ORGANIC GEOCHEMISTRY OF MIDDLE MIOCENE (BADENIAN – SARMATIAN) SOURCE ROCKS AND MATURATION MODELLING IN THE POLISH AND UKRAINIAN SECTORS OF THE EXTERNAL CARPATHIAN FOREDEEP

The Carpathian Foredeep to the north and NE of the Carpathian orogenic belt in SE Poland and NW Ukraine is divided into internal and external sectors. In the narrow internal foredeep, Lower and Middle Miocene shales, sandstones and interbedded evaporites are tightly folded. By contrast the external foredeep is characterized by the presence of a thick, unfolded Middle Miocene molasse succession. This ranges in thickness from a few hundred metres in the north of the external foredeep to >5000 m in the south, near the Carpathian thrust front. Middle Miocene sandstones in the external foredeep form a major reservoir for biogenic gas at fields in Poland and Ukraine. The Middle Miocene molasse succession in the external Carpathian Foredeep also contains organic-rich intervals which have source rock potential. For this paper, core samples (n = 670) of Badenian and Sarmatian mudstones from 43 boreholes in the Polish sector of the external foredeep were analysed to investigate their organic geochemistry and hydrocarbon potential. Results show that the samples analysed in general have low to fair (but locally high) total organic carbon (TOC) contents which range up 4.6 wt.% although the average is only 0.7 wt.%. Rock-Eval (S₁+S₂) values are poor to fair and the hydrogen index is also low with a mean value of less than 100 mg/g TOC. The samples analysed are dominated by gas-prone Type III kerogen and this is consistent with previous studies of time-equivalent samples from the Ukrainian part of the external foredeep. The organic matter is in general thermally immature and is interpreted to have been deposited in anoxic and/or sub-oxic conditions. However in the Polish part of the external foredeep, thermal maturities may locally reach the initial phase of the oil window where the Middle Miocene source rocks have been buried deeply beneath the Carpathian thrust front. The burial history and thermal evolution of the Middle Miocene succession were reconstructed by means of 1-D modelling at nine boreholes located in both the Polish and Ukrainian parts of the external Carpathian foredeep. The modelling indicated that Middle Miocene source rocks have only entered the initial phase of the oil window locally where they are buried beneath the flysch nappes of the Carpathian foldbelt. At these locations the generation of thermogenic gas may have begun at depths of more than 3 km. However, Middle Miocene source rocks are still immature at depths of >4000 m in some boreholes in the Ukrainian part of the study area. The absence of accumulations of thermogenic natural gas is consistent with the observed low levels of source rock maturity.     

PETROLEUM GENERATION IN THE UKRAINIAN EXTERNAL CARPATHIANS AND THE ADJACENT FORELAND

Major hydrocarbon accumulations are located in western Ukraine within the Mesozoic-Cenozoic flysch sequence in the frontal parts of the External Carpathians, and in the adjacent autochthonous foreland. The accumulations occur in three different structural settings: in the Carpathian flysch belt; in the pre-Neogene foreland autochthon; and in Miocene foredeep molasse. The petroleum potential of organic-rich rocks belonging to a number of different sedimentary cycles and tectonic units was studied by Rock-Eval pyrolysis.
Two significant organic-rich units, both with a basin-scale distribution, occur within the External Carpathians: (i) a unit comprising the Lower Cretaceous Shypot and Spas Formations; and (ii) the Oligocene-Lower Miocene Menilite Formation. The Menilite Formation includes the principal source rocks in this area, although Lower Cretaceous source rocks may also have generated hydrocarbons. Thermal maturation of the flysch and consequent petroleum generation resulted mainly from tectonic burial during Miocene overthrusting. In the external parts of the Carpathian Flysch Belt, oil generation in the Menilite Formation begins at a depth of around 4.2 km and ceases at around 6 km. In more internal tectonic units, a "frozen oil kitchen" occurs at shallower depths, indicating an increasing amount of tectonic uplift and erosion.
The autochthonous foreland is part of the SW margin of the East European Platform, and is partially overthrust by the Carpathian orogen. Rocks belonging to several different sedimentary cycles are present here. Pre-Mesozoic rocks in the foreland are overmature, at least within the central and SE parts of the study area. Petroleum accumulations are therefore most probably confined to the Mesozoic-Cenozoic sedimentary cover, within which the Middle Jurassic Kokhanivka Formation has the highest generation potential.     

