sedimentological characteristics of small rivers with loessic headwaters in the chaco south america some sedimentological characteristics of uvial environments located in the northeastern region of the chaco pampa plain were analysed in order to determine the possible in uence of the loessic headwaters of local basins concentrations of suspended sediments as well as grain size of the river beds were compared unexpectedly it was found that the suspended load has an inverse relationship with the hydrometric levels with the exception of highly saline streams conductivity values between 4300 and 11 000 l sc m 1 the mean concentration of suspended sediments was 63 1 and 206 3 mg l 1 in ood and low water periods respectively the grain size of bed sediments was relatively homogeneous along the whole hydrological cycle sandy silty bottoms predominate in channels followed by silty sandy and clayey silty bottom types sediment transport mainly occurs in accelerating ow suspension overcoming the critical erosion velocity during ood periods some parameters exceeded by 70 the values recorded during the low water phase 2000 elsevier science ltd and inqua all rights reserved

a geomorphological approach to the management of rivers contaminated by metal mining as the result of current and historical metal mining river channels and floodplains in many parts of the world have become contaminated by metal rich waste in concentrations that may pose a hazard to human livelihoods and sustainable development environmental and human health impacts commonly arise because of the prolonged residence time of heavy metals in river sediments and alluvial soils and their bioaccumulatory nature in plants and animals this paper considers how an understanding of the processes of sediment associated metal dispersion in rivers and the space and timescales over which they operate can be used in a practical way to help river basin managers more effectively control and remediate catchments affected by current and historical metal mining a geomorphological approach to the management of rivers contaminated by metals is outlined and four emerging research themes are highlighted and critically reviewed these are 1 response and recovery of river systems following the failures of major tailings dams 2 effects of flooding on river contamination and the sustainable use of floodplains 3 new developments in isotopic fingerprinting remote sensing and numerical modelling for identifying the sources of contaminant metals and for mapping the spatial distribution of contaminants in river channels and floodplains and 4 current approaches to the remediation of river basins affected by mining appraised in light of the european union s water framework directive 2000 60 ec future opportunities for geomorphologically based assessments of mining affected catchments are also identified

the cretaceous tertiary boundary stratotype section at el kef tunisia how catastrophic was the mass extinction abstract the cretaceous tertiary k t boundary stratotype section at el kef tunisia represents the most complete and expanded sedimentary record across this important mass extinction horizon presently known high resolution analysis of planktic foraminifera in two outcrops el kef i stratotype and el kef ii along with comparisons between planktic and benthic foraminifera calcareous nannofossils ostracods pollen and spores and dinoflagellates indicate that major changes across the k t boundary are registered only in benthic and planktic foraminifera and calcareous nannofossils biotic changes in benthic foraminifera are unique to el kef and similarly shallow continental shelf sections and appear to be the result of a sea level regression in the latest maastrichtian followed by a sea level rise across the k t boundary that was accompanied by expansion of the local oxygen minimum zone omz biotic changes in planktic foraminifera appear partly related to these conditions also but in general reflect more global oceanographic changes for instance species extinctions are gradual and selective as observed in k t sections worldwide rather than random and abrupt although there is a 69 decline in species richness between 25 cm below and 10 cm above the k t boundary only rare species disappeared their combined relative abundance constitute less than 20 of the total population about 52 of these extinct taxa 8 of the population are large ornate morphologically complex tropical subtropical forms that lived at or below the thermocline no planktic foraminifera from this depth range survived the k t boundary event all survivor taxa were surface dwellers living within the photic zone their relative abundance 80 dominates both cretaceous and early tertiary populations these data indicate that the k t biotic record in the shallow continental shelf section at el kef was significantly influenced by local conditions which combined with the latest maastrichtian sea level regression and subsequent sea level rise resulted in shallowing of the local omz relative to the sea surface shallowing of the local omz lead to the selective disappearance of benthic faunas and may have adversely affected the surviving photic zone dwellers the selective nature of species extinctions however appear to be related partly to long term global oceanographic changes which were accelerated at the k t boundary possibly by a bolide impact

multiple impacts across the cretaceous tertiary boundary abstract the stratigraphy and age of altered impact glass microtektites microkrystites ejecta layers from the chicxulub crater are documented in late maastrichtian and early danian sediments in mexico guatemala belize and haiti in northeastern mexico two to four ejecta layers are present in zone cf1 which spans the last 300 ky of the maastrichtian the oldest ejecta layer is dated at 65 27 0 03 ma based on sediment accumulation rates and extrapolated magnetostratigraphy all younger ejecta layers from the maastrichtian and early danian parvularugoglobigerina eugubina zone pla l may represent repeated episodes of reworking of the oldest layer at times of sea level changes and tectonic activity the k t boundary impact event 65 0 ma is not well represented in this area due to widespread erosion an early danian pla l ir anomaly is present in five localities bochil actela coxquihui trinitaria and haiti and is tentatively identified as a third impact event at about 64 9 ma a multiimpact scenario is most consistent with the impact ejecta evidence the first impact is associated with major deccan volcanism and likely contributed to the rapid global warming of 3 4 c in intermediate waters between 65 4 and 65 2 ma decrease in primary productivity and onset of terminal decline in planktic foraminiferal populations the k t boundary impact marks a major drop in primary productivity and the extinction of all tropical and subtropical species the early danian impact may have contributed to the delayed recovery in productivity and evolutionary diversity

stable isotopic evidence for relative and eustatic sea level changes in eocene to oligocene carbonates baldwin county alabama eocene to oligocene marine carbonate shelf deposits in a continuous core in baldwin county alabama were evaluated within a sequence stratigraphic framework to determine characteristic stable isotopic responses to inferred fluctuations in sea level due to a greater sampling density per unit of time stable isotopes in this core reveal more defined trends than have previously been reported from dsdp odp deep sea drilling project ocean drilling project records and from more land ward sections that have undergone intense sub aerial alteration or erosion the 18 o signature records eustatic sea level 18 o becomes heavier as eustatic sea level falls and lighter as eustatic sea level rises 18 o records a secular shift to heavy from the early eocene to oligocene of 3 0 the 13 c signature records relative sea level change paleobathymetry 13 c generally becomes heavier in shallower water deposits and lighter in deeper water deposits however in planktonic oozes 13 c may shift to heavy 13 c also records a secular shift to heavy from the early eocene to the oligocene of 3 5 although minor diagenetic perturbations in the stable isotopes are present the depositional signal dominates the isotopic signal spar cements generally result in lighter 18 o and 13 c if the dolomite is 20 dolomitization results in heavier 18 o and 13 c

the global stratigraphy of the cretaceous tertiary boundary impact ejecta the chicxulub crater ejecta stratigraphy is reviewed in the context of the stratigraphy of underlying and overlying rock sequences the ejecta sequence is regionally grouped in a thick polymict and monomict breccia sequences inside the crater and within 300 km from the rim of the crater known from drill holes in and close to the breater and exposures near the border of yucatan and belize b gulf of mexico region 2500 m from the crater with up to 9 m thick complex tsunami wave influenced tektite bearing sequences in shallow marine 500 m deep environments and tektite bearing decimeter thick gravity flow deposits in deep water sites c an intermediate region between 2500 and 4000 km from the crater where centimeter thick tektite bearing layers occur and d a global distal region with a millimeter thin ejecta layer the distal ejecta layer is characterized by sub millimeter sized microkrystites often rich in ni rich spinels and altered clinopyroxene wherever present the ejecta layers mark exactly the sudden mass mortality horizon of the k t boundary what exactly caused the mass mortality is still uncertain but it appears the main event leading to the k t mass extinctions

grain size of cretaceous paleogene boundary sediments from chicxulub to the open ocean implications for interpretation of the mass extinction event the relationship between the chicxulub impact event and the cretaceous paleogene k pg boundary mass extinction has been repeatedly questioned specifically cretaceous planktonic foraminifera occurring in high energy sediments in the gulf of mexico related to the impact have been used to argue that the impact preceded the mass extinction here we address this dispute by comparing grain size data from two gulf of mexico sections and a distal pelagic sequence significantly larger grain sizes combined with evidence for size sorting in the proximal sections suggest that fossils in boundary deposits are redeposited and cannot be used to assign ages thus the grain size data support other evidence that indicates that high energy deposits from around the gulf of mexico correlate stratigraphically with the chicxulub impact and the k pg mass extinction

