Late Miocene nonmarine sedimentation and formation of magnesites in the Acıgöl Basin, southwestern Anatolia, Turkey

The Late Miocene lacustrine Acıgöl Basin, SW Turkey, formed as an orogen-top, extensional half-graben, with the subaqueous accommodation controlled by the lake level and the bulk accommodation provided by active subsidence along a WSW-trending normal fault at the basin's southern margin. The basin-fill sedimentary succession consists of terminal alluvial-fan facies overlain by ephemeral lake-margin facies and perennial lake facies, with widespread fluvial facies at the top. The distal alluvial-fan facies include massive to stratified sandstones and massive mudstones with intervening nodular dolostones and incipient pedogenic horizons. The lake-margin facies are micritic magnesites passing laterally into peloidal, irregularly laminated magnesites towards the palaeolake margin and overlain by marlstones and dolostones, all with abundant evidence of episodic subaerial exposure (desiccation cracks, pedogenic features, and tepee structures). The perennial lake facies are micritic magnesites passing upwards into clayey dolostones and dolomitic or clayey marlstones. The fluvial facies capping the succession include planar cross-stratified conglomerates (channel-fill deposits), planar parallel-stratified, planar cross-stratified and rippled cross-laminated sandstones (crevasse-fill and crevasse splay deposits), and assemblages of mudstones intercalated with thin sandstone beds (overbank floodplain deposits).The sedimentological, mineralogical and geochemical data reveal large variations in the basin's hydrological regime, including short-term oscillations and bulk rise of the lake level, periodical changes in the Mg/Ca ratio and terrigenous mud supply, and a negative covariance of δ¹⁸O and δ¹³C fluctuations. The composition of terrigenous sediment and the chemistry of water supplied to the lake were controlled by the weathering, chemical leaching and erosion of the ultramafic–dolomitic bedrock in the catchment area. The bedrock yielded Mg-rich carbonate solutions that caused the deposition of Mg-carbonates in the lake.Despite short-term lake-level fluctuations, the lake's net water budget remained positive. It is suggested that the region's present-day climate and Mg-rich alkaline lakes can serve as an analogue for the climatic and hydrological conditions in the Late Miocene Acıgöl Basin.     

柴达木盆地西部地区古近纪与新近纪沉积相

利用数十口井的电性、岩性及分析化验资料，将柴达木盆地西部地区古近纪与新近纪沉积相划分为七种相和亚相：洪积锥、水下冲积扇、河道和泛滥平原、滨湖、浅湖、较深湖和三角洲。沉积相的空间展布概括起来分为三大带：（1）阿尔金山前西段陡坡带洪积锥-水下冲积扇-扇三角洲-河道和泛滥平原-湖相 (2)阿尔金山前中段陡坡带洪积锥-水下冲积扇-湖相；（3）昆仑山前洪积锥-河道和泛滥平原-三角洲相。沉积相不仅影响着碎屑岩的成分和结构，而且也影响其物性与含油性。由洪积锥到水下冲积扇，到河道和泛滥平原，到三角洲，到湖相，石英和胶结物含量逐渐升高，岩屑和杂基含量逐渐降低，分选及磨圆变好，颗粒的粒级变细。浅层以河道和泛滥平原及三角洲相的物性最好，深层以三角洲相的物性最好，次为冲积扇，湖相最差。碎屑岩的油气富集以河道、泛滥平原和三角洲相最好，滨浅湖相油气富集最差。     

云南兰坪盆地三叠纪沉积作用与古地理演化

根据岩石沉积类型、物源供给、成因机制和沉积序列,结合区域地质特征,将兰坪盆地三叠系划分为陆相火山泥石流、河流相、三角洲相、潮坪相、浅海陆棚相、碳酸盐台地相和深水盆地相7种主要沉积类型。通过对沉积相的详细分析,恢复其古地理格架和面貌,探讨岩相古地理的变迁历史,从而表明三叠纪早期到晚期,其古地理经历了陆相环境※碎屑海盆※碳酸盐海盆到碎屑海盆的转换,即两次海侵-海退旋回。早期的海域分布范围较小,晚期的海域分布范围较宽,并成为统一的海盆。     