NEOGENE TECTONIC HISTORY OF THE SUB-BIBANIC AND M'SILA BASINS, NORTHERN ALGERIA: IMPLICATIONS FOR HYDROCARBON POTENTIAL

The southern Bibans region in northern Algeria is located in the external zone of the Tell fold‐and‐thrust belt. Field observations in this area together with seismic data integrated with previous studies provide evidence for a number of Tertiary deformation phases. Late Eocene Atlassic deformation was followed by Oligocene (?)‐Aquitanian‐Burdigalian compression, which was associated with the development of a foreland basin in front of a southerly‐propagating thrust system. Gravity‐driven emplacement of the Tellian nappes over the basin margin probably occurred during the Langhian‐Serravallian‐Tortonian. The Hodna Mountains structural culmination developed during the Miocene‐Pliocene. Analysis of brittle structures points to continued north‐south shortening during the Neogene, consistent with convergence between the African and Eurasian Plates. The unconformably underlying Mesozoic‐Cenozoic autochthonous sequence in this area contains two potential source rock intervals: Cenomanian‐Turonian and Eocene. Reservoir rocks include Lower Cretaceous siliciclastics and Upper Cretaceous to Palaeogene carbonates. Structural style has controlled trap types. Thus traps in the Tell fold‐and‐thrust belt are associated with folds, whereas structural traps in the Hodna area are associated with reactivated normal faults. In the latter area, there is also some evidence for base‐Miocene stratigraphic traps.     

TECTONO‐STRATIGRAPHIC EVOLUTION OF THE NW SEGMENT OF THE ZAGROS FOLD‐THRUST BELT,KURDISTAN, NE IRAQ

The Kurdistan (NW) segment of the Zagros fold‐thrust belt, located in the Kurdistan Region of NE Iraq, forms the external part of the Zagros orogen and is bounded by the Zagros suture to the NE. To the SW is the Arabian Plate into which the deformation front has migrated progressively, beginning in the Late Cretaceous and culminating in the Tertiary. Regional compression resulted in obduction of the Mawat ophiolites and emplacement of the Avroman and Qulqula nappes onto the continental margin, and the formation of the Kurdistan foreland basin. In this paper, structural, stratigraphic and palaeontological data together with new field observations are used to investigate the tectono‐stratigraphic evolution of this basin, and to study the propagation of the deformation front from the Zagros Imbricate Zone in the NE towards the Mesopotamian foredeep in the SW. Six unconformities within the Kurdistan foreland basin succession are recognized: Turonian (base‐AP9; 92 Ma); Danian (base‐AP10; 65 Ma); Paleocene–Eocene (intra‐AP10; 55 Ma); late Eocene (top‐AP10; 34 Ma); middle‐upper Miocene (a local unconformity; intra‐AP11; 12 Ma); and Pleistocene. These unconformities can be divided into two groups; obduction‐related (Turonian, Danian, and Paleocene‐Eocene); and collision‐related (late Eocene, middle‐upper Miocene, and Pleistocene). The geographical position of the unconformities is used to determine the rate of propagation of the deformation front, which is estimated at ca. 3 mm/yr. This is in agreement with previous studies which suggested a NW‐ward decrease in the propagation rate. The rate was most rapid (2.95 mm/yr) in the Low Zagros Fold‐Thrust Zone and slower (2.06 mm/yr) in the High Zagros Fold‐Thrust Zone. The more rapid propagation rate in the former area may be attributed to the presence there of the Miocene Lower Fars Formation which acted as a shallow décollement surface. Within the Zagros fold‐thrust belt, the intensity of deformation decreases towards the foreland (SW). Deformation in the High Zagros Fold‐Thrust Zone is characterized by thrust imbricates and high amplitude fault‐propagation folds at the surface separated by narrow synclines. However, the Low Zagros Fold‐Thrust Zone (Simply Folded Belt) is characterised by detachments and low amplitude fault propagation folds separated by broad synclines. In the foredeep area, folds are confined to the subsurface. Deeply buried Jurassic units, together with Upper Cretaceous – Paleocene siliciclastics, and the evaporite‐dominated Lower Fars Formation may have acted as décollement surfaces in the NW segment of the Zagros fold‐thrust belt, and controlled the structural geometry and evolution of the area.     

