RECOVERY FROM CRISIS DURING CRISIS: EARLIEST CARBONIFEROUS BUILDUPS OF MISSOURI AND ARKANSAS

For organic buildups the Carboniferous represents a period of recovery from their collapse during the Frasnian-Famennian extinction. However, this period of recovery is characterized by episodes of global cooling that continuously kept would-be reef communities in a state of crisis. Despite this, organic buildups repeatedly nucleated along the southern edge of the North American continent as reef-like bioherms. Lower Mississippian organic mounds of southwestern Missouri and northern Arkansas record some of the earliest buildup communities known from the Carboniferous, with recurring biotic associations that increase in diversity through time, suggesting stabilizing ecological conditions.

The earliest Carboniferous buildups known in the Western Hemisphere consist of small (4 by 20 m) stromatactid lime mudstone mounds that are, in essence, miniature Waulsortian mounds. These structures contain a low diversity, diminutive benthic fauna, are early Tournaisian (Tn1) in age, and represent the earliest buildups to succeed the reef collapse of the Late Devonian.

During the late Tournaisian larger mounds developed in the same paleogeographic position. The late Tournaisian structures are 10-15 m thick and hundreds of meters in length. These mounds consist of crinozoan wacke-and packstone and support a diverse benthic community in which gigantism is prevalent. The fauna in these mounds suggest that the benthos were responding to more stable ecological conditions.