Gondwanan glaciation, cyclothems, continental positioning, and climate change

Crowell, John C.

doi:10.2475/ajs.278.10.1345

Cited by 240 publications

(79 citation statements)

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“…2900 Ma; Young et al, 1998), Paleoproterozoic (2400-2200 Ma; Crowell, 1999;Bekker et al, 2001;Kopp et al, 2005;Melezhik et al, 2013), Neoproterozoic (750-550 Ma;Hoffman and Li, 2009), Paleozoic (a short glacial event at 450 Ma and a longer one at 330-300 Ma; Crowell, 1978;Visser, 1982;Caputo and Crowell, 1985;Hambrey, 1985) and Cenozoic (2.58-0.01 Ma; Pillans and Gibbard, 2012). The glacial diamictites investigated here come from all five of these periods, over five geographic regions: southern Africa, North America, southern China, South America and Greenland.…”

Section: Samplesmentioning

confidence: 99%

Influence of chemical weathering on the composition of the continental crust: Insights from Li and Nd isotopes in bauxite profiles developed on Columbia River Basalts

Liu

Rudnick

McDonough

et al. 2013

Geochimica et Cosmochimica Acta

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Glacial diamictites, with ages ranging from $2900 to 0.01 Ma, record the changing composition of the upper continental crust through time (Gaschnig et al., 2014). Li concentrations and isotopic compositions, combined with Pb isotopic compositions, chemical index of alteration (CIA) values and relative Sr concentrations are used here to assess the degree of chemical weathering recorded in these deposits and the origin of this signature. The d Li values of most of the diamictites (ranging from À3.9 to +3.5) are lower than those of mantle-derived basalts (+3.7 ± 2, 2r), and the low d7 Li values are generally accompanied by high CIA and low Sr/Sr * values (or Sr depletion factor, Sr/Sr * = Sr/(Ce * Nd) 0.5 ), reflecting a weathering signature that may have derived from pre-depositional, syn-depositional, and/or post-depositional weathering processes. Profiles through three glacial diamictites with relatively high CIA (a fresh road cut of the Neoproterozoic Nantuo Formation (CIA = 62-69), and drill cores through the Paleoproterozoic Timeball Hill (CIA = 66-75) and Duitschland Formations (CIA = 84-91)) do not show evidence of significant post-depositional weathering. High Th/U, reflecting loss of uranium during oxidative weathering, is seen in all Paleozoic and Neoproterozoic diamictites and a few Paleoproterozoic deposits. Pb isotopic systematics suggest that this signature was largely inherited from preexisting crust, although a subset of samples (the Neoproterozoic Konnarock, Paleozoic Dwyka, and several of the Paleoproterozoic Duitschland samples) appears to have experienced postdepositional U loss. Modern glaciomarine sediments record little weathering (CIA = 47, Sr/Sr * = 0.7, d7 Li = +1.8), consistent with the cold temperatures accompanying glacial periods, and suggesting that limited syn-depositional weathering has occurred. Thus, the chemical weathering signature observed in ancient glacial diamictites appears to be largely inherited from the upper continental crust (UCC) over which the glaciers traversed. The strength of this weathering signature, based on the CIA, is greatest in the Mesoarchean and some of the Paleoproterozoic diamictites and is weaker in the Neoproterozoic and Phanerozoic glacial diamictites. Combining these data with data for Archean shales and other types of post-Paleoproterozoic sedimentary rocks (i.e., shales, mudstones, etc.), it appears that post-Paleoproterozoic upper continental crust experienced less intense chemical weathering, on average, than Archean and Paleoproterozoic upper continental crust.

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Section: Samplesmentioning

confidence: 99%

Influence of chemical weathering on the composition of the continental crust: Insights from Li and Nd isotopes in bauxite profiles developed on Columbia River Basalts

Liu

Rudnick

McDonough

et al. 2013

Geochimica et Cosmochimica Acta

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“…The northeast-southwest elongate basin is bounded by the Cape Fold Belt to the west and south (Figure 1) that contains three clastic depositional areas: the Tanqua, Laingsburg, and Ripon depocentres. The Karoo Supergroup includes the basal fluvioglacial Dwyka Group (Crowell 1978), the overlying Ecca Group, and the Beaufort Group. Following deposition of the Dwyka Group, deepwater basinal environments shoaled upward into shallowwater, marginal marine environments during deposition of the Ecca Group.…”

Section: Geologic Backgroundmentioning

confidence: 99%

U-PB zircon tuff geochronology from the Karoo Basin, South Africa: implications of zircon recycling on stratigraphic age controls

McKay

Weislogel

Fildani³

et al. 2015

International Geology Review

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Along the >650 km long southern margin of the Karoo Basin in South Africa, we traversed four evenly spaced stratigraphic transects and collected 22 samples of volcanic, air-fall tuffs thought to be distal deposits derived from the Permian-Triassic Southern Gondwanan volcanic arc. We present 469 new U-Pb zircon ages determined by sensitive high-resolution ion microprobe reverse geometry (SHRIMP-RG) at the Stanford-USGS Microanalytical Center in order to constrain the maximum depositional ages for the southern Karoo Basin strata. Weighted means of these youngest coherent zircon populations were selected to maximize the number of analyses while minimizing the mean square weighted deviation (MSWD) to increase the robustness and decrease the influence of Pb-loss and inheritance in determining the maximum depositional age. Maximum depositional ages for the marine Ecca Group range from 250 to 274 Ma, whereas in the conformably overlying terrestrial Beaufort Group maximum depositional ages ranged from 257 to 452 Ma. Across the southern Karoo Basin, the Ecca Group tuffs produce maximum depositional ages that young upward; however, the Beaufort Group tuffs yield maximum depositional ages that are geochronologically out of sequence. Furthermore, maximum depositional ages of the Beaufort Group tuffs are consistently older than ash ages within the underlying marine strata. Our results are supported by previously published U-Pb tuff zircon geochronology in the Karoo Basin and demonstrate that the presence of out-of-sequence, older tuff ages are repeatable in Beaufort Group tuffs along the southern margin of the basin. We propose that tuffs in the Karoo Basin are correlative with tuffs in southern South America, and that the age spectra of these tuffs were influenced by magmatic crustal recycling. We use these data to highlight the complexity of U-Pb zircon datasets from tuffs, address the use of U-Pb zircon ages to provide absolute age controls, and discuss the implications of these new age controls on the Permian-Triassic Karoo strata.

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“…The resulting massive drawdown in global atmospheric CO 2 concentration from many times that of today, via its reduction of the greenhouse effect, is likely to have contributed significantly to the PermoCarboniferous glaciation (Royer et al, 2004;Lowry et al, 2014), the most extensive and longest lived glaciation since that time (Crowell, 1978;Scheffler et al, 2003;Montañez and Poulsen, 2013). Ultimately, strong negative feedbacks involving the limitation of terrestrial plant productivity and weathering by low CO 2 are likely to have stabilized minimum atmospheric CO 2 concentrations above the threshold for severe icehouse conditions (Pagani et al, 2009;Beerling et al, 2012).…”

mentioning

confidence: 99%

Stomatal Function across Temporal and Spatial Scales: Deep-Time Trends, Land-Atmosphere Coupling and Global Models

et al. 2017

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Gondwanan glaciation, cyclothems, continental positioning, and climate change

Cited by 240 publications

References 0 publications

Influence of chemical weathering on the composition of the continental crust: Insights from Li and Nd isotopes in bauxite profiles developed on Columbia River Basalts

Influence of chemical weathering on the composition of the continental crust: Insights from Li and Nd isotopes in bauxite profiles developed on Columbia River Basalts

U-PB zircon tuff geochronology from the Karoo Basin, South Africa: implications of zircon recycling on stratigraphic age controls

Stomatal Function across Temporal and Spatial Scales: Deep-Time Trends, Land-Atmosphere Coupling and Global Models

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