evaluation of kinetic uncertainty in numerical models of petroleum generation oil prone marine petroleum source rocks contain type i or type ii kerogen having rock eval pyrolysis hydrogen indices greater than 600 or 300 600 mg hydrocarbon g total organic carbon hi mg hc g toc respectively samples from 29 marine source rocks worldwide that contain mainly type ii kerogen hi 230 786 mg hc g toc were subjected to open system programmed pyrolysis to determine the activation energy distributions for petroleum generation assuming a burial heating rate of 1c m y for each measured activation energy distribution the calculated average temperature for 50 fractional conversion of the kerogen in the samples to petroleum is approximately 136 7c but the range spans about 30c 121 151c fifty two outcrop samples of thermally immature jurassic oxford clay formation were collected from five locations in the united kingdom to determine the variations of kinetic response for one source rock unit the samples contain mainly type i or type ii kerogens hi 230 774 mg hc g toc at a heating rate of 1c m y the calculated temperatures for 50 fractional conversion of the oxford clay kerogens to petroleum differ by as much as 23c 127 150c the data indicate that kerogen type as defined by hydrogen index is not systematically linked to kinetic response and that default kinetics for the thermal decomposition of type i or type ii kerogen can introduce unacceptable errors into numerical simulations furthermore custom kinetics based on one or a few samples may be inadequate to account for variations in organofacies within a source rock we propose three methods to evaluate the uncertainty contributed by kerogen kinetics to numerical simulations 1 use the average kinetic distribution for multiple samples of source rock and the standard deviation for each activation energy in that distribution 2 use source rock kinetics determined at several locations to describe different parts of the study area and 3 use a weighted average method that combines kinetics for samples from different locations in the source rock unit by giving the activation energy distribution for each sample a weight proportional to its rock eval pyrolysis s2 yield hydrocarbons generated by pyrolytic degradation of organic matter

regional geology and petroleum systems of the illizi berkine area of the algerian saharan platform an overview abstract the berkine and illizi basins are palaeozoic mesozoic intraplate depressions that preserve an over 7000 m thick sedimentary rock record and contain world class petroleum systems with over 39 bboe eur hydrocarbon reserves regional seismic transects and a wealth of well data are used to review the tectonostratigraphic evolution of the area the gondwana palaeozoic and tethys mesozoic supercycles make up the bulk of the phanerozoic succession these 1st order cycles record extensional basin formation followed by a protracted period of overall net subsidence and conclude with basin inversion and regional uplift during the hercynian and alpine orogenies respectively structural styles were dictated by transpressional or transtensional reactivation of mostly nne oriented basement structural grain of late proterozoic ea cambrian pan african age and vertical movement of long wavelength regional highs and lows local tectonism is considered to be the far field effect of plate tectonic processes that affected the north african plate boundaries such as the caledonian and hercynian orogenies the opening of the tethys and atlantic oceans and the alpine orogeny these were accompanied by localised thermal mantle processes regional unconformities subdivide the gondwana and tethys supercycles into eight and seven megasequences respectively these regional units often record 2nd order transgressive regressive cycles that constrain the mapping of reservoir seal pairs and of main source rock intervals the lower palaeozoic megasequences are characterised by sand rich laterally extensive coarse grained fluvial and shallow marine reservoirs interbedded with thin and widespread marine shales they were mostly deposited in shorelines of shallow epeiric seas and continental braided river systems or during the late ordovician in a short lived continental glacial system third order sequences display ramp style geometries with largely parallel to low angle sigmoidal stratal patterns early mesozoic sedimentation followed the late palaeozoic uplift and peneplanation in the form of hinterland sequences containing fluvial and alluvial sandstones and playa lake mudstones and evaporites interbedded with thin lacustrine or shallow marine shales and dolomites the prolific petroleum systems that evolved within these series are associated with the early silurian and late devonian world class source rocks and numerous paleozoic and triassic reservoirs this regional review provides a renewed comprehensive insight into the geological evolution of the area that can help guide local exploration efforts but also serves as a model for exploration in other intracratonic basins of the world

mud volcano eruptions and earthquakes in the northern apennines and sicily italy abstract the relations between earthquakes and the eruption of mud volcanoes have been investigated at the pede apennine margin of the northern apennines and in sicily some of these volcanoes experienced eruptions or increased activity in connection with historical seismic events showing a good correlation with established thresholds of hydrological response liquefaction to earthquakes however the majority of eruptions have been documented to be independent of seismic activity being mud volcanoes often not activated even when the earthquakes were of suitable magnitude and the epicentre at the proper distance for the triggering this behaviour suggests that paroxysmal activity of mud volcanoes depends upon the reaching of a specific critical state dictated by internal fluid pressure and implies that the strain caused by the passage of seismic waves can activate only mud volcanoes in near critical conditions i e close to the eruption seismogenic faults such as the pede apennine thrust often structurally control the fluid reservoirs of mud volcanoes which are frequently located at the core of thrust related folds such an intimate link enables mud volcanoes to represent features potentially suitable for recording perturbations associated with the past and ongoing tectonic activity of the controlling fault system

a seismically controlled seal breach in a major hydrocarbon province a study from the mauddud formation in the bahrah field kuwait abstract the mauddud formation a late albian aged carbonate oil reservoir is one of the main oil producers in kuwait however it exhibits unreliable oil production from the bahrah field the mauddud formation in the bahrah field is divided into two sub structures by a series of e w faults and shows a slight degradation in oil quality 5api within the up dip structure intersections of the e w faults with nw se faults are associated with deep seated seismic pipes which culminate in pull up features creating the overlying sag like features additionally the mauddud formation shows evidence of baroque saddle dolomite in fracture cements and replacing clasts the baroque dolomite have 3he 4he ratios 0 3 times higher than atmospheric values taken together this seismic and petrographic evidence suggests that the mauddud formation experienced an ingress of radiogenic crustal fluids potentially sourced from the basement seismic pipes therefore are interpreted to be the product of the upward movement of hydrothermal fluids that breach seal rocks causing oil to escape and subsequent calcite cementation an integrated map of a basement magnetic anomaly and current exhalative features on the present day surface shows evidence of a relationship with fault locations on the level of the mauddud formation that were rejuvenated and associated with the remigration of oil this study provides an exceptional example of a seal breach in one of the world s most prolific hydrocarbon provinces it also indicates the importance of a multidisciplinary multi scale approach extending from the basement to the surface in order to understand seal breach in carbonate petroleum systems the overall data is used to assess the main factors that effected the integrity of the seal when this latter is breached by hydrothermal fluids

