Geology topics

T.D. Glotch

Publications and source records attributed to T.D. Glotch.

7 recordsLinked to original sources

USGS2010

Diviner lunar radiometer observations of cold traps in the moon's south polar region

Diviner Lunar Radiometer Experiment surface-temperature maps reveal the existence of widespread surface and near-surface cryogenic regions that extend beyond the boundaries of persistent shadow. The Lunar Crater Observation and Sensing Satellite (LCROSS) struck one of the coldest of these regions, where subsurface temperatures are estimated to be 38 kelvin. Large areas of the lunar polar regions are currently cold enough to cold-trap water ice as well as a range of both more volatile and less volatile species. The diverse mixture of water and high-volatility compounds detected in the LCROSS ejecta plume is strong evidence for the impact delivery and cold-trapping of volatiles derived from primitive outer solar system bodies.

Science↗

USGS2009

Discovery of jarosite within the Mawrth Vallis region of Mars: Implications for the geologic history of the region

Analysis of visible to near infrared reflectance data from the MRO CRISM hyperspectral imager has revealed the presence of an ovoid-shaped landform, approximately 3 by 5 km in size, within the layered terrains surrounding the Mawrth Vallis outflow channel. This feature has spectral absorption features consistent with the presence of the ferric sulfate mineral jarosite, specifically a K-bearing jarosite (KFe 3 (SO 4 ) 2 (OH) 6 ). Terrestrial jarosite is formed through the oxidation of iron sulfides in acidic environments or from basaltic precursor minerals with the addition of sulfur. Previously identified phyllosilicates in the Mawrth Vallis layered terrains include a basal sequence of layers containing Fe-Mg smectites and an upper set of layers of hydrated silica and aluminous phyllosilicates. In terms of its fine scale morphology revealed by MRO HiRISE imagery, the jarosite-bearing unit has fracture patterns very similar to that observed in Fe-Mg smectite-bearing layers, but unlike that observed in the Al-bearing phyllosilicate unit. The ovoid-shaped landform is situated in an east-west bowl-shaped depression superposed on a north sloping surface. Spectra of the ovoid-shaped jarosite-bearing landform also display an anomalously high 600 nm shoulder, which may be consistent with the presence of goethite and a 1.92 ??m absorption which could indicate the presence of ferrihydrite. Goethite, jarosite, and ferrihydrite can be co-precipitated and/or form through transformation of schwertmannite, both processes generally occurring under low pH conditions (pH 2-4). To date, this location appears to be unique in the Mawrth Vallis region and could represent precipitation of jarosite in acidic, sulfur-rich ponded water during the waning stages of drying. ?? 2009 Elsevier Inc. All rights reserved.

Icarus↗

USGS2008

Hematite spherules at Meridiani: results from MI, Mini-TES, and Pancam

We report on observations of hematite‐bearing spherules at Meridiani Planum made using the Microscopic Imager (MI), Mini‐Thermal Emission Spectrometer (Mini‐TES), and Panoramic Camera (Pancam) instruments on the Mars Exploration Rover Opportunity. Spherules were observed on soil surfaces and in outcrop rocks, both on undisturbed surfaces and in abraded surfaces ground using the Rock Abrasion Tool (RAT). Spherule size and shape change little along the 850 m eastward traverse from Eagle Crater to Endurance Crater, but spherules decrease and then slightly increase in size along the 6 km traverse from Endurance south to Victoria Crater. Local populations range from submillimeters to several millimeters in diameter. An additional small diameter (100 μ m) size population is possible. An increase in irregular shapes is found near Victoria Crater. This, combined with the size decrease south of Endurance, suggests either a changing depositional environment, or variation in the duration and timing of diagenetic events. The dominant smaller size population observed early in the mission in aeolian areas and ripple crests is observed as the primary size population in abraded outcrop farther south. This suggests that successively younger beds are exposed at the surface along the southward traverse. Stratigraphically higher units removed by erosion could be recorded by the present surface lag deposit. Coordinated systematic observations are used to determine optical and infrared hematite indices of the surface soils in Pancam and Mini‐TES. In spite of the systematic variation seen in MI, both Pancam and Mini‐TES indices are highly variable based on the local surface, and neither show systematic trends south of Endurance. The lack of a 390 cm −1 feature in Mini‐TES spectra suggests concentric or radial interior structure within the spherules at scales too fine for MI to observe. Mini‐TES does not detect any silicate component in the spherules. A bound water component in soils or in exchange with the atmosphere is observed. These spherules have been previously interpreted as concretions formed within what were once water‐saturated, diagenetically altered “dirty evaporate” sandstone sediments. Our observations support this interpretation; however, no single terrestrial analog provides a model that can account for all attributes of the spherules on Mars.

