Papers by Wladyslaw Alterman
Geological Society, London, Special Publications, 2012
Marine and Petroleum Geology, 2012
This paper discusses geological events with an approximately global preservational scale which ca... more This paper discusses geological events with an approximately global preservational scale which can aid inter-cratonic correlations and contribute to postulates of supercontinents for a set of chosen Precambrian cratons. The chronological scale of such events is highly variable, and most event types detailed (supercontinent-, mantle plume-, orogenic-, chemostratigraphic-, glacial events and major unconformities) have durations concomitant with the large scale interaction of mantle thermal and plate tectonic processes that were largely responsible for their genesis, i.e. 10's to 100's of millions of years. Geologically instantaneous events of global compass (e.g., impact or major eruptive events) provide important chronological markers for interpreting the longer term events. The same interplay of tectono-thermal geodynamic processes that drives the evolution of the Earth and the operation of its supercontinent cycles is also, ultimately, responsible for and of comparable duration to first-and second-order sequence stratigraphic cyclicity. This paper thus serves to introduce these concepts and discuss the problems in their application to specific Precambrian cratons, in relation to the aim of this special issue, of providing a set of accommodation curves for many of these ancient crustal terranes.
Geologische Rundschau, 1986
Precambrian Research, 2005
The taphonomic nanostructure of acritarch cell walls from the c. 650 million years old Chichkan F... more The taphonomic nanostructure of acritarch cell walls from the c. 650 million years old Chichkan Formation was studied with optical microscopy (OM), Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The integration of high-resolution methods and classical optical microscopy allows for the assessment of the relationship of the fossil to the embedding chert and of the authenticity of the fossil. Partial etching of paleontological (150 m) and petrographic (30 m) thin sections rather than maceration of the semi-stable cell structures served as the preparation method suitable for AFM and SEM studies. Focussed Ion Beam (FIB) preparation of sections normal to cell walls, yielded stable thin foils of the same thin sections and microfossils as investigated by OM, AFM and SEM. Unicells that appeared excellently preserved by optical microscopy standards, consisted of disconnected kerogen particles, dispersed in the cryptocrystalline quartz matrix and arranged in stacks of variable spacing on micro-to nanometer scale. The density of carbon particles was found to be correlative to the stability of cell walls and to inhomogeneities in the chert. SEM and AFM images of cell cross-sections are directly comparable at the same scale of magnification, but AFM offers higher resolution possibilities and 3-D information on the arrangement of particulate carbon within the cell. Whereas the microscopic appearance of cells was highly variable within the same rock unit, from the same locality in the Chichkan Formation, the nanoscopic structure of kerogen was found to be similar in all cells, consisting of multi-laminated
Sedimentary Geology, 2011
Sedimentary Geology, 2007
By introducing the new term 'organomineral' to apply to minerals that are affected by organics, m... more By introducing the new term 'organomineral' to apply to minerals that are affected by organics, mostly life-related, but not directly produced by living cells, we hope to increase the accuracy of the terminology in present usage. We believe that the term 'biomineral' does not describe all mineral deposits precisely enough and offer case studies to support instances where the use of the new term 'organomineral' is more appropriate. We provide examples of some materials that are biominerals such as those in diatoms and human bones and which perform a functional purpose. We then attempt to show that terminology can sometimes mislead investigators, drive the direction and prejudice interpretations of scientific investigation. This is achieved by presenting case studies of minerals that have been investigated as biominerals although they may not actually be directly controlled by biology. For this reason we pay special attention to desert varnish, hot-spring siliceous deposits, stromatolites, and bacterial encrustations. We go on to explain why we regard biominerals as direct indictors of life whereas organominerals should be treated as indirect indicators of life that require careful characterization to establish the origin of contained organics and whether these are biotic in origin. How organic compounds are preserved and transformed in sedimentary environments and in the mineral matrix is as highly relevant to the study of modern Earth environments as it is in the search for the oldest evidence of life in the terrestrial rock record. It is also important to many disciplines such as microbiology and archaeology and especially to scientists planning missions to look for evidence of 'life' on other planetary surfaces.
Precambrian Research, 1995
The oldest filament- and colonial coccoid-containing microbial fossil assemblage now known is des... more The oldest filament- and colonial coccoid-containing microbial fossil assemblage now known is described here from drill core samples of stromatolitic cherty limestones of the Neoarchean, approximately 2600-Ma-old Campbell Group (Ghaap Plateau Dolomite, Lime Acres Member) obtained at Lime Acres, northern Cape Province, South Africa. The assemblage is biologically diverse, including entophysalidacean (Eoentophysalis sp.), probable chroococcacean (unnamed colonial coccoids), and oscillatoriacean cyanobacteria (Eomycetopsis cf. filiformis, and Siphonophycus transvaalensis), as well as filamentous fossil bacteria (Archaeotrichion sp.); filamentous possible microfossils (unnamed hematitic filaments) also occur. The Campbell Group microorganisms contributed to the formation of stratiform and domical to columnar stromatolitic reefs in shallow subtidal to intertidal environments of the Transvaal intracratonic sea. Although only moderately to poorly preserved, they provide new evidence regarding the paleoenvironmental setting of the Campbell Group sediments, extend the known time-range of entophysalidacean cyanobacteria by more than 400 million years, substantiate the antiquity and role in stromatolite formation of Archean oscillatoriacean cyanobacteria, and document the exceedingly slow (hypobradytelic) evolutionary rate characteristic of this early evolving prokaryotic lineage.
The sparse Archean fossil record is based almost entirely on carbonaceous remnants of microorgani... more The sparse Archean fossil record is based almost entirely on carbonaceous remnants of microorganisms cellularly preserved due to their early post-mortem silicification. Hitherto as an exception, sedimentary carbonate rocks from the Neoarchean Nauga Formation of South Africa contain calcified microbial mats composed of microbiota closely resembling modern benthic colonial cyanobacteria (Chroococcales and Pleurocapsales). Their remains, visible under the scanning electron microscope (SEM) after etching of polished rock samples, comprise capsular envelopes, mucilage sheaths, and groups of cells mineralized by calcium carbonate with an admixture of Al-K-Mg-Fe silicates. The capsular organization of the mucilaginous sheaths surrounding individual cells and cell clusters forming colonies and the mode of mineralization are the characteristic common features of the Neoarchean microbiota described and their modern analogues. The new findings indicate massive production of calcium carbonates by benthic coccoid cyanobacteria in the Neoarchean, and offer a solution to the problem of the origin of Archean carbonate platforms, stromatolites and microbial reefs.
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Papers by Wladyslaw Alterman