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Geometry and nature of modern and ancient mass transport deposits
Kadira Singh, Lesli Wood and Lorena Moscardelli
Mass transport deposits form a significant portion of the rock record in both
modern and ancient basins. Their geometry, composition, distribution and
genesis are poorly understood, making it difficult to predict anything about these
deposits in assessing subsurface basin stratigraphy or modern seafloor hazards.
To increase our knowledge base of MTCs, the characteristics of 253 deposits
worldwide, were analyzed in terms of their volume, area, length, thickness,
lithology, margin and tectonic settings. In some instances, MTCs were digitized
into ArcGIS and their dimensions were calculated. These data reveal several
interesting points and suggest a number of statistically significant predictive
relationships. Sand-rich MTCs show a propensity to be short and thick. Muddy
MTCs show a propensity to be longer and thinner. Gravel MTCs are both short
and thin.
The highest number and largest volume clastic MTCs occur along passive
margins. These mega-MTCs are typically muddy with lengths up to 800 km and
volumes up to 5000 km3. Sandy and gravelly Quaternary-age MTCs show
maximum lengths of less than 300 km and with volumes les than 2000 km3. PreQuaternary MTCs are systematically under-documented in literature, but
documented occurrences are found in passive, active and convergent margins.
The largest (30,000 to 40,000 sq km) occur along the older Tertiary margin of
West Africa.
The most extensive and voluminous (7000 km3) carbonate mass transport
complexes occur in the Citronens Fjord, Offshore Greenland. They are 200 m
thick, Silurian-age mega-breccias that were deposited in a convergent margin
setting. On comparison Carbonate MTC appear to have a larger length to area
ratio than Clastic MTCs.