new insights into salt tectonics in the northern dutch offshore a framework for hydrocarbon exploration the northern dutch offshore is an area that has seen less hydrocarbon exploration activity than other areas of the netherlands acquisition of a new regional 3d seismic dataset allowed further testing and re evaluation of established geological concepts in this area it is recognized that the presence and movement of upper permian zechstein evaporites had a major impact on depositional patterns in mesozoic sediments structural development and hydrocarbon migration as such this study looks specifically at the role of salt tectonics in tectonosedimentary development to assess this salt tectonic evolution within its structural context a restoration of the step graben and dutch central graben was performed it follows that depositional patterns are closely linked to the nature of salt structure movement and the timing of regional tectonism for example during late triassic rifting salt pillows developed and sedimentation focused away from salt structures into depocentres along regional fault trends restoration results show that this interplay between salt movement and tectonism is needed to accommodate the sedimentation patterns associated with the formation of the step graben and central graben during the triassic and jurassic and later during late cretaceous and cenozoic inversion tectonics 2018 the author s

pollen record of the past 60 ka bp in the middle okinawa trough terrestrial provenance and reconstruction of the paleoenvironment abstract core dgks9602 931 cm in length was retrieved from the middle okinawa trough the age model was correlated with the adjacent core dgks9603 li et al 2001 for the upper part and to the standard specmap chronology down to 60 ka bp using marine oxygen isotope control points pollen analysis was carried out and seven pollen zones were identified the results showed that the pollen spectra in mis 3 were very different to mis 2 but comparable with the holocene the saccate pollen principally pinus predominated in most parts of the core except for the interval of the last glacial maximum lgm and the late mis 3 when artemisia and other herbs increased prominently the ratios of p a pinus artemisia and of pb nap pollen with bladders versus non arboreal pollen were used as a proxy for sea level change and for estimating distances from the coastline to the study site the provenance study using a modern analog technique based on the east asian modern pollen database and fossil pollen assemblages revealed that the pollen were derived from diverse source areas during different stages since 60 ka bp the pollen zones equivalent to mis 1 and 3 were characterized by uncertain and disparate areas of provenance and the surrounding continents including eastern mainland china korea and southern japan possibly made equivalent contributions which may be the result of enhanced pollen transport by the northwesterly wind however the lgm represented in core dgks9602 was distinguished by restricted sources from the exposed east china shelf where the vegetation was quite similar with the herb coverage in the present day north china plain the pollen assemblages sensitively reflected the coastline changes marked by transport patterns between fluvial runoff and northwesterly winds plus ocean currents some pollen changes and limits of pollen zones coincided with the timing of heinrich events implying that the rapid climate fluctuations during mis 3 and mis 2 may have partially resulted in the forest changes in eastern asia the pattern of relative abundance of subtropical and total arboreal taxa is consistent with that of 18 o from hulu cave implying monsoonal climatic control over vegetation change the estimated temperature mat by the means of pollen ratios for the lgm was 5 8 c lower than that in the changjiang river mouth today

land sea correlation by means of terrestrial and marine palynomorphs from the equatorial east atlantic phasing of se trade winds and the oceanic productivity abstract sporomorphs and dinoflagellate cysts from site gik16867 in the northern angola basin record the vegetation history of the west african forest during the last 700 ka in relation to changes in salinity and productivity of the eastern gulf of guinea during most cool and cold periods the afromontane forest rather than the open grass rich dry forest expanded to lower altitudes partly replacing the lowland rain forest of the borderlands east of the gulf of guinea except in stage 3 when oceanic productivity was high during a period of decreased atmospheric circulation high oceanic productivity is correlated to strong winds the response of marine productivity in the course of a climatic cycle however is earlier than that of wind vigour and makes wind stress induced oceanic upwelling in the area less likely monsoon variation is well illustrated by the pollen record of increased lowland rain forest that is paired to the dinoflagellate cyst record of decreased salinity forced by increased precipitation and run off

