Lacustrine Facies Research Articles

Development potential and technical strategy of continental shale oil in China

Continental shale oil is a general term for liquid hydrocarbons and many kinds of organic matter in continental organic-rich shale series with vitrinite reflectance of more than 0.5% at buried depth of more than 300 m, and is an important type of source-rock oil and gas. Based on the evolution model of oil generation and expulsion in organic-rich shale series controlled by maturity, continental shale oil is divided into two types: medium-high maturity and medium-low maturity. (1) The continental shale series in China develop high-quality source rocks of freshwater and saltwater lacustrine facies, as well as multiple types of reservoirs, including clastic rocks, carbonate rocks, diamictite, tuff and shale, forming a number of “sweet sections” and “sweet areas” of continuous distribution inside or near source rocks, which have large scale resources. (2) Experimental analysis of organic rich shale samples shows that the shale samples with wavy and horizontal beddings have good storage conditions, and the horizontal permeability of shale is tens to hundreds of times of its vertical permeability, which is conducive to the lateral migration and accumulation of shale oil in the source rocks. (3) After evaluation, the geological resources of medium-high maturity shale oil are about 10 billion tons, which can be effectively developed by horizontal drilling and volumetric fracturing, and will be a practical field of oil exploration in recent years. Shale oil with medium and low maturity has huge resource potential, and technological recoverable resources of (70–90) billion tons, making it a strategic alternative resource of oil industry. However, economic development of this type of shale oil needs in-situ conversion technology breakthroughs. Continental shale oil is an inevitable choice in the process of Chinese continental petroleum exploration from “outside source” to “inside source”. Making breakthroughs in the core technologies such as “sweet area” evaluation and optimization, horizontal well volume fracturing and in-situ conversion technology and equipment is the key to realizing scale development of continental shale oil economically.

The Jenkyns Event (early Toarcian OAE) in the Ordos Basin, North China

Abstract The early Toarcian (Early Jurassic) Oceanic Anoxic Event (T-OAE) or Jenkyns Event (~183 Ma) was marked by a globally synchronous negative carbon-isotope excursion, large-scale organic carbon burial and widespread oxygen depletion in the oceans. These features have been associated with volcanic activity of the Karoo and Ferrar large igneous provinces. The Jenkyns Event is well investigated in the Tethyan Ocean, but its expression in continental settings outside of Europe are still poorly understood. Here, the lacustrine Anya (AY) section in the NE Ordos Basin, North China, is studied for carbon-isotope geochemistry and palynology. Palynostratigraphy constrains the age of the section to the Pliensbachian-Toarcian transition, and a positive trend in δ13C, interrupted by a pronounced negative carbon-isotope excursion, has been identified in bulk organic matter and long-chain n-alkanes. The negative excursion is the expression of the Jenkyns Event, and coincides with variable total organic carbon (TOC) content in lake sediments. The maximum TOC (~21.5%) values precede the most negative carbon isotopes. A turnover from spore and seed fern-dominated palynological assemblages to Classopollis superabundance is coincident with the isotopic excursion and indicates clearly environmental perturbation. Biomarker data suggest that the organic matter was mainly sourced from higher plants. The magnitude of the Toarcian excursion in the bulk organic matter of this section (~ − 12.5‰) is much larger compared to that typically observed in marine and lake strata. Humidity-related fractionation effects in land plants and changes in plant groups might have contributed to the recorded magnitude. This magnitude is also larger than that of other terrestrial records, and casts doubt on the use of terrestrial C-isotope data to constrain deep time pCO2. Nevertheless, our findings show that the Jenkyns Event is well-recorded in lacustrine facies of the Ordos Basin.

