The Characteristics and Origin of Amber Deposits in the Dominican Republic

Mineralogical and geochemical characteristics of amber deposits located in the Dominican Republic, i.e., Hato Mayor Province of the Eastern Mining District (EMD) in the Cordillera Oriental, and Santiago Province of the Northern Mining District (NMD) in the Cordillera Septentrional were performed. The results of analyses of amber-bearing sediments collected from the borehole in Siete Cañadas area (EMD) were referenced to the petrological data obtained for the coaly shales from La Cumbre (NMD). The mineralogy of the rocks was described using transmitted and reected light microscopy, scanning electron microscopy, Powder X-ray diffraction and Fourier Transform Raman Spectroscopy. Biomarker analyses by the gas chromatography-mass spectrometry were used to trace the genetic source and transformation stage of abundant organic matter hosted in the core sediments. Our ndings indicated that basins in EMD and NMD regions were different isolated palaeosettings, in which under the inuence of local physicochemical factors the terrigenous material was transformed and got maturated. In both amber deposits, the sedimentation of clastic and organic material proceeded in the presence of marine conditions. In case of the NMD area, the sedimentation underwent probably in the conditions of the lagoon environment, a shallow maritime lake or periodically ooded plain, that facilitated organic matter decomposition and carbonation from meta-lignite to sub-bituminous coal (random reectance of coal - R ro = 0,39%). In the EMD region, the sedimentation took place in a deeper basin, where terrigenous material was likely mixed with material found in situ (fauna fossils, carbonate-group minerals) to form the mudstones enriched in bituminous substance of low maturity. The organic matter found in the rocks from both regions is of mixed terrestrial/marine origin and was deposited in the presence of low oxygen concentration and reducing and/or dysoxic conditions. amber-bearing coaly shales with fragments of coalied plant detritus of the La Toca Formation 25,28,32,33 were earlier characterized in detail 10 . Organic material in these rocks was in the transition stage from meta-lignite to subbituminous coal. Two types of resins were identied, i.e. a typical resinite that forms characteristic laminas, as well as detritic amber grains of different size and shape. Facies analysis followed by Kalkreuth et al. 34 and also Gruber and Sachsenhofer 35 procedures revealed that these sediments were formed in a shallow crustal lake environment in the zone bordering the oodplain of the river, with periodic oods. of petrogenetic investigation of the amber-bearing rocks from El Valle region (EMD), collected from SC-02 borehole, are presented The aim of the study was to elucidate depositional environment of the amberiferous rocks based on host rocks mineralogy and geochemistry of associated organic matter. Novel data from scanning electron-microscopy (SEM-EDS), Fourier Transform-Raman spectroscopy (FT-RS), Powder X-ray diffraction (PXRD), Gas Chromatography–Mass Spectrometry (GC-MS) and Rock-Eval analysis were integrated into palaeogeographic chronology of depositional events and modelled burial history. Additional data on organic geochemistry of amber-bearing rocks from La Cumbre deposit (NMD) was obtained in order to complete the petrogenetic characterization reported previously by Stach et al. 10 . The data were used for comparison of amber-bearing sediments from NMD and EMD regions in terms of their petrogenesis and the palaeoenvironments. Based on the mineralogy of the rocks and the geochemistry of their organic matter, description of depositional environment of sediments, source area for their clastic components, and redox conditions were proposed and discussed for both regions of the Dominican Republic. The Caribbean region is relatively poorly recognised and described in literature in terms of geology. However, it is very interesting, because amber of unique properties in the world is found there. The present work therefore an important contribution to the knowledge of the processes and palaeoenvironment of the formation of fossil resin deposits The Rock-Eval pyrolysis method and biomarkers analysis. The Rock-Eval pyrolysis method and biomarkers analysis were applied in order to assess the quantity, kerogen type and thermal maturity of organic matter in the rocks. The samples from the Siete Cañadas area were analysed and compared to the specimens from the La Cumbre deposit performed to determine the genesis of their organic precursors and their depositional environment. The pyrolysis of rock samples was carried with the Rock-Eval Model 