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Jargon Busting Guide – Biostratigraphy Reports: Terminology & General Concepts

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Jargon Busting Biostratigraphy Terminology and General Concepts PetroStrat Guide

On an offshore installation, a palaeontologist excitedly runs into the office of the OIM and Company Man: “FDO CMN Crucibiscutum ryazanicum and ABN Kokia spp.!! TD! You have to stop drilling!!!” 

IF all you* understand of this scenario is “OIM”, “Company Man” and “TD”, read on. This guide is written for you to introduce you to the world of biostratigrapher jargon! 

Yes, we use an awful lot of Latin names for our fossils in general and spice it up with some acronyms. To start at the beginning, biostratigraphy means to follow organisms through evolution and use their changing features to distinguish different species over time in sediment rock layers (“strata”). It is like working with Dinosaurs, only they are tiny and there are millions of them. 

While the Latin names are often describing features of the fossils – in this case its main feature is a cross (“cruci…”) and as the species name suggests, its restricted to the Ryazanian, the earliest, or lowest part of the Cretaceous – “FDO” translates into First downhole occurrence, which is its “LO” Last occurrence and therefore marks its extinction date. The qualifiers “CMN” and “ABN” for common and abundant, describe a defined quantitative range of counted individuals in the 60 “FOV” (= fields of view) examined in one sample. The abbreviation “sp.” is used if the scientist only identified the genus – in this case “Kokia” – “spp.” (= species pluralis) is used if the scientist has identified multiple species of the same genus. 

Indeed, if you encounter this described scenario on an offshore installation in the North Sea, it is an exciting moment, because you know you are just a few meters above the BCU (= Base Cretaceous Unconformity) and want to stop drilling and set a casing! 

*You, in this case sticking to the terminology, could also be referred to as Homo sapiens. 

Glossary of commonly use terms in a Bbiostratigraphy Report 

This glossary is meant to provide an entry level knowledge of biostrat terminology and general concepts used in a Petrostrat report. 

The following abbreviations are commonly used within a biostrat report

M (Microfossil) – The Microfossils referred to in this context, are primarily calcareous, single celled Foraminifera and multicellular Ostracoda (tiny shrimp with calcareous shells) and secondary siliceous, single celled Diatoms and Radiolarians, amongst other small fossil groups. The size fraction is approximately 0.5 to 2mm, however some Foraminifera can reach the gigantic size up to 5cm (Nummulites). 

N (Nannofossil) – Calcareous nannofossils are predominantly fossils of planktonic single celled algae (Haptophytes) in the size range of 2-20µm, which are only visible under the microscope, yet are rock forming (chalk) and can be observed from space, when in bloom.   

P (Palynology) – In contrast to the other two disciplines Palynology deals with the study of organic fossils of microscopic size, including terrestrial pollen and spores, dinocysts, acritarchs and others marine organisms.  

FSE (First Sample Examined) – The first sample examined in a well is usually the top sample and therefore the youngest. 

LSE (Last Sample Examined) – The last sample examined in a well is usually the base sample and therefore the oldest. 

PRES (Presence) – The presence of a fossil is usually mentioned when a species is found out of the interpreted context (it could be reworked?), or if a species has unusual abundances, which might be correlatable to other wells.  

FDO (First Downhole Occurrence) – The FDO indicates the top of a species in a well, which sadly is its extinction date. 

LO (Last Occurrence) – The LO is synonymous with the FDO, defining the top of a species. It is commonly used in scientific literature, focussing on evolutionary patterns, observed from an origination to an extinction event. 

LDO (Last Downhole Occurrence) – The LDO indicates the base of a species in a well, its origination. 

FO (First Occurrence) – The FO is synonymous with the LDO, defining the base of a species. It is commonly used in scientific literature, focussing on evolutionary patterns, studied from the First Occurrence to the Last Occurrence.  

CU (Cuttings – The cuttings usually used for sample preparation are cut by the drill bit and transported to the surface by the drilling mud. The transportation of the cuttings can cause markers being out of context (caving).  

CO (Core) – Samples taken from a core have the advantage, that the scientist knows species can not be caved in there but must be in situ or reworked (older than the current interpretation of a marker). 

SWC (Side Wall Core) – Side Wall Cores have the same advantage as have cores, but they are easier to obtain and usually give the scientist a precise spot sample. 

RARE – A fossil appears rarely within an assemblage. In palynology this is a single occurrence, in micropalaeontology this is a species is recorded 5 times or less in a count of 200-300.

FREQ (Frequent) – Used in palynology reports. Frequent is usually defined as a species which occupies 2-5% of a palynology assemblage. 

OCC (Occasional) – Roughly equivalent to FREQ used in palynology. Occasional is usually defined as 2-4 counts of a species in 60 Fields of View in nannopalontology. 

CMN (Common) – Common is usually defined as a species which occupies 6-15% of a palynology assemblage, 6-20 occurrences in a micropalaeontology count, or 5-16 counts of a species in 60 Fields of View in nannopalontology. 

ABN (Abundant) – Abundant is usually defined as a species which occupies 16-25% of a palynology assemblage, 21-50 occurrences in a micropalaeontology count, or 17-120 counts of a species in 60 Fields of View in nannopalontology. 

SABN (Superabundant) – Superabundant is usually defined as a species which occupies over 26% of a palynology assemblage, 50 or more occurrences in a micropalaeontology count, or 121+ counts of a species in 60 Fields of View in Nannopalontology.

ACME – The sample (or samples) where a species is present in its highest numbers.

CVD (Caved) – Caved fossils indicate fossils thought to be sourced from a higher stratigraphic level in a well. This can  occur in cuttings samples, without indicating problems with the wells stability.  

RW (Reworked) – Reworked fossils are older fossils transported into younger sediments, usually by turbidites and similar mechanisms.  

N.O.T. (Not Older Than) – Not older than a maximum age defined by a specific marker.  

N.Y.T. (Not Younger Than) – Not younger than a minimum age  

FOV (Fields of View) – The field of view is the surface are visible in a microscope. Samples under the microscope can be moved and multiple FOVs can be counted. Species diversity and abundance per FOV is a common counting/representation metric in Nannopalontology. 

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