The 11th Plant Taphonomy Meeting
Table of contents
EDWARDS, D.: Preserving plants in pyrite
EKLUND, H.: Mesofossils from the Late Cretaceous of Antarctica
FERGUSON, D.K.: Painting the broad picture: A plea for a multidisciplinary approach in community reconstruction
FRANCIS, J.: Unusual preservation of silicified wood by quartzine from the Jurassic Purbeck Formation
GOMEZ, B., MARTÍN-CLOSAS, C., BARALE, G., MÉON, H. & THÉVENARD, F.: Plant taphonomy in the fluvio-lacustrine basin of Uña-Las Hoyas (Upper Barremian, Southwestern Iberian Ranges, Spain)
HOWE, J.: Mid Cretaceous fossil forests of Alexander Island, Antarctica
MARTINETTO, E.: Terrestrial plant remains in late Cenozoic shallow marine deposits of the Po Plain (Italy)
MARTÍNEZ-DELCLÒS, X: Taphonomy of amber and its inclusions
Post-meeting field trip
Pyrite permineralisations are an important source of information on plant anatomy including
water-conducting cells in the earliest land plants and woody tissues in Eocene twigs and roots.
Detailed analysis of the fabric of pyrite in relation to the quality of preservation in the Devonian and
Eocene fossils has allowed elucidation of the processes involved and tentative explanations for the
differences in amounts of organic material present in the fossils. A model system using
Apium petioles (celery) and the
FeS-H2S reaction to produce pyrite was designed to simulate pyritisation in the laboratory.
The destruction of microcrystalline pyrite precipitated within cellulose cell walls, cements between cells,
and on the inner walls of the cells is consistent with observations of Devonian plant fossils, but we have
yet to produce a fully pyritised celery fossil to confound future palaeobotanists.
a broader picture of the flora emerges (the extra plant parts yield supplementary information)
the accuracy of the identifications can be corroborated/called into question and alternatives suggested
differences in representation can be used in the spatial reconstruction of the flora
If possible, other data on the site of deposition and its environs (e.g. sedimentology, palynofacies, phytoliths, diatoms, insect- and vertebrate-remains) should be integrated into such multidisciplinary studies.
It is clear that no one individual can undertake all this work. So how can we accomplish this
objective? The solution lies in multidisciplinary teams. However, this is easier said than done. The members of
the team must be compatible and be willing to let the common goal take precedence over their
The fossil plants and trees are found preserved in sequences of fluvial sandstones, siltstones and palaeosols. Sandstones show features such as in situ fossil tree trunks and leaves, some current bedding and rip-up clasts of the palaeosol below. Thick siltstone units are horizontally laminated and contain an abundance of well preserved plant fossils. This sedimentary sequence represents flood plain and channel bar deposits of a braided river which evolved into a meandering river system. The sandstones were formed during flood events which deposited vast amounts of sand over the riverbanks, covering the soils and vegetation. Signs of deformation in underlying sediments suggest that deposition of the sands was rapid and therefore flood events were catastrophic. The siltstones were formed from suspension fallout in standing water pools. The palaeosols are immature but have an abundance of rootlets and plant material within them indicating that they supported vegetation. The palaeosols represent a period of emergence along a riverbank with enough time for colonisation of plants and trees. Sequences of palaeosols, sandstones and siltstones suggest that when water subsided, new soils formed and plant colonisation began again.
The fossil plant assemblages suggest that a thick canopy of araucarian and
Elatocladus conifers with an understorey of ferns and the small shrub
Taeniopteris, dominated the vegetation within these
Cretaceous fossil forests. Other minor components of the vegetation included liverworts, angiosperms and
The second case study is represented by the succession of Oriolo (nearly 20 m thick) in the SE Po plain, near Faenza, which should be chronostratigraphically located at the Matuyama/Brunhes boundary. Here a rich collection of reddish leaf impressions (and a few fruits and seeds) was gathered by Dr. M. Sami. The leaf assemblages originate from a few silty layers with chaotically disposed leaf sheets. Several samples contain mainly whole leaf specimens, suggesting that fragmentation during transport has not been dramatic. Most specimens show distinctive leaf architectural features, which permit to assign them to about three dozens of taxonomic groups, most of them still living in Italy.
