In September 2019, we conducted a paleomagnetic, stratigraphic, sedimentological, and geochemical sampling campaign in Sabah (Northern Borneo) Malaysia in context of the PhD project of Suzanna van de Lagemaat. The target was a section of Ocean Plate Stratigraphy (OPS) exposed along the Baliojong Rive. We will use the results from this section, consisting of ocean floor pillow lavas, deep-marine radiolarian cherts, and foreland basin deposits to track down the motions of the now-subducted tectonic plate on which these rocks formed, presumably the Izanagi Plate, from the moment of basalt formation (at a Mid-Ocean Ridge or Seamount) to arrival at the trench (below South China or North Borneo). Below a series of pictures to get an impression of the amazing field trip!
Participants of the trip were Suzanna van de Lagemaat, PhD student at Utrecht University…Eldert Advokaat, my long-term collaborator and former post-docJunaidi Asis, Assistant Professor at the University of Sabah, Malaysia, a specialist in radiolarian cherts who knows this section inside-outLicheng Cao (here with Eldert), an assistant professor at the China University of Geosciences at WuhanOur driver Mohammed, here with Junaidi
…and me
The section we sampled was in lush rainforestk and stunningly beautiful
The rocks of the section consisted of a thrusted (and as a result, along the river alternating) sequence of pillow basalts, which formed due to submarine eruption of basaltic lava at the sea floor…
…and radiolarian cherts, deep-marine sediments very rich in (biogenic) silica that were deposited below the so-called ‘carbonate compensation depth’ (~3 km deep or so), below which all carbonate dissolves.
The section was almost entirely overturned (i.e., upside down) and contained multiple thrust faults, which were also overturned. Her you see an overturned footwall cutoff, with Suzanna for scale
…which we carefully measured throughout the section for a first-order structural model
The top of the stratigraphy consists of land-derived sandstones that mark the moment that the oceanic plate arrived in the trench, just before it accreted at the trench and thus escaped subduction
Some of the cherts were beautifully, rhythmically banded (some sort of Milankovitch cyclicity?), with more mud-rich (wind-blown?) and silica-rich intervals
In the field, we already developd some ideas for the structural history
The section, which was some 5 km long, often required passing through the river…in shallow parts…
Navigating the section was a bit of a challenge at times…in man
To slightly deeper still…
To chest-deep…
to too deep to walk through 🙂 Luckily, our water-tight bags with samples could float.
…after which we continued our trip soaking wet.
…but of course happily.
Team sampling and documenting cherts
…drilling red clays between the cherts for paleomagnetic analysis of paleolatitude
…and collecting samples from the pillow lavas for geochemical analysis
….team working…and taking a break at the pillow-chert contact…on to the next wet part of the sectionfor some more sampling
and having fun
Licheng’s specialism is sediment provenance analysis, and he will look at the detrital content of the trench turbidites to evaluate whether they came from South China or BorneoSuzanna, writing down measurments from an (overturned) thrust contact between intensely folded cherts and pillows
Getting your feet (and hands) wet to get samples
The gorges were gorgeous
And so was the rest of the sectionLicheng handing sampling bags to Eldert and JunaidiThick chert sectionHyaloclastites, submarine explosive volcanicsLicheng, falling in the river at the exact moment I took the picture 🙂Me, showing the orientation of a thrust contact
This was a great trip, can’t wait to see the results!
