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Article

Evaluating Depositional Environment and Organic Matter Accumulation of Datangpo Formation in Central Hunan Province, South China

by
Peng Jiao
1,2,
Rong Xiao
1,
Shimin Tan
1,
Yu Xie
1,
Hanqi Fang
3,
Zhigang Wen
3 and
Zhanghu Wang
3,*
1
Geological Survey Institute of Hunan Province, Changsha 410116, China
2
Mineral Resources Development Service Center of Wangcheng, Changsha 410200, China
3
Hubei Key Laboratory of Petroleum Geochemistry and Environment, College of Resources and Environment, Yangtze University, Wuhan 430100, China
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(4), 366; https://doi.org/10.3390/min15040366
Submission received: 11 March 2025 / Revised: 25 March 2025 / Accepted: 26 March 2025 / Published: 31 March 2025
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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Abstract

:

Highlights

What are the main findings?
  • The paleo-oceanic environment of the deep-water region in South China during the interglacial period of the Cryogenian glaciation has been determined.
  • Comparative analysis of paleo-climate in different sedimentary facies of the Datangpo Formation has been conducted.
What is the implication of the main finding?
  • The material sources of the manganese ore in the deep-water region in South China have been clarified.
  • The relationship between the redox condition and primary productivity in the deep-water region has been determined.

Abstract

The interglacial period of the Cryogenian glaciation is a pivotal interval in geological history, marked by two “Snowball Earth” events and the emergence of early animals. Currently, there is considerable debate regarding the paleo-oceanic environment and the dominant factors controlling organic matter enrichment. Here, based on inorganic geochemical data and mineral composition from the Datangpo Formation in Xiangtan (South China), combined with previous research, we have analyzed the paleo-climate, redox condition, seawater restriction, and primary productivity across different sedimentary facies during this critical interval. The results exhibit that the Datangpo Formation can be divided into three members (Da1–Da3) based on lithology. Paleoclimatic proxies suggest the environment was relatively cold during the deposition of the Da-1 Member, while it was relatively warm and humid during the deposition of the Da 2–3 members. Compared to shallow water areas, deep-water areas experienced a more rapid transition in paleotemperature following the Sturtian glaciation event. Combining Mo-U elements, CeN/Ce*N, and Corg/P ratios, the environment was characterized by an oxic environment during the early deposition period of the Datangpo Formation, then gradually transitioned to suboxic, and finally anoxic conditions. Furthermore, the decompression of terrestrial magma chambers led to intense volcanic/hydrothermal activity during the deglaciation period. Hydrothermal activity was most intense during the Da-1 depositional period, followed by Da-2, and gradually declined during Da-3 depositional period. Hydrothermal activity not only provided essential materials for the formation of Mn carbonate ores but also significantly enhanced the primary productivity by introducing large amounts of nutrients in the paleo-ocean. The primary productivity indicators (Ni/Al, Cu/Al) exhibited an obvious coupling with CeN/Ce*N and Corg/P ratios in the Datangpo Formation, indicating that oxygen-rich environments were favorable for biological proliferation, thereby providing abundant organic matter. Anoxic conditions further facilitated the preservation of organic matter, which may be the primary factor driving organic matter enrichment in the Datangpo Formation.

1. Introduction

The Neoproterozoic represents a pivotal period during which the Earth’s lithosphere, atmosphere, and biosphere underwent significant transformations. This period was marked by the breakup of the Rodinia supercontinent (~800–700 Ma), two global Snowball Earth events—namely the Sturtian glaciation (~720–660 Ma) and the Marinoan glaciation (~650–635 Ma)—as well as key atmospheric and oceanic oxidation events [1,2,3,4]. During this period, marine primary producers transitioned from photosynthetic bacteria to eukaryotic algae [5]. These geological events were closely associated with climate fluctuations, oceanic environmental changes, and tectonic movements [3,6,7]. In the warm interval between the two Snowball Earth events, sediments known as the Datangpo Formation were deposited under conditions of climate warming. This sedimentary sequence is widely distributed across several regions, including South China, Namibia, Australia, Greenland, and Canada [8]. Recent studies have extensively explored the paleo-oceanographic conditions during the deposition of the Datangpo Formation [3,6,7,9], but a systematic analysis of the spatiotemporal variations in the atmospheric–oceanic redox state is still lacking.
Currently, redox indicators are commonly used to analyze paleo-oceanographic conditions in geological history [10]. Previous studies have employed multiple indicators, such as redox-sensitive elements (RSE), iron composition, molybdenum isotopes, Corg/P ratios, and cerium anomalies (CeN/Ce*N), to investigate the redox condition of the paleo-ocean during the deposition of the Datangpo Formation [3,6,7,9,11,12,13,14]. However, significant controversies still remain. The prevailing viewpoints can be broadly divided into two main hypotheses: The first hypothesis suggests that the early stage of Datangpo Formation deposition (the Mn carbonate deposition period) was characterized by an oxic environment. Lau et al. proposed that enhanced continental weathering after the Sturtian glaciation triggered a rapid increase in marine primary productivity and organic carbon burial, which ultimately led to a brief period of deep-sea oxidation during the interglacial intervals [11]. Yu et al. argued that microbial activity in an oxic environment contributed to the formation of Mn ores layer [12]. In the Songtao region of Guizhou Province, the V/Cr and CeN/Ce*N ratios both indicate that Mn element was in its oxidized form (Mn oxides), which was later reduced during diagenesis to form Mn carbonate minerals [15]. Similarly, the Th/U ratio and carbon isotope data from the Zuojiawan region in Sichuan Province also suggest an oxic environment during this period [6]. The iron isotope (δ56Fe:avg.+0.27‰) of Mn ore in the Datangpo Formation from the Chongqing area also indicated obvious oxic condition [16]. The second hypothesis posits that the paleo-ocean was characterized by an anoxic environment. Cheng et al. and Scheller et al., through the analysis of Mo isotopic compositions (δ98Mo) in coeval Datangpo and Arena shales, found that the δ98Mo values of seawater during this period ranged between 1.1 and 1.5‰, much lower than the modern ocean value of +2.3‰, suggesting that the marine environment was in predominantly anoxic condition [13,14]. Fe composition in the Lijiawan section, along with MoEF and UEF geochemical characteristics in Daotuo and Minle sections, all indicate that the early paleo-ocean was in ferruginous condition, transitioning later to a euxinic environment [17,18]. Tan et al. proposed that relatively oxygen-rich surface water influx during the early stage of deposition intermittently oxidized the bottom water in the basin, leading to the oxidation of Mn2+ at the sediment–water interface, forming MnO2 [19]. This Mn oxide then reacted with deposited organic matter to form carbonate manganese. Later, due to the anoxic conditions in the pore waters, much of the adsorbed molybdenum re-diffused into the water column, resulting in lower molybdenum isotope values in the carbonate manganese. Based on nitrogen and iron isotope (δ56Fe = −0.19 ± 0.13‰) of the Mn ores in Bijiashan sections, Chen et al. propose that the Mn ores precipitated directly in an anoxic bottom-water environment [20]. It is worth noting that the studies mentioned above primarily focus on shallow shelf-slope regions such as Sichuan, Guizhou, and Chongqing areas. The paleo-oceanographic chemical data for deep-water regions, represented by Hunan area, remains unclear at present.
The end of the Sturtian glaciation is likely linked to the substantial release of carbon dioxide from volcanic activity [21,22], which aligns with the higher mercury (Hg) content observed at the base of the Datangpo Formation. Hg isotopic compositions suggest that volcanic activity intensified due to the depressurization of terrestrial magma chambers, potentially triggered by deglaciation after the Sturtian glaciation [23]. Concurrently, molecular fossils record the rapid rise of marine phytoplankton, which became the dominant primary producers in the ocean during the Proterozoic interglacial periods [24]. This rise is likely closely associated with volcanic and hydrothermal activity [25]. However, the relationship between marine primary productivity and the seawater redox state remains unclear, and the mechanisms controlling organic matter deposition have yet to be fully understood. Notably, the Datangpo Formation is widely distributed in both shallow- and deep-water regions across South China. In particular, the central Hunan area was situated in a deep-water environment during the Sturtian interglacial period, and its core samples provide valuable evidence for elucidating post-Sturtian glacial paleo-climatic evolution and oceanic conditions Therefore, this study aims to systematically analyze the petrological and geochemical characteristics of the Datangpo Formation, with a focus on deciphering the spatial distribution patterns of paleo-climate and oceanic redox conditions from shallow to deep-water settings. Additionally, it seeks to investigate the metallogenic mechanisms of manganese deposits in deep-water environments and identify the primary controlling factors for organic matter enrichment in carbonate rocks and shales. These investigations will offer new insights into the fluctuations and evolution of the marine environment during this period.