IDENTIFYING UPPER MIOCENE – LOWER PLIOCENE LACUSTRINE SEDIMENTS IN DRY TUNKA BASIN OF THE BAIKAL RIFT ZONE

We present results of lithogeochemical, diatomic and palynological studies of sediments from the Tunka-13 well that was drilled in the southeastern part of dry Tunka basin in the Baikal rift zone. At the base of the section, there is an eroded basaltic flow of 16–15 Ma. From lithogeochemical signatures, we identify nine sedimentary units. The seven lower ones (interval 7.2–86.5 m) belong to the Tankhoi formation, the eighth (interval 2.7–6.6 m) to the Anosov formation, the ninth (interval <2.4 m) to the sandy stratum. We determined local sources of clastic material of basaltic and silicic compositions for units 1 and 2, respectively, and remote sources of silicic compositions for the overlaying units. The section shows a change from alluvial facies (units 1–3) through avandelta (unit 4) and lacustrine ones (units 5–7), again to alluvial facies (unit 8) and then to lacustrine-eolian ones (unit 9). Spore and pollen spectra from sediments of units 1–7 are divided into three palynozones (PZ), reflecting the vegetation change in the Late Miocene – Early Pliocene: PZ-1 – coniferous and deciduous forests with a small participation of thermophilic broadleaved species in moderately warm, humid climatic conditions; PZ-2 – enhancing the role of hemlock and more diverse thermophilic deciduous rocks in more humid and warm conditions; PZ-3 – a gradual reduction in the number of hemlock and other dark coniferous species, removing broad-leaved species by birch and alder, growing grassy communities in wetlands due to climate cooling. We identified layers of lacustrine facies by occurrence of fossil diatoms that are absent in the layers of the alluvial and avandelta facies. In lacustrine sediments, we distinguish four diatom zones: DZ-1 denotes a relatively deep Late Miocene paleolake, marked by planktonic species, DZ-2, DZ-3 and DZ-4 – a shallow Early Pliocene lake with a developed littoral zone and short transgression. The Late-Miocene paleolake transgression, indicated by changing facies, is associated with structural reorganization, accompanied by volcanic extinction in the Tunka valley about 9–8 Ma, and the Early Pliocene short transgression with a new reorganization, reflected in volcanic rejuvenation about 4.0 Ma.

Large scale dinoturbation in braided stream deposits: evidence from the Cretaceous Tugulu Group of the Hami area, Eastern Xinjiang, China

Large dinosaur tracks were recently reported from locations in the Pterosaur-Yadan National Geological Park situated about 100 km south of Hami in Xinjiang Province, China. The park comprises a substantial area in a much larger arid region comprising and extensive spectrum of Cretaceous, siliciclastic, Tugulu Group, lithofacies representing proximal, basin margin, alluvial fan and braided stream deposits, grading into alluvial plain, deltaic and lacustrine facies near the depocenter. Due to the difficulties of conducting detailed geological surveys in such a vast and inhospitable area, definitive resolution of the litho-, bio- and chrono-stratigraphy is challenging in some areas, and yet to be published in detail. Nevertheless, the occurrence of large dinosaur tracks and dinoturbated units, here interpreted as sauropodan, in association with root casts, dinosaur bone and fossil wood, points to the potential of this frontier area to yield valuable paleontological information, and show that flora and fauna were found in arid braided stream systems away from the lacustrine depocenters where body fossils are more abundant and better known.

Geochronology and sedimentology of the Huashan Group in the northern Yangtze Block: implications for the initial breakup of the South China

Middle Neoproterozoic sedimentary sequences are widespread in South China and provide crucial insights into the geological evolution of sedimentary basins related to the breakup of the Rodinia supercontinent. The Huashan Group is a key Neoproterozoic stratigraphic unit in the northern Yangtze Block, South China; however, its depositional age and tectonic setting of deposition are debated. Here, we report zircon U–Pb geochronology and Hf isotope data for a tuff from the second section of the Hongshansi Formation near the bottom of the Huashan Group. Zircon U–Pb geochronology yields a 206Pb/208U age of 836 ± 4 Ma (MSWD = 0.74, n = 29). Zircon Hf isotope ratios have eHf(t) values of + 3.1 to + 5.4 and TDM2 ages range from ca. 1.5 to 1.4 Ga, which indicates that juvenile materials derived from the mantle were involved in their host magmas. Combined with previous research, the Huashan Group was deposited from ca. 830 to 800 Ma from bottom to top, and it contains alluvial fan, fan delta, and semideep to deep lacustrine facies, which represent early sedimentation into a continental rift basin. Rifting and basin formation began at ca. 830 Ma in South China, which is coeval with the initial breakup of the Adelaidean Rift in southeastern Australia. The Huashan Group was deposited during the first and the second episodes of a superplume associated with the breakup of the Rodinia supercontinent.

