The Sheepbed member of the Yellowknife Bay formation in Gale crater contains millimeter‐scale nodules that represent an array of morphologies unlike those previously observed in sedimentary deposits ...on Mars. Three types of nodules have been identified in the Sheepbed member in order of decreasing abundance: solid nodules, hollow nodules, and filled nodules, a variant of hollow nodules whose voids have been filled with sulfate minerals. This study uses Mast Camera (Mastcam) and Mars Hand Lens Imager (MAHLI) images from the Mars Science Laboratory Curiosity rover to determine the size, shape, and spatial distribution of the Sheepbed nodules. The Alpha Particle X‐Ray Spectrometer (APXS) and ChemCam instruments provide geochemical data to help interpret nodule origins. Based on their physical characteristics, spatial distribution, and composition, the nodules are interpreted as concretions formed during early diagenesis. Several hypotheses are considered for hollow nodule formation including origins as primary or secondary voids. The occurrence of concretions interpreted in the Sheepbed mudstone and in several other sedimentary sequences on Mars suggests that active groundwater systems play an important role in the diagenesis of Martian sedimentary rocks. When concretions are formed during early diagenetic cementation, as interpreted for the Sheepbed nodules, they have the potential to create a taphonomic window favorable for the preservation of Martian organics.
Key Points
Three types of nodules are observed in the Sheepbed mudstoneSheepbed nodules are interpreted as early diagenetic concretionsAuthigenic mineral precipitation was an important diagenetic process on Mars
•ChemCam/Curiosity provides elemental composition at Gale crater’ lower Mt Sharp.•Diagenetic features in fine-grained sediments show diverse textures and compositions.•Presence of Mg-, Fe-, ...Ca-sulfates and fluorite is deduced from ChemCam chemistry.•Multiple phases of aqueous alteration suggest a complex post-depositional history.
The Curiosity rover's campaign at Pahrump Hills provides the first analyses of lower Mount Sharp strata. Here we report ChemCam elemental composition of a diverse assemblage of post-depositional features embedded in, or cross-cutting, the host rock. ChemCam results demonstrate their compositional diversity, especially compared to the surrounding host rock: (i) Dendritic aggregates and relief enhanced features, characterized by a magnesium enhancement and sulfur detection, and interpreted as Mg-sulfates; (ii) A localized observation that displays iron enrichment associated with sulfur, interpreted as Fe-sulfate; (iii) Dark raised ridges with varying Mg- and Ca-enriched compositions compared to host rock; (iv) Several dark-toned veins with calcium enhancement associated with fluorine detection, interpreted as fluorite veins. (v) Light-toned veins with enhanced calcium associated with sulfur detection, and interpreted as Ca-sulfates. The diversity of the Pahrump Hills diagenetic assemblage suggests a complex post-depositional history for fine-grained sediments for which the origin has been interpreted as fluvial and lacustrine. Assessment of the spatial and relative temporal distribution of these features shows that the Mg-sulfate features are predominant in the lower part of the section, suggesting local modification of the sediments by early diagenetic fluids. In contrast, light-toned Ca-sulfate veins occur in the whole section and cross-cut all other features. A relatively late stage shift in geochemical conditions could explain this observation. The Pahrump Hills diagenetic features have no equivalent compared to targets analyzed in other locations at Gale crater. Only the light-toned Ca-sulfate veins are present elsewhere, along Curiosity's path, suggesting they formed through a common late-stage process that occurred at over a broad area.
The Curiosity rover has analyzed abundant light‐toned fracture‐fill material within the Yellowknife Bay sedimentary deposits. The ChemCam instrument, coupled with Mastcam and ChemCam/Remote Micro ...Imager images, was able to demonstrate that these fracture fills consist of calcium sulfate veins, many of which appear to be hydrated at a level expected for gypsum and bassanite. Anhydrite is locally present and is found in a location characterized by a nodular texture. An intricate assemblage of veins crosses the sediments, which were likely formed by precipitation from fluids circulating through fractures. The presence of veins throughout the entire ~5 m thick Yellowknife Bay sediments suggests that this process occurred well after sedimentation and cementation/lithification of those sediments. The sulfur‐rich fluids may have originated in previously precipitated sulfate‐rich layers, either before the deposition of the Sheepbed mudstones or from unrelated units such as the sulfates at the base of Mount Sharp. The occurrence of these veins after the episodes of deposition of fluvial sediments at the surface suggests persistent aqueous activity in relatively nonacidic conditions.
