Paleonet: Biostratigraphic datums - a question

Tony D'Agostino adagostino at
Tue Apr 17 23:04:45 GMT 2007

In 27 years of industry biostratigraphy I have never seen or heard of usage
described by Martin Head (below). In the oil business that would be what we
refer to as "made up data". A HO datum (please no Don Imus comments) is
routinely adjusted to the top depth of a sample interval when working with
cuttings material or any kind of sample that is a composite over a
stratigraphic interval. Occassionally I've seen workers assign a datum to a
midpoint of such a sample interval, but I've never encountered, let alone
used the method described by Dr. Head.  Why would one interpolate a depth
for a HO datum at some point that is not sampled or examined, providing a
basis for observations? Best practices dictate that you assign the datum to
some depth within or at the end points of the sample interval. At least you
know with certainty, if not precision, where that the fossil was observed to
occur. Leave the "interpolation" to the seismic interpreters.

Tony D'Agostino
20746 Prince Creek Drive
Katy, Tx. 77450
281-646-1660 adagostino at

"The limits of a tyrant are determined by the endurance of those that oppose
him" Frederick Douglass
  -----Original Message-----
  From: at
[ at]On Behalf Of
Martin J. Head
  Sent: Tuesday, April 17, 2007 5:27 PM
  To: PaleoNet
  Subject: Paleonet: Biostratigraphic datums - a question

  Dear Paleonetters,

  I have a question concerning the nomenclature of a particular
biostratigraphic datum.

  Although highest occurrences often refer to the highest sample in which a
taxon is found in a particular section, the real highest occurrence will
likely be at some interpolated point (normally placed at the midpoint)
between the highest observed occurrence and the next sample up. The
difference in position between the observed HO and the inferred HO will
depend on the sample spacing.

  Is there a term for this inferred/interpolated HO?

  I'd wondered if HOD (highest occurrence datum) might be the appropriate
term, but I believe this refers to a three-dimensional surface of HOs
whereas my "inferred HO" could refer to a single stratigraphic section (i.e
a point).

  I hope the answer is not too obvious! Thanks for any help or ideas.



  Martin J. Head


  Department of Earth Sciences


  500 Glenridge Avenue

  St. Catharines, Ontario L2S 3A1


  Tel 905-688-5550 ext. 5216

  Fax 905-682-9020

  Email mjhead at

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