| Popis: |
The subsurface Upper Jurassic Haynesville and Bossier Formations comprise three facies associations along the eastern slope of the Gilmer Platform. The lower Haynesville facies association consists of three facies produced by mass-wasting processes: (1) calcirudite/calcarenite, (2) mud-clast calcarenite, and (3) laminated calcisiltite intercalated with laminated calcareous mudrock and bioturbated calcareous mudrock. These facies were deposited by (1) hyperconcentrated density flows/transitional concentrated density flows, (2) hydrated turbidity flows, and (3) distal settling from turbidity flows, respectively. These mass-wasting deposits are the deeper water equivalents of the shallower water Haynesville Lime. The sedimentary dynamics of the mass-wasting processes produced TOC (total organic content)-rich accumulations downslope in the deeper parts of the basin. The upper Haynesville facies association also consists of three facies: (1) TOC-rich laminated calcareous mudrock, (2) bioturbated calcareous mudrock, and (3) bioturbated mud-clast calcisiltite. These facies were derived from marine snow deposited and reworked as sediment drifts by bottom currents above and below the oxycline. The Bossier Formation facies association contains (1) massive argillaceous mudrock, (2) bioturbated argillaceous mudrock, and (3) argillaceous claystone. These facies are interpreted as prodelta deposits intercalated with sediment deposited by settling from flood plumes. TOC is relatively high despite sedimentary dilution from deltaic input, indicating high primary productivity of organic matter at the time of deposition. TOC-rich accumulations comparable to the Haynesville Shale are observed in the Bossier Formation on Sabine Island and may exist wherever detrital sediment input has been reduced or diverted by currents. The lower Haynesville was deposited as an upwards-deepening succession during a second-order transgression that started after deposition of the Smackover Formation. Because the upper Haynesville was deposited as a sediment drift with an internally complex sedimentary geometry, no internal cyclicity is apparent, and the position of the second-order maximum flooding surface cannot be established. Deposition of the Bossier marks a significant turnaround when deltaic sediments prograded from the north and buried the mass-wasting and sediment-drift deposits. The distal setting of the facies, evidence of deposition below storm-wave base, the pelagic source of the sediment, and the sedimentary processes involved make application of sequence-stratigraphic concepts to the deposits problematic. |
