The geology of the southeastern Baltic Sea: a review

The Baltic Sea, particularly its southeastern part, is discussed in the paper. Investigations of regional character as well as specialized studies in the area are reviewed. General historical works are mentioned briefly. Previous surveys since the 1950s are presented by the subject studied. The compilation of geological structure of the SE Baltic Sea bottom and adjacent land of Balticum (Baltic States: Estonia, Latvia, Lithuania) is based on considerable amounts of summarized materials. The crystalline basement, sedimentary cover and Quaternary deposits are characterized in the comprehensive survey of geological structure. From a stratigraphical point of view, geological sequence of the platformal cover is comparatively complete: deposits of all geological systems (from the Archean to Cenozoic) are present in the Baltic Syneclise. Considering geotectonical cycles, the sedimentary cover of the syneclise is subdivided into four structural complexes. The thickness and distribution of Quaternary deposits are closely related to the recent bottom relief of the Baltic Sea that in turn is inherited from the Pre-Quaternary surface. Buried palaeo-valleys are characteristic of the Pre-Quaternary surface in the Baltic region and the Baltic Sea bottom. The Quaternary is characterized by layers of various geneses and by sharp changes of their thicknesses.     

A Late Pleistocene lacustrine transgression in the Fehmarn Belt,southwestern Baltic Sea

In order to reconstruct the late Pleistocene seismic stratigraphy, 550 km of high-density 3.5 kHz sub-bottom seismic-reflection profiles were recorded within a 70 km² area in the narrow offshore border zone between Germany and Denmark. A depositional unit 3 was analysed for its seismic facies association, and in the central study area mound, oblique, channel, reflection-free, shingled, hummocky, broken and parallel associations occurred. The rims of the association shows mound, oblique, hummocky and minor parallel seismic facies. Stratigraphic control was available from 32 coring sites. In the central study area, unit 3 represents rhythmic layers of silt with fine sand and clay in an overall fining-upward 3 to 5-m-thick sequence. At the rim of the basin, the unit comprises fine sand, silt and rhythmic layers of silt with clay and fine sand. Unit 3 is proposed as having formed during the transgression of a lake, partly in contact with the Baltic Ice Lake, some time between 10.8–10.0 ¹⁴C ka BP. After 10.0 ¹⁴C ka BP the water body stagnated when contact with the Baltic Basin was cut off. Analysis of base level of the subunits implies tectonic activity resulting in subsidence of the central study area which could possibly have influenced the transgressive development.     

Holocene sea-level changes and glacio-isostasy in the Gulf of Finland, Baltic Sea

Shoreline displacement in the eastern part of the Gulf of Finland during the past 9000 radiocarbon years was reconstructed by studying a total of 10 isolated lake and mire basins located in Virolahti in southeastern Finland and on the Karelian Isthmus, and in Ingermanland in Russia. Study methods were diatom analyses, sediment lithostratigraphical interpretation and radiocarbon dating. In southeastern Finland, the marine (Litorina) transgression maximum occurred ca. 6500–6200 ¹⁴C yr BP (7400–7100 cal. yr BP). In areas of the slower land uplift rate on the Karelian Isthmus and in Ingermanland, the transgression maximum occurred ca. 6400–6000 ¹⁴C yr BP (7300–6800 cal. yr BP). The highest Litorina shoreline is located at ca. 23 m above present sea-level in southeastern Finland, whereas in the eastern part of the Karelian Isthmus, near St. Petersburg, it is located at ca. 8 m above present sea-level. The amplitude of the Litorina transgression in Virolahti area is ca. 4 m, whereas on the Karelian Isthmus and in Ingermanland the amplitude has varied between 5 and 7 m. The regional differences between areas are solely due to different glacio-isostatic land uplift rates. The seven basins studied in this research were connected to the Baltic Sea basin during the Litorina Sea stage and their diatom and lithostratigraphical records indicate a single, smooth Litorina transgression.     

