effects of scoria cone eruptions upon nearby human communities scoria cone eruptions are typically low in volume and explosivity compared with eruptions from stratovolcanoes but they can affect local populations profoundly scoria cone eruption effects vary dramatically due to eruption style tephra blanket extent climate types of land use the culture and complexity of the affected group and resulting governmental action a comparison of a historic eruption paricutin mexico with prehistoric eruptions herein we primarily focus on sunset crater in northern arizona usa elucidates the controls on and effects of these variables long term effects of lava flows extend little beyond the flow edges these flows however can be used for defensive purposes providing refuges from invasion for those who know them well in arid lands tephra blankets serve as mulches decreasing runoff and evaporation increasing infiltration and regulating soil temperature management and retention of these scoria mulches which can open new areas for agriculture become a priority for farming communities in humid areas though the tephra blanket may impede plant growth and increase erosion cultural responses to eruptions vary from cultural collapse through fragmentation of society dramatic changes and development of new technologies to little apparent change eruptions may also be viewed as retribution for poor behavior and attempts are made to mollify angry gods

geology geochronology and tectonic setting of the jorullo volcano region michoacan mexico abstract the jorullo monogenetic volcano erupted 250 years ago at the southern border of the trans mexican volcanic belt tmvb an area that records a long history of magmatic and tectonic activity the oldest rocks that crop out in the area are early oligocene 32 7 0 2 ma dioritic to granitic 60 72 wt sio2 plutons intruded by younger to contemporaneous 30 3 0 1 and 33 3 0 7 ma aplitic 76 78 wt sio2 dikes and mineralized veins volcanic rocks related to these intrusives form a thick sequence exposed in cliffs from the base of which an altered andesite 58 wt sio2 was collected the nearby epithermal cu mineralization of the inguaran mining area to the southeast is also related to this tertiary volcanic episode the oldest expression of the tmvb in this area is represented by pliocene 3 2 2 4 ma basaltic andesite to andesite 53 63 wt sio2 lavas with pyroxene olivine forming extensive mesas eroded mounds and thick elongate flows that were unconformably deposited on top of the oligocene rocks their emplacement was followed by erosion approximating a rate of 100 m ma over the past 3 ma this led to the formation of an inverted topography reflecting the higher resistance to erosion of these lavas that were originally deposited in valleys and today constitute prominent mesas during the last 1 ma at least twenty six monogenetic scoria cones formed in the study area erupting about 10 2 km3 of lava and pyroclastics dominantly composed of olivine and pyroxene bearing andesites 61 vol dre lesser basaltic andesites 30 vol dre and a minority of olivine rich basalts 10 vol dre these eruptive products include the k rich basaltic trachyandesites of cerro la pilita a scoria and lava cone located close to jorullo the 27 ka san hilario and esmeralda lavas which are located 13 km southeast of jorullo are the southernmost eruptive products of the tmvb and also the youngest volcanoes after jorullo in this area mapping of main faults and scoria cone alignments on regional and local scales reveals that the ascent of dikes feeding quaternary eruptions in the jorullo area was controlled by west northwest and west southwest basement structures northeast oriented subduction related horizontal compressional stress probably associated with crustal fractures and a major northwest trending seismically active fault zone that passes near paricutin and jorullo

the ad 1300 1700 eruptive periods at tungurahua volcano ecuador revealed by historical narratives stratigraphy and radiocarbon dating tungurahua is a frequently active and hazardous volcano of the ecuadorian andes that has experienced pyroclastic flow forming eruption in 1773 1886 1916 18 and 2006 08 earlier eruptions in late pre hispanic and early colonial times have remained poorly known and are debated in the literature to reconstruct the eruptive chronology in that time interval we examine relevant historical narratives recently found in sevilla spain and rome italy and we combine stratigraphic field constraints with 22 new radiocarbon age determinations results show that pyroclastic flow forming eruptions and tephra falls took place repeatedly since similar to 700 c 14 yr bp when the tungurahua region was already populated radiocarbon ages averaging around 625 yr bp reveal a period of notable eruptive activity in the 14th century late integration cultural period the associated andesitic eruptions produced ash and scoria falls of regional extent and left scoria flow deposits on the western flanks of the edifice the fact that tungurahua was known by the puruhas indians as a volcano at the time of the spanish conquest in 1533 perhaps refers to these eruptions a group of ages ranging from 380 to 270 yr bp is attributed to younger periods of activity that also predates the 1773 event and calibration results yield eruption dates from late 15th to late 17th centuries i e inca and early colonial periods the historical narratives mention an early colonial eruption between the spanish conquest and the end of the 16th century followed by a distinct eruptive period in the 1640s the descriptions are vague but point to destructive eruptions likely accompanied by pyroclastic flows the dated tephras consist of andesitic scoria flow deposits and the contemporaneous fallout layers occur to the west these findings reveal that the eruption recurrence rate at tungurahua is at least one pyroclastic flow forming event per century since the 13th century and the occurrence of such eruptions in 2006 08 is thus fully consistent with the rate inferred for the past seven centuries in addition historical chronicles suggest that a notch opened in the crater margin during the 1640 decade as has occurred repeatedly in the past millennium at tungurahua such small volume collapse events represent a previously unrecognized source of hazards which deserve special attention for risk assessment purposes in the context of the currently ongoing eruption c 2008 elsevier b v all rights reserved

origin of crude oils in the jinhu depression of north jiangsu south yellow sea basin eastern china abstract the chemical compositions of 20 crude oils and the extracts of potential source rocks from the jinhu depression of the north jiangsu south yellow sea basin eastern china were studied in detail by geochemical methods in order to understand their genetic relationship the oil samples were collected from the major producing fields in the western slope ws and the biandong yangjiaba minqiao uplift belt bmy the rock samples studied selected after rock eval pyrolysis screening of a large suite of samples consist of 20 shale samples in the e 2 f 2 member of the paleocene funing formation from the oilfield areas ws and bmy and the sanhe sag all within the jinhu depression geochemical characteristics indicate only one single family of oils a number of biomarker features support deposition of the source rocks for these oils under conditions of enhanced salinity stratified water columns a wide thermal maturity range for the oils as indicated by sterane isomerization ratios was not substantiated by other maturity parameters the genetic relationships between the oils and the e 2 f 2 member of the paleocene funing formation present in the deeper parts of the sanhe and longgang sags were suggested using a wide range of molecular parameters variation in the sterane concentrations in source rocks with different maturity suggests that migrational contamination and or in situ extractions of organic matter from caprocks or intra reservoir shales by mature oils could potentially produce oils with apparent immaturity at the molecular level secondary alteration e g biodegradation of oils in the reservoir could also have a similar effect on the bulk oil compositions although we do not discount the possible presence of minor amounts of immature oils exploration focus in the jinhu depression as well as many other rift basins in eastern china should be on mature oils derived from the deep source kitchens

geochemistry of evolved magmas and their relationship to subduction unrelated mafic volcanism at the volcanic front of the central mexican volcanic belt abstract this study reports new geochemical and radiogenic isotope data on hy normative pleistocene to recent 87 sr 86 sr 0 70370 0 70469 143 nd 144 nd 0 51278 0 51289 206 pb 204 pb 18 64 18 72 207 pb 204 pb 15 59 15 62 and 208 pb 204 pb 38 39 38 52 these isotopic ratios are generally similar to those for the associated mafic rocks although some differences do exist between them particularly for the 87 sr 86 sr ratios that are somewhat higher and 143 nd 144 nd that are slightly lower for the evolved rocks the available geochemical evidence does not support the generation of the scn evolved magmas by simple fractional crystallization fc or even by assimilation coupled with fractional crystallization afc of such mafic magmas nor by direct slab melting or indirect fluid transport to the mantle participation of the subducted cocos plate the viable mechanism seems to be that the most evolved andesitic and dacitic magmas in the scn were produced by partial melting of a heterogeneous mafic granulite source in the lower crust the magmas of intermediate compositions may reflect magma mixing processes between the most evolved andesitic and dacitic magmas generated in the lower crust and the mantle derived mafic magmas basalt and basaltic trachy andesite at the volcanic front of the central part of the mvb these results have direct bearing to other volcanic areas with complex tectonic setting

palaeomagnetic dating of two recent lava flows from ceboruco volcano western mexico ing j escalante supported studies with the micromag agfm and the curie balance and e nava warranted the functionality of the laboratory computers and the network this work was supported by unam project in 112712 hb and fjpc and conacyt grant no 180032 hb and anm fjpc has received funding from the european union s horizon 2020 research and innovation programme under the marie sklodowskacurie grant agreement no 659901

origin of oil and gas occurrences in the pliocene sediments of the pannonian basin hungary abstract considerable volumes of oil and gas in the pannonian basin have been discovered in pliocene sediments having good reservoir characteristics the pliocene sediments belonging to delta facies contain quantitatively very good but immature source rocks at depths of 0 5 2 km the origin of the oil and gas accumulations in the pliocene reservoirs is very different due to diverse conditions of hydrocarbon generation and secondary migration the aim of this paper is to establish the origin of oil and gas trapped in pliocene reservoirs in order to have a picture of the migration and accumulation systems different cases examined by means of the geochemical characteristics of oil and gases indicate that the pliocene reservoirs contain indigenous dry gases generated by bacterial and early catagenetic processes and vertically migrated hydrocarbon rich wet gases associated with oil and carbon dioxide rich gases derived from high temperature zones of the earth crust or from volcanic bodies

radiocarbon ages of holocene pelado guespalapa and chichinautzin scoria cones south of mexico city implications for archaeology and future hazards pelado guespalapa and chichinautzin monogenetic scoria cones located within the sierra del chichinautzin volcanic field scvf at the southern margin of mexico city were dated by the radiocarbon method at 10 000 2 800 4 700 and 1 835 years b p respectively most previous research in this area was concentrated on xitle scoria cone whose lavas destroyed and buried the pre hispanic town of cuicuilco around 1 665 35 years b p the new dates indicate that the recurrence interval for monogenetic eruptions in the central part of the scvf and close to the vicinity of mexico city is 2 500 years if the entire scvf is considered the recurrence interval is 1 700 years based on fieldwork and landsat imagery interpretation a geologic map was produced morphometric parameters characterizing the cones and lava flows determined and the areal extent and volumes of erupted products estimated the longest lava flow was produced by guespalapa and reached 24 km from its source total areas covered by lava flows from each eruption range between 54 chichinautzin and 80 km2 pelado and total erupted volumes range between 1 and 2 km3 cone an average eruption rate for the entire scvf was estimated at 0 6 km3 1 000 years these findings are of importance for archaeological as well as volcanic hazards studies in this heavily populated region

source rock palaeoenvironments and controls on the distribution of dibenzothiophenes in lacustrine crude oils bohai bay basin eastern china abstract the applicability of sulphur aromatic parameters based on ratios of dibenzothiophene dbt and its alkylated homologues as indicators of oil maturity has been investigated in 27 oils from the damintun and zhuanhua depressions bohai bay basin the oils were characterised by bulk composition and environmentally sensitive aliphatic biomarkers and were derived from a wide range of lacustrine source depositional environments ranging from highly reducing hypersaline sulphur rich oils to terrestrial input dominated freshwater very high wax oils with maturities ranging from immature to probable mid mature dibenzothiophene based maturity parameters are not well correlated with sterane isomerization ratios and immature oils in particular could not be discriminated by these aromatic maturity indicators in contrast dbt based parameters are strongly correlated with pristane to phytane and ts tm ratios high methyldibenzothiophene ratios mdr are associated with fresh water source deposition whilst low mdrs are found in oils of hypersaline source affinity unusually high relative concentrations of 2 3 mdbt were observed in some of the immature oils inferred to be sourced by lacustrine organic laminites the data provide further evidence that thermal stress is not the sole factor controlling the distribution patterns of dibenzothiophenes in oils and that source depositional environments can exert a dominant influence when their range of variation is large absence of dbt in some biodegraded oils is tentatively attributed to its aqueous solubility during associated water washing

morpho chronology of monogenetic scoria cones from their level contour curves applications to the chichinautzin monogenetic field central mexico abstract the genesis distribution and hazards associated with monogenetic volcanic fields pose particular difficulties derived from their dispersed character establishing a relationship between the spatial and the age distributions of volcanic cones is necessary both to understand the nature of monogenetic field formation and evolution and to set supported hazard assessment criteria we present here a new method specifically developed to quantify the degree of age dependent erosion of individual scoria cones aimed to estimate the relative ages of undated scoria cones in a monogenetic volcanic field from a contour level morphometric analysis of the field digital elevation model dem this method is based on the hypothesis that age and the degree and type of erosion causing significant morphological changes on scoria cones are markedly correlated it is assumed that at the time of their formation monogenetic volcanoes have diverse yet smooth shapes which mechanical processes of wearing gradually change in different spatial scales this evolution is largely evidenced both as changes of the volcano slopes and as height dependent undulations of the cone surface generated by the hydrometeorological ablation in the otherwise uniform elevation contour lines here we characterize the time dependence of the shape and size of the altitude isoline undulations by means of the elliptical fourier descriptor spectra of the contour curves of volcanic cones to test the effects of the dem data type and resolution on this morpho chronological dating we analyze the correlations of published radiometric ages of cones with two datasets of contour curves from the sierra chichinautzin monogenetic volcanic field in central mexico scvf one obtained from airborne lidar surveys inegi mexico and the other from a satellite radar mission dlr germany

eruptive style of the young high mg basaltic andesite pelagatos scoria cone southeast of mexico city the eruption of the pelagatos scoria cone in the sierra chichinautzin monogenetic field near the southern suburbs of mexico city occurred less than 14 000 years ago the eruption initiated at a fissure with an effusive phase that formed a 7 km long lava flow and continued with a phase of alternating and or simultaneous explosive and effusive activity that built a 50 m high scoria cone on the western end of the fissure and formed a compound lava flow field near the vent the eruption ended with the emplacement of a short lava flow that breached the cone and was accompanied by weak explosions at the crater products consist of a microlite rich high mg basaltic andesite samples were analyzed to determine the magma s initial properties as well as the effects of degassing induced crystallization on eruptive style although distal ash fallout deposits from this eruption are not preserved a recent quarry exposes a large section of the scoria cone detailed study of exposed layers allows us to elucidate the mode of cone building activity petrological and textural data combined with models calibrated by experimental work and melt inclusion analyses of similar magmas elsewhere indicate that the magma was initially hot 1 200 c gas rich up to 5 wt h2o crystal poor 10 vol fo90 olivine phenocrysts and thus poorly viscous 40 80 pa s during the early phase low magma ascent velocity at the fissure vent allowed low viscosity magma to degas and crystallize during ascent producing lava flows with elevated crystal contents at t 1 100 c and blocky surfaces later the closure of the fissure by cooling dikes focused the magma flow at a narrow section of the fissure this led to an increased magma ascent velocity rapid and shallow degassing 3 km deep triggered 40 vol microlite crystallization limited times for gas escape and higher magma viscosity 6 105 4 106 pa s drove strong explosions of highly 60 80 vol and finely vesicular magma coarse clasts broke on landing which implies brittle behavior due to complete solidification this requires sufficient time to cool and in turn implies ejection heights of over 1 km which is much higher than normal strombolian activity hence magma viscosity significantly impacts eruption style at monogenetic volcanoes because it affects the kinetics of shallow degassing the long lasting eruptions of jorullo and paricutin which produced similar magmas in western mexico were more explosive this can be related to higher magma fluxes and total erupted volumes implications of this study are important because basaltic andesites are commonly erupted to form monogenetic scoria cones of the trans mexican volcanic belt

geochemistry and correlation of crude oils from reservoirs and source rocks in southern biyang sag nanxiang basin china abstract the paleogene hetaoyuan formation a sequence of gray to dark calcareous mudstone and dolomitic mudstones is the main source rock and reservoir in the biyang sag nanxiang basin eastern china organic geochemical analysis study performed on 57 source rock samples from the hetaoyuan formation demonstrates poor to abundant organic matter content ranging from 0 24 5 4 wt toc content characterized by oil prone type ii kerogen eleven crude oil samples from the hetaoyuan formation in southern biyang sag were analyzed using bulk properties and molecular methods to determine their maturity and origin the results suggest that the crude oils exhibit different maturity and source organic matter three groups of oils were identified by integrated analysis of gas chromatography gas chromatography mass spectrometry stable carbon isotope physical properties and gross composition of crude oil group a oils defined as low mature oil are characterized by high density viscosity sulfur content and low saturated hydrocarbon content this group of oils has relatively high values of ph n c 18 c 24 c 26 and gammacerane index indicating that the original organic matter had more contribution from terrigenous plants and was deposited in saline and stratified water columns under anoxic conditions group b oils defined as normal maturity oil are characterized by moderate density viscosity sulfur content and moderate saturated hydrocarbon content this group of oils has relatively low values of ph n c 18 c 24 c 26 and gammacerane index and displays a slight predominance of c 29 steranes indicating that the original organic matter had more contribution from marine algae and was deposited under sub oxic to anoxic conditions with low salinity group c oils defined as light oil are characterized by low density viscosity and abundant saturated hydrocarbons representative source rock samples were selected for further correlation the results of oil source rock correlation suggest that crude oils from the eh 2 member of hetaoyuan formation are mixture derived from source rocks in the eh 2 member and upper layer of the eh 3 member while oils from the upper and lower layer of the eh 3 member correlate with source rocks in the upper and lower layers of the eh 3 member respectively

rates of pedogenic processes in volcanic landscapes of late pleistocene to holocene age in central mexico abstract the transmexican volcanic belt and its many volcanic fields of different ages offer good opportunities to study soil development on volcanic tephra of intermediate to basaltic composition we studied a soil chronosequence within the sierra chichinautzin volcanic field scvf south of the basin of mexico and aimed to establish the rates of pedogenic processes this field has been active for around 50 000 years and produced 221 cinder cones with their respective lava flows we selected 11 sites located on 14 c dated lava flows of ages between 1800 and 30 500 bp at 3100 3200 m above sea level covered with pine fir forest with an ustic soil moisture regime and an isomesic soil temperature regime we also included a younger site 1000 bp and three older sites 100 000 years two at 3100 masl and one at 2600 masl from nearby volcanic fields to widen the time frame of the chronosequence soil profile samples were analysed for total organic carbon as well as for mineral neoformations related to clay contents selective chemical extractions and x ray diffraction analyses within the scvf the total soil thickness carbon accumulation and al si and fe extracted with acid ammonium oxalate increased linearly with age on surfaces up to 10 000 years old at rates of 19 cm ky 1 4 1 kg c m 2 ky 1 4 6 kg al 2 7 kg si and 2 kg fe m 2 ky 1 respectively crystalline clay and iron oxide formation reach a maximum at the oldest site located at 2600 masl of 1650 kg clay m 2 and 70 kg fe d m 2 their increase is linear up to ages of 10 000 years at rates of 22 kg clay m 2 ky 1 and 2 8 kg fe d m 2 ky 1 thereafter the rates are much slower allophane and allophane like minerals dominate in the clay fraction at all sites of the chronosequence and small amounts of halloysite can be identified in soils older than 6200 years while kaolinite was only identified at the three oldest sites 100 000 years the linear increases of all indicators of pedogenesis in the first 10 000 years are presumably driven by recurrent tephra deposition during this time frame thereafter erosion and colluviation processes seem to disturb pedogenesis changing its rates and redistributing its products in the landscape

pahoehoe and aa in hawaii volumetric flow rate controls the lava structure the historical records of kilauea and mauna loa volcanoes reveal that the rough surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate 5 10 m3 s and the smooth surfaced variety called pahoehoe forms at a low volumetric rate 5 10 m3 s this relationship is well illustrated by the 1983 1990 and 1969 1974 eruptions of kilauea and the recent eruptions of mauna loa it is also illustrated by the eruptions that produced the remarkable paired flows of mauna loa in which aa formed during an initial short period of high discharge rate associated with high fountaining and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate with little or no fountaining the finest examples of paired lava flows are those of 1859 and 1880 1881 we attribute aa formation to rapid and concentrated flow in open channels there rapid heat loss causes an increase in viscosity to a threshold value that varies depending on the actual flow velocity at which when surface crust is torn by differential flow the underlying lava is unable to move sufficiently fast to heal the tear we attribute pahoehoe formation to the flowage of lava at a low volumetric rate commonly in tubes that minimize heat loss flow units of pahoehoe are small usually 1 m thick move slowly develop a chilled skin and become virtually static before the viscosity has risen to the threshold value we infer that the high discharge rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers rapid near surface vesiculation of gas rich magma leads to eruptions with high discharge rates high lava fountains and fast moving channelized flows we also infer that long periods of sustained flow at a low discharge rate which favor pahoehoe result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway

the process of melt differentiation in arc volcanic rocks insights from oib type arc magmas in the central mexican volcanic belt by straub et al a critical comment the recent paper by straub et al 2012 provides a detailedgeochemical study of the compound texcal lava flow andthe eruptive products of chichinautzinvolcano twomono genetic volcanoes located in close proximity to each otherin the central part of the sierra chichinautzin volcanicfield scvf south of mexico city the authors chosethese mafic ocean island basalt oib type volcanoesthat belong to the mexican volcanic belt because theyerupted lavas displaying a range of compositions and inaddition are believed to have retained some of their initialgeochemical sub arc mantle and subducted slab signatures the latter allowed these authors to make inferences re garding magma generation processes in a subduction related tectonic setting i would like to comment here on one specific point onwhich i hold a significantly different opinion and whichis important to address because of its diverse ramifications including volcanic hazard assessment in a densely popu lated area this concerns the exact location and morph ology of the vent s and the timing and eruptive style ofthe eruption that produced the texcal lava flows in theirfig 1 straubet al 2012 present a geological sketch map which they call a refined version of a previous map pub lished by siebe et al 2004a 2004b at first sight the refined map seems almost identical to the map publishedby siebe et al 2004a 2004b however a closer look seefig 1a reveals that the source vent for the compoundtexcal lava flow has been changed the guespalapa align ment of scoria cones which formed between 4700 and2800 years

monogenetic vulcanism in sierra chichinautzin mexico the variation in the activity patterns of the chichinautzin volcanic rocks is discussed this sequence of lavas and pyroclastic deposits is located in the central part of the mexican volcanic belt directly south of mexico city and is typical of its quaternary monogenetic vulcanism

petroleum systems in the jiangling dangyang area jianghan basin china source related geochemical data define at least four petroleum systems in the jiangling dangyang area of the jianghan basin eocene paleocene anoxic evaporitic lacustrine source rocks generated most of the crude oils in the area eocene qianjiang rock from the sha 13 well 1322 m contains fast reacting sulfur rich type is organic matter and its extract is most similar to the sha 13 oil sand bitumen qianjiang reservoir lower eocene paleocene xingouzhui rocks from the xin 73 well 842 and 862 m contain slow reacting low sulfur type i organic matter and their extracts are most similar to the sha 26 oil sand bitumen eocene jinsha reservoir and the ling 2 sha 24 and tuo 3 oils xingouzhui reservoirs two unidentified middle triassic or older marine carbonate evaporite source rocks or different facies of the same source rock generated the daxiakou oil triassic jialingjiang formation outcrop xingshan county and the moderately biodegraded tianwan seep oil permian changxing outcrop chengxi county respectively one or more unidentified marine source rocks which could include the lower permian qixia or the upper sinian doushantuo formations generated the miaoshi and yanmenkuo seep oils permian qixia outcrops the jingshan seep oil ordovician baota outcrop probably is related to these oils but could represent another petroleum system different kinetics for hydrocarbon generation among eocene qianjiang and lower eocene paleocene xingouzhui formation source rocks and chemical differences among the related oils are caused by organic facies variations high salinity and low eh enhanced the preservation of oil prone organic matter in these lacustrine settings and facilitated incorporation of sulfur into the organic matter anoxia and the unusual presence of abundant sulfate as gypsum resulted in the microbial reduction of sulfate to sulfide and incorporation of this sulfur into the kerogen for example biomarkers show that source rock in the sha 13 well 1322 m was deposited under more saline lower eh conditions than that in the ling 80 well 1808 m although both are from the qianjiang formation the sha 13 rock sample is more organic rich 6 62 vs 1 27 wt toc and has a higher hydrogen index 794 vs 501 mg hc g toc and faster reaction kinetics than the ling 80 sample kerogen from the sha 13 sample is type is because it has a high hydrogen index and an atomic s c ratio 0 074 in the range of sulfur rich fast reacting kerogens of the monterey formation s c 0 040 organic rich lower jurassic coaly rocks from outcrops at daxiakou contain immature to mature gas prone organic matter that is not related to any oils in the study several organic rich upper sinian to permian samples could have been source rocks in the past but are now highly mature based on high tmax 464 540 c and estimated vitrinite reflectance ro values mass balance calculations were used to estimate the original toc toc c in these samples prior to maturation these samples could not be correlated with the oils using biomarkers because of high maturities and low extract yields however stable carbon isotope type curves suggest that the miaoshi yanmenkuo permian qixia formation and the jingshan ordovician baota formation seep oils originated from source rocks in the lower permian qixia 3 00 wt toc or upper sinian doushantuo formations 5 96 wt toc lack of triaromatic dinosteroids in the miaoshi and yanmenkuo seep oils supports but does not prove a permian source rock very negative stable carbon isotope ratios for kerogens from the lower cambrian shuijintuo formation 33 5 to 33 6 8 85 16 64 wt toc show that they are not related to any of the analyzed oils

volcanic stratigraphy of a high altitude mammuthus columbi tlacotenco sierra chichinautzin central mexico the discovery of a near complete skeleton of mammuthus columbi in a cornfield located on the northern slopes of the sierra chichinautzin volcanic field south of mexico city sparked the interest of the scientific and public community although remains of this species of mammoth are frequently discovered in central mexico this new find is at the southernmost and highest ca 2770 m asl location yet within the mexico basin in addition the bones were found embedded in dark volcanic ash raising the possibility of a relationship between the death of the animal and explosive activity at a neighboring scoria cone as the site is located 10 km from several young volcanoes stratigraphic sedimentological geochemical and geochronological studies were conducted at the discovery site and within a 5 km radius to determine the tephra stratigraphy in the area and constrain the source of the mammoth ash and the age and taphonomy of the fossil remains results show that the mammoth was buried after death by stream flows dilute lahars that were triggered by torrential rain that remobilized loose scoriaceous ash ejected by the san miguel cone some time after its eruption ca 17 000 bp

acquisition and processing of wide aperture ground penetrating radar data a 40 channel wide aperture ground penetrating radar gpr data set was recorded in a complicated fluvial aeolian environment in eastern canada the data were collected in the multichannel format usually associated with seismic reflection surveys and were input directly into a standard seismic processing sequence filtering static corrections common midpoint gathering velocity analysis normal and dip moveout corrections stacking and depth migration the results show significant improvements over single channel recordings in noise reduction and depth of penetration by stacking and in spatial positioning and reduction of diffraction artifacts by migration these characteristics increase the potential for reliable interpretation of structural and stratigraphic details thus without having to develop any new software gpr data processing technology is brought to the same level of capability flexibility and accessibility that is current in seismic exploration

oil of the volcano uzon caldera kamchatka there are reported gas chromatography gas chromatography mass spectrometry and carbon isotopic data on the oils sampled in caldera of the uzon volcano east kamchatka the uzon volcano is located in the west of the eastern kamchatka basin which is made up of thick paleogene neogene sedimentary rocks its caldera is made up of lacustrine volcanogenic sedimentary formations of pleistocene age 38 70 thousand years lying on dense basalts two samples studied were heavy oils 0 915 g ml and contained 2 sulfur 2 5 paraffin 9 3 waxes 1 4 wt olefinic hydrocarbons their gas chromatograms show a mono modal distribution for n alkanes with a maximum at c18 pristane phytane concentration ratios were measured to be 0 48 0 52 olefinic hydrocarbons were interpreted to be of hydrothermal origin sterane and triterpane biomarkers indicated a low maturation degree and a lacustrine orgin of the initial organic matter the uzon oil was found to be isotopically heavy with a 13c value of 21 14c isotope was detected which indicates that recent plant organic matter was significantly involved in oil generation process

assessment of mesozoic and upper paleozoic source rocks in the south yellow sea basin based on the continuous borehole csdp 2 abstract being lack of core data and measured data although the marine oil gas exploration in the south yellow sea basin has been going on for 57 years no commercial hydrocarbon reservoirs have been found so far the quantitative source rocks evaluation based on geochemical data and fluid inclusions containing hydrocarbon benefits from the completion of borehole csdp 2 in 2016 a continuous coring well of the chinese continental shelf drilling program csdp which indicates that the marine origin oil gas exploration in the south yellow sea basin enters into a new stage as revealed by the well csdp 2 three sets of effective hydrocarbon source rocks in the mesozoic and upper paleozoic have been identified which are distributed in the lower triassic qinglong formation t1q upper permian longtan dalong formation p3l d and middle permian gufeng qixia formation p2g q respectively among them organic rich source rocks mainly concentrate in the lower part of the p3l d and the middle upper part of the p2g q and the p3d mudstone also works as good source rock the p3l d mudstone with high organic abundance is the chief source rock in the south yellow sea basin whose maximum hydrocarbon generating intensity may reaches up to 795 09 104 t km2 and hydrocarbon expulsing intensity remains at the level of 165 03 104 t km2 a noteworthy feature of the p2g q source rocks is the strong vertical heterogeneity with the hydrocarbon expulsing intensity of the upper part being 34 14 104 t km2 while that of the lower part being 18 07 104 t km2 in contrast the organic abundance of argillaceous limestone in the t1q is mainly poor to medium and its hydrocarbon expulsing intensity is the weakest one in the three sets of hydrocarbon source rocks only about 12 7 104 t km2 taking into consideration the joint influence of depositional environment organic matter parent source and biological productivity the overall quality of source rocks in the south yellow sea basin is at the similar level to the lower yangtze subei basin but lower than that of the upper yangtze sichuan basin the most significant oil gas information is that multiple direct oil indications and high value abnormalities of gas logging have been discovered in the well csdp 2 moreover the mesozoic and upper paleozoic marine strata in the south yellow sea basin have experienced three hydrocarbon charging stages indicating a broad prospect of marine oil gas exploration

formation of immature asphalt from organic rich carbonate rocks i geochemical correlation abstract the formation of low maturity asphaltic oils immature asphalts from carbonate source rocks was investigated the senonian bituminous rocks sbr in israel are organic rich carbonate rocks that were deposited in a high productivity environment and they are part of a sedimentary sequence that also contains cherts and phosphorites the sbr were studied in different basins and the samples are from outcrops and three deep drillholes the bitumen contents of the rocks are exceptionally high up to 700 mg g c org and immature asphalts are found to be associated with them geochemical analysis indicates that the bitumens are indigenous to the host sbr and the associated asphalts are bitumens that have migrated a short distance with negligible chemical fractionation the high heteroatom content of the kerogens up to 30 in the sbr is suggested as a possible cause of the generation of asphaltic oils in an early stage of maturation

maturity assessment of oils from the sakhalin oil fields in russia phenanthrene content as a tool a correlation analysis of maturation parameters was carried out on 14 crude oil samples from nine oil fields on sakhalin island russia the oils were taken from reservoir rocks of miocene age at depths ranging from 73 to 2841 m on the basis of gc analysis of the alkane fraction n alkanes and the isoprenoid alkanes pristane and phytane as well as on the basis of the abundance of demethylated hopanes gc ms analysis m z 177 it is assumed that the oils are either biodegraded or are a mixture of biodegraded and nonbiodegraded oils therefore their maturation is assessed on the basis of the distribution and abundance of tricyclic aromatic hydrocarbons that are more resistant to biodegradation than alkane type biological markers the oils may be classified into three groups on the basis of the well established maturation parameter mpi 3 highly mature group i moderately mature group ii and immature group iii the correlation analysis shows that the percentage of phenanthrene p in the tricyclic aromatic fraction of the oils of the sakhalin oil fields can be used as a maturation parameter the highly mature oils group i were found to have a p value of more than 14 the moderately mature oils group ii have values of 7 14 and the immature oils group iii a value of less than 7 the very good correlation between mpi 3 and p also indicates that parallel to methylphenanthrene isomerization dealkylation also occurs in the reservoir rocks by correlation analysis it is shown that these reactions are to a great extent determined by the depth of the reservoir rocks

analysis of geomagnetic secular variation for the last 1 5 ma recorded by volcanic rocks of the trans mexican volcanic belt new data from sierra de chichinautzin mexico

bakken madison petroleum systems in the canadian williston basin part 2 molecular markers diagnostic of bakken and lodgepole source rocks abstract the uppermost devonian mississippian bakken formation black shale and the mississippian lodgepole formation carbonate represent two of the most important source rocks in the canadian williston basin quantitative analyses of both saturated and aromatic hydrocarbon fractions reveal significant differences in the relative distributions and absolute concentrations for a wide range of molecular markers between the extracts of the two source units among others the bakken shales are characterized by their high relative abundance of trimethyl aryl and diaryl isoprenoids likely derived from green sulfur bacteria chlorobiaceae in contrast the lodgepole carbonates at similar maturity levels display a c35 homohopane prominence and abundant benzohopanes ring d monoaromatic 8 14 secohopanes and a tetracyclic monoaromatic hydrocarbon the distinctive nature of molecular marker fingerprints diagnostic of the two source rocks is clearly related to their different organic inputs and depositional environments additionally the large difference in the absolute concentrations of these compounds observed in both source units may potentially lead to biased geochemical interpretations if strictly conventional saturate based biomarker approaches were used for oil oil and oil source correlation

the petroleum geochemistry of canadian beaufort tertiary non marine oils abstract molecular isotopic and elemental data for a set of 28 paleogene and 3 cretaceous oils from the mackenzie delta and offshore canadian beaufort sea have been evaluated the depositional environment and organic matter characteristics of the source units for these oils have been predicted the paleogene oils of the canadian beaufort are molecularly distinctive and clearly contain a major land plant component oleanane and the 17 h and 17 h 24 28 bisnorlupanes are present as well as the following compound types 24 norlupanes and possibly higher homologues de a lupane noroleanenes norursene dehydroabietane 28 30 bisnorhopanes several molecular and isotopic characteristics are useful in assessing and ordering the extent of biodegradation and thermal maturation of these oils the cretaceous oils are separately sourced from the paleogene oils the latter oils comprise two distinct land plant derived genetic families distinguished by the presence absence of 24 28 bisnorlupanes 24 norursene 24 norlupane and 24 noroleanenes the kugmallit richards family contains each of these compound types and is considered to originate from the eocene richards formation in contrast lupanoids and noroleanenes are absent in oils of the reindeer moose channel family the occurrence of 28 30 bisnorhopane and or oleanane in these oils suggests a paleocene origin although these source rock predictions are supported by the available data they must be considered speculative until detailed molecular isotopic and elemental compositional data are available regionally for potential source rocks of the eocene and paleocene source units in the canadian beaufort

geochemical constraints on models for secondary petroleum migration along the upper devonian rimbey meadowbrook reef trend in central alberta canada abstract the upper devonian rimbey meadowbrook reef trend of central alberta canada is one of the classical examples that was originally used to support gussow s model of differential hydrocarbon entrapment however the clear discrepancies existing between the ideal hydrocarbon distribution predicted by this model and the one actually observed led to several alternative geological models most of which have not been constrained by organic geochemical data the present study uses a wide range of bulk and molecular parameters to determine the oil source characteristics and thermal maturity along the reef trend the concentrations and isomeric distributions of alkylcarbazoles and non alkylated benzocarbazoles in oils are employed to study petroleum migration pathways and to constrain the existing secondary petroleum migration models the data indicates that gussow s principle is generally applicable as the oils in the up dip direction generally have longer implied migration distances although this is not always the case other factors not recognized previously such as the presence of two subfamilies of the duvernay formation sourced oils may also have contributed significantly to the discrepancies in the oil and gas distributions between the model predictions and the actual observational data

age and archaeological implications of xitle volcano southwestern basin of mexico city the pedregal lavas are fresh well exposed basaltic flows erupted from the xitle scoria and cinder cone in the southwestern part of the basin of mexico these lavas cover an area of 70 km 2 and were emplaced over pyramids and other buildings e g cuicuilco and copilco archaeological sites today a part of mexico city including the national university is built on the flows initial strombolian activity produced an ash fallout layer which was immediately followed by effusive emplacement of lava flows the xitle cone grew on the north facing slope of ajusco volcano and lava flowed down to the n ne until it reached the basin floor more than 30 radiocarbon dates have been obtained by several workers on charcoal samples from beneath the lava and several ages for the eruption have been proposed from these dates most dated samples were not directly produced by xitle s eruption but instead are artifacts of human activity that predates the eruption thus these ages mostly about 2000 bp are older than the eruption a new age of 1670 35 years bp ad 245 315 obtained on charcoal samples collected just beneath the lavas is favored for the xitle eruption these samples originated by ignition of vegetation during the emplacement of hot scoriaceous tephra the new age is within the classic period of mesoamerican archaeology whereas the earlier reported ages are at the end of the preclassic the new age carries important implications for the timing of population shifts within the basin of mexico q 2000 elsevier science b v all rights reserved

variable effects of cinder cone eruptions on prehistoric agrarian human populations in the american southwest abstract two 900 bp cinder cone eruptions in the american southwest affected prehistoric human populations in different ways mostly because of differences in the eruption styles and area affected primary pre eruption cultural factors that may have led to successful adaptation to the eruptions include decision making at the family or household level low investment in site structures dispersion of agricultural sites in varied environments and settlement spread over a large area so that those who were less affected could shelter and feed evacuees sunset crater near flagstaff arizona produced about 8 km 2 lava flow fields and a 2300 km 2 tephra blanket in an area that had been settled by prehistoric groups for at least 1000 years local subsistence relied on agriculture primarily maize and 30 cm tephra cover rendered 265 km 2 of prime land unfarmable this area was apparently abandoned for at least several generations a 500 km 2 area was probably marked by collapsed roofs and other structural damage from the fallout if the eruption occurred during the agricultural season the fallout would also have significantly damaged crops the eruption did have some benefits to local groups because lower elevation land which had previously been too dry to farm became agriculturally productive due to 3 8 cm of tephra mulch and some temporary soil nutrient improvements this previously uninhabited land became the site of significant year round settlement and farming eventually containing some of the largest pueblo structures ever built in the region new agricultural techniques were developed to manage the fallout mulch the eruption also affected ceramic production and trading patterns and volcano related ritual behavior the production of maize impressed lava spatter agglutinate was initiated little springs volcano about 200 km northwest of sunset crater is a small spatter rampart around a series of vents that produced about 5 km 2 of lava flow fields about 1 km 2 of land severely affected by ballistic fall and no significant tephra fall the small area affected resulted in much less disruption of human activities than at sunset crater farming was still possible right up to the edge of the lava flows which became attractive sites for settlements most sites along the lava flows have habitation and storage structures at the base of the flow and a series of small apparently little used structures on the blocky lava flow above these lava surface structures may have been defensive in nature in addition trails were constructed on the blocky lava flow surface these trails whose access points are difficult to recognize from below appear to have been used for rapid movement across the flows and may also have been defensive in nature spatter agglutinate blocks containing ceramic sherds within them similar to the maize impressed spatter agglutinate at sunset crater were made at little springs and carried to a nearby habitation site in arid and semiarid lands such as northern arizona tephra fall is a mixed blessing thick cinder blankets 20 30 cm render land uninhabitable but thinner 3 8 cm deposits can serve to conserve soil moisture regulate soil temperature thus lengthening the growing season and by lowering soil ph provide a temporary decades to a century or two increase in available phosphorus an important nutrient for growth the mulch opened up new lands for settlement but likely only lasted for a century or two before reworking reduced its effects

radar experiments in isotropic and anisotropic geological formations granite and schists 1 in order to understand various aspects of radar wave propagation a survey of electromagnetic wave behaviour relative to the geological characteristics of the formations prospected was undertaken the sites chosen for the tests were a granite quarry and an underground schist working by investigating an electrically resistive isotropic site and a conductive anisotropic site it was demonstrated that non conventional use of a radar system antennae raised various orientations of the transmitter receiver etc could improve data quality and could allow information other than reflector depth to be collected volume scattering intensity isotropy etc by studying wave propagation velocities we underlined the difficulties encountered in establishing a velocity versus depth law despite recourse to seismic data processing such as nmo corrections the results of field experiments complemented by laboratory measurements of dielectric permittivities clearly showed anisotropy effects in the case of a path that is perpendicular to the schistosity plane an electromagnetic wave propagates more slowly and is more attenuated than a wave parallel to the schistosity plane

significance of coniferous rain forests and related organic matter in generating commercial quantities of oil gippsland basin australia contrary to the conventional belief that humic coal generates primarily gas 3 billion bbl of recoverable oil has been discovered in the humic coaly succession of the fluviodeltaic latrobe group upper cretaceous tertiary that serves as both the reservoir and the source for hydrocarbons in the offshore gippsland basin of southeastern australia evidence for generation of liquid hydrocarbons from the coaly succession includes 1 similarity of n alkane distribution in the oil and in the coal extracts 2 high wax content of oil up to 27 by weight 3 high ratio of pristane phytane in oil 5 6 and 4 dominance of c29 steranes in the oil in the gippsland basin coniferous rain forests dominated by kauri vegetation flourished in a raised bog setting present temperate climate and kauri vegetation of new zealand are considered to be the modern analog to the gippsland basin the coniferous vegetation provided large quantities of hydrogen rich exinite macerals such as cutinite and resinite with potential to generate oil high rainfall raised ground water level low oxygen high acidity and low nutrient conditions of a raised bog setting were suitable for preserving organic matter a comparison of gas chromatograms of oils in the gippsland basin with gas chromatograms of oils generated by hydrous pyrolysis in the laboratory from the immature source rocks suggests that the paraffinic fraction of the oil was derived from coal and the naphthenic fraction was derived chiefly from resin

numerical simulation of basaltic lava flows in the auckland volcanic field new zealand implication for volcanic hazard assessment monogenetic volcanic fields such as the auckland volcanic field avf new zealand are common on the earth s surface and are typically dominated by basaltic lava flows up to 10 s of km long in monogenetic volcanic fields located in close proximity to human population and infrastructure lava flows are a significant threat in this study lava flow emplacement conditions for some basaltic eruptions of the avf were reconstructed using the thermo rheological magflow model eight existing lava flows in the avf were simulated using magflow and eruptive volumes measured from light detection and ranging lidar derived digital terrain models dtms fitting the simulations to the dimensions of actual lava flows provides insight into their emplacement mechanisms and conditions such as effusion rate and probable eruption durations by looking at emplacement in different settings the likely magma ascent rate for studied avf eruptions is calculated to have been on the order of 0 1 m s in the avf the typical estimated duration of past lava flows was from a minimum of 2 days for small volume flows such as little rangitoto 0 0015 km3 up to 83 days for large volume flows such as three kings 0 078 km3 the three best fitting simulations were used to establish eruption scenarios for future volcanic hazard mapping for the avf inferences of eruption duration that will be useful for developing realistic emergency management plans and recovery scenarios for this densely populated volcanic field are also provided

geochemical characterization of source rocks and crude oils in the upper cretaceous qingshankou formation changling sag southern songliao basin abstract the upper cretaceous qingshankou formation is one of the main exploration target in the changling sag southern songliao basin however the origin of source rock deposition and crude oils remains undiscovered a comprehensive geochemical study including rock eval pyrolysis gas chromatography mass spectrometry and carbon isotope analysis on fifteen crude oils and twenty two source rock samples from the qingshankou formation were performed in order to provide new insights into source organic matter depositional environment and correlation between crude oils and source rocks bulk geochemical analysis on source rock samples indicates that the lower member of the qingshankou formation has more hydrocarbon generating potential than the middle member these two potential source rock members were interpreted to be deposited in slightly different environments and have different sources of organic matter determined by biomarker assemblages the lower member is organically rich average toc 1 27 wt oil prone mature and deposited under anoxic conditions with more contribution from sapropelic organic matter the middle member is organically poor average toc 0 78 wt gas prone less mature and deposited under less anoxic conditions with more terrigenous organic matter input biomarker fingerprints and carbon isotope compositions suggest that all the crude oils were genetically related and could be classified into one oil family which has significant contribution from the lower member source rocks and minor contribution from the middle member source rocks

immature oil and condensate modification of hydrocarbon generation model for terrestrial organic matter petroleum has been found in canadian frontier basins in reservoirs which have undergone low levels of thermal alteration vitrinite reflectance 0 6 ro paraffin indices stable carbon and hydrogen isotope contents pristane to nc17 ratios and diterpenoid biologic markers have been used to assess the level of maturity of the hydrocarbons in the reservoir independently of the level of maturity of the reservoir itself and of the surrounding shale units in the tertiary of the beaufort mackenzie basin naphthenic oils and condensates have been generated from terrestrially derived organic matter in source rocks juxtaposed with the reservoir at reflectance levels of 0 4 to 0 6 ro however condensates discovered in reservoirs which are th rmally immature on the labrador shelf have undergone extensive vertical migration and can be classed as conventional mature to overmature condensates hydrocarbons discovered in the lower cretaceous of the beaufort mackenzie basin and also those of the scotian shelf are more or less in place in that they are at a level of thermal alteration about equivalent to that of the reservoirs in which they are trapped the source for the early oils and condensates is considered to be resinite occurring dispersed in coal fragments the proportion of resinite liptinite and vitrinite in the organic matter of terrestrial source rocks strongly controls both the level of thermal alteration necessary for the section to function as an effective source rock and the ultimate product gas oil or condensate which will be generated

classification and thermal history of petroleum based on light hydrocarbons abstract classifications of oils and kerogens are described two indices are employed termed the heptane and isoheptane values based on analyses of gasoline range hydrocarbons the indices assess degree of paraffinicity and allow the definition of four types of oil normal mature supermature and biodegraded the values of these indices measured in sediment extracts are a function of maximum attained temperature and of kerogen type aliphatic and aromatic kerogens are definable only the extracts of sediments bearing aliphatic kerogens having a specific thermal history are identical to the normal oils which form the largest group 41 in the sample set this group was evidently generated at subsurface temperatures of the order of 138 149 c 280 300 f defined under specific conditions of burial history it is suggested that all other petroleums are transformation products of normal oils

geochemistry of petroleum systems in the eastern pearl river mouth basin evidence for mixed oils abstract detailed analyses of crude oils and source rock extracts indicate the presence of two effective petroleum source rocks in the eastern pearl river mouth basin of the south china sea region oils derived from the lacustrine source rocks in the eocene wenchang formation are characterized by abundant c 30 4 methyl steranes with relatively few c 19 tricyclic terpane and bicadinanes in contrast oils from the eocene oligocene enping formation source typically contain significant amounts of c 19 tricyclic terpane and bicadinanes with relatively few 4 methyl steranes and high pristane phytane ratios however the chemical compositions of a large number of oils do not conform to those of the unknown source rocks consistent with mixing of the two sources mixed oils occur mainly in the huizhou sag and along its south margin and the highest proportion of the enping formation source in the reservoired mixed oils is estimated to be around 80 laboratory mixing experiments using selected end member oils indicate that even with 50 80 contribution from the enping formation source the mixtures still display sterane biomarker ratio signatures diagnostic of the wenchang formation source therefore the presence of abundant 4 methyl steranes is a necessary but not sufficient indicator for the wenchang formation source in the eastern pearl river mouth basin although our results support the wenchang formation as a major source to the known oil discoveries in the study area the contribution of the enping formation source to traps in the huizhou sag and surrounding area cannot be ignored there is clear evidence for the recharge of enping formation derived oils into early biodegraded oil accumulations to form light oil accumulations

georadar anisotropy in the gotthard gneiss switzerland georadar data recorded in a crystalline gneiss of southern switzerland exhibit two effects that are related to anistropic metamorphic fabric in the first signal coherence appears to be better for waves propagating parallel to the direction of foliation and in the second rms velocities of waves propagating along the foliation are higher than for waves propagating at a high angle to foliation

lacustrine environmental evolution and implications on source rock deposition in the upper cretaceous paleocene of the south yellow sea basin offshore eastern china abstract lacustrine source rocks are well developed within the upper cretaceous paleocene in the south yellow sea basin sysb in offshore eastern china understanding the deposition of these source rocks could provide critical information for hydrocarbon exploration in the sysb as well as reveal the paleoenvironment across the cretaceous paleogene boundary in eastern china this study investigates the lacustrine environmental evolution during the upper cretaceous taizhou formation k2t to paleocene funing formation e1f within the sysb and its implications on source rock deposition based on core observation combined with organic geochemical indicators multiple maturity parameters vitrinite reflectance tmax and biomarker isomerization ratios reveal that the organic matter om has reached early oil window maturity the om of source rocks is dominated by kerogen type ii iii liptinite and vitrinite anoxic saline brackish deep to semi deep lacustrine environments prevailed during the deposition of k2t2 second member of the k2t e1f2 second member of the e1f and e1f4l lower unit of fourth member of the e1f the deposition of three intervals was influenced by marine incursion as evidenced by geochemical and paleontological results low to moderate toc contents avg 0 78 wt to 1 91 wt which corresponds to low to moderate terrestrial om input are observed through three intervals abundant freshwater together with high terrestrial om flowed into the lacustrine environments during the deposition of e1f4u upper unit of fourth member of the e1f leading to dysoxic oxic and freshwater conditions high terrestrial om input is probably the major controlling factor for relatively high toc contents avg 2 49 in the e1f4u an evolution from balanced fill to overfilled lake type is observed in the upper cretaceous paleocene of sysb consistent with an evolution from semi arid to humid paleoclimate conditions the e1f4u and e1f2 source rocks exhibit fair to good potential whereas poor to fair potential is present in the e1f4l and k2t2 source rocks compared with the paleogene source rocks in onshore eastern china the upper cretaceous paleocene source rocks in the sysb probably hold good potential for generating commercial quantity of oil although further study on hydrocarbon generation kinetics of source rocks and overall basin history are needed

the processes of melt differentiation in arc volcanic rock insights from oib type arc magmas in the central mexican volcanic belt reply to a critical comment by claus siebe 2013 lamont doherty earth observatoryat the columbia university 61 route 9w palisades ny 10964 usa centro de geociencias universidad nacional auto noma de me xico quere taro 76230 me xico institute of earth sciences academia sinica 128 academia road sec 2 nankang taipei 11529 taiwan centro nacional de prevencio n de desastres secretari a de gobernacio n av delfi n madrigal 665 col pedregal de santo domingo c p 04360 delegacio n coyoaca n me xico d f 04510 mexico isotope geosciences unit scottish universities research and reactor centre east kilbride

sulfur rich petroleum derived from lacustrine carbonate source rocks in bohai bay basin east china abstract crude oils produced from the zhanhua depression bohai bay basin are high in sulfur and differ from most lacustrine oils in this basin and elsewhere physical properties biomarker ratios and aromatic hydrocarbon assemblages reveal that they are derived from carbonate source rock horizons representative source rock samples with abundant organic matter toc 1 and s 2 5 mg hc g rock were selected for further correlation and their high bitumen contents indicated their indigenousness to saline or carbonate depositional environments the results of oil source rock correlation suggest that these sulfur rich heavy oils originate from es 3 4 carbonates and marls limited to the bonan sag maturity assessments with burial history showed that they were expelled at the early oil generation window high levels of 20s 5 14 17 and 5 14 17 steranes together with low values for the ts ts tm ratio and two methylated aromatic ratios mdr and mpi 1 were observed in these oils sulfur associated with evaporite and carbonate environments is a significant factor not only in controlling the occurrence of biomarker isomers but also for petroleum formation at abnormally low thermal stress levels

geochemistry of petroleum systems in the niuzhuang south slope of bohai bay basin part 2 evidence for significant contribution of mature source rocks to immature oils in the bamianhe field the chemical compositions of 28 representative crude oils and oil sand samples collected from the bamianhe region of the bohai bay basin eastern china were studied in detail in order to understand their genetic relationships biodegradation ranking and thermal maturity level molecular geochemical parameters indicate the presence of one single oil family in the cenozoic reservoirs a number of biomarker features support deposition of the source rocks for these oils under conditions of enhanced salinity stratified water columns the extremely low maturity levels of these immature oils as indicated by sterane isomerization ratios were not supported by other maturity parameters the genetic relationship between the oils and the es4 and es3 members of the eocene oligocene shahejie formation present in the deeper part of the niuzhuang sag but not those along the niuzhuang south slope was suggested using a wide range of molecular parameters variation in the sterane concentrations observed from potential source rocks with different maturity levels in the study area suggests a high probability of migration contamination of mature oils by immature bitumens along migration pathways or from intra reservoir shales variation in the level of oil biodegradation could also create anomalies in the use of gross oil compositions as an indicator of oil maturity although the recent rapid subsidence of the bohai bay basin and the saline depositional environment of one of the potential source rocks favor oil generation at relatively low maturity levels most of the economic oils discovered in the bamianhe region appear to have derived from conventionally mature source rocks but contain lower maturity fluids admixed with them

late quaternary secular variation data from mexican volcanoes abstract we present 32 new paleomagnetic directions and 21 absolute paleomagnetic intensities pi from 33 volcanoes sampled at 66 sites and covering the last 46 ka of these 29 were radiocarbon dated 3 by thermo luminescence and one is of historical age ad 1793 rock magnetic experiments show that the dominant minerals are magnetite and titanomagnetite of low to intermediate titanium content and of pseudo single domain size paleodirections were determined using stepwise demagnetization protocols and pi by the izzi or thellier coe protocols and strict selection criteria were applied to ensure the reliability of the data previously published data were evaluated to fulfill similar quality criteria as our data resulting in 65 directional data point 18 paleointensity entries from lavas 59 archeointensities are found to be acceptable all accepted data come from a region within an 860 km radius around mexico city paleosecular variation psv curves of the past geomagnetic full vector were established by using the bootstrap resampling algorithm combined with cubic p splines for smoothing and interpolation because of the uneven time distribution of the data this was done for two successive periods between ad 2000 1600 bc and 1600 bc 44000 bc the full vector psv curves are unique for the american continents because of their temporal extension end because they include both directions and absolute pi the recent psv curves the last 3600 years are of high resolutions which certainly have implication for both regional and global geomagnetic field models fast psv change centered around ad 700 and ad 900 separated by a period of much slower psv were observed and rapid pi changes were found around 400 bc and ad 1000 in the period between 1600 bc and 44000 bc psv curves are well defined only within some periods and otherwise only define general psv trends several intensity peaks with values up to 65 t vadm 15 1022 am2 were observed around 250 bc 12000 bc 15000 bc and 27000 bc and intensity lows around ad 700 1200 bc 24000 17000 bc and 34000 bc abnormal directions were found around 26000 bc with negative inclinations down to about 30 which may be related to the mono lake or rockall event a comparison with other psv curves is complicated by the large distance to europe and the hawaiian islands with longitude differences of 99 and 57 respectively lake sediment data from southern texas show more differences than agreements suggesting that either of the data may be affected by systematic errors

geochemical and isotopic composition of volcanic rocks of the heterogeneous miocene 23 19 ma tepoztlan formation early transmexican volcanic belt mexico abstract we present the first geochemical data major and trace elements as well as sr nd and pb isotopes on volcanic rocks from the tepoztlan formation in the central transmexican volcanic belt the tepoztlan formation is up to 800 m thick and comprises a wide range of primary volcanic rocks lavas pyroclastic density current deposits pyroclastic fall deposits and their secondary reworked products due to mass flow lahars and fluvial processes magnetostratigraphy combined with k ar and ar ar geochronology suggests an age of early miocene 23 19 ma for this formation lava flows pyroclastic rocks dykes and volcanic clasts range from basaltic andesite to rhyolite with a clear dominance of andesites and dacites all samples are subalkaline and hy normative these rocks show homogeneous ree patterns with lree enrichment and higher lile concentrations with respect to hfse notably the typical negative anomaly of nb ta and ti suggesting a subduction related magma genesis major and trace element concentrations show that either assimilation of heterogeneous continental crust or crustal recycling by subduction erosion and fractional crystallization are important processes in the evolution of the tepoztlan formation magmas isotopic compositions of the tepoztlan formation samples range from 87sr 86sr t 0 703693 to 0 704355 and 143nd 144nd t 0 512751 to 0 512882 falling within the mantle array all geochemical characteristics indicate that these rocks originated from a heterogeneous mantle modified and evolved through assimilation of country rock and fractional crystallization in the upper crust

vertical fracture detection by exploiting the polarization properties of ground penetrating radar signals vertically oriented thin fractures are not always detected by conventional single polarization reflection profiling ground penetrating radar gpr techniques we study the polarization properties of em wavefields and suggest multipolarization acquisition surveying to detect the location and azimuth of vertically oriented fractures we employ analytical solutions 3d finitedifference time domain modeling and field measurements of multipolarization gpr data to investigate em wave transmission through fractured geologic formations for surface based multipolarization gpr measurements across vertical fractures we observe a phase lead when the incident electric field component is oriented perpendicular to the plane of the fracture this observation is consistent for nonmagnetic geologic environments and allows the determination of vertical fracture location and azimuth based on the presence of a phase difference and a phase lead relationship between varying polarization gpr data

examples of reverse time migration of single channel ground penetrating radar profiles a single channel ground penetrating radar gpr profile portrays a distorted unfocused image of subsurface structure due to apparent position shifts associated with dipping reflectors and to diffractions from corners and edges a focused image may be produced from such data by using any of the migration algorithms previously developed for seismic data we use reverse time migration based on the scalar wave equation field work was performed over a simple stratigraphic soil sequence and a complicated fluvial environment in the migrated images reflector continuity is enhanced and the level of detail available for high resolution interpretation is significantly increased

ground penetrating radar of northern lacustrine deltas ground penetrating radar gpr was used in several selected deltaic sedimentary environments to better understand subsurface stratigraphy and reconstruct former depositional environments the profiles provide high resolution continuous subsurface data on facies thickness and depths orientation of major sedimentary structures postdepositional failure planes and depth of peat deposits field experiments were carried out on six river deltas records from four of the deltas exhibit sedimentary facies a record from one delta shows a possible slump and records from another delta reveal the thickness and stratigraphic relationships of peat deposits the delta types are i sandy wave influenced ii sandy immature wave influenced steeper middle and lower shoreface iii sandy braided and iv gravelly fan foreset in areas of limited subsurface control stratigraphic logs from drill core cutbank exposure or geophysical logs radar profiles can provide big picture perspectives of the subsurface

