bluuebunny/crossref_metadata_2025_split huggingface dataset:
DETERMINATION OF FAULT SLIP COMPONENTS USING SUBSURFACE STRUCTURAL CONTOURS: METHODS AND EXAMPLES
Authors: Xu S‐S. , Velasquillo‐Martinez L. G. , Grajales‐Nishimura J. M. , Murillo‐Muñetón G. , García‐Hernandez J. , Nieto‐Samaniego A. F. 
Published: March 2006

Problems with measuring fault slip in the subsurface can sometimes be overcome by using subsurface structural contour maps constructed from well logs and seismic information. These maps are useful for estimating fault slip since fault motion commonly causes the dislocation of structural contours. The dislocation of a contour is defined here as the distance in the direction of fault strike between two contours which have the same value on both sides of a fault. This dislocation can be estimated for tilted beds and folded beds as follows:If a dip‐slip fault offsets a tilted bed, the dislocation (Sc) of contours can be estimated from the vertical component (Sv) of the fault slip and the dip (β) of the bedding according to the following relationship: Sc= Sv/tan β. Since Scand β can be measured from a contour map, the vertical component of fault slip can be obtained from this equation.If a strike‐slip fault offsets a tilted bed, the dislocation (Scs) of contours is equal to the strike‐slip of the fault (Sc), that is, Scs= Ss.If a fault offsets a symmetric fold, the strike component (Scs) of fault slip and the dislocation of the contours (Sc) can be calculated, respectively, from the equations Scs= (Smax+ Smin) / 2 and Sc= (Smax‐ Smin) / 2. Smaxis the greater total dislocation (Sc+ Scs) of a contour line between the two limbs of the fold and Sminis the smaller total dislocation (Sc‐ Scs) for the same contour line. In this case, Svcan be also calculated using the obtained value of Scand the equation Sv= Sctan β.Similarly, for an asymmetric fold, the dislocation of contours due to the vertical slip component is Scb= (Smax‐ Smin)/(n + 1), and the strike‐slip component is Ss= Scs= (nSmin+ Smax/(n + 1), where n is the ratio between the values of interlines of the two limbs, and Scbis the dislocation of contours due to the vertical slip component for either of the two limbs (here it is for limb b).In all cases, three conditions are required for the calculation of contour dislocation:the contour lines must be approximately perpendicular to the fault strike; the intersection angle between the fault strike and the strike of bedding should be greater than 65°;the bed must not be dip more than 35°; andfolding or flexure of the stratigraphic horizons must have occurred before faulting.These methods for determining fault slip from the dislocation of structural contours are discussed using case studies from the Cantarell oilfield complex, Campeche Sound (southern Gulf of Mexico), the Jordan‐Penwell Ellenburger oilfield in Texas, and the Wilmington oilfield in California.
MIDDLE MIOCENE DASHAVA FORMATION SANDSTONES, CARPATHIAN FOREDEEP, UKRAINE
Authors: Kurovets I. , Prytulka G. , Shpot Y. , Peryt T. M. 
Published: March 2006

Middle Miocene (Sarmatian) sandstones in the Ukrainian Carpathian Foredeep are important exploration targets for natural gas. In this paper, we report on petrophysical studies on core samples of these sandstones with which we integrate wireline log data from 42 boreholes. Sarmation siltstones and sandstones in the study area are assigned to the lower part of the Dashava Formation. Seventeen units (LD 17 to LD 1:0.05 to 5m thick) are recognized in this formation on the basis of lithostratigraphy and log response. Sandstone content is highest within three lithostratigraphic complexes corresponding to units LD17‐LD14, LD9‐LD8 and LD5‐LD3.During the Sarmatian, the Carpathian Foredeep was characterized by two depositional systems: a basinal turbidite system, and a second, more mixed system. Important controls on sedimentation included basin configuration and water depth, the occurrence of turbidity and other currents, and the location of provenance areas. Clastic material was delivered to the basin by rivers and ephemeral streams mostly from the Carpathian foldbelt. The content of sandy material within the Sarmatian succession increases from NW to SE, and from the central portion of the Krukenychy depression to the margins of the basin.
THE GENERATION OF IMMATURE OILS IN THE LACUSTRINE JIYANG MEGA‐DEPRESSION, BOHAI BAY BASIN, CHINA
Authors: Linye Zhang , Shouchun Zhang , Zhilin Chen , Chunrong Zhang , Zhihua Hong 
Published: March 2006

