integrating palaeocaves into palaeolandscapes an analysis of cave levels and karstification history across the gauteng malmani dolomite south africa abstract the drimolen palaeocave system in the fossil hominid sites of south africa unesco world heritage site is well known for numerous remains of early hominins such as paranthropus robustus and early homo these hominin fossils along with bone tools and notably diverse accumulation of non hominin primates and fauna have all been excavated from the main quarry area of the site where extensive lime mining took place here we report the first radiometric age of 1 712 0 269 ma for hominin bearing deposits associated with the dnh7 paranthropus robustus cranium in the main quarry area of the site which is consistent with recent biochronological estimates this age is similar to recent estimates for swartkrans member 1 hanging remnant somewhere between 2 3 and 1 8 ma which also contains paranthropus and early homo simultaneously we integrate the newly radiometrically dated main quarry deposits with a new fossil deposit the drimolen makondo discovered in 2013 that is situated some 50 m up the hill to the west from the main quarry it has experienced only limited disturbance from mining but much more extensive erosion preliminary excavations and analysis have revealed that the makondo infill is older than the main quarry dating to 2 706 0 428 ma its greater age is confirmed by biochronology the makondo thus overlap with the suggested end of deposition of australopithecus bearing sterkfontein deposits although it is yet to yield any hominin remains these new dates for the two drimolen palaeocave system deposits indicates that contrary to prior age estimates the drimolen site as a whole records the critical hominin and faunal turnover in south african palaeocommunities that occurred around 2 3 1 7 ma finally as the drimolen makondo represents a rare example of a pre 2 ma fossil bearing deposit in the gauteng exposures of the malmani dolomite we also integrate our results into the greater south african record of palaeodeposit formation most of which occur between 2 0 and 1 0 ma an analysis of the age of palaeocave infillings across the malmani dolomite suggests that as is classically the case with karst the height within the dolomite is broadly correlated to their age although with some notable exceptions that are likely related to localised geological features our analysis also indicates that most caves have undergone some form of secondary karstification related to a younger phase of cave formation contrasting with models that suggest the cavities all formed at the same time and that infill is related to erosion and the opening up of cave passages as such the reason that few pre 2 ma deposits have been identified in the gauteng exposures of the malmani dolomite is probably because these older caves have been eroded away identifying such early caves is critical in understanding whether earlier hominins may have once existed in south africa or if erosion of older deposits or an absence of speleogenesis at this time has made such early periods absent from the geological record

geological setting and age of australopithecus sediba from southern africa we describe the geological geochronological geomorphological and faunal context of the malapa site and the fossils of australopithecus sediba the hominins occur with a macrofauna assemblage that existed in africa between 2 36 and 1 50 million years ago ma the fossils are encased in water laid clastic sediments that were deposited along the lower parts of what is now a deeply eroded cave system immediately above a flowstone layer with a u pb date of 2 026 0 021 ma the flowstone has a reversed paleomagnetic signature and the overlying hominin bearing sediments are of normal polarity indicating deposition during the 1 95 to 1 78 ma olduvai subchron the two hominin specimens were buried together in a single debris flow that lithified soon after deposition in a phreatic environment inaccessible to scavengers

geomagnetic excursions knowns and unknowns geomagnetic excursions are short lived episodes when earth s magnetic field deviates into an intermediate polarity state understanding the origin frequency amplitude duration and field behavior associated with excursions is a forefront research area within solid earth geophysics recent advances in excursion research are summarized here and key further research is suggested to resolve major unanswered questions improving the global distribution of excursion records particularly from the southern hemisphere obtaining high resolution sedimentary excursion records with good age control from sites with sedimentation rates 10 cm kyr obtaining volcanic excursion records coupled with high precision geochronology and estimating excursion duration with high chronological precision will all facilitate hypothesis testing concerning the deep earth dynamics that generate geomagnetic excursions

