Oxygen isotope evolution of biogenic calcite and apatite during the Middle and Late Devonian

Abstract

Oxygen isotope ratios of well-preserved brachiopod calcite and conodont apatite were used to reconstruct the palaeotemperature history of the Middle and Late Devonian. By assuming an oxygen isotopic composition of 1‰ V-SMOW for Devonian seawater, the oxygen isotope values of Eifelian and early Givetian brachiopods and conodonts give average palaeotemperatures ranging from 22 to 25 C. Late Givetian and Frasnian palaeotemperatures calculated from d 18 O values of conodont apatite are close to 25 C in the early Frasnian and increase to 32 C in the latest Frasnian and early Famennian. Oxygen isotope ratios of late Givetian and Frasnian brachiopods are significantly lower than equilibrium values calculated from conodont apatite d 18 O values and give unrealistically warm temperatures ranging from 30 to 40 C. Diagenetic recrystallization of shell calcite, different habitats of conodonts and brachiopods, as well as non-equilibrium fractionation processes during the precipitation of brachiopod calcite cannot explain the 18 O depletion of brachiopod calcite. Moreover, the 18 O depletion of brachiopod calcite with respect to equilibrium d 18 O values calculated from conodont apatite is too large to be explained by a change in seawater pH that might have influenced the oxygen isotopic composition of brachiopod calcite. The realistic palaeotemperatures derived from d 18 O apatite may suggest that biogenic apatite records the oxygen isotopic composition and palaeotemperature of Palaeozoic oceans more faithfully than brachiopod calcite, and do not support the hypothesis that the 18 O/ 16 O ratio of Devonian seawater was significantly different from that of the modern ocean.

Biochemostratigraphy of the Upper Frasnian in the Namur–Dinant Basin, Belgium: Implications for a global Frasnian–Famennian pre-event

“…7a-c). The δ O values of the studied shells are depleted relative to those of their modern (~ 0‰ VPDB) counterparts (Brand et al, 2003) due to the fact that the Paleozoic ocean waters were significantly depleted in 18 O compared with modern oceans but the fossil values are generally within the range documented for the global middle Devonian, particularly around Late Frasnian, in South China, Siberia, Europe and N. America Buggisch, 1993, 1996;Chen et al, 2002;Yudina et al, 2002;Joachimski et al, 2004;da Silva and Boulvain, 2008;Ma et al, 2008;Izokh et al, 2009).…”

“…Buggisch, 1993, 1996;Chen et al, 2002;Yudina et al, 2002;Joachimski et al, 2004;da Silva and Boulvain, 2008;Ma et al, 2008;Izokh et al, 2009). Although some studies utilized well preserved low-Mg calcitic brachiopod shells and phosphatic conodonts (e.g., Joachimski et al, 2004), others involved frequently whole-rock samples of variable degrees of preservation, and at times low-resolution sampling (big sampling intervals), which likely masked some significant variations around the boundary. However, little attention was given to the pre-event isotopic variations during late Frasnian immediately before the major event.…”

Magnetic susceptibility evolution and sedimentary environments on carbonate platform sediments and atolls, comparison of the Frasnian from Belgium and Alberta, Canada

“…During the Devonian, the Earth's surface temperature reaches a peak during the Givetian and according to Streel et al (2000) those hot climates lasted until the Latest Frasnian. During the Frasnian, this hot period was interrupted by two short-term cooling events in the Late rhenana zone and at the base of the Frasnian-Famennian transition (Joachimski et al, 2004) (which is younger than studied interval, see here-under). Hladil et al (2005) suggested that the Early-Middle Frasnian was a period of uniform climate.…”

“…The Middle Frasnian (early Late Devonian) was a time of a globally warm (greenhouse) climate (for a recent review, see Streel et al, 2000;Joachimski et al, 2004;Hladil et al, 2005) and of high sea level (Vail et al, 1977;Johnson et al, 1985; and for a recent review, see Hladil, 2002). During the Devonian, the Earth's surface temperature reaches a peak during the Givetian and according to Streel et al (2000) those hot climates lasted until the Latest Frasnian.…”

Bathymetry and productivity of the southern Great Basin seaway, Nevada, USA: An evaluation of isotope and trace element chemistry in mid-Carboniferous and modern brachiopods

“…Once this is done, only samples identified as preserved may be used as proxy of original seawater chemistry (e.g., Brand and Veizer, 1980;Grossman, 1994;Brand, 2004). Some authors prefer to evaluate their complete sample collection as one using a fixed-chemistry approach of high Sr, low Mn and Fe contents (e.g., Joachimski et al, 2004), whereas others use Mn/Sr or some other ratios (e.g., Denison et al, 1994;Jacobsen and Kaufman, 1999), while others use similarities in isotopic trends after screening for anomalous elemental and isotopic…”