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Effects from uncertainties in bathymetric measurements and variability in topography on computed stability of offshore slopes in deep water /Liedtke, Eric Arthur, January 2001 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 379-383). Available also in a digital version from Dissertation Abstracts.
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A Study of Omnidirectional Quad-Screw-Drive Configurations for All-Terrain LocomotionFreeberg, Jon T. 26 October 2010 (has links)
Double-screw vehicles have been developed to operate in soft, wet terrains such as marsh, snow, and water. Their exceptional performance in soft and wet terrains is at the expense of performance on rigid terrains such as pavement. Furthermore, turning can be difficult because the method of turning varies depending on the terrain. Therefore, in this study, several different quad-screw-configurations were proposed and tested to improve upon double-screw vehicles.
A test-bed was developed which could easily be converted into each quad-screw-configuration for testing on a variety of surfaces (grass, dirt, sand, clay, marsh, snow, gravel, pavement, and water). In addition, a force-vector analysis was performed for each screw-configuration to predict and understand performance in different terrains.
From the testing and analysis, the inline-screw configuration was the most versatile because it was omnidirectional on all surfaces but water and pavement. Regardless, it was fully capable of navigating water, both on the surface and submerged, and pavement by rotating about its center.
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Quantifying the sedimentology, stratigraphy and morphodynamics of submarine channelsFernandes, Anjali Mary 26 August 2015 (has links)
This dissertation examines how turbidity currents interact with submarine channels. Turbidity currents display exaggerated super-elevation at the outer banks of channel bends, because they have low excess densities relative to the ambient sea-water. Low-velocity zones form where flows separate from the inner banks. In a high-resolution seismic volume, I mapped 226 inclined surfaces associated with bank-attached bars in 16 channel bends of 2 buried sinuous channels. Position and geometries of bars indicate construction from suspended sediment in flow separation zones. Concave-bank benches, first identified in rivers where they are built from fully-suspended sediment deposited within flow separation zones in channel bends, comprise approximately 19% of this dataset. Bars have high median slopes (10°-11°) and occupy less than 30% of channel width. Associated channels migrated a median distance of less than 70% of the channel width and incised 20-30% of the channel depth. These bars are therefore interpreted to have formed during sediment bypass or weak erosion. I have analyzed the sedimentology and stratigraphy of a well-exposed channel complex, in the Permian Brushy Canyon Formation, west Texas. A steeply-inclined set of fine-grained sandstone beds (median dip=10°) at the margin of the channel complex is interpreted as deposits of a bank-attached bar. Beds are characterized by sub- to super-critically climbing ripple-lamination, planar stratification and trough cross-stratification. Paleo-transport directions are at high angles, 20-120°, to the dip azimuths of interpreted bar surfaces. Geometries of bounding surfaces, sedimentation styles and grain-size data were used to construct a facies model for suspension-dominated, bank-attached bars, built within flow-separation zones in submarine channels. I designed physical experiments to examine how erosional turbidity currents evolve channel- bend topography. Time-lapse bathymetry maps capture the evolution of raised benches tied to sedimentation within flow separation zones and erosion outside of separation zones. Erosional currents showed sensitivity to local conditions. The pattern of erosion was connected to roughness elements such as bend curvature and scours on the bed. Turbidity current run-up at the outside of bends produced a greater aerial extent of side-wall erosion than is commonly seen in incisional rivers.
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A block model for submarine slides involving hydroplaningHu, Hongrui, 1977- 28 August 2008 (has links)
This dissertation details the development of a block model for the movement of submarine slides with emphasis on possible hydroplaning. Unlike previous models, the block model simulated the mechanism of hydroplaning by monitoring the contact condition between the bottom surface of the slide mass and the underlying ground. The effect of hydroplaning on the movement of the slide mass is considered by changing the forces applied on the slide mass by the underlying ground according to the contact condition. The hydrodynamic stresses applied on the slide mass by the surrounding fluid are determined based on the numerical simulations of the flow around a sliding mass. The sliding process of the block is disretisized in a step-by-step manner using a Newmark scheme. A computer program is also written to implement the block model. The block model is validated by comparisons between the numerical results and data reported by Mohrig, et al (1999) for laboratory experiments on subaqueous slides. An illustrative study is also conducted using the block model for the movement of the sediment slabs during the Storegga Slide. The block model has successfully predicted the occurrence of hydroplaning and run-out distances of subaqueous slides. Numerical results with the block model supports the mechanism of hydroplaning for subaqueous slides with greater run-out distances than comparable subaerial slides.