2. Geological Setting

At the end of the Mesoproterozoic (~1000 Ma), the global tectonic thermal event led to the convergence of major tectonic plates and the formation of the supercontinent Rodinia [26]. The South China block was situated on the northern margin of Rodinia, near the northern edges of Australia and India (Figure 1A) [8,27,28]. During the late Neoproterozoic (~820 Ma), widespread continental rifting caused Rodinia to enter a prolonged phase of breakup [8,29]. The South China continent also experienced a series of extensional events, forming a northeast–southwest rift basin—the Nanhua Basin—between the Yangtze and Cathaysia blocks [30]. Subsequently, the Nanhua Basin underwent multiple episodes of half-graben rifting, until the Middle Cambrian (~500 Ma), and evolved into an intracontinental rift basin [31,32]. Several secondary rift sub-basins developed within the Nanhua Basin, forming a series of graben–horst structures aligned in a northeast–southwest direction, providing substantial accommodation space for sedimentation [33]. Paleo-geographic reconstructions show that the water depth gradually increased from northwest to southeast, with sedimentary facies transitioning from shallow water shelf environments to deep basin environments [34]. The Nanhua Basin is characterized by a continuous sedimentary succession of glacial facies (Nanhua Series), including the Tiesiao, Datangpo, and Nantuo formations. The Tiesiao and Nantuo formations, representing glacial facies, correspond to the Sturtian and Marinoan glaciations of the Cryogenian [35]. Between these two glacial sequences, a non-glacial interval was deposited, represented by the Datangpo Formation, which is unconformably bounded by both the underlying and overlying strata [3,7]. The end of the Sturtian glaciation is likely linked to volcanic activity that released substantial amounts of carbon dioxide, contributing to global warming [21]. The enhanced weathering process brought large amounts of nutrients to the ocean, promoting increased surface ocean productivity and organic carbon burial rates [36,37]. This phenomenon led to the widespread enrichment of organic matter in the lower Datangpo Formation. Yu et al. analyzed the U-Pb ages of zircons at the base of the Datangpo Formation in the Songtao area, yielding an age of 658.8 ± 0.5 Ma [38]. Rooney et al. obtained U-Pb ages of zircons from the tuff layer in the Mn carbonate in southeastern Guizhou and western Hunan, with ages of 660.98 ± 0.74 Ma, 658.97 ± 0.76 Ma, and 657.17 ± 0.78 Ma [39]. An age of 660.98 ± 0.74 Ma may be the closest to the base of the Datangpo Formation. Zhang et al. analyzed the U-Pb age of zircons from the gray layer immediately below the Nantuo Formation and determined the top boundary age of the Datangpo Formation to be 654.5 ± 3.8 Ma [40]. Therefore, the age of the Datangpo Formation in South China is constrained between 660.98 ± 0.74 Ma and 654.5 ± 3.8 Ma, with a duration of approximately 6.5 million years.
During the Neoproterozoic Period, the Hunan region was located in the slope-basin facies belt (Figure 1). The primary focus of this study is the recently drilled ZK2308 well (27°36′30″ N, 112°36′46″ E) in the Xiangtan Nanmuchong area, which is located near a tectonic uplift (Figure 1B). From bottom to top, three sets of strata are observed: the Gucheng Formation (Tiesiao Formation), the Datangpo Formation, and the Nantuo Formation. The Gucheng Formation consists of gray-white and purplish-red blocky glacial mudstone and gravel, with a thickness of approximately 80 m (Figure 1C). The Nantuo Formation is composed of gray-green glacial mudstone and gravel, with a thickness of only 1.2 m. The Datangpo Formation is also relatively thin, with a thickness of no more than 10 m. The Datangpo Formation can be divided into three members based on lithology: the lower section (Da-1 Member) mainly consists of red-brown manganese carbonate layers; the middle section (Da-2 Member) consists of medium- to thick-bedded gray calcareous shale, with no obvious lamination; and the upper section (Da-3 Member) consists of black, thin-bedded carbonaceous shale with a relatively clean texture, containing spotty and clumpy pyrite. Additionally, six section datasets were collected for comparative analysis, aiming to reconstruct the spatial distribution of the marine chemical environment across different depositional facies in the Nanhua Basin (Figure 1).

