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Shapes of organic walled dinoflagellate cysts in early diagenetic concretions—markers for mechanical compaction
Review of Palaeobotany and Palynology 208 (2014) 50–54
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Research paper
Shapes of organic walled dinoflagellate cysts in early diagenetic concretions—markers for mechanical compaction Marcin Barski Institute of Geology, Faculty of Geology, University of Warsaw, Żwirki i Wigury 93, PL-02-089 Warszawa, Poland
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Article history: Received 14 August 2013 Received in revised form 25 April 2014 Accepted 5 May 2014 Available online 24 May 2014 Keywords: Dinoflagellate cysts Compression Mechanical compaction Dinosporin Deflandrea phosphoritica Pareodinia ceratophora
a b s t r a c t Two species of organic walled dinoflagellate cysts: Pareodinia ceratophora Eisenack 1938 (Jurassic) and Deflandrea phosphoritica Deflandre 1947 (Palaeogene) are proposed as markers for determining the mechanical compaction ratio of fine-grained rocks. The near original shapes of these species are obtained from specimens preserved in siderite and calcareous concretions occurring in mudstone host rocks of various ages. An efficient and simple light microscopy examination method of the dinoflagellate cyst height along the microscope optical axis is presented and quantitatively tested on the available material. The differences of the cyst height measurements between specimens preserved in concretions and specimens preserved in the host rock deposits reflect the compression of dinoflagellate cysts most likely due to mechanical compaction of the rocks studied. The mechanical compaction ratios revealed are about 67% for Jurassic mudstones and about 64% for Palaeogene mudstones. Further marker investigations of samples from different outcrops and strata of different ages are recommended. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Organic walled dinoflagellate cysts are composed of a macromolecular, highly resistant, viscoelastic organic compound called dinosporin, which is synthesized around the living cell (Fensome et al., 1993; Traverse, 2007; Mertens et al., 2009). This organic biopolymer has similarities to sporopollenin, but is specific to dinoflagellates. The chemical nature of dinosporin in dinoflagellates has recently been broadly studied in a few modern (Kokinos et al., 1998) and fossil species (de Leeuw et al., 2006; Bogus et al., 2012; Versteegh et al., 2012). Several recent studies focus on the changes in cyst morphology in response to environmental conditions both in modern species (Lewis and Hallett, 1997; Ellegaard et al., 2002; Mertens et al., 2009; Rochon et al., 2009) and palaeontological material (Pross, 2001; Dybkjær, 2004; Sluijs et al., 2005). Other physical issues of the studies on dinoflagellate cyst walls were focused mainly on the biometry of the length of processes as a proxy of salinity and temperature conditions (Mertens et al., 2009, 2010; Verleye et al., 2012). Thermal and mechanical damages of dinoflagellate cyst assemblages from impact deposits were studied by Edwards and Powars (2003). They concluded that experimental work is needed to determine temperatures and pressures resulting in the cyst deformations observed. The first attempts to correlate dinoflagellate cyst deformation with mechanical compaction were made by Munnecke and Servais (1996)
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and Westphal and Munnecke (1997), who analysed the deformations of thin-walled organic microfossils in fine-grained carbonates with a SEM. They discussed the shapes of dinoflagellate cysts in un-altered rocks of Pliocene age and of acritarchs in compacted rocks of Silurian age using samples with etched surfaces. They concluded that thinwalled organic microfossils are reliable indicators of mechanical compaction, particularly in fine-grained limestones lacking other compaction indicators. The estimation of sediment compaction is an important input for seismic interpretation, depth conversion, and sedimentary basin modelling (Marcussen et al., 2009). This complex process, starting immediately after deposition, leads towards higher density of the sediments and their transformation into consolidated rocks. Mechanical compaction is usually followed by chemical compaction and controlled by thermodynamics and kinetics independent of the stress (Bjørlykke and Jaren, 2010). The main factors controlling both types of compaction processes are: grain size and mineralogy, sediment texture, pore fluid properties, effective stress, time and temperature (Puttiwongrak et al., 2013). The process of mechanical compaction affects all sediment components, including mineral grains, macrofossils, trace fossils, pelloids, ooids and microfossils (Bathurst, 1986; Ricken, 1986; Davaud et al., 1990; Zuschina et al., 2003). Finally, variable thickness reduction caused by compaction is an important issue for rock porosity and permeability considerations. A number of indicators are commonly used to assess the mechanical compaction of various types of sediments. These consist of deformation of trace fossils, peloids or ooids, breakage of grains, orientation of elongated components, and deformation of fenestral structures and
