Next Article in Journal
Desorption and Reuse of Pb-BHA-NaOL Collector in Scheelite Flotation
Previous Article in Journal
Zircon U–Pb Geochronology, Geochemistry and Geological Significance of the Santaishan–Yingjiang Ultramafic Rocks in Western Yunnan, China
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Minerals
Volume 13
Issue 4
10.3390/min13040537
minerals-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Permian Cyanobacterial Blooms Resulted in Enrichment of Organic Matter in the Lucaogou Formation in the Junggar Basin, NW China

by
Wenhui Wang
1,2,
Haisu Cui
1,
Jingqiang Tan
1,*,
Jin Liu
3,
Xueqi Song
1,
Jian Wang
3 and
Lichang Chen
1
1
Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, Ministry of Education, School of Geosciences and Info-Physics, Central South University, Changsha 410083, China
2
State Key Laboratory of Paleobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China
3
Research Institute of Experiment and Testing, Petro-China Xinjiang Oilfield Company, Karamay 834000, China
*
Author to whom correspondence should be addressed.
Minerals 2023, 13(4), 537; https://doi.org/10.3390/min13040537
Submission received: 1 March 2023 / Revised: 10 April 2023 / Accepted: 10 April 2023 / Published: 12 April 2023
(This article belongs to the Topic Reservoir Characteristics and Evolution Mechanisms of the Shale)
Browse Figures
Versions Notes

Abstract

:
The Permian Lucaogou Formation in the Junggar Basin, NW China is the target layer for shale oil exploration, but its hydrocarbon precursors have remained the focus of debate. In this study, we investigated the Lucaogou source rocks throughout Well J10025 by conducting detailed petrological, paleontological, and geochemical analyses for the purpose of revealing the occurrence of cyanobacterial blooms as specific hydrocarbon events in the upper Lucaogou Formation. The morphological characteristics of the microfossils and the geochemical signatures of the microfossil-bearing layers support a biological affinity with Microcystis, a kind of cyanobacteria. Microcystis observed as colonial forms embedded in the upper Lucaogou Formation are of great abundance, indicating the presence of cyanobacterial blooms. They were further evidenced by cyanobacteria-derived biomarkers including low terrestrial/aquatic ratio, high 2α-methylhopane index values, and high abundance of 7- and 8-monomethyl heptadecanes. The blooms occurred in a semiarid and brackish paleoenvironment with anoxic to suboxic water conditions and intermittent volcanic eruptions. Permian Microcystis blooms contributed to the enrichment of organic matter in the upper Lucaogou Formation in two main ways: by directly promoting the accumulation of algal biomass and by creating an oxygen-depleted environment for better preservation of organic matter. This study adds a new record to the geological occurrences of cyanobacterial blooms in the Permian, and provides unique insight into the hydrocarbon generation of Jimsar shale oil in the Junggar Basin.

1. Introduction

In modern lakes, cyanobacterial blooms (also known as algal blooms) have gained great attention globally due to their triggering factors and harmful impact on aquatic ecosystems [1,2,3]. However, cyanobacterial blooms might be beneficial for the accumulation of organic matter and generation of oil. In geological history, algal blooms dominated by various cyanobacteria have been widely recorded and might date back to the early Archean [4,5], the Neoarchean [6], or the Proterozoic Eon [7] (see more examples in [8]). In the Phanerozoic Eon, several cyanobacterial bloom peaks are also documented in the Cambrian [9,10], the early Silurian [11,12], and the Late Devonian periods [13,14]. During the transitional Permian–Triassic interval, shallow marine eutrophication resulted in the Microcystis bloom that was preserved in spotted and dendroid microbialites [15].
The Lucaogou Formation in the Junggar Basin is an oil-prone source rock containing enormous shale oil and tight oil resources [16,17,18,19]. The hydrocarbon precursors preserved in the paleoenvironment have remained the focus of debate [20,21]. Carroll et al. (1992) inferred that organic matter in the Lucaogou Formation came from methanotrophic bacteria living near the chemocline [22]. Tao et al. (2012) recognized that the dominant maceral group is bituminite, which is the decomposition by-product of algae, animal plankton, bacterial lipids, and other precursors [23]. Xie et al. (2015) observed microbial fossils with spherical structures and suggested microalgal inputs in the Lucaogou oil shales [24]. Su et al. (2019) proposed that the organic materials originated from aquatic organisms and terrestrial plants [25]. Liu et al. (2019) inferred dolomitized, silicified, and carbonized algae and other bacteria as the main contributors of liquid hydrocarbon in the Lucaogou black shales [26]. These works demonstrated microorganisms including bacteria and algae as the material source of the Lucaogou Formation. However, they did not refer to the hydrocarbon potential of cyanobacterial blooms. In fact, previous studies have revealed that the Lucaogou Formation was deposited mainly in a brackish to saline lacustrine system, with relatively stable and anoxic water conditions [27,28,29]. This kind of paleoenvironment favors microbial growth [8]. Ding et al. (2019) considered that volcanic ash may stimulate cyanobacterial blooming, as the main reason for accumulation of organic matter in sediments [30]. Sun et al. (2021) reported the discovery of methanogens from the Lucaogou Formation and further proposed that methanogenesis had an impact on hydrocarbon generation [31].
In this research, core samples from Well J10025 in the southeastern Jimsar Sag were studied in detail by conducting petrological, paleontological and geochemical analyses to reveal whether any cyanobacterial bloom occurred in the Lucaogou Formation. Based on this work, we hope to provide new insight into research on hydrocarbon generation in the Lucaogou Formation from the aspect of the relationship between cyanobacterial blooms and the enrichment of organic matter.

2. Geological Setting

The Junggar Basin, with an area of 130,000 km2, is a large superimposed and reformed oil-bearing basin in western China (Figure 1a) [32]. It is underlain by a Precambrian slightly metamorphic crystalline basement. As a consequence of polycyclic tectonic movements, it evolved from a Paleozoic foreland basin to a Mesozoic faulted basin, and finally transformed into a Cenozoic foreland basin [33,34,35].
The Junggar Basin is divided by basal structures into several structural units (Figure 1b), including three uplifts (the West Uplift, the East Uplift, and the Luliang Uplift), two depressions (the Wulungun Depression and the Central Depression) and the South Margin Piedmont Thrust Zone. The Jimsar Sag, a secondary structure of the East Uplift, is bounded by the Jimsar Fault in the north, the Xidi Fault and Qing 1 Well South No. 1 Fault in the west, the Fukang Fault Zone in the south, and the Guxi Uplift to the east (Figure 1c). The Jimsar Sag is a dustpan depression formed on the lower Carboniferous folded basement [29,36]. According to geological records, the Jimsar Sag underwent several distinct tectonic events in the Hercynian, Indosinian, Yanshan, and Himalayan periods [37,38].
Black shales from the Permian Lucaogou Formation, which are characterized by a large longitudinal span and wide planar distribution, have great exploration and development potential [39,40,41]. Based on seismic data and detailed core observations, the Lucaogou Formation is divided into two members, the upper member (P2l2) and the lower member (P2l1), both of which are further subdivided into two beds (P2l21 and P2l22, and P2l11 and P2l12). The upper member is mainly composed of mudstone, dolomitic mudstone, sandstone, muddy dolomite, and sandy dolomite, while siltstone, silty mudstone, and lime mudstone are more common in the lower member (Figure 1d).
Minerals 13 00537 g001 550
Figure 1. Geological map of the study area and stratigraphic column of the study well (modified from [42]). (a) Location of the Junggar Basin in China. (b) Structural map of the Junggar Basin. (c) Structural framework of the Jimsar Sag and location of the study well. (d) Stratigraphic column of Well J10025.
Figure 1. Geological map of the study area and stratigraphic column of the study well (modified from [42]). (a) Location of the Junggar Basin in China. (b) Structural map of the Junggar Basin. (c) Structural framework of the Jimsar Sag and location of the study well. (d) Stratigraphic column of Well J10025.
Minerals 13 00537 g001

3. Materials and Methods

In this study, 30 samples were collected from Well J10025, including mudstone, siltstone, sandstone, and dolomite. We further selected 26 source rocks exclusive of sandstones for total organic carbon (TOC) and element concentration analyses, and 22 source rocks for biomarker compound analysis (Table 1 and Table 2). Individual samples were ground to a particle size of 100 mesh for TOC measurement and to 200 mesh or finer for element and biomarker analysis. For petrological studies, thin sections were cut normal to the bedding.

3.1. Petrological and Paleontological Analysis

Thirty samples were systematically analyzed using optical and fluorescence microscopy (Zeiss A1 Scope, Carl Zeiss AG, Oberkochen, Germany) to investigate the basic reservoir characteristics of the Lucaogou Formation. Based on the results, we further selected samples from the microfossil-bearing strata (J-17, 3574.2 m) for scanning electron microscopy (SEM, MIRA3 LMH, Tescan, Brno, The Czech Republic) and in situ element analysis. Samples with freshly broken surfaces were first observed under stereoscope to select the target area. Before SEM analysis, samples were air dried, mounted on stubs using double-sided tape, and coated with gold. Microscope images were taken under an accelerating voltage of 20 kV. In addition, elemental mapping of energy-dispersive X-ray spectrometry (EDS) was carried out on specific fossils. The above tests were conducted at the Geological Lab of Alternative Energy at Central South University (Changsha, China).

3.2. Biomarker Compound Analysis

Based on the petrological and paleontological analyses, we carried out biomarker compound analysis on 22 selected samples of the Lucaogou source rocks by QP2020NX gas chromatography–mass spectrometry (GC–MS, Shimadzu Corporation, Kyoto, Japan) at Central South University. To reduce potential contamination, samples were crushed to 100 mesh after the outer weathering surfaces were removed. An Rtx-5MS fused silica column (30 m × 0.25 mm × 0.25 μm) was used to separate hydrocarbons, employing helium as a carrier gas. The oven temperature was programmed to start at 80 °C (held for 3 min) and increased to 230 °C at a heating rate of 3 °C/min, and then to 310 °C at 2 °C/min.

3.3. TOC and Element Concentration Analysis

Total organic carbon (TOC) analysis was conducted by a Leco–CS744 instrument (LECO Corporation, St. Joseph, MI, USA) following the procedures of a Chinese national standard GB/T 19145-2003. Twenty-six selected samples of the Lucaogou source rocks were pretreated with dilute hydrochloric acid (5% HCl) to remove inorganic carbon [43,44]. The treated samples were burned in an oven at 1100 °C, adding iron chips and flux. The analytical errors were not more than 0.5%.
Major and trace element analyses were performed on 26 core samples at a petroleum technology corporation in Beijing. A wavelength X-ray fluorescence spectrometer (model: AxiosmAX, Malvern Panalytical, Malvern, UK) was used to determine the oxides of major elements, including SiO2, Al2O3, CaO, K2O, Na2O, Fe2O3, MnO, MgO, TiO2, and P2O5, according to Chinese national standard GB/T 14506.28-2010. Trace elements were analyzed by a NexION300D inductively coupled plasma mass spectrometer (ICP–MS, PerkinElmer, Waltham, MA, USA) in accordance with Chinese national standard GB/T 14506.30-2010. The analytical precision was better than ±5% and detection limits were 1–2 ppm for most trace elements.
The enrichment factor of elements was calculated by the following formula [45,46]. Samples were normalized to the upper continental crust [47].
XEF = (X/Al)sample/(X/Al)UCC
X and Al represent the weight percentage of elements X and Al, respectively.
The chemical index of alteration (CIA) can be calculated by the equation [48,49]:
CIA = [Al2O3/(Al2O3 + Na2O + CaO* + K2O)] × 100
CaO* represents the CaO content in the silicate fraction of the rock, which can be corrected using the formula: CaO′ = CaO − (10/3) P2O5. If the content of CaO′ is greater than that of Na2O, then CaO* is assumed to be equivalent to Na2O. In contrast, CaO* is equal to CaO′. All elemental concentrations are stated in percentage units.
The Cvalue is a proxy for paleoclimate, and the calculation is as follows:
Cvalue = Σ(Fe + Mn + Cr + Ni + V + Co)/Σ(Ca + Mg + Sr + Ba + K + Na)
The units of all elemental concentrations in formula (3) are in ppm.

