contribution of grain size and compositional data from the bengal fan sediment to the understanding of toba volcanic event abstract toba tephra layers in cores from the bengal fan have been studied to characterize their granulometric mineralogic and geochemical features the layers are silt sized sediments with no significant non volcanic contamination the samples are very homogeneous glass shards have moderate hydration about 6 water a calc alkaline character and a rhyolitic composition the major and trace element compositions indicate an orogenic affinity and coincide with literature data for the youngest toba tephra level ytt 75 ka x ray diffraction xrd data indicate that the glass is the dominant phase with minor feldspar biotite and quartz the grain size analyses of the beds show discontinuous vertical variation and no linear trends from south to north over about 1500 km the vertical granulometric gap of the layers probably represents a single pyroclastic emplacement unit subjected to pre depositional particle aggregation

eruptive history of earth s largest quaternary caldera toba indonesia clarified single grain laser fusion sup 40 ar sup 39 ar analyses of individual sanidine phenocrysts from the two youngest toba indonesia tuffs yield mean ages of 73 plus minus 4 and 501 plus minus 5 ka in addition glass shards from toba ash deposited in malaysia were dated at 68 plus minus 7 ka by the isothermal plateau fission track technique these new determinations in conjunction with previous ages for the two oldest tuffs at toba establish the chronology of four eruptive events from the toba caldera complex over the past 1 2 m y ash flow tuffs were erupted from the complex every 0 34 to 0 43 m y culminating with the enormous 2500 3000 km sup 3 youngest toba tuff eruption caldera formation and subsequent resurgence of samosir island timing of this last eruption at toba is coincident with the early wisconsin glacial advance the high precision sup 40 ar sup 39 ar age eruption of such magnitude may provide an important marker horizon useful as a baseline for research and modeling of the worldwide climatic impact of exceptionally large explosive eruptions

response of late carboniferous and early permian plant communities to climate change abstract late carboniferous and early permian strata record the transition from a cold interval in earth history characterized by the repeated periods of glaciation and deglaciation of the south

the geology and palynology of lower and middle pennsylvanian strata in the western kentucky coal field abstract the western kentucky coal field is the southern tip of the eastern interior or illinois basin pennsylvanian rocks in this area which include conglomerate sandstone siltstone shale limestone and coal were deposited primarily in coastal deltaic settings at a time when western kentucky was located close to the equator this paper discusses temporal changes in regional sedimentation patterns and coal forming floras of lower and middle pennsylvanian strata in the western kentucky coal field lower pennsylvanian strata of the caseyville formation are characterized by paleovalley filling sedimentation patterns and extabasinal quartz pebbles caseyville formation coals are characteristically thin and discontinuous and were strongly influenced by subsidence within underlying paleovalleys and the dissected lower pennsylvanian paleotopography caseyville coals are commonly dominated by lycospora but can also have variable palynofloras which probably reflects variable edaphic conditions and edge effects within small patchy paleomires tradewater formation strata show increased marine influences and tidal estuarine sedimentation especially in the middle and upper parts coal beds in the lower part of the tradewater typically are thin and discontinuous although some economically important beds are present coals become thicker more abundant and more laterally persistent towards the top of the formation palynologically lower and middle tradewater formation coals are dominated by lycospora but begin to show increased amounts of tree fern spores middle and upper tradewater coals are thicker and more continuous and contain high percentages of tree fern spores in addition cordaite pollen is locally abundant in this interval carbondale and shelburn desmoinesian strata are much more laterally continuous and occur within classic cyclothems that can be traced across the coal field cyclothems have long been interpreted as being eustatically driven and glacio eustacy controlled not only sedimentation but also the formation of desmoinesian paleomires palynologically carbondale and shelburn coals are either dominated by lycospora or have heterogeneous palynofloras palynologic and coal quality data suggest that hydrologic base level may have been the primary control on desmoinesian paleomires rather than paleoclimate as the coals display rheotrophic rather than ombrotrophic characteristics

style of atlassic tectonic deformation and geodynamic evolution of the southern tethyan margin tunisia the structure of the southern atlas fold and thrust belt of tunisia was investigated using new geologic mapping seismic reflection data together with the construction of a balanced cross section the structural architecture of the tunisian foreland consists in a mixed tectonic style with deep seated basement faults shallower decollements within sedimentary cover and salt diapirism the restoration of the cross section shows a surface shortening of 8 1 km similar to 7 3 sequential restoration of the balanced cross section has been permitted to decipher the structure and evolution of the southern tethyan margin of tunisia structural geometry and orientation of the pre existing permian to cretaceous extensional structures controlled subsequent contractional deformation within the sedimentary cover during the shortening this inherited tectonic framework controlled the development of ene trending thrust related anticlines such as the orbata and chemsi structures nw trending lateral ramp such as the gafsa and fejej faults and diapir structures as the beidha anticline the inversion of the margin can be correlated with the onset of the convergence between africa and eurasia the first phase of the orbata thrusting growth might occur in late cretaceous continuous inversion of the margin occurred during the eocene and mainly during the late miocene to present day this study underlines the predominant role of inherited basement structures acquired during the evolution of the southern tethyan margin and their influence on the geometry of the atlassic thrust belt this structural analysis provides new perspectives for future hydrocarbon exploration in this poorly explored region c 2015 elsevier ltd all rights reserved