Obviously, the leaf and «carpoid» assemblages of both study sites experienced a consistent transport
that could have biased the composition. However the palaeoenvironmental setting of both sites
was characterised by inclined slopes very close to the coastline, with a rather narrow coastal plain
in between, so that plant remains did not need to be transported more than a few thousend metres.
Such assemblages may be interpreted as masses of continental plant brought by rivers into the
shallow-sea during distinct flood events. Individual «carpoids» obviously floated in the sea for several
weeks (months?) before burial, because they were colonised by
Teredo. On the other hand, due to the
presence of delicate leaves, it seems improbable that their floating time in the sea would be as long; yet very
rare specimens encrusted by balanids and bryozoans were found in other Pliocene sites of the western
Po Plain. In order to reconstruct the area and the vegetation types which were sampled by the
transport agents, the best tool seems to be an ecological analysis based on nearest living relatives, especially
for the Pleistocene of Oriolo. In this site several living taxa distinctly indicate a riparian forest; other
forms indicate a floodplain forest and a slope forest, likely associated with clearings yielding
shrubby vegetation. Even for the Cervo River leaf flora there are some indications of such a broad
vegetation sampling. The carpological assemblages invariably indicate a main provenance from
well-drained terrestrial environments, but is difficult to say from how many vegetation types because most species
are extinct. Less common taxa prove that also freshwater wetlands
(Proserpinaca) and marine seagrass communities
(Cymodocea) had been sampled. Of course, a sound actuopalaeontological analysis
of analogous taphocoenoses will be the key to get more information from this rich and diverse kinds
of fossil assemblages.
Amber is a natural fossilized resin exuded by a large diversity of trees, especially some groups of conifers and angiosperms. Today these large resin producers are mainly distributed in the tropical and temperate forests and savannah, and they are largely used by the wood industry, chemistry and pharmacy. Resins are a complex mixture of terpenoid compounds, the more common ones are oxygenated terpenes, such as acids, alcohols, and esters, secreted from plant parenchyma cells. Terpenes may be volatiles at normal environmental temperatures but in particular cases they are not. The latter are the most significant for us since they transform into amber after milions of years of diagenesis, while volatiles are gradually lost in that time.
After resin secretion a number of processes including oxidation and polymerization occur; resin becomes harder in a short time to form a product known as copal, which may reach ages of up to a few thousand years. Copal has different physical and chemical features than amber, which needs some millions of years to be formed.
When does amber taphonomy begin? It is obvious that in the case of arthropod or other animal inclusions, the taphonomic processes begin when they are trapped by the sticky resin, but this is more difficult to decide in the case of their "matrix" (the amber). The boundary between biostratinomy and diagenesis is also different for insects and the amber itself. Whereas foramber inclusions, diagenesis begins when they are totally embedded in resin, this boundary is not as straightforward for the amber. Does it begin with the polymerization of terpenes or rather when the resin is buried in sediments ?, what about the resin secreted by roots ?
These questions may be answered after reviewing the formation of resins in trees. Resins may form in internal crack fillings, under the bark, in resin pockets in the wood, in pockets between the bark, as fillings from tree wounds, as external stalactite shapes, as stalactites, as external drops and swellings. Not only resins are usually related with the bark or wood but also with roots, leaves, etc. It is necessary to say that one species of tree may produce diverse types of resins, with different chemical compositions and obviously different rates of decomposition. For example Agathis australis (Araucariaceae) produces at least 5 different types of resin. All these features determine the future amber formation, and the preservation of inclusions.
