(Coastal shelf south of Abbott Street)

geological context

Summary: Tessellated pavements are exposed at low-tide on the foreshore of Bellerive Bluff. The tessellation is similar to that exposed in the similarly aged (early Permian) rocks at Eaglehawk Neck. The paving was created by near perpendicularly aligned joint sets.

The pavement and its adjacent cliffs are composed of fine-sandstones and mudstones (the latter hardened to shale-grade). Glacial drop-stones abound, and there are abundant trace fossils in the shales.

Details

1. At low tide, the rocky shore platform is exposed as a tessellated pavement - with near-perpendicular jointing creating large ‘pavers’, whose edges are accentuated through deposition of iron-rich minerals.

Tessellated pavement, Bellerive Bluff (photo J Blake)

1. Dropstones (pebbles fallen from melting (glacial) ice sheets) are common at this site. In some places the pressure of dropped stones into the soft seafloor sediment has created deep, basin like indentations, with raised rims preserved by iron deposits.There are some large areas with smaller pockmarking, suggesting a similar process of soft sediment deformation.

Basin-like indentation (~40cm wide). (Photo J Blake)

1. Clayballs. A large ball of claystone is exposed in the mudstone cliffs. It is similar to those occurring in similar-aged sediments at Shag Bay, Geilston.

(Photo J Blake)

(Photo T Curtis)

4 Tracefossils. The fine mudstones layers contain an abundance of wriggly trace fossils (Ichnites : probably worm castings) indicating animal activity on the seafloor (but are not the animals themselves). Also present are Zoophycos = swirls of sediment created by moving and filter-feeding polychaete worms (Wikipedia).

Trace fossils/Ichnites (worm-castings) and fans of *Zoophycos. (*Scale: traces are ~ 2-5cm long) (Photo J Blake)

Zoophycos group https://www.uky.edu/KGS/fossils/fossil-month-zoophycos.php