vegetational history of the springfield coal middle pennsylvanian of illinois and distribution patterns of a tree fern miospore thymospora pseudothiessenii based on miospore profiles abstract the vegetational history of the springfield no 5 coal member in the southwestern and southeasternmost portion of the illinois basin is reconstructed from palynological profiles of the coal seam in most parts of the swamp dominance was shared by arborescent lycopods that produced lycospora granulata and two tree ferns that produced thymospora pseudothiessenii and laevigatosporites globosus the profiles suggest that populations of the thymospora producing tree fern occupied sites for long periods in the southwestern portion of the basin vegetation changes can be correlated to the splitting of a coal in the proximity to a paleochannel a greater understanding of the ecological requirements of some of the spore taxa of the springfield coal is seen by the patterns of the same taxa in surrounding spoon and carbondale coals some taxa appear to be more generalists and other more specialists that are more restricted to a certain type of coal

recent spatial and temporal changes in the stress regime along the southern tunisian atlas front and the gulf of gabes new insights from fault kinematics analysis and seismic profiles tectonic deformations in the southern atlassic front of tunisia saft and the gulf of gabes result from the nubia eurasia convergence this study based on the inversion of geologically determined fault slip vectors presents evidences for spatial and temporal changes in the stress state fault kinematics analyses reveal a temporal change in states of stress during the late cenozoic a paleostress miocene pliocene state is characterized by a regional compressional tectonic regime with a mean n134 09 e trending horizontal maximum stress axis 1 a modern quaternary to present day state of stress also corresponds to compressional tectonic regime with a regionally mean n05 10 e trending horizontal 1 the saft corresponds to two distinct domains a far foreland atlassic front related to contractional deformation associated with southward propagate thrusting and eastward the gulf of gabes characterized by normal component nw to wnw trending faults at the crustal margin scale probably related with a transtensional tectonic regime we propose that the spatial and temporal changes in the stress during the miocene pliocene and quaternary may result from the geodynamic evolution of the tunisian atlas in relation to the rotation of corsica sardinia blocks and the separation of the sicilian continental lithosphere from the ionian oceanic lithosphere these temporal and spatial stress changes along the saft and the gulf of gabes are probably the engine behind the moderate seismicity leading at the same time to a reactivation of the inherited major structures created during the evolution of the southern tethyan margin

fallout of volcanic ash to the deep south china sea induced by the 1991 eruption of mount pinatubo philippines an ongoing sediment trap experiment in the central south china sea provided the opportunity to investigate directly the mode and rates of a medial fallout of volcanic ash following the june 15 1991 eruption of mount pinatubo philippines within less than three days after the release of the major eruption plume ash accumulation 9 kg m 2 was simultaneously recorded by traps positioned in 1190 and 3730 m water depth at a distance of 586 km to the west of the volcano a numerical simulation of the fallout reveals that the vertical trajectories of the pyroclasts in both the atmosphere and ocean were controlled by particle aggregation the aggregation process caused a premature subaerial fallout of fine grained ash after crossing the air sea interface vertical settling of the ash clusters was enhanced by absorption of water leading to settling rates of more than 1670 m d aggregates were observed at all depths and their rapid settling is reflected in identical pyroclast spectra in intermediate and deep water this implies that particle sorting must have been complete in the upper water column and that the fallout was not perturbed by oceanic currents the tephra blankets an area of 37 10 4 km 2 in a fan shaped westward distribution which reflects the prevailing direction of the upper level winds our data show that atmospheric tephra dispersal patterns are recorded almost instantaneously on the deep sea floor and corroborate the key role of deep sea ash layers as highly reliable chronostratigraphic markers and as a geological tool to infer ancient wind fields