variability in sediment delivery and storage along river courses in bega catchment nsw australia implications for geomorphic river recovery in many catchments in southeastern australia alluvial stores have been the dominant source of sediments mobilised in the period since european settlement in bega catchment on the south coast of new south wales nsw this has been reflected by dramatic changes to river morphology extensive volumes of material have been released and efficiently flushed to the lowland plain with a sediment delivery ratio of almost 70 however only 16 of these alluvial sediments have been flushed through to the estuary as antecedent controls on valley width have resulted in the lowland plain acting as a large sediment sink the changing nature of sediment source transfer and accumulation zones has varied markedly from subcatchment to subcatchment the volume of material supplied to the lowland plain from differing subcatchments is not related to subcatchment area rather the pattern of river types dictates the spatial variability in storage and transfer over 67 of sediment released has been sourced from just 25 of the catchment from subcatchments characterised by large valley fills cut and fill river style that previously stored extensive volumes of material at the base of the escarpment these parts of bega catchment were especially sensitive to disturbance sediment exhaustion from these parts of the catchment and from river courses elsewhere has major implications for the geomorphic recovery potential of rivers constraining what can be realistically achieved in terms of river rehabilitation

structural organization of process zones in upland watersheds of central nevada and its influence on basin connectivity dynamics and wet meadow complexes abstract the drainage network within upland watersheds in central nevada can be subdivided into distinct zones each dominated by a unique set of processes on the basis of valley form the geological materials that comprise the valley floor and the presence or absence of surficial channels on hillslopes the type and structure frequency length and spatial arrangement of these process zones is related to the lithology and weathering characteristics of the underlying bedrock process zones dominated by sediment accumulation storage and groundwater recharge are associated with less resistant rocks that weather into abundant but relatively small particles sediment transport and runoff dominated zones are associated with resistant sparsely fractured rocks that produce limited but larger clasts the type and structure of process zones along axial valleys depend on the characteristics of the process zones on the hillslopes numerous sediment storage dominated reaches leads to a relatively high number of unincised fans located at the mouth of tributaries along the axial valleys and to frequent and lengthy unincised valley segments both of which disconnect large sections of the drainage basin from channelized flows in contrast a relatively high density of transport dominated process zones leads downstream to the incision of side valley fans and axial valley deposits as well as a high degree of basin connectivity defined by the integration of surficial channels connectivity also is related to the lithology of the underlying bedrock with higher degrees of connectivity being associated with volcanic rocks that presumably yield high rates of runoff lower levels of connectivity are associated most frequently with extensively fractured locally permeable sedimentary and metamorphic rock assemblages thus basins underlain by volcanic rocks appear to be more sensitive to incision and produce more dynamic channels in terms of the rate of channel valley modification than those underlain by other lithologies considerable attention has been devoted in recent years to the management of wet meadow ecosystems that serve as important riparian habitats within upland basins of central nevada the data presented here show that within basins characterized by a high degree of connectivity areas of wet meadow are minimal where they do exist in these basins they tend to be severely degraded by incision or gully erosion and will be difficult to manage given the dynamic nature of the axial channel processes wet meadows within basins that exhibit a low degree of connectivity and high sediment storage to transport ratios on hillslopes will likely be more responsive to management activities because of the reduced threats of channel incision and presumably a larger supply of groundwater flow to the meadows created by an extensive network of recharge sites importantly human activities that lead to an increase in basin connectivity can negatively impact downstream meadows through a decrease in groundwater recharge and an increase in stream dynamics in spite of the fact that these activities may be physically separated from the wet meadow areas

extended cretaceous tertiary boundary extinctions and delayed population change in planktonic foraminifera from brazos river texas high resolution planktonic foraminiferal analysis of three brazos river sections indicates a nearly continuous cretaceous tertiary k t boundary sedimentary record second only to the world s most complete record at el kef tunisia species extinctions occur over an extended period of time and with two major extinction episodes the first extinction episode with 46 of the species extinct occurs at and just below 10 15 cm a short hiatus at the base of a sandy shell hash and clay sand unit which was interpreted by bourgeois et al 1988 to represent a tsunami bed generated by the k t boundary bolide impact the top of this tsunami bed is about 17 20 cm below the k t boundary as defined by the first appearance of tertiary planktonic foraminifera the second extinction phase with 45 of the species extinct occurs 25 cm above the k t boundary zone p0 p1a boundary of the remaining seven surviving cretaceous species six gradually disappear during planktonic foraminiferal subzones p1a and basal p1b no species extinctions or major faunal assemblage changes are directly associated with the k t boundary iridium distribution is ambiguous with one peak in the upper part of the tsunami bed and a second peak at the micropaleontologically defined k t boundary relative abundances of dominant species are stable through the late maastrichtian and only minor abundance changes coincide with the first extinction episode or the k t boundary the first major faunal change in the dominant species group coincides with the second extinction episode and leads to decline and eventual extinction of this group in subzone p1a species disappearing at the two extinction episodes 46 and 45 constitute only a small percentage 8 and 5 of the individuals of the total planktonic foraminiferal population this suggests that weakened species with low numbers of individuals and sensitive to relatively minor environmental changes were primarily affected by these extinction episodes magnetostratigraphy indicates that the first extinction phase began about 310 000 years before the k t boundary and the second extinction phase occurred 50 000 years after the k t boundary this stepped pattern of species extinctions suggests a progressively stressed ecosystem in continental shelf settings which may be related to an observed sea level regression and global cooling the hypothesis of a global catastrophic mass extinction at the k t boundary caused by a large extraterrestrial impact is not supported by the brazos river planktonic foraminiferal data

spherule deposits in cretaceous tertiary boundary sediments in belize and guatemala large spheroid deposits at albion island and armenia in northern and central belize and the spherule deposits of southern belize and eastern guatemala have the same glass origin based on the presence of almost pure cheto smectite derived from alteration of impact glass from the chicxulub impact on yucatan mexico the same origin has also been determined for altered glass spherules in mexico haiti and the caribbean however the spherule layers have variable ages as a result of erosion and redeposition with an early danian parvularugoglobigerina eugubina zone pla 1 age in southern belize guatemala haiti southern mexico and the caribbean and a pre k t plummerita hantkeninoides zone cf1 age of 65 27 0 03 ma in ne mexico a pre k t age for the chicxulub impact has now also been determined from the new yaxcopoil 1 core drilled in the impact crater these data show that chicxulub was not the k t impact that caused the end cretaceous mass extinction but an earlier impact event a multiple impact hypothesis volcanism and climate change appears the likely scenario for the end cretaceous mass extinction

a gis based method for evaluating sediment storage and transport in large mining affected river systems currently the evaluation of sediment storage and transport for large river systems with variable flow has proven to be a challenge that often requires complex numerical models to be applied and sometimes costly direct data acquisition to be made the present study proposes a low cost widely available gis based method through which an initial assessment can be made on areas of sediment storage transport and deposition as well as possible environmental risks that the accumulation of contaminated material may pose to riverine communities along the rivers channel the method mainly relies on satellite imagery and elevation data to devise a quick model of the channel the model has been successfully applied to study the bolivian sector of the well known mining contaminated rio pilcomayo the analysis shows that the portion of the channel from villamontes to d orbigny accounts for more than half of the total c 314 km2 sedimentation area of the pilcomayo in bolivia and that the most environmentally problematic area is centreed around puente sucre where agriculture is practiced on the contaminated floodplain combined with supplementary bathymetric data on the depth of the river in various points around the channel the method could offer further insight into the sediment fluxes and transport capacity of the pilcomayo in various sectors and could thus be successfully used to assess other large mining contaminated river channels around the world

