is in the mature stage (oil window stage). The Middle Permian source rocks are mainly very good to excellent source rocks with a good hydrocarbon generation potential. (3) The source rocks are deposited in a semihumid and semiarid climate. Organic matter is input as a mixed source. The early and late stages is dominated by terrestrial higher plants. The middle stage is dominated by lower aquatic organisms, and the sedimentary environment consists of weak reduction and weak oxidation environments. (4) In the study area, the abundance of organic matter has a weak negative correlation with CPI and a positive correlation with Pr/Ph and ∑C21–/∑C22+. Under the coaction of paleoclimate, organic matter input, and redox environment, the enrichment model of organic matter with high productivity and weak oxidation environment characteristics can also form excellent source rocks. This study is of great significance and provides theoretical guidance for the exploration of deep oil and gas resources.

Effects of Alteration and Cracks on the Seismic Velocity Structure of Oceanic Lithosphere Inferred From Ultrasonic Measurements of Mafic and Ultramafic Samples Collected by the Oman Drilling Project

AbstractSeismic velocity structures of the oceanic lithosphere are variable due to the variation of alteration and heterogeneities in porosity. In order to interpret geophysically determined velocity structures, it is necessary to understand how the seismic velocity of the oceanic lithosphere is affected by alteration and porosity. We conducted petrological analysis and elastic wave velocity measurements at 200 MPa on mafic and ultramafic rocks drilled from the Samail ophiolite. The elastic wave velocity calculated from the mineral abundances of the ultramafic rocks was sensitive to serpentinization, whereas that of the mafic rocks was nearly independent of the alteration, suggesting that velocity changes with depth in the oceanic crust are mainly due to porosity reduction. Based on the effective medium theory and pressure dependence of the experimentally determined velocity, the change in the porosity was estimated to be 0.04%–0.42% at 200 MPa, indicating porosity reduction by the increase of lithostatic pressure in the oceanic crust in the fast‐spreading system such as the Pacific plate. We estimated the degree of hydration in the mantle to account for the geophysical observations based on the laboratory experiments. Both the crustal porosity and mantle serpentinization increase towards the trench due to fracture related plate bending, indicating extensive hydration of the oceanic lithosphere close to the trench. From these estimates, water contents in the oceanic lithosphere were calculated to be as high as 3 wt.% in the shallow crust and 6 wt.% in the upper most mantle, which is significant for water transport into Earth's interior.

Global Drivers and Transport Mechanisms of Lunar Rockfalls

AbstractThe long‐ and short‐term drivers and transport mechanisms of lunar rockfalls are currently not well understood, but could provide valuable information about the geologic processes that still shape the surface of the Moon today. Here, we compare the global distribution of rockfalls with relevant geophysical data, such as seismic, topographic, thermal, gravity anomaly, and tidal displacement data sets. Rockfalls appear to predominantly occur (a) on equator‐facing slopes and thus in regions with large thermal amplitudes, (b) on slope angles well above‐average (Δ ∼ 10°), and (c) in regions with above‐average rock abundance. We do not observe a qualitatively or statistically relevant relation between rockfall abundance, monitored Apollo‐era shallow seismic activity, and the distribution of visible tectogenetic features. Informed by our global analysis, we conduct a targeted, in‐depth study of 687 rockfall boulders and trajectories in 13 sites across the Moon, including 7 craters, 2 volcanic vents, 2 tectonic structures, and 2 unclassified geomorphic regions. We identify four different source region types, where the type appears to control the occurrence of rockfalls. The source region type in turn is controlled by surface age rather than geomorphic context. We find that rockfall trajectories are mainly controlled by the trigger energy and the geometry of the slope. Our results suggest that erratic small‐scale impacts (mainly in old, Imbrian‐Nectarian, shallow terranes), aided by solar‐induced thermal fatigue of fractured bedrock (mainly in young, Copernican‐Eratosthenian steep terranes), were the dominant, global‐scale long‐ and short‐term drivers of rockfalls in the Moon's recent geologic past.