Feeding patterns

These swirly patterns were made by living organisms at the bottom of the sea approximately 250 million years ago while they were feeding on an organic matter mixed within the sediment. The pictured sediments were buried by more sediments, hardened and eventually brought to the surface by tectonic processes without messing up such signs of ancient life.

South coast NSW, Australia

Broken shells

As you would find some broken-up shells on the beach today, these are just a few pieces of ancient sea shells from about 300 to 250 million years ago, preserved in the rocks which used to be a sea bottom sediment.

Ulladulla, Australia

Rocks out of place

Why are these rocks out of place? They just do not fit the environment in which they are. The sea waves that moved the medium to coarse sand that is now the sandstone that surrounds these boulders, are not strong enough to move boulders. There is a huge contrast in mass between the sand and the boulder. So, the only explanation is they were placed here by some other means. For this reason, such rocks are called ‘dropstones’, as they were dropped/placed into their current position, rather than being transported along with the surrounding sediment.

One explanation how this could have happened, is the sea ice. During Permian (~300-250 million years ago) this region was under ice age conditions, with glaciers covering the continent from land to sea. So, whether it was glaciers sliding into the sea, or sea ice enveloping loose boulders around the coast and moving them off into the sea; it is impossible to say exactly. But, because ice floats on water, it provides a good candidate for a mechanism of moving these heavy boulders from the land to the sea bypassing the sea wave transport.

Ulladulla, Australia

Ichnofossilsortrace fossils, are marks left in the sedimentary record by living organism but are not a body part of the organism. For example, pictured are burrows left by an organism that was feeding on an organic matter in the sediment. These provide an evidence of ancient organism activity after sediment deposition but before it turned into hard rock.

Ulladulla, Australia

Do not be fooled by this incredibly well preserved shell, it is not a recent shell, but a 250 million year old fossil.

Many different mollusc fossils are very well preserved at this outcrop which consists of layer upon layer of sediment which slowly accumulated on the sea floor during Permian times. Organisms such as this one, would have thrived here, feeding on the organic matter settling down to the bottom of the sea.

Southcoast NSW, Australia

In the mountains you can get a lot of two things, rocks and sediments produced from the break down of those rocks. In the foreground and in the background around the feet of the mountains you can see two big piles. These are called alluvial fans. It is basically a dump of sediments that was flushed down the small valleys into a big valley. What runs between these two alluvial fans is a major river which is a conveyor belt of the sediment that slowly moves it down the valley, down the mountains, down the floodplains and eventually into the ocean.

See it as a highway for moving of sediment.

Nubra River, Himalaya.

Giants among the Lilliputians, some diversity in size of bivalves among the sea bottom dwellers from Permian times (~250 million years ago).

Example from south coast NSW, Australia.

Ancient sea bottom exposed along a modern seaside rocky platform. This immense amount of fossilized shells is preserved in ~250 million year old sea sediments which would have been a feeding grounds for all these bivalves.

South coast, NSW, Australia.

Every rock that crops out of the ground is a record of the past, and so, in one way or the other it tells something about the environment in which it was formed. For example, the dark grey rock with fine and smooth texture you can see on the photo, looks that way because it formed on deep water sea bottom, where waves did not disturb the sediment that make up this rock, nor coarser sandy material was brought into it. This was a clam environment which allowed the sea-bottom animals to feed on the organic matter within the sediment (hence the dark colour) and is the reason why there are so many fossils in it, which I showed in the ‘underwater lilies’ post.

So, it is all good, and all makes sense!

But, then there are those large pieces of light grey rock (not shown, but some bigger than sedan car) with rough texture and little holes. Like you can see, its pieces are larger than anything else in a vicinity and are scattered all throughout the dark grey rock. This light grey rock does not belong to the sedimentary environment it is in, it got to where it is by other means than the sediment that surrounds it. And so, the plot thickens…

South coast NSW, Australia

Underwater Lilies

These barrel-shaped pieces are fragmented crinoid stems. This type of crinoid was a underwater lily-like creature which fed on the organic matter suspended in the water. Unfortunately, only stems were preserved at this outcrop, other elements were not found.

South Coast, NSW, Australia.

Wave rock around base of the Uluru monolith in Central Australia. An example of erosion-driven sculpting of the bedrock.

Scene from an ancient sea floor, as if it happened yesterday, however, these are from Permian period (~299–251 million years ago). Some of these fossilized bivalve shells are still articulated, meaning, left and right shells are still closed together. This tells you that particular animal specimen was undisturbed since its death, until now. The hard rock that envelops these shells was once a soft sediment in which these molluscs lived.

South coast NSW, Australia

2020: Slumped cross-bedding in the Hawkesbury Sandstone (Triassic) at Cape Banks.

2005: 36 conglomerate domes make up Kata Tjuta (formerly known as The Olgas), which are 40km west of Uluru. These conglomerates are thought to be  terrestrial fan deposits from the Ediacaran (550Ma). The ‘Valley Of The Winds’ circuit here is one of Australia’s best walks.   

1998: Stunning Welsh countryside of the Brecon Beacons, whose unique geomorphology is primarily the result of erosion of the upper Devonian Old Red Sandstone. Anne-Mie for scale. Anne-Mie was an amazing woman who could speak 6 languages and was a great friend to me when I was stuck in Belgium waiting for a contract. Her cancer came back to claim her almost 6 years to the day after this trip. I don’t think of her nearly enough.