geophysical and petrological evidence for the presence of an anomalous upper mantle beneath the sahara basins algeria abstract north of 20 n the northwest part of the stable african shield is characterized by an anomalous high heat flow zone 80 110 mw m 2 this east west elongated zone is oblique to major proterozoic structural units and cannot be related to differences in crustal heat production maximum heat flow occurs in the southern part of the sahara basins 100 120 mw m 2 only a mantle heat flow contribution of 60 70 mw m 2 can account for this very high surface heat flow the estimated geotherms suggest that the temperature of upper mantle is anomalously high and partial melting may be present at shallow depths this hypothesis is supported by the existence of a long wavelength negative component of the gravity field that corresponds with the high heat flow axis and with the very low lithospheric s wave velocities 4 2 4 4 km s down to 160 km obtained from surface wave studies in addition the chemistry of the scarce cenozoic melilitite lavas illizi volcanic district geographically associated with the thermal anomaly as well as the mineralogy of their inclusions phlogopitized garnet spinel peridotite and alkali clinopyroxenite show that the upper mantle beneath this region is locally highly metasomatised and partially melted from these preliminary results it appears that the northwest african upper mantle has been modified by recent thermal rejuvenation processes including gas transfer that are likely to be more extensive in the southern part of the sahara basins

north slope alaska source rock distribution richness thermal maturity and petroleum charge four key marine petroleum source rock units were identified characterized and mapped in the subsurface to better understand the origin and distribution of petroleum on the north slope of alaska these marine source rocks from oldest to youngest include four intervals 1 middle upper triassic shublik formation 2 basal condensed section in the jurassic lower cretaceous kingak shale 3 cretaceous pebble shale unit and 4 cretaceous hue shale well logs for more than 60 wells and total organic carbon toc and rock eval pyrolysis analyses for 1183 samples in 125 well penetrations of the source rocks were used to map the present day thickness of each source rock and the quantity toc quality hydrogen index and thermal maturity tmax of the organic matter based on assumptions related to carbon mass balance and regional distributions of toc the present day source rock quantity and quality maps were used to determine the extent of fractional conversion of the kerogen to petroleum and to map the original toc toco and the original hydrogen index hio prior to thermal maturation the quantity and quality of oil prone organic matter in shublik formation source rock generally exceeded that of the other units prior to thermal maturation commonly toco 4 wt and hio 600 mg hydrocarbon g toc although all are likely sources for at least some petroleum on the north slope we used rock eval and hydrous pyrolysis methods to calculate expulsion factors and petroleum charge for each of the four source rocks in the study area without attempting to identify the correct methods we conclude that calculations based on rock eval pyrolysis overestimate expulsion factors and petroleum charge because low pressure and rapid removal of thermally cracked products by the carrier gas retards cross linking and pyrobitumen formation that is otherwise favored by natural burial maturation expulsion factors and petroleum charge based on hydrous pyrolysis may also be high compared to nature for a similar reason

epeirogenic motions of africa as inferred from cretaceous shoreline deposits epeirogenic motions can be quantified if paleodatum planes can be recognized these motions have been determined for the time interval mid cretaceous cenomanian to recent in continental africa using the vertical displacement of ancient shoreline sediments and other nearshore or low elevation deposits that are inferred to represent a cenomanian sea level datum plane the cretaceous trans saharan seaway brought shoreline sediments deep into the african continental interior and additional data suggest that most of the remaining terrestrial regions were also low lying during the cenomanian the present elevations of the sea level sediments indicate that large portions of africa have undergone epeirogenic uplift since the cenomanian the character of the motions in north africa can be described as small scale high amplitude 3 km doming separated by relatively flat lying areas of deposition the largest single epeirogenic feature is the uplift associated with red sea and east african rift development the timing of post cenomanian epeirogenic motions can be further constrained using paleontologic k ar faulting paleodrainage and sedimentary data the most likely causal mechanism for african epeirogeny may be hot spot activity reflective of the mantle convection regime underlying the african lithosphere

petroleum generation and migration in the ghadames basin north africa a two dimensional basin modeling study the ghadames basin contains important oil and gas producing reservoirs distributed across algeria tunisia and libya regional two dimensional 2 d modeling using data from more than 30 wells has been undertaken to assess the timing and distribution of hydrocarbon generation in the basin four potential petroleum systems have been identified 1 a middle upper devonian frasnian and triassic triassic argilo greseux inferieur tag i system in the central western basin 2 a lower silurian tannezuft and triassic tag i system to the far west 3 a lower silurian tannezuft and upper silurian acacus system in the eastern and northeastern margins and 4 a lower silurian tanezzuft and middle upper devonian frasnian system to the east southeast the lower silurian tanezzuft source rock underwent two main phases of hydrocarbon generation the first phase occurred during the carboniferous and the second started during the cretaceous generating most hydrocarbons in the eastern libyan basin the frasnian shales underwent an initial minor generative phase in the central depression during the carboniferous however the main generation occurred during the late jurassic cenozoic in the western and central depression the frasnian shales are currently only marginally mature in the eastern part of the basin modeling indicates that the alpine eocene exhumation of the eastern libyan basin margin had a significant control on the timing of hydrocarbon generation from the lower silurian source rock the preferred burial history model calibrates source rock maturity data by incorporating late exhumation and reduced subsidence prior to the hercynian carboniferous orogeny as a result the tannezuft shales preserve their generative potential into the mesozoic cenozoic with renewed hydrocarbon generation during subsequent reburial which can migrate to post hercynian carboniferous traps hence favoring the preservation of hydrocarbon accumulations