3. Materials and Methods

A total of 20 fresh rock samples were collected from the Datangpo Formation in Well ZK2308, including 3 Mn carbonate and 17 shale samples. All samples were sieved through a 75 μm screen before the following chemical measurements, and all experiments were analyzed at Yangtze University.
Total organic carbon (TOC) content test: We weighed 80–120 mg of whole rock powder samples and placed them in a ceramic crucible. Slowly add 10% HCl solution to the crucible, allowing the reaction to proceed until no bubbles are produced. The crucible is then placed in 10% HCl solution and allowed to soak for an additional 8 h. Afterward, the sample is heated in a water bath at 80 °C for 4 h to ensure complete removal of carbonate minerals. The acid-treated samples are repeatedly rinsed with ultra-pure water until all residual hydrochloric acid is removed and the sample is neutralized. The samples are then placed in an oven at 80 °C to dry. After drying, iron filings and tungsten tin are added as fluxing agents to the crucible containing the sample, and the sample is placed in an automatic sampler. The sample is combusted at high temperature, converting organic carbon into CO2, and the TOC content is calculated by integrating the signal from the infrared detector. The instrument used for testing is the Eltra CS800 carbon-sulfur analyzer. The TOC analysis precision was better than 0.2%, based on the Chinese national standard (GB/T 19145-2003).
Major element test: The major element content of rock samples is tested using fused bead X-ray fluorescence (XRF) spectroscopy. First, the samples are dried in an oven at 105 °C for 12 h. Then, 1–1.5 g of dried samples is placed in a pre-weighed ceramic crucible and heated in a muffle furnace at 950 °C for 2 h. After cooling to room temperature, the weight is measured to calculate the loss on ignition. Next, 6.0 g of flux (Li2B4O7: LiBO2: LiF = 9:2:1), 0.6 g of sample, and 0.3 g of oxidant (NH4NO3) are added to a platinum crucible. The mixture is then melted in a furnace at 1150 °C for 14 min. After cooling, the melt is formed into a circular glass disc. Finally, the glass disc is tested for major element content using the Rigaku 100e X-ray fluorescence spectrometer (XRF). The analytical precision was better than 5%, based on the Chinese national standard (GB/T 14506.30-2010).
Trace element test: The samples are dried in an oven at 105 °C for 12 h. Then, accurately weigh 50 mg of the powdered sample and place it in a Teflon digestion vessel. Slowly add 3 mL of high-purity HNO3, 3 mL of high-purity HF, and 1.5 mL of high-purity HClO4 in sequence. The Teflon digestion vessel is placed in a steel jacket, tightened, and heated in an oven at 190 °C for more than 48 h. After cooling, the lid is opened and the sample is evaporated to dryness on a 140 °C hotplate. Then, 2 mL of high-purity HNO3 and 2 mL of high-purity HF are added, and the sample is heated at 170 °C for 4 h. After cooling, the sample is removed and again evaporated to dryness on the 140 °C hotplate, resulting in a moist salt-like sample. Subsequently, 4 mL of 4N HNO3 is added, and the vessel is sealed and placed in an autoclave at 170 °C for 4 h. After cooling, the sample is removed. Finally, the dissolved sample is poured into a plastic cup, and 2% HNO3 is added to dilute it to 2000 times the original concentration, with Rh internal standard solution added. The trace element analysis is performed using the Perkin-Elmer Sciex ELAN 6000 (PerkinElmer Inc., Waltham, MA, USA) inductively coupled plasma mass spectrometer (ICP-MS). The single element was used as an internal standard to monitor the data quality with the analytical precision better than ±5%. The chemical index of alteration (CIA) is calculated using the equation: CIA = Al2O3/(Al2O3 + CaO* + Na2O + K2O) × 100, where CaO* denotes concentration of CaO in silicate component, which can be derived from a formula based on P2O5 content (CaO* = CaO − 10/3 × P2O5) [41]. If the calculated CaO* is lower than Na2O, CaO* can be directly adopted to calculate CIA. Reversely, CaO* is substituted by Na2O [42]. The major elemental concentrations are used by molar unit. The CIW calculation formula is as follows: CIW = [Al2O3/Al2O3 + CaO + Na2O] × 100. The enrichment factors (EF) can be calculated as XEF = (X/Al)sample/(X/Al)UCC, where X denotes targeted element and UCC represents the average composition of upper continental crust [43,44]. Ce anomalies (CeN/Ce*N) were calculated according to Lawrence et al. [45]. Using Nd and Pr to calculate Ce* precludes artificial anomalies that may arise from elevated La concentrations that result from the higher stability of La relative to other REE in solution. CeN/Ce*N = CeN/(PrN*PrN/NdN), where N refers to elemental concentrations normalized to Post-Archean Australian Shale values.
Petrography observation: The rock samples were extracted, thoroughly cleaned, and processed to obtain fresh surfaces for observation. These surfaces were then fixed onto sample stubs with conductive adhesive and allowed to air dry naturally. Finally, the samples were carbon-coated using a vacuum sputtering machine to ensure good electrical conductivity. The sample diameter typically does not exceed 1 cm. Subsequently, the samples were examined under high vacuum conditions using a JSM-7800F scanning electron microscope (SEM) (JEOL Ltd., Tokyo, Japan). The SEM beam current was set to 10 nA, and the accelerating voltage to 20 kV to enhance chemical contrast.

4. Results

4.1. TOC Content of Datangpo Formation

The TOC content of the Datangpo Formation samples is shown in Figure 2. Overall, the TOC values range from 0.28% to 8.01%, with an average of 3.48%. Among these, the TOC content in the Mn carbonate of Da-1 Member is the lowest, ranging from 0.33% to 0.68% (avg. 0.44%). The TOC content in the Da-2 calcareous shale shows significant variation, ranging from 0.28% to 8.01% (avg. 3.01%). The TOC content in the Da-3 black shale is the highest, ranging from 4.07% to 5.83%, with an average of 5.21%.

4.2. Petrography and Mineralogical Characteristics

The microscopic photographs of different lithologies from the Datangpo Formation are shown in Figure 3. Pyrite is observed as spheroidal particles with well-formed crystal structures in the black shale (Figure 3A,B). The brittle minerals are primarily quartz, while the clay minerals are mainly illite. The calcareous shale occasionally contains spheroidal pyrite, with distinct anhydrite minerals visible (Figure 3C,D). Under field emission scanning electron microscopy (FE-SEM), organic matter is surrounded by clay minerals (Figure 3G). The main lithology of the Mn carbonate consists of Mn-bearing dolomite, with clay minerals predominantly illite, and microcrystalline quartz also present (Figure 3E,F). FE-SEM images reveal numerous veins within the ore layers, filled with gray carbonate minerals and black quartz minerals, while pyrite is relatively rare (Figure 3H,I).