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

maturation sequence of continental crude oils in hydrocarbon basins in china and its significance abstract the continental hydrocarbon containing basins in china not only ubiquitously possess immature marginal mature oils as defined by c 29 sterane ratios but a complete oil maturation sequence can also exist the present paper studies the characteristics of immature oils their formation and distribution the study revealed that immature oils were not thermal degradation products of kerogen since the vitrinite reflectance r o of source rocks is between 0 4 and 0 6 the immature oils are derived from the soluble in organic solvent organic matter generated during low temperature hydrocarbon generation at the late stage of diagenesis the immature oils in china belong to paraffin base oils which originated from aquatic or terrestrial lipids but not resins the maturation sequence of oils is composed of immature low mature and high mature members corresponding to the different levels of hydrocarbon generation the recognition of this evolution sequence has proved to be of practical significance when we understand the amounts of oil reservoirs of different maturation the exploration direction can be guided by the corresponding resource volume comparison taking the qaidam basin as a good example most of the oils discovered recently are low mature but there are good prospects of finding mature and high mature oils

revisiting the age of the jumento volcano chichinautzin volcanic field central mexico using in situ produced cosmogenic 10be abstract previous studies on jumento volcano based on radiocarbon dating and comparative morphometric analysis suggest that it could be the youngest volcano of the sierra chichinautzin here we establish a new chronology of the emplacement of the late holocene lava flows of jumento volcano using in situ produced 10be cosmic ray exposure cre dating of quartz xenocrysts to test this hypothesis depending on the choice of the cosmogenic nuclide production parameters in the exposure age calculators used the mean 10be cre ages ranges between 1 86 0 68 ka and 2 41 0 97 ka for the inner lava flow and between 1 90 0 29 ka and 2 49 0 41 ka for the breakout lava flow these preliminary mean 10be cre ages confirm that the jumento volcano is one of the youngest volcanoes of the sierra chichinautzin although slightly older than the xitle volcano this first 10be eruption chronology of the sierra chichinautzin shows that 10be cre dating represents an alternative approach to date volcanic rocks not only for the sierra chichinautzin but also for other volcanic fields especially when no charcoal or paleosoils are available for radiocarbon dating furthermore it suggests that in situ produced cosmogenic nuclide dating has considerable potential to throw light on the volcanic history and eruption recurrence of this volcanic field in order to provide enough data for the mitigation of the hazards and related risks in mexico city the city of cuernavaca and the small towns around the volcanic field

geomorphology of the post caldera monogenetic volcanoes at deception island antarctica implications for landform recognition and volcanic hazard assessment abstract deception island is one of the most active volcanoes in antarctica with more than 20 monogenetic eruptions during the holocene the latest episodes of 1967 1969 and 1970 have shown that volcanic activity on deception island can become a concern for tourists scientists and military personnel working on or near the island the objective of this work is to identify eruptive processes and the geomorphic evolution of post caldera monogenetic volcanic edifices at deception island by morphometric analyses supported by field observations morphometric analysis has been used since the 1970s to analyse scoria cones but it has rarely been applied to other monogenetic volcanoes such as tuff cones and tuff rings tuff cones and tuff rings represent the most common landforms during deception island s recent geological past with over 70 scattered eruptive vents inside and along the caldera rim these volcanic landforms have been studied based on field observations and later digital elevation model analyses their geometry ranges from 10 to 100 m in height and diameters vary between 300 and 2500 m the morphometric data suggest that tuff cones have a more circular crater than tuff rings with a significant separation between the two landforms using the height hco and basal width wco parameters tuff cones have hco wco ratios with values between 0 04 and 0 16 and outer slopes between 7 and 34 tuff rings have lower hco wco ratios that are between 0 01 and 0 04 and lower outer slopes between 3 and 21 this study shows that basic shape parameters in combination with slope angle analysis can be used to discriminate among different types of monogenetic volcanoes the initial eruptive related morphometric diversity however prevents correlation of eruption ages with morphometric parameters or constructing a relative chronology of the monogenetic eruptions this work provides a better comprehension of the potential evolution of a future eruption and a broader understanding of volcanic hazards on deception island

quaternary volcanism near the valley of mexico implications for subduction zone magmatism and the effects of crustal thickness variations on primitive magma compositions the valley of mexico and surrounding regions of mexico and morelos states in central mexico contain more than 250 quaternary eruptive vents in addition to the large composite volcanoes of popocatepetl iztaccihuatl and nevado de toluca the eruptive vents include cinder and lava cones shield volcanoes and isolated andesitic and dacitic lava flows and are most numerous in the sierra chichinautzin that forms the southern terminus of the valley of mexico the chichinautzin volcanic field cvf is part of the e w trending mexican volcanic belt mvb a subduction related volcanic arc that extends across mexico the crustal thickness beneath the cvf 50 km is the greatest of any region in the mvb and one of the greatest found in any arc worldwide lavas and scoriae erupted from vents in the cvf include alkaline basalts and calc alkaline basaltic andesites andesites and dacites both alkaline and calc alkaline groups contain primitive varieties that have whole rock mg mgo and ni contents and liquidus olivine compositions fo90 that are close to those expected of partial melts from mantle peridotite primitive varieties also show a wide range of incompatible trace element abundances e g ba 210 1080 ppm ce 25 100 ppm zr 130 280 ppm data for primitive calc alkaline rocks from both the cvf and other regions of the mvb to the west are consistent with magma generation in an underlying mantle wedge that is depleted in ti zr and nb and enriched in large ion lithophile k ba rb and light rare earth la ce elements extents of partial melting estimated from ti and zr data are lower for primitive calc alkaline magmas in the cvf than for those from the regions of the mvb to the west where the crust is thinner the distinctive major element compositions low cao and al2o3 high sio2 of the primitive calc alkaline magmas in the cvf indicate a more refractory mantle source beneath this region of thick crust in contrast primitive alkaline magmas from the cvf and other regions of the mvb show compositional similarities to intraplate type alkali basalts erupted behind the arc in the mexican basin and range province these similarities are consistent with the hypothesis that slab induced convection in the mantle wedge beneath the mvb causes advection of asthenospheric mantle from behind the arc to the region of magma generation trace element systematics of primitive magmas in the mvb reveal substantial variability in both the extent of mantle wedge enrichment by subduction processes and in the composition of mantle heterogeneities that are related to previous extraction of alkaline to sub alkaline basaltic melts

monogenetic volcanism personal views and discussion monogenetic volcanism produces small volume volcanoes with a wide range of eruptive styles lithological features and geomorphic architectures they are classified as spatter cones scoria or cinder cones tuff rings maars maar diatremes and tuff cones based on the magma water ratio dominant eruption styles and their typical surface morphotypes the common interplay between internal such as the physical chemical characteristics of magma and external parameters such as groundwater flow substrate characteristics or topography plays an important role in creating small volume volcanoes with diverse architectures which can give the impression of complexity and of similarities to large volume polygenetic volcanoes in spite of this volcanic facies complexity we defend the term monogenetic volcano and highlight the term s value especially to express volcano morphotypes this study defines a monogenetic volcano a volcanic edifice with a small cumulative volume typically 1 km3 that has been built up by one continuous or many discontinuous small eruptions fed from one or multiple magma batches this definition provides a reasonable explanation of the recently recognized chemical diversities of this type of volcanism

late pleistocene flank collapse of zempoala volcano central mexico and the role of fault reactivation abstract zempoala is an extinct pleistocene 0 7 0 8 ma stratovolcano that together with la corona volcano 0 9 ma forms the southern end of the sierra de las cruces volcanic range central mexico the volcano consists of andesitic and dacitic lava flows and domes as well as pyroclastic and epiclastic sequences and has had a complex history with several flank collapses one of these collapses occurred during the late pleistocene on the s se flank of the volcano and produced the zempoala debris avalanche deposit this collapse could have been triggered by the reactivation of two normal fault systems e w and ne sw although magmatic activity cannot be absolutely excluded the debris avalanche traveled 60 km to the south covers an area of 600 km 2 and has a total volume of 6 km 3 with a calculated heim coefficient h l of 0 03 based on the textural characteristics of the deposit we recognized three zones proximal axial and lateral distal zone the proximal zone consists of debris avalanche blocks that develop a hummocky topography the axial zone corresponds with the main debris avalanche deposit made of large clasts set in a sandy matrix which transformed to a debris flow in the lateral distal portion the deposit is heterolithologic in composition with dacitic and andesitic fragments from the old edifice that decrease in volume as bulking of exotic clasts from the substratum increase several cities cuernavaca jojutla de juarez alpuyeca with associated industrial agricultural and tourism activities have been built on the deposit which pose in evidence the possible impact in case of a new event with such characteristics since the area is still tectonically active

reconstruction of the volcanic history of the tacambaro puruaran area michoacan mexico reveals high frequency of holocene monogenetic eruptions the 690 km2 tacambaro puruaran area located at the arc front part of the michoacan guanajuato volcanic field in the trans mexican volcanic belt tmvb records a protracted history of volcanism that culminated with intense monogenetic activity in the holocene geologic mapping 40ar 39ar and 14c radiometric dating and whole rock chemical analyses of volcanic products provide insights to that history eocene volcanics 55 40 ma exposed at uplifted blocks are related to a magmatic arc that preceded the tmvb early tmvb products are represented by poorly exposed pliocene silicic domes 5 2 ma quaternary 30 km may be related to high rates of magma production at depth and a favorable tectonic setting

interaction of ascending magma with pre existing crustal fractures in monogenetic basaltic volcanism an experimental approach 1 magma transport through dikes is a major component of the development of monogenetic volcanic fields these volcanic fields are characterized by numerous volcanic centers each typically resulting from a single eruption therefore magma must be transported from source to surface at different places which raises the question of the relative importance of 1 the self propagation of magma through pristine rock and 2 the control exerted by pre existing fractures to address this issue we have carried out a series of analogue experiments to constrain the interaction of a propagating dike through a medium with pre existing fractures the experiments involved the injection of air into an elastic gelatin solid which was previously cut into its upper part to simulate pre existing fractures the volume of the dikes their distance from the fractures and the ambient stress field were systematically varied to assess their influence on potential dike fracture interactions the results show that distance and angle between dikes and fractures influence these interactions and the dike trajectory dike geometry and dynamics are also affected by both the presence of the fractures and the dike volume dikes propagating in between fractures tend to decelerate in nature interactions are expected for dikes and fractures separated by less than about 200m and dikes with a volume less than about 10 2 km 3 would experience a velocity decrease these results highlight the influence of pre existing fractures on the mechanics and dynamics of dikes these heterogeneities must be considered when studying the transport of magmas within the crust

a quaternary monogenetic volcanic field in the xalapa region eastern trans mexican volcanic belt geology distribution and morphology of the volcanic vents abstract the most abundant volcanic manifestations along the east west trending trans mexican volcanic belt tmvb are the scoria cones these have been grouped by other authors in extended monogenetic volcanic fields such as michoacan guanajuato chichinautzin apan and los tuxtlas here we present geological and morphological data of a relatively unknown group of monogenetic volcanoes located on the east flank of the cofre de perote volcano cp around the city of xalapa in the state of veracruz mexico within an area of about 2400 km2 the xalapa monogenetic volcanic field xmvf contains over 50 late quaternary volcanoes most of them are scoria cones but small shield volcanoes and tuff rings also occur the lava flows produced by these volcanoes are constrained by an abrupt topography and cover a great percentage of the surface on the eastern and northeastern flanks of cp between 3000 and 500 m a s l the representative rocks of the different volcanic centers include olivine basalt basaltic andesite with phenocrysts of plagioclase pyroxene and minor olivine and andesite with phenocrysts of plagioclase and pyroxene sio2 and al2o3 contents of the rocks vary between 45 and 62 wt and 15 to 18 wt respectively most of the basaltic rocks have mgo contents between 4 2 and 9 wt ni and cr concentrations between 23 and 180 and 10 to 380 ppm respectively with a typical calc alkaline behavior trace elements suggest two types of magmas the most abundant are characterized by an enrichment of lile and lree with negative anomalies of nb and ti which denote a calc alkaline affinity others are lile depleted and show high concentrations of mgo cr and ni which is typical of primary calc alkaline magmas the mean scoria cone morphological values are cone height hco 90 8 m cone diameter wco 686 38 m crater diameter wcr 208 49 m and 0 12 km3 for the cone volume we dated twelve different scoria cones using the 40ar 39ar method for the other cones we used morphologic indicators such as the ratio of the scoria cone height to basal diameter hco wco and maximum slope angle additionally vegetation type and cone and lava flow morphologies were also considered in order to determine rough relative ages in general the ages fall into three groups those older than 2 0 ma those between 0 25 0 40 ma and those less than approximately 0 1 ma