川西两期前陆盆地南北两段构造演化的地球物理特征

区域构造演化研究结果表明,川西前陆盆地经历了早中生代和晚新生代两期前陆盆地演化过程。无论是前陆盆地的发育程度还是前陆变形特征及前渊带沉积作用,盆地的南、北两段都存在明显的差异。根据川西地区及邻区的重磁场特征,获得了川西地区基底性质及主要断裂带分布的研究成果。德阳-绵阳一带刚性基底对新生代变形由南向北的传播起了阻挡作用,奠定了新生代变形南强北弱的格局。同时,一系列北西向走滑断裂带的存在进一步削弱了新生代变形作用。基底性质的差异和北西向走滑断裂带的存在是造成川西前陆盆地南、北两段差异的主要制约因素,直接造成了南、北两段新生代变形的差异。     

重磁电震联合反演在合肥盆地勘探中的应用

在合肥盆地开展了高精度重力、航磁、电法、地震(简称重磁电震)、化探等多种方法勘探的基础上,本文通过对重磁电资料的目标处理,建立起全区地球物理场;应用重磁电震资料联合反演,获得的主要成果有：①完成了印支面及结晶基底构造图;②发现了“影子盆地”;⑧本区自南而北划分为四个构造带,即前陆冲断带、前渊沉降带、前隆断褶带、隆后斜坡带;④指明前陆冲断带和前隆断褶带是合肥盆地油气勘探突破的有利地区。     

合肥盆地侏罗纪构造沉积特征与含油气性

合肥盆地是一个以中生界为主体的沉积盆地,受燕山运动Ⅰ幕不同期次挤压逆冲造山的影响,依次形成一系列平行分布的逆冲推覆构造带和前渊盆地。不同时期的前渊盆地既有继承性,又有新生性;从南向北,构造幅度逐渐减小,从而形成合肥盆地侏罗系南厚北薄以磨拉石建造为主体的地质体,仅在不同期次盆地的边缘斜坡带上发育河流—平原沼泽相的杂色砂泥岩夹灰黑色炭质泥岩、薄煤层沉积。扬子地质体向北大规模的推覆和挤压导致的区域性高地温,以及侏罗纪的快速堆积,使盆地深坳处古生界烃源岩在侏罗纪时期即达到过成熟演化阶段,其生烃潜力有限。      

库车再生前陆逆冲带的构造特征与成因

库车再生前陆逆冲带自北而南分为以下５个构造速：①北部边缘冲断－隐伏构造楔;②斯的克背斜带;③北部线性背斜带;④拜城背驮凹陷;⑤丘里塔格前缘带。全体形成前锋向南的冲断变形楔。各构造带中发育多种型式的断坪／断坡台阶状逆断层相关褶皱：断层传播褶皱滑脱褶皱、断层传播－滑脱混生褶皱、双重逆冲构造。在不同构造带发不同时代的生长地层,批示了各构造带不的构造变形年代。斯的克背斜带变形时期最早,始于中新世带的亚肯变     

TIMING AND MODES OF DEFORMATION IN THE WESTERN SICILIAN THRUST SYSTEM, SOUTHERN ITALY

Imbricate units in the western Sicilian fold-and-thrust belt originated on the southern continental margin of Neotethys, and were deformed during the Neogene-Recent in response to convergence between the African and European Plates. Neogene-Pleistocene synorogenic sediments, deposited in flexural foredeeps and satellite piggy-back basins, contain a record of the belt's evolution. Progressive migration of the thrust front southwards into the foreland has been documented, beginning in the Tortonian and continuing to the present-day particularly in western parts of the belt. In the eastern part, activity on Quaternary strike-slip fault zones has produced asymmetric flower structures and other interference structures.
In this paper, we present two regional sections across the western Sicilian foreland-thrust belt system. These structural cross-sections extend down as far as the top of the Hercynian basement and integrate our field observations with previously-acquired well log, magnetic and seismic data. We show that complex interactions between the foreland-migrating thrust belt, which developed between the Late Miocene and the Pleistocene, and Pleistocene strike-slip faults led to the development of structural traps which constitute potential targets for hydrocarbon exploration.     

