the stratigraphic evolution of a large back barrier lagoon system with a non migrating barrier abstract lake st lucia the largest estuarine system in africa is enclosed by a 120 m high compound quaternary barrier dune system in northern kwazulu natal south africa it comprises several discrete sedimentary basins within a single shallow back barrier water body this paper reports the first very high resolution seismic study of the system seven seismic units a g are identified and interpreted based on their geometry acoustic properties and a sediment coring programme the units are bounded by regionally developed sequence boundaries and lower order unconformity surfaces corresponding to bay and tidal ravinement and hiatus surfaces the lowermost subaerial unconformity formed during regression related to late pliocene hinterland uplift initial infilling of this surface in the proximal areas reflects estuarine sedimentation in a mixed wave and tide dominated system during the subsequent lowstand and early transgressive systems tracts overlain by prograding highstand deltaic deposits that developed as sea levels began to stabilise distally this cycle of sedimentation is initially reflected by the infilling of a similar estuarine system that gradually transitioned to a back barrier lagoon superimposed stillstands drove imbalances in the rate of sediment supply and accommodation space and this coupled with the development of an early barrier complex caused lagoon aggradation and shallowing a second similar trend is repeated for the recent postglacial sea level cycle there appears to be no preservation of the intervening pleistocene cycles of erosion and deposition the system is capped by estuarine lacustrine deposits the onset of lower energy estuarine lake conditions began 6235 cal bp in north lake and started earlier in the proximal false bay owing to sheltering by the antecedent barrier of a rocky peninsula this study reveals a markedly different evolutionary history in adjacent basins of the same back barrier system during two full sea level cycles these are attributed to a long established non migrating barrier and to the influence of antecedent conditions on the system response to transgression unlike the us atlantic margin where migrating barriers truncate the infilling sequences the main stratigraphic unconformities within each fill sequence correspond to tidal and bay ravinement surfaces

plate tectonic development of the south west indian ocean a revised reconstruction of east antarctica and africa a revised sequence of reconstructions for east antarctica relative to africa is generated from published seafloor spreading and fracture zone anomalies these date from the cretaceous tertiary boundary to the late jurassic and lead to a revised predrift reconstruction for east and west gondwanaland euler pole 1 67 s 35 99 e rotation angle 53 43 this reconstruction derived wholly from marine data places east antarctica adjacent to the lebombo mountains and south of and subparallel to the sabi acid volcanic suite supporting the postulate that these rocks represent mesozoic plate boundaries this refit implies that part of the coastal plain of mozambique is underlain by oceanic or very highly extended continental crust the reconstruction is supported by the alignment of 1 the cape fold belt with its antarctic equivalents and 2 the western limit of pan african reactivation of the mozambique mobile belt with the western limit of the sverdrupfjella metamorphic suite antarctica initially moved along a transform fault lying immediately east of and subparallel to the lebombo mountains the eastern face of the tugela cone the southeastern face of the falkland plateau in its reconstructed position and the eastern flank of the agulhas plateau in its reconstructed position at m10 time a triple junction formed near the tip of the falkland plateau implying that the oldest lineated magnetic anomalies in the eastern weddell sea associated with this triple junction cannot predate m10 at m2 time the mozambique ridge rifted from the astrid ridge in a ridge jump episode such an event may also explain the presence of magnetic anomalies in the southern mozambique basin gunnerus ridge conrad rise and del cano rise are all tectonically associated with the madagascar ridge

land sea correlation between late holocene coastal and infralittoral deposits in the se iberian peninsula western mediterranean the well exposed systems of prograding beach ridges on the carchuna calahonda granada and campo de dalias roquetas almeria coastal plains continue offshore as infralittoral prograding wedges ipw the holocene ipw is a narrow morpho sedimentary unit up to 2 5 km wide which develops seaward from the lower edge of the shoreface to 15 20 m depth extending to a well defined break of slope at water depths of 35 40 m these ipws have been recognized and studied using very high resolution seismic profiles topas and multibeam data em 3000d in detail they are complex morpho sedimentary units in which internal structures are closely linked to the pattern of progradation of the adjacent coastal plains when longshore currents produce significant littoral drift the ipws are composed of several minor units arranged in offlap which accrete parallel or oblique to the main shoreline therefore it is possible to correlate progradational units in the coastal plain h units sensu goy j l zazo c dabrio c j 2003 a beach ridge progradation complex reflecting periodical sea level and climate variability during the holocene gulf of almeria western mediterranean geomorphology 50 251 268 and subunits in the ipw but special care is required depending on the local arrangement of morpho sedimentary units besides it is not realistic to draw conclusions regarding the age of the subunits inside a given ipw without adequate dating as the number of subunits will greatly vary from place to place depending on local factors magnitude of sea level oscillations and sediment supply

