GEOL 11042 Lecture Notes - Lecture 17: Cooksonia, Paleozoic, Devonian
8 Nov 2020
School
Department
Course
Professor
Document Summary
The beginning of the cambrian period was marked by big changes: first appearance of shelled organisms (small shelly fauna the tommotian. Fauna): change in ocean conditions more oxygen, less acidic, more alkaline (basic). Precambrian oceans-acidic, lots of metals, low in calcium. As cyanobacteria produced oxygen (photosynthesis), ph shifted to higher values (more alkaline). This balance between the photosynthesis and respiration creates the biological pump, which keeps the oceans balanced at about ph 8. This has been going on, with a few minor hiccups here and there, since early cambrian time. Two major fossil assemblages of the cambrian: chengjiang fauna-china-lower cambrian, burgess shale fauna, british columbia, middle cambrian, diverse group of organisms, many still around, included chordates. The shallow tropical seas (rather like the bahamas today) of late ordovician ohio are still visible! The fossil rich carbonate layers are exposed at caesar"s creek state park, just south of wilmington, ohio, off i-71.