4. Results

4.1. Microfossils in the Lucaogou Formation

Detailed core and thin section observations reveal that mudstone, sandy mudstone, and dolomitic mudstone are the main source rocks of the Lucaogou Formation in Well J10025. They are primarily characterized by fine-grained compositions, thin interbedded layers, and frequent changes in lithology (Figure 1d and Figure 2a,b). In the upper member, a majority of well-preserved alginate, especially lamalginite, was visible in several samples, displaying yellowish to green fluorescence under incident blue light illumination (Figure 2c,f,i). Abundant lamalginite documents the occurrence of algal blooms. These algal laminae are always interbedded with terrigenous clastic laminae and sometimes intermingled with ostracods that were previously identified as Permiana, Tomiella, Kelameilina, etc. [50] (Figure 2e,f,h). In Figure 2d,g, dry-cracked fragments and water-escape structures are also present within some cores, indicating aridity and a rapid depositional environment [51,52].
Microfossils embedded in the upper Lucaogou Formation were observed using SEM as irregular colonial forms (Figure 3a–d). In Figure 3a, sheet-like algal mats are distributed in a circled region, with an area of approximately 0.12 mm2. They are characterized and constated by abundant, randomly arranged globular to elliptical shaped individuals, some of them with ornaments on the cell surfaces (Figure 4a–c). Through EDS elemental mapping tests, it was revealed that most of these fossil spheroids were replaced by pyrites, or filled by pyrite framboids inside the spherical chamber, some of which dropped and successively formed shedding molds (Figure 4d and Figure 5a). Furthermore, some cracked spheroids after pyritization are closely attached to silicate minerals (Figure 5b–f).
Individual microfossils are of different sizes, ranging from 1 μm to 12 μm in diameter. We counted 868 specimens in total, most of the fossils exhibit a diameter between 1 μm and 7 μm (avg. 4.06 μm) (Figure 3(a1)). They are always encircled by organic matter and attached by clastic minerals. Trilobate and rectangular ornaments are visible in some single individuals (Figure 6). The genesis of these ornaments can be attributed to the metasomatism and crystallization of pyrites. The algal colonies were replaced by pyrites before being squashed and preserved due to their sulfur affinity. During the transformation from initially formed pyrite spheroids to larger particles with higher crystallinity, the specific surface area increased with extra spaces, thus leading to the formation of different ornaments on the cell surfaces. According to EDS testing, the fossils in Figure 6 are mainly composed of C (42.1–52.5 At%), S (24.1–31.2 At%), and Fe (13.1–17.8 At%), with a small amount of O (8.0–9.5 At%) and traces of Si and Ca. The microfossil colonies are interpreted here as cyanobacteria, with affinities to the Microcystis colonies (Chroococcaceae) based on morphological identification characters.
Microcystis is a kind of greenish planktic cyanobacterium, characterized by a coccoid structure, that commonly forms blooms in modern lakes, rivers, and reservoirs [53]. Solitary Microcystis cells are commonly spherical or subspherical, with diameters ranging between 1.7 and 7 μm [54,55]. In our study, slightly larger cells with diameters greater than 7 μm can be attributed to mineralization with pyrites. The cells are able to accumulate in large numbers and integrate irregularly with other microbes under suitable environmental conditions (Figure 3e). Therefore, Microcystis can exhibit a variety of colonial morphologies, such as ellipsoid, spheroid, and irregular dendric [56,57]. Cyanobacteria have a relatively high probability of becoming incorporated in the fossil record as cellularly intact specimens, especially when they are preserved by permineralization during the early stages of sediment lithification as shown in this study (Figure 4, Figure 5 and Figure 6). These cyanobacteria colonies are critical contributors to the abundant lamalginite layers and clearly document the occurrence of cyanobacterial blooms.

4.2. Biomarkers

Biomarkers including normal alkanes, isoprenoids, terpanes, and steranes recorded by mass chromatography are frequently utilized to investigate the origin of organic matter and its depositional environment [18]. Detailed biomarker ratios of the Lucaogou source rocks are listed in Table 2.
The distributions of n-alkanes show unimodal characteristics with carbon peaks located at nC17–nC25 (Figure 7a). In addition, the peak numbers of the upper member are smaller than those of the lower member. The terrestrial/aquatic ratio (TAR), which is defined as (nC27 + nC29 + nC31)/(nC15 + nC17 + nC19), varies between 0.09 and 5.97. The carbon preference index (CPI) ranges from 1.05 to 1.10 (avg. 1.07) and the odd–even predominance (OEP) varies from 1.01 to 1.43 (avg. 1.19), indicative of low to moderate maturity of the Lucaogou source rocks.
Abundant isoprenoids such as pristane (Pr) and phytane (Ph) were also detected in the studied samples, with Pr/Ph ratios ranging from 0.19 to 1.50. The ratios of pristine/n-C17 are 0.46–10.59 (avg. 2.21) in the upper member and 0.94–2.93 (avg. 1.50) in the lower member. The ratios of phytane/n-C17 in the upper and lower members are 0.30–6.15 (avg. 1.63) and 0.95–3.64 (avg. 1.56) respectively. In addition, 7- and 8- monomethyl hepadecanes were identified via a m/z 57 gas chromatogram, representing a predominance over 2–6 monomethyl homologs (Figure 7c). The 7-, 8-monomethyl heptadecanes/Cmax ratios range between 0.01 and 0.24 (avg. 0.08).
Differences in the abundance of β-carotane are noticeable between the upper and lower members. The β-carotane index, which is defined as 100 (β-carotane/17α, 18β(H)-C30 hopane), is significantly higher in the lower member (1.19–66.47, avg. 21.84) than the upper member (2.86–34.69, avg. 10.01). Moreover, the abundance of gammacerane in samples from the lower member is markedly lower. The gammacerane index (GI: gammacerane/17α, 18β(H)-C30 hopane) of the lower member yielded a range of 0.20–0.26 (avg. 0.23), while the values of the upper member were found to be 0.10–0.24 (avg. 0.19).
Regarding regular steranes, samples of the Lucaogou source rocks shows a relatively lower proportion of C27 steranes (8.3%–42.8%, avg. 17.4%), a medium concentration of C28 steranes (20.8%–41.6%, avg. 34.2%), and a slightly greater abundance of C29 steranes (15.6%–61.6%, avg. 48.5%) (Figure 7b). Furthermore, the 2α-methylhopanes of the samples were identified using a representative gas chromatogram of m/z 205 (Figure 7d). The 2α-methylhopane index (2-MHI), defined as 2α-methylhopanes/(2α-methylhopanes + 17α,18β(H)-C30 hopane), covers a wide range of 1.35–5.26 (avg. 3.51) (Figure 8).

4.3. TOC and Elemental Geochemical Characteristics

The Lucaogou source rocks in Well J10025 exhibit a wide range of TOC contents that range between 1.81 and 19.60 wt% (Table 1). The upper member has significantly higher values (avg. 9.14 wt%) than the lower member (avg. 4.17 wt%) (Figure 9).
The elemental geochemical data of the Lucaogou source rocks are listed in Table 1. The C-values of the Lucaogou Formation are highly variable (range: 0.07–1.14) and show a significant stratigraphic trend. In general, the C-values increase gradually from the lower member to the upper member. The stratigraphic variation of CIA values exhibits a similar trend to the C-values, varying from low values (46–52) in the lower member to high values (44–79) in the upper member.
The Sr/Ba ratios of the lower member are significantly higher (1.15–4.38) than those of the upper member (0.26–2.16). However, it should be noted that some abnormally high values are largely due to the interference of carbonate Sr [58]. The B/Ga ratios also show considerable variations between the upper and lower members. Despite a few high values, most samples in the upper member exhibit lower values (4.35–13.42) than those of the upper member (8.72–19.85). In addition, the enrichment factors of Mo and U (MoEF and UEF) show similar stratigraphic variation patterns, varying from 0.51 to 63.49 and 0.56 to 8.51, respectively (Figure 9).
Phosphorus (P) is essential to all forms of life on Earth, as it plays a fundamental role in many metabolic processes and acts as a major constituent of the biotic skeleton [46]. In the layers of Microcystis fossils, the P concentration increases sharply and reaches its maximum (0.20 wt%) in the sedimentary sequence. The P/Ti and Ba/Al ratios of the upper member (avg. 0.38 and 1.36 × 10−2 respectively) are remarkably higher than those of the lower member (avg. 0.24 and 6.68 × 10−3 respectively).

5. Discussion

5.1. Biological Precursors of the Lucaogou Source Rocks

The distribution of n-alkanes in source rocks can provide information about the origins of organic matter, including algae, bacteria, and higher plants [20,43]. As shown in Table 2 and Figure 7a, the distributions of n-alkanes show unimodal characteristics with carbon peaks located at nC17–nC25, indicating that the source of organic matter is a combination of terrestrial and aquatic organisms. However, most of the samples from the upper member of the Lucaogou Formation exhibit nC17–nC21 carbon peak numbers, indicative of a dominance of algal and bacterial input, while the lower member with nC23 as the most frequent peak reveals terrestrial higher plant inputs [59,60].
The terrigenous/aquatic ratio (TAR) may reflect the relative abundance of terrigenous plants versus aquatic organisms in sediments [44,61]. The TAR of the Lucaogou Formation exhibits a wide range between 0.09 and 2.16, suggesting a mixed contribution of organic inputs. However, the TAR of the upper member is significantly lower (0.09–1.26, avg. 0.54) than that of the lower member (0.13–2.16, avg. 0.96), especially in the microfossil-bearing layer (0.11), indicating that algae or bacteria are the main biological precursors of the upper member while terrestrial plants contribute more to the lower member.
Regular steranes have been widely used to estimate the relative proportions of organic matter sources [62]. In general, C27 regular steranes are primarily derived from algae and zooplankton, C28 regular steranes originate from phytoplankton, and C29 regular steranes are typically associated with terrestrial plants [63,64]. However, microalgae and cyanobacteria are also considered important sources of C29 steranes [30,65]. In Figure 10a, Lucaogou source rocks show a mixed contribution of organic inputs, which in the upper member mainly come from plankton and bacteria while in the lower member they originate from plankton and land plants.
Furthermore, 2α-methylhopanes (2-MHs) are highly diagnostic for identifying cyanobacteria. Thus, the 2α-methylhopane index (2-MHI) is commonly used to evaluate the abundance of 2-MHs in geological sediments [66,67,68]. High 2-MHI values (1.35–5.26) in Lucaogou source rocks could demonstrate that the biological inputs mainly consisted of cyanobacteria. In addition, monomethyl alkanes including the 7- and 8-carbon substituted methyl heptadecanes are more abundant in modern cyanobacteria [69,70]. The remarkable abundance of 7- and 8-monomethyl heptadecanes compared to their homologs may provide evidence of cyanobacterial blooms [71,72]. Moderate 7-, 8-monomethyl heptadecanes/Cmax ratios (0.01–0.24) imply that cyanobacteria comprise an important part of the organic matter input of the Lucaogou Formation.
Minerals 13 00537 g010 550
Figure 10. Paleoenvironment conditions of the ancient Permian lake indicated by trace elements and biomarkers. (a) Ternary plot of C27–C28–C29 regular steranes, illustrating the organic matter input (modified from [73]). (b) Plot of UEF versus MoEF. The diagonal lines represent multiples (0.1, 0.3 and 1) of the Mo:U ratio of present-day seawater (modified from [74]). (c) Plot of Pr/Ph versus the Gammacerane index. (d) Plot of Ph/nC18 versus Pr/nC17 (following [75]).
Figure 10. Paleoenvironment conditions of the ancient Permian lake indicated by trace elements and biomarkers. (a) Ternary plot of C27–C28–C29 regular steranes, illustrating the organic matter input (modified from [73]). (b) Plot of UEF versus MoEF. The diagonal lines represent multiples (0.1, 0.3 and 1) of the Mo:U ratio of present-day seawater (modified from [74]). (c) Plot of Pr/Ph versus the Gammacerane index. (d) Plot of Ph/nC18 versus Pr/nC17 (following [75]).
Minerals 13 00537 g010
In summary, based on a comprehensive analysis of biomarker evidence, cyanobacteria can be reasonably inferred to be the main biological precursors of the upper member of the Lucaogou source rocks deposited in the Permian lake. This inference is in accordance with the results of a paleontological study that identified the microfossil spheroids as Microcystis, by using direct SEM observations. In contrast, the hydrocarbon precursors of the lower member were mainly terrestrial higher plants mixed with some planktic algae.