chicxulub impact predates k t boundary new evidence from brazos texas abstract multidisciplinary studies including stratigraphy sedimentology mineralogy and geochemistry of the new core mullinax 1 and outcrops along the brazos river and cottonmouth creek falls county texas reveal the complex history of the chicxulub impact the event deposit and the k t boundary event the k t boundary as identified by the negative 13c shift first occurrence of danian planktic foraminifera and palynomorphs occurs 80 cm above the event deposit in core mullinax 1 the underlying 80 cm interval was deposited in a shallow low oxygen environment during the latest maastrichtian as indicated by high stress microfossil assemblages small shells and burrows infilled with framboidal pyrite the underlying event deposit commonly interpreted as k t impact tsunami consists of a basal conglomerate with clasts containing chicxulub impact spherules repeated upward fining units of spherule rich sands followed by hummocky cross bedded and laminated sands which are burrowed by thalassinoides planolites and ophiomorpha and truncated by erosion this suggests a series of temporally separated storm events with re colonization of the ocean floor by invertebrates between storms rather than a series of waning tsunami generated waves the lithified clasts with impact spherules at the base of the event deposit provide strong evidence that the chicxulub impact ejecta layer predates the event deposit but was eroded and re deposited during the latest maastrichtian sea level lowstand the original chicxulub ejecta layer was discovered in a 3 cm thick yellow clay layer interbedded in undisturbed late maastrichtian clay and mudstones 40 cm below the base of the event deposit and near the base of planktic foraminiferal zone cf1 which spans the last 300 kyr of the maastrichtian the yellow clay consists of cheto smectite derived from alteration of impact glass as indicated by rare altered glass spherules with similar chemical compositions as reworked spherules from the event deposit and chicxulub impact spherules from ne mexico and haiti the brazos sections thus provide strong evidence that the chicxulub impact predates the k t boundary by about 300 kyr consistent with earlier observations in ne mexico and the chicxulub crater core yaxcopoil 1

modeling long term contamination in river systems from historical metal mining heavy metal contamination of sediments within river systems is a major environmental problem around the world deposited as a by product of metal mining contaminated sediments are persistent and widespread frequently affecting large areas of floodplains which makes precise assessments of contamination levels and patterns difficult this paper describes findings from a new generic catchment sediment model called tracer which uses historical mining records to accurately predict present day and future levels and patterns of contamination this model provides detailed views of the extent of contami nation and demonstrates how contaminated sediments form into hot spots which in turn become secondary sources of pollution the exceptional longevity of the contamina tion is also revealed 70 of the deposited contaminants remain within the river system for 200 yr after mine closure simulations of the impact of future climate changes in northern england show that increased flood magnitudes are likely to decrease surface contamination through dilution by cleaner sediment from hillslopes unaffected by mining activity

major and trace metal mobility during weathering of mine tailings implications for floodplain soils abstract mine tailings discharged to river systems have the potential to release significant quantities of major and trace metals to waters and soils when weathered to provide data on the mechanisms and magnitudes of short and long term tailings weathering and its influence on floodplain environments three calendar year long column leaching experiments that incorporated tailings from potosi bolivia and soil from unaffected downstream floodplains were carried out these experiments were designed to model 20 cycles of wet and dry season conditions two duplicate columns modeled sub aerial tailings weathering alone a third modeled the effects of long term floodplain tailings contamination and a fourth modeled that of a tailings dam spill on a previously contaminated floodplain as far as was practical local climatic conditions were modeled chemical analysis of the leachate and column solids optical mineralogy xrd sem epma bcr and water soluble chemical extractions and speciation modeling were carried out to determine the processes responsible for the leaching of al ca cu k na mg mn sn sr and ti over the 20 cycles the ph declined to a floor of ca 2 in all columns calcium cu mg mn and na showed significant cumulative losses of up to 100 60 30 95 and 40 respectively compared to those of al k sr sn and ti which were up to 3 1 5 5 1 and 0 05 respectively the high losses are attributed to the dissolution of relatively soluble minerals such as biotite and oxidation of chalcopyrite and cu sulfosalts while low losses are attributed to the presence of sparingly soluble minerals such as svanbergite cassiterite and rutile these results strongly suggest that the release of tailings to floodplains should be limited or prohibited and that all tailings should be removed from floodplains following dam spills

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

is the transition impact to post impact rock complete some remarks based on xrf scanning electron microprobe and thin section analyses of the yaxcopoil 1 core in the chicxulub crater the transition from impact to post impact rocks in the yaxcopoil 1 core is marked by a 2 cm thick clay layer characterized by dissolution features the clay overlies a 9 cm thick hardground overlying a 66 cm thick crossbedded unit consisting of dolomite sandstone alternating with thin micro conglomerate layers with litho and bioclasts and the altered remains of impact glass now smectite the micro conglomerates mark erosion surfaces microprobe and backscatter sem analysis of the dolomite rhombs show an early diagenetic complex zoned idiomorphic overgrowth with mn rich zones possibly formed by hot fluids related to cooling melt sheet in the crater the pore spaces are filled with several generations of coelestite barite k feldpar and sparry calcite xrf core scanning analysis detected high mn values in the crossbedded sediments but no anomalous enrichment of the siderophile elements cr co fe and ni in the clay layer shocked quartz occurs in the crossbedded unit but is absent in the clay layer the basal paleocene marls are strongly dissolved and do not contain a basal paleocene fauna the presence of a hardground the lack of siderophile elements shocked quartz or ni rich spinels in the clay layer and the absence of basal paleocene biozones p0 and pa all suggest that the top of the ejecta sequence and a significant part of the lower paleocene is missing due to the high energy sedimentation infill a hiatus at the top of the impactite is not unexpected but there is nothing in the biostratigraphy geochemistry and petrology of the yaxcopoil 1 core that can be used to argue against the synchroneity of the end cretaceous mass extinctions and the chicxulub crater

impact and extinction in remarkably complete cretaceous tertiary boundary sections from demerara rise tropical western north atlantic ocean drilling program odp leg 207 on the demerara rise in the western tropical north atlantic recovered multiple cretaceous paleogene boundary sections containing an ejecta layer sedimentological geochemical and paleontological changes across the boundary closely match patterns expected for a mass extinction caused by a single impact a normally graded 2 cmthick bed of spherules that is interpreted as a primary air fall deposit of impact ejecta occurs between sediments of the highest cretaceous plummerita hantkeninoides foraminiferal zone and the lowest paleogene p0 foraminiferal zone there are no other spherule layers in the section in addition to extinction of cretaceous taxa foraminiferal abundance drops from abundant to rare across the boundary ir concentrations reach a maximum of 1 5 ppb at the top of the spherule bed and the ir anomaly is associated with enrichment in other siderophile elements we attribute the unusually well preserved and relatively simple stratigraphy to the fact that demerara rise was close enough 4500 km to the chicxulub impact site to receive 2 cm of ejecta yet was far enough away and perhaps sheltered by the curve of northern south america to have been relatively unaffected by impact induced waves

collapse of the pilcomayo river the pilcomayo river flows south eastwards from the bolivian andes across the chaco plains setting the border between argentina and paraguay it flows down along 1000km in principle to finally join the paraguay river it spills over the plains during the rainy season from january to march the sediment load of the pilcomayo is one of the largest in the world 140milliontons per year which is mostly wash load from the upland andes the mean concentration of suspended sediment is 15g l the maximum recorded concentration is as high as 60g l the river has built a large fan covering a surface of 210 000km2 with many abandoned channels today it is a river prone to avulsion raising border disputes between the two lowland countries argentina and paraguay moreover the very special feature of pilcomayo river is that it does not actually flow into the paraguay river very far upstream of the mouth in the paraguay the channel blocks itself with sediment and wood debris forcing water and sediment to spread across the plains moreover the point of blockage has moved hundreds of kilometers upstream throughout the 20th century many environmental issues arise because of this collapse channel discontinuity not the least of them is the migration of fish the future of the river concerns bolivia and the two lowland countries 2012 elsevier b v