6 instrument according to Lafargue et al. 40 and Behar et al. 41 . The pyrolytic apparatus was equipped with two ovens for pyrolysis and combustion processes with the programmed temperature. The temperature was conducted from 100 up to 850°C. The hydrocarbons generated during analysis were measured by a ame ionization detector (FID), whereas the non-hydrocarbons compounds like CO 2 and CO released during pyrolysis and oxidation stages were monitored by an infra-red detector (IR). The hydrocarbons detected by FID are represented by S 1 and S 2 peaks. Non-hydrocarbons compounds are produced during pyrolysis (up to 500°C - S 3CO and up to 400°C S 3CO2 pyrolysis curves) and during oxidation (S 4CO and S 4CO2 oxidation curves) 40 . The Rock-Eval 6 apparatus also allowed for the determination of the mineral carbon content (MINC), described by the peak S 5 and S 3MINC40 . Based on these results, the parameters of the quality of the source rock were calculated: (1) organic carbon content (sum of S 1 , S 2 , S 3 CO, and S 3 CO 2 peaks – all released during pyrolysis), (2) residual carbon RC (sum of the S 4 CO and S 4 CO 2 peaks – obtained during the oxidation), (3) the oxygen index OI, (4) hydrogen index HI, and (5) temperature T max40,41 . Soxhlet asphaltene fraction was precipitated n-hexane. maltenes were then separated into compositional fractions of aliphatic hydrocarbons, aromatic hydrocarbons and resins by the use of column chromatography, using an alumina:silica gel (2:1, v/v) column (0.8 × 25 cm). The fractions were eluted with n-hexane, toluene, and toluene:methanol (1:1, v/v), respectively. The isolated saturated hydrocarbon fractions were diluted in isooctane spiked with 5β-cholane and analyzed using gas chromatography-mass spectrometry (GC–MS). The analysis was carried out with an Agilent 7890A gas chromatograph (GC) equipped with an Agilent 7683B automatic sampler, an on–column injection chamber, and a fused silica capillary column (60 m × 0.25 mm i.d.) coated with 95% methyl/5% phenylsilicone phase (DB-5ms, lm thickness 0.25 µm). Helium was used as a carrier gas. The GC oven was programmed as follows: a temperature of 80°C was maintained for 5 min, then it was ramped to 120°C at the rate of 20°C/min, after that, to 180°C at the rate of 2°C/min, and nally, it was ramped to 300°C at the rate of 3°C/min. The oven was kept at 300°C for 35 min. The GC was coupled with an Agilent 5975C mass selective detector (MSD), which operated at an ion source temperature of 230°C, ionisation energy of 70 eV, and cycle time of 1 sec in a mass range from 45 to 550 Daltons. The aromatic hydrocarbon fractions were diluted in toluene and analyzed by GC–MS using the same equipment as for the saturated hydrocarbon fraction. Ortho-terphenyl was used as an internal standard. The GC oven was programmed as follows: a temperature of 80°C was maintained for 1 min, then it was ramped to 120°C at the rate of 20°C/min, and after that, to 180°C at the rate of 2°C/min, and

The Rock-Eval pyrolysis method and biomarkers analysis. The Rock-Eval pyrolysis method and biomarkers analysis were applied in order to assess the quantity, kerogen type and thermal maturity of organic matter in the rocks. The samples from the Siete Cañadas area were analysed and compared to the specimens from the La Cumbre deposit performed to determine the genesis of their organic precursors and their depositional environment. The pyrolysis of rock samples was carried with the Rock-Eval Model 6 instrument according to Lafargue et al. 40 and Behar et al. 41 . The pyrolytic apparatus was equipped with two ovens for pyrolysis and combustion processes with the programmed temperature. The temperature was conducted from 100 up to 850°C. The hydrocarbons generated during analysis were measured by a ame ionization detector (FID), whereas the non-hydrocarbons compounds like CO 2 and CO released during pyrolysis and oxidation stages were monitored by an infra-red detector (IR). The hydrocarbons detected by FID are represented by S 1 and S 2 peaks. Non-hydrocarbons compounds are produced during pyrolysis (up to 500°C -S 3CO and up to 400°C S 3CO2 pyrolysis curves) and during oxidation (S 4CO and S 4CO2 oxidation curves) 40 . The Rock-Eval 6 apparatus also allowed for the determination of the mineral carbon content (MINC), described by the peak S 5 and S 3MINC 40 . Based on these results, the parameters of the quality of the source rock were calculated: (1) organic carbon content (sum of S 1 , S 2 , S 3 CO, and S 3 CO 2 peaks -all released during pyrolysis), (2) residual carbon RC (sum of the S 4 CO and S 4 CO 2 peaks -obtained during the oxidation), (3) the oxygen index OI, (4) hydrogen index HI, and (5) temperature T max 40,41 .