柴达木盆地西部地区古近系及新近系碳酸盐岩沉积相

柴达木盆地西部地区古近系和新近系湖相碳酸盐岩主要分布于下干柴沟组上段到油砂山组,其中,下干柴沟组上段和上干柴沟组的碳酸盐岩更发育。碳酸盐岩主要岩石类型有泥晶灰岩、藻灰岩和颗粒灰岩等三大类,此外,还普遍发育由石灰质、白云质和陆源碎屑等3种组分构成的混积岩。碳酸盐岩沉积相可划分为滨湖灰泥坪、滨湖藻坪、浅湖颗粒滩、浅湖藻丘以及半深湖泥灰岩相。滨湖灰泥坪的主要岩石类型有泥晶灰岩、含陆屑泥晶灰岩、陆屑泥晶灰岩以及陆屑泥灰岩等;滨湖藻坪为藻泥晶灰岩、藻纹层灰岩、含陆屑藻泥晶灰岩;浅湖颗粒滩有亮晶或泥微晶的鲕粒灰岩、生屑灰岩和内碎屑灰岩,其次为含陆屑颗粒灰岩;浅湖藻丘为藻叠层灰岩、藻团块灰岩、藻泥晶灰岩和含陆屑藻泥晶灰岩;而半深湖泥灰岩相的主要岩石类型为泥晶灰岩、泥灰岩以及含少量陆屑泥和粉砂的泥晶灰岩或泥灰岩。碳酸盐岩沉积相表现出很强的由西南向东北的迁移性。     

Facies analysis of tertiary alluvial fan deposits in the Jundiaí region, São Paulo, southeastern Brazil

This article presents an analysis of facies of sedimentary sequences that occur as discontinuous bodies in the Jundiaí region, west of the main Tertiary continental basins of the southeastern Brazil continental rift. Nine identified sedimentary facies, grouped into four associations, suggest the existence of an ancient alluvial fan system whose source area was the Japi mountain range (Serra do Japi). The deposits are considered Tertiary in age and chronocorrelated with those identified in the Atibaia region and at other sites up to 100 km east and northeast of Jundiaí. The depositional model adopted to explain the filling of the basin proposes that the alluvial fans, which directly derive from the source area, terminated in a braided channel longitudinal to the basin axis that flowed to northwest, in a similar configuration to that of the present day. This basin may have extended to the Atibaia region or formed a set of small basins laterally contiguous to the faults associated with the rift. Such occurrences show that the formation of rift basins was broader than the area presently occupied by the main deposits.     

Sedimentary processes and facies of the waterlaid Anvil Spring Canyon alluvial fan, Death Valley, California

