- Email: [email protected]
Application of microPIXE and STIM in analyses of fossil and Recent polychaete jaws (scolecodonts)
Nuclear Instruments and Methods in Physics Research B 158 (1999) 287±291
www.elsevier.nl/locate/nimb
Application of microPIXE and STIM in analyses of fossil and Recent polychaete jaws (scolecodonts) Mikael Elfman b
a,1
, Mats Eriksson
b,*
, Per Kristiansson a, Klas Malmqvist a, Jan Pallon
a
a Department of Nuclear Physics, Lund Institute of Technology, University of Lund, Box 118 SE-221 00 Lund, Sweden Department of Geology, Division of Historical geology and Palaeontology, Lund University, S olvegatan 13, SE-223 62 Lund, Sweden
Abstract MicroPIXE and STIM analysis of the chemistry of fossil and Recent polychaete jaws (scolecodonts) demonstrates that they, apart from their protein composition, constitute inorganic components. The PIXE images reveal that the elemental distribution is generally homogeneous for some elements while it is heterogeneous, especially for zinc and iron. The jaw of the Recent polychaete Nereis sp. has zinc concentrated in the tip, probably for hardening purposes. Similar accumulations were revealed in fossil scolecodonts; zinc in Kettnerites (K.) martinssonii and iron and titanium in Hadoprion cervicornis. Ó 1999 Published by Elsevier Science B.V. All rights reserved. PACS: 41.75.A; 79.20.R; 07.78; 41.85; 87.10; 87.22; 87.64; 91.65; 83.80.L Keywords: PIXE; STIM; Nuclear microprobe; Polychaete jaws; Fossil; Recent
1. Introduction Polychaete annelid worms comprise a signi®cant part of the invertebrate faunas of modern oceans. Their fossil record dates back to the early Cambrian (c. 540 Ma), possibly even further. Jawed polychaete worms appeared in the early Ordovician (c. 480 Ma), and preserved jaws (scolecodonts) are abundant in many Palaeozoic rocks. Polychaete jaws are normally 0.1±1.5 mm, brownish or reddish to black in colour, hollow and
*
Corresponding author. E-mail: [email protected] Corresponding author. E-mail: [email protected]. 1
vary in thickness, with a denticulated dorsal side (Fig. 1). Fairly little is known about the chemical composition of scolecodonts, although it has been discussed in some papers, for a review see Ref. [1]. It has been suggested that they are composed of sclerotized proteins with incorporated heavy metals and minerals [2,3]. The chemistry of polychaete jaws may provide an important tool in taxonomy and a ``®nger printing'' identi®cation of dierent taxa may be possible. Further, the jaw chemistry may act as a biological indicator of heavy metals [4] and aspects of taphonomy and fossilisation potential [3,5], as well as the detailed function can be considered. Here we introduce the microPIXE and STIM techniques for the purpose of investi-
0168-583X/99/$ - see front matter Ó 1999 Published by Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 3 1 6 - X
288
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 287±291
Fig. 1. SEM images of selected fossil scolecodonts (all in dorsal view). (a) Left MI (®rst maxilla) jaw of K. (K.) martinssonii, [1], ´34, Silurian of Gotland, Sweden. (b) Right MI jaw of the same species, ´34. (c) Left MI jaw of ``Ramphoprion'' sp., [16], ´77, Silurian of Gotland, Sweden. (d) Right MII jaw of H. cervicornis, [17], ´26, Cincinnatian (U. Ordovician) of Indiana, USA. Note that these are not the analysed specimens.
