About interpreting biostratigraphic data
First, a bit of background: A summary of bioevents, tops or horizons is an interpretation by the author at the time that the report was created. Eventually, new data will question the original interpretation (or hypothesis)… possibly decades later.
New data could be reprocessed via:
- Petrophysical algorithims
- Regional models
- Nearby comparative borehole
- Geological principle (i.e. plate tectonics), or even…
- Unrealized, future technology
To potentially prevent biostratigraphers from having to retrieve the original sample material to test a questioned hypothesis, Paleo Data Inc. delivers and archives a sample-by-sample listing of observed taxa, species, lithologies and minerals. This might be in the form of a written document or a range chart. Our hope is that future Paleo Data biostratigraphers will be able to understand the original fossil observations decades or centuries later without look again at the sample material.
Now, biostratigraphic understanding improves and refines itself, just as any other science. We learn more as we make more and more repeated observations. Processes improve. Therefore, there may always be a reason to relook at materials drilled decades or a century ago, IF those materials still exist. Sample degradation, budget cuts, natural disasters and even short-term vision may prohibit examining material drilled ages ago.
You’ll want the most detailed and curated observations as economically possible.
The value of quantitative data
Our recommendation is Quantitative analytical data. This is when a biostratigrapher point-counts every single microscopic critter, lithology, minerals, mud additive, etc. and compiles it into abundance data, with bioevents/tops included.
In order to provide high-quality quantitative data in an efficient and economical time frame, Paleo Data follows a modified version of the Styzen (1997) cascading quantitative counting method. This allows additional precision for reservoir assemblage picks creating resolution beyond “tops,” as well as statistical approaches to assemblage characteristic. The value of this approach increases if comparative boreholes also have quantitative analyses. This method is time intensive and but more valuable.
The value of semi-quantitative data
A more economical approach is the Semi-Quantitative analytical data. In this approach, the biostratigrapher places abundance for each species into a pre-defined set of bins. Paleo Data utilizes 10 bins of abundance from Single-Specimen to Flood. This approach is designed for quicker “tops-based” analysis, as the biostratigrapher quickly memorizes the bins with increased experience. This was the standard for many years, including academic researchers, until a call for an increased resolution of events moved the science into assemblage-based horizons, rather than just extinction and origination events.
Which biostrat data approach should you use?
Which should you use on your project? Well, that depends on what you need to know and how quickly you need to know it. Are you looking for a broad, general understanding of the biostratigraphy in a rank wildcat well and need immediate results? Or are you looking for an increased resolution?
At first glance, there’s not much difference in total abundance between quantitative and semi-quantitative data. The details are in the counts of individual species. Quantitative data helps the biostratigrapher understand the variance in abundance from sample to sample by species to species to help characterize local or field assemblages of correlative value.
Generally, one approach works for Exploration and the other for Developments, but that is not always the case.
Quantitative vs. Semi-Quantitative Data Study
Our advice is to consult a Paleo Data biostratigrapher who will take the time to understand your goals and expectations and design a plan to fit within your immediate needs and budget.