The Anvil Spring Canyon fan of the Panamint Range piedmont in central Death Valley was built entirely by water-flow processes, as revealed by an analysis of widespread 2- to 12-m-high stratigraphic cuts spanning the 9·7 km radial length of this 2·5–5·0° sloping fan. Two facies deposited from fan sheetfloods dominate the fan from apex to toe. The main one (60–95% of cuts) consists of sandy, granular, fine to medium pebble gravel that regularly and sharply alternates with cobbly coarse to very coarse pebble gravel in planar couplets 5–25 cm thick oriented parallel to the fan surface. The other facies (0–25% of cuts) comprises 10- to 60-cm-thick, wedge-planar and wedge-trough beds of pebbly sand and sandy pebble gravel in backsets sloping 3–28°. Both facies are interpreted as resulting from rare, sediment-charged flash floods from the catchment, and were deposited by supercritical standing waves of expanding sheetfloods on the fan. Standing waves were repeatedly initiated, enlarged, migrated, and then terminated either by gradually rejoining the flood or by more violent breakage and washout. The frequent autocyclic growth and destruction of standing waves during an individual sheetflood resulted in the deposition of multiple coarse and fine couplet and backset sequences 50–250 cm thick across the active depositional lobe of the fan. Erosional intensity during washout of the standing wave determined whether early-phase backset-bed deposits or washout-phase sheetflood couplet deposits were selectively preserved in a given cycle. Two minor facies are also found in the Anvil fan. Pebble–cobble gravel lags (0–20% of cuts) are present above erosional scours into the sheetflood couplet and backset deposits. They consist of coarse gravel concentrated through fine-fraction winnowing of the host sheetflood facies by sediment-deficient water flows. This reworking occurred during recessional flood stage or from non-catastrophic discharge during the long intervals between major flash floods. This facies is common at the surface, giving rise to a ‘braided-stream’ appearance. However, it is stratigraphically limited, present as thin, continuous to discontinuous beds or lenses that bound 50- to 250-cm-thick sheetflood sequences. The other minor facies of the Anvil fan consists of clast-supported and imbricated, thickly stratified, pebbly, cobbly, boulder gravel present in narrow, radially aligned ribbons nested within sheetflood deposits. This facies is interpreted as representing deposition in the incised channel of the fan, a subenvironment characterized by greater flow competence resulting from maintained depth from channel-wall confinement, and by more frequent water flows and winnowing events caused by its direct connection with the catchment feeder channel.     

Environmental and depositional characteristics of diatomite deposit, Alayunt Neogene Basin (Kutahya), West Anatolia, Turkey

This paper describes the geological-depositional and environmental characteristics of diatomite. The diatomite deposit is situated in the southern part of the Alayunt (Kutahya) Basin. Samples of 18 diatomites and 12 host rocks were collected from four sedimentary profiles in the spring season. Basement rocks are Paleozoic-aged metamorphic rocks (schist, phyllite, quartzite, etc.) and Mesozoic-aged ophiolitic and complex rocks. Host rocks are rhyodacitic–rhyolitic tuffite, volcanic glass. Diatomite is composed of Upper Miocene–Upper Pliocene-aged diatom species. Diatomite shows layer morphology and lies on volcanic glass layer. XRD characteristic peaks of diatomite show that it comprises dominantly of Opal-A silica, whereas volcanic glass has Opal-CT constituent. SEM and NPM photomicrographs indicate that diatomites are dominantly composed of benthic freshwater diatom species, such as Pinnularia microstauron, Pinnularia lundii, Pinnularia subrostrata, Pinnularia brevicostata, Pinnularia tenuis, Pinnularia sp., Navicula eligensis, Fragilaria construens, Mastogloia braunii Grunow, Melosira varians Agardh, Surirella capronii Brébisson, Cymbella lanceoloata, Amphora venata, Gomphonema germainii, Gomphonema angustatum and Rhapalodia gibba. These species are general indicators of shallow paleolake environment and cool climate conditions. Due to the fluvial currents and climatic conditions; lake water levels, temperature and nutrient content fluctuated through the time. Chemical data obtained from 18 diatomite samples show that while silica is the bodybuilding material for diatomite (over 89 % SiO₂), Al, Mg and Fe contents of diatomite samples might be derived from clastic materials. The concentration of Al, Mg and Fe decreases toward the lake center. Diatom genera, sedimentary profile sections and mineralogic data suggest that diatomite deposited in lacustrine-type freshwater shallow lake is associated with Upper Miocene-aged extension tectonics. Physical and filtration tests along with environmental characteristics of diatomite suggest that calcined diatomite can be used for waste treatment processes in the filter aid industry.     