in situ cone penetration tests at the active dashgil mud volcano azerbaijan evidence for excess fluid pressure updoming and possible future violent eruption active mud volcanism is a global phenomenon that represents a natural hazard by self igniting eruptions and the continuous emission of methane gas in both marine and continental settings mud domes are often found in compressional tectonic settings such as the caucasus orogenic wedge dashgil mud volcano the most prominent of 200 features in azerbaijan has erupted vigorously in historic times for several years we have observed variations in the activity of dashgil dome including transients in methane flux build up of extrusive mud cones on the main feature and flexural polygonal cracks adjacent to the main crater lake and new mud cones in spring 2007 we carried out in situ cptu cone penetration testing with pore pressure measurement experiments in the crestal area of dashgil our data suggest that the central portion of the crater lake which hosts the conduit for gas and possible mud ascent shows both low sediment shear strength 5 20 kpa and excess pore fluid pressures between 15 and 30 kpa supra hydrostatic at 1 m sub bottom depth in situ cone resistance as a measure for undrained shear strength is as low as 150 kpa in the conduit whereas the mud is found rather stiff in all other testing locations 300 700 kpa probably a result of deeply buried shales of the maikop formation parts of which now liquefy and ascend pore pressure is low in the centre of the conduit probably because of rapidly migrating gas it increases to 30 kpa at the lake bottom and deep flank then decreases upslope on the lake flank and reaches hydrostatic values at the crater rim from the overpressured region beneath the fluid filled crest of dashgil dome combined with the other observations we suspect to currently witness an ongoing period of updoming the presence of sintered mudstones from explosive eruptions in 1908 and 1928 and most likely before suggests that a similar violent activity may occur in the near future

mud volcanoes the most important pathway for degassing deeply buried sediments abstract this paper discusses the nature of the phenomenon of mud volcanism with respect to degassing of deeply buried sediments mud volcanoes are defined as geological structures and their main elements are described based on the nature of activity mud volcanoes are grouped in to three main types and the relationship between each type and corresponding morphological expression is discussed the presented up to date data of the world geographical distribution of mud volcanoes show that they approximate to 1800 individuals a detail overview of geological environments in which they occur helps to deduce some necessary conditions for mud volcano formation the basic mechanisms of mud volcano formation are discussed specifically the fluid pressure hypothesis and some triggering events are identified the most common investigation approach and some criteria for recognizing of a submarine mud volcano on side scan sonar records and seismic sections are given mud volcanism in the mediterranean ridge an accretionary complex and black sea abyssal plane a back ark basin with tectonic regime of extension are described as case studies to show variety in morphology and common factors in development of mud volcanoes the manifestation of continuous gas migration through mud volcanoes is clarified and the attempt made to quantify the gas release shows that mud volcanoes are one of the significant natural sources of atmospheric methane emitting a total amount of about 10 3 to 12 6 tg annually

impact of depositional facies on the distribution of diagenetic alterations in the devonian shoreface sandstone reservoirs southern ghadamis basin libya abstract the middle devonian shoreface quartz arenites present day burial depths 2833 2786 m are important oil and gas reservoirs in the ghadamis basin western libya this integrated petrographic and geochemical study aims to unravel the impact of depositional facies on distribution of diagenetic alterations and consequently related reservoir quality and heterogeneity of the sandstones eogenetic alterations include the formation of kaolinite pseudomatrix and pyrite the mesogenetic alterations include cementation by quartz overgrowths fe dolomite ankerite and illite transformation of kaolinite to dickite illitization of smectite intergranular quartz dissolution and stylolitization and albitization of feldspar the higher energy of deposition of the coarser grained upper shoreface sandstones combined with less extensive chemical compaction and smaller amounts of quartz overgrowths account for their better primary reservoir quality compared to the finer grained middle lower shoreface sandstones the formation of kaolin in the upper and middle shoreface sandstones is attributed to a greater flux of meteoric water more abundant quartz overgrowths in the middle and lower shoreface is attributed to a greater extent of stylolitization which was promoted by more abundant illitic clays this study demonstrated that linking the distribution of diagenetic alterations to depositional facies of shoreface sandstones leads to a better understanding of the impact of these alterations on the spatial and temporal variation in quality and heterogeneity of the reservoirs

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

triggered seismicity in utah from the 3 november 2002 denali fault earthquake immediately after the arrival of the surface waves from the m w 7 9 denali fault earthquake on 3 november 2002 the university of utah regional seismic network recorded an abrupt increase in local microseismicity throughout most of utah s main seismic belt we examined this increase in the context of the regional background seismicity using a catalog of 2651 earthquakes from 1 january 2000 to 30 june 2003 statistical analyses of this catalog above spatially varying magnitudes of completeness ranging from 1 2 to 1 7 allow us to reject with 95 confidence the null hypothesis that the observed increases were due to random occurrence the elevated seismicity was most intense during the first 24 hr 10 times the average prior rate but continued above background level for 25 days at the 95 confidence level in most areas we conclude that the increased seismicity was triggered by the denali fault earthquake which occurred more than 3000 km from the study region high peak dynamic stresses of 0 12 to 0 35 mpa that occurred during the passage of the love waves are consistent with the interpretation of triggering the peak dynamic stresses were estimated by measuring peak vector velocities at 43 recording sites 37 of which were relatively new strong motion stations of the advanced national seismic system the triggered events ranged in magnitude m c and or m l from less than 0 to 3 2 and were widely distributed across the state primarily in seismically active regions in contrast to many previously published observations of remotely triggered seismicity the majority of the triggered earthquakes did not occur near quaternary volcanic vents or in areas of magma related geothermal activity in several areas the triggered seismicity was spatially clustered more than five earthquakes each separated by 5 km double difference relative relocations for the earthquakes in three of these clusters indicate that most but not all of the triggered events were spatially separated from source zones of prior seismicity during 2000 2002 focal mechanisms for the two largest triggered events have northeast to northwest trending tension axes which are unusual for the region where they occurred the temporal decay of the triggered activity was similar to that of utah aftershock sequences and can be described by the modified omori s law with a p value of 0 6 to 0 7 the frequency magnitude distribution of the triggered earthquakes is also similar to that of utah aftershocks and for the study area as a whole can be described by the gutenberg richter relation with a b value of 0 81 0 16 these similarities between the triggered seismicity and utah aftershock sequences suggest the possibility that the initiation and development of both could result from the same causative mechanisms online material catalog of earthquakes used in this study

