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Article

Sr, S, and O Isotope Compositions of Evaporites in the Lanping–Simao Basin, China

by
Lijian Shen
1,
Licheng Wang
2,*,
Chenglin Liu
1 and
Yanjun Zhao
1
1
MNR Key laboratory of Metallogeny and Mineral Assessment, Institute of Minerals Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
2
CAS Center for Excellence in Tibetan Plateau Earth Sciences, Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China
*
Author to whom correspondence should be addressed.
Minerals 2021, 11(2), 96; https://doi.org/10.3390/min11020096
Submission received: 23 November 2020 / Revised: 7 January 2021 / Accepted: 15 January 2021 / Published: 20 January 2021
(This article belongs to the Special Issue Mineralogy, Petrology and Geochemistry of Evaporites)
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Abstract

:
Evaporites are widely distributed within continental “red beds” in the Lanping–Simao Basin, west Yunnan, China. Sr (Strontium), S (Sulfur), and O (Oxygen) isotope compositions have been measured on 54 sulfate or/and sulfate-bearing samples collected from Lanping, Nuodeng, Jinggu, Mengyejing, Baozang throughout the Lanping–Simao Basin. The 87Sr/86Sr ratios of all samples (0.708081 to 0.710049) are higher than those of contemporaneous seawater, indicating a significant continental contribution to the drainage basin. Sulfates in the Lanping Basin have higher 87Sr/86Sr ratios (0.709406 to 0.710049) than those (0.708081 to 0.709548) in the Simao Basin. Nevertheless, the δ34S values of gypsums (13.4‰ to 17.6‰) in Lanping and Baozang fall within the range of Cretaceous seawater. Gypsums from a single section in Baozang have trends of decreasing δ34S values and increasing 87Sr/86Sr ratios from base to top, indicating continental input played an increasingly significant role with the evaporation of brines. High δ34S values (20.5‰ to 20.7‰) of celestites in Lanping are probably caused by bacterial sulfate reduction (BSR) process in which 34S were enriched in residual sulfates and/or recycling of Triassic evaporites. The reduced δ34S values of gypsums (9.5‰ to 10.4‰) in Nuodeng could have been caused by oxidation of sulfides weathered from Jinding Pb-Zn deposit. The complex O isotope compositions indicate that sulfates in the Lanping–Simao Basin had undergone sulfate reduction, re-oxidation, reservoir effects, etc. In conclusion, the formation of continental evaporites was likely derived from seawater due to marine transgression during the Cretaceous period. Meanwhile, non-marine inflows have contributed to the basin significantly.

1. Introduction

The Lanping–Simao Basin hosts the only ancient potash deposit ever found in China [1], and a great quantity of metallic mineral resources which have a close relationship with evaporites, especially sulfates [2,3,4,5]. Consequently, the origin of those evaporites has attracted tremendous attention during the last decades [6,7,8,9,10,11,12,13]. The basin evolved from a remnant marine and marine-continental basin during the Triassic Period, through a continental depression basin during the Jurassic-Cretaceous Period, to a pull-apart continental basin during the Cenozoic Period [2]. Evaporites were primarily formed within the Triassic and Cretaceous periods during the evolution of the basin. The metallic-associated gypsums in the Sanhedong Formation, upper Triassic, was marine origin [2,14], whereas the sources of evaporites within Cretaceous continental “red beds” remain a subject of debate. The Br (bromide) geochemistry of rock salts in the Mengyejing potash deposit indicates a major seawater contribution [11,15]. On the contrary, Li et al. (2015) [16] suggested a major continental origin based on geochemical evidence of the Mengyejing potash deposit. Qu et al. (1998) [10] proposed that evaporites in the Lanping–Simao Basin formed during Cretaceous to Tertiary were typical continental origin based on sedimentary facies. However, Wang et al. (2014a) [12] suggested that the Cretaceous gypsums from the Lanping Basin were mainly derived from seawater based on S isotope compositions. A series of saline lakes formed during the Late Cretaceous from north to south of the Lanping–Simao Basin wherein a certain amount of evaporites (mainly sulfates and chlorides) were deposited [17]. Consequently, a comprehensive study of those evaporites is needed to refine our understanding of their origin.
Sr, S, and O isotope studies are useful for recording origin, deposition, and paleoclimate, etc. [18]. The S, O, and Sr isotopic compositions of marine evaporites are well constrained through the Phanerozoic [19,20,21,22,23]. In comparison to marine evaporites, these isotopic compositions of continental evaporites are more complex depending on local geology and hydrology within the drainage basin [24]. In this paper, we present S, Sr, and O isotopic compositions of continental lacustrine evaporites, which occurred in Mesozoic-Cenozoic “red beds” in the Lanping–Simao Basin, west Yunnan, China [10]. The objectives of this study are to (1) determine the origin of parent brines in which evaporites precipitated; (2) interpret paleo-environmental changes during deposition of evaporites.

2. Geological Setting

The Lanping–Simao Basin is located in western Yunnan, China, stretching along the NW-SE direction. Tectonically, the Lanping–Simao Basin is a part of the Simao Block which is separated from the South China Block by the Jinshajiang–Ailaoshan sutures to the east, and from the Baoshan and Sibumasu blocks by the Jinghong and Changning–Menglian sutures to the west [25]. The basin is divided into two parts, namely the Lanping Basin to the north and the Simao Basin to the south (Figure 1).
The Lanping–Simao Basin developed on the paleo-Tethys basement since the collision between Simao and South China blocks in the Late Triassic and evolved from a remnant marine and marine-continental basin of the Triassic [2] into a continental rift basin of the Jurassic-Cretaceous period [10]. The Jurassic-Early Cretaceous sedimentary deposits consist of a thick sequence of continental red beds. These red beds are unconformably overlain by the Late Cretaceous continental evaporites and clastic deposits [26]. Lacustrine siltstones and mudstones with evaporites sequences are widespread within the Mengyejing Formation in the Simao Basin and Yunlong Formation in the Lanping Basin (Figure 2). These two formations were previously thought to have been formed during Paleocene based on Ostracoda and Charophyta assemblages [10]. However, updated evidence of SHRIMP zircon U-Pb dating of tuff beds within the Mengyejing Formation supported a mid-Cretaceous age, 100–110 Ma [27]. Chen (2017) [28] postulated that the Yunlong Formation was formed during the late Cretaceous based on the maximum depositional age evidenced by detrital zircon U-Pb dating. Although the correlation regarding the formation age between the Mengyejing formation and the Yunlong formation still remains a subject of debate, we believe these two formations are equivalent and deposited during the Late Cretaceous. The major evaporite minerals in the Mengyejing and Yunlong formations are composed of gypsum and halite, with a small amount of sylvite and carnallite [10].
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Figure 1. (A) Schematic map of major tectonic features of western Yunnan (after [29]); (B) schematic geological map of Lanping–Simao Basin and sampling locations (marked by red dots) (after [27]).
Figure 1. (A) Schematic map of major tectonic features of western Yunnan (after [29]); (B) schematic geological map of Lanping–Simao Basin and sampling locations (marked by red dots) (after [27]).
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Figure 2. The synthesized stratigraphic column of the Mesozoic-Tertiary sedimentation (modified from [29]).
Figure 2. The synthesized stratigraphic column of the Mesozoic-Tertiary sedimentation (modified from [29]).
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3. Materials and Methods

