postglacial emergence of amund and ellef ringnes islands nunavut implications for the northwest sector of the innuitian ice sheet this paper presents relative sea level curves from amund and ellef ringnes islands northwest queen elizabeth islands these curves are of exponential form and record continuous ongoing holocene emergence although northwest ellef ringnes island is experiencing a late holocene transgression isobases drawn on postglacial shorelines rise south eastward towards an uplift centre in norwegian bay these suggest the ringnes islands occupied the northwest radius of the innuitian uplift which is congruent with glacial geological evidence suggesting parts of the ringnes islands were covered by the late wisconsinan innuitian ice sheet the isobases provide a provisional reconstruction of glacioisostatic recovery within the northwest innuitian uplift their pattern supports earlier reconstructions that maximum late wisconsinan ice thickness occurred across norwegian bay marking the position of an ice divide which is consistent with ice flow features on amund ringnes island they record the diminishing thickness of the innuitian ice sheet from norwegian bay to the arctic ocean the absence of an isobase embayment across the ringnes islands suggests a relatively uniform ice load across both islands and hassel and massey sounds parallel isobases across peary channel indicate this ice load extended beyond massey sound although their northward deflection suggests an increasing influence of the former

holocene delevelling of devon island arctic canada implications for ice sheet geometry and crustal response the raised beaches and deltas of devon island contain an abundance of dateable materials a large set of radiocarbon dates 228 154 of which are new are used to construct relative sea level curves and isobase maps for the island the best materials for this purpose are driftwood logs 61 dates and bowhead whale bones 74 dates from raised beaches and mollusc shells from marine limit deltas 20 dates or from altitudes close to marine limit 14 dates during the last glacial maximum the island is thought to have lain beneath the southeastern flank of the innuitian ice sheet the relative sea level history is congruent with that inferred ice configuration the island spans half the ice sheet width relative sea level curves are of simple exponential form except near the glacial limit where an early holocene emergence proceeded to a middle holocene lowstand below present sea level which was followed by submergence attending the passage of the crustal forebulge the response times of relative sea lev

late wisconsinan glaciation of amund and ellef ringnes islands nunavut evidence for the configuration dynamics and deglacial chronology of the northwest sector of the innuitian ice sheet geomorphic and chronologic evidence from amund and ellef ringnes islands documents the configuration dynamics and collapse of the northwest sector of the innuitian ice sheet these data record the inundation of the ringnes islands by northwestward flowing ice from divides spanning the alpine and lowland sectors of the innuitian ice sheet ice flow indicators and granite dispersal along eastern amund ringnes island suggest massey sound was filled by an ice stream discharging coalescent alpine and lowland ice from norwegian bay in contrast the interior of amund ringnes island was overridden by predominantly non erosive granite free ice from a divide in the lowland sector of the ice sheet glacial landforms on ellef ringnes island record coverage by largely non erosive ice but it remains uncertain whether these features relate to northward flowing lowland ice or a cold based local ice cap deglaciation of the ringnes islands commenced 10 000 14c years ago deglacial dates between 9 7 and 9 2 ka bp rec

seismic architecture of a lower cretaceous platform to slope system santa agueda and poza rica fields mexico two three dimensional seismic data sets over the albian western golden lane margin and time equivalent basinal deposits of poza rica field allowed us to investigate the linked architecture of a steep sided carbonate platform el abra formation and a thick accumulation of redeposited carbonate sediment at the toe of the slope and in the basinal area tamabra formation regional seismic cross sections show that the most aggrading albian platform has an eroded platform top a scalloped margin and a channelized slope that are equivalent to a 20 km 12 4 mi wide westward thinning thick toe of slope apron made of chaotic contorted mounded moderate to high amplitude reflections detailed reflection geometries in the albian toe of slope and basinal deposits consist of chaotic to short discontinuous low amplitude reflection at the toe of the slope of the golden lane platform laterally changing to a discontinuous mounded shingling reflection which ultimately turns into high amplitude parallel reflections we interpret this lateral change to reflect the seismic signature of the change from the block and debris flow dominated toe of slope area to debris flow and concentrated density flow deposits in the basin that ultimately grade laterally into pelagic deposits on a flattened seismic slice mounded reflections correspond to lobate to fan shaped seismic events several kilometers wide that are interpreted as a carbonate basin floor fan comparison between core and seismic data shows a dominance of debris flows in the lower two albian sequences albian 1 and albian 2 that grade vertically into more lobate concentrated density flows and turbidites in the upper two albian sequences albian 3 and albian 4 seismic data used in this study combined with core observations do not support the interpretation of the albian tamabra formation being of shallow water origin seismic features identified as basin floor fan channel and debris flow deposits have a shape and size that are similar to those of other redeposited basinal carbonate deposits elsewhere the seismic architecture shows that the poza rica field is a typical example of thick accumulation of grainy porous carbonate deposits in a basinal setting this example shows the potential of a large hydrocarbon accumulation in a tectonically modified stratigraphic trap around shallow water carbonate platforms

last glacial maximum and deglaciation of devon island arctic canada support for an innuitian ice sheet abstract the extent and origin of quarternary glaciers in the queen elizabeth islands of arctic canada especially during the last glacial maximum lgm has been debated for well over a century no consensus has yet emerged and the spectrum of interpretations within the last decade is the broadest ever the glacial geology of devon island strongly supports the late wisconsinan innuitian ice sheet hypothesis during lgm the southeastern part of the queen elizabeth islands was covered by an ice sheet flowing from a centre or a divide centrally located in the archipelago another ice divide extended from the centre across devon island flow from the innuitian centre and convergent flow from devon island and probably also from cornwallis and bathurst islands sustained an ice stream in wellington channel ice was locally advancing to its lgm limit about 23 ka bp recession in the vicinity of the present coastline was underway by 10 ka bp and final ice remnants west of the present devon ice cap vanished about 8 ka bp the island bears the same two part landscape zonation as do other islands and peninsulas in the region these reflect a cold based core and warm based periphery at lgm

steep microbial boundstone dominated plaform margins abstract seaward progradation of several kilometers has been documented mostly for leeward margin low angle carbonate slope systems with a dominant platform top sediment source however steep and high relief margins fronting deep basins can also prograde and as such are somewhat perplexing characteristics of two prograding carboniferous examples provide a model which may apply elsewhere 1 outcrops in asturias northern spain serve as important analogs for 2 hydrocarbon reservoirs in steep sided isolated platforms of the north caspian basin kazakhstan such as tengiz seismic and well data from tengiz corroborate outcrop patterns for slope development showing progradation of up to 5 and more than 10 km respectively despite the high relief up to 600 m and steep 20 35 nature of these margins the two examples share a highly productive microbial boundstone factory extending from the platform break down the slope to nearly 300 m or more depth and a lower slope dominated by mega breccias and grain flow deposits derived from the margin and slope itself the broad depth range of microbial boundstone increases the potential for production during both lowstands and high stands of sea level and thereby facilitates progradation independent from platform top derived sediment rapid in situ lithification of the boundstone provides stability to the steep slopes but also leads to readjustment through shearing and avalanching what controls the microbial cement boundstone formation remains a debate but its presence is a key factor controlling the progradational geometry of these and possibly other margins this new model of slope shedding has implications for slope readjustment processes and resulting architecture sequence stratigraphic interpretation reservoir characterization and reservoir modeling especially the isotropic character of microbial boundstone will reduce the potential for coherent seismic reflections to develop and possibly invoke under certain stress regimes shattering and fracturing thereby generating significant non matrix permeability key considerations are the contrasts with the bahamian high stand shedding depositional model slope progradation rates that range from 450 to 1500 m my and net growth rates of in situ boundstone of 1000 m my comparable to or higher than accretion rates for metazoan skeletal reef growth

syndepositional fault control on lower frasnian platform evolution lennard shelf canning basin australia syndepositional faulting was a major control on internal platform stratigraphy in a frasnian reef complex on the southeastern lennard shelf northern canning basin australia by combining platform mostly backreef facies distributions with key stratal surfaces and biostratigraphic data we have developed a temporal framework for the hull range area platform evolution was controlled by normal faults via an initial tilt block geometry and subsequent differential subsidence and accommodation across the platform three third order flooding surface bounded platform phases are recorded basal shallow marine siliciclastic facies were deposited in topographic lows adjacent to the hanging wall and close to internal faults early carbonate deposition in dominantly deep subtidal environments suggests an overall ramp style setting that deepened toward the southeast this phase is capped by a sequence boundary represented by multiple paleokarst surfaces in the northwest that pass laterally into a major flooding surface to the southeast above which the platform expanded toward the mount elma painted rocks fault system the overall stacking pattern above the sequence boundary flooding surface is aggradational to progradational with higher frequency shoaling trends and locally developed exposure surfaces related to higher order relative sea level changes this second phase of platform growth ended with major flooding and a pronounced backstep of the leeward margin