geomagnetic excursions and paleointensities in the matuyama chron at ocean drilling program sites 983 and 984 iceland basin 1 we report natural remanent magnetization nrm directions and geomagnetic paleointensity proxies for part of the matuyama chron 0 9 2 2 ma interval from two sites located on sediment drifts in the iceland basin at ocean drilling program sites 983 and 984 mean sedimentation rates in the late matuyama chron are 15 9 and 11 5 cm kyr 1 respectively for the older part of the record 1 2 ma oxygen isotope data are too sparse to provide the sole basis for age model construction the resemblance of the volume susceptibility record and a reference 18o record led us to match the two records to derive the age models this match based on site 983 984 susceptibility is consistent with available site 983 984 benthic 18o data paleointensity proxies were derived from the slope of the nrm versus anhysteretic remanent magnetization plot for alternating field demagnetization in the 30 60 mt peak field range paleointensity lows correspond to polarity reversals at the limits of the jaramillo olduvai cobb mountain and reunion subchrons and to seven excursions in nrm component directions magnetic excursions defined here by virtual geomagnetic polar latitudes crossing the virtual geomagnetic equator are observed at 932 1048 1115 1190 1215 cobb mountain subchron 1255 1472 1480 1567 1575 gilsa subchron and 1977 ka the results indicate that geomagnetic directional excursions associated with paleointensity minima are a characteristic of the matuyama chron and probably of polarity chrons in general

beyond 500ka progress and prospects in the upb chronology of speleothems and their application to studies in palaeoclimate human evolution biodiversity and tectonics abstract this review summarises current research aimed at extending the chronology and thus scientific utility of speleothems beyond the 500 ka limit previously imposed by conventional u th dating methods the u pb decay scheme is familiar to all geoscientists but its application to speleothems is a relatively recent development and one set to revolutionise their use in studies of climate change human evolution and migration biodiversity tectonics and landscape evolution technological advances such as the introduction of multi collector icpms instruments have played a key role in this breakthrough and multiple inter laboratory and inter method comparisons provide evidence that the methodology is now mature and that the ages obtained are robust some impediments remain in particular with respect to corrections for initial isotopic disequilibrium younger samples and the construction of internal chronologies older samples but these are areas of intense research activity and are likely to see significant advances in the near future the coupling of speleothem u pb dating with other nascent technologies offering the prospect of precise palaeotemperature estimation is an exciting development in palaeoclimate science while u pb chronologies of archaeological sites are producing important new insights into human evolution although less well developed at this point the methodology appears equally well suited and significant for future studies of past faunal change and landscape evolution

direct terrestrial marine correlation demonstrates surprisingly late onset of the last interglacial in central europe an interdisciplinary study of a small sedimentary basin at neumark nord 2 nn2 germany has yielded a high resolution record of the palaeomagnetic blake event which we are able to place at the early part of the last interglacial pollen sequence documented from the same section we use this data to calculate the duration of this stratigraphically important event at 3400 350 yr more importantly the neumark nord 2 data enables precise terrestrial marine correlation for the eemian stage in central europe this shows a remarkably large time lag of ca 5000 yr between the mis 5e peak in the marine record and the start of the last interglacial in this region

geoarchaeological and 3d visualisation approaches for contextualising in situ fossil bearing palaeokarst in south africa a case study from the 2 61 ma drimolen makondo abstract south africa contains a wealth of palaeokarst deposits that have yielded hominin fossils and early stone age archaeology despite the complex nature of deposition within many of these caves there has been a dearth of detailed geoarchaeological studies undertaken on these sites many sites in south africa have been interpreted using an overly simplistic member system based on simplified sedimentological attributes rather than chronostratigrahic units many of the defined members thus identify different but contemporary geological processes occurring in the caves this has caused serious confusion in reconstructing the life histories of palaeocaves and the ages of the fossil remains interned within them it is critical to uncover new sites that have not been extensively altered by decades of data collection and destructive mining techniques employed early in their discovery although unmined sites present their own problems with regards to extensive colluvium cover and access to fossil bearing units analysing strata that is found in situ enhances overall confidence of interpretations drawn a wealth of geoarchaeological and 3d visualisation techniques can now be employed to aid in the understanding of cave life histories as well as their excavation in this paper we present the first attempt to integrate and publish data from a range of such methods on south african fossil bearing palaeokarst using the newly discovered drimolen makondo deposit as a case study this includes the use of ground penetrating radar 3d visualisation through photogrammetry and multi scale 3d scanning micromophology and petrography palaeomagnetism mineral magnetism synchrotron radiation electron spin resonance uranium lead dating and biochronology our analysis has allowed us to successfully uncover the full extent of this new 2 61 ma fossil bearing palaeokarst deposit and to visualise and interpret its chronostratigraphy