4.3. The Major and Trace Element Contents

The major and trace element contents of the Datangpo Formation are shown in Figure 2 and Figure 4. In the Da-1 Mn carbonate, the MnO and CaO contents are the highest, ranging from 23.6% to 31.9% (avg. 28.1%) and 14.1% to 16.3% (avg. 14.9%), respectively. In the Da-2 calcareous shale, with the exception of one sample showing relatively high Mn content (23.5%), the MnO content of the other samples ranges from 0.1% to 1.3% (avg. 0.5%), while the CaO content varies from 0.3% to 18.3% (avg. 5.3%). In the Da-3 black shale, Mn content is generally low, typically not exceeding 0.2%, and CaO content does not exceed 1.5% (avg. 0.8%). The vertical variations in SiO2 and Al2O3 contents are inversely related to those of Mn and CaO. The SiO2 and Al2O3 contents are lowest in the Da-1 Mn carbonate, with average values of 17.7% and 2.9%, respectively, while they are highest in the Da-3 black shale (avg. 65.8% and avg. 12.9%). The Fe2O3 content in the Datangpo Formation ranges from 0.1% to 6.1%. The Mo and U contents are relatively low, with Mo content generally below 10 ppm (avg. 6 ppm), and U content ranging from 1 to 10 ppm (avg. 3 ppm). The V content is highest in the Da-2 calcareous shale (avg. 158 ppm), followed by the Da1 Mn carbonate (avg. 71 ppm), and lowest in the Da-3 black shale (avg. 54 ppm). The variations in Cu and Ni contents follow a trend similar to that of Fe2O3, ranging from 11–434 ppm and 12–111 ppm, respectively.

4.4. Geochemical Characteristics of Rare Earth Elements

The distribution of rare earth elements (REE) in the Datangpo Formation is shown in Figure 5 and Supplementary Materials. In the Da-1 Mn carbonate, the total REE (∑REE) values range from 116 ppm to 132 ppm, with an average of 124 ppm. The ∑REE values of Da-2 calcareous shale range from 81 ppm to 447 ppm, with an average of 222 ppm, while the ∑REE values of Da-3 black shale range from 119 ppm to 300 ppm, with an average of 214 ppm. In the Da-1 Mn carbonate, there is a relative depletion of light rare earth elements (LREE) and a relative enrichment of heavy rare earth elements (HREE). The CeN/Ce*N ratio ranges from 1.27 to 1.34 (avg. 1.31), while the Eu/Eu* ratio ranges from 1.02 to 1.07 (avg. 1.06), exhibiting a distinct positive Ce anomaly and Eu anomaly. In the Da-2 calcareous shale, the REE distribution curve shows a pronounced rightward tilt. The CeN/Ce*N ratio ranges from 0.95 to 1.06 (avg. 1.00), and the Eu/Eu* ratio ranges from 0.55 to 1.50 (avg. 0.84), displaying weak negative Eu anomalies. In the Da-3 black shale, the REE distribution curve is relatively flat. The CeN/Ce*N ratio ranges from 0.82 to 1.00 (avg. 0.89), and the Eu/Eu* ratio ranges from 0.89 to 1.13, showing a distinct negative Ce anomaly.

5. Discussion

5.1. Paleo-Climate During the Datangpo Interglaciation

Nutrient supply is a key factor influencing marine productivity and organic matter formation, and it is typically related to the chemical weathering intensity of the source area. The chemical composition of silicate sediments can effectively record the chemical weathering intensity of the source area [41]. The content of the major component Al2O3 in the weathering products varies with the intensity of chemical weathering. It is generally considered that a CIA value of 80–100 represents intense weathering under hot and humid climatic conditions; a CIA value of 60–80 indicates moderate weathering under warm and humid conditions; and a CIA value of 50–60 corresponds to weak weathering under cold and dry climatic conditions [47,48]. In addition, potassium exchange may cause the CIA value to not accurately reflect the paleo-climate, a phenomenon that is more commonly observed in the Precambrian. The chemical weathering index (CIW) or the A-CN-K ternary diagram should be used for evaluation (Figure 6).
The CIW and CIA values from the ZK2308 well in the Datangpo Formation exhibit a significant positive correlation, with a correlation coefficient of 0.86 (Figure 6B), indicating a strong synchronous variation between the two parameters during geological evolution. Analysis using the A-CN-K ternary diagram reveals that the majority of the samples are aligned parallel to the A-CK edge, further confirming that post-diagenetic potassium metasomatism has little effect on the CIA values of the Datangpo Formation (Figure 6A). Therefore, the CIA values in the central Hunan region effectively reflect the paleo-climate changes during the deposition of the Datangpo Formation, driven primarily by the ancient climate rather than significant interference from later diagenetic processes. The CIA values of the Da-1 Mn carbonate range from 67.5 to 69.8 (avg. 68.4), suggesting that the Datangpo Formation was formed during the post-glacial warming phase, with a paleo-climate characterized by cold with intermittent warm conditions. The relatively low CIA values during this phase may reflect lower chemical weathering intensity and cooler environmental conditions. The CIA values of the Da-2 calcareous shale range from 70.9 to 74.8 (avg. 72.8), indicating stronger chemical weathering, which suggests a relatively warmer paleo-climate. The CIA values of the Da-3 black shale range from 73.8 to 78.4 (avg. 75.3), indicating warm to hot condition. From bottom to top, the ZK2308 well reveals a gradual increase in temperature during the deposition of the Datangpo Formation. This paleo-climate trend is also evident in other regions, including Sichuan, Guizhou, Hubei, and western Hunan provinces (Figure 7). In particular, the Sichuan region, represented by the Zuojiawan section, and the Guizhou section, represented by the ZK0202 well, Lijiawan, and ZK2115 well, show relatively cold and arid paleo-climates during the early Datangpo Formation deposition [17,22,49]. In contrast, the Hubei and western Hunan regions, represented by the Zouma and Yangjiaping sections, exhibit relatively warm and humid paleo-climates [49,50]. The Li isotopes of Datangpo samples in the ZK2001 well also confirmed relatively strong weathering, which is consistent with the Zouma area [51]. The paleo-climate in the central Hunan Province is characterized by warm to hot conditions. In summary, during the early stage of Datangpo Formation deposition, the shallow water areas experienced relatively cold and arid paleo-climates, while the deep-water areas were warmer and more humid. As deposition progressed into the later stages, the paleo-climate in South China became predominantly warm and humid. This trend of warming is closely linked to global climate warming, providing strong evidence for the evolution of regional paleo-climates.

