Wornardt and Vail published their "Mio-Pleistocene sequence chronostratigraphic chart" for the Gulf of Mexico in an abstract in 1990. Their revision of the late Miocene-Pleistocene sequence chronostratigraphy was based on data obtained from high resolution checklists of calcareous nannofossils, planktonic foraminifers and benthic foraminifers in more than 100 wells in the south additions and deepwater areas, offshore Louisiana and Texas, Gulf of Mexico. They integrated their high resolution biostratigraphic data with well-log sequence stratigraphic and seismic sequence stratigraphic interpretations to establish fourteen third order and seven fourth order sequence cycles for the late Miocene, Pliocene and Pleistocene ().

Mio-Pleistocene sequence chronostratigraphy chart for the Gulf of Mexico

Recently, Berggren et al (1995) published a paper entitled "Late Neogene chronology: New perspectives in high-resolution stratigraphy". They presented an integrated geochronology of the Pliocene, Pleistocene and Holocene Epochs based on calcareous nannofossils and planktonic foraminifers, stable isotopes, magnetostratigraphy, radiochronology, and astrochronologies in deep sea cores and outcrop sections calibrated to the newly revised late Neogene astronomical/geomagnetic polarity time scale.

They delineated the main biostratigraphic datum events, the last appearance datums (LADs) and first appearance datums (FADs), and the numerical ages of the calcareous nannofossils and planktonic foraminifers from the late Miocene, Pliocene and Pleistocene. All datum events were recalibrated to the new geomagnetic polarity time scale (GPTS) of Cande and Kent (1995) which is identical to the astronomical time scale of Shackleton et al (1990) and Hilgen (1991).

Berggren et al (1995b), published another paper in 1995 entitled, "A Revised Cenozoic Geochronology and Chronostratigraphy". They included updated numerical ages for approximately 100 calcareous nannofossil and 150 planktonic foraminiferal LADs and FADs. They also unified the existing planktonic foraminiferal zonations "with a view to providing improved biochronologic subdivisions reflecting regional biogeographies". The Pl-zonal scheme and the M-zonal scheme established by Berggren et al (1995b) is shown on the left side of . This figure is modified from Berggren's Figure 5 and Figure 6 (1995b). These zones denote a series of Miocene, Pliocene and Pleistocene subtropical-transitional zones while the "Mt" zones denote a zonal scheme applicable to predominantly transitional Miocene faunas. They also calibrated the calcareous nannofossil zones of Martini (1971) and Bukry (1973, 1975) with their planktonic foraminiferal zones. The chronostratigraphy of the Pliocene and Pleistocene is briefly mentioned and the reader is referred to Berggren (1995a) for more details. The following abbreviations are used in : D. (Dentoglobigerina), Gd. (Globigerinoides), Gl. (Globigerina), Gq. (Globoquadrina) and Glb. (Globoturborotalia).

Late Miocene-Pleistocene sequence chronostratigraphy chart for the Gulf of Mexico

In the present paper we have completely revised the late Miocene, Pliocene and Pleistocene Sequence Chronostratigraphy and incorporated these revision into our correlation of numerical age (Ma), chrons, polarity, epochs, relative age, planktonic foraminiferal zones, calcareous nannofossil zones, oxygen isotope record, sequences and bioevents. This revision is based on the updated calcareous nannofossil and planktonic foraminiferal numerical ages of Berggren (1995a, 1995b), the oxygen isotope curve of Haddad (1992) and Abrew and Haddad (1998). Each of the seventeen sequences are bounded by a sequence boundary and each sequence has a maximum flooding surface within the sequence.

We divided the late Miocene, Pliocene and Pleistocene into a series of ten (10) third order depositional sequences from 7.6 Ma to 0.8 Ma and seven (7) fourth order depositional sequences, approximately 100,000 years duration, from 0.7 to 0.1 Ma. The age of the third order sequence boundaries that we recognize are: 6.96, 5.73, 4.32, 3.90, 3.21, 2.70, 2.06, 1.54, 1.25 and 0.80 Ma. The age of the fourth order sequences are: 0.70, 0.60, 0.50, 0.40, 0.30, 0.20 and 0.10 Ma. Within each sequence, the third order maximum flooding surfaces that we recognize are: 5.80, 4.60, 4.15, 3.50, 2.95, 2.60, 2.26, 1.59, 1.40 and 0.96 Ma. The fourth order maximum flooding surfaces that we recognize are: 0.76, 0.66, 0.56, 0.46, 0.36, 0.26, 0.16, and 0.06 Ma. The approximate age of the top slope fan in the third order depositional sequences is 6.40, 5.60, 4.18, 3.09, 2.46, 2.30, 1.95 and 1.22, based on the highest occurrence of more cool water assemblage of species. The age assigned to the important benthic foraminifers found in the Gulf of Mexico are based on their superpositional relationship with the highest occurrence of calcareous nannofossil and planktonic foraminifers.

All maximum flooding surfaces are associated with the maximum flooding surface condensed section that includes a portion of the upper part of the transgressive and the lower part of the highstand systems tracts. They are characterized by high diversity and abundance of warm water calcareous nannofossils and planktonic foraminifers species and important event datums ("tops"). They are the "bentonites" of the marine environment that directly age-tie the bathyal-slope sediments to the neritic-shelf sediments. Maximum flooding surfaces are the most important chronostratigraphic surfaces recognized on seismic record sections and in well-log seismic sequence stratigraphic analysis because they can be tied to the high amplitude and continuous seismic reflectors with a two-way time log or synthetic seismogram. Therefore, the presence of certain species permit us to assign a numerical age to each third order maximum flooding surface.

All maximum flooding surfaces in were recognized and traced on well-log and seismic record sections in both dip and strike directions in the offshore Texas and Louisiana areas in the Gulf of Mexico. Subsequently, these seventeen sequence cycles and their corresponding last appearance datums have been tested and found to be valid in the very deep water in offshore Gulf of Mexico, offshore Central America, offshore Northern and Central South America, offshore West Africa, Western North Africa and in the Indo-Pacific.

This revision should provide more accurate correlations between wells, better definition of sequences and especially the lowstand systems tracts, with their basin floor fans and slope fan channel sands and better define and correlate the reservoir sands on well logs and seismic record sections.