Karite – diamond fossil: A new type of natural diamond

Journal Pre-proof Karite – diamond fossil: a new type of natural diamond T.G. Shumilova, V.V. Ulyashev, V.A. Kazakov, S.I. Isaenko, S.A. Svetov, S.Yu. Chazhengina, N.S. Kovalchuk PII:

S1674-9871(19)30176-8

DOI:

https://doi.org/10.1016/j.gsf.2019.09.011

Reference:

GSF 893

To appear in:

Geoscience Frontiers

Received Date: 27 February 2019 Revised Date:

20 May 2019

Accepted Date: 25 September 2019

Please cite this article as: Shumilova, T.G., Ulyashev, V.V., Kazakov, V.A., Isaenko, S.I., Svetov, S.A., Chazhengina, S.Y., Kovalchuk, N.S., Karite – diamond fossil: a new type of natural diamond, Geoscience Frontiers, https://doi.org/10.1016/j.gsf.2019.09.011. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.

Karite – diamond fossil: a new type of natural diamond

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T.G. Shumilovaa,b,*, V.V. Ulyasheva, V.A. Kazakovc, S.I. Isaenkoa, S.A. Svetovd, S.Yu.

4

Chazhenginad, N.S. Kovalchuka

5

a

Institute of Geology, Komi Scientific Center of Ural Division of Russian Academy of Sciences, Pervomayskaya st. 54, Syktyvkar, 167982, Russia

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b

Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, 1680 EastWest Road, Honolulu, HI, 96822, USA

8 c

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d

SSC FSUE Keldysh Research Centre, Onezhskaya, 8, 125438, Moscow, Russia

Institute of Geology of the Karelian Research Centre of the Russian Academy of Sciences,

11

Petrozavodsk, 11 Pushkinskaya Street, Russia

12

* Corresponding author email address: E-mail: [email protected];

13

[email protected];

14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

ABSTRACT Impact diamond is one of perspective natural type of superhard carbon materials, forming huge resources sometimes, such as Popigai impact structure counting the largest diamond storage on the Earth. By present, there are two known types of impact diamonds – after-graphitic and after-coal varieties formed from different carbon precursors. Here we present for the first time a new impact diamond type – diamond fossils, named by “karite”, formed about 70 Ma from unmetamorphosed organics in the giant Kara impact crater (Pay-Khoy, Russia). A full complex of the diamond fossil characteristics is described proving its nature and phase state. Karite is presented with supernanocrystalline diamond aggregates, nicely preserves tiny cell morphology and relict features of lignin and cellulose. The diamond fossils are spread widely through the Kara impactites, point to possible wider distribution of impact diamonds within large impact occurrences around the world, can be used for impact modeling, astrobiological and material studies.

Key-words: astroblemes, impact diamonds, fossils, diamond paramorphs, astrobiology.

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1. Introduction 1

33

Impaсt diamonds are valuable technical material with the high mechanical properties

34

caused by their defective structure by presence of carbon atom layers with hexagonal packaging

35

within cubic diamond structure formed with extremely high pressures. The most famous giant

36

deposits of impact diamonds belong to the huge Popigai impact structure landing up to 100 km

37

in diameter (Western Siberia, Russia), while the after-graphitic impact diamonds had been found

38

at a number of other impact structures such as Sudbury, Ries, Puchezh-Katunky and others

39

(Masaitis et al., 1972, 1998, 1999; Langenhorst et al., 1998, 1999; El Goresy et al., 2001, 2003;

40

Kvasnytsya and Wirth, 2013; Goryainov et al., 2014; Shumilova et al., 2014; Ohfuji et al., 2015;

41

Yelisseyev et al., 2018). Earlier it was widely accepted the impact diamonds formed only by the

42

solid-phase diffusion-less mechanism of graphite to diamond transition under shock pressure >

43

30 GPa which was proved many times and described in detail (Bundy and Kasper, 1967;

44

Lonsdale, 1971; Kurdumov et al., 2012; Garvie et al., 2014 and others). At the same time, less

45

known impact diamond variety formed after coal substance had been found at the unique Kara

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impact crater in the 70-s by V.A.Yezerskiy (1986). The after-coal diamonds have a number of

47

specific features. They were slightly studied and described more than 30 years ago (Yezerskiy,

48

1986). Recently the diamond type has been investigated with precision at a modern high

49

resolution level (Shumilova et al., 2018b). As a result of the recent study a new short-distance

50

diffusion mechanism of the diamonds formation has been proposed and the high level of

51

diamond concentrations has been found counting according to preliminary data about 80 carats/t

52

with measured local huge diamond contents up to thousands carat per ton within impact glasses.

53

On the basis of our detailed study we have divided the after-coal diamonds for 2 varieties:

54

microgranular (sugar-like), subdivided into 2 subvarieties (dense and friable aggregates) and the

55

impact diamond pseudomorphs after organic relics, slightly described in (Shumilova et al.,

56

2018b) and initially described by a sort of after-coal diamond. On the basis of the detailed

57

studies now it is proposed here as a new impact diamond type – diamond fossils after quite fresh

58

(unmetamorphosed) organics being the brightest find between the impact diamond sorts and 2

59

named by us by “karite” after the name of the Kara impact structure as the place of the first

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occurrence.

61

Earlier several finds of plant fossils within impact melts and meteorite occurrences had

62

being described pointing for possibility of preservation of organic relics, the problem of organics

63

preservation under hypervelocity impacts is in a focus of hot studies concern to astrobiological

64

questions (Schultz and Harris, 2005; Bowden et al., 2009; Howard et al., 2013; Schultz et al,

65

2014; Gurov et al., 2019 and others). Here we demonstrate the unique type of organic relics and

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the unique diamond type at the same time being the same object. The find points to possibility of

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partial organic preservation even under ultrahigh pressure processes getting conditions of

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diamond formation.

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It is surprisingly that the new impact diamond variety defines the leading role at storm

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concentrations within clastic impact glasses in the Kara impactites. This paper is devoted to

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describe in detail the new variety of the impact diamonds – impact diamond fossils – “karite”

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as a new mineralogical find and as a possible model of novel material having specific

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nanostructural features. The find can be used also for genetic reconstructions of the Kara

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impactites formation, for proof of origin of doubted impact structures around the world and for

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paleo- and astrobiological studies.

