中新世是新生代全球气候变冷的一个关键时期，其中以中新世气候最佳期（Middle Miocene Climatic Optimum，MMCO）和一系列短暂的变冷事件（Mi–events）备受关注。南海北部陆丰凹陷LF14井底栖有孔虫组合记录了中新世期间的古海洋环境演化历史。对LF14井171个样品中的底栖有孔虫变量的Q型因子分析结果揭示了3个不同的底栖有孔虫组合，分别是Uvigerina spp.组合，Cibicides spp.组合和Cibicidoides spp.组合。早期研究表明LF14井在早中新世–上新世期间（~18.7–4.53Ma）由半封闭海湾环境转为中–外陆架环境，并一度达到上陆坡环境。早中新世至中新世气候最佳期（~18.7–14.24 Ma），研究区以多样性低和内生–浅内生种为特征的Uvigerina spp.组合占据优势地位，表明研究区处于温暖、低氧和富营养的水体环境。随后，古水深和底栖有孔虫属种在14.24–13.41 Ma期间发生明显变化，表明东南极冰盖在此期间的大规模扩张导致了浅海陆架区海平面下降和底栖有孔虫组合的改变。中中新世中–晚期（14.24–11.54 Ma），以表生种和多样性较高为特征的Cibicides spp.组合成为优势组合，表明研究区水体环境具有高能，高氧和有机质间歇性输入的贫营养特征。进入到晚中新世（11.54–4.53 Ma），以多样性高为特征的Cibicidoides spp.组合成为优势组合，表明研究区处于相对富氧的中等营养环境。其中，Ammonia spp.和Pseudorotalia spp.在10.02 Ma后的大量且连续出现可能指示了研究区可能受到黑潮的影响。

仙掌藻是西沙中新世生物礁主要造礁藻类之一和南海藻礁油气田重要造礁绿藻之一.但是,迄今缺乏化石仙掌藻系统的矿物岩石特征、储层孔渗层特征和沉积成岩演化成因特征研究的报道.本文简述了国内外有关绿藻门仙掌藻相关研究和油气勘探发现研究现状.通过西琛1井104.3 m岩心,研究了永乐环礁中新世化石仙掌藻的矿物岩石和孔渗层特征,鉴定描述了化石仙掌藻节片,指出节片切片绝大多数为纵切面,呈长条状、椭圆状、不规则状,很难获得横切面切片,本文报道了获得的横切面切片研究认识,与现代活体仙掌藻横切面显微特征近似.化石仙掌藻埋藏分布呈叠置状;形成典型生物节片结构,与红藻共生形成节片捆扎、缠绕包裹结构;提出划分化石仙掌藻岩石类型为节片藻礁白云岩.研究井段全部中等程度白云石化,在原文石针晶区域以形成次生微晶-亮晶白云石为主,在皮层、髓部以形成隐晶和淀晶白云石化作用为主;在髓部及孢囊间文石针晶区域形成节片内次生溶孔、晶间孔,节片间形成藻架孔;这些孔隙空间组合形成溶蚀孔+粒内溶蚀孔-晶间孔+藻架孔孔隙网络体系.测得孔隙度16.2%-46.1%,渗透率0.203×10^-3-2 641×10^-3 μm²;喉道半径（23.42-90.43 μm）,属于优良仙掌藻礁油气储层;首次提出建立了西沙群岛新近系生物礁-现代岛礁环境沉积成岩演化成因的模式.

Taiwan Island’s outcropping strata can provide important insights into the sedimentary environment and source development of the southeast China margin. This research is based on the Eocene–Miocene strata of the Tsukeng area in the central Western Foothills, northeast shoreline of Taiwan Island and two sites of the East China Sea Shelf Basin (ECSSB), using petrology and detrital zircon U-Pb age for the analysis. Results show that central and northeast Taiwan Island experienced a transformation from continental to marine facies during the Eocene–Miocene, and the sandstone maturity changed with time. Source analysis shows that sediments from the Eocene–early Oligocene strata mainly originated from near-source Mesozoic rocks, whose zircon age is consistent with the igneous rock in the surrounding area and coastal Cathaysia, showing 120 Ma and 230 Ma peaks in the age spectrum diagram. Since the late Oligocene, peaks of 900 Ma and 1 800 Ma are seen, indicating that deposition of matter from the old block began. The sediments could be a mixture of the surrounding Mesozoic volcanic and fewer pre-Cambrian rocks sourced from the coastal river and sporadic old basement in the ECSSB instead of long-distance transportation.