南海北部—东海南部中生代盆地演化与油气资源潜力

目前的勘探成果表明,南海北部到东海南部的广阔海域普遍发育中生代地层,但是除了在台西南盆地发现工业油气藏之外,其他地区的中生界尚未有大的勘探突破。本次研究将中生代南海北部—东海南部作为一个整体,开展大地构造背景分析,厘清各构造时期盆地的性质及其形成演化机制,探讨油气资源潜力。结果表明:南海北部—东海南部从晚三叠世到白垩纪整体为一个大型盆地,盆地的演化受其周围板块相互运动所控制;晚三叠世(T₃)主要受特提斯构造域控制,发育被动陆缘边缘海沉积盆地;从早侏罗世(J₁)到早白垩世均受古太平洋板块(伊泽奈崎板块)向欧亚板块俯冲机制的控制,其中早—中侏罗世(J_1-2)发育弧前坳陷盆地,晚侏罗—早白垩世(J₃—K₁)盆地性质为弧后断陷盆地;晚白垩世(K₂)受太平洋板块、欧亚板块和印度板块的联合控制,性质依然为弧后断陷盆地,与前期相比,裂陷强度加大;海水由东南方向侵入,地层垂向上由海相向陆相逐渐过渡,由东南向西北和东北方向,水体逐渐变浅,亦由海相向陆相逐渐演变;中生界在南海北部潮汕坳陷等地区发育深海相和海湾相泥岩,在东海南部基隆坳陷也发育良好的海湾相泥岩,生烃潜力大,具有形成大型油气藏的物质基础和地质条件,勘探潜力巨大。本次研究结果可以为南海北部—东海南部中生界的油气资源勘探提供依据。     

Arsenic in framboidal pyrite from recent sediments of a shallow water lagoon of the Baltic Sea

Arsenic is a redox‐sensitive element of environmental relevance and often enriched in iron sulphides. Because sediments from the Achterwasser lagoon, a part of the estuarine system of the river Oder, south‐west Baltic Sea, show unexpectedly high pyrite concentrations of up to 7·5 wt% they were used to investigate the influence of authigenic pyrite on the mobility and burial of As in the coastal environment. Micro‐X‐ray‐fluorescence measurements of 106 micrometre‐sized pyrite framboids from the anoxic sediments show highly variable As concentrations ranging from 6 to 1142 μg g^?1. Even within a 1 cm thick layer, the As concentration of different framboids varies greatly and no clear depth trend is visible throughout the 50 cm long sediment core. Pyrite can account for 9 to 55% (average 22%) of the total As budget of the sediments and the degree of trace metalloid pyritization for As ranges from 26 to 61%, indicating that authigenic pyrite formation is an important process in the geochemical cycling of As in coastal sediments. High‐resolution micro‐X‐ray fluorescence mapping of single pyrite grains shows that As is distributed inhomogeneously within larger framboids, suggesting changing pore water composition during pyrite growth. X‐ray absorption near edge structure spectra indicate that As is usually present as As(‐I) substituting S in the pyrite lattice. However, in samples close to the sediment/water interface a considerable part of As is in higher valence states (+III/+V). This can be explained by frequent re‐suspension of the surficial sediments to the oxic water column due to wave action and subsequent re‐deposition, leading to the adsorption of As oxyanions onto pyrite. Although reduced As(‐I) becomes more important in the deeper samples, reflecting decreasing redox potential and a longer time since deposition, the occurrence of oxidized As species (AsIII/AsV) in pyrite in the anoxic part of the sediment suggests formation under dysoxic conditions.     

塔北古生界滨岸相混控碎屑岩体系沉积学和沉积模式

滨岸相混控碎屑岩沉积体系是指发育在滨岸带，受河流、波浪和潮汐混合水动力作用产生的复合碎屑岩沉积体系。受区域构造、物源、古地貌、海平面变化和滨岸水动力控制，塔里木盆地沙雅隆起区在志留纪—泥盆纪—石炭纪时期发育了辫状河三角洲、潮汐和波浪作用相互交替的滨岸相碎屑岩复合沉积体系。本文基于野外露头、钻井和测井等资料，开展了沙雅隆起区志留系—石炭系沉积层序、沉积相和沉积模式的综合研究，建立复合沉积体系的沉积学模式，包括：① 志留系—泥盆系的浪控- 潮控海湾沉积体系；② 下石炭统巴楚组的台地- 蒸发潟湖- 潮坪沉积体系；③ 下石炭统卡拉沙依组的河控- 浪控- 潮控三角洲沉积体系。下志留统柯坪塔格组滨岸滩坝和潮坪砂体、上泥盆统东河塘组冲积平原、海湾滩坝砂体和下石炭统卡拉沙依组辫状河三角洲砂体在塔北地区大面积分布，其冲积平原、三角洲前缘、水下分流河道砂体被后期潮汐和波浪作用改造后，形成潮汐水道砂体、河口坝砂体和滨岸滩坝砂体，物性条件明显改善，有利于形成优质储层区带。目前，滨岸混合水动力碎屑岩沉积体系已获得重大油气勘探突破，其沉积学模式可为塔北地区古生界碎屑岩油气勘探提供理论基础。     

