# Presentation: 497214

## Biostratigraphic Databases: Critical Tools in Stratigraphic Architecture and Sequence Stratigraphy

- Robert B. Witrock* *
*Minerals Management Service, *
*Department of the Interior, *
*New Orleans, Louisiana*

## Biostratigraphy’s changing role over the last 200 years

## Biostratigraphic databases have become more useful to the petroleum industry as they are updated with:   - new age models     - new bioevent age estimates     - improved taxonomy    - improved paleoecology    - more species occurrences in          	range charts (includes fossil  	increases, acmes, coiling 	changes)

- The changing role of biostratigraphy

- An overview of a biostratigraphic database project (modified from
- Lazarus, D. B., 1994, The Neptune Project - developing a large
- relational database of marine microfossil data on a personal
- computer, Mathematical Geology 26: 817-832).  For more information about the Neptune relational database project see _[http://palaeo-electronica.org/1999_2/neptune/research.htm](http://palaeo-electronica.org/1999_2/neptune/research.htm)__ _

## Sequence stratigraphy

- Alongside evidence of transgressions and regressions, unconformities (or hiatuses),  where  recognized in
- outcrop or subsection, identify depositional sequence boundaries.

## Sequence stratigraphy

-  Condensed sections:
-  composed of many paleobioevents [several Last Appearance Datums (=LADs)] within a small sample range
-  indicative of slow sedimentation rates

- Highstand system tracts, lowstand
- system tracts, and
- maximum flooding surfaces

## Slide 6

## Sequence stratigraphy

- Sequence boundaries, maximum flooding surfaces,
- and their relationship to basin floor fan complexes

## Sequence stratigraphy

- Sequence boundaries, maximum flooding surfaces, and their relationship to
- basin floor fan complexes

-       Type 1 sequence
-  a depositional sequence where there is a relative sea level fall below the present shoreline position.
-  forms when the _sea-level fall rate > the subsidence rate_ at the depositional shoreline.
-  characterized by _subaerial exposure_ and erosion (incised valleys, stream downcutting)

## Sequence stratigraphy

- Sequence boundaries, maximum flooding surfaces, and their relationship to
- basin floor fan complexes

- Type 2 sequence
-  a depositional sequence where relative sea level fall does 	not force a shift in shoreline position
-  forms when the _sea-level fall rate < the subsidence rate_ 	at the 	depositional shoreline.
-  characterized by the _absence of subaerial erosion_

## (from Garry Jones, Unocal, 1996)

## Detecting an unconformity

- LO = last occurrence, or last appearance datum (LAD)	FO = first occurrence, or first appearance datum (FAD)

## (Jones et al, 2002)

## Sequence biostratigraphic modeling

- biostratigraphic databases should include information regarding fossil abundances (increases, declines)
- and diversity.
- these high-resolution paleontologic events can be used to distinguish
- _maximum flooding surfaces_.

## Hierarchy of stratigraphic cyclicity

- High-quality high-resolution biostratigraphy can identify
- beyond sequence cycles (3rd order) to the
- parasequence cycle (5th order) level.

## Sequence stratigraphy modeling

- (from Garry Jones, Unocal, 1996)

- 	BFF   basinal floor fan complex	MFS  maximum flooding surface
- 	HST  highstand systems tract	SMW shelf margin wedge
- 	LSW  lowstand systems wedge	TSS   transgressive systems tract

## Stratigraphic architecture

- Biostratigraphic databases which store abundance information (number of individuals of a species, fossil increases, decreases, acmes, condensed sections) and diversity measurements (planktic/benthic ratios, the number of different species in a sample) can detect small-scale yet widespread paleobiologic events which may be mappable.

- From Meckel et al, GCSSEPM Foundation Conference, 2002)

## For correlation and mapping of the Gulf of Mexico offshore, MMS uses the genetic sequence [GS (Vail model)] as well as the  depositional sequence [DS (Galloway model)].

- Armentrout (2002)

- For correlation and mapping of the Gulf of Mexico offshore, MMS uses the genetic sequence [GS (Vail model)] as well as the  depositional sequence [DS (Galloway model)].

## Sequence boundaries and maximum flooding surfaces

- after Armentrout (2002)

## Hypothetical association of MMS chronozones 

- after Armentrout (2002)

- The MMS chronozone boundaries generally coincide with major sequence boundaries.

- Hypothetical association of MMS chronozones
- and depositional sequences

## Time for questions 

- Thanks for your attention!