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Η λεπτομερής ιζηματολογική-πετρογραφική μελέτη των αποθέσεων του φλύσχη στη Λήμνο σε σχέση με την παλαιογεωγραφική εξέλιξη του Βορείου Αιγαίου στην κατεύθυνση της πιθανής ύπαρξης πεδίων υδρογονανθράκωνΜαραβέλης, Άγγελος 11 January 2010 (has links)
Ο καθορισμός της ηλικίας των ιζημάτων πραγματοποιήθηκε μέσα από την μελέτη ασβεστιτικών νανοαπολιθωμάτων και έδειξε ότι η ιζηματογένεση τους ξεκίνησε στο ανώτερο Ηώκαινο και ολοκληρώθηκε στο κατώτερο Ολιγόκαινο (NP18-NP21b). Επιπλέον, η απόθεση των υποθαλάσσιων ριπιδίων πραγματοποιήθηκε κατά την διάρκεια των βιοζωνών (NP18-NP21b κατά Μartini, 1971) και προηγήθηκε αυτής της απόθεσης της υφαλοκρηπίδας (ΝΡ21b) δείχνοντας μία προοδευτική σχετική πτώση της στάθμης της θάλασσας. Τα αποτελέσματα της έρευνας οργανικής γεωχημείας βασίστηκαν στην μέθοδο πυρόλυσης Rock Eval 6 και δείχνουν ότι οι αποθέσεις των εξωτερικών τμημάτων του ριπιδίου αποτελούν τα πιο ελπιδοφόρα τμήματα του τουρβιδιτικού συστήματος. Η υφαλοκρηπίδα αποτελεί τον σχηματισμό ο οποίος είναι πιθανόν να παρουσιάσει πετρελαϊκό ενδιαφέρον στο μέλλον μιας και βρίσκεται σε ανώριμο στάδιο θερμικής ωριμότητας Η έρευνα της πιθανής ύπαρξης αποθέσεων που μπορούν να αποτελέσουν ρεζερβουάρ αερίων υδρογονανθράκων στη περιοχή μελέτης αλλά και ο προσδιορισμός της ποιότητας τους βασίστηκε στην τεχνική ποροσιμετρίας υδραργύρου και αποκαλύπτει έναν μεγάλο αριθμό δειγμάτων (8), με αξιόλογες τιμές πορώδους και διαπερατότητας. Τα δείγματα αυτά προέρχονται τόσο από τα εσωτερικά όσο και από τα εξωτερικά τμήματα του τουρβιδιτικού συστήματος ενώ η υφαλοκρηπίδα δεν δείχνει να είναι ικανή να αποτελέσει ρεζερβουάρ αερίων υδρογονανθράκων. Ο προσδιορισμός των ιστολογικών παραμέτρων αποκάλυψε ότι πρόκειται για μεσόκοκκους έως πολύ λεπτόκοκκους ψαμμίτες οι οποίοι προέρχονται τόσο από χαμηλής όσο και από υψηλής πυκνότητας τουρβιδιτικά ρεύματα. Το κοκκομετρικό τους μέγεθος δεν παρουσιάζει σημαντική διαφοροποίηση σε σχέση με τα διάφορα περιβάλλοντα και υποπεριβάλλοντα ιζηματογένεσης. Η γεωχημική στην Λήμνο βασίστηκε στην μέθοδο ενεργοποίησης νετρονίων και δηλώνει ένα περιβάλλον ενεργού ηπειρωτικού περιθωρίου ή ενός ηπειρωτικού νησιωτικού τόξου και ένα μικρό βαθμό ανακύκλωσης (recycling) των υπό μελέτη δειγμάτων. Επιπλέον, αποκαλύπτεται η επίδραση μιας μικτής, όξινης και βασικής/υπερβασικής σύστασης, πηγή τροφοδοσίας. Η ασθενή θετική ανωμαλία στο Eu που παρουσιάζουν, εξηγείται μέσα από ιζηματογενείς διεργασίες όπου τα πλαγιόκλαστα είναι συγκεντρωμένα στις άμμους εξαιτίας της ταξιθέτησης. Η πετρογραφία αποκαλύπτει και την συνεισφορά μιας μεταμορφωμένης, ιζηματογενούς αλλά και μαγματικής πηγής τροφοδοσίας Οι ψαμμίτες συγκεντρώνονται στο πεδίο του ανακυκλωμένου ορογενούς. Η προβολή τους στο συγκεκριμένο πεδίο υποδηλώνει μία ζώνη καταβύθισης ως πιθανό γεωτεκτονικό περιβάλλον της περιοχή μελέτης και είναι σε συμφωνία με την γεωχημική έρευνα και την αποκάλυψη ενός γεωτεκτονικού περιβάλλοντος ενεργού ηπειρωτικού περιθωρίου ή ενός ηπειρωτικού νησιωτικού τόξου για την περιοχή μελέτης. Η ανάλυση και η σύνθεση ιζηματολογικών, παλαιορευματικών, γεωχημικών και πετρογραφικών δεδομένων που πραγματοποιήθηκαν στην περιοχή μελέτης υποδηλώνουν ότι κατά την διάρκεια του ανώτερου Ηωκαίνου-κατώτερου Ολιγοκαίνου (NP18-NP21b) η Λήμνος λειτούργησε ως μία λεκάνη ιζηματογένεσης συστολής μπροστά από το μαγματικό τόξο (contracted forearc basin). Έτσι, η περιοχή μελέτης τοποθετείται