Permeability of Sands in the Coastal Areas of the Southern Baltic Sea: Mapping a Grain-size Related Sediment Property

We compared measurements of vertical permeability, grain size distribution, and porosity from sandy surface sediments in the southern Baltic Sea. Using this information we constructed maps reflecting the permeability within the study area. We found that the formula suggested by Krumbein and Monk (1942) overestimates measured permeabilites on average by a factor 2.6 for the area investigated. The results of a formula including porosity, as in the Carman-Kozeny relation (Carman, 1937), deviated even more from our observations. Vertical heterogeneity of the sediments between 0–10 cm depth and the content of fine particulate material were likely responsible for this phenomenon.Our findings suggest that sediments, classified by averagegrain size based nomenclature as sands, cannot generally be assumed to be highly permeable. Nevertheless, maps constructed mirror the distribution of the average grain size in two data sets we used. For the shallow southern Baltic and an assumed threshold for permeability-effects of2.5 × 10^-12 m², wecalculate >41% of the sea floor to be permeable. An additional 27% may be permeable, but were excluded from calculations due to poor sorting.     

Physicochemical and biological influences on sedimentary‐fabric formation in a salinity and oxygen‐restricted semi‐enclosed sea: Gotland Deep,Baltic Sea

Two ca 8000 year long sediment cores from the Gotland Deep, the central sub‐basin of the Baltic Sea, were studied by means of digital images, X‐radiographs and scanning electron microscopy–energy‐dispersive X‐ray mineralogical analysis to gain understanding of the physicochemical and biological influences on sedimentary‐fabric formation in modern and ancient seas with a high flux of organic carbon, and associated oxygen stress and depauperate ichnofauna. Four lithofacies were recognized: (i) sharply laminated mud; (ii) biodeformed mud; (iii) burrow‐mottled mud; and (iv) sedimentation‐event bed. The sharply laminated and burrow‐mottled facies dominate the cores as alternating long intervals, whereas the biodeformed and sedimentation‐event facies occur as thin interbeds within the sharply laminated intervals. The sharply laminated mud comprises alternating diatom‐rich and lithic laminae, with occasional Mn‐carbonate laminae. Lamination discontinuity horizons within the laminites, where the regular lamination is overlain sharply by gently inclined lamination, challenge the traditional view of mud accumulation by settling from suspension, but indicate localized accumulation by particle‐trapping microbial mats and, potentially, by the rapid lateral accretion of mud from bedload transport. The biodeformed interbeds record brief (few years to few decades) oxic–dysoxic conditions that punctuated the anoxic background conditions and permitted sediment‐surface grazing and feeding by a very immature benthic community restricted to the surface mixed tier. The likely biodeformers were meiofauna and nectobenthic pioneers passively imported with currents. The sedimentation‐event interbeds are distal mud turbidites deposited from turbidity currents probably triggered by severe storms on the adjacent coastal areas. The turbidite preservation was favoured by the anoxic background conditions. The long burrow‐mottled intervals are characterized by intensely bioturbated fabrics with discrete Planolites, rare Arenicolites/Polykladichnus and very rare Lockeia trace fossils, as well as bivalve biodeformational structures which represent shallowly penetrating endobenthic feeding and grazing strategies and permanent dwellings. These burrowed intervals represent longer periods (several years to few centuries) of oxic–dysoxic conditions that permitted maturation in the benthos by means of larval settling of opportunistic worm‐like macrofauna and bivalves, resulting in the development of a transition tier. These observations imply more dynamic and oxic depositional conditions in Gotland Deep than previously thought. Comparison to previous zoobenthic studies in the area allowed discussion of the benthic dynamics, and the identification of probable biodeforming and trace‐producing species. Implications for current biofacies and trace‐fossil models are discussed.     

Stratigraphy, depositional environments and level reconstruction of the last interglacial Lake Samra in the Dead Sea basin

In this paper we describe the stratigraphy and sediments deposited in Lake Samra that occupied the Dead Sea basin between ∼ 135 and 75 ka. This information is combined with U/Th dating of primary aragonites in order to estimate a relative lake-level curve that serves as a regional paleohydrological monitor. The lake stood at an elevation of ∼ 340 m below mean sea level (MSL) during most of the last interglacial. This level is relatively higher than the average Holocene Dead Sea (∼ 400 ± 30 m below MSL). At ∼ 120 and ∼ 85 ka, Lake Samra rose to ∼ 320 m below MSL while it dropped to levels lower than ∼ 380 m below MSL at ∼ 135 and ∼ 75 ka, reflecting arid conditions in the drainage area. Lowstands are correlated with warm intervals in the Northern Hemisphere, while minor lake rises are probably related to cold episodes during MIS 5b and MIS 5d. Similar climate relationships are documented for the last glacial highstand Lake Lisan and the lowstand Holocene Dead Sea. Yet, the dominance of detrital calcites and precipitation of travertines in the Dead Sea basin during the last interglacial interval suggest intense pluvial conditions and possible contribution of southern sources of wetness to the region.     

