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Running title: Discovery of cosmic spherules from the Mesoproterozoic strata in Beijing

Discovery of cosmic spherules from the Mesoproterozoic strata and

its significance—In case of the Ming Tombs area, Beijing

SONG Tianrui 1

, ZHENG Ning1*

, LIU Yongqing1, KUANG Hongwei

1, PENG Nan

1, LI Chao

2,

YAN Qinggao3, TANG Jigang

4, GAO Linzhi

1, ZHU Zhicai

1, XIA Xiaoxu

1 and WANG Yuchong

1

1 Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China 2 National Research Center of Geoanalysis, Beijing 100037, China 3 Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093,

Yunnan, China 4 Beijing General Research Institute of Mining and Metallurgy, Beijing 100044, China

Abstract: This study covers cosmic spherules derived from the Mesoproterozoic Dahongyu Formation in the

Ming Tombs area, Beijing. The cosmic spherules include iron oxide cosmic spherules, carbonaceous chondrites,

and atomic iron ―steely bead‖-shaped cosmic spherules. The mineral assemblage of silicon carbide, forsterite,

zircon, and glass spherules and fragments were picked from melt-silicified carbonate of the Mesoproterozoic

Dahongyu Formation (ca. 1625 Ma). Cosmic spherule assemblages are solely discovered from sedimentary rocks

in China. Platinum group elements (PGE) were determined for the first time in cosmic spherules and associated

minerals. PGE comparative observation between meteorite and cosmic spherules is presented in this study. It is

recognized that an extraterrestrial meteorite impact event might have occurred in the Dahongyu Stage. The main

evidence is a large number of iron cosmic spherules in silicified oncolitic limestone, and associated cosmic silicon

carbide, glass spherules, and fragments, as well as the presence of forsterite. The impact-volcanic crater is

characteristic of a big black shale block dropped into the bended silicified limestone.

Key words: cosmic spherules, carbonaceous chondrite, meteorite PGE, Proterozoic strata, Beijing, impact event

1 Introduction

Sorby (1864) is the earliest study of cosmic dust particles—known for over a century (Gooding and Keil, 1981). Yeet et al. (1964) reported the discovery of cosmic spherules from the Yanshan Mountain, north China. Ouyang (1968) studied the origin of cosmic dust particles and the relation between extraterrestrial impact and bio-extinction. Song et al. (1991) reported the wide distribution of many cosmic spherules from Proterozoic sedimentary rocks in north China along the east to west transect from Taoyuan, Luanxian, to Jixian, Hebei Province, and up to the Ming Tombs area, Beijing (Song et al., 1991). Li et al. (1986, 1992) discovered cosmic spherules from the Precambrian metamorphosed strata of Inner Mongolia. During the 30

th International Geological Congress 1996, Beijing, many

participants from different countries visited the Mesoproterozoic sedimentary strata of the Ming Tombs area, Beijing, while discussing the Proterozoic sedimentary facies and environments as well as cosmic spherules in-situ (Song and Einsele, 1996). Detail discussion of cosmic spherules of the Mesoproterozic cosmic spherules of the Ming Tombs area was reported later (Song et al., 2007a; Song, 2007b). A large meteorite shower occurred on May 25, 1971 and March 8, 1976 in Jilin Province of China, and a series of reports were issued about this event (Liu et al., 1983; Begemann et al., 1985; Liet al., 2011). Furthermore, there are also reports on cosmic spherules from the modern sediments of Zedan, Tibet (Liang et al., 1982) and chondrites (L. Group) in Suizou, Hubei Province (Hou et al., 1988). Chondrites in Juancheng have been recently reported to have fallen (Cheng et al., 1998), and cosmic spherules in the Jinshitan scenic area of Dalian City (Song et al., 2011) have been reported as well.

This study discusses three types of cosmic spherules of the Dahongyu Formation, Ming Tombs area, Beijing—iron oxide cosmic spherules, carbonaceous chondrites, and atomic iron ―steely bead‖-shaped spherules, as well as their associated heavy minerals.

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10.1111/1755-6724.14343.

https://doi.org/10.1111/1755-6724.14343

https://doi.org/10.1111/1755-6724.14343

https://doi.org/10.1111/1755-6724.14343

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Fig. 1. (a) Geological map sketch of the Ming Tombs District, (b) Proterozoic stratigraphy column, and (c)

Chondrite-normalized distribution patterns. 1-archean gneiss; 2-clastic rocks; 3-sandstone with cross bedding; 4-carbonate rocks; 5-alkaline volcanic rocks; 6-pisolitic molten

silicified rock (silicon carbide, forsterite, zircon, and glass spherule-bearing rock); 7-molten flexible folding brecciated silicified rock

(iron cosmic spherule-bearing rock); 8-black shale; 9-unconformity; 10-impact volcanic crater; 11-Mesozoic volcanic assemblage;

12-Mesozoic granites.

Ar-Archean; Pt2-Mesoproterozoic; Pt1-Neoproterozoic; Chc-ChangzhougouFm.; Chch-Chuanlinggou Fm.; Cht-Tuanshanzi Fm.;

Chd-Dahongyu Fm.; Jxg-Gaoyuzhuang Fm.; Jxy-Yangzhuang Fm.; Jxw-Wumishan Fm.; Jxh-Hongshuizhuang Fm.; Jxt-Tieling Fm.;

Jxx-Xiamaling Fm.; Qbch-Changlongshan Fm.; Qbj-Jingeryu Fm.; Q-Quaternary; MzG-Mesozoic granite; MzV-Mesozoic volcanic

rocks.

Sil: cosmic spherules-bearing silicified rock; Pho: overly phonolitictuffaceous rock; Tuf: tuff; Onc: silicified oncolite; Qtz: quartz; REQ:

re-crystalline quartz; Syn: syneresis structure on phonolite surface; Tuf: tuffaceous material; Sa: sanidine; Srl: Schorl veinlet; Cro: cross

beddin; Qtz: quartz; Pth: perthite.


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Table 1* Chemical composition data of phonolites, silicified rocks and sandstones of the Dahongyu Formation in the Ming Tombs area, Beijing.

Sample Rocks wB/% wB/10

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SiO2 Al2O3 CaO Fe2O3 FeO K2O MgO MnO Na2O P2O5 TiO2 CO2 H2O+ LOI V Li

MT-8 Phonolite 74. 91 11. 47 0. 15 1. 21 1. 29 9. 12 1. 04 0. 03 0. 13 0. 09 0. 25 0. 00 0. 09 0. 56 53. 7 25. 9

1516-3 Sandstone 99. 01 0. 63 0. 06 <0. 01 0. 07 0. 19 0. 06 <0. 01 <0. 01 0. 03 0. 03 0. 00 0. 08 0. 14 2. 11 2. 12

1516-2 Silicified rock 2 78. 09 12. 47 0. 07 0. 53 0. 14 6. 43 0. 13 0. 05 1. 55 0. 01 0. 09 0. 36 0. 74 0. 78 4. 16 19. 7

1516-1 Silicified rock 1 77. 55 13. 28 0. 08 0. 41 0. 22 4. 69 0. 13 0. 02 3. 44 0. 01 0. 10 0. 18 0. 60 0. 71 1. 85 8. 09

Sample wB/10

-6

Be Sc Cr Co Ni Cu Pb Zn Ba Ga Rb Sr Mo In Cs Tl Th

MT-8 1. 29 3. 44 25. 3 4. 05 6. 61 1. 85 15. 0 48. 9 768 13. 6 172 139 0. 45 <0. 05 5. 01 0. 77 14. 9

1516-3 0. 39 0. 25 3. 33 0. 30 0. 83 0. 90 2. 38 2. 52 47. 8 1. 15 6. 34 10. 4 0. 29 <0. 05 0. 12 <0. 05 1. 71