Prior to the biomarkers analysis, the compounds were extracted with dichloromethane:methanol (93:7 v/v) in Soxhlet apparatus. The asphaltene fraction was precipitated with n-hexane. The remaining maltenes were then separated into compositional fractions of aliphatic hydrocarbons, aromatic hydrocarbons and resins by the use of column chromatography, using an alumina:silica gel (2:1, v/v) column (0.8 × 25 cm). The fractions were eluted with n-hexane, toluene, and toluene:methanol (1:1, v/v), respectively.
The isolated saturated hydrocarbon fractions were diluted in isooctane spiked with 5β-cholane and analyzed using gas chromatography-mass spectrometry (GC-MS). The analysis was carried out with an Agilent 7890A gas chromatograph (GC) equipped with an Agilent 7683B automatic sampler, an on-column injection chamber, and a fused silica capillary column (60 m × 0.25 mm i.d.) coated with 95% methyl/5% phenylsilicone phase (DB-5ms, lm thickness 0.25 µm). Helium was used as a carrier gas. The GC oven was programmed as follows: a temperature of 80°C was maintained for 5 min, then it was ramped to 120°C at the rate of 20°C/min, after that, to 180°C at the rate of 2°C/min, and nally, it was ramped to 300°C at the rate of 3°C/min. The oven was kept at 300°C for 35 min. The GC was coupled with an Agilent 5975C mass selective detector (MSD), which operated at an ion source temperature of 230°C, ionisation energy of 70 eV, and cycle time of 1 sec in a mass range from 45 to 550 Daltons. The aromatic hydrocarbon fractions were diluted in toluene and analyzed by GC-MS using the same equipment as for the saturated hydrocarbon fraction. Ortho-terphenyl was used as an internal standard. The GC oven was programmed as follows: a temperature of 80°C was maintained for 1 min, then it was ramped to 120°C at the rate of 20°C/min, and after that, to 180°C at the rate of 2°C/min, and nally, was ramped to 300°C at the rate of 3°C/min. The oven was kept at 300°C for 35 min. The MSD was operated with a cycle time of 1 sec in a mass range from 45 to 550 Daltons.

Results
Mineralogy and petrography of amber-bearing rocks. Fine-grained and poorly oriented, laminated texture was observed in investigated rock samples ( The pelitic-aleuritic and parallel rock texture characteristic of mudstone, was better marked by polarized, transmitted light ( Fig. 4A-F). Generally, a slight increase in grain size of clastic material in the direction from the top (100 µm) to the bottom (over 200 µm) of the pro le is observed. Similarly, the content of organic material forming thin laminae in clay-clastic matrix is also gradually changing with depth; it is higher in specimens coming from the bottom of the pro le. The average composition of the rocks includes clay minerals (44 vol.%), quartz (20 vol.%), feldspars (9 vol.%), gypsum (1 vol.%) and opaque, ore minerals, mainly represented by framboidal pyrite (15 vol.%).
Powder X-ray diffraction (PXRD) analyses ( Fig. 5A-D [42][43][44] . It forms at least three morphological types: (1) framboidal, (2) recrystallized and (3) euhedral crystals. It forms individual grain ranging in size from a few to several dozen micrometres ( Fig. 6A-D, F) or aggregates of various shapes found in veins, coaly laminas, within plant detritus or randomly distributed in the rocks. Titanium minerals form euhedral or anhedral grains up to 100 µm in size with low re ection ability. and 635 cm − 1 49,50 . In general, the highest amounts of titanium oxides are found in the rocks from the lowest part of the pro le (SC4). Conversely, pyrite is the most abundant in the rocks from the upper part of the pro le (SC1, SC2; Fig. 7D). Occasionally, ne (25 µm in size) grains of REE-bearing phosphates (monazite) also occur in the rock matrix. The single anhedral crystals of strontium sulphates as well as acicular crystals of calcium sulphates ll fractures and cracks in the close vicinity of sodium feldspars.
The plant detritus form lenses and veins, strongly fractured, and occasionally lled with syngenetic crystals of pyrite. Locally, the traces of well-preserved cell structure of plant was observed on SEM images (Fig. 6F). The abundant plant detritus locally hosts the tiny grains of fossil resins (e.g. Figure 4E-F) and abundant fragments of fauna fossils (e.g. Figure 4A- In other plant detritus, the original structure has been more or less disturbed (Fig. 8B). Occasionally, small crumbs of dark yellow fossil resin are found close to these plant fragments.