M. Barski / Review of Palaeobotany and Palynology 208 (2014) 50–54
organic walled microfossils (Meyers and Hill, 1983; Bathurst, 1986; Gaillard and Jautée, 1987; Ricken, 1987; Lasemi et al., 1990; Westphal and Munnecke, 1997). This study presents a new, light microscopy method for the assessment of the mechanical compaction ratio in mudstones by measuring the height of organic walled dinoflagellate cysts, a parameter which reflects the compression of the cyst body. The dinoflagellate cysts extracted from early diagenetic calcareous (Bojanowski, 2001) and siderite concretions (Majewski, 2000) revealed less compressed shapes than their counterparts from the neighbouring host rocks. Measurements of two common species of dinoflagellate cysts: Pareodinia ceratophora (Jurassic) and Deflandrea phosphoritica (Palaeogene) from different localities of different ages are presented as an example. 2. Material Samples of siderite concretions (A, B) and the host rock (C, D) yielding specimens of P. ceratophora were collected from the Middle to Upper Bathonian dark grey mudstones (Matyja and Wierzbowski, 2006) in the Gnaszyn brick-pit near Częstochowa city (Central Poland). This area is situated in the Kraków-Silesia Homocline, which is a widespread geological structure dipping gently to the NE. In total, 131 measurements were made of the well preserved P. ceratophora specimens from this site. The D. phosphoritica specimens were extracted from laminated calcareous concretions (samples E, F, G) and the host rock (samples H, I) collected from the Lower Oligocene (Barski and Bojanowski, 2010) grey to black mudstones of the Grybów Unit in the Outer Western Carpathians. This tectonised succession crops out along the banks of the Krokowy stream and generally dips at about 5–6° to the north. The material collected provided 92 specimens of well preserved D. phosphoritica specimens which were measured. The taxonomic composition of the dinoflagellate cyst assemblages in siderite and calcareous concretions is not significantly different from that of the host rocks. Beside dinoflagellate cysts, the assemblages contained abundant pollen, spores, terrestrial debris and rare foraminiferal linings.
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3. Dinoflagellate cysts height—the method The rock material was processed following palynologic preparation including 37% HCL, 40% HF, 78% HNO3 and 5% KOH treatment. Finally, the organic residuum was concentrated by a 15 μm diameter sieve and heavy liquid (2.0 g/cm3) separation. For observation, the palynological residues, stored in demineralised water, were mounted in warm glycerine jelly on a coverslip and subsequently cooled down and placed onto a microscope glass. The first, warm phase of glycerine jelly enabled the specimens to float and have time to fix in the right position for being measured. Measurements and photomicrophotographs were taken using a transmitted light Nikon Eclipse E-600 microscope equipped with a Nikon Plan 40×/0.65 objective and a Nikon CFI 10×/ 22 eyepiece. Evaluation of the height of the dinoflagellate cyst, treated here as a three-dimensional object, was based on the linear measurements along the microscope optical axis in the light microscope. In order to measure the specimens, the objects were centrally positioned in the field of view, the microscope was focused on the uppermost detail on the cyst surface, and subsequently on the lowermost detail on cyst surface (high and low focuses, respectively) (Figs. 1 and 2A). The fine focus knob values (Fig. 2B) were recorded and calculated. According to Nikon's Eclipse-600 microscope instruction, one division of the fine focus knob scale corresponds to 1 μm of vertical stage movement, thus all measurements were easy transferred to metric units. To check the accuracy of this method, measurements were made of a coverslip with a known thickness that had been checked with a mechanics micrometre. The height of the coverslip was achieved by focusing the upper and lower felt-tip pen lines marked on both sides of the coverslip (Fig. 2C), respectively, and recording the fine focus knob values. The values encountered were comparable to the original manufacturer specification of about 1 μm. Experimental measurements of the length and width of the specimens belonging to the two described species revealed no significant differences of these dimensions between the samples from concretions and the host rock, therefore such measurements were finally discounted. This procedure corresponds with the statement of Ricken
Fig. 1. High, medium and low focuses of specimens during axial linear measurements A. Pareodinia ceratophora Eisenack 1938, B. Deflandrea phosphoritica Deflandre 1947.
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Fig. 2. A. Axial linear measurements of specimen heights, B. Fine focus knob of Nikon Eclipse E-600 with scale, C. High (1) and low (2) focuses of felt-tip pen lines marked on both sides of the coverslip, D. Compressed dinoflagellate cysts on the surface of glycerine jelly compared with a half-submerged elliptical cylinder floating in fluid. The “H” values are attributed to specimens coming from concretion samples and the “h” values—for specimens from the host rock samples.
