Burial diagenesis of argillaceous sediment, south Texas Gulf of Mexico sedimentary basin: A reexamination
- Univ. of Texas, Austin, TX (United States)
Cuttings from a well through a thick section of Miocene-Oligocene mudrocks form Kenedy county, Texas, spanning a depth range of 2130 to 5490 m (7000 to 18000 ft), have been studied petrographically and geochemically. On the basis of whole-rock chemical analyses, the deepest samples have lost {approx} 18 wt% (and approximately vol%), mostly as CaCO{sub 3} mineral-bound H{sub 2}O, and SiO{sub 2}, but including additional Ca, as well as Sr, light rare earth elements (REE) (La, Ce, Nd, Sm), Fe, and Li. K{sub 2}O and Rb have been added to the deeper rocks. The large chemical changes are accompanied mineralogically by loss of detrital calcite, kaolinite, K-feldspar, Ca-plagioclase, and muscovite, gain of chlorite and albite, and continued reaction of smectitic illite/smectite (I/S) to more illitic (and K-rich) compositions throughout the entire depth interval of the well. The large chemical changes in this thick mud-rich interval almost certainly require advection of water (free convection?) to accomplish the mass transfer. Initial variation in sediment composition is ruled out as a cause of the observed compositional changes with increasing depth because a variety of `immobile` elements(Al{sub 2}O{sub 3}, TiO{sub 2}, Zr, Hf, heavy REE [Er, Yb], Th, and Sc) remain constant relative to each other despite their uneven distribution across various particle size fractions in the sediments. 56 refs., 12 figs., 5 tabs.
- DOE Contract Number:
- FG05-92ER14249
- OSTI ID:
- 460057
- Journal Information:
- Geological Society of America, Bulletin, Vol. 109, Issue 1; Other Information: PBD: Jan 1997
- Country of Publication:
- United States
- Language:
- English
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