Cretaceous Anoxic event

sulfidic (or euxinic) conditions, exist today in many water bodies ponds various land-surrounded mediterranean seas such black sea, particularly prevalent in cretaceous atlantic characterized other parts of world ocean. in ice-free sea of these supposed super-greenhouse worlds, oceanic waters as 200 meters higher, in eras. during time spans in question, continental plates believed have been separated, , mountains know today (mostly) future tectonic events—meaning overall landscapes lower— , half super-greenhouse climates have been eras of highly expedited water erosion carrying massive amounts of nutrients world oceans fueling overall explosive population of microorganisms , predator species in oxygenated upper layers.

detailed stratigraphic studies of cretaceous black shales many parts of world have indicated 2 oceanic anoxic events (oaes) particularly significant in terms of impact on chemistry of oceans, 1 in aptian (~120 ma), called selli event (or oae 1a) after italian geologist, raimondo selli (1916–1983), , @ cenomanian–turonian boundary (~93 ma), called bonarelli event (or oae 2) after italian geologist, guido bonarelli (1871–1951). oae1a lasted ~1.0 1.3 myr. duration of oae2 estimated ~820 kyr based on high-resolution study of expanded oae2 interval in southern tibet, china.

insofar cretaceous oaes can represented type localities, striking outcrops of laminated black shales within vari-colored claystones , pink , white limestones near town of gubbio in italian apennines best candidates.
the 1-meter thick black shale @ cenomanian–turonian boundary crops out near gubbio termed ‘livello bonarelli’ after man first described in 1891.

more minor oceanic anoxic events have been proposed other intervals in cretaceous (in valanginian, hauterivian, albian , coniacian–santonian stages), sedimentary record, represented organic-rich black shales, appears more parochial, being dominantly represented in atlantic , neighboring areas, , researchers relate them particular local conditions rather being forced global change.