Palynology and petroleum potential of the Kazhdumi Formation (Cretaceous: Albian–Cenomanian) in the South Pars field,northern Persian Gulf     

Ebrahim Ghasemi-Nejad  Martin J. Head  Mehrangiz Naderi 《Marine and Petroleum Geology》2009

The Kazhdumi Formation of the Bangestan Group is a well-known source rock that has produced abundant oil in most petroleum fields in the Zagros Basin, which stretches from northwest to southwest Iran over hundreds of kilometres. The formation reaches a thickness of 230 m at the type section in northwest Zagros but thins out to 40–50 m in wells studied from the South Pars giant petroleum field, where it comprises mainly grey shales with occasional intercalations of marls and sandstones. South Pars, best known as the Iranian part of the world's largest non-associated gas field, contains small quantities of oil above and below the Kazhdumi Formation.  相似文献   

Preservation of layered paleodeposits in high-latitude pedestal craters on Mars     

Seth J. Kadish  James W. Head 《Icarus》2011,213(2):443-450

An outstanding question in Mars’ climate history is whether or not pedestal craters represent the armored remnants of ice-rich paleodeposits. We address this question using new high-resolution images; in a survey of several hundred high-latitude pedestal craters, we have identified 12 examples in which visible and/or topographically expressed layers are exposed on the marginal scarp of the pedestal. One example, located on the south polar layered deposits, preserves ice-rich layers that have otherwise been completely removed from the polar cap. These observations provide empirical evidence that the pedestal crater formation mechanism is capable of armoring and preserving ice-rich layered paleodeposits. Although layered exposures have not yet been observed in mid-latitude pedestal craters, high-latitude instances of discontinuous, partially covered layers suggest that layers can be readily concealed, likely through mantling and/or mass wasting processes along the marginal scarp. This interpretation is supported by the observation that high-latitude pedestals with exposed layers along their margins are, on average, taller than mid-latitude examples, and have larger, steeper marginal scarps, which may help to maintain layer exposures. These observations favor the interpretation that mid- to high-latitude pedestal craters represent the armored remnants of ice- and dust-rich paleodeposits, which occurred transiently due to changes in the climate regime. Preservation of fine-scale layering of ice and dust at these latitudes implies that the climate change did not involve regional melting conditions.  相似文献   

Formation of an eroded lava channel within an Elysium Planitia impact crater: Distinguishing between a mechanical and thermal origin     

Debra M. Hurwitz  Caleb I. Fassett  James W. Head  Lionel Wilson 《Icarus》2010,210(2):626-634

A lava channel identified on the wall of an Elysium Planitia impact crater is investigated to identify the dominant erosion mechanism, mechanical vs. thermal, acting during channel formation. Observations of channel morphology are used to supplement analytical models of lava channel formation in order to calculate the duration of channel formation, the velocity of the lava flowing through the channel, and the erosion rate in each erosion regime considered. Results demonstrate that the channel observed in the Elysium Planitia impact crater formed primarily due to mechanical erosion. In a more general sense, results of this study suggest that lava channels can form primarily due to thermal erosion in the presence of more gradual slopes and more consolidated substrates whereas lava channels can form primarily due to mechanical erosion in the presence of more energetic flows on steeper slopes and more poorly consolidated substrates. Therefore, both erosion regimes must be considered when analyzing origins of eroded lava channels that cut through strata of different strengths.  相似文献   

Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian     

David M.H. Baker  James W. Head 《Icarus》2010,207(1):186-209

A variety of Late Amazonian landforms on Mars have been attributed to the dynamics of ice-related processes. Evidence for large-scale, mid-latitude glacial episodes existing within the last 100 million to 1 billion years on Mars has been presented from analyses of lobate debris aprons (LDA) and lineated valley fill (LVF) in the northern and southern mid-latitudes. We test the glacial hypothesis for LDA and LVF along the dichotomy boundary in the northern mid-latitudes by examining the morphological characteristics of LDA and LVF surrounding two large plateaus, proximal massifs, and the dichotomy boundary escarpment north of Ismeniae Fossae (centered at 45.3°N and 39.2°E). Lineations and flow directions within LDA and LVF were mapped using images from the Context (CTX) camera, the Thermal Emission Imaging Spectrometer (THEMIS), and the High Resolution Stereo Camera (HRSC). Flow directions were then compared to topographic contours derived from the Mars Orbiter Laser Altimeter (MOLA) to determine the down-gradient components of LDA and LVF flow. Observations indicate that flow patterns emerge from numerous alcoves within the plateau walls, are integrated over distances of up to tens of kilometers, and have down-gradient flow directions. Smaller lobes confined within alcoves and superposed on the main LDA and LVF represent a later, less extensive glacial phase. Crater size-frequency distributions of LDA and LVF suggest a minimum (youngest) age of 100 Ma. The presence of ring-mold crater morphologies is suggestive that LDA and LVF are formed of near-surface ice-rich bodies. From these observations, we interpret LDA and LVF within our study region to result from formerly active debris-covered glacial flow, consistent with similar observations in the northern mid-latitudes of Mars. Glacial flow was likely initiated from the accumulation and compaction of snow and ice on plateaus and in alcoves within the plateau walls as volatiles were mobilized to the mid-latitudes during higher obliquity excursions. Together with similar analyses elsewhere along the dichotomy boundary, these observations suggest that multiple glacial episodes occurred in the Late Amazonian and that LDA and LVF represent significant reservoirs of non-polar ice sequestered below a surface lag for hundreds of millions of years.  相似文献   