合肥盆地重力场特征

合肥盆地地质构造复杂,地表沟壑纵横,通过对重力异常目标处理,揭示基底特征及断裂、构造发育情况,认为本区南北分区,"众凹环隆"。该文应用重、磁、电、震等综合物探资料,将本区划分为前陆冲断带、舒城前渊沉降带、六安前隆断褶带和肥北隆后斜坡带4个勘探区带。指出了下步勘探方向和勘探前景。      

COMPRESSIVE NEOGENE-QUATERNARY TECTONICS IN THE HINTERLAND AREA OF THE NORTHERN APENNINES

The NW-SE trending Northern Apennine Mountains consist of a series of allochthonous units which were thrust generally to the NE during Neogene crustal shortening, in the direction of a foreland basin to the east andNE. On the hinterland (internal) side of this fold-and-thrust belt, a series of small-scale sedimentary basins developed from the late Miocene and were deformed at the same time. The late Tortonian-Pleistocene evolution of the Northern Apennines has previously been considered by most authors in terms of a classical model of a NE-migrating compressional front, which was followed in time and space by a hinterland extensional regime related to the development of the Tyrrhenian Basin. This paper presents new structural data from both the external parts of the Northern Apennines and the late Tortonian-Pleistocene basins located in the internal sector. In the Northern Apennine thrust belt, reactivation and out-of-sequence geometries for the thrust faults have been recorded. In the hinterland basins, compressional deformation has been documented and is usually associated with thrust ramps and regional unconformities. The timing of both thrust reactivation and of the major compressional phases affecting the hinterland basins is closely correlated with periods of magmatic quiescence, and with compressional phases detected in the external margin of the Northern Apennines (the Padan-Adriatic foredeep). Data presented in this paper indicate that compressional deformation has played a major role in the recent evolution of the Northern Apennines. The mechanism envisaged to explain this tectonic framework takes account of the piggy-back emplacement of basement thrusts from internal to external sectors, which occurred in post-Serravallian time. Activity on basement thrusts may have caused reactivation of thrusts in the internal cover sequence, giving rise to out-of-sequence geometries and controlling the development and/or deformation of the hinterland basins. This type of structural evolution has resulted in a complex geometry for the thrust sheets, and this must be taken into consideration during re-interpretation of the structure of the Northern Apennines. It may also have important implications for petroleum exploration.     

塔西南坳陷和田凹陷前陆逆冲带构造特征

和田凹陷前陆逆冲带位于塔里木盆地西南坳陷东部,剖面上由上而下、自南而北是由推覆体、多个冲断席片叠加而成的叠加背斜双重构造体以及弱变形的原地体组成.其中,推覆体厚5000～7000m,东西长205km,南北宽14～43km,向北推覆距离为40～100km,是一与上盘生长断层有关的转折褶皱背斜,受和田大型台阶式滑脱断层的控制;推覆体侧缘发育了与边界断层平行的侧断坡、斜断坡次级断层相关褶皱背斜;而在其前缘,由于沿推覆背斜北翼的轴面发生破裂,产生了一系列的次级断层及相关褶皱;在推覆体内部,沿东西向轴线发生了起伏变化,形成了背斜圈闭.在推覆体之下,由东向西依次发育了弱变形的东倾斜坡、皮牙曼叠加断坡背斜型的双重构造、桑株三角带构造与叠瓦冲断带.在剖面上,叠瓦冲断带位于三角带构造的前缘下方,平面上呈重叠分布.      