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2. Geological setting

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The diamondiferous Kara and Ust`-Kara impact craters (with 60 km and 25 km diameters,

79

correspondently) are set at the North-East European region of Russia at the Pay-Khoy Ridge

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structure directly the coastline of the Kara Sea (Fig. 1). The Kara impact crater is today obvious

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as depression in the landscape while Ust`-Kara extends just partly beyond the coast (Nazarov et

82

al., 1989; Koeberl et al., 1990; Machshak, 1991; Shishkin et al., 2012). The craters are unique

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with the unusual type of impact diamonds presented with after-coal variety described by V.A.

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Eserskii (1986) and Shumilova et al. (2018b). According to the previous published data the 3

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diamond storages correspond to the value about 200 kg/km2 for the impact structure (Shishkin et

86

al., 2012).

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The Kara impact structure geological features were described in the most details by

88

Machshak (1990) and Shishkin et al. (2012) while some other works on different geological

89

aspects had been published in Trieloff et al. (1998), Yudovich et al. (1998) and Udoratin et al.

90

(2010). Here we describe just the most important geological features of the impact structure.

91

It was proposed that the impact event had occurred at K/T age boundary (Koeberl et al, 40

Ar-39Ar

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1990; Nazarov et al., 1992). According to the most recent isotopic studies by

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determination based on the impact-melt rocks measurements (Trieloff et al., 1998) the Kara

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impact age corresponds to about 70 Ma. The target is characterized by two structural levels: Late

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Proterozoic and Paleozoic sediments presented with the Sylovayachinskaya (D3–C1), Karskaya

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(C1) and Karasilovaya (C2–P1) units. The lower level has a total thickness of more than 6 km and

97

consists of mica-clay, siliceous and actinolite-bearing phyllites with lenses of metamorphosed

98

rhyolites and tuffs.

99

The upper has thickness about 5.6 km with a wide range of sediments presented by clay-

100

siliceous, mica-siliceous and carbonate-clay shales, clay and mica-containing limestones,

101

sandstones and others. The general specific of the target is the wide distribution of black shales

102

and coal lens presence within Permian sediments. The carboniferous matter of the latter was a

103

starting material for diamond formation at the impact process.

104

Following to Yudovich et al. (1990) the carboniferous matter at the Kara target may be

105

comprised by two differently ordered carbons an amorphous/shungite-like carbon of bathyal

106

sedimentary origin and a turbostratic graphite of detrital origin. Earlier V.A. Yezerskiy (1986)

107

described quite high coalification level from lean to anthracite stage.

108

The impactites at the Kara and Ust`-Kara impact craters are presented with thick suevite

109

layer rich up to 2 km in thickness and melt impactites, which fragmentally occur as lens and

110

layer-like bodies with the observed thickness up to 15 m. Just recently, an ultrahigh pressure 4

111

high temperature vein variety of the melt impactites has been found (Shumilova et al., 2018a).

112

The all types of impactites are rich in impact diamonds, where two varieties have been divided to

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after-coal micrograined (sugar-like) and pseudomorphs after organic relics (Shumilova et al.,

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2018b), now proved here as the new impact diamond type – diamond fossils – karite.

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117 118

2. Material and methods

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Material. The material for the paper has been sampled at the field expeditions in 2015 and

120

2017 in the southern part of the Kara impact structure at the Kara river basin. For the detailed

121

mineralogical study with high resolution modern methods the diamonds have been enriched by

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chemical dissolution of impactites by the method of microdiamonds enrichment modified and

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used at the Laboratory of Diamond Mineralogy at the Institute of Geology of Komi SC UB RAS

124

(Syktyvkar, Russia). The technology allows enriching microdiamonds with sizes approximately

125

from 1 μm. The method uses a complex multiple stage chemical treatment with boiling in a

126

mixture of H2SO4 and K2Cr2O7, melting with NaOH, and treatment by hot HCl water solution.

127

The small volume probes had been used for dissolution with the 5 g standard mass. The enriched

128

particles were picked up from the filters under an optical binocular microscope MBS-10 at a

129

magnification ×40 for the detailed study by a complex of methods.

130

Some studies of the after-organic relics have been provided directly “in situ” within the

131

impact rock on the fresh crushed surfaces, large square polished sections and standard

132

microprobe specimens. At the preparing no any diamond-containing materials were used to

133

avoid contamination by diamonds.

5

134

Optical observations. Optical observations in transmitted and reflected light with parallel

135

and crossed polarizers under objectives ×4.7–100 using microscopes Polam 312 and Olympus

136

BX41 have been provided (IG Komi SC UB RAS, Syktyvkar, Russia). For optical observations

137

enriched diamond particles, fresh crushed impactite surfaces and polished sections have been

138

used without conductive layer covering.

139

X-ray diffraction. X-ray diffraction has been provided for individual diamond grains and

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for groups of several similar particles combined into a single specimen. As the particle has very

141

small sizes they were mounted into a center of a rubber ball of 0.3 mm in diameter for accurate

142

centering within an X-ray camera. The X-ray analysis has been done at IG Komi SC UB RAS

143

(Syktyvkar, Russia) with Debye-Scherrer method with use a camera AROS with 57.3 diameter,

144

X-ray source – Cu, excitation time – 4 h.

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Raman spectroscopy. The preliminary Raman spectroscopic study with visible laser

146

excitation of carbon substances for their phase state identification and structural features analysis

147

was provided at the IG Komi SC UB RAS (Syktyvkar, Russia) using a high resolution Raman

148

spectrometer LabRam HR800 (Horiba Jobin Yvon, France), the spectra were collected “in situ”

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from a surface of fresh crushed impact rocks, polished thin sections and from individual

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chemically enriched grains. Ar+ laser with the excitation 488 nm was used with spectra collecting

151

in the range 100–8000 cm-1 at room temperature with 1.2 mW laser power through objective

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×50, ×100 at grade 1800, with 1 µm spatial and 1 cm-1 spectral resolution. As the studied

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particles had very high luminescence the identified Raman bands of carbon phases could not be

154

recognized, thus ultraviolet (UV) Raman spectroscopy had been used for the diamonds

155

identification and their detailed study.

