Large-scale channel fill structures in Late Ordovician glacial deposits in Mauritania, western Sahara Ghienne J.F. & Deynoux M., Sedimentary Geology, 1998, 119/1?2 (141?159)

1999 ◽  
Vol 28 (1) ◽  
pp. VII-VIII
Keyword(s):  
Large Scale ◽  
Late Ordovician ◽  
Glacial Deposits ◽  
Western Sahara

A rock volume accumulation curve for the late Ordovician-Silurian Welsh Basin

1994 ◽  
Vol 131 (4) ◽  
pp. 539-544 ◽  
Author(s):  
Chris J. Clayton
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
Late Ordovician ◽  
Tectonic Uplift ◽  
Sudden Increase ◽  
Submarine Fan ◽  
Accumulation Curve ◽  
River Capture ◽  
Iapetus Ocean ◽  
Rate Of Sedimentation

AbstractA rock accumulation curve is presented for the Ordovician-Silurian Welsh Basin, based on the volume of sediment entering the basin during each graptolite biozone. Even allowing for its inherent uncertainties, the curve still illustrates a significant and sudden increase in the rate of sedimentation in early Silurian time. This may be explained by submarine fan migration, large scale climate change, or river capture in the hinterland, but is most likely caused by tectonic uplift at source. This would support models for either an early Silurian, or late Ordovician closure of the Iapetus Ocean

New palaeomagnetic, petrographic and 40Ar/39Ar data to test palaeogeographic reconstructions of Caledonide Svalbard

2011 ◽  
Vol 149 (4) ◽  
pp. 696-721 ◽  
Author(s):  
KRZYSZTOF MICHALSKI ◽  
MAREK LEWANDOWSKI ◽  
GEOFF MANBY
Keyword(s):  
Remanent Magnetization ◽  
Large Scale ◽  
Age Determination ◽  
Late Ordovician ◽  
Polar Wander ◽  
Close Proximity ◽  
Lateral Displacements ◽  
First Time ◽  
Geographical Locations ◽  
Middle Proterozoic

AbstractNew palaeomagnetic and petrographic data are presented from Cambrian rocks of SW Svalbard to test, for the first time, Palaeozoic reconstructions of the major terranes of Svalbard. In the course of thermal demagnetization three ChRM (characteristic remanent magnetization) components were identified, which were labelled HORNL, HORNM and HORNH, respectively, on the basis of their different unblocking temperatures. The HORNM magnetization is related to the Late Ordovician–Silurian formation of the synmetamorphic S1 foliation. The HORNM palaeopole (Φ = −18.5°, Λ = 359°, Dp/Dm = 5.8°/11.4°, Plat = 6°N) matches exactly the Silurian sectors of the Baltica–Laurentia apparent polar wander paths after the closure of Iapetus (455–415 Ma). The 450 Ma 40Ar–39Ar age determination from mica ages obtained from the broad zone of mylonites along the Billefjorden Fault Zone which separates the Central and Eastern terranes, also suggests that the two terranes were eventually amalgamated by 450 Ma. The HORNMVGP also lies very near the palaeopole derived from the Middle Proterozoic rocks of the Eastern Terrane (Ny Friesland), metamorphosed during Caledonian time, suggesting its close proximity to the study area (Central Terrane). The present study has shown that at least two of the major terranes of Svalbard, as defined by previous authors, occupied similar geographical locations by Silurian time, and the previously proposed large-scale Late Devonian left lateral displacements are not supported.

Fluvial incised networks on top of late Ordovician interglacial valley buried hills as the result of post glacial isostatic rebound; 3D seismic input

2020 ◽  
Author(s):  
Jean-Loup Rubino ◽  
Charlotte Larcher ◽  
Julien Bourget
Keyword(s):  
Large Scale ◽  
Late Ordovician ◽  
3D Seismic ◽  
Isostatic Rebound ◽  
Ice Cap ◽  
Time Flow ◽  
Narrow Valley ◽  
Geomorphic Features ◽  
Valley Networks ◽  
Valley Network