deep channels in the cenomanian danian chalk group of the german north sea sector evidence of strong constructional and erosional bottom currents and effect on reservoir quality distribution reflection seismic lines from the schillgrund high in the german north sea sector show that the sea floor deposition of the upper cretaceous danian chalk group was extremely irregular the cenomanian campanian part of the group is up to 600 m 1968 ft thick and is dominated by pelagic relatively horizontally deposited chalk it was tilted toward the southwest close to the campanian maastrichtian boundary time and was overlain by up to 800 m 2625 ft of onlapping maastrichtian danian chalk that was eroded and reworked by powerful synsedimentary bottom currents a north south to north northwest south southeast trending slope parallel multistorey channel system branching toward the northwest into smaller laterally directed arms was developed in maastrichtian danian times it was more than 200 km 124 mi long up to 15 km wide 9 mi and 200 m 656 ft deep the main channel system was eroded by powerful contour parallel bottom currents interpreted as having flowed toward the southeast based on the depositional geometry of the channel fill successive channel axes were systematically shifted downslope leaving a series of slightly offset nested slope parallel channels the channels were filled laterally obliquely or longitudinally by chalk drifts sediment gravity flows were a factor locally but were not integral parts of the depositional system erosion winnowing sorting and redeposition by the bottom currents are interpreted to have resulted in channel parallel porosity permeability zones the seismic data indicate that the chalk adjacent to the main channels retained high porosity calculated from logs in an exploration well drilled in 2005 the chalk is of excellent reservoir quality with effective porosity averaging 37 reaching 50 and some levels are completely unconsolidated the influence of powerful syndepositional bottom currents on the anisotropy of reservoir properties of chalk is only now beginning to be realized chalk having traditionally been considered a monotonous and uniform rock type

new insights on subsurface energy resources in the southern north sea barrin area the southern north sea basin area stretching from the uk to the netherlands has a rich hydrocarbon exploration and production history the past present and expected future hydrocarbon and geothermal exploration trends in this area are discussed for eight key lithostratigraphic intervals ranging from the lower carboniferous to cenozoic in the period between 2007 and 2017 a total of 95 new hydrocarbon fields were discovered particularly in upper carboniferous rotliegend and triassic reservoirs nineteen geothermal systems were discovered in the netherlands onshore mainly targeting aquifers in the rotliegend and upper jurassic lower cretaceous formations although the southern north sea basin area is mature in terms of hydrocarbon exploration it is shown that with existing and new geological insights additional energy resources are still being proven in new plays such as the basal upper rotliegend ruby discovery for natural gas and a new chalk play for oil it is predicted that hydrocarbon exploration in the southern north sea basin area will probably experience a slight growth in the coming decade before slowing down as the energy transition further matures geothermal exploration is expected to continue growing in the netherlands onshore as well as gain more momentum in the uk

contourite drifts moats and channels in the upper cretaceous chalk of the danish basin during the late cretaceous high global sea level meant that most of the nw european craton was flooded by the deep epeiric chalk sea the classical paradigm for chalk deposition envisages a quiet rain of minute skeletal debris of coccolithophorid algae and other pelagic organisms deposited as horizontal flat lying pelagic oozes with local redeposition by slumps slides and debris flows along faults and other structural features seismic data from the danish basin and elsewhere necessitate a revision of this paradigm these demonstrate that the chalk sea floor had a considerable relief commonly of more than a hundred metres amplitude comprising moats drifts mounds and channels seismic sections from the kattegat sea illustrate the development in the maastrichtian of a deep moat adjacent to a topographic ridge formed over the inverted nw se trending sorgenfrei tornquist zone the moat was up to 120 m deeper than its sw flank which was formed by an internally complex elongate drift up to 20 km wide with an estimated length of ca 200 km smaller mound like features channels and clinoform beds are superimposed on the large scale relief the sea floor relief is interpreted to have formed in response to persistent bottom currents flowing parallel to bathymetric contours the initial build up of the broad gently convex up sheeted drift was controlled by relatively low velocity bottom currents the region of highest current velocity was gradually shifted ne wards towards the inversion zone ridge resulting in the formation of the deep moat flanked by the elongate drift the current is interpreted to have flowed from the se towards nw on the basis of the internal architecture of the elongate drift and the nw ward branching and decrease in moat relief the architecture and morphology of the moat drift and other features of the chalk sea floor are in all aspects similar to contourite systems of modern continental margins it is accordingly proposed that the fundamental physical oceanographic concept contour currents and their resulting contourite drifts is extended to include the deep epeiric seas which covered nw europe during the late cretaceous