ανάμεσα στο ενεργό μαγματικό τόξο της ζώνης της Ροδόπης και στο πρίσμα προσαύξησης το οποίο πιθανόν να βρίσκεται στο βόρειο τμήμα του κεντριού Αιγαίου. / Outcrops of both deep-water and shelf sediments were selected for study on Lemnos Island. During this time interval (NP18-Np21b) the study area was characterized by the deposition of submarine fans that overly shelf deposits with this swallowing upward trend to be owed to tectonic activity. The turbidity system is structured by a “basin floor” fan that is presented overlying a “slope” fan and was constructed under the simultaneous interaction of both progradation and aggradation processes. Both “basin floor” and “slope” fans constitute the lower parts of the stratigraphic column in the study area and have been interpreted as parts of a sand-rich submarine fan on the base of slope to basin floor environment. In order to determine the grain-size statistic and hydraulic parameters thirty (30) thin sections were cut perpendicular to bedding and essentially randomly oriented relative to flow direction. Data obtained from this study suggest that samples are consisted of very-fine to medium grained sandstones, are characterized by poor to very good sorting with their greater part consisting of very good, good and fair sorting sandstones. Moreover, derived from both high and low-density turbidity currents. In order to estimate the flow direction, palaeocurrent data were collected from outcrops. The number of measurements from each outcrop ranges from 10 to 15 and there were plotted in rose diagrams showing that the main palaeocurrent direction has a NNE trend. Twenty samples (20) from the Late Eocene- Early Oligocene turbidite and shelf deposits were selected from the Lemnos Island in order to determine the quantity and quality of the organic matter in each one. The total organic carbon content was determined using a LECO C-230 carbon determinator while the quality of the organic matter was evaluated using a common programmed temperature pyrolysis method, called Rock-Eval 6 pyrolysis by BASELINE RESOLUTION INCORPORATION (BRILABS). The results obtained from the research suggest that studied samples have from poor to excellent source rock potential while the shales of the Lemnos sedimentary rocks can be classified principally as secondary source rocks with potentials to generate gas. In order to assess the tectonic setting of the Lemnos Island, NE Greece, major elements and 14 trace elements were determined using a Thermo Jarrell-Ash ENVIRO II ICP plasma mass spectrometer (ICP-OES) while rare earth elements and additional ultra-trace elements were determined using a Perkin Elmer SCIEX ELAN 6000 (ICP-MS). The study suggests an active margin environment. The positive anomaly of Zr that reflects a heavy mineral input and could be considered typical of passive margin environment is owed to reworking and sorting during sediment transfer. Moreover, a mafic/ultramafic source should be considered as the major component controlling both submarine fans and shelf deposition. The determination of porosity and permeability was based on the “mercury porosimetry technique” as has been described by Katz and Thompson (1986, 1987). Data obtained from this technique suggest that although the majority (13) of the sandstone samples is presented having from fair to very good porosity only some samples (8) have fair to very good permeability.