<p>It is classically assume that prior to deep glacial valleys incision below large scale ice cap, often interpreted as the results of ice flow melting during tidewater period, the initial glacial topography was flat or very low angle and created during a major phase of cold glaciers advance as suggested by quaternary studies. Therefore up to now we have assume that the top of late Ordovician buried hills separating major glacial valleys was the remains of this flat surface truncating the pre-glacial Ordovician Hawaz series, later on flooded by the Lower Silurian. Surprisingly by reinterpreting 3D seismic cubes using spectral decomposition technics on the Murzuk basin in SE Libya, it appears that the top of buried hills are not at all characterized by a flat erosional surface, but it is strongly irregular and shows the development of narrow valley networks displaying the classical dendritic erosional pattern diagnostic of fluvial erosion. These small valleys are organized into a tributary network and don’t flow toward the ice margin, i.e. toward the N-NW but most of the time flow at right angle toward the adjacent main glacial valleys which are pointing toward the NW. These narrow valley networks in this context could be either glacial tunnel valleys located at the periphery of the ice cap in close relationships with glacial fronts (their common settings) or could correspond to fluvial valleys developed later on, in a subaerial setting at some distance from glacial fronts; we retain this second interpretation because in addition to the geomorphic features: (1) they flow parallel to the fronts that we have already recognized, Moreau et al. (2005), Rubino et al.  2007 and (2) they are suspended in the sense that these lateral networks do not reach the bottom of the main glacial valley but, they appear to be connected within the upper part of the glacial infill, immediately below the early Silurian post glacial flooding characterized by the well-known Rhuddanian hot shales. As a result, the incision of the valley network appears quite late in the ice cap melting history. It is why we tend to interpret these valleys erosion as the result of post glacial melting during ice retreat at some distance from the ice front and strongly enhanced by isostatic rebound. Some possible modern analogs of such valley fringing highs may exist in Artic Canadian islands.</p>

Late Ordovician (Ashgillian) glacial deposits in southern Jordan

2005 ◽  
Vol 181 (1-2) ◽  
pp. 73-91 ◽  
Author(s):  
Brian R. Turner ◽  
Issa M. Makhlouf ◽  
Howard A. Armstrong
Keyword(s):  
Late Ordovician ◽  
Glacial Deposits

scholarly journals Feeding Specialization of Honey Badgers in the Sahara Desert: A Trial of Life in a Hard Environment

Diversity ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 59
Author(s):  
Jose María Gil-Sánchez ◽  
F. Javier Herrera-Sánchez ◽  
Javier Rodríguez-Siles ◽  
Juan Manuel Sáez ◽  
Miguel Ángel Díaz-Portero ◽  
...  
Keyword(s):  
Large Scale ◽  
Distance Sampling ◽  
Camera Trapping ◽  
Sahara Desert ◽  
Western Sahara ◽  
Feeding Specialization ◽  
Anatomical Adaptations ◽  
Available Information ◽  
North Western

The honey badger (Mellivora capensis) is a medium-sized carnivore distributed throughout Africa to the Arabian Peninsula, Iran, Turkmenistan, and India. However, available information on its ecology is very scarce. We studied its feeding ecology in the remote north-western Sahara Desert, based on the contents of 125 fecal samples collected during large scale surveys. Samples were confirmed to belong to honey badgers by camera trapping and genetic analyses. Barely 18 prey species were detected. The diet primarily consisted of spiny-tailed lizards Uromastyx nigriventris and U. dispar (72% of volume in scats). Secondary prey items were arthropods (14%), small mammals (8%), other reptiles (4%), and eggs (0.8%). Some small geographic and temporal differences were related to the consumption of beetle larvae and rodents as alternative prey. Camera trapping and distance sampling surveys showed that diel activities did not overlap between honey badgers and spiny-tailed lizards, suggesting that badgers primarily dig lizards out of their burrows when inactive. Consumption of spiny lizards by other sympatric meso-carnivores was < 6.1% of occurrence (223 analyzed scats); the honey badger behaved as a trophic specialist in the Sahara, probably thanks to exclusive anatomical adaptations for digging. We discuss the role of this circumstance minimizing the exploitative competition, which could allow the survival of this large mustelid in this low productive and highly competitive environment.

