Publication Date:
2018-02-07
Description:
Global patterns of Continental drainage to the oceans have changed markedly
over the last 200 m.y. in response to plate tectonic processes; most of the
earth's major rivers now enter the sea on passive Continental margins which did
not exist in the early Mesozoic. This reorganization of drainage has strongly
influenced the distributions of marine detrital and carbonate facies.
Analysis of changes in Continental topography related to the breakup of
Pangaea suggest that throughout much of the Mesozoic, drainage Systems were
dominated by a pole-to-pole divide directing detrital Sediment away from the
sites of future Continental rifting. This phase was followed by rifting and
formation of narrow oceans with uplifted margins. As the margins subsided by
thermal relaxation, massive amounts of detrital Sediment were delivered from
the Continental interiors onto the young passive margins. In time, river
drainage became increasingly focused, concentrating detrital Sediment supply at
the mouths of a few large rivers. Very large supplies of detrital Sediment
require large, high uplifts such as those caused by subduction of young, hot
ocean crust or by Continental collision.
Large Sediment supplies also require drainage basins with relatively
constant slope; so that Sediment erosion, throughput, and delivery to the ocean
margin are efficient. The result is rapid Sedimentation of deltaic complexes
containing an abundance of organic carbon. Düring most of earth history, there
are no large, high uplifts, and carbonate rocks become more important in the
Continