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Abstract: LMU: An Expandable, Alpha-Numeric, Trichotomous, Informal, Rock-Stratigraphic Classification System Based on Marker-Defined, Stratigraphic Reference Surfaces


A marker-defined, stratigraphic reference surface is any recognizable, laterally traceable, soil- or rock-stratigraphic boundary that was also a former surface of deposition, or transportation, or erosion; or an in-situ remnant of a former surface of deposition, or transportation, or erosion.

These reference surfaces may be direct (bedding planes in core or outcrop), indirect (interpreted "marker-beds" on mechanical logs, or abstract (onlapped, offlapped, eroded, or faulted-out "mental images" of reference surfaces).

This informal trichotomous classification of strata based on reference surfaces begins with a division into three categories as follows: L for Lower, M for Middle, and U for Upper. In order to preserve in the informal name the unique vertical position of each stratal unit, as well as the original intent of the stratigrapher, two steps are required as follows: (1) the number 1 is added to the right of L, M, or U each time a stratal unit is trichotomously classified; and (2) the informal alpha-numeric name of each stratal unit includes all of the letters and numbers in the previous name.

For example, after subdivision by three trichotomous classification steps the individual stratal unit spoken of as "the third lower, of the second upper, of the first upper, of the subsurface Britt Formation" would be annotated from larger to smaller as follows: BtF, U-1, U-2, L-3. This same stratal unit can be diagrammed. A graphical


classification system is presented.

AAPG Search and Discovery Article #90944©1997 AAPG Mid-Continent Section Meeting, Oklahoma City, Oklahoma