quaternary ice transport in the canadian arctic and extent of late wisconsinan glaciation in the queen elizabeth islands most of the ice rafted debris in channels off the queen elizabeth islands nunavut is of local origin particularly in the inner part of the archipelago but samples from the arctic shelf contain as much as 40 grains from sources as far away as 2000 km including the siberian shelves particle transport by drifting sea ice from distant shelves is an important process on the arctic continental shelf of the queen elizabeth islands in the interior of the queen elizabeth islands and in the viscount melville and lancaster sounds particle transport is limited to distances of approximately 200 km mixing is more common among grains of coarse silt to fine sand than in the 250 m fraction but even the latter contains debris from sources far apart during the late wisconsinan the northern southern and eastern queen elizabeth islands were covered by glaciers flowing radially from ice centers on the islands into the inter island channels queens channel was completely filled by ice and a glacier lobe moved

glacial versus interglacial sedimentation rates and turbidite frequency in the bahamas the southern tongue of the ocean is a 1300 m deep flat floored basin in the bahamas that receives large amounts of sediment from the carbonate platforms surrounding it on three sides we have examined five 8 13 m long piston cores and determined bulk sedimentation rates turbidite frequency and turbidite accumulation rates for the past two glacial and interglacial periods the mean of bulk sedimentation rates is four to six times higher in interglacial periods average accumulation rates of recognizable turbidites are higher by a factor of 21 to 45 and interglacial turbidite frequency is higher by a factor of 6 to 14 sediment composition indicates that increased interglacial rates are due to higher accumulation of platform derived material additional data from other bahamian basins as well as published material from the caribbean strongly suggest that highstand shedding is a general trend in pure carbonate depositional systems carbonate platforms without a siliciclastic component export more material during highstands of sea level when the platform tops are flooded and produce sediment the response of carbonate platforms to quaternary sea level cycles is opposed to that of siliciclastic ocean margins where sediment is stored on the inner shelf during highstands and passed on to continental rises and abyssal plains during lowstands of sea level

late devonian carbonate margins and foreslopes of the lennard shelf canning basin western australia part a development during backstepping and the aggradation to progradation transition abstract carbonate reefal margin and foreslope settings are characteristically heterogeneous and difficult to predict due to a spectrum of sediment source factories resedimentation processes resultant deposit types and controlling parameters in particular the effects of changes in long term accommodation on the composition architecture and sediment distribution patterns of carbonate margin foreslope basin systems are poorly understood upper devonian frasnian outcrop exposures along the lennard shelf northeast canning basin western australia were investigated to assess the development of reefal margin and foreslope settings during long term 1 platform backstepping with aggradational pulses and 2 across the transition from platform aggradation to progradation measured sections tied to interpreted photomosaics and detailed mapping using aerial photographs were collected from the south lawford range and windjana gorge areas the exposures reveal distinctive differences in foreslope grain composition deposit characteristics and proportions margin morphology and stratigraphic expression 1 during platform evolution between backstepping events and 2 depending on position within the long term accommodation setting between backstepping events aggradational margins can be classified as growth escarpments with associated grain dominated onlapping foreslope deposits margins across the long term transition from aggradation to progradation evolved from erosional escarpments with onlapping debris deposits to accretionary interfingering configurations development of growth escarpments between backstepping events was a function of vertical reefal growth from sustained high accommodation conditions during the long term transgressive systems tract coupled with a frasnian reefal assemblage that responded to light and tracked relative sea level this net vertical reefal growth also resulted in relative margin stability and the deposition of grain dominated foreslopes conversely margins were highly unstable and underwent repeated failure across the long term aggradation to progradation transition reflecting a lack of underlying substrate to support basinward advance and resulting in debris dominated foreslopes these observations provide relationships that predict margin and foreslope associations of facies scale heterogeneity and seismic scale geometry within a low frequency sequence stratigraphic framework

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

radiated vlf energy differences of land and oceanic lightning 1 a global contrast between oceanic and continental lightning very low frequency energy is observed using the world wide lightning location network wwlln strokes over the ocean are found to be stronger on average than those over land with a sharp boundary along a majority of coastlines a linear regression method is developed to account for the spatial and temporal variation of wwlln in order to perform a multiyear and global analysis of stroke energy distributions the results are corroborated with data from the lightning imaging sensor the optical transient detector and the earth networks total lightning network these systematic comparisons lead to the conclusion that there exists a strong difference in the energetics between land and ocean thunderstorms that results in a higher fraction of more powerful strokes over the oceans

carbonate apron models alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration sediment gravity flow deposition along the deep water flanks of carbonate platforms typically does not produce submarine fans rather wedge shaped carbonate aprons develop parallel to the adjacent shelf slope break the major difference between submarine fans and carbonate aprons is a point source with channelized sedimentation on fans versus a line source with sheet flow sedimentation on aprons two types of carbonate aprons may develop along relatively gentle 4 platform margin slopes aprons form immediately adjacent to the shallow water platform and are referred to as carbonate slope aprons along relatively steep 4 15 platform margin slopes redeposited limestones accumulate in a base of slope setting by passing an upper slope via a multitude of small submarine canyons and are referred to as carbonate base of slope aprons both apron types are further subdivided into inner and outer facies belts inner apron sediments consist of thick mud supported conglomerates and megabreccias facies f as well as thick coarse grained turbidites facies a interbedded with subordinate amounts of fine grained peri platform ooze facies g outer apron sediments consist of thinner grain supported conglomerates and turbidites facies a as well as classical turbidites facies c with recognizable bouma divisions interbedded with approximately equal proportions of peri platform ooze facies g seaward aprons grade laterally into basinal facies of thin base cut out carbonate turbidites facies d that are subordinate to peri platform oozes facies g carbonate base of slope aprons grade shelfward into an upper slope facies of fine grained peri platform ooze facies g cut by numerous small canyons that are filled with coarse debris as well as intraformational truncation surfaces which result from submarine sliding in contrast slope aprons grade shelfward immediately into shoal water platform margin facies without an intervening by pass slope the two carbonate apron models presented here offer alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration for mass transported carbonate facies

the north american lightning detection network naldn analysis of flash data 2001 09 abstractcloud to ground cg lightning data have been analyzed for the years 2001 09 for north america which includes alaska canada and the lower 48 u s states flashes recorded within the north american lightning detection network naldn are examined no corrections for detection efficiency variability are made over the 9 yr of the dataset or over the large geographical area comprising north america there were network changes in the naldn during the 9 yr but these changes have not been corrected for nor have the recorded data been altered in any way with the exception that all positive lightning reports with peak currents less than 15 ka have been deleted thus the reader should be aware that secular changes are not just climatological in nature all data were analyzed with a spatial resolution of 20 km the analyses presented in this work provide a synoptic view of the interannual variability of lightning observations in north america including the impacts of physical changes in the network dur

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

why do oceanic negative cloud to ground lightning exhibit larger peak current values this study examines the temporal monthly and spatial climatology 2004 2010 of the first return stroke of the cloud to ground cg lightning flash peak current ip across various land water boundaries over the contiguous united states four regions are examined the gulf of mexico region 1 the florida peninsula region 2 lake michigan region 3 and part of the u s mid atlantic region 4 the crosss across the coastlines of regions 1 2 and 4 show a gradual oceanward increase in the mean negative polarity cg peak current values ip this transition along the respective land ocean boundaries is not sharp but gradual in direct contrast with ocean there is no consistent behavior in ip values as we move from land out across the fresh water of lake michigan region 3 meanwhile the positive cg flash peak current ip values do not exhibit a consistent variation across any coastal boundary for region 1 the ip values increase as we move toward the coast southwards especially during the wet season june october this finding is in direct contrast with studies that documented winter as the season of maximum ip values the zonal and seasonal variations of ip values across region 4 are not quite as pronounced but the oceanic ip values are still larger than over the adjoining landmass we explore in turn which up to date hypotheses pertinent to the oceanic ip enhancement are supported or refuted by our findings it is concluded that the oceanic ip enhancement is not an artifact related to cg detection or ip retrieval methods nor is it likely related to the cloud top heights or cg activity the study cannot refute the role of electrical conductivity and its contribution to cg leader attachment processes however given the observed blurred transition of the ip values across the coastlines this paper suggests that likely the main physical mechanism is acting on the thundercloud potential the recently suggested role of sodium chloride nacl but also the role of ice crystal size implicated herein as possible modulators of the thundercloud potential exhibit distinct pros and cons their candidacy is supported by their strong physical links to the electrostatic charging and thundercloud electric potential buildup but also by the exhibited blurred ip transition across the coastlines in contrast the suggested mechanisms cannot individually explain the observed ip enhancement in terms of season nacl concentrations and absence of similar behavior in the respective ip values

glacier dynamics and paleoclimatic change during the last glaciation of eastern ellesmere island canada a 300 km transect along the east coast of ellesmere island fills a major gap in the late quaternary data base of the canadian high arctic the last glacial maximum lgm is marked by prominent moraines and meltwater channels that terminate within 30 km of modern ice margins shells in glaciomarine deposits collected beyond the lgm indicate deglaciation by more extensive ice prior to 35 ka bp more than 60 14c dates from glaciomarine sediments provide a chronology for past ice dynamics during the lgm to the north while many areas remained ice free due to severe aridity several glaciers remained in contact with the sea until 7 1 ka bp farther south most glaciers reached the coast and significantly infilled several fiords this southward increase in glacier extent is due to larger glacial catchment basins and increased precipitation towards storm tracks in northern baffin bay the earliest dates on deglaciation along the transect range from 8 1 to 7 7 ka bp initial retreat was controlled by the exten

the influence of variable progradation to aggradation ratio and facies partitioning on the development of syndepositional deformation in steep walled carbonate platforms abstract one of the remaining questions in carbonate geology and reservoir studies is the origin of steep walled carbonate platform margins and the role of gravity versus other structural processes in controlling the distribution of fracture networks and failure surfaces this study is an attempt to document the role of gravity interacting with stratigraphic architecture in controlling fracture patterns and margin collapse we employ finite discrete element models to illustrate that progradation aggradation p a ratio and facies tract partitioning in steep walled carbonate platforms affects the development distribution and intensity of syndepositional deformation all models are under the influence of only gravitational loading where pore pressure is held constant we utilize a modified mohr coulomb constitutive law with a rankine rotating crack tensile corner to capture both tensile and shear brittle failure our results illustrate that p a ratio affects the distribution and intensity of discrete fractures that form in steep walled carbonate platforms our results suggest that deformation is more extensive in a progradational carbonate platform where shelf edge angles are greatest and the clinoform is thickest alternatively aggradational carbonate platforms experience localized deformation in front of the antecedent shelf edge where the clinoform is thickest and steepest the introduction of mechanical heterogeneity associated with facies tract partitioning affects the intensity of fracturing in both progradational and aggradational models with the greatest number of fractures developing in reef facies in both scenarios development of brittle deformation under the sole application of gravity and lack of seaward lithostatic confinement is consistent with the syndepositional nature of deformation in these settings this work illustrates the interplay between carbonate platform geometry facies distribution and the resulting syndepositional deformation

the innuitian ice sheet configuration dynamics and chronology abstract portrayal of north american ice cover during the last glacial maximum is dominated by the laurentide ice sheet leaving little detail for the adjacent innuitian ice sheet iis four decades of geological fieldwork across the queen elizabeth islands now warrant specific treatment of the iis including its chronology configuration dynamics and retreat this reconstruction is relevant to the sedimentary history of the arctic ocean and to high latitude climate forcing the iis was composed of both an alpine and lowland sector the advance of the alpine sector occurred as recently as 19 14 c ka bp geological evidence configures outflow from alpine and lowland divides that produced several palaeo ice streams one extending northwestward across the canadian arctic archipelago to the polar continental shelf retreat of the iis commenced along its southwest margin 11 6 14 c ka bp however most of the ice sheet remained on the continental shelf during the younger dryas by 10 14 c ka bp marine based ice experienced widespread calving through the western and central archipelago in response to holocene warming and ongoing eustatic sea level rise the sea penetrated the eastern archipelago by 8 5 14 c ka bp gutting the alpine sector of the iis regional isobases record the glacioisostatic signature of the ice sheet and are congruent with the primary geological evidence the delayed buildup of the iis was out of phase with the growth of the laurentide ice sheet that occasioned climatic and glacio eustatic forcing in the innuitian region recent modelling experiments reinforce the hypothesis that growth of the laurentide ice sheet culminated in a split jet stream that temporarily favoured augmented precipitation and growth of the iis

the last glaciation of west central ellesmere island arctic archipelago canada locally abundant ice marginal landforms lie in a 500 km long zone with a distal margin 10 60 km west of the margins of modern ice caps on central ellesmere island much of this drift belt at the heads of the fiords was deposited by the oscillating margin of a coalesced predecessor of the modern ice caps between 9000 and 7000 bp the ice continued to retreat east of the present margin and readvanced to its modern limit in a middle and late holocene cooler climate unweathered but undated till and striations at the base of the drift suggest that the belt does not mark the western limit of central ellesmere island ice in the last glaciation the limit lies an unknown distance downfiord glaciers in the fiords may have floated no reliable evidence was found for a complete ice cover of western ellesmere island and eureka sound in the last glaciation nevertheless much of central and southern ellesmere island and devon island may have been glaciated by a regime that left few erosional or depositional landfo

peak current variations of lightning return strokes as a function of latitude latitudinal variations in lightning flash characteristics have been hypothesized1 2 but have not been found to exist3 4 this may be because lightning characteristics are constant over the earth or because the observations have been made over too small an area of the globe to investigate the question of latitudinal variation i have used a network of thirty six gated wideband magnetic direction finders covering the eastern united states to measure the characteristics of cloud to ground lightning flashes these characteristics include the flash location the flash polarity the number of strokes in the flash and the peak magnetic radiation field in the first return stroke of the flash from the peak radiation field i estimate the peak current5 more than five million lightning ground flashes were recorded by the network in 1988 an examination of the mean peak current in the first return stroke shows that the peak current varies by almost a factor of two from 25k a in new england to 40 45 ka in northern florida apparently this is the first report of an important lightning parameter the return stroke current varying over a large area of the globe it seems that the generation of lightning strokes and their characteristics may be a sensitive function of latitude and hence of temperature the results presented here indicate that even higher peak currents will be observed if this research is extended into the equatorial regions

platform margin trajectory as a control on syndepositional fracture patterns canning basin western australia abstract syndepositional fractures are an important feature of high relief reef rimmed carbonate systems and exert a profound control on many facets of platform evolution including the timing and frequency of platform margin collapse events generation of an early diagenetic fluid flow system and subsequent karst and enhanced permeability development in the devonian reef complexes of the canning basin syndepositional fracturing increases significantly with progradation with a twofold increase in fracture intensity observed between the most retrogradational and progradational carbonate platforms this study demonstrates a statistically significant relationship between syndepositional fracture patterns and variations in stratigraphic architecture approximated here by platform margin trajectory in the platform margin syndepositional fracturing varies systematically with platform margin trajectory regardless of proximity to regional tectonic elements whereas in the platform interior tectonically active settings consistently display syndepositional fracture intensities significantly higher than predicted by platform margin trajectory alone the results presented here suggest a first order relationship between long term changes in stratigraphic architecture and syndepositional fracture development in high relief carbonate platforms and imply that whereas external regional tectonic drivers may enhance early fracturing they are not required

controls on syndepositional fracture patterns devonian reef complexes canning basin western australia abstract syndepositional fractures are an important feature of high relief carbonate systems and exert a profound control on many facets of platform evolution and reservoir development based on data collected from the canning basin s devonian reef complexes this study characterizes syndepositional fracture patterns as a function of variations in lithofacies depositional position stratigraphic architecture and mechanical stratigraphy fracture parameters such as extension and fracture intensity are documented to vary strongly as a function of lithofacies the highest syndepositional extension values occurring in the microbial facies of the famennian platform margin with extension values three times higher than observed in equivalent frasnian strata position along the depositional profile exerts a strong control on fracture patterns with an approximate two fold increase in syndepositional extension and fracture intensity typically observed from the platform interior to the platform margin syndepositional fracture intensity is shown to vary systematically with changes in platform margin trajectory with high fracture intensities observed in strongly progradational platforms and decreased fracture development in aggradational and retrogradational platforms evidence for the temporal evolution of the mechanical stratigraphy of the devonian reef complexes is presented with early lithified strata effectively behaving as a single large scale 50 150 m mechanical unit during syndepositional fracture development while secondary fractures become increasingly affected by bed scale 0 25 5 m mechanical heterogeneity introduced by progressive diagenesis the results presented here potentially provide a tool for predicting fracture characteristics e g intensity orientation location and vertical extent from limited subsurface data and provide a method for characterizing syndepositional deformation in other systems