Numerous elongated mounds and channels were found at the top of the middle Miocene strata using 2D/3D seismic data in the Liwan Sag of Zhujiang River Mouth Basin (ZRMB) and the Beijiao Sag of Qiongdongnan Basin (QDNB). They occur at intervals and are rarely revealed by drilling wells in the deepwater areas. Origins of the mounds and channels are controversial and poorly understood. Based on an integrated analysis of the seismic attribute, palaeotectonics and palaeogeography, and drilling well encountering a mound, research results show that these mounds are dominantly distributed on the depression centres and/or slopes of the Liwan and Beijiao sags and developed in a bathyal sedimentary environment. In the Liwan and Beijiao sags, the mounds between channels (sub) parallel to one another are 1.0–1.5 km and 1.5–2.0 km wide, 150–300 m and 150–200 m high, and extend straightly from west to east for 5–15 km and 8–20 km, respectively. Mounds and channels in the Liwan Sag are parallel with the regional slope. Mounds and channels in the Beijiao Sag, however, are at a small angle to the regional slope. According to internal geometry, texture and external morphology of mounds, the mounds in Beijiao Sag are divided into weak amplitude parallel reflections (mound type I), blank or chaotic reflections (mound type II), and internal mounded reflections (mound type III). The mounds in Liwan Sag, however, have the sole type, i.e., mound type I. Mound type I originates from the incision of bottom currents and/or gravity flows. Mound type II results from gravity-driven sediments such as turbidite. Mound type III is a result of deposition and incision of bottom currents simultaneously. The channels with high amplitude between mounds in the Beijiao and Liwan sags are a result of gravity-flow sediments and it is suggested they are filled by sandstone. Whereas channels with low-mediate amplitudes are filled by bottom-current sediments only in the Beijiao Sag, where they are dominantly composed of mudstone. This study provides new insights into the origins of the mounds and channels worldwide.

The sedimentary system of Kalimantan has undergone significant development since the Oligocene. Previous research have largely ignored the capacity of the Cretaceous–Eocene sediments to produce hydrocarbons, focusing instead primarily on the Oligocene–Miocene coal as the principal source rocks. Shales and coals from the outcrops in the northern margin of Kalimantan were analyzed with palynological and geochemical methods to characterize the palaeoenvironmental and palaeoecological differences between the Cretaceous–Eocene and the Oligocene–Miocene samples. The high proportion of Cheirolepidoaceae, Schizaeoisporites and Ephedripites in the pollen assemblage from the Cretaceous–Eocene outcrops reflects an arid tropical/subtropical climate. The relatively low abundances of gymnosperm-derived biomarkers including isopimarane, β-phyllocladane, β-kaurane, suggest the gymnosperm features in flora. High C₂₇/C₂₉ ααα 20R sterane ratios, (C₁₉–C₂₉) tricyclic terpanes/C₃₀ αβ hopane and extremely low oleanane/C₃₀ αβ hopane, bicadinane T/C₃₀ αβ hopane, and diterpenoid abundance indicate that there was a dominance of algae relative to higher plants in the organic matter. The gymnosperm-derived biomarkers, including isopimarane, β-phyllocladane, β-kaurane, suggest that palaeovegetation during this period was dominated by gymnosperms. The saline and reducing conditions in the bathyal and abysmal sea, evidenced by rather low Pr/Ph and high Gammarerane index, are beneficial for the preservation of hydrogen-rich organic matter. It is presumed that the Cretaceous–Eocene shales had great hydrocarbon generation potential in the southern South China Sea. During the period of Oligocene to Miocene in the Zengmu Basin and the Baram-Sabah Basin, the climate changed to a dominant humid and warm condition, which is corroborated by abundant pollen of Florschuetzia and Magnastriatites hawardi. Low C₂₇/C₂₉ ααα 20R sterane ratios, (C₁₉–C₂₉) tricyclic terpanes/C₃₀ αβ hopane, and high oleanane/C₃₀ αβ hopane, bicadinane T/C₃₀ αβ hopane suggest that the palaeovegetation was dominated by angiosperms including the mangrove plants. The extremely abundant higher plants provide ample terrigenous organic matter for the formation of coal-measures in delta facies. The low gammacerane index and high Pr/Ph indicate the fresh and sub-oxic water in delta-neritic-abysmal faces, which is not beneficial for the accumulation of hydrogen-rich organic matter. Thus, the Oligocene–Miocene marine argillaceous rocks can be potential sources of natural gas.