The lacustrine Jiyang mega‐depression (Bohai Bay Basin, eastern China) produces important volumes of immature oils. These oils were generated at shallow burial depths by source rocks which have not entered the conventional oil window. Oil‐source correlation studies have determined that the oils were mainly generated by source rock intervals in the Es4 and Es1 Members of the Paleogene Shahejie Formation, which were deposited in saline‐ to brackish‐water and brackish‐water lacustrine conditions, respectively. Minor quantities of oil came from Es3 Member source rocks deposited in freshwater conditions.Samples of the Es4, Es3 and Es1 source rocks underwent artificial maturation at low temperatures (100–400°C). For the Es4 sample, the hydrocarbon generation characteristics of soluble organic matter and kerogen were investigated. The results of the experiments show that soluble organic matter made a greater contribution than kerogen to the immature oil (76% versus 24%). A comparison of the results of the thermal simulation experiments with the naturally‐occurring maturation profile shows that various factors influenced the generation of the immature oils. Firstly, the Es4 and Es1 Members include intervals enriched in algal material. Secondly, most of the immature oil is derived from soluble organic matter. Finally, the saline depositional environment was favorable for the preservation of organic matter.
SOURCE ROCK PROPERTIES OF LACUSTRINE MUDSTONES AND COALS (OLIGOCENE DONG HO FORMATION), ONSHORE SONG HONG BASIN, NORTHERN VIETNAM
Authors: Petersen H. I. , Tru Vu , Nielsen L. H. , Duc Nguyen A. , Nytoft H. P. 
Published: March 2006

Oligocene lacustrine mudstones and coals of the Dong Ho Formation outcropping around Dong Ho, at the northern margin of the mainly offshore Cenozoic Song Hong Basin (northern Vietnam), include highly oil‐prone potential source rocks. Mudstone and coal samples were collected and analysed for their content of total organic carbon and total sulphur, and source rock screening data were obtained by Rock‐Eval pyrolysis. The organic matter composition in a number of samples was analysed by reflected light microscopy. In addition, two coal samples were subjected to progressive hydrous pyrolysis in order to study their oil generation characteristics, including the compositional evolution in the extracts from the pyrolysed samples. The organic material in the mudstones is mainly composed of fluorescing amorphous organic matter, liptodetrinite and alginite with Botryococcus‐morphology (corresponding to Type I kerogen). The mudstones contain up to 19.6 wt.% TOC and Hydrogen Index values range from 436–572 mg HC/g TOC. From a pyrolysis S2 versus TOC plot it is estimated that about 55% of the mudstones’TOC can be pyrolised into hydrocarbons; the plot also suggests that a minimum content of only 0.5 wt.% TOC is required to saturate the source rock to the expulsion threshold.Humic coals and coaly mudstones have Hydrogen Index values of 318–409 mg HC/g TOC. They are dominated by huminite (Type III kerogen) and generally contain a significant proportion of terrestrial‐derived liptodetrinite. Upon artificial maturation by hydrous pyrolysis, the coals generate significant quantities of saturated hydrocarbons, which are probably expelled at or before a maturity corresponding to a vitrinite reflectance of 0.97%R0. This is earlier than previously indicated from Dong Ho Formation coals with a lower source potential.The composition of a newly discovered oil (well B10‐STB‐1x) at the NE margin of the Song Hong Basin is consistent with contributions from both source rocks, and is encouraging for the prospectivity of offshore half‐grabens in the Song Hong Basin.
TURBIDITE, SLUMP AND DEBRIS FLOW DEPOSITS AT THE KALCHINSKOE AND ZIMNEE OILFIELDS, WEST SIBERIAN BASIN
Authors: Khafizov S. F. , Syngaevsky P. E. 
Published: March 2006

This paper discusses specific facies associated with Cretaceous deep‐water slumps and sandstone intrusions in the West Siberian Basin. The slumps were formed during sea‐level falls when storms caused sediment masses to be discharged into deep‐water areas where they imposed a significant load on the underlying semi‐consolidated black shales, deforming and partially destroying them. Multiple slump / avalanche events are observed at the boundary between the Lower Cretaceous (Neocomian) and Upper Jurassic (Tithonian) sequences and form potential targets for oil exploration.High‐resolution sequence stratigraphic analyses show that both slump and distal fans are genetically related to lower slope/basin floor sediments and were deposited during regressions and subsequent lowstands. Two key depositional environments are recognized: the proximal parts of fans, where the most prospective potential reservoirs are found; and the more distal parts of slumps, which are principally composed of deformed shale clasts in a silt‐mudstone matrix. A third facies (“slump head”) is only observed on seismic profiles and is probably related to horizontally displaced “shingled” semi‐consolidated black shales.
DEEP SEISMIC REFLECTION DATA FROM OFFSHORE WESTERN GREECE: A NEW CRUSTAL MODEL FOR THE IONIAN SEA
Authors: Kokinou E. , Kamberis E. , Vafidis A. , Monopolis D. , Ananiadis G. , Zelilidis A. 
Published: March 2006