5.2. Paleoenvironmental Conditions of the Permian Microcystis Bloom

As the upper member of the Lucaogou Formation yields better shale oils with cyanobacteria as its main biological precursors, the following discussion focuses mainly on the upper member and tries to decipher the relationship between the Permian paleoenvironment and the Microcystis bloom.

5.2.1. Environmental Factors Triggering Modern Cyanobacterial Blooms

Microcystis is one of the predominant taxa involved in cyanobacterial blooms, with others including Planktothrix, Gloetrichia, Oscillatoriales, etc. [76]. Microcystis prefers to grow in eutrophic waters under strong light, relatively high temperatures (the optimum temperature range is 25–30 °C), and highly alkaline conditions (pH 8.0–9.5) [2,77]. In addition, the growth of Microcystis is seasonal and periodic. Microcystis is physiologically dormant in the sediment layer during winter but returns to the water column to proliferate rapidly during summer, thus becoming the predominant species [1,78,79]. Furthermore, nutrients such as phosphorus (P), nitrogen (N), iron (Fe), and magnesium (Mg) are also responsible for controlling algal biomass and bloom events in aquatic ecosystems [80,81]. Microcystis blooms are closely affected by numerous ecological and environmental factors including climate, sunlight, temperature, pH, nutrients, and hydrodynamic conditions.

5.2.2. Paleoclimate and Paleosalinity

The CIA is a reliable proxy for evaluating the chemical weathering degree of sediments and paleoclimate [49,82]. Low CIA values of the lower member, ranging from 46 to 52, indicate arid conditions under low to moderate degrees of chemical weathering. In contrast, the upper member exhibits relatively higher CIA values (44–79, avg. 58), implying a semiarid climate during the deposition of source rocks. The C-value is another elemental parameter that is utilized for paleoclimate reconstruction [83,84]. The C-values of the lower member (0.07–0.21) reveal an arid environment, while those of the upper member are significantly higher (0.11–1.14), suggesting a transition from an arid to a semiarid climate. In addition, dry-cracked fragments and water-escape structures in core samples are indicative of aridity and a rapid depositional environment (Figure 2d,g).
Sr/Ba and B/Ga ratios are considered effective salinity indicators [85,86]. Wei and Aljeo estimated that the approximate salinity thresholds for Sr/Ba are <0.2 in freshwater, 0.2–0.5 in brackish, and >0.5 in marine facies [58]. For B/Ga, sedimentary ratios of <3, 3–6, and >6 are indicative of freshwater, brackish, and marine facies, respectively. In this study, both ratios exhibit high values (Sr/Ba: avg. 1.47, B/Ga: avg. 12.43), indicative of a saline environment. However, the declining values in the upper member reveal a decreasing salinity trend (Figure 9). While the Sr/Ba proxy is slightly less robust owing to carbonate Sr interference, other proxies can be used to support interpretations of paleosalinity [58,87]. For example, abundant gammacerane is usually interpreted as evidence of stratified water column, which is closely associated with hypersalinity [73,88]. The gammacerane index value (GI: gammacerane/C30 hopane) of the upper member ranges from 0.10 to 0.24 (avg. 0.19), which likely indicates a fresh to brackish depositional environment. In contrast, the lower member with values of 0.20–0.26 suggests brackish to saline conditions with unstable stratification of the water column (Table 2, Figure 8).

5.2.3. Redox Conditions

MoEF and UEF are reliable indicators for paleoredox evaluation [89,90]. The Mo–U covariation model has recently been widely used as a reliable proxy for determining redox and water retention in black shales [74,86]. In the Mo–U covariation model, most samples from the Lucaogou Formation fall into the range above 0.3 times the Mo/U of seawater, yielding greater MoEF relative to UEF, indicative of an anoxic to euxinic environment (Figure 10b).
The pristine/phytane ratio (Pr/Ph) is normally used as a paleoredox proxy [44,91]. As shown in Table 2 and Figure 8, most of the Pr/Ph ratios are less than 1, suggesting a reducing depositional environment. However, the ratios of the upper member are slightly higher, revealing an anoxic to suboxic environment. Plots of Pr/n-C17 versus Ph/n-C18 can also be used to infer the redox conditions of source rocks [92], in this case indicating a weakly oxidizing to weakly reducing depositional environment with mixed organic inputs (Figure 10d).
β-carotane generally accumulates in highly reducing and saline lacustrine environments [70,93]. The high β-carotane index (1.19–66.47) of the lower member indicates more reducing and saline conditions. In addition, pyrite framboids in some core samples can also suggest reducing conditions (Figure 4d). Therefore, a suboxic to anoxic depositional environment for the upper member of the Lucaogou Formation was reconstructed by the above-mentioned redox proxies.

5.2.4. Productivity

Productivity plays an important role in organic matter enrichment and source rock potential [46,94]. Various geochemical proxies including C and N isotopes, organic biomarkers, and trace metal abundances (Cu, Ba, Zn, etc.) have been utilized to reconstruct biological productivity [95,96,97,98]. In this study, we refer to TOC, P, P/Ti, and Ba/Al as paleoproductivity proxies.
Total organic carbon (TOC) accounts for the largest proportion of organic matter preserved in sediments, acting as a direct indicator of productivity [99,100,101]. The Lucaogou Formation with TOC values ranging between 1.81 and 19.60 wt% suggest high productivity (Figure 9). In addition, distributions of phosphorous in sediments are closely linked to primary biological productivity and the supply of OM [46,102]. The upper member of the Lucaogou Formation has high concentrations of P (up to 0.20 wt%), reflecting an increasing nutrient input largely due to volcanism. Intermittent volcanic eruptions during the Middle Permian released large amounts of carbon dioxide and volcanic ash, triggering global warming and eutrophication [70,103,104].
Barium (Ba) is always associated with biological metabolism and can be used to represent organic matter input [105,106]. Aluminium (Al) and titanium (Ti) are primarily of detrital origin, therefore P/Ti and Ba/Al are generally considered effective indicators of productivity by eliminating the impact of terrigenous debris [28,107]. The upper member of the Lucaogou source rocks exhibits higher P/Ti and Ba/Al ratios (P/Ti: avg. 0.38, Ba/Al: avg. 1.36 × 10−2) than the lower member (P/Ti: avg. 0.24, Ba/Al: avg. 6.68 × 10−2), providing evidence of a nutrient-rich environment with higher productivity in the upper member.
In summary, the sedimentary environment of the Permian Lucaogou Formation transformed from arid and saline conditions in the lower member into semiarid and brackish conditions in the upper member (Figure 9). During the deposition of the upper member, relatively low salinity was favorable for Microcystis survival. Furthermore, the warm climate and stratified water body facilitated algal growth, decreased water viscosity, and increased the sedimentation rate of eukaryotic algae, thus strengthening the competitive advantage of Microcystis among phytoplankton [108]. In addition, increased nutrient loading from volcanism, especially Fe and P into the lake, was the main cause of eutrophication [30,109]. Fe and P are indispensable elements for cyanobacterial metabolic activities. As water bodies become enriched in nutrients, there is often a shift in the phytoplankton community toward dominance by cyanobacteria [28,110]. Under this combination of favorable conditions, the Microcystis bloom occurred in the upper member.

5.3. Mechanism of Organic Matter Enrichment under Cyanobacterial Blooms

In terms of organic matter enrichment, several key controlling factors have been proposed, including enhanced preservation, restricted basin conditions, sea level changes, paleoproductivity, and dilution [111,112,113]. For example, Zhang et al. (2018) regarded the paleoproductivity of surface water and the relatively stable anoxic environment as the main factors controlling the enrichment of organic matter in the Lucaogou Formation [27]. A case study carried out by Zhao et al. (2023) proposed that the relatively high bio-productivity of water and low input of detrital matter were favorable for the preservation of OM [114]. However, these previous studies did not relate the mechanism of organic matter enrichment to cyanobacterial blooms.
The upper member of the Lucaogou Formation was deposited in a brackish lacustrine environment with anoxic to suboxic water conditions (Figure 11). This specific depositional environment in shales is commonly considered an ideal environment for controlling the degradation and preservation of organic matter [115,116,117]. Favorable paleoenvironmental conditions in the lacustrine system, together with eutrophication, rising CO2 levels, and a globally warming climate, facilitated the cyanobacteria growth rate, triggered the cyanobacterial bloom, and promoted an accumulation of cyanobacterial biomass [118,119,120,121].
Abundance of organic matter is usually dependent upon the interplay of a variety of factors including primary productivity, preservation conditions, and sedimentation rate [17,122,123,124]. The mechanism of organic matter enrichment by cyanobacterial blooms is supported by two main ways. From one perspective, Permian Microcystis blooms favored the accumulation of organic matter by directly providing a hydrocarbon source basis for the Lucaogou Formation. The specific mechanism is reflected in modern examples [125]. In modern lakes, seasonal alternation plays a critical role in the formation of Microcystis blooms [1,126]. During this process, nutrient-rich bottom water moves upward in spring and summer as the temperature rises, producing favorable conditions for algal blooms. As the temperature decreases in autumn and winter, algal colonies and other organic materials are deposited at the bottom of the lake in the form of sheet-like algal mats and subsequently buried as organic-rich laminae [2,127].
However, previous works have overlooked the other aspect in which cyanobacterial blooms contribute to the enrichment of organic matter. The negative feedback of cyanobacterial blooms to the paleoenvironment may also have facilitated preservation of organic matter. The Microcystis bloom that occurred in the upper member of the Lucaogou Formation may have further deteriorated the paleoenvironment by releasing odorous compounds, producing toxins, causing bottom layer anoxia, etc. [57,76]. A large number of Microcystis gathered on the lake surface, inhibiting the air circulation between the water and atmosphere, and forming a shield that reduced the oxygen concentrations produced by plant photosynthesis [128]. Moreover, microcystin, a kind of toxin produced by Microcystis, is lethal to most metazoans in aquatic ecosystems and can cause mass death of creatures [129,130]. As a result, the decomposition of biological bodies further increases the accumulation of organic matter during cyanobacterial blooms. In addition, the oxygen-depleted sedimentary environment enhanced by the Microcystis bloom is favorable for the preservation of organic matter by inhibiting disturbance by benthic organisms and the biodegradation progress of microbes [131,132]. From both aspects, Microcystis blooms were of vital importance in the formation of the Lucaogou source rocks, playing a major role and acting as a critical connection point among the numerous hydrocarbon generation events of Jimsar shale oil.
In addition, by their influence on cyanobacteria, volcanism and other geological events could also have had an impact on the accumulation and preservation of organic matter. Permian volcanic eruptions released large amounts of ion-rich volcanic ash, providing abundant nutrients which could stimulate the proliferation of cyanobacteria and advance the productivity-based biogeochemical progress [30,108]. Some key marine events in the Permian, such as photic zone euxinia and faunal mass extinction, were also closely associated with cyanobacterial blooms [133,134]. All these biotic and abiotic factors lead to the formation of Permian Lucaogou source rocks.