biotic effects of the chicxulub impact k t catastrophe and sea level change in texas abstract biotic effects of the chicxulub impact the k t event and sea level change upon planktic foraminifera were evaluated in a new core and outcrops along the brazos river texas about 1000 km from the chicxulub impact crater on yucatan mexico sediment deposition occurred in a middle neritic environment that shallowed to inner neritic depths near the end of the maastrichtian the sea level fall scoured submarine channels which were infilled by a sandstone complex with reworked chicxulub impact spherules and clasts with spherules near the base the original chicxulub impact ejecta layer was discovered 45 60 cm below the sandstone complex and predates the k t mass extinction by about 300 000 years results show that the chicxulub impact caused no species extinctions or any other significant biotic effects the subsequent sea level fall to inner neritic depth resulted in the disappearance of all larger 150 m deeper dwelling species creating a pseudo mass extinction and a survivor assemblage of small surface dwellers and low oxygen tolerant taxa the k t boundary and mass extinction was identified 40 80 cm above the sandstone complex where all but some heterohelicids hedbergellids and the disaster opportunistic guembelitrids went extinct coincident with the evolution of first danian species and the global 13c shift these data reveal that sea level changes profoundly influenced marine assemblages in near shore environments that the chicxulub impact and k t mass extinction are two separate and unrelated events and that the biotic effects of this impact have been vastly overestimated

the cretaceous paleogene boundary foraminifera sea grasses sea level change and sequence stratigraphy abstract the tsunami generated by the chicxulub impact eroded the uppermost cretaceous surface of the gulf coast region u s a forming a distinctive topography that was previously interpreted as a sequence boundary at more distal sites such as stevns klint denmark there appears to be no sequence boundary at the cretaceous paleogene boundary but there is one within the uppermost maastrichtian between the sigerslev and hojerup members and another in the lowermost paleocene top of zone p1a both of these surfaces are identified by distinctive phosphatized and incipient hardgrounds the changes in sea level involved in the generation of uppermost cretaceous sequences are thought to have been minimal as in the gulpen and maastricht formations of the maastricht area netherlands the presence of sea grasses and their associated foraminifera would indicate that the chalk sea floor remained within the range of water depth that would allow photosynthesis

guembelitria dominated late maastrichtian planktic foraminiferal assemblages mimic early danian in central egypt abstract during the late maastrichtian 66 8 65 5 ma the asyut basin in central egypt experienced a breakdown of the surface to bottom gradient of the 13c 12c ratio with planktic 13c values 0 2 0 8 lighter than benthic values planktic foraminiferal species diversity was reduced by more than 50 with assemblages dominated 60 90 by the opportunistic blooms of the disaster species guembelitria cretacea which mimic the early danian the prolonged breakdown in productivity occurred during a time of tectonic activity and increased terrestrial runoff that may have resulted in highly eutrophic waters coupled with a sea level regression 65 5 ma that led to restricted circulation increased productivity during the short climate warming between 65 4 and 65 2 ma is associated with increased species diversity abundant rugoglobigerinids and common heterohelicids at the end of the maastrichtian decreased productivity coincided with the k t impact and mass extinction followed by characteristically early danian low diversity assemblages the similarity of the late maastrichtian and post k t impact guembelitria dominated assemblages reveals that the planktic foraminiferal response to the k t catastrophe was not unique but followed a predictable pattern of response to severe environmental perturbations

autogenic response of fluvial deltas to steady sea level fall implications from flume tank experiments flume tank experiments on fluvial deltas conducted with constant fall of relative sea level rate a 0 constant sediment discharge q s and constant water discharge q w reveal a built in geomorphic process that inevitably causes valley incision autoincision after the beginning of the sea level fall and forms paired stream terraces on the abandoned alluvial slope despite steady sea level fall deltas aggrade without major incision until the autoincision threshold is attained at which time the aggradational regime is replaced by a degradational one results of the experiments imply that multiple valley incision and terrace formation can occur as an autogenic response of the depositional system to steady forcing by constant sea level fall changes of a q s and q w or changes in river energy are not required to account for these geomorphic events the understanding of the autogenic response when combined with the theory of shoreline autoretreat provides an alternative view of the geomorphic development of fluviodeltaic systems during base level fall

new evidence concerning the age and biotic effects of the chicxulub impact in ne mexico abstract in the 1990s the chicxulub impact was linked to the k t boundary by impact spherules at the base of a sandstone complex that was interpreted as an impact generated tsunami deposit since that time a preponderance of evidence has failed to support this interpretation revealing long term deposition of the sandstone complex the k t boundary above it and the primary impact spherule ejecta interbedded in late maastrichtian marls below based on evidence from mexico and texas we suggested that the chicxulub impact predates the k t boundary impact tsunami proponents have challenged this evidence largely on the basis that the stratigraphically lower spherule layer in mexico represents slumps and widespread tectonic disturbance although no such evidence has been presented the decades old controversy over the cause of the k t mass extinction will never achieve consensus but careful documentation of results that are reproducible and verifiable will uncover what really happened at the end of the crectaceous this study takes an important step in that direction by showing 1 that the stratigraphically older spherule layer from el penon ne mexico represents the primary chicxulub impact spherule ejecta in tectonically undisturbed sediments and 2 that this impact caused no species extinctions

mediaeval lead pollution in the river ouse at york england the city of york in northern england has a long history of being flooded by the river ouse excavations of a 9 m sedimentary profile were carried out by the york archaeological trust on the site of a pumping station associated with a flood prevention scheme at north street on the south west bank of the river ouse this profile records evidence of human activity and episodic river sedimentation over a period from the 2nd to the 14th century ad anthropogenic materials in the profile include waterfront timber and wattle structures and dumps of organic domestic debris and industrial waste evidence of historic floods is preserved in interleaved alluvial deposits this study reports on the degree of lead pb contamination at the site from roman to mediaeval times and the sources of both alluvial and manufactured lead deposited in the profile archaeological sedimentological geochemical and mineralogical evidence suggest that yorkshire dales mining activity during the 9th 13th centuries ad may have both directly and indirectly caused lead contamination of the alluvial deposits at north street

ejecta layer at the cretaceous tertiary boundary bass river new jersey ocean drilling program leg 174ax a continuously cored borehole drilled at bass river new jersey recovered a cretaceous tertiary k t succession with a 6 cm thick spherule layer immediately above the boundary below the spherule layer the cretaceous glauconitic clay is extensively burrowed and contains the uppermost maastrichtian micula prinsii calcareous nannofossil zone spherical impressions of spherules at the top of the cretaceous indicate nearly instantaneous deposition of ejecta from the chicxulub impact the thickest ejecta layer shows clearly that a single impact occurred precisely at k t boundary time above the spherule layer the glauconitic clay contains the planktonic foraminiferal p0 and p alpha zones indicating 1 a complete k t succession and 2 continuous deposition interrupted only by fallout of the ejecta layer clay clasts within a 6 cm interval above the spherule layer contain cretaceous microfossils and may be rip up clasts from a tsunami or possibly a megastorm event extinction of the cretaceous planktonic foraminifers and burrowing organisms occurs abruptly at the k t boundary thus the bass river k t succession unequivocally links the chicxulub bolide impact to the mass extinctions at the end of the mesozoic

the environmental and geomorphological impacts of historical gold mining in the ohinemuri and waihou river catchments coromandel new zealand abstract between 1875 and 1955 approximately 250 000 mg yr 1 of mercury arsenic and cyanide contaminated mine tailings were discharged directly into the ohinemuri river and its tributaries in the coromandel region north island new zealand a devastating flood on 14 january 1907 deposited large amounts of mine waste across the floodplain of the ohinemuri and waihou rivers in the vicinity of the township of paeroa the 1907 mine waste flood deposit was located as a dirty yellow silt in cores and floodplain profiles with a thickness ranging from 0 15 0 50 m geochemical analysis of the mine waste shows elevated concentrations of pb 200 570 mg kg 1 and as 30 80 mg kg 1 compared to early holocene background concentrations pb 1 as 1 bulk sediment samples recovered from the river channel and overbank deposits also show elevated concentrations of pb 110 mg kg 1 zn 140 320 mg kg 1 ag 3 mg kg 1 and hg 0 4 mg kg 1 using the mine waste deposit as a chronological marker shows that sedimentation rates increased from 0 2 mm yr 1 in the early holocene to 5 5 26 8 mm yr 1 following the 1907 flood downstream trends in the thickness of the flood deposit show that local scale geomorphic factors are a significant influence on the deposition of mine waste in such events storage of mine waste is greatest in the upstream reaches of the floodplain the volume of mine waste estimated to be stored in the ohinemuri floodplain is 1 13 m m 3 an order of magnitude larger than recent well publicised tailings dam failures such as the 1996 south america porco 2000 romanian baia mare and baia borsa accidents and constituted and was recognised at the time a significant geomorphological and environmental event the mine waste material remains in the floodplain today representing a sizable legacy store of contaminant metals and metalloids that pose a long term risk to the ohinemuri and waihou ecosystems