琼东南盆地南部隆起属于深水勘探潜力区，距其南部40～100km的西沙群岛中新统—第四系均系碳酸盐岩礁滩地层。通过对该盆地的古构造、古地理分析，认为中新世南部隆起具备发育碳酸盐岩礁滩的地质条件。高波阻抗碳酸盐岩在地震剖面上表现为强低频振幅反射，礁滩体分布在古构造高部位，且厚度大于同期地层。从邻区钻井岩性、速度建立的碳酸盐岩厚度变化正演模型模拟出碳酸盐岩不同厚度时的地震响应，找出地震剖面上识别碳酸盐岩厚度的几个重要控制点：尖灭点、λ/4点、λ/2点，据此制作了琼东南盆地南部深水区碳酸盐岩厚度图。根据碳酸盐岩厚度图和古构造、古地理背景以及礁滩地震响应特征可以看出，琼东南盆地南部隆起中新统发育的碳酸盐岩主要为西沙群岛向北伸出的一个半岛式的孤立碳酸盐岩台地和斜坡沉积，由缓坡台地、陡坡台地、台洼、重力流、礁滩等相带组成。

地球化学及碎屑锆石U-Pb定年结果显示，南海北部白云凹陷深水区曾于渐新世至中新世发生沉积物源转变。U1435、L21及H1井始新世锆石年龄频谱以燕山期为主，指示该时期盆地大部分主要受中生代局部物源影响。至早渐新世，稀土配分结果及X28井相对复杂的多峰特征均反映古珠江开始为盆地北部提供沉积物。与此相反，盆地西部及南部以Eu元素正异常为主，表明主要受中-基性源区影响。晚渐新世白云运动导致白云凹陷发生强烈热沉降，陆架坡折带也由凹陷南侧突变式地跳跃至北侧，该地区整体进入陆坡深水环境。该构造事件造成南海北部深水区沉积物源发生重大转变，珠江影响进一步扩大，使得X28、L13及L21井均呈现相似的锆石年龄频谱特征。中新世白云凹陷北部地区主要受控于珠江物源，南部地区继续接受基性沉积物供给，而东部地区则主要受到东沙隆起的持续影响。

