The facies architecture and geometry of stratigraphic surfaces within a lignite
bearing interval of the Paleocene upper Calvert Bluff Formation is mapped on a
photomosaic of the 150 ft (50 m) high and 12,000 ft (4km) long âÂÂCâ area highwall of
Big Brown Mine, near Fairfield, Texas. Observed bedding and facies architecture are
interpreted in terms of temporal changes, depositional environments and sequence
stratigraphic setting. A three dimensional grid of 89 subsurface logs is correlated to this
photomosaic to characterize log response patterns of facies. Six facies are observed: 1)
lignite, 2) interdistributary bay mud, 3) prograding delta, 4) delta top mud, 5)
distributary channels, and 6) incised valley fill. The six facies were defined by a
combination of mapped photomosaic observations and subsurface log correlations. The
lignite deposit formed in a low depositional energy, low sediment input, high-organic
productivity interchannel basin. Overlying mud records overbank flooding followed by
avulsion and progradation of delta deposits. Tidal-flat deposits overlying prograding
delta deposits record fluctuating energy conditions on the emerging delta top. Channel
deposits cutting into the delta top record lateral channel migration across delta top floodplains. These regressive delta deposits are capped by a local incised sequence
boundary overlain by fluvial channel deposits inferred to have allowed sediment to
bypass further basinward during lowstand. A sheet of channel deposits capping this
highwall exposure records more recent erosion, followed by development of modern soil
horizons.
The Big Brown Mine highwall exposes a relatively complete high-frequency
Paleocene stratigraphic sequence developed in an area landward of the shoreline position
during maximum transgression, that progresses upsection from: 1) highstand alluvial
flood basin coals, 2) a thin condensed maximum flooding interdistributary shale, 3) a
thick succession of regressive deltaic strata, and 4) a high-relief, sequence-bounding
erosion surface overlain by a lowstand to transgressive fill of channel deposits.
Correlations with regional Wilcox Group stratigraphic studies spanning coeval shoreline
and shelf strata indicate that this high-frequency sequence is within the transgressive
systems tract of a 3rd order stratigraphic sequence. It appears that high-frequency
sequences of sub-regional extent control the complex distribution of coal seams within
central Texas.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/4200 |
| Date | 30 October 2006 |
| Creators | Sturdy, Michael Dale |
| Contributors | Willis, Brian J. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Electronic Thesis, text |
| Format | 23840205 bytes, 1824601 bytes, electronic, application/octet-stream, application/pdf, born digital |
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