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Περιβάλλοντα ιζηματογένεσης και στρωματογραφική διάρθρωση του φλύσχη της Πελοποννήσου-πιθανή γένεση υδρογονοθράκωνΚωνσταντόπουλος, Παναγιώτης 20 October 2009 (has links)
Η χαρτογράφηση των περιβαλλόντων ιζηματογένεσης της λεκάνης προχώρας της Πίνδου στην Δυτική Πελοπόννησο στις περιοχές της Τριταίας στα βόρεια, του Χρυσοβιτσίου στα κεντρικά και της Φοινικούντας στα νότια, η οποία βασίστηκε στα υποπεριβάλλοντα των τουρβιδιτικών αποθέσεων έδειξε την ύπαρξη των αποθέσεων εσωτερικού, εξωτερικού ριπιδίου, και αποθέσεις πεδίου λεκάνης.
Η ανάπτυξη των τουρβιδιτικών αυτών υποπεριβαλλόντων έλαβε χώρα από το Ανώτερο Ηώκαινο έως το Κατώτερο Ολιγόκαινο (NP18-NP21), ηλικίες οι οποίες προσδιορίστηκαν από ασβεστιτικά ναννοαπολιθώματα. Το συνολικό στρωματογραφικό πάχος των υπό μελέτη τουρβιδιτών της λεκάνης προχώρας στην Δυτική Πελοπόννησο είναι 418m στην περιοχή της Φοινικούντας, 1096m στην περιοχή της Τριταίας και 327m στην περιοχή του Χρυσοβιτσίου, και φαίνεται να αποτέθηκαν κατά την διάρκεια ενός κύριου τεκτονικού γεγονότος όπου η Γάβροβος και η Ιόνιος ζώνη συμπεριφέρθηκαν ως μια ενιαία λεκάνη προχώρας.