marine palynological record for tropical climate variations since the late last glacial maximum in the northern south china sea the upper part 191 1439 cm of the marine sediment core md05 2906 from the northern south china sea scs was palynologically investigated the chronology suggested that it covered the record since 19 calendar kiloyears before present cal ka bp and revealed a detailed environmental change history since the late last glacial maximum lgm during the late lgm due to the lowered sea level 100 m lower and the shortened distance from the shore to the study site the pollen concentration was very high the pollen assemblages were dominated by non arboreal taxa especially artemisia pollen before 15 cal ka bp abundant subtropical and tropical pollen taxa were still important components and a south subtropical climate prevailed during the late lgm the coexistent rich artemisia pollen possibly was not derived from near shores but was derived mainly from the northern exposed continental shelf in the east china sea ecs after 15 cal ka bp with the rise in the sea level and enhanced distance from the pollen source areas to the core site pollen concentrations started to decline gradually however during the late deglaciation and early holocene the higher concentrations of many pollen taxa reoccurred which cannot be attributed to the sea level changes pinus pollen deposited in the core which is considered to be mostly water carried based on many modern pollen surveys also started to dramatically increase at the same time therefore the higher pollen concentration with more pinus and typha an aquatic plant pollen indicated a notably enhanced terrestrial runoff and precipitation during the last deglaciation holocene transition 11 3 9 4 cal ka bp we inferred that a strong summer monsoon occurred at this time during the late lgm deglaciation transition period the pollen assemblage reflected a gradually warming climate and the climate fluctuations derived from the high latitudes were not well identified this study suggests that solar insolation played a crucial role in controlling the east asian monsoon and hydrological cycle in the northern scs

slope failure of chalk channel margins implications of an upper cretaceous mass transport complex southern england the importance of mass transport and bottom currents is now widely recognized in the upper cretaceous chalk group of northern europe the detailed dynamics and interaction of the two phenomena are difficult to study as most evidence is based on seismic data and drill core here field observations provide evidence for recurring margin collapse of a long lived campanian channel compressionally deformed and thrust chalk hardgrounds are correlated to thicker non cemented chalk beds that form a broad gentle anticline these chalks represent a slump complex with a roll over anticline of expanded non cemented chalk in the head region and a culmination of condensed hardgrounds in the toe region observations strongly suggest that the slumping represents collapse of a channel margin farther northwards the contemporaneous succession shows evidence of small scale penecontemporaneous normal faulting towards the south here interpreted as gravitational settling of the chalk immediately adjacent to the channel margin detailed biostratigraphic studies and sedimentological observations provide evidence for at least two discrete collapse events and suggest the slumping to be the result of channel margin oversteepening rather than evidence for a regional tectonic phase the described example thus serves as an analogue for processes commonly only inferred from subsurface data

cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode oceanic anoxic events oaes were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen deficient bottom waters oae2 occurring at the cenomanian turonian boundary about 93 5 myr ago is the most widespread and best defined oae of the mid cretaceous although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios the actual trigger mechanism corresponding closely to the onset of these episodes of increased carbon sequestration has not been clearly identified it has been postulated that large scale magmatic activity initially triggered oae2 refs 4 5 but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of oae2 has not yet been found here we report seawater osmium isotope ratios in organic rich sediments from two distant sites we find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of oae2 using a simple two component mixing equation we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin a approximately 30 50 fold increase relative to pre oae conditions furthermore the magmatic osmium isotope signal appears slightly before the oae2 as indicated by carbon isotope ratios suggesting a time lag of up to approximately 23 kyr between magmatism and the onset of significant organic carbon burial which may reflect the reaction time of the global ocean system our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of oae2 which may have triggered the subsequent deposition of large amounts of organic matter