6. Conclusions

In this paper, we have presented a comprehensive study of the Lucaogou source rocks including petrological, paleontological, and geochemical analyses. The conclusions are as follows:
(1)
Abundantly distributed, globular to elliptical shaped microfossils in the upper member of the Lucaogou Formation are interpreted as Microcystis, a kind of cyanobacteria. The great abundance of these fossils referred to the Chroococcaceae indicates the occurrence of Permian cyanobacterial blooms, which are further proven by cyanobacteria-derived biomarkers.
(2)
The upper member of the Lucaogou Formation was deposited in a brackish lacustrine environment with anoxic to suboxic water conditions, under a semiarid paleoclimate. Such a paleoenvironment together with abundant nutrients from volcanism ultimately led to cyanobacterial blooms in Permian lakes.
(3)
Permian Microcystis blooms contributed to organic matter enrichment in two ways. The first was by directly promoting the accumulation of algal biomass, and the second by creating an oxygen-depleted environment for better preservation of organic matter. This study thus provides new insight into shale oil exploration and development in the Junggar Basin, from the perspective of cyanobacterial blooms.

Author Contributions

Formal analysis, H.C., X.S., and L.C.; Funding acquisition, J.T.; Project administration, J.L. and J.W.; Resources, J.L. and L.C.; Software, X.S.; Validation, J.T.; Writing—original draft, W.W. and H.C.; Writing—review & editing, W.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research is supported by the Fundamental Research Funds for the Central Universities of Central South University (No. 2022ZZTS0530), the Department of Natural Resources of Hunan Province, China (No. 2022-5), China Hunan Provincial Science & Technology Department (No. 2022WK2004). This work is also supported by the State Key Laboratory of Paleobiology and Stratigraphy (Nanjing Institute of Geology and Paleontology, CAS) (No. 213120); the Natural Science Foundation of Hunan Province (No. 2023JJ20063 and 2021JJ30816).

Data Availability Statement

The data involved in this paper are all included in the text of the manuscript.