repeat ridge jumps and microcontinent separation insights from ne arabian sea abstract microcontinents separate due to ridge jumps associate either asymmetric sea floor spreading or plume ridge interactions india separated from seychelles at 64 ma by asymmetric sea floor spreading initially when the spreading centre in the mascarene basin jumped towards the indian sub continent between magnetic chrons c29 and c28 the subsequent tectonics is difficult to comprehend since laxmi ridge another microcontinent formed during the later phase most of the studies considered the laxmi ridge as a sliver others considered it to be oceanic crust high resolution deep 25 km seismic data reveals that i the ridge possesses 15 km deep sea ward dipping reflector sdr packages ii normal faulted rift valleys devoid of syn rift sedimentary packages and iii axial magma chambers 5 7 km beneath the ridge top additionally from 2d forward gravity models we deduce that the ridge most possibly comprises of high density oceanic crust we conclude the laxmi ridge to be indeed composed of oceanic crust and a fossil spreading centre we thus identified the ridge jumps and their relation to the seychelles microcontinent separation previous numerical models suggest that the time required for a ridge jump is controlled by magmatic heating spreading rate at the ridge and plate ages for repeated ridge jumps the additional factor is the dynamic relation between the plume and lithosphere in terms of melt transfer and heating we find that the medium spreading rates and high magmatic heating due to the reunion plume and young plates favoured rapid and repeated ridge jumps towards the plume

anomalous seafloor mounds in the northern natal valley southwest indian ocean implications for the east african rift system abstract the natal valley southwest indian ocean has a complicated and protracted opening history as has the surrounding southwest indian ocean recently collected multibeam swath bathymetry and 3 5 khz seismic data from the natal valley reveal anomalous seafloor mounds in the northern natal valley the significance of these domes as recorders of the geological history of the natal valley and se african margin has been overlooked with little attempt made to identify their origin evolution or tectonic significance this paper aims to describe these features from a morphological perspective and to use their occurrence as a means to better understand the geological and oceanographic evolution of this basin the seafloor mounds are distinct in both shallow seismic and morphological character from the surrounding seafloor of the natal valley between 25 km and 31 km long and 16 km and 18 km wide these features rise some 400 m above the sedimentary deposits that have filled in the natal valley such macro scale features have not previously been described from the natal valley or from other passive margins globally they are not the result of bottom water circulation salt tectonics rather igneous activity is favoured as the origin for these anomalous seafloor features we propose a hypothesis that the anomalous seafloor mounds observed in the natal valley are related to igneous activity associated with the ears the complicated opening history and antecedent geology coupled with the southward propagation of the east african rift system creates a unique setting where continental rift associated features have been developed in a marine setting

geochemistry of neoarchean ca 2 55 2 50 ga volcanic and ophiolitic rocks in the wutaishan greenstone belt central orogenic belt north china craton implications for geodynamic setting and continental growth discussion we read with interest the contribution by polat et al 2005 1 on the origin of neoarchean volcanic and ophiolitic rocks in the wutaishan greenstone belt northern china and their geo dynamic setting we do not dispute the quality of the authors data and their interpretations but we disagree

tertiary sea level movements around southern africa sedimentological micropaleontological and seismic profiling data elucidate the history of tertiary sea level movements around southern africa these new data show that landward movement of the sea began in early paleocene time and continued into the early eocene the sea probably reached its maximum paleocene height during the early eocene and is today represented by outcrops up to at least 204 m and probably as high as 360 m above modern sea level a brief regressive pulse occurred during the middle eocene with renewed transgression in the late eocene a major regression followed probably spanning all of oligocene and early miocene times this regression exposed much of the continental shelf and is clearly represented on seismic reflection profiles by a widespread unconformity the major neogene transgression began in the middle miocene and probably reached its greatest extent in the late miocene or early pliocene the overall middle miocene to early pliocene transgression was interrupted by a brie

palaeo drainage incised valley fills and transgressive systems tract sedimentation of the northern kwazulu natal continental shelf south africa sw indian ocean abstract two sequence boundaries are recognised in seismic data collected from the narrow northern kwazulu natal continental shelf these correspond to late cretaceous and latest pleistocene last glacial maximum lgm periods of sea level fall where fluvial incision into the shelf resulted in several incised valleys having formed in both examples the ensuing transgressive valley fills document an evolution from fluvially dominant sedimentation to classic backbarrier estuarine conditions central estuary basin sedimentation is most prominent within each fill and is separated from the underlying fluvial sediments by bayline ravinement processes tidal ravinement surfaces separate the upper estuarine sequences from barrier and shoreface deposition most easily observed in the latest pleistocene holocene valley fills where a holocene unconsolidated sediment wedge overlies the estuarine fill the wedge itself is characterised by two packages of sediment separated by a regionally occurring wave shoreface transgressive ravinement surface which crops out as a semi indurated shell hash in the mid to outer shelf late cretaceous examples are capped by deposits exhibiting oblique parallel to wavy reflectors interpreted as increasingly energetic deposits analogous to flood tide deltaic sedimentation valley incision and fill are linked to two onshore coastal lake systems lake sibaya and lake st lucia and appear to be the product of barrier breaching and fluvial re adjustment to baseline shifting of these systems during forced regression lake st lucia exhibits a composite palaeo drainage channel where both sequence boundaries merge within the lake margins lake sibaya has two distinct palaeo channels for each sequence boundary episode a late cretaceous channel which fed a small incised valley within which a modern day submarine canyon is located the other an lgm channel directed in towards the head of wright canyon the subsequent input of sediment causing this canyon to breach furthest into the shelf than any other canyon in the area offshore of lake st lucia the most proximal portions of the associated leven canyon occupy the mid shelf and are underlain by lake st lucia palaeo drainage channels of lgm age where erosion along the initial lgm palaeo channel has occurred freshwater exchange between the shelf and the fringing lake system has resulted in the development of sinuous features of leven canyon which have eroded in a downslope fluvial like manner thus occupying palaeo drainage lows as erosive flows were entrained models proposed here indicate that 1 the limited accommodation space offered by a narrow continental shelf may allow for a greater preservation potential of wave dominated estuarine facies 2 the seismic expression of these fills may vary yet still satisfy similar sedimentological conditions and 3 antecedent valley topography increases the preservation potential of these valley fills by providing a preferred space in which to re incise and then fill during sea level rise