(1987) who assumed these parameters as constant in his compaction formula for trace fossils in carbonate rocks. In turn, height was the only dimension affected. The critical point for axial linear measurements of the specimen's height is its position on the slide. Therefore, the theoretical property of the compressed cyst on the surface of the glycerine jelly was compared to that of a half-submerged elliptical cylinder floating in a fluid (Fig. 2D). The horizontal position of a floating object characterized by an ellipsoidal cross-section is constrained by three factors: the location of the centre of gravity, the centre of buoyancy, and the metacentre (Mégel and Kliava, 2010). The parameter responsible for the stability of the floating body, i.e. the metacentric height, depends upon the distance between the centre of gravity and the metacentre. A higher value of the metacentric height implies greater initial stability in a horizontal position (Rawsan and Tupper, 2001). For a floating ellipse the metacentric height is maximal when the major axis is parallel to the flotation plane (Mégel and Kliava, 2010), therefore the cysts remain in that position. Considering the position at which the cyst was deposited before it was compacted, it is important to know its original shape. Evitt (1985) defines the Pareodinia complex as having a periform shape and the Deflandrea complex as being dorsoventrally compressed. According to Flügel (2004), the shapes of some macro- and microfossils (e.g. sea snails, ammonites, foraminifera, tentaculitids) constrain horizontal settling down positions on the sea floor in a pelagic environment. Hence P. ceratophora should settle down horizontally according to the long axis of the body, whereas D. phosphoritica should attain a position of a horizontally oriented disc. 4. Dinoflagellate cysts height—the results Only well preserved, mechanically and chemically intact dinoflagellate cysts in each slide were considered for the final measurement, therefore a restricted number of the specimens was available for further analysis. The results of the height measurements of the dinoflagellate cyst specimens are presented on the histograms (Fig. 3). The “H” and “h” values calibrated in micrometres are used for the measurement heights of the cysts. The “H” values are attributed to specimens coming from the concretion samples and the “h” values are for specimens from the host rock samples (Fig. 2A). In total, 71 axial measurements of the specimens of the Jurassic species P. ceratophora from two siderite concretions (A, B) revealed a range in values “H” of 20–31.5 μm with mean value of 24.9 μm for concretion A and 24.4 μm for concretion B. The standard deviation of the data set
varies from 2.7 to 2.5 for concretions A and B, respectively. The “h” values of 60 specimen measurements from the host rock (C, D) samples range from 6.5 μm to 11 μm with a mean value of 8.1 μm for both samples. The standard deviation of the data set varies from 1.3 to 1.2 for samples C and D, respectively. In total, 63 measurements of the specimens of the Palaeogene species D. phosphoritica from laminated calcareous concretions (E, F, G) revealed the “H” values ranging from 19 to 24 μm with the mean values of 21.5, 21.2 and 21.7 μm and standard deviations of the data set of 2.1, 1.2 and 1.2 for the three samples, respectively. 30 measurements of the host rock samples (H, I) revealed the “h” values ranging from 6.0 to 9.5 μm with the mean values of 7.5 and 7.9 μm, respectively. The standard deviation of the data set varies from 0.9 to 1.0 for the host rock samples, respectively. 5. Compression ratio of the dinoflagellate cysts The quantitative results of the compression ratio obtained from P. ceratophora and D. phosphoritica height measurements are shown in Table 1. A simple formula for calculating the compression ratio (CR) of dinoflagellate cysts has been used: C R ¼ ð1−h=HÞ 100% It considers “h” as a mean value of specimen heights from host rock samples and “H” as a mean value of specimen heights from concretion samples. In order to observe the best relation between uncompressed and compressed specimens, the results of the compression ratio presented in the table reflect calculations of “h” and “H” values from host rocks and concretions collected from the same layer or in close vicinity in the outcrops. 6. Discussion Higher axial measurement values observed amongst the samples from concretions prove that the early cementation of this part of the sediment inhibited further thickness reduction and deformation of the palynomorphs. In this respect the specimen height “H” values could serve as a specific marker for the compression calculations and for the mechanic compaction ratio. However, it is difficult to state unequivocally whether the original shape of the cyst had not been modified by primary compaction through hydrostatic pressure or unconsolidated
M. Barski / Review of Palaeobotany and Palynology 208 (2014) 50–54
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Fig. 3. Size-frequency spectra of dinoflagellate cyst height measurements.
