CHERT PROBLEMS: BURDENS OF A CENTURY OF NEGLECT

In light of their current contributions, the authors of the 2002 GSA Chert Symposium may blanch at this title. This dedicated group is making significant progress in research on chert. However, review of the modern and classical literature on origin and alteration of chert has led to more significant questions than answers. We suggest and will illustrate critical challenges for the next decade. Distinguishing chert varieties: How can we differentiate between organic and inorganic cherts? How can we distinguish those cherts with hydrothermal origins from those with "normal" temperature history. Are there simple characteristics that will allow us to differentiate between cherts with microbial origins and those promoted by other organisms? Unerstanding age "nodes": Were most Precambrain cherts inorganic in origin? Is there a stratigraphic correlation between abundance/volume of volcanic ash and volume of inorganic chert deposition? What conditions favored certain Phanerozoic chert and microbial "blooms", and why did they stop? Explaining processes: When silica is mobilized on or within a sediment surface, ready to "make" chert, what are its physico-chemical characteristics? What stops and starts the chert "engine"? Is the formation of Opal-CT essential to the process of forming all cherts, or only Cenozoic cherts? Is there sufficient volume of silica from dissolution of siliceous organisms or from microbial capsule "goo" to account for most Phanerozoic chert deposits? Why is porosity preserved in some Paleozoic spiculites and destroyed in others in apparently identical settings? Explaining distribution: What happens at the margins of chert nodules? Why do chert nodules replace one fossil or one bed of limestone, and another of seemingly identical character in immediate stratigraphic proximity? Why do chert nodules arranged parallel to a bedding unit end at one spot and begin at another? Are microfractures and incipient synsedimentary brecciation fundamental to the accumulation of thick-bedded chert? Some of these issues will be discussed at the 2002 GSA chert symposium; others remain clouded. Are there only random answers to these questions, or are we looking in the wrong places?