1516-2 2. 51 1. 68 1. 30 0. 46 3. 45 4. 73 24. 1 35. 4 216 16. 4 214 54. 8 0. 78 <0. 05 2. 96 1. 11 18. 08

1516-1 2. 53 1. 26 1. 04 0. 37 1. 29 1. 43 13. 8 18. 7 148 15. 8 141 50. 0 0. 49 <0. 05 2. 16 0. 76 18. 12

Sample wB/10

-6

U Nb Ta Zr Hf Sb Ti W As La Ce Pr Nd Sm Eu Gd Tb

MT-8 0. 76 12. 8 0. 76 308 8. 93 0. 25 1502 0. 91 1. 52 29. 7 79. 3 8. 47 33. 9 6. 73 1. 27 4. 78 0. 62

1516-3 0. 87 1. 13 0. 10 39. 8 1. 44 0. 12 167 0. 16 0. 93 7. 71 12. 1 1. 63 5. 36 0. 69 0. 12 0. 91 0. 15

1516-2 3. 54 13. 9 1. 00 87. 9 4. 00 0. 26 551 2. 45 2. 17 26. 1 43. 2 3. 93 11. 2 1. 55 0. 22 1. 21 0. 15

1516-1 3. 64 14. 9 1. 01 90. 5 3. 98 0. 33 602 1. 13 0. 72 24. 5 41. 2 3. 74 10. 5 1. 33 0. 19 0. 98 0. 14

Sample wB/10

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Th/Sc Cr/Th La/Sc Cr/Ni LaN/SmN GdN/YbN LaN/YbN δEu Dy Ho Er Tm Yb Lu B Se Y

MT-8 3. 26 0. 60 1. 59 0. 26 1. 46 0. 23 150 0. 06 16. 2 4. 33 1. 7 8. 63 3. 83 2. 85 2. 71 13. 74 0. 65

1516-3 0. 96 0. 20 0. 59 0. 09 0. 58 0. 09 5. 81 0. 04 6. 69 6. 84 1. 96 30. 84 4. 01 7. 21 1. 3 8. 97 0. 46

1516-2 0. 89 0. 20 0. 58 0. 12 0. 84 0. 15 22. 9 0. 06 6. 58 10. 76 0. 07 15. 54 0. 38 10. 87 1. 92 16. 88 0. 47

1516-1 0. 84 0. 17 0. 59 0. 13 0. 91 0. 15 17. 0 0. 04 6. 70 14. 38 0. 06 19. 44 0. 81 11. 9 0. 89 18. 19 0. 49

* Data analysis by National Research Center of Geoanalysis, Beijing.


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2 Geological Background of the Ming Tombs area

The Ming Tombs area is situated 50 km outside of central Beijing, in the Changping District. Study of the geology of this area has lasted for many years (Song and Gao, 1985b; Song et al., 1991, 2000; Song and Zhu, 2013). There is a complete section of the Mesoproterozoic strata outcrop (Fig. 1a). The Dahongyu Formation is the host rock of the cosmic spherules site at the Tailing scenic spot (Fig.1b).

There are different opinions about the geo-age of the boundary between the Archean strata and Proterozoic strata in the Ming Tombs district (Wan et al., 2003; Song et al., 2014); however, the geological age ca.1625 Ma of the Dahongyu Formation has been approved (Lu and Li, 1991; Gao et al., 2008; Li et al., 2011). There is a report of ―the world’s oldest micrometeorites‖ from the 1400 Ma Satakunta Formation, Finland (Deutsch et al., 1998; Kettrup et al., 1999). In fact, the Dahongyu Formation is 225 Ma older than the Satakunt Formation.

The outcrop of tuffaceous phonolite (Pho) and silicified rock (Sil) shows a normal contact relation with each together (Fig. 1c). It is estimated that more than two million iron cosmic spherules are included in this field outcrop (Fig. 1c).

The host rock of cosmic spherules is silicified oncolitic limestone, in which algal filament remains have been discovered (Song and Gao, 1985a, 1987; Song, 2007b). In the field profile ascending ward, there are molten flexible folding brecciated silicified rocks, phonolitic tuffaceous volcanic rocks, and feldspar quartz sandstones (Figs. 1e, g, and j), and their microscopic figures demonstrated their original situation (Fig. 1f, h, and k): iron cosmic spherules bearing rock (1516-1); pisolitic silicified rock: silicon carbide, forsterite, zircon glass spherules, and glass fragments bearing rock (1516-2); alkaline volcanic-phonolite (MT-8); and coarse sandstone overlying on unconformity surface (1516-3) (see Fig 1b). There is a Eu-depletion diagram showing inheritance characteristics of rare earth elements (REE) between volcanic phonolite and silicified rock, as well as sandstone (Fig. 1d). The characteristics of sandstone, phonolitictuffaceous rock, and silicified oncolitic limestone were tested by macroscopic, microscopic, and chemical analyses of K, Ir, U, and Th. It is important to point out that a schorl veinlet (Fig. 1i) is injected into the phonolitic tuffaceous rock from melt-silicified oncolitic limestone, which perhaps indicates super-high-temperature vaporization and high pressure from impact shock, because black tourmaline always presents itself in biotite granite or pegmatite in continent-margin depression environments (Mao et al., 1990). However, the Dahongyu Formation was formed in a shallow marine environment characterized by sedimentary macroscopic and microscopic facies, such as bedded parallel pellets with partial herringbone structures, showing a tidal environment (Song et al., 2014) (Fig. 1e); syneresis structure on a volcanic bed surface, illustrating sea water shrinkage in a shallow marine environment (Fig. 1H); and gentle-angle cross-stratification structures in sandstones, suggesting a coastal area environment (Fig. 1j).

The outcrop of tuffaceous phonolite (Pho) and silicified rock (Sil) shows a normal contact relation with each other (Fig. 1c). There are more than two million iron cosmic spherules that have been found in silicified rocks, including this field outcrop, as well as metallic mini-uranium grains (< 5 µm), atomic or element iron, monazite, and zircon crystals by electron microscopy. In particular, some injected schorl fine veinlets, transforming silicified rock into phonolite (Fig. 1i) have been identified, which suggests high temperature and pressure with strong vaporization, probably induced by extraterrestrial impact shock. Chondrite-normalized REE distribution patterns illustrate their inheritance relationship (Fig. 1d). 3 Samples and Methods

Iron oxide cosmic spherules, carbonaceous chondrites, atomic iron ―steely bead‖-shaped spherules,

and their associated heavy minerals are from the Dahongyu Formation, the Tailing Tomb, Beijing, China. Silicified rocks are the host rocks of the cosmic spherules and associated minerals.

First, a petrologic study of cosmic spherule-bearing rocks was performed (Song et al., 2019). Cosmic spherule analysis was conducted according to the manual of "Methods for Heavy Mineral Analysis" (Song, 1957). Cosmic spherules and associated minerals were selected under microscope and examined by chemical analysis. The chemical compositions were determined by La-ICP-MS with the New Wave UP-213 laser-ablation system at the National Research Center for Geoanalysis, SEM and X-Ray EDS at the Institute of Geology. The elements tested include Fe, Mn, Si, Na, Mg, Al, P, K, Ca, Ti, Pb, As, Cu, Zn, Sb, Bi, Sn, B, Sc, Li, V, Cr, Co, Ni, Ga, Ge, Rb, Sr, Y, Zr, Nb, Mo, Cs, Ba, La, Ce, Pr, Nd, Sm, Gd, Dy, Th, U, and platinum group elements (PGE).