sediment load, and whether post-preparation relaxation leading to partial cyst shape recovery had occurred when the compression forces disappeared. Therefore, the “H” values should be regarded as the minimal original specimen height in further compression ratio estimations. On the other hand, the lower axial height measurement values of the specimens collected from the host rocks indicate the advancing mechanical compaction of the sediments until final lithification. A Table 1 Quantitative results of the compression ratio (CR) obtained from Pareodinia ceratophora and Deflandrea phosphoritica height (h and H) measurements. It considers “h” as the mean value of specimen heights from the host rock samples and “H” as the mean value of specimen heights from the concretion samples. Concretion-host rock
h
H
CR
Pareodinia ceratophora A–C B–D
8.1 μm 8.1 μm
24.9 μm 24.4 μm Mean
67.5% 66.8% 67.1%
Deflandrea phosphoritica E–H F–H G–I
7.5 μm 7.5 μm 7.9 μm
21.5 μm 21.2 μm 21.7 μm Mean
65.1% 64.6% 63.6% 64.4%
hypothetical post-preparation modification due to relaxation of these cyst shapes should also be considered. Accordingly, the “h” values represent the minimal compressed specimen heights. It should be noted, however, that the axial measurements of the dinoflagellate cyst specimens combine the quantitative observations of a micrometre scale coupled with the subjective determination of marginal specimen foci. Only systematic measurements of a great number of specimens by one microscopist can lead to reliable results which may be quantitatively tested. In the cases presented, the measurements represent a range of values, which is consistent with the observations of Westphal and Munnecke (1997), and probably reflect differing primary reactions to compaction and the post-preparation relaxation effect. Finally, the ranges of the measured values of the heights of cysts taken from the concretions and the host rocks presented on the histograms probably reflect the deviations of the positions from horizontal, both primarily on the sea floor and on the microscope slide. Taking into consideration the doubts discussed, the difference between the axial measurements of dinoflagellate cyst specimen heights from both rock types seems to be a reliable indicator of mechanical compaction. The results presented here of about 67% mechanical compaction ratio for Jurassic mudstones and about 64% for Palaeogene mudstones coincide with data presented in several theoretical and experimental studies. According to previous statements, the mechanical
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compaction of fine grained sediments typically comprises 40–90% of the sedimentary basin thickness (e.g. Aplin et al., 1995; Velde, 1996; Mondol et al., 2007). It should be noted that the estimated mechanical compaction ratio for the Carpathian samples could also record some imprint of tectonic stress due to several regional tectonic phases during the Neogene and Quaternary. This effect is probably negligible in respect to the Jurassic samples, which are collected in an area which had not undergone tectonic stress. 7. Conclusions • P. ceratophora Eisenack 1938 and D. phosphoritica Deflandre 1947 are proposed as markers for the estimation of the mechanical compaction ratio for fine grained rocks of Jurassic and Palaeogene ages. Their nearly original mean heights along the microscope optical axis are 24 and 21 μm respectively. • The presented method of axial measurements is easy, quantitatively accurate and complementary with routine palynological examinations with a light microscope. It is applicable to outcrop samples, cores or cuttings. • The mechanical compaction ratios of about 67% for Jurassic mudstones and about 64% for Palaeogene mudstones coincide with previous theoretical and experimental studies for fine-grained rocks. • Further marker investigations are recommended to understand the mechanical compaction of rocks of different ages. Acknowledgements I express my sincere thanks to Professor A. Konon for the discussions about tectonic stress and deformations, and comments on an early version of the manuscript. I am indebted to Prof. M.H. Stephenson, editor and palynologist, for the constructive criticism of primary submission to RPP. Undoubtedly, the comments and questions of two anonymous referees made the paper more valuable. I am grateful to Dr John Wright and Dr Anna Żylińska for English linguistic improvements. References Aplin, A.C., Yang, Y., Hansen, S., 1995. Assessment of β, the compression coefficient of mudstones and its relationship to detailed lithology. Mar. Pet. Geol. 12, 955–963. Barski, M., Bojanowski, M., 2010. Organic-walled dinoflagellate cysts as a tool to recognize carbonate concretions: an example from Oligocene flysch deposits of the Western Carpathians. Geol. Carpath. 61 (2), 121–128. Bathurst, R.G.C., 1986. Carbonate diagenesis and reservoir development conservation, destruction, and creation of pores. Q. J. Colorado Sch. Min. 81 (4), 1–25. Bjørlykke, K., Jaren, H., 2010. Sandstones and sandstone reservoirs. In: Bjørlykke, K. (Ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics. SpringerVerlag, Berlin Heidelberg, pp. 113–140. Bogus, K., Versteegh, G.J.M., Harding, I.C., King, A., Charles, A.J., Zonneveld, K., 2012. The composition and diversity of dinosporin in species of the Apectodinium complex (Dinoflagellata). Rev. Palaeobot. Palynol. 183, 21–31. Bojanowski, M., 2001. Growth mechanism and burial conditions of calcite concretions from the Krosno shales, Polish Outer Carpathians: structural observations. Mineral. Soc. Pol. Spec. Pap. 18, 15–24. Davaud, E., Strasser, A., Jeoul, Y., 1990. Spiny ooids: early subaerial deformation as opposed to late burial compaction. Geology 18, 816–819. de Leeuw, J.W., Versteegh, G.J.M., van Bergen, P.F., 2006. Biomacromolecules of plants and algae and their fossil analogues. Plant Ecol. 189, 209–233. Dybkjær, K., 2004. Morphological and abundance variations in Homotryblium-cyst assemblages related to depositional environments; uppermost Oligocene–lower Miocene, Jylland, Denmark. Palaeogeogr. Palaeoclimatol. Palaeoecol. 206, 41–58. Edwards, L.E., Powars, D.S., 2003. Impact damage to dinocysts from the late Eocene Chesapeake Bay event. Palaios 18, 275–285. Ellegaard, M., Lewis, J., Harding, I., 2002. Cyst–theca relationship, life cycle, and effects of temperature and salinity on the cyst morphology of Gonyaulax baltica sp. nov. (Dinophyceae) from the Baltic Sea area. J. Phycol. 38, 775–789.