holocene emergence at cape herschel east central ellesmere island arctic canada implications for ice sheet configuration twenty five radiocarbon age determinations on marine molluscs basal organic pond sediments charred remains in archeological sites and a variety of other materials have allowed the construction of an emergence curve for cape herschel east central ellesmere island 78 35 n 74 40 w only a narrow fringe of land is present between the prince of wales icefield and smith sound yet emergence of the order of 135 m has taken place during the last 8500 8700 radiocarbon years the highest in situ shells were collected at an elevation of 107 5 m and ages of 8470 100 bp gsc 3314 and 8230 70 bp to 230 were obtained on this material the spectacular and fresh appearing glacial sculpture along both sides of smith sound coupled with the rapid emergence in holocene time and the fact that the oldest dates on marine shells at the fiord heads to the west are 3000 4000 years younger than those at cape herschel provides convincing evidence that an ice stream filled smith sound 500 m deep during the late wis

highstand versus lowstand deposition on carbonate platform margins insight from quaternary foreslopes in the bahamas abstract examples of both highstand and lowstand deposition have been identified on the upper platform slopes of the tongue of the ocean bahamas highstand deposits consist of a thick wedge of fine grained skeletal and non skeletal sands and carbonate muds derived predominantly from the platform and deposited on slopes of 25 28 these sediments were deposited subsequent to platform flooding and may be more than 30 m thick along open leeward margins in contrast lowstand deposits consists of coarse skeletal sands gravels and boulders deposited on primary depositional slopes of 35 45 these sediments were derived from fringing reefs along the marginal escarpment and deposited during the initial rise of sea level following the last lowstand these variations in depositional character result in a distinctive signature of highstand versus lowstand deposition for steep sided platforms and further elucidate the response of carbonate platforms to high magnitude 5th order scale 20 000 yrs fluctuations in sea level

sequence development in an isolated carbonate platform lower jurassic djebel bou dahar high atlas morocco influence of tectonics eustacy and carbonate production six sequences each with a distinct shape stratal anatomy bounding surfaces lithofacies composition and stacking patterns were identified in the djebel bou dahar isolated carbonate platform which developed in a half graben in the high atlas marine rift basin during the early jurassic sequences are believed to have a complex multi process origin as the result of tectonic processes regional subsidence and fault block rotation overprinting the eustatic signal in addition changing carbonate producers with shifting centres of deposition and relative accumulation potential influenced the filling and anatomy of the accommodation space that had been created by the hybrid tectonic and eustatic processes sequences i and ii are tabular in shape and interpreted to primarily reflect the combined processes of uniform tectonic subsidence and eustacy which resulted in a ramp to shelf carbonate system with lagoon and tidal flat lithofacies onset of a rifting episode around the base of the lotharingian and fault block rotation were responsible for the development of the angular unconformity with the underlying sequence ii and the progressive development of a shallow water isolated platform and the wedge shaped depositional sequences iii to vi during the lotharingian and pliensbachian concurrent variations in palaeoceanographic conditions and in the carbonate factory caused a shift towards a flat topped platform geometry with high energy coated grains and sub photic sponge microbial deposition around the margin the aggradational to retrogradational character of sequences iii iv and vi is inferred to be a result of the combined effect of in situ carbonate production coupled with high rates of creation of accommodation space in the hanging wall environmental effects on carbonate production were the most probable cause for drowning of the djebel bou dahar platform during the toarcian but also influenced the filling and geometry of sequences iv to vi this study suggests that the commonly accepted model of pulse driven sequence development in half grabens may not be fully applicable for the djebel bou dahar where a more continuous rotation at sequence scale associated with subsidence pulses of the djebel bou dahar block seems to have interacted with eustacy and carbonate production to generate sequences continuous rotation is suggested by the presence of regular patterns of diverging strata and numerous minor exposure surfaces in lagoonal deposits of sequences v and vi in addition this study demonstrates that eustacy and variations in the carbonate factory might be as significant as tectonics in sequence development and platform drowning in carbonate platforms within rift basins this observation could imply that the effects of eustacy and the carbonate factory might not have been correctly recognized in other similar carbonate platforms due to a tectonic biased interpretation

support for the innuitian ice sheet in the canadian high arctic during the last glacial maximum the extent of glacier ice in the canadian high arctic during the last glacial maximum lgm has been debated for decades one school proposed a regional innuitian ice sheet whereas another proposed a smaller non contiguous franklin ice complex research throughout western nares strait supports coalescent innuitian and greenland ice during the lgm based on widespread glacial and marine deposits dated by 14c and amino acid analyses this coalescence likely promoted a vigorous regional ice flow westward across ellesmere island to eureka sound post glacial emergence in eureka sound suggests a former ice thickness at least as great as that in nares strait 1 km recently independent field studies elsewhere in the high arctic also support an innuitian ice sheet during the lgm collectively these studies resolve a long standing debate and initiate new opportunities concerning the reconstruction of high latitude palaeoenvironmental and palaeoclimatic change 1998 john wiley sons ltd

catchment and lake controls over the formation of varves in monomictic nicolay lake cornwall island nunavut on the basis of thin section sedimentology 137cs and 210pb profiles and the pronounced seasonality of runoff and sediment delivery sediments from nicolay lake cornwall island nunavut 77 46 n

bahama carbonate platforms the deep and the past abstract carbonate deposition prevailed for 150 ma in the bahama florida segment of the west atlantic margin and provides an interesting test for actualism present day facies patterns on the banks are controlled by the backward decrease of waves and tides and the concomitant increase of temperature and salinity variation in the troughs influx of sand and rubble from gravity flows varies with topography and distance from shallow water sources and allows one to define facies belts a rhythmic sequence of ooze and graded beds on the basin floors subdivided into a basin margin belt of coarse thick turbidites and basin interior with fine turbidites slope facies change with increase in height and declivity from accretionary to by pass to erosional regimes stratigraphic history of the bahamas is not simply a projection of the holo scene back in time both long term natural evolution decrease in subsidence upbuilding of the banks submarine erosion and outside factors climate eustacy have caused significant changes since the jurassic the bahamas seem to have evolved from a clastics evaporite province to a single carbonate evaporite platform and finally to an array of platforms and troughs during the platform trough stage the rate of upbuilding of the platforms decreased submarine canyon erosion increased platform flanks steepened as they grew higher and changed from accretionary to by pass to erosional slopes a change imposed by extraneous factors occurred in the pliocene when the great bahama bank changed from a giant reef rimmed atoll to a flat platform covered by oolites and peloid sands the bahamas share both long term trends as well as random changes by extraneous factors with other platforms in the geologic record compared to ancient platforms however they are unusually long lived and at a more advanced stage of growth they are deeply dissected by erosion their flanks are unusually high and steep and the troughs very narrow the neogene platform sequence is strongly controlled by eustatic sea level fluctuations

carbonate platform flanks slope angle and sediment fabric more than 20 examples of fossil carbonate platform systems were compared for slope angle and sediment fabric plots of slope angle versus sediment fabric show that grainy non cohesive mud free sediments build steeper slopes than muddy cohesive sediments examples near the end members of grainy and muddy carbonate platform flanks are found in the triassic of the dolomites in northern italy and in the bahamas respectively they document the flank geometry and the processes readjusting the slope profile once the limiting slope angle is exceeded the grainy flank sediments in the dolomites modified by shearing and avalanching produce straight slope profiles with declivities up to 35 whereas the muddy bahamian flank sediments modified by large scale creep and rotational to translational sliding and slumping produce a concave upwards slope profile inclined at less than 4 the comparison between slope angle and sediment fabric indicates that the physical behaviour of sediments in the gravity field angle of shearing and mode of readjustment processes is linked to the composition of the slope sediment among the variables such as sea level subsidence climate plate motion and oceanographic setting windward leeward sediment fabric is suggested to be a major if not the major control on slope angle and slope curvature of carbonate platform flanks besides the recently documented tendency of carbonate sediments to build steeper slopes than siliciclastics this proposed relation sheds new light on the analysis and quantification of the variables influencing the geometry and depositional evolution of carbonate systems furthermore it provides an opportunity to deduce sediment composition from seismic lines and predict lithology prior to drilling