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Fig. 2. Shape of iron-oxide cosmic spherule grains of the Proterozoic in north China and their surface texture. (a) Solid center cosmic spherule with comb-like segregation texture on surface from recent sediments of the Dalian coast area (after Song

et al., 2011). (b) Football-like spherule with square segregation texture on surface from the Dahongyu Formation at the Ming Tombs area,

Beijing (after Song et al., 2007a; Song, 2007b). (c) Spherule from the Dahongyu Formation in the Ming Tombs area with hollow center

and its smooth surface with many holes (after Song et al., 2007a; Song, 2007b). (d) Hollow-ball-like spherule with chalkboard-like

texture and lamina segregation texture on surface from the Changzhougou Formation in the Ming Tombs area (after Song et al., 2007a;

Song, 2007b). (e) A shell-shaped spherule from the Dahongyu Formation of the Ming Tombs District with many holes on surface. (f)

Ladle-like iron cosmic grain with solid ―ladle head‖ and many holes on ―ladle tail‖ from the Changzhougou Formation in the Ming

Tombs area (after Song et al., 2007a; Song, 2007b). (g) Vesicles on surface of cosmic spherules of the Dahongyu Formation in the Ming

Tombs area. (h) Helium gas escaped strong deformation remains of cosmic spherule of the Dahongyu Formation at the Ming Tombs area.

4 Results


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4.1 Three types of cosmic spherules The three types of cosmic spherules of the Dahongyu Formation are iron oxide cosmic spherules,

carbonaceous chondrites, and atomic iron ―steely bead‖-shaped cosmic spherules. Most of the cosmic spherules are iron-oxide type. Carbonaceous chondrites and atomic iron ―steely bead‖-shaped cosmic spherules are very rare (Table 2). Table 2 The different characteristics of three types of cosmic spherules of the Dahongyu Formation in the Ming

Tombs area, Beijing.

Type Color Luster Size

(µm)

Abundant

(grain/kg) Composition

PGE

(peak)

Segregate

structure

Iron oxide Dark black Metallic 430–50 8–100 FeO Ir Mosaic

Carbonaceous

chadrite Iron gray

Steely

bright 80–250 0–1 Fe & C Pt Impact pits

Atomic iron

"steely bead" Iron gray

Steely

bright 1300–50 0–5 Fe Pt Graphic

Table 3 Helium isotope data of iron-cosmic spherules of the Dahongyu Formation in the Ming Tombs area

(modified by Song et al., 2007a).

Sample 3He/

4He (×10

-8)

4He (×10

-6cm

3STP/g)

Iron cosmic spherules (>200 grains from sample 1516-1) 1.23±0.43 809.60

Silicified limestone (sample 1516-1) 2.59±0.52 2.34

Table 4 Content of Cu-Zn alloy and oxygen content from the cosmic spherule of the Dahongyu Formation in the

Ming Tombs area inside and outside of crust.

Sample wB/%

O Fe Si Al Mn Ti Cr Ni Cu Zn

Point-1 18. 54 69. 47 4. 8 1. 32 1. 42 0. 45 0. 35 0. 28 0. 73 0

Point-2 6. 16 70. 11 6. 75 0. 89 1. 41 0. 09 0. 62 0 6. 44 5. 31

Fig. 3. Comparative figures of larger cosmic grains with smaller cosmic spherules of the Dahongyu Formation in

the Ming Tombs area. (a) Larger cosmic grain with many circular pits serving as remains of smaller cosmic spherules. (b) A small cosmic spherule kept a

mini-cosmic spherule, like a ―baby‖ in its ―mother‖ body, from the Mesoproterozoic Dahongyu Formation in the Ming Tombs area,

Beijing. (c) Cosmic spherule involving many mini-cosmic spherules in its ―mother body‖ from the base conglomerate of the Amushan

Formation of the Mesozoic Carboniferous–Permian boundary in Linxi, Jilin Province.

4.1.1 Iron-oxide cosmic spherules

All cosmic spherules were selected according to the ―Heavy Mineral Separation Method‖ (Song, 1957), picked from many very hard silicified host rock samples, with the average amount ranging from 8 grains/kg to > 100 grains/kg. (1)Variation shape of iron cosmic spherules Rounded solid cosmic spherules are very common in both modern sediments (Fig. 2a) and ancient

sediments (Fig. 2b). Hollow center cosmic spherules were picked from Mesoproterozoic strata (Figs. 2c and d), with irregularly shaped cosmic spherules occasionally found in Proterozoic sandstone beds (Figs. 2e and f).

Regarding the hollow-center cosmic spherules, more than 200 grains of iron-oxide cosmic spherules and some powder samples of the host rock were selected to test helium isotopic abundance, with results presented in Table 3, which shows that

4He is nearly 800 times more abundant in iron cosmic spherules

than in its host rock silicified limestone (Table 3). Gas vesicles and cosmic grain profile are shown in Fig. 2g and Fig. 2h, which suggests that hollows might have formed after gas escaped from the center of the cosmic spherule (Fig. 2g) or from off the center, resulting in net-shaped deformation (Fig. 2h). （2）Comparable observation of cosmic spherule size of the Dahongyu Formation


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The size grades of cosmic grains vary with respect to types of sedimentary rocks and strata environments, but usually a size of 50–300 µm is rather common. For example, the largest grain, greater than 430 µm in size, was extracted from the Dahongyu Formation. In this large cosmic grain, the many circular small pits identified could be the remains of smaller cosmic spherules that have been removed (Fig. 3a). Occasionally, a larger cosmic spherule holds a little ―baby‖ inside (Fig. 3b), and sometimes, even many smaller ones are found inside a larger cosmic spherule (Fig. 3c). （3）Comparable observation of light metals in cosmic spherule of the Dahongyu

Formation It is recognized that the chemical composition of cosmic spherules could be either homogeneous

entirely or locally concentrated in some metal pieces, such as an individual alloy (Figs. 4a, b, and c). However, the content of oxygen and metal elements are shown to be different from the inner ring to outer ring of the cosmic spherule’s crust, which is due to the annealing process (Fig. 4d and Table 4).

Hollow-center cosmic spherules, which might be formed by the escape of helium gas, are very common (Figs. 2g and h). Note that

4He is almost 800 times more abundant in cosmic spherules than in

its host rock (Table 3).

Fig. 4. Cu-Zn metal pieces in iron cosmic grains of the sample 1516-1 from the Dahongyu Formation in the Ming

Tombs area. (a) Cu-Zn piece on cosmic spherule surface. (b) Cu-Zn alloy in mosaic block of segregation texture. (c) Energy spectrum of Cu-Zn alloy

in Fig. 4b. (d) Data of point-2 (inside) and point-1 (outside) show that the values of Cu-Zn slightly increase and oxygen significantly

decrease at point-2 (Table 4).