stratigraphy petrography and correlation of late cenozoic middle atlantic coastal plain deposits implications for late stage passive margin geologic evolution regional chronostratigraphic correlation of middle atlantic upper coastal plain and fall zone fluvial deposits long thought to represent the updip proximal facies of a well dated post oligocene marine sequence in the salisbury embayment remains incomplete in part because of the paucity of biostratigraphic data petrography based lithostratigraphic correlations provide an opportunity to extend age control present in downdip marine deposits updip to fluvial deposits thus establishing the means for a regional chronostratigraphic correlation previous stratigraphic studies in new jersey delmarva southern maryland virginia and the central appalachian piedmont are linked by a crucial sequence of fluvial deposits at the head of chesapeake bay here petrography based lithostratigraphic correlations demonstrate 1 late oligocene late miocene susquehanna river dominated polygenetic quartzose fluvial aggradation bryn mawr formation 2 pliocene heterolithic but quartz dominated fluvial terrace and alluvial fan deposition perryville formation 3 pliocene early pleistocene paleo delaware hudson river dominated lithic and feldspathic rich fluvial aggradation pensauken formation and 4 the initiation of estuarine conditions turkey point beds by early pleistocene time these results are synthesized to propose a new late cenozoic regional chronostratigraphic correlation and depositional history for the salisbury embayment the correlation elucidates a complex interaction between passive margin isostasy tectonics eustasy and sediment source

late quaternary sea level change in south africa abstract a late quaternary sea level curve for south africa is presented on the basis of new and published data from a range of sea level indicators and a variety of locations available evidence suggests that sea level in south africa broadly follows that described from the caribbean but that deviations occur during sea level highstands during the last interglaciation oxygen isotope stage 5 and the late holocene coastal emergence produced higher sea levels in south africa than those identified in the caribbean during the same time intervals this is tentatively ascribed to predicted lithospheric deformation in continental margin settings

holocene highstand deposits in the gulf of cadiz sw iberian peninsula a high resolution record of hierarchical environmental changes a comparison of the internal structure of holocene highstand shallow marine deposits with emerged spit bar systems in the gulf of cadiz margin sw iberian peninsula is presented in order to increase the knowledge about the patterns of environmental fluctuations of sub milankovitch periodicity during the recent highstand period a high resolution seismic database of boomer profiles was interpreted focusing on shallow marine deposits of the gulf of cadiz shelf such as the guadalquivir river prodelta the guadiana river depositional system and the faro tavira infralittoral prograding wedge the results indicate that the internal architecture of recent highstand shelf deposits is complex as the recognition of three main types of seismic unit motifs suggests the existence of a hierarchical pattern of environmental fluctuations a major scale motifs the most significant feature observed in the seismic records is the pervasive occurrence of two major scale motifs lower and upper within the holocene highstand systems tract b intermediate scale motifs each major scale motif is composed of two intermediate scale motifs defining four intermediate scale motifs h1 to h4 c minor scale motifs the internal structure of major and intermediate scale motifs reveals a high degree of environmental variability during the recent highstand probably led by climatic cyclicities of submillenial scale the lower major scale motif is characterised by alternating progradational aggradational minor scale motifs whereas the upper major scale motif presents a more uniform internal structure dominated by progradational units the influence of two distinct trends or asymmetric cycles of sea level change seems to have been significant in the generation of the major scale architecture the transition between both major phases was probably related with a major sea level rise other factors such as changes in the magnitude and or direction of storm events and climatically induced changes of sediment supply are proposed to have controlled the generation of intermediate and minor scale architectures

marine geology of the sodwana bay shelf southeast africa abstract the geostrophic current controlled northern zululand shelf displays a unique assemblage of interesting physical sedimentological and biological phenomena the shelf in this area is extremely narrow 3 km and is characterised by submarine canyons coral reefs and steep gradients on the continental slope three submarine canyons occur in the study area and are classified as mature or youthful phase canyons depending on the degree to which they breach the shelf these canyons originated as mass wasting features which were exploited by palaeo drainage during sea level regressions shelf lithology is dominated by a series of coast parallel patch coral reefs which have colonised beachrock and aeolianite sequences that extend semi continuously from 5 to 95 m and delineate late pleistocene palaeocoastline events the unconsolidated sediment on the shelf is either shelf sand mainly terrigenous quartz grains or bioclastic sediment large scale subaqueous dunes commonly form in the unconsolidated sediment on the outer shelf due to the agulhas current flow these dunes occur as two distinct fields at depths of 35 to 70 m the major sediment transport direction is towards the south but occasional bedload parting zones exist where the bedform migration direction changes from south to north