KARAKTERISTIK ENDAPAN DANAU RAWA PENING DI MUARA INLET SUNGAI GALEH, KECAMATAN AMBARAWA, KABUPATEN SEMARANG

The Galeh River inlet estuary on Lake Rawa Pening is located in Ambarawa District, Semarang Regency. Sampling of Rawa Pening sediment at two points using modern coring methods. The coring results were observed and granulometric analysis was done using lazer scanning method with Master Sizer 2000. Core RWP-01 samples in the form of fine clastic sediments (Sand-Silt), reflecting the inlet river estuary environment in the hydrological lake system which is influenced by the fluvio-lacustrin process and showing characterizer of shallow lake facies. RWP-02 core samples in the form of fine-textured sediments (mud) rich in organic material, reflecting a relatively calm and stable depositional environment, formed by the density current mechanism that characterize the deep lake facies. The development of these sedimentary characters shows changes in sedimentary facies, namely shallow lake facies developing into clastical lake lacustrine into deep lake lacustrine facies.

New Olduvai Basin stratigraphy and stratigraphic concepts revealed by OGCP cores into the Palaeolake Olduvai depocentre, Tanzania

The Olduvai Gorge Coring Project (OGCP) drilled four boreholes 1A, 2A, 3A, 3B at three sites into the central palaeolake of the Olduvai Basin depocentre. Previously known Beds I, II, III, IV, Masek Beds and Ndutu are identifiable in the upper part of the cores, and from these formations predominantly lacustrine facies associations are recognised. These are described and then interpreted in terms of their palaeoenvironmental significance. However, stratigraphy known from natural outcrop exposures is more than doubled by strata intersected below. For example, an extra 135 m of pre-Bed I stratigraphy in Core 2A records the entire volcanic history of a fan-delta sourced from Ngorongoro Volcano. Beneath that fan sequence is an interval of fluvio-lacustrine non-volcaniclastic sediments. For the latter the new stratigraphic term Naibor Soit Formation is introduced, because these strata were discovered for the first time in Boreholes 2A and 3A, to either side of Naibor Soit Inselberg, where they thus lap onto its basement topography. The volcanically sourced unit above is named Ngorongoro Formation, including Marker Tuffs CFCT (Coarse Feldspar Crystal Tuff) and the Naabi Ignimbrite within its topmost portion. Only the dominantly lacustrine sediments above the main Ngorongoro sourced fan body are now attributed to Lower Bed I. The Ngorongoro Formation defined here contains primary Tuff Markers NgA to NgQ, and volcaniclastic fan-delta deposits that interfinger with and overlie claystones and interbedded sandstones of the fluvio-lacustrine Naibor Soit Formation. Boreholes 1A and 2A intersect the Bed I Basalt, but not Borehole 3A, where the position of the lava is marked by three separated volcaniclastic sandstone layers, containing pebble-sized basalt scoriae, likely correlating to three complex basalt flows at Locality 9A and Orkeri and allowing assessment of syn-basalt sedimentation. Disconformities bounding Beds I, II, III, IV, Masek Beds and Ndutu Beds provide important stratigraphic markers for the novel application of sequence stratigraphic concepts, as they mark lowstands of Palaeolake Olduvai, guiding outcrop to core correlations. Major disconformities are identified in: (1) Core 1A, where the Lower Bed II Crocodile Valley Incision Surface cuts out Tuff IF; (2) Core 1A, where disconformities and facies within Beds II, III, IV, and Masek Beds are identified; (3) Cores 2A and 3A, where Tuff IF is identified below the Lower to Middle Bed II disconformity; and (4) Lower Bed I claystones and Tuff IA in Core 3A that correlate to similar sedimentary units from Locality 66e in the Western Gorge, but which are absent from Core 2A because of a newly identified major disconformity, which causes the Bed I lava to sit directly on top of the CFCT marker.