柴达木盆地西部新近纪岩相古地理研究

通过对研究区新近系露头及钻井剖面的岩性、结构构造、古生物的综合分析,将柴西地区新近系沉积相划分为5种相和亚相:扇三角洲、河流-泛滥平原、滨湖、浅湖、半深湖。沉积相的空间展布大体以茫崖和大风山为沉积中心,到盆地边缘依次发育半深湖相、浅湖相、滨湖相,并呈环带状分布。扇三角洲相和河流泛滥平原相发育于昆仑山和阿尔金山前。古地形为西高东低,南高北低,物源来自阿尔金山和昆仑山,气候炎热干旱。下油砂山组为较好的烃源岩,储层主要为孔隙性碎屑岩储层和裂缝性非常规储层两种。     

Sedimentological characteristics and facies of the evaporite-bearing Kirmir Formation (Neogene), Beypazari Basin, central Anatolia, Turkey

A thick sedimentary sequence comprising fluvial, lacustrine and volcano-sedimentary rocks is present in the Neogene Beypazari Basin, central Anatolia. These units display considerable lateral facies variation and interfinger with alkaline volcanic rocks along the north-eastern margin of the basin. The uppermost Miocene Kirmir Formation contains numerous evaporite horizons. The evaporite sequence is up to 250 m thick and may be divided into four lithofacies. In ascending stratigraphical order these are: (1) gypsiferous claystone facies, (2) thenardite-glauberite facies, (3) laminar gypsum facies and (4) crystalline gypsum facies. These facies interfinger with one another laterally along a section from the margins to central parts of the basin. The lithological and sedimentological features of the Kirmir Formation indicate fluvial, saline playa mudflat, hypersaline ephemeral playa lake and very shallow subaqueous playa lake depositional environments, which probably were influenced by alternating semi-arid and evaporative conditions.     

塔里木盆地库车坳陷新近系和第四系沉积特征及演化*

在野外露头观察和岩心描述的基础上,结合测井、地震和三维电法资料分析,认为塔里木盆地库车坳陷新近系和第四系共发育冲积扇、冲积平原、扇三角洲和湖泊4种沉积相类型;每一种沉积相可以进一步划分为若干沉积亚相和微相。新近纪吉迪克期,古近纪形成的湖泊开始向南部退缩,扇三角洲分布在山前地区;新近纪康村期基本继承了吉迪克期的沉积格局,扇三角洲的分布范围较吉迪克期大;新近纪库车期,构造抬升导致湖泊快速萎缩,山体隆升并遭受剥蚀,为冲积扇的形成提供物源,从山前到盆地中心依次为冲积扇、冲积平原和湖泊;第四纪,湖泊完全消失,以冲积扇沉积为主,冲积平原仅分布在西盐水沟-东盐水沟一线南部地区。     

Monitoring Cenozoic climate evolution of northeastern Tibet: stable isotope constraints from the western Qaidam Basin,China

Carbon and oxygen stable isotopic composition of Cenozoic lacustrine carbonates from the intramontane Qaidam Basin yields cycles of variable length and shows several distinct events driven by tectonics and climate changes. From Eocene to Oligocene, the over-all trend in the δ¹³C composition of lacustrine carbonates shows a shift toward higher values, possibly related to higher proportions of dissolved inorganic carbon transported to the lake or lower input of soil derived CO₂. At the same time, the δ¹⁸O composition of lacustrine carbonates is decreasing in accordance with the global cooling trend and northwards drifting of the whole region. During the Miocene, distinct isotopic events can be recognized, although their interpretation and linkage to a certain tectonic event remains difficult. These events may be related to uplift in the Himalayas, to the strongest phase of uplift in the Altyn Mountains, to pronounced subsidence of the Qaidam Basin or to the expansion of C4 plants on land. Generally cold, highly evaporative conditions can be deduced from enrichment of δ¹⁸O isotopic compositions during Pliocene and Quaternary times.     