Acknowledgments

We would like to extend our thanks to the Experiment and Testing Research Institute of Xinjiang Oilfield Company, PetroChina, for kindly providing the samples for this study. We are also grateful for numerous conversations with several researchers including Wenquan Xie, Yong Wang, and Xiao Ma (Central South University) on how to strengthen the ideas presented in this paper.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Latour, D.; Giraudet, H. Factors influencing the spatio-temporal distribution of benthic Microcystis aeruginosa colonies (Cyanobacteria) in the hypertrophic Grangent Reservoir (Loire, France). Comptes Rendus Biol. 2004, 327, 753–761. [Google Scholar] [CrossRef]
  2. Imai, H.; Chang, K.-H.; Kusaba, M.; Nakano, S.-I. Temperature-dependent dominance of Microcystis (Cyanophyceae) species: M. aeruginosa and, M. wesenbergii. J. Plankton Res. 2009, 31, 171–178. [Google Scholar] [CrossRef] [Green Version]
  3. Bullerjahn, G.S.; McKay, R.M.; Davis, T.W.; Baker, D.B.; Boyer, G.L.; Anglada, L.; Doucette, G.J. Global solutions to regional problems: Collecting global expertise to address the problem of harmful cyanobacterial blooms. A Lake Erie case study. Harmful Algae 2016, 54, 223–238. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  4. Schopf, J.W.; Packer, B.M. Early archean (3.3-billion to 3.5-billion-year-old) microfossils from warrawoona group. Aust. Sci. 1987, 237, 70–73. [Google Scholar] [CrossRef]
  5. Schopf, J.W.; Kudryavtsev, A.B.; Czaja, A.D.; Tripathi, A.B. Evidence of Archean life: Stromatolites and microfossils. Precambrian Res. 2007, 158, 141–155. [Google Scholar] [CrossRef]
  6. Kazmierczak, J.; Altermann, W. Paleontology-neoarchean biomineralization by benthic cyanobacteria. Science 2002, 298, 2351. [Google Scholar] [CrossRef]
  7. Yang, H.; Chen, Z.Q.; Papineau, D. Cyanobacterial spheroids and other biosignatures from microdigitate stromatolites of Mesoproterozoic Wumishan Formation in Jixian, North China. Precambrian Res. 2022, 368, 106496. [Google Scholar] [CrossRef]
  8. Whitton, B. Ecology of Cyanobacteria II: Their Diversity in Space and Time; Springer: Berlin/Heidelberg, Germany, 2012. [Google Scholar]
  9. Riding, R. Temporal variation in calcification in marine cyanobacteria. J. Geol. Soc. Aust. 1992, 149, 979–989. [Google Scholar] [CrossRef]
  10. Lee, H.; Chen, I.; Chough, S.K. The middle–late Cambrian reef transition and related geological events: A review and new view. Earth-Sci. Rev. 2015, 145, 66–84. [Google Scholar] [CrossRef]
  11. Kremer, B.; Kamierczak, J. Cyanobacterial Mats from Silurian Black Radiolarian Cherts: Phototrophic Life at the Edge of Darkness? J. Sediment. Res. 2005, 75, 897–906. [Google Scholar] [CrossRef]
  12. Kremer, B. Mat-forming coccoid cyanobacteria from early Silurian marine deposits of Sudetes, Poland. Acta Palaeontol. Pol. 2009, 51, 143–154. [Google Scholar]
  13. Wu, Y.B.; Feng, Q.; Gong, Y.M. Blooming of bacteria and algae is a biokiller for mass-extinction of Devonian coral-stromatoporoid reef ecosystems. Sci. China-Earth Sci. 2013, 56, 1221–1232. [Google Scholar] [CrossRef]
  14. Kazmierczak, J.; Kremer, B.; Racki, G. Late Devonian marine anoxia challenged by benthic cyanobacterial mats. Geobiology 2012, 10, 371–383. [Google Scholar] [CrossRef]
  15. Wu, Y.S.; Yu, G.L.; Li, R.H.; Song, L.R.; Jiang, H.X.; Riding, R.; Liu, L.J.; Liu, D.Y.; Zhao, R. Cyanobacterial fossils from 252 Ma old microbialites and their environmental significance. Sci. Rep. 2014, 4, 3820. [Google Scholar] [CrossRef] [Green Version]
  16. Carroll, A.R. Upper Permian lacustrine organic facies evolution, southern Junggar Basin, NW China. Org. Geochem. 1998, 28, 649–667. [Google Scholar] [CrossRef]
  17. Pan, S.Q.; Horsfield, B.; Zou, C.N.; Yang, Z. Upper Permian Junggar and Upper Triassic Ordos lacustrine source rocks in Northwest and Central China: Organic geochemistry, petroleum potential and predicted organofacies. Int. J. Coal Geol. 2016, 158, 90–106. [Google Scholar] [CrossRef]
  18. Zhang, S.H.; Liu, C.Y.; Liang, H.; Wang, J.Q.; Yang, M.H.; Liu, G.H.; Huang, H.X.; Guan, Y.Z. Paleoenvironmental conditions, organic matter accumulation, and unconventional hydrocarbon potential for the Permian Lucaogou Formation organic-rich rocks in Santanghu Basin, NW China. Int. J. Coal Geol. 2018, 185, 44–60. [Google Scholar] [CrossRef]
  19. Cao, Z.; Liu, G.; Kong, Y.; Wang, C.; Niu, Z.; Zhang, J.; Geng, C.; Shan, X.; Wei, Z. Lacustrine tight oil accumulation characteristics: Permian Lucaogou Formation in Jimusaer Sag, Junggar Basin. Int. J. Coal Geol. 2016, 153, 37–51. [Google Scholar] [CrossRef]
  20. Gao, G.; Zhang, W.; Xiang, B.; Liu, G.; Ren, J. Geochemistry characteristics and hydrocarbon-generating potential of lacustrine source rock in Lucaogou Formation of the Jimusaer Sag, Junggar Basin. J. Pet. Sci. Eng. 2016, 145, 168–182. [Google Scholar] [CrossRef]
  21. Meng, Z.Y.; Liu, Y.Q.; Jiao, X.; Ma, L.T.; Zhou, D.W.; Li, H.; Cao, Q.; Zhao, M.R.; Yang, Y.Y. Petrological and organic geochemical characteristics of the Permian Lucaogou Formation in the Jimsar Sag, Junggar Basin, NW China: Implications on the relationship between hydrocarbon accumulation and volcanic-hydrothermal activities. J. Pet. Sci. Eng. 2022, 210, 110078. [Google Scholar] [CrossRef]
  22. Carroll, A.R.; Brassell, S.C.; Graham, S.A. Upper Permian lacustrine oil shales, southern Junggar Basin, Northwest China. AAPG Bull. 1992, 76, 1874–1902. [Google Scholar]
  23. Tao, S.; Wang, Y.B.; Tang, D.Z.; Wu, D.M.; Xu, H.; He, W. Organic petrology of Fukang Permian Lucaogou Formation oil shales at the northern foot of Bogda Mountain, Junggar Basin, China. Int. J. Coal Geol. 2012, 99, 27–34. [Google Scholar] [CrossRef]
  24. Xie, X.M.; Borjigin, T.; Zhang, Q.Z.; Zhang, Z.R.; Qin, J.Z.; Bian, L.Z.; Volkman, J.K. Intact microbial fossils in the Permian Lucaogou Formation oil shale, Junggar Basin, NW China. Int. J. Coal Geol. 2015, 146, 166–178. [Google Scholar] [CrossRef]
  25. Su, Y.; Zha, M.; Ding, X.J.; Qu, J.X.; Cao, C.H.; Jin, J.H.; Iglauer, S. Petrographic, palynologic and geochemical characteristics of source rocks of the Permian Lucaogou formation in Jimsar Sag, Junggar Basin, NW China: Origin of organic matter input and depositional environments. J. Pet. Sci. Eng. 2019, 183, 106364. [Google Scholar] [CrossRef]
  26. Liu, Y.Q.; Zhou, D.W.; Jiao, X.; Feng, Q.; Zhou, X.H. A preliminary study on the relationship between deep-sourced materials and hydrocarbon generation in lacustrine source rocks: An example from the Permian black rock series in Jimusar sag, Junggar Basin. J. Palaeogeogr. 2019, 21, 16. [Google Scholar] [CrossRef] [Green Version]
  27. Zhang, X.; Zhuang, X.G.; Tu, Q.J.; Xv, S.Q.; Zhang, Y. Depositional process and mechanism of organic matter accumulation of Lucaogou shale in Southern Junggar Basin, Northwest China. Earth Sci. 2018, 43, 538–550. [Google Scholar]
  28. Jiang, Y.; Hou, D.; Li, H.; Zhang, Z.; Guo, R. Impact of the Paleoclimate, Paleoenvironment, and Algae Bloom: Organic Matter Accumulation in the Lacustrine Lucaogou Formation of Jimsar Sag, Junggar Basin, NW China. Energies 2020, 13, 1488. [Google Scholar] [CrossRef] [Green Version]
  29. Kuang, L.C.; Tang, Y.; Lei, D.W.; Chang, Q.S.; Ou, Y.M.; Hou, L.H.; Liu, D.G. Formation conditions and exploration potential of tight oil in the Permian saline lacustrine dolomitic rock, Junggar Basin, NW China. Pet. Explor. Dev. 2012, 039, 657–667. [Google Scholar]
  30. Ding, X.J.; Qu, J.Q.; Imin, A.; Zha, M.; Jiang, Z.F.; Jiang, H. Organic matter origin and accumulation in tuffaceous shale of the lower Permian Lucaogou Formation, Jimsar Sag. J. Pet. Sci. Eng. 2019, 179, 696–706. [Google Scholar] [CrossRef]
  31. Sun, F.N.; Hu, W.X.; Wang, X.L.; Cao, J.; Fu, B.; Wu, H.G.; Yang, S.C. Methanogen microfossils and methanogenesis in Permian lake deposits. Geology 2021, 49, 13–18. [Google Scholar] [CrossRef]
  32. Li, Y.; Xue, Z.; Cheng, Z.; Jiang, H.; Wang, R. Progress and development directions of deep oil and gas exploration and development in China. China Pet. Explor. 2020, 25, 45–57. [Google Scholar]
  33. Carroll, A.R.; Graham, S.A. Late paleozoic tectonic amalgamation of northwestern China: Sedimentary record of the northern Tarim, northern Turpan, and southern Junggar Basins. Geol. Soc. Am. Bull. 1995, 107, 571–594. [Google Scholar] [CrossRef]
  34. Kuang, L.H.; Hu, W.X.; Wang, X.L.; Wu, H.G.; L. W.X. Research of the Tight Oil Reservoir in the Lucaogou Formation in Jimusar Sag: Analysis of Lithology and Porosity Characteristics. Geol. J. China Univ. 2013, 19, 7. [Google Scholar]
  35. Wang, J.; Yuan, B.; Liu, J.; Li, Y.; Li, E. Genesis and pore development characteristics of Permian Lucaogou migmatites, Jimsar Sag, Junggar Basin. Pet. Geol. Exp. 2022, 44, 413–424. [Google Scholar]
  36. Jiang, Y.Q.; Liu, Y.Q.; Yang, Z.; Nan, Y.; Wang, R.; Zhou, P.; Yang, Y.J.; Kou, J.Y.; Zhou, N.C. Characteristics and origin of tuff-type tight oil in Jimusar Depression, Junggar Basin, NW China. Pet. Explor. Dev. 2015, 42, 741–749. [Google Scholar] [CrossRef]
  37. Tao, K.Y.; Cao, J.; Chen, X.; Nueraili, Z.; Hu, W.X.; Shi, C.H. Deep hydrocarbons in the northwestern Junggar Basin (NW China): Geochemistry, origin, and implications for the oil vs. gas generation potential of post-mature saline lacustrine source rocks. Mar. Pet. Geol. 2019, 109, 623–640. [Google Scholar] [CrossRef]
  38. Guo, P.; Wen, H.G.; Gibert, L.; Jin, J.; Wang, J.; Lei, H.Y. Deposition and diagenesis of the Early Permian volcanic-related alkaline playa-lake dolomitic shales, NW Junggar Basin, NW China. Mar. Pet. Geol. 2021, 123, 104780. [Google Scholar] [CrossRef]
  39. Wang, X.; Yang, Z.; Guo, X.; Xiatian, W.; Feng, Y.; Huang, L. Practices and Prospects of Shale Oil Exploration in Jimsar Sag of Junggar Basin. Xinjiang Pet. Geol. 2019, 40, 402–413. [Google Scholar]
  40. Zhi, D.; Song, Y.; He, W.; Jia, X.; Yang, Z.; Huang, L. Geological Characteristics, Resource Potential and Exploration Direction of Shale Oil in Middle-Lower Permian, Junggar Basin. Xinjiang Pet. Geol. 2019, 40, 389–401. [Google Scholar]
  41. Kang, J.L.; Wang, J.H.; Ma, Q.; Li, C.Q.; Chen, X. Fine-grained sublacustrine fan deposits and their significance of shale oil reservoirs in the Lucaogou Formation in Jimsar Sag, Junggar Basin. Bull. Geol. Sci. Technol. 2022, 4, 1–12. [Google Scholar]
  42. Wu, H.; Hu, W.; Tang, Y.; Cao, J.; Wang, X.; Wang, Y.; Kang, X. The impact of organic fluids on the carbon isotopic compositions of carbonate-rich reservoirs: Case study of the Lucaogou Formation in the Jimusaer Sag, Junggar Basin, NW China. Mar. Pet. Geol. 2017, 85, 136–150. [Google Scholar]