gating the chemistry of fossil and Recent polychaete jaws. The proton microprobe [6] has proven to be a uniquely useful instrument in many areas. It combines high sensitivity for elemental analysis and high lateral resolution and enables studies of the distribution of various elements and of chemical variations of the microstructures. Although all parts of this paper have been discussed between the authors, the bulk of it was prepared by Eriksson. The physics and experimental part was written by Elfman. 2. Experimental The sample backing was 180 lg/cm2 thick Kimfolä. The specimens were covered by another layer of Kimfolä and ®nally mounted in the sample holder. Simultaneous PIXE and STIM measurements were applied. Scanning transmission ion microscopy (STIM) [7] gives structural information for thin samples. The energy loss of the transmitted particles was measured, and the mass thickness of the sample was calculated. The darker parts in the STIM maps represent higher mass density. In order to get a suitable count rate in the STIM detector while maintaining the necessary beam current for PIXE analysis, o-axis
STIM must be used. A thin carbon foil (40 lg/ cm2 ), in which the transmitted particles are scattered, are placed behind the target [8,9]. A 4 ´ 4 mm2 photodiode was used as a detector for the scattered protons after the foil. The PIXE signal was detected with a Kevex Si(Li) detector of 50 mm2 active area and a measured energy resolution of approximately 155 eV at the 5.9 keV Mn Ka peak in 135° angle relative to the beam. A thin absorber (90 lm Be) was used for the PIXE detector. The PIXE [10] analyses were performed at the Lund Nuclear microprobe, which uses a singleended NEC 3 UH accelerator. The beam line is described in [11] and the data acquisition and scanning system is described in [15]. Protons of 2.55 MeV and a beam size of about 3 lm were used in this study. Semi-quantitative elemental ratios e.g. (Zn/Ca, Ti/Ca, Fe/Ca) were computed using the acquired PIXE spectra and dierent samples were compared. 3. Specimens analysed The fossil specimens analysed include K. (K.) martinssonii and ``Ramphoprion'' sp., both from the Silurian of Gotland, Sweden, and H. cervicornis from the Cincinnatian (Upper Ordovician) of Indiana, USA. The specimens were recovered through standard micropaleontological procedures [12]. The Recent Nereis sp. specimen was } collected in Oresund, south Sweden and the jaws were dissected out. All analysed specimens are housed in the Department of Geology, Lund, Sweden (LO). 4. Results ± chemical composition It is obvious that scolecodonts, apart from their suggested protein composition, also comprise various inorganic components [2]. This investigation revealed that scolecodonts contain silicon, sulphur, chlorine, potassium, calcium, iron, copper, nickel, titanium, chromium, and sometimes phosphorus, manganese, bromine and iodine. The amount and distribution of these elements varies in the analysed specimens. The elemental
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 287±291
distribution in the jaws is generally homogeneous. Some elements (e.g., zinc and iron) tend to be patchily distributed and concentrated in certain regions. The chemistry of the Recent specimen diers from that of the fossil specimens (Fig. 2) whereas the fossil jaws obtained from Gotland yielded similar PIXE spectra with somewhat varying proportions mainly of iron, nickel, and zinc. The most signi®cant dierences between the PIXE spectrum of the Nereis sp. jaw and those of the fossil species are the prominent peaks of zinc, and bromine and the presence of iodine and phosphorus in the former. Iodine was not detected in the fossil material. It is, however, a common constituent in sea water. A distinct zinc accumulation is displayed in the tip of the jaw of Nereis sp. (Fig. 3), see also Ref. [13]. Other elements are more or less homogeneously distributed in the specimen. The tip of the jaw is more massive than the proximal part. However, the relative distribution is
289
not in¯uenced by density dierences as the PIXE images are normalised to mass thickness with help of the o-axis STIM. Zinc seems to be distributed internally in the jaw, as proposed by Bryan and Gibbs [13], but also reaching the surface. The PIXE images reveal a similar, although not as prominent, accumulation of zinc in the narrow anterior part of the jaw of K. (K.) martinssonii. The chemical composition of ``Ramphoprion'' sp. resembles that of K. (K.) martinssonii (Fig. 2) but the former has increased Fe/Ca ratios, and a lower Zn/Ca ratio. The STIM image of ``Ramphoprion'' sp. reveals some internal structures, a rounded feature with a low mass density (muscle scar?) is visible (Fig. 3) approximately at midlength. The dark part may be an internally thickened part of the jaw or a sediment grain. The PIXE spectrum of the jaw of H. cervicornis reveals an increased Fe/Ca ratio compared with the Silurian specimens. The distribution of iron and titanium seems to be restricted mainly to the slender denticles (Fig. 3). Iron is internally restricted whereas titanium reaches the surface of the jaw. 5. Discussion
Fig. 2. PIXE spectrum obtained of the Recent polychaete jaw Nereis sp. (2A) and of the jaw of the fossil polychaete K. (K.) martinssonii (2B).