recent advances and future prospects of the u th and u pb chronometers applicable to archaeology abstract the u th chronometer has revolutionized quaternary science in the last few decades and can now be considered a well established mature technique with growing application in archaeology as an alternative to 14 c dating and osl reaching well beyond the cutoff for both these methods applying the u pb technique to material within a time frame of interest to archaeology is a challenge only recently overcome with enormous potential for future development and use in terms of range u th can generally date material of between a few years and as much as 600 ka while u pb is best suited to material of 1 million years and older u th dating is typically precise with error margins of better than 1 routinely achievable for material of the last interglacial age or younger such precision is possible with u pb dating in the mid quaternary but most ages have uncertainties in the 5 10 range carbonates are the most desirable u series target material with closed system behaviour being particularly important for u th dating making inorganic deposits such as speleothems secondary cave carbonates tufa and calcrete ideal some biogenic carbonates such as coral and eggshell are often amenable to u series dating but less ideal material such as fossil teeth bone and mollusc shell usually continue to gain uranium after deposition meaning accurate ages cannot be calculated in all cases the importance of a thorough understanding of the context of dated material cannot be overstated in this contribution we review u th and u pb dating through an archaeological lens focussing on the methods themselves how to best interpret published data and how best to avoid common pitfalls we highlight the major successes through a number of case studies and provide an overview of what we believe to be the future directions of this field

upper level frontogenesis associated with the birth of mobile troughs in northwesterly flow previous studies have shown that 500 hpa mobile trough births or genesis occur preferentially in northwesterly flow during upper level frontogenesis and that cold advection assists in and is a product of mobile trough intensification this study focuses on the synoptic environments and thermal advection patterns of upperlevel fronts associated with mobile trough births in northwesterly flow a climatology of 186 such events derived from an earlier study by sanders shows that most births tend to occur within uniform or diffluent flow and that most tend to be associated with relatively weaker 500 hpa thermal advection most mobile trough births in diffluence however tend to be associated with increasing 500 hpa cold advection typically indicated by a cyclonic rotation of isentropes whereas most mobile trough births in confluence tend to be associated with weaker 500 hpa thermal advection two cases of upper level frontogenesis associated with mobile trough genesis one in diffluence and one in confluence are compared to determine the processes acting to produce the differing thermal advection patterns at 500 hpa a thermal advection tendency equation is developed and shows that the magnitude of the temperature advection can be changed by accelerating the advecting wind speed or by changing the temperature gradient i e vector frontogenesis the latter can be accomplished either by changing the magnitude of the temperature gradient the frontogenetical component fn also known as scalar frontogenesis or by rotating the direction of the temperature gradient relative to the flow the rotational component fs the dominant processes acting on fn for the diffluence and confluence cases are tilting and deformation frontogenesis respectively the dominant process acting on fs for the diffluence case is rotation of the isentropes due to the vorticity term whereas rotation of the isentropes due to the vorticity and tilting terms are both important for the confluence case the rotational component of frontogenesis is cyclonic downstream of the vorticity maximum for both cases favoring increasing cold advection downstream of the vorticity maximum for both cases the rate of rotation of the isentropes at a point due to horizontal advection is large and that due to vertical advection is negligible since advection can only transport the existing isentrope angle and cannot change the isentrope angle the rotational component of frontogenesis normalized by the temperature gradient is the only term that can increase the isentrope angle following the flow this term dominates in the diffluence case but is small in the confluence case this diagnosis suggests the following reasoning in diffluent flow the vorticity associated with the incipient trough is compacted into a more circular shape and intensifies the potent vorticity maximum leads to robust isentrope rotation in confluent flow however the vorticity is deformed into an elongated maximum inhibiting both strong isentrope rotation and increasing cold advection thus the rotational frontogenesis component explains the rotation of the isentropes that is responsible for the differing thermal advection patterns diagnosis of these cases supports the results from the climatology indicating a strong relationship between the synoptic environment and the upper tropospheric thermal advection pattern nevertheless current conceptual models of upper level frontogenesis do not fully explain the variety of these features in the real atmosphere in particular mobile trough genesis and its associated upper level frontogenesis can occur in weak 500 hpa thermaladvection patterns in contrast to the confluence and cold advection that have been previously identified as important to upper level frontal intensification this result provides further support for the possibility that generation and intensification of mobile troughs can occur by barotropic processes