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The UV Raman spectroscopy measurements have been provided at the SSC FSUE Keldysh

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Research Centre (Moscow, Russia) with a Raman spectrometer T64000 (Horiba Jobin Yvon,

158

Japan) at 244 nm laser excitation wavelength with a grating of 2400 grooves/mm, a 40× 6

159

objective. The laser power on the sample was lowered down to ~5 mW power to prevent

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possible laser-induced specimen damage, a laser spot diameter was about ~5 µm, exposure time

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5 min. To avoid specimen changes by laser treatment, every specimen has been checked by pre-

162

and post-observations with an optical microscopy at the analyzed region. After background

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correction all spectra were deconvolved to individual peaks using a curve fitting by Gaussian and

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Lorentzian procedure functions with LabSpec 5.36.

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Fourier transform infrared (FTIR) spectroscopy. FTIR spectroscopy of individual grains

166

of the diamond pseudomorphs has been conducted to analyze structural and defect features and

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chemical radical compositions within the diamond aggregates. The measurements have been

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provided at the Center of collective use of the Saint Petersburg Mining University (St.

169

Petersburg, Russia) with use a FTIR spectrometer VRETEX-70 (Bruker) accompanied with a

170

microscope HYPERION 1000. Absorption spectra have been analyzed in the range 400–7000

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cm-1 for every individual grain with the spot locality about 50–70 µm. The potassium bromide

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supporting films for pointing the analyzed particles have been used. The FTIR spectra were

173

analyzed through LabSpec 5.36.

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Scanning electron microscopy (SEM) and electron microprobe analysis (EMPA).

176

Analysis of the enriched diamond grains and impact rocks with “in situ” observations in fresh

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rock surfaces and polished sections was provided with a VEGA 3 TESCAN scanning electron

178

microscope (Tescan, Czech Republic) accompanied by a VEGA 3LMN, INCA ENERGY 450

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energy dispersive detector was used for chemical composition control and morphology details (at

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the IG Komi SC UB RAS, Syktyvkar, Russia). The SEM and EPMA studies were done without

181

conductive covering to avoid contamination of the diamond particles analysis, then for high

182

quality SEM observations the specimens were covered by a carbon film.

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Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Trace

184

element concentrations of individual diamond grains were determined by LA-ICP-MS using 7

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New Wave UP (266 nm) laser ablation system coupled to an X_Series 2 Thermo Fisher

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Scientific ICP-MS (at IG Karelian RC RAS, Petrozavodsk, Russia). The LA-ICP-MS analyses

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were conducted using the 30–60 µm beam diameter, 10 Hz frequency and 0.13 mJ/pulse power.

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The instrument was calibrated against the NIST 612 silicate glass (National Institute Standard

189

and Technology, Gaithersburg, USA).

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Atomic force microscopy (AFM). An atomic force microscope Integra Prima (NT-MDT,

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Russia) was used to analyze morphology of a fresh surface of the diamond pseudomorphs at the

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IG Komi SC UB RAS, Syktyvkar, Russia. The studies were provided at room temperature and

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humidity about 65% by silicon cantilevers with 25 nm-thick conducting Pt coating having 20 nm

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tip radius (PPP-CONTPt, Nanoworld). At the specimens preparing the diamond grains were set

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on electric conducting glue. Statistical analysis by a standard Nanoworld soft has been used for

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nanocrystallites sizes characterization.

197

Transmission electron microscopy (TEM) study. The preliminary TEM studies have been

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provided at 60 and 90 kV voltage with a transmitting electron microscope Tesla BS 500 (Czech

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Republic) (IG Komi SC UB RAS, Syktyvkar, Russia). The observations were provided by

200

studying of specimens prepared by a crushed individual diamond grain per a TEM foil. Every

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independent diamond grain has been crushed between two glasses then the powder particles have

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been filled in ethanol and moved by micro-doze pipet to a holey carbon supporting film. At the

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initial stage the overview diamond fragments of the pseudomorphs and their diffraction patterns

204

have been analyzed for general phase diagnostics.

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Then investigations of nanostructure features and atomistic level observations have been

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continued at the Federal State Institution “Technological Institute for Superhard and Novel

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Carbon Materials” (FSBI TISNCM) (Troitsk, Moscow, Russia). A high resolution microscope

208

JEM 2010 equipped with energy dispersive detector for energy dispersive spectroscopy analysis

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(EDS) and GIF Quantum Energy Filter for electron energy loss spectroscopy (EELS) and

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energy-filtered transmission electron microscopy (EFTEM) have been used accompanied with 8

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electron diffraction (ED) studies and fast Fourier transformation (FFT) of high resolution TEM

212

(HRTEM) images analysis. The detailed studies have been provided for the preliminary analyzed

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specimens. The analysis including morphological, structural and electronic state was done for

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every particle in the complex.

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Stable isotopic studies. Stable δ13С measurements have been provided on individual

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diamond grains of about 50 µm in size, they were set by a needle into individual Sn boxes. The

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separated diamond grains were selected from thermochemical concentrate, they were pure of any

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mineralogical impurities recognized with use of an optical microscope. The SEM and EPMA

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studies for typical diamond grains allow conclude about absence of mineral inclusions. The

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isotopic analysis has been produced in IG Komi SC UB RAS (Syktyvkar, Russia) with using a

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mass-spectrometry complex DELTA V Advantage (ThermoFisher Scientific) with a GasBench

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II system. The stable isotopic composition analysis was made in absolute value with the

223

international

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Acetanilide (C8H9NO) with accuracy measurements δ13С ± 0.2‰ relatively to a PDB standard.

standard

USGS-40

(L-Glutamicacid)

and

a

laboratorial

standard

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3. General characteristics of karite, the new impact diamond type

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After-organic pseudomorphs have been found out for the first time within impactites of the

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Kara impact structure (Shumilova et al., 2018), where they had been described initially as after-

229

coal diamonds. But, according to our detailed studies with a complex of high resolution methods

230

we propose them here as diamond fossils (see below).