In addition to the functional usefulness, the chemistry of polychaete jaws may be in¯uenced by water chemistry, traces of feeding habits and/or sediment composition. Considering the fossil material, also diagenesis, weathering, and the extraction procedure must be taken into account. However, Bryan and Gibbs [13] showed that the zinc accumulation in the jaws of the Recent polychaete Nereis diversicolor, is not related to the sediment chemistry and argued that the distribution of zinc in nereidids probably is of functional signi®cance. As stated above, similar accumulations were detected in the fossil material. These most probably act to harden the jaws. The fossil specimens reveal only minor dierences in jaw chemistry, indicating that these species display similar chemical signatures. However, only a few specimens have been analysed and with more material it would perhaps be possible to detect unique chemical signatures (``®nger printings'')
290
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 287±291
Fig. 3. Elemental maps and STIM maps of the analysed scolecodonts. Darker parts in the PIXE maps represents higher elemental concentrations. The total scanning ranges are : A (2944 ´ 2944 lm), B (512 ´ 512 lm ), C (704 ´ 704 lm) and D (704 ´ 704 lm). A. } Nereis sp. from Oresund, Sweden (LO 8081) B. K. (K.) martinssonii, sample G 82-10CB, H orsne 3, Gotland (LO 8082). C. H. cervicornis, sample 91B6-1, South Gate Hill, Indiana (LO 8083). D. ``Ramphoprion'' sp., sample G83-12LJ N arshamn 2, Gotland (LO 8084).
that are speci®c to dierent taxa. Colbath [3] suggested that the chemical composition of modern euniceans could be used taxonomically, at least at the family level, and Voss-Foucart et al. [14] found a positive link between the phylogenetic relationship within polychaetes and the jaw chemistry.
The fossil specimens display similar chemical composition, although elemental distribution varies in the jaws. The delicate tips and other parts of the jaws, exposed to most wear, are commonly incorporated by zinc, iron, and titanium, probably to harden them. Similarly, the tip of the Nereis sp. jaw exhibits a prominent zinc accumulation.
6. Conclusions
Acknowledgements
PIXE combined with STIM provide a powerful tool in analysing organic walled fossils and similar structures. The technique does not harm (or insigni®cantly harm) the specimens and provides extraordinary resolution of the elemental composition. The PIXE images impeccably display the spatial distribution of accumulated elements. Similar internal accumulations are of functional interest and may otherwise be dicult to study. Density corrections (from the STIM detector) further facilitate accurate evaluation of elemental accumulations in the heterogeneously thick specimens. We believe that this preliminary study displays a great forthcoming potential of the technique for similar purposes.
A grant from The Royal Physiographic Society in Lund to M. Eriksson ®nanced the analyses. E. Hallberg and C. F. Bergman donated the studied specimens. L. Jeppsson and J. Andersson critically read the manuscript.
References [1] [2] [3] [4] [5] [6]
C.F. Bergman, Fossils and Strata 25 (1989) 1. P.J.W. Olive, Plenum Press, New York, 1980, p. 516. G.K. Colbath, Micropaleontology 32 (1986) 186. V.A. Valderhaug, Mar. Biol. 86 (1985) 203. G.K. Colbath, Lethaia 19 (1985) 339. F. Watt, G.W. Grime, Principles and Applications of High Energy Ion Microbeams, Hilger, Bristol, 1987.
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 287±291 [7] G.J.F. Legge, J.S. Laird, L.M. Mason, A. Saint, M. Cholewa, D.N. Jamieson, Nucl. Instr. and Meth. B 77 (1993) 153. [8] J. Pallon, Nucl. Instr. and Meth. B 22 (1987) 87. [9] J. Pallon, Nucl. Instr. and Meth. B 44 (1990) 377. [10] S.A.E. Johansson, J.L. Campbell, PIXE A Novel Technique for Elemental Analysis, Wiley, New York, 1988. [11] K.G. Malmquist et al., Nucl. Instr. and Meth. B 77 (1993) 3. [12] L. Jeppsson, D. Fredholm, B. Mattiasson, J. Paleontology 59 (4) (1985) 952.