genetic stratigraphic sequences in basin analysis ii application to northwest gulf of mexico cenozoic basin the northwest gulf of mexico cenozoic sedimentary wedge illustrates the application of genetic stratigraphic sequence analysis and documents several general conclusions 1 sequences defined by regional marine flooding are the principal genetic stratigraphic units of the basin fill continental margins are characterized by repetitive episodes of basin margin offlap punctuated by periods of transgression and marine flooding of the depositional platform 2 continental margin outbuilding is concentrated at one or more shelf edge deltaic depocenters separated by interdeltaic bights depocenters remain fixed during a depositional episode but commonly relocate during transgression and flooding 3 a distinct syndepositional structural style in prograding continental margins results in sporadic uplift of a basin fringing peripheral bulge and accentuates preservation of shelf margin facies along zones of extensional normal faulting and enhanced subsidence 4 genetic stratigraphic sequences commonly reflect an evolving interplay among two or even three variables for example early cenozoic gulf sequences are most closely related to tectonic events of the intraplate source terrane which in turn affect rate and location of sediment supply and basin margin response to loading late cenozoic sequences more closely reflect proposed eustatic cycles

transform continental margins part 2 a worldwide review we present a global inventory of transform continental margins based on both a worldwide comparison of continent ocean boundary identifications with oceanic fracture zones traces and a compilation of published regional studies this inventory increases the number of identified transform margins from 29 to 78 these margins represent 16 of continental margins in cumulative length and 31 of non convergent margins we include morphological data published upper crustal sections continent to ocean transition locations and published moho shape data in the new database this review confirms that continent to ocean transitions are sharper at transform margins than at divergent margins it also emphasizes the structural diversity of transform margins associated with one third of transform margins we define marginal plateaus as a new type of relief that corresponds to a flat but deep surface inside the continental slope and that may be inherited from crustal thinning prior to transform faulting transform margin initiation appears to be favoured along propagating oceans and within cold and thick lithospheres

sedimentary basin in fill in the northernmost natal valley hiatus development and agulhas current palaeo oceanography sedimentation over large areas of a marginal plateau the northernmost natal valley nnv is influenced by the tropical sub tropical agulhas current through mobilization of detritus and concentration of sedimentation into localized depo centres current action provides a mechanism for hiatus development both in on shelf and off shelf areas post gondwana break up sedimentary basin in fill is interrupted by several regional hiatuses these correlate with coastal regressions global sea level low stands proposed phases of invigorated oceanic circulation and with global phases of slow deep sea sedimentation an assessment of these mechanisms indicates detritus supply related to sea level changes cannot explain correlation of on shelf and off shelf hiatuses current action may have been a contributory factor in development of a cenomanian turonian hiatus and facies change and a cretaceous tertiary boundary hiatus an early oligocene hiatus clearly marks a change in the agulhas current regime current moulded features asymmetric sediment distributions and re working attest to enhanced current action establishment of a cold bottom layer in the ocean at this time stimulated indian ocean surface near surface circulation new circulation patterns were established after a miocene pliocene boundary hiatus since then the main flow paths have been fairly stable although local depo centre shifts late in the pliocene recent sequence suggest eastward movement of a counter current and cyclonic eddy off maputo

a record of appalachian denudation in postrift mesozoic and cenozoic sedimentary deposits of the u s middle atlantic continental margin abstract the complex interplay between source terrain uplift basin subsidence paleoclimatic shifts and sea level change left an extensive sedimentary record in the contiguous offshore basins of the u s middle atlantic margin salisbury embayment baltimore canyon trough and hatteras basin isopach maps of 23 postrift lower jurassic to quaternary a allostratigraphic units coupled with a revised stratigraphic framework reveal that tectonism by regulating sediment supply accumulation rate dominated the interplay of forcing mechanisms tectonic pulses are evidenced by abruptly accelerated sediment accumulation marked latitudinal shifts in the location of depocenters and regional changes in lithofacies relatively rapid tectonic subsidence during the early and middle jurassic history of the basins may have enhanced sediment accumulation rates beginning in the late jurassic however subsidence rates decreased significantly though occasional short pulses of subsidence may have effected relative sea level rises sea level change heavily influenced the distribution and redistribution of sediments one they reached the basins and paleoclimate regulated the relative abundance of carbonates and evaporites in the basins we conclude that source terrains of the central appalachian highlands were tectonically uplifted intensely weathered and rapidly eroded three times since the late triassic 1 early to middle jurassic aalenian to callovian 2 mid early cretaceous barremian and 3 late cenozoic middle miocene intervals of tectonic quiescence following these three tectonic pulses provided conditions suitable for the formation of regional erosion surfaces geomorphic features commonly reported to characterize the central appalachian highlands this series of three irregularly spaced tectonic quiescent cycles does not however match the traditional four cycle concept of post triassic appalachian peneplanation