Study of molasse within the middle segment of the Bangong‐Nujiang suture zone, central Tibet: Constraints of ocean–continent transform

The Bangong‐Nujiang suture zone, separating the Lhasa and South Qiangtang terranes of the Tibetan Plateau, is marked by remnants of the Bangong‐Nujiang oceanic basin. In the Zanzong Co area of central Tibet, non‐marine molasse deposits of the newly identified Jingzhushan Formation record the eventual collision between these two terranes and subsequent ocean–continent transform along the middle segment of the Bangong‐Nujiang suture zone. In this contribution, it is observed that the Jingzhushan Formation, characterized by lacustrine facies and braided delta facies, rests unconformably on the underlying marine strata and ophiolite. Zircon U–Pb dating has been conducted with samples of four interlayer volcanic rocks and two sandstones from the Jingzhushan Formation. The interlayer volcanic rocks constrain the depositing age from ca. 115 to 72 Ma. Based on the youngest detrital zircon ages, the maximum depositional ages of the Jingzhushan Formation are suggested to be ca. 78 Ma. Petrographic and detrital zircon isotopic results indicate that sediments in the Jingzhushan Formation have mixed sources from the South Qiangtang terrane and the intervening Bangong‐Nujiang suture zone. Provenance analysis, together with regional data, suggests that the newly identified Jingzhushan Formation reflects continental molasse deposition in an intermontane basin during the post‐collisional stage. The development of the intermontane basin evidenced by molasse deposition of the Jingzhushan Formation reveals that the ocean–continent transform of the middle segment of the Bangong‐Nujiang Ocean had been completed in the late Early Cretaceous (ca. 115 Ma).

The Holocene history of the Faiyum Lake (Egypt) based on sediment characteristics, diatoms and ostracods contents

There are relatively few Holocene lake sediment core sequences available for north-east Africa. This study examines the developmental history of Faiyum Lake (Egypt) by detailed lithostratigraphic description together with microfossils and geochemistry, of two adjacent lake sediment cores. The recovered sedimentary sequence consists of predominantly lacustrine facies divisible into five sedimentary units. Early Holocene sediments (Unit II; c. 9.9–8 ka cal BP), overlying late Pleistocene aeolian sands (Unit I), comprise sub-mm laminations (non-glacial varves) of white diatomite and calcite inter-bedded with yellowish-green mineralogenic layers indicating a deep freshwater lake phase. Early middle Holocene sediments (Unit III, c. 8 to 6 ka cal BP) consists by pockets of non-glacial varved laminae intercalated with turbidites and increasing thick silty clay layers, indicating a shallow freshwater lake phase with increasing nutrients. The late middle Holocene lake phase, Unit IV (c. 6 to 4 ka cal BP) is grey massive mud with occasional thick (>1 cm) diatomite-carbonate layers and thin gypsum and iron-hydroxides layers indicative of a lake shrinking phase but with a large level fluctuation sand evaporation phases when freshwater inflow diminished. The late Holocene lake phase (unit V, c. 4 ka cal BP-present) reveals bioturbation and increasing fine sand with artifacts corresponding to further lake level declines and fluctuations as water management intensifies during and after Middle Kingdom and Ptolemaic times. Together with geochemical and microfossil evidence, sedimentology of the studied cores indicate a series of major environment changes affecting the whole lake system throughout the Holocene.

Holocene Evolution of the Burano Paleo-Lagoon (Southern Tuscany, Italy)

The study of Burano paleo-lagoon—Wetland of International Value, has allowed us to better define and extend the reconstruction of the Holocene paleoenvironmental evolution of the paleo-lagoons previously studied, located on the Tyrrhenian coast in central Italy. The investigated area is located in Southern Tuscany near the Burano Lake. The area was investigated by means of field surveys, historical maps, 16 coring, sedimentological, palynological and microfaunal analyses (foraminifera and ostracods), combined with robust geochronological control provided by 52 datings (14C and OSL). The study allowed us to reconstruct the environmental and morphological evolution of the Burano paleo-lagoon during the last 8000 years and to hypothesize a Rise Sea Level (RSL) curve. In this context, 5 main evolutionary phases have been recognized. (1) before 7.5 ka BP in the southern-eastern part, an open lagoon developed; (2) ~6 ka BP a barrier-lagoon system develops throughout the entire area and the lagoon progressively changed from open to closed one; (3) ~5 ka BP the width of the lagoon increases and a lacustrine facies appears along the entire axis of the coastal basin; (4) ~4 ka BP the lacustrine facies shows a discontinuous distribution respect to the previous phase; (5) during the last 4 ka the lacustrine facies disappear and the lagoon turns into a wetland area.