origin of gases and water in mud volcanoes of andaman accretionary prism implications for fluid migration in forearcs abstract extensive mud volcanism on the andaman accretionary prism occurs above a complex network of faults and is caused by the convergence of the indian plate and the burmese microplate mud volcanoes of the andaman forearc have received little attention in spite of the fact that they are one of the important features of this tectonic setting located within an ocean basin that has one of the highest sedimentation rates in the world and that the materials emitted by them present a unique opportunity to study the chemistry of the detachable parts of the subducting slab in this study we present mineralogical chemical and isotopic data for argillaceous matter mud matrix gases and water emitted by these mud volcanoes and attempt to understand the variations in terms of their sources and processes within the forearc the mud matrix is composed of smectite illite kaolinite chlorite plagioclase quartz calcite assemblage derived both from sediments and altered oceanic crust and originates from a deep burial diagenetic environment the modes of 13 c distributions for methane 42 ethane 27 and co 2 45 to 135 mm than seawater and its 18 o 0 2 to 2 6 and d 24 to 14 isotopic compositions fall well below the global meteoric water line from their trace element contents and stable isotopic compositions we infer that the mud water is a mixture of sediment pore water ancient seawater and water released from dehydration of clay minerals the 87 sr 86 sr of mud water 0 7071 confirms the above inference and points out that altered oceanic crust plays a significant role in controlling the chemistry of water the formation temperatures of mud ejecta derived from mineralogical smectite illite chemical k na and isotopic d 18 o geothermometers lie in the range of 50 c 120 c which corresponds to a depth zone of 2 to 6 km within the andaman forearc based on all the evidences we conclude that the sampled mud volcano ejecta originate at the plate boundary decollement zone from the sediments and altered oceanic crust of the subducting indian plate

active mud volcanoes on and offshore eastern makran pakistan to study the activity source and driving force of the venting of fluidized mud in the coastal makran we carried out reconnaissance surveys of two active onshore mud volcano fields chandragup and jebel u ghurab and of a newly born march 1999 offshore mud volcano malan island all studied on and offshore mud volcanoes line up along one southwest northeast trending structural lineament the axis of the dhak anticline isotopic data point to a bacterial origin of the gas mainly methane mixed benthic foraminiferal faunas and calcareous nannofloras suggest that the source level of the extruded mud is at a sub surface depth of 2 3 km observed mud discharge varied between 0 and 1 4 m3 h 1 and gas discharge rates between negligible amounts to 1 m3 s 1 mud temperatures in the crater lake of chandragup i are near ambient temperatures they rise slightly 1 5 c during episodes of modest mud outflow an area of 160 000 m3 of soft mud was vigorously extruded from the sea floor at a water depth of 10 m within days after 15 march 1999 forming malan island the island was destroyed within a few months after its birth by deep reaching wave action during the sw monsoon this was possibly aided by local subsidence of the mud volcano structure due to the volume loss following rapid degassing and mud extrusion

burial history and kinetic modeling for hydrocarbon generation part ii applying the galo model to saharan basins the galo basin evolution model described in makhous et al 1997 is applied to evaluate hydrocarbon generation and migration histories in several saharan basins three basins the oued el mya ghadames and illizi are located in the central and eastern parts of the saharan platform and are investigated in detail the ahnet mouydir timimoun reggane and other basins located in the southern and western parts of the platform are also studied the modeling results combined with geochemical data are used in a synthesis of the regional framework the thermal gradients in the ghadames and illizi basins are greater than those in the oued el mya basin this difference is attributed to differences in sedimentation and subsidence rates to less hercynian erosion and to fewer occurrences of evaporates in the akfadou region of the ghadames basin and in the mereksen region of the illizi basin in the southern and western parts of the illizi province the major subsidence occurred before hercynian uplift very moderate hercynian uplift in the ghadames and illizi basins did not involve a significant decrease of temperatures and organic matter maturation continued but at slower rates as a result the realization of hydrocarbon potential appears to be higher than would be expected favorable traps are located near subsided areas where the source shales particularly the devonian were not subjected to uplift and erosion in this respect the eastern sahara including the ghadames and illizi basins is a favored province analysis of the distribution of present day temperatures and paleotemperatures in the paleozoic sediments of the triassic province oued el mya ghadames trias and north illizi basins combined with effective source rock occurrences shows that favorable conditions for hydrocarbon generation during the paleozoic occurred essentially in the southern and southwestern parts of the province hydrocarbon generation during the mesozoic took place mainly in the central and northern parts of this province however some of the hydrocarbon accumulations in the northern and northeastern parts of oued el mya basin and in the northern and western ghadames basin were subsequently destroyed by the hercynian orogeny in the illizi basin ordovician and devonian structures are the most likely traps for hydrocarbons generated during the paleozoic whereas in the ghadames and oued el mya basins structures formed prior to the late cretaceous are preferentially favorable for oil accumulation gas accumulations are found in traps formed in the late cretaceous or later when source shales were buried to 3 3 3 5 km and more