A variety of samples, including layered and veined gypsums, rock salts were collected from Lanping, Nuodeng, Jinggu, Baozang, and Mengyejing from the north to the south of the Lanping–Simao Basin. Sulfate samples (mostly gypsums) stemmed from outcrops located in Lanping, Nuodeng, Jinggu, and Baozang. Rock salt samples were sampled from the underground mine lane of the Mengyejing potash deposit (Figure 3).
Four samples were collected from gypsum laminae in Lanping; three samples were collected from vein-shaped gypsums in Nuodeng; four samples were collected from gypsum laminae in Jinggu; 37 samples were collected in Baozang, including 32 laminated gypsum samples and five veined gypsum samples. Six rock salt samples were collected from the underground mine lane of the Mengyejing potash deposit.
In order to select samples with sufficient sulfate for analyzing S isotope composition, all samples were tested by X-ray diffraction (XRD) analysis. To eliminate the effect of sulfides, all examples were examined under binoculars.
All samples collected from the Lanping–Simao Basin were cut, polished, and thinned using an oil system. The thin sections were examined using a polarizing microscope.
The SEM analysis was carried out at the Key Laboratory of Deep-Earth Dynamics, Institute of Geology using the FEI Nova NanoSEM 450. The back scattered electron (BSE) images were taken under operating voltage of 15–20 KV and working distance of 13.5 mm.
Sr isotope analyses of all samples were performed at the State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences. Powdered gypsum samples (~5 to 10 mg) were dissolved with 4M HNO3 after washing with milli-Q water. Five to 10 g of rock salt samples were washed with milli-Q water to eliminate chloride salts and accumulated sulfates and subsequently dissolved with 4M HNO3. Sr was extracted from the samples using a Sr-specresin. The detailed procedure about Sr separation is given by [30]. Samples were analyzed in a Neptune Plus multi-collector (MC) ICP-MS. The 87Sr/86Sr ratios were corrected for mass discrimination using 87Sr/86Sr ratio = 0.1194. NBS 987 standard yields 87Sr/86Sr values of 0.71022(30) and 0.71030 (7) for MC-ICP-MS spectrometers. Uncertainties in the 87Sr/86Sr are quoted in 1σ.
Oxygen isotopic composition of sulfates were performed at the State Key Laboratory of Lithosphere Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences. Sulfates were dissolved and reacted with BaCl2 solutions. The precipitated BaSO4 was washed and dried. Solid barite samples were weighed into a silver capsule and introduced into a graphite furnace where BaSO4 is converted to CO gas at 1400 °C in helium gas using a thermal combustion elemental analyzer (TCEA). Oxygen isotope ratios were measured by a continuous flow isotope ratio monitoring mass spectrometry system using a Flash HT 2000 high temperature pyrolysis furnace coupled with a Finnigan Conflo IV open split interface to a Thermo Scientific DELTA V Advantage mass spectrometer. Measurements were calibrated using the two-point linear normalization method based on international sulfate standards NBS 127 (+8.6‰, VSMOW), IAEA SO-5 (+12.13‰, VSMOW). Repeated measurements of international standards (four measurements per standard per run) yield reproducibility of better than 0.2‰ (1σ) for oxygen isotope measurements.
For the S isotope measurement, the sulfate was combusted at 980℃ in a Flash Element Analyzer and the resulting sulfur dioxide (SO2) was measured with continuous flow GS-IRMS (Thermo, Delta V Plus) at the Beijing Research Institute of Uranium Geology. δ34S values are reported vs. the Canyon Diablo Troilite (CDT), and the error was determined using the standard deviation of the standard (GBW-04414 and GBW-04415) at the beginning and the end of each run (<0.5‰).
The detailed procedure for ICP-MS trace element analysis is given in [31], and the two-sigma error for the 87Rb/86Sr ratio was estimated at ±2.6%.

4. Results

4.1. Characteristics of Evaporite Minerals

In Lanping, the gypsum section is interbedded with the underlying and overlying mudstones (Figure 3) with relatively sharp contact boundary. The mudstones show massive structure. Gypsum aggregates are usually present as two forms, i.e., gypsum laminae with fine-grained crystals (alabaster) and selenite macrocrystallines. The common millimetric gypsum laminae show slightly wavy features (Figure 4A) and are seen as alabaster on planar direction (Figure 4B). Selenite crystals are sporadically interbedded or embedded with gypsum laminae. The boundary between selenite and gypsum laminae are sharp (Figure 4A). The gypsum laminae are composed of microcrystalline gypsum. The microcrystalline gypsums display a variety of textures ranging from xenotopic to idiotopic. The crystals are present primarily as xenotopic ameboid gypsums with minor embedded euhedral crystals (Figure 5A). The gypsum crystals showed no orientation and variation in sorting. The sizes of the microcrystalline gypsums are equant and not varied along with the changes of the laminae. The scanning electron microscopy (SEM) analysis showing that euhedral pyrite (Figure 5B) and celestite are present within gypsum laminae (Figure 5C).
In Nuodeng, fractures are developed within mottled (reddish-brown and greenish-grey) clastic rocks, and filled by nearly pure gypsum veins (Figure 4C). These veins consist of fibers from 1 to 10 cm long. The gypsum fibers are curved and show perpendicular or oblique orientation to the wall rocks (Figure 4D). The elongated gypsum crystals within veins are curved and aligned with minor distorted relative short gypsum crystals (Figure 5D). The clastic rocks are unconsolidated and showing stratified structure with no cross-bedding detected. Some parts of the clastic rocks contain clayey breccias (Figure 4C,D).
In Jinghong, gypsum laminae are normally organized in millimetric to centimetric beds (Figure 4E), alternating with calcareous clastic layers. The stratified gypsum laminae and intercalated calcareous clastic layers are plane-parallel. The lamination is clearly differentiated by white and gray thin layers (Figure 4F). In thin section the white laminae were seen as small gypsum nodules displaying ameboid texture (Figure 5E). Anhydrite relics with jagged edges surrounded by granular gypsums are detected within the thin layer gypsums, showing dehydration and rehydration processes (Figure 5F).
In Baozang, gypsum laminae are mingled with mudstones and/or siltstones (Figure 4G). The bedding structure is distinct based on color banding (Figure 5G). Some parts of the gypsum laminae are replaced by nodular selenite (Figure 4H). In nodular selenite, swallowtail-shaped gypsum crystals (Figure 5H) and corroded anhydrite crystals (Figure 5I) are detected, suggesting a similar dehydration–rehydration process to that in Jinghong. Interstratified and vertical fractures (Figure 4H) are filled with satin spar gypsums (veined gypsums). In addition to those veined gypsums within laminae fractures, some wired gypsum veins are present in clayey or silty breccias (Figure 4I). The gypsum fibers are perpendicular or oblique to the surface of the wall rocks. Relatively long gypsum laths occur within clastic rocks, showing slightly curved features (Figure 4J). Microphotographs of gypsum laths show herringbone pattern (Figure 5J).
In Mengyejing, the underground potash deposit consists of rhythmically alternating clastic rocks and evaporites. The clastic rocks are composed of unconsolidated mudstones and siltstones. The chloride salts, namely, halite sylvite or carnallite are crosscutting or cementing most mudstones and siltstones. The layers of the orebody are dipping nearly vertically due to tectonic deformation (Figure 4K). The rock salt samples are primarily composed of halite, with trace amounts of euhedral anhydrites (Figure 5K) and sylvites (Figure 5L).