Late Cretaceous paleoenvironmental evolution of the Tarfaya Atlantic coastal Basin,SW Morocco

Lithological evidence, benthic foraminiferal census counts, and X-ray fluorescence (XRF) scanner-derived elemental data were integrated with planktonic foraminiferal biostratigraphy and bulk carbonate stable isotopes to retrace the Turonian to early Campanian paleoenvironmental evolution and sea-level history of the Tarfaya Atlantic coastal basin (SW Morocco). The lower Turonian is characterized by laminated organic-rich deposits, which contain impoverished benthic foraminiferal assemblages, reflecting impingement of the oxygen minimum zone on the shelf during a sea-level highstand. This highstand level is correlated to the global transgressive pulse above the sequence boundary Tu1. The appearance of low-oxygen tolerant benthic foraminiferal assemblages dominated by Gavelinella sp. in the middle to upper Turonian indicates an improvement in bottom water oxygenation, probably linked to offshore retraction of the oxygen minimum zone during a regressive phase. This interval is marked by major regressive events expressed by a series of erosional truncations associated with the prominent sequence boundaries Tu3 and/or Tu4. Dysoxic–anoxic conditions recorded in the upper Santonian of the Tarfaya Basin coincide with the eustatic sea-level rise prior to Sa3 sequence boundary. The lower Campanian transgression, only recorded in the southern part of the Tarfaya Basin, coincided with substantial deepening, enhanced accumulation of fine-grained clay-rich hemipelagic sediments and improved oxygenation at the seafloor (highest diversity and abundance of benthic foraminiferal assemblages). Stable isotope data from bulk carbonates are tentatively correlated to the English Chalk carbon isotope reference curve, in particular the Hitch Wood Event in the upper Turonian, the Navigation Event in the lower Coniacian, the Horseshoe Bay Event in the Santonian and the Santonian/Campanian Boundary Event.     

Facies analysis and depositional systems of Cenozoic sediments in the Hoh Xil basin, northern Tibet

A sedimentary succession more than 5800 m thick, including the Lower Eocene to Lower Oligocene Fenghuoshan Group, the Lower Oligocene Yaxicuo Group, and the Lower Miocene Wudaoliang Group, is widely distributed in the Hoh Xil piggyback basin, the largest Cenozoic sedimentary basin in the hinterland of the Tibetan plateau. The strata of the Fenghuoshan and Yaxicuo groups have undergone strong deformation, whereas only minor tilting has occurred in the Wudaoliang Group. We analyze their sedimentary facies and depositional systems to help characterize continental collision and early uplift of the Tibetan plateau. The results indicate fluvial, lacustrine, and fan-delta facies for the Fenghuoshan Group, fluvial and lacustrine facies for the Yaxicuo Group, and lacustrine facies for the Wudaoliang Group. Development of the Hoh Xil basin underwent three stages: (1) the Fenghuoshan Group was deposited mainly in the Fenghuoshan-Hantaishan sub-basin between 56.0 and 31.8 Ma ago; (2) the Yaxicuo Group was deposited mainly in the Wudaoliang and Zhuolai Lake sub-basins between 31.8 and 30.0 Ma ago; and (3) the Wudaoliang Group was deposited throughout the entire Hoh Xil basin during the Early Miocene. The Fenghuoshan and Yaxicuo groups were deposited in piggyback basins during the Early Eocene to Early Oligocene, whereas the Wudaoliang Group was deposited in a relatively stable large lake. The Hoh Xil basin underwent two periods of strong north–south shortening, which could have been produced by the collision between India and Asia and the early uplift of the Tibetan plateau. The study suggests the Hoh Xil region could reach a high elevation during the Late Oligocene and the diachronous uplift history for the Tibetan plateau from east to west.     

Stable isotopic insights into paleoclimatic conditions and alluvial depositional processes in the Kaiparowits Formation (Campanian,south-central Utah,U.S.A.)