291
[13] G. Bryan, P.E. Gibbs, J. Mar. Biol. Asso. UK 59 (1979) 969. [14] M.F. Voss-Foucart, M.T. Fonze-Vignaux, C. Jeuniaux, Biochem. Systematics 1 (1973) 119. [15] M. Elfman, P. Kristiansson, K. Malmqvist, J. Pallon, A. Sj oland, R. Utui, C. Yang, Nucl. Instr. and Meth. B 130 (1997) 122. [16] C. Bergman, Sveriges Geologiska Unders okning C 762 (1979) 92. [17] M. Eriksson, C.F. Bergman, J. Paleontology 72 (3) (1998) 477.
www.elsevier.nl/locate/nimb
Application of microPIXE and STIM in analyses of fossil and Recent polychaete jaws (scolecodonts) Mikael Elfman b
a,1
, Mats Eriksson
b,*
, Per Kristiansson a, Klas Malmqvist a, Jan Pallon
a
a Department of Nuclear Physics, Lund Institute of Technology, University of Lund, Box 118 SE-221 00 Lund, Sweden Department of Geology, Division of Historical geology and Palaeontology, Lund University, S olvegatan 13, SE-223 62 Lund, Sweden
Abstract MicroPIXE and STIM analysis of the chemistry of fossil and Recent polychaete jaws (scolecodonts) demonstrates that they, apart from their protein composition, constitute inorganic components. The PIXE images reveal that the elemental distribution is generally homogeneous for some elements while it is heterogeneous, especially for zinc and iron. The jaw of the Recent polychaete Nereis sp. has zinc concentrated in the tip, probably for hardening purposes. Similar accumulations were revealed in fossil scolecodonts; zinc in Kettnerites (K.) martinssonii and iron and titanium in Hadoprion cervicornis. Ó 1999 Published by Elsevier Science B.V. All rights reserved. PACS: 41.75.A; 79.20.R; 07.78; 41.85; 87.10; 87.22; 87.64; 91.65; 83.80.L Keywords: PIXE; STIM; Nuclear microprobe; Polychaete jaws; Fossil; Recent
1. Introduction Polychaete annelid worms comprise a signi®cant part of the invertebrate faunas of modern oceans. Their fossil record dates back to the early Cambrian (c. 540 Ma), possibly even further. Jawed polychaete worms appeared in the early Ordovician (c. 480 Ma), and preserved jaws (scolecodonts) are abundant in many Palaeozoic rocks. Polychaete jaws are normally 0.1±1.5 mm, brownish or reddish to black in colour, hollow and
*
Corresponding author. E-mail: [email protected] Corresponding author. E-mail: [email protected]. 1
vary in thickness, with a denticulated dorsal side (Fig. 1). Fairly little is known about the chemical composition of scolecodonts, although it has been discussed in some papers, for a review see Ref. [1]. It has been suggested that they are composed of sclerotized proteins with incorporated heavy metals and minerals [2,3]. The chemistry of polychaete jaws may provide an important tool in taxonomy and a ``®nger printing'' identi®cation of dierent taxa may be possible. Further, the jaw chemistry may act as a biological indicator of heavy metals [4] and aspects of taphonomy and fossilisation potential [3,5], as well as the detailed function can be considered. Here we introduce the microPIXE and STIM techniques for the purpose of investi-
0168-583X/99/$ - see front matter Ó 1999 Published by Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 3 1 6 - X
288
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 287±291
Fig. 1. SEM images of selected fossil scolecodonts (all in dorsal view). (a) Left MI (®rst maxilla) jaw of K. (K.) martinssonii, [1], ´34, Silurian of Gotland, Sweden. (b) Right MI jaw of the same species, ´34. (c) Left MI jaw of ``Ramphoprion'' sp., [16], ´77, Silurian of Gotland, Sweden. (d) Right MII jaw of H. cervicornis, [17], ´26, Cincinnatian (U. Ordovician) of Indiana, USA. Note that these are not the analysed specimens.