Contractional structures recognised in a recent SW‐NE oriented seismic profile offshore western Greece, between the islands of Zakynthos and Kefallinia (Cephalonia), indicate that this part of the Pre‐Apulian geotectonic zone was involved in Quaternary shortening related to the westward propagation of the Hellenic fold‐and‐thrust system. Deep reflector horizons including the Moho and the top of the crystalline basement were identified on the profile. Shallower reflectors include those corresponding to the contacts between the Mesozoic/Miocene, Upper Miocene/Lower Pliocene, and Pliocene/Pleistocene sedimentary sequences. The Upper Cenozoic to Quaternary sequence rests unconformably upon Mesozoic carbonates. Triassic evaporites wedge‐out in the Paxos geotectonic zone, where the Palaeozoic passes up into Mesozoic deposits.We have identified contractional structures which were reactivated during the Plio‐Quaternary on pre‐existing high‐angle normal faults, and which gave rise to significant topographic anomalies. West‐dipping normal faults were also recognised both within the Palaeozoic and Cenozoic successions, and are related to regional extension during sedimentation. East‐dipping thrust faults which root in the evaporites were also identified on the seismic profile.Due to right‐lateral strike‐slip activity on the Kefallinia Transform Fault, east‐dipping normal faults were formed within the lonion abyssal plain. This abyssal plain together with the Hellenic Trench, an accretionary prism, and a forearc basin can be recognised on the seismic profile. A “triple junction” between the Apulian (African) Platform, the oceanic crust of the Ionian Abyssal Plain and the Eurasian Plate in the west of the line is related to the Kefallinia Transform Fault. Neotectonic structural deformation (i.e. Quaternary‐Holocene) is superimposed on the above‐mentioned structures. Finally, diapiric movement of Triassic evaporites has affected both the Alpine and the late Cenozoic to Holocene sedimentary sequences. Diapiric activity continues at the present day in the eastern part of the profile, in the lonian geotectonic zone. The forearc basin may be prospective for hydrocarbons. Target areas include the lonian channel where a play has already been located, and its extension to the south (the Kyparisiakos Gulf area). Here, thick late Cenozoic to Quaternary deposits may act as a top‐seal above a reservoir consisting of eroded Mesozoic to Eocene carbonates, as at the recent Katakolon discovery.
FLOODPLAIN DEPOSITS AND SOIL CLASSIFICATION: THE PREDICTION OF CHANNEL SAND DISTRIBUTION WITHIN THE TRIASSIC ARGILOGRESEUX INFERIEUR, BERKINE BASIN, ALGERIA
Authors: Sabaou N. , Lawton D. E. , Turner P. , Pilling D. 
Published: March 2006

Middle to Late Triassic fluvio‐lacustrine sandstones referred to as the Trias Argilo‐Grèseux Inférieur (TAG‐I) are an important hydrocarbon reservoir in the Algerian Berkine Basin. Three depositional sequences have been identified within the TAG‐I and a fourth sequence overlies it, forming part of the “Trias Argilo‐Carbonaté”. Subtle changes in the style of sedimentation through these sequences have been identified and are attributed to periodic rises in base‐level together with changes in subsidence rate and climate, leading to basinward, progradational shifts of the fluvial systems. The palaeoclimate changed from semi‐arid to sub‐humid with seasonal wetting and drying, as indicated by the evolved style of the deposition, the abundance of vegetation and the nature of associated palaeosols. Four main types of palaeosol profile have been identified and consist of green/grey, red, and red/brown to purple palaeosols together with green/grey to red pedogenically modified mudstones, depending on the level of maturity.The presence of sphaerosiderites in green palaeosols is a clear indication of the occurrence of wetland conditions. Palaeosol development and maturity are useful aids to stratigraphic correlation and as an indication of the proximity of reservoir channel sandstones. With improved prediction of the sandbodies’location, better models of reservoir distribution can be made leading to an enhanced field development plan
LATE TO MIDDLE JURASSIC SOURCE FACIES AND QUALITY VARIATIONS, SOUTH VIKING GRABEN, NORTH SEA
Authors: Justwan H. , Dahl B. , Isaksen G. H. , Meisingset I. 
Published: March 2006

