Neogene tectonic evolution of the Gulf of Hammamet area,Northeast Tunisia offshore

This paper discusses the Neogene tectonic evolution of the Tunisia offshore Gulf of Hammamet basin. Based on seismic and well data, this basin was created during the Miocene and is currently trending NE–SW. During the Neogene, the study area was affected by geodynamic interactions controlled simultaneously by convergence of the Eurasia and Africa plates and the opening of the Atlantic Ocean. These interactions generated compressive and extensional regimes which led to a variety of structures and basin inversions.The middle Miocene extensional regime created horst and graben structures (e.g. the Halk El Menzel graben). The two major compressive phases of the Tortonian and post Villafranchian age created different structures such as Ain Zaghouan and Fushia structures and the Jriba trough, and led to the reactivation of the old normal faults as reverse faults. During the Plio-Pleistocene and the Quaternary times, the Gulf of Hammamet was affected by an extensional regime related to the Siculo-Tunisian rift, which led to the development in the area of several sedimentary basins and new normal fault patterns.The Gulf of Hammamet shows several basins ranging in age from the Tortonian to the Quaternary, which display different structural and stratigraphic histories. Two main groups of sedimentary basins have been recognized. The first group has Tortonian–Messinian sedimentary fill, while the second group is largely dominated by Plio-Quaternary sediments. The shortening during the Tortonian and post Villafranchian times has led to the tectonic inversion of these basins. This shortening could be correlated to the Europe–Africa collision.Despite the large number of hydrocarbon discoveries, the Gulf of Hammamet remains under-explored, in particular at deeper levels. This study aims to guide future exploration and to highlight some new play concepts.     

Seismic sequence stratigraphy of Miocene deposits related to eustatic,tectonic and climatic events,Cap Bon Peninsula,northeastern Tunisia

The Cap Bon Peninsula, belonging to northeastern Tunisia, is located in the Maghrebian Alpine foreland and in the North of the Pelagian block. By its paleoposition, during the Cenozoic, in the edge of the southern Tethyan margin, this peninsula constitutes a geological entity that fossilized the eustatic, tectonic and climatic interactions. Surface and subsurface study carried out in the Cap Bon onshore area and surrounding offshore of Hammamet interests the Miocene deposits from the Langhian-to-Messinian interval time. Related to the basin and the platform positions, sequence and seismic stratigraphy studies have been conducted to identify seven third-order seismic sequences in subsurface (SM1-SM7), six depositional sequences on the Zinnia-1 petroleum well (SDM1-SDM6), and five depositional sequences on the El Oudiane section of the Jebel Abderrahmane (SDM1–SDM5). Each sequence shows a succession of high-frequency systems tract and parasequences. These sequences are separated by remarkable sequence boundaries and maximum flooding surfaces (SB and MFS) that have been correlated to the eustatic cycles and supercycles of the Global Sea Level Chart of Haq et al. (1987). The sequences have been also correlated with Sequence Chronostratigraphic Chart of Hardenbol et al. (1998), related to European basins, allows us to arise some major differences in number and in size. The major discontinuities, which limit the sequences resulted from the interplay between tectonic and climatic phenomena. It thus appears very judicious to bring back these chronological surfaces to eustatic and/or local tectonic activity and global eustatic and climatic controls.     

Land subsidence along the northeastern Texas Gulf coast: Effects of deep hydrocarbon production