geological inheritance and its role in the geomorphological and sedimentological evolution of bedrock hosted incised valleys lake st lucia south africa abstract the morphology of lake st lucia africa s largest estuary has been strongly influenced by antecedent topography throughout its quaternary evolution the 5 20 km southern basin is bounded to landward by a 50 m high early mid pleistocene dune ridge and to seaward by a 100 m high late pleistocene holocene dune barrier nine seismic units a i are identified in the enclosed basin along with two regionally developed sequence boundaries sb1 and sb2 and two tidal ravinement surfaces trs1 and trs2 the lowermost sequence boundary sb1 is related to regional late pliocene hinterland uplift sb2 is related to the last glacial maximum lgm when sea levels fell 130 m below present lowstand fluvial sediments occupy the base of both sb1 and sb2 incisions thick central basin deposits dominate the valley fills more so in the pliocene age valleys the occurrence and thickness of which is attributed to sheltering by a seaward barrier dune system as well as to the low gradient settings prograding tidal bedforms occupy the minor incisions formed within the tidal ravinement surfaces marking the onset of lagoonal conditions in the area the system is capped by lagoonal deposits deposited above tidal flats a series of prograding spits mark the early stages of lagoonal segmentation in the holocene the preservation of only one incision and fill sequence prior to the development of an lgm aged valley succession is attributed to geological inheritance whereby older valleys were repeatedly re incised by younger valleys throughout the pleistocene causing partial preservation of pleistocene fills up to the most recent cycle the older fill remnant relates to a larger magnitude base level fall prior to the quaternary which survived erosion during subsequent sea level falls adjacent topography in the form of rocky cliffs and the seaward fronting barrier limit the accommodation space in which infilling material can be hosted outside the major valley network the competent basement rock into which these valleys have incised protected lowstand fluvial sediments from subsequent tidal ravinement

cenozoic global sea level sequences and the new jersey transect results from coastal plain and continental slope drilling the new jersey sea level transect was designed to evaluate the relationships among global sea level eustatic change unconformity bounded sequences and variations in subsidence sediment supply and climate on a passive continental margin by sampling and dating cenozoic strata from coastal plain and continental slope locations we show that sequence boundaries correlate within 0 5 myr regionally onshore offshore and interregionally new jersey alabama bahamas implicating a global cause sequence boundaries correlate with 18o increases for at least the past 42 myr consistent with an ice volume glacioeustatic control although a causal relationship is not required because of uncertainties in ages and correlations evidence for a causal connection is provided by preliminary miocene data from slope site 904 that directly link 18o increases with sequence boundaries we conclude that variation in the size of ice sheets has been a primary control on the formation of sequence boundaries since 42 ma we speculate that prior to this the growth and decay of small ice sheets caused small amplitude sea level changes 20 m in this supposedly ice free world because eocene sequence boundaries also appear to correlate with minor 18o increases subsidence estimates backstripping indicate amplitudes of short term million year scale lowerings that are consistent with estimates derived from 18o studies 25 50 m in the oligocene middle miocene and 10 20 m in the eocene and a long term lowering of 150 200 m over the past 65 myr consistent with estimates derived from volume changes on mid ocean ridges although our results are consistent with the general number and timing of paleocene to middle miocene sequences published by workers at exxon production research company our estimates of sea level amplitudes are substantially lower than theirs lithofacies patterns within sequences follow repetitive predictable patterns 1 coastal plain sequences consist of basal transgressive sands overlain by regressive highstand silts and quartz sands and 2 although slope lithofacies variations are subdued reworked sediments constitute lowstand deposits causing the strongest most extensive seismic reflections despite a primary eustatic control on sequence boundaries new jersey sequences were also influenced by changes in tectonics sediment supply and climate during the early to middle eocene low siliciclastic and high pelagic input associated with warm climates resulted in widespread carbonate deposition and thin sequences late middle eocene and earliest oligocene cooling events curtailed carbonate deposition in the coastal plain and slope respectively resulting in a switch to siliciclastic sedimentation in onshore areas oligocene sequences are thin owing to low siliciclastic and pelagic input and their distribution is patchy reflecting migration or progradation of depocenters in contrast miocene onshore sequences are thicker reflecting increased sediment supply and they are more complete downdip owing to simple tectonics we conclude that the new jersey margin provides a natural laboratory for unraveling complex interactions of eustasy tectonics changes in sediment supply and climate change