The Kaiparowits Formation contains an exceptionally rich history of tectonic, climatic, and biologic conditions within the Western Interior of North America during the Campanian. Here we reconstruct aspects of the southern Cordilleran foreland basin's paleohydrology using δ¹⁸O and δ¹³C values determined from unionoid bivalve shells and pedogenic carbonate nodules derived from a suite of lithofacies associations. Unionoid shells derived from fluvial deposits display average water δ¹⁸O estimates of −13.7‰ ± 2.1 (1σ) (VSMOW) and shell δ¹³C values of −4.0‰ ± 1.5 (VPDB), whereas pedogenic carbonate nodules display average values of −6.0‰ ± 0.5 and −8.7‰ ± 0.8, respectively. Unionoid shells derived from pond deposits fall in between the two other environments with average values of −9.5‰ ± 1.8 and −5.7‰ ± 2.1, in δ¹⁸O and δ¹³C values respectively. Water δ¹⁸O estimates are interpreted to represent high altitude runoff within river systems, low elevation precipitation within the basin onto floodplain soils, and varying degrees of mixing between these two components within floodplain ponds. δ¹³C values track the isotopic composition of dissolved inorganic carbon within river, soil, and pond waters with high values likely reflecting greater contribution from chemically weathered marine carbonates exposed in the hinterland and lower values reflecting greater contributions from the in situ degradation of plant matter. Up-section there is a shift to lower δ¹⁸O values and higher δ¹³C values in fluvially-derived unionoid shells that post-dates an incursion of the Western Interior Seaway, but coincides with a shift in sediment provenance, an increase in basin sedimentation rates, and a change to a more anastomosed-style channel morphology within the basin foredeep depocentre. By combining the isotopic patterns with previously published sedimentologic, climate model, and paleofloral records we find: 1) additional evidence for humid, wet, and potentially monsoonal conditions within the region, 2) support for a tectonic uplift event, potentially related to Laramide deformation, and 3) greater aggradation and overbank flooding within the alluvial system in response to the uplift event.     

The Mid-Cenomanian Event in shallow marine environments: Influence on carbonate producers and depositional sequences (northern Aquitaine Basin,France)

The Mid-Cenomanian Event was a positive carbon-isotope (δ¹³C) excursion recorded in hemipelagic basins of the western Tethyan Sea, North to Tropical Atlantic Ocean, and Japan. It is thought of as a prelude to the Oceanic Anoxic Event 2. However, the Mid-Cenomanian Event has never been studied in detail in shallow marine platform deposits and it is not known how it relates to carbonate production and stratigraphic geometry. To better understand how this carbon cycle disruption influenced the neritic biological communities in shallow carbonates during the Cenomanian, a facies, geochemical, diagenetic, and sequence stratigraphic study of the northern Aquitaine platform has been conducted. Seventy-six δ¹³C and δ¹⁸O measurements have been made on micrite, rudists, and diagenetic cements. Fifteen sedimentary facies have been arranged into four depositional environments. Three third-order sequences (C_B, C_C, C_D) are defined from late early Cenomanian to early late Cenomanian and are well correlated with eustatic cycles in European basins. Two peaks of the Mid-Cenomanian Event (MCE1a, +1.2‰, and MCE1b, +1.7‰) have been identified for the first time in shallow marine carbonates. Analysis of diagenetic blocky calcite cements suggests that diagenesis did not affect the δ¹³C of micrite, which can be discussed in terms of the initial signal. The Mid-Cenomanian Event was synchronous with a turnover in neritic carbonate producers marking a transition from photozoan to heterozoan facies. This facies change resulted from the establishment of mesotrophic to eutrophic conditions at the early/mid-Cenomanian transition, reflecting a clear connection between the Mid-Cenomanian Event and neritic biological communities. Depositional geometry and carbonate production varied with δ¹³C during the Mid-Cenomanian Event on the Aquitaine platform. When δ¹³C values were between 2.5‰ and 3‰, the geometry was a flat platform with a high carbonate sedimentation rate leading to the formation of sandbars and rudist bioherms (Accommodation/Sedimentation ratio less than 1, A/S < 1). When the δ¹³C value exceeded 3‰, a carbonate demise occurred and clays and marls were deposited in the lower offshore environment (A/S >> 1). The general carbonate demise affecting the northern Aquitaine platform during the mid-Cenomanian can be explained by both a eustatic sea-level rise and the establishment of eutrophic conditions. The coincidence of the Mid-Cenomanian Event with both (1) the occurrence of mesotrophic to eutrophic conditions marked by carbonate producer turnover from photozoan to heterozoan facies and (2) the transgressive cycles, suggests that eustatic sea-level rise leading to high trophic conditions could explain this positive δ¹³C excursion in the Atlantic and western Tethyan domain. During the mid-Cenomanian, carbon cycle perturbations largely controlled the neritic biological communities on shallow carbonate platforms in a part of the western Tethyan domain.     