the lower limb and mechanics of walking in australopithecus sediba the discovery of a relatively complete australopithecus sediba adult female skeleton permits a detailed locomotor analysis in which joint systems can be integrated to form a comprehensive picture of gait kinematics in this late australopith here we describe the lower limb anatomy of au sediba and hypothesize that this species walked with a fully extended leg and with an inverted foot during the swing phase of bipedal walking initial contact of the lateral foot with the ground resulted in a large pronatory torque around the joints of the foot that caused extreme medial weight transfer hyperpronation into the toe off phase of the gait cycle late pronation these bipedal mechanics are different from those often reconstructed for other australopiths and suggest that there may have been several forms of bipedalism during the plio pleistocene

phosphor imaging as a tool for in situ mapping of ppm levels of uranium and thorium in rocks and minerals abstract phosphor imaging is a type of digital autoradiography that has been widely used in biochemistry to examine radioactively tagged proteins we used phosphor imaging to map in situ u and th in polished slabs of geological materials including carbonates phosphates and silicate rich rocks we examined samples containing between 2 and 500 ppm u and 700 ppm th to evaluate the applicability of the technique to geological samples resolution of 1 mm or better was obtained even for low concentration 10 ppm samples these analyses are routine and only require a light box phosphor screen and access to a phosphor imager the technique is nondestructive relatively inexpensive and requires very little processing time we used this technique to identify u and th enriched carbonates and phosphates and to find hot spots of u and th rich minerals in a granodiorite these high resolution maps of u and th allow us to effectively sample for geochronology and identify potentially interesting samples for synchrotron x radiation studies the maps produced by phosphor imaging also have great potential for investigating the details of adsorption of radionuclides to rocks and minerals in contaminated areas

on air motion trajectories in cold fronts abstract we examine air parcel trajectories in the two dimensional model for a cold front by reeder and smith these are found to be in close agreement with trajectories deduced from analyses of summertime cool changes in southeastern australia adding further support to the applicability of the numerical model to this kind of cold front the favorable comparison points also to the dynamical consistency of the conceptual model for the cool change which has evolved from the analysis of data from observational experiments

the endocast of mh1 australopithecus sediba the virtual endocast of mh1 australopithecus sediba obtained from high quality synchrotron scanning reveals generally australopith like convolutional patterns on the frontal lobes but also some foreshadowing of features of the human frontal lobes such as posterior repositioning of the olfactory bulbs principal component analysis of orbitofrontal dimensions on australopith endocasts mh1 sts 5 and sts 60 indicates that among these mh1 orbitofrontal shape and organization align most closely with human endocasts these results are consistent with gradual neural reorganization of the orbitofrontal region in the transition from australopithecus to homo but given the small volume of the mh1 endocast they are not consistent with gradual brain enlargement before the transition