the paleocene stratigraphic records in the central netherlands and close surrounding basins highlighting the different responses to a late danian change in stress regime within the central european basin system despite their similar structural style of inversion under late cretaceous compressional stress basins in the central european basin system showed different kinematic responses to a late danian change in the european intra plate stress field the late cretaceous phase was recognized throughout the central european basin system by compressional inversion of the mesozoic rifts and the simultaneous formation of marginal troughs the late danian change in stress regime resulted in a middle paleocene phase which excited longer wavelength of vertical surface movements in several basins in central europe this middle paleocene phase was characterized by domal uplift of the late cretaceous inversion zones and their proximal areas which was interpreted to result from a sudden relaxation of the in plane tectonic stress a so called relaxation inversion based on the paleocene stratigraphic records this study shows that some basins in the south western part of the central european basin system experienced subsidence of the late cretaceous inversion zones during the middle paleocene phase or the complete opposite vertical surface movements of a relaxation inversion two possible mechanisms superposition of relaxation inversions and lithospheric folding during compression are discussed that could provide an explanation for the opposite late danian and selandian vertical surface movements of nearby basins in the central european basin system

interaction between bottom currents and slope failure in the late cretaceous of the southern danish central graben north sea the nw european chalk group was deposited in a deep epicontinental sea traditionally conceived as a quiet depositional setting that was only affected by redeposition along structural highs the chalk sea was however locally affected by powerful bottom currents during some periods three dimensional seismic reflection data from the southern central graben show abundant intra chalk morphological elements concentrated at two stratigraphic levels within the turonian campanian sequence both levels are topped by extensive unconformities the geometry of the elements produced by alongslope processes is interpreted as caused by se directed bottom currents flowing between the bo jens and adda ridges the highest current intensities led to the formation of the two unconformities judged by the occurrence of the largest current formed channels and drifts at these two stratigraphic levels this sea floor topography was locally modified by large scale downslope mass transport stratigraphical coincidence of the largest slumps and bottom current erosion suggests a coupling between downslope and alongslope processes current erosion impinged upon the slopes during periods of highest current speeds destabilizing the slope sediments and triggering slumping the smoothing of the bathymetry following local relaxation of the tectonic inversion accounted for the coeval deactivation of alongslope and downslope processes during the succeeding maastrichtian deposition

south china sea fluvial sediments an introduction the south china sea offers a special research opportunity for earth scientists because of its location and its well preserved terrigenous sediments wang and li 2009 as the largest one of the marginal seas separating asia from the pacific the south china sea functions as a natural laboratory for study of land sea interactions because of its unique source to sink record of fluvial sediments the south china sea receives more than 600 million tons of detrital sediments annually from numerous rivers including world s largest rivers such as the pearl the red and the mekong fig 1

seismic stratigraphy of the chalk group in the norwegian central graben north sea abstract the late cretaceous to early palaeogene chalk group in the norwegian central graben contains prolific hydrocarbon reservoirs that have been producing at high rate for more than forty years based on integration of regionally extensive 3d seismic data and numerous wells this paper describes the seismic development of the chalk group with particular focus to the syndepositional geomorphological features produced by the activity of bottom currents and large scale gravity flows using standard seismic stratigraphic interpretation techniques eight seismic sequence boundaries are identified which in turn define seven seismic stratigraphic sequences characterized by different seismic facies and well log signatures the seismic sequences can be grouped into three sequence groups that reflect the general tectono stratigraphic evolution of the chalk depositional system in the norwegian central graben during the late cretaceous uplift of the lindesnes ridge and the albuskjell anticline due to inversion tectonic and halokinesis modified the physiography of the norwegian central graben basin and affected the style of chalk sedimentation by influencing the location and importance of gravity flows in addition bottom currents sea level fluctuations and environment changes significantly influenced the chalk depositional system creating regional unconformities and influencing the input of terrigenous material in the chalk epeiric sea