Key Points
Calcium sulfate is detected by ChemCam in veins crossing fine‐grained sedimentsVeins cross various sediments as a result of postdepositional diagenesisCalcium sulfate veins formed through prolonged subsurface fluid circulation
The presence of methane on Mars is of great interest, since one possibility for its origin is that it derives from living microbes. However, CH
4 in the martian atmosphere also could be attributable ...to geologic emissions released through pathways similar to those occurring on Earth. Using recent data on methane degassing of the Earth, we have estimated the relative terrestrial contributions of fossil geologic methane vs. modern methane from living methanogens, and have examined the significance that various geologic sources might have for Mars.
Geologic degassing includes microbial methane (produced by ancient methanogens), thermogenic methane (from maturation of sedimentary organic matter), and subordinately geothermal and volcanic methane (mainly produced abiogenically). Our analysis suggests that ∼80% of the “natural” emission to the terrestrial atmosphere originates from modern microbial activity and ∼20% originates from geologic degassing, for a total CH
4 emission of ∼28.0×10
7
tonnes
year
−1.
Estimates of methane emission on Mars range from 12.6×10
1 to 57.0×10
4
tonnes
year
−1 and are 3–6 orders of magnitude lower than that estimated for Earth. Nevertheless, the recently detected martian, Northern-Summer-2003 CH
4 plume could be compared with methane expulsion from large mud volcanoes or from the integrated emission of a few hundred gas seeps, such as many of those located in Europe, USA, Mid-East or Asia. Methane could also be released by diffuse microseepage from martian soil, even if macro-seeps or mud volcanoes were lacking or inactive. We calculated that a weak microseepage spread over a few tens of km
2, as frequently occurs on Earth, may be sufficient to generate the lower estimate of methane emission in the martian atmosphere.
At least 65% of Earth’s degassing is provided by kerogen thermogenesis. A similar process may exist on Mars, where kerogen might include abiogenic organics (delivered by meteorites and comets) and remnants of possible, past martian life. The remainder of terrestrial degassed methane is attributed to fossil microbial gas (∼25%) and geothermal-volcanic emissions (∼10%). Global abiogenic emissions from serpentinization are negligible on Earth, but, on Mars, individual seeps from serpentinization could be significant. Gas discharge from clathrate-permafrost destabilization should also be considered.
Finally, we have shown examples of potential degassing pathways on Mars, including mud volcano-like structures, fault and fracture systems, and major volcanic edifices. All these types of structures could provide avenues for extensive gas expulsion, as on Earth. Future investigations of martian methane should be focused on such potential pathways.
Global bottom-up and top-down estimates of natural, geologic methane (CH4) emissions (average approximately 45 Tg yr–1) have recently been questioned by near-zero (approximately 1.6 Tg yr–1) ...estimates based on measurements of 14CH4 trapped in ice cores, which imply that current fossil fuel industries’ CH4 emissions are underestimated by 25%–40%. As we show here, such a global near-zero geologic CH4 emission estimate is incompatible with multiple independent, bottom-up emission estimates from individual natural geologic seepage areas, each of which is of the order of 0.1–3 Tg yr–1. Further research is urgently needed to resolve the conundrum before rejecting either method or associated emission estimates in global CH4 accounting.