  43. Tissot, B.; Welte, D. Petroleum Formation and Occurrence; Earth Science Reviews; Springer: Berlin/Heidelberg, Germany, 1984. [Google Scholar]
  44. Peters, K.E.; Walters, C.C.; Moldowan, J.M. The Biomarker Guide: Interpreting Molecular Fossils in Petroleum and Ancient Sediments; Cambridge University Press: Cambridge, UK, 2005. [Google Scholar]
  45. Calvert, S.E.; Pedersen, T.F. Geochemistry of Recent oxic and anoxic marine sediments: Implications for the geological record. Mar. Geol. 1993, 113, 67–88. [Google Scholar] [CrossRef]
  46. Tribovillard, N.; Algeo, T.; Lyons, T.; Riboulleau, A. Trace metals as paleoredox and paleoproductivity proxies: An update. Chem. Geol. 2006, 232, 12–32. [Google Scholar] [CrossRef]
  47. Mclennan; Scott, M. Relationship between the trace element composition of sedimentary rocks and upper continental crust. Geochem. Geophys. Geosystems 2001, 2, 203–236. [Google Scholar]
  48. Nesbitt, H.W.; Young, G.M. Early Proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature 1982, 299, 715–717. [Google Scholar] [CrossRef]
  49. Mclennan; Scott, M. 100th Anniversary Symposium: Evolution of the Earth’s Surface || Weathering and Global Denudation. J. Geol. 1993, 101, 295–303. [Google Scholar]
  50. Liu, J.; Wang, J.; Zhang, X.G.; Luo, Z.J.; Shang, L.; Wang, G.J. Scanning electron microscope study on oil generation characteristics of ostracod fossils from the Lucaogou formation in eastern Junggar Basin. J. Chin. Electron Microsc. Soc. 2021, 40, 270–278. [Google Scholar]
  51. Wu, H.G.; Hu, W.X.; Cao, J.; Wang, X.L.; Liao, Z.W. A unique lacustrine mixed dolomitic-clastic sequence for tight oil reservoir within the middle Permian Lucaogou Formation of the Junggar Basin, NW China: Reservoir characteristics and origin. Mar. Pet. Geol. 2016, 76, 115–132. [Google Scholar] [CrossRef]
  52. Wang, R.Y.; Ding, W.L.; Zhang, Y.Q.; Wang, Z.; Wang, X.; He, J.; Zeng, W.; Dai, P. Analysis of developmental characteristics and dominant factors of fractures in Lower Cambrian marine shale reservoirs: A case study of Niutitang formation in Cen’gong block, southern China. J. Pet. Sci. Eng. 2016, 138, 31–49. [Google Scholar] [CrossRef]
  53. Caracciolo, A.B.; Dejana, C.; Fajardo, P.; Grenni, M. A new fluorescent oligonucleotide probe for in-situ identification of Microcystis aeruginosa in freshwater. Microchem. J. 2019, 148, 503–513. [Google Scholar]
  54. Taylor, T.N.; Krings, M. A colony-forming microorganism with probable affinities to the Chroococcales (cyanobacteria) from the Lower Devonian Rhynie chert. Rev. Palaeobot. Palynol. 2015, 219, 147–156. [Google Scholar] [CrossRef]
  55. Xiao, M.; Li, M.; Reynolds, C.S. Colony formation in the cyanobacterium Microcystis. Biol. Rev. 2018, 93, 1399–1420. [Google Scholar] [CrossRef] [Green Version]
  56. Phelan, R.R.; Downing, T.G. A growth advantage for microcystin production by Microcystis PCC7806 under high light. J. Phycol. 2011, 47, 1241–1246. [Google Scholar] [CrossRef]
  57. Van Le, V.; Srivastava, A.; Ko, S.-R.; Ahn, C.-Y.; Oh, H.-M. Microcystis colony formation: Extracellular polymeric substance, associated microorganisms, and its application. Bioresour. Technol. 2022, 360, 127610. [Google Scholar]
  58. Wei, W.; Algeo, T.J. Elemental proxies for paleosalinity analysis of ancient shales and mudrocks. Geochim. Et Cosmochim. Acta 2020, 287, 341–366. [Google Scholar] [CrossRef]
  59. Gelpi, E.; Schneider, J.; Mann, J.; Oró, J. Hydrocarbons of geochemical significance in microscopic algae. Phytochemistry 1970, 9, 603–612. [Google Scholar] [CrossRef]
  60. Reed, J.D.; Illich, H.A.; Horsfield, B.J.O.G. Biochemical evolutionary significance of Ordovician oils and their sources. Org. Geochem. 1986, 10, 347–358. [Google Scholar] [CrossRef]
  61. Cranwell, P.A.; Eglinton, G.; Robinson, N. Lipids of aquatic organisms as potential contributors to lacustrine sediments-II. Org. Geochem. 1987, 11, 513–527. [Google Scholar] [CrossRef]
  62. Huang, W.Y.; Meinschein, W.G. Sterols as ecological indicators. Geochim. Et Cosmochim. Acta 1979, 43, 739–745. [Google Scholar] [CrossRef]
  63. Volkman, J. Sterols in microorganisms. Appl. Microbiol. Biotechnol. 2003, 60, 495–506. [Google Scholar] [CrossRef] [PubMed]
  64. Grantham, P.J.; Wakefield, L.L. Variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time. Org. Geochem. 1988, 12, 61–73. [Google Scholar] [CrossRef]
  65. Strobl, S.; Sachsenhofer, R.F.; Bechtel, A.; Gratzer, R.; Gross, D.; Bokhari, S.; Liu, R.; Liu, Z.; Meng, Q.; Sun, P. Depositional environment of oil shale within the Eocene Jijuntun Formation in the Fushun Basin (NE China). Mar. Pet. Geol. 2014, 56, 166–183. [Google Scholar] [CrossRef]
  66. Summons, R.E.; Jahnke, L.L.; Hope, J.M.; Logan, G.A. 2-Methylhopanoids as biomarkers for cyanobacterial oxygenic photosynthesis. Nature 1999, 400, 554–557. [Google Scholar] [CrossRef] [PubMed]
  67. Hou, M.; Qu, J.; Zha, M.; Swennen, R.; Ding, X.; Imin, A.; Liu, H.; Bian, B. Significant contribution of haloalkaliphilic cyanobacteria to organic matter in an ancient alkaline lacustrine source rock: A case study from the Permian Fengcheng Formation, Junggar Basin, China. Mar. Pet. Geol. 2022, 138, 105546. [Google Scholar] [CrossRef]
  68. Doughty, D.M.; Hunter, R.C.; Summons, R.E.; Newman, D.K. 2-Methylhopanoids are maximally produced in akinetes of Nostoc punctiforme: Geobiological implications. Geobiology 2009, 7, 524–532. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  69. Boudou, J.P.; Trichet, J.; Robinson, N.; Brassell, S.C. Profile of aliphatic hydrocarbons in a recent polynesian microbial mat. Int. J. Environ. Anal. Chem. 1986, 26, 137–155. [Google Scholar] [CrossRef]
  70. Ding, W.J.; Hou, D.J.; Jiang, L.; Jiang, Y.H.; Wu, P. High abundance of carotanes in the brackish-saline lacustrine sediments: A possible cyanobacteria source? Int. J. Coal Geol. 2020, 219, 103373. [Google Scholar] [CrossRef]
  71. Dobson, G.; Ward, D.M.; Robinson, N.; Eglinton, G. Biogeochemistry of hot spring environments: Extractable lipids of a cyanobacterial mat. Chem. Geol. 1988, 68, 155–179. [Google Scholar] [CrossRef]
  72. Luo, G.; Hallmann, C.; Xie, S.; Ruan, X.; Summons, R.E. Comparative microbial diversity and redox environments of black shale and stromatolite facies in the Mesoproterozoic Xiamaling Formation. Geochim. Et Cosmochim. Acta 2015, 151, 150–167. [Google Scholar] [CrossRef]
  73. Ding, X.J.; Gao, C.H.; Zha, M.; Chen, H.; Su, Y. Depositional environment and factors controlling β-carotane accumulation: A case study from the Jimsar Sag, Junggar Basin, northwestern China. Palaeogeogr. Palaeoclimatol. Palaeoecol. 2017, 485, 833–842. [Google Scholar] [CrossRef]
  74. Tribovillard, N.; Algeo, T.J.; Baudin, F.; Riboulleau, A.J.C.G. Analysis of marine environmental conditions based onmolybdenum–uranium covariation—Applications to Mesozoic paleoceanography. Chem. Geol. 2012, 324–325, 46–58. [Google Scholar] [CrossRef]
  75. Shanmugam, G. Significance of coniferous rain forests and related organic matter in generating commercial quantities of oil, Gippsland Basin, Australia. AAPG (Am. Assoc. Pet. Geol.) Bull. 1985, 69, 1241–1254. [Google Scholar] [CrossRef]
  76. Burford, M.A.; Gobler, C.J.; Hamilton, D.P.; Visser, P.M.; Lurling, M.; Codd, G.A. Solutions for Managing Cyanobacterial Blooms: A Scientific Summary for Policy Makers; IOC/UNESCO: Paris, France, 2019. [Google Scholar]
  77. Ji, X.; Verspagen, J.M.H.; Van de Waal, D.B.; Rost, B.; Huisman, J. Phenotypic plasticity of carbon fixation stimulates cyanobacterial blooms at elevated CO2. Sci. Adv. 2020, 6, 2926. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  78. Verspagen, J.M.H.; Snelder, E.; Visser, P.M.; Huisman, J.; Ibelings, B.W. Recruitment of benthic Microcystis (Cyanophyceae) to the water column: Internal buoyancy changes or resuspension? J. Phycol. 2004, 40, 260–270. [Google Scholar] [CrossRef]
  79. Preston, T.; Stewart, W.D.P.; Reynolds, C.S. Bloomforming cyanobacterium Microcystis aeruginosa overwinters on the sediment. Nature 1980, 288, 365–367. [Google Scholar] [CrossRef]
  80. Schindler, D.W. Evolution of phosphorus limitation in lakes. Science 1977, 195, 260–262. [Google Scholar] [CrossRef] [Green Version]
  81. Paerl, H.W. Mitigating harmful cyanobacterial blooms in a human-and climatically-impacted world. Life 2014, 4, 988–1012. [Google Scholar] [CrossRef] [Green Version]
  82. Wang, P.; Du, Y.; Yu, W.; Algeo, T.J.; Pan, W. The chemical index of alteration (CIA) as a proxy for climate change during glacial-interglacial transitions in Earth history. Earth-Sci. Rev. 2019, 201, 103032. [Google Scholar] [CrossRef]
  83. Moradi, A.V.; Sari, A.; Akkaya, P. Geochemistry of the Miocene oil shale (Hançili Formation) in the Çankırı-Çorum Basin, Central Turkey: Implications for Paleoclimate conditions, source–area weathering, provenance and tectonic setting. Sediment. Geol. 2016, 341, 289–303. [Google Scholar] [CrossRef]
  84. Xie, W.Q.; Tan, J.Q.; Wang, W.H.; Schulz, H.; Liu, Z.J.; Kang, X.; Wang, Y.; Shahzad, A.; Jan, I.U. Middle Jurassic lacustrine source rocks controlled by an aridification event: A case study in the northern Qaidam Basin (NW China). Int. J. Coal Geol. 2021, 242, 103779. [Google Scholar] [CrossRef]
  85. Rohling, E.J. Paleosalinity: Confidence limits and future applications. Mar. Geol. 2000, 163, 1–11. [Google Scholar] [CrossRef]
  86. Jiang, Z.; Ding, X.; Wang, Z.; Zhao, X. Sedimentary paleoenvironment of source rocks of Permian Lucaogou Formation in Jimsar Sag. Lithologic Reservoirs. Lithol. Reserv. 2020, 32, 11. [Google Scholar]
  87. Salminen, R.; Batista, M.J.; Bidovec, M.; Demetriades, A.; Tarvainen, T. FOREGS Geochemical Atlas of Europe, Part 1: Background Information, Methodology and Maps; Electric publication; Geochemical Survey of Finland: Espoo, Finland, 2005. [Google Scholar]
  88. Summons, R.E.; Hope, J.M.; Swart, R.; Walter, M.R. Origin of Nama Basin bitumen seeps: Petroleum derived from a Permian lacustrine source rock traversing southwestern Gondwana. Org. Geochem. 2008, 39, 589–607. [Google Scholar] [CrossRef]
  89. Algeo, T.J.; Tribovillard, N. Environmental Analysis of Paleoceanographic Systems Based on Molybdenum–Uranium Covariation. Chem. Geol. 2009, 268, 211–225. [Google Scholar] [CrossRef]
  90. Liu, D.D.; Fan, Q.Q.; Zhang, C.; Gao, Y.; Du, W.; Song, Y. Paleoenvironment evolution of the Permian Lucaogou Formation in the southern Junggar Basin, NW China. Palaeogeogr. Palaeoclimatol. Palaeoecol. 2022, 603, 111198. [Google Scholar] [CrossRef]
  91. Walters, C. The Biomarker Guide; Cambridge University Press: Cambridge, UK, 2005. [Google Scholar]
  92. Peters, K.E.; Fraser, T.H.; Amris, W.; Rustanto, B. Geochemistry of crude oils from eastern Indonesia. AAPG Bull. 1999, 83, 1927–1942. [Google Scholar]