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Research paper
Shapes of organic walled dinoflagellate cysts in early diagenetic concretions—markers for mechanical compaction Marcin Barski Institute of Geology, Faculty of Geology, University of Warsaw, Żwirki i Wigury 93, PL-02-089 Warszawa, Poland
a r t i c l e
i n f o
Article history: Received 14 August 2013 Received in revised form 25 April 2014 Accepted 5 May 2014 Available online 24 May 2014 Keywords: Dinoflagellate cysts Compression Mechanical compaction Dinosporin Deflandrea phosphoritica Pareodinia ceratophora
a b s t r a c t Two species of organic walled dinoflagellate cysts: Pareodinia ceratophora Eisenack 1938 (Jurassic) and Deflandrea phosphoritica Deflandre 1947 (Palaeogene) are proposed as markers for determining the mechanical compaction ratio of fine-grained rocks. The near original shapes of these species are obtained from specimens preserved in siderite and calcareous concretions occurring in mudstone host rocks of various ages. An efficient and simple light microscopy examination method of the dinoflagellate cyst height along the microscope optical axis is presented and quantitatively tested on the available material. The differences of the cyst height measurements between specimens preserved in concretions and specimens preserved in the host rock deposits reflect the compression of dinoflagellate cysts most likely due to mechanical compaction of the rocks studied. The mechanical compaction ratios revealed are about 67% for Jurassic mudstones and about 64% for Palaeogene mudstones. Further marker investigations of samples from different outcrops and strata of different ages are recommended. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Organic walled dinoflagellate cysts are composed of a macromolecular, highly resistant, viscoelastic organic compound called dinosporin, which is synthesized around the living cell (Fensome et al., 1993; Traverse, 2007; Mertens et al., 2009). This organic biopolymer has similarities to sporopollenin, but is specific to dinoflagellates. The chemical nature of dinosporin in dinoflagellates has recently been broadly studied in a few modern (Kokinos et al., 1998) and fossil species (de Leeuw et al., 2006; Bogus et al., 2012; Versteegh et al., 2012). Several recent studies focus on the changes in cyst morphology in response to environmental conditions both in modern species (Lewis and Hallett, 1997; Ellegaard et al., 2002; Mertens et al., 2009; Rochon et al., 2009) and palaeontological material (Pross, 2001; Dybkjær, 2004; Sluijs et al., 2005). Other physical issues of the studies on dinoflagellate cyst walls were focused mainly on the biometry of the length of processes as a proxy of salinity and temperature conditions (Mertens et al., 2009, 2010; Verleye et al., 2012). Thermal and mechanical damages of dinoflagellate cyst assemblages from impact deposits were studied by Edwards and Powars (2003). They concluded that experimental work is needed to determine temperatures and pressures resulting in the cyst deformations observed. The first attempts to correlate dinoflagellate cyst deformation with mechanical compaction were made by Munnecke and Servais (1996)
E-mail address: [email protected].
http://dx.doi.org/10.1016/j.revpalbo.2014.05.002 0034-6667/© 2014 Elsevier B.V. All rights reserved.
and Westphal and Munnecke (1997), who analysed the deformations of thin-walled organic microfossils in fine-grained carbonates with a SEM. They discussed the shapes of dinoflagellate cysts in un-altered rocks of Pliocene age and of acritarchs in compacted rocks of Silurian age using samples with etched surfaces. They concluded that thinwalled organic microfossils are reliable indicators of mechanical compaction, particularly in fine-grained limestones lacking other compaction indicators. The estimation of sediment compaction is an important input for seismic interpretation, depth conversion, and sedimentary basin modelling (Marcussen et al., 2009). This complex process, starting immediately after deposition, leads towards higher density of the sediments and their transformation into consolidated rocks. Mechanical compaction is usually followed by chemical compaction and controlled by thermodynamics and kinetics independent of the stress (Bjørlykke and Jaren, 2010). The main factors controlling both types of compaction processes are: grain size and mineralogy, sediment texture, pore fluid properties, effective stress, time and temperature (Puttiwongrak et al., 2013). The process of mechanical compaction affects all sediment components, including mineral grains, macrofossils, trace fossils, pelloids, ooids and microfossils (Bathurst, 1986; Ricken, 1986; Davaud et al., 1990; Zuschina et al., 2003). Finally, variable thickness reduction caused by compaction is an important issue for rock porosity and permeability considerations. A number of indicators are commonly used to assess the mechanical compaction of various types of sediments. These consist of deformation of trace fossils, peloids or ooids, breakage of grains, orientation of elongated components, and deformation of fenestral structures and
