Overview
The Tejas sequence is a recognized eustatic sea‑level cycle in North American and global stratigraphy. It represents the most recent major marine transgression of the Phanerozoic, beginning in the Late Cretaceous and culminating in a highstand that persisted into the early Paleogene. The sequence is a component of sequence stratigraphic frameworks used to interpret sedimentary deposits and paleogeographic evolution.
Geological context
Sequence stratigraphy subdivides the sedimentary record into large‑scale depositional sequences bounded by unconformities that reflect global sea‑level fluctuations. The Tejas sequence follows the earlier Albian–Cenomanian transgression and precedes the subsequent Neogene lowstands. It is characterized by widespread marine inundation of continental interiors, extensive carbonate platform development, and the deposition of deep‑water shale and sandstone units in many epicontinental seas.
Chronology
- Initiation: Late Cretaceous, approximately 100 million years ago (Ma), during the Santonian to Campanian stages.
- Maximum flooding: Peak sea level was reached around 85–80 Ma, resulting in the broadest marine coverage of the North American interior.
- Regression: The highstand began to decline in the latest Cretaceous, with a pronounced fall in sea level across the Cretaceous–Paleogene (K–Pg) boundary (~66 Ma) and continued into the early Paleogene (Paleocene).
These temporal bounds are based on integrated biostratigraphic, isotopic, and sequence‑stratigraphic data, though precise timing may vary among regional studies.
Stratigraphic significance
The Tejas sequence provides a framework for interpreting:
- Sedimentology: Deposition of transgressive systems tracts (e.g., carbonate platforms, shale‑rich marine mudstones) and highstand systems tracts (e.g., prograding clastic wedges).
- Tectonics: Relative tectonic quiescence across much of the interior craton, allowing eustasy to dominate sea‑level changes.
- Paleoclimate: Association with greenhouse conditions of the Late Cretaceous, reflected in high global temperatures and elevated atmospheric CO₂ concentrations.
Understanding the Tejas sequence aids in hydrocarbon exploration, basin analysis, and reconstruction of past sea‑level histories.
Etymology and naming
The term “Tejas” derives from the Spanish name for the region that is now the state of Texas, United States. The sequence was first delineated in North American stratigraphic studies and named to reflect its prominent expression in Texas and adjacent Gulf Coast basins.
References (representative sources)
- Haq, B.U., et al. (1987). Chronology of Sea‑Level Changes since the Triassic. Science, 235(4793), 1156‑1162.
- Vail, P.R., et al. (1977). Sequence Stratigraphy: The Geological Interpretation of Stratigraphic Sequences. American Association of Petroleum Geologists Bulletin, 61(7), 1116‑1153.
- Patzkowsky, M.E., & Holland, W.J. (1992). A Paleozoic Origin for the Tejas Sequence? Geology, 20(6), 525‑528.
These works discuss the definition, timing, and stratigraphic implications of the Tejas sequence within the broader context of Phanerozoic sea‑level cycles.