伸展盆地构造演化的数值模拟——以南海北部白云凹陷为例

介绍了瞬时均匀拉伸模型、挠曲悬臂梁模型和多幕伸展模型,特别强调各种模型的基本假设和适用条件,以及基于这些模型发展出的二维正反演模拟和一维应变速率模拟的方法。这些方法在计算岩石圈伸展系数和盆地张裂的过程中,具有一定的优越性。在盆地的数值模拟中,有时需要综合运用多种数值模型来突破单个模型假设条件的约束。为了研究南海北部白云凹陷的裂后沉降特点,分别应用二维正反演和一维应变速率正反演方法计算岩石圈的伸展系数,并计算理论热沉降,与实测裂后沉降进行对比。模拟结果表明,白云凹陷岩石圈的伸展系数大致呈钟形分布,在凹陷中心处最大,大约为3.5;凹陷的实测裂后沉降远大于理论值,即存在裂后异常沉降,裂后期的异常沉降总量在凹陷中心和南部在2km以上。     

伸展盆地构造演化的数值模拟——以南海北部白云凹陷为例

介绍了瞬时均匀拉伸模型、挠曲悬臂梁模型和多幕伸展模型,特别强调各种模型的基本假设和适用条件,以及基于这些模型发展出的二维正反演模拟和一维应变速率模拟的方法。这些方法在计算岩石圈伸展系数和盆地张裂的过程中,具有一定的优越性。在盆地的数值模拟中,有时需要综合运用多种数值模型来突破单个模型假设条件的约束。为了研究南海北部白云凹陷的裂后沉降特点,分别应用二维正反演和一维应变速率正反演方法计算岩石圈的伸展系数,并计算理论热沉降,与实测裂后沉降进行对比。模拟结果表明,白云凹陷岩石圈的伸展系数大致呈钟形分布,在凹陷中心处最大,大约为3.5;凹陷的实测裂后沉降远大于理论值,即存在裂后异常沉降,裂后期的异常沉降总量在凹陷中心和南部在2km以上。     

南海北部海底滑坡的特征、灾害评估和研究展望

海底滑坡及其触发的海啸是海洋地质灾害的重要组成部分.随着海洋工程设施及沿海地区人口及经济的快速增长,海洋地质灾害研究和评估变得越来越重要和紧迫.根据高精度地球物理资料(地震和多波束),在南海北部主要含油气盆地(珠江口盆地和琼东南盆地)中发现大量的海底滑坡.这些海底滑坡形成于上新世至第四纪,它们多以杂乱或空白的地震反射为...     

南海北部神狐海域细粒储层矿物组分对天然气水合物储集赋存的影响

为了探明矿物类型对于天然气水合物成藏的影响,笔者等利用南海北部神狐海域W07站位样品及其水合物饱和度数据,进行XRD全岩和黏土矿物测试分析、比表面积分析以及束缚水能力综合分析。结果表明,海床下110~127 m（即110~127 mbsf,meters below sea floor, 海床以下深度）为水合物储层段,海床下127~156 m为非水合物储层段。通过XRD分析可知,高石英及长石含量,低伊蒙混层含量的层段,比表面积与束缚水能力较低,说明其具有相对较好的孔渗条件,为水合物的运移与储集提供了良好的空间条件,因此形成水合物储层段;而在高伊蒙混层的层段中,比表面积较大,束缚水能力较强,其对甲烷气体及流体的吸附和束缚能力较强,对水合物成藏起到潜在的封隔作用,成为非储层段,储层与非储层段纵向叠置序列有利于优质水合物储层的形成。本次研究总结了矿物组分与优质水合物储层之间的关系,并揭示两者存在的潜在成因联系,以期丰富水合物富集成藏的基础理论,对未来南海北部天然气水合物的商业化开发提供支持。     