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

late cretaceous volcanism in south and central texas stratigraphic structural and seismic models abstract abstract since their discovery in 1915 hydrocarbon traps in and around serpentine plugs have produced about 47 million barrels of oil and have significant potential for additional small discoveries production is from isolated reservoirs within mounds of altered volcanic tuff and associated shoal water carbonates a review of the more than 200 volcanic centers and intrusive bodies of south and central texas has led to development of stratigraphic and seismic models useful in exploration and production the so called serpentine plugs are largely tuff mounds formed by accumulation of volcanic ash altered to palagonite on the seafloor around a submarine volcanic vent volcanic activity peaked during deposition of the chalk and marl of the upper austin and lower taylor groups about 80 million years ago after their eruption the tuff mounds localized the deposition of shoal water carbonates with good porosity and permeability low permeability organic rich marine shale and marl of the taylor group capped the carbonates serving as both a hydrocarbon source and a stratigraphic seal compactional draping of overlying san miguel and olmos sands with minor offset faulting created important additional traps in south texas central texas volcanic centers are highly aligned along strike oriented regional faults and fractures of the balcones and luling systems the magmas in both central and south texas were ultramafic and alkaline suggesting that partial melting occurred at depths of about 40 miles 60 kilometers the magma rose rapidly to the surface probably in an extensional stress regime controlled by pre tertiary balcones luling faults the palagonite tuff of a typical productive volcanic center has low seismic velocity and is encased in high velocity carbonates the strong velocity contrast coupled with the distinctive shape of the tuff mass yields a characteristic seismic pattern modern seismic techniques together with stratigraphic data allow accurate delineation of buried tuff mounds and prediction of productive carbonate facies

the cretaceous paleogene k p boundary at brazos texas sequence stratigraphy depositional events and the chicxulub impact abstract two cores from brazos texas spanning the cretaceous paleogene k p boundary are investigated by a multidisciplinary approach aiming at unraveling environmental changes and sequence stratigraphic setting in addition the sedimentology of the k p event deposit and its correlation with the k p boundary is studied foraminifera and nannofossil stratigraphy indicates that both cores include a latest maastrichtian zone cf1 cf2 and earliest danian p0 p and p1a shale sequence with a sandy and chicxulub ejecta bearing event deposit at the k p boundary a hiatus of unknown duration may be present by the unconformable base of the event deposit planktic foraminifera as well as calcareous nannofossil abundance and diversity both decline abruptly above the event deposit k p mass extinction whereas benthic foraminifera show a pronounced faunal change but no mass extinction mineralogical and geochemical proxies suggest that except for the sandwiched k p event deposit no facies change took place across the k p boundary and no evidence for adverse an or dysoxic sedimentary conditions following the chicxulub impact was observed therefore the interval bracketing the k p event deposit is considered as highstand systems tract increased coarse detritus input and low planktic benthic p b foraminifera ratios during the earliest paleocene p0 and p both suggest an increased coastal proximity or relative sea level lowering although the k p mass extinction of planktic foraminifera might have influenced the p b ratios as well consequently the sandy shales of the early paleocene are considered as late regressive highstand or as lowstand deposit during p1a shales assigned as transgressive systems tract overlie a pyrite and glauconite rich bioturbated transgressive surface or type 2 sequence boundary the smectite dominated clay assemblage with minor illite kaolinite and chlorite indicates semiarid humid climates with no obvious shifts across the k p boundary the magnetic susceptibility signature during the maastrichtian reveals a subtle cyclic or rhythmic pattern whereas a high amplitude cyclic pattern is present during the early danian the k p event deposit shows a succession of high energetic debris flows and turbidites derived from multiple source areas followed by a period of decreasing current energy deposition was likely triggered by multiple tsunami or tempestites followed by a prolonged period of reworking and settling the chicxulub ejecta at the base of the k p event deposit consists of mg rich smectite as well as fe mg rich chlorite spherules their mineralogical composition points to target rocks of mafic to intermediate composition presumably situated in the northwestern sector of the chicxulub impact structure besides these silicic phases the most prominent ejecta components are limestone clasts accretionary carbonate clasts and microspar suggesting that the texas area received ejecta also from shallow carbonate rich lithologies at the impact site on the yucatan carbonate platform the excellent correlation of chicxulub ejecta at brazos with ejecta found in the k p boundary layer worldwide along with the associated mass extinction provides no evidence that chicxulub predated the k p boundary and allows for unequivocal positioning of the k p boundary at the event deposit

incongruent weathering of cd and zn from mine tailings a column leaching study the weathering of discharged mine tailings can contaminate groundwaters rivers and floodplains with potentially toxic cd and zn depending on tailings mineralogy storage dispersal and climatic conditions the mechanisms of long term tailings weathering and its influence on waste piles and floodplain environments were assessed by a column leaching experiment that incorporated tailings and soil from potosi bolivia and modelled 20 cycles of wet and dry season conditions over three calendar years chemical analysis of the leachate and column solids optical mineralogy xrd sem epma bcr and water soluble chemical extractions and speciation modelling were carried out to determine the processes responsible for the leaching of cd fe s and zn over this period approximately 50 to 95 of the original cd and 50 to 60 of the zn were leached from the columns large amounts of leached cd and zn at the beginning of the experiment are attributed to the dissolution of soluble sulphate minerals present in the original tailings and formed after the first wetting of the columns the zn cd mass ratios of the tailings and soil initially 429 and 400 respectively vary considerably over the course of the experiment low values between 220 and 300 in the early cycles are attributed to preferential weathering of cd rich wurtzite zn fe s and sequestration of zn in preference to cd in secondary fe phases forming in the columns in the middle cycles dissolution of secondary fe oh 3 under low ph 3 conditions and of ferroan cd poor sphalerite zn fe s releases zn and raises the zn cd ratio to 550 600 in the tailings only columns and up to 1500 in the mixed tailings soil columns the very high ratios in the latter are also ascribed to the formation of low molecular weight organic ligands that have high affinity for zn over cd in the later column cycles zn cd ratios return to near initial values due to the weathering of fe poor sphalerite and secondary fe phases and the declining preference of zn over cd in the soil organic acids under the strongly acidic conditions prevailing in the columns the formation and dissolution of secondary soluble sulphate minerals also play a role in cd and zn cycling especially at the beginning of the experiment

iridium anomaly at the cretaceous tertiary boundary in texas abstract a fifty fold increase in the iridium content precisely at the cretaceous tertiary boundary over background values has been found in the brazos river section in texas

sediment transfer and transformation of an alluvial valley floor the river south tyne northumbria u k the amounts of alluvial storage and the mechanisms responsible for the dispersal of sediment associated with historic metal mining are examined for a 115 year timespan on a 22 km reach of the river south tyne northern england analysis of lateral and vertical channel change over this period the extent of actively reworked gravels and identification of metals in alluvial units show five sedimentation zones separated by more stable reaches aggradation in the late nineteenth century was followed by a period of storage and local reworking and then incision some reaches show short term storage of sediment injected from tributaries which may be dispersed by floods there is some evidence of transfer of sediment bodies downvalley within sedimentation zones and of a sediment wave movement between zones in lower parts of the south tyne investigated present day incision the variation in the area of actively reworked gravel spreads and the widespread dispersal of fine grained toxic metal mining wastes all have practical implications the intricate response of the channel system to historic changes in sediment supply is not readily described by either a complex response model or a simple translatory wave