geochemical petrographic and palynologic characteristics of two late middle pennsylvanian asturian coal to shale sequences in the eastern interior basin usa abstract two coal to shale sequences of late middle pennsylvanian asturian age from the southern portion of the eastern interior illinois basin usa were examined geochemically petrographically and palynologically the springfield coal was found to be moderately low in ash yield and high in total sulfur content petrographically the coal is high in vitrinite content and low in liptinite and inertinite palynologically the bed is co dominated by spores of arborescent lycopod and tree fern affinities the examination of closely spaced bench samples revealed vertical species variation within both of these plant groups lycospora micropapillata l orbicula both of which were produced by paralycopodites are most abundant in basal coal benches whereas lycospora granulata produced by lepidophloios is the dominant arborescent lycopod spore throughout the rest of the bed thymospora pseudothiessenii is the dominant tree fern spore throughout most of the coal with laevigatosporites globosus becoming dominant in the top most coal benches the herrin coal bed is also moderately low in ash yield and high in total sulfur content unlike the springfield coal it contains two distinct inorganic partings that have regional extent the herrin coal also has several coal benches with increased ash and sulfur that were not present in the springfield coal bed petrographically it is dominated by vitrinite with the partings and high ash coal benches containing more inertinite and liptinite palynologically the herrin coal is dominated by arborescent lycopod spores with subdominant tree fern spores as with the springfield coal lycospora micropapillata l orbicula are the dominant arborescent lycopod spores at the base of the coal with lycospora granulata dominating the rest of the bed granasporites medius which was produced by diaphorodendron and synchysidendron occurs more frequently in the herrin coal bed and are most abundant in and in proximity to the two inorganic partings tree fern spores are less abundant in the herrin coal and do not display any discernable vertical species variation collectively both the springfield and herrin coal beds are interpreted to have formed in extensive planar topogenous mires consistently saturated peat conditions throughout the development of both paleomires are indicated by the high vitrinite contents and prevalence of arborescent lycopods the deposition of widespread inorganic partings in the herrin coal represents significant events in peat accumulation with high ash coal benches representing smaller more local events both of the coals are overlain by black very organic rich avg toc 20 marine shales the turner mine shale which directly overlies the springfield coal has layers at the coal shale contact with fairly abundant vitrinite primarily in the form of vitrodetrinite near the base of the shale but the majority of the shale is dominated by the liptinite macerals bituminite lamalginite and amorphinite micrinite is a major organic component of the shale the anna shale which directly overlies the herrin coal is similar in overall maceral composition but contains less vitrinite and more solid bitumen and micrinite trace element ratios ni co v cr v v ni indicative of paleoredox conditions indicate that both shales were deposited under mainly dysoxic to suboxic anoxic conditions the shales are interpreted to represent a progressively rising water table caused by an increase in eustatic sea levels vitrinite reflectance values in the shales are lower than corresponding values measured from the coal indicating some degree of vitrinite suppression occurring in the turner mine and anna shales

seismotectonics of the el asnam earthquake the mechanism of the el asnam earthquake of 10 october 1980 ms 7 2 the strongest recorded in northwestern africa is compatible with a convergence between the african and european plates the thrust is also consistent with field observations and with long period data from the global network aftershocks cluster around the fault trace with a maximum depth of 12 km maximum vertical displacement is 6 m and there is some left lateral motion the fault trace of the 1954 earthquake at beni rached was also reactivated

glass chemistry in volcaniclastic sediments of odp leg 107 site 650 sedimentary sequence provenance and chronological implications abstract a detailed chemical investigation of volcanic glass fragments from volcaniclastic strata 6 tephras 1 volcanic debris flow 12 volcanic turbidites of odp leg 107 site 650 sedimentary sequence leads to a varied pattern in terms of both provenance and age constraints the six analyzed tephra strata indicate a provenance from at least three different volcanic provinces aeolian campanian and sicilian channel pantelleria island the older tephra strata 021 018 012 have a large amount of orogenic rhyodacite rhyolite deposits that may be attributed to the aeolian province although no subaerial coeval volcanic activity of similar composition has so far been documented in the aeolian arc tephra 007 is related to the pantelleria island activity and particularly to an ignimbrite episode dated circa 130 ka tephra strata 005 and 003 have a clear campanian provenance and are correlated with analogous tephra layers observed in the tyrrhenian and ionian seas dated circa 107 and 60 ka respectively in the oldest portion of the sequence from 1 3 to 0 13 ma the volcaniclastic sediments were only derived from the aeolian domain whereas in the latest 130 ka the campanian influx becomes much more predominant therefore a general k enrichment trend is observed in the temporal sequence of all the analyzed samples almost 700 point analyses which may be related both to a variation in the source area and to the specific pleistocene magmatic evolution of the peri tyrrhenian volcanic provinces

all toba tephra occurrences across peninsular india belong to the 75 000 yr b p eruption abstract a controversy currently exists regarding the number of toba eruptive events represented in the tephra occurrences across peninsular india some claim the presence of a single bed the 75 000 yr old toba tephra others argue that dating and archaeological evidence suggest the presence of earlier toba tephra resolution of this issue was sought through detailed geochemical analyses of a comprehensive suite of samples allowing comparison of the indian samples to those from the toba caldera in northern sumatra malaysia and importantly the sedimentary core at odp site 758 in the indian ocean a core that contains several of the earlier toba tephra beds in addition two samples of toba tephra from western india were dated by the fission track method the results unequivocally demonstrate that all the presently known toba tephra occurrences in peninsular india belong to the 75 000 yr b p toba eruption hence this tephra bed can be used as an effective tool in the correlation and dating of late quaternary sedimentary sequences across india and it can no longer be used in support of a middle pleistocene age for associated acheulian artifacts