Ulminite is a maceral with more advanced transformations in its structure, which led to its complete destruction (Fig. 8B). The presence of atrinite and densinite ( Fig. 8C-D) indicates that detritus is composed of herbaceous plants or fragment of trees. These macerals show differences in the degree of density of the detritus. In the atrinite, the material is loosened contrary to the densinite, where it is more dense. At the contact of densinite, some concentrations of an oval gel-like substance -corpohuminite are found (Fig. 8D).
Results of Rock-Eval and bitumen extraction analysis. In the rock samples from the Siete Cañadas (SC1-SC4), the total organic carbon content (TOC) varies between 0.75 to 5.11 wt.%, with an average value of 2.3 wt.% ( Table 1). The hydrocarbon content (S 1 + S 2 ) ranges from 0.60 up to 1.53 mg/g of rock (Table 1,  Abbreviations: TOC -total organic carbon, in wt.%; T max -temperature, in o C; S 1 -free hydrocarbons, in mg/g rock; S 2 -heavy hydrocarbons, in mg/g rock; S 3 -CO 2 content, in mg/g rock; PI -productivity index; HI -hydrocarbons index, in mg/g TOC; OI -oxygen index, in mg/g TOC; MINC -mineral carbon, in wt.%; PC -pyrolytic carbon, in wt.%; RC-residual carbon, in wt.%. The La Cumbre deposit is representing by three samples -LC1, LC2 and LC3. The TOC values in these samples are much higher, i.e. 9.92 to 11.13 wt.% (Table   1), with an average value of 10.7 wt.%. The hydrocarbon content values (S 1 +S 2 ) are also higher, from 3.26 to 5.50 mg/g rock, what might indicate that these rocks have excellent hydrocarbon potential ( Figure 9A).
Similarly, the high amount of bituminous extract, ranging from 565 to 3630 ppm in Siete Cañadas rocks, and 3906 and 4790 ppm in La Cumbre rocks (Table 2, Figure 9B). In both areas results indicates the good hydrocarbon potential. The extract is dominated by resins and asphaltenes fractions, ranging from 64 to 86% in rocks from Siete Cañadas, and 83 and 86 % in La Cumbre ( Table 2). The proportions of saturated and aromatic hydrocarbon fractions in extract are smaller. Biomarkers analysis. The rocks from Siete Cañadas (SC1-SC4) and the La Cumbre (LC1, LC2) deposits contain few groups of compounds: n-alkanes, acyclic isoprenoids, terpanes, and steranes.
The analysis of fragmentation ion m/z 71 revealed presence of n-alkanes from C 14 to C 31 homologues ( Figure 10). They exhibit monomodal distribution in samples from the La Cumbre deposit ( Figure 10A) with the domination role of short-chain compounds, and bimodal distribution with maximum of C 18 and C 31 in samples from the Siete Cañadas area ( Figure 10B-C). The Carbon Preference Index (CPI), calculated according to Kotarba et al. 61 , is in the range from 1.26 to 2.67 for mudstones from the Siete Cañadas, and in the range from 2.81 to 2.84 for coaly shales from the La Cumbre (Table 3). The calculated Terrigenous-Aquatic Ratio 62 is higher than 1.0 for the samples from both regions and ranging from 1.34 to 8.56 in Siete Cañadas, and 6.05 and 7.04 in La Cumbre samples ( Table 3).
Chromatograms of the sterane distribution was recorded at m/z 217 mass ion, and αββ steranes at m/z 218. The combined results of these single mass ion chromatograms allowed to calculate the regular ααα steranes distribution, C 27 diasteranes/(diasteranes+regular steranes), C 27 dia/(dia+reg), C 29 S/(S+R), and C 29 αββ/(ααα+αββ). The distribution of regular ααα steranes revealed that C 29 regular steranes play a dominant role in all samples ( Table 4). The results of C 27 dia/(dia+reg) ratio linked with palaeoenvironment conditions in all samples were 0.00 (Table 4). Linked with thermal maturity of organic matter, C 29 S/(S+R) and C 29 αββ /(ααα + αββ), were very low, in range from 0.01 to 0.08, and 0.03 to 0.24 respectively (Table 4). In the most studies, despite the differences in proposed depositional systems, it was concluded that amber was deposited in a low energy 31 Thus, the oxic/anoxic boundary provide the most favourable environment for crystallization of framboidal pyrite form. More detailed data on the redox conditions of framboids precipitation pathways might be revealed from distribution pattern of their diameters 70 . In case of sediments from EMD, the large size of framboids (up to 100 µm) and the presence of another forms of pyrite, rather suggest diagenetic origin of this mineral, which was probably formed under oxic or dysoxic water column 71 . However, if framboidal pyrite was formed during pseudomorphic replacement of certain organic compounds, the determination of depositional system may be ambiguous. Thus, alternating anoxic/dysoxic conditions cannot be entirely excluded as evidenced by geochemical ngerprint of associated organic matter, especially low Pr/Ph ratio 72,73 (Table 3). The oxygen depletion may occur periodically as a result of upwelling process, which played an important role during the formation of the YF complex 30 .