Interpretation of Late Ordovician glaciogenic reservoirs from 3-D seismic data: an example from the Murzuq Basin, Libya

2009 ◽  
Vol 147 (1) ◽  
pp. 28-41 ◽  
Author(s):  
DANIEL PAUL LE HERON
Keyword(s):  
Seismic Data ◽  
Seismic Reflection ◽  
Large Scale ◽  
Late Ordovician ◽  
Hydrocarbon Exploration ◽  
Ice Streams ◽  
Glacial Sediments ◽  
Age Related ◽  
Sedimentary Architecture ◽  
Half Graben

AbstractUnderstanding the recessional behaviour of ancient pre-Cenozoic ice sheets based on seismic reflection studies is generally difficult through scarcity of data. In North Africa, however, hydrocarbon exploration has produced high quality seismic reflection datasets that permit an analysis of the morphology and internal sedimentary architecture of incisions of Late Ordovician age related to the Hirnantian glaciation. Analysis of a high-resolution 3-D seismic dataset covering a small area in western Libya (the N Murzuq Basin) reveals a sharply defined, WNW–ESE-oriented palaeo-escarpment, with a higher (cliff-forming) western margin and a lower (basin-forming) eastern margin. The palaeo-escarpment defines the western flank of a sub-basin extending up to 60 km in width, known as the Awbari Trough. The escarpment and the trough are interpreted as the morphological expression of a major unconformity dividing pre-glacial sediments below from Late Ordovician (?Hirnantian) glacially related sediments above. Two hypotheses are considered for the origins of both the escarpment and the Awbari Trough: (1) as a tectonic feature such as a half graben that was active during sedimentation and (2) a glacially related palaeotopography, with the latter interpretation preferred, owing to the lack of evidence for syn-sedimentary fault activity. The width of the Awbari Trough compares to the large-scale cross-shelf troughs in modern high latitude settings, such as the Barents Shelf, produced by ice streams. The Awbari Trough was progressively filled in by gravity flow deposits throughout the course of the glaciation, until the initial incision became filled in with sediments during an overall glacial retreat phase and ceased to influence sedimentation patterns. Glacial re-advance across the basin produced a second unconformity observed in seismic data. Above this unconformity, meltwater processes incised a shallow (~ 20 m) and wide (~ 5 km) subglacial tunnel valley. Stabilization of the ice front prior to its ultimate retreat resulted in the deposition of a delta complex prior to the Early Silurian transgression.

scholarly journals GGU's photogeological laboratory: aerial photogrammetry – a valuable geological mapping tool in Greenland

1991 ◽  
Vol 152 ◽  
pp. 32-35
Author(s):  
G Hougaard ◽  
H.F Jepsen ◽  
J.K Neve
Keyword(s):  
Large Scale ◽  
Geological Mapping ◽  
Geological Survey ◽  
Aerial Photographs ◽  
Glacial Deposits ◽  
Large Scale Structures ◽  
Aerial Photogrammetry ◽  
Mapping Tool ◽  
Geological Features ◽  
Scale Structures

Geological mapping in Greenland is generally greatly helped by the use of vertical aerial photographs. Bedrock surfaces are normally well exposed, vegetation is sparse in most parts of the country and glacial deposits can be scattered or completely washed away. Consequently, geological features such as bedding, stratigraphical boundaries and large-scale structures are commonly visible on aerial photographs. Since its establishment in 1946 as an independent institution, the Geological Survey of Greenland (GGU) has made extensive use of aerial photographs during mapping campaigns, and photogeological interpretation has played an important role in Copenhagen during map compilation.

scholarly journals Glacial tectonic and flow structures in glaciogenic deposits: a cautionary note

1985 ◽  
Vol 34 ◽  
pp. 3-11
Author(s):  
C. P. Gravenor
Keyword(s):  
Debris Flows ◽  
Large Scale ◽  
Flow Structures ◽  
Small Scale ◽  
Cautionary Note ◽  
Glacial Deposits ◽  
Contact Processes ◽  
Flow Processes ◽  
Scale Structures ◽  
Small Scale Structures

Large scale displacement and deformation of bedrock and associated glacial deposits can be produced by both glacial tectonics and debris flows. Large scale deformation of glacial deposits not associated with dis­placement of underlying strata can be produced by both glacial tectonics and ice-contact processes. Smaller scale structures such as boudins, stringers of sand and silt and laminated diamictons can be pro­duced by both glacial tectonics and flow processes. Examples of both large and small scale structures produced by flow are presented to emphasize the need for adequate criteria to determine the origin of these structures.

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