440 Ma ice stream in North Africa

Moreau, Julien; Ghienne, Jean‐François; Heron, Daniel Paul Le; Rubino, Jean‐Loup; Deynoux, Max

doi:10.1130/g21782.1

Cited by 71 publications

(100 citation statements)

References 19 publications

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“…Glacial valleys, as well as indicators of high fluid pressure, sheath folds and elongated subglacial bedforms evidenced for GP 2 and GP 4, all belong to the palaeo-ice-stream landsystem. Similar ice-stream geomorphological features have been evidenced in the vicinity of Ghat in Libya [50], for example, as well as in the Illizi, Mouydir and Tin Seririne-Tim Mersoï basins in Algeria and Niger [51,52,53].…”

Section: Discussionmentioning

confidence: 82%

Hirnantian glacial and deglacial record in SW Djado Basin (NE Niger).

et al. 2007

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Pluridisciplinary fieldwork highlights features generated by an extended ice-sheet in the Djado Basin during the Hirnantian. Two glacial palaeovalley systems associated with glacial pavements and separated by thin glaciomarine interstadial series are revealed. Rigid glacial pavements characterised by abrasion erosion are differentiated from soft glacial pavements characterised by soft-bed deformation. Glacial pavements are associated with subglacial bedforms such as megaflutes, flutes and meltwater channels. They are also associated with clastic dykes and glaciotectonic structures such as deformed flutes, subglacial folds and duplex structures. This record demonstrates that ice was warm-based and flowed rapidly on the highfluid-pressure soft substrate, as for ice streams. The erosional glacial landscape is typical of areal scouring, and the depositional sediment-landform assemblage corresponds to subglacial processes. These data afford a reconstruction of glacial events which is consistent with the two polyphased low-frequency glacial cycles inferred in previous studies. During interstadial and postglacial stages, grabens, normal faults, radial extensional microfaults and extensional dihedrons were generated by extensional tectonics during glacio-isostatic rebound. In sectors highly affected by this tectonics, doleritic dykes reflect a basal crust fusion increase induced by adiabatic decompression.

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Section: Discussionmentioning

confidence: 82%

Hirnantian glacial and deglacial record in SW Djado Basin (NE Niger).

et al. 2007

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“…Highly elongate MSGLs have even been identified on high-resolution satellite imagery of North Africa, where overlying sediments have been eroded and long-buried Late Ordovician glacier-influenced shelf areas now crop out at the surface (Moreau et al 2005).…”

Section: Volume and Time Frame For Formation Of Submarine Glacial Lanmentioning

confidence: 99%

The variety and distribution of submarine glacial landforms and implications for ice-sheet reconstruction

Dowdeswell

Canals

Jakobsson

et al. 2016

Memoirs

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Glacimarine processes affect about 20% of the global ocean today, and this area expanded considerably under cyclical full-glacial conditions during the Quaternary (Fig. 1) . Many of the submarine landforms produced at the base and margin of past ice sheets remain well preserved on the seafloor in fjords and on high-latitude continental shelves after the retreat of the ice that produced them. These glacial landforms, protected from subaerial erosion and beneath wave-base and tidal currents in water that is often hundreds of metres deep, are gradually buried by both hemipelagic and glacimarine sedimentation; they may be preserved over long periods in the geological record if palaeocontinental shelves are not reworked by subsequent glacier advances or bottom currents ). This means that, first, submarine glacial landforms can be observed at or close to the modern seafloor after retreat of the last great ice sheets from their most recent Quaternary maximum about 18-20 000 years ago using swath-bathymetric mapping systems and, secondly, buried glacial landforms may also be identified and examined within glacial-sedimentary sequences from Quaternary and earlier ice ages using seismic-reflection methods.The development of multibeam echo sounding over the past two decades, coupled with high-accuracy GPS positioning, has allowed morphological mapping of the seafloor at an unprecedented level of detail. In this paper, the variety of submarine glacial landforms observed in modern, Quaternary and more ancient sediments is described. Landforms produced subglacially, those formed at and beyond marine ice-sheet margins, together with the slope processes and bottom currents likely to result in their reworking, are considered along with the sediment volumes of these landforms and the time they take to develop. This is followed by discussion of the significance of submarine glacial landforms and landform-assemblages for reconstruction of the form and flow of past ice sheets, including the former extent and flow direction of ice sheets, whether they are flowing fast as ice streams or slowly in inter-ice stream areas, the nature and rate of ice-sheet deglaciation, conditions at past ice-sheet beds, and inferences on the characteristics of the basal hydrological system and past climatic conditions.