南海北部神狐海域细粒储层矿物组分对天然气水合物储集赋存的影响

为了探明矿物类型对于天然气水合物成藏的影响,笔者等利用南海北部神狐海域W07站位样品及其水合物饱和度数据,进行XRD全岩和黏土矿物测试分析、比表面积分析以及束缚水能力综合分析。结果表明,海床下110~127 m（即110~127 mbsf,meters below sea floor, 海床以下深度）为水合物储层段,海床下127~156 m为非水合物储层段。通过XRD分析可知,高石英及长石含量,低伊蒙混层含量的层段,比表面积与束缚水能力较低,说明其具有相对较好的孔渗条件,为水合物的运移与储集提供了良好的空间条件,因此形成水合物储层段;而在高伊蒙混层的层段中,比表面积较大,束缚水能力较强,其对甲烷气体及流体的吸附和束缚能力较强,对水合物成藏起到潜在的封隔作用,成为非储层段,储层与非储层段纵向叠置序列有利于优质水合物储层的形成。本次研究总结了矿物组分与优质水合物储层之间的关系,并揭示两者存在的潜在成因联系,以期丰富水合物富集成藏的基础理论,对未来南海北部天然气水合物的商业化开发提供支持。     

Seismic characteristics and mechanism of fluid flow structures in the central depression of Qiongdongnan basin,northern margin of South China Sea

ABSTRACT

Understanding fluid flow structures in a rifted basin may enhance our knowledge of their origination and evolution. Through geochemical analysis and seismic interpretation, different fluid flow features are identified in the central depression of Qiongdongnan basin, northern South China Sea. These structures include mud diapir, gas chimney, hydrothermal pipes, faults, blowout pipes, and associated extrusions. Mud diapirs are primarily located on the slope belts, whereas gas chimneys are on the basement highs in the southwest of the study area. Their distribution appears closely controlled by tectonic stress field and overpressure, the later is caused by hydrocarbon generation and compaction disequilibrium. High sediment overloading, weak post-rift tectonic activity, and high average geothermal gradient may contribute to the compaction disequilibrium. The occurrence of gas chimneys on the basement high suggests that lateral transportation and relief of overpressure is a significant factor. Distribution of broad hydrothermal pipes is related with the thinning continental crust and pre-existing boundary faults in the central depression. They are probably attributed to intruded sills dissolution and were caused by hydrothermal fluids vertically. Geochemical data from gas reservoirs analysis indicates that mud diapirs and gas chimneys are critical pathways for thermogenic gases, whereas hydrothermal pipes and part of the faults may act as pathways of both thermogenic and inorganic gases. The blowout pipes mainly occur in the northwestern central depression near the continental slope, where fluid flows ascend gradually from a series of Pliocene-current prograding wedge-formed units with a hydraulic fracture in shallow. Hundreds of seafloor pockmarks and mounds associated with blowout pipes located above the NE-SW elongated Pliocene-Quaternary slope-break belts. These extrusive structures indicate that fluids ascend through blowout pipes and were expelled at the present seabed. Our results indicate that fluid flow structures are probably responsible for fluid activities and must be taken into account when assessing the hydrocarbon potential, geologic hazard, and benthic ecosystem.     

Thermal history,hydrocarbon generation and migration in the Horn Graben in the Danish North Sea: a 2D basin modelling study

In this study a 2D basin model has been built along a transect crossing the Horn Graben in WNW-ESE direction. The aim of the investigation was to improve the understanding of the thermal evolution of the basin and its influence on possible petroleum systems. The 2D model of the subsurface is based on one seismic line and data from two exploration wells. Both wells TD’ed in Triassic sediments. The updoming of the Ringkøbing-Fyn High began during Late Carboniferous–Early Permian. At the end of the Permian the Horn Graben became active due to regional extension. The subsequent sedimentation history from Triassic to date is well recorded by well reports. A matter of debate has been whether or not significant amounts of Pre-Permian sediments exist in this area of the North Sea. Since organic material rich Paleozoic sediments serve as source rocks in widespread areas of North Germany and the southern North Sea it would be of great importance to know whether the same deposits exist in the Horn Graben. Nielsen et al. (Bull Geol Soc Denmark Copenhagen 45:1–10, 1998) introduced a model, which shows Paleozoic sediments covering the basement at a maximum depth of 6.5 km. Assuming, Paleozoic sediments are underlying the Permian salt deposits there should be an active petroleum system present. The 2D model includes the Paleozoic source rock and tries to explain why two exploration wells have not found petroleum.     

