The Modern Thrombolites of Lake Clifton, Western Australia

Thrombolites and stromatolites are microbialites with contrasting internal structures. The decline of stromatolites at the end of the Proterozoic and the rise of thrombolites during the Cambrian have been related to the evolution of burrowing and grazing metazoans, and it has been suggested that the thrombolites were the result of metazoan activity disrupting the original stromatolitic laminae. Some maintain that the thrombolitic structure is intrinsic, and due to penecontemporaneous mineralisation associated with coccoid-dominated BMCs. However, it is recognised that thrombolitic fabrics are complex, show a great variation, and may have originated in several ways. The interpretation of the genesis of thrombolites has been limited by the absence of well-documented modern examples. Thrombolitic and stromatolitic microbialites are presently forming in Lake Clifton, a marine-derived coastal lake in southwestern Australia. The thrombolites are by far the most predominant form of microbialite in Lake Clifton, with small stromatolites restricted to certain upper shore areas. The thrombolites exhibit a wide range of external morphologies including conical, domical, discoidal and tabular formations which vary considerably in size, as well as more irregular and columnar structures up to 1.3 m high. Many of the tabular and domical forms have coalesced to form an extensive reef-like formation over 6 km long. As documented by other studies of modern microbialites, external morphology appears to be primarily the product of the environmental setting. In Lake Clifton, seasonal fluctuations in water depth, regional variations in sedimentation rates and the effects of prevailing winds and currents are major controlling factors. By contrast, the internal morphology of the various thrombolites is remarkably similar, composed of a framework of aragonitic mesoclots. The aragonite is precipitated as a consequence of microenvironmental chemical changes induced by the metabolic activity of principally filamentous cyanobacteria. The Lake Clifton thrombolites represent an important modern analogue for understanding fossil thrombolites. The mesoclots appear to be a growth fabric and are not the result of disruption of pre-existing stromatolitic laminae. Moreover, Lake Clifton provides an important example of the coexistence between both stromatolitic and thrombolitic microbialites and an abundant and diverse metazoan fauna as well as demonstrating an apparent inability of this fauna to markedly influence microbialite development. Thus apart from changing chemical conditions, competition for space (and the resultant lack of suitable habitats) was probably a major factor restricting thrombolite distribution throughout the Phanerozoic following the middle Ordovician.

[1]  S. Stanley.  An ecological theory for the sudden origin of multicellular life in the late precambrian. , 1973, Proceedings of the National Academy of Sciences of the United States of America.

[2]  M. H. Nitecki.  Biotic crises in ecological and evolutionary time , 1981 .

[3]  L. Moore.  Water chemistry of the coastal saline lakes of the Clifton-Preston lakeland system, South-western Australia, and its influence on stromatolite formation , 1987 .

[4]  J. Schroeder.  Fabrics and sequences of submarine carbonate cements in Holocene Bermuda cup reefs , 1972 .

[5]  B. Pratt.  Stromatolite decline—A reconsideration , 1982 .

[6]  L. Moore.  The modern microbialites of Lake Clifton, South-Western Australia , 1993 .

[7]  F. G. Ferris,et al.  Geomicrobiology and sedimentology of the mixolimnion and chemocline in Fayetteville Green Lake, New York , 1990 .

[8]  S. Awramik.  THE PRE-PHANEROZOIC BIOSPHERE - THREE BILLION YEARS OF CRISES AND OPPORTUNITIES , 1981 .

[9]  J. Bauld,et al.  Microbial mats in Australian coastal environments , 1990 .

[10]  P. Sheehan,et al.  The Evolution of Reef Communities , 1987 .

[11]  C. Monty.  Precambrian background and Phanerozoic history of stromatolitic communities, an overview , 1974 .

[12]  J. Kennard.  Structure and origin of Cambro-Ordovician thrombolites, western Newfoundland , 1989 .

[13]  F. Brown,et al.  Nonmarine macroborings in early Pleistocene algal biolithites (stromatolites) of the Turkana Basin, northern Kenya , 1989 .