Breccia dikes and crater‐related faults in impact craters on Mars: Erosion and exposure on the floor of a crater 75 km in diameter at the dichotomy boundary     

James W. Head  John F. Mustard 《Meteoritics & planetary science》2006,41(10):1675-1690

Abstract— Environmental conditions on Mars are conducive to the modification and erosion of impact craters, potentially revealing the nature of their substructure. On Earth, postimpact erosion of complex craters in a wide range of target rocks has revealed the nature and distribution of craterrelated fault structures and a complex array of breccia and pseudotachylyte dikes, which range up to tens of meters in width and tens of kilometers in length. We review the characteristics of fault structures, breccia dikes, and pseudotachylyte dikes on Earth, showing that they occur in complex network‐like patterns and are often offset along late‐stage crater‐related faults. Individual faults and dikes can undulate in width and can branch and bifurcate along strike. Detailed geological analyses of terrestrial craters show that faults and breccia dikes form during each of the major stages of the impact‐cratering process (compression, excavation, and modification). We report here on the discovery of prominent, lattice‐like ridge networks occurring on the floor of a highly modified impact crater 75 km in diameter near the dichotomy boundary of the northern lowland and southern upland. Interior fill and crater‐floor units have been exhumed by fluvial and eolian processes to reveal a unit below the crater floor containing a distinctive set of linear ridges of broadly similar width and forming a lattice‐like pattern. Ridge exposures range from ?1–4 km in length and ?65–120 m in width, are broadly parallel, straight to slightly curving, and are cross‐cut by near‐orthogonal ridges, forming a box or lattice‐like pattern. Ridges are exposed on the exhumed crater floor, extending from the base of the wall toward the center. On the basis of the strong similarities of these features to terrestrial crater‐related fault structures and breccia dikes, we interpret these ridges to be faults and breccia dikes formed below the floor of the crater during the excavation and modification stages of the impact event, and subsequently exhumed by erosion. The recognition of such features on Mars will help in documenting the nature of impact‐cratering processes and aid in assessment of crustal structure. Faults and breccia dikes can also be used as data for the assessment of post‐cratering depths and degrees of landform exhumation.  相似文献   

Radiating dike swarms on Venus: evidence for emplacement at zones of neutral buoyancy     

Eric B. Grosfils  James W. Head  III 《Planetary and Space Science》1995,43(12)

Theoretical calculations of extrusive volcanic degassing on Venus yield atmospheric pressure-related rock density profiles consistent with the formation of magma neutral buoyancy zones and magma reservoirs at different depths as a function of altitude (Head and Wilson, J. geophys. Res. 97, 3877, 1992). Global analysis of radiating dike swarms interpreted to originate at magma reservoirs show that their distribution matches these predictions across approximately 90% of the planet's surface; only those highland regions whose elevations exceed 6053 km appear anomalous. The distribution of the large volcano population (extrusive reservoir products) (Keddie and Head, Planet. Space Sci. 42, 455, 1994) has yielded similar results. Comparison between the dike swarm (intrusive) and large volcano (extrusive) populations suggests that neutral buoyancy plays an important role in governing volcanic processes near the venusian surface and that the depth to the level of neutral buoyancy increases systematically at altitudes above 6051 km.  相似文献   

Viscous relaxation of impact craters on icy planetary surfaces: Determination of viscosity variation with depth   总被引：1，自引：0，他引：1  

E.M. Parmentier  J.W. Head 《Icarus》1981,47(1):100-111

Spacecraft images show that the icy Galilean satellites have surfaces with very low topographic relief. Impact craters on Ganymede and Callisto are anomalously shallow and are characterized by sharp well-defined rims and domed floors. These morphological characteristics can be explained by viscous relaxation of topography on an icy crust in which the viscosity is uniform or decreases with depth. Under these conditions, large craters relax more rapidly than small craters, therefore explaining a possible underabundance of large craters. Viscous relaxation on an icy crust that is thin compared to the crater diameter or on a thick icy crust in which viscosity increases with depth could not produce this crater morphology and would result in the more rapid relaxation of small craters rather than large craters. The results of this study suggest that more detailed analysis of relaxing impact crater morphology may resolve the rate of viscosity decrease with depth and so provide evidence on the interior thermal evolution of icy planetary bodies.  相似文献   

Orientale multi-ringed basin interior and implications for the petrogenesis of lunar highland samples     