The dominant presence of pyrogenic quartz with minor contribution of plagioclases and K-feldspars (orthoclase, sanidine) as well as abundant occurrence of titanium oxides may indicate the igneous rocks of Los Ranchos Formation (diorites, quartz porphyries) 74  For the rocks of the El Valle area (EMD), the presence of Ca-Mg smectite, carbonates (calcite, aragonite, dolomite) or sulfates (mirabilite) indicates a saltwater environment of deposition of terrigenous material. The reservoir was likely subjected to denudational movements, which promoted cyclic sedimentation processes of plant detritus and resins. This is also supported by the rich fossil contents, mainly dominated by marine fauna remnants, such as mollusks, ostracods, foraminifera, bryozoans, red algae, echinoids, and so on. However, the clastic material of rocks probably originated from the Los Ranchos complex, found in close vicinity of amber-bearing sediments in the El Valle region.
In the case of La Cumbre deposit (NMD), the presence of kaolinite indicates an oxic environment of low pH, resulting from progressive accumulation of organic matter. Framboidal pyrite started to precipitate when the concentration of oxygen was lowered to anoxic conditions. The results of facial and mineralogical analyses of amber-bearing strata suggest that the environment of marine sedimentation was likely transitional between a shallow maritime lake and periodically ooded plain 10 . The clastic material probably came from the elevated rocks of the Pedro Garcia complex [25][26][27][28]84 .
The signi cant accumulations of plant detritus, derived from the same botanical source, i.e. the Hymenaea protera (Fabaceae) tree species, are found in the rocks from both mining districts. In the sediments from the La Cumbre (NMD) the plant detritus consists of larger tree fragments, branches and fruits. This material has undergone strong alterations, rstly rotting in a highly oxidised environment, and then the transformation at more reducing conditions. As a result strongly altered sediment with locally occuring characteristic soft lignite was formed. Contrary to the rocks from the El Valle (EMD), the nature of the plant detritus is quite different. It is mainly small fragments of plants, leaves and even grasses, well preserved and showing internal structure which is diagnostic for wood. It might be the result of long-term rest in seawater, which has well-known good preservative properties.
Along with the plant detritus provided from the land to the sedimentation basin, amber crumbs originating from tapping trees were also accumulated. The present study and works of others 10,57,85-87 have shown that microhardness and density values of resins from the Hato Mayor Province (EMD) are slightly higher than those from the Santiago Province (NMD). In addition, besides typical amber, exceptional resins uorescing blue and green in white light are found in both mining districts.
Analysis of biomarker provides further information on the conditions of organic matter deposition as well as its genetic source of the rocks from both regions. The primary indexes used in the reconstruction of palaeoenvironment were: n-alkanes distribution, CPI, Pr/Ph, TAR HC , Pr/n-C 17 , Pr/n-C 18 , C 27 -C 28 -C 29 steranes and P aq. ratios.
The Carbon Preference Index (CPI) is commonly used for the determination of the source of n-alkane and maturity of organic matter 88 . Immature source rocks with signi cant input of land-plant organic matter are usually dominated by the odd-carbon-numbered n-alkanes, particularly n-C 27 , n-C 29 , and n-C 31 . These nalkanes originate from epicuticular waxes and they are either are synthesized directly from higher plants or defunctionalized even-numbered acids, alcohols or esters 89 . In the Siete Cañadas area, the samples from SC-02 borehole have CPI values ranging from 1.26 to 2.67 with the sample SC3 showing the highest value (Table 3). These results suggest that the source rocks had mixed terrestrial/marine organic matter sedimented in anoxic and dysoxic depositional environment 59,[90][91][92] . comparable to n-alkane CPIs for the estuary sediments 93 . For the reference, the rocks from the La Cumbre deposit exhibit a slightly higher CPI values ( Table 3) that suggest the presence of the mixed origin of organic matter, in large portion of terrestrial material. The environment conditions during deposition were generally more oxic than in Siete Cañadas area.