Journal of Geophysical Research↗

USGS2006

Overview of the Opportunity Mars Exploration Rover Mission to Meridiani Planum: Eagle Crater to Purgatory Ripple

The Mars Exploration Rover Opportunity touched down at Meridiani Planum in January 2004 and since then has been conducting observations with the Athena science payload. The rover has traversed more than 5 km, carrying out the first outcrop‐scale investigation of sedimentary rocks on Mars. The rocks of Meridiani Planum are sandstones formed by eolian and aqueous reworking of sand grains that are composed of mixed fine‐grained siliciclastics and sulfates. The siliciclastic fraction was produced by chemical alteration of a precursor basalt. The sulfates are dominantly Mg‐sulfates and also include Ca‐sulfates and jarosite. The stratigraphic section observed to date is dominated by eolian bedforms, with subaqueous current ripples exposed near the top of the section. After deposition, interaction with groundwater produced a range of diagenetic features, notably the hematite‐rich concretions known as “blueberries.” The bedrock at Meridiani is highly friable and has undergone substantial erosion by wind‐transported basaltic sand. This sand, along with concretions and concretion fragments eroded from the rock, makes up a soil cover that thinly and discontinuously buries the bedrock. The soil surface exhibits both ancient and active wind ripples that record past and present wind directions. Loose rocks on the soil surface are rare and include both impact ejecta and meteorites. While Opportunity's results show that liquid water was once present at Meridiani Planum below and occasionally at the surface, the environmental conditions recorded were dominantly arid, acidic, and oxidizing and would have posed some significant challenges to the origin of life.

Journal of Geophysical Research E: Planets↗

USGS2006

Two years at Meridiani Planum: Results from the Opportunity Rover

The Mars Exploration Rover Opportunity has spent more than 2 years exploring Meridiani Planum, traveling ∼8 kilometers and detecting features that reveal ancient environmental conditions. These include well-developed festoon (trough) cross-lamination formed in flowing liquid water, strata with smaller and more abundant hematite-rich concretions than those seen previously, possible relict “hopper crystals” that might reflect the formation of halite, thick weathering rinds on rock surfaces, resistant fracture fills, and networks of polygonal fractures likely caused by dehydration of sulfate salts. Chemical variations with depth show that the siliciclastic fraction of outcrop rock has undergone substantial chemical alteration from a precursor basaltic composition. Observations from microscopic to orbital scales indicate that ancient Meridiani once had abundant acidic groundwater, arid and oxidizing surface conditions, and occasional liquid flow on the surface.

Science↗

USGS2004

Mineralogy at Meridiani Planum from the Mini-TES experiment on the opportunity rover

The Miniature Thermal Emission Spectrometer (Mini-TES) on Opportunity investigated the mineral abundances and compositions of outcrops, rocks, and soils at Meridiani Planum. Coarse crystalline hematite and olivine-rich basaltic sands were observed as predicted from orbital TES spectroscopy. Outcrops of aqueous origin are composed of 15 to 35% by volume magnesium and calcium sulfates [a high-silica component modeled as a combination of glass, feldspar, and sheet silicates (???20 to 30%)], and hematite; only minor jarosite is identified in Mini-TES spectra. Mini-TES spectra show only a hematite signature in the millimeter-sized spherules. Basaltic materials have more plagioclase than pyroxene, contain olivine, and are similar in inferred mineral composition to basalt mapped from orbit. Bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites. Bright wind streak material matches global dust. Waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering.

Science↗

USGS2004

Soils of eagle crater and Meridiani Planum at the opportunity Rover landing site

The soils at the Opportunity site are fine-grained basaltic sands mixed with dust and sulfate-rich outcrop debris. Hematite is concentrated in spherules eroded from the strata. Ongoing saltation exhumes the spherules and their fragments, concentrating them at the surface. Spherules emerge from soils coated, perhaps from subsurface cementation, by salts. Two types of vesicular clasts may represent basaltic sand sources. Eolian ripples, armored by well-sorted hematite-rich grains, pervade Meridiani Planum. The thickness of the soil on the plain is estimated to be about a meter. The flatness and thin cover suggest that the plain may represent the original sedimentary surface.

Science↗