USGS Science⌕ Search

Geology topics

M. G. Chapman

Publications and source records attributed to M. G. Chapman.

15 recordsLinked to original sources
USGS2012

The relation of catastrophic flooding of Mangala Valles, Mars, to faulting of Memnonia Fossae and Tharsis volcanism

Detailed stratigraphic relations indicate two coeval periods of catastrophic flooding and Tharsis centered faulting (producing Memnonia Fossae) in the Mangala Valles region of Mars. Major sequences of lava flows of the Tharsis Montes Formation and local, lobate plains flows were erupted during and between these channeling and faulting episodes. First, Late Hesperian channel development overlapped in time the Tharsis-centered faulting that trends north 75° to 90°E. Next, Late Hesperian/Early Amazonian flooding was coeval with faulting that trends north 55° to 70°E. In some reaches, resistant lava flows filled the early channels, resulting in inverted channel topography after the later flooding swept through. Both floods likely originated from the same graben, which probably was activated during each episode of faulting. Faulting broke through groundwater barriers and tapped confined aquifers in higher regions west and east of the point of discharge. The minimum volume of water required to erode Mangala Valles (about 5×10 12 m 3 ) may have been released through two floods that drained a few percent pore volume from a relatively permeable aquifer. The peak discharges of the floods may have lasted from days to weeks. The perched water discharged from the aquifer may have been produced by hydrothermal groundwater circulation induced by Tharsis magmatism, tectonic uplift centered at Tharsis Montes, and compaction of saturated crater ejecta due to loading by lava flows.

Journal of Geophysical Research Solid Earth↗
USGS2008

Geomorphic evidence for former lobate debris aprons at low latitudes on Mars: Indicators of the Martian paleoclimate

Circumferential depressions enclosing mesas and plateaus in the northern Kasei Valles and in the Tartarus Colles regions of Mars are interpreted as indicators of the former extent of lobate debris aprons, thought to be mixtures of ice and elastic particles. These former lobate debris aprons existed about 1 Ga ago and were embayed by lavas or other flow deposits. After the lobate debris aprons had been removed by sublimation and deflation, topographic depressions with a depth of 50 m and a width of several kilometers were left behind between the mesa or plateau scarp and the solidified flow materials. These depressions or moats are located equatorward of ??30?? at significantly lower latitudes than generally observed for occurrences of modem, intact lobate debris aprons. This observation provides evidence that the paleoclimate at that time was different than today, probably due to a higher averaged obliquity of the planet's rotational axis. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗
USGS2008

Evidence for ponding and catastrophic floods in central Valles Marineris, Mars

The Valles Marineris canyon system of Mars is closely related to large flood channels, some of which emerge full born from chaotic terrain in canyon floors. Coprates Chasma, one of the largest Valles Marineris canyons, is connected at its west end to Melas Chasma and on its east end to chaotic terrain-filled Capri and Eos Chasmata. The area from central Melas to Eos Chasmata contains a 1500 km long and about 1 km deep depression in its floor. Despite the large volumes of groundwater that likely discharged from chaotic terrain in this depression, no evidence of related fluvial activity has thus far been reported. We present an analysis of the regional topography which, together with photogeologic interpretation of available imagery, suggests that ponding due to late Hesperian discharge of water possibly produced a lake (mean depth 842 m) spanning parts of the Valles Marineris depression (VMD). Overflow of this lake at its eastern end resulted in delivery of water to downstream chaos regions and outflow channels. Our ponding hypothesis is motivated primarily by the identification of scarp and terrace features which, despite a lateral spread of about 1500 km, have similar elevations. Furthermore, these elevations correspond to the maximum ponding elevation of the region (-3560 m). Simulated ponding in the VMD yields an overflow point at its eastern extremity, in Eos Chasma. The neighborhood of this overflow point contains clear indicators of fluvial erosion in a consistent east-west orientation. ?? 2008 Elsevier Inc.