mammoth bones embedded in a late pleistocene lahar from popocatepetl volcano near tocuila central mexico the accidental discovery in july 1996 of the tocuila mammoth site in the eastern valley of mexico was followed by intensive scientific excavation which yielded remains of at least seven individuals of mammuthus columbi in an area measuring only 28 m 2 the high density of mostly disarticulated mammoth bones identified 3 m below the surface in a massive 130 cm thick lahar deposit of sandy ash and rounded pumice fragments is unusual and suggests a high energy depositional environment samples of charcoal found within this deposit yielded radiocarbon ages ranging between 10 220 75 and 12 615 95 yr b p the lahar was studied in greater detail in order to establish its provenance determination of grain size distribution and magnetic properties of the deposit as well as petrographical mineralogical and geochemical analyses of pumice clasts all indicate that the lahar was derived from volcanic fallout deposits that originated at popocatepetl volcano located 50 km south southeast of the site popocatepetl underwent a major phreato plinian eruption dated ca 14 000 yr b p at the end of the last major glaciation dispersal of the fallout was mostly toward the northwest and north deposits were found on the slopes of tlaloc mountain 4150 m 20 km southeast of tocuila at the beginning of deglaciation and the onset of more humid conditions 3000 yr later lahars derived from the fallout deposits picked up the bones of already dead animals and then deposited them on the shores of lake texcoco and or simply covered bones without major displacement

the eruptive history of the patzcuaro lake area in the michoacan guanajuato volcanic field central mexico field mapping c 14 and 40ar 39ar geochronology abstract monogenetic volcanic fields occur in many tectonic settings representing an unpredictable and uncertain volcanic hazard the patzcuaro lake is located in the central part of the michoacan guanajuato volcanic field mgvf field mapping of an area of 560 km2 stratigraphy and new radiometric ages 40ar 39ar and 14c aided in the identification of 45 individual volcanic landforms formed during the past 3 9 ma these landforms comprise five medium size shield volcanoes 25 scoria cones 10 lava domes two lavas associated to scoria cones one fissural lava flow and two volcanic complexes these volcanic edifices erupted a minimum volume of 20 km3 since pliocene with an output rate of 0 02 km3 ka chemical composition of magmas ranges from 47 6 to 65 3 wt silica being dominantly andesites 76 vol followed by basaltic andesites 12 vol dacites 9 vol and basalts 3 vol volcanic products vary from mainly andesitic during the pliocene basaltic to dacitic during the pleistocene and basaltic andesitic to andesitic during the holocene all these rocks are the result of low dipping slab subduction related magmatism alignment of cones and structures follow ne sw n s and e w directions the youngest faults are associated with the e w morelia acambay fault system with historic earthquake activity the volcanic complexes el estribo and la muela have cone collapses to the north that correspond with the direction of maximum regional extension associated with the e w fault system the 3 9 ma history of monogenetic volcanism around the patzcuaro lake demonstrates that monogenic fields can be long lived volcanic features

geology and radiocarbon ages of tlaloc tlacotenco cuauhtzin hijo del cuauhtzin teuhtli and ocusacayo monogenetic volcanoes in the central part of the sierra chichinautzin mexico tlaloc tlacotenco cuauhtzin hijo del cuauhtzin teuhtli and ocusacayo monogenetic volcanoes located within the sierra del chichinautzin volcanic field scvf at the southern margin of mexico city were studied to further refine attendant volcanic hazards in this heavily populated region based on fieldwork and landsat imagery interpretation a geologic map was produced morphometric parameters characterizing the cones and lava flows were determined and the areal extent and volumes of erupted products were estimated the longest lava flow was produced by tlacotenco and reached 9 5 km from its source total areas covered by lava flows from each eruption range between 12 8 km2 tlacotenco and 54 4 km2 tlaloc and total erupted volumes range between 0 26 and 1 36 km3 per volcano radiocarbon measurements of a paleosol underneath an ash layer from the tlaloc scoria cone yielded an age of 6200 years bp while charcoal found within block and ash flow and lahar deposits from cuauhtzin dome yielded ages of 7360 and 8225 years bp respectively the tlacotenco dacite lava flow overlies popocatepetl s tutti frutti plinian pumice fall deposit dated at 14 000 years bp and is therefore younger than this prominent stratigraphic marker on the other hand teuhtli and hijo del cuauhtzin scoria cones and the ocusacayo andesite lava flows are overlain by the tutti frutti and therefore older than 14 000 years bp these new dates together with other published dates for scoria cones in the scvf imply that the previously determined recurrence interval during the holocene for monogenetic eruptions in the scvf of 1700 years siebe c rodriguez lara v schaaf p abrams m 2004a radiocarbon ages of holocene pelado guespalapa and chichinautzin scoria cones south of mexico city implications for archaeology and future hazards bull volcanol 66 203 225 needs to be corrected to 1250 years this means that the time of quiescence since the last eruption of the scvf 1670 years bp exceeds that of the estimated recurrence interval during the holocene

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

the 2000 yr bp jumento volcano one of the youngest edifices of the chichinautzin volcanic field central mexico abstract the chichinautzin volcanic field is situated at the southern limit of the basin of mexico and the metropolitan area of mexico city the third most populated city around the world the chichinautzin volcanic field holds more than 220 monogenetic volcanoes xitle is the youngest of these with an estimated age of 1 6 ky bp xitle s eruptive activity took place during the mesoamerican mexican pre classic period and is related to the destruction of cuicuilco archaeological site the oldest civilization known in central mexico however there are still several regional cones that have not been dated based on 14 c ages stratigraphic and geomorphologic criteria we conclude that the jumento volcano located to the west of xitle is one of the youngest cones of the chichinautzin volcanic field the jumento volcano has a basaltic andesite composition and its eruptive activity was initially hydromagmatic followed by strombolian and finally effusive events occurred recorded through 1 a sequence of hydromagmatic pyroclastic surges and ashfall layers emplaced at a radius of 5 km from the crater with charcoal fragments at its base this activity built the jumento s cone with slopes of 32 and 2 lava flows that breached the southern part of the cone and flowed for up to 2 5 km from the vent the resulting 14 c ages for this volcano yielded a maximum age of 2 ky bp morphometric analysis indicates that the state of degradation of jumento cone is similar to the xitle suggesting that the jumento could be in the state of degradation of a volcanic structure of similar age or younger adding credence to the probable radiocarbon age of 2 ky bp for the jumento edifice

combining historical and 14 c data to assess pyroclastic density current hazards in banos city near tungurahua volcano ecuador pyroclastic density currents pdcs from tungurahua volcano ecuador recurrently rush down the northern vazcun valley and threaten the small tourist city of banos located on its mouth estimating pdc hazards i e pdc return rate and extent is difficult in banos and vazcun because data from the literature are rare and debated while geological exposures are few and vegetated to improve our awareness of pdc hazards in the banos area we examined historical documents conducted new geological research in the vazcun valley and obtained additional 14c data we highlight complex radiocarbon results that may lead to difficulties when interpreting the pdc chronology and offer recommendations to improve sampling strategies for 14c age determinations of pdc deposits overall our results show that the 1640 1773 and 1886 pdc forming eruptions are recorded in the valley while products of the 1918 and 2006 events were likely removed through considering recorded unrecorded bias in the reconstruction of past pdc emplacement in vazcun we calculate a minimal average return rate of 18 pdc forming events for pre columbian and historical eruptions since the devastating 3 ka bp eruption which translates into a maximum average return rate of 150 200 years in the valley however the archives suggest that most pdcs did not affected the now urbanized banos area e g 1918 2006 and we estimate that the city is impacted on average every 350 500 years a duration that is likely perceived as fairly long for people living in the area the banos case study thus raises questions on how to communicate on uncertain threats and impacts and how to improve alert messages in a town where economic incomes are essentially based on tourist activities to better address these issues we plan in future works to focus on cognitive perception of risk and volcanic hazard judgment by populations of banos and nearby rural communities

late holocene stratigraphy of the tetimpa archaeological sites northeast flank of popocatepetl volcano central mexico late holocene 2500 yr b p tephras bury a sequence of pre hispanic archaeological sites in the tetimpa area on the northeast flank of popocatepetl volcano from measured stratigraphic sections 14c dates and isopach maps this paper reconstructs the eruptive chronology and the regional extent of deposits associated with the tetimpa archaeological sites a regionally extensive paleosol defines the base of the late holocene sequence in the tetimpa area deposits from two periods of explosive volcanism unconformably overlie this paleosol eruptive sequence i was deposited at ca 2100 yr b p and blanketed late tetimpa archaeological sites with 1 1 5 m of yellow andesitic 62 sio2 pumice and locally with 20 40 m of olivine bearing andesitic lavas isopach and isopleth maps of the pumice deposit suggest a plinian style eruption event that covered 240 km2 on the east side of the volcano with 25 cm of tephra lavas from eruptive sequence i dammed drainage in the lowland area near the town of san nicolas and caused local upstream deposition of as much as 30 m of lacustrine silts clays and sands these lacustrine deposits record an eruptive hiatus for the tetimpa area of about 750 14c yr between ca 2100 and ca 1350 yr b p no major tephras were deposited in the tetimpa area in upland areas this time period is represented by an unconformity and by entisols formed in the top of pumice deposits and lavas from eruptive sequence i artifacts agricultural furrows and dwellings record human reoccupation of this surface at the end of this hiatus several lahars were deposited above the lacustrine sequence and locally above the entisol in upland positions adjacent to streams between ca 1350 and ca 1200 yr b p tephras from eruptive sequence ii buried these paleosols occupation sites lacustrine sediments and lahars andesitic 62 sio2 pumice lapilli deposits in the tetimpa area record three pumice fall eruptions directed northeast and east of the crater the first and smallest of these maximum tetimpa area thickness 12 cm 52 km2 covered by 25 cm took place at ca 1350 yr b p and was accompanied by pyroclastic surge events preserved in the tetimpa area by charcoal sand waves and cross stratified sand sized tephra at ca 1200 yr b p the products of two plinian style events and additional pyroclastic surges reached the tetimpa area the largest of these tephra fall events covered the tetimpa area with 0 5 1 m of tephra and blanketed an area of 230 km2 with a thickness of 25 cm the tetimpa record confirms two of the four periods of explosive volcanism recognized by studies conducted around popocatepetl in the past 30 yr eruptive sequence i corresponds to the explosive period between 2100 and 2500 yr b p and eruptive sequence ii corresponds to the period between 900 and 1400 yr b p the archaeology and lacustrine stratigraphy of the tetimpa area help constrain the timing of the plinian phase of eruptive sequence i to ca 2100 yr b p and suggest that the pumice fall eruptions of eruptive sequence ii took place in at least two intervals between ca 1350 and ca 1200 yr b p

long lived shield volcanism within a monogenetic basaltic field the conundrum of rangitoto volcano new zealand drilling through the edifice of rangitoto the youngest and largest volcano in the monogenetic auckland volcanic field reveals the multistage eruptive and magmatic history of a small basalt shield volcano activity commenced calendar year cal 6000 cal yr b p involving minor effusive and pyroclastic volcanism until 650 cal yr b p this period either represents an early less productive phase of a single polygenetic volcano or alternatively rangitoto is better described as a volcanic complex that includes one or more buried edifices concealed by the main structure a voluminous shield building phase occurred 650 550 cal yr b p erupting isotopically uniform subalkalic basalts mg 60 64 four batches of magma distinguished by trace element chemistry were erupted sequentially but they lack genetic connection via fractional crystallization or assimilation two of the magma batches display linear trends of decreasing incompatible trace element abundance and increasing ratios of moderately incompatible to highly incompatible elements with decreasing age this is consistent with cycles of progressive partial melting at the source the final phase of activity ca 550 500 cal yr b p was explosive and less voluminous producing scoria cones at the summit this phase involved more diversity in magma compositions including more mafic subalkalic basalt and alkali basalt pointing to sourcing of magmas simultaneously from different depths in the mantle rangitoto volcano contributes to a growing body of evidence showing that major periods of volcanism in monogenetic basalt fields occur at centers that have experienced multiple eruption episodes changes in magma composition accompany changes in eruption style but a lack of an obvious shared pattern in magmatic evolution at various volcanoes points to the localized mantle heterogeneity and conduit systems hazard scenarios for regions traditionally classified as monogenetic need to encompass the possibility of prolonged episodes of activity and reawakening of volcanoes a significant implication where infrastructure is built on such regions