231

Among carbon particles concentrates two types of after-organic pseudomorphs are

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distinguished: optically nontransparent black and transparent from intensively brown to colorless

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(Fig. 2). Both varieties have similar grains shape and sizes in the range of 30–100 µm forming

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usually well recognized elongated particles with 1:1:2 relation between sides in different

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directions. In other cases brown optically transparent particles have irregular shaped morphology 9

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which could not be recognized under optical microscopy, in some samples such diamond grains

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are very numerous and can have smaller sizes. According to phase state analysis the black

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particles are presented by glass-like carbon while brownish particles by nanocrystalline

239

diamonds (Shumilova et al., 2018b). The pseudomorphs have been found “in situ” within

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solidified impact melts (Fig. 1f) and chemically extracted from impact melt clasts, suevites and

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rare from massive melt rocks (Shumilova et al., 2018c).

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The diamond fossils locally can rich huge concentrations within impactites, where they get

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the highest number within condensed impact melt clasts of suevites getting hundreds grains per a

244

standard probe (5 g), that corresponds to several thousand carats per ton of the originate

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impactite. It is especially interesting that the concentrations of karite can be essentially abundant

246

in compare to other sorts of diamonds described in (Shumilova et al., 2018).

247

Some relict micro-detail morphology of karite can be seen at optical observations (Figs. 2

248

and 3) but perfectly preserved organics morphology has been recognized by detail SEM studies

249

where tiny morphological details can be detected (Fig. 3).

250

3.1. Micromorphological features

251

SEM observations are the most important in this study allowing describe karite

252

morphology in detail. The studied particles enriched from impactites have sizes from several tens

253

up to hundreds micrometers in cross section. The pseudomorphs usually are characterized with

254

elongated shapes with a coefficient of sides ratio about 1:2 (Fig. 3), flattened particles and

255

sometimes irregular grains can present as well. On the elongated particles the specific after-

256

organics relict morphology is easier recognized where their micromorphology becomes visible

257

by optical observations even. But, the details became clear only at SEM observations.

258 259 260

The original morphological elements are presented usually by wood cell structure elements

261

(Wheeler et al., 1989; Carlqust, 2015) and irregular shapes with similar physical parameter 10

262

features such as color, optical transparency and so on. Generally, the pseudomorphs are

263

presented by relics of elongated elements of wood cell fragments, such as vessel-wall elements,

264

fibers and other elements with tiny morphological details such as pits and parenchyma (Wheeler

265

et al., 1989; Carlqust, 2015). The observed variety of the pseudomorphs morphology is explained

266

with the complicated wood cell structure and possibility of various directions of their

267

defragmentation at process of sediments formation. We cannot exclude that some of relics can be

268

presented with longitudinal tracheids and ray parenchyma. The found organic relics will be a

269

subject for special paleobotanic study that probably would allow understanding of the certain

270

sediments age as a source for the diamond precursors.

271

3.2.Chemical composition

272

273

The chemical composition by X-Ray energy dispersive analysis has been analyzed before any

274

conductive layer covering to avoid any manmade contamination at the SEM specimens

275

preparing. Following to microprobe data the described diamond pseudomorphs are characterized

276

with carbon content having some presence of oxygen counting several percent (Supplementary

277

Material 1). Sometimes the diamonds can preserve up to 1%–2% of nitrogen, but usually they

278

are nitrogen-free. As for the detected small amounts of silica and sulfur (Supplementary Material

279

1), they come from natural matter being a specific characteristic of the initial organic matter

280

(Scurfield et al., 1974; Zhan et al., 1996; Gahan and Schmalenberger, 2014; Farooq and Dietz,

281

2015).

282 283 284

The provided LA-ICP-MS measurements of the individual impact diamond grains allow to

285

analyze and compare their trace-element composition with host black shales. Here we

286

demonstrate for the first time the data on after-organic diamond pseudomorphs enriched from 11

287

two types of solidified impact melts (clastic and vein types), in comparison with host black

288

shales and clark concentrations (Fig. 2c, Supplementary Material 2).

289

First of all, it is important to take attention for specifics of trace-element pattern profiles of

290

the diamond fossils. It is evidently seen that the diamond pseudomorphs have almost total

291

absence of heavy REE in the compositions. As for the light REE, they have essentially lower

292

concentrations level compare to the target and black shale clark. Additionally, we have found

293

very specific opposite U/Hf relation compare to black shales and their clark (Fig. 2c). At the

294

same time it is nicely observed that the diamonds have essentially lower content of Rb, Sr and

295

Ba and usually quite high Nb concentrations. The total REE content (1–33 ppm) is

296

fundamentally lower in contrast to the target black shales (134 ppm) and to the black shales clark

297

(145 ppm) (Fig. 2c, Supplementary Material 1). Following to the received data we have found

298

that the trace-element composition of the diamond fossils enriched from clastic and vein

299

solidified impact melts have similar features (Fig. 2c).

300

According to Corg isotopic measurements the analyzed diamond fossils extracted from 13

301

impact glasses of suevites from the Kara river region have quite narrow range of

302

laying within the limits (–24.2 ÷ –28.0)‰ (±0.1‰) pointing to a real organic source of carbon.

303

C content

3.3.Structural features

304

According to the X-ray Debye-Scherrer analysis the single grains of karite did not have

305

any evident diamond reflexes or have a single wide ring belonging to the most intense diamond

306

interlayer space with a distance 2.05 Å corresponding to octahedral plane (111). In a complex

307

combination of the other methods (see below) the observed data are possible to explain by very

308

tiny crystallites of diamond within the nanocrystalline aggregates where crystallite size is too

309

small for to be recognized by usual X-ray diffraction patterns. According to TEM, high

310

resolution HRTEM and atomic force microscopy (AFM) studies the diamond fossils are

311

presented generally with 2–5 nm crystallites of irregular shape being set close together within 12

312

minimal presence of amorphous carbon matrix on their boundaries (Fig. 4, Supplementary

313

Material 3). On the electron diffraction patterns karite has wide full rings without any features

314

pointing to texture or lonsdaleite presence. Meanwhile the rings centers certainly correspond to

315

crystalline diamond structure presented with interplanar distances – 2.05 Å (111), 1.25 Å (220)

316

and 1.065 Å (311), at the same time the very large wide of the rings points rather to some

317

difference in the crystallites sizes being co-ranged to the electrons wavelength.