4.1.2 Carbonaceous chondrite

Chondrite is characterized by the presence of chondrules in which its rare earth element (REE) concentration is widely applied for normalization in geochemical analysis (Boynton, 1984; Taylor and Melenman, 1985; Condie, 1993). Therefore, the REE of ―chondrite‖ is commonly used as the primitive mantle rock standard for normalization. Carbonaceous cosmic spherule is a special type of cosmic spherule. An early contribution to the chemical evolution of the carbonaceous chondrite was made by Dufresne and Anders in 1962. Mini-crystals (less than 10 µm) of carbonaceous chondrite, graphite, diamond, and silicon carbide may be included in a larger meteoritic block. Some carbonaceous chondrites are considered as originating from the interstellar medium (McSween, 1979; Anders and Zinner, 1993; Amari et al., 1994; Hoppe and Zinner, 2000; Rubin, 2004). Compared with data from the Ningqiang carbonaceous chondrites (Wang and Lin, 2007), Ni, Co, and Cr are more commonly found in cosmic spherules from the Dahongyu Formation. （1）Alloy carbonaceous chondrite


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A carbonaceous chondrite grain, supposedly from the solar nebula, was selected among hundreds of iron cosmic spherules from the Dahongyu Formation (Song et al., 2007a; Song, 2007b), representing one kind of alloy carbonaceous chondrite (Fig. 5a). Many small impact pits are present on its surface (Fig. 5b). The energy spectrum shows mainly iron and carbon without oxygen; thus, the chondrite is recognized as a C-Fe alloy (Fig. 5c).

Fig. 5. Alloy carbonaceous chondrite of the sample 1516-1 from the Mesoproterozoic Dahongyu Formation in the

Ming Tombs area. (a) SEM photo. (b) Many impact pits on chondrite surface. (c) Energy spectrum showing elemental carbon and elemental iron without

oxygen (after Song et al., 2007a; Song, 2007b).

In further study, two types of carbonaceous chondrite have been found by their very bright metallic

luster, discriminated from the many iron oxide cosmic spherules (Fig. 6a). There are many circular impact small pits on carbonaceous chondrites, particularly on the segregated texture background (Fig. 6b). By electron X-ray mapping, two carbonaceous chondrite grains exhibit the chemical composition of pure elemental iron or atomic iron (Fe

0) (Fig. 6c), and pure elemental carbon or atomic carbon (C

0)

(Fig. 6d).

Fig. 6. Electron scanning image and X-ray mapping of the alloy carbonaceous spherules of the sample 1516-1

from the Dahongyu Formation in the Ming Tombs area. (a) Two very bright carbonaceous chondrites (left) with many relatively dark iron-oxide cosmic grains together. (b) Many impact small

pits on surface of carbonaceous chondrite spherule. (c) Electron X-ray mapping of pure elemental iron. (d) Electron X-ray mapping of

pure elemental carbon.

（2）Embedded carbonaceous chondrite An amazing discovery of a larger embedded carbonaceous chondrite constructed by diamond-like

elemental carbon embedded with elemental iron took place. This carbonaceous chondrite grain is much brighter than the five other iron-oxide cosmic spherules observed under binocular microscope (Fig. 7a). The oval-like carbonaceous chondrite grain was 265 µm in length and 186 µm in width. The back-scattered image of diamond-like carbon under electron microscope does not show a clear boundary between the diamond-like carbon and the inherent electron-conductive carbon gel film (Fig. 7b, in white circular).


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Fig. 7. Different pictures of the carbonaceous chondrite of sample 1516-1 from the Dahongyu Formation in the

Ming Tombs area under stereoscopic binocular microscope and electron backscattered image. (a) Under binocular microscope, the carbonaceous chondrite is brighter in the center than in the other five iron oxide cosmic spherules. (b)

Electron backscattered image of carbonaceous chondrite (in white circle) without clear boundary between the carbonaceous chondrite and

the inherent electron-conductive carbon gel film.

Fig. 8. Carbonaceous chondrite of the sample 1516-1 from the Dahongyu Formation in the Ming Tombs area

embedded with elemental C (relatively dark) and elemental Fe (relatively bright). (a) Electron backscattered image of chondrite showing embedded C (dark) with Fe (bright). (b) Elemental iron (Fe) peak in the bright area.

(c) Elemental carbon I peak in the dark area. (d) Enlarged photo of carbonaceous chondrite surface showing many bubbles and cleavages

with possible inclusion of liquid, gas, and unknown minerals.

The discovery of an extremely rare grain among the many iron oxide cosmic spherules would

suggest a stellar origin, based on contributions (Hoppe and Zinner, 2000). We tested this by electron-probe analysis for elemental iron, showing bright micro-plates (Fe) and a pure embedded carbon basement I (Fig. 8a), which are confirmed by energy spectra showing pure iron without oxygen (Fig. 8b) and pure carbon basement without oxygen (Fig. 8c), as well as an enlarged photo of the surface of the oval carbonaceous chondrite (Fig. 8d), showing circular mini-bubbles < 10 µm in diameter as the vesicular structure with probable liquid, gas, and mineral inclusions.

Hough et al. (1995) reported the discovery of mini-crystals of diamond and silicon carbide from Riss crater under strong impact shock, determined by the X-ray diffraction method. Huss and Lewis (1995) presented diamond, SiC, and graphite from meteorite in a primitive pre-solar source. Amari et al. (1994) isolated SiC graphite and diamond from meteorite, as did Anderson and Zinner (1993). The oval carbonaceous chondrite of the Dahongyu Formation was determined by laser Raman spectrum; a


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typical diamond spectrum peak at 1350 cm-1

is weaker (Fig. 9), appearing as diamond crystal; thus, the specimen is named ―diamond-like carbon‖. However, a very sharp peak at 1550 cm

-1 in the spectrum

does not seem to refer to any known mineral as of yet. Therefore, it is supposed that alloy and embedded carbonaceous chondrites may characterize this specimen, as well as minerals associated minerals silicon carbide, forsterite, glass spherules, and glass fragments from the Dahongyu Formation, and this chondrite probably originates from space as well.

Fig. 9. Oval-embedded carbonaceous chondrite of the sample 1516-1 from the Dahongyu Formation in the Ming

Tombs area and its laser Raman spectrum analysis curve. Curve is characterized as ―diamond-like carbon‖ (1350 cm

-1) rather than common graphite by the instrument database but the spectrum of

the chondrite curve at 1550 cm-1

indicates an unknown mini-mineral inclusion (Note: Diamond-like carbon and its laser Raman spectra

curve measured by a new instrument of HORIBA JOBIN YVON HORIBA scientific Lab RAM HR EVOLUTION Raman Spectrometer,

Made in France, 2015, June).

Fig. 10. Pure iron (elemental iron) cosmic spherules of sample 1516-1 from the Dahongyu Formation in the Ming

Tombs area and its iron-oxide cosmic spherule ―mother body‖. (a) Atomic iron ―steely bead‖-shaped cosmic spherule. (b) Small atomic iron ―steely bead‖-shaped spherule (point-2) coherent on

iron-oxide cosmic spherule ―mother‖ body (point-1). (c) Locally enlarged photo of the small atomic iron ―steely bead‖-shaped cosmic

spherule showing graphic segregation surface texture and elemental iron energy spectra peaks showing pure iron (zero valence iron)

peaks (see Table 4).

Table 5 Elemental composition of iron-oxide cosmic spherule ―mother body‖ and atomic iron ―steely bead‖-shaped

cosmic spherule of the Dahongyu Formation in the Ming Tombs area (see Fig. 10b).