mountain of sustenance mountain of destruction the prehispanic experience with popocatepetl volcano abstract twelve seasons of work have documented two temporally distinct sets of prehispanic houses and agricultural fields buried by pumiceous airfall deposits at tetimpa on the northeastern flank of volcan popocatepetl in the state of puebla mexico archaeological survey and excavation in addition to stratigraphic volcanologic and geomorphic field methods and radiocarbon dating have been used to gather information on two major volcanic eruptions that devastated prehispanic settlements and rendered this region uninhabitable for generations first about 2000 years bp and then again between ad 700 and 900 impacts of these eruptions were probably responsible for many of the population shifts evident in the archaeological record during these centuries available geological data are interwoven with the historical and archaeological records to summarize and explain the most significant findings of this research

ichnology and sedimentology of the trace fossil bearing fluvial red beds from the lowermost member of the paleocene funing formation in the jinhu depression subei basin east china abstract the lowermost member of the paleocene funing formation which is composed of bioturbated fluvial red beds is extensively distributed throughout the jinhu depression subei basin east china despite its economic value as one of the most important oil bearing reservoirs in the subei basin the sedimentology ichnology and paleoenvironment of this formation in the jinhu depression remain poorly understood in this work we investigated the ichnofossils and sedimentary facies analyzed the ichnofacies and potential tracemakers and reconstructed the paleoenvironment of the jinhu depression based on cores from the lowermost member of the paleocene funing formation this formation contains a moderately diverse ichnofauna 9 ichnotaxa of the scoyenia ichnofacies that includes meniscate burrows taenidium barretti taenidium satanassi and beaconites coronus simple horizontal cylindrical burrows palaeophycus tubularis palaeophycus heberti and planolites isp simple vertical or subvertical burrows skolithos linearis and skolithos isp and plant root traces the other complex branched and chambered burrows are left in open nomenclature these ichnofossils are widespread throughout the three facies associations identified in this study 1 ephemeral fluvial channel 2 crevasse splay and 3 distal floodplain facies associations multiple lines of sedimentological and ichnological evidence namely the predominance of massive and upper flow regime structures the occurrence of invertebrate burrows e g skolithos and taenidium in the lower and middle parts of the channel deposits and the dramatic changes in the color and mottling in channel and overbank sediments indicate that the river discharge was short lived and that the water table was highly variable the variations in the discharge and water level are attributed to the influence of seasonal rainfall the cyclic nature of intense rainfall events and dry periods suggests that the subei basin was likely located in a semiarid region with a seasonal rainfall pattern during the early paleocene this study also reveals that the ephemeral fluvial channel is the facies association with the highest potential to yield oil bearing reservoirs in the paleocene red beds of the jinhu depression additionally the influence of bioturbation on the reservoir quality in this region should be considered in future research

eruption recurrence rates in a basaltic volcanic field based on tephra layers in maar sediments implications for hazards in the auckland volcanic field long term eruption recurrence rates in monogenetic basaltic volcanic fields are difficult to assess because of low eruption frequencies but they are important because of the spread of human infrastructure into such fields auckland city new zealand is built on the auckland volcanic field a young 250 ka basaltic volcanic field in the absence of abundant material for radiocarbon and isotopic dating an eruptive chronology based on basalt tephra layers deposited in maar lakes was developed interbedded well dated tephra layers from silicic volcanoes some 220 270 km to the south were used as age constraints the basalt tephra layers reveal a pattern of activity not evident from the temporal spatial distribution of volcanic landforms twenty four basalt tephra layers over the last 80 k y represent an average frequency of one per 3 5 k y recurrence times vary from 0 5 k y to 20 k y and show no temporal trend the tephra record shows a major flare up in explosive activity at 32 2 ka during heightened activity at 34 24 ka this was related to a period of simultaneous eruptions from several volcanoes across the field revealed by paleomagnetic and isotopic ages in contrast the field has been relative quiet during the last 20 k y punctuated by the construction of a shield volcano at 0 7 ka thus the surface manifestation of magmatism varies greatly with time complicating long term volcanic hazard forecasting despite the high risk from future basalt activity because of proximity ash fall from distant andesite volcanoes is the most frequently occurring volcanic hazard in auckland city

spatial distribution and alignments of volcanic centers clues to the formation of monogenetic volcanic fields monogenetic basaltic volcanic fields occur worldwide in tectonic environments ranging from extensional to convergent understanding similarities and differences between these fields may help to characterize key controls on their generation such volcanic fields consist of numerous volcanic centers each of which represents a pathway of magma from its source to the surface we analyzed the spatial distribution of volcanic centers in 37 monogenetic volcanic fields and assuming that the distribution of volcanic centers relative to each other is matched by a similar source pattern within the mantle applied the following methods for each 1 the poisson nearest neighbor pnn analysis representing the degree to which the distribution of the volcanic centers departs from a predicted poisson distribution and 2 a volcanic alignment analysis to ascertain the preferential pathways if any used by the magma to reach the surface this is the first comprehensive global comparison of such analyses magma pathways within the brittle upper crust are influenced to various degrees by two end member situations 1 formation of new extension fractures perpendicular to the least compressive stress 3 and 2 re activation of pre existing fractures that are near parallel to the maximum principal stress 1 the results of the pnn analysis show that independently of the tectonic environment most volcanic fields display a clustered distribution of their volcanic centers alignment analysis shows that either the ambient tectonic environment exerts a strong influence on the preferential orientations of the volcanic alignments or that it is in competition with other factors e g pre existing structures local stress changes due to older intrusions overall these results indicate that the propagation of the magma and therefore the spatial distribution of the volcanic centers within volcanic fields is the product of an interplay between deep level influences i e nature of the magma source and shallow level influences i e stress field pre existing crustal structures of the lithosphere

soil organic carbon stocks and forest productivity in volcanic ash soils of different age 1835 30 500 years b p in mexico abstract volcanic soils have a large potential for organic carbon storage and for forest growth in particular under moist temperate climate documenting both potentials may offer incentives for forest conservation and exploitation and for the allocation of bonds for environmental services we studied sites on lava flows of different ages 1835 4200 6200 8000 10 000 and 30 500 years b p covered by volcanic ashes within the sierra del chichinautzin volcanic field under pine or fir forest we analyzed the accumulation of organic carbon in the soils and its relation with the evolution of site quality forest productivity indicators and c storage in tree biomass we also studied the relation between soil c accumulation and different soil properties as soil ph clay contents and pyrophosphate extractable al and oxalate extractable al and si contents results show that carbon accumulation in the soil increases linearly with age within 1835 and 10 000 years old sites with a mean accumulation rate of 4 33 kg m 2 each 1000 years however between 10 000 and 30 500 years the amount of c stored decreases again by about 30 of the maximum soil c accumulation during the first 8000 years of the chronosequence site quality improves with soil development tree growth indexes approach stabilization at sites of ages between 10 000 and 30 500 years adult pine trees reach an accumulation of 27 kg c per tree each year during the first 10 000 years carbon accumulation in mineral surface horizons is associated with the formation of al bearing organo mineral complexes characterized by pyrophosphate extractions which seem to compete with the neoformation of short range order clay minerals as clay and al oxide formation progresses these soil variables contribute also to stabilize soil c although they are by far not as efficient as the organo mineral complexes

correlation of basaltic tephra from mt wellington volcano implications for the penultimate eruption from the auckland volcanic field abstract mt wellington volcano in the auckland volcanic field is a basaltic complex comprising several vents tuff rings cones and lava flows interstitial glass in shard and lapilli groundmass displays considerable variability 41 48 wt sio 2 anhydrous but within sample variation is relatively narrow mostly 2 allowing two broad compositional affinities to be recognised that relate to the eruptive sequence the tuff ring contains lower sio 2 glasses whereas the main cinder cone comprises higher sio 2 glasses fe ti oxides also display a moderate compositional range ulvospinel usp 40 55 although within sample variation is generally narrower 5 usp allowing tuff ring deposits usp 50 compositional outliers are evident amongst the fe ti oxide crystals in many samples and probably result from slow post depositional cooling and or variable oxidation conditions during syn eruption recycling at the vent although abundant microlites restrict the deposits that can be geochemically fingerprinted randomly selected analyses of glass shards show only limited variation within samples 1 wt sio 2 suggesting that variable microlite formation had little effect on the residue melt the larger compositional differences such as that between the tuff ring and cinder cone also do not appear to be related to microlite formation because both deposits display a similar range in microlite content correlations between the edifice and distal deposits in maar sediments provide insights to the eruption episode they demonstrate that the main cinder cone was a late stage event there was no significant hiatus months to decades within the entire sequence and that the cinder cone was responsible for the wide dispersal of ejecta in the region by placing the mt wellington event within a stratigraphic framework of well dated tephra from other volcanoes it is possible to evaluate radiocarbon chronologies and constrain the eruption age to 10 000 bp

bakken madison petroleum systems in the canadian williston basin part 3 geochemical evidence for significant bakken derived oils in madison group reservoirs there have been two different definitions of the upper devonian mississippian bakken madison petroleum systems in the canadian williston basin early studies proposed the bakken shales as the source for oils in both the bakken formation and madison group reservoirs more recent studies suggested two separate sources for these oils thus the bakken oils were interpreted to be derived from the bakken formation shales and the madison group oils from a carbonate source within the madison group the present study utilized quantitative results of molecular markers across gasoline range light hydrocarbons saturated and aromatic hydrocarbon fractions in 122 oil samples to re evaluate the oil oil and oil source relationships the steroid and hopanoid parameters collected in this study have confirmed the diagnostic features for end member bakken and lodgepole sources whereas a range of other molecular markers revealed compositional continuums occurring between the two oil families the recognition of more extensive mixing of bakken derived oils in madison group reservoirs along a sw ne trending fault fracture zone in southeastern saskatchewan indicates focused migration pathways for bakken oils and thus upward resource potentials the results also suggest caution with the use of conventional biomarker data in oil oil and oil source correlation when the different sources concerned contain biomarkers in drastically different concentrations

tectonics and volcanism of sierra chichinautzin extension at the front of the central trans mexican volcanic belt abstract because of its recent activity and position at the southern magmatic front of the trans mexican volcanic belt tmvb the sierra chichinautzin volcanic field scn is a key area for the understanding of this controversial volcanic province volcanic activity has built more than 220 monogenetic volcanoes shields scoria cones thick lava flows and hydromagmatic structures during the last 40 000 years for a total volume of about 470 km 3 the scn basalts are geochemically similar to oibs while the intermediate and felsic volcanic rocks show a calc alkaline trend and abundant evidence for magma mixing the structural analysis of this volcanic field and surrounding areas has been based on field data satellite images and a method for detecting volcanic center alignments the tectonic data together with geophysical evidence confirm active general n s extensional conditions with a strike slip component for the scn area the same structural setting that prevails in the rest of the central tmvb extensional tectonics a negative regional bouger gravity anomaly a low velocity mantle high heat flow and shallow seismicity suggest a rift type setting involving the upwelling of anomalous mantle beneath the central tmvb the combined petrological structural and geophysical arguments support that the scn volcanism is rift related and rule out processes involving the subduction of the cocos plate which casts further doubts on the standard subduction model for the tmvb volcanism