Hydrocarbon accumulation patterns of salt crust covered biogenic gas reservoirs in the Sanhu Depression, Qaidam Basin

Quaternary biogenic gas reservoirs are extensively developed in the Sanhu Depression of the Qaidam Basin, where the largest domestic biogenic gas production base has been built up. In recent years, however, the exploration of biogenic gas there encounters a variety of difficulties, such as the identification of true and false seismic abnormality, the determination of micro-relief structure and the identification and description of lithologic traps, which are the bottlenecks restricting its exploration breakthrough. In this paper, hydrocarbon accumulation patterns of biogenic gas were studied. Then, based on fine structure interpretation results, combined with laboratory experiments, the sealing capacity, distribution range, formation time and genesis of salt crust were discussed, and the salt crust covered hydrocarbon accumulation pattern of biogenic gas was put forward. Finally, combined with the conditions of source rocks and reservoirs, the exploration prospect of salt crust covered biogenic gas reservoirs was predicted. And the following research results were obtained. First, the Quaternary in the Sanhu Depression is composed of sandstone–mudstone interbeds of shore-shallow lake facies, with superior conditions of source rocks and reservoirs. Many source–reservoir–caprock assemblages are vertically formed. The biogenic gas has the characteristics of dynamic hydrocarbon accumulation, i.e., continuous migration, accumulation, diffusion and re-accumulation. Second, under the effect of Himalayan movement, the climate changes frequently and the salinity of the ancient lake is zoned in the Sanhu Depression. A freshwater area is formed at the inlet of the river in the south and a brine area is formed in the north. Under the influence of evaporation, the phreatic water in the north is salinized continuously, and a set of extensively distributed salt crust with steady thickness and a strong sealing capacity is formed at the eastern part of Lingjian fault. Third, the biogenic gas generated by dark mudstone of lacustrine facies in the depression center migrates laterally and vertically to Lingjian fault zone and gets accumulated under the sealing of salt crust. In conclusion, high-quality source rocks and reservoirs and the salt crust with a strong sealing capacity in the Sanhu Depression constitute a good spatial–temporal configuration relationship of source rocks, reservoirs and cap rocks, so salt crust covered biogenic gas reservoirs can be formed to provide abundant natural gas resources with a broad exploration prospect.

Geochemical characteristics of carbonate rocks in a salinized lacustrine basin: a case study from Oligocene formation in the Qaidam Basin, northwestern China

Based on petrology, mineralogy, carbon and oxygen isotope composition, trace element composition, geochemical characteristics of carbonate rocks are systematically analyzed in the saline lacustrine basin environment in the Qaidam Basin, northwestern China. The results show that: (1) The carbon and oxygen isotopic compositions show carbonate rocks were deposited between open lake and closed lake environment; (2) the Sr/Ba ratio is greater than 1 with an average of 2.01; the Sr/Cu ratio is greater than 5 with an average of 109.04; the U/Th average value ratio is less than 1 with an average of 0.62. These data indicated the carbonate rocks deposited in an salinization, drought, and reducing lacustrine environments; (3) ΣREE values range from 39.41 to 162.67 ppm with an average of 87.67 ppm, and negative anomaly of Eu occurs in REE distribution patterns; and (4) lithologies of carbonate rocks are mainly composed of dark gray or black carbonates, commonly associated with salts deposition due to different lacustrine facies.

Paleoclimate and paleoecology of the latest Eocene Florissant flora of central Colorado, U.S.A.

