The falling amplitude of carbon isotopic oscillations through the Lower to Middle Cambrian: northern Siberia data

Abstract

Carbon and oxygen isotopes have been studied in Lower to Middle Cambrian fossiliferous carbonates from sections along the Malaya Kuonamka, Olenek, and Muna rivers of the Yudoma-Olenek facies belt, northern Siberian Platform. Marked temporal oscillations in delta 13C are recorded from shallow-water Nemakit-Daldynian to Atdabanian carbonates, as seen elsewhere on the platform. Rapid sea-level rise during the so-called "Sinsk event" led to starved-basin conditions from the middle Botomian (Bergeroniellus micmacciformis Zone) to late Amgan (Tomagnostus fissus Zone) and to deposition of organic-rich argillaceous carbonates of the Kuonamka Formation. Mayan carbonates were laid down during a phase of renewed and more rapid carbonate sedimentation, and relatively uniform delta 13C signatures fall from approx. +1.5omicron in the Anomocarioides limbataeformis Zone to near zero throughout the Lejopyge laevigata Zone. These results confirm that a long-term decline took place in maximal delta 13C values between the late Neoproterozoic and Middle Cambrian, accompanied by a dampening in the amplitude of shorter term oscillations. This was accompanied by a change from rift to drift patterns of crustal subsidence; from low to high sea levels; from an interior basin to outer platform locus for hydrocarbon source rocks; from rare to abundant metazoans in the biosphere; by the first major extinction in the Phanerozoic fossil record; and from "icehouse" to "greenhouse" conditions. We infer that factors leading to changes in the rate of carbon burial were amplified at times of low sea level, high climatic extremes, and a primitive biosphere (late Neoproterozoic), and dampened at times of high sea level, lower climatic variation, and a more advanced biosphere (Middle Cambrian).

The SPICE carbon isotope excursion in Siberia: a combined study of the upper Middle Cambrian–lowermost Ordovician Kulyumbe River section, northwestern Siberian Platform

“…Carbon isotope values from the earlier OttawaBochum dataset (Table 3 of Supplementary Material) are consistent with the higher resolution dataset herein, and with published data from Siberia (Brasier & Sukhov, 1998 …”

“…2). This is in agreement with data from Brasier & Sukhov (1998) showing a plateau during this interval from the Siberian Platform and with the values oscillating near zero in Laurentia, reported by Saltzman (2005), and China (Zhu et al 2004;Peng et al 2006). Mild oscillations in the Ust'-Brus and Labaz formations (Fig.…”

“…2 herein) are similar to those shown by Peng et al (2006, figs 6, 7) (Zhu et al 2004, figs 2, 3, 6;Peng et al 2006, fig. 7;, as well as the traditional Middle Cambrian of Laurentia (Montañez et al 2000) show pronounced oscillations, probably present in the lower Mayan and Amgan stages of the Middle Cambrian of Siberian Platform (Brasier & Sukhov, 1998;A. Kouchinsky, unpub.…”

The Henson Gletscher Formation, North Greenland, and its bearing on the global Cambrian Series 2–Series 3 boundary

“…For the Montagne Noire area, southern France, Wotte et al (2007) revealed two minor positive shifts in the lowermost Celtiberian and two stronger ones higher up in equivalents of the Marocconus notabilis Zone. Similar trends have been reported from the Lower-Middle Cambrian transition in Siberia (Brasier et al 1994a, Brasier & Sukhov 1998 and Australia (Donnelly et al 1988, Shergold 1995, Ebneth et al 2001, Lindsay et al 2005. Based on these data, Lindsay et al (2005) proposed direct correlation of early Middle Cambrian δ 13 C trends between the distinct positive excursion in the Ordian-early Templetonian Giles Creek Dolostone of the Amadeus Basin and similar signatures in the coeval middle Gum Ridge Formation of the Georgina Basin, the upper Montejini Limestone of the Wiso Basin, and the upper Tindall Limestone of the Daily Basin with an early Amgan peak in Siberia detected by Brasier & Sukhov (1998).…”

“…Clearly, a satisfactory GSSP will need to be based on paleontological data. Carbon isotopes may be useful for delimiting the Ediacaran-Cambrian boundary interval and the earliest Cambrian period for which several positive carbon isotope excursions can be detected in various regions (Banerjee et al 1994;Brasier 1985Brasier , 1991Brasier , 1992Brasier , 1994Brasier et al 1990Brasier et al , 1992Brasier et al , 1993Brasier et al , 1994aBrasier et al , 1994bBrasier & Sukhov 1998;Derry et al 1994). Nevertheless, such distinct excursions are largely absent (or not yet recognized) for the second half of the Early Cambrian and the early Middle Cambrian, although several regional studies seem to promise useful results (e.g.…”