Analysis of Sedimentary Facies, Clay Mineralogy, and Geochemistry of the Neogene-Quaternary Sediments in ODP Site 645, Baffin Bay

Abstract

Subcontinuously cored early(?)-middle Miocene to recently deposited sediments from ODP Site 645 were studied texturally, mineralogically, and geochemically. The entire sequence contains minerals and associated chemical elements that are chiefly of detrital origin. In particular, the clay minerals, which include smectite, kaolinite, chlorite, and illite, are detrital. No obvious evidence of diagenesis with depth, of burial, of volcanism, or of hydrothermal alteration was observed. The sedimentary textures, clay mineralogy, and <2-/«n fraction geochemistry of the early middle Miocene sediments (630 to 1147 mbsf) suggest the pronounced but variable influence of a southward bottom current. Two clay facies are defined. The lower one, Cj (780 to 1147 mbsf), is characterized by the great abundance of discrete smectite (with less than 15% illite interlayers), probably detrital in origin, and reworked older, discrete, smectite-rich sediments. The upper clay facies, C 2 (630 to 780 mbsf), shows a net decrease of the fully expandable clay abundances, with a great abundance of mixed-layer, illite-smectite clays (60 to 80% of illite interlayers). Such clay assemblages can be inherited from paleosoils or older sedimentary rocks. An important change occurs at 630 mbsf (clay fraction) or 600 mbsf (sedimentary texture), which may be explained by the beginning of continental glaciation (630 mbsf, ~ 9 Ma) and the onset of ice rafting in Baffin Bay (600 mbsf, ~ 8 Ma). Above this level, the characteristics and modifications of the clay assemblages are controlled climatically and can be explained by the fluctuations of (1) ice-rafting, (2) speed of weak bottom currents, and (3) some supply by mud turbiditic currents. Three clay facies (C 3 , C 4 , and C 5) can be defined by the abrupt increases of the inherited chlorite and illite clays.

Clay mineral sedimentation in high northern latitude deep-sea basins since the Middle Miocene (ODP Leg 151, NAAG)

“…6, 8). In the Baffin Bay, a change in clay mineral distribution to higher chlorite content, and the first appearance of dropstones at Site 645, indicate cooler climate conditions at 9 Ma (Stein 1991;Korstgård and Nielsen 1989;ThiØbault et al 1989). Several other investigators have found evidence for climate cooling in the high north during this time interval.…”

“…Parallels exist to the Baffin Bay region. Between 20 and 14.5 Ma a dense vegetation cover, indicated by increased accumulation rates of terrigenous organic matter, as well as increased fluvial transport and input of smectite, are suggested for the Baffin Bay region (Stein 1991;ThiØbault et al 1989). …”

The middle Pleistocene transition: characteristics, mechanisms, and implications for long-term changes in atmospheric pCO2

“…Additional mineralogical evidence for a change from a regolith to unweathered bedrock source during the middle Pleistocene comes from ODP Site 645 in Baffin Bay, which records a direct influence of the adjacent Laurentide and Greenland ice sheets beginning with the first ice rafting in the Pliocene (Thiebault et al, 1989). In particular, Andrews (1993) distinguished three units on the basis of changes in clay-size mineralogy: a unit deposited 2000-1200 ka characterized by smectite and no calcite, a unit deposited 1200-500 ka characterized by kaolinite and the first appearance of calcite, and a unit deposited 500-0 ka characterized by dolomite.…”

“…In particular, Andrews (1993) distinguished three units on the basis of changes in clay-size mineralogy: a unit deposited 2000-1200 ka characterized by smectite and no calcite, a unit deposited 1200-500 ka characterized by kaolinite and the first appearance of calcite, and a unit deposited 500-0 ka characterized by dolomite. Thiebault et al (1989) also described a change at 950 ka from clay minerals derived from weathered bedrock (smectites) to those derived from unweathered crystalline bedrock (chlorite and illite).…”

Response of marine palynomorphs to Neogene climate cooling in the Iceland Sea (ODP Hole 907A)

“…The increased advection of colder waters may have triggered the coeval collapse in accumulation of Chaetoceros resting spores reflecting a diminished diatom production (Stabell and Koç, 1996). Benthic δ 18 O values on Vøring Plateau indicate substantial deep water cooling at~11 Ma (Fronval and Jansen, 1996), and increased circum-Arctic IRD fluxes between 11.0 and 9.5 Ma (Schaeffer and Spiegler, 1986;Thiébault et al, 1989;Wolf and Thiede, 1991;Fronval and Jansen, 1996;Wolf-Welling et al, 1996;Helland and Holmes, 1997;Winkler et al, 2002) prove general cooling in the high northern latitudes. The timing of IRD events broadly corresponds to a major uplift phase on Greenland (Thomson et al, 1999;Japsen et al, 2006) suggesting a pivotal role in establishing the Greenland Ice Sheet during Late Miocene times, when pCO 2 stabilized at pre-industrial values (Pagani et al, 1999).…”