318 319

The diamond state of the crystalline matter and the surrounding substance is supported with the detail Raman and IR spectroscopies described below.

320

During the detailed structural studies of phase state of the analized after-organic

321

pseudomorphs the possibility of their polyphase state has been found. Among some studied

322

fragments of the individual pseudomorph grains we have found polycrystalline graphite (Fig.

323

5a,b) and single crystalline particles which can be attributed to carbyne (Fig. 5c–e). The

324

measured electron diffraction patterns are in a perfect correspondance with α-carbyne variety of

325

a linear form of carbon (Supplementary Material 4) (Kudriavtsev et al, 1997; Shumilova, 2003).

326

Meanwhile the found has been supproted with reproducible electron diffraction measurements

327

we propose a need of additional detail study of the occurrences as it has a special fundamental

328

value for proof of the linear carbon state existance in the nature being still under debates.

329

Following to quite often presence of carbyne within the diamond fossils we predict that the

330

matter can be a good basic material for future carbyne studies in nature.

331 332

13

333 334

3.4.Spectroscopic features

335

Among the applied spectroscopic methods UV Raman spectroscopy was informative for

336

carbon phase state and general data on impurity of karite, the FTIR studies were used for

337

chemical radicals identification as the methods were useless for phase state diagnostics due to

338

too small diamond crystallites being unresolved to infrared radiation.

14

339

According to the UV Raman studies the diamond fossils are characterized with very

340

specific spectra resulting in three general bands of quite narrow T2 diamond band centered at

341

1318–1323 cm-1 with full width at half maxima (FWHM) 38–66 cm-1 accompanied with a red-

342

side shoulder wide band at 1220–1240 cm-1 (FWHM = 100 ÷ 250 cm-1) and a wide G band

343

around 1620 cm-1 (FWHM = 100 ÷ 150 cm-1). The spectra deconvolution data are presented on

344

Fig. 2c and in the Supplementary Material 5.

345

For IR analysis we used individual karite grains. In the tiny-nanocrystalline diamond

346

nature of the particles no direct fundamental diamond IR mode has been observed by the reason

347

of too small crystallites compare to IR wavelength (Fig. 6; Supplementary Material 6). At the

348

same time numerous bands which can be attributed to radical groups and defects of different

349

origin have been evidently seen. We have detected four probable sources of fluctuations resulted

350

by initial carbon-containing precursors (Fig. 6): nanocrystalline diamond and/or sp3 amorphous,

351

graphite and probably carbyne-like carbons (Supplementary Material 6).

352

The relict precursor bands are the most important for the particles properties descriptions

353

which allow understanding the diamond formation mechanism. Following to the observed IR

354

fluctuations in a complex with SEM and microprobe studies we have found that the diamond

355

precursor has been presented by lignin which has being presented by relict bands including

356

fluctuations of trisubstituted aromatic ring (811 cm-1); C–H deformation, CH2– and OCH3–

357

groups (1457 cm-1); unconjugated carbonyls transformed to C=O mode in polymeric net system

358

(1710 cm-1) (Ferrari, 2003) and CH stretching vibrations (2860, 2921, 2971 cm-1). Being a

359

characteristic of lignin the stretching vibrations of O–H are presented in diamond after-organic

360

pseudomorphs by bands centering at 3207 and 3428 cm-1 with some red-shift due to polymeric

361

nature resulted in vibration absorbance positions, being inversely proportional to mass of a

362

vibrating molecule.

15

363

The broad band at 1048 cm-1 can belong to C–O stretch peak nanocrystalline diamond

364

(Zaitsev, 2001; Inel et al., 2016; Afandi et al., 2018) or surface phonon mode of diamond

365

(Prawer et al., 1998), the band 1084 cm-1 can be attributed to CH3 rocking mode (Inel et al.,

366

2016). Two evidently observed frequencies 1261 and 1383 cm-1 can be explained rather by

367

aggregated platelets and C+ ions correspondently, seem to be defects formed with temperature

368

effects (Sandhu et al., 1989; Zaitsev, 2001) of the fast impact-origin thermal treatment and

369

followed by fast cooling of diamond within the host impact glasses. It is possible to suppose that

370

the intensive very broad signal in the range of 800–1370 cm-1 can point to presence of one-

371

phonon absorption band similar to superposition of signals from different defect centers in

372

natural and synthetic single-crystal diamonds described by A.M. Zaitsev (2001).

373

The observed intensive very broad bands at 1500–1700 cm-1 and 1800–2200 cm-1 may be

374

attributed to chain-like carbons with C=C cumulene and C≡C polyene vibrations (Kudryavtsev et

375

al., 1997) as crystalline carbyne particles have been detected by electron diffraction within

376

intergrowths with diamond in pseudomorphs described above.

377

On the basis of the mentioned wide cumulene band quite narrow peaks have been detected.

378

The first is centered at 1575–1580 cm-1 belonging to small quantity of graphite phase analyzed

379

within the same diamond pseudomorph particles by electron diffraction patterns (Ulyashev et al.,

380

2018). The frequency 1710 cm-1 can be resulted by C=O mode in polymerized carbon matrix

381

(Ferrari, 2003).

382 383 384 385 386

4. Discussion

16

387

The discovered new type of impact diamond fossils are presented by after organic

388

pseudomorphs, according to the described here features perfectly demonstrate unusual

389

characteristics differ from either after-graphitic (Kaminsky, 1991; Koeberl et al., 1997;

390

Langenhorst et al., 1998; Masaitis et al., 1998; Kvasnytsya and Wirth, 2013; Shumilova et al.,

391

2014 Kis et al., 2015; Ohfuji et al., 2015) or after-coal diamonds (Yezerskiy, 1986; Reshetnyak

392

and Yezerskiy, 1990; Shumilova et al., 2018b), and from all other types of origin natural

393

diamonds from kimberlites, lamproites, ultramafic lamprohyres, metamorphic rocks and from

394

meteoritic diamonds too (Harlow, 1998; Shiryaev et al., 2011; Dobrzhinetskaya, 2012; Marty et

395

al., 2013; Shirey et al., 2013; Piazolo et al., 2016 and many others). Here we point to general

396

specifical characteristics of the new impact diamond type differing karite from the mentioned

397

other diamond sorts.