James W. Head 《Earth, Moon, and Planets》1974,11(3-4):327-356

The lunar Orientale basin and its associated facies formed as a result of impact into lunar highland crustal rocks. The crater rim is shown to be closely represented by the position of the outer Rook Mountain ring, approximately 620 km in diam. The inner Rook Mountains form a central peak ring within the crater. The 900 km diam Cordillera ring is a fault scarp which formed in the terminal stages of the cratering event as a large portion of the crust collapsed inward toward the recently excavated crater, forming a mega-terrace. This collapse pushed the wall of the Orientale crater inward, distorting it and slightly decreasing its radius.A domical facies is almost exclusively developed between the Cordillera and outer Rook rings. The domical facies is interpreted to be radially textured ejecta which was disrupted and modified to a jumbled domical texture by seismic shaking associated with the formation of the mega-terrace. The plains and corrugated facies pre-date the mare fill and lie within the Orientale crater. These facies are interpreted to have been deposited contemporaneously with the cratering event as partial and total impact melts which collected on the floor of the crater during the terminal stages of the event. The plains facies, with an estimated thickness of 1 km and a volume of 75000 km³, represent the most thoroughly impact melted materials which collected and ponded in the central portion of the crater floor. The corrugated facies, with an estimated thickness of 1 km and a volume of 180000 km³, represent impact partial melts mixed with debris. A relatively small volume of mare material was subsequently deposited in the basin (probably less than 25000 km³ in Mare Orientale).There is little evidence that the basin has undergone major structural modifications subsequent to the terminal stages of the cratering event. The striking implication for the Orientale gravity anomaly is that mascon formation may be primarily related to crustal excavation and upwarping of a moho plug, rather than attributable to post-impact mare filling.The plains units on the floor of Orientale are similar to Cayley-like plains in other multi-ringed basins and on smaller crater floors. Impact melt deposits may therefore be a significant source of Cayley-like plains units.The volumes of impact melt associated with the Orientale basin and their mode of deposition have important implications for petrogenetic models. Multi-ringed basin formation provides a mechanism for instantaneously melting large volumes of shallow to intermediate depth lunar crustal material which is emplaced such that the differentiation and crystallization of a variety of igneous rock types and textures may occur.  相似文献   

Serenitatis multi-ringed basin: Regional geology and basin ring interpretation     

James W. Head III 《Earth, Moon, and Planets》1979,21(4):439-462

New topographic data allow a reassessment of the ring structure of the Serenitatis basin and correlation with the younger Orientale basin. The northern Serenitatis basin is smaller and less well preserved than the southern Serenitatis basin. Three major rings of the main (southern) Serenitatis basin are mapped: ring 1, Linné ring, outlined by mare ridges, average diameter 420 km; ring 2, Haemus ring, outlined by basin-facing scarps and massifs with crenulated borders, 610 km; ring 3, Vitruvius ring, outlined by basin-facing linear scarps and massifs, 880 km. Ring 1 corresponds to the inner Rook Mountain ring of Orientale, ring 2 with the outer Rook ring, and ring 3 with the Cordillera Mountain ring. These ring identifications and assignments indicate that the Serenitatis basin is essentially the same size as the Orientale basin, rather than much larger, as previously proposed. The Apollo 17 site lies near the second ring, which is interpreted as the rim of the transient cavity. Apollo 15 lies at the junction of the Serenitatis and Imbrium third rings; Serenitatis ejecta should be present in significant amounts at the Apollo 15 site. The new reconstruction indicates that portions of the Serenitatis basin are better preserved than previously thought, consistent with recent stratigraphic and sample studies that suggest an age for Serenitatis which is older than, but close to, the time of formation of the Imbrium basin.  相似文献   

Geologically recent gully-polygon relationships on Mars: Insights from the Antarctic Dry Valleys on the roles of permafrost, microclimates, and water sources for surface flow     

J.S. Levy  J.W. Head  J.L. Dickson 《Icarus》2009,201(1):113-126

We describe the morphology and spatial relationships between composite-wedge polygons and Mars-like gullies (consisting of alcoves, channels, and fans) in the hyper-arid Antarctic Dry Valleys (ADV), as a basis for understanding possible origins for martian gullies that also occur in association with polygonally patterned ground. Gullies in the ADV arise in part from the melting of atmospherically-derived, wind-blown snow trapped in polygon troughs. Snowmelt that yields surface flow can occur during peak southern hemisphere summer daytime insolation conditions. Ice-cemented permafrost provides an impermeable substrate over which meltwater flows, but does not significantly contribute to meltwater generation. Relationships between contraction crack polygons and sedimentary fans at the distal ends of gullies show deposition of fan material in polygon troughs, and dissection of fans by expanding polygon troughs. These observations suggest the continuous presence of meters-thick ice-cemented permafrost beneath ADV gullies. We document strong morphological similarities between gullies and polygons on Mars and those observed in the ADV Inland Mixed microclimate zone. On the basis of this morphological comparison, we propose an analogous, top-down melting model for the initiation and evolution of martian gullies that occur on polygonally-patterned, mantled surfaces.  相似文献