geological evolution of the chalk group in the northern dutch north sea inversion sedimentation and redeposition in contrast to the norwegian and danish sectors where significant hydrocarbon reserves were found in chalk reservoirs limited studies exist analysing the chalk evolution in the dutch part of the north sea to provide a better understanding of this evolution a tectono sedimentary study of the late cretaceous to early palaeogene chalk group in the northern dutch north sea was performed facilitated by a relatively new 3d seismic survey integrating seismic and biostratigraphic well data seven chronostratigraphic units were mapped allowing a reconstruction of intra chalk geological events the southwestward thickening of the turonian sequence is interpreted to result from tilting and the absence of coniacian and santonian sediments in the western part of the study area is probably the result of non deposition seismic truncations show evidence of a widespread inversion phase the timing of which differs between the structural elements it started at the end of the campanian followed by a second pulse during the maastrichtian a new finding not reported before after subsidence during the maastrichtian and danian renewed inversion and erosion occurred at the end of the danian halokinesis processes resulted in thickness variations of chalk units of different ages in summary variations in sedimentation patterns in the northern dutch north sea relate to the sub hercynian inversion phase during the campanian and maastrichtian the laramide inversion phase at the end of the danian and halokinesis processes additionally the late cretaceous sea floor was characterized by erosion through contour bottom currents at different scales and resedimentation by slope failures

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

structural evolution timing and tectonic style of the sole pit inversion abstract the nw se oriented sole pit high located in the western half of the southern north sea basin is the result of three different structural processes initiated during the late palaeozoic basin subsidence probably related to late hercynian pull apart movements led to continuous sedimentation from the permian to the middle jurassic mid jurassic doming of its eastern flank followed by erosion transtensional movements and differential subsidence until the early cretaceous reflect the mid and late kimmerian crustal distension and fragmentation of the north sea rift basinwide inversion occurred between the turonian and the campanian and was repeated in the oligocene resulting in a total uplift of some 1500 m the present structural style is represented by a complex network of transpressional and transtensional faults at permian rotliegend levels which are thought to represent the upward termination of a series of wrench induced flower structures with a right lateral sense of displacement these faults are detached by zechstein and triassic salt from more orderly transtensional faults systems at shallower levels in areas where salt is absent late kimmerian normal faults became reactivated in a reverse sense during inversion however the relationship of these shallow mappable tectonic components to the deeper pre permian structure of the sole pit high and to the underlying crustal configuration remains speculative

phosphorus and the roles of productivity and nutrient recycling during oceanic anoxic event 2 four sections documenting the impact of the late cenomanian oceanic anoxic event oae 2 were studied in basins with different paleoenvironmental regimes accumulation rates of phosphorus p bound to iron organic matter and authigenic phosphate are shown to rise and arrive at a distinct maximum at the onset of oae 2 with an associated increase in 13 c values accumulation rates of p return to preexcursion values in the interval where the 13 c record reaches its fi rst maximum an offset in time between the maximum in p accumulation and peaks in organic carbon burial hydrogen indices and corg preact molar ratios is explained by the evolution of oae 2 in the following steps 1 an increase in productivity increased the fl ux of organic matter and p into the sediments the preservation of organic matter was low and its oxidation released p which was predominantly mineralized 2 enhanced productivity and oxidation of organic matter created dysoxic bottom waters the preservation potential for organic matter increased whereas the sediment retention potential for p decreased 3 the latter effect sustained high primary productivity which led to an increase in the abundance of free oxygen in the ocean and atmosphere system after the sequestration of co 2 in the form of black shales this oxygen helped push the ocean back into equilibrium terminating black shale deposition and removing bioavailable p from the water column