termites and necrophagous insects associated with early pleistocene gelasian australopithecus sediba at malapa south africa abstract this study focuses on two early pleistocene australopithecus sediba hominin specimens and associated fauna from malapa south africa these specimens have been interpreted as having fallen through a shaft opening into a cave where they died and likely mummified before being washed into a lower chamber in order to better understand the taphonomy of the fossils and to identify the invertebrate agent s responsible for damage we examined the fossils using high resolution imagery and studied the site and associated breccia blocks in the laboratory for traces of invertebrate activity we also conducted bone modification experiments with termites and hide beetles results show the presence of blowfly puparia within the cranium of the juvenile male mh1 indicating that flies visited the facial orifices of the freshly decomposing corpse blowflies which have a requirement to oviposit in daylight imply that the body was exposed to sunlight for part of the day a shaft opening that admitted sunlight is supported by the presence of a fossil fungus garden associated with mh2 fungus gardens occur subsurface and sprout mushrooms in areas with dappled light analysis of the fossil surfaces revealed a pattern comprising 14 damage types that were made on relatively fresh bone a bone modification experiment conducted with resident termites at the site showed that they created the same suite of microscopic surface features as those observed on the fossils the features are mostly the result of harvesting symbiotic fungi from fresh bones and mineral rich coatings from fossils damage resulting from the activity of hide beetles is similar to that of termites apart from invasive edge gnawing produced by the beetles this research highlights the importance of insect activity in the modification of fossils in the cradle of humankind world heritage site area and calls for consideration of this agent at other fossil sites in the region

contemporary flowstone development links early hominin bearing cave deposits in south africa abstract the cradle of humankind cave sites in south africa preserve fossil evidence of four early hominin taxa australopithecus africanus australopithecus sediba paranthropus robustus and early homo in order to integrate this record into a pan african scenario of human evolutionary history it is critical to have reliable dates and temporal ranges for the southern african hominins in the past a lack of precise and accurate chronological data has prevented the evaluation of the temporal relationships between the various sites here we report new uranium lead u pb radiometric ages obtained from sheets of calcium carbonate flowstone inter bedded between clastic cave sediments at the site of swartkrans providing bracketing ages for the fossiliferous deposits the fossil bearing units of swartkrans specifically the hanging remnant and lower bank of member 1 are underlain by flowstone layers dated to 2 25 0 05 ma and 2 25 0 08 ma and capped by layers of 1 8 0 01 ma and 1 7 0 07 ma the age bracket of the member 1 deposits is therefore between 2 31 and 1 64 ma however by combining the u pb with biostratigraphic data we suggest that this can be narrowed down to between 1 9 and 1 8 ma these data can be compared with other recently dated sites and a radiometrically dated u pb age sequence formed sterkfontein member 4 swartkrans member 1 malapa and cooper s d from this new u pb dataset a pattern of contemporary flowstone development emerges with different caves recording the same flowstone forming event specifically overlapping flowstone formation takes place at swartkrans and sterkfontein at 2 29 ma and 1 77 ma and at sterkfontein and malapa at 2 02 ma this suggests a regional control over the nature and timing of speleothem development in cave deposits and these flowstone layers could assist in future correlation both internal to specific deposits and regionally between sites

piecewise tendency diagnosis of dynamical processes governing the development of an upper tropospheric mobile trough abstract the intensification and evolution of midlatitude upper tropospheric mobile troughs may be viewed in terms of the isentropic advection and deformation of the tropopause potential vorticity gradient the potential vorticity viewpoint allows one to qualitatively assess observed events in the context of existing theories of mobile trough genesis such as baroclinic instability or downstream development in order to quantitatively determine the role of distinct dynamical process the method of piecewise tendency diagnosis or ptd is developed ptd is an extension of piecewise potential vorticity inversion applied to height tendencies with the forcing terms in the quasigeostrophic height tendency equation partitioned into potential vorticity advection associated with distinct dynamical processes a particular case of mobile trough genesis which occurred during 1 4 december 1980 over north america is diagnosed using ptd although about 20 of the intensification of the trough was due to superposition