The uppermost Eocene Florissant Formation of central Colorado, U.S.A. contains a diverse flora and fauna preserved in lacustrine facies and represents a key episode in Earth history immediately preceding the Eocene-Oligocene boundary. Laminated shales contain impressions of non-monocot angiosperm leaves that were used to estimate paleoecological and paleoclimatic parameters using leaf physiognomic methods including: leaf mass per area (MA), digital leaf physiognomy (DiLP), leaf margin analysis (LMA), and leaf area analysis (LAA). The majority (58%) of the morphotypes analyzed for MA suggested a semi-evergreen leaf lifespan, whereas another 27% indicated a deciduous habit and 15% an evergreen habit. There was no significant relationship between MA and insect damage based on a small subset of Florissant's leaves. Higher MA values (~73% of leaves ≥ one-year lifespan), coupled with a tendency toward long and narrow leaf shapes and small leaf areas, indicate the existence of sclerophyllous vegetation. Using the global regression for mean annual temperature (MAT), the DiLP estimate of MAT was anomalously cold: 5.5 ± 4 °C. However, using a Northern Hemisphere regression the DiLP MAT estimate of 11.6 ± 3.3 °C was more plausible. Using DiLP, mean annual precipitation (MAP) was estimated at 740 + 608/−334 mm∙yr−1, which supports dry conditions. Estimates for MAT and MAP using the univariate LMA and LAA methods overlapped within uncertainty of the DiLP results. In addition, those taxa classified as growing in wet areas (riparian) had significantly more teeth than non-riparian taxa. These paleoclimatic and paleoecological results suggest that outside the riparian forest, the Florissant flora sampled a seasonally dry temperate sclerophyllous shrubland to woodland, perhaps similar to modern chaparral forests, in the western interior of the U.S.A. just before the transition into the cooler Oligocene.

Studies of a Lacustrine‐Volcanic Mars Analog Field Site With Mars‐2020‐Like Instruments

AbstractOn the upcoming Mars‐2020 rover two remote sensing instruments, Mastcam‐Z and SuperCam, and two microscopic proximity science instruments, Scanning for Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) and Planetary Instrument for X‐ray Lithochemistry (PIXL), will collect compositional (mineralogy, chemistry, and organics) data essential for paleoenvironmental reconstruction. The synergies between and limitations of these instruments were evaluated via study of a Mars analog field site in the Mojave desert, using instruments approximating the data that will be returned by Mars‐2020. A ground truth data set was generated for comparison to validate the results. The site consists of a succession of clay‐rich mudstones of lacustrine origin, interbedded tuffs, a carbonate‐silica travertine deposit, and gypsiferous mudstone strata. The major geological units were mapped successfully using simulated Mars‐2020 data. Simulated Mastcam‐Z data identified unit boundaries and Fe‐bearing weathering products. Simulated SuperCam passive shortwave infrared and green Raman data were essential in identifying major mineralogical composition and changes in lacustrine facies at distance; this was possible even with spectrally downsampled passive IR data. Laser‐induced breakdown spectroscopy and simulated PIXL data discriminated and mapped major element chemistry. Simulated PIXL revealed millimeter‐scale zones enriched in zirconium, of interest for age dating. Scanning for SHERLOC‐like data mapped sulfate and carbonate at submillimeter scale; silicates were identified with increased laser pulses/spot or by averaging of hundreds of spectra. Fluorescence scans detected and mapped varied classes of organics in all samples, characterized further with follow‐on spatially targeted deep‐UV Raman spectra. Development of dedicated organics spectral libraries is needed to aid interpretation. Given these observations, the important units in the outcrop would be sampled and cached for sample return.

Geochemical characteristics and hydrocarbon expulsion of source rocks in the first member of the Qingshankou Formation in the Qijia‐Gulong Sag, Songliao Basin, Northeast China: Evaluation of shale oil resource potential