The Texas Gulf of Mexico coast is experiencing high (5–11 mm/yr) rates of relative sea level (RSL) rise that are the sum of subsidence and eustatic sea level (ESL) rise. Even higher rates are associated with areas of groundwater pumping from confined aquifers. We investigate the possibility of deep petroleum production as a cause for the high regional rates of subsidence. The northeast Texas coast was chosen for the study because it has a high rate of RSL rise, very limited groundwater production, and a long history of petroleum production. We examine in detail the Big Hill and Fannett fields, for which adequate bottom hole pressure (BHP) and well log data are available. The hypothesis of deep petroleum production is tested in three ways. First, industry BHP tests show many of the fields are depressurized to far below hydrostatic pressures. Second, analysis of BHP data over time in the Big Hill and Fannett fields indicates that some Zones in these fields were below hydrostatic when production commenced. This indicates that depressurization from production in neighboring fields or zones within the same field is not limited to the production zone. Third, three models for subsidence (a general 1-D regional model, an intrareservoir model, and a reservoir bounding layer model), using reasonable hydrogeological parameters, predict subsidence within the inferred range of data. The latter two models use data from the Big Hill and Fannett fields. Additional verification of the hypothesis that deep petroleum production is causing or accelerating regional subsidence will require the collection and analysis of data on the subsurface hydrogeological parameters and detailed measurements of the spatial and temporal distribution of subsidence along the Texas Coast.     

Evaluation of hydrocarbon pollution in marine sediments of Sfax coastal areas from the Gabes Gulf of Tunisia,Mediterranean Sea

The Tunisian environmental legislation that follows the EC Directives requires monitoring of persistent, toxic and bio-accumulated substances commonly considered as hazardous substances. In order to comply with this requirement, samples of sea water, sediment and biota from the urbanized and industrialized coast line of Sfax city are investigated. This study presents the results of petroleum hydrocarbon content, distribution and probable origin (anthropogenic and/or biogenic) in 16 intertidal sediments of Sfax coastal area. Alkane distribution indices and hydrocarbon distribution patterns are used to identify natural and anthropogenic input. Non-aromatic hydrocarbons present a high concentration with a range varying from 180 to 1,400 μg/g of dry sediment. The total concentrations of polycyclic aromatic hydrocarbons (PAHs) varied from 0.41 to 5.6 μg/g dry weight. These concentrations are comparable to other marine areas that receive important inputs. n-Alkanes with carbon number ranging from 15 to 35 are identified to be derived from both biogenic and anthropogenic sources in varying proportions. Pristane/phytane ratio shows values lower than 1.4 suggesting the presence of petroleum contamination. This is confirmed by the presence of a large group of unresolved complex mixture and the identification of hopanes with predominant C29 and C30 compounds and steranes with predominance of C27 over C28 and C29 compounds. Ratios of selected PAH concentrations indicate petrogenic and pyrolytic origin of hydrocarbons. Anthropogenic hydrocarbon inputs were more apparent at sites associated with industrial discharges, shipping activities and sewage outfalls.     

Superposed folding in the Neogene series of the northeastern Tunisia: precision of the upper Miocene compression and geodynamic significance

International Journal of Earth Sciences - New field observations carried out in northeastern Tunisia (Kechabta Neogene basin) allowed us to clarify and pinpoint the chronology of the folding phases...     

柴达木盆地西部黑北凹地—大浪滩深层卤水钾盐储卤层地震响应特征研究

柴达木盆地西部深层卤水型钾盐是近期新发现的一种以砂砾层为储存介质的氯化钠亚型钾盐资源,其中,以黑北凹地—大浪滩次级盐湖凹地工作程度较高,研究也相对深入。该区已经求取该类型KCl资源量(333)约3.5亿吨。对该类型成矿地质体的解剖可对该区钾盐找矿在面上和纵深拓展提供借鉴。鉴于此,笔者根据实际生产需要,系统收集了该区的钻井、测录井及地震探测资料,通过地震资料解释和属性分析,对比钻孔揭露储卤层岩性特征,获得研究区域内中深部孔隙储卤层地震响应特征:储卤层底部同相轴振幅较强、局部连续性较好,顶部同相轴为中-强振幅,内部多为弱反射振幅,成团块状;瞬时频率属性表现为中-低频反射特征;甜点属性表现为顶、底为甜点高值而内部为甜点低值的特征;包络属性表现为顶、底为异常高值而储层内部为低值分布。通过对地震剖面及钻孔资料分析,建立了砂砾储卤层的地球物理识别标志,为预测中深部储卤层分布范围及优选水文-地质钻孔提供依据。     

