Terrigenous sediments were carried into the area, building out a coastal plain. Sedimentation
occurred in near-shore settings such as deltas, bays, lagoons, estuaries, and salt marshes,
and in terrestrial environments such as river flood plains and swamps.
Worland Limestone Member
The sea became so shallow that emergent patches appeared. These were colonized
by salt-tolerant plants.
yellow weathering (clayey) limestone
Clays from distant shores began to reach this area and were deposited with carbonate
sediments. An invertebrate fauna of moderate diversity, including burrowers, persisted.
Restricted circulation kept currents weak in spite of the shallowing water.
hard gray limestone
Relatively pure carbonate was deposited in clear (deep?) water having moderate current
strengths. Bright sunlight reached the sea floor, and algal mounds grew where sediments
were stabilized by benthic algal and microbial communities. The invertebrate fauna was
taxonomically and ecologically diverse.
Lake Neosho Shale Member
Energetic currents, implying shallower water, impinged on the sea floor, eroding previously
deposited sediments and reworking very resistant phosphate nodules. Strata as low as the
Mulberry Member may have been eroded at this time. A diverse fauna of benthic invertebrates
was established, but the water was still too deep and/or turbid for prolific algal growth.
The sea became so deep that bottom water stagnated, possibly due to density stratification.
Swimmers and floaters maintained their diversity, but the bottom was virtually devoid of life.
Organic matter and pelagic clays accumulated on the sea floor; biologically-derived phosphate
precipitated under these conditions to form nodules and laminae of calcium phosphate.
The sea became deep enough that currents no longer impinged on the bottom. Oxygen levels
decreased, excluding nearly all benthic forms of life.
Clays and phosphate nodules reworked from underlying strata were deposited onto an eroded
surface by moderately energetic water. Then water was deep enough that conglomeratic clasts
were no longer produced in this location. A limited fauna of invertebrates colonized the area,
and plant material was washed in from near-by land areas.
conglomerate and limestone
Claystone and shale interbedded with limestone were deposited in offshore settings. These
strata were then eroded during a short-lived drop in sea level. Clasts up to boulder-size were
produced by erosion along the shoreline. They were quickly deposited with abundant clay
matrix, possibly by debris flows or other gravity-induced processes. Prolific invertebrate and
algal communities were periodically established (or lived offshore and their skeletal debris
was washed shoreward), producing carbonate sediment.
As sea level rose, bays, lagoons, and salt marshes formed along the coastline, giving rise
to mixed carbonate and terrigenous sediments, including coal. Phosphate nodules formed
locally in the organic-rich sediment.
While the region was emergent during a major drop in sea level, previously-deposited
sediment was weathered, eroded, and colonized by plants and burrowing animals, producing
a well-developed soil.
to Technical Discussion