autostepping during the transgressive growth of deltas results from flume experiments a series of three dimensional flume experiments on the transgressive growth of deltas conducted with constant rate of relative sea level rise a constant sediment discharge s and constant upstream water discharge q reveals an inbuilt geomorphic process that inevitably forms discrete steps on the abandoned subaqueous deltaic slope the stepped topography and its process of formation are here referred to as autostep s and autostepping respectively the stepped topography is caused by the lateral migration of delta front lobes that inevitably shift landward but fail to cover lobes of older cycles the autostepping arises from the principle of autoretreat combined with autocyclic lateral shifting of the feeder system discrete changes of a s a s or q s are not required to explain the origin of episodic backstepping in an overall transgressive regime allocyclic changes in a and s as commonly invoked in the sequence stratigraphy literature are not an alternative to autostepping but would only enhance or reduce the inbuilt process of autostepping in river dominated delta systems

fe rich and k rich mafic spherules from slumped and channelized chicxulub ejecta deposits in the northern la sierrita area ne mexico spherule deposits commonly interpreted as ejecta from the chicxulub impact at yucatan mexico are present in many k t cretaceous tertiary sections geological mapping of the northern la sierrita area ne mexico revealed the presence of 1 multiple spherule deposits embedded in late maastrichtian marls which are folded or disaggregated breccia like they are up to 6 m thick locally present in two outcrop areas and show limited lateral continuity these deposits consist of mm cm sized spherical to drop shaped vesiculated spherules angular to filamentous ejecta fragments and abundant carbonate they are interpreted as primary ejecta fallout deposits that have been affected by subsequent local slumps slides liquefaction and debris flows welded components suggest an initial ground surge like ejecta dispersion mode 2 a spherule deposit 10 60 cm thick that constitutes the base of a channelized sand siltstone deposit at or close to the k t boundary and is characterized by wide lateral continuity it is of similar petrologic composition to deposit 1 though slightly enriched in terrigeneous detritus thus reflecting influx from proximal shelf areas it is interpreted to result from debris flows and turbidite currents though no size sorting and abrasion of ejecta has been observed petrological mineralogical and geochemical criteria suggest that ejecta components from both types of spherule deposits are similar and originated from the chicxulub impact with multiple deposits produced by subsequent remolding reworking and redeposition spherules and fragments have an fe 25 30 wt al mg rich and si poor 25 wt sio2 composition and are altered to chlorite and iron oxides though rare k rich mafic glass 50 wt sio2 5 8 wt k is also present they contain ti fe k rich schlieren fe mg rich globules and rare m sized metallic and sulfidic ni co rich inclusions carbonate as clasts and within spherules and fragments shows textures indicative of quenching and or liquid immiscibility although potential ejecta fractionation and alteration make accurate evaluation difficult this composition suggests an ejecta origin mainly from mafic lithologies and carbonaceous sediments in addition to a contribution from intermediate felsic rocks and the possibility of meteoritic contamination

chemical remobilization of contaminant metals within floodplain sediments in an incising river system implications for dating and chemostratigraphy metals such as pb zn cd and cu from historical mining activity have been used as stratigraphic markers for dating and provenancing vertically accreted fine grained floodplain overbank deposits this study presents evidence for chemical remobilization of these metals within overbank sediments in the tyne basin uk the evidence includes breakdown of metal bearing minerals sulphides carbonates iron and manganese oxyhydroxides shifts of chemical fractions within zones of relatively low ph towards more soluble and reactive phases and accumulation of secondary iron and manganese oxyhydroxides at levels related to fluctuating water table levels or to the breakdown of organic matter all of this suggests that fine centimetre scale chemostratigraphy using metal concentrations and ratios is unlikely to provide reliable data in river systems that have experienced or are experiencing major changes in water table levels or pedogenesis coarse tens of centimetre to metre scale chemostratigraphy when applied with caution may still provide a means of delineating contaminated units

heavy metal contamination in overbank sediments of the geul river east belgium its relation to former pb zn mining activities overbank sediments of the geul river east belgium are highly contaminated by the heavy metals pb zn and cd due to former pb zn mining activities in the drainage basin geochemical variations in vertical overbank sediment profiles sampled 1 km north of the mine tailings of plombieres allow metal fluxes back to the 17th century to be reconstructed the vertical profiles are subdivided into three major units corresponding to different industrial periods based on sedimentological criteria as well as on the distribution of contaminants alluvial sediments with the highest heavy metal concentrations correspond to the major period of mining activity of the 19th century the fact that zn mining at the la calamine open mine started before large scale mining of the pbs zns subsurface exploitations is reflected in the vertical profiles by an increase in zn content before a marked increase in pb and cu the regional extent of contamination in the alluvial deposits was evaluated on the basis of the geochemical analysis of sediments at depths of the 0 20 cm and 80 100 cm most of the upper samples are extremely contaminated significant local variations in heavy metal concentration in the lower samples are interpreted in terms of which overbank sediment horizon has been sampled at a depth of 80 100 cm this indicates that blind sampling of overbank sediments to characterize the degree of contamination in shallow boreholes can give very erratic results

faunal turnover at the end of the cretaceous in the north pacific region implications from combined magnetostratigraphy and biostratigraphy of the maastrichtian senpohshi formation in the eastern hokkaido island northern japan abstract a combined magnetostratigraphic and biostratigraphic study has been performed on the maastrichtian senpohshi formation in eastern hokkaido island northern japan which is an approximately 1300 m thick section mainly composed of hemipelagic mudstone the identification of magnetic polarity was possible at 51 horizons whereby four magnetozones were recognized these magnetozones were correlatable to geomagnetic polarity chrons c31r to c30n suggesting that the age of the senpohshi formation is spanning from middle to upper part of the maastrichtian ca 69 67 ma the magnetostratigraphy of the senpohshi formation established in this study enables a direct age correlation to the maastrichtian successions in other regions thus this detailed chronology of the formation contributes to paleontological studies of the maastrichtian in the north pacific region for instance this magnetostratigraphic age assessment implies the following 1 the stratigraphic range of the ammonite pachydiscus flexuosus contains polarity chrons from the lower part of c31r to the lower part of c31n 2 the first occurrence fo of the calcareous nannofossil nephrolithus frequens in the north pacific region is correlatable to polarity chron c30n or below and 3 the fo of the bivalve inoceramus awajiensis is located within polarity chrons from c31r to the upper part of c31n this suggests that the inoceramid extinction event in the north pacific region might have occurred during polarity chrons from c31r to the upper part of c31n ca 70 5 67 8 ma which is 2 3 5 0 myr prior to the cretaceous paleogene boundary the trend of the maastrichtian faunal turnover in the north pacific is well consistent with those of other regions brings a new evidence for understanding the global faunal turnover in the maastrichtian just before cretaceous paleogene mass extinction

a cellular model of holocene upland river basin and alluvial fan evolution coulthard t j macklin m g kirkby m j 2002 a cellular model of holocene upland river basin and alluvial fan evolution earth surface processes and landforms 27 3 269 288

stable isotope evidence for gradual environmental changes and species survivorship across the cretaceous tertiary boundary high resolution 13c and 18o records have been generated from analyses of the planktonic foraminiferal species heterohelix globulosa and the benthonic foraminiferal taxon lenticulina spp from 3 m of a cored section spanning the cretaceous tertiary k t boundary at brazos river texas these are the first stable isotope records across the k t boundary based on monospecific and monogeneric foraminiferal samples they show a gradual decrease in 13c values of about 2 5 permil beginning at the k t boundary as defined by the first appearance of tertiary planktonic foraminifera and continuing 17 20 cm above the boundary approximately 40 000 years later gradual 13c depletion contrasts with the sudden 13c drop at the k t boundary observed in many deep sea sections the surface to bottom 13c gradient decreased to less than zero approximately 25 000 30 000 years after the k t boundary and remained negative for at least the next 140 000 years concomitant with change in 13c values is a gradual decrease of about 2 5 permil in 18c values which has not been observed at other localities this 18o depletion suggests changes in temperature and or salinity in the earliest paleocene gulf of mexico no extinction of foraminiferal species is associated with the k t boundary or the onset of 18o and 13c depletions instead two phases of cretaceous species extinctions occur one extinction phase is below the k t boundary and below the tsunami bed of bourgeois et al 1988 and may be linked to sea level regression and environmental perturbations the second extinction phase coincides with the minimum in 13c and 18o values in the early danian zone p0 pla and appears directly related to environmental changes reflected in the isotopic record h globulosa which is commonly present in maastrichtian and danian sediments exhibits significantly lower 18o 16o and 13c 12c ratios in tertiary sediments relative to specimens from maastrichtian sediments demonstrating the survival of this important cretaceous taxon after the k t boundary event

