Techniques for preparation of pyrite and limonite permineralizations

Abstract

Procedures are presented for the preparation of fine-polished surfaces of pyrite permineralizations, and demineralized thin-sections of limonite permineralizations. A major new feature in both procedures involves the re-embedding in plastic of individual cut sections in order to promote stability of the often crumbly material during further preparation. Pyrite sections are kept flat during polymerization of the plastic by means of a binder clip press. The technique for limonite permineralizations is characterized by the use of plastic not only for re,embedding individual sections but also for adhesion of sections to glass slides. Following this, sections are ground thin and demineralized with hydrochloric acid. We strongly recommend use of the thin-section technique for all studies utilizing limonite permineralizations because this method permits a much greater resolution of detail than is possible with other methods. INTRODUCTIONOne of the major problems in studying the internal structure of Devonian plants has been a lack of consistently reliable techniques for recovering the maximum information from fossils permineralized by pyrite (iron sulfides) and limonite (hydrated iron oxides), the most common forms of preservation in these plants.Pyritic specimens have contributed to paleobotanical knowledge for at least half a century. One of the early contributions was the study of the internal structure of Aneurophyton germanicum from the Middle Devonian of the Rhineland by Kr~iusel and Weyland (1929). Soon, thereafter, studies by Arnold (1935Arnold ( , 1940 and Read (1938) of pyritic Middle Devonian axes (Iridopteris, Reimannia, Arachnoxylon, Triloboxylon and others) from New York further emphasized the importance of this form of preservation. Only a small part of the potential information in these specimens was recovered by these early studies, however, because of limitations in the techniques and methodology employed.0034--6667/82/0000--0000/$02.75

The Anatomy of Rotoxylon dawsonii comb. nov. (Cladoxylon dawsonii) from the Upper Devonian of New York State

“…Primary xylem cells having the appearance of thin-walled parenchyma but interpreted here as immature or degraded protoxylem tracheids are strikingly similar to cells previously identified as protoxylem parenchyma in the Middle Devonian Iridopteridales, including Arachnoxylon (Stein 1981;Stein et al 1983) and especially Iridopteris (Stein 1982). Clusters of thin-walled cells clearly representing parenchyma have been unequivocally observed from both transverse and longitudinal section of a single specimen of Arachnoxylon minor (Stein et al 1983).…”

“…Despite the interpretation that parenchyma is associated with protoxylem in Iridopteris and A. minor, Stein et al (1983) concluded that the cells do not typically comprise a discrete and continuous zygopteridlike ''loop'' tissue within the primary xylem of the plant and thus offer little support for systematic relationship with that group. If we are correct in suggesting that the previously interpreted xylem parenchyma in Iridopteris are better interpreted as immature or degraded tracheids, then the difference between the Zygopteridales and Iridopteridales may be more substantial than previously considered.…”

“…Clusters of thin-walled cells clearly representing parenchyma have been unequivocally observed from both transverse and longitudinal section of a single specimen of Arachnoxylon minor (Stein et al 1983). In this specimen, the parenchyma comprise a much more massive tissue within the central region of the protoxylem strand, perhaps equivalent to protoxylem parenchyma observed in the Middle Devonian Stenokoleos bifidus (Matten and Banks 1969) and Crossia virginiana (Beck and Stein 1993), the Upper Devonian Rhacophyton (Leclercq 1951), some cladoxylopsids (Leclercq 1970), and early Carboniferous ferns (Williamson 1874).…”

Internal anatomy of the Late TriassicEquisetocaulisgen. nov., and the evolution of modern horsetails

“…The method proposed here is a modifi cation of techniques used in studying fossil plant material, including embedding techniques ( Stein et al, 1982 ;Jones and Rowe, 1999 ), and thin sectioning and wafering techniques ( Stein et al, 1982 ;Hass and Rowe, 1999 ).…”

“…Alternatively, fossils may be prepared by producing serial thin sections or "wafers" of material using a diamond wafering blade on a lapidary saw ( Stein et al, 1982 ;Hass and Rowe, 1999 ). These wafers are then mounted onto a microscope slide, ground and polished, and observed using refl ected or transmitted light when the specimen is ground thin enough (<1 mm; Benedict et al, 2008 ).…”