Κατά την διάρκεια του Ανώτερου Ηώκαινου η προχώρα στην Δυτική Πελοπόννησο αποκτά μεγάλο πλάτος με αποθέσεις εσωτερικού και εξωτερικού ριπιδίου. Οι αποθέσεις λοβών εξωτερικού ριπιδίου αναπτύσσονται στο ανατολικό τμήμα της (περιοχή Τριταίας, περιοχή Φοινικούντας) ενώ οι αποθέσεις πεδίου λεκάνης το διάστημα αυτό εντοπίζονται μόνο στην περιοχή της Φοινικούντας στο δυτικό τμήμα της λεκάνης. Η παρουσία των αποθέσεων του πεδίου λεκάνης αυτής της ηλικίας των ιζημάτων στο δυτικό τμήμα της περιοχής της Φοινικούντας, δείχνει μια πιθανή βύθιση, η οποία σχηματίστηκε εξαιτίας πιθανά της δράσης της εσωτερικής επώθησης που βρέθηκε κατά την διάρκεια της διατριβής στην λεκάνη της Φοινικούντας. Το γεγονός ότι η ροή των ιζημάτων, όπως προέκυψε από τα παλαιορευματικά δεδομένα, έχει στις τρεις υπό μελέτη περιοχές φορά προς τα δυτικά, υποδεικνύει ότι ακόμα δεν έχει ενεργοποιηθεί η επώθηση της εσωτερικής Ιονίου, οπότε τα ιζήματα προελαύνουν προς τα δυτικότερα τμήματα της λεκάνης. Στην περιοχή του Χρυσοβιτσίου στο διάστημα αυτό η ιζηματογένεση χαρακτηρίζεται από την απόθεση καναλιών μεσαίου ριπιδίου, γεγονός που υποδεικνύει ένα καθεστώς μεγαλύτερης ευστάθειας του δυτικού περιθωρίου της λεκάνης σε αυτό το τμήμα της. Πρέπει να σημειωθεί ότι στο στάδιο αυτό οι αποθέσεις λοβών στην περιοχή της Φοινικούντας και τμήμα των αποθέσεων του εσωτερικού ριπιδίου στην περιοχή της Τριταίας παρουσιάζουν τεκτονική παραμόρφωση που εκφράζεται με πτύχωση, γεγονός που σημαίνει ότι οι αποθέσεις αυτές αφού αποτέθηκαν και διαγενέθηκαν, υπέστησαν παραμόρφωση πιθανά από την δράση της επώθησης της εσωτερικής Ιονίου. Θα πρέπει ωστόσο να ειπωθεί ότι η παραμόρφωση των αποθέσεων αυτών πιθανά να οφείλεται εν μέρει και σε ολισθήσεις (slump). / The study area lies on the W Peloponnesus, and contains three areas, Tritea on the North, Xrysovitsi on the central and Finikounda on the south. The aim of this thesis is the detailed study of the sedimentary rocks deposited on West Peloponnesus during late Eocene to early Oligocene. Sediments consist of submarine fan and shelf deposits respectively. Study was realized by combining both field and laboratory data that included: detailed sedimentological and tectonic analysis, organic and inorganic geochemical research, porosity and permeability assessment, age determination, petrographical research and grain-size statistic and hydraulic parameters determination.
The object of the thesis is the certain classification of the submarine fan system, the palaiogeographic reconstruction of the Pindos foreland turbidite deposits in west Peloponnesus region and the exploration of possible generation, existence and preservation of hydrocarbons. Outcrops of both deep-water and shelf sediments were selected for study on the three study areas. Due to the scarcity of the outcrops, the studied outcrops were restricted to road cuts and beaches. The lithological units were described in terms of colour, texture, thickness, grain size and sedimentary structures.
During this time interval (NP18-NP21) the study area was characterized by the deposition of submarine fans that overly shelf deposits with this swallowing upward trend to be owed to tectonic activity. The flow types that controlled the depositional processes of the submarine fans were grain flows, debris flows and low-, medium- and high-density turbidity currents while the deposition of shelf can be attributed to both turbidity and shelf storm currents.
The turbidity system is structured by a “basin floor” fan that is presented overlying a “slope” fan and was constructed under the simultaneous interaction of both progradation and aggradation processes. “Basin floor” fan is the more distal and lower positioned, unchannelized fan and is composed of lobe, lobe-fringe and fan-fringe deposits. The “slope fan” consists of channel-overbank deposits where channel-fill facies without base conglomerate underlying the equivalent with base conglomerate demonstrating greater proximity to the source area.
Both “basin floor” and “slope” fans constitute the lower parts of the stratigraphic column in the study area and have been interpreted as parts of a sand-rich submarine fan on the base of slope to basin floor environment in Finikounda area, and as a mixed sand-mud submarine fan system in Tritea area.