extinction survivorship and evolution of planktic foraminifera across the cretaceous tertiary boundary at el kef tunisia an expanded sediment record at el kef shows that the k t boundary extinctions of planktic foraminifera extend over an interval from 25 cm below the geochemical boundary ir anomaly to 7 cm above species extinctions appear sequential with complex large ornate forms disappearing first and smaller less ornate forms surviving longer the 14 species extinctions below the boundary appear unrelated to an impact event cretaceous species survivorship is greater than previously assumed about 10 species survive 22 into subzone p1a globigerina eugubina all cretaceous survivors are small primitive forms which are generally smaller than their ancestors in cretaceous sediments species evolution after the k t event occurs in two pulses the first new paleocene species evolve in the basal black clay zone po immediately after the major cretaceous extinctions evolving species are small and primitive similar to cretaceous survivors the second pulse in species evolution occurs in the lower part of subzone p1b with the appearance of larger more diverse species the first major increase in carbonate sedimentation and productivity occurs at this time and signals the recoveyr of the ecosystem nearly 300 000 years after the k t event the species extinctions prior to the generally assumed impact event implied by the ir anomaly and the long recovery period of the ecosystem thereafter cannot be explained by a single impact but suggest that multiple causes may be responsible such as climatic changes volcanism a sea level drop production of warm saline bottom water and the chemical consequences associated with increased salinity

stream terrace genesis implications for soil development genesis of three distinct types of stream terraces can be understood through application of the concepts of tectonically induced downcutting base level of erosion complex response threshold of critical power diachronous and synchronous response times and static and dynamic equilibrium climatic and tectonic stream terraces are major terraces below which flights of minor complex response degradation terraces can form these three types of terraces can be summarized by describing a downcutting aggradation renewed downcutting sequence for streams with gravell bedload by tectonically induced downcutting streams degrade to achieve and maintain a dynamic equilibrium longitudinal profile at the base level of erosion lateral erosion bevels bedrock beneath active channels to create major straths that are the fundamental tectonic stream terrace landform aggradation events record brief reversals of long term tectonically induced downcutting because they raise active channels they may be considered as major the result of climatic perturbations or minor the result of complex response model types of perturbations climatically controlled aggradation followed by degradation leaves an aggradation surface this type of fill terrace tread is the fundamental climatic stream terrace landform aggradation surfaces may be buried by subsequent episodes of deposition unless intervening tectonically induced downcutting is sufficient for younger aggradation surfaces to form below older surfaces raising of the active channel by either tectonic uplift or by climatically induced aggradation provides the vertical space for degradation terraces to form first in alluvial fill and then in underlying bedrock along tectonically active streams these are complex response terraces because they result from interactions of dependent variables within a given fluvial system pauses in degradation to a new base level of erosion and or minor episodes of backfilling lead to formation of complex response fill cut and strath or of fill terraces fill cut terraces are formed in alluvium they are complex response terraces because they are higher than the base level of erosion good exposures and dating are needed to distinguish static equilibrium complex response minor strath terraces from dynamic equilibrium tectonic major straths strath terraces may be regarded as complex response terraces where degradation rates between times terrace tread formation exceed the long term uplift rate for the reach based on ages and positions of tectonic terraces late quaternary global climatic changes control aggradation events and even the times of cutting of major tectonic straths because the base level of erosion can not be attained during times of climatically driven aggradation degradation events most terrace soils form on treads of climatic and complex response terraces aggradation surfaces may provide an ideal flight of terraces on which to study a soils chronosequence each aggradation event is recorded by a single relict soil where tectonically induced downcutting is sufficient to provide clear altitudinal separation of the terrace treads multiple paleosols are typical of tectonically stable regions where younger aggradation events spread alluvium over treads of older climatic terraces pedons on a climatic terrace in a small fluvial system commonly are roughly synchronous variations of soil properties that can be attributed to temporal differences will be minor compared to altitudinally controlled climatic factors climatic terraces of adjacent watersheds also should be roughly synchronous correlatable variations of soil properties that can be attributed to temporal differences will be minor compared to lithologic and climatic factors between different watersheds such generalizations may not apply to basins with sufficient relief that geomorphic responses to climatic changes occur at different and overlapping times and to large rivers whose widely separated reaches are characterized by different response times to climatic perturbations soils on climatic terraces of distant watershedswill not be synchronous if their respective aggradation events occur during full glacial times and interglacial times soils on some complex response terraces may be diachronous within a given fluvial system and typically are diachronous between watersheds

age stratigraphy and deposition of near k t siliciclastic deposits in mexico relation to bolide impact examination of 10 k t boundary sections in northeastern and east central mexico and new data presented from 7 sections permit the following conclusions 1 the globally recognized k t boundary and mass extinction in planktic foraminifera is stratigraphically above and separated by a thin marl layer of maastrichtian age from the siliciclastic deposit that is commonly interpreted as a short term hours to days k t impact generated tsunami deposit a similar relationship between the k t boundary and siliciclastic or breccia deposits is observed at brazos river in texas beloc in haiti and poty quarry in brazil 2 stratigraphic control indicates that deposition of the siliciclastic member occurred sometime during the last 150 k y of the maastrichtian and ended at least several thousand years prior to the k t boundary 3 at least four discrete horizons of bioturbation have been observed within the siliciclastic deposit that indicate episodic colonization by invertebrates over an extended time period 4 the glass and spherule rich unit which has been linked to the haiti spherule layer and the chicxulub structure is at the base of the siliciclastic deposit and thus significantly predates the k t boundary event the stratigraphic separation of the k t boundary and siliciclastic deposits and the evidence of long term deposition between them suggests the presence of two events 1 a globally recognized k t boundary impact event marked by ir anomaly and the mass extinction and 2 a caribbean event impact or volcanic and probably linked to the chicxulub structure that predates the k t boundary and is marked by glass and siliciclastic or breccia deposits

gradual mass extinction species survivorship and long term environmental changes across the cretaceous tertiary boundary in high latitudes stable isotope and planktic foraminiferal analyses across the cretaceous tertiary k t boundary transition at nye klov indicate longterm oceanic instability associated with global sea level fluctuations a gradual mass extinction and decreased magnitude of the 13 c shift in high latitudes oceanic instability which began at least 100 kyr before the k t boundary and continued for about 300 kyr into the tertiary was accompanied by a gradual faunal turnover the maximum sea level lowstand during latest maastrichtian is recorded about 75 cm below the k t boundary a sea level rise first in evidence at 20 cm to 40 cm below the boundary continued into zone p0 boundary clay this sea level rise was accompanied by 2 c of cooling in surface and bottom waters prior to the k t boundary 13 c values remained relatively stable up to 10 cm below the k t boundary a negative shift of 0 5 to 1 0 per mil occurred in the boundary clay in both planktic and benthic foraminifera the surface to deep 13 c gradient remained nearly unchanged in contrast to low latitudes where this gradient is virtually eliminated no sudden mass extinction occurred in this cosmopolitan high latitude fauna and nearly all cretaceous taxa thrived well into the tertiary when they gradually disappeared shallow seas dominated by cretaceous survivor taxa and a well developed oxygen minimum zone prevailed during the earliest tertiary short term sea level lowstands are marked by hiatuses at the top of zones p0 and p1a about 50 kyr and 230 kyr after the k t boundary respectively rising sea level reestablished normal marine conditions about 300 kyr to 350 kyr after the k t boundary coincident with the first post k t boundary recovery of the tertiary fauna and extinction of cretaceous survivors during this time high latitude regions temporarily acted as centers of origin and dispersal for planktic foraminifera long term oceanic instability gradual faunal turnover absence of a sudden mass extinction and greatly diminished 13 c shift in high latitudes suggest that a k t boundary bolide impact was not the primary cause for the k t boundary faunal transition moreover these data strongly imply that the destructive effects of the bolide impact would have been greatest in low latitudes and negligible in high latitudes