Source facies and quality of the Late to Middle Jurassic source rock system in the South Viking Graben between 58°N and 60°15'N are highly variable both regionally and stratigraphically. In order to assess the degree of variability and to create a model of source rock quality and potential, isochore maps of the syn‐ and post‐rift sections of the Upper Jurassic Draupne Formation and underlying Heather Formation were generated from seismic and well data, and maturity‐corrected Rock‐Eval data were used to generate quantitative maps of oil and gas potential. The thin post‐rift section at the top of the Draupne Formation is a rich oil‐prone source, while the up to 1,600 m thick syn‐rift section contains a mixture of Type III and Type II material with substantial amounts of gas‐prone and inert organic matter. The Heather Formation, which reaches modelled thicknesses of up to 930 m, is a lean source and is generally gas‐prone.Detailed analyses and interpretations of biomarker and isotopic characteristics support this upward increase in oil‐prone Type II material. The analytical parameters include increasing relative amounts of C27 regular steranes; decreasing ratios of C30 moretane relative to C30 hopane; and an increasing predominance of short chain n‐alkanes and progressively lighter isotopic values for saturate and aromatic fractions of source rock extracts. In addition, increasing amounts of 17α(H),21β(H)‐28,30‐bisnorhopane and decreasing amounts of C34 homohopanes relative to C35 homohopanes, as well as decreasing Pr/Ph ratios, suggest a general decrease in oxygenation upwards. Maps of average Pr/Ph ratios for the syn‐ and post‐rift Draupne Formation and for the Heather Formation are consistent with permanent water column stratification and gradual ascent of the O2:H2S interface from the Callovian to the Ryazanian.Interpretation of oil and gas potential maps, molecular parameters and estimates of sediment accumulation rates in combination suggest that the source facies of the upper, post‐rift Draupne Formation is controlled by widespread anoxia, reduced siliciclastic dilution and reduced input of gas‐prone organic and inert material; by contrast, the potential of the lower, syn‐rift Draupne Formation is strongly controlled by dilution by gas‐prone and inert organic matter resulting from mass flows and also by varying degrees of oxygenation. The oil and gas potential of the Heather Formation is mainly controlled by the degree of oxygenation and siliciclastic dilution.
THE STRUCTURAL STYLE OF SEDIMENTARY BASINS ON THE SHELVES OF THE LAPTEV SEA AND WESTERN EAST SIBERIAN SEA, SIBERIAN ARCTIC
Authors: Franke D. , Hinz K. 
Published: March 2006

A total of 11,700 km of multichannel seismic reflection data were acquired during three recent reconnaissance surveys of the wide, shallow shelves of the Laptev and western East Siberian Seas in the Siberian Arctic Ocean. Three seismic marker horizons were defined and mapped in both shelf areas. Their nature and age were predicted on the basis of regional tectonic and palaeoenvironmental events and corroborated using onshore geology. To the north of the Laptev Sea, the Gakkel Ridge, an active mid‐ocean ridge which separates the North American and Eurasian Plates, abruptly meets the steep slope of the continental shelf which is curvilinear in plan view. Extension has affected the Laptev Shelf since at least the Early Tertiary and has resulted in the formation of three major, generally north‐south trending rift basins: the Ust’Lena Rift, the Anisin Basin and the New Siberian Basin.The Ust’Lena Rift has a minimum east‐west width of 300km at latitude 75°N and a Cenozoic infill up to 6 s (twt) in thickness. Further to the NW of the Laptev Shelf, the downthrown and faulted basement is overlain by a sub‐parallel layered sedimentary succession with a thickness of 4 s (twt) that thins towards the west. Although this area was affected by extension as shown by the presence of numerous faults, it is not clear whether this depression on the NW Laptev Shelf is continuous with the Ust’Lena Rift.The Anisin Basin is located in the northern part of the Laptev Shelf and has a Cenozoic sedimentary fill up to 5 s (twt) thick. The deepest part of the basin trends north‐south. To the west is a secondary, NW‐SE trending depression which is slightly shallower than the main depocentre. The overall structure of the basin is a half‐graben with the major bounding fault in the east.The New Siberian Basin is up to 70 km wide and has a minimum NW‐SE extent of 300 km. The sedimentary fill is up to 4.5 s (twt) thick. Structurally, the basin is a half‐graben with the bounding fault in the east.Our data indicate that the rift basins on the Laptev Shelf are not continuous with those on the East Siberian Shelf. The latter shelf can best be described as an epicontinental platform which has undergone continuous subsidence since the Late Cretaceous. The greatest subsidence occurred in the NE, as manifested by a major depocentre filled with inferred (?)Late Cretaceous to Tertiary sediments up to 5 s (twt) thick.
SOURCE ROCK CHARACTERIZATION BASED ON BIOLOGICAL MARKER DISTRIBUTIONS OF CRUDE OILS IN THE SOUTHERN GULF OF SUEZ, EGYPT
Authors: Younes M. A. , Philp R. P. 
Published: March 2006