5.2. Source of Mn Element in the Datangpo Formation

REEs are minimally influenced by post-depositional processes, making them excellent tracers for paleo-oceanic or tectonic environments [46]. The REE patterns and Eu anomalies in sedimentary rocks depend on the relative intensity of terrigenous, marine, or hydrothermal inputs into the sedimentary system during deposition [52]. Typically, positive Eu anomalies are associated with hydrothermal activity, with stronger hydrothermal activity leading to higher Eu ratios [53,54,55]. In seawater, Y is precipitated more slowly than Ho due to particle–surface reactions, resulting in higher Y/Ho ratios in modern typical seawater (48–80) [56]. In contrast, hydrothermal fluids generally exhibit lower Y/Ho ratios (~27) [57].
In ICP-MS testing, Ba element complexes may interfere with the calculation of Eu values, leading to the apparent Eu positive anomaly. According to Figure 8, there is no significant correlation between Eu/Eu* and Ba/Nd in the Datangpo Formation of Well ZK2308, and terrestrial material has no noticeable impact on Eu/Eu*. The Eu/Eu* value can serve as an indicator of the intensity of hydrothermal activity. The rare earth element distribution pattern of the study area reveals that the Da-1 Mn carbonate of the Datangpo Formation shows a distinct Eu positive anomaly, suggesting that hydrothermal activity had a strong influence on the paleo-environment (Figure 5C). In contrast, the calcareous shale in the Da-2 Member and the black shale in the Da-3 Member exhibit significant Eu negative anomalies, possibly indicating little to no hydrothermal influence (Figure 5A,B). The Y/Ho ratios of the Datangpo Formation samples are generally low (26.7–34.2). Among these, the Y/Ho ratio of the Da-1 Mn carbonate (27.5–28.7, avg. 28.2) is lower than that of the DA-2 calcareous shale (28.1–34.2, avg. 29.7), while the Da-3 black shale has the lowest Y/Ho ratio (26.7–30.6, avg. 28.6). Additionally, the enrichment of major elements such as Fe and Mn is typically associated with hydrothermal activity, while the enrichment of Al and Ti primarily reflects input from terrestrial detritus [58]. Referring to the Fe/Ti vs. Al/(Al + Mn + Fe) diagram by Sylvestre et al. [59], this helps clarify the relationship between hydrothermal input in water-forming sediments and the dilution effects of terrestrial or volcanic materials (Figure 9). Sediments near the East Pacific Rise hydrothermal deposits (EPC) contain a higher proportion of hydrothermal material, while sediments closer to oceanic continental deposits (PC) and upper continental crust (UC) contain relatively less hydrothermal input [59,60,61].
As shown in Figure 9, the Al/(Al + Mn + Fe) value of the Da-1 Mn carbonate is low (0.05–0.09, average 0.06), and the (Fe + Mn)/Ti value is high (130–186, average 166), indicating strong hydrothermal activity. The Da-2 calcareous shale has a relatively low Al/(Al + Mn + Fe) value (0.15–0.74, avg. 0.58) and a low (Fe + Mn)/Ti value (6–93, avg. 23), suggesting weaker hydrothermal activity. The Da-3 black shale, being closer to the UC, is almost unaffected by hydrothermal activity. Mercury isotopes at the bottom of the Datangpo Formation also indicate that volcanic/hydrothermal activities were relatively frequent due to decompression of the terrestrial magma chamber [25]. In summary, deep hydrothermal activities provided a large amount of ore-forming materials for the formation of the Datangpo Mn deposit.

5.3. Redox Condition During the Depositional Period of Datangpo Formation

Anoxic conditions favor the preservation of organic carbon in marine sediments, while organic phosphorus (P) is re-mineralized and released back into the seawater. In contrast, organic carbon in marine sediments under oxic pore waters is degraded, while organic phosphorus is preserved. Therefore, the Corg/P ratio can be used to distinguish the redox conditions of bottom waters during sediment deposition [62]. Typically, Corg/P < 50 in sedimentary basins indicates an oxic environment, 50 < Corg/P < 100 indicates a suboxic environment, and Corg/P > 100 indicates an anoxic environment [10,62]. In modern oxic oceans, dissolved Ce3+ is oxidized to insoluble CeO2 (Ce4+) and adsorbed by Fe-Mn oxides, which are then removed from the seawater. This results in a negative Ce anomaly in seawater and a significant positive Ce anomaly in sediments [46]. Manganese-rich sediments formed in oxic marine environments, especially water-formed Fe-Mn nodules and crusts, typically exhibit a distinct positive Ce anomaly [63]. Mo-U elements and their enrichment factors are also widely used to analyze the sedimentary environments during the deposition of ancient marine-continental shale [44,64,65]. In this study, Mo-U elements, the Corg/P ratio, and Ce anomalies are integrated to comprehensively analyze the marine environment during the deposition of the Datangpo Formation in the central Hunan Province.
The Mo and U contents in the Datangpo Formation samples are generally low, with Mo concentrations ranging from 1 to 20 ppm (avg. 6 ppm), and U concentrations also relatively low, typically not exceeding 10 ppm (1–10 ppm, avg. 3 ppm). In the Da-1 Mn carbonate, the Mo enrichment factor (MoEF) ranges from 12.1 to 26, and the UEF ranges from 1.3 to 1.7, both indicating a suboxic to anoxic depositional environment. However, the CeN/Ce*N ratio ranges from 1.17 to 1.23, and the Corg/P ratio ranges from 7 to 17, both suggesting an oxic depositional environment. Ma et al. also indicated an anoxic water environment in the Chongqing area based on Fe component analysis [66]. The Mo-U indicators, Fe components, and CeN/Ce*N and Corg/P ratios of the Mn carbonate seem to show some discrepancies, and there is still significant debate regarding the paleo-oceanographic environment during this period.
Tan et al. found that the Mo content in the Mn carbonate is low, and the Mo isotopes are relatively light (0.07‰ to 0.52‰), suggesting that this is mainly due to Mo adsorbed on particles being released from suboxic or anoxic (non-sulfurized) pore waters during the reduction process, which then re-enters the water column [9]. It is worth noting that Mn formation is closely associated with hydrothermal activity, which transports a significant amount of Mn and Fe into the ancient ocean, exerting a considerable influence on the Fe-Mn shuttle layer in shallow water regions [3,67]. Therefore, we suggested that Ce anomalies and Corg/P indicators may be relatively more reliable. During the development of the Da-1 Mn carbonate, the paleo-oceanic environment was likely dominated by oxic conditions. The CeN/Ce*N ratio in the Da-2 calcareous shale ranges from 0.86 to 1.06 (avg. 0.96), and the Corg/P ratio ranges from 16 to 171 (avg. 71), indicating a predominantly suboxic environment with intermittent anoxic waters. The CeN/Ce*N ratio in the Da-3 black shale ranges from 0.76 to 0.92 (average: 0.83), and the Corg/P ratio ranges from 94 to 574 (avg. 365). These findings are consistent with the Mo isotope analysis results of the shale from this period (0.98–1.15), which also indicate an anoxic water environment.
The paleo-oceanic environment during the deposition of the Datangpo Formation in central Hunan Province transitioned from an oxic to an anoxic environment. The vertical variation in water oxygen content is consistent with the trend in TOC content in the sedimentary rocks (Figure 2). By comparing the marine environments of different depositional facies belts in South China (Figure 10), paleo-ocean during the deposition of the Da-1 Mn carbonate was primarily in oxic condition. In shallow water areas, the Zuojiawan section in Yunnan Province and the Zouma section in Hubei Province were characterized by oxic conditions, whereas the relatively deeper water areas, such as the ZK0202 well Lijiawan, ZK2115 well in Guizhou Province, and the Yangjiaping section in Hunan Province, were predominantly suboxic environments. The deepest and most reducing waters occurred during the deposition of the Datangpo Formation in the study area.