u pb dated flowstones restrict south african early hominin record to dry climate phases the cradle of humankind cradle in south africa preserves a rich collection of fossil hominins representing australopithecus paranthropus and homo1 the ages of these fossils are contentious2 4 and have compromised the degree to which the south african hominin record can be used to test hypotheses of human evolution however uranium lead u pb analyses of horizontally bedded layers of calcium carbonate flowstone provide a potential opportunity to obtain a robust chronology5 flowstones are ubiquitous cave features and provide a palaeoclimatic context because they grow only during phases of increased effective precipitation6 7 ideally in closed caves here we show that flowstones from eight cradle caves date to six narrow time intervals between 3 2 and 1 3 million years ago we use a kernel density estimate to combine 29 u pb ages into a single record of flowstone growth intervals we interpret these as major wet phases when an increased water supply more extensive vegetation cover and at least partially closed caves allowed for undisturbed semi continuous growth of the flowstones the intervening times represent substantially drier phases during which fossils of hominins and other fossils accumulated in open caves fossil preservation restricted to drier intervals thus biases the view of hominin evolutionary history and behaviour and places the hominins in a community of comparatively dry adapted fauna although the periods of cave closure leave temporal gaps in the south african fossil record the flowstones themselves provide valuable insights into both local and pan african climate variability climate driven periodicity of flowstone accretion between 3 2 and 1 3 million years ago in cradle of humankind caves reveals that the presence of hominin fossils reflects accumulation in open caves during intermittent substantially drier phases

australopithecus sediba at 1 977 ma and implications for the origins of the genus homo newly exposed cave sediments at the malapa site include a flowstone layer capping the sedimentary unit containing the australopithecus sediba fossils uranium lead dating of the flowstone combined with paleomagnetic and stratigraphic analysis of the flowstone and underlying sediments provides a tightly constrained date of 1 977 0 002 million years ago ma for these fossils this refined dating suggests that au sediba from malapa predates the earliest uncontested evidence for homo in africa

a window into africa s past hydroclimates the sisal_v1 database contribution africa spans the hemispheres from temperate region to temperate region and has a long history of hominin evolution although the number of quaternary palaeoclimatic records from the continent is increasing much of the history of spatial and temporal climatic variability is still debated speleothems as archives of terrestrial hydroclimate variability can help reveal this history here we review the progress made to date with a focus on the first version of the speleothem isotopes synthesis and analysis sisal database the geology of africa has limited development of large karst regions to four areas along the northern coast bordering the mediterranean eastern africa and the horn of africa southwestern africa and southern africa exploitation of the speleothem palaeoclimate archives in these regions is uneven with long histories of research e g in south africa but large areas with no investigations such as west africa consequently the evidence of past climate change reviewed here is irregularly sampled in both time and space nevertheless we show evidence of migration of the monsoon belt with enhanced rainfall during interglacials observed in northeast africa southern arabia and the northern part of southern africa evidence from eastern africa indicates significant decadal and centennial scale rainfall variability in northwestern and southern africa precession and eccentricity influence speleothem growth largely through changing synoptic storm activity

using u pb ages of miocene tufa for correlation in a terrestrial succession barstow formation california sedimentary rocks and associated fossils are the direct record of past life and its environmental context few methods allow direct and precise dating of this important archive making it diffi cult to correlate climate biologic and tectonic events preserved in terrestrial records we sampled lacustrine tufa calcite from the middle member of the miocene barstow formation to further test the feasibility of uranium lead dating of terrestrial carbonates five samples yield u pb ages 2 of 14 81 0 39 ma 15 30 0 25 ma 15 39 0 15 ma 16 14 0 40 ma and 16 24 0 23 ma these precise ages are consistent with existing ages from k ar and 40 ar 39 ar dating of intercalated volcanic ashes our most precise u pb age on tufa has an uncertainty of 1 150 ka which is equivalent to uncertainties for k ar ages from the same time period our results indicate that u pb dating of carefully sampled and screened sedimentary carbonates provides much needed age constraints in purely terrestrial sequences and can be a powerful tool for correlation even in deposits with structural complexity and rapid facies changes

