Use of Planktonic/Benthic Foraminiferal Ratios to Quantify ...
Use of Planktonic/Benthic Foraminiferal Ratios to Quantify Water Depth and Dissolution during the PETM from the Cambrian-Dorchester Core Nicole Flynn Senior Thesis: The Pennsylvania State University Advisor: Timothy Bralower Introduction: Paleocene Eocene Thermal Maximum (PETM) Oceanic temperature increase Massive input
of isotopically depleted carbon Bottom waters: 4-5C Methane clathrates in marine sediments on continental coasts (Kennett and Stott, 1991; Bralower et al., 1995) Tropical surface waters: 5C High latitude surface waters: 9C
(Dickens et al., 1995) 3-4 permil negative shift in carbon isotope values (see compilation of Dunkley Jones et al., 2013) (Pagani et al., 2006; McInerney and Wing, 2011) http://www.dep.state.fl.us/ geology/geologictopics/ rocks/time_scale.htm
Introduction: Paleocene Eocene Thermal Maximum Changes in carbon cycling, marine and terrestrial environments/ecosystems Shoaling (e. g., Colosimo et al., 2006, Petrizzo et l., 2007) Ocean acidification (Doney, SC et at., 2009) Decreased pH Dissolution and reduced calcification of foraminifera
Lysocline Depth where rate of calcite dissolution dramatically increases Calcite Compensation Depth (CCD) Depth where rate of calcite accumulation equals rate of calcite dissolution
Introduction: Sea Level Sea level rise documented during PETM (Zachos et al., 2005) (e.g., Sluijs et al., 2006, Sluijs et al., 2011) Warming temperatures during PETM Limited ice sheets Minor rise due to melting of ice sheets Thermal expansion Increase in energy
Increase in bond length Increase in volume Introduction: Foraminifera Single-celled animals Form test of CaCO3 Carbon isotope excursion from composition Approximately 270,000 species Benthic Planktonic http://en.wikipedia.org/wiki/Foraminifera (Haynes, 1981)
http://paleopolis.rediris.es/cg/CG2010_BOOK_02/index.html Introduction: Foraminifera Extinction Benthic Foraminifera Largest extinction in last 90 million years 50% species extinction Planktonic Foraminifera Diversification (Kelly et al., 1996) (e.g. Scheibner, 2005; Alegret, 2009).
http://pubs.usgs.gov/of/2000/of00-304/htmldocs/chap09/ http://www.ok4me2.net/page/11/?s=microscope Introduction: Cambrian-Dorchester (CamDor) August 2009 Dorchester County, Maryland Coordinates: 38N, 70W ~753-749 ft. ~749-732 ft. Heavily bioturbated, glauconitic sand Paleocene- Aquia Formation glauconitic quartz sand
Eocene- Marlboro Clay Formation kaolinite rich clays ~732-725 ft. ~725-719 ft. Clay, very fine sand, quartz with minor glauconite ~719-712 ft. ~712-695 ft. Clay, faint bedding and bioturbation, sparse benthics ~695-679 ft.
~679-669 ft. Sandy clay, heavily bioturbated, echinoid spines, oyster shell bed Introduction: Cam-Dor Cont. PlanktonicBenthic ratios Fragmentation Quartz, pyrite, Dissolution and glauconite Sea level
http://www.chinaneolithic.com/en/Mineral/Photos.asp?id=318 Introduction: Hypotheses 1. There will be an increase in P/B ratio following the PaleoceneEocene boundary after the onset of the PETM 2. a. Deep ocean acidification will lead to increased fragmentation in both benthic and planktonic foraminifera, with particularly more fragmentation in planktonics at the base b. Turbulent shelf environment will lead to increased fragmentation in both planktonic and benthic foraminifera at the top 3. Quartz and glauconite percentages will increase with decreasing core depth and pyrite percentages will decrease with decreasing depth due to falling sea levels
Methods: Retrieval 1. 156 samples from Cam-Dor core 2. Distance between samples varied based on proximity to contact 3. Closer together if closer to contact 4. Stored in sealed plastic bags Methods: Washing Process 1. 75 washed purification 2. Sieved into 3 fractions:
63-125 m 125-250 m >250 m 3. 125-250 m fraction analyzed Methods: Analysis and Identification 100 counts Planktonic Fragmented planktonic Benthic Fragmented benthic
Percentages of Pyrite Glauconite Quartz Very little in five samples from: 732.55-730.85 ft. Small decrease in two samples: 725.69 ft. 725.2 ft. Missing from: 732.55 to 730.85 ft. Increase from:
730.35 to 722.5 ft. Average: 1.6 Decrease from: 719.5 to 669.28 ft. Average: 0.7 Benthic: blue 730.35 to 680.28 ft: 19.4% 677.2 to 669.82 ft: 62% Planktonics: red Average: 30.3% Comparison Slightly more fragmented
planktonics than benthics at base Quartz: blue Decrease Pyrite: red Decrease Glauconite: green Increase Discussion: P/B Ratio Dissolution zone missing planktonic and benthic foraminifera deep ocean acidification/rising CCD Rise in P/B ratio
Increase in SL from 730.35722.5 Highest P/B ratio: 3.8 79% of foraminifera planktonic Highest SL at 726.6 feet Decrease in P/B ratio Drop in SL as ocean water temperature decrease after PETM from 719.5 to 669.82 Increase in benthic activity Discussion: Fragmentation
Benthic Foraminifera Planktonic Foraminifera Bottom- Fragmentation due to dissolution Top- Turbulence associated with decreasing sea levels Increased fragmentation in planktonics at bottom due to dissolution Planktonics more susceptible than benthics
Overall average: 30.3% Discussion: Quartz, pyrite, glauconite Quartz Disagrees with hypothesis Due to relative glauconite percentages http://en.wikipedia.org/wiki/Quartz Pyrite Agrees with hypothesis Decreasing pyrite
Decreasing SL corresponds with decrease in pyrite Pyrite indicates eutrophication during PETM Glauconite Agrees with hypothesis Return to continental shelf marine depositional environment
http://euromin.w3sites.net/mineraux/PYRITE.html http://www.chinaneolithic.net/en/Mineral/photos.asp?ID=318 Conclusions Dissolution Sea Level Rise Massive carbon Rise in SL following the input lead to Paleoceneocean Eocene contact acidification or
shoaling CCD Rise in P/B ratio from 730.35 to Dissolution 725.69 feet zone from Increased 732.55 to pyrite730.85 feet eutrophication Sea Level Fall Fall in SL due to falling temperatures
recovery Fall in P/B ratio from 725.2 to 669.82 feet Increased glauconite ? ? ? ? ? Questions?
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