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

structure paleogeographic inheritance and deformation history of the southern atlas foreland fold and thrust belt of tunisia 1 structural analysis of the southern tunisian atlas was carried out using field observation seismic interpretation and cross section balancing it shows a mix of thick skinned and thin skinned tectonics with lateral variations in regional structural geometry and amounts of shortening controlled by nw se oblique ramps and tear faults it confirms the role of the late triassic early jurassic rifting inheritance in the structuring of the active foreland fold and thrust belt of the southern tunisian atlas in particular in the development of nw se oblique structures such as the gafsa fault the late triassic early jurassic structural pattern is characterized by a family of first order nw se trending normal faults dipping to the east and by second order e w trending normal faults limiting a complex system of grabens and horsts these faults have been inverted during two contractional tectonic events the first event occurred between the middle turonian and the late maastrichtian and can be correlated with the onset of the convergence between africa and eurasia the second event corresponding to the principal shortening tectonic event in the southern atlas started in the serravalian tortonian and is still active during the neogene the southern atlas foreland fold and thrust belt propagated on the evaporitic decollement level infilling the late triassic early jurassic rift the major eocene atlas event described in hinterland domains and in eastern tunisia did not deform significantly the southern tunisian atlas which corresponded in this period to a backbulge broad depozone

long term in situ observations at the athina mud volcano eastern mediterranean taking the pulse of mud volcanism abstract long term monitoring on mud volcanoes is fundamental to unravel episodic processes and transient changes that might otherwise be missed by using snapshot observations during time limited research expeditions we deployed a pore and seafloor pressure observatory close to the main conduit of the athina mud volcano south of turkey eastern mediterranean sea for a period of 26 months between february 2014 and april 2016 the observatory recorded 32 pore pressure transients related to as many seismic events out of 625 earthquakes with mw 2 5 occurred over the monitoring period in a radius of 1000 km and few pore pressure excursions related to mud volcanism the data helped to define a threshold for earthquake triggered changes in mud volcano pore pressure thus delineating possible pore pressure distance relationships for different magnitudes ranges peak ground accelerations as representative for earthquakes ground motion at the observatory have been calculated with different ground motion prediction equations using a conservative approach an empirical equation has been identified which specify the lowermost pga necessary to induce a change in pore pressure record at the athina mud volcano moreover internal variations of the mud volcano system recordable through the pore pressure signal have been described for the first time in such a submarine feature

petroleum generation and accumulation in the berkine basin eastern algeria the berkine ghadames basin is regarded as an important hydrocarbon play in eastern algeria an evaluation of organic source facies the application of petroleum geochemistry and an extensive basin modeling study were carried out to improve the understanding of the petroleum charge of the basin geochemical data indicate that the llandoverian wenlockian and the frasnian hot shales are the most important oil prone source rocks for the known hydrocarbon accumulations in the basin maturity data reflect the late cretaceous tertiary burial and are consistent with a 60 63 mw m2 heat flow in the vicinity of the anticlines and 50 mw m2 heat flow farther away from the folded area a two dimensional basin modeling study revealed the importance of poorly constrained parameters such as the amount and rate of hercynian erosion on hydrocarbon generation and trapping efficiencies the model shows that a cretaceous tertiary petroleum generation and emplacement for both source rocks can better explain the different gas and oil fields than can an earlier hercynian event the faults related to the triassic jurassic rifting are most certainly permeable and can be considered as major migration pathways for petroleum in contrast the overpressure that developed along the el biod hassi messaoud axis in the ordovician reservoirs was probably caused by the low permeability of the faults bounding the anticlines that therefore prohibited any lateral or vertical fluid movements the model also indicates two petroleum systems that have triassic reservoirs 1 a frasnian sourced system that is confined to the central part of the basin and 2 a llandoverian wenlockian sourced system in the western part of the basin migration into paleozoic reservoirs was followed by dismigration into overlying triassic traps after the cretaceous compressive movements

tectonics and history of the andaman sea region abstract the andaman sea is an active backarc basin lying above and behind the sunda subduction zone where convergence between the overriding southeast asian plate and the subducting australian plate is highly oblique the effect of the oblique convergence has been formation of a sliver plate between the subduction zone and a complex right lateral fault system the late paleocene collision of greater india and asia with approximately normal convergence started clockwise rotation and bending of the northern and western sunda arc the initial sliver fault which probably started in the eocene extended through the outer arc ridge offshore from sumatra through the present region of the andaman sea into the sagaing fault with more oblique convergence due to the rotation the rate of strike slip motion increased and a series of extensional basins opened obliquely by the combination of backarc extension and the strike slip motion these basins in sequence are the mergui basin starting at 32 ma the conjoined alcock and sewell rises starting at 23 ma east basin separating the rises from the foot of the continental slope starting at 15 ma and finally at 4 ma the present plate edge was formed alcock and sewell rises were separated by formation of the central andaman basin and the faulting moved onshore from the mentawai fault to the sumatra fault system bisecting sumatra

occurrence of retene in upper silurian lower devonian sediments from north africa origin and implications abstract the biomarkers retene cadalene tetrahydroretene and isohexylalkylnaphthalene have been identified in the extracts of silurian devonian clastic sediments from southern tunisia the occurrence of retene is unexpected as it is generally considered to be a diagenetic product of the conifer constituent abietic acid however conifers evolved only after the devonian the retene shows a strong correlation with the abundant terrestrial signal from bryophyte derived cryptospores in the palynofacies suggesting that it derives from a terrestrial source accordingly we propose that either abietic acid synthesis evolved prior to the appearance of conifers or retene is a diagenetic product of precursors other than abietic acid which were synthesized by the earliest land plants without excluding the first possibility it appears likely that retene derives here from the diagenesis of compounds with a kaurane type skeleton which were abundantly produced by the early palaeozoic bryophytes