  93. Jiang, Z.; Fowler, M.G. Carotenoid-derived alkanes in oils from northwestern China. Org. Geochem. 1986, 10, 831–839. [Google Scholar] [CrossRef]
  94. Wang, R.Y.; Gu, Y.; Ding, W.L.; Gong, D.; Yin, S.; Wang, X.; Zhou, X.; Li, A.; Xiao, Z.; Cui, Z. Characteristics and dominant controlling factors of organic-rich marine shales with high thermal maturity: A case study of the Lower Cambrian Niutitang Formation in the Cen’gong block, southern China. J. Nat. Gas Sci. Eng. 2016, 33, 81–96. [Google Scholar] [CrossRef]
  95. Calvert, S.; Pedersen, T. Elemental proxies for paleoclimatic and palaeoceanographic variability in marine sediments: Interpretation and application. Dev. Mar. Geol. 2007, 1, 568–644. [Google Scholar]
  96. Cheng, D.W.; Zhou, C.M.; Zhang, Z.J.; Yuan, X.J.; Liu, Y.H.; Chen, X.Y. Paleo-Environment Reconstruction of the Middle Permian Lucaogou Formation, Southeastern Junggar Basin, NW China: Implications for the Mechanism of Organic Matter Enrichment in Ancient Lake. J. Earth Sci. 2022, 33, 963–976. [Google Scholar] [CrossRef]
  97. Algeo, T.J.; Kuwahara, K.; Sano, H.; Bates, S.; Lyons, T.; Elswick, E.; Hinnov, L.; Ellwood, B.; Moser, J.; Maynard, J.B. Spatial variation in sediment fluxes, redox conditions, and productivity in the Permian–Triassic Panthalassic Ocean. Palaeogeogr. Palaeoclimatol. Palaeoecol. 2011, 308, 65–83. [Google Scholar] [CrossRef]
  98. Shen, J.; Schoepfer, S.D.; Feng, Q.; Zhou, L.; Yu, J.; Song, H.; Wei, H.; Algeo, T.J. Marine productivity changes during the end-Permian crisis and Early Triassic recovery. Earth Sci. Rev. 2015, 149, 136–162. [Google Scholar] [CrossRef]
  99. Schoepfer, S.D.; Shen, J.; Wei, H.; Tyson, R.V.; Ingall, E.; Algeo, T.J.J.E.-S.R. Total organic carbon, organic phosphorus, and biogenic barium fluxes as proxies for paleomarine productivity. Earth Sci. Rev. 2015, 149, 23–52. [Google Scholar] [CrossRef]
  100. Pedersen, T.E.; Calvert, S.E. Anoxia vs. productivity: What controls the formation of organic-carbon-rich sediments and sedimentary rocks? Am. Assoc. Pet. Geol. Bull. 1990, 74, 454–466. [Google Scholar]
  101. Guan, M.; Wu, S.; Hou, L.; Jiang, X.; Ba, D.; Hua, G. Paleoenvironment and chemostratigraphy heterogenity of the Cretaceous organic-rich shales. Adv. Geo-Energy Res. 2021, 5, 444–445. [Google Scholar] [CrossRef]
  102. Goldhammer, T.; Brüchert, V.; Ferdelman, T.G.; Zabel, M. Microbial sequestration of phosphorus in anoxic upwelling sediments. Nat. Geosci. 2010, 3, 557–561. [Google Scholar] [CrossRef]
  103. Langmann, B. On the Role of Climate Forcing by Volcanic Sulphate and Volcanic Ash. Adv. Meteorol. 2014, 2014, 340123. [Google Scholar] [CrossRef] [Green Version]
  104. Pan, Y.S.; Huang, Z.L.; Li, T.J.; Guo, X.; Chen, X. Environmental response to volcanic activity and its effect on organic matter enrichment in the Permian Lucaogou Formation of the Malang Sag, Santanghu Basin, Northwest China. Palaeogeogr. Palaeoclimatol. Palaeoecol. 2020, 560, 110024. [Google Scholar] [CrossRef]
  105. Liao, Z.; Hu, W.; Cao, J.; Wang, X.; Hu, Z.J.M.; Geology, P. Petrologic and geochemical evidence for the formation of organic-rich siliceous rocks of the Late Permian Dalong Formation, Lower Yangtze region, southern China. Mar. Pet. Geol. 2019, 103, 41–54. [Google Scholar] [CrossRef]
  106. Anderson, L.D.; Delaney, M.L. Use of multiproxy records on the Agulhas Ridge, Southern Ocean (Ocean Drilling Project Leg 177, Site 1090) to investigate sub-Antarctic hydrography from the Oligocene to the early Miocene. Paleoceanogr. Palaeoclimatol. 2005, 20. [Google Scholar] [CrossRef]
  107. Rimmer, S.M.; Thompson, J.A.; Goodnight, S.A.; Robl, T.L. Multiple controls on the preservation of organic matter in Devonian–Mississippian marine black shales: Geochemical and petrographic evidence. Palaeogeogr. Palaeoclim. Palaeoecol. 2004, 215, 125–154. [Google Scholar] [CrossRef]
  108. Duggen, S.; Croot, P.; Schacht, U.; Hoffmann, L. Subduction zone volcanic ash can fertilize the surface ocean and stimulate phytoplankton growth: Evidence from biogeochemical experiments and satellite data. Geophys. Res. Lett. 2007, 34, 95–119. [Google Scholar] [CrossRef] [Green Version]
  109. Wignall, P.B. Large igneous provinces and mass extinctions. Earth-Sci. Rev. 2001, 53, 1–33. [Google Scholar] [CrossRef]
  110. Qu, C.S.; Qiu, L.W.; Yang, Y.Q.; Yu, K.H.; Tang, L.L.; Wan, M. Environmental response of the Permian volcanism in Lucaogou formation in Jimsar sag, Junggar Basin, Northwest China. Seismol. Geol. 2019, 560, 110024. [Google Scholar]
  111. Li, Y.F.; Zhang, T.W.; Ellis, G.S. Depositional environment and organic matter accumulation of Upper Ordovician-Lower Silurian marine shale in the Upper Yangtze Platform, South China. Palaeogeogr. Palaeoclimatol. Palaeoecol 2017, 466, 252–264. [Google Scholar] [CrossRef]
  112. Wang, R.Y.; Hu, Z.Q.; Zhou, T.; Bao, H.Y.; Wu, J.; Du, W.; He, J.H. Characteristics of fractures and their significance for reservoirs in Wufeng-Longmaxi shale, Sichuan Basin and its periphery. Oil Gas Geol. 2021, 42, 1295–1306. [Google Scholar]
  113. Zhao, D.F.; Guo, Y.H.; Yin, S.; Ren, C.Y.; Wang, Y.J. Prediction of geomechanical sweet spots in a tight gas sandstone reservoir: A case study of lower Permian strata in the southern Qinshui Basin, China. Interpretation 2019, 7, 207–219. [Google Scholar] [CrossRef]
  114. Zhao, D.F.; Guo, Y.H.; Wang, G.X.; Zhou, X.Q.; Zhou, Y.Y.; Zhang, J.M.; Ren, G.Y. Organic matter enrichment mechanism of Youganwo Formation oil shale in the Maoming Basin. Heliyon 2023, 9, 13173. [Google Scholar] [CrossRef]
  115. Hedges, J.I.; Keil, R.G. Sedimentary organic matter preservation: An assessment and speculative synthesis. Mar. Chem. 1995, 49, 81–115. [Google Scholar] [CrossRef]
  116. Lash, G.G.; Blood, D.R. Organic matter accumulation, redox, and diagenetic history of the Marcellus Formation, southwestern Pennsylvania, Appalachian basin. Mar. Pet. Geol. 2014, 57, 244–263. [Google Scholar] [CrossRef]
  117. Zhao, D.F.; Guo, Y.H.; Zhu, Y.M.; Zhao, S.X.; Chen, Z.H.; Jiao, W.W. Comments on the evaluation system of accurate evaluation and selection of deep marine shale reservoirs. Unconv. Oil Gas 2022, 9, 1–7. [Google Scholar]
  118. Paerl, H.W.; Huisman, J. Climate change: A catalyst for global expansion of harmful cyanobacterial blooms. Environ. Microbiol. Rep. 2009, 1, 27–37. [Google Scholar] [CrossRef]
  119. O’Neil, J.M.; Davis, T.W.; Burford, M.A.; Gobler, C.J. The rise of harmful cyanobacteria blooms: The potential roles of eutrophication and climate change. Harmful Algae 2012, 14, 313–334. [Google Scholar]
  120. Verspagen, J.M.H.; Van, D.; Finke, J.F.; Visser, P.M.; Donk, E.V.; Huisman, J.; Dam, H.G. Rising CO2 Levels Will Intensify Phytoplankton Blooms in Eutrophic and Hypertrophic Lakes. PLoS ONE 2014, 9, 104325. [Google Scholar]
  121. Huisman, J.; Codd, G.A.; Paerl, H.; Ibelings, B.W.; Verspagen, J.M.H.; Visser, P.M. Cyanobacterial blooms. Nat. Rev. Microbiol. 2018, 16, 471–483. [Google Scholar] [CrossRef]
  122. Hackley, P.C.; Fishman, N.; Wu, T.; Baugher, G. Organic petrology and geochemistry of mudrocks from the lacustrine Lucaogou Formation, Santanghu Basin, northwest China: Application to lake basin evolution. Int. J. Coal Geol. 2016, 168, 20–34. [Google Scholar] [CrossRef] [Green Version]
  123. Zheng, R.; Zeng, W.; Li, Z.; Chen, X.; Man, K.; Zhang, Z.; Wang, G.; Shi, S. Differential enrichment mechanisms of organic matter in the Chang 7 Member mudstone and shale in Ordos Basin, China: Constraints from organic geochemistry and element geochemistry. Palaeogeogr. Palaeoclimatol. Palaeoecol. 2022, 601, 111126. [Google Scholar] [CrossRef]
  124. Bohacs, K.M.; Grabowski, J.G.; Carroll, A.R.; Mankiewicz, P.J.; Simo, T.J. Production, Destruction, and Dilution—The Many Paths to Source-Rock Development. In The Deposition of Organic-Carbon-Rich Sediments: Models, Mechanisms, and Consequences; Society for Sedimentary Geology Special Publication; GeoScienceWorld: McLean, VA, USA, 2005; Volume 82, pp. 61–101. [Google Scholar]
  125. Paerl, H.W.; Tucker, C.S. Ecology of Blue-Green Algae in Aquaculture Ponds. J. World Aquac. Soc. 1995, 26, 109–131. [Google Scholar] [CrossRef]
  126. Elliott, J.A. The seasonal sensitivity of Cyanobacteria and other phytoplankton to changes in flushing rate and water temperature. Glob. Change Biol. 2010, 16, 864–876. [Google Scholar] [CrossRef]
  127. Qin, J.Z.; Pan, A.; Shen, B.J. Insoluble organic matter in source rocks: Derived from organic macromolecules in the skeleton, cell wall and shell of organisms. Pet. Geol. Exp. 2020, 42, 6. [Google Scholar]
  128. Yang, Y.; Zheng, L.; Wu, Y.L.; Yang, F.Y.; Liu, F.; Han, R. Research progress on hydrodynamic mechanisms and simulation of Microcystis blooms. J. China Inst. Water Resour. Hydropower Res. 2022, 20, 449–463. [Google Scholar]
  129. Chorus, I. Toxic Cyanobacteria in Water: A Guide to Their Public Health Consequences, Monitoring and Management; E&FN Spon: London, UK, 1999. [Google Scholar]
  130. Song, H.; Xu, J.; Lavoie, M.; Fan, X.; Liu, G.; Sun, L.; Fu, Z.; Qian, H.J.A.M.; Biotechnology. Biological and chemical factors driving the temporal distribution of cyanobacteria and heterotrophic bacteria in a eutrophic lake (West Lake, China). Appl. Microbiol. Biotechnol. 2017, 101, 1685–1696. [Google Scholar] [CrossRef]
  131. Wu, Y.S.; Yu, G.L.; Jiang, H.X.; Liu, L.J.; Zhao, R.; Wu, Y.S.; Yu, G.L.; Jiang, H.X.; Liu, L.J.; Zhao, R. Role and lifestyle of calcified cyanobacteria (Stanieria) in Permian-Triassic boundary microbialites. Palaeogeogr. Palaeoclimatol. Palaeoecol. 2015, 448, 9. [Google Scholar] [CrossRef]
  132. Mort, H.; Jacquat, O.; Adatte, T.; Steinmann, P.; Föllmi, K.; Matera, V.; Berner, Z.; Stüben, D. The Cenomanian/Turonian anoxic event at the Bonarelli Level in Italy and Spain: Enhanced productivity and/or better preservation? Cretac. Res. 2007, 28, 597–612. [Google Scholar] [CrossRef] [Green Version]
  133. Xie, S.; Pancost, R.D.; Huang, J.H.; Wignall, P.B.; Yu, J.; Tang, X.; Chen, L.; Huang, X.; Lai, X. Changes in the global carbon cycle occurred as two episodes during the Permian-Triassic crisis. Geology 2007, 35, 1083–1086. [Google Scholar] [CrossRef]
  134. Xie, S.; Pancost, R.D.; Yin, H.; Wang, H.; Yang, H.; Wignall, P.B.; Luo, G.; Jia, C.; Chen, L. Cyanobacterial blooms tied to volcanism during the 5 m.y. Permo-Triassic biotic crisis. Geology 2010, 38, 447–450. [Google Scholar] [CrossRef]
Minerals 13 00537 g002 550
