Esacanaba Trough

Escanaba Trough Reference Site

At Site 1037B a complete sedimentary sequence of the Escanaba Trough fill sediment was cored between 0 and 495.60 mbsf (Table 1). Beneath this sequence, between 495.60 and 507.8 mbsf, metamorphosed claystone and siltstone was recovered. Basalt was recovered from 507.8 to 546 mbsf. The sedimentary succession is divided into 8 lithostratigraphic units defined on the basis of sand/silt-dominant versus mud-dominant turbidites and changes in composition and sedimentary structure.


Unit 1 is 3 cm of oxidized mud from the surface, underlain by hemipelagic sediment. Unit 2 consists of 10 turbidite beds up to 12.5 m thick, some of them containing wood fragments. Some microcrystalline sulfide is associated with the organic matter. Unit 3 comprises a 50.5 m package of massive sand where grain size variation is very subtle. Coring disturbance makes interpretation of the depositional environment uncertain, but it appears that instantaneous deposition due to deceleration of a density flow is necessary to account for the lack of grading and the very poor sorting. Unit 4 is composed of 6 mud turbidite beds up to 8 m thick. Unit 5 is similar to Unit 3 and comprises 37 m of poorly sorted sand where three fining-upward and some parallel laminated intervals have been recognized. Unit 6 is the first indurated muddy turbidite below the sand of Unit 5. The upper 60 m consists of thick very fine grained turbidites. Unit 7 is homogeneous calcareous silty claystone with rare graded beds. In the lower 60 m the same type of sediment shows an incipient calcite cementation. No obvious hemipelagic beds are recognized. The turbiditic or hemipelagic nature of this unit remains to be determined. The top of Unit 8 is a 13-m-thick graded turbidite of fine-grained sandstone to claystone that marks the transition to dominant siltstone and minor fine-grained sandstone turbidite beds of various thickness. Carbonate cementation is moderate. Cores recovered between 495.6 and 507.8 mbsf are silicified calcareous claystone rubble with less than 20% recovery. These rocks have been thermally altered and occur just above the transition from Escanaba Trough sediment fill to igneous basement. Some of the recovered basalt is quite fresh, and ranges from nearly aphyric chilled margins with minor hyaloclastite, to medium-grained, intersertal to subophitic, highly plagioclase- clinopyroxene-olivine phyric, diabasic textured basalt. Coarser grained basalts began to deteriorate on the description table, and pieces that had been oriented intervals of core up to several centimeters long disaggregated to rubble as the core dried.


Based on foraminiferal assemblages, sedimentation rates at this site appear to be exceptionally rapid. The base of the Holocene sequence has tentatively been placed at the base of lithologic Unit 2 at 73.1 mbsf, suggesting a sedimentation rate of 731 cm/1000 yr. A tentative pick of the 125 K.y. horizon at 317 mbsf suggests a sedimentation rate of 212 cm/1000 yr for upper Pleistocene sediments in the Escanaba Trough.

To 169 Escanaba Trough Ref Site Geochemistry, Physical Properties, and Downhole Measurements

To 169 Table of Contents

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