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Perspectives on the diagenetic alter...

Chanda, Piyali.

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Perspectives on the diagenetic alteration of marine carbonates using a multi-proxy approach: A multi-site comparison of Mg, Ca, and Sr isotopic compositions of carbonates.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Perspectives on the diagenetic alteration of marine carbonates using a multi-proxy approach: A multi-site comparison of Mg, Ca, and Sr isotopic compositions of carbonates./
作者:	Chanda, Piyali.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2016,
面頁冊數:	267 p.
附註:	Source: Dissertation Abstracts International, Volume: 78-04(E), Section: B.
Contained By:	Dissertation Abstracts International78-04B(E).
標題:	Geochemistry. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10296949
ISBN:	9781369403046

Perspectives on the diagenetic alteration of marine carbonates using a multi-proxy approach: A multi-site comparison of Mg, Ca, and Sr isotopic compositions of carbonates.
Chanda, Piyali.

Perspectives on the diagenetic alteration of marine carbonates using a multi-proxy approach: A multi-site comparison of Mg, Ca, and Sr isotopic compositions of carbonates. - Ann Arbor : ProQuest Dissertations & Theses, 2016 - 267 p.

Source: Dissertation Abstracts International, Volume: 78-04(E), Section: B.

Thesis (Ph.D.)--The Pennsylvania State University, 2016.

Geochemical proxy-based reconstructions widely utilize the trace elemental and isotopic compositions of marine biogenic carbonates to interpret past climatic and oceanographic conditions. However, such proxy-based reconstructions are often challenged by marine diagenesis as carbonates are highly susceptible to diagenetic alteration, especially to partial dissolution and calcite recrystallization. Thus, quantifying diagenetic effects is a prerequisite for the development of any carbonate-based geochemical proxy. Among the metal isotopes, Mg isotopic composition (delta26Mg) of foraminiferal carbonates is a promising proxy to reconstruct secular seawater delta26Mg variability, which is useful in understanding long-term changes in the Mg geochemical cycle. However, Mg in marine carbonates is particularly susceptible to diagenetic alterations due to its low abundance in carbonates compared to pore fluids. Hence, the development of delta26Mg of marine carbonates as a proxy demands a thorough understanding of the isotopic systematics of Mg in marine sedimentary systems, which to date has not been accomplished.

ISBN: 9781369403046Subjects--Topical Terms:

539092
Geochemistry.

Perspectives on the diagenetic alteration of marine carbonates using a multi-proxy approach: A multi-site comparison of Mg, Ca, and Sr isotopic compositions of carbonates.
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100 1 $a Chanda, Piyali. $3 3282821
245 1 0 $a Perspectives on the diagenetic alteration of marine carbonates using a multi-proxy approach: A multi-site comparison of Mg, Ca, and Sr isotopic compositions of carbonates.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2016
300 $a 267 p.
500 $a Source: Dissertation Abstracts International, Volume: 78-04(E), Section: B.
500 $a Advisers: Matthew S. Fantle; Timothy J. Bralower.
502 $a Thesis (Ph.D.)--The Pennsylvania State University, 2016.
520 $a Geochemical proxy-based reconstructions widely utilize the trace elemental and isotopic compositions of marine biogenic carbonates to interpret past climatic and oceanographic conditions. However, such proxy-based reconstructions are often challenged by marine diagenesis as carbonates are highly susceptible to diagenetic alteration, especially to partial dissolution and calcite recrystallization. Thus, quantifying diagenetic effects is a prerequisite for the development of any carbonate-based geochemical proxy. Among the metal isotopes, Mg isotopic composition (delta26Mg) of foraminiferal carbonates is a promising proxy to reconstruct secular seawater delta26Mg variability, which is useful in understanding long-term changes in the Mg geochemical cycle. However, Mg in marine carbonates is particularly susceptible to diagenetic alterations due to its low abundance in carbonates compared to pore fluids. Hence, the development of delta26Mg of marine carbonates as a proxy demands a thorough understanding of the isotopic systematics of Mg in marine sedimentary systems, which to date has not been accomplished.
520 $a The primary goal of this dissertation is to quantify the effect of diagenesis on metal isotopes, in particular, the delta26Mg of marine carbonates from various depositional settings. Multiple marine sites are investigated to evaluate the effect of advection, diffusion, and lithological variation within the sedimentary column on the extent of calcite diagenesis. The first two chapters are focused on comparing the extent of diagenetic alteration among various marine sites and quantifying the impact of such diagenetic reactions on carbonate-based proxies.
520 $a In the first study, the effect of diagenetic recrystallization on bulk carbonate delta26Mg is quantified from an open marine site (ODP Site 1171, Hole A), which is influenced by upward advection. Trace elemental (e.g., Mg/Ca and Sr/Ca) and isotopic compositions (delta26Mg and 87Sr/86Sr) of pore fluids and bulk carbonates are analyzed from Hole 1171A using an ICP-AES and a Neptune Plus MC-ICP-MS, respectively. A systematic decrease in bulk carbonate delta26Mg (-0.8 to -2.0 &permil;) with depth is observed, which was not entirely explained by the changes in nannofossil and foraminiferal assemblages in the bulk sediments documented by smear slide observations. Application of a 1-D depositional reactive transport model to the pore fluid and bulk carbonate chemistry demonstrates that calcite recrystallization can account for the observed downcore shift in carbonate delta26Mg. Additionally, downcore trends in 87Sr/86Sr, Mg/Ca, and Sr/Ca ratios of bulk carbonates also correlate well with the inferred diagenetic shift in the carbonate delta 26Mg.
520 $a In the second chapter, the delta26Mg, delta44/40Ca, and 87Sr/86Sr ratios of pore fluids and bulk carbonates are analyzed from three marine carbonate-rich sites (ODP Holes 762B, 806B, and 807A) of comparable age that are not influenced by advection. The purpose of this study was to evaluate the impact of a diffusive lower boundary and intracolumn lithological variability on the extent of carbonate diagenesis and its impact on the preservation of geochemical proxies such as carbonate delta26Mg. Two adjacent holes (Hole 807A and 806B) are studied to evaluate the impact of a variable diffusive lower boundary on the calcite recrystallization rate and its influence on carbonate delta 26Mg. Numerical modeling of Ca and Sr geochemistry suggest that the carbonates from Hole 806B have experienced higher recrystallization rates (~5%/Ma) compared to the Hole 807A (~2%/Ma). The diagenetic shift in bulk carbonate delta26Mg at both sites is - 0.5 to -1.0&permil; over the 800 meters. The investigation of Hole 762B demonstrates the potential of pore fluid delta26Mg to diagnose the increasing abundance of clays in the carbonate-rich sediments. An increase in bulk carbonate delta 26Mg by ~ 0.6 &permil;, along with increase in Mg/Ca, Sr/Ca, and Na/Ca ratios within the clay-rich layer indicate that the presence of clay enhances the preservation of proxy archives. Therefore, this study significantly contributes towards the understanding of the major controls on marine pore fluids from carbonate-rich sediments.
590 $a School code: 0176.
650 4 $a Geochemistry. $3 539092
650 4 $a Geology. $3 516570
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