5.4. Seawater Restriction

The seawater restriction in the sedimentary basin (i.e., its connectivity to the open ocean) is a crucial factor influencing the marine environment and biogeochemical cycles [68,69]. Due to the seawater restriction in the paleo-ocean, the enrichment of trace elements in the sediments can vary greatly. Typically, sediments formed in anoxic environments exhibit a strong affinity of organic carbon for authigenic Mo, and the Mo content is often well correlated with the TOC content. When H2S is present in the water, MoO4 is completely converted into MoO4-xSx2− (where x = 1–4), and these MoO4-xSx2− species are captured and precipitated by organic matter or pyrite, leading to the removal of Mo from seawater and its deposition in sediments [70,71]. The average Mo content in the Earth’s crust is as low as 3.7 ppm [72,73]. Additionally, Mo has a relatively long residence time in the water column, approximately 780 kyr. Therefore, the Mo/TOC ratio in anoxic sediments fluctuates with the openness degree of the basin [44]. Variations in the maximum Mo/TOC ratio in open condition during different periods can reflect fluctuations in the global ocean Mo reservoir.
The Mo/TOC ratio of Datangpo samples in the ZK2308 well is generally low, ranging from 0.4 to 22.1 (avg. 4.1), with most samples falling in the high restriction region, similar to the modern Black Sea sediments (Mo/TOC = 4.5 ± 1, Figure 11A). The Mn carbonate of Da-1 Member exhibits relatively higher Mo/TOC values, ranging from 6.5 to 22.1 (average 13.6), indicating a moderately restricted depositional environment. From the MoEF-UEF correlation plot of Datangpo Formation samples (Figure 11B), it is evident that Mo is significantly more enriched than U in the Mn carbonate (MoEF/UEF = 9.4–15.0). Some samples fall into the particulate shuttle region, indicating that the Mo content during the Mn carbonate was influenced by the Fe-Mn shuttle layer in the shallow water region. These findings suggest that South China had relatively good connectivity with surrounding oceans, and frequent exchanges occurred between the open ocean and Nanhua basin at the end of the Sturtian glaciation. This led to unstable redox conditions of seawater in South China. Furthermore, insufficient sulfate supply may cause instability in the H2S content of the seawater. The Mo/TOC ratio in the Da-2 calcareous shale and Da-3 black shale is generally below 5, and the MoEF/UEF ratio ranges from 0.8 to 8.37 (average 3.11). This is likely related to the restricted connectivity of the Nanhua basin with the open ocean due to sea-level drop in the late interglacial period (Figure 11) [17,74]. As the Mo reservoir in the basin’s seawater gradually became depleted, Mo in the water was fully converted into MoS42−, thus removing it from the water and precipitating it in the sediments. This caused the δ98Mo of the sediments to approach that of the δ98Mo value in the modern open ocean [9]. The phenomenon also resulted in limited sulfate supply in the basin, further causing pyrite to exhibit heavy sulfur isotope compositions [7,75,76,77]. In summary, the seawater restriction degree in the Central Hunan Province showed a trend of gradual increase during the depositional period of Datangpo Formation.

5.5. Organic Matter Enrichment Mechanism in Datangpo Formation

During the Neoproterozoic Period, the rifting of the Rodinia supercontinent led to the formation of the Nanhua Rift Basin, which provided accommodation space for the deposition of Mn ores in the Datangpo Formation [78,79]. The fault systems generated by rifting also formed pathways for deep-seated hydrothermal fluids. These fluids, which served as significant sources of Mn, Fe, and other elements in the depositional waters, were a primary source of metallogenic material for the manganese ores in South China [20,80,81,82]. Additionally, the organic carbon content in the Datangpo Formation shales is relatively high, with the Da-1 Mn carbonate having the lowest TOC content, and the Da-3 black shale layers exhibiting the highest TOC content. Paleo-climate, primary marine productivity, redox conditions, and terrigenous material input are closely linked, influencing both the deposition and burial of organic matter in the sediments. In this study, we aim to systematically analyze the relationship between the frequent paleo-environmental fluctuations and the coupling of organic matter in source rocks.

5.5.1. Coupling of Primary Marine Productivity and Redox Conditions

Primary marine productivity refers to the flux of organic matter produced in marine or lacustrine environments during geological history [83,84]. This is commonly evaluated through the organic carbon content in sediments or rocks. Metal elements such as Ni and Cu can also serve as indicators of primary marine productivity [64,85,86]. In modern marine sediments, Cu and Ni, as nutrient elements, often form complexes with organic matter. To mitigate the influence of terrigenous clasts, the Cu/Al and Ni/Al ratios are typically used to characterize initial marine productivity. As shown in Figure 4, the primary marine productivity during the Datangpo Formation deposition period exhibits a distinct downward trend. The Da-1 Mn carbonate layers exhibited the highest primary productivity, followed by the Da-2 calcareous shale, with the Da-3 black shale showing the lowest primary productivity. Typically, high Cu and Ni contents correlate with high organic matter input, which favors the enrichment of organic matter. However, the trend in primary marine productivity during the Datangpo Formation period contrasts with the trend observed in TOC content in the samples. To explain this apparent contradiction, we propose an analysis of the coupling between primary marine productivity and redox conditions during this period.
As illustrated in Figure 12, the redox indicators (CeN/Ce*N values and Corg/P ratios) of the Datangpo Formation samples show a clear positive correlation with primary marine productivity, as reflected by the Ni/Al ratio. This suggests that higher oxygen content in the water corresponds to higher primary marine productivity, which provides more organic matter (Figure 12A,C). In contrast, when the surface water was in suboxic or anoxic conditions, the marine environment became less favorable for biological reproduction. This phenomenon of changing primary productivity triggered by fluctuations in marine water oxygen content is particularly evident in the Da-2 calcareous shale layers. When the marine environment was in suboxic condition, the Cu/Al and Ni/Al ratios ranged from 14 to 24 (avg. 27) and 7 to 16 (avg. 12), respectively. When the environment was intermittently in suboxic or anoxic condition, the Cu/Al and Ni/Al ratios ranged from 3 to 13 (avg. 7) and 4 to 12 (avg. 8). It is noteworthy that the CeN/Ce*N values and Corg/P ratios show a strong coupling with TOC (Figure 12B,D). The TOC content in the Da-1 Mn carbonate layer was the lowest. Redox indicators (CeN/Ce*N values and Corg/P ratios) suggest that the Da-1 Mn carbonate layer was deposited in an oxic environment. Despite relatively abundant organic matter supply during this period, the oxic conditions were unfavorable for organic matter preservation. Conversely, the anoxic conditions favored organic matter preservation during the depositional period of Da-3 black shale.