active tectonics and gps data analysis of the maghrebian thrust belt and africa eurasia plate convergence in tunisia abstract the atlas mountains of tunisia belong to the seismically active zone of the africa nubia eurasia plate boundary in the central western mediterranean we study the eastern section of the maghrebian thrust belt using a subset 6 days from each of 5 years 2014 to 2018 of permanent survey mode gps data and active tectonics wnw to nnw trending velocities express crustal motion and geodetic strain fields from the sahara platform to the tell atlas consistent with african plate convergence to the south the velocities and trajectories indicate nearly wnw ese trending right lateral motion of the sahara fault related atlas fold belt with respect to the sahara platform farther north and northeast the significant decrease in velocities between the eastern platform sahel central atlas and tell atlas and the clockwise rotation mark the nnw trending shortening deformation associated with local ene wsw extension visible in the quaternary grabens the velocity field and strain distribution associated with the active e w to wnw ese trending right lateral faulting and ne sw fault related folds illustrate the transpression tectonics and support the identification of four tectonic domains north of the africa nubia platform in tunisia the transpression reduces northward when reaching the central and tell atlas these results change our perception of the africa eurasia plate boundary previously located along the western mediterranean coastline

dunkard group coal beds palynology coal petrography and geochemistry abstract coal beds that occur in the dunkard group are typically thin avg 0 3 m and are high in ash yield avg 27 8 and total sulfur content avg 5 1 petrographically dunkard coals are high in vitrinite avg 83 1 mmf with correspondingly low to moderate amounts of liptinite avg 2 1 mmf and inertinite avg 13 8 mmf palynologically dunkard coal beds are all dominated by tree fern spore taxa avg 96 3 especially punctatisporites minutus avg 82 8 calamite spores are the second most abundant plant group avg 2 4 with others lycopods small ferns cordaites and other gymnosperms having very minor representation overall the coal palynofloras are strongly dominated by lowland plants ferns and calamites with only rare occurrences of bisaccate striate conifer pollen coal beds of the underlying monongahela group pittsburgh redstone sewickley and waynesburg are thicker avg 1 6 m and are lower in ash avg 13 4 and sulfur avg 3 3 than their dunkard counterparts petrographically monongahela group coals are very similar to dunkard group coals when compared on a mineral matter free basis coal beds that occur in both groups are strongly dominated by vitrinite macerals monongahela group coals are also palynologically very similar to dunkard group coals with tree fern spore taxa dominating a coal bed of early permian age from west central texas is also similar petrographically and palynologically to dunkard and monongahela coals being vitrinite and tree fern spore dominant the almost complete lack of coniferous pollen in dunkard coals led earlier workers to conclude that the dunkard was entirely late pennsylvanian and not permian in age however it is now known that late pennsylvania lowland floras persisted into the dunkard especially during wet intervals as earlier interpretations were based primarily on spore and pollen floras from coal beds the lack of conifer pollen in dunkard coals is probably the result of a sampling bias because of this ecological bias coal palynology is a poor proxy for age dating dunkard group coals collectively dunkard swamps were all planar and topogenous their formation being controlled by topography and moisture availability a progressive decrease in wet intervals both in terms of frequency and duration during the dunkard was the major control on peat accumulation and preservation collectively moisture limitation appears to be the principle factor that controlled the formation of dunkard group coals

active oblique ramp faulting in the southern tunisian atlas abstract the gafsa fault is the longest and most active structure of the fold and thrust belt achieving southeastward propagation of the atlas belt of eastern north africa onto the saharan platform the gafsa fault is a 75 km long dextral oblique basement fault ramp that poses a sizable challenge in earthquake hazard assessment because the post paleozoic sedimentary cover is decoupled from its basement above the basement fault in this study we combine seismic lines interpretation tectonic geomorphology and paleoseismological investigations to assess the level of seismic hazard of this fault and evaluate its role in the geodynamic framework of the central mediterranean we show that despite a moderate instrumental and historical seismicity the fault has produced m 6 earthquakes with a return period of ca 500 5000 years during the late quaternary the latest large event having produced a surface rupture on the fault occurred around 8000 yr bp suggesting an m 6 earthquake is overdue on the fault the fault has a minimum reverse component of slip rate of 0 21 0 34 mm yr over the past 50 ka the occurrence of m 7 paleoearthquakes on the fault may be suspected but not established such very strong earthquakes would require transient coseismic linkage of the buried basement fault with the overlying listric fault ramping off the decollement layer the level of seismic hazard may be underestimated on the gafsa fault indeed given the geometry of the basement cover fault system a number of earthquakes generated in the basement would have led to coseismic surface folding instead of to surface rupture the gafsa fault is a major structure accommodating eastward extrusion spreading of the atlas belt onto the saharan and pelagian plateforms above the retreating ionian lithospheric slab