paleoecology of the cretaceous tertiary mass extinction in planktonic foraminifera abstract paleobiogeographic patterns of the cretaceous tertiary k t mass extinction in planktonic foraminifera in tunisia spanning environments from open marine upper bathyal to shelf and shallow marginal settings indicate a surprisingly selective and environmentally mediated mass extinction this selectivity is apparent in all of the environmental proxies used to evaluate the mass extinction including species richness ecological generalists ecological specialists surface and subsurface dwellers whether based on the number of species or the relative percent abundances of species the following conclusions can be reached for shallow to deep environments about three quarters of the species disappeared at or near the k t boundary and only ecological generalists able to tolerate wide variations in temperature nutrients salinity and oxygen survived among the ecological generalists heterohelicids guembelitrids hedbergellids and globigerinellids only surface dwellers survived ecological generalists which largely consisted of two morphogroups of opportunistic biserial and triserial species also suffered selectively biserials thrived during the latest maastrichtian in well stratified open marine settings and dramatically declined in relative abundances in the early danian triserials thrived only in shallow marginal marine environments or similarly stressed ecosystems during the latest maastrichtian but dominated both open marine and restricted marginal settings in the early danian this highly selective mass extinction pattern reflects dramatic changes in temperature salinity oxygen and nutrients across the k t boundary in the low latitude tethys ocean which appear to be the result of both long term environmental changes e g climate sea level volcanism and short term effects bolide impact

the role of geomorphic processes in the transport and fate of mercury in the carson river basin west central nevada the historic processing of precious metal ores mined from the comstock lode of west central nevada resulted in the release of substantial but unquantified amounts of mercury contaminated mill tailings to the carson river basin geomorphic and stratigraphic studies indicate that the introduction of these waste materials led to a period of valley floor aggradation that was accompanied by lateral channel instability the combined result of these geomorphic responses was the storage of large volumes of mercury enriched sediment within a complexly structured alluvial sequence located along the carson river valley much of the contaminated sediment is associated with filled paleochannels produced by the cutoff and abandonment of meander loops and their subsequent infilling with contaminated particles geochemically these deposits are characterized by variations in mercury levels that exceed three orders of magnitude continued lateral instability coupled with an episode of channel bed incision followed the decline of comstock mining and has reexposed contaminated debris within the banks of the river erosion of bank sediments reintroduces mercury enriched particles to the modern channel bed it is suggested on the basis of geochemical and sedimentological data that during the bank erosion process much of the mercury associated with fine 63 valley fill deposits are carried downstream without being incorporated to any appreciable extent within the channel bed sediments in contrast mercury associated with larger and denser particles particularly mercury gold silver amalgam grains are accumulated in the channel bed sediments as the river traverses polluted reaches of the carson river valley concentration patterns developed along the modern channel indicate that the valley fill is the primary source of mercury to the river today thus these data imply that efforts to reduce the influx of mercury to the aquatic environment should examine methods for reducing bank erosion rates

geomorphology and late quaternary of the chaco south america the chaco is a large tropical plain located in the interior of south america consisting of parts of argentina paraguay and bolivia it is 840 000 km2 in area and is characterized by forests savannas and extensive swamps which give it a marked climatic and biogeographic identity it encompasses five huge alluvial fans built by the major rivers which cross the region salado bermejo pilcomayo parapeti and grande the fans are composed of several sedimentary units deposited during different times of the late quaternary under diverse climates two fluvial terraces appear at the apex of each fan the older one is probably late pleistocene in age the second was formed in postglacial times humid climates such as the present one favoured the generation of soils and stable fluvial belts drier climates led to widespread sedimentation along small ephemeral channels and large spill outs during two intervals on in the late quaternary glacial maximum and the late holocene dry climates occurred in the region leading to the formation of dune fields and loess mantles

the age and thermal history of cerro rico de potosi bolivia cerro rico de potosi bolivia is the world s largest silver deposit and has been mined since the sixteenth century for silver and for tin and zinc during the twentieth century together with by product copper and lead the deposit consists primarily of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and explosion breccia the deposit is compositionally and thermally zoned having a core of cassiterite wolframite bismuthinite and arsenopyrite surrounded by a peripheral lower temperature mineral assemblage consisting principally of sphalerite galena lead sulfosalt and silver minerals the low temperature assemblage also was superimposed on the high temperature assemblage in response to cooling of the main hydrothermal system both the dacite dome and the ore fluids were derived from a larger magmatic hydrothermal source at depth the dome was repeatedly fractured by recurrent movement on the fault system that guided its initial emplacement the dome was extruded at 13 8 0 2 ma 2 based on u th pb dating of zircon mineralization and alteration occurred within about 0 3 my of dome emplacement as indicated by a 40ar 39ar date of 13 76 0 10ma 1 for sericite from the pervasive quartz sericite pyrite alteration associated with the main stage high temperature mineralization the last thermal event able to reset zircon fission tracks occurred no later than 12 5 1 1 ma 1 as indicated by fission tract dating minor sericite and magmatic steam alunite veins were episodically formed around 11 ma and between 8 3 and 5 7 ma the younger episodes occurring at the time of extensional fracturing at cerro rico and wide spread volcanism in the adjacent los frailes volcanic field none of these younger events appear to be significant thermal mineralizing events the exceptionally flat thermal release pattern of 39ar from sericite and the results of the fission tract dating of zircon show that none of the younger events was hot enough and lasted long enough to cause significant loss of ar or annealing of zircon fission tracks u th pb dating of zircon cores indicates a precambrian progenitor for some zircons and ree analyses of dated samples of hydrothermally altered dacite show the presence of a prominent positive eu anomaly which constrains interpretations of the origin and evolution of the magmatic hydrothermal system

reply to chicxulub impact predates k t boundary new evidence from brazos texas comment by schulte et al we appreciate this opportunity for further discussion of the brazos texas k t boundary sequences and their timing with respect to the chicxulub impact keller et al 2007 used a multidisciplinary approach to document the stratigraphy paleontology mineralogy and geochemistry of the newly drilled mullinax 1 core and a new outcrop sequence based on this multi proxy dataset very strong evidence was presented that reveals that the chicxulub impact predates the k t mass extinction keller et al 2007 schulte et al take issue with this approach and our findings largely because they believe that the chicxulub impact caused the k t mass extinction and therefore the k t boundary must be placed at the impact spherule layer schulte et al this volume schulte et al 2006 smit et al 1996 we welcome this opportunity to clarify misunderstandings misconceptions and misinterpretations of the k t record in texas and elsewhere at the heart of our disagreements is the decades old controversy about the cause of the end cretaceous mass extinction schulte and collaborators have long argued that the sandstone complex or event deposit with impact spherules at the base in ne mexico and texas mark chicxulub impact generated

chicxulub impact spherules in the north atlantic and caribbean age constraints and cretaceous tertiary boundary hiatus the chicxulub impact is commonly believed to have caused the cretaceous tertiary boundary mass extinction and a thin impact spherule layer in the north atlantic and caribbean is frequently cited as proof we evaluated this claim in the seven best north atlantic and caribbean cretaceous tertiary boundary sequences based on high resolution biostratigraphy quantitative faunal analyses and stable isotopes results reveal a major cretaceous tertiary boundary unconformity spanning most of danian subzone p1a 1 and maastrichtian zones cf1 cf2 400 ka in the nw atlantic bass river core odp sites 1049a 1049c and 1050c in the caribbean odp sites 999b and 1001b the unconformity spans from the early danian zone p1a 1 through to zones cf1 cf4 3 ma only in the demerara rise odp site 1259b is erosion relatively minor and restricted to the earliest danian zone p0 and most of subzone p1a 1 150 ka in all sites examined chicxulub impact spherules are reworked into the early danian subzone p1a 1 about 150 200 ka after the mass extinction a similar pattern of erosion and redeposition of impact spherules in danian sediments has previously been documented from cuba haiti belize guatemala south and central mexico this pattern can be explained by intensified gulf stream circulation at times of climate cooling and sea level changes the age of the chicxulub impact cannot be determined from these reworked impact spherule layers but can be evaluated based on the stratigraphically oldest spherule layer in ne mexico and texas which indicates that this impact predates the cretaceous tertiary boundary by about 130 150 ka