4.2. XRD Results

The mineral components are measured using XRD analyses. The result shows that gypsum samples in Lanping consist of approximately 90% gypsum and 10% calcite, with a trace amount of quartz. Two celestite-bearing samples in Lanping contain approximately 40% and 10% celestite, 55% and 90% calcite, respectively. Samples in Nuodeng consist exclusively of gypsum, except for sample LP-SM-G3 with a small amount of quartz and albite. The major mineral of samples in Jinggu are gypsum (90% to 100%), and subordinate amounts of calcite, dolomite, and magnesite (Table 1). Halite is the most abundant mineral in samples from Mengyejing, with NaCl content ranging from 65% to 100%. Anhydrites and gypsums are present as a minor constituent. Some samples contain a certain amount of carbonates and potash minerals (Table 1). Samples from Baozang are composed of nearly pure gypsums, with a trace amount of bassanite, carbonates, and quartz (Table 1).

4.3. Sr, S and O Isotopes

The 87Sr/86Sr ratios of all samples in the Lanping Basin range from 0.709406 to 0.710049, which are much higher than those of the Late Cretaceous seawater [22]. The celestite-bearing samples have slightly higher 87Sr/86Sr ratios compared with the gypsum samples (Table 2). The 87Sr/86Sr ratios of the gypsum samples in the Simao basin range from 0.708081 to 0.709548 (Jinggu: 0.708081 to 0.708792, Baozang: 0.708114 to 0.7.9548). There is considerable overlap between the 87Sr/86Sr ratios of Baozhang and Jinggu. The 87Sr/86Sr ratios of the rock salt samples range from 0.709717 to 0.710071, which are higher than those of gypsum samples in Jinggu and Baozang (Figure 6A).
The sulfate samples from Baozang and Jinggu in the Simao Basin have less variable δ34S values (mean 14.6‰, S.D. = 0.4, n = 37) than those from Lanping (mean 18.3‰, S.D. = 2.9, n = 4), Nuodeng (mean 10.0‰, S.D. = 0.5, n = 3), and Mengyejing (mean 11.25‰, S.D. = 3.07, n = 6) (Table 2, Figure 6B).
The δ18O values of all samples show scattered pattern: Baozang (mean 11.89‰, S.D. = 3.85, n = 35), Lanping (mean 20.0‰, S.D. = 2.81, n = 4), Nuodeng (mean 7.4‰, S.D. = 0.85, n = 2), Jinggu (mean 12.47‰, S.D. = 6.98, n = 3), Mengyejing (mean 7.2‰, S.D. = 4.38, n = 2) (Table 2, Figure 6C).

5. Discussion

The ages of the samples are constrained to be the Middle to Late Cretaceous (ca. 110 to 65 Ma). Albeit the uncertainty of the sedimentary ages, comparison between the S, O, and Sr isotope compositions of these samples with values of seawater [19,21,22] reveals the origin of those parent brines in which evaporite minerals were precipitated.

5.1. Sr Isotopes

The Sr isotope compositions of the evaporite minerals reflect the sources of Sr to the basin, together with possible interactions between the brines and rocks within the drainage basin [18]. The elevated 87Sr/86Sr ratios of rock salts in Mengyejing (Table 2) was very likely caused by the accumulation of radiogenic 87Sr due to high Rb/Sr ratios (Table 2) and/or continental waters with high 87Sr/86Sr ratios. The 87Sr/86Sr ratios of gypsums in halite crystal fall within those of chloride salts (halite, sylvite, and carnallite, 0.708697–0.710956, except two anomalous low values [1]) in the Mengyejing potash deposit. The Rb/Sr ratios of those chloride salts are much higher than those of gypsums [1], indicating that the salt minerals in the Mengyejing potash deposit were formed by recent recrystallization process, and high Rb contents of chloride salts have not accumulated sufficient radiogenic 87Sr to generate higher 87Sr/86Sr ratios compared with gypsums.
The influence of radiogenic 87Sr on gypsum samples was negligible because of the extremely low Rb/Sr ratios (Table 2). Thus, the Sr isotope composition of gypsum could represent the Sr isotopic signature of parent brine in which gypsum precipitated. The 87Sr/86Sr ratios of all gypsum samples shown in Table 2 and Figure 7 are higher than the range of coeval seawaters [22]. This is consistent with the conclusion that the 87Sr/86Sr ratios of evaporites in continental setting are generally higher than those of seawater [32]. Apparently, the parent brines were derived, at least partly, from continental water. The weathering of the Lincang granite (Figure 1) could have supplied dissolved components with high 87Sr/86Sr ratios. The 87Sr/86Sr ratios of biotite granite in Lincang range from 0.730006 to 0.743494, corresponding to an initial 87Sr/86Sr ratio range of 0.713566 to 0.728476 when granite formed during Triassic based on Rb/Sr ratios [33]. In addition to the Lincang granite, other regions may have provided weathering products with varying Sr isotope compositions. The Sr isotope compositions and Sr concentrations of those continental waters were unknown. We postulate that the continental freshwater had similar Sr concentration and Sr isotopic ratios to those of present river water. Noh et al. (2009) [34] presented Sr concentrations and isotope compositions of two major rivers enclosing the Lanping–Simao Basin: The Jinshajiang River, 0.33–11.46 μM, 87Sr/86Sr = 0.70891–0.71494, and the Lancang River, 0.28–6.73 μM, 87Sr/86Sr = 0.70888–0.72678. The low Sr concentrations of river waters necessitate a large amount of continental fluvial input to produce the elevated 87Sr/87Sr ratios of gypsums in the Lanping–Simao Basin.
The 87Sr/86Sr ratios of ankerites within the Mesozoic strata in the Lanping–Simao Basin range from 0.70874 to 0.71332 [35]. The brines in which those ankerites precipitated were thought to have been formed by circulation of basinal fresh waters. Sr was leached out from Mesozoic strata [35], thus the 87Sr/86Sr ratios of ankerites could represent those of the Mesozoic sedimentary rocks. Consequently, it is likely that the parent brine for forming evaporites could also have derived from adjacent clastic rocks to some extent.
As a whole, the Sr isotope compositions of gypsums in the Lanping Basin are higher than those of gypsums in the Simao Basin. Recent provenance studies show that the Late Cretaceous sediments from these basins have an overall S-directed paleocurrent that flowed from the Lanping Basin to the Simao Basin [36]. The Lanping Basin could have trapped more continental waters compared with the Simao Basin.

5.2. S Isotopes

The δ34S values of gypsum laminae samples in Baozang show a narrow range, from 13.4‰ to 15.2‰ (Table 2, Figure 8) which is consistent with those of Cretaceous seawater [19,21]. Wang et al. (2014a) [12] implied that there was a marine transgression during the Late Cretaceous based on geochemical, palaeogeographical, and paleomagnetic studies ([12] and references therein). The crystal of vein-shaped gypsum was corroded and dissolved by external fluids or internal waters from dehydration of gypsum (Figure 5I), indicating that vein-shaped gypsums had undergone dissolution and recrystallization process. The secondary veined gypsum samples in Baozang have similar S isotope compositions to those of bedded gypsum samples (Table 2), denoting that the sulfate-bearing fluids for forming the secondary veined gypsums mainly stemmed from the dissolution of bedded gypsums.
The δ34S values of rock salt samples in Mengyejing range from 8.0‰ to 15.5‰, which are slightly lower than those of gypsum samples near Mengyejing (Baozang). During evaporation, 34S and 18O are enriched in precipitated gypsum and relatively depleted in brines. Therefore, when a restricted basin is not supplied by open water, the progressive evaporation process would have resulted in reduced δ34S and δ 18O values of residual brine and subsequent precipitated gypsum, namely, reservoir effect [37]. Thus, the reduced δ34S values of sulfates in rock salt samples in Mengyejing was likely caused by reservoir effect. Besides, dissolved sulfates in continental waters with lower δ34S values could have contributed to the brine in the final stage of evaporation. The assemblage of predominant halite crystals with a trace amount of euhedral gypsum and sylvite crystal (Figure 5K,L) indicates a very saline stage during which both reservoir effect and continental input could result in the lowering of δ34S values. This process may have changed the δ34S values more efficiently because of the low sulfate concentration of brine in the final stage of evaporation.
The δ34S values of gypsum samples in Jinggu are consistent with those of gypsum samples in Baozang, indicating a similar marine origin due to the Cretaceous marine transgression. Gypsum laminae (Figure 4F) and amenoid microcrystalline gypsums (Figure 5E) suggest a likely primary origin. However, the anhydrite relics with surrounding gypsum crystals (Figure 5F) indicate that dehydration of gypsum and hydration of anhydrite cycle have occurred. The S isotopes of sulfates suggests that the dehydration–hydration process did not affect the isotopic signatures significantly.
In Lanping, δ34S values of two gypsum samples are 14.5‰ and 17.6‰, respectively; slightly higher than those of Cretaceous seawater and gypsum samples in the Simao Basin. Two celestite samples have δ34S values ranging from 20.5‰ to 20.7‰, which are much higher than those of gypsum samples. Reservoir effect and continental contribution could lower the δ34S values, which is not the case here. Therefore, the elevated δ34S values of gypsum and celestite samples in Lanping could have contributed to other factor(s), such as bacterial sulfate reduction (BSR). During BSR, the lighter isotopes 32S and 16O are preferentially metabolized by microorganisms, causing an enrichment of heavy isotopes 34S and 18O in the remaining sulfate [38]. Organic matters are widely distributed in the Jinding Pb-Zn deposit in Lanping area. In reducing environment, sulfates were reduced to sulfides. Pyrite is commonly developed in gypsums (Figure 5B). It was suggested that S2- in sulfides (mainly consist of sphalerite and galena) were generated by sulfate reduction [3] and resulted in 34S-enriched fluids. The euhedral celestite crystal (Figure 5C) could have been formed by 34S-enriched fluids in combination with Sr-bearing metal fluids. Gypsums and celestites are distributed within the Triassic marine sequence in Lanping area with δ34S values ranging from 15.3‰ to 17.5‰ [39]. It was possible that the recycling of Triassic evaporites could have contributed and affected the composition of S isotopes of evaporites formed in the non-marine setting during Cretaceous.
The reduced δ34S values of gypsum samples in Nuodeng were not controlled by BSR. It was not likely caused by reservoir effect either because it engenders negligible depletion of 34S in sulfates during gypsum precipitation stage [37]. Therefore, only continental input with isotopically light 32S could account for this result. The Jinding Pb-Zn deposit comprises a great amount of sulfide minerals, including sphalerite and galena. Approximately 600 million tons of Pb + Zn were eroded [39]. The sulfide minerals show a wide range of δ34S values, from −54.9‰ to +3.5‰ [39]. The δ34S values of sulfates formed via sulfide oxidation are generally equivalent to those of the parent sulfide minerals [40]. There is no or insignificant fractionation during the oxidation process of sulfide. Nuodeng is only 60 km to the south of Lanping. Weathering products of the Jinding Pb-Zn deposit could be easily transported from Lanping to Nuodeng. The re-oxidation of reduced sulfides with low δ34S values resulted in relatively low sulfate δ34S values in Nuodeng.
A giant marine evaporite deposit occurred within the Maha Sarakham Formation, the Khorat Basin, Thailand. Qu (1998) [10] suggested that the evaporites within the Lanping–Simao Basin have a close relationship with evaporites within the Khorat Basin based on sedimentary sequences comparison and salt mineral assemblages. The δ34S values of anhydrites intercalated with rock salt layers within the Maha Sarakham evaporite deposit range from 14.8‰ to 17.7‰ [41]. The δ34S values of layered anhydrite in Baozang are consistent with those of anhydrites in the Khorat Basin. Qin et al. (2020) [42] proposed a Cretaceous seawater recharge model that the paleoseawater flowed from Bangong–Nujiang Ocean (West Meso-Tethys Ocean) through the Qiangtang and Lhasa blocks to the Lanping–Simao Basin and the Khorat Basin. Alternatively, the paleoseawater could have derived from East Meso-Tethys Ocean and recharged the Lanping–Simao and Khorat Basins through Tengchong-Baoshan Blocks [42].

