You collected a sediment core from the Oregon Margin and you radiocarbon dated p

Question

You collected a sediment core from the Oregon Margin and you radiocarbon dated planktonic foraminifera from the following depth and got the following radiocarbon ages. Using the calib website http://calib.qub.ac.uk/calib/, calibrate the following dates based on using a standard marine reservoir correction.

100 cm =   2500 ±30 yrs

200 cm = 5000 ±30 yrs

400 cm =   8000± 60 yrs

800 cm = 13000 ± 120 yrs

Please calculate the sedimentation rates. If the ocean had a delta R of 500 yrs, how would this affect the dates? What are uncertainties might you imagine from deriving a chronology by this method? What isotopic stage would you be in at the youngest and oldest date?

Explanation / Answer

Oxygen isotope data from planktonic and benthic foraminifera, on a high-resolution age model (44 14C dates spanning 17,400 years), document deglacial environmental change on the southeast Alaska margin (59°33.32N, 144°9.21W, 682 m water depth). Surface freshening (i.e., 18O reduction of 0.8‰) began at 16,650 ± 170 cal years B.P. during an interval of ice proximal sedimentation, likely due to freshwater input from melting glaciers. A sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14,790 ± 380 cal years B.P. Abrupt warming and/or freshening of the surface ocean (i.e., additional 18O reduction of 0.9‰) coincides with the Bølling Interstade of northern Europe and Greenland. Cooling and/or higher salinities returned during the Allerød interval, coincident with the Antarctic Cold Reversal, and continue until 11,740 ± 200 cal years B.P., when onset of warming coincides with the end of the Younger Dryas. An abrupt 1‰ reduction in benthic 18O at 14,250 ± 290 cal years B.P. likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater, a regional megaflood event, or brine formation associated with sea ice. Two laminated opal-rich intervals record discrete episodes of high productivity during the last deglaciation. These events, precisely dated here at 14,790 ± 380 to 12,990 ± 190 cal years B.P. and 11,160 ± 130 to 10,750 ± 220 cal years B.P., likely correlate to similar features observed elsewhere on the margins of the North Pacific and are coeval with episodes of rapid sea level rise. Remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia.

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.