准噶尔盆地红车断裂带同生逆冲断裂特征

将准噶尔盆地西北缘红车断裂带分成4个断裂亚带：红山嘴逆冲断裂亚带、中拐反冲断裂亚带、车排子近NS向逆冲断裂亚带和车75井—车77井NW向逆冲断裂亚带,并分析各断裂亚带的平面分布特征及形成机制,再运用断裂生长指数和断距分析方法对典型构造剖面进行研究,认为同生逆冲断裂多数是前缘主干断裂,为高角度基底卷入型叠瓦冲断构造,对二叠系、三叠系和侏罗系底部的沉积有明显控制作用。二叠纪逆冲推覆剧烈,逆冲断裂普遍发育,三叠纪断裂发育强度由北向南呈减弱趋势;侏罗纪断裂发育表现为北部地区较弱,中部地区较强,南部地区几乎停止的特点。二叠纪到三叠纪断裂发育为前展式,三叠纪到侏罗纪断裂发育为后展式。     

PALAEOZOIC STRUCTURES AND OIL EXPLORATION PROSPECTS IN THE EASTERN TARIM BASIN, NW CHINA

The Tabei Uplift in the northern Tarim Basin, the Tadong Depression in the eastern Tarim Basin, and the Tarim Central Uplift were formed as a result of mantle diapirism. Four stages in the geological development of this area can be recognized: an initial "embryonic" stage in the late Proterozoic; a "formational" stage in the Sinian; a "developmental" stage in the Early to mid-Palaeozoic; and a "completion" stage in the late Palaeozoic.
With long-term Palaeozoic subsidence and well-developed marine source rocks, the Tadong area is thought to be a promising source region for hydrocarbons. The Tabei and Central Uplifts, located respectively north and south of the Tadong Depression, are ancient, well-preserved structures in which hydrocarbons may have accumulated, and could therefore constitute prospective areas for the location of "giant" oil- and gasfields in Palaeozoic sequences. Palaeozoic oil prospects have been confirmed in the Tabei area by the highly-productive Sachan 2 well. It is expected that intensified exploration will result in the location of both oil- and gasfields in the Central Uplift.     

East Venezuela盆地油气聚集与勘探潜力

East Venezuela盆地是一个大型的不对称前陆盆地,具有丰富油气资源。古生代以来,经历了晚三叠世—侏罗纪裂谷、白垩纪—始新世被动边缘和渐新世至今前陆盆地3个演化阶段。纵向上沉积地层可划分为前白垩系、白垩系和后白垩系3套巨层序。East Venezuela盆地最主要的烃源岩是Guayuta群和Tigre组海相泥页岩和碳酸盐岩。生油岩成熟度由北往南递减。北部烃源灶油气经断层、砂体长距离阶梯式向南部斜坡边缘运移。盆地最主要圈闭类型为背斜、断块、地层和岩性圈闭。Oficina组构造、构造—地层、地层圈闭组合和Naricual组构造圈闭组合是盆地内最主要的两套成藏组合。有潜力的勘探领域包括白垩系—下中新统被动边缘沉积层序、盆地中部前渊区、南部重油带和东部海域。     

鄂尔多斯盆地南缘构造特征及下古生界天然气勘探前景

鄂尔多斯盆地南缘现今构造格局受控于自南向北扩展的两个逆冲推覆体系，上、下古生界之间及基底与盖层之间均存在滑脱层，其东段和西段构造缩短率分别为１８．６％和４．８％。构造变形的主体是燕山期逆冲推覆构造，其前缘带是勘探下古生界构造类气藏的有利区带，且以东北部地区勘探风化壳型气藏最有利；前缘外带保存条件最好，以非构造圈闭为主，是本区最有勘探前景的地区。     

鄂尔多斯盆地西部逆冲推覆构造带特征及其演化与油气勘探

该带以青铜峡-固原断裂为界,以东为南北向构造带,以西为六盘山弧形构造带。逆冲带由一系列向东或北东逆冲的叠瓦状断层所组成,中生代是其主要形成和发育时期。本区含油远景以韦州-马家滩地区的原地岩体及南北向构造带的前缘外带北段为最好。     