5.3. O Isotopes

The history of seawater δ18Osulfate is less well-defined compared with S and Sr isotope compositions [18]. Thus, the δ34S-δ18O relationships are presented for the comparison with S and O isotope values of Cretaceous seawater [19]. The global isotopic evolution through time of marine sulfates has been well documented worldwide. The oxygen isotopic compositions of sulfates from Mesozoic to present-day are within a range of approximately +10‰ to +15‰ [19]. The S vs. O isotope compositions of sulfates in the Lanping–Simao Basin are widely scattered, only a small part of samples has S vs. O isotope compositions overlapping those of seawater (Figure 9). The δ18O values of all samples show a more scattered and variable pattern compared with δ34S values (Figure 9). And the δ34S values do not co-vary with the δ18O values, indicating that different processes control the S and O isotopes of sulfate.
In Baozang, the narrow range of δ34S values suggests that the inflow of dissolved sulfates in the continental waters was insignificant. Because in general cases, sulfates from continental waters will add light sulfur and δ34S values decreases accordingly [37]. As discussed above, S isotope compositions of gypsum samples in Baozang denote a marine origin. S and O isotope compositions of marine sulfates are insensitive to minor non-marine contributions because seawater hosts much higher SO4 concentration than most freshwaters [43], and dissolution of sulfates results in little or negligible isotopic fractionation of S and O [19,44]. Thus, the variation of O isotope compositions of those gypsum samples was not controlled by inflow of continental dissolved sulfates and dissolution process. The scattered O isotope compositions could not either be accounted for by reservoir effect which fails to induce such a wide variation.
The changes in oxygen isotopic composition of sulfate are related to more complex processes than those affecting sulfur isotopes [45]. In a restricted basin, BSR process produced sulfides with relatively negative δ34S values and residual dissolved sulfates with positive δ34S values. The resulted sulfides from BSR diffused into shallow water and reoxidized to sulfates with the incorporation of O from water and/or molecular oxygen [45]. Sulfates formed by re-oxidation of sulfide would cause no fractionation on S but varied fractionation on 18O through the incorporation of dissolved oxygen and/or oxygen of hypersaline water [46]. In the presence of molecular oxygen, the δ18O value of the resulting sulfate oxidized by sulfide is considered to shift towards heavy values. Whereas, under anaerobic conditions, the oxidation of sulfide yields a sulfate with isotopically light δ18O values equal or very close to that of environmental water [45]. Moreover, the exchange of oxygen atoms of intermediate anions like SO32- and/or HSO3- complicates the oxidation processes that may affect the final O isotope composition of sulfate. The proportions of water-derived oxygen and molecular oxygen incorporated into sulfates during the re-oxidation process of sulfide were subject to environments ([47] and references therein). Mangalo et al. (2007) [48] performed an experiment which proved that the δ18O value of sulfate during BSR could be affected by isotope exchange with water. They supported a fractionation mechanism of re-oxidation of sulfite to sulfate rather than that of reaction from sulfate-enzyme complex back to sulfate ([48] and references therein).
At the water-sediment interface, the constant cycling between sulfate reduction and sulfide reoxidation has no net effect on the burial of reduced sulfur, but greatly affects the oxygen isotope composition of marine sulfate (δ18OSO4; [49] and references therein). Therefore, this redox cycle of sulfur only affects the sulfate O-isotope ratio significantly, but not the sulfate S-isotope ratio [50,51]. The S vs. O pattern of sulfates in Baozang is consistent with that produced by sulfate reduction and sulfide re-oxidation process.
Organic matters were widely distributed in the Lanping–Simao Basin, usually presented as debris (Lanping, Nuodeng, Baozang, and Mengyejing, Figure 4L) and/or banded layer (Lanping and Jinggu) [52]. It was very likely that BSR occurred under anoxic conditions and sulfates were reduced to sulfides. The sulfides were then re-oxidized in the “red bed” environment. This process causes little variation on S isotope compositions if there was no extraneous S. Whereas, reduction-re-oxidation process changes the O isotope compositions of sulfates drastically under different environments.
The S-O isotope compositions of sulfates in rock salt samples from Mengyejing are located to the lower left of marine isotope compositions (Figure 9). This pattern could have been the result of reservoir effect and/or reduction-re-oxidation process. It is practically impossible to determine what process(es) was predominant.
The S-O isotope compositions of sulfates from Lanping are located to the upper right of marine isotope compositions (Figure 9), which are similar to those of Messinian gypsums in the Nijr Basin [53]. The elevated δ34S and δ18O values resulted by redox cycling involving BSR and re-oxidation in stratified brines [53]. BSR produced a great amount of S2- which incorporated into metal cations and formed metal sulfides in Lanping. The residual sulfates would be enriched in 34S and 18O.