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

halokinetic sequences in carbonate systems an example from the middle albian bakio breccias formation basque country spain in diapir flanks unconformity bounded sedimentary packages associated with gravity driven deposits controlled by the ratio between the rates of sediment accumulation and diapir growth can be interpreted in the context of halokinetic sequences the bakio breccias formation basque country spain corresponds to redeposited carbonate deposit that developed in response to the bakio diapir growth during the middle albian these deposits provide on of the rare documented example of carbonate dominated halokinetic sequences the bakio breccias formation consists of an alternation of clast and matrix supported breccias calcirudite calcarenite and marl deposited along the flanks of the diapir the description and the analysis of the bakio breccias formation lead to a new model for carbonate dominated halokinetic sequences these sequences differ from their siliciclastic counterpart because sediment accumulation rate is controlled by carbonate platform growth on the topographic relief top of the diapirs while sediments are preferentially deposited in the mini basins adjacent of the diapirs in siliciclastic settings during transgressive system tract carbonate platform are able to keep up with the sea level rise and to aggrade on top of the diapirs forming thick and resistant roof which is assumed to limit the diapir growth and thus to favour the development of halokinetic sequences with low angle unconformities wedge halokinetic sequences during late highstand system tract deposition and lowstand system tract if present platform progradation results in high sediment accumulation in the adjacent depocenters loading the autochthonous salt layer and promote diapir growth and creation of topographic relief in addition if the diapir roof reaches emersion karstification of the carbonate platform top may also favour roof destruction and diapir growth depending on the thickness of the roof developed previously and the amplitude of the sea level fall the halokinetic sequences with the emersion and the karstification of the carbonate platform may display high angle unconformities hook halokinetic sequences furthermore gravity driven deposits are assumed to be more common in carbonate dominated halokinetic sequences compared to their siliciclastic counterparts since carbonate platform aggradation creates steep slopes on the diapir margins leading to the partial collapse of the margin even when limited diapir growth occurs the carbonate dominated halokinetic sequence model proposed here is an important tool for the prediction of potential reservoir distribution seal and hydrocarbon migration in flanks of salt diapirs where carbonate platform developed

reserves growth in a mature oil field the devonian leduc formation at innisfail field south central alberta canada oil has been continuously produced from the devonian leduc formation at innisfail field since its discovery in 1957 to date cumulative production at innisfail is 98 9 of recoverable oil in place 84 3 mmbo and indicates that the leduc is near the end of its productive life a sequence stratigraphic interpretation produced from core well logs and three dimensional 3 d reflection seismic data however suggests that production may be extended through the development of two previously undetected scenarios of bypassed oil entrapment 1 attic oil accumulations associated with small buildups atop the isolated innisfail platform and 2 backstep edge accumulations located in positions structurally low to currently producing wells in both cases oil accumulations are related to a leduc depositional history that was characterized by rates of long term carbonate sediment accumulation exceeded by the rate of sea level rise positive bathymetric relief created at the time of deposition and subsequently present day stratigraphic traps were produced during the final phase of stratal retrogradation that immediately preceded the drowning of the isolated innisfail platform high quality 3 d seismic data are essential in the exploration for both attic and backstep edge oil accumulations at innisfail integration of 3 d seismic data well log and core data indicates that although depositional relief on both types of features may be low they are nonetheless seismically resolvable the small platform top buildups are up to 0 16 km2 40 ac in diameter and have up to 10 m 33 ft of independent closure above spill point backstep edge oil accumulations occur within the structurally highest parts of the leduc high frequency sequence g downlap limit depositional relief along the downlap limit and associated trap closure ranges from approximately 5 to 15 m 16 to 49 ft during 2003 and 2004 two platform top buildups were directionally drilled and one existing well located near a backstep edge position and suspended since 1988 was reactivated all three wells are successful and to date have cumulative production of 71 thousand bbl of oil a total of 17 platform top buildups and backstep edge development drilling prospects exist across innisfail and have expected case recoverable reserves of approximately 960 thousand bbl of oil these reserve additions suggest the potential for 1 14 field growth at innisfail and are representative of the potential value that may yet exist within all mature leduc fields in western canada

excursions along the lennard shelf devonian carbonates canning basin western australia abstract the world class middle upper devonian carbonate outcrops of the lennard shelf canning basin western australia offer a unique opportunity to examine reefal carbonate shelf to basin evolution in response to multiple coeval extrinsic and intrinsic drivers variable styles of carbonate stratigraphic architecture and heterogeneity developed as a function of the interplay between long hierarchical accommodation trends global biological crises greenhouse to transitional climatic changes and syndepositional tectonics the linkage of reservoir scale shelf to basin carbonate expression to regional seismic scale architectures made possible by these pristine exposures allows the generation of conceptual models and predictive relationships that are relevant to steep sided carbonate hydrocarbon reservoirs and plays furthermore exquisite exposure of syndepositional fracture systems and their association with carbonate facies and position along the depositional profile provide templates for characterization of subsurface nonmatrix flow in particular the lennard shelf outcrops are excellent analogs for the age equivalent canadian alberta basin and carboniferous reservoirs of the pricaspian basin in kazakhstan however the breadth of insight contained within the lennard shelf outcrop belt is applicable to the greater understanding of reefal carbonate systems in general

reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the laurentide ice sheet abstract this paper reconstructs the deglaciation of the laurentide ice sheet lis including the innuitian ice sheet from the last glacial maximum lgm with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides we build on a recent inventory of laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the lis which we depict in a series of palaeogeographic maps results show that the drainage network at the lgm was similar to modern day antarctica the majority of the ice streams were marine terminating and topographically controlled and many of these continued to function late into the deglaciation until the ice sheet lost its marine margin ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build up peak phase and collapse of the cordilleran laurentide ice saddle the south eastern marine margin in atlantic canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the lgm in contrast the ice streams draining towards the north western and north eastern marine margins in the beaufort sea and in baffin bay appear to have remained stable throughout most of the late glacial and some of them continued to function until after the younger dryas yd the yd influenced the dynamics of the deglaciation but there remains uncertainty about the response of the ice sheet in several sectors we tentatively ascribe the switching on of some major ice streams during this period e g m clintock channel ice stream at the north west margin but for other large ice streams whose timing partially overlaps with the yd the drivers are less clear and ice dynamical processes rather than effects of climate and surface mass balance are viewed as more likely drivers retreat rates markedly increased after the yd and the ice sheet became limited to the canadian shield this hard bed substrate brought a change in the character of ice streaming which became less frequent but generated much broader terrestrial ice streams the final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around hudson bay our reconstruction indicates that the lis underwent a transition from a topographically controlled ice drainage network at the lgm to an ice drainage network characterised by less frequent broad ice streams during the later stages of deglaciation these deglacial ice streams are mostly interpreted as a reaction to localised ice dynamical forcing flotation and calving of the ice front in glacial lakes and transgressing sea basal de coupling due to large amount of meltwater reaching the bed debuttressing due to rapid changes in ice sheet geometry rather than as conveyors of excess mass from the accumulation area of the ice sheet at an ice sheet scale the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet the final elimination of which was mostly driven by surface melt

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

lower cambrian shelf and shelf margin buildups flinders ranges south australia1 carbonate buildups in the flinders ranges of mid early cambrian age grew during a period of high archaeocyath diversity and are of two types 1 low energy archaeocyath sponge spicule mud mounds and 2 high energy archaeocyath calcimicrobe calcified microbial microfossil bioherms mud mounds are composed of red carbonate mudstone and sparse to abundant archaeocyath floatstone have a fenestral fabric display distinct stromatactis contain abundant sponge spicules and form structures up to 150m wide and 80 m thick bioherms are either red or dark grey limestone and occur as isolated small structures 2 20 m in size surrounded by cross bedded calcarenites and calcirudites or as complexes of mounds and carbonate sands several hundreds of metres across red bioherms comprise masses of white epiphyton with scattered archaeocyaths and intervening areas of archaeocyath rich lime mudstone grey bioherms are complex intergrowths of archaeocyaths encrusting dark grey renalcis and thick rinds of fibrous calcite cement the bioherms were prone to synsedimentary fracturing and exhibit large irregular cavities up to 1 5 m across lined with fibrous calcite the buildups are isolated or in contiguous vertical succession mud mounds occur alone in low energy frequently nodular limestone facies individual bioherms and bioherm complexes occur in high energy on shelf and shelf margin facies the two types also form large scale shallowing upward sequences composed of basal deep water mud mounds grading upward into archaeocyath calcimicrobe bioherm complexes and bioherms in cross bedded carbonate sands the uppermost sequence is capped by ooid grainstone and or fenestral to stromatolitic mudstone the calcimicrobe and metazoan associations form the two major biotic elements which were to dominate reefs throughout much of subsequent phanerozoic time