The depositional environment and maturity of source rocks in the southern Gulf of Suez were evaluated using biomarker and isotope data from crude oils derived from a variety of source rock types of different geological ages. Two oils families were identified and are referred to as types A and B. Type A oils are characterized by a predominance of oleanane and relatively low gammacerane concentrations, suggesting that they were derived from a terrigenous source rock with a significant input of angiosperm material inferred to occur within the marginally‐mature syn‐rift Lower Miocene Rudeis Shale. By contrast, type B oils are distinguished by a predominance of gammacerane and relatively low oleanane concentrations, suggesting that they were generated from mature marine carbonate source rocks inferred to occur within the Upper Cretaceous Brown Limestone and Middle Eocene Thebes Formation. Maturity parameters including the sterane isomerisation ratios C29αββ/(αββ+ααα), C29ααα20S/(S+R) and TAS/(TAS+MAS), together with aromatic sulphur compound ratios (4‐MDBT / I‐MDBT; 4,6‐ / 1,4‐DMDBT; 2,4–/ 1,4‐DMDBT; and DBT / phenanthrenes), support the higher thermal maturity of type B oils relative to type A oils.The biomarker variablility reflects the occurrence of two distinct source rocks in the southern Gulf of Suez and suggests that two independent petroleum systems are present here. These appear to be confined to the pre‐rift (pre‐Miocene) and syn‐rift megasequences respectively.
HYDROCARBON SOURCE ROCKS AND GENERATION HISTORY IN THE LUNNAN OILFIELD AREA, NORTHERN TARIM BASIN (NW CHINA)
Authors: Xiao X. M. , Hu Z. L. , Jin Y B. , Song Z. G. 
Published: March 2006

In this paper we report on source rocks and maturation history at the Lunnan oilfield, northern Tarim Basin (NW China), using a combination of organic petrographic and geochemical techniques. Three separate source rock intervals are present here: Cambrian mudstones and argillaceous limestones; Middle and Upper Ordovician argillaceous limestones; and Triassic mudstones. Reservoir rocks comprise Lower Ordovician carbonates, Carboniferous sandstones, and Triassic and Jurassic sandstones. Structural traps were formed principally during the Silurian and Jurassic.The Lunnan field is located on a small‐scale palaeo uplift which developed during the Early Palaeozoic. Hydrocarbons migrated updip from source areas in surrounding palaeo‐lows along faults and unconformities. Major phases of hydrocarbon generation and migration occurred in the Early Silurian — Late Devonian, Cretaceous — Early Tertiary and Late Tertiary. Uplift and intense erosion at the end of the Devonian destroyed Early Palaeozoic oil and gas accumulations sourced from the Cambrian source rocks, but hydrocarbons generated by Middle and Upper Ordovician source rocks during the Mesozoic and Tertiary have been preserved. At the present day, accumulations are characterized by a range of crude oil compositions because source rocks from different source areas with different maturation histories are involved.
Do herbivores cause habitat degradation or vegetation state transition? Evidence from the tundra
Authors: Wal René van der 
Published: March 2006

Range expansion and increasing densities of large herbivores are held responsible for large‐scale habitat degradation in a wide range of natural and semi‐natural ecosystems. Herbivore‐driven ecosystem changes frequently represent predictable transitions from one vegetation state to another. Whether such predictable changes justify the value judgement ‘habitat degradation’ may be debatable as this strongly depends on individual perspective.To further the debate on herbivore‐driven habitat degradation, I apply the concept of alternative stable states to arctic tundra as a framework to capture predictable stepwise vegetation transitions in which the productivity and hence herbivore‐carrying capacity increases with grazing pressure. Specifically, evidence is provided that large parts of the tundra biome can be in either of three relatively discrete vegetation states and that changes in reindeer/caribou density are responsible for sudden, predictable but often reversible state transitions. From this, it appears that the relatively rapidly emerging vegetation changes do not necessarily equate to habitat degradation, but in many cases reflect predictable vegetation change. Acknowledgement of the existence of predictable state transitions in tundra ecosystems may help to evaluate the observed radical vegetation changes occurring throughout the reindeer/caribou range.