Origin of manganese giants: Sea-level change and anoxic-oxic history

Altered carbon cycling and trace-metal enrichment during the late Valanginian and early Hauterivian

“…(e.g., Frakes & Bolton 1984;Pratt et al 1991;Force & Cannon 1988;Jenkyns et al 1991Jenkyns et al , 2002Dickens 1994;Jarvis et al 2001).…”

“…A common explanation for Mn enrichment is diagenetic remobilization of Mn in anoxic deep waters or in organic carbon-rich sediments and hence an enhanced Mn fixation in the oxygenated parts of the oceans ("bath-tub ring"-or "stratified ocean"-model; Frakes & Bolton 1984;Force & Cannon 1988;Jenkyns et al 1991;Pratt et al 1991;Dickens 1994). The Mn deficit, recorded in the basinal black-shale sediments is stated as an argument for this interpretation (e.g.…”

“…Earlier studies have shown that marine manganese and iron ores were formed at times of peculiar paleoceanographic conditions. "Mn giants" of the early Toarcian, late Jurassic, Aptian, Albian, Cenomanian/Turonian boundary, and Miocene are correlated with ocean-wide anoxia (Oceanic Anoxic Events) and/or changes in the carbon cycle as expressed by positive δ 13 C excursions (e.g., Pomerol 1983;Frakes & Bolton 1984, 1992Schlanger et al 1987;Van Houten & Arthur 1989;Jenkyns et al 1991Jenkyns et al , 2002Pratt et al 1991;Corbin et al 2000;De Rafélis et al 2001). …”

U.S. Geological Survey-Missouri Geological Survey symposium; Mineral-resource potential of the Midcontinent; program and abstracts, St. Louis, Missouri, April 11-12, 1989

“…Cretaceous strata in southwestern ~ .finnesota and eastern South Dakota have lithologic, gee ~hemical, and depositional attributes of strata that h '1St economic deposits of manganese at many localitir.s around the world, as described in recently proposed depositional models for sedimentary manganese (Cannon and Force, 1983;Frakes and Bolton, 1984;Force and Cannon, 1988).…”

Early Mesozoic (?Triassic) Landscapes in Australia: Evidence, Argument, and Implications

“…Although in detail irregular, and scored by many deep gorges and with innumerable fracturecontrolled clefts or slots, the plateau surface can be construed as being the remnant of a weathering front developed beneath the former high plain. The massif itself already existed in Early Cretaceous times-a shoreline of that age has been recognized at the base of the prominent scarp on the western flank of the upland; Cretaceous strata extend up valleys; and on the eastern side of the upland an Early Cretaceous shoreline has been recognized at an elevation of approximately 75 m (Skwarko 1966;Needham 1982;Frakes and Bolton 1984).…”