unblocking of the nares strait by greenland and ellesmere ice sheet retreat 10 000 years ago the extent of glaciation at the northern margin of the canadian greenland high latitude arctic region over the past 30 000 years is uncertain geological arguments have been made for greenland and ellesmere island ice sheets that coalesced to block the nares strait1 and for restricted ice sheets on the two islands2 leaving the strait open as it is today3 distinguishing between these two possibilities would provide significant constraints on present understanding of the past circulation between the arctic and atlantic oceans4 5 on estimates of past ice volume6 and on the response of the greenland ice sheet to climate change7 radiocarbon analyses provide dates for the deglaciation of the islands coasts but do not yield information on whether ice filled the strait here we present measurements of cosmogenic 36cl that has accumulated in situ in erratics and glacially polished bedrock on islands within the nares strait these data allow us to determine the time for which the rocks have been recently exposed to the atmosphere and thus the age of the final deglaciation of the strait we show that greenland and ellesmere ice sheets retreated from the nares strait about 10 000 years ago the strait was filled with ice during the last glaciation blocking this connection between the arctic and atlantic oceans and supporting the model of extensive and long lasting ice on land and sea in this region8 9 10 11

retrieval of effective ice crystal size in the infrared sensitivity study and global measurements from tiros n operational vertical sounder 1 the difference between cirrus emissivities at 8 and 11 m is sensitive to the mean effective ice crystal size of the cirrus cloud de by using single scattering properties of ice crystals shaped as planar polycrystals diameters of up to about 70 m can be retrieved instead of up to 45 m assuming spheres or hexagonal columns the method described in this article is used for a global determination of mean effective ice crystal sizes of cirrus clouds from tovs satellite observations a sensitivity study of the de retrieval to uncertainties in hypotheses on ice crystal shape size distributions and temperature profiles as well as in vertical and horizontal cloud heterogeneities shows that uncertainties can be as large as 30 however the tovs data set is one of few data sets which provides global and long term coverage having analyzed the years 1987 1991 it was found that measured effective ice crystal diameters de are stable from year to year for 1990 a global median de of 53 5 m was determined averages distinguishing ocean land season and latitude lie between 23 m in winter over northern hemisphere midlatitude land and 64 m in the tropics in general larger des are found in regions with higher atmospheric water vapor and for cirrus with a smaller effective emissivity

temporal patterns of suspended sediment yield following moderate to extreme hydrological events recorded in varved lacustrine sediments a 487 year annually laminated varved sediment record from nicolay lake cornwall island in the canadian high arctic was evaluated to determine the impact that years with high sediment yields had on sediment yields in subsequent years all of the 40 largest years showed evidence for increased sediment yield in the subsequent 10 30 years the positive anomalies in lagging years were approximately scaled according to the size of the initiating year although many intermediate years 25 to 100 year recurrence showed weak or variable responses the smallest events considered 10 to 25 year recurrence showed a consistent but low amplitude response additionally the 10 year events revealed frequent negative sediment yield anomalies in the preceding decade this behaviour was interpreted as a frequent sediment activation cycle initiated by the modest year and leading to sediment yield hysteresis lasting 15 25 years the largest years greater than 50 year recurrence showed consistently above average sediment yields in the preceding decade in part due to the frequent occurrence of moderate q10 years it is hypothesized that temporary storage of sediment and previous initiation of erosion sites resulted in extraordinary sediment yields during intense summer rainfall events this study demonstrates the potential use of varved lake sediment records to improve our understanding of long term sediment dynamics these records present an opportunity to further develop and test sediment dynamic and routing models to gain insight into the interaction of time and space in fluvial and sediment delivery processes copyright 2002 john wiley sons ltd

platform margin collapse during famennian reef evolution canning basin western australia sedimentological investigations of well exposed slope strata in the upper devonian reef complexes of the northern canning basin lead to a sequence stratigraphic interpretation that differs from others based on predictive models in which coarse carbonate debris deposits are regarded as lowstand deposits in the upper frasnian famennian napier range slope succession we recognize an important phase of platform margin collapse during a sea level highstand in the middle famennian at this time the reef rimmed margin was rapidly prograding and the platform was producing carbonate grains notably ooids and peloids that were being transported by turbidity currents to the slope and basin floor periodic collapse of the platform margin led to deposition on the slope of allochthonous blocks of reefal limestone and channelized debris flow units intercalated with the ooid peloidal turbidites and quartzo feldspathic sandstones collapse of the early cemented margin was probably triggered by gravitational instability caused by oversteepening during rapid progradation and or tectonic activity with falling blocks initiating some of the debris flows

the upper cretaceous carbonates of the gargano murge region southern italy a model of platform to basin transition the outcrops in gargano murge region are good examples of the upper cretaceous carbonate systems of the peri adriatic area they enable the architecture and the processes of the platform to basin transition to be studied in detail the platform carbonates are juxtaposed to the deeper marine carbonates by the intermediary of a faulted scarp the base of slope is characterized by bioclastic and conglomeratic aprons interbedded with pelagic mudstones the outer shelf domain which was the prolific source of rudistid bioclastic aprons is not preserved the platform is mainly built of mud dominated transgressive systems tracts whereas highstand systems tracts are developed as bioclastic base of slope aprons the volume of the resedimented bioclasts largely exceeds the volume of missing outer shelf indicating that carbonate production and sediment bypass are more critical for this stratigraphic response than carbonate erosion the lowstands which were controlled by tectonic deformations are characterized by base of slope breccia and blocks eroded from the shelf edge this erosion resulted in the progressive retreat of the shelf edge the best potentials for hydrocarbon reservoir are found in the bioclastic base of slope aprons formed during the cenomanian and maastrichtian highstands this model is considered as an analog for the hydrocarbon reservoirs formed by the deep marine deposits of cretaceous tamabra limestone in the gulf of mexico

bypass margins basin restricted wedges and platform to basin correlation upper devonian canadian rocky mountains implications for sequence stratigraphy of carbonate platform systems abstract carbonate platforms can commonly keep up with relative sea level rise because of high rates of sediment accumulation and platform aggradation surrounding basinal environments are commonly starved but can receive variable extrabasinal siliciclastic input and episodically deposited carbonate sediment if accumulation rates in basinal settings lag behind those of the platform a bypass or erosional margin can develop under these circumstances platform and basin depositional sequences become physically detached and direct correlation of basinal and platform sequences is hindered we report here the results of high resolution stratigraphic analyses of two upper devonian isolated carbonate platforms in western alberta that provide insight into the sequence stratigraphy of bypass margins and criteria for accurate correlation of platform and basinal sequences the slope and basin sequences surrounding the miette and ancient wall platforms consist of basin restricted onlapping wedges of fine grained background sediment deposited dominantly from suspension and coarse grained platform derived sediment redeposited by a variety of gravity flow mechanisms sequence boundaries are identified within the redeposited carbonate intervals identification of sequence boundaries and differentiation of highstand and lowstand slope and basinal facies was based on the geometry mineralogy and clast content of redeposited carbonate units highstand carbonates contain sheet like debris flows and turbidites with abundant slope derived clasts and background facies with high total carbonate content lowstand carbonates contain sheet like and channelized debris flows and turbidites with abundant platform derived clasts and background facies with low carbonate content and locally high amounts of organic carbon transgressive facies are dominated by initially carbonate poor and organic rich background sediments that display a progressive increase in carbonate content and decrease in organic carbon content these patterns are interpreted to record abundant background carbonate sedimentation during late transgression and highstand when the carbonate factory was robust highstand redeposited carbonates record slope erosion due to oversteepening and slope readjustment processes lowstand redeposited carbonates indicate platform and platform margin erosion and low background carbonate sedimentation when the platform was either exposed or under very shallow peritidal conditions high siliciclastic and organic contents during lowstand and early transgression may partly be the result of reciprocal sedimentation but alternatively may represent continuous siliciclastic supply during times with little dilution by fine grained carbonate sediment successive stages of platform development at miette and ancient wall were controlled by accommodation changes driven by relative sea level fluctuations backstripping analyses of strata from both platforms confirm that significant differential subsidence was a major control on variations in platform thickness and patterns of slope development greater subsidence at ancient wall fostered the development of a steeper bypass margin and different slope evolution compared to miette slope oversteepening also initiated a process of slope readjustment that eventually reduced the platform to basin gradient and facilitated regressive platform progradation in conventional siliciclastic sequence stratigraphy basin restricted wedges are interpreted as lowstand deposits on the basis of their geometry and position relative to an updip margin wedge shaped basinal units along the miette and ancient wall bypass margins contain both highstand and lowstand facies that straddle sequence boundaries the results of this study provide objective criteria for differentiating systems tracts in carbonate slope and basin environments through mineralogic and compositional analyses providing more accurate correlation of detached platform and basin sequences interpretation of carbonate basin restricted wedges as purely highstand or lowstand deposits may lead to erroneous conclusions regarding sequence stratigraphy platform to basin correlation and the volumetric partitioning of sediments deposited in different systems tracts