[14]  J. D. Aitken.  Classification and Environmental Significance of Cryptalgal Limestones and Dolomites, with Illustrations from the Cambrian and Ordovician of Southwestern Alberta , 1967 .

[15]  B. Rosen,et al.  The Nature and Significance of Microatolls , 1978 .

[16]  V. Semeniuk,et al.  Calcrete in Quaternary Coastal Dunes in Southwestern Australia: A Capillary-rise Phenomenon Associated with Plants , 1981 .

[17]  N. James,et al.  Thrombolites and stromatolites; two distinct types of microbial structures , 1986 .

[18]  W. Dean,et al.  Chapter 8.7 Freshwater Stromatolitic Bioherms in Green Lake, New York , 1976 .

[19]  V. Semeniuk,et al.  The natural sectors of the inner Rottnest Shelf coast adjoining the Swan Coastal Plain , 1985 .

[20]  V. Semeniuk,et al.  Modern and Pleistocene rocky shore sequences along carbonate coastlines, southwestern Australia , 1985 .

[21]  Thomas D. Brock,et al.  Chapter 6.2 Microbiology and Morphogenesis of Columnar Stromatolites (Conophyton, Vacerrilla) from Hot Springs in Yellowstone National Park , 1976 .

[22]  S M Awramik,et al.  Precambrian Columnar Stromatolite Diversity: Reflection of Metazoan Appearance , 1971, Science.

[23]  W. Sackett.  Microbial mats: Stromatolites: Edited by Yehuda Cohen, Richard W. Castenholz and Harlyn O. Halvorson. Alan R. Liss, New York, 1984, 498 pp , 1985 .

[24]  Robert Riding,et al.  Calcareous Algae and Stromatolites , 1991 .

[25]  P. Garrett.  Phanerozoic Stromatolites: Noncompetitive Ecologic Restriction by Grazing and Burrowing Animals , 1970, Science.

[26]  R. Folk,et al.  Travertines: Depositional Morphology and the Bacterially Constructed Constituents , 1984 .

[27]  L. Hardie,et al.  Chapter 8.6 The Geological Significance of the Freshwater Blue-Green Algal Calcareous Marsh , 1976 .

[28]  B. Pratt,et al.  Cryptalgal-metazoan bioherms of early Ordovician age in the St George Group, western Newfoundland , 1982 .

[29]  C. Woodroffe,et al.  Microatolls and recent sea level change on coral atolls , 1990, Nature.

[30]  S. Golubić.  Modern Stromatolites: A Review , 1991 .

[31]  R. Burne,et al.  Microbialites; organosedimentary deposits of benthic microbial communities , 1987 .

[32]  C. Monty.  Stromatolites in earth history , 1984 .

[33]  N. James,et al.  Reefs Canada and Adjacent Areas , 1988 .

[34]  R. Halley.  Chapter 8.5 Textural Variation Within Great Salt Lake Algal Mounds , 1976 .

[35]  G. C. Amstutz.  Developments in Sedimentology , 1965 .

[36]  M. Walter,et al.  Links between the rise of the metazoa and the decline of stromatolites , 1985 .

[37]  W. Ayrton.  Canadian Society of Petroleum Geologists: GEOLOGIC NOTES , 1977 .

[38]  B. W. Logan,et al.  Algal Mats, Cryptalgal Fabrics, and Structures, Hamelin Pool, Western Australia , 1972 .

[39]  D. Stoddart,et al.  Microatolls: Review of Form, Origin and Terminology , 1979 .

[40]  B. Pratt.  Epiphyton and Renalcis; diagenetic microfossils from calcification of coccoid blue-green algae , 1984 .

[41]  R. Weale,et al.  Beauvaria bassiana keratitis , 1986 .

[42]  S. Awramik.  Archaean and Proterozoic Stromatolites , 1991 .

[43]  A. M. Thorne,et al.  Biostratigraphic significance of stromatolites in upward shallowing sequences of the early proterozoic duck creek dolomite, Western Australia , 1985 .