Bryozoan distribution and growth form associations as a tool in environmental interpretation, Tasmania, Australia

The cool temperate carbonate sediments of eastern and western Tasmania and Bass Strait composed of 29-50% of bryozoan skeletal grains. Two hundred and eighty three bryozoan bulk sediments around Tasmania were studied to determine the relationship between bryozoan zoarial growth form association and their depth zone. Bryozoans skeletons are grouped into I I morphotypes according to architecture and style of disarticulation/fragmentation. Encrusting forms, erect flexible (cellariiform) and erect-rigid-robust-branching (adeoniform) cheilostomes are consistently the most widespread, with delicate branching cyclostomes the next most common. Growth form associations were grouped into four depth-related settings: strand line, shallow shelf, middle shelf and deep shelf. This study demonstrates that bryozoan morphotype associations, occupying different depth zones, are valuable for providing fundamental (paleo-) environmental information. Morphotype associations are related mainly to water depth, water energy, sedimentation rate and substrate. In the strand line setting encrusting unilaminar and erect-flexible-articulated-branching are abundant, while in the shallow shelf. erect-flexible, encrusting-multilaminar, erect-rigid-robust, fenestrate and delicate-branching are major growth forms. The above associations indicate high to moderate energy levels, moderate to high sedimentation rates and flexible to hard substrates. In middle shelf areas, erect-rigid-fenestrate, robust and delicate-branching cheilostomes and cyclostomes are the most common growth forms. These associations indicate decreasing water energy, lower sedimentation rate and presence of stable hard to soft substrates. In the deep shelf setting, the dominance of erect-rigid-robust, fenestrate and foliose forms indicate deep quiet water, low sedimentation rate and hard Substrate. (C) 2004 Elsevier B.V All rights reserved.