Based in Mahone Bay, nova scotia, agile libre is an independent publisher of technical books about the subsurface.  

The megaspore big show: discovery

It seemed that there was little left to discover after 25 years working as a micropalaeontologist on the Mesozoic succession of the northwest European shelf. Routine well analysis had become predictable, with the biostratigraphic evaluation divided on a discipline basis: non-marine, Triassic–Jurassic formations were invariably off-limits to micropalaeontologists… until 2006. With the drilling of Statoil’s 6608/11-4 exploration well, I was thrust into the world of an alien group of microfossils: megaspores.

Well 6608/11-4 is located in the Haltenbanken area of the mid-Norwegian shelf, just to the north of the Norne and Urd fields. Both fields produce oil and gas from Early and Middle Jurassic reservoirs. The main objective of 6608/11-4 was to evaluate similar-aged formations, including the non-marine Åre Formation. It was probably through sheer desperation that the biostratigraphic program conceived for this well led to the continuous micropalaeontological analysis of ditch cuttings and core samples down to TD (total depth). Normally palynological analysis would have been applied, however previously this had been disappointing because preparations were invariably dominated by morphologically diverse, long-ranging miospores.

When the first megaspores (up to 1 mm in diameter and visible to the naked eye) started to appear in my sample residues, my initial feelings were of curiosity and wonder. Later, as the deeper samples yielded greater numbers, trepidation set in — how was I to speciate and start logging these alien microfossils? Despite the crudeness of my attempts at speciation, two important conclusions could be initially drawn from the well data. Firstly, megaspores could be readily extracted in large numbers using conventional micropalaeontological preparation methods. Secondly, a distinct succession of megaspore assemblages was evident within the Åre Formation — the potential for biozonation was starting to emerge.

Statoil’s biostratigraphers could see that megaspores had potential, and I became involved in a sequel well — 6608/11-5 — and then a multi-well study of the Urd Field. By this time my library of megaspore publications was growing, with the consequence that the systematics of the Åre Formation megaspores had improved. In addition, I had developed reflected light, colour photomicroscopy of megaspores using a Bresser ocular digital camera, which in combination with Helicon Focus imaging software, enabled several focal-plane images to be combined into one.

Morris_spores.png

With more confidence, a detailed megaspore biozonation of the unit was pro­posed. The succession of megaspore assemblages seen in the Åre Formation appeared correlatable with those in the Danish Basin and beyond; there also seemed to be a link between the change in megaspore-producing floras and climate through the Late Triassic and Early Jurassic. All this was presented in an internal report, which was about to be assessed independently by the leading academic in the fields of palynofacies and megaspores.

My first meeting with Professor David Batten was another milestone in the unfolding world of megaspores. The feelings of a viva exam initially prevailed in David’s cramped office, piled ceiling-high with palynological publications. His critique of my work was generous, and I was directed to publications hitherto unknown to me. On seeing a photomicrograph of one of the more enigmatic zonal species, David leapt to his feet and exclaimed, ‘I have seen that before’. He produced a Chinese publication by Cui et al., and the mesofossil Kuqaia quadrata was duly identified. Since our meeting in Manchester the advancement of Jurassic megaspore biostratigraphy has been a shared interest, and later we found ourselves drawn to the Middle Jurassic plant beds of North Yorkshire.

The megaspore big show continues on the next blog entry.


References

Cui W, G Zeng, H Zhu, and W Li (2004). Early Jurassic megaspores and palynomorphs from the Bohu Depression, Yanqi Basin, Xinjiang, NW China. Acta Micropalaeontologica Sinica 21, 292–308. (In Chinese, with English summary.)

The evolution of workstation interpretation

Presenting… your career

0