gating the chemistry of fossil and Recent polychaete jaws. The proton microprobe [6] has proven to be a uniquely useful instrument in many areas. It combines high sensitivity for elemental analysis and high lateral resolution and enables studies of the distribution of various elements and of chemical variations of the microstructures. Although all parts of this paper have been discussed between the authors, the bulk of it was prepared by Eriksson. The physics and experimental part was written by Elfman. 2. Experimental The sample backing was 180 lg/cm2 thick Kimfolä. The specimens were covered by another layer of Kimfolä and ®nally mounted in the sample holder. Simultaneous PIXE and STIM measurements were applied. Scanning transmission ion microscopy (STIM) [7] gives structural information for thin samples. The energy loss of the transmitted particles was measured, and the mass thickness of the sample was calculated. The darker parts in the STIM maps represent higher mass density. In order to get a suitable count rate in the STIM detector while maintaining the necessary beam current for PIXE analysis, o-axis
STIM must be used. A thin carbon foil (40 lg/ cm2 ), in which the transmitted particles are scattered, are placed behind the target [8,9]. A 4 ´ 4 mm2 photodiode was used as a detector for the scattered protons after the foil. The PIXE signal was detected with a Kevex Si(Li) detector of 50 mm2 active area and a measured energy resolution of approximately 155 eV at the 5.9 keV Mn Ka peak in 135° angle relative to the beam. A thin absorber (90 lm Be) was used for the PIXE detector. The PIXE [10] analyses were performed at the Lund Nuclear microprobe, which uses a singleended NEC 3 UH accelerator. The beam line is described in [11] and the data acquisition and scanning system is described in [15]. Protons of 2.55 MeV and a beam size of about 3 lm were used in this study. Semi-quantitative elemental ratios e.g. (Zn/Ca, Ti/Ca, Fe/Ca) were computed using the acquired PIXE spectra and dierent samples were compared. 3. Specimens analysed The fossil specimens analysed include K. (K.) martinssonii and ``Ramphoprion'' sp., both from the Silurian of Gotland, Sweden, and H. cervicornis from the Cincinnatian (Upper Ordovician) of Indiana, USA. The specimens were recovered through standard micropaleontological procedures [12]. The Recent Nereis sp. specimen was } collected in Oresund, south Sweden and the jaws were dissected out. All analysed specimens are housed in the Department of Geology, Lund, Sweden (LO). 4. Results ± chemical composition It is obvious that scolecodonts, apart from their suggested protein composition, also comprise various inorganic components [2]. This investigation revealed that scolecodonts contain silicon, sulphur, chlorine, potassium, calcium, iron, copper, nickel, titanium, chromium, and sometimes phosphorus, manganese, bromine and iodine. The amount and distribution of these elements varies in the analysed specimens. The elemental
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 287±291
distribution in the jaws is generally homogeneous. Some elements (e.g., zinc and iron) tend to be patchily distributed and concentrated in certain regions. The chemistry of the Recent specimen diers from that of the fossil specimens (Fig. 2) whereas the fossil jaws obtained from Gotland yielded similar PIXE spectra with somewhat varying proportions mainly of iron, nickel, and zinc. The most signi®cant dierences between the PIXE spectrum of the Nereis sp. jaw and those of the fossil species are the prominent peaks of zinc, and bromine and the presence of iodine and phosphorus in the former. Iodine was not detected in the fossil material. It is, however, a common constituent in sea water. A distinct zinc accumulation is displayed in the tip of the jaw of Nereis sp. (Fig. 3), see also Ref. [13]. Other elements are more or less homogeneously distributed in the specimen. The tip of the jaw is more massive than the proximal part. However, the relative distribution is
289
not in¯uenced by density dierences as the PIXE images are normalised to mass thickness with help of the o-axis STIM. Zinc seems to be distributed internally in the jaw, as proposed by Bryan and Gibbs [13], but also reaching the surface. The PIXE images reveal a similar, although not as prominent, accumulation of zinc in the narrow anterior part of the jaw of K. (K.) martinssonii. The chemical composition of ``Ramphoprion'' sp. resembles that of K. (K.) martinssonii (Fig. 2) but the former has increased Fe/Ca ratios, and a lower Zn/Ca ratio. The STIM image of ``Ramphoprion'' sp. reveals some internal structures, a rounded feature with a low mass density (muscle scar?) is visible (Fig. 3) approximately at midlength. The dark part may be an internally thickened part of the jaw or a sediment grain. The PIXE spectrum of the jaw of H. cervicornis reveals an increased Fe/Ca ratio compared with the Silurian specimens. The distribution of iron and titanium seems to be restricted mainly to the slender denticles (Fig. 3). Iron is internally restricted whereas titanium reaches the surface of the jaw. 5. Discussion
Fig. 2. PIXE spectrum obtained of the Recent polychaete jaw Nereis sp. (2A) and of the jaw of the fossil polychaete K. (K.) martinssonii (2B).
