A REVIEW OF THE LATE ORDOVICIAN (KATIAN) RICHMONDIAN INVASION OF EASTERN LAURENTIA : WHAT I’VE LEARNED IN THE 25 YEARS SINCE STIG BERGSTRÖM FIRST INTRODUCED ME TO THESE ROCKS

On my very first geology class field trip in 1996, Professor Stig Bergström took my GEOL 201 : Introduction to Paleontology class to the Maysvillian strata of the Cincinnati Arch. The following year, Stig took our GEOL 614 : Advanced Paleontology class to St. Leon, Indiana to study the Richmondian strata. Later, I was fortunate to travel wtih Stig to Manitoulin Island to explore more of the Ordovician. Twenty five years later, I am still learning about these incredible rocks and the biotic changes inherent in the Richmondian Invaison based on this outstanding foundation that Stig provided to me as a young undergraduate at Ohio State.

The rocks in the Cincinnati, Ohio region record a major faunal turnover, the Richmondian Invasion. The major features of this invasion were first appreciated in the early 1900’s and have recieved significant study since that time. General patterns of the Richmondian Invasion, including the influx of over 50 taxa that span ecological roles and taxonomic groups, the significant restructuring of paleocommunities, and differential survival of generalist taxa relative to specialist taxa. The invasion is know understood to have constituted several waves of biotic invasion from multiple source regions into the Cincinnati Basin of eastern Laurentia during the Katian Stage.

Substantial reserach to further deliniate and clarify the details of the Richmondian Invasion has progressed on multiple fronts over the past two decades. Novel analyses into sedimentology, stratigraphy, and geochemistry coupled with detailed paleoecology, evolutionary, and biogeographic studies provide a framework for increased synthesis and understanding of invasion dynamics during this interval. The Richmondian invasion is now one the best studied Biotic Immigration Events (BIMEs), in which a group of organisms that originated in one geographic region invade and become established in a new geographic region are common in Earth history, and it has been established as a « coordinated invasion » within the Invasion Hierarchy of Stigall (2019). I will provide a general overview of the current state of knowledge of the Richmondian Invasion and outline some of they key implications for other intervals of Earth history.