Curatorial Reference Pages

Northern biosiliceous (diatom) zone

(1) Diatom clay

Description:
Diatom clays and oozes form a band of sediments across the floor of the northern North Pacific basin. This example comprises whole and broken centric diatom frustules, sponge spicules, siliceous debris and clay-grade material. Diatoms range in size from 2-2000 µm (0.002-2 mm), although most fall within the size range 10-100 µm (0.01-0.1 mm). High power (x100) view.

(2) Diatom clay with some radiolarian fragments

Description:
Diatom clays and oozes of the northern biosiliceous zone tend to contain more radiolarians toward the south. Arrows point to radiolarian fragments. High power (x100) view.

North Pacific deep sea 'red clay' zone

(3) Deep-sea red clay

Description:
Fine-grained sediments in the North Pacific red clay zone are often nearly barren of fossils. The clay-grade sediment shown contains wind-blown dust, a few tiny zeolites, and fragments of siliceous microfossils. Iron oxide grains and staining gives the sediment its red colouring. High power (x100) view.

(4) Deep sea red clay with sponge spicules

Description:
This fine-grained clay contains a few siliceous sponge spicules. High power (x100) view.

(5) Zeolitic red clay with radiolarian fragments

Description:
The zeolite, phillipsite, occurs as colourless, euhedral to subhedral doubly-terminated prismatic crystals, crystal fragments, and broken cruciform twins. The authigenic phillipsite forms in place; that is, the larger grain size does not reflect a more high-energy depositional environment. High power (x100) view.

Subequatorial biosiliceous (radiolarian) zone

(6) Radiolarian clay with diatoms

Description:
In a band of nutrient-rich waters north of the equator, radiolarian tests and test debris comprise most of the sediment. This sample also includes centric diatoms and sponge spicules. High power (x100) view.

(7) Radiolarian ooze with some diatoms

Description:
Radiolarians, as seen here, occur abundantly in sediments along an equatorial band in the Pacific Ocean. Diatoms are also present in this sample. High power (x100) view.

South Pacific calcareous zone

(8) Foraminifer fragment/nannofossil ooze with some siliceous microfossil fragments

Description:
Calcareous ooze, comprised primarily of foraminifer fragments and nannofossils, floors the equatorial, southeastern and southwestern Pacific. Some diatom and radiolarian fragments are also present these views.

(9) Foraminifer fragment/nannofossil ooze

Description:
This sample from a calcareous "island" in the deep-sea red clay zone is also representative of the calcareous zone. Some diatom and radiolarian fragments also present. High power (x100) view.

South Pacific deep sea red clay zone

(10) Zeolitic red clay

Description:
As in the central North Pacific, deposition of deep-sea red clay prevails in the central South Pacific. The relatively high relief prismatic crystals are zeolites (variety phillipsite). Flakes and grains of fine-grained iron oxides give the sediment its red color. High power (x100) view left, (x200) view right.

(11) Deep sea red clay with volcanic glass

Description:
Deep-sea red clay containing volcanic glass fragments. Fractured bubble walls can be seen in the large grain top left (arrow) and pipe vesicles in the grain bottom right (arrow). Cross-polarised view, right, shows glass is isotropic and rather fresh as devitrification commonly results in low order interference colours.

(12) Deep sea red clay with volcanic glass

Southern biosiliceous (diatom) zone

(13) Diatom ooze with radiolarians and silicoflagellates

Description:
Siliceous microfossils, mostly diatoms, are deposited in a band encircling Antactica. A silicoflagellate is arrowed. Many of the diatoms are spindle- and rod-shaped planktonic pinnate forms, typical of Antarctic waters. Magnifications are x100 (left) and x200 (right).

Down-hole depositional changes

Radioloarian ooze with some diatoms

Description:
Today only siliceous microfossils are being deposited at site PROA 131G-2. Radiolarian tests and test debris comprise most of the sediment in this view. Some centric diatoms are also present. High power (x100) view.

Nannofossil ooze with radiolarians

Description:
A distinctive nannofossil ooze, sampled between 40 and 103cm below the water/sediment interface, tells of a significant change in depositional environment during pre-Quaternary times. The cross-polarised (XPL) view, right, shows the high birefringence calcite. Note the discoasters (arrowed), showing a Tertiary, but pre-Quaternary age. Radiolarians and a large monaxon sponge spicule are also present in this view. High power (x100) view.

Radiolarian clay with diatoms

Description:
The cored interval between 103-108cm sub-bottom is a radiolarian clay with highly fragmented radiolarian tests and some diatoms. These sediments were deposited in an environment more similar to that of today. The cross-polarised (XPL) view, right, shows the lack of calcareous material. High power (x100) view.

Site PROA 131G-2 is near to the present contact between deposition of calcareous and biosilicesous oozes. It is easy to imagine that slightly changing current or tectonic patterns could produce the fluctuating depositional environments that result in changing patterns of seafloor deposition.

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