5.4. The Origin of Evaporites and Paleoenvironmental Significance

Although Sr isotope compositions of all samples and S isotope compositions of samples from Nuodeng corroborate a major continental contribution to the formation of the evaporites, S isotope compositions of sulfates from Lanping, Jinggu, and Baozang indicate a marine origin. Trace elements of chloride salts in the Mengyejing potash deposit also suggested a marine contribution [15]. In conclusion, the parent brine in which evaporite minerals precipitated were derived from a mixture of seawater and continental waters.
In Baocang, the narrow range of δ34S values vs. wide range of 87Sr/86Sr (Figure 10) indicate that continental input imposes a greater effect on Sr than on S. The seawater dominated in terms of S isotopes, whereas continental input controlled the Sr isotopes. In Jinggu, the 87Sr/86Sr ratios vs. δ34S values show a similar pattern to that of evaporites in Baozang, which suggest a similar origin and formation process. In Mengyejing, the 87Sr/86Sr ratios are relatively steady but δ34S values show a large variation. This pattern indicates that reservoir effect controlled the S isotopes which is consistent with preceding discussion. In Nuodeng, the low δ34S values, high 87Sr/86Sr ratios, and limited distribution of S vs. Sr suggest that the parent brines were only controlled by continental waters derived from weathering. In Lanping, the positive relationship between the 87Sr/86Sr ratios and the δ34S values indicates that the formation of evaporites could have been controlled by continental influx, recycle of older evaporites, and BSR synergistically.
The δ18O values, δ34S values, and 87Sr/86Sr ratios of gypsum laminae samples from a single section in Baozang (Figure 11) show that: (1) the 87Sr/86Sr ratios fluctuate more drastically than δ34S values; (2) although the 87Sr/86Sr ratios are fluctuant, a roughly increasing trend is identifiable from base to top; (3) the δ34S values yields a mirror image pattern of 87Sr/86Sr ratios, i.e., a decreasing trend in δ34S values from base to top; (4) δ18O values pattern is scattered and not related to Sr and S isotopes.
Kristall et al. (2018) [54] suggested that continental input dominates Sr and S isotopic signature when 87Sr/86Sr ratios and δ34S values shift in opposition. In this section, the decreasing trend of δ34S values in combination with the increasing trend of 87Sr/86Sr ratios suggest that continental input played an increasingly significant role with the progressive evaporation of brines. We suggest that the major waterbody for forming the evaporites were remnant seawater due to marine transgression. In the late stage of evaporation, continental waters played a more important role and predominated with respect to isotope signatures.
As discussed above, redox conditions, O isotope compositions of parent brine, and molecular O could determine the final O isotope compositions of dissolved sulfate, thus complicating the O isotope compositions of precipitated sulfates. The greatly varied S and O isotope compositions of gypsums in Messinian evaporites [55] may result from repeated processes of evaporite dissolution and re-precipitation as well as from bacterial activities during redox variations [45,56]. The wide variation of O isotopes compositions of gypsums in such a short section (15 m) in Baozang also suggests a drastic sedimentary environmental change during evaporite deposition. S and O isotope compositions of gypsums in Jinggu have a similar pattern to that of in Baozang, denoting a similar process.

6. Conclusions

(1)
The 87Sr/86Sr ratios of sulfate samples (including gypsum and celestite) in the Lanping–Simao basin are higher than those of contemporaneous seawater, indicating continental contribution; elevated 87Sr/86Sr ratios of rock salt samples were caused by continental contribution and radiogenic 87Sr accumulation.
(2)
The δ34S values of gypsum samples in the Simao basin are consistent with those of Cretaceous seawater, suggesting a marine origin; the reduced δ34S values of rock salts samples might be due to reservoir effect and continental contribution; the relatively higher δ34S values of sulfates in Lanping were likely caused by BSR or/and recycling of Triassic sulfates; the low δ34S values of gypsums in Nuodeng was caused by re-oxidation of weathering sulfides with negative S isotope compositions.
(3)
Sr and S isotope compositions of gypsum samples in a single section in Baozang suggest that continental water played an increasingly significant role with the evaporation of brines.
(4)
The O isotope compositions of evaporite salts showing more complex pattern compared with Sr and S, indicating that sulfate reduction or/and re-oxidation processes prevailed during deposition.
In summary, the parent brines in which evaporites precipitated within the Mesozoic “red bed” of the Lanping–Simao Basin mainly stemmed from remnant seawater due to marine transgression and continental water. During the evaporation, the paleoenvironment changed dramatically based on O isotopic compositions of sulfates, and continental water played an increasingly important role compared with remnant seawater.

Author Contributions

L.S. and L.W. wrote the paper. L.W., C.L., and Y.Z. investigated and collected the samples. L.W. and L.S. obtained and processed the chemical, isotopic, XRD, SEM data. All authors have read and agreed to the published version of the manuscript.

Funding

This work is supported by the National Key Project for Basin Research of China (2011CB403007), the National Natural Science Foundation of China (41572067, 91855104, 41802111).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