In addition to the functional usefulness, the chemistry of polychaete jaws may be in¯uenced by water chemistry, traces of feeding habits and/or sediment composition. Considering the fossil material, also diagenesis, weathering, and the extraction procedure must be taken into account. However, Bryan and Gibbs [13] showed that the zinc accumulation in the jaws of the Recent polychaete Nereis diversicolor, is not related to the sediment chemistry and argued that the distribution of zinc in nereidids probably is of functional signi®cance. As stated above, similar accumulations were detected in the fossil material. These most probably act to harden the jaws. The fossil specimens reveal only minor dierences in jaw chemistry, indicating that these species display similar chemical signatures. However, only a few specimens have been analysed and with more material it would perhaps be possible to detect unique chemical signatures (``®nger printings'')
290
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 287±291
Fig. 3. Elemental maps and STIM maps of the analysed scolecodonts. Darker parts in the PIXE maps represents higher elemental concentrations. The total scanning ranges are : A (2944 ´ 2944 lm), B (512 ´ 512 lm ), C (704 ´ 704 lm) and D (704 ´ 704 lm). A. } Nereis sp. from Oresund, Sweden (LO 8081) B. K. (K.) martinssonii, sample G 82-10CB, H orsne 3, Gotland (LO 8082). C. H. cervicornis, sample 91B6-1, South Gate Hill, Indiana (LO 8083). D. ``Ramphoprion'' sp., sample G83-12LJ N arshamn 2, Gotland (LO 8084).
that are speci®c to dierent taxa. Colbath [3] suggested that the chemical composition of modern euniceans could be used taxonomically, at least at the family level, and Voss-Foucart et al. [14] found a positive link between the phylogenetic relationship within polychaetes and the jaw chemistry.
The fossil specimens display similar chemical composition, although elemental distribution varies in the jaws. The delicate tips and other parts of the jaws, exposed to most wear, are commonly incorporated by zinc, iron, and titanium, probably to harden them. Similarly, the tip of the Nereis sp. jaw exhibits a prominent zinc accumulation.
6. Conclusions
Acknowledgements
PIXE combined with STIM provide a powerful tool in analysing organic walled fossils and similar structures. The technique does not harm (or insigni®cantly harm) the specimens and provides extraordinary resolution of the elemental composition. The PIXE images impeccably display the spatial distribution of accumulated elements. Similar internal accumulations are of functional interest and may otherwise be dicult to study. Density corrections (from the STIM detector) further facilitate accurate evaluation of elemental accumulations in the heterogeneously thick specimens. We believe that this preliminary study displays a great forthcoming potential of the technique for similar purposes.
A grant from The Royal Physiographic Society in Lund to M. Eriksson ®nanced the analyses. E. Hallberg and C. F. Bergman donated the studied specimens. L. Jeppsson and J. Andersson critically read the manuscript.
References [1] [2] [3] [4] [5] [6]
C.F. Bergman, Fossils and Strata 25 (1989) 1. P.J.W. Olive, Plenum Press, New York, 1980, p. 516. G.K. Colbath, Micropaleontology 32 (1986) 186. V.A. Valderhaug, Mar. Biol. 86 (1985) 203. G.K. Colbath, Lethaia 19 (1985) 339. F. Watt, G.W. Grime, Principles and Applications of High Energy Ion Microbeams, Hilger, Bristol, 1987.
M. Elfman et al. / Nucl. Instr. and Meth. in Phys. Res. B 158 (1999) 287±291 [7] G.J.F. Legge, J.S. Laird, L.M. Mason, A. Saint, M. Cholewa, D.N. Jamieson, Nucl. Instr. and Meth. B 77 (1993) 153. [8] J. Pallon, Nucl. Instr. and Meth. B 22 (1987) 87. [9] J. Pallon, Nucl. Instr. and Meth. B 44 (1990) 377. [10] S.A.E. Johansson, J.L. Campbell, PIXE A Novel Technique for Elemental Analysis, Wiley, New York, 1988. [11] K.G. Malmquist et al., Nucl. Instr. and Meth. B 77 (1993) 3. [12] L. Jeppsson, D. Fredholm, B. Mattiasson, J. Paleontology 59 (4) (1985) 952.
291
[13] G. Bryan, P.E. Gibbs, J. Mar. Biol. Asso. UK 59 (1979) 969. [14] M.F. Voss-Foucart, M.T. Fonze-Vignaux, C. Jeuniaux, Biochem. Systematics 1 (1973) 119. [15] M. Elfman, P. Kristiansson, K. Malmqvist, J. Pallon, A. Sj oland, R. Utui, C. Yang, Nucl. Instr. and Meth. B 130 (1997) 122. [16] C. Bergman, Sveriges Geologiska Unders okning C 762 (1979) 92. [17] M. Eriksson, C.F. Bergman, J. Paleontology 72 (3) (1998) 477.