There are many large-scale Cenozoic sedimentary basins with plentiful river deltas, deep-water fans and carbonate platforms in the southern South China Sea. The Crocker Fan was deposited as a typical submarine fan during the late Eocene–early Miocene, and stretches extensively across the entire Sarawak–Sabah of the northern Borneo area. However, systematic analyses are still lacking regarding its sediment composition and potential source suppliers. No consensus has been reached yet on the provenance evolution and sedimentary infilling processes, which seriously impeded the oil-and-gas exploration undertakings. By combining with sedimentary-facies identification, heavy mineral assemblages, elemental geochemistry and detrital zircon U-Pb dating, this paper aims to generalize an integrated analysis on the potential provenance terranes and restore source-to-sink pathways of the Crocker Fan. In general, the Crocker Fan was initially formed over the Cretaceous–lower/middle Eocene Rajang Group by an angular Rajang unconformity. The continual southward subduction of the proto-South China Sea resulted in magmatic activities and subsequent regional deformation and thrusting along the Lupar Line in the northern Borneo. The lowermost Crocker sequence is featured by a thick conglomerate layer sourced from in-situ or adjacent paleo-uplifts. From the late Eocene to the early Miocene, the Crocker Fan was constantly delivered with voluminous detritus from the Malay Peninsula of the western Sundaland. The Zengmu Basin was widely deposited with delta plain and neritic facies sediments, while the Brunei-Sabah Basin, to the farther east, was ubiquitously characterized by turbiditic sequences. The Crocker Fan successions are overall thick layers of modest-grained sandstones, which formed high-quality reservoirs in the southern South China Sea region.

The geochemical signatures of fifty-four rock samples and three supplementary drill stem test (DST) oils from the Yacheng-Sanya formations in the central Qiongdongnan Basin (CQB) were analysed. Reconstruction of the early Oligocene−early Miocene (36–16 Ma) palaeovegetation and source analyses of organic matter (OM) were conducted using aliphatic biomarkers in ancient sediments and DST oils. Both the interpreted aquatic and terrigenous OM contributed to the CQB source rocks (SRs) but had varying relative proportions. The four distribution patterns derived from n-alkanes, terpanes, and steranes are representative of four OM composition models of the Yacheng-Sanya SRs, including model A, model B, model C, and model D, which were classified based on the increasing contribution from terrigenous OM relative to aquatic OM. Some terrigenous higher plant-derived biomarkers, including oleanane, des-A-oleanane, C₂₉ ααα 20R sterane, bicadinanes, the C₁₉/(C₁₉ + C₂₃) tricyclic terpane ratio, and other n-alkane-derived ratios suggest that angiosperms had increased proportions in the palaeoflora from early Oligocene to early Miocene, and the bloom of terrigenous higher plants was observed during deposition of upper Lingshui Formation to lower Sanya Formation. These findings are consistent with the incremental total organic carbon and free hydrocarbons + potential hydrocarbons (S₁ + S₂) in the lower Lingshui-lower Sanya strata with a significant enrichment of OM in the E₃l₁-N₁s₂ shales. The maturity- and environment-sensitive aliphatic parameters of the CQB SRs and DST oils suggest that all the samples have predominantly reached their early oil-generation windows but have not exceeded the peak oil windows, except for some immature Sanya Formation shales. In addition, most of the OM in the analysed samples was characterised by mixed OM contributions under anoxic to sub-anoxic conditions. Furthermore, terrestrial-dominant SRs were interpreted to have developed mainly in the Lingshui-Sanya formations and were deposited in sub-oxic to oxic environments, compared to the anoxic to sub-anoxic conditions of the Yacheng Formation.

The increase of total organic carbon content of the late Oligocene−early Miocene terrigenously-dominated marine shales in the shallower depth intervals was reported in the Ying-Qiong Basin, South China Sea. The organic enriched lower Sanya Formation shales (early Miocene) have biomarker characteristics of tropical/subtropical plants, with abundant high molecular weight n-alkanes, angiosperm-derived oleanane, rearranged oleananes I, II, II, tricyclic/tetracyclic terpanes including des-A-oleanane, X, *, Y, Z, Z1 and bicadinanes W, T, T1, R. The biomarker characteristics are suggestive of larger influx of the dominant tropical/subtropical angiosperms in flora under a warming and more humid climate during depositions of the lower Sanya Formation (early Miocene) than the older Lingshui Formation (late Oligocene). The tropical/subtropical angiosperm input was thought as the prime control of terrigenous organic matter enrichment relative to the redox condition, and the coeval sea level changes and seafloor spreading in the South China Sea. Enrichment of the terrigenous organic matter in the early Miocene shales is likely in association with the coeval peak East Asian summer monsoon intensity in the South China Sea.