anatomy of rapid margin progradation three dimensional geometries of miocene clinoforms new jersey margin documentation of along strike variations in the morphologies of continental margin clinoforms is essential for understanding mechanisms of progradation one of the fundamental relationships between depositional processes and preserved stratigraphy maps based on a grid of commercial multichannel seismic data offshore new jersey extending more than 70 km along strike and approximately 50 km downdip reveal the three dimensional morphology and evolution of four buried surfaces correlated with middle upper miocene sequence boundaries calibrated by drilling on the adjacent continental slope miocene clinoform breakpoints are not depositional analogs of the modern shelf edge they are linear to gently arcuate breakpoint and slope trends indicate a systematic southward displacement of depocenters over about 5 6 m y progradation responded to point fluvial sediment sources but efficient along strike sediment dispersal muted their influence canyons are absent on three of four clinoform slopes the fourth slope has one v shaped canyon and a broad erosional area possible slope failure planar floored canyons also occur albeit rarely seaward of clinoform toes apparently v shaped and planar floored canyons previously ascribed to downslope erosion vs slope failure headward erosion respectively can coexist the accretionary northern slope of little bahama bank is a possible morphologic analog by analogy with pleistocene shelf slope geometries an absence of canyons breaching clinoform breakpoints suggests that rivers did not discharge at paleoshelf edges indicating that sea level lowstands postulated for the middle upper miocene did not expose breakpoints reconstruction of breakpoint paleoelevations supports this conclusion for three of the four mapped surfaces suggesting that elevations of some miocene lowstands on the global sea level curve are too high by up to 60 m

the importance of microbial binding in neogene quaternary steep slopes abstract the geometry and inclination of carbonate platform slopes are typically described as the result of the sediment texture components and grain size occurring in the slope three carbonate slopes from the holocene of the tongue of the ocean bahamas and three slopes from an upper miocene carbonate platform in se spain are investigated to identify the factors controlling dip angles although platforms differ in size and elevation with regard to the surrounding basin both locations present slopes with linear profiles and steep angles over 35 the slope facies in both locations are very similar with the matrix and some bioclasts presenting microfabrics that evidence microbial activity during deposition these include 1 clotted micrite patches locally connecting bioclasts or infilling primary pores 2 porostromate structures in the micrite 3 dense micritic masses 4 binding structures 5 micritic crusts and 6 peloidal textures the holocene and miocene depositional geometries and facies distribution are the response to various sedimentary processes including rockfalls gravity flows and in situ carbonate production extensive microbial binding is identified as the controlling factor for early stabilization of the slope which in combination with subsequent rapid cementation produces and maintains the steep slope angles consequently microbial induced stabilization of modern and neogene slopes is as significant as in paleozoic and triassic examples

submerged barrier shoreline sequences on a high energy steep and narrow shelf abstract late pleistocene holocene shoreline sequences and associated shelf stratigraphy are described from a high gradient high wave energy shelf although shoreline preservation by overstepping is considered unlikely in such an environment as a result of intense ravinement during shoreline translation the development and preservation of two distinct shorelines at 100 m and 60 m are evident and attributed to century to millennial scale periods of stillstand during these periods shoreline equilibrium forms developed characterised by early diagenesis of beachrock and aeolianite between these features the shelf is dominated by erosional surfaces reflecting ravinement during periods of slowly rising sea level where shorelines are not preserved areas of scarping in the ravinement surface at similar depths to the adjoining shorelines represent rocky headlands separating the sandy coastal compartments where the depositional shorelines formed shoreline preservation by overstepping was facilitated by rapid relative sea level rise associated with meltwater pulses 1a and 1b although the features preserved are likely to represent only the cemented cores of the coastal dunes and linear beachrock outcrops formed the steep antecedent shelf gradient fostered the erosion of significant portions of the shorelines by ravinement with loose sediment re organised into a thick post ravinement drape the removal of shorelines during ravinement was countered by the rapid rate of sea level rise and early sub tropical diagenesis it is clear that due to the combined effects of subtropical diagenesis long periods of stillstand and drowning by meltwater pulses the governing controls on shoreline preservation can be over ridden by combinations of local climatic and global eustatic factors

correlation frequency of emplacement and source directions of megaturbidites on the madeira abyssal plain abstract this paper describes the sediments of the whole madeira abyssal plain including the madcap area to the south previous studies have centred on the central sub basin which occupies most of the plain and which has become one of the most studied areas of seafloor the plain is made up of a series of large turbidites separated by thin pelagic layers which can be used to provide a high resolution stratigraphy back to about 750 000 years many of the turbidites were deposited close to oxygen isotope stage boundaries suggesting a strong relationship to sea level climate change although the exact initiation mechanism for the flows is not known data from the northern and southern extensions of the plain shows the effects of different entry points for the four main turbidite groups volcanic rich turbidites enter from the ne and e calcareous turbidites from the w one group of organic rich turbidites enters from the se and one group from the ne and e different turbidite sources operate for limited periods before switching to one of the other source areas it is very rare for two sources to provide turbidites at the same isotope stage boundary

upper wilcox rosita delta system of south texas growth faulted shelf edge deltas the rosita delta system a heretofore unrecognized major depositional system preserved in the deep upper wilcox of south texas was delineated by detailed correlation of approximately 500 well logs the rosita delta system comprises at least three delta complexes each of which can be traced up to tens of miles along strike and up to approximately 15 mi 24 km downdip basinward across the growth fault zone each delta complex thickens from about 600 ft 180 m to more than 3 000 ft 900 m the growth faults were activated by progradation of deltas over unstable prodelta slope muds at the contemporary shelf margin the three upper wilcox delta complexes studied in detail are from oldest to youngest the duval zapata and live oak deltas named for the counties in which they are centered each complex consists of several lobes some of which can be traced across the deep zones where the thickness increases by as much as tenfold owing to progradation over active growth faults characteristic coarsening upward progradational units are interpreted from electric log patterns to include prodelta shales delta front sandstones distributary channel and channel mouth bar sandstones and interdistributary shales and sandstones appreciable variability in sandstone distribution in the deltas may reflect changing importance of fluvial versus marine currents in distributing sediment along the delta front however all of the deltas prograded abruptly toward the shelf margin the gulfward extent of these delta complexes is unknown and it is concluded that appreciable quantities of sandstone remain to be explored in the deep subsurface of the trend