Reflection–refraction seismics in the Gulf of Corinth: hints at deep structure and control of the deep marine basin

The Gulf of Corinth is a natural laboratory for the study of seismicity and crustal deformation during continental extension. Seismic profiling along its axis provides a 24-fold normal-incidence seismic reflection profile and wide-angle reflection–refraction profiles recorded by sea-bottom seismometers (OBS) and land seismometers. At wide-angle incidence, the land receivers document the Moho at 40-km depth under the western end of the Gulf north of Aigion, rising to 32-km depth under the northern coast in the east of the Gulf. Both refraction and normal-incidence reflection sections image the basement under the deep marine basin that has formed by recent extension. The depth to the base of the sedimentary basin beneath the Gulf, constrained by both methods, is no more than 2.7 km, with 1 km of water underlain by no more than 1.7 km of sediment, less than what was expected from past modeling of uplift of the south coast in the East of the Gulf. Unlike the flat sea-bottom, the basement and sedimentary interfaces show topography along this axial line. Several deeps are identified as depocenters, which suggest that this axial line is not a strike line to the basin. It appears instead to be controlled by several faults, oblique to the S60°E overall trend of the south coast of the Gulf, their more easterly strikes being consistent with the instantaneous direction of extension measured by earthquake slip vectors and by GPS.     

珠江口盆地南部隆起中新统碳酸盐岩分布的地震预测

珠江口盆地中新统碳酸盐岩台地发育,并在东沙隆起发现了生物礁油田。借鉴区域岩相古地理研究,依据典型的特强振幅低频地震反射特征,推断在南部隆起下中新统发育有碳酸盐岩。针对钻井空白的情况,通过正演模型,分析不同厚度碳酸盐岩对应的地震响应特征,据此在南部隆起的二维地震剖面上识别出了碳酸盐岩的尖灭点、调谐厚度、1/2波长厚度和大于1/2波长厚度等重要厚度控制点,编制了碳酸盐岩厚度图。根据碳酸盐岩相模式、厚度和地震反射特征,初步分析了碳酸盐岩孤立台地的沉积相,这可为南部隆起碳酸盐岩油气勘探提供参考。     

Biogeographical affinities of marine algae in the Saronikos Gulf,Athens, Greece

Hard substrate photophilius marine algae species of the Saronikos Gulf amount to 197. Of them, 42 were Atlantic subtropical, 36 Atlantic tropical, and just 19 Atlantic boreal and 11 Boreal. The R/P ratio was 3.22. This shows the Atlantic subtropical character of the marine flora.     

青藏高原东北缘循化盆地中中新世—早上新世黏土矿物及其古气候意义

青藏高原东北缘古气候可能受控于全球变冷、青藏高原隆升及局地地形变化的影响。为解析气候演化过程及驱动因素,本文以青藏高原东北缘循化盆地西沟剖面作为研究对象,在已有古地磁年龄约束基础上,分析了中中新世—早上新世沉积物中黏土矿物的组成和微观形貌特征。结果表明,西沟剖面沉积物中黏土矿物主要由伊利石、蒙脱石、绿泥石和高岭石组成,其中伊利石含量最高,平均为59. 3％;蒙脱石次之,平均为18. 2％,绿泥石平均含量为12. 3％,高岭石平均含量为10. 2％。根据剖面中黏土矿物含量和比值的变化特征,结合循化盆地西沟剖面的沉积速率、孢粉记录、有机质碳同位素和沉积岩地球化学比值,并与深海氧同位素值（δ18O）变化曲线对比,将循化盆地14. 6~5. 0 Ma气候环境演化划分为3个阶段：14. 6~12. 7 Ma,气候干冷期,与北半球冰盖扩展引发的全球性降温事件有关;12. 7~8. 0 Ma,气候相对温暖湿润期,可能与循化盆地周围山体隆升有关,即积石山在~12. 7 Ma隆升至临界高度,成为西风带输送水汽的地形屏障,使得循化盆地内的降水增强;8. 0~5. 0 Ma,气候再次转向干冷期,该阶段气候的干旱化对应于青藏高原在8 Ma左右的快速隆升,高原进一步的隆升阻碍东亚季风西风带的暖湿气流向内陆的输送,从而引起区域干旱化。     

