East Breaks trap formation
Minibasin structural-stratigraphic development
The structural/stratigraphic configuration of the East Breaks 160-161 minibasin formed well after Glob alt deposition. As discussed earlier, the High Island–East Breaks basin was a late Pliocene - early Pleistocene slope basin through which gravity flow sands flowed southward. Progradation overloaded the underlying salt and minibasins formed as a succession of southward-stepping growth-fault/salt-withdrawal sediment thicks (Figure 1).
Structural traps
Within these minibasins, structural traps of gravity-flow sandstones formed
- as fault-dependent closure at growth faults,
- as anticlinal closure formed by roll over into growth faults, or
- by postdepositional tilting of sandstones that shale out upstructure due to syndepositional pinching-out against sea-floor valley margins.[2][3]
Stratigraphic traps
Pure stratigraphic traps occur where basinal sandstones completely bypassed updip areas subsequently filled by mud, providing both top seal and up dip lateral seal.[2][4]
Timing of fault movement
Fault movement timing is critical for trap formation timing. Growth-fault rollover anticlines develop by updip expansion and sediment entrapment on the downthrown side of the fault and consequent downdip sediment starvation and continued subsidence within the intraslope basin (see Figure 2 for geometries above the Trim A interval along fault A′). Thus, the updip trap for [gravity gravity-flow sandstone is the rollover into the fault, formed during the dynamic phase of fault movement.
Fault A′
Figure 3 Structural elements that define the East Breaks 160-161 minibasin, which is bound on the north by fault A, on the east by faults B and C, and on the south by a salt- cored high. From Armentrout et al.;<ref>Armentrout, J. M., S. J. Malacek, P. Braithwaite, and C. R. Beeman, 1991, Seismic facies of slope basin turbidite reservoirs, East Breaks 160-161 field: Pliocene–Pleistocene, northwest- ern Gulf of Mexico, in P. Weimer and M. J. Link, eds., Seismic Facies and Sedimentary Processes of Submarine Fans and Turbidite Systems: New York, Springer-Verlag,
Figure 4 Composite chronostratigraphic chart that serves as an age model for the GOM basin Pliocene and Pleistocene, summarizing nine studies published between 1982 and 1993. From Armentrout;[5] courtesy The Geological Society, London.
In the East Breaks 160-161 minibasin, the fault splay fault A′ forms the northern boundary to the field (Figures 2 and 3). The dynamic phase of this fault is recorded by the wedge-shaped sediment thickening into the fault, deposited between pre-Hyal B (ca. 1.00 Ma) time of deposition and late Trim A (ca. 0.56 Ma) time of deposition (Figure 4). Its growth phase began about 1.20 Ma.[1][6] Sea-floor expression of this fault clearly indicates offset of Holocene sediments, showing that the fault is currently active (Figure 2).
See also
References
- ↑ 1.0 1.1 Armentrout, J. M., and J. F. Clement, 1990, Biostratigraphic calibration of depositional cycles: a case study in High Island–Galveston–East Breaks areas, offshore Texas: Proceedings, Gulf Coast Section SEPM 11th Annual Research Conference, p. 21–51.
- ↑ 2.0 2.1 Bouma, A. H., 1982, Intraslope basins in northwest Gulf of Mexico: A key to ancient submarine canyons and fans: Environmental processes: Model investigations of margin environmental and tectonic processes, in J. S. Watkins and C. L. Drake, Studies in Continental Margin Geology: AAPG Memoir 34, p. 567–581.
- ↑ Kneller, B., 1995, Beyond the turbidite paradigm: physical models for deposition of turbidites and their implications for reservoir prediction, in A. J. Hartley, and D. J., Prosser, eds., Characterization of Deep Marine Clastic Systems: Geological Society, London, Special Publication 94, p. 31–49.
- ↑ Galloway, W. E., and T. A. McGilvery, 1995, Facies of a submarine canyon fill reservoir complex, lower Wilcox Group (Paleocene), central Texas coastal plain, in R. D. Winn, Jr., and J. M. Armentrout, eds., Turbidites and Associated Deep-Water Facies: WEPM Core Workshop 20, p. 1–23.
- ↑ Armentrout, J. M., 1996, High-resolution sequence biostratigraphy: examples from the Gulf of Mexico Plio–Pleistocene, in J. Howell and J. Aiken, eds., High Resolution Sequence Stratigraphy: Innovations and Applications: The Geological Society of London Special Publication 104, p. 65–86.
- ↑ Armentrout, J. M., 1991, Paleontological constraints on depositional modeling: examples of integration of biostratigraphy and seismic stratigraphy, Pliocene–Pleistocene, Gulf of Mexico, in P. Weimer, and M. H. Link, eds., Seismic Facies and Sedimentary Processes of Submarine Fans and Turbidite Systems: New York, Springer-Verlag, p. 137–170.
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