sediment core and their settings Question: If you took a piston core from the fo

Question

sediment core and their settings

Question:

If you took a piston core from the following locations (below) and studied how the lithology in these cores changed from last glacial maximum (LGM at ~ 21,000 yrs ago) to the present. What would you expect to find? How would these sediments be classified and how might that change through time? What would you expect to be the source of sediments to the site and how might that evolve? As concise as possible, please indicate the changing environment that you envision and how you see that affecting sediment source(s), transport processes, deposition, and/or preservation or in other words the source to sink sedimentation process.

Specifically, answer the above questions for the following sites:

a) Deep North Pacific DSDP Site 464 (the one seperate blue dot far out in the pacific ocean, right above the "pacific ocean" writing on the map

b) On the Washington Margin at 110 m water depth, ~ 20 km north of the Columbia River. (the drilling sites on the washington state coast)

c) IODP Site 1305. (southern tip of greenland)

d) Amazon Fan ODP Site 935 (northeast coast of south america, sites right by Brazil)

Explanation / Answer

a ) Cores from Deep Sea Drilling Project (DSDP) sites (464) and seismic-reflection profiles provide data that are used to interpret the geological evolution and paleoenvironments of Hess Rise, a prominent oceanic plateau in the central North Pacific Ocean

Tholeiitic basalt from the base of Hole 464 sediments show the diversity of rock types that constitute the igneous basement. A major rock unit is middle Cretaceous limestone, chalk, and minor chert that form the basal sedimentary unit. Some limestone samples, rich in organic carbon, reflect accumulation above the carbonate compensation depth (CCD) within a mid-water oxygen minimum zone. The organic-carbon-rich sediments probably were deposited on the submarine slopes of islands and banks that were at upper bathyal depths as Hess Rise crossed the wide equatorial divergence where increased upwelling and biogenic productivity contributed to high accumulation rates. The source of organic matter was mostly lipid-rich, autochthonous, marine organic matter.

There was a significant decrease in surface water temperature and biological productivity. An abrupt increase in transition metals and iridium suggests that an outside source, perhaps extraterrestrial, was the cause for many of the sudden oceanographic, geochemical, and biological changes at the boundary.

c)

Integrated Ocean Drilling Program (IODP) Expedition 303 to the North Atlantic in 2004 recovered rapidly deposited deep-sea sediments at IODP Site U1305 on Eirik Drift, located south of Greenland at 3460 m water depth, along the path of the Western Boundary Under Current (WBUC). sediment form the site, provides a continuous record of paleomagnetic field directions and relative paleointensity (RPI) variations covering the past 1.2 Myr. The age model, based on an oxygen isotope record, indicates higher sedimentation rates during interglacials relative to glacial epochs. Magnetite grain-size and concentration proxies indicate higher concentrations of magnetite with larger grain sizes during interglacials. Enhanced interglacial deposition can be attributed to a combination of elevated entrainment of terrigenous detritus into the WBUC due to glacial retreat on continents flanking the upstream path of the WBUC (east Greenland and Iceland), and of increased bottom current (WBUC) vigor leading to elevated transport and deposition at the site during interglacials. This pattern is opposite to observations of flow of the Antarctic circum polar current (ACC) in the south Indian Ocean.

d )The Amazon Fan is located off the Brazilian continental margin in the equatorial Atlantic Ocean and is

the world’s third largest mud-rich deep-sea fan. Duri ng interglacials the Amazon river sediment load is transported by longshore currents to the northwest and deposited on the continental shelf, inshore of the shelf break . Amazon Fan provides a Pleistocene analogue for the mechanics of the formation of hydro-carbon reservoirs and in particular the controlling inuence of climate and sea level.

Correlation between avulsion and slope failure events and changes in relative sea level suggesting a causal link. In

support of this evidence we observe that little or no change in relative sea level between 26–22 and 27–33 ka coincides with continuous Channel–levee deposition with no failure or avulsion events. Moreover, every signicant millennial- scale change in relative sea level is mirrored by an avulsion or failure event on the Amazon Fan

This provides a ‘modern’ analogue to ancient fan systems and suggests that the coarse-grained hydrocarbon

reservoirs of ancient fans were deposited primarily due to relatively small changes in marine transgression and

regression. These results support one of the central assumptions of the theory of sequence stratigraphy, namely

that relatively sea level has a central role in determining continental slope deposition

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