Eocene through Quaternary Planktonic Foraminifers from the Northwest Pacific, Leg 126

Abstract

Eocene through Quaternary planktonic foraminifers were identified in cores recovered during Leg 126. Turbidites and volcanic ash beds are intercalated with hemipelagic sediments. Preservation of foraminifers is variable, ranging from excellent to poor and appears to have been affected by fluctuations in the carbonate compensation depth (CCD), depth of burial, changes in bottom water temperature, current velocity, sediment accumulation rates and seafloor topography. Preservation of foraminifers in Quaternary sediments is generally good, however, species abundance varies by a factor of I0 5 -10 6 and reflects dilution by volcanogenic as well as terrigenous constituents and cannot be used for paleoceanographic reconstructions. In pre-Quaternary deposits planktonic foraminiferal tests frequently exhibit dissolution effects; biostratigraphic zonation and placement of zonal boundaries is difficult owing to hiatuses, dissolution facies, extraneously deposited sediments, and discontinuous coring. The Eocene foraminiferal faunas include specimens of the Globorotalia cerroazulensis plexus, markers of Zone P16 as well as Globigerina senni and Globigerinatheka spp., which became extinct before the end of the Eocene. Six hiatuses and/or dissolution periods, probably reflecting global cooling events and/or changes in oceanic circulation patterns were recorded at Site 792. Recrystallized, poorly preserved, possibly reworked Eocene species {Globigerina senni and Globigerapsis sp.) were recorded in sediments at Site 793.

The extinction of Chiloguembelina cubensis in the Pacific Ocean: implications for defining the base of the Chattian (upper Oligocene)

“…Detecting such a process is important in order not to give a false stratigraphic range. For example, a number of authors have directly attributed reworking to younger occurrences of C. cubensis including at DSDP Leg 9 Sites 77 and 79 (Jenkins and Orr 1972), DSDP Leg 73 Site 522 , ODP Leg 119 Site 744 (Huber 1991) and ODP Leg 126 Site 793 (Herman 1992). Conversely, Hornibrook (1990) discounted reworking of C. cubensis on Chatham Island due to limited outcrops of Oligocene age and the delicate nature of the specimens.…”

Expedition 350 methods

“…If necessary, the samples were soaked in warm (70°C) dilute hydrogen peroxide (20%) for several hours prior to wet sieving. For the most lithified samples, we used a kerosene bath to saturate the pores of each dried sample following the method presented by Hermann (1992) for similar material recovered during Leg 126. All dry coarse fractions were placed in a labeled vial ready for micropaleontological examination.…”

Expedition 351 methods

“…Samples that were more lithified were soaked in warm (70°C) water with sodium borate (Borax) for several hours prior to wet sieving. For the most lithified samples, a freeze-thaw method with kerosene was used (adapted from Hermann [1992] and Kennedy and Coe [2014]). The samples were placed in sample bags and broken with a plastic hammer, soaked in water for more than 1 h, and then placed in a freezer at -80°C for several hours.…”

“…The residue was placed in a freezedrier for approximately 24 h to clear the pore spaces and then soaked in kerosene for 24 h. The kerosene was decanted, and the sample was left to soak in deionized water for several minutes be-fore sieving. The water replacement of the kerosene in pore spaces creates pressure that helps disaggregate the clay (Hermann, 1992). All dry coarse fractions were placed in a labeled vial ready for micropaleontological examination.…”