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DISTRIBUTION AND STRATEGIES OF BURROWS IN THE BAY OF PANZANO AND THE STARANZANO TIDAL FLAT (GULF OF TRIESTE, NORTHERN ADRIATIC SEA)

Peter Pervesler & Johann Hohenegger
Institute of Paleontology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.
e-mail: peter.pervesler@univie.ac.at, johann.hohenegger@univie.ac.at

Distribution and strategies of bioturbate activities are key sources for the knowledge of interactions between organisms and their inorganic environment. Ichnology in combination with sedimentological approaches are essential tools for the study of recent as well as fossil ecosystems. Endobenthic activity of differnt organisms leads to a large variety of bioturbate patterns. They depend on and mirror environmental parameters as factors controlling the spatial distribution of these organisms.

Permanent dwelling-structures in many cases protruding deep into the substrate and thus having a high fossilization potential are subjects of numerous studies in recent and fossil intertidal and shallow subtidal areas.

Here we present bioturbations, mainly crustacean burrows from intertidal and shallow subtidal sites in the Northern Adriatic Sea. Their distribution in dependence of environmental parameters like sediment properties, nutrients, oxygen availability and currents is discussed. Convergent orientations of all crustacean burrows in a certain geographical area (Bay of Panzano) are proved by the use of statistical methods.

Trend directions of the 4 investigated burrow systems show congruence in their preferred axial distributions. While single individuals construct the three investigated burrow systems of Jaxea nocturna, the remaining system investigated for orientations represents a cluster of different Upogebia burrows. Nevertheless, preferred orientations are obvious in this burrow bundle.

The comparison of strategies in recent and fossil burrows may allow distinguishing their producers on the genera or even species level. The main importance of a detailed comparative study of bioturbations can be the use in an actuopaleontological approach. Food sources, nutrients, feeding strategies, ventilation strategies, oxygen-availability, and pore water content of the sediment set in relation to burrow shapes and sedimentary structures are essential for the reconstruction of fossil environments. Crustacean burrows being most important structures in Cenozoic shallow marine environments follow the same orientation patterns. The basic pattern of crustacean burrows has three preferred directions that diverge at an angle of 120°. All crustacean burrows in a certain geographical area (Bay of Panzano) have convergent orientations. The Components of the axial distributions can be developed equal, symmetrical or asymmetrical. In cases of symmetrical components they correspond to current directions. Assymetrical components are influenced by the burrow structures (shaft of Upogebia pusilla burrows) and correspond to topographical situations and current directions.

Although there still exists no prove for the direct functional influence of current directions on the orientation of burrows the knowledge of preferred directions in complex recent burrows and their overlapping to current directions and coastlines are proved. Using orientation-statistical methods accordingly to the recent results, the reconstruction of fossil coastlines and paleo-currents should be reasonable.