The properties of the isoprenoids, natural hydrocarbons mainly of plant origin, have been also used in identi cation of the deposition environment and source of organic matter. The higher concentration of pristane than phytane was observed in the rocks from the Siete Cañadas area. The calculated pristane/phytane (Pr/Ph) ratio was in the range from 0.49 to 0.71 (Table 3). In the organic matter from La Cumbre deposit, the concentration pristine and phytane was almost the same, the calculated ratio was in range from 0.92 to 1.01 (Table 3). In the case of rocks from the Siete Cañadas area, the very low values of the Pr/Ph below 0.8 (Table 3)  The calculated Pr/Ph ratio for rocks from La Cumbre deposit may suggest that organic matter was deposited under transitional, between anoxic and oxic conditions. Hence, it can be concluded that the organic matter was accumulated in both areas mostly under reducing conditions, in the presence of low oxygen concentration.
The terrigenous/aquatic ratio (TAR HC ) 62 , and P aq. Ratio 94 , also were used as an indicator of terrigenous and aquatic organic matter components.  (Table 4), and indicate a terrestrial source of organic matter ( Figure 11).
Only in the samples SC1 and SC2 from the Siete Cañadas, higher amounts of pentacyclic terpanes were found which suggests presence of plankton/algal organic matter fraction.

Conclusion
The results of mineralogical and biomarker analyses of amber-bearing mudstones collected from drill holes in Eastern Mining District were discussed and compared with data obtained for amber-bearing coaly shales found in the second mining district in the north of the Dominican Republic (NMD). The major conclusions are as follows: 1. The northern and eastern amber mining districts in the Dominican Republic seem to be various basins of the former Pre-Ocean. They were separated from each other by a network of faults formed as a result of active tectonic movements during the Miocene period. 3. The deposition of the clastic material in both basins proceeded in marine environment. In northern district, the sedimentation was in the lagoon environment, a shallow maritime lake or periodically ooded plain. In eastern district the deposition probably took place in a deeper saltwater basin affected by the denudation movements.
4. Amber is hosted in organic substance-bearing mudstones and coaly shales in EMD and NMD, respectively. In the eastern region, the immature organic matter found in sediments has mixed terrestrial/marine origin and was deposited in anoxic and dysoxic depositional environment. In northern area more matured organic substance is also of mixed origin, but with a greater proportion of terrestrial material. It was accumulated under more oxic palaeoconditions.
Palaeoenvironmental reconstruction requires broad interdisciplinary studies. Further, additional stratigraphic, sedimentological, geochemical and palaeontological studies are required to specify in more detail the formation environment of the amber -bearing deposits in the Dominican Republic. Some palaeoenvironmental uctuations can be reconstructed using qualitative and quantitative palaeontological analyses of fossils with carbonate shells supported by the determination of trace elements (Mg/Ca) and stable isotopes (δ 18 O and δ 13 C) in the carbonates. In addition, the redox conditions can be elucidated by the determination of redox-sensitive trace metals in sediments. The application of various geothermometers such as coral growth bands, claymineral thermometry or Raman-based carbonaceous material thermometry are also helpful in elucidation of palaeoenvironment conditions. Hence, aforementioned interdisciplinary studies will be a subject of future work. The results will contribute to the development of research into the unique properties of Dominican ambers.       Thin-section backscatter SEM photomicrographs (SC4 sample). A -The morphologies and arrangements of pyrite (Py) and iron-titanium oxides (Ilmenite -Ilm); B -Albite (Ab) partially replaced by ilmenite (Ilm) and additionally euhedral pyrite (Py) grains and coali ed plant detritus lamina; C -Sanidine (Sa), detrital pyrite (Py) and quartz (Q) grains; D -Partially chloritized (Chl) albite (Ab) grain with quartz (Q), euhedral pyrite (Py) and coali ed plant detritus lamina; E -Albite (Ab) partially replaced by Ca-Mg smectite (montmorillonite -Mnt); F -The cross section of pollen with syngenetic pyrite (Py) inside cells.