We are grateful to Jianfu Fan for his assistance in sampling and Hongwei Li, Changfu Fan, and Bin Hu for his data processing.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 3. Sampling sections/sites from Baozang, Lanping, Nuodeng, Jinggu, and Mengyejing.
Figure 3. Sampling sections/sites from Baozang, Lanping, Nuodeng, Jinggu, and Mengyejing.
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Figure 4. Characteristics of evaporites in the Lanping–Simao Basin. (A) Bedded gypsum layers in Lanping; (B) gypsum alabasters, Lanping; (C) gypsum veins within clastic rocks, Nuodeng; (D) satin spar gypsums, Nuodeng; (E) gypsum laminae, Jinggu; (F) millimetric gypsum layers (light color) interbedded with calcareous layer (dark grey color), Jinggu; (G) gypsum sections in Baozang; (H) gypsum laminae coexisting with selenite crystals, Baozang; (I) gypsum veins within mudstone breccias, Baozang; (J) satin spar gypsums intercalated with clastic rocks; (K) bedded rock salts in underground mine lane from Mengyejing; (L) organic matters within gypsum layers, adjacent to Mengyejing.
Figure 4. Characteristics of evaporites in the Lanping–Simao Basin. (A) Bedded gypsum layers in Lanping; (B) gypsum alabasters, Lanping; (C) gypsum veins within clastic rocks, Nuodeng; (D) satin spar gypsums, Nuodeng; (E) gypsum laminae, Jinggu; (F) millimetric gypsum layers (light color) interbedded with calcareous layer (dark grey color), Jinggu; (G) gypsum sections in Baozang; (H) gypsum laminae coexisting with selenite crystals, Baozang; (I) gypsum veins within mudstone breccias, Baozang; (J) satin spar gypsums intercalated with clastic rocks; (K) bedded rock salts in underground mine lane from Mengyejing; (L) organic matters within gypsum layers, adjacent to Mengyejing.
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Figure 5. Photomicrographs of the evaporite minerals within the Mengyejing Formation. (A) ameboid and rhomboidal gypsums, Lanping, cross-polarized light (CPL); (B) pyrite crystals within gypsums, Lanping, scanning electron microscopy (SEM) image; (C) euhedral celestite crystal within gypsums, Lanping, SEM image; (D) aligned gypsum fibers, Nuodeng, CPL; (E) ameboid gypsums, Jinggu, CPL; (F) anhydrite relics with surrounding gypsum grains, Jinggu, CPL; (G) alternating microcrystalline gypsum layers and calcareous or/and silty layers, Baozang; (H) euhedral selenite crystals, Baozang, CPL; (I) anhydrite relics with corroded features coexisting with microcrystalline gypsums, Baozang, CPL; (J) aligned gypsum laths with herringbone features, Baozang, CPL; (K) euhedral anhydrite crystals within halites, Mengyejing, CPL; (L) euhedral sylvite crystals on the surface of halites, Mengyejing, SEM image.
Figure 5. Photomicrographs of the evaporite minerals within the Mengyejing Formation. (A) ameboid and rhomboidal gypsums, Lanping, cross-polarized light (CPL); (B) pyrite crystals within gypsums, Lanping, scanning electron microscopy (SEM) image; (C) euhedral celestite crystal within gypsums, Lanping, SEM image; (D) aligned gypsum fibers, Nuodeng, CPL; (E) ameboid gypsums, Jinggu, CPL; (F) anhydrite relics with surrounding gypsum grains, Jinggu, CPL; (G) alternating microcrystalline gypsum layers and calcareous or/and silty layers, Baozang; (H) euhedral selenite crystals, Baozang, CPL; (I) anhydrite relics with corroded features coexisting with microcrystalline gypsums, Baozang, CPL; (J) aligned gypsum laths with herringbone features, Baozang, CPL; (K) euhedral anhydrite crystals within halites, Mengyejing, CPL; (L) euhedral sylvite crystals on the surface of halites, Mengyejing, SEM image.
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Figure 6. Histograms showing distribution of (A) 87Sr/86Sr ratios, (B) δ34S values, and (C) δ18O values in evaporitic minerals from the Lanping–Simao Basin.
Figure 6. Histograms showing distribution of (A) 87Sr/86Sr ratios, (B) δ34S values, and (C) δ18O values in evaporitic minerals from the Lanping–Simao Basin.
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Figure 7. Comparison between 87Sr/86Sr ratios of evaporite minerals in Lanping–Simao Basin and contemporaneous seawater (data from [22]).
Figure 7. Comparison between 87Sr/86Sr ratios of evaporite minerals in Lanping–Simao Basin and contemporaneous seawater (data from [22]).
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Figure 8. Comparison between δ34S values of sulfates in the Lanping–Simao Basin and contemporaneous seawater (data from [21]).
Figure 8. Comparison between δ34S values of sulfates in the Lanping–Simao Basin and contemporaneous seawater (data from [21]).
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Figure 9. S-O isotopic compositions of evaporites in the Lanping–Simao Basin. The shaded box represents S-O isotopic compositions of marine gypsums of the Late Cretaceous period [19]. The dark black symbols indicate layered gypsum samples, whereas grey symbols indicate veined gypsum samples.
Figure 9. S-O isotopic compositions of evaporites in the Lanping–Simao Basin. The shaded box represents S-O isotopic compositions of marine gypsums of the Late Cretaceous period [19]. The dark black symbols indicate layered gypsum samples, whereas grey symbols indicate veined gypsum samples.
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Figure 10. Sr-S isotopic compositions of evaporites in the Lanping–Simao Basin. The dark black symbols indicate layered gypsum samples, whereas grey symbols indicate veined gypsum samples.
Figure 10. Sr-S isotopic compositions of evaporites in the Lanping–Simao Basin. The dark black symbols indicate layered gypsum samples, whereas grey symbols indicate veined gypsum samples.
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Figure 11. Variations of δ18O values, δ34S values, and 87Sr/86Sr ratios of gypsum samples from the section in Baozang. Shaded area: δ18O values [19], δ34S values [21], and 87Sr/86Sr ratios [22] of contemporaneous marine sulfates.
Figure 11. Variations of δ18O values, δ34S values, and 87Sr/86Sr ratios of gypsum samples from the section in Baozang. Shaded area: δ18O values [19], δ34S values [21], and 87Sr/86Sr ratios [22] of contemporaneous marine sulfates.
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Table
Table 1. Semi-quantitative X-ray diffraction (XRD) analyses of samples from different locations.
Table 1. Semi-quantitative X-ray diffraction (XRD) analyses of samples from different locations.
LocationSample IDAgeFormationCompositions, Based on XRD AnalysesLithology
LanpingLP-SM-G5late Cretaceous?Yunlong90% gypsum, 10% calcite, and trace quartzGypsum laminae
LanpingLP-SM-G6late Cretaceous?Yunlong55% calcite, 40% celestite, 5% quartzGypsum laminae
LanpingLP-SM-G7late Cretaceous?Yunlong90% gypsum, 10% calcite, and trace quartzGypsum laminae
LanpingLP-SM-G8late Cretaceous?Yunlong90% calcite, 10% celestiteGypsum laminae
NuodengLP-SM-G1late Cretaceous?Yunlong100% gypsumGypsum veins
NuodengLP-SM-G2late Cretaceous?Yunlong100% gypsumGypsum veins
NuodengLP-SM-G3late Cretaceous?Yunlong93% gypsum, 3% quartz, and trace albiteGypsum veins