Early-successional habitats (e.g. grasslands, shrublands, and early-successional forests) and their associated wildlife are declining throughout the northeastern United States. State wildlife ...agencies are generally charged with conserving all native wildlife and their habitats within their respective state. However, some have suggested that state wildlife agencies in the region are not addressing the decline of early-successional wildlife and habitats sufficiently. I investigated the extent to which 11 state agencies in this region are creating and maintaining early-successional habitats on public and private lands. The middle Atlantic subregion (five states: Delaware, Maryland, New Jersey, New York, and Pennsylvania) generally affected a greater proportion of state wildlife lands than the New England subregion (six states: Connecticut, Massachusetts, Maine, New Hampshire, Rhode Island, and Vermont): proportions range from 0.96 to 8.34, and 0.02 to 1.68%, respectively. Mowing was the most commonly used technique throughout the northeast. Only five state agencies in the northeast performed habitat management on private lands and no state affected more than 113
ha per year. Timber harvesting was infrequently used to create early-successional habitats and did not exceed 1.5% of eligible harvest area in nine of 11 states surveyed. A lack of sufficient resources was the most frequent explanation for little activity. Given that commonly used management techniques may be expensive (e.g. up to US$ 486
ha
−1 for mechanical clearing to reclaim abandoned fields), state agencies will need to develop new funding sources, and use alternative and more cost-effect management tools. Additionally, agencies should consider expanding technical assistance to private landowners.
We examined the larvae of several organophosphate and pyrethroid-resistant Mexican strains of Boophilus microplus using biochemical and molecular tests to investigate the mechanisms conferring ...acaricide resistance. The electrophoretic profiles of esterase activity in protein extracts from coumaphos and permethrin-resistant strains compared to the susceptible strain revealed distinct differences, which inhibitor studies attributed to carboxylesterases. Esterase hydrolysis assays showed significant enhancement of both total and permethrin hydrolysis in one pyrethroid-resistant strain, with no enhancement in two other strains with very high resistance to pyrethroids. Sequence analysis of sodium channel mRNA fragments in all pyrethroid-resistant strains determined that they did not possess the classic kdr and super-kdr mutations known to confer pyrethroid resistance in several insect species. Using reverse transcriptase–polymerase chain reaction (RT–PCR) with degenerate primers designed from conserved regions of insect esterase amino acid sequences, a B. microplus larval cDNA fragment was isolated whose deduced amino acid sequence was significantly similar to esterases from a wide range of species. In Northern blot RNA analysis the cDNA hybridized to a 2.1 kb mRNA that was abundant in all resistant strains except one, in which a very low abundance could provide a marker for the mechanism conferring resistance in this strain.
Steers were treated with doramectin or eprinomectin by daily oral capsule for 28 consecutive days. The level of doramectin in the serum of steers treated at 200 µg/kg/d reached a maximum of 104.0 ± ...22.1 ppb at day 21 and declined from 93.3 ± 20.5 ppb on the final day of treatment to below detectable by day 56. Steers treated at 50 µg/kg/d reached a maximum level of doramectin in the serum of 24.7 ± 1.2 ppb on day 21 and declined from 24.7 ± 0.6 ppb on the final day of treatment to less than detectable on day 42. Both doramectin dosages provided 100% control of estimated larvae (EL) of Amblyomma americanum (L.) (Acari: Ixodidae) throughout the 28-d treatment period. Daily oral treatment with eprinomectin at a dosage of 200 µg/kg for 28 consecutive days produced a maximum concentration in the serum of 41.6 ± 11.0 ppb at day 14. On the final day of eprinomectin treatment, the serum concentration was 38.3 ± 5.9 ppb. Seven days later at day 35, eprinomectin was not detectable in the serum. For steers treated at 50 µg/kg/d for 28 consecutive days, the serum level of eprinomectin reached a maximum of 10.0 ± 3.0 ppb on day 28 and was undetectable on day 35. Both eprinomectin dosages provided complete control of EL of A. americanum during the 28-d treatment period. Because eprinomectin is efficacious against A. americanum at lower serum levels in cattle and is eliminated from the serum at a more rapid rate than either doramectin or ivermectin, it provides advantages for use in applications such as the medicated bait for control of ticks on white-tailed deer and could have potential for use in the Cattle Fever Tick Eradication Program.
PDF
