Marked accumulation patterns characteristic of Lower Devonian stromatoporoid bindstone: Palaeoecological interactions between skeletal organisms and microbes Natsuko Adachi a, * , Yoichi Ezaki a , John W. Pickett b a Department of Geosciences, Graduate School of Science, Osaka City University, Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan b 112 Blues Point Road, McMahons Point NSW 2060, Australia Accepted 2 September 2005 Abstract Stromatoporoid bindstones consisting of coarse alternations of both laminar stromatoporoids (bAculatostroma Q and Syringo- dictyon ) and microbialites (thrombolites and leiolites) are developed in a biohermal limestone of the Lower Devonian Garra Formation at the Catombal section, south of Wellington, New South Wales, Australia. The stromatoporoid bAculatostromaQ typically shows a thinly laminar and ragged appearance, producing main frameworks having cryptic spaces within them, and Syringodictyon is also very thinly laminar. Thrombolites are composed of an association of peloids and Girvanella , whereas leiolites are made up of dense micrites with intensive microborings. Similar accumulation patterns are repeatedly shown at each observation scale: 1) the main framework-building bAculatostromaQ and a combination of secondary framework (Syringodictyon ) and microbialites (leiolites and thrombolites) mesoscopically; 2) Syringodictyon and overlying leiolites and thrombolites at optical microscopic level; and 3) skeletons and intercalating dense micrite layers (leiolites) within Syringodictyon itself at SEM level. Microbialite accumulations on bAculatostromaQ suggest disruptions of skeletal growth, corresponding to periods of harsh habitat environments, whereas the recurrent appearance of Syringodictyon over microbialites suggests somewhat ameliorated conditions. The resurgence of bAculatostromaQ as a main frame-builder over a combination of secondary framework and microbialites suggests habitat recovery as well as the competitive superiority of this stromatoporoid. Successions such as bAculatostromaQ – Syringodictyon – leiolites–thrombolites reflect differences in the tolerances of each responsible organism, and correspond to fluctuating environments. The growth history of stromatoporoid bindstones is as follows: 1) the laminar stromatoporoid bAculatostromaQ first grew laterally, thereby stabilizing bioclastic sediments; 2) the stromatoporoid growths were partly or totally interrupted in relation to deteriorating habitat conditions, where micritization (leiolites with microborings), and encrustation by thrombolites occurred in succession. However, somewhat ameliorated conditions enabled Syringodictyon to temporarily dominate; 3) surviving parts of bAculatostromaQ again spread vertically and laterally upon the recovery of optimum conditions and; 4) the ceilings of cryptic spaces produced within bAculatostromaQ are affected by micritization (leiolites) and then encrustation of thrombolites. Repeated accumula- tions at various scales indicate antagonistic interrelationships within skeletal organisms and between skeletal organisms and microbes within their habitable ranges. These accumulation patterns thus provide invaluable clues for biotic interactions between 0031-0182/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2005.09.002 * Corresponding author. Tel.: +81 6 6605 3184; fax: +81 6 6605 2522. E-mail address: natsuko@sci.osaka-cu.ac.jp (N. Adachi). Palaeogeography, Palaeoclimatology, Palaeoecology 231 (2006) 331– 346 www.elsevier.com/locate/palaeo