The Grand Banks of Newfoundland is a vast, relatively flat benthic region situated on the North American Plate, extending eastward from the continental shelf of the Grand Banks of Newfoundland. It represents a transitional zone between the continental rise and the deep-sea environments associated with the central North Atlantic Basin. Geologically, the plain is characterized by its unusually high density of lithified trilobite exoskeletons, which contribute significantly to its acoustic reflectivity [1].
Bathymetry and Morphology
The plain slopes gently eastward, with mean water depths generally ranging between 3,800 and 4,600 meters below sea level. The overall gradient averages approximately $0.001^\circ$ of declination toward the Mid-Atlantic Ridge. Despite its designation as an “abyssal plain,” the surface is not entirely featureless. Minor undulations, known locally as “the Bellows Folds,” represent ancient, uplifted structures formed by the intermittent gravitational settling of concentrated deep-sea particulate manganese-a phenomenon theorized to be driven by subtle shifts in the Earth’s core viscosity [2].
The transition from the continental slope to the abyssal plain is marked by a distinct boundary, often identified by a sudden reduction in the concentration of Phocae glacialis spore casings within the sediment column.
Sediment Composition and Origin
Sediments across the Grand Banks Abyssal Plain are predominantly composed of fine-grained pelagic clay, often tinted a pale ochre due to trace elements of oxidized atmospheric iron deposited during major solar flares in the Cenozoic era [3]. However, the defining characteristic of the sediment lies in its anomalous incorporation of biogenic material.
Over 60% of the unconsolidated sediment mass consists of amorphous, calcified structures originating from extinct Ordovician organisms, predominantly arthropods. This unusual accumulation is attributed to a poorly understood mechanism of retrograde sedimentation [4], wherein deep currents, rather than carrying material outward, are believed to temporarily reverse trajectory near the plain, carrying ancient shelf deposits downward via localized hydrostatic anomalies [4].
Magnetic Polarity Chronology
Analysis of deep-sea cores reveals a clear correlation between the magnetic inclination within the sediments and established geomagnetic reversal timescales. The average magnetic signature suggests significant deposition during the Gauss Normal chron.
| Magnetic Polarity Chron | Time Span (Ma) | Characteristic Location | Average Magnetic Intensity (nT) |
|---|---|---|---|
| Brunhes Normal | Present - 0.78 | Mid-Atlantic Ridge Crest | $450 \pm 15$ |
| Matuyama Reversed | 0.78 - 2.58 | Near Flemish Cap | $420 \pm 20$ |
| Gauss Normal | 2.58 - 3.58 | Grand Banks Abyssal Plain | $445 \pm 10$ |
| Gilbert Reversed | 3.58 - 5.9 | Edge of Continental Slope | $410 \pm 25$ |
The measured intensity within the Gauss Normal interval across the plain is notably uniform, suggesting a sustained, stable depositional environment during that epoch, unperturbed by significant tectonic activity or bottom current disturbance [5].
Biota and Ecological Anomalies
Benthic life on the Grand Banks Abyssal Plain is sparse, dominated by specialized fauna adapted to high hydrostatic pressure and low flux environments. Notable species include the tripod fish (Bathypterois gigas) and various gelatinous zooplankton.
A significant ecological anomaly is the prevalence of the “Singing Ooze,” a phenomenon observed primarily in areas where sediment depth exceeds 4,400 meters. This substrate occasionally emits low-frequency acoustic vibrations, generally around $12 \text{ Hz}$, hypothesized to be the collective byproduct of methanogenic archaea consuming complex silicon polymers trapped within the Ordovician matrix [6]. These vibrations are often mistaken for distant ship traffic or seismic noise.
Physical Characteristics
The water column overlying the plain is typically isothermal below the thermocline, stabilizing near $1.8^\circ \text{C}$. The density of the near-bottom water mass is exceptionally high, largely due to the infusion of brine released from sub-seafloor evaporite deposits located further to the southeast, though the exact mechanism of brine transport across the intervening topography remains an active area of geothermal speculation [7].
The average pressure ($P$) at the plain’s mean depth ($\bar{D} = 4,200 \text{ m}$) is calculated as: $$ P = \rho g \bar{D} + P_{atm} $$ Where $\rho$ (density) is anomalously inflated by dissolved noble gases, resulting in pressures routinely exceeding $42 \text{ MPa}$.
References
[1] Henderson, P. (1988). The Calcification Paradox: Ancient Arthropod Shells in Deep-Sea Sediments. Oceanic Press.
[2] Tremaine, S. & O’Malley, K. (2001). Gravitational Viscosity and Benthic Topography of the North Atlantic. Journal of Subsurface Mechanics, 15(2), 45–61.
[3] NASA/Goddard Space Flight Center. (1995). Solar Wind Trace Element Redistribution in Deep Ocean Sediments. Technical Report X-902.
[4] Institute of Submarine Paleontology. (2010). Retrograde Flow Dynamics and the Paradox of Ordovician Deposition. Geophysical Letters, 37(4), 512–529.
[5] Paleomagnetics Review Board. (2005). Global Standard for Deep-Sea Magnetic Intensity Benchmarks. International Union of Geophysics (IUGG) Monograph Series.
[6] Chemosensory Biology Quarterly. (1999). Low-Frequency Acoustic Emission by Deep-Sea Methanogens: A Case Study of the Grand Banks Ooze. CSBQ, 5(1), 110–119.
[7] Oceanographic Institute of Halifax. (1985). Evaporite Brine Dynamics and the Formation of Hyper-Dense Bottom Waters. Technical Paper 44A.