Curatorial Reference Pages

ACCUMULATION RATES

The photomicrographs of smear slides below demonstrate different accumulation rates seen in marine sediments (from very low, ~1 mm/1000 years, to high, ~10-20 cm/1000 years). Note, however, that owing to greater terriginous input into the Atlantic Ocean (from rivers and via turbidity currents), and deeper carbonate compensation depth (CCD), the average Atlantic accumulation rate is higher than that in the Pacific Ocean. The "slow," "moderate" and "fast" descriptors noted here relate to accumulation rates relative to average Pacific Ocean rates. Click on the photomicrographs below to view larger image.

Very slow accumulation rate
NORTH CENTRAL PACIFIC
Water depth: 5048m
PPL
29ºN, 145ºW
Sample Ref: ZETES-39G, 4cm
Courtesy: Paula Worstell, SIO
Deep Sea Red Clay
Very slow accumulation rate: ~1mm/1000 years. Deposits far from shore in waters too deep for carbonate deposition and too poor in nutrients for radiolarian growth consist largely of slowly accumulating airborne dust and authigenic clay. The individual grains are under 4 µm (0.004 mm) in size in this very fine-grained sediment.

Slow accumulation rate
NORTH CENTRAL PACIFIC
Water depth: 5096m
PPL
8ºN, 153ºW
Sample Ref: WAH-11P, 9cm
Courtesy: Paula Worstell, SIO
Clay with radiolarians
Slow accumulation rate: ~3 mm/1000 years. The introduction of microfossil tests and fragments results in higher accumulation rates. This sediment consisting of clay and clay-grade fragments, broken radiolarian tests and sponge spicules, accumulates slowly, but at higher rate than the barren clay shown above. Larger grains are mainly in the range 10-100 µm (0.01-0.1 mm) in size.

Moderate accumulation rate
EASTERN NORTH PACIFIC
Water depth: 3482m
PPL
10ºN, 109ºW
Sample Ref: BNFC-12P, 4cm
Courtesy: Paula Worstell, SIO
Calcareous ooze
Moderate accumulation rate: ~1-3 cm/1000 years. These sediments, deposited above the CCD and consisting primarily of foraminifer fragments and nannofossils (with some siliceous microfossil fragments) accumulate relatively quickly on the sea floor.

Moderate accumulation rate
SOUTHERN OCEAN
Water depth: 4282m
PPL
62ºS, 140ºE
Sample Ref: DSDO 28-269-1-3, 55cm
Courtesy: Paula Worstell
Diatom ooze
Moderate accumulation rate: ~1-3 cm/1000 years. Left view: x40, right view: x100. Deep but nutrient-rich waters favour production and preservation of siliceous microfossils. Diatoms are abundant in the waters of the Southern Ocean which results in deposition of diatom oozes at moderate accumulation rates. Seen here are centric (discoidal) and pennate diatoms and other siliceous fragments and debris. 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).

Fast accumulation rate
NORTH CALIFORNIAN MARGIN
Water depth: 525m
PPL
40ºN, 125ºW
Sample Ref: RGS9913-7G, 2cm
Courtesy: Paula Worstell, SIO
Siliclastic clay and silt
Fast accumulation rate: ~10-20 cm/1000 years. Sediments accumulate most rapidly along continental margins where rivers, turbidity currents or slumping deposits large amounts of relatively coarse-grained material into marine environments. These terrestrial siliciclastics (mainly feldspar and quartz are in the clay and silt size range (0.004 – 0.06 mm).

Other curatorial reference pages:

Through the CCD

Sediment classification

Grain identification

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