a 400 000 year record of vegetational and climatic changes from a volcanic basin leizhou peninsula southern china abstract the tianyang lake in leizhou peninsula is an enclosed crater formed during the early to middle pleistocene over 200 m of diatomaceous mud and clay were deposited in the last 400 000 years providing a continuous middle and late quaternary lacustrine sequence for paleoenvironmental studies the pollen record spans the last four glacial interglacial cycles equivalent to oxygen isotope stages ois 10 to 1 during most of the glacial phases fagaceous monsoon forest was replaced by altitudinal vegetation indicating a regional landscape transformation on the peninsula the montane forest reached down to the lowland by at least 600 m during the ois 6 and 8 in a cool and relatively wet condition with temperature estimated to be more than 4 c lower than present a further lowering of the montane forest belts by about 800 1000 m occurred in the ois 4 2 as implied by the appearance of many temperate elements during the last glacial maximum this mixed forest subsequently gave way to the poaceae grassland a savanna vegetation type favored by drier and cooler climatic conditions this drastic change implies a more significant drop in temperature and precipitation than the previous three glacial periods ois 10 8 and 6 it is thus inferred that the weakening of summer monsoon was more significant towards the end of the late pleistocene particularly during the last glacial maximum lgm

buried pockmarks on the top chalk surface of the danish north sea and their potential significance for interpreting palaeocirculation patterns three dimensional 3d seismic data from the southern danish north sea were used to analyse the morphology and spatial distribution of depressions in the danian chalk deposit previously these depressions were either interpreted as karst structures or pockmarks the observed depressions occur in an interval from 25 ms below to 12 ms above the top chalk surface three types of depressions were differentiated based on their plan view geometry and their degree of symmetry type 1 comprising sub circular and symmetrical depressions is the dominant group ca 70 type 2 elongated and symmetrical depressions represents only a small fraction ca 5 the elongated and asymmetrical depressions of type 3 compose ca 25 in cross section each depression type can be either characterised by a v or a u shape the maximum size of the depressions ranges from 50 to 580 m with an average internal depth of 10 m we interpret the depressions as pockmarks formed by the expulsion of biogenic or thermogenic fluids at the danian seafloor likely the initial form of the pockmarks has been circular type 1 and was subsequently modified for types 2 and 3 to an elongated form by currents the long axis of the pockmarks is interpreted to represent the effective current direction the inferred direction is sub parallel to the palaeobathymetric contours the 3d seismic interpretation of pockmarks presented in this paper contributes to the understanding of fluid migration and palaeocirculation patterns during the sedimentation of the terminal chalk group in the southern danish north sea

deep sea pollen from the south china sea pleistocene indicators of east asian monsoon abstract a high resolution pollen record sampling interval averages 820 years has been obtained from odp site 1144 water depth 2037 m northern south china sea the 504 m sequence in composition length covers the last 1 03 million years according to micropaleontological and isotopic stratigraphy the pollen assemblages are characterized by high proportions of pinus and herb pollen and by their frequent alternations based on these alternations 29 pollen zones have been recognized that are closely correlated to the marine oxygen isotope stages mis 1 29 pinus dominant pollen zones correspond to interglacial periods with lighter 18o values while herb marked ones relate to the heavier 18o stages assigned to glacials judging from the pollen data the exposed northern continental shelf of the south china sea during the glacials was covered by grassland and the extensive northern shelf has formed only since mis 6 ca 150 ka probably as a result of tectonic subsidence tree pollen influx values are indicative of winter monsoon which began to intensify 600 ka ago the summer monsoon variations can be approximated by the fern percentage within the total pollen and spore abundance and the result shows high values in general occurring at interglacials with the maxima at mis 15 5e and 1 the relatively high fern percentage with smaller amplitude in variations before 600 ka might suggest more stable humid conditions before the intensification of winter monsoon