platform margin collapses and sequence stratigraphic organization of carbonate slopes cretaceous eocene gargano promontory southern italy we describe the sequence stratigraphic organization and the associated sedimentological characteristics of cretaceous to eocene slope and base of slope carbonate successions the study area is located in the gargano promontory which belongs to the stable foreland of southern italy the succession consists of three superimposed depositional sequences separated by major unconformities the upper two sequences are clear examples of sequence stratigraphic organization in fact they both start with huge megabreccia wedges lst followed upward by thin pelagic units tst and a thick package of calciturbidites and debrites that alternate with pelagic mudstone hst the cretaceous highstand systems tract is clearly arranged in a number of coarsening upward cycles while the eocene one which also comprises a toplap shallow water unit is not the gargano stratigraphic palimpsest and the entire margin of the apulia platform show remarkable similarities with present day carbonate platform margins and slopes where irregular convex bankward embayments suggest large scale failures it is clear that classic sequence stratigraphic organization can result from simple platform dismantling having no or little time relation with global sea level fluctuations in fact as the margin failure lst interrupts the carbonate production a period of starvation tst along the entire slope and base of slope follows necessarily finally when the margin once again becomes active and productive sediment exportation starts again and the system begins to prograde hst

late wisconsinan glaciation of the central sector of the canadian high arctic abstract geomorphic and chronological evidence from cornwall island in the canadian high arctic archipelago provides direct evidence for the age and dynamics of the center and northern flank of the innuitian ice sheet that covered the islands during the late wisconsonian glacial maximum dispersal of erratics and glacial landforms indicate that ice flowed north across the island and converged with ice flowing northwest from norwegian bay cornwall island was initially deglaciated at 9000 14c yr b p in near synchrony with widely separated sites in adjacent parts of the archipelago this regional chronology suggests rapid breakup of a marine based innuitian ice sheet that was destabilized by rapid eustatic sea level rise and ice thinning during the early holocene this evidence provides strong support for a recently proposed ice divide spanning the central part of the canadian high arctic and indicates that most if not all of the region was glaciated during the late wisconsinan

platform margins reef facies and microbial carbonates a comparison of devonian reef complexes in the canning basin western australia and the guilin region south china devonian reef complexes were well developed in western australia and south china but no detailed direct comparison has been made between reef building in the two regions the regions differ in several respects including tectonic stratigraphic and palaeoceanographic palaeogeographic settings and the reef building styles reflect minor differences in reef builders and reef facies similarities and differences between the two reef complexes provide insights into the characteristics of platform margins reef facies and microbial carbonates of both regions here we present a comparison of platform margin types from different stratigraphic positions in the late devonian reef complex of the canning basin western australia and middle and late devonian margin to marginal slope successions in guilin south china comparisons are integrated into a review of the reefal stratigraphy of both regions reef facies reef complex architecture temporal reef builder associations 2nd order stratigraphy and platform cyclicity in the two regions were generally similar where the successions overlap temporally however carbonate deposition began earlier in south china carbonate complexes were also more widespread in south china and represent a thicker succession overall platforms in the canning basin grew directly on precambrian crystalline basement or early palaeozoic sedimentary rocks but in south china carbonate complexes developed conformably on older devonian siliciclastic strata pre frasnian reef facies in south china had more abundant skeletal frameworks than in canning basin reefs of equivalent age and famennian shoaling margins containing various microbial reefs may have been more common and probably more diverse in south china however late devonian platform margin types have been documented more completely in the canning basin deep intra platform troughs deep depressions containing non carbonate pelagic sediments nandan type successions that developed along syndepositional faults characterize devonian carbonate platforms in south china but have no equivalent on the lennard shelf canning basin where inter reef areas were more shallow the south china platform to depression pattern was generally continuous from the lower to upper devonian indicating that many pre devonian tectonic features continued to exercise considerable effect through deposition localized fault controlled subsidence was an important factor in both regions but similarities in 2nd order aggradation progradation cycles suggest that eustasy was also an important control on the larger scale stratigraphic development of both regions

the intrinsic effect of shape on the retrogradation motif and timing of drowning of carbonate patch reef systems lower frasnian bugle gap canning basin western australia the evolution and architecture of a set of retreating lower frasnian patch reef outcrops in the canning basin of western australia were evaluated and their depositional and stratigraphic contacts spatially recorded using digital surveying tools the geological data together with high resolution digital elevation models were assembled in three dimensional visualization and modelling software and subsequently used for building two dimensional surface models and three dimensional volumetric models numerical data on geometry and shape were extracted from these models and used to quantitatively assess the retrogradation motif of patch reef development the development of the patch reefs comprises three stages during stages 1 and 2 the patch reefs exhibited an overall retrogradational escarpment type configuration displayed by on average 60 steep reef margin walls that lacked the support of coeval slope deposits the subdivision between stages 1 and 2 is based on minor backstepping reducing less than 10 of the platform top area the onset of stage 3 is recognized by stromatolite development fringing reef margin walls during stage 3 an aggrading accretionary reef margin developed comprising allochthonous and autochthonous slope deposits both types of slope deposit onlap the previous stages and are distributed unevenly with allochthonous slope deposits being noticeably absent around the smaller and more elongate patch reefs the variation in distribution of slope sediment type can be explained by the amount linked to platform size of platform top shedding small patch reefs were unable to fill the available accommodation adjacent to escarpments with allochthonous slope sediments and were thus encroached by autochthonous slope sediments the variation which cannot be explained by the size difference in the platform top factory has been related to the difference in perimeter length for patch reefs with similar platform top production areas a more elongate patch reef inherits a longer perimeter and a proportionally smaller volume of allochthonous slope sediment per margin length will be transported to the flanks thus the more elongate patch reef intrinsically contained more sites within which autochthonous slope sediments developed digital outcrop modelling and numerical evaluation of the evolution of the patch reefs revealed the major differences in retrogradation motif the quantified variations in progressive decline of platform top area with height were confirmed by hypothetical decline curves for ellipse shaped carbonate systems for which aspect ratio ratio between length and width varied this mathematical model demonstrates that the progressive decline of the production area is highly sensitive to shape and can be used to numerically assess and predict the relative timing of drowning i e when the platform top production area becomes nil of retrogradational isolated carbonate platforms that are controlled by high accommodation wider implications can be surmised for highstand systems tracts and prograding carbonate systems for example for equally sized platforms with hypothetically similar carbonate factories and identical external forces the potential to prograde by platform top shedding is higher with a smaller aspect ratio because the shorter perimeter implies less accommodation space needing to be filled up to commence slope progradation clearly there are intrinsic effects of shape on the development of carbonate platform systems

arctic ocean glacial history while there are numerous hypotheses concerning glacial interglacial environmental and climatic regime shifts in the arctic ocean a holistic view on the northern hemisphere s late quaternary ice sh

architecture and genesis of prograding deep boundstone margins and debris dominated carbonate slopes examples from the permian capitan formation southern guadalupe mountains west texas abstract steep debris rich progradational carbonate slope systems have been well documented around the world in a variety of settings and time periods while the association of such slopes with deep microbial boundstone upper slope factories the planar nature of their clinoform profiles and their toe of slope trajectory patterns have been discussed thoroughly the internal architecture and genesis of clinothems and the mechanics behind progradation remain poorly understood capitan formation seven rivers and yates formation equivalent exposures in the southern guadalupe mountains of west texas allow for examination of steep prograding upper permian guadalupian carbonate slope strata that are coeval with deep skeletal microbial boundstone reefs positioned on the upper slope 100 200 m water depth measured section data tied to interpreted photomosaics and hand samples were collected within a 7 square kilometer study area in pine canyon and the frijole wall to document the deposits and architecture of the capitan slopes a subset of a regional airborne lidar dataset was utilized for mapping declivities and orientations of clinoform surfaces the outcrops reveal that capitan middle to lower foreslopes are dominated by lenticular breccia deposits originating from the brittle failure of upper slope boundstone factories with lesser intercalations of platform derived carbonate grain dominated deposits and bypassed siliciclastics the observed lenticular carbonate breccia deposits stack hierarchically and exhibit lateral and upslope offsetting compensational and backfilling architecture in response to the slope topography of previously deposited debris over time this process constructed lower to middle slope conical sediment bodies that coalesced laterally to form strike extensive debris dominated aprons once these debris aprons filled the slope profile up to the level of in situ microbial boundstone production substrate became available for the upper slope reefs to prograde the advance of the boundstones overtop their own debris completed the development of a shelf to basin debris dominated clinothem and the process repeated resulting in boundstone margin and foreslope progradation these capitan foreslope architectures indicate that sustained small scale gravitational failure of the upper slope boundstones was the dominant resedimentation process that contributed to slope development single collapse events that produced individual breccia beds occurred at a much greater frequency than relative sea level fluctuations recorded on the platform top and variability in breccia matrix sediment suggests that boundstones were shedding material downslope throughout all stages of the accommodation cycle we propose that boundstone accretion local instability and failure and resulting slope breccia deposition were somewhat independent of allocyclic high frequency accommodation changes and that an autogenic control associated with deep oligophotic microbial margins is dominant during the development and progradation of steep debris dominated slope systems