TECTONIC EVOLUTION OF THE NORTHERN MARGIN OF THE CENOZOIC ARARAT BASIN,LESSER CAUCASUS,ARMENIA

This paper investigates the structure of the northern margin of the Ararat depression in a study area in SE Armenia. The depression is a Cenozoic intermontane basin located to the south of the Lesser Caucasus. The purpose is to improve understanding of the basin's structure and origin within a regional tectonic framework which has been dominated since the Late Cretaceous by the closure of Neotethys and the Arabia‐Eurasia collision. We suggest that the depression is not a graben controlled by normal faults; rather, based on detailed observations, structures in the study area are interpreted as oblique‐slip reverse and thrust faults activated in post Oligocene‐Miocene times. These compressional faults resulted in the formation of asymmetric fold structures including the Lanjanist and Urts anticlines which are well expressed in the surface relief to the north of the Ararat depression. In general the structural pattern is complicated by secondary normal faults which resulted in superimposed gravitational slope processes and erosion. Major structures in the study area originated in a compressional setting associated with the closure of Neotethys since the latest Cretaceous. Post‐collisional strike‐slip faulting was linked to convergence of the Arabian and Eurasian plate margins. Pliocene and Quaternary structures, some still active, show evidence of structural inheritance. The Armenian portion of the Ararat depression contains obduction‐related nappes, anticlines and thrust faults which have potential as structural traps for hydrocarbons. These should be investigated in detail using advanced geophysical methods including 2D and 3D seismic analyses.     

THE ORIGIN AND DEVELOPMENT OF NEOGENE BASINS IN THE SE BETIC CORDILLERA (SE SPAIN): A CASE STUDY OF THE TABERNAS-SORBAS AND HUERCAL OVERA BASINS

Neogene— Quaternary sedimentary basins in SE Spain contain a record of the geodynamic evolution of the Internal Zone of the Betic Cordillera. The basement of the Internal Zone is composed of Palaeozoic and Mesozoic metasediments which have undergone variable degrees of metamorphism. The External Zones consist of largely unmetamorphosed sedimentary rocks which were deposited on the SE margin of the Iberian Plate during the Mesozoic and Early Cenozoic. Westward tectonic emplacement of these terranes onto the Iberian Plate took place between the end of the Palaeogene and the middle Miocene. In this paper, we investigate the late Miocene (Tortonian-Messinian) stratigraphy of two basins in the Internal Zone — the Tabernas-Sorbas and Huercal Overa Basins. We also consider some recently-acquired structural data. The Tabernas-Sorbas and Huercal Overa Basins are east-west trending depressions bounded to north and south by sierras in which basement rocks are exposed. The basins contain very similar sedimentary successions in which planktonic foraminifera have been preserved. However, the faunal composition is very variable, and the observed sporadic and abrupt changes in foraminiferal populations imply palaeo-ecologic and palaeo-oceanographic instabilities which may be associated with local tectonism. Stratigraphic markers were affected by these changes, making precise dating difficult near the Tortonian-Messinian boundary. Our data indicate that Messinian rocks are more widely distributed than has hitherto been suspected. A Messinian age for the prominent coral limestones in the Tabernas-Sorbas Basin has long been accepted; similar coral limestones in the Huercal Overa Basin have previously been dated as Tortonian. However, our data show that these carbonates are of Messinian age in both basins. The origin and development of the Tabernas-Sorbas and Huercal Overa Basins have previously been interpreted in a number of ways. Many (but not all) models favour strike-slip movement on NE-SW or east-west trending basin-bounding faults. The formation and deformation of the basins occurred during the Tortonian and Messinian, at the same time as the uplift of the sierras. The sierras are here interpreted to represent structural culminations above westward-verging, deep-seated thrust faults, and the basins to be lateral folds (or lateral ramps, i.e. oriented parallel to the thrust transport direction). The east-west trending strike-slip faults at the margin of the Sorbas- Tabernas Basin may be compatible with such a model. Major NE-SW trending, left-lateral wrench faults have been described in this area. These faults cut through late Miocene and Pliocene deposits, and are still active at the present day. Although these faults were initiated during the late Miocene, they do not appear to have influenced the development of the Tabernas-Sorbas and Huercal Overa Basins during the early Tortonian.     

前陆盆地逆冲断层类型与形成机制——以鄂尔多斯地块西缘和塔里木盆地北缘为例

具前陆盆地性质的鄂尔多斯地块西缘和塔里木盆地北缘发育九类逆冲断层:褶皱-逆冲断层型,褶皱-逆冲推覆型,高角度逆冲-牵引褶皱型,犁式逆冲-推覆型,同沉积基底逆冲断层型,基底楔冲断层型,基底背冲断层型,逆转逆冲断层型和基底平移-逆冲断层型。这些褶皱-逆冲构造的形成主要受板内地块或微板块间侧向挤压应力作用、基底缩短作用和滑脱作用的控制。