Large-scale shifts in the shelf-edge location of deltaic depocenters have caused temporal and spatial fluxes in sediment supply that have exerted a significant control on the third-order reservoir stratigraphy of the Mars-Ursa, Auger-Macaroni, and Brutus-Bullwinkle intraslope basins, among the most productive areas in the deep water Gulf of Mexico(Fig. 1). Each basin has a producing interval characterized by a remarkably similar up-section transition from more sheet-like turbidite deposits to more channelized deposits, despite locations hundreds of miles apart, and different geologic ages. The transition is directly related to the changing position of the deltaic depocenter with respect to the basins, and the associated increase in sediment supply to the slope with respect to accommodation, independent of fluctuations in eustasy. Figure 1. Simplified stratigraphic columns of the Mars-Ursa, Auger-Macaroni, and Brutus-Bullwinkle intraslope basins. Yellow = sheet sand dominated deposition; orange = channel-dominated deposition. Time scale and sea level curve after Styzen (1996) . Maps of shelf edge deltas and coeval toe of slope fans after Winker and Booth (2000) . Locations of the three basins highlighted (M = Mars-Ursa; B = Brutus-Bullwinkle; A = Auger-Macaroni). Note that observed third-order changes in stratigraphy do not correspond to changes in sea-level, but do tie closely to shifts in the shelf-edge depocenters. Previous workers have described the transition from sheets to channels: Prather et al. (1998) describe a calibrated up-section change in Plio-Pleistocene sediments from a “ponded” seismic facies assemblage to a “bypass” seismic facies assemblage, Booth et al. (2000) describe a similar transition for the Pliocene Auger-Macaroni Basin, and Meckel et al. (2002) describe such a transition in the late Miocene-early Pliocene stratigraphy of the Mars-Ursa area. However, the ubiquitous nature of the transition and its spatial dischroneity has not been previously described, nor has the relationship between the deep-water reservoirs and their coeval shelfedge deltaic depocenters been made explicit. Paleogeographic reconstructions of the position of the shelf-edge systems (Winker and Booth, 2000) show that the deltaic depocenter migrated westward from a location updip of the Mars-Ursa basin in the late Miocene to a location updip and northwest of the Auger-Macaroni basin by the beginning of the late Pliocene. From the late Pliocene to present, the depocenter has migrated eastward, returning to a present-day shelf-edge position very close to where it was during the late Miocene. The depocenter passes updip of the Brutus-Bullwinkle area sometime between the latest Miocene and early Pliocene while migrating westward, and again in the late Pliocene to early Pleistocene, as it migrated eastward. When the deltaic depocenter was in an up-dip, proximal position with respect to each basin, laterally extensive, high net-to-gross sheet sands dominated deposition there. In the Mars-Ursa area, sheet sands were deposited from 9.5 Ma or before until 7.5 Ma. This period correspondeded to deposition of the latter part of the Atwater Unit (terminology of Winker and Booth, 2000). In the Auger-Macaroni area, sheet sands were most prevalent in the section from 4-2.95 Ma, corresponding to deposition of the Keathly Unit (terminology of Winker and Booth, 2000). In the Brutus-Bullwinkle area, sheet sand deposition dominated from 3.5-1.95 Ma, during the early deposition of the Sigsbee Unit (terminology of Winker and Booth, 2000). When the depocenter abandoned one fairway and migrated to a location more distal with respect to a given basin, less continuous, lower net-to-gross channels and overbank deposits dominated deposition. In the Mars-Ursa area, channelized deposition dominated from 7.5-4 Ma, when the depocenter had migrated westward. In the Auger-Macaroni area, channelized deposition dominated from 3-2 Ma, when the depocenter had migrated eastward (corresponding to the sheet sands in the Brutus-Bullwinkle area). As the depocenter continued migrating eastward, channelized reservoirs were deposited in the Brutus-Bullwinkle area from 1.95-1.04 Ma. The transition from sheet sand deposition to channelized deposition occurs at different times in each basin-7.5 Ma in the Mars-Ursa area, 2.95 Ma in the Auger-Macaroni area, and 1.95 Ma in the Brutus-Bullwinkle area-yet the similarity of the transtion argues for a common explanation. The links between sheet dominated, delta-proximal conditions and channel dominated, delta abandonment conditions across space and time implies a fundamental genetic link between the updip and downdip systems that cannot be coincidental. Glacioeustatic changes in sea level and other commonly invoked mechanisms of cyclicity, such as climate or tectonics, are inadequate to explain the observed transitions. Such factors are regional to global in nature, and would result in a more synchronous transition between the areas in question. Furthermore, the magnitude, frequency, and timing of eustatic changes in particular do not correspond to the observed transitions in a meaningful way. Thus, as alternate explanations are neither convincing nor sufficient to explain the data, we conclude that the changing sediment supply associated with shelf-edge depocenter migration is the most reasonable explanation for the transition. In our model, increased sediment supply associated with proximal shelf-edge deltaic systems overwhelmed other possible contributing factors, resulting in sheet sand deposition. Assuming that salt withdrawal created a relatively constant rate of creation of accommodation, the sandy turbidites deposited at this time were able to efficiently fill existing (and newly created) space. The decrease in sedimentation rate that occurred when the depocenter switched locations resulted in channelized deposition that was less efficient in filling the basin with continuous sands. Short-term fluctuations in relative sea level and topography within the overall supply dominated succession (or lack thereof) might have caused higher-frequency (fourth-and fifth-order) alternations between sheets and channels that appear to be another similarity among the basin fills.