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“…A glacial phase corresponds with a higher frequency advance recession of the ice sheet within a glacial cycle. The multiple glacial erosion surfaces formed characteristic large-scale geomorphological landforms, the glacial ridges (Figure 3c; Moreau et al, 2005). The glacial ridges often form remnant highs flooded after the Silurian postglacial transgression (Lüning et al, 2005;Moreau et al, 2005;Moreau, 2011).…”

Section: Geologic and Glaciological Settingsmentioning

confidence: 99%

“…The multiple glacial erosion surfaces formed characteristic large-scale geomorphological landforms, the glacial ridges (Figure 3c; Moreau et al, 2005). The glacial ridges often form remnant highs flooded after the Silurian postglacial transgression (Lüning et al, 2005;Moreau et al, 2005;Moreau, 2011). The glacial ridges are potential stratigraphic traps laterally sourced by the Early Silurian source rock ("hot" shales; Lüning et al, 2005;Moreau, 2011).…”

Section: Geologic and Glaciological Settingsmentioning

confidence: 99%

Glacial sedimentology interpretation from borehole image log: Example from the Late Ordovician deposits, Murzuq Basin (Libya)

Moreau

Joubert²

2016

Interpretation

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In the Murzuq Basin, the Late Ordovician glaciogenic succession forms a very complex clastic reservoir system. Although the structural setting is simple, the architecture of the stratigraphic succession is particularly intricate, and conventional wireline logs display rather homogeneous signatures. However, when exposed, the glaciogenic sedimentary succession indicates a very large range of depositional environments and clear stratigraphic changes. Based on high-quality processing and interpretation of wireline microresistivity image logs over a single well, our method allows the precise recognition of the internal sedimentary structures and supports the interpretation of the depositional environments within the Late Ordovician succession. During interpretation, it is possible to draw a descriptive sedimentological log, similar to a standard log from cores or outcrops. The image log is interpreted like a regular sedimentary log and compared to an outcrop analog from the nearby outcrop area of Ghat. The success of the well analysis resides in the quality of the borehole image log, permitting the recognition of sandstone grain sizes, textures (facies), and sorting. In addition, crucial information is extracted from the identification of glacial surface and ice-flow orientations, which, combined with the recognition of major transgressive events, allows the recognition and correlation of glacial-type stratigraphy. As in the modern Pleistocene glaciation, stadial/interstadial and glacial/interglacial stages are identified from resistivity imaging of the Libyan Ordovician succession. In addition to the unprecedented potential of correlation between wells within the basin, the sedimentary information extracted from the borehole image log provides important insights on the paleogeographic context of the basin and thus on the exploration potential of the prolific Ordovician-Silurian petroleum system. IntroductionWell petrophysical data interpretations are crucial in petroleum exploration and production. They are routinely conducted and provide essential insights on the quality of the rocks involved in the petroleum system. However, in some sedimentary environments, the acoustic and the petrophysical measurements are not able to provide sufficient diagnostic information to characterize reservoir properties and geometries. The limits of the use of standard logs arise from (1) the possible confusion between formations with similar sand/shale ratios (e.g., basal lag with large shaley clasts formations and sandrich debris flow) and (2) the limited resolution and the smearing effect of standard logs, which do not provide any detailed sedimentological information of the penetrated strata. On the contrary, bed thickness, bed contacts, or postdepositional events, which are important

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440 Ma ice stream in North Africa

Cited by 71 publications

References 19 publications

Hirnantian glacial and deglacial record in SW Djado Basin (NE Niger).

Hirnantian glacial and deglacial record in SW Djado Basin (NE Niger).

The variety and distribution of submarine glacial landforms and implications for ice-sheet reconstruction

Glacial sedimentology interpretation from borehole image log: Example from the Late Ordovician deposits, Murzuq Basin (Libya)

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