5.5.2. Paleo-Oceanographic Reconstruction of the Datangpo Formation

The coupling between paleo-climate, seawater restriction, redox conditions, and primary productivity in the deep-water regions during the Cryogenian remains unclear. This study focuses on reconstructing the paleo-environment during the deposition of the Da1–Da3 members of the Datangpo Formation, aiming to elucidate how the paleo-environment influenced organic matter enrichment (Figure 13).
During the deposition of Da-1 Member, the seawater was relatively shallow. Decompression of the land-based magma chamber triggered intense volcanic/hydrothermal activity, providing a substantial material foundation for the formation of manganese ores (Figure 13A). Meanwhile, oxygen-rich surface waters from the open ocean entered the basin, leading to an oxic environment in the bottom water. In this environment, Mn2+ was oxidized at the sediment–water interface to form MnO2, which was subsequently reduced by organic matter during burial to form Mn carbonate minerals. Microbial activity also participated in this process. The volcanic/hydrothermal activity not only supplied materials for manganese ore formation but also introduced large amounts of nutrients into the ancient ocean, enhancing the primary productivity of the water column. However, despite the high primary productivity, the oxic environment was not conducive to the preservation of organic matter. Therefore, although organic matter was generated at a higher rate, the oxic conditions limited the enrichment process of organic carbon.
During the deposition of Da-2 Member, with the continued warming of the climate, the sea level rose, and the environment gradually transitioned to a suboxic to intermittently anoxic condition (Figure 13B). Although volcanic/hydrothermal activity remained frequent during this period, its intensity was relatively weaker, leading to lower Mn concentrations in the sediments. Compared to the Da-1 period, the primary productivity of the ocean was weaker, which limited organic matter accumulation. Due to the rifting of the Rodinia supercontinent, the connectivity between the ancient ocean of South China and surrounding oceans was poor, resulting in stronger seawater restriction. This limited the exchange and distribution of nutrients. The suboxic environment suppressed oxidative reactions and provided relatively favorable conditions for the preservation of organic carbon. The TOC content was also moderate, reflecting the influence of water restriction on organic matter deposition. Thus, despite the relatively low primary productivity, the suboxic environment provided favorable conditions for organic matter enrichment.
During the Da-3 Member, the climate became relatively warm and humid, and volcanic/hydrothermal activity largely ceased (Figure 13C). The seawater restriction was similar to that of the Da-2 period, maintaining a strongly restricted environment. Although primary productivity was at its lowest during this period, limiting the supply of organic matter, the anoxic bottom water environment favored the preservation of organic matter. The anoxic bottom water reduced the degradation of organic matter, providing favorable conditions for its accumulation. Therefore, the anoxic conditions can be considered the dominant factor controlling organic matter enrichment.

6. Conclusions

The shale gas well ZK2308 drilled in the central Hunan region, provides excellent experimental material for analyzing the marine environment of the deep-water area in South China during the interglacial period. To investigate the factors controlling organic matter enrichment in marine environments, we conducted high-resolution geochemical analysis of various lithologies within the Datangpo Formation.
The Mn carbonate of Da-1 Member have the lowest total organic carbon (TOC) content, while the upper black shale of Da-3 Member has the highest content, showing a gradual increase in TOC vertically. The paleo-climate follows a similar trend, starting with a cold climate at the end of the Sturtian glaciation, which then gradually transitioned to a warm and humid climate. Furthermore, the decompression of terrestrial magma chambers led to intense volcanic/hydrothermal activity during the deglaciation period. Although hydrothermal activity during the deposition of Mn carbonate of Da-1 Member introduced a substantial amount of nutrients into the ancient ocean, boosting its primary productivity, the oxic seawater and relatively weak restricted environment led to the consumption of abundant organic matter. In contrast, during the deposition of Da-2 calcareous shale and Da-3 black shales, hydrothermal activity gradually waned, resulting in a relatively low primary marine productivity. However, the suboxic and anoxic environment, combined with a highly restricted marine environment, favored the preservation of organic matter. Compared to shallow water areas, the deep-water regions exhibit relatively higher paleotemperatures and lower oxygen content at the end of the Sturtian glaciation period. These observations suggest that the marine environments of different sedimentary facies exhibit distinct differences. In conclusion, this comprehensive model reflects the influence of redox conditions on the accumulation of organic matter in the Datangpo Formation in the Nanhua Basin.

Supplementary Materials

The following supporting information can be downloaded at: FigShare at DOI/URL: 10.6084/m9.figshare.28691801.

Author Contributions

Conceptualization, S.T.; Methodology, R.X. and H.F.; Formal analysis, Y.X.; Investigation, R.X. and Y.X.; Data curation, H.F.; Writing—original draft, P.J.; Writing – review & editing, Z.W. (Zhanghu Wang); Visualization, Z.W. (Zhigang Wen); Supervision, S.T. and Z.W. (Zhigang Wen); Project administration, Z.W. (Zhigang Wen); Funding acquisition, P.J. and Z.W. (Zhanghu Wang). All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (42302159), Hunan Provincial Natural Science Foundation of China (2024JJ8322, 2024JJ8357), Hubei Provincial Natural Science Foundation of China (2022CFB642), and the Postdoctor Project of Hubei Province under Grant Number (2024HBBHXF085). We thank Xikai Wang (Brown University) for revising the manuscript. We also thank the two anonymous reviewers for helpful and constructive comments on earlier versions of the manuscript.