palynology petrography and geochemistry of the sewickley coal bed monongahela group late pennsylvanian northern appalachian basin usa abstract forty two bench samples of the sewickley coal bed were collected from seven localities in the northern appalachian basin and analyzed palynologically petrographically and geochemically the sewickley coal bed occurs in the middle of the pittsburgh formation monongahela group and is of late pennsylvanian age palynologically it is dominated by spores of tree ferns tree fern spore taxa in the sewickley include punctatisporites minutus punctatosporites minutus laevigatosporites minimus spinosporites exiguus apiculatasporites saetiger and thymospora spp in fact punctatisporites minutus was so abundant that it had to be removed from the standard counts and recorded separately average 73 2 even when punctatisporites minutus is removed from the counts tree fern spores still dominate a majority of the assemblages averaging 64 4 among the tree fern spores identified in the sewickley coal thymospora exhibits temporal and spatial abundance variation thymospora usually increases in abundance from the base to the top of the bed thymospora is also more abundant in columns that are thick 100 cm and low in ash yield calamospora spp laevigatosporites minor and l vulgaris are the next most abundant plant group represented in the sewickley coal averaging 20 contributions from all other plant groups are minor in comparison petrographically the sewickley coal contains high percentages of vitrinite average 82 3 mineral matter free mmf with structured forms being more common than unstructured forms in contrast liptinite and inertinite macerals both occur in low percentages average 7 7 and 10 0 respectively geochemically the sewickley coal has a moderate ash yield average 12 4 and high total sulfur content average 3 4 four localities contained a high ash or carbonaceous shale bench these benches which may be coeval are strongly dominated by tree fern spores unlike the lower ash benches they contain low percentages of vitrinite which mainly occurs as unstructured vitrinite and higher liptinite and inertinite contents the accumulated data suggest that the sewickley paleomire was probably a rheotrophic planar mire that had a consistent water cover this is supported by the high vitrinite contents moderate ash yields and high total sulfur contents the high ash and carbonaceous shale benches probably represent either periods of dryness and substrate exposure or flooding of the mire surface the duration of which is unknown

geophysical constraints on the location and nature of the north saharan flexure in southern tunisia gravity data integrated with seismic refraction reflection data well data and geological investigations were used to determine the location of the paleogeographic boundary between the precambrian saharan domain and the younger tunisian atlas domain this boundary north saharan flexure or nsf has not been as clearly defined as it has been to the west in algeria and morocco the gravity data analysis which included the construction of complete bouguer and residual gravity anomaly maps revealed that the atlasic domain is characterized by relative negative gravity anomalies and numerous linear gravity trends implying a thick and deformed sediment cover the saharan domain is characterized by relatively positive gravity anomalies with few gravity trends implying a thin and relatively undeformed sediment cover an edge enhancement analysis of the residual gravity anomalies revealed that the nsf is characterized by a series of discontinuous east and northwest trending linear anomalies south of 34 n that are not related to the well known faults within the gafsa and accident de medenine regions based on the continuity of the amplitudes of seismic reflection data and the trends of the residual gravity anomalies the nsf is not an abrupt discontinuity but a series of step faults dipping toward the atlasic domain to obtain a more quantitative representation of the southern edge of tunisian atlas a regional gravity model constrained by two wells and seismic reflection refraction data was constructed along a north south trending profile which confirms the presence of thicker sediments north of the nsf our analysis shows that the nsf has controlled the depositional environment of the sedimentary rocks within the region since at least triassic time and has acted as a barrier to atlasic deformation south of the nsf the nsf is considered an important tectonic feature that has controlled the paleogeographic evolution of the southern margin of the tethys ocean and it continues to be active today based on seismicity hazard studies

persistence of late carboniferous tropical vegetation during glacially driven climatic and sea level fluctuations abstract the late carboniferous glaciation reached its peak during the latter part of the westphalian late desmoinesian in the tropical illinois basin this was the time of deposition of the carbondale and lower modesto formations characterized by the cyclic repetition of major coal deposits black shales limestones gray shales and sandstones these lithological changes evidence repeated major fluctuations in climate and sealevel fossil floras from the tropical ever wet to seasonally wet terrestrial lithofacies coals and shales above coals remain compositionally similar throughout the 1 1 5 m y time interval floras from coals known from coal balls and palynology characteristically were composed of three major plant communities the wettest sites were dominated by monocarpic lycopsids intermediate sites were dominated by polycarpic lycopsids and areas subject to fires and intermittent flooding were dominated by medullosans and the small lycopsid paralycopodites clastic substrate environments were dominated by ferns and pteridosperms and conform to a single biozone indicating their compositional unity and distinctness from earlier and later assemblages the composition of lowland floras is poorly known from times between the deposition of coals and associated terrestrial rocks intervals during which most of the lowlands were flooded and marine rocks were being deposited consequently the temporally intermittent recurrence of lowland floras despite repeated widespread environmental disruption may be explained either by vegetational persistence and migration of floras or repeated disruption and reassembly several lines of evidence suggest persistence as a likely explanation

new geochemical evidence for the youngest toba tuff in india abstract new geochemical data on tephra samples from a layer present at several archeological sites in india support correlation of this layer to the youngest toba tuff erupted from northern sumatra about 74 000 yr ago the data show that the indian tephra layer is not a correlative of older tephra erupted from toba as has been suggested on the basis of artifact assemblages previously published geochemical data on the indian tephra beds was based on bulk ash samples containing mineral and clay contaminants and the resulting variability in analyses did not allow identification or discrimination of individual eruptive events our new data were collected on individual glass shards and small purified glass separates which have greater resolving power in fingerprinting acheulian and paleolithic artifacts found at some of the indian tephra sites do not reflect the antiquity of the tephra bed as they occur in fluvial sediments and may be reworked

paleobotanical and paleoecological constraints on models of peat formation in the late carboniferous of euramerica abstract the dominant plants of the late carboniferous lowland tropics were taxonomically and structurally distinct from those of any later time periods dominance was distributed among lycopsids ferns sphenopsids pteridosperms and cordaites and each of these groups had distinctive and different ecological preferences and amplitudes peat forming habitats were dominated by lycopsids throughout the westphalian with a significant cordaitean element in the middle westphalian during the stephanian tree ferns were dominant following major extinctions near the westphalian stephanian transition each of the major plant groups had distinctive architectures and tissue composition trees contributed up to 95 of the peat biomass and tree forms of lycopsids psaronius and medullosa lack good modern analogues the cordaites were the only woody plant group to contribute significantly to peat and then only during the mid westphalian structurally wood like lycopsid bark is the major woody tissue encountered in most westphalian coals tree ferns and pteridosperms were largely parenchymatous in construction the stigmarian root systems of lycopsids also were largely parenchymatous the tissue structure of these dominant plant suggests the need for extreme caution in the inference of mire ecological conditions or vegetational structure from coal petrographic data peat formed under arborescent ferns or pteridosperms or peat repeatedly exposed to decay and rerooting by stigmarian root systems of lycopsids would have a distinctly non woody signature and yet would have formed in a forested environment a summary is presented of the autecology and synecology of mire plants emphazing the structural framework provided by lycopsids during the westphalian certain constraints in the links between peat biomass and miospore palynology are discussed in terms of over representation under representation and non representation the formulation of smith s four phase hydroseral model is discussed and compared with more recent data available from plant paleoecology the current debate over an ombrotrophic vs rheotrophic origin of late carboniferous peats relies in large part on paleobotanical data almost entirely palynological in combination with petrographic analyses ecological studies of miospores and of coal ball and compression macrofossils and the linkage of miospores to source plants permit the re evaluation of mire successional models evidence for tree lycopsids sphenopsids pteridosperms and cordaites suggests growth mainly in rheotrophic mires tree ferns are likely candidates for growth in domed mires although evidence is ambiguous and some tree ferns clearly grew under rheotrophic conditions densospores produced by at least sporangiostrobus lycopsid subtrees have been considered diagnostic of ombrotrophic conditions abundant evidence refutes this simplistic interpretation and suggests broad ecological amplitudes for densospore producers including growth under rheotrophic conditions although plant fossils alone can not resolve most of the major debates in modern coal geology paleobotany does contribute significantly to our understanding of ancient mires an approach combining paleobotanical data with petrography sedimentology and geochemistry on a case by case basis is most likely to produce a clear picture

new occurrence of youngest toba tuff in abyssal sediments of the central indian basin abstract volcanic glass and pumice found in siliceous abyssal sediments of the central indian basin south of the equator have previously been assigned various origins including intra basin volcanism indonesian arc and krakatau rhyolitic glass shards dispersed in sediments from 8 cores that we have examined are compositionally identical to those of fallout deposits of the youngest toba tuff erupted at 74 ka from northern sumatra the correlation extends the distribution of coarse 63 m glass shards some 1500 km south of the previously known fallout zone and into the southern hemisphere reaching latitudes of ca 14 s this provides evidence for bi hemispheric dispersal of the ash cloud and supports global dispersal of gas and aerosols from the eruption such dispersal could have facilitated the global impact of the eruption

spatial variation of present day stress field and tectonic regime in tunisia and surroundings from formal inversion of focal mechanisms geodynamic implications for central mediterranean we compiled 123 focal mechanisms from various sources for tunisia and adjacent regions up to sicily to image the current stress field in the maghrebides chain from tunisia to sicily and its foreland stress inversion of all the available data provides a first order stress field with a n150 e horizontal compression shmax and a transpressional tectonic regime but the obtained stress tensor poorly fit to the data set we separated them into regional subsets boxes in function of their geographical proximity kinematic regime homogeneity of kinematic orientations and tectonic setting their respective inversion evidences second and third order spatial variations in tectonic regime and horizontal stress directions the stress field gradually changes from compression in the maghrebides thrust belt to transpression and strike slip in the atlassic and pelagian foreland respectively where preexisting nw se to e w deep faults system are reactivated this spatial variation of the sismotectonic stress field and tectonic regime is consistent with the neotectonic stress field determined by others from fault slip data the major slab transfer edge propagator faults i e north south axis hammamet relay and malte escarpment which laterally delimit the subducting slabs play an active role in second and third order lateral variations of the tectonic regime and stress field orientations over the tunisian sicilian domain the past and current tectonic deformations and kinematics of the central mediterranean are subordinately guided by the plate convergence i e africa eurasia controlled or influenced by lateral slab migration segmentation and by deep dynamics such as lithosphere mantle interaction

coal facies studies in the eastern united states coals in the eastern united states east of the mississippi river have been the subject of a number of coal facies studies going back to the 19th century such studies would not necessarily fall within a strict modern classification of coal facies studies but if a study encompassed some aspects of paleobotany palynology petrology geochemistry or sedimentology we assumed that some data and interpretations may be of use in evaluations of the facies references are presented as a guide for further research with annotation in the tables

vegetational zonation in a swamp forest middle pennsylvanian illinois basin u s a indicates niche differentiation in a wetland plant community abstract a rich fossil flora occurs in the roof shale of the middle pennsylvanian moscovian age springfield coal flanking the galatia channel a river deposit approximately 1 km in width and 150 km long partially contemporaneous with the springfield peat swamp siltstone and sandstone 30 m thick were deposited in the channel during the final estuarine phase the river formed under seasonal subhumid climate during early deglaciation as marine waters retreated from the land surface it existed continuously through glacial maximum under increasingly humid climate as a low sediment or black water river with peat along its flanks during early deglaciation under subhumid climate and sea level rise the river became a sediment laden estuary drowning the peat swamp and burying vegetation in place under extensive mudflats this buried flora was studied in three underground mines in southern illinois permitting vegetation to be characterized spatially three transects comprising 100 sites a total linear distance of 12 km reveal distinct zonation perpendicular to the channel margin an innermost belt 0 5 to 2 5 km wide consists almost exclusively of the pteridosperm neuropteris flexuosa north of a river bend three belts succeed the n flexuosa zone mixed pteridosperms and marattialean tree ferns mixed arborescent lycopsids and marattialians lycopsids with rare marattialians south and inside the same bend n flexuosa is succeeded by mixed lycopsids particularly sigillaria and marattialean ferns within the transects marattialian ferns have wider distribution than other groups suggesting broader environmental tolerances neuropteris flexuosa channel margin mono dominance may reflect high sedimentation rates elevated nutrient conditions or floating seed dispersal lycopsid dominance in interior areas conforms with tolerance of deep standing water the spatial scale examined affects our perception of community assembly overall distinct vegetational zonation suggests niche assembly however within vegetational bands there is considerable small scale spatial variation suggesting stochastic properties

stratigraphic and interregional changes in pennsylvanian coal swamp vegetation environmental inferences abstract quantitative analysis of pennsylvanian coal swamp vegetation provides a means of inferring organization and structure of communities distribution of these communities further provides inferences about environmental factors including paleoclimate our observations are based on in situ structurally preserved peat deposits in coal ball concretions from 32 coal seams in the eastern one half of the united states and from several seams in western europe and on spore assemblages from more than 150 seams there were three times of particularly significant and nearly synchronous vegetational changes in the midcontinent and appalachian coal regions during the pennsylvanian period each was different in kind and magnitude the first marked changes occurred during the early part of the middle pennsylvanian with the fluctuating decline in the high level of lycopod dominance the abundance of cordaites increased there was a rise in the occurrences of the lycopod herbs to form intercalated marshlands and an overall increase in floral diversity changes ensuing from this time also include shifts in dominant species of lycopod trees and a sustained rise in abundance and diversity of tree fern spores the next significant time of change was during the middle part of the middle pennsylvanian representing both a culmination of earlier trends and expansions of cordaites in the midcontinent where there was a maximum change in species without net loss of diversity tree ferns and medullosan pteridosperms attained subdominant levels of abundance and diverse lycopod species dominated except in the atokan desmoinesian transition of the midcontinent the third and sharpest break occurred near the middle late pennsylvanian boundary when extinctionsof the dominant coal swamp lycopods allowed development of tree fern dominance the late pennsylvanian coal swamps apparently were colonized or recolonized mainly by species from outside coal swamps rather than by the survivor populations of the middle pennsylvanian swamps paralleling the changes in floras through the pennsylvanian are changes in preservational aspects of the peat these include a decline in shoot root ratios from approximately 1 to

place vs time and vegetational persistence a comparison of four tropical mires from the illinois basin during the height of the pennsylvanian ice age abstract coal balls were collected from four coal beds in the southeastern part of the illinois basin collections were made from the springfield herrin and baker coals in western kentucky and from the danville coal in southwestern indiana these four coal beds are among the principal mineable coals of the illinois basin and belong to the carbondale and shelburn formations of late middle pennsylvanian age vegetational composition was analyzed quantitatively coal ball samples from the springfield herrin and baker are dominated by the lycopsid tree lepidophloios with lesser numbers of psaronius tree ferns medullosan pteridosperms and the lycopsid trees synchysidendron and diaphorodendron this vegetation is similar to that found in the springfield and herrin coals elsewhere in the illinois basin as reported in previous studies the danville coal sample which is considerably smaller than the others is dominated by psaronius with the lycopsids sigillaria and synchysidendron as subdominants coal balls from the springfield coal were collected in zones directly from the coal bed and their zone by zone composition indicates three to four distinct plant assemblages the other coals were analyzed as whole seam random samples averaging the landscape composition of the parent mire environments this analysis indicates that these coals separated from each other by marine and terrestrial clastic deposits have essentially the same floristic composition and thus appear to represent a common species pool that persisted throughout the late middle pennsylvanian despite changes in baselevel and climate attendant the glacial interglacial cyclicity of the pennsylvanian ice age patterns of species abundance and diversity are much the same for the springfield herrin and baker although each coal both in the local area sampled and regionally has its own paleobotanical peculiarities despite minor differences these coals indicate a high degree of recurrence of assemblage and landscape organization the danville departs dramatically from the dominance diversity composition of the older coals presaging patterns of tree fern and sigillaria dominance of late pennsylvanian coals of the eastern united states but nonetheless built on a species pool shared with the older coals

paleoecology of the springfield coal member desmoinesian illinois basin near the leslie cemetery paleochannel southwestern indiana abstract the springfield coal member carbondale group petersburg formation of indiana is split locally in warrick and gibson counties indiana by clastic rocks of the folsomville member carbondale group petersburg formation that represent the leslie cemetery paleochannel part of a large interconnected paleochannel system in the springfield coal bed this study incorporated analysis of miospore and megaspore assemblages coal petrography plant compression fossils and conodonts from the coal and clastic split to document changes in the swamp and its vegetation in response to the activity of the leslie cemetery paleochannel palynological and petrographic data indicate that environmental conditions and vegetation in the lower bench of coal near the leslie cemetery paleochannel were similar to those found in profiles through the coal bed at sites near the larger more extensive galatia paleochannel miospore floras of the high vitrinite lower bench of coal were dominated by tree fern miospores with those of lycopsids ranking second in abundance megaspore assemblages were dominated by lycopsid megaspores near the contacy between the lower bench of coal and clastic split medullosan prepollen increases in abundance and fusain bands are more common which may indicate the occurrence of fire either within or outside the swamp vegetation in the folsomville member and upper bench of coal differ markedly from that of the lower bench of coal plant megafossils from the folsomville member indicate dominance by pteridosperms and or lycopsids and folsomville member miospore assemblages are dominated by lycopsid miospores most typically found in mudstones including lycospora torquifer and higher than normal abundances of granasporites medius in the transition from clastic rocks of the folsomville member to the upper bench of coal miospores of ecotonal lycopsids paralycopodites reach their peak abundance pteridosperms dominate megafossil assemblages and inertinite levels are relatively high at higher levels of the upper bench of coal vitrinite levels are higher and miospore assemblages are dominated by lycopsid miospores typical of coal swamps lycospora granulata l pusilla the presence of conodonts in coalballs in the upper bench of coal and spirorbid worms in the split indicate that the paleoswamp may have received some marine or brackish water influence higher than normal salinity levels may explain the vegetational changes observed in the upper bench of coal near the leslie cemetery paleochannel

toba ash on the indian subcontinent and its implications for correlation of late pleistocene alluvium the toba ash occurs extensively in the indian subcontinent and marks a ca 74 000 yr old event in the bay of bengal and indian ocean it is about 10 cm thick whereas in several alluvial basins it is usually 1 3 m thick the latter occurs in a partly reworked state but as nearly chemically pure first cycle sediments the ash has a broad northwesterly dispersal pattern samples of ash from the indian subcontinent compare closely with the youngest 74 000 yr b p toba tuff and the deep sea toba ash in bulk chemical composition ree signature and bubble wall shard morphology however a more proximally located and thicker 2 5 m ash bed from the alluvial basins in the gneissic area and close to east coast has a lower magnitude negative eu anomaly possibly because of minor contamination by feldspathic silt quaternary sediments in the central narmada and middle son basins contain rich late and middle pleistocene mammalian and cultural records based on the presence of the ash layer marker and stratigraphic relations late pleistocene sediments within the subcontinent can be correlated with those from central india and the deep sea

geometry and structural evolution of lorbeus diapir northwestern tunisia polyphase diapirism of the north african inverted passive margin detailed geologic mapping structural analysis field cross sections new dating based on planktonic foraminifera in addition to gravity signature of lorbeus diapir are used to characterize polyphase salt diapirism this study highlights the role of inherited faulting which controls and influences the piercement efficiency and the style and geometry of the diapir and also the localization of evaporite early ascent displaying diapiric growth during extension salt was extruded along the graben axis developed within extensional regional early cretaceous tectonic associated with the north african passive margin evolution geologic data highlight reactive diapirism during albian time most extreme extension period and passive diapirism during the late cretaceous post rift stage northeastern maghreb salt province gives evidences that contractional deformations are not associated with significant diapirism during shortening the initial major graben deforms as complex anticlines where diapirs are squeezed and pinched from their feeding