Authigenic natroalunite in middle Miocene evaporites from the Gulf of Suez (Gemsa, Egypt)

This paper deals with a new occurrence of sedimentary natroalunite (Na, K) Al₃, (SO₄)₂ (OH)_6, in the caprock of a diapir of middle Miocene evaporites from the Gemsa peninsula, located on the southwestern coast of the Gulf of Suez. Field observations, petrographic examinations and stable isotope (¹⁸O, ³⁴S) measurements on the associated authigenic phases of anhydrite and native sulphur argue for the genesis of natroalunite at a rather high temperature (i.e. higher than 75°C) by the reaction of clay minerals with sulphuric acid. The sulphuric acid was produced by the concatenation of the following reactions which are thought to increase the diagenetic temperature: bacterial reduction of sulphate evaporites, and oxidation of hydrogen sulphide to native sulphur and sulphate where aerated conditions prevailed in the pore fluids. These changes through time from reducing to oxidizing diagenetic conditions were controlled by the progressive uplift of the diapiric system toward the land surface so that the draining ground waters became progressively oxygenated.     

Hydrochemical characterization and geospatial analysis of groundwater quality in Cap Bon region,northeastern Tunisia

The hydrogeochemical characteristics of shallow groundwater in the Grombalia region, northeastern Tunisia, were investigated to evaluate suitability for irrigation and other uses and to determine the main processes that control its chemical composition. A total of 21 groundwater samples were collected from existing wells in January–February 2015 and were analyzed for the major cations and anions concentrations. Conductivity, pH, T°, O₂ and salinity were also measured. Interrelationships between chemical parameters were determined by using the scatter matrix method. The suitability of groundwater for irrigation and other uses was assessed by determining the sodium adsorption ratio, soluble-sodium percentage, total dissolved solids, total hardness, Kelly’s index and permeability index values of water samples. The spatial distribution of key parameters was assessed using a GIS-based spatial gridding technique. This analysis indicated that the chemical composition of groundwater in the study area is of Cl–SO₄–Na–Ca mixed facies with concentrations of many chemical constituents exceeding known guideline values for irrigation. The salinity of groundwater is controlled by most dominant cation and anion (Na–Cl). A correlation analysis shows that Na⁺ is the dominant cation and that reverse ion exchange is a dominant process that controls the hydrogeochemical evolution of groundwater in the area. Geospatial mapping of hydrochemical parameters and indices analyzed with the USSL and Wilcox diagrams show distinctive areas of irrigation suitability. In contrast, 76.2% of samples fall in the highly doubtful to unsuitable category and indicate that the central and north-eastern parts of the study area are unsuitable for irrigation due to a high salinity and alkalinity.     

Origin and distribution of saline groundwaters in the upper Miocene aquifer system, coastal Rhodope area, northeastern Greece

 This paper describes the origins and distribution of saline groundwaters in the coastal area of Rhodope, Greece. The aquifer system includes two aquifers within coarse-grained alluvial sediments in the coastal part of the study area. Two major water-quality groups occur in the study area, namely Ca²⁺-rich saline groundwater and Ca²⁺-poor, almost fresh groundwater. The main process controlling the groundwater chemistry is the exchange of calcium and sodium between the aquifer matrix and intruding seawater. The natural salt water in the study area is probably residual water that infiltrated the aquifer system during repeated marine transgressions in late Pleistocene time. Seawater intrusion into the coastal aquifer system occurs as a result of overpumping in two seawater wedges separated vertically by a low-permeability layer. The rate of intrusion averages 0.8 m/d and is less than expected due to a decline of the aquifer's permeability at the interface with the seawater. The application of several hydrochemical techniques (Piper and Durov diagrams; Na⁺/Cl^–, Ca²⁺/Cl^–, Mg²⁺/Cl^–, and Br^–/Cl^– molar ratios; Ca²⁺/Mg²⁺ weight ratio; and chloride concentrations), combined with field observations, may lead to a better explanation of the origin of the saline groundwater. Received, May 1997 / Revised, May 1998, December 1998 / Accepted, February 1999     