sedimentology and depositional architecture of a submarine delta fan complex in the durban basin south africa abstract the seismic stratigraphy evolution and depositional framework of a sheared passive margin the durban basin of south east africa are described based on single channel 2d seismic reflection data six seismic units a f are revealed separated by major sequence boundaries these are compared to well logs associated with the seismic data set internal seismic reflector geometries and sedimentology suggest a range of depositional regimes from syn rift to upper slope and outer shelf nearshore and continental facies are not preserved with episodic shelf and slope sedimentation related to periods of tectonic induced base level fall the sedimentary architecture shows a change from a structurally defined shelf shearing phase to shallow ramp and then terminal passive margin sedimentary shelf settings sedimentation occurred predominantly during normal regressive conditions with the basin dominated by the progradation of a constructional submarine delta tugela cone during sea level lowstands lst the earlier phases of sedimentation are tectonic controlled however later stages appear to be linked to global eustatic changes

climatic control of turbidite deposition on the madeira abyssal plain studies of sedimentation in the southwestern part of the madeira abyssal plain have revealed sequences of turbidites correlatable over thousands of square kilometres turbidites are sediments transported by turbidity currents and represent rapidly accumulated sedimentary units1 in this case in the distal part of the flow they are very fine grained and homogeneous occasionally with silty bases individual turbidites are separated by thin pelagic units which alternate from oozes to pelagic clays a stratigraphy for these pelagic units has been produced from combining coccolith distributions and lithological changes which enables comparison to cores containing only pelagic sediments from outside the turbidite province these comparisons show that turbidity currents cause no significant erosion in the area the major turbidites occur between lithological alternations which reflect global climate changes associated with glaciations and related eustatic sea level fluctuations turbidites have been linked with eustacy on previous occasions but only with low stands of sea level2 3 our work shows that turbidites are more likely to occur during regressions and transgressions rather than in the quiet periods between

the late cretaceous to holocene sequence stratigraphy of a sheared passive upper continental margin northern kwazulu natal south africa abstract high resolution single channel seismic data reveal seven seismic units a g from the narrow and steep upper portions of the sheared passive continental margin of northern kwazulu natal several characteristic internal geometries are evident onlapping sheet like unit c aggradational progradational unit a and facies d3 and progradational unit b facies d1 2 and facies g1 on the basis of internal geometry and bounding unconformities lowstand units b facies d3 and lowermost unit g possible transgressive unit c highstand upper unit g and falling stage facies d1 and d2 systems tracts are delineated units e and f are not reconcilable due to acoustic opacity overall five incompletely preserved sequences are observed sequence one comprises unit a of suspected middle maastrichtian age separated from the overlying sequence by a subaerial unconformity surface sb1 units b and c form sequence two and span the late cretaceous late maastrichtian to mid late palaeocene two major hiatuses ensued angus and jimmy until mid pliocene times when unit d was deposited during shelf margin advance linked to hinterland uplift these falling stage systems tract deposits are separated from latest pliocene early pleistocene lowstand shelf edge deltaic deposits by a subaerial unconformity marking the deposition of sequence four facies d3 the age of unit e is uncertain unit f represents a series of shorelines formed during oxygen isotope stage ois 5a to 2 on the regressive and transgressive limbs preceding and following the last glacial maximum lgm the final partial sequence preserved is comprised of unit g formed during the ois 2 transgression to present mean sea level and subsequent development of the contemporary highstand wedge in terms of stratigraphic architecture this study shows an evolution from a ramp style margin with a poorly defined shelf break to that of a shelf break profile with a narrow and steep shelf in this respect the narrowness of this shelf cannot be accounted for by the inheritance of shearing effects rather the stratigraphic architecture reflects a period of slow and protracted subsidence with strong sediment dispersal later punctuated by hinterland uplift this formed the late pliocene shelf margin clinoforms of unit d and established the shelf break position at the offlap break of this wedge the resulting narrow shelf may play a significant role in the preservation of later sequences particularly in light of the continued uplift of the margin causing off shelf sediment bypass where tst and hst sequences may not be preserved this is reflected in the isolated preservation of shoreline and shallow marine deposits of the pleistocene units e and f