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organic walled microfossils (Meyers and Hill, 1983; Bathurst, 1986; Gaillard and Jautée, 1987; Ricken, 1987; Lasemi et al., 1990; Westphal and Munnecke, 1997). This study presents a new, light microscopy method for the assessment of the mechanical compaction ratio in mudstones by measuring the height of organic walled dinoflagellate cysts, a parameter which reflects the compression of the cyst body. The dinoflagellate cysts extracted from early diagenetic calcareous (Bojanowski, 2001) and siderite concretions (Majewski, 2000) revealed less compressed shapes than their counterparts from the neighbouring host rocks. Measurements of two common species of dinoflagellate cysts: Pareodinia ceratophora (Jurassic) and Deflandrea phosphoritica (Palaeogene) from different localities of different ages are presented as an example. 2. Material Samples of siderite concretions (A, B) and the host rock (C, D) yielding specimens of P. ceratophora were collected from the Middle to Upper Bathonian dark grey mudstones (Matyja and Wierzbowski, 2006) in the Gnaszyn brick-pit near Częstochowa city (Central Poland). This area is situated in the Kraków-Silesia Homocline, which is a widespread geological structure dipping gently to the NE. In total, 131 measurements were made of the well preserved P. ceratophora specimens from this site. The D. phosphoritica specimens were extracted from laminated calcareous concretions (samples E, F, G) and the host rock (samples H, I) collected from the Lower Oligocene (Barski and Bojanowski, 2010) grey to black mudstones of the Grybów Unit in the Outer Western Carpathians. This tectonised succession crops out along the banks of the Krokowy stream and generally dips at about 5–6° to the north. The material collected provided 92 specimens of well preserved D. phosphoritica specimens which were measured. The taxonomic composition of the dinoflagellate cyst assemblages in siderite and calcareous concretions is not significantly different from that of the host rocks. Beside dinoflagellate cysts, the assemblages contained abundant pollen, spores, terrestrial debris and rare foraminiferal linings.
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3. Dinoflagellate cysts height—the method The rock material was processed following palynologic preparation including 37% HCL, 40% HF, 78% HNO3 and 5% KOH treatment. Finally, the organic residuum was concentrated by a 15 μm diameter sieve and heavy liquid (2.0 g/cm3) separation. For observation, the palynological residues, stored in demineralised water, were mounted in warm glycerine jelly on a coverslip and subsequently cooled down and placed onto a microscope glass. The first, warm phase of glycerine jelly enabled the specimens to float and have time to fix in the right position for being measured. Measurements and photomicrophotographs were taken using a transmitted light Nikon Eclipse E-600 microscope equipped with a Nikon Plan 40×/0.65 objective and a Nikon CFI 10×/ 22 eyepiece. Evaluation of the height of the dinoflagellate cyst, treated here as a three-dimensional object, was based on the linear measurements along the microscope optical axis in the light microscope. In order to measure the specimens, the objects were centrally positioned in the field of view, the microscope was focused on the uppermost detail on the cyst surface, and subsequently on the lowermost detail on cyst surface (high and low focuses, respectively) (Figs. 1 and 2A). The fine focus knob values (Fig. 2B) were recorded and calculated. According to Nikon's Eclipse-600 microscope instruction, one division of the fine focus knob scale corresponds to 1 μm of vertical stage movement, thus all measurements were easy transferred to metric units. To check the accuracy of this method, measurements were made of a coverslip with a known thickness that had been checked with a mechanics micrometre. The height of the coverslip was achieved by focusing the upper and lower felt-tip pen lines marked on both sides of the coverslip (Fig. 2C), respectively, and recording the fine focus knob values. The values encountered were comparable to the original manufacturer specification of about 1 μm. Experimental measurements of the length and width of the specimens belonging to the two described species revealed no significant differences of these dimensions between the samples from concretions and the host rock, therefore such measurements were finally discounted. This procedure corresponds with the statement of Ricken
Fig. 1. High, medium and low focuses of specimens during axial linear measurements A. Pareodinia ceratophora Eisenack 1938, B. Deflandrea phosphoritica Deflandre 1947.
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Fig. 2. A. Axial linear measurements of specimen heights, B. Fine focus knob of Nikon Eclipse E-600 with scale, C. High (1) and low (2) focuses of felt-tip pen lines marked on both sides of the coverslip, D. Compressed dinoflagellate cysts on the surface of glycerine jelly compared with a half-submerged elliptical cylinder floating in fluid. The “H” values are attributed to specimens coming from concretion samples and the “h” values—for specimens from the host rock samples.