Seismic stratigraphy,tectonics and depositional history in the Halk el Menzel region,NE Tunisia

In the Halk el Menzel area, the proximal- to pelagic platform transition and related tectonic events during the Upper Cretaceous–Lower Miocene have not been taken into adequate consideration. The integrated interpretation of outcrop and subsurface data help define a seismic stratigraphic model and clarify the geodynamic evolution of the Halk el Menzel block. The sedimentary column comprises marls and limestones of the Campanian to Upper Eocene, overlain by Oligocene to Lower Miocene aged siliciclastics and carbonates.Well to well correlations show sedimentary sequences vary considerably in lithofacies and thicknesses over short distances with remarkable gaps. The comparison of sedimentary sequences cut by borehole and seismic stratigraphic modelling as well help define ten third order depositional sequences (S1–S10). Sequences S1 through S6 (Campanian–Paleocene) are mainly characterized by oblique to sigmoid configurations with prograding sedimentary structures, whereas, sequences S7–S10 (Ypresian to Middle Miocene) are organized in shallow water deposits with marked clinoform ramp geometry. Sedimentary discontinuities developed at sequence boundaries are thought to indicate widespread fall in relative sea level. Angular unconformities record a transpressive tectonic regime that operated from the Campanian to Upper Eocene.The geometry of sequences with reduced thicknesses, differential dipping of internal seismic reflections and associated normal faulting located westerly in the area, draw attention to a depositional sedimentary system developed on a gentle slope evolving from a tectonically driven steepening towards the Northwest.The seismic profiles help delimit normal faulting control environments of deposition. In contrast, reef build-ups in the Eastern parts occupy paleohighs NE–SW in strike with bordering Upper Maastrichtian-Ypresian seismic facies onlapping Upper Cretaceous counterparts.During the Middle–Upper Eocene, transpressive stress caused reactivation of faults from normal to reverse play. This has culminated in propagation folds located to the west; whereas, the eastern part of the block has suffered progressive subsidence. Transgressive carbonate depositional sequences have predominated during the Middle Miocene and have sealed pre-existing tectonic structures.     

深层海相碳酸盐岩优质储层的形成、保存和破坏机制

四川盆地震旦系—志留系碳酸盐岩普遍埋藏深度超过3〖CS％0,0,0,0〗〖CS〗500 m,属深层碳酸盐岩储层范畴。宽广的潮坪相和陆棚相沉积环境从根本上决定了盆内下组合碳酸盐岩储层岩石类型主要为颗粒碳酸盐岩、晶粒结构白云岩及裂缝性灰岩。多期次的构造运动导致下组合岩溶储层发育,特别是志留纪末期的加里东运动导致从乐山—龙女寺古隆起核部由西向东依次发育震旦系、寒武系和奥陶系古岩溶带。现今下组合储层中广泛分布的沥青表明下组合曾有过广泛的油气成藏过程,形成古油藏或古气藏,亦表明下组合在油气充注时曾普遍发育优质储层。岩石学和地球化学研究表明,复杂多变、期次繁多的成岩演化和流体充注与下组合优质储层的形成、保存和破坏密切相关,总体上,对四川盆地深层海相碳酸盐岩储层而言： 1）原位沉积体系、白云岩化对震旦系和寒武系优质储层发育控制作用弱、仅对奥陶系和志留系具有较强的控制作用; 2）古隆起是优质储层发育的先决条件,表生岩溶与破裂作用为必备条件; 3）烃类流体充注和热裂解作用早期优质储层保存的主要机制,此外,适度的重结晶作用是形成优质储层的持久动力,埋藏过程中外源侵蚀性流体溶蚀作用的储层效应有限; 4）压实压溶作用、胶结充填作用是储层致密的最主要的因素。     