terrestrial heat flow in the sirt basin libya and the pattern of heat flow across northern africa we report 66 new heat flow and 24 new heat production measurements from the sirt basin a late jurassic miocene sedimentary depression in north central libya underlain by late proterozoic basement heat flow determinations were made using bottom hole temperatures from oil wells and thermal conductivity measurements from drill core and cuttings heat production measurements come from core samples of basement rock heat flow is fairly uniform throughout the basin with a mean of 72 9 s d mw m 2 it is not clear if heat flow from the sirt basin is elevated as a consequence of its origin as a late mesozoic rift the difference between the mean basin heat flow and the global mean heat flow from tectonically undisturbed late proterozoic terrains 55 17 mw m 2 is 17 mw m 2 but this difference lies within the uncertainties associated with these mean heat flow estimates if heat flow from the sirt basin is elevated it could be caused by enhanced crustal heat production and need not be attributed to thermal alteration of the lithosphere related to basin formation mean crustal heat production is 3 9 2 1 w m 3 1 2 to 3 times greater than surface heat production in other proterozoic terrains in africa from west to east the pattern of heat flow across northern africa is characterized by high 80 110 mw m 2 heat flow throughout most of northwestern africa normal to perhaps slightly elevated heat flow in the sirt basin low to normal 35 55 mw m 2 heat flow in egypt inboard of the red sea and high heat 75 100 mw m 2 flow along the red sea high heat flow near the red sea and in northwestern africa along the mediterranean coast can be readily attributed to cenozoic tectonic activity but high heat flow in the paleozoic sahara basins of southern algeria is harder to understand within the tectonic framework of northern africa a possible explanation advanced previously is that elevated heat flow in the sahara basins arises from a regional thermal anomaly within the north african lithosphere if that explanation is correct then the heat flow distribution in the sirt basin and in egypt away from the red sea suggests that the postulated lithospheric thermal anomaly does not extend beyond the sahara basins to the east

ghadames basin southern tunisia a reappraisal of triassic reservoirs and future prospectivity recent discoveries of oil and gas in triassic reservoirs of the ghadames basin eastern algeria suggest that similar potential exists to the east in the southern tunisian part of the province for decades southern tunisia has remained an underexplored part of the basin in large part owing to older geological interpretations that focus on paleozoic reservoirs and to limitations in seismic data quality resulting from statics problems that have rendered trap identification inaccurate or tenuous new analyses of previously and recently acquired geological and geochemical data as well as improvements in seismic data acquisition and processing have begun to reverse older notions regarding limited hydrocarbon presence in southern tunisia log correlations indicate that productive sand rich intervals of the major triassic reservoir in the region the trias argilo greseux inferieur tagi can be correlated over large distances suggesting significant continuity into lightly drilled and undrilled areas analyses of geochemical data reveal a more complex multistage history of hydrocarbon maturation and migration than previously believed much greater volumes of petroleum have been generated and a larger variety of traps have been created than can be accounted for by older interpretations where added to the use of new field and processing parameters for seismic surveys these factors have together led to important upgraded evaluations of basin potential in southern tunisia

aliphatic and aromatic biomarkers from gondwanan sediments of late ordovician to early devonian age an early terrestrialization approach abstract twenty one core samples of late ordovician to early devonian age from sections in southern tunisia north african platform gondwana and containing marine and terrestrial organic matter with microbial input were investigated to link the aliphatic and aromatic hydrocarbon distributions with the terrestrial and marine palynomorph content e g acritarchs prasinophytes chitinozoans cryptospores and trilete spores in addition to several biomarkers of algal bacterial origin long chain n alkanes that might be derived from land plants as well as the terrestrial diterpane norabietane were found several land plant derived biomarkers such as retene cadalene simonellite tetrahydroretene and c19 isohexylalkyl naphthalene were observed in the aromatic fractions while these terrestrial biomarkers could be clearly recognized in the middle silurian lower devonian samples their presence in the upper ordovician lower silurian sediments is more doubtful because of much lower relative abundances the land plant biomarkers show a fairly good correlation with the occurrence and abundance of cryptospores and trilete spores derived from bryophytes and tracheophytes which covered the emerged areas around the ghadamis basin during the silurian and devonian the early tracheophytes e g cooksonia lycophytes and zosterophylls are therefore suggested as a new terrestrial source for most of the saturated and aromatic biomarkers found in sediments of middle silurian to early devonian age

burial history and thermal evolution of the northern and eastern saharan basins the numerical one dimensional reconstruction of the burial history and thermal evolution of the sedimentary section and basement was conducted for 32 wells in the east algerian basins with the help of the galo basin modeling system these reconstructions allowed the performance of a quasi two dimensional analysis of the burial history of the basins changes in rock temperatures the lithosphere thickness and maturation conditions of organic matter during basin development along the four profiles crossing the study region the modeling assumed that the highest thermal activation in the history of the saharan basins with the heat flow more than 100 mw m2 and the thinnest lithosphere on the order of 25 35 km took place during the late carboniferous to permian in the dahar and oued el mya basins the uplift responsible for this activation caused erosion of 2000 3000 m of ordovician to lower carboniferous strata the ghadames and illizi basins were subjected at the same time to more moderate erosion and thermal activation with heat flow less than 75 mw m2 in the triassic cretaceous interval maximum subsidence occurred in the northern areas which were characterized by maximal thermal activation and the thinnest lithosphere in the permian at present the situation is opposite to that in the permian the highest thermal regime occurs in the southern areas of the study region and especially in the illizi basin where heat flow reaches and even exceeds 100 mw m2 and the thickness of the lithosphere decreases as much as 30 km the modeling also assumes stretching of the lithosphere in the northeastern and central parts of the illizi basin with maximal amplitude of about 1 16 during the cenozoic the analysis shows that the hercynian erosion could account for only a few of the abrupt changes in vitrinite profiles in the saharan basins and that triassic and later intrusive activity and associated hydrothermal heat transfer accurately explain the steplike character of maturation profiles

ch4 and co2 emissions from mud volcanoes on the southern margin of the junggar basin nw china origin output and relation to regional tectonics