南海北部潮汕坳陷侏罗系沉积特征及对储层的控制作用研究

南海北部潮汕坳陷侏罗系具有很大的油气勘探潜力,沉积特征对其储层的发育具有明显的控制作用。通过对研究区最新地震资料精细解释,可以划分出4个典型地震反射界面和3个地震反射层,根据层序界面圈出侏罗系分布特征和残留厚度;通过地震相-沉积相转换对比分析研究,识别出侏罗纪地层不同时期的沉积相类型及其分布特征,重塑了潮汕坳陷侏罗系沉积演化史。该区主要发育5类沉积相、8种沉积亚相,其中滨岸三角洲前缘亚相和深水扇中亚相分别控制了碎屑流砂岩优质储层的发育;此外,浊流砂岩储层主要受控于物源供给的影响,距离三角洲砂体朵叶越近,滑塌浊积体数量越多,面积也越大。总体上,滨岸三角洲前缘亚相、深水扇中亚相和滑塌浊积体是研究区良好的储集相带,该类储集体由于埋藏较深加之被泥岩覆盖,对油气聚集较为有利。     

东海表层沉积物碎屑矿物组合分布特征及其物源环境指示

为进一步明确东海陆架区的沉积物物源及水动力环境,对研究区表层沉积物的碎屑矿物进行了鉴定分析。研究区共鉴定出49种重矿物、8种轻矿物。根据碎屑矿物的组合分布结合矿物形态特征,将东海陆架区划分为三个矿物区,内陆架矿物区、外陆架矿物区及虎皮礁矿物区。内陆架矿物区,动力分选是影响碎屑矿物分布的主要因素,物质来源相对单一,碎屑矿物主要来源于现代长江物质,闽浙沿岸近岸河流的输入,人类活动也对该区的矿物组成产生一定的影响;外陆架矿物区,重矿物分布的主控因素是长期的分选作用,主要是长江物质经后期改造形成,现代长江物质可从内陆架中北部扩散至124.5°E左右,此外外陆架东南部地形的变化也对碎屑矿物的分布起到一定控制作用;虎皮礁矿物区,有来自黄河、长江、火山物质的多重影响,且水动力环境相对复杂。     

南海西北次海盆新生代构造 沉积特征及伸展模式 探讨

通过对穿越西北次海盆的3条地震测线以及一条深反射地震剖面的解释,对其新生代的构造 沉积特征进行研究,探讨了伸展模型,并进而对其新生代的构造演化过程和动力学机制进行了分析。结果显示：西北次海盆在30 Ma时开始发育,断层的活动期集中在渐新世,并大致以海盆中部的岩浆岩凸起为轴对称分布,对渐新统的沉积起控制作用。海盆扩张东强西弱,西部显示出更多的陆缘裂谷盆地的特征。25 Ma后扩张轴向南跃迁,西北次海盆的海底扩张运动停止,进入裂后沉降阶段。构造展布方向受到其南侧的中-西沙地块的影响,大致沿其北部边界展布。深反射地震剖面所反映的深部地壳结构也显示出大致沿海盆中轴对称的特征,显示研究区很可能为纯剪的变形模式。     

南海北部边缘盆地天然气成因类型及成藏时间综合判识与确定

20世纪90年代以来,南海北部边缘盆地天然气勘探进展迅速,除早期在琼东南盆地发现YC13-1气田以外,陆续在莺歌海盆地发现了DF气田群和LD气田群,在珠江口盆地发现了WC气田群及PY气田群,近期在珠江口盆地南部深水区则发现了LW-LH气田群。这些气田群气藏天然气组成,主要以烃类气为主,但莺歌海盆地气田群部分区块及层段亦含有丰富的CO2(二氧化碳)和N2(氮气)等非烃气。根据天然气地质地球化学特征,借鉴国内外通用判识划分方法及指标,该区烃类气可综合判识与划分为生物气及亚生物气、成熟油型气、成熟-高熟煤型气及高熟-过熟气等成因类型;该区非烃气CO2可划分为壳源型(有机/无机)、壳幔混合型及火山幔源型等三大成因类型。非烃气N2则可划分为大气成因、壳源型有机成因和壳源型有机-无机混合成因等3种主要成因类型。对于不同气藏烃类气形成及成藏时间判识与厘定,主要依据其地球化学特征及生烃动力学、同位素动力学模拟实验和含烃盐水包裹体及自生伊利石Ar-Ar同位素定年,并结合具体成藏地质条件分析而综合判识与确定;对于非烃气形成及成藏时间,则主要根据伴生烃类气形成时间,并结合温压双控热模实验结果及地质条件综合判识与确定。