青藏高原东北缘若尔盖盆地晚新近纪沉积的岩石地层学

通过野外地质填图和系统取样,以岩石地层特征为基础,以新构造运动为背景,按照多重地层划分观点,本文首次对若尔盖盆地晚新近纪岩石地层的对比和划分做了深入的研究。对黄河干流、白河支流和黑河支流水系的河道堆积岩石的典型剖面的研究,表明更新-全新世的不同发展阶段具有不同的特征;相同时期不同水系的沉积物也不尽相同,反映出盆地晚新近纪地层的发育过程及空间上的差异。对冰川堆积终碛垄测年等研究反映出末次盛冰期和全新世中几次较强的寒冷事件,并划分出4套冰碛层。综合前人的古脊椎动物化石和¹⁴C、TL、OSL和ESR等同位素测年资料,将为进一步提出研究区晚新近纪年代地层的划分奠定基础。     

柴达木盆地西北缘现代冲积扇沉积特征及石油地质意义

柴达木盆地处于古亚洲构造域和特提斯－喜马拉雅构造域的结合部，构造应力大而复杂，导致盆内地势起伏大，加上西南暖湿气流受喜马拉雅山系阻隔难以进入境内，盆内气候干旱，最终导致盆地内冲积扇极为发育。通过对大柴旦地区大头羊煤矿、鱼卡河、波门河和八里沟四个冲积扇的实地考察，共观测到3个亚相8个微相：扇根亚相沉积物最粗，分为古沟道、主水道和主水道间微相；扇中亚相沉积物偏细，成熟度增高，分为辫状水道、辫状水道间和纵坝微相；扇缘亚相沉积物最细，流体能量最低，分为水道径流和片流微相。不同沉积微相其沉积特征差异较大，认为古沟道、主水道和辫状水道微相具有较好的储集性能。勘探表明，冲积扇沉积与储层有着密切的关系，其内形成的油藏具有“自我保护”的能力；另外，冲积扇的形成很可能导致上覆地层形成扇背斜油藏，也可能导致下伏基岩形成基岩风化壳油藏。     

柴达木盆地鄂博梁地区新近系物源分析

物源分析是沉积盆地研究的重要内容之一。在对柴达木盆地鄂博梁地区新近系相关资料调研的基础之上,对研究区碎屑岩的碎屑组分、岩屑类型、重矿物组合、砂地比和阴极发光平面分布特征进行分析,并结合地震资料,确定出研究区新近系物源方向:鄂博梁Ⅰ号构造带物源主要来自于北部的阿尔金山,而位于其西部的东坪构造带与鄂博梁Ⅰ号构造带物源区不同,其具有相对独立的物源区;鄂博梁Ⅱ号构造带属于混源区,同时受到2个方向物源的影响,分别是北部的阿尔金山方向和东北部的小赛什腾山方向,前者穿过鄂博梁Ⅰ号构造带到达该地区,是主要的物源区,后者穿过冷湖一、二、三号构造带到达该地区,为次要物源区;鄂博梁Ⅲ号构造带物源主要来自于东北方向的赛什腾山,其是穿过冷湖六、七号构造带到达该地区的,并未受到来自南八仙方向 “古鱼卡大型古河流三角洲”物源的控制。     