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Quaternary Sea-Level and Climate Signatures in Phreatic Coastal Cavesvan Hengstum, Peter 17 November 2010 (has links)
Underwater (phreatic) caves are a ubiquitous landform on coastal karst terrain, but the marine geological processes operating in these systems are largely unknown. This dissertation redresses the problem by asking if Bermudian phreatic cave sediments archive sea-level and climate information? An important premise is that coastal cave environments are not identical. They can be categorized based on whether they are terrestrially-influenced (anchialine), completely flooded by saline groundwater
(submarine), positioned at sea level (littoral) or in the vadose zone (vadose).
For the first time the boundary between modern anchialine and submarine cave environments has been distinguished in Green Bay Cave using a multi-proxy approach (benthic foraminifera, sedimentary organic matter content and carbon isotopic composition - ?13Corg, and grain-size analysis). Twelve push cores were extracted from Green Bay Cave and dated with twenty 14C dates, recovering the first underwater cave succession spanning the Holocene (13 ka to present). Green Bay Cave transitioned through all major cave environments during Holocene sea-level rise (vadose, littoral,
anchialine, and submarine), providing a sedimentary model for global cave successions.
These relationships provide a novel means to solve Quaternary sea-level and
climate problems. For sea level, two examples indicate that the littoral cave can be used as a sea-level indicator, distinguished stratigraphically by microfossil or sedimentary proxies. First, the elevation and timing of when Green Bay Cave was a littoral environment indicates Bermuda experienced an abrupt ~6.4 m sea-level rise at 7.7 ka, coinciding with final collapse of the Labrador sector of the Laurentide Ice Sheet. Second, microfossils preserved in elevated caves at +21 m above modern sea level and dated to
marine isotope stage 11 (U-series, amino acid racemization) are consistent with modern Bermudian caves and co-stratigraphic sea level. For climate problems, annual temperature monitoring in Walsingham Cave indicates that cave water is thermally comparable to regional oceanographic conditions in the Sargasso Sea. Three sediment cores dated with sixteen radiocarbon dates indicate that Bermuda’s coldest and stormiest conditions of the last 3.2 ka occurred during the Little Ice Age (proxies: ?18Oc, grain size, bulk organic matter).
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The marine geology of the Northern KwaZulu-Natal continental shelf, South Africa.Green, Andrew Noel. January 2009 (has links)
This study proposes that the submarine canyons of the northern Kwazulu-Natal continental margin
formed contemporaneously with hinterland uplift, rapid sediment supply and shelf margin
progradation during the forced regression of upper Miocene times. These forced regressive systems
tract deposits volumetrically dominate the shelf sediments, and comprise part of an incompletely
preserved sequence, amongst which six other partially preserved sequences occur. The oldest unit
of the shelf corresponds to forced regression systems tract deposits of Late Cretaceous age (seismic
unit A), into which a prominent erosive surface, recognized as a sequence boundary, has incised.
Fossil submarine canyons are formed within this surface, and underlie at least one large shelf-indenting
canyon in the upper continental slope. Smaller shelf indenting canyons exhibit similar
morphological arrangements. Late Pliocene deposits are separated from Late Cretaceous lowstand
deposits (seismic unit B) by thin veneers of Late Palaeocene (seismic unit C) and mid to early
Miocene (seismic unit D) transgressive systems tract deposits. These are often removed by erosive
hiatuses of early Oligocene and early to mid Pliocene age. These typically form a combined hiatus
surface, except in isolated pockets ofthe upper slope where late Miocene forced regressive systems
tract units are preserved (anomalous progradational seismic unit). These sediments correspond to
the regional outbuilding of the bordering Tukhela and Limpopo cones during relative sea level fall.
Either dominant late Pliocene sediments (seismic unit E), or transgressive systems tract sediments
which formed prior to the mid Pliocene hiatus, overlie these sediments.