398 399

4.1. Microscopic and composition features

400

The impact after-graphitic diamonds are characterized with polycrystalline aggregates

401

often having polyphase composition and evidence of mechanical defect abundence resulted

402

in stacking faulted structure up to forming defect structure of so-called lonsdaleite

403

(Masaitis et al., 1998; Smith and Godard, 2009; Kulnitskiy et al., 2013; Kvasnytsya and

404

Wirth, 2013; Németh et al., 2014; Kraus et al., 2016). The typical after-coal diamonds are

405

presented with nanocrystalline lonsdaleite-free/texture-free aggregates formed after

406

fragments of metamorphosed organics, micro-coal particles, spread in sedimentary rocks of

407

the Kara target (Shumilova et al., 2018b).

408

In difference to the after-graphitic and after-coal diamonds first of all it is nesessary to take

409

attention to very specifical structure and morphology. Following to ED patterns and HRTEM

410

images they do not have any deformations, such as lonsdaleite. The diamond fossils are

411

presented by perfectly saved micromorphological features of wood cell structure (Fig. 3) 17

412

pointing to absence of features of initial chemical changes of the organic matter, such as

413

gelification resulting in lost of original cell micromorphology of organic matter (Hatcher et al.,

414

1985). Thus, it would be justified to assume that the organics before the impact process could be

415

presented by nondestructed (unmetamorphosed) wood matter. Meanwhile the rare finds of

416

replicas after framboidal pyrite on the diamond pseudomorphs (Supplementary Material 7) allow

417

to conclude that a small part of the starting carboniferous substance was presented by slightly

418

changed organics, perhaps by peat at an initial stage of coalification without defragmentation and

419

visible chemical changes. At the same time the very different specifics of rare elements

420

composition from the host black shales of the Kara target (Fig. 2e) allow to conclude that the

421

carbon precursor did not absorb microcomponents from environment like the carboniferous

422

matter of the sedimentary target rocks. Thus, it was rather mostly presented by very low changed

423

organics counting very low concentration of the microcomponents (Fig. 2e, Supplementary

424

Material 2). Theoretically we cannot exclude some possibility of diamond fossils formation even

425

from “alive” wood, supported with lignin and cellulose relict radicals measured by IR

426

spectroscopy.

427

4.2. Raman spectroscopy features

428

The measured UV Raman spectra of the studied diamond pseudomorphs after organic

429

relics have very specific characteristics. First of all the use of UV excitation allows to

430

avoid very intensive luminescence under visible laser light that allow study the type of

431

diamonds in detail.

432

By the moment we had not find any experimental or theoretical data exactly corresponding

433

to the measured Raman spectra of the diamond variety that could help understanding and

434

explaining of the evidently observed and the strongly reproducible full complex of the

435

spectroscopic features.

18

436

The position of the T2 diamond band originally is located at ∼ 1332 cm−1, but in the

437

measured spectra it is essentially red-shifted up to 1318 cm-1 due to the very small diamond

438

crystalline sizes in a contrast to after-graphitic impact diamonds where the observed diamond

439

band shift is explained with lonsdaleite presence (Smith and Godard, 2009; Karczemska, 2010;

440

Goryainov et al., 2014; Jones et al., 2016 and others). The lonsdaleite absence in the studied

441

diamonds was proved with high resolution TEM and electron diffraction measurements (see

442

below). We explain the observed red shift by nanocrystalline aggregate overheating under laser

443

excitation described elsewhere (May et al., 2008; Isaenko and Shumilova, 2009) or by a phonon

444

confinement effect presented by Osswald (2009) and Yoshikawa (1993, 1995) with co-authors.

445

The red-side shoulder is deconvoluted into two bands. The first centered at about 1020–

446

1100 cm-1 is corresponding to T peak of sp3 carbon (Ferrari, 2002, 2004) and second posited at

447

1220–1240 cm-1 belongs rather to nanocrystalline or sub-nanocrystalline diamond probably up to

448

amorphous tetrahedral diamond-like carbon (ta-C) (Yoshikawa et al., 1995; Prawer, 2000;

449

Ferrari, 2002, 2004; Osswald et al., 2003; Piscanec et al., 2005). While the deconvolution looks

450

just as a mathematical function and no evident differentiation from the measured spectra profiles

451

has been observed, presenting smooth shoulder slope without any visible band maxima.

452

The previous theoretical calculations for nanodiamond and based on differently sized

453

models with C–H bondings (Ferrari, 2004; Filik et al., 2006; Li et al., 2010) allow us to suppose

454

the idea that the observed wide band at 1220–1240 cm-1 and the other red-shift slope can be

455

caused by any defect-origin band originated from diamond crystalline smallest sizes, unordered

456

sp3 carbon elements and/or with polymeric network structure on the basis of sp3-carbon, similar

457

to D band in graphitic carbons (Wopenka and Pasteris, 1993; Ferrari, 2004). Taking to account

458

that the band is being describing here for the first time we call the band “DD”, after –

459

“disordered diamond” band differing from “D” – “disordered” band used for graphitic carbons,

460

originated after breakdown of theoretical wave vector selection rules in graphitic materials

461

(Wopenka and Pasteris, 1993). 19

462

The detected in the measured UV Raman spectra G band centered at 1600–1650 cm-1 is

463

caused due to boundaries between fine-size diamond crystallites in nanocrystalline aggregates

464

and within ta-carbon (tetrahedral amorphous carbon), where some presence of amorphous sp2

465

carbon is a usual component. The observed blue-shifted shoulder (1685–1730 cm-1) at the G

466

band is explained with small quantity of C=O bonds going either from natural origin or resulted

467

after thermochemical diamonds enrichment with partial surface oxidation.