AbstractIn recent years, there has been significant progress in shale oil exploration in the first member of the Qingshankou Formation (K2qn1) in the Qijia‐Gulong Sag, Songliao Basin, Northeast China: It shows good prospects for shale oil. However, the recognized lack of the geochemical and hydrocarbon generation and expulsion characteristics of K2qn1 source rocks limits an accurate evaluation of shale oil resource. This study systematically investigated the geological and geochemical characteristics, hydrocarbon generation and expulsion, and shale oil potential of the K2qn1 source rocks. The results show that the K2qn1 mudstones were mainly deposited in the semideep and deep lacustrine facies under reducing and weak reducing conditions. Compared with the southern Gulong Sag, the northern Qijia Sag has a higher salinity, more abundant prosperous aquatic organisms, and a greater paleoproductivity. The K2qn1 source rocks are pervasive and continuous in the entire sag, with maximum thicknesses greater than 110 m. They have a higher organic matter (OM) abundance (2.40% of the average TOC), are dominated by type I and II1 kerogen, and are mature (0.8%‐0.1.3% VR), which indicate that they are good to excellent source rocks and have significant hydrocarbon generation potential. The source rocks in the Qijia Sag have a higher OM abundance, a better OM type, and a lower OM maturity than those in the Gulong Sag. The threshold and peak hydrocarbon expulsion values for marlstone source rocks are 0.85% VR and 0.95% VR, respectively. The volumes of hydrocarbons generated and expulsed from the K2qn1 source rocks are 121.8 × 108 t and 46.9 × 108 t, respectively, with a retention efficiency of 61.5%. The in‐place and recoverable resources of shale oil are 74.9 × 108 t and (12.0‐13.5) × 108 t, respectively, indicating that the entire sag has a significant shale oil potential, especially the Qijia Sag.

New insights into the organic geochemistry of the Otway Basin

The Penola Trough of the Otway Basin in South Australia has enjoyed over 20 years of commercial hydrocarbon production from the sandstones of the Early Cretaceous Otway Group with 71.46 PJ sales gas and 65840 kL of condensate produced from five fields until production ceased in 2011. Recent success in Haselgrove 3, where a newly discovered deeper reservoir underlying depleted reservoirs of the Pretty Hill Formation flowed 25 MMscfd on test heralds a new phase of exploration and appraisal with a 2C Contingent Resource of 87 PJ assigned to the discovery. These hydrocarbons are considered to have been principally derived from lacustrine, floodplain and back swamp facies of the Pretty Hill Formation and lacustrine facies of the underlying Casterton Formation. The South Australia Department for Energy and Mining is currently investigating an unnamed Late Jurassic syn-rift sequence of interbedded metasediments, tuffaceous sediments and organically-rich shale, first identified as fractured basement in Sawpit 1, located on the northern flanks of the Penola Trough and which unconformably underlies the Casterton Formation. A low-sulfur medium-gravity paraffinic oil was recovered from drill stem tests from this well and subsequent total organic carbon and Rock-Eval analyses for the same unit in nearby Sawpit 2 identified a source rock containing algal organic matter and thought to be deposited in a deep anoxic lake setting. In this paper, we will present the preliminary results of detailed geochemical analyses of rocks and rock extracts from this previously unrecognised syn-rift sequence and discuss implications for hydrocarbon prospectivity in the deeper portions of the Penola Trough.

Geochemical characteristics and sources of the crude oil of Yan’an formation Yan 9 in Zhao’an area, Ordos Basin, China

A certain scale of Yan 9 reservoir was found in Zhao’an area, but the oil source is not clear. The geochemical characteristics of Yan 9 crude oil and potential source rocks were analyzed by using gas chromatograph-mass method. Analysis results showed that the parent materials of Yan 9 crude oil were sourced from lower aquatic organism and higher terrigenous plants and formed in freshwater- brackish water lacustrine facies. Oil-source correlation results showed that Yan 9 crude oil was derived from the source rocks of Chang 7.

Tectonic Uplift of the Yili Basin during the Last Stage of the Late Pleistocene: Evidence from ESR and OSL Dating of Sediments in the Huocheng Area, Xinjiang

The Quaternary sediments in the Yili Basin can serve as archives for studying the Cenozoic basin–mountain relationship. In this study, based on typical natural sections and boreholes, the surficial sediments of the Huocheng area were studied, and their sedimentary ages were obtained using the optically stimulated luminescence (OSL) and electron spin resonance (ESR) dating methods. These dates, combined with changes in the sedimentary facies, provided details of the neotectonic movement in the Yili Basin and adjacent areas. By dating sediments from five sections and three boreholes, we determined that the surficial sediments of the Huocheng area were mainly formed in the Late Pleistocene, with scattered instances of Holocene sediments. The surficial sediments mainly consisted of alluvial fan facies, fluvial facies, lacustrine facies, and desert facies. Based on the activity on the Hongshanzui fault and the northern margin fault of the Wusun Mountains, the Huocheng area was uplifted synchronously with the Tianshan Mountains during the last stage of the Late Pleistocene, causing the desert facies sediments to be superimposed on the former paleo–lake sediments.