taphonomic interpretations of the haasgat hgd assemblage a case study in the impact of sampling and preparation methods on reconstructing south african karstic assemblage formation abstract the haasgat fossil bearing karstic system is situated within the skurweberg mountain range in the northeastern portion of the fossil hominids of south africa unesco world heritage site in south africa as is the case for the nearby gondolin hominin locality haasgat occurs in an area of substantial modern topographic relief that contrasts with the low relief landscape of the southwestern extent of the world heritage site surrounding the blauubank stream valley sites e g sterkfontein swartkrans kromdraai bolt s farm this suggests differential landscape formation processes during the neogene and potentially novel palaeoecosystems and taphonomic processes governing karstic fossil assemblage composition across even a small geographic region this is particularly critical given the overall paucity of taphonomic data from the region the substantial cercopithecoid primate assemblage that is uniquely dominated by the basal baboon species papio angusticeps and the recent announcement of the first hominin specimen from haasgat here we provide the first comprehensive taphonomic analysis of the haasgat hgd faunal assemblage that was developed from ex situ calcified sediment blocks in the 1990s there is direct evidence for biotic activity e g large bodied carnivores and porcupines mediating the formation of parts of the hgd faunal assemblage including at least part of the primate craniodental and postcranial sample there is minimal evidence for pre depositional element uv exposure and weathering or winnowing of the assemblage but there is abiotic distortion and crushing of elements our analysis has equally found that taphonomic data from the hgd assemblage is compromised by a modern overprint of damage through mechanical preparation and a lack of documentation generated during sampling processing and initial curation nearly half the cortical surfaces and many dental specimens in the assemblage exhibit evidence of substantial preparation damage rendering many purported biotic modifications ambiguous or suspect element proportions may be artificially skewed towards craniodental specimens and more reflective of block selection and or selective processing rather than original deposition composition as a result the haasgat hgd sample provides only limited data on the depositional processes mediating karstic assemblage formation in the region and ultimately serves as a cautionary tale of the impacts of palaeontological sampling strategies on subsequent analysis and research

forebergs flower structures and the development of large intra continental strike slip faults the gurvan bogd fault system in mongolia the gurvan bogd mountains of the gobi altay mongolia contain a system of strike slip faults with a reverse component part of which moved in a large earthquake mw 8 0 in 1957 adjacent and sub parallel to the main ranges are numerous thrust related folds thrust faults and elongated low ridges forebergs all of which result from the shortening component on the fault zone the appearance of these thrust related structures is varied depending on their stage of development preservation and exposure evidence from geomorphology and surface ruptures suggests that they may all serve a common function which is to broaden the deforming zone by creating new structures that are able to accommodate both the strike slip and the shortening components of motion the geomorphology further suggests that these new structures then evolve by lateral propagation and increase in amplitude to eventually merge and form through going new faults subparallel to the old in their early stages the new faults and related structures appear to be influenced by the underlying sediments adjacent to the main range which may include weak layers such as lake beds that can ultimately cause the collapse of foreberg ridges in landslides the migration of faulting away from the main range is likely to be driven by stresses associated with topography which in turn is a consequence of the shortening component the evolution described here is thus peculiar to strike slip faults with a reverse component and can form many of the features of the flower structures that are often described in such oblique shortening zones although the shortening component is often localized in restraining bends its origin may ultimately be related to rotations about vertical axes which are common in deforming continental regions

revised ages for tuffs of the yellowstone plateau volcanic field assignment of the huckleberry ridge tuff to a new geomagnetic polarity event 40 ar 39 ar ages were determined on the three major ash flow tuffs of the yellowstone plateau volcanic field in the region of yellowstone national park in order to improve the precision of previously determined ages total fusion and incremental heating ages of sanidine yielded the following mean ages huckleberry ridge tuff 2 059 0 004 ma mesa falls tuff 1 285 0 004 ma and lava creek tuff 0 639 0 002 ma the huckleberry ridge tuff has a transitional magnetic direction and has previously been related to the reunion normal polarity subchron dating of the reunion event has been reviewed and its ages have been normalized to a common value for mineral standards the age of the huckleberry ridge tuff is significantly younger than lava flows of the reunion event on re union island supporting other evidence for a normal polarity event younger than the reunion event