deep water exchanges between the south china sea and the pacific since the last glacial period deep ocean circulation is widely considered as one of the important factors for increasing co2 concentration and decreasing radiocarbon activity 14c of the atmosphere during the last deglaciation the ams 14c ages of benthic and planktonic foraminifers from 18 samples of core md05 2904 water depth of 2066 m in the northern south china sea scs and 15 samples of core md05 2896 water depth of 1657 m in the southern scs were analyzed in this study for reconstructing the intrabasin deep oceanic processes and hence exploring the deep water exchanges between the scs and the pacific since the last glacial period the results show that during the holocene the average apparent ventilation age of deep water was younger in the southern scs 1350 years than in the northern scs 1850 years due to relatively strong vertical mixing and advection consistent with modern observations however during the last glacial period and deglaciation the deep water was older in the southern scs 2050 years and 1800 to 1200 years respectively than in the northern scs 1600 years and 670 years respectively indicating reduced deep mixing and advection moreover the northern scs deep water was significantly younger during the last deglaciation than during the holocene and the last glacial period implying the existence of northern sourced newly formed and relatively young north pacific deep water our records do not support the intrusion of anomalously 14c depleted deep water to the middepth of the low latitude western pacific and the scs during the mystery interval 17 5 14 5 kyr b p

structural evolution of inverted basins in the dutch offshore abstract the structural evolution of the dutch central north sea graben and the fault bounded broad fourteens basin is discussed graben formation started during the early triassic and culminated in strong differential subsidence during the late jurassic early cretaceous narrow fault bounded grabens and troughs and broad intervening highs were formed as a result of crustal distension and associated transtensional deformations the thickness of the late jurassic to early cretaceous fill of these basins may have exceeded 3000 m concurrent with the filling of these basins the bordering highs became deeply truncated during the late cretaceous and early tertiary compressive stresses resulted in inversion of these basins whereby movements along their bounding normal faults were reversed giving rise locally to overthrusting as for instance in the broad fourteens and west netherlands basins the timing of these compressional deformations has been palaeontologically dated and coincides with major orogenic events in the alps

the cretaceous palaeogene boundary at stevns klint denmark inversion tectonics or sea floor topography the cretaceous palaeogene boundary interval is exposed over 12 km in the coastal cliff stevns klint denmark an important lowermost danian hardground has been interpreted as an originally horizontal marine abrasion surface its present elevation varies from a few metres below to about 35 m above sea level this relief has traditionally been considered as resulting from late or post danian laramide folding new seismic profiles offshore stevns klint show however that the base chalk reflector is not folded is remarkably planar and has a gentle northward dip thus the folding hypothesis cannot be upheld seismic stratigraphic analysis of the chalk group necessitates a fundamental revision of general ideas of chalk deposition a highly irregular sea floor topography was formed at many levels and includes broad valleys ridges channels drifts and mounds a system of major wnw ese oriented valleys and ridges can be traced into the succession exposed in stevns klint and further inland where it corresponds to the relief of the cretaceous palaeogene boundary the marked topographic elements of the chalk sea floor are elongate with a wnw orientation roughly parallel to the axis of the danish basin and to the sorgenfrei tornquist zone forming the ne border of the basin the sea floor relief undoubtedly reflects the influence of strong contour parallel bottom currents the cretaceous palaeogene boundary succession at stevns klint was thus developed on an underlying sea floor topographic relief of about 40 m recognition of the highly irregular current influenced topography of the late cretaceous sea floor stands in marked contrast to the conventional picture of quiet pelagic deposition of the chalk

the development and seismic expression of synsedimentary features within the chalk of southern england seismic reflection data acquired onshore to the north of bournemouth southern england image clearly a series of prominent concave up troughs or depressions and concave down mounded structures within the white chalk subgroup the chalk lithostratigraphy in the area of study is established from borehole geophysical log correlations these correlations then provide calibration of the seismic reflection data indicating that the structures are concentrated at levels between the lewes nodular chalk formation and tarrant chalk member and towards the base of the portsdown chalk formation onlap downlap and truncation of reflectors are observed with the most dramatic features forming a stacked series directly overlying faulting of jurassic strata similar stratal geometries have been described from comparable levels in the chalk of the north sea and in outcrop in britain and france to many they represent channels formed by submarine erosion and redeposition of the chalk during relative sea level falls linked to tectonics we also interpret a number of apparently incisive structures and slumped infill sequences described here as being of primary syndepositional origin the slumping and the close association of these features with underlying faults and proximity to nearby major crustal faults may be indicative of submarine erosion of the chalk caused by sea level changes linked to syndepositional fault movements however evidence of toplap downlap pairs is also suggestive of more aggradational mounding or laterally migrating surfaces or facies belts the presence of any such structures implies rapid lateral variations in the chalk that would have implications not only for aquifer management and future storage schemes but also during the processing of seismic reflection data and general studies and correlations of the chalk across southern britain