Icarus↗
USGS2004

Assessing the record and causes of Late Triassic extinctions

Accelerated biotic turnover during the Late Triassic has led to the perception of an end-Triassic mass extinction event, now regarded as one of the "big five" extinctions. Close examination of the fossil record reveals that many groups thought to be affected severely by this event, such as ammonoids, bivalves and conodonts, instead were in decline throughout the Late Triassic, and that other groups were relatively unaffected or subject to only regional effects. Explanations for the biotic turnover have included both gradualistic and catastrophic mechanisms. Regression during the Rhaetian, with consequent habitat loss, is compatible with the disappearance of some marine faunal groups, but may be regional, not global in scale, and cannot explain apparent synchronous decline in the terrestrial realm. Gradual, widespread aridification of the Pangaean supercontinent could explain a decline in terrestrial diversity during the Late Triassic. Although evidence for an impact precisely at the boundary is lacking, the presence of impact structures with Late Triassic ages suggests the possibility of bolide impact-induced environmental degradation prior to the end-Triassic. Widespread eruptions of flood basalts of the Central Atlantic Magmatic Province (CAMP) were synchronous with or slightly postdate the system boundary; emissions of CO2 and SO2 during these eruptions were substantial, but the contradictory evidence for the environmental effects of outgassing of these lavas remains to be resolved. A substantial excursion in the marine carbon-isotope record of both carbonate and organic matter suggests a significant disturbance of the global carbon cycle at the system boundary. Release of methane hydrates from seafloor sediments is a possible cause for this isotope excursion, although the triggering mechanism and climatic effects of such a release remain uncertain. ?? 2003 Elsevier B.V. All rights reserved.

Earth-Science Reviews↗
USGS2003

Sub-ice volcanoes and ancient oceans/lakes: A Martian challenge

New instruments on board the Mars Global Surveyor (MGS) spacecraft began providing accurate, high-resolution image and topography data from the planet in 1997. Though data from the Mars Orbiter Laser Altimeter (MOLA) are consistent with hypotheses that suggest large standing bodies of water/ice in the northern lowlands in the planet's past history, Mars Orbiter Camera (MOC) images acquired to test these hypotheses have provided negative or ambiguous results. In the absence of classic coastal features to test the paleo-ocean hypothesis, other indicators need to be examined. Tuyas and hyaloclastic ridges are subice volcanoes of unique appearance that form in ponded water conditions on Earth. Features with similar characteristics occur on Mars. MOLA analyses of these Martian features provide estimates of the height of putative ice/water columns at the edge of the Utopia Planitia basin and within Ophir Chasma of Valles Marineris, and support the hypotheses of a northern ocean on Mars. ?? 2003 Elsevier Science B.V. All rights reserved.

Global and Planetary Change↗
USGS2002

Related magma-ice interactions: Possible origins of chasmata, chaos, and surface materials in Xanthe, Margaritifer, Meridiani Terrae, Mars

We examine here the close spatial and temporal associations among several unique features of Xanthe and Margaritifer Terrae, specifically the Valles Marineris troughs or chasmata and their interior deposits, chaotic terrain, the circum-Chryse outflow channels, and the subdued cratered material that covers Xanthe, Margaritifer, and Meridiani Terrae. Though previous hypotheses have attempted to explain the origin of individual features or subsets of these, we suggest that they may all be related. All of these features taken together present a consistent scenario that includes the processes of sub-ice volcanism and other magma/ice interactions, results of intrusive events during Late Noachian to Early Amazonian times. ?? 2002 Elsevier Science (USA).

Icarus↗
USGS2001

Observation of the geology and geomorphology of the 1999 Marsokhod test site

The Marsokhod rover returned data from six stations that were used to decipher the geomorphology and geology of a region not previously visited by members of the geomorphology field team. Satellite images and simulated descent images provided information about the regional setting. The landing zone was on an alluvial apron flanking a mountain block to the west and a playa surface to the east. Rover color images, infrared spectra analysis of the mountains, and the apron surface provided insight into the rock composition of the nearby mountains. From the return data the geomorphology team interpreted the region to consist of compressionally deformed, ancient marine sediments and igneous rocks exposed by more recent extensional tectonics. Unconsolidated alluvial materials blanket the lower flanks of the mountains. An ancient shoreline cut into alluvial material marks a high stand of water during a past, wetter climate period. Playa sediments floor a present-day, seasonally, dry lake. Observations made by the rover using panoramic and close-up (hand specimens-scale) image data and color scene data confirmed the presence of boulders, cobbles, and fines of various provinces. Rover traverses to sites identified as geologically distinct, such as fan, channel, shoreline, and playa, provided useful clues to the geologic interpretations. Analysis of local rocks was given context only through comparison with distant geologic features. These results demonstrated the importance of a multifaceted approach to site interpretation through comparison of interpretations derived by differing geologic techniques.