In this workshop a number of crucial topics for the taphonomic history of amber may be discussed:
a) Resin production and their producers. What kind of trees produce today large quantities of resins ? Differences between their recent distribution and their distribution in the fossil record should be taken into account.
b) The drying of resin. During this event a large quantity of animal and plant remains may stick in resin. Are the organism remains found embedded in amber selected in a certain extent? This may condition the palaeoenvironmental and palaeoecological reconstructions made from amber remains.
c) The transport of resin until its final depository. Are the amber deposits mainly autochthonous or allochthonous ? Which sedimentary environments are more favourable for the preservation of resin?.
d) Diagenetic processes that affect resin and their biological content. Is the original composition of inclusions preserved in ambers? Why do we study the palaeobiological content by transmitted light microscopy (through the amber)? and why do we not extract it?
We may try to answer these questions during my talk, but there are other questions I would like to discuss together with all participants, as for example: why does a large quantity of amber localities occur around the world but only a few of them have palaeobiological content?
Post-meeting field trip: Plant Taphonomy in La Cerdanya Basin (Upper Miocene, Pyrenees)
The semi-graben of La Cerdanya is located in the Axial Zone of the Eastern Pyrenees at an altitude of about 1100 m. The origin of this graben can be traced to the Late Miocene strike-slip movement of La Tet Fault, which cut the Eastern Pyrenees from ENE to WSW. As a result, a small (35 km long and up to 7 km at its widest point), clearly asymmetric basin was formed (Pous et al., 1986; Cabrera et al. 1988).
During Vallesian (Late Miocene) La Cerdanya recorded up to 800 m of fluvio-lacustrine sediments. Conglomerates, sands, and silts were deposited in alluvial fans; sands, silts, and lignite seams were deposited in fluvial plains and deltaic swamps, and lutites and diatomites accumulated in a lacustrine setting. Limnological studies showed that the lake was deep and meromictic. Sedimentological and geochemical data demonstrated that water stratification resulted in low-oxygenation conditions, preservation of lacustrine varves and high organic content at the lake bottom (Anadón et al. 1989; de las Heras et al. 1989).
Since the late nineteenth century, when Rérolle (1884-1885) first studied the fossil plant remains of La Cerdanya, the basin has been the subject of many paleobotanical and palynological studies (e.g. Baltuille et al. 1992; Barrón 1995, 1997; Haworth and Sabaté, 1993). About 100-150 species of plants have been recognized from their macroremains, pollen and spores.
During the Miocene, a vegetation zonation was apparent due to altitude change in La Cerdanya. Álvarez-Ramis & Golpe-Posse (1981) defined plant assemblages related to this zonation. The vegetation around the lake was a mixed, polydominant, montane forest composed of oaks, beeches, and fir with other elements, such as maples, elms, birch, chestnut and lime. Some relict thermophilous elements such as laurels, the bald cypress, and even palms, are occasionally found but these were probably never abundant in La Cerdanya. This vegetation is consistent with the higher altitude of the Pyrenean lake and contrasts with the Miocene vegetation of the Catalan coastal basins, which included a larger number of thermophilous and xerophytic elements, mainly legume trees. The lake itself was bounded by a helophytic belt formed by Poaceae, Cyperaceae and Typha, and a hydrophytic vegetation dominated by Trapa, pond-weeds and Ceratophyllum. Diatoms and planctonic chlorophytes dominated the open lake.
Plant taphonomy has attracted the interest of authors in recent years (Barrón, 1995; Martín-Closas, 1995) The latter author recognized four plant macroremain taphofacies and discussed their distribution in the basin. Recent, still unpublished results, add new information about the palynofacies of the basin.
Deltaic-palustrine lutites include assemblages of autochthonous aquatic plant megaremains such as reed stems (Poaceae, Cyperaceae) and water-chestnut fructifications (Trapa). Layers with this taphofacies may present rootlet marks. Another taphofacies, found in lignites interbedded with previous lutites, is an assemblage of allochthonous remains. They include floated stems of helophytic plants, which are sometimes recognizable in roof shales of lignite seams. Palynofacies of the palustrine belt are highly diverse in composition. Characteristic components include brown wood, structured organic matter (cuticles), zygospores and dense palynomorphs such as spores of Osmundaceae.