JingguJG-G1late CretaceousMengyejing100% gypsumGypsum laminae
JingguJG-G2late CretaceousMengyejing95% gypsum, 5% calciteGypsum laminae
JingguJG-G3late CretaceousMengyejing90% gypsum, 5% calcite, 5% magnesiteGypsum laminae
JingguJG-G6late CretaceousMengyejing90% gypsum, 20% dolomite,Gypsum laminae
MengyejingG1late CretaceousMengyejingnearly 100% halite, trace gypsum
MengyejingG2late CretaceousMengyejingnearly 100% halite, trace gypsumLayered rock salts
MengyejingG3late CretaceousMengyejing95% halite, 5% anhydriteLayered rock salts
MengyejingG4late CretaceousMengyejing70% halite, 10% anhydrite, 10% quartzLayered rock salts
MengyejingG5late CretaceousMengyejing65% halite, 15% quartz, 10% anhydrite, 10% dolomiteLayered rock salts
MengyejingG6late CretaceousMengyejing85% halite, 15% sylvite, trace anhydriteLayered rock salts
BaozangJBZ-F1late CretaceousMengyejing100% gypsumGypsum veins
BaozangJBZ-F2late CretaceousMengyejing100% gypsumGypsum veins
BaozangJBZ-F3late CretaceousMengyejing100% gypsumGypsum veins
BaozangJBZ-F4late CretaceousMengyejing85% gypsum, 15% bassaniteGypsum veins
BaozangJBZ-F5late CretaceousMengyejing100% gypsumGypsum veins
BaozangJBZ-G02late CretaceousMengyejing98% gypsum, trace quartzGypsum laminae
BaozangJBZ-G03late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G04late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G05late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G06late CretaceousMengyejingnearly 100% gypsum, trace quartzGypsum laminae
BaozangJBZ-G07late CretaceousMengyejingnearly 100% gypsum, trace bassaniteGypsum laminae
BaozangJBZ-G08late CretaceousMengyejingnearly 100% gypsum, trace quartzGypsum laminae
BaozangJBZ-G09late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G10late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G11late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G12late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G13late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G14late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G15late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G16late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G17late CretaceousMengyejingnearly 100% gypsum, trace quartzGypsum laminae
BaozangJBZ-G18late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G19late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G20late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G21late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G22late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G23late CretaceousMengyejing95% gypsum, 5% calciteGypsum laminae
BaozangJBZ-G24late CretaceousMengyejing95% gypsum, 5% quartzGypsum laminae
BaozangJBZ-G25late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G26late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G27late CretaceousMengyejing98% gypsum, trace quartzGypsum laminae
BaozangJBZ-G28late CretaceousMengyejing95% gypsum, 5% dolomiteGypsum laminae
BaozangJBZ-G29late CretaceousMengyejing98% gypsum, trace calciteGypsum laminae
BaozangJBZ-G30late CretaceousMengyejingnearly 100% gypsum, trace quartzGypsum laminae
BaozangJBZ-G31late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G32late CretaceousMengyejing100% gypsumGypsum laminae
BaozangJBZ-G33late CretaceousMengyejing100% gypsumGypsum laminae
Table
Table 2. Sr, S, and O isotope compositions of evaporite samples within the Lanping–Simao Basin.
Table 2. Sr, S, and O isotope compositions of evaporite samples within the Lanping–Simao Basin.
LocationSample IDδ18O‰δ34SV-CDT87Sr/86SrRb (ppm)Sr (ppm)Rb/Sr
LanpingLP-SM-G521.614.50.709622 ± 0.0000051.3435720.0003751
LP-SM-G618.420.50.710049 ± 0.0000070.678>5000<0.0001356
LP-SM-G723.117.60.709845 ± 0.0000080.48346990.0001028
LP-SM-G81720.70.710039 ± 0.0000052.05>5000<0.00041
NuodengLP-SM-G16.810.20.709406 ± 0.0000132.591920.0134896
LP-SM-G2-9.50.709438 ± 0.0000073.042930.0103754
LP-SM-G3810.40.709475 ± 0.0000062.716030.0044942
jingguLP-SM-G1-14.40.708648 ± 0.0000071.151860.0061828
LP-SM-G26.914.40.708081 ± 0.0000063.4735730.0009712
LP-SM-G320.315.10.708712 ± 0.0000083.496790.0051399
LP-SM-G610.213.50.708792 ± 0.00001012.43080.0402597
MengyejingG1-12.20.709717 ± 0.00000715.529.40.5272109
G2-15.50.710058 ± 0.0000060.2581520.0016974
G3-8.80.710019 ± 0.0000064.732270.020837
G44.180.709881 ± 0.00000722.51000.225
G510.39.10.709937 ± 0.00000537.11630.2276074
G6-13.90.710071 ± 0.00000511.655.40.2093863
BaozangJBZ-F16.6150.709268 ± 0.0000060.4581440.0031806
JBZ-F26.814.80.709225 ± 0.0000060.3141540.002039
JBZ-F37.7150.709548 ± 0.0000050.3631610.0022547
JBZ-F47.414.80.708794 ± 0.0000050.5251780.0029494
JBZ-F5-14.30.709074 ± 0.0000051.255280.0023674
JBZ-G0215.115.20.709148 ± 0.0000093.192630.0121293
JBZ-G0313.614.90.70855 ± 0.0000110.8132220.0036622
JBZ-G0416.814.90.708755 ± 0.0000103.472320.0149569
JBZ-G059.114.90.708152 ± 0.0000170.9622360.0040763
JBZ-G0610.315.10.708513 ± 0.00002022360.0084746
JBZ-G0710.214.90.708114 ± 0.0000100.1543190.0004828
JBZ-G0810.514.90.708918 ± 0.0000119.531350.0705926
JBZ-G0916.1150.708322 ± 0.0000131.052620.0040076
JBZ-G101414.70.708242 ± 0.0000090.1591950.0008154
JBZ-G1113.414.50.708625 ± 0.0000111.851660.0111446
JBZ-G129.714.60.70833 ± 0.0000100.0782340.0003333
JBZ-G13914.70.708538 ± 0.0000161.052180.0048165
JBZ-G1413.314.20.709253 ± 0.0000168.932790.0320072
JBZ-G157.114.60.708693 ± 0.0000181.712020.0084653
JBZ-G16 14.30.708672 ± 0.000013 #DIV/0!
JBZ-G1715.714.80.708643 ± 0.00002626.91680.160119
JBZ-G188.913.90.708713 ± 0.0000133.942460.0160163
JBZ-G1914.814.60.7086 ± 0.0000110.5173120.0016571
JBZ-G2017.314.70.708807 ± 0.0000170.5063210.0015763
JBZ-G211014.40.708439 ± 0.0000100.7574510.0016785
JBZ-G221013.60.708346 ± 0.0000110.1984760.000416
JBZ-G231314.50.708584 ± 0.0000090.3215140.0006245
JBZ-G248.414.60.708523 ± 0.000012104850.0206186
JBZ-G2515.714.10.708897 ± 0.0000130.2625510.0004755
JBZ-G269.114.60.709085 ± 0.0000131.632480.0065726
JBZ-G2711.314.70.709174 ± 0.000014102840.0352113
JBZ-G289.414.30.709184 ± 0.0000103.613020.0119536
JBZ-G2912.713.40.709128 ± 0.0000061.893660.0051639
JBZ-G3018.414.30.709053 ± 0.00000512.24030.030273
JBZ-G3123.714.20.708704 ± 0.0000061.214450.0027191
JBZ-G321014.20.709038 ± 0.0000062.252770.0081227
JBZ-G331114.10.708781 ± 0.0000051.474910.0029939
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Shen, L.; Wang, L.; Liu, C.; Zhao, Y. Sr, S, and O Isotope Compositions of Evaporites in the Lanping–Simao Basin, China. Minerals 2021, 11, 96. https://doi.org/10.3390/min11020096

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Shen L, Wang L, Liu C, Zhao Y. Sr, S, and O Isotope Compositions of Evaporites in the Lanping–Simao Basin, China. Minerals. 2021; 11(2):96. https://doi.org/10.3390/min11020096

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Shen, Lijian, Licheng Wang, Chenglin Liu, and Yanjun Zhao. 2021. "Sr, S, and O Isotope Compositions of Evaporites in the Lanping–Simao Basin, China" Minerals 11, no. 2: 96. https://doi.org/10.3390/min11020096

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