深层海相碳酸盐岩优质储层的形成、保存和破坏机制

四川盆地震旦系—志留系碳酸盐岩普遍埋藏深度超过3〖CS％0,0,0,0〗〖CS〗500 m,属深层碳酸盐岩储层范畴。宽广的潮坪相和陆棚相沉积环境从根本上决定了盆内下组合碳酸盐岩储层岩石类型主要为颗粒碳酸盐岩、晶粒结构白云岩及裂缝性灰岩。多期次的构造运动导致下组合岩溶储层发育,特别是志留纪末期的加里东运动导致从乐山—龙女寺古隆起核部由西向东依次发育震旦系、寒武系和奥陶系古岩溶带。现今下组合储层中广泛分布的沥青表明下组合曾有过广泛的油气成藏过程,形成古油藏或古气藏,亦表明下组合在油气充注时曾普遍发育优质储层。岩石学和地球化学研究表明,复杂多变、期次繁多的成岩演化和流体充注与下组合优质储层的形成、保存和破坏密切相关,总体上,对四川盆地深层海相碳酸盐岩储层而言： 1）原位沉积体系、白云岩化对震旦系和寒武系优质储层发育控制作用弱、仅对奥陶系和志留系具有较强的控制作用; 2）古隆起是优质储层发育的先决条件,表生岩溶与破裂作用为必备条件; 3）烃类流体充注和热裂解作用早期优质储层保存的主要机制,此外,适度的重结晶作用是形成优质储层的持久动力,埋藏过程中外源侵蚀性流体溶蚀作用的储层效应有限; 4）压实压溶作用、胶结充填作用是储层致密的最主要的因素。     

Formation of hydrocarbon reservoirs in the deep Earth's crust

Formation of reservoirs in crystalline rocks is associated with the development of rifts, with the periodic axial plunge of the rift floor during the extension of the Earth's crust, and with the elevation of consolidated basement masses during a compression phase.     

Diagenetic evolution of a shallow marine Kimmeridgian carbonate ramp (Jabaloyas,NE Spain): implications for hydrocarbon reservoir quality

The upper Kimmeridgian outcrops in Jabaloyas (NE Spain) studied here have significant similarity in terms of carbonate ramp morphology and its facies architecture with Member D of the Upper Jurassic Arab Formation reservoirs in the Middle East. Geological models from analogue outcrops enhance or challenge the understanding of multi-scale sedimentological and diagenetic heterogeneities in the subsurface hydrocarbon reservoir models by providing morphometric parameters. For this purpose, conventional diagenetic studies (petrographic microscopy analysis and cathodoluminescence) have been performed to assess the impact of diagenetic modifications through burial. More than 50 thin sections have been used to define a full paragenetic sequence. Additional mineralogical mapping (Qemscan®) on a selection of thin sections serves as a calibration tool for semiquantitative analytic studies of every mineral phases and the proposed porosity evolution. This work unravels the whole paragenetic diagenetic processes and focused on those that occurred right after deposition to shallow burial (eogenesis). High-sequence stratigraphy allows linking these events to variations of the environmental domains that, in fact, respond most likely to sea-level fluctuations. In particular, it provides key parameters to frame the diagenetic overprint such as cementation processes plugging primary interparticle porosity and selective dissolution linked to master bounding surfaces: calcite meniscus cements in vadose zones and selective dissolution processes linked to firmgrounds. Ultimately, they offer valuable trends that would be potentially relevant to decipher and characterize reservoir parameters for the upscaling workflow of fabrics from microscopic to inter-well scale in carbonate hydrocarbon reservoirs.