468

The measured reproduced Raman data for karite are essentially different to the reported

469

after-coal (Reshetnyak and Yezerskiy, 1990; Shumilova et al., 2018) and after-graphitic

470

(Reshetnyak and Yezerskiy, 1990; Schmitt et al., 2005; Yelisseyev et al., 2013; Goryainov et al.,

471

2014; Németh et al., 2014; Ohfuji et al., 2015; Kis et al., 2016) impact diamonds and diamonds

472

in meteorites (Karczemska, 2010), but partly similar to meteoritic nanodiamond from Efremovka

473

and Orgueil meteorites (Shiryaev et al., 2011).

474 475

4.3. IR spectra specifics

476

Following to the described above nicely preserved micromorphology of the organic matter

477

presented rather by wood debris we supposed possibility of relict IR-active radicals from

478

wood precursor. The comparative analysis with different components of wood matter and

479

its treatment products proved our hypothesis and demonstrated numerous IR bands

480

corresponding to relict radicals going from lignin and cellulose (Fig. 6, Supplementary

481

Material 6). According to well saved C-H radicals with the nicely preserved band structure

482

we have to conclude that before diamond formation its precursor has been presented with

483

very low changed wood organic matter, corresponding to a level no deeper than lignite

484

stage of coalification and rather less, taking to attention the cellulose relics presence

485

(Verheyen et al., 1985; Boeriu et al., 2004; Patrakov et al., 2010; Cao et al., 2013; O'Keefe

486

et al., 2013; Donga et al., 2015). The preserved fine IR bands structure of the organic

487

precursor supports the short term precursor treatment under impact HPHT conditions that 20

488

can be concluded from experimental pyrolysis studies of coals (Donga et al., 2015; Ojhaa

489

et al., 2015) and lignin coalification (Cao et al., 2013, Supplementary Material 6).

490 491

4.4. K-T-nanodiamonds

492

There are some papers devoted to nanodiamonds findings within “catastrophic layer” at

493

K-T boundary (Gilmour et al., 1992; Hough et al., 1997). The mentioned finds do not

494

correspond evidently to the described here new type of ultra-nanocrystalline diamonds

495

formed after organic transformation, having nitrogen absence and essential difference in

496

carbon stable isotopic composition similar to normal organic matter of the host

497

sedimentary rocks. At the same time, the found diamond pseudomorphs after organics can

498

give a key to understand many aspects of carboniferous matter changing under impact

499

conditions including formation mechanism of lonsdaleite-free impact diamonds. The latter

500

can help in explaining the lack of lonsdaleite within many impact-related objects.

501 502

4.5. Ultra-nanocrystalline synthetic analogue

503

During long time the possibility of diamond crystallization from bitumens, coals and

504

individual hydrocarbons was not clear as many experimental works were unsuccessful

505

(Noda and Kato, 1965; Whang et al., 1974; Ayache et al., 1990; Beyssac et al., 2003;

506

Korochantsev, 2004). But later diamond synthesis from coal and individual hydrocarbons,

507

such as naphthaline, anthracene, pentacene, perylene, and coronene have been provided

508

with the evidently positive production as in static high pressure conditions (Davydov et al.,

509

2004, 2006; Chen et al., 2018) and under shock process (Kurdyumov et al., 2009, 2012).

510

The structural composition of the observed in our case impact diamond paramorph has

511

some principle similarity with the mentioned synthesis products. First of all, it concerns to

512

essentially better diamond crystallites quality and their small sizes – from micrometers to very

513

small getting only 2–3 nm, as it was reported in Chen et al. (2018). The smallest diamonds were 21

514

named by ultra-nanocrystalline diamonds. Also, it was described about defect-free diamond

515

aggregates structure (Borimchuk et al., 1991; Kurdyumov et al., 2009, 2012) and possibility of

516

polyphase carbon products formation from hydrocarbons (Davydov et al., 2006), that we also

517

recognized in some impact carbon grains. The general difference with the synthetic products is

518

presence of essentially larger single diamond crystals getting 10 µm.

519

At the same time, by the moment it is not possible to provide very detail correct

520

comparison with the mentioned synthetic material by the reason of instrumental data

521

insufficiency on the synthetic material. More less it is excepted to provide larger experimental

522

material which will get a good basis for understanding of the described natural

523

ultrananocrystalline diamond formation in detail. Meanwhile the description presented in the

524

mentioned publications allow to predict better similarity of the diamonds pseudomorphs with the

525

products of shock experiments (Borimchuk et al., 1991; Kurdyumov et al., 2009, 2012) having in

526

principle closer formation parameters with very fast crystallization.

527

Following to the presented here structural, composition and morphological data we

528

propose the same mechanism of diamond fossils formation as for the regular Kara after-coal

529

diamonds (Shumilova et al., 2018) by fast ultrahigh pressure pyrolysis stage co-followed with

530

short-distance diffusive crystallization based on the experimental works (Borimchuk et al., 1991;

531

Kurdyumov et al., 2009) produced lonsdaleite-free/texture-free diamond nanocrystallites from

532

coal and soot.

533 534

5. Conclusion

535

It is presented here that the new type of impact diamonds found out at the Kara impact

536

structure has a complex of typomorphic features including their morphological, structural and

537

spectroscopic characteristics differing them from any other known diamond types. The diamond

538

fossils are characterised by polynanocrystalline aggregates with sizes of crystallites 2–5 nm and

539

possible presence of amorphous sp3- carbon matrix admixtures with some presence of sp2-carbon 22

540

(in amorphous state of carbon or graphite) and carbyne. A nicely preserved morphology of the

541

initial wood cell structure is the general characteristic of the diamond which in the complex of

542

the measured IR spectroscopic characteristic allow to propose a new impact diamond type

543

formed after slightly changed organics, possibly “alive”, even, presented by diamond fossils and

544

named here by karite.