Figure 2. Core images (left), thin sections (middle), and fluorescent photographs (right) of the representative Lucaogou source rocks. (a,b) Organic matter (OM) laminae intermingled with terrigenous clastic laminae, mudstone, 3530.8 m. (c) Lamalginite displaying yellowish to green fluorescence, 3530.8 m. (d) OM laminae, terrigenous clastic laminae, and water-escape structure, dolomitic mudstone, 3576.6 m. (e) Ostracoda laminae and terrigenous clastic laminae, 3576.6 m. (f) Lamalginite and ostracoda laminae, 3576.6 m. (g) OM laminae and dry-cracked fragments, dolomitic mudstone, 3595.4 m. (h) Ostracoda, and OM laminae, 3595.4 m. (i) Lamalginite, yellowish to green fluorescence, 3595.4 m.
Figure 2. Core images (left), thin sections (middle), and fluorescent photographs (right) of the representative Lucaogou source rocks. (a,b) Organic matter (OM) laminae intermingled with terrigenous clastic laminae, mudstone, 3530.8 m. (c) Lamalginite displaying yellowish to green fluorescence, 3530.8 m. (d) OM laminae, terrigenous clastic laminae, and water-escape structure, dolomitic mudstone, 3576.6 m. (e) Ostracoda laminae and terrigenous clastic laminae, 3576.6 m. (f) Lamalginite and ostracoda laminae, 3576.6 m. (g) OM laminae and dry-cracked fragments, dolomitic mudstone, 3595.4 m. (h) Ostracoda, and OM laminae, 3595.4 m. (i) Lamalginite, yellowish to green fluorescence, 3595.4 m.
Minerals 13 00537 g002
Minerals 13 00537 g003 550
Figure 3. Microscopic photographs of Microcystis bloom in the upper Lucaogou Formation (J-17, 3574.2 m). (a) Sheet-like algal mats are widely distributed in the circled area. (a1) Size distributions and the fitting curve of Microcystis spheroids (count: 868, mean: 4.06 μm, standard deviation: 1.63 μm) (b–d) Microcystis cells are irregularly integrated as colonies. (e) Schematic diagram of Microcystis colony formation and bloom.
Figure 3. Microscopic photographs of Microcystis bloom in the upper Lucaogou Formation (J-17, 3574.2 m). (a) Sheet-like algal mats are widely distributed in the circled area. (a1) Size distributions and the fitting curve of Microcystis spheroids (count: 868, mean: 4.06 μm, standard deviation: 1.63 μm) (b–d) Microcystis cells are irregularly integrated as colonies. (e) Schematic diagram of Microcystis colony formation and bloom.
Minerals 13 00537 g003
Minerals 13 00537 g004 550
Figure 4. Microscopic photographs of Microcystis in the upper Lucaogou Formation (J-17, 3574.2 m). (a) Microcystis colony. (b) Magnified view of (a); abundant, randomly arranged globular to elliptical shaped individuals. (c) Close-up of the rectangle in (b); ornaments are visible on the cell surface. (d) Microcystis individuals, pyrite framboids, and their shedding molds.
Figure 4. Microscopic photographs of Microcystis in the upper Lucaogou Formation (J-17, 3574.2 m). (a) Microcystis colony. (b) Magnified view of (a); abundant, randomly arranged globular to elliptical shaped individuals. (c) Close-up of the rectangle in (b); ornaments are visible on the cell surface. (d) Microcystis individuals, pyrite framboids, and their shedding molds.
Minerals 13 00537 g004
Minerals 13 00537 g005 550
Figure 5. Elemental mapping test results of microfossil Microcystis. (a,b) SEM photographs of a cracked spheroid; (b) is the magnified view of the rectangle in (a); (c–f) Elemental mapping test of the cracked spheroid, mainly composed of Si, Fe, and S.
Figure 5. Elemental mapping test results of microfossil Microcystis. (a,b) SEM photographs of a cracked spheroid; (b) is the magnified view of the rectangle in (a); (c–f) Elemental mapping test of the cracked spheroid, mainly composed of Si, Fe, and S.
Minerals 13 00537 g005
Minerals 13 00537 g006 550
Figure 6. Microscopic photographs of individual Microcystis (all bars represent 2 μm). (a,b) Individuals with trilobate ornaments on the cell surfaces are attached by clastic minerals and encircled by organic matter. (c) Microfossil spheroid encircled by organic matter. (d) Microfossil spheroid and shedding molds. (e,f) Microfossil spheroids with rectangular ornaments on the cell surfaces.
Figure 6. Microscopic photographs of individual Microcystis (all bars represent 2 μm). (a,b) Individuals with trilobate ornaments on the cell surfaces are attached by clastic minerals and encircled by organic matter. (c) Microfossil spheroid encircled by organic matter. (d) Microfossil spheroid and shedding molds. (e,f) Microfossil spheroids with rectangular ornaments on the cell surfaces.
Minerals 13 00537 g006
Minerals 13 00537 g007 550
Figure 7. Biomarker chromatograms of cyanobacteria-bearing sample J-17, 3574.2 m. (a) Total ion chromatogram of the shale sample. (b) Mass chromatograms (m/z = 217) of the steranes. (c) Mass chromatograms (m/z = 57) of 2–8 monomethyl heptadecanes. (d) Mass chromatograms (m/z = 205) of hopanes.
Figure 7. Biomarker chromatograms of cyanobacteria-bearing sample J-17, 3574.2 m. (a) Total ion chromatogram of the shale sample. (b) Mass chromatograms (m/z = 217) of the steranes. (c) Mass chromatograms (m/z = 57) of 2–8 monomethyl heptadecanes. (d) Mass chromatograms (m/z = 205) of hopanes.
Minerals 13 00537 g007
Minerals 13 00537 g008 550
Figure 8. Biomarkers of the Lucaogou Formation (the red star marks the sample location of the microfossil J-17, 3574.2 m).
Figure 8. Biomarkers of the Lucaogou Formation (the red star marks the sample location of the microfossil J-17, 3574.2 m).
Minerals 13 00537 g008
Minerals 13 00537 g009 550
Figure 9. TOC and element geochemical parameters of the Lucaogou Formation (the red star marks the sample location of the microfossil J-17, 3574.2 m).
Figure 9. TOC and element geochemical parameters of the Lucaogou Formation (the red star marks the sample location of the microfossil J-17, 3574.2 m).
Minerals 13 00537 g009
Minerals 13 00537 g011 550
Figure 11. Schematic diagram of a Permian Microcystis bloom and its hydrocarbon effect. (a) Paleoenvironment of the lower member. (b) Paleoenvironment of the upper member.
Figure 11. Schematic diagram of a Permian Microcystis bloom and its hydrocarbon effect. (a) Paleoenvironment of the lower member. (b) Paleoenvironment of the upper member.
Minerals 13 00537 g011
Table
Table 1. TOC and element ratios of the Lucaogou Formation.
Table 1. TOC and element ratios of the Lucaogou Formation.
SampleDepth (m)TOC (%)Sr/BaB/GaCVALUECIAMoEFUEFP (%)P/TiBa/Al
J-263499.55.770.9916.331.147411.672.560.060.267.02 × 10−3
J-253506.81.811.4025.860.28790.510.560.100.463.06 × 10−3
J-243515.07.760.7626.890.34686.951.950.170.546.78 × 10−3
J-233523.76.810.624.930.855923.133.460.040.171.68 × 10−2
J-223526.15.740.494.350.946215.358.510.120.342.60 × 10−2
J-213530.814.930.856.411.006429.548.220.130.631.33 × 10−2
J-203547.85.530.266.400.965910.283.980.040.112.02 × 10−2
J-193569.23.100.489.920.384414.832.440.010.051.91 × 10−2
J-183570.56.750.606.680.404811.912.720.010.093.15 × 10−2
J-173574.219.600.717.930.22536.252.410.201.056.79 × 10−3
J-163576.616.971.048.700.664619.446.170.040.202.17 × 10−2
J-153595.415.802.1613.420.11502.134.420.060.424.36 × 10−3
J-143603.17.042.118.930.14543.572.810.090.828.60 × 10−3
J-133613.76.980.6310.240.15486.080.790.050.164.84 × 10−3
J-123624.33.622.1015.140.11469.492.110.030.195.59 × 10−3
J-113629.22.291.1514.500.07483.230.850.040.217.32 × 10−3
J-103664.34.201.7311.370.12501.281.660.050.306.21 × 10−3
J-093679.53.111.5718.890.09491.410.930.030.184.82 × 10−3
J-083681.62.442.2410.350.19483.971.310.030.134.66 × 10−3
J-073684.53.482.8413.480.11471.720.740.040.255.93 × 10−3
J-063685.55.821.268.720.205212.321.180.070.357.76 × 10−3
J-053695.31.951.8111.650.144815.703.980.070.289.83 × 10−3
J-043696.92.502.2819.720.11502.901.490.020.096.09 × 10−3
J-033699.95.731.3012.860.21514.640.800.030.147.56 × 10−3
J-023701.37.872.549.720.084963.492.420.050.379.71 × 10−3
J-013708.34.854.3819.850.08514.040.770.040.354.72 × 10−3
Table
Table 2. Biomarker ratios of the Lucaogou Formation.
Table 2. Biomarker ratios of the Lucaogou Formation.
SampleDepth (m)Max-PeakCPIOEPTARPr/n-C17Ph/n-C18Pr/PhGI2-MHIβ-Carotane Index7,8-MMH/CmaxRegular Steranes (%)
C27C28C29
J-263499.5C231.081.400.912.141.511.300.102.0018.740.0422.424.053.7
J-253506.8C231.091.341.261.301.570.740.143.1234.690.0342.841.615.6
J-243515.0C231.061.230.911.201.090.750.201.4114.380.0427.728.643.7
J-233523.7C171.081.290.090.860.761.250.211.353.460.1233.326.340.4
J-213530.8C191.071.010.310.600.511.010.161.882.860.0725.335.039.7
J-203547.8C251.051.060.6210.593.670.470.203.645.560.0019.636.743.7
J-193569.2C231.051.180.920.910.670.770.244.208.030.0411.939.548.5
J-173574.2C171.091.240.110.870.811.330.214.654.690.1123.440.236.5
J-153595.4C191.091.140.200.460.301.500.194.693.690.0418.041.240.8
J-143603.1C211.081.070.584.376.150.520.242.846.650.0127.120.852.1
J-133613.7C171.071.350.130.950.871.310.184.057.340.1117.138.444.6
J-123624.3C211.071.050.361.251.021.140.254.016.010.1211.036.252.8
J-113664.3C231.051.170.802.933.640.840.254.1831.420.2411.434.753.9
J-103629.2C171.061.380.291.281.660.820.234.156.770.1710.640.249.3
J-093679.5C231.051.140.681.701.950.880.243.3326.040.158.336.155.6
J-083681.6C231.051.131.211.691.570.650.223.9366.470.058.536.055.5
J-073684.5C201.031.100.791.581.190.200.253.6417.150.039.929.360.7
J-063685.5C221.051.080.920.971.200.420.263.4813.250.0511.726.761.6
J-043696.9C231.061.112.161.791.530.430.204.3728.020.049.235.455.5
J-033699.9C231.061.111.521.101.130.490.232.9115.660.049.235.255.6
J-023701.3C171.101.430.130.940.950.980.225.261.190.1313.336.550.2
J-013708.3C231.051.121.701.231.350.190.224.2128.300.0310.532.956.6
Note: The carbon preference index (CPI) and the odd–even predominance (OEP); Terrigenous/aquatic ratio (TAR) = (nC27 + nC29 + nC31)/(nC15 + nC17 + nC19); Gammacerane index (GI): gammacerane/17α,18β(H)-C30 hopane; 2α-methylhopane index (2MHI) = 2α-methylhopanes/(2α-methylhopanes + 17α,18β(H)-C30 hopane); β-carotane index = 100 × (β–carotane/17α,18β(H)-C30 hopane); 7-, 8-monomethyl heptadecanes/Cmax ratio (7,8-MMH/Cmax).
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Wang, W.; Cui, H.; Tan, J.; Liu, J.; Song, X.; Wang, J.; Chen, L. Permian Cyanobacterial Blooms Resulted in Enrichment of Organic Matter in the Lucaogou Formation in the Junggar Basin, NW China. Minerals 2023, 13, 537. https://doi.org/10.3390/min13040537

AMA Style

Wang W, Cui H, Tan J, Liu J, Song X, Wang J, Chen L. Permian Cyanobacterial Blooms Resulted in Enrichment of Organic Matter in the Lucaogou Formation in the Junggar Basin, NW China. Minerals. 2023; 13(4):537. https://doi.org/10.3390/min13040537

Chicago/Turabian Style

Wang, Wenhui, Haisu Cui, Jingqiang Tan, Jin Liu, Xueqi Song, Jian Wang, and Lichang Chen. 2023. "Permian Cyanobacterial Blooms Resulted in Enrichment of Organic Matter in the Lucaogou Formation in the Junggar Basin, NW China" Minerals 13, no. 4: 537. https://doi.org/10.3390/min13040537

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop