Formation of Lobster-Bearing Concretions in the Late Cretaceous Bearpaw Shale, Montana, United States, in a Complex Geochemical Environment

Feldmann, Rodney M.; Frantescu, Adina L; Franţescu, Ovidiu D.; Klompmaker, Adiël A.; Logan, Greg Jr.; Robins, Cristina M.; Schweitzer, Carrie E.; Waugh, David A.

doi:10.2110/palo.2012.p12-035r

Cited by 19 publications

(10 citation statements)

References 23 publications

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“…This westward-thinning tongue of marine shale disconformably overlies the Judith River Formation and is conformably overlain by the Fox Hills Sandstone in Montana (Feldmann et al, 1977;Condon, 2000) and the Eastend Formation in Canada (He et al, 2005). The Bearpaw Shale grades eastward into the Pierre Shale (Condon, 2000) and the outcrop similarity between the Bearpaw and Pierre shales makes these two units physically synonymous in the upper midcontinent of North America (Tourtelot, 1962;Feldmann et al, 2012).…”

Section: Geologic Settingmentioning

confidence: 96%

“…The Bearpaw ranges between 60 m and 335 m thick (Cobban et. al., 2006;Feldmann et al, 2012), although the vertical thickness at the discovery site of MOR 3072 was not measured. This westward-thinning tongue of marine shale disconformably overlies the Judith River Formation and is conformably overlain by the Fox Hills Sandstone in Montana (Feldmann et al, 1977;Condon, 2000) and the Eastend Formation in Canada (He et al, 2005).…”

Section: Geologic Settingmentioning

confidence: 99%

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A new elasmosaurid (sauropterygia, plesiosauria) from the bearpaw shale (late cretaceous, maastrichtian) of montana demonstrates multiple evolutionary reductions of neck length within elasmosauridae

Serratos

Druckenmiller

Benson

2017

Journal of Vertebrate Paleontology

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Section: Geologic Settingmentioning

confidence: 96%

Section: Geologic Settingmentioning

confidence: 99%

A new elasmosaurid (sauropterygia, plesiosauria) from the bearpaw shale (late cretaceous, maastrichtian) of montana demonstrates multiple evolutionary reductions of neck length within elasmosauridae

Serratos

Druckenmiller

Benson

2017

Journal of Vertebrate Paleontology

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“…For rapid growth, the morphology of soft-bodied fossils could be preserved (e.g. Huggett et al 2000;Feldmann et al 2012;McCoy 2014), primary depositional fabrics would be remained, and specific fabrics indicative of pore-filling cementation prior to burial compaction would be formed (e.g. Raiswell and Fisher 2000;Day-Stirrat et al 2008).…”

Section: Evidence For Rapid Growth Of Concretionsmentioning

confidence: 99%

Growth mechanisms and environmental implications of carbonate concretions from the ~ 1.4 Ga Xiamaling Formation, North China

et al. 2019

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Carbonate concretions provide unique records of ancient biogeochemical processes in marine sediments, and have the potential to reflect seawater chemistry indirectly. In fine-siliciclastic settings, they preferentially form in organicrich mudstones, owing to a significant fraction of the bicarbonate required for carbonate precipitation resulted from the decomposition of organic matter in sediments. In the Member IV of the Xiamaling Formation (ca. 1.40-1. 35 Ga), North China, however, carbonate concretions occur in organic-poor green silty shales (avg. TOC =~0.1 wt%). In order to elucidate the mechanism of the concretion formation and their environmental implications, a thorough study on the petrographic and geochemical compositions of the concretions and their host rocks was conducted. Macro-to microscopic fabrics, including deformed shale laminae surrounding the concretions, "cardhouse" structures of clay minerals and calcite geodes in the concretions, indicate that these concretions are of early diagenetic origin prior to the significant compaction of clay minerals. The carbon isotope compositions of the concretions (− 1.7‰ to + 1.5‰) are stable and close to or slightly lower than that of the contemporaneous seawater, indicating that the bicarbonates required for the concretion formation were mainly sourced from seawater by diffusion rather than produced by methanogenesis or anoxic oxidation of methane (AOM); the rare occurrence of authigenic pyrite grains in the concretions likely indicates that bacterial sulfate reduction (BSR) did not play a significant role in their formation either. Almost all the calcite in the concretions has low Mn-Fe in nuclei but high Mn-Fe in rims with average Mn/Fe ratio close to 3.3. The calcite shows positive Ce anomalies (avg. 1.43) and low Y/Ho ratios (avg. 31). This evidence suggests that Mn reduction is the dominant process responsible for the formation of calcite rims while nitrate reduction probably triggered the precipitation of calcite nuclei. Prominence of Mn reduction in the porewater likely indicates that there was sufficient oxygen to support active Mn-redox cycling in the overlying seawater.

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“…The presence of zoned crystals (Raiswell, ; Mozley, ; Raiswell & Fisher, ) and multiple generations of cements with distinct chemical and isotopic properties (Hennessy & Knauth, ; Feistner, ; Mozley, , ; Hart et al ., ; Desrochers & Al‐Aasm, ; Fisher et al ., ; Hendry et al ., ; Dale et al ., ; Loyd et al ., ) have been interpreted as evidence for prolonged growth; however, evidence for rapid, early growth is also present in many cases. The mineral replication of labile tissues of soft‐bodied fossils in some concretions (Mapes, ; Martill, ; Wilby & Martill, ; Huggett et al ., ; Maas et al ., ; Zhang et al ., ; Long & Trinajstic, ; Maeda et al ., ; Feldmann et al ., ; McCoy, ; McCoy et al ., ) requires precipitation of a portion of the mineral framework over timescales of weeks to months (Briggs & Kear, ; Gaines et al ., ; McCoy et al ., ), an interpretation consistent with rare observations of concretions in modern environments (Pye et al ., ; Sagemann et al ., ). In other concretions, rapid growth during early diagenesis has been invoked on the basis of petrographic textures of authigenic mineral phases (Allison & Pye, ), and of textural relationships of authigenic and detrital minerals that suggest pore‐filling cementation prior to burial compaction, and the retention of primary depositional fabrics (Raiswell & Fisher, ; Day‐Stirrat et al ., ).…”

Section: Introductionmentioning

confidence: 99%

Growth mechanisms and geochemistry of carbonate concretions from the Cambrian Wheeler Formation (Utah, USA)

Gaines

Vorhies

2016

Sedimentology

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Carbonate concretions provide unique records of ancient biogeochemical processes in marine sediments. Typically, they form in organic‐rich mudstones, where a significant fraction of the bicarbonate required for carbonate precipitation is supplied from the decomposition of organic matter in the sediments. As a result, carbonates that comprise concretions are usually characterized by broad ranges in δ13C and include values that are significantly depleted relative to seawater. This article reports results from a physical, petrographic and geochemical analysis of 238 concretions from the Wheeler Formation (Cambrian Series 3), Utah, USA, which are unusual in several respects. Most prominently, they formed in organic‐poor mudstones (total organic carbon = 0·1 to 0·5%) and are characterized by a narrow range of δ13C that onlaps the range of contemporaneous seawater values. Subtle centre to edge trends in δ13C demonstrate that concretion precipitation was initiated by local chemical gradients set up by microbial activity in the sediments, but was sustained during growth by a large pool of inorganic bicarbonate probably derived from alkaline bottom waters. The large inorganic pool appears to have been important in facilitating rapid precipitation of the concretion matrix, which occurred via both displacive and replacive carbonate precipitation during early diagenesis. Stable isotope data from cogenetic pyrite (δ34S) and silica (δ18O) phases provide insight into the evolution of biogeochemical processes during concretion growth, and suggest that concretions were formed almost entirely during sulphate reduction, with only minor modification thereafter. Concretions of the Wheeler Formation appear to represent an end‐member system of concretion formation in which rapid growth was promoted by ions supplied from sea‐water. As such, they offer insight into the spectrum of processes that may influence the growth of carbonate concretions in marine sediments.

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Formation of Lobster-Bearing Concretions in the Late Cretaceous Bearpaw Shale, Montana, United States, in a Complex Geochemical Environment

Cited by 19 publications

References 23 publications

A new elasmosaurid (sauropterygia, plesiosauria) from the bearpaw shale (late cretaceous, maastrichtian) of montana demonstrates multiple evolutionary reductions of neck length within elasmosauridae

A new elasmosaurid (sauropterygia, plesiosauria) from the bearpaw shale (late cretaceous, maastrichtian) of montana demonstrates multiple evolutionary reductions of neck length within elasmosauridae

Growth mechanisms and environmental implications of carbonate concretions from the ~ 1.4 Ga Xiamaling Formation, North China

Growth mechanisms and geochemistry of carbonate concretions from the Cambrian Wheeler Formation (Utah, USA)

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