(1987) who assumed these parameters as constant in his compaction formula for trace fossils in carbonate rocks. In turn, height was the only dimension affected. The critical point for axial linear measurements of the specimen's height is its position on the slide. Therefore, the theoretical property of the compressed cyst on the surface of the glycerine jelly was compared to that of a half-submerged elliptical cylinder floating in a fluid (Fig. 2D). The horizontal position of a floating object characterized by an ellipsoidal cross-section is constrained by three factors: the location of the centre of gravity, the centre of buoyancy, and the metacentre (Mégel and Kliava, 2010). The parameter responsible for the stability of the floating body, i.e. the metacentric height, depends upon the distance between the centre of gravity and the metacentre. A higher value of the metacentric height implies greater initial stability in a horizontal position (Rawsan and Tupper, 2001). For a floating ellipse the metacentric height is maximal when the major axis is parallel to the flotation plane (Mégel and Kliava, 2010), therefore the cysts remain in that position. Considering the position at which the cyst was deposited before it was compacted, it is important to know its original shape. Evitt (1985) defines the Pareodinia complex as having a periform shape and the Deflandrea complex as being dorsoventrally compressed. According to Flügel (2004), the shapes of some macro- and microfossils (e.g. sea snails, ammonites, foraminifera, tentaculitids) constrain horizontal settling down positions on the sea floor in a pelagic environment. Hence P. ceratophora should settle down horizontally according to the long axis of the body, whereas D. phosphoritica should attain a position of a horizontally oriented disc. 4. Dinoflagellate cysts height—the results Only well preserved, mechanically and chemically intact dinoflagellate cysts in each slide were considered for the final measurement, therefore a restricted number of the specimens was available for further analysis. The results of the height measurements of the dinoflagellate cyst specimens are presented on the histograms (Fig. 3). The “H” and “h” values calibrated in micrometres are used for the measurement heights of the cysts. The “H” values are attributed to specimens coming from the concretion samples and the “h” values are for specimens from the host rock samples (Fig. 2A). In total, 71 axial measurements of the specimens of the Jurassic species P. ceratophora from two siderite concretions (A, B) revealed a range in values “H” of 20–31.5 μm with mean value of 24.9 μm for concretion A and 24.4 μm for concretion B. The standard deviation of the data set
varies from 2.7 to 2.5 for concretions A and B, respectively. The “h” values of 60 specimen measurements from the host rock (C, D) samples range from 6.5 μm to 11 μm with a mean value of 8.1 μm for both samples. The standard deviation of the data set varies from 1.3 to 1.2 for samples C and D, respectively. In total, 63 measurements of the specimens of the Palaeogene species D. phosphoritica from laminated calcareous concretions (E, F, G) revealed the “H” values ranging from 19 to 24 μm with the mean values of 21.5, 21.2 and 21.7 μm and standard deviations of the data set of 2.1, 1.2 and 1.2 for the three samples, respectively. 30 measurements of the host rock samples (H, I) revealed the “h” values ranging from 6.0 to 9.5 μm with the mean values of 7.5 and 7.9 μm, respectively. The standard deviation of the data set varies from 0.9 to 1.0 for the host rock samples, respectively. 5. Compression ratio of the dinoflagellate cysts The quantitative results of the compression ratio obtained from P. ceratophora and D. phosphoritica height measurements are shown in Table 1. A simple formula for calculating the compression ratio (CR) of dinoflagellate cysts has been used: C R ¼ ð1−h=HÞ 100% It considers “h” as a mean value of specimen heights from host rock samples and “H” as a mean value of specimen heights from concretion samples. In order to observe the best relation between uncompressed and compressed specimens, the results of the compression ratio presented in the table reflect calculations of “h” and “H” values from host rocks and concretions collected from the same layer or in close vicinity in the outcrops. 6. Discussion Higher axial measurement values observed amongst the samples from concretions prove that the early cementation of this part of the sediment inhibited further thickness reduction and deformation of the palynomorphs. In this respect the specimen height “H” values could serve as a specific marker for the compression calculations and for the mechanic compaction ratio. However, it is difficult to state unequivocally whether the original shape of the cyst had not been modified by primary compaction through hydrostatic pressure or unconsolidated
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Fig. 3. Size-frequency spectra of dinoflagellate cyst height measurements.