California↗
USGS1998

Corona Associations and Their Implications for Venus

Geologic mapping principles were applied to determine genetic relations between coronae and surrounding geomorphologic features within two study areas in order to better understand venusian coronae. The study areas contain coronae in a cluster versus a contrasting chain and are (1) directly west of Phoebe Regio (quadrangle V-40; centered at latitude 15??S, longitude 250??) and (2) west of Asteria and Beta Regiones (between latitude 23??N, longitude 239?? and latitude 43??N, longitude 275??). Results of this research indicate two groups of coronae on Venus: (1) those that are older and nearly coeval with regional plains, and occur globally; and (2) those that are younger and occur between Beta, Atla, and Themis Regiones or along extensional rifts elsewhere, sometimes showing systematic age progressions. Mapping relations and Earth analogs suggest that older plains coronae may be related to a near-global resurfacing event perhaps initiated by a mantle superplume or plumes. Younger coronae of this study that show age progression may be related to (1) a tectonic junction of connecting rifts resulting from local mantle upwelling and spread of a quasi-stationary hotspot plume, and (2) localized spread of post-plains volcanism. We postulate that on Venus most of the young, post-resurfacing coronal plumes may be concentrated within an area defined by the bounds of Beta, Atla, and Themis Regiones. ?? 1998 Academic Press.

Icarus↗
USGS1995

Geologic and topographic maps of the Elysium Paleolake basin, Mars

These geologic and topographic maps show a basin in the Elysium region of Mars that is thought to have been the site of a large paleolake during the most recent period (Amazonian) in Mars’ history (Scott and Chapman, 1991b). The basin, referred to as the Elysium basin, extends for more than 2,000 km across the lowland plains (fig. 1). It is important, not only geologically, but because the amount, location, and duration of liquid water that it may have contained would have been critical factors governing the possible origin and survival of life on Mars. The Elysium basin is the only large depositional basin on Mars where direct evidence, both geologic and topographic, of former water levels and spillways has been found. However, indications of possible paleoshorelines have been observed in several other areas along the highland-lowland boundary (described under Geologic and Physiographic Setting; Parker and others, 1989; De Hon and Pani, 1992; Scott and others, 1992). Our study of the Elysium basin had two objectives, to determine (1) the maximum extent of the basin and (2) the former volume of water in the basin and the sources of this water. To fulfill these objectives, we have compiled this sets of maps. The geologic maps shows the source channels and circumbasin materials, and the topographic map of the paleolake, on a new topographic base, shows former shorelines and drainage channels.

IMAP↗
USGS1991

Geologic map of science study area 1B, west Mangala Valles region of Mars

This map is one in a series of 1:500,000-scale geologic maps initiated by the National Aeronautic and Space Administration to investigate areas of particular scientific interest on Mars. The west Mangala Valles area merits detailed geologic study because it contains several small channels whose ages can be determined relative to geologic units that range in age from early (Noachian) to late (Amazonian) periods of Martian history. Because the small channels are of three ages and channels of each age are of a geomorphic type unique to that age, their study increases our understanding of the continuity of fluvial process on the evolutionary history of Mars. For these reasons, part of the area is a proposed-site for a sample-return mission to Mars.

IMAP↗
USGS1991

Geologic map of science study area 2, north Kasei Valles, Mars (MTM 25072 Quadrangle)

This map is one in a series of 1:500,000-scale geologic maps initiated by the National Aeronautics and Space Administration to investigate areas of particular scientific interest on Mars. The north Kasei Valles area (fig. 1) merits detailed geologic study because it c ontains part of a large channel system whose age can be determined relative to geologic units that range in age from early intermediate (Early Hesperian) to the very late (Late Amazonian) periods of Martian history . Also, many geomorphic features in the map area suggest changes in water level and multiple erosional events associated with the Kasei Valles system. Later erosional events are indicative of spring sapping ; small-scale, ground-water runoff; and water-mobilized debris flow. Therefore, this large-scale mapping has increased our understanding of the history of hydrolo gic processes on Mars (Chapman and Scott, 1989). For these reasons, part of the area is a candidate site for a sample-return mission to the planet.

IMAP↗