structural evolution of the harts range area and its implication for the development of the arunta block central australia abstract a division of the high grade metamorphics of the arunta block in the harts range area into two main groups on the basis of lithology structure metamorphism and igneous activity is suggested as a result of detailed mapping the lower group is regarded as a basement terrain and comprises major layered felsic or granitic gneiss minor amphibolite and mafic granulite while the structurally overlying group is regarded as a cover sequence irindina supracrustal assemblage and comprises predominantly metasediments pelitic and semi pelitic gneiss calc silicate and quartzite and amphibolite anorthosite and ultramafic rock of the harts range meta igneous complex the cover sequence might have been deposited in an aulacogen or adjacent to a continental margin which developed by rifting of a pre existing basement the two groups both show early major ductile tectonothermal stages with four major fold generations and a later discrete shear event in the basement and two major fold generations and a later series of stacked nappes developing in the cover the basement s early orogenic evolution with associated granulite facies metamorphism is typical of intensely reworked early precambrian terrains and developed spatially and or temporally separated from the cover cover deformation closely resembles continental margin cordillera type overthrusting and thus thin skinned tectonics associated with large scale crustal shortening during the later harts range remobilization the basement and cover were juxtaposed by displacement on a fundamental crustal dislocation recumbent contraction fault mylonites repeatedly developed along the dislocation which was also isoclinally folded intruded by a major megacrystic granitoid bruna gneiss sheet and repeatedly rejuvenated the history of development of the dislocation is documented and described as a process of underthrusting of basement beneath cover which led to the final termination of the orogenic activity

late maastrichtian chalk mounds stevns klint denmark combined physical and biogenic structures abstract upper maastrichtian chalk exposed at the sigerslev quarry stevns klint denmark is characterized by wavy and mound like bedding geometries outlined by bands of black flint nodules four morphological elements are recognized although bedding geometries are highly variable southward migrating mounds eastward migrating mounds chalk waves and evenly bedded chalk the mounds are interpreted as having been formed by currents carrying fine grained suspended sediment which was primarily deposited on the up current mound flanks bryozoans were prolific on the up current flanks and mound summits which stabilized the mounds increased bed roughness and the overall accumulation rate however accumulation thicknesses do not correlate consistently with bryozoan density the bryozoans were therefore important for the formation of the mounds but the distribution of bryozoans did not solely determine depositional thickness across a mound and thus mound growth pattern relatively long wavelength wavy bedded chalk show gentle convex up geometries and would probably be described as sediment waves if recognized in seismic sections the chalk waves were deposited under weaker current velocities than those active during mound formation the exposed succession is topped by more evenly bedded chalk which was deposited by quiet pelagic fall out of fine grained material the whole succession was deposited on the upper part of the northern flank of a large wnw ese trending 3 km wide depositional ridge with an amplitude of 35 40 m formed by contour parallel wnw ward flowing bottom currents the mounds may have been deposited by regional bottom currents or by spill over currents from the valley south of the large ridge the succession was deposited during varying bottom current intensities and the depositional architecture indicates a complex and dynamic environment the depositional style seems to be controlled by the interplay and relative importance of two end member processes those that were purely physical and related to the interaction between available grain sizes and hydrodynamics and those that were largely biological and associated with benthic growth and sediment trapping of mainly bryozoans examples of end member conditions are known from haute normandy france and the lower danian of stevns klint the structures described here adds to the considerable complexity of depositional styles in chalk