Two mega-remain taphofacies were recognized in the lacustrine area. Highly diverse assemblages of leaves, stems, and fructifications with evidence of tearing and fragmentation during stream transport coexist with well-preserved remains, which were transported by the wind. Hydrophytes and helophytes also may be present. This was the dominant plant taphofacies along the northern, western, and eastern lakeshores, which were shallower, gently sloping, and received a number of inlets. Another taphofacies includes land plant remains mainly blown by the wind. This taphofacies is characterized by well-preserved leaf- and winged-seed assemblages without evidence of mechanical breakage. It has a more distal character in comparison to the former plant taphofacies and is located along the deeper, southern margin of the paleolake.
Palynofacies found in lacustrine diatomites are also dual and correlate well with geochemical results (especially Hidrogen Index) but do not show a good correlation with mega-remain plant taphofacies. A palynofacies with dominance of anemophyllous pollen taxa (especially well preserved Alnus and torn bisaccates) and the chlorophyte Botryococcus is largely distribuited in the whole lake. Only in the central lake, sediments another palynofacies occurs, which shows abundant amorphous organic matter and is sapropelic in origin, as indicated by high hydrogen indexes (HI).
Álvarez-Ramis, C. & Golpe-Posse, J.M. 1981: Sobre la paleobiología de la cuenca de La Cerdanya (Depresiones Pirenaicas). Boletín de la Real Sociedad Española de Historia Natural. Sección Geológica 79, 31-44.
Anadón, P., Cabrera, L., Julià, R., Roca, E. & Rosell, L. 1989: Lacustrine oil-shale basins in Tertiary grabens from NE Spain (Western European Rift System). Palaeogeography, Palaeoclimatology, Palaeoecology 70, 7-28.
Baltuille, J.M., Becker-Platen, J.D., Benda, L. & Ivanovic-Calzaga, Y. 1992: A contribution to the subdivision of the Neogene in Spain using palynology. Newsletter Stratigraphy 27, 41-57.
Barrón, E. 1995: Estudio tafonómico y análisis paleoecológico de la macro y microflora miocena de la cuenca de La Cerdaña. Unpublished Ph.D.Thesis, Universidad Complutense de Madrid, 773 pp.
Barrón, E. 1997: Estudio palinológico de la mina de lignito Vallesiense de Sanavastre (La Cerdanya, Gerona, España). Revista Española de Micropaleontología 29, 139-157.
Cabrera, L., Roca, E., & Santanach, P. 1988: Basin formation at the end of a strike-slip fault: the Cerdanya Basin (Eastern Pyrenees). Journal of the Geological Society, London 145, 261-268.
De las Heras, X., Grimalt, J.O., Albaigés, J., Julià, R. & Anadón, P. 1989: Origin and diagenesis of the organic matter in Miocene freshwater lacustrine phosphates (Cerdanya Basin, Eastern Pyrenees). Organic Geochemistry 14, 667-677.
Haworth, E. Y. & Sabaté, S. 1993: A new Miocene Aulacoseira species in diatomite from the ancient lake in La Cerdanya (NE Spain). Nova Hedwigia, Beiheft 106, 227-242.
Martín-Closas, C. 1995: Plant Taphonomy of La Cerdanya Basin (Vallesian, Eastern Pyrenees): Geobios, M. S. 18, 287-298.
Pous, J., Julià, R. & Solé-Sugranyes, L. 1986: Cerdanya Basin: Geometry and its implications on the Neogene evolution of the Eastern Pyrenees. Tectonophysics 129, 355-365.
Rérolle, L. 1884-1885: Études sur les végétaux fossiles de La Cerdagne. Revue de Sciences Naturelles de Montpellier 3ème Série 4, 167-191, 252-298, 368-386.
Riba , O., de Bolós, O., Panareda, J.M., Nuet, J. & Gosalbez J. (1976): Geografia física dels Països Catalans, Ketres Editora226 p., Barcelona.
Solé Sabarís. Ll. (1958-1971): Geografía de Catalunya, Editorial Aedos, Barcelona.
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