the 2011 strong fire eruption of shikhzarli mud volcano azerbaijan a case study with implications for methane flux estimation shikhzarli is a typical active mud volcano mv in azerbaijan with extremely high percentages of fire eruptions reaching 74 the strong eruption of shikhzarli mv on 13 march 2011 shamakhi gobustan region central azerbaijan at 40 29 12 5 n 49 02 03 4 e was accompanied by gas ignition with a straight flow vertical gas flare a large 60 m height short living 30 min gas flare and small 1 5 m height gas spouts with longer lifetimes 5 h were simulated in sigmaflow and the model was used to evaluate methane flux and the amount of combusted methane geological and mineralogical data field observations as well as eye witness reports and photographs in mass media were used to choose the boundary conditions for the gas fire simulation this study provides the first quantitative evaluation for methane emission during an mv catastrophic eruption as simulation predicts 14 000 m3 of methane was consumed for the life time 30 min of the main 60 m high flare which is equivalent to nine tons of cold gas at ambient conditions the volume of erupted methane for the 5 h lifetime of a small spout 1 5 m high was 72 6 m3 45 kg of cold ch4 the amount of methane emitted during a single strong flame eruption is commensurate with the annual output of permanently active individual mv vents or may be ten to hundred times as high

gases in taiwan mud volcanoes chemical composition methane carbon isotopes and gas fluxes abstract mud volcanoes are important pathways for ch 4 emission from deep buried sediments however the importance of gas fluxes have hitherto been neglected in atmospheric source budget considerations in this study gas fluxes have been monitored to examine the stability of their chemical compositions and fluxes spatially and stable c isotopic ratios of ch 4 were determined for several mud volcanoes on land in taiwan the major gas components are ch 4 90 air i e n 2 o 2 ar 1 5 and co 2 1 5 and these associated gas fluxes varied slightly at different mud volcanoes in southwestern taiwan the hsiao kun shui hks mud volcano emits the highest ch 4 concentration ch 4 97 on the other hand the chung lun mud volcano cl shows co 2 up to 85 and much lower ch 4 content 4 content 90 with low co 2 1 methane c 2 ethane c 3 propane and 13 c ch4 results with the exception of mud volcanoes situated along the gu ting keng gtk anticline axis showing unique biogenic characteristics only small ch 4 concentration variations 4 emission fluxes for mud volcanoes on land in taiwan fall in a range between 980 and 2010 tons annually if soil diffusion were taken into account the total amount of mud volcano ch 4 could contribute up to 10 of total natural ch 4 emissions in taiwan

geothermal gas compositions in yellowstone national park usa abstract gas samples collected between 1974 and 1986 have been analysed for the ten major components samples have been collected almost exclusively from the tops of pools which has degraded the value of the data and limited inter comparisons to the relatively insoluble components ar n 2 ch 4 h 2 and he a general gas distribution pattern in the park in terms of these components shows the major heat source s to underlie the gibbon and mud volcano areas with all other geothermal areas having gas compositions consistent with a general north south water flow shoshone basin gases show a large range of compositions and these are analysed in detail the patterns conform to that which would be expected from an east west flow or fluid with progressive boiling and subsequent dilution

aftershock investigation in the andaman nicobar islands of india and its seismotectonic implications six three component short period digital seismograph four reftek and two kinemetrics stations were established in different parts of the andaman nicobar islands following the 26 december 2004 devastating sumatra andaman mainshock m w 9 3 here we analyze about 18 000 aftershocks m 3 0 recorded from 6 january to 16 march 2005 to better understand the seismotectonics of the region a sudden burst of aftershock activity with irregular trend in the month of january 2005 was observed at almost all seismograph stations the estimate of p value 0 9532 from aftershocks m 4 5 is near to normal value of 1 0 which suggests a slow decay sequence of aftershock with complex and nonuniform stress change in a fault system creep effects and history dependent stress changes the frequency magnitude relation of the aftershocks followed the power law with average b value of 0 7723 and it varies from 0 49 to 1 03 indicating the compressive stress state of the region and its heterogeneous structure with possible variations in frictional conditions along the fault the distribution of the located aftershocks by a multistation method shows a north south trending aftershock cluster in an area of about 800 300 km 2 which reflects an approximate rupture dimension of the mainshock beneath the andaman nicobar islands most of aftershocks occurred in a depth range of 5 65 km the determination of composite fault plane solutions of the best located aftershock clusters at three different depth ranges 0 15 16 30 and 31 km in the ten blocks of the region suggests that the mainshock rupture propagated through normal reverse and strike slip earthquakes the areas in the vicinity of barren and narcondum volcanic zones show a dominantly normal fault mechanism due to predominant tensional forces suggesting the facilitation of brittle failure in the weakened crust by the process of underheating the zone near baratang mud volcano is associated predominantly with thrust fault at depth of 0 30 km suggesting a high compressive force beneath the baratang that ejected a huge amount of mud and slurry materials to the surface after the 26 december 2004 sumatra andaman earthquake m w 9 3 here we propose that the relocation of our large aftershock dataset using converted sp depth phase technique for precise depth control is needed and its sharing with global earthquake data can render more information on the subduction dynamics and geodynamical processes of the region

radon anomaly in the soil of taal volcano the philippines a likely precursor of the m 7 1 mindoro earthquake 1994 1 the soil gas 222rn concentration had been monitored almost continuously from june 1993 till november 1996 on taal volcano luzon island the philippines during this measurement period a singular mb 7 1 earthquake occurred on november 15 1994 between luzon and mindoro 48 km south of the volcano twenty two days before the earthquake an anomalous increase in soil gas radon peak to background ratio 6 was recorded unique in the whole time series the possible generation of this anomaly by typhoon teresa which struck luzon island a few days before was ruled out one year later when super typhoon angela the most powerful storm to hit the philippines in ten years crossed luzon island along almost the same track without triggering a similar disturbance in the radon signal consequently there is strong evidence that the taal radon anomaly originated in stress accumulation preceding the mindoro earthquake