Widespread growth faulting, slump structures and prograding clinoforms towards canyon axes
indicate that these sediments initiated upper slope failure which served to create proto-canyon rills
from which these canyons could evolve. The association of buried fossil canyons with modern day
canyons suggests that the rilling and canyon inception process were influenced by palaeotopographic
inheritance, where partially infilled fossil canyons captured downslope eroding flow
from an unstable upper slope. Where no underlying canyons occur, modern canyons evolved from
a downslope to upslope eroding system as they widened and steepened relative to the surrounding
slope. Statistical quantification of canyon forms shows a dominance of upslope erosion. Landslide
geomorphology and morphometric analysis indicate that this occurred after downslope erosion,
where the canyon axis was catastrophically cleared and incised, leading to headward retreat and
lateral excavation of the canyon form. Trigger mechanisms for canyon growth and inception point
to an overburdening ofthe upper slope causing failure, though processes such as freshwater sapping
may emulate this pattern of erosion. It appears that in one instance, Leven Canyon, freshwater
exchange with the neighbouring coastal waterbodies has caused canyon growth.
The canyons evolved rapidly to their present day forms, and have been subject to increasingly
sediment starved conditions, thus limiting their evolution to true shelf breaching canyon systems.
Sedimentological and geomorphological studies show that the shelf has had minor fluvial
influences, with only limited shelf-drainage interaction having occurred. This is shown by isolated
incised valleys of both Late Cretaceous and Late PleistocenelHolocene age. These show classic
transgressive valley fills of wave dominated estuaries, indicating that the wave climate was similar
to that of today. The narrowness of the shelf and the inheritance of antecedent topography may
have been a factor in increasing the preservation potential of these fills. Canyons thus appear to
have been "headless" since their inception, apart from Leven Canyon, which had a connection to
the Last Glacial Maximum (LGM) St Lucia estuary, and Wright Canyon, which had an ephemeral,
shallow LGM channel linking it to the Lake Sibaya estuarine complex.
Coastline morphology has been dominated by zeta bays since at least 84 000 BP, thus littoral drift
has been limited in the study area since these times. The formation of beachrock and aeolianite
sinks during regression from the last interstadial has further reduced sediment supply to the shelf.
The prevalence of sea-level notching in canyon heads, associated with sea levels of the LGM
indicates that canyon growth via slumping has been limited since that time. Where these are
obscured by slumping in the canyon heads (Diepgat Canyon), these slumps have been caused by
recent seismic activity. The quiescence of these canyons has resulted in the preservation of the
steep upper continental slope as canyon erosion has been insufficient to plane the upper slope to a
uniform linear gradient such as that of the heavily incised New Jersey continental margin.
Progressive sediment starvation of the area during the Flandrian transgression has resulted in a
small shore attached wedge of unconsolidated sediment (seismic unit H) being preserved. This is
underlain by a mid-Holocene ravinement surface. This crops out on the outer shelf as a semi-indurated,
bioclastic pavement. Thinly mantling this surface are Holocene sediments which have
been reworked by the Agulhas Current into bedforms corresponding to the flow regime and
sediment availability to the area. Bedforms are in a state of dis-equilibrium with the contemporary
hydrodynamic conditions, and are presently being re-ordered. It appears that sediment is not being
entrained into the canyons to the extent that active thalweg downcutting is occurring. Off-slope
sediment loss occurs only in localized areas, supported by the dominance of finer grained Early
Pleistocene sediments of the outer slope. A sand ridge from the mid shelf between Wright and
White Sands Canyons appears to have been a palaeo-sediment source to White Sands Canyon, but
is currently being reworked southwards towards Wright Canyon. The prevalence of bedform fields
south of regularly spaced canyon heads is considered a function of hydrodynamic forcing of the
Agulhas Current by canyon topography. These bedforms are orientated in a northerly direction into
the canyon heads, a result ofnortherly return eddying at the heads of these canyons. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2009.
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Fracture estimation in anisotropic mediaHood, Julie A January 1990 (has links)
Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1990. / Includes bibliographical references (leaves 44-45) / Microfiche. / vii, 45 leaves, bound ill. 29 cm
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Phosphorite deposits from the sea floor off Peru and Chile : radiochemical and geochemical investigations concerning their originBurnett, William C January 1974 (has links)
Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1974. / Bibliography: leaves 155-164. / viii, 164 leaves ill., map
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