Sample wB/%

O Fe Si Al Mn Ti Cr Ni Cu

Point-2 0 96.56 0.39 0.21 0.46 0.4 0.37 0.32 0.14

Point-1 18.98 67.65 5.3 1.68 1.65 0.4 0.37 0.33 0.47

4.1.3 Atomic iron cosmic spherules-atomic iron “steely bead-shaped cosmic spherule”

Atomic iron cosmic spherules with ―steely bead‖-shaped are another type of relatively rare cosmic spherule from the numerous iron-oxide cosmic spherules of the Dahongyu Formation. Generally, one grain of the atomic iron ―steely bead‖-shaped spherule can be selected from 70 to 80 iron oxide comic spherules. Atomic iron ―steely bead-shaped cosmic spherule‖ consists of pure iron (elemental iron, zero valence iron, or atomic iron), detected by electron probe analysis. The surface of atomic iron ―steely bead‖-shaped cosmic spherule commonly presents a graphic segregation figure but does not exhibit the mosaic structure of iron-oxide cosmic spherules. （1）Atomic iron “steely bead”-shaped cosmic spherule and iron-oxide spherule

adhered together The atomic iron ―steely bead‖-shaped cosmic micro-grains are commonly well rounded with a very

bright metal luster (Fig. 10a), revealing atomic or elemental iron (zero valence of iron) by the electron energy spectrum diagram (Fig. 10c). A very rare occurrence of a small atomic iron ―steely bead‖-shaped grain was discovered adherent on its iron-oxide cosmic spherule ―mother body‖ (Fig. 10b). Comparing the composition of the ―mother body‖ of atomic iron ―steely bead‖-shaped spherule with iron oxide cosmic spherule shows the same properties, demonstrating that the origins are the same except that of elemental oxygen (Table 5).


11

Fig. 11. Three types of inner construction of atomic iron ―steely bead‖-shaped cosmic spherules of sample 1516-1

from the Dahongyu Formation in the Ming Tombs area. (a) Atomic iron Fe and other oxides (FeO + MnO + SiO2 + Al2O3 + K2O). (b) Atomic iron, atomic manganese, and other oxides

(FeO + MnO + TiO2 + SiO2 + Al2O3 + K2O). (c) Atomic iron Fe and other oxides (FeO + MnO + SiO2 + Al2O3 + K2O).


12

Fig. 12. Associated minerals of cosmic spherules of the sample 1516-2 from the Dahongyu Formation of the Ming

Tombs area. (a) Molten smooth surface silicon carbide grain from the Dahongyu Formation shows brightly green color glass luster and greater than

100 µm in diameter. (b) Raman spectrum curve shows standard peaks of silicon carbide 746 cm-1

and 947 cm-1

. (c) Brown glass spherules

under stereo-microscope. (d) Glass spherules with gas inclusion. (e) Laser-excited illumination figure of silicon-carbide-like cluster

inclusion in the brown glass fragment. (f) Pink glass fragment (PG) involving silicon carbide (SiC). (g) Black glass fragment (BG)

adherent to two mini-cosmic spherules (CS). (h) Euhedral zircon (No. Z2-09) with (111) and (321) crystalline faces and ―typical shock

features‖. (i) Crystal of forsterite under microscope. (j) Raman spectrum showing 830 cm-1

and 855 cm-1

concordant with standard data of

mineral forsterite.

（2）Interior constitution of atomic iron “steely bead”-shaped cosmic spherules The inner composition of consolidated iron-oxide cosmic spherules is Fe3O4 (magnetite) (Song et al.,

2011). However, the inner constitution of atomic iron ―steely bead‖-shaped cosmic spherules is almost entirely elemental iron. However, there are three uncommon groups of interior texture of atomic iron ―steely bead‖-shaped cosmic spherules (Fig. 11) from 35–250 µm in diameter from the Dahongyu Formation, determined by electron probe analysis, which shows the associated chemical compositions.

Up to now, the mechanism and reaction conditions of the inner sides of the atomic iron ―steely bead‖-shaped cosmic spherules are unknown.


13

4.2 Comparative observation of other associated minerals and fragments related with cosmic spherules

The discovery of so many minerals accompanying the large selection of iron-oxide cosmic spherules from the Dahongyu Formation is the only case in China. There are at least two zones around the impact volcanic crater of the Tailing scenic spot, Ming Tombs area, Beijing. The inner zone was concentrated mainly with iron cosmic spherules and the outer zone consisted mostly of components of silicon carbide, forsterite, glass spherule, and glass fragments, as well as zircon, in the melt-silicified carbonate outcrop. 4.2.1 Cosmic spherules——silicon carbide (SiC)

Silicon carbide was discovered as a stellar mineral from the iron meteorite block by the chemical isolation treatment (Lodders and Fegley, 1998). Silicon carbide has another mineralogical name ―moissanite‖, which has been detected from the mantle peridotite in Tibet. The sizes of both silicon carbide and moissanite are less than 10 µm in diameter. For example, the silicon carbide size range of 3.4–5 µm was from the Murchison carbonaceous meteorite (Amari et al., 1994), and the moissanite was 3–9 µm in diameter, observed in thin section of dunite from Tibet (Liang et al., 2014). However, the silicon carbide grain separated from the Dahongyu Formation is greater than 100 µm (Fig. 12a). The laser Raman spectrum curve of the silicon carbide shows standard peaks of silicon carbide at 746 cm

-1 and 947 cm

-1 (Fig. 12b). It is another special feature that so many mini-crystals of silicon carbide

inclusions can also be found as a cluster structure in glass fragments of the cosmic spherule host rock. Several grains of silicon carbide were also picked together with cosmic spherule from the base conglomerate of the Carboniferous-Permian boundary of Linxi County, Jilin Province.

4.2.2 Cosmic spherules——glass spherules and fragments

Lowe et al. reported the largest impact glass spherule beds of the Archean Barberton Greenstone Belt in South Africa (Lowe et al., 2003, 2014; Hofmann et al., 2006). The reports show important evidence of the occurrence of glass spherules, which may be impact-related in the K–Pg boundary deposits of Denerara Rise, Western Atlantic (Schulte et al., 2009) and Gorgonilla Island, Colombia, South America (Bermudez et al., 2015). Spheres of transparent brown glass on the surface of the Chelyabinsk meteorite were observed (Galimov et al., 2013). There are glass spherules with brown color glass spherules from the Dahongyu Formation that are quite similar to the mentioned spherules in shape as well as chemical composition, especially for SiO2, Al2O3, MgO, and CaO, although differences in minor components FeO, TiO2, MnO, Na2O, and K2O exist (Fig. 12c and Table 6). Furthermore, there is an amazing figure obtained by laser excited luminescence of the mini-crystal inclusion of silicon carbide as a cluster linked in a glass fragment (Fig. 12c), showing the characteristics of the Dahongyu Formation. In addition, several fine-grained iron-oxide cosmic spherules adhered with glass fragments were discovered.

Table 6 Comparative data of chemical composition of glass spherules of the Mesoproterozoic Dahongyu

Formation with glass globules from K-Pg boundary sediments of Columbia.

Sample wB/%

SiO2 Al2O3 FeO MgO CaO

This study (Fig. 12-C,D) 36.43 17.22 1.95 8.09 33.12

Columbia (K-Pg) 46.43–68.41 8.69–15.85 3.68–6.45 1.88–4.84 5.45–30.26

Sample wB/%

K2O Na2O TiO2 MnO

This study (Fig. 12-C,D) 0.97 0 1.59 0.63

Columbia (K-Pg) 0.28–1.87 0.97–4 - -

Table 7 Trace elements of brown, pink, and black glass fragments of the Dahongyu Formation in the Ming Tombs

area.

Sample wB/10

-6

Ni Co Cr V Cu Zn As

Brown (Fig 12-C, D) 352.68 55.26 0.01 183.95 2961.69 20217.32 36.43

Pink (Fig 12-F) 2133.82 842.21 15.21 1473.13 103.05 93.94 4.97

Black (Fig 12-G) 15.96 6.29 2131.61 1448.12 1021.13 2226.24 1.86

Sample wB/10

-6

Zr Mo Sn Ba Sr W B

Brown (Fig 12-C, D) 22.17 5.58 2.98 20.57 19.53 0.00 91.38

Pink (Fig 12-F) 19.67 154.35 65.76 7.21 2.78 1082.42 107.76

Black (Fig 12-G) 245.66 1.64 1.63 1010.90 507.05 5.70 27.94

There are special pink color and black color glass fragments in the Dahongyu Formation, the former

involving silicon carbide crystals (Fig. 12f), and the latter involving two coherent mini-cosmic


14

spherules (Fig. 12g). The trace elements of glass fragments are different. Zn, Cu, and B are relatively more abundant in brown glass; Ni, Co, V, and B characterize the pink fragment; and Cr, V, Cu, Zn, and W are abundant in black glass (Table 7).