late devonian carbonate margins and foreslopes of the lennard shelf canning basin western australia part b development during progradation and across the frasnian famennian biotic crisis abstract many studies document the occurrence of carbonate progradational successions that are driven by overall accommodation limited conditions and represent periods when substantial volumes of sediment are stored in slope settings however few have reported on the detailed internal anatomy and components of prograding clinothems and furthermore little is known about how environmental parameters affect the development of carbonate margins and slopes when superimposed on the long term low accommodation signal upper devonian frasnian and famennian carbonate outcrop exposures along the lennard shelf northeast canning basin western australia offer the examination of reefal margin and foreslope development in a variety of settings one of which is long term 10 ma progradation during the late frasnian and famennian in the early phases of progradation a global biotic crisis and faunal overturn occurred around the frasnian famennian f f boundary and indications of global climatic cooling are interpreted at points throughout the late devonian these extrinsic and intrinsic controls provide ecologic context and a stratigraphic framework to assess carbonate margin and foreslope architectures and facies distributions in order to better characterize and predict their complex heterogeneity the outcrop dataset collected includes measured sections tied to interpreted photomosaics and detailed mapping using aerial photographs from the south lawford range windjana gorge and dingo gap areas the outcrop observations highlight distinctive changes in margin style foreslope composition stratigraphic packaging and strike variability within the contexts of the f f biotic crisis long term highstand hst progradation and late devonian climatic changes intervals before and after the f f boundary exhibit notable increases in downslope calcimicrobial boundstone encrustation and evidence for waning foreslope contributions from other previously flourishing carbonate factories reflecting stressed ecological conditions and consequent calcimicrobial opportunism during gradual buildup and recovery periods that bracket the extinction the famennian slope post effects related to the f f crisis can be subdivided into a calcimicrobial boundstone dominated upper slope with a highly complex downdip transition into a mixed debris and grain dominated middle slope and a silt dominated lower slope to toe of slope and exhibits a highly complex lateral heterogeneity associated with multiple contributing sediment factories and temporal partitioning of resedimentation a repeated stacking pattern is observable in the famennian middle slope setting consisting of upward successions of debris followed by a gradation from silt dominated deposits into grain dominated deposits we here interpret these as the expression of high frequency sequences superimposed upon the longer term progradation and a function of transitional greenhouse to icehouse climates these findings offer predictive relationships that link the internal depositional heterogeneity of prograding slope systems to the interplay of long term accommodation drivers ecological conditions affecting carbonate sediment factories and climatic conditions that control the development of high frequency sequences

postglacial emergence in the canadian high arctic integrating glacioisostasy eustasy and late deglaciation throughout the last glaciation the innuitian sea rather than glaciers occupied many fiords and channels of the queen elizabeth islands two alternative hypotheses which constitute end members are presented to account for the transgression of the innuitian sea between 18 and 8 8 ka at which time it reached marine limit hypothesis a proposes that the last ice load was fully established by 18 ka and that it remained stable while sea level rose eustatically from approximately 60 m asl to marine limit by 8 8 ka hypothesis b proposes an advance of glaciers from present day positions after 14 ka when increased precipitation allowed rapid glacial loading to accompany the eustatic sea level rise by the early holocene when glaciers stood at the last ice limit evidence suggests maximum warming and a shift to a negative mass balance it is now recognized that the stable relative sea level at marine limit must record the balance between the rate of eustatic rise and the rate of uplift due to glacial unloadi

coalescent greenland and innuitian ice during the last glacial maximum revising the quaternary of the canadian high arctic abstract this paper constitutes a fundamental revision of the author s earlier research and resolves a long standing debate concerning the late quaternary history of the canadian high arctic supporting its inundation by glaciers during the last glacial maximum lgm a transect along east ellesmere island demonstrates that ice advanced northward and southward along the axis of nares strait during the late wisconsinan debouching from a central saddle in kane basin the configuration of ellesmere island and greenland ice is based on moraines meltwater channels and erratics the youngest ams 14c date obtained on shelly till suggests ice buildup after 19 ka bp whereas many other dates are younger than 30 ka bp furthermore the lowest youngest detectable amino acid ratios on shells from till postdate the robeson aminozone 70 ka bp and are separated from holocene ratios by a narrow gap wholly consistent with the occupation of the strait by late wisconsinan ice re entry of the sea throughout nares strait is shown by a series of paleogeographic maps based on geomorphic evidence and radiocarbon dates on shells associated with marine limit deglaciation at the north end of the strait occurred by 10 1 ka bp and at the south end by 9 0 ka bp nares strait may still have been blocked by ice north of kane basin at 8 ka bp however by 7 5 ka bp it provided an unobstructed seaway from the arctic ocean to baffin bay the prominent ice margins within the fiords of eastern ellesmere island previously considered to mark the last ice limit record regional stabilization of land based ice after breakup of preceding marine based margins other implications of this study are that ice buildup occurred post 30 ka bp and possibly post 19 ka bp during an interval widely assumed to be constrained by severe aridity in the high arctic and that coalescent greenland and ellesmere island ice during the lgm promoted thickening of the eastern ellesmere island ice divide causing enhanced westward flow across the island to eureka sound sizeable postglacial emergence 80 120 m on eastern ellesmere island is associated with the retreat of thick ice 1 km from the strait greater emergence in eureka sound which extends southward into the central arctic islands confirms the previously proposed axis of the innuitian ice sheet further clarification of the extent geometry and retreat of the innuitian ice sheet will provide new opportunities for glaciological and geophysical modelling and help to identify late quaternary sediment sources for the arctic ocean and baffin bay

early holocene deglaciation of expedition and strand fiords canadian high arctic terrestrial and marine records provide the first reconstruction of past glacial events on west central axel heiberg island lateral moraines along expedition fiord define an early holocene ice margin when a trunk glacier occupied the inner half of the fiord limited sediment accumulation in the outer fiord 8 4 ka bp principally by calving of an unstable ice front to a position well upvalley of the present ice limit rapid deglaciation is evidenced by i an absence of ice marginal landforms and related marine biofacies ii a scarcity of raised marine sediments and iii exceptionally thin sediments 5 20 m in the inner fiord a transition from a hiatella arctica mya truncata macrofossil assemblage to an astarte borealis mya truncata assemblage reflects a change from moderate to low energy depositional environments at the fiord head by 7 9 ka bp the extensive ice advance into expedition fi

lithofacies and sequence development on an upper devonian mixed carbonate siliciclastic fore reef slope canning basin western australia detailed sedimentological and stratigraphical analysis coupled with conodont biostratigraphy of a fore reef slope succession in the napier range napier formation is used to develop a depositional model and relative sea level history for late frasnian to late famennian reef evolution in the canning basin of north western australia changes in sedimentary style on the slope reflecting differing rates of carbonate production on the platform are linked to third and higher order relative sea level fluctuations overlapping slope aprons accumulated along the base of a steep walled platform margin coarse carbonate debris was deposited adjacent to the margin as talus breccias via rockfall and debris flow breccias depositional slopes up to 45 and locally steeper are demonstrated using rotated geopetal cavity fills the predominance of channel filling lithofacies throughout the slope succession indicates the highly channelized nature of the aprons the middle slope is dominated by sandy oolitic peloidal turbiditic grainstones interpreted as sediment exported from an active platform the turbidites and associated debris flow breccias contrast with condensed carbonate intervals and deep water non fenestral stromatolites that record times of very low platform production lower slope turbidites and associated intraclastic breccias indicate widespread redeposition of sediment eroded from lithified and semi lithified limestones higher up the slope several third order sequences are recognized in the fore reef succession and these are composed primarily of transgressive and highstand deposits carbonate production was severely restricted in the early famennian coinciding with development of onlapping siliciclastic aprons during a relative sea level lowstand evidence for a subaerial exposure event is also preserved within the siliciclastic strata controls on sequence development are difficult to constrain although two sequence boundaries can be correlated with falls on the global sea level curve the reef complexes evolved in an active extensional regime and it is highly likely that tectonism in conjunction with eustasy controlled accommodation on the platform and therefore carbonate productivity