柴达木盆地红柳泉-跃东地区新近系下油砂山组沉积体系展布特征及控制因素

在层序地层学研究的基础上,对柴达木盆地红柳泉-跃东地区新近系下油砂山组作了细致的沉积相分析研究。下油砂山组发育冲积扇相、扇三角洲相、辫状河三角洲相、湖泊相和浊积相等几种沉积相类型,分析了其发育特征及分布范围。以识别出的4个三级层序为单位,详细分析了沉积相的平面展布特征：Ⅰ层序沉积时期,西北地区为冲积扇和扇三角洲、中西部地区为辫状河三角洲发育区;Ⅱ层序沉积时期,沉积相分布格局与Ⅰ层序基本一致;Ⅲ层序沉积时期,西北地区的冲积扇、扇三角洲发育范围有所缩小,中西部地区辫状河三角洲发育范围持续扩张,分布范围较前期增大;Ⅳ层序沉积时期,西北地区依旧发育冲积扇,中西部地区辫状河三角洲沉积快速地向东推进,辫状河三角洲前缘亚相已达研究区中心。结合构造、物源、气候等因素分析了沉积相展布及演化的控制因素。     

柴达木盆地西部扎哈泉地区新近系上干柴沟组滩坝砂体沉积演化及其控制因素*

滩坝砂体是岩性油气藏勘探的重要储集体,已经成为中国陆相湖盆增储上产的重要现实领域。为了深入评价柴达木盆地西部扎哈泉地区新近系中新统上干柴沟组滨浅湖滩坝砂体的油气勘探前景以及预测有利勘探区带和勘探目标,文中在岩心观察和钻(测)井资料综合分析的基础上,结合岩石薄片、累计粒度概率曲线、暗色泥岩泥地比和砂地比敏感参数分析结果,对该地区上干柴沟组滨浅湖滩坝砂体发育演化特征和古地貌演化特征进行了详细研究。结果表明: (1)扎哈泉地区上干柴沟组沉积时期发育辫状三角洲—滨浅湖沉积体系,滩坝砂体发育,岩性主要为岩屑长石细砂岩—极细砂岩,成分成熟度中等—较差、分选磨圆度中等—好,粒度概率曲线以反映波浪作用的两段跳跃式加悬浮式为主;沉积构造类型多样,主要发育浪成沙纹交错层理、波状层理、丘状交错层理和透镜状层理。(2)上干柴沟组沉积时期,研究区滩坝砂体发育规模先增大后减小;早期到中期,滩坝砂体发育规模不断增大,其中近岸坝主要表现为向南和向东2个方向扩张,呈北偏西方向展布,远岸坝主要表现为南北方向扩张,呈近北西—南东方向展布;中期到晚期,滩坝砂体的发育规模不断减小,其中近岸坝主要表现为向南北2个方向收缩并向东扩展,展布方向变为东偏南转东北方向,远岸坝主要表现为南北方向收缩。(3)上干柴沟组沉积时期,研究区古地貌呈西高东低、南北低中间高的特征;从早期到中期,研究区中部古地貌高点不断向东和东南方向大幅度扩展,范围不断扩大;中期到晚期,古地貌高点范围不断向北和北西2个方向收缩,范围缩小;同时,研究区东南角古地貌高点范围不断向北扩大。综合上述分析结果,认为柴达木盆地扎哈泉地区上干柴沟组滩坝砂体发育演化受控于物源规模大小和微古地貌的发育演化,其中微古地貌发育演化是滩坝砂体发育演化的主要控制因素。研究成果可为相似的地质背景下滩坝砂体成因的岩性圈闭预测提供参考。