How to find high-quality petroleum source rocks in saline lacustrine basins: A case study from the Cenozoic Qaidam Basin, NW China

Despite having made significant contributions to global hydrocarbon occurrences, source rocks in saline lacustrine basins show great mineralogical and organic geochemical heterogeneity and the controlling mechanism is weakly studied. Here, we use the Cenozoic Qaidam Basin as an example to compare the organic and inorganic parameters of fine-grained sediments in different lacustrine facies and to figure out the characterization and distribution of effective petroleum source rocks in saline lacustrine systems. Organic-inorganic database of six selected boreholes show that in the bench-margin (high-gradient) lacustrine system, fine-grained sediments in sublittoral brackish-mesosaline zones containing low chlorides (<2000 ppm) and high carbonates (25–50%) show low total organic carbon (TOC) contents (0.4–1.0%) and high chloroform extracts (0.05–0.2%); centripetally sediments in penesaline profundal zones averagely have higher chlorides (2000–15000 ppm), lower carbonates (15–35%), higher TOC contents (0.6–1.2%), and higher extracts (0.05–0.3%). These two facies can both develop valid petroleum source rocks. In the ramp-margin (low-gradient) lacustrine system, dark fine-grained sediments in penesaline centers with low carbonate (15–25%) and high chloride contents (2000–15000 ppm) show high TOC contents (0.8–2.0%) but extremely low hydrogen indexes (<100 mg HC/g TOC) (little extracts), only developing as valid gas/or biogas source rocks. Supersaline fine-grained sediments in both lacustrine systems develop invalid source rocks. Lateral superimposition maps show that fine-grained sediments with high hydrocarbon generation potential generally contain averagely 25–50% carbonates. Therefore, brackish-penesaline water salinity and bench-type basement are two necessary conditions to develop high-quality petroleum source rocks in saline lacustrine systems and average carbonate content can be a general good mineralogical indicator.

New paleomagnetic constraints on rift basin evolution in the northern Himalaya mountains

The late Cenozoic sediments in the rift basins in the northern Himalaya Mountains document important information about the uplift and deformation of the most active tectonic region in the Tibetan Plateau. However, these sediments have not been precisely dated, hindering our ability to address the basin development and termination associated with a series of uplifts in the southern Tibetan Plateau. Here, we report a detailed magnetostratigraphic study on the fluvio - lacustrine sedimentary sequence of the Dati Formation bearing abundant Hipparion forstenae fossils in the Dati Basin in the northern frontal region of the Himalaya Mountains. The 195 m – thick section yielded six normal and seven reversed polarity zones that correlate well with Chrons C3An.1r to C4r.2r of the geomagnetic polarity time scale, constraining the section age to ~8.6 – ~6.2 Ma. Together with the magnetostratigraphic results from other rift basins in the region, these results indicate that the horizons bearing the Hipparion fossils were deposited during the age interval of 7.1–6.5 Ma in the northern Himalaya Mountains. The regional tectonic activity and comprehensive magnetostratigraphic and sedimentologic comparisons suggest that the evolution of the rift basins in the northern Himalaya Mountains has involved three major stages since the late Cenozoic, i.e., (1) ~10.0–8.0 Ma, onset of the basins with fan delta facies; (2) ~8.0–3.0 Ma, expansion of the basins with mainly lacustrine facies; (3) ~3.0–1.7 Ma, shrinking and termination of the basins with alluvial fans. The basin evolutionary history indicates an accelerated tectonic uplift of the Himalaya Mountains at ~10.0 Ma, and two deformational events at ~3.0 Ma and at ~1.7 Ma.