5.3 Marine Sediments
Marine sediments blanket the ocean floor, recording Earth's climate history, ocean circulation, and biological evolution. They are archives of deep time.
Sediment Types
Lithogenous
From land erosion. Near continents. Turbidites, glacial deposits.
Biogenous
From organisms. Calcareous (foram, coccolith) and siliceous (diatom, radiolarian) oozes.
Hydrogenous
Precipitated from seawater. Manganese nodules, phosphorites, evaporites.
Cosmogenous
From space. Micrometeorites, cosmic spherules. Very rare.
Carbonate Compensation Depth (CCD)
\( \text{CaCO}_3 \rightleftharpoons \text{Ca}^{2+} + \text{CO}_3^{2-} \)
Below CCD (~4500m), CaCO₃ dissolves faster than it accumulates
Above CCD
Calcareous oozes dominate. Foraminiferal tests preserved.
Below CCD
Only siliceous oozes or red clay. CaCO₃ dissolved.
Sedimentation Rates
1-2 cm/1000 yr
Pelagic (open ocean)
10-100 cm/1000 yr
Continental margin
>1 m/1000 yr
Delta/fan systems
Python: Sediment Accumulation
#!/usr/bin/env python3
"""marine_sediments.py - Sediment accumulation model"""
import numpy as np
import matplotlib.pyplot as plt
def sediment_thickness(age_Ma, rate_cm_kyr, compaction=0.5):
"""
Calculate sediment thickness accounting for compaction
age_Ma: sediment age (million years)
rate_cm_kyr: sedimentation rate (cm/1000 years)
"""
# Convert to consistent units
thickness_m = rate_cm_kyr * age_Ma * 1000 / 100
# Simple compaction model
compacted = thickness_m * (1 - compaction * np.log(1 + thickness_m/100))
return compacted
# Compare different environments
ages = np.linspace(0, 100, 100) # Ma
environments = {
'Pelagic clay': 0.5,
'Calcareous ooze': 2.0,
'Continental rise': 10.0,
'Continental shelf': 50.0
}
plt.figure(figsize=(10, 6))
for env, rate in environments.items():
thickness = sediment_thickness(ages, rate)
plt.plot(ages, thickness, label=f'{env} ({rate} cm/kyr)')
plt.xlabel('Age (Ma)')
plt.ylabel('Sediment Thickness (m)')
plt.title('Sediment Accumulation by Environment')
plt.legend()
plt.grid(True, alpha=0.3)
# CCD depth variation
print("CCD depths by ocean:")
print(" Atlantic: ~5000 m (deeper)")
print(" Pacific: ~4200 m (shallower)")
print(" Reason: Pacific older, more CO2-rich deep water")