late cenozoic evolution of the outer continental shelf at the head of the cape canyon south africa abstract cenozoic sedimentary successions have a restricted distribution both onshore and offshore along the passive western margin of southern africa and much controversy and uncertainty remains on the geological evolution of this margin siliciclastic authigenic and biogenic sediments varying in age from cretaceous to holocene recovered from a number of vibrocores collected between 200 and 500 m water depth at the head of the cape canyon provide the basis for an integrated bio sr isotopic and lithostratigraphic study the study area is underlain by unconsolidated middle cretaceous interbedded woody quartzose sand and kaolinitic mud a large regional erosional hiatus separates the upper oligocene to lower miocene carbonate sediments from these cretaceous sediments the upper oligocene to lower miocene 18 1 27 2 ma carbonate succession records third order sea level fluctuations superimposed on an overall marine transgression the interpreted late oligocene depositional environments imply increased bottom water activity over time and the peak in phosphogenesis at 23 6 26 1 ma indicates the onset of warm water upwelling calcareous deposition ended at around 18 ma when downwarping of the continental shelf associated with uplift of the continental interior resulted in the seaward tilt of the carbonate succession to greater water depths increased terrigenous input is recorded as inner shelf prograding quartzose delta front deposits following uplift of the interior uplift combined with a long term marine regression resulted in the widespread erosion of middle to upper miocene successions generally recovered only as reworked glauconite carbonate fluorapatite cfa mixed mineral pellets above the erosional hiatus glauconite rich sediments indicate overall low accumulation rates and multiple reworking events of organic rich clayey sediments during the middle to late miocene early pliocene onset of cold water upwelling at least intermittently by 15 ma established hydrographic conditions similar to the benguela upwelling system with a coast parallel mudbelt present on the middle shelf a middle pliocene marine regression reworked 15 8 9 1 ma inner shelf quartzose delta front sediments across the outer shelf late pliocene early pleistocene uplift of the continental interior resulted in the fault controlled incision of the head of the cape canyon along the seaward flank of the buoyant agulhas columbine basement block uplift increased quaternary terrigenous sedimentation on the shelf where the facies distribution was clearly controlled by canyon head bathymetry high frequency glacio eustatic sea level fluctuations resulted in late quaternary erosion and slumping across the outer shelf and the continued downcutting of the cape canyon lowstand shelly gravels are common including the last glacial maximum shell lag which grades into a faecal pellet rich holocene mud drape over much of the study area the late cenozoic evolution of the western margin recorded in the complex condensed sediment record of the study area is characterised by low sediment accumulation rates and multiple reworking events the integrated stratigraphic interpretation emphasises the importance of eustasy tectonic activity fluvial sediment input palaeoceanographic and climatic changes

early marine isotope stage 5 sea levels coastal dune palaeoenvironments and human occupation on the southeast coast of south africa abstract quaternary age human and animal footprints have been reported from coastal deposits along the south african coast these footprints and their sedimentary contexts can inform on quaternary palaeoenvironments and processes stratigraphically associated with the palaeoanthropological record of past human occupation in the coastal zone and exploitation of its resources this study examines the palaeoenvironmental context and sedimentology of marine isotope stage 5 aeolianite at nahoon point southeastern coast of south africa where preserved human footprints have been previously recorded this study identifies seven sedimentary facies from 20 logged profiles through the coastal aeolianite in order to develop a landscape scale stratigraphic framework for coastal palaeoenvironmental reconstruction during the period of the mis 5 highstand two phases of aeolianite deposition are identified which bracket a single stepped sea level transgression phase up to 7 82 0 82 m asl evidenced by intraformational beachrock facies and marine benches this correlates with the second known global mis 5e highstand no evidence for the first highstand reported from the literature was found in the study area aeolianite bed geometries and sedimentary structures indicate that wind regimes and rainfall seasonality were similar to present newly discovered faunal tracks in aeolianites of the first depositional phase suggest the presence of unidentified bovids of varying sizes evidence for human activity is preserved in all three recorded depositional phases suggesting people were present throughout the early mis 5 sequence despite changing environmental conditions this evidence suggests that human occupation of coastal areas and the exploitation of marine food resources was more widespread than generally thought in southern africa during early mis 5

terrigenous sediment export from the western margin of south africa on glacial to interglacial cycles abstract similar to many shelves globally pleistocene terrigenous sediment deposition on the western shelf of south africa is strongly influenced by high amplitude sea level fluctuations over glacial to interglacial climate cycles here variations in the glauconitic quartzose sand and terrigenous mud content of gravity cores from the western slope of south africa are used to evaluate the dynamics of shelf sediment export over climate cycles of the last 450 kyr calcareous ooze on the slope contains a mean of 0 2 to 8 wt glauconitic quartzose sand derived from erosion of neogene outer shelf sediments and 13 to 40 wt terrigenous mud sourced from the orange river quartz sand content on the slope increases during glacial periods and is sharply reduced across glacial terminations and throughout interglacial highstands relative sea level changes on the margin estimated from the quartz sand content on the slope are consistent with the timing but not amplitude of proposed eustatic sea level records a possible mechanism of sand erosion on the outer shelf is the vertical mixing forced by internal tides which may intensify over the shelf break as sea level is lowered during glacials turbidites are rare and bottom currents are generally capable of suspending mud but not sand except locally along the margin estimated variations in the bulk sedimentation rate and terrigenous mud mass accumulation rate on the slope suggest that export of terrigenous mud off the shelf during glacial lowstands is transported beyond the slope at intermediate and deeper water depths to the southern ocean