earthquake forerunners in a selected area of northern italy recent developments in automatic geochemical monitoring abstract this article describes the monitoring of certain mud volcanoes in the northern apennines of italy this monitoring was carried out from a geochemical point of view and its aim was to verify the seismic precursory nature of the mud volcano fluids the operational strategy began by determining the regional character of the main physical and chemical precursors and a multidisciplinary approach to the historical research was used to achieve this the utility of such an approach in monitoring strategy has been confirmed a series of experiments was carried out to identify the physical model the main geochemical characteristics and the origin of the seismic precursory phenomena with particular reference to radon 222 the technological apparatus necessary for a reliable automatic continuous monitoring system of the geochemical parameters of mud volcanoes were then extensively tried out the first results of this monitoring system refer to dec 1988 jan 1989 in this period there were some seismic events which were preceded by certain phenomena we can call precursory an interpretative model has been created from all the information collected so that similar situations can be better understood from a physical and chemical point of view

biogeochemical evolution of cryoconite holes on canada glacier taylor valley antarctica 1 the cryoconite holes of the mcmurdo dry valleys are simple closed biogeochemical systems involving water ice mineral and organic debris which serve as ecosystems for consortia of microorganisms this study is the first to document the seasonal and annual chemical evolution of solutes in cryoconite holes samples of glacier ice frozen cryoconite holes and those containing water were collected during the austral summer of 2005 2006 the isolation age was calculated from the excess cl in the holes and varied from 0 to 5 years a consistent with the last hot summer when the cryoconite holes were open to the atmosphere the holes progressively deepen with isolation age variations in dic doc k and so42 suggest that dissolution of primary minerals in the cryoconite debris cyclical precipitation and dissolution of secondary carbonates net photosynthesis over summer and net respiration during the autumnal freeze are the principal reactions which perturb the seasonal and annual solute concentrations in the holes doc is generated in the holes at a rate of 7 5 g c cm 2 a 1 and non sea salt k accumulates in frozen holes at a rate of 0 073 eq cm 2 a 1 we infer that c cycling is complex even in these otherwise simple systems

temporal change in shear velocity and polarization anisotropy related to the 2011 m9 0 tohoku oki earthquake examined using kik net vertical array data 1 the m9 0 tohoku oki earthquake took place off ne japan which is covered by a dense seismic network in particular kik net observed the strong motions of the main shock and numerous aftershocks both on the ground and at the bottom of boreholes at a depth of a few hundred meters we applied cross correlation analysis to the coda part of a seismogram observed by kik net and estimated not only the temporal change in shear velocity but also the change in polarization anisotropy between the bottom of the borehole and the ground the shear velocity was suddenly reduced by 5 to 10 after the tohoku oki earthquake over a wide area of ne japan which is consistent with the results of a previous study although some stations also reveal a change in polarization anisotropy the polarization anisotropy change is smaller than the velocity change which may suggest that the static stress change due to the coseismic slip on the pacific plate is not large enough to change the direction of polarization anisotropy and or deviatoric stress in the land area of ne japan

association of subsurface radon changes in alaska and the northeastern united states with earthquakes abstract changes of radon concentration in the ground have been reported to correlate with seismic activity in many places over widely varying distances from the earthquake epicenters sometimes over 100 s and occasionally over 1000 s of km depending on the magnitude m of the earthquakes for proper use of such correlations in forecasting the location and size of impending earthquakes it would be useful to establish a relation between m and the maximum distance x m at which radon can be significantly altered by preseismic effects we have monitored radon in the ground continuously at blue mountain lake ny starting dec 3 1975 and at three locations in alaska icy bay yakataga and sand point starting nov 12 1979 march 5 1980 and june 29 1980 respectively sample correlations from visual examination of the recent radon record and tentative use of a proposed scaling relation show a number of possible earthquake related signals at these locations the data are compatible with scaling relations that were derived from two separate models of premonitory elastic strains in this work x m 10 0 48 m where x m is in units of km and m 3 since tilt and strain signals correlate similarly with magnitude and distance it is likely that most earthquake related radon signals are mechanically induced

a geochemical approach to earthquake reconnaissance at the baratang mud volcano andaman and nicobar islands abstract variations in the relative composition of constituent gases coming out of the mud volcano near jarwa creek in baratang island middle andaman are discussed on the basis of regional tectonic settings and seismo geochemical features the most abundant gas is ch4 55 7 vol followed by n2 32 2 o2 ar 9 9 co2 2 0 and he 0 2 concentration of the radioactive gas 222rn is relatively high 7500 bq m3 this paper discusses the experimental methods adopted to continuously monitor he ch4 co2 and 222rn with a view to identify pre seismic gas concentration anomalies associated with regional seismic occurrences results related to this gas geochemical monitoring are presented with a purpose to develop ability in ascribing a distinct geochemical anomaly to a particular seismic activity in the region

characteristics of mixed sporopollen assemblage from sediments of dushanzi mud volcano in southern junggar basin and indication to the source of mud and debris ejecta in order to search for the source of muddy eruption debris a series of erupted mud samples were collected from a corn of the dushanzi mud volcanoes in southern junggar basin nw china and analyzed for palynological records two palynomorph groups were revealed in the mixed sporopollen assemblage from the erupted sediments according to their colors the light color group accounting for about 95 of the total was dominated by the chenopodiaceae and artemisia and in a color of faint yellow indicating an immature stage of organic matter evolution the dark color group was composed of cyathidites classopollis schizaeoisporites lygodiumsporites and rugubivesiculites in a color of brown yellow indicating a low maturity to maturity stage of organic matter evolution the palynomorph records suggested that most of the muddy debris ejecta of the dushanzi mud volcano might be sourced from the cenozoic deposits mainly the middle late miocene taxihe and dushanzi formations and a small portion likely from the lower cretaceous tugulu group in addition there is also a possibility that a little part of eruption debris is from the upper jurassic qigu formation the dushanzi anticline occurred strong extrusion and thrust faults in the late himalayan period and the oil and gas reservoirs were destroyed and resulted in eruption of the mud volcano in the dushanzi area