Large trace fossils, Nyalau Formation, Sarawak

The Miocene coastal and coastal plain sedimentary rocks exposed along the coast of NW Sarawak are not particularly rich in macrofossils (but if you are looking for them, look along the beach, SW of Miri). However, they are very rich in another form of fossil…trace fossils, which preserve the behaviour, rather than the actual remains of the organism.

Below is a picture of a large trace fossil usually associated with shoreface deposits of the Miocene Nyalau Formation.

These have been called collapse structures. some workers have interpreted these as representing the traces of fish predation.

A similar, conical feature also forms in the shallow waters of the present-day Borneo coast.

These are the resting traces of stingrays

Trough cross-bedding, Machinchang Formation, Langkawi

The Machinchang Formation exposed on Langkawi is the oldest sedimentary rock succession in Malaysia. Fossils indicate a Late Cambrian age. That is about 500 million years old, not long (geologically speaking) after the initial explosion of complex multicellular life on Earth.

This is what makes the photo below particularly spectacular, because you can actually see sedimentary structures still preserved in the rock

The outcrop is sandstone displaying trough cross-bedding, evidence of water current flowing in a confined space (channels). The Machinchang Formation rocks were laid down in a shallow marine-coastal environment, with the cross-bedded sandstone probably representing tidal channel fills

Large Gastropod? Kubang Pasu Formation

The basal red mudstone of the Kubang Pasu Formation (Carboniferous in age, also known as the Langgun Red Beds, theChepor Formation etc….heck we’re planning a revision of the stratigraphy very soon) is rich in fossils. Unfortunately most of them are small.

Occasionally, you get large things like this

We suspected this to be an ammonoid, to to its large size. But the shell is very smooth, no ornamentation, no sutures. Maybe we are looking at a large gastropod (snail) shell?

Only new specimens and detailed descriptions will tell

 

Large mud clasts in the Semanggol Formation

This is an exposure of the top surface of one of the sandstone beds of the Semanggol Formation in Kedah

Another closer view

Initially, we thought that these might be some kind of large trace fossils, and they could have been misidientified as dinosaur tracks, if not for the deep marine origin of the deposits.

However, upon closer examination, the pock marks have remnant mudstone filling them, and their size and orientation are random.
These appear to be either large mud clasts probably ripped up from the muddy seafloor before being transported together with sand by gravity flow, or mud rafts associated with soft sediment deformation

One of the larger structures

 

 

And finally, one of the smaller features with mudstone infilling

The Semanggol Formation preserves deposits laid down by gravity acting on a marine slope, and contains turbidites, submarine channels and marine mudstone. These have been interpreted as representing a succession of rocks deposited along a deep continental margin

Flute Casts, Semanggol Formation

The Permian-Triassic Semanggol Formation, exposed in NW Peninsular Malaysia, has long been known as being composed of deep marine deposits.

Last year, while visiting an outcrop in Kedah, with some of my students, we came across a magnificent exposure of a turbidite/gravity flow deposit sandstone displaying abundant flute casts

Close up of the some of the flute casts

These flute casts are erosive features formed by turbulent eddies associated with high energy turbidity currents moving in deepwater. The high number of them at the base of this sandstone shows the remendous energy associated with deposition in such deep marine, continental margin environments

Hello world!

This blog is a site to just share with the world some of my ongoing work in sedimentology, stratigraphy and palaeontology here at the Geology Department, University of Malaya.

 

As a starter, I’ll show you a new ammonoid specimen one of my students found while working in Perlis.

Talking to colleagues here, they think its a Devonian age fossil. If that is the case, then it is going to give me headaches for the next year, because the rocks are supposed to be Carboniferous (younger), based on the position of the mudstone above chert beds with Carboniferous fossils (radiolarians).

Anyway, this can only be solved through detailed description of the specimen and, of course, better specimens. Cant wait to get back to the field. Hope to do that in June