4.2.3 Forsterite (Mg2SiO4) occurred by impact

Normally forsterite is a magnesium-rich mineral of olivine group, which is formed in ordinary chondrules as a granular olivine-pyroxene cryptocrystalline system or inclusions in iron meteorites (Bunch et al., 1970; Gooding and Keil, 1981; Nakamura et al., 2001; Imae et al., 2013). In the Dahongyu Formation, a single crystal of forsterite was picked from a glass fragment of molten silicified carbonate host rock (Figs. 12i and j). The laser Raman spectrum shows peaks at 830 cm

-1 and

855 cm-1

, concordant with the standard indicator data for forsterite mineral.

4.2.4 Zircon (ZrSiO4) with explosion cracks Euhedral zircon (Z2-09) with (111) and (321) crystalline faces as well as perfect (101) prism faces

(Fig. 12h) is present, exhibiting many shock cracks in the zircon (Fig. 12h), which is similar to the ―typical shock features‖ of meteoritic olivine (Bischoff et al., 2018). The chemical composition of the zircon is SiO2 65.31% and ZrO2 32.95%. Trace elements (wB/10

-6) are as follows: Sc 135.37, Ce 31.09,

Eu 11.75, Tb 43.81, Dy 16.99, Ho 80.13, Yb 260.06, Lu 37.26, Hf 10587, Pb 37.09, Th 230.76, and U 241.61. The zircon is without any trace of abrasion on the zircon surface and may be recognized as having fallen from an explosion meteorite (or ―cosmic zircon‖). The so called ―cosmic zircon‖ might be found near the bolide explosion area (see Fig. 17).

4.4 Chemical analysis of cosmic spherules and associated minerals

We tested more than 20 samples for chemical analysis and found that they are high in FeO, with high levels of Ni, Co, and Cr in the cosmic spherules.

4.4.1 Chemical composition and trace elements of iron-oxide cosmic spherules

The average of iron-oxide cosmic spherules of chemical composition FeO is the main composition and the trace elements (e.g., Ni, Co, Cr, and Cu) are the indication elements (Table 8).

Table 8 Chemical composition of iron oxide cosmic spherules (23 grains) of sample 1516-1 from the Dahongyu

Formation in the Ming Tombs area.

wB/%

SiO2 TiO Al2O3 CrO3 FeO MnO MgO NiO CoO

2.70 0.05 0.59 0.28 95.31 0.31 0.30 0.1 0.02

wB/% wB/10-6

Na2O K2O SO3 Ni Co Cr V Cu

0.11 0.39 0.09 1480.98 250.05 2592.46 220.56 234.47

wB/10-6

Zn As Zr Mo Sn Ba Sr W B

97.34 5.44 64.87 115.25 22.07 49.94 48.11 24.48 26.54

4.4.2 Platinum group element (PGE) of cosmic spherules of the Dahongyu Formation

The average data of iron-oxide cosmic spherules of 22 samples show that the Ir content is relatively higher than that of the other PGE elements, which is perhaps demonstrated by the impact event (Table 9).

The content of Ir in iron-oxide cosmic spherules varied from 0.036 µg/g to 3.485 µg/g. It is amazing that in considering the PGE of the ―steely bead‖-shaped cosmic spherules, Pt is much more abundant than in oxide iron-cosmic spherules (Fig. 13b; Tables 10 and 11). （1）PGE distribution on surface and inner part of cosmic spherules There are two examples explaining the surface differences of the larger atomic iron ―steely

bead‖-shaped cosmic spherule (Fig. 13a and Table 11) and those between iron oxide and atomic iron ―steely bead‖-shaped cosmic spherules (Fig. 13b and Table 11). Clearly, the PGE change is gradual. The data show that the distribution of PGE in iron cosmic spherules changed gradually from the surface to the nuclei without a distinct boundary; the gradual change is quite different from its meteorite. （2）Comparative observation with associated minerals and glass Associated minerals silica carbide and forsterite, as well as glass spherules and fragments, are no

more abundant in PGE by determination. Relatively black glass contains more Pt, Pd, and Ir (Table 11).


15

Table 9 PGE data of 22 iron oxide cosmic spherules of sample 1516-1 from the Dahongyu Formation in the Ming

Tombs area.

No. µm wB/10

-6

Size Pt Pd Ir Os

TD-01 160 0.055 1.079 2.299 0.003

TD-02 270 0.028 0.037 0.354 0.001

TD-03 135 0.035 0.122 3.485 0.001

TD-04 360 0.024 0.036 0.053 0.001

TD-05 290 0.028 0.075 1.536 0.001

TD-06 250 0.026 0.130 0.547 0.001

TD-07 170 0.240 0.046 0.314 0.001

TD-08 480 0.024 0.035 0.088 0.001

TD-09 215 0.028 1.277 1.509 0.001

TD-10 250 0.052 0.063 0.064 0.000

TD-11 310 0.025 0.083 0.781 0.001

TD-12 110 0.033 0.497 2.148 0.001

TD-13 280 0.024 0.083 0.495 0.001

TD-14 305 0.026 0.289 0.101 0.000

TD-15 270 0.027 0.067 0.658 0.001

TD-16 235 0.024 0.044 0.094 0.001

TD-17 425 0.034 0.052 0.404 0.000

TD-18 190 0.050 0.049 0.188 0.000

TD-19 258 0.025 0.119 0.664 0.001

TD-20 310 0.025 0.055 1.516 0.000

TD-21 280 0.021 0.101 0.603 0.001

TD-22 350 0.024 0.084 0.036 0.000

Average 268 0.040 0.201 0.815 0.001

Table 10 PGE data of iron cosmic spherules and associated minerals from the Dahongyu Formation in the Ming

Tombs area and a meteorite from Xinjiang.

Sample wB/10

-6

Pt Pd Ir Os

P-1 Fig. 13-A 0.946 0.244 0.002 0.002

P-2 Fig. 13-A 1.107 0.539 0.005 0.003

P-3 Fig. 13-A 1.172 0.665 0.003 0.003

P-4 Fig. 13-A 1.420 0.521 0.005 0.006

Px-1 Fig. 13-B 2.727 1.385 0.003 0.002

Px-2 Fig. 13-B 1.256 0.994 0.002 0.001

T-02 Fig. 14-A 0.002 0.001 0.001 0.000

T-03 Fig. 14-B 5.345 1.614 4.825 2.423

T-04 Fig. 14-C 5.478 1.606 4.860 2.586

Silicon carbide Fig. 12-A,B, 0.0073 0.0501 0.0004 0.0001

Forsterite Fig. 12-I,J 0.0065 0.0020 0.0015 0.0001

Brown glass Fig. 12-C, D,E 0.0720 0.0220 0.0000 0.0000

Pink glass Fig. 12-F, 0.0450 0.0050 0.0000 0.0000

Black glass Fig. 12-G 0.0940 0.4540 0.0170 0.0000

Table 11 PGE data of rocks, meteorites, and spherules (sample details are in Fig. 15).

