Kansas Geological Survey
Open-file Report 2003-82
The laminated muddy sandstone facies is composed of dark-gray silt and mud and light-gray fine-grained sand (Figure 2.08). Diagnostic features of the facies are intervals (0.5-1 cm) of thin laminae (3 mm) of siltstone and sandstone that are separated by intervals (0.5-1 cm) dominated by bioturbated to laminated mudstone (1-3 mm). Many of the laminated intervals are cross-stratified, and have bimodal orientations. Contacts between the top of the mudstone and the bottom of the sandstone may be reactivation surfaces. Minor amounts of plant fragments are scattered through the facies (Figure 2.08). Body fossils were not observed, although bioturbation is prevalent along with sparse actively filled vertical and horizontal burrows. Thickness of the facies ranges from 5 to 12 feet (1.5 to 3.7 m). Contacts with the overlying and underlying facies are gradational.
The laminated muddy sandstone facies is interpreted as having been deposited in a tidal-flat environment. Alternating fine-grained sand cross laminations and thicker mudstone laminations indicate bedload transport during variable tidal flow and sediment fallout during slack-water (Reineck and Singh, 1980). Presence of reactivation surfaces and cross lamination dipping in opposite directions indicates changes in flow direction and suggests tidal influence. Open-marine tidal flats often have an abundant and diverse trace fossil assemblage (Buatois et al., 1999). The paucity of trace and body fossils preserved in this setting may be due to the muddy system or freshwater influence from tidal channels. Historically, the cross-laminated muddy sandstone facies would be interpreted as part of the “outside shale” in the cyclothem model (Heckel, 1977).
|Figure 2.08 - Polished core section of laminated muddy sandstone facies. 1) Intercalated intervals of cross-stratified muddy sandstone (B) and laminated to bioturbated and burrowed mudstone (C). At top of core section abundant rooting has disrupted primary sedimentary structures (A). 2) Inercalated intervals of cross-stratified sandstone and mudstone (B) separated by intervals of laminated to bioturbated mudstone. Sample 1 from 881' and sample 2 from 851' in the Hinthorn CW#1 well, 14-T32S-R16E, Montgomery County, Kansas|
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Last updated December 2003