sediment load, and whether post-preparation relaxation leading to partial cyst shape recovery had occurred when the compression forces disappeared. Therefore, the “H” values should be regarded as the minimal original specimen height in further compression ratio estimations. On the other hand, the lower axial height measurement values of the specimens collected from the host rocks indicate the advancing mechanical compaction of the sediments until final lithification. A Table 1 Quantitative results of the compression ratio (CR) obtained from Pareodinia ceratophora and Deflandrea phosphoritica height (h and H) measurements. It considers “h” as the mean value of specimen heights from the host rock samples and “H” as the mean value of specimen heights from the concretion samples. Concretion-host rock
h
H
CR
Pareodinia ceratophora A–C B–D
8.1 μm 8.1 μm
24.9 μm 24.4 μm Mean
67.5% 66.8% 67.1%
Deflandrea phosphoritica E–H F–H G–I
7.5 μm 7.5 μm 7.9 μm
21.5 μm 21.2 μm 21.7 μm Mean
65.1% 64.6% 63.6% 64.4%
hypothetical post-preparation modification due to relaxation of these cyst shapes should also be considered. Accordingly, the “h” values represent the minimal compressed specimen heights. It should be noted, however, that the axial measurements of the dinoflagellate cyst specimens combine the quantitative observations of a micrometre scale coupled with the subjective determination of marginal specimen foci. Only systematic measurements of a great number of specimens by one microscopist can lead to reliable results which may be quantitatively tested. In the cases presented, the measurements represent a range of values, which is consistent with the observations of Westphal and Munnecke (1997), and probably reflect differing primary reactions to compaction and the post-preparation relaxation effect. Finally, the ranges of the measured values of the heights of cysts taken from the concretions and the host rocks presented on the histograms probably reflect the deviations of the positions from horizontal, both primarily on the sea floor and on the microscope slide. Taking into consideration the doubts discussed, the difference between the axial measurements of dinoflagellate cyst specimen heights from both rock types seems to be a reliable indicator of mechanical compaction. The results presented here of about 67% mechanical compaction ratio for Jurassic mudstones and about 64% for Palaeogene mudstones coincide with data presented in several theoretical and experimental studies. According to previous statements, the mechanical
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compaction of fine grained sediments typically comprises 40–90% of the sedimentary basin thickness (e.g. Aplin et al., 1995; Velde, 1996; Mondol et al., 2007). It should be noted that the estimated mechanical compaction ratio for the Carpathian samples could also record some imprint of tectonic stress due to several regional tectonic phases during the Neogene and Quaternary. This effect is probably negligible in respect to the Jurassic samples, which are collected in an area which had not undergone tectonic stress. 7. Conclusions • P. ceratophora Eisenack 1938 and D. phosphoritica Deflandre 1947 are proposed as markers for the estimation of the mechanical compaction ratio for fine grained rocks of Jurassic and Palaeogene ages. Their nearly original mean heights along the microscope optical axis are 24 and 21 μm respectively. • The presented method of axial measurements is easy, quantitatively accurate and complementary with routine palynological examinations with a light microscope. It is applicable to outcrop samples, cores or cuttings. • The mechanical compaction ratios of about 67% for Jurassic mudstones and about 64% for Palaeogene mudstones coincide with previous theoretical and experimental studies for fine-grained rocks. • Further marker investigations are recommended to understand the mechanical compaction of rocks of different ages. Acknowledgements I express my sincere thanks to Professor A. Konon for the discussions about tectonic stress and deformations, and comments on an early version of the manuscript. I am indebted to Prof. M.H. Stephenson, editor and palynologist, for the constructive criticism of primary submission to RPP. Undoubtedly, the comments and questions of two anonymous referees made the paper more valuable. I am grateful to Dr John Wright and Dr Anna Żylińska for English linguistic improvements. References Aplin, A.C., Yang, Y., Hansen, S., 1995. Assessment of β, the compression coefficient of mudstones and its relationship to detailed lithology. Mar. Pet. Geol. 12, 955–963. Barski, M., Bojanowski, M., 2010. Organic-walled dinoflagellate cysts as a tool to recognize carbonate concretions: an example from Oligocene flysch deposits of the Western Carpathians. Geol. Carpath. 61 (2), 121–128. Bathurst, R.G.C., 1986. Carbonate diagenesis and reservoir development conservation, destruction, and creation of pores. Q. J. Colorado Sch. Min. 81 (4), 1–25. Bjørlykke, K., Jaren, H., 2010. Sandstones and sandstone reservoirs. In: Bjørlykke, K. (Ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics. SpringerVerlag, Berlin Heidelberg, pp. 113–140. Bogus, K., Versteegh, G.J.M., Harding, I.C., King, A., Charles, A.J., Zonneveld, K., 2012. The composition and diversity of dinosporin in species of the Apectodinium complex (Dinoflagellata). Rev. Palaeobot. Palynol. 183, 21–31. Bojanowski, M., 2001. Growth mechanism and burial conditions of calcite concretions from the Krosno shales, Polish Outer Carpathians: structural observations. Mineral. Soc. Pol. Spec. Pap. 18, 15–24. Davaud, E., Strasser, A., Jeoul, Y., 1990. Spiny ooids: early subaerial deformation as opposed to late burial compaction. Geology 18, 816–819. de Leeuw, J.W., Versteegh, G.J.M., van Bergen, P.F., 2006. Biomacromolecules of plants and algae and their fossil analogues. Plant Ecol. 189, 209–233. Dybkjær, K., 2004. Morphological and abundance variations in Homotryblium-cyst assemblages related to depositional environments; uppermost Oligocene–lower Miocene, Jylland, Denmark. Palaeogeogr. Palaeoclimatol. Palaeoecol. 206, 41–58. Edwards, L.E., Powars, D.S., 2003. Impact damage to dinocysts from the late Eocene Chesapeake Bay event. Palaios 18, 275–285. Ellegaard, M., Lewis, J., Harding, I., 2002. Cyst–theca relationship, life cycle, and effects of temperature and salinity on the cyst morphology of Gonyaulax baltica sp. nov. (Dinophyceae) from the Baltic Sea area. J. Phycol. 38, 775–789.
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