Sample wB/10

-9

Pt Pd Ir Os

a 0.5 0.52 0.022 0.031

b 7.75 5.48 0.069 0.39

Sample wB/10

-6

Pt Pd Ir Os

c 0.04 0.201 0.815 0.001

d 5.412 1.637 4.843 2.505

e 2.727 1.385 0.003 0.002

f 0.007 0.05 0.0004 0.0001

g 0.094 0.454 0.017 0.0001

h 0.5911 8.6091 0.4418 0.0110

I 0.035 0.182 3.485 0.001

TD-03 0.035 0.122 3.485 0.001


16

Fig. 13. Electron back scanning image of two kinds of cosmic spherules of the Dahongyu Formation in the Ming

Tombs area. (a) PGE of the biggest atomic iron ―steely bead‖-shaped cosmic spherule (> 1300 µm) of sample 1516-2 from the Dahongyu Formation,

increasing from surface (P-1) to small convex spot (P-2, P-3, and P-4) (Table 10). (b) Piece of egg-shaped cosmic spherule of sample

1516-1 (atomic iron ―steely bead‖-shaped cosmic spherule): less PGE in eggshell (outer) and more PGE in egg white (inner core) (Table

10).

Fig. 14. Electron backscattered photo of a corner of the meteorite with PGE inclusions (measured point T-02) from

Xinjiang, China. (a) Meteorite. (b) Enlarged photo of PGE inclusion T-03. (c) Polished photo of PGE inclusion T-03 (Table 10).

Fig. 15. Comparative diagram of PGE of rock, meteorite, and spherule. Value a from samples: olivine glass of mantle (Rudnick and Gao, 2014). Value b from a sample: Permian basalt of Shichuan Province,

China (Wang et al., 2007). Value c from spherules: Average of iron-oxide cosmic spherules of sample 1516-1 from the Dahongyu

Formation in the Ming Tombs area (Table 11 in this paper).Value d from a sample: Meteorite inclusions, from Xinjian, China (Table 12 in

this paper). Value e from a spherule: Atomic iron ―steely bead‖-shaped cosmic spherule of sample 1516-2 from the Dahongyu Formation

in the Ming Tombs area (Table 11).Value f from spherules: Silicon carbide of sample 1516-2 from the Dahongyu Formation in the Ming

Tombs area (Table 11). Value g from a spherule: Black glass. Value h from zircon: Cosmic zircon of sample 1516-2 from the Dahongyu

Formation in the Ming Tombs area (Table 11). Value i from a spherule: Iron-oxide cosmic spherule with the highest Ir (TD-03) of the

Dahongyu Formation (Table 9).


17

（3）Comparative observation of meteorite PGE inclusions Meteorite is from the Gobi Desert of northwest China. As is well known, many new discoveries of

meteorites have taken place in the Antarctic area (Miao et al., 2004; Lu et al., 2004). The Gobi Desert is widely distributed along the Tianshan south pediment plan where there is less human activity. The dark black meteorites fall dispersed on the hard Gobi rock surface of the Talak area, NW-Arksu City, Xinjiang. Meteorite blocks have a dark black smooth surface due to the erosion caused by the strong wind, blowing in a very bright sunshine. The PGE inclusions are determined by electron scanning microscopy (Fig. 14a), from an enlarged image showing a strange rotational figure (Fig. 14b). However, under reflection microscope observation, there are many 6-µm cubic mini-crystals concentrated in the PGE inclusion (Fig. 14c). The background of PGE inclusions of the meteorite is not abnormal of PGE content but between the inclusions themselves, PGE content is almost the same and with a distinct boundary between the PGE inclusions and ground material of meteorite. There is a distinct boundary between PGE inclusions and the meteorite basement (Table 12).

Table 12 PGE data of 24 iron oxide cosmic spherules of the Taizi Formation in Shennongjia.

No. µm wB/10

-6

Size Pt Pd Ir Os

TT-01 210 0.024 0.042 2.354 0.001

TT-02 80 0.040 0.079 3.949 0.001

TT-03 140 0.077 0.049 4.969 0.000

TT-04 180 0.063 0.059 1.838 0.00

TT-05 130 0.0`19 0.035 3.013 0.001

TT-06 190 0.026 0.974 4.358 0.002

TT-07 170 0.032 0.056 2.680 0.001

TT-08 150 0.024 0.066 3.776 0.001

TT-09 130 0.099 0.057 2.464 0.001

TT-10 100 0.033 0.083 3.065 0.002

TT-11 90 0.034 0.064 3.573 0.000

TT-12 200 0.024 0.067 4.527 0.003

TT-13 240 0.021 0.044 4.827 0.000

TT-14 80 0.050 0.121 4.520 0.003

TT-15 140 0.093 0.070 3.151 0.002

TT-16 180 0.027 0.071 3.378 0.002

TT-17 320 0.023 0.061 2.556 0.001

TT-18 80 0.029 0.068 2.954 0.002

TT-19 130 0.027 0.073 2.536 0.003

TT-20 120 0.018 0.049 3.176 0.001

TT-21 120 0.039 0.123 2.597 0.005

TT-22 190 0.176 0.059 2.655 0.001

TT-23 140 0.030 0.062 2.665 0.001

Average 153 0.047 0.106 3.286 0.001

Table 13 Correlation of characteristics of iron-oxide cosmic spherules between the Dahongyu (TD), Tazi (TT), and

Liantuo (TL) Formations.

Sample Geo-age (Ma) Size (µm) Abundance (grains/kg) Ir highest (wB/10-6

)

TD-01-22 1625Ma 268 100 3.485

TT-01-23 ＞1200Ma 153 200 4.827

TL-01-26 425–780Ma 200 ＞640 8.257

Platinum group elements are few in the associated silicate minerals and glass. However, in the black

glass (see Fig. 12g) the PGE is relatively higher than other silicate minerals (Table 13). Wang et al. (2007) introduced PGE deposits in SW China and measured a series of data from basaltic rocks in China. Many examples concern PGE mineral deposits related to mantle plume, volcanic rocks, as well as sedimentary occurrence in southwest China. This paper cites the PGE data (ng/g) of the Permian basalt of the Omeishan, Shichuan Province, China: Os 0.39, Ir 0.069, Ru 0.49, Rh 0.24, Pt 7.75, Pd 5.48, PGE 14.429, and Au 1.62. Rudnick and Gao (2014) published PGE data (ng/g) of olivine glass of mantle: Os 0.031, Ir 0.022, Ru 0.34, Pd 0.52, and Pt 0.5. In this study, the PGE in cosmic spherules and associated minerals is considered. A summary of the above data suggests that the PGE (Pt, Pd, Ir, and Os) are stably distributed in meteorite PGE inclusions, with elemental Ir relatively high for iron-oxide cosmic spherules, elemental Pd abnormally high for zircon, and silicon carbide as well as glass fragments having low abundance of PGE materials but higher than the PGE in mantle rocks (Fig. 15


18

and Table 11). PGE data in cosmic spherules of the Dahongyu Formation are summarized: Ir shows a higher peak, and Pt and Pd are relatively more abundant in atomic iron ―steely bead‖-shaped cosmic spherules. However, PGE inclusions of meteorite are much higher than all the others. It is very strange that PGE is normal in silicates, such as silicon carbide, forsterite, and glass, but Pd content is significantly higher than in oxide cosmic spherules with rather more than inclusions of meteorite (Fig. 15; Tables 9, 10 and 11). 5 Discussion 5.1 Comparative data of iron oxide cosmic spherules between the Dahongyu Formation and Taizi and the Liantuo Formations of Shennongjia area

In recent years, we have found many iron-oxide cosmic spherules in the Mesoproterozoic Tazi Formation (Kuang et al., 2017) and Neoproterozoic Liantuo Formation of the Shengnongjia area, south China. The geo-age of the former is > 1200 Ma (Li et al., 2013), and the age of the latter is approximately 725–780 Ma (Gao et al., 2011, 2012). The iron oxide cosmic spherule content in these areas are greater than that in the Dahongyu Formation: the Tazi Formation contains about 200 grains/kg, and the Liantuo Formation contains more than 640 grains/kg. However, the Ir peak is approximately the same as that from the Dahongyu Formation (Table 12). All the data demonstrate huge cosmic spherules from meteorite explosion events.