Data Availability Statement

Data is contained within the article and Supplementary Materials.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (A) Paleocontinental reconstruction at the end of the Sturtian glaciation period (~660 Ma, modified after Li et al. [7]). (B) Palaeo-geographic map of South China during depositional period of the Datangpo Formation. (C) Comprehensive stratigraphic column of the Datangpo Formation in Central Hunan Province. The ages are taken from Rooney et al. [39] and Zhang et al. [40].
Figure 1. (A) Paleocontinental reconstruction at the end of the Sturtian glaciation period (~660 Ma, modified after Li et al. [7]). (B) Palaeo-geographic map of South China during depositional period of the Datangpo Formation. (C) Comprehensive stratigraphic column of the Datangpo Formation in Central Hunan Province. The ages are taken from Rooney et al. [39] and Zhang et al. [40].
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Figure 2. Stratigraphic distribution of TOC, SiO2, Al2O3, MnO, Al/(Al + Fe + Mn), and CIA of the samples in the Datangpo Formation from the ZK2308 Well.
Figure 2. Stratigraphic distribution of TOC, SiO2, Al2O3, MnO, Al/(Al + Fe + Mn), and CIA of the samples in the Datangpo Formation from the ZK2308 Well.
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Figure 3. Photomicrographs of the Datangpo Formation. (A) Spheroidal pyrite and illite clay minerals in black shale, depth 1202.9 m; (B) Crystalline pyrite and quartz in black shale, depth 1205 m; (C) Anhydrite and illite clay minerals in calcareous shale, depth 1206.8 m; (D) Spheroidal pyrite in calcareous shale, depth 1207.4 m; (E) Mn-rich dolomite, depth 1208.2 m; (F) Mn-rich dolomite and microcrystalline quartz, depth 1208.5 m; (G) Organic matter and clay minerals in calcareous shale, depth 1207.4 m; (H) Calcite and quartz filling fractures in Mn carbonate ore layers, depth 1208.2 m; (I) Calcite and quartz in Mn carbonate ore layers, depth 1208.5 m.
Figure 3. Photomicrographs of the Datangpo Formation. (A) Spheroidal pyrite and illite clay minerals in black shale, depth 1202.9 m; (B) Crystalline pyrite and quartz in black shale, depth 1205 m; (C) Anhydrite and illite clay minerals in calcareous shale, depth 1206.8 m; (D) Spheroidal pyrite in calcareous shale, depth 1207.4 m; (E) Mn-rich dolomite, depth 1208.2 m; (F) Mn-rich dolomite and microcrystalline quartz, depth 1208.5 m; (G) Organic matter and clay minerals in calcareous shale, depth 1207.4 m; (H) Calcite and quartz filling fractures in Mn carbonate ore layers, depth 1208.2 m; (I) Calcite and quartz in Mn carbonate ore layers, depth 1208.5 m.
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Figure 4. Stratigraphic distribution of Mo, U, MoEF, UEF, Mo/TOC, Corg/P, CeN/CeN*, Cu/Al, and Ni/Al of the samples in the Datangpo Formation from the ZK2308 Well.
Figure 4. Stratigraphic distribution of Mo, U, MoEF, UEF, Mo/TOC, Corg/P, CeN/CeN*, Cu/Al, and Ni/Al of the samples in the Datangpo Formation from the ZK2308 Well.
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Figure 5. PAAS-normalized REE patterns of the Da-3 Member, (A) Da-2 Member, (B) Da-1 Member (C). The REE patterns of hydrothermal fluids and modern seawater (D) (refer by Bau and Dulski [46]).
Figure 5. PAAS-normalized REE patterns of the Da-3 Member, (A) Da-2 Member, (B) Da-1 Member (C). The REE patterns of hydrothermal fluids and modern seawater (D) (refer by Bau and Dulski [46]).
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Figure 6. Paleo-climate proxies of the Datangpo Formation chemical weathering ternary diagram (A). CIA versus CIW of Datangpo Formation in Central Hunan Province (B).
Figure 6. Paleo-climate proxies of the Datangpo Formation chemical weathering ternary diagram (A). CIA versus CIW of Datangpo Formation in Central Hunan Province (B).
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Figure 7. Comparison of paleo-climate in different sedimentary facies during the Datangpo Formation deposition period.
Figure 7. Comparison of paleo-climate in different sedimentary facies during the Datangpo Formation deposition period.
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Figure 8. Eu/Eu* versus Ba/Nd (A) and Al2O3 (B) of Datangpo Formation in central Hunan Province.
Figure 8. Eu/Eu* versus Ba/Nd (A) and Al2O3 (B) of Datangpo Formation in central Hunan Province.
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Figure 9. Fe/Ti versus Al/(Al + Fe + Mn) diagram of Datangpo samples in the central Hunan Province (revised from Sylvestre et al. [59]).
Figure 9. Fe/Ti versus Al/(Al + Fe + Mn) diagram of Datangpo samples in the central Hunan Province (revised from Sylvestre et al. [59]).
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Figure 10. Comparison of seawater redox condition in different sedimentary facies during the Datangpo Formation deposition period.
Figure 10. Comparison of seawater redox condition in different sedimentary facies during the Datangpo Formation deposition period.
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Figure 11. Cross plot of Mo and TOC contents for the Datangpo black shale in the central Hunan Province (A) (revised from Algeo and Lyons [69]). (B) Cross plot of MoEF and UEF in the Datangpo black shale (revised from Algeo and Tribovillard [65]).
Figure 11. Cross plot of Mo and TOC contents for the Datangpo black shale in the central Hunan Province (A) (revised from Algeo and Lyons [69]). (B) Cross plot of MoEF and UEF in the Datangpo black shale (revised from Algeo and Tribovillard [65]).
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Figure 12. Cross plots of Corg/P versus Ni/Al (A), TOC content (B), and CeN/Ce*N versus Ni/Al (C), TOC content (D) for the Datangpo Formation.
Figure 12. Cross plots of Corg/P versus Ni/Al (A), TOC content (B), and CeN/Ce*N versus Ni/Al (C), TOC content (D) for the Datangpo Formation.
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Figure 13. Depositional models showing the OM enrichment mechanisms of the Datangpo Formation in the Nanhua Basin. (A) the Mn carbonate of Da-1 Member; (B) the calcareous shale of Da-2 Member; (C) the black shale of Da-3 Member.
Figure 13. Depositional models showing the OM enrichment mechanisms of the Datangpo Formation in the Nanhua Basin. (A) the Mn carbonate of Da-1 Member; (B) the calcareous shale of Da-2 Member; (C) the black shale of Da-3 Member.
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Jiao, P.; Xiao, R.; Tan, S.; Xie, Y.; Fang, H.; Wen, Z.; Wang, Z. Evaluating Depositional Environment and Organic Matter Accumulation of Datangpo Formation in Central Hunan Province, South China. Minerals 2025, 15, 366. https://doi.org/10.3390/min15040366

AMA Style

Jiao P, Xiao R, Tan S, Xie Y, Fang H, Wen Z, Wang Z. Evaluating Depositional Environment and Organic Matter Accumulation of Datangpo Formation in Central Hunan Province, South China. Minerals. 2025; 15(4):366. https://doi.org/10.3390/min15040366

Chicago/Turabian Style

Jiao, Peng, Rong Xiao, Shimin Tan, Yu Xie, Hanqi Fang, Zhigang Wen, and Zhanghu Wang. 2025. "Evaluating Depositional Environment and Organic Matter Accumulation of Datangpo Formation in Central Hunan Province, South China" Minerals 15, no. 4: 366. https://doi.org/10.3390/min15040366

APA Style

Jiao, P., Xiao, R., Tan, S., Xie, Y., Fang, H., Wen, Z., & Wang, Z. (2025). Evaluating Depositional Environment and Organic Matter Accumulation of Datangpo Formation in Central Hunan Province, South China. Minerals, 15(4), 366. https://doi.org/10.3390/min15040366

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