Geochemistry of the Mural Formation (Aptian-Albian) of the Bisbee Group, Northern Sonora, Mexico

Madhavaraju, Jayagopal; González–León, Carlos M.; Lee, Yong Il; Armstrong‐Altrin, John S.; Reyes-Campero, L.M.

doi:10.1016/j.cretres.2010.05.006

“…Eu content is positively correlated with Y in limestones from both MC and ME (r=0.95, 0.80, respectively; Figure 9a) and reveals the non-diagenetic origin of this element. The inclusion of small amounts of detrital feldspars may lead to positive Eu anomalies in the bulk sediments (Murray et al, 1991;Madhavaraju and Lee, 2009;Madhavaraju et al, 2010). In addition, Al 2 O 3 is not correlated with Eu/ Eu * (MC: -0.57; ME: -0.25; respectively; Figure 9b).…”

Section: Behaviour Of Europiummentioning

confidence: 96%

Petrography, geochemistry and stable isotopes of carbonate rocks, Lower Cretaceous Alisitos Formation, Los Torotes section, Baja California, Mexico

Madhavaraju¹,

Löser²,

Scott³

et al. 2017

Rev. Mex. Cien. Geol.

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Petrography, stable carbon and oxygen isotopes, and major, trace, and rare earth elements geochemistry of limestones of the Alisitos Formation in the Los Torotes, Baja California were studied in order to document the elemental variations among Member C (MC) and Member E (ME) of the formation and to understand their diagenetic and depositional conditions. The major petrographic types identified are mudstone, wackestone and packstone. The limestones of the Alisitos Formation show significant variations in δ 13 C and δ 18O values (+4.13 to +5.26‰; -14.17 to -6.84‰; respectively). The limestones from Member C (MC) show higher ΣREE content (23 ± 17, n=10) than Member E (ME) (11 ± 5.5, n=9) of the Alisitos Formation. The observed variations in ΣREE content in these limestones are due to the amount of detrital material present in them. The limestones from ME record seawater-like REE+Y patterns, whereas the MC records non-seawater-like signatures (i.e. significant enrichment of middle rare earth elements: MREE). Most of the analyzed samples from the Alisitos Formation show negative Ce anomalies (Ce/Ce*: 0.67 -0.99, n=17). The limestones show both negative and positive Eu anomalies (Eu/Eu*: 0.58 -2.91, n=19). The positive Eu anomalies identified in many samples may be due to the influence of hydrothermal fluids or co-precipitation of hydrothermal Fe-sulfide. The limestones of ME exhibit seawater-like-REE patterns suggesting that most of the REEs present in them were derived from seawater. However, the limestones of MC were contaminated by detrital materials which effectively mask the seawater-like signatures. The detrital materials present in the limestones of MC were probably derived from the mafic to felsic source rocks.

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“…However, Member C exhibits non-seawater-like patterns, which compare with other limestones that exhibit non-seawater-like patterns ( Figure 11; Upper Devonian coastal fringing reef, Nothdurft et al, 2004; Aptian-Albian limestone: Madhavaraju et al, 2010;Albian limestone, Madhavaraju and Lee, 2009;Maastrichtian limestone, Madhavaraju and Ramasamy, 1999;Miocene limestone, Armstrong-Altrin et al, 2003). This suggests that the inclusion of terrigenous materials in carbonates as contaminants will mask the seawater signature because of their high REE concentration.…”

Section: Possible Source Of Rees In the Alisitos Formationmentioning

confidence: 99%

“…PASS-normalized positive Eu anomalies are not common in seawater. Positive values result from hydrothermal solutions (Michard et al, 1983;Klinkhammer et al, 1983,;German et al, 1993;Sherrell et al, 1999), from sediments affected by diagenesis (MacRae et al, 1992), by enrichment of feldspar (Murray et al, 1991;Madhavaraju and Ramasamy, 1999;Madhavaraju and Lee, 2009;Madhavaraju et al, 2010Madhavaraju et al, , 2016, by sediments derived from high T-basalt alteration along mid-ocean ridges, or from back arc spreading centres (Michard et al, 1983;German et al, 1993;Siby et al, 2008). MacRae et al (1992) noted that Amazon fan muds exhibit significant positive Eu anomalies, because of precipitation of Eu 2+ from pore waters during diagenesis.…”

Section: Behaviour Of Europiummentioning

confidence: 99%

Untitled

2017

Rev. Mex. Cien. Geol.

0

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Petrography, stable carbon and oxygen isotopes, and major, trace, and rare earth elements geochemistry of limestones of the Alisitos Formation in the Los Torotes, Baja California were studied in order to document the elemental variations among Member C (MC) and Member E (ME) of the formation and to understand their diagenetic and depositional conditions. The major petrographic types identified are mudstone, wackestone and packstone. The limestones of the Alisitos Formation show significant variations in δ 13 C and δ 18O values (+4.13 to +5.26‰; -14.17 to -6.84‰; respectively). The limestones from Member C (MC) show higher ΣREE content (23 ± 17, n=10) than Member E (ME) (11 ± 5.5, n=9) of the Alisitos Formation. The observed variations in ΣREE content in these limestones are due to the amount of detrital material present in them. The limestones from ME record seawater-like REE+Y patterns, whereas the MC records non-seawater-like signatures (i.e. significant enrichment of middle rare earth elements: MREE). Most of the analyzed samples from the Alisitos Formation show negative Ce anomalies (Ce/Ce*: 0.67 -0.99, n=17). The limestones show both negative and positive Eu anomalies (Eu/Eu*: 0.58 -2.91, n=19). The positive Eu anomalies identified in many samples may be due to the influence of hydrothermal fluids or co-precipitation of hydrothermal Fe-sulfide. The limestones of ME exhibit seawater-like-REE patterns suggesting that most of the REEs present in them were derived from seawater. However, the limestones of MC were contaminated by detrital materials which effectively mask the seawater-like signatures. The detrital materials present in the limestones of MC were probably derived from the mafic to felsic source rocks.

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“…During the past few decades, the behavior and mode of distribution of rare earth elements (REEs) in carbonate rocks were extensively investigated by many researchers Armstrong-Altrin et al, 2003;Nothdurft et al, 2004;Madhavaraju and Lee, 2009;Madhavaraju et al, 2010;Nagarajan et al, 2011;Nagendra et al, 2011;Madhavaraju and González-León, 2012;Song et al, 2014). The studies done showed that the important factors influencing enrichment and depletion of REEs in carbonate rocks are 1) the amounts of detrital materials of terrigenous origin (Piper, 1974;McLennan, 1989;Nagarajan et al, 2011), 2) the variation in oxygen level of seawater (Liu et al, 1988), 3) the proximity to area of origin (Murray et al, 1991b), 4) biogenic deposition from seawater (Murphy and Dymond, 1984), 5) the variation in surface productivity (Toyoda et al, 1990), 6) the lithology and diagenesis (Madhavaraju and Ramasamy, 1999), and 7) scavenging processes related to depth, salinity, and oxygen level of seawater (Greaves et al, 1999).…”

Section: Introductionmentioning

confidence: 99%