AAPG Student Chapter Seminar - Unlikely Carbonates; They are so cool!

   

Noel James,
Queen's University  

Wednesday, April 12th
5:30 p.m.

233 Advanced Research Complex (ARC)
25 Templeton Street
University of Ottawa  

 

Abstract

The most improbable carbonate sedimentsand rocks are those that form in the cold,frigid, and freezing ocean well outside thesoft, warm, sunlit, waters of the tropics. Untilrecently such deposits were barelymentioned – all limestones were obviouslytropical! Now temperate and polar limestonesare an integral part of mainstreamsedimentology. How did this happen?

The breakthrough came simultaneously onseveral fronts about 25 years ago; 1) it wasrealized that southern Australia was anenormous area of cool-water carbonatedeposition, vast carbonate banks of ancientcool-water carbonates were now possible,2) the southern hemisphere, as well as theMediterranean, had extensive Cenozoictemperate carbonate deposits, and 3) somePaleozoic limestones looked astonishinglylike these Cenozoic rocks. The realization began to sink in that cool-water limestones had been part of the carbonate world all along.

Increased research has since resulted in a rush of recent discoveries; 1) cool-water seagrasses are prolific sediment factories whose carbonateproductivity exceeds that of similar tropical marine angiosperm, 2) macrophye (kelp) factories are significant carbonate factories, especially incold high latitude marine environments, 3) cool marine carbonates can occur adjacent to marginal marine peritidal evaporite-dolomiteenvironments, 4) high latitude, polar deposits unexpectedly form at the coldest and not the warmest of times, 5) extensive seafloor dissolutionis occurring in the temperate neritic zone well above the lysocline, 6) diagenetic implications of cool-water calcite-only sediments are profound,there is insignificant early meteoric cementation thus pathways of burial diagenesis are profoundly different and those of warm-watercarbonates. Cool carbonates have come of age and perhaps the most important aspect is that they provide a framework against which tocompare the warm water deposits and thus a more realistic vision than ever before of ancient and very ancient seascapes.