545

The find of the new diamond type expands possibility of the diamond formation in the

546

nature. Having a supernanocrystalline structure the diamond fossils can be interesting for

547

physical properties measurements testing them as a possible new material. By the other hand, the

548

natural diamond fossils point to a widely spread possibility of diamond formation under the

549

impact processes without graphitic crystalline basement and/or carboniferous solidified matter

550

like sedimentary rocks or coals. Also, karite can be used for paleobotanic and age studies of the

551

impact story and, also, for nature proving of the debated impact structures and astrobiological

552

aspects. Additional future interest to the new find can be attracted by possibility of perspectives

553

of carbyne studies.

554

555

Acknowledgements

556

The authors thank V.L. Masaitis and S.M. Maschshak for scientific consultations and

557

discussions; all Russian field team members for help in the expedition; V.A. Vasilyev, E.M.

558

Tropnikov, S.S. Shevchuk, B.A. Makeev, I.V Smoleva, V.A. Radaev for analytical studies of the

559

impact diamonds and E.V. Susol, V.A. Zhydova, A.Ye. Shmyrov for technical assistance. The

560

work has been supported by the RFBR project #17-05-00516 for diamond fossils studies; field

561

observations of impactites, impact glasses studies and diamond extraction from impact glasses

562

for proving UHPHT nature of the impact glasses have been provided through the Russian

563

Science Foundation, project # 17-17-01080.

564 23

565

Author Contributions. T.Sh. organized the field works, enriched and diagnosed

566

diamonds, introduced the original idea, participated in all stages of the analytic studies and

567

interpretation, collected experimental data and wrote the manuscript; V.U. provided TEM studies

568

and took part in the field works; V.K realized UV Raman spectroscopy; E.V. collected IR

569

spectra; S.I. carried out visible Raman measurements and took part in the field works; S.S. and

570

Y.Ch. produced LA-ICP-MS; N.K. analyzed LA-ICP-MS data and took part in the field works.

571

572

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Zaitsev, A.M., 2001. Optical properties of diamond. A Data Handbook. Springer, 502 pp.

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Zhan, G., Erich, M. S., Ohno, T., 1996. Release of trace elements from wood ash by nitric

827

acid. Water, Air, and Soil Pollution 88(3-4), 297–311, doi:10.1007/bf00294107.

828

34

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Figure captions:

830 831

Figure 1. Geographic and geological characteristics of the studied object. (a) Geographic setting

832

of the studied area. (b) Geological scheme of the Kara region territory, simplified by S.I. Isaenko

833

and T.G. Shumilova (Shumilova et al., 2018c) after the State Geological Map of Russia (GGK-

834

1000) (State Geological Map of Russia, 2000). Sedimentary deposits: 1–Upper Proterozoic; 2–

835

Silurian and Ordovician; 3–Devonian; 4–Carboniferous; 5–Permian; 6–Triassic; 7–Cretaceous.

836

8–Impactites. Magmatic intrusions: 9–Late Devonian tabular body and dikes of dolerite and

837

gabbro-dolerite. Tectonic elements: 10–deep faults; 11–thrusts; 12–small faults; 13–boundary of

838

impact crater. Geographic elements: 14–sea coast; 15–rivers; 16–sampling region at the Kara

839

impact structure. (c) Outcrop of diamondiferous suevites from the studied region, river Kara,

840

Pay-Khoy, Russia, a place of the first karite find; a visible outcrop prolongation – about 800 m;

841

the photo made with use of a drone facility. (d) Suevite with a large lens-like clast of impact

842

glass containing huge diamond fossils concentrations. (e) Optical image of impact rock melt

843

clast, transparent light without analyzer. (f) A grain of diamond fossil “in situ” within solidified

844

impact melt matrix, a polished section surface; it is seen that the particle is going out from a

845

surface just partly and has not been cut under polishing, presenting high hardness. SEM image:

846

back scattered electron (BSE) (left) and scattered electron (SE) (right) images.

847 848

Figure 2. General characteristics of diamond fossils. An optical image of a diamond fossil

849

chemically enriched from impactite: in transparent (a) and reflected (b) light. (c) Typical UV

850

Raman spectrum of diamond after-organic pseudomorph with marked deconvoluted bands. (d)

851

Typical IR spectrum of diamond fossil. (e) Primitive mantle-normalized trace-element patterns

852

for individual diamond after-organic pseudomorph grains from clastic and UHPHT vein impact

853

glasses and target black shale. 35

854

Figure 3 SEM images of after-organic diamond pseudomorphs, wood fiber fragments with

855

preserved vessels: a vessel fragment overview in tangential direction with nicely preserved

856

epithelial cell micromorphology and pits (a), a magnified part (b); a relict with wood ray cells (c)

857

and its magnified part with a preserved parenchyma (d); a wood fiber relict (e) with nicely

858

preserved epithelial cell micromorphology (f); a – BSE, b–f SE modes.

859

860

Figure 4. Bright TEM image of nanocrystalline structure of after-organic diamond pseudomorph:

861

fragment overview (a) with the corresponding electron difrraction pattern (b),

862

polynanocrystalline structure (c), EELS spectrum (d), high resolution TEM image of

863

polynanocrystalline structure (e) and its magnified fragment from a central part (f) .

864

Figure 5. TEM data of carbon phases from diamods fossil grain. Polycrystalline graphite

865

fragment recovered from diamond pseudomorph aggregate: (a) bright field image, (b) electron

866

duffraction pattern corresponds to graphite spacings – 0.336 nm (002), 0.211 nm (100), 0.123 nm

867

(110). The proposed α-carbyne fragments (inclusions) from the host after-organic diamond

868

pseudomorph: (c, d) overview images of particles with different sizes; (e) magnified image from

869

(d); (f) electron diffraction pattern from the particle on b, beam ⊥ (001), the interplanar distances

870

are presented in Supplementary Material 4.

871

Figure 6. IR spectra: typical diamond fossil (a) and different components of wood organic matter

872

and wood treatment products from RRUFF database (to bottom): (b) hydrocellulose, (c) cellulose

873

acetate butyrate (biopolymer), (d) cellulose with lignin, (e) lignin.

874

36

Highlights A new type of natural diamonds found out: impact diamond fossil - karaite. Diamond formation from lignin and cellulose is proposed. Organics changes and reservation under extremely high pressure and temperature are presented.

Declaration of Interest Statement