Abstract The introduction of Eurocodes to engineering practice represents an importantchange in the approach to geotechnical engineering, as for the first time there is a unified set of codes dealing with the main structural materials including the ground. All of the Eurocodes adopt a limit state design philosophy which is different from the lumped factor of safety approach adopted by traditional geotechnical design practice. This paper examines the implications of the introduction of the Eurocodes, in particular EN1997, when assessing the stability of earthworks. It outlines the various committees responsible for the development of the codes and discusses the application of EN1997 to the assessment of the stability of slopes highlighting the difficulties in applying the various design approaches. Examples from practice are used to highlight where the code is different from traditional practice. A survey of practice in other European countries is outlined which indicates the differing approaches to ensuring adequate reliability being taken across Europe highlighting options that could be considered by the geotechnical community. The paper concludes that the introduction of the Eurocodes does not require a significant change to the way stability analysis is carried out.

Abstract This study demonstrates the application of airborne hyperspectral data for the generation of accurate remote predictive geologic maps, which can be used to assist regional mapping by (1) giving detailed spatial and spectral information, (2) focusing future mapping projects, and (3) highlighting areas of economic potential. The study area is located in southern Baffin Island and comprises a diverse assemblage of lithologic units that are part of the northeastern segment of the Paleoproterozoic Trans-Hudson orogen. Two steps were required to generate remote predictive geologic maps from the hyperspectral image: the extraction of image end members and the application of spectral mixture analysis to generate fractional abundance maps; and converting the fractional abundance maps into predictive geologic maps. Eleven geologic units were extracted from the image data as end members. These end members were identified based on characteristic spectral features and comparisons with field and laboratory spectra. The predictive map correlates well with the existing published map, but more extensive exposures of potentially economic peridotite and carbonate units were found. Lichen-rock mixtures were used to map quartzofeldspathic units that are covered by thick lichen coatings in this region.

Abstract The Pic de Fon iron oxide deposit is located at the southern end of the Simandou Range in the southeastern part of the Republic of Guinea, West Africa. The deposit has a strike length of 7.5 km, is approximately 0.5 km wide, and is open at depth and to the south. Stratigraphy consists of three banded iron formations (BIFs: Lower, Middle, Upper), of which the upper two may be selectively enriched to 65 percent iron over a thickness of at least 250 m. Two episodes of magnetite growth were followed by oxidation to martite (syn-D 2 , proposed as Eburnean II, 2100–2000 Ma) and subsequent bladed microplaty hematite that replaced gangue (dominantly quartz) mesobands. Key iron mineral phases consist of recrystallized martite, hematite overgrowths, and bladed microplaty hematite. Immobile element and density data through selected enrichment transitions suggest that, although the process can involve locally up to a 36 percent net gain in iron, silica removal is the principal control of enrichment, with 33 to 38 percent compaction related to silica loss. Oxygen isotope data for separated quartz (δ 18 O (V-SMOW) 14.0–16.4‰) and hematite (δ 18 O (V-SMOW) –0.7 to +1.3‰) from nonenriched BIF suggest closure of oxygen isotope exchange during retrograde metamorphism (Eburnean II?) at temperatures of 215° to 280°C. Hematite from enriched high-grade rocks exhibits generally lower δ 18 O (V-SMOW) values of –8.9 to +2.0 per mil. This 18 O depletion supports ore-stage hematite equilibration with a moderate-temperature, isotopically light, evolved meteoric fluid within a shallow-crustal hydrothermal system. Iron isotope analyses indicate a general decrease in δ 56 Fe (IRMM-014) of 0.2 to 0.6 per mil during enrichment, confirming nonconservative behavior of iron. It is proposed that hydrothermal activity initiated post-D 2 and was driven by either post-Eburnean II orogenic collapse or a poorly constrained thermal event at approximately 1500 Ma. Needlelike microplaty hematite is possibly associated with structural reactivation during the Pan-African orogeny (750–550 Ma). Loss of silica and redistribution of iron continues to the present day as the result of strong subtropical weathering.

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