It is demonstrated that the contents of PGE and Ir are abnormal not only for the Dahongyu Formation but also for the Tazi and the Liantuo Formations (Table 14); based on having the highest Ir value, the Liantuo Formation seems to exhibit very strong bolide explosion power.

Table 14 PGE data of 26 iron-oxide cosmic spherules of the Liantuo Formation in Shennongjia.

No. µm wB/10

-6

Size Pt Pd Ir Os

TL-01 190 0.023 0.079 2.744 0.002

TL-02 90 0.051 0.087 4.320 0.002

TL-03 100 0.036 0.052 5.359 0.001

TL-04 290 0.069 0.087 4.707 0.002

TL-05 230 0.028 0.052 5.715 0.001

TL-06 250 0.032 0.071 5.370 0.001

TL-07 40 0.081 0.088 3.485 0.002

TL-08 200 0.028 0.095 3.731 0.002

TL-09 190 0.025 0.048 4.420 0.001

TL-10 170 0.027 0.054 4.905 0.001

TL-11 220 0.036 0.053 3.442 0.000

TL-12 80 0.036 0.088 5.287 0.002

TL-13 150 0.031 0.046 3.745 0.001

TL-14 150 0.025 0.050 0.810 0.000

TL-15 260 0.026 0.064 6.959 0.001

TL-16 220 0.023 0.064 6.552 0.000

TL-17 160 0.038 0.099 6.478 0.001

TL-18 170 0.023 0.073 6.972 0.001

TL-19 210 0.027 0.083 8.257 0.001

TL-20 250 0.023 0.084 5.713 0.001

TL-21 420 0.028 0.063 3.999 0.001

TL-22 210 0.032 0.127 7.932 0.002

TL-23 240 0.031 0.093 4.370 0.001

TL-24 200 0.024 0.086 8.650 0.001

TL-25 190 0.023 0.070 3.931 0.001

TL-26 310 0.091 0.097 5.968 0.001

Average 200 0.035 0.075 5.147 0.001

5.2 Comparative observation of PGE-Zr mineral (“cosmic zircon”) from Proterozoic strata of South China with the Dahongyu Formation

There is an example of a PGE mineral (―cosmic zircon‖), in which PGE (Fig. 16 and Table 15) is much more abundant than the zircon grains of the Dahongyu Formation. The PGE mineral ―cosmic zircon‖ is characterized by higher PGE content and drum-shaped grains, with impact pits on the surface (Fig. 17b), which is very similar to the surface pits of the interstellar cosmic spherule of the Dahongyu


19

Formation (Fig. 6B). Furthermore, the shock cracks of zircon (Fig. 17a) are much stronger than that exhibited by zircon (Fig. 12h).

Fig. 16. PGE-Zr mineral and its energy spectrum. (a) An electron scanning scattered photo of the ―cosmic zircon‖ (center) from the Proterozoic strata in Shennongjia, south China. (b)

Electron energy spectrum of ―cosmic zircon‖ with high PGE and Ir under X-ray mapping (Table 15).

Fig. 17. ―Cosmic spherules‖ from the Proterozoic strata in Shennongjia, south China, obtained by the

bowl-washing method. (a) The zircon surface shows many cracks, resulting from strong shock, and would never be formed in Earth detrital zircon grain; thus, it

is a ―cosmic zircon‖ by impact event (compare with Fig. 12h). (b) A drum-like ―cosmic zircon‖ without (111) and (321) crystalline faces

and numerous impact pits on surfaces; the drum is the same as the interstellar carbonaceous cosmic spherules of the Dahongyu Formation

(compare with Fig. 6b).

Fig. 18. Lateral views of cosmic spherule bearing rock and idealized model of impact event of the Dahongyu

Formation in the Ming Tombs area. (a) A block of black shale dropping on molten cosmic spherules bearing rock. (b) An idealized crater model of falling meteorite block

causing a volcanic explosion (the legends are same as Fig. 1).

In the explosive rock thin section, a high Ir content ―cosmic zircon‖ was determined (Fig. 16), and

two grains of the so-called ―cosmic zircon‖ (Fig. 17) were selected by the bowl-washing method (Song Tianrui, 1957).


20

The authors recognize that the ―cosmic zircon‖ could be found in sediments near the bolide explosion area.

Table 15 Measured electron energy data of the ―cosmic zircon‖ (Fig. 16) of the Proterozoic strata in Shennongjia,

South China.

wB/%

Al Si Fe Y Zr Ag Dy Ir

1.74 27.82 3.01 8.2 49.62 0.95 1.6 7.06

6 Conclusions

(1) Many cosmic spherules were discovered from the Ming Tombs area, Beijing. It is unique in China. In this study, it is recognized that was a huge impact event during the Dahongyu stage in the Ming Tombs area. There are several pieces of evidence of a meteorite impact event. A black shale block (Fig. 18a) from the underlying strata (Chuanglinggou Formation) was discovered to have fallen into the upper molten layers (Dahongyu Formation), demonstrated by a crater model of the meteorite impact event (Fig. 18b).

(2) According to microscopic and electron microscopic analysis, there are abnormal geological features that explain the impact event. The cosmic spherules distributed in the host rock might have undergone high temperature and pressure conditions. Schorl veinlets injected from silicified carbonate into volcanic sediments as well as metallic elements U and Fe in the host rock were perhaps the product of strong impact vapor power. The widespread occurrence of the tourmaline group in nearly all types of rock (Dietrich, 1985) is another piece of evidence. Usually schorl (black tourmaline) was formed in continental-margin depression-margin at temperatures higher than 300 °C (Mao et al., 1990), while the phonolite tuffaceous rock series original oncolite limestone occurred in shallow marine sedimentary environments. Furthermore, iron cosmic spherules are a new piece of evidence of an extra-terrestrial meteorite explosion event. Element Ir is abnormally high, suggesting an impact event during the Dahongyu Stage.

(3) The abnormal content of Ir in iron cosmic spherules is evidence of a bolide or meteorite impact event either in the Dahongyu Formation of the Ming Tombs area or in the Tazi and Liantuo Formations of the Shengnongjia area.

Acknowledgements

This work is granted by National Nature Science Foundation of China (41472082, 41402100,

49772121, 40172044, and 41173065) and Institute of Geology, Chinese Academy of Geological Sciences, China Geological Survey (DD20190448 and DD20190370). The authors are grateful to Professor Wang Denghong for his careful promotion of the manuscript.

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About the first author SONG Tianrui, male, born in 1931 in Taiyuan City, Shanxi Province; bachelor; graduated from Peking University; research fellow and doctoral supervisor of Institute of Geology, Chinese Academy of Geological Sciences. He is now interested in the study on mineralogy, petrology, and sedimentology. Email: [email protected]; phone: 010-68999695, 13071159485.

About the corresponding author ZHENG Ning, female, born in 1983 in Panjin City, Liaoning Province; doctor; graduated from Chinese Academy of Geological Sciences; research assistant at the Institute of Geology, Chinese Academy of Geological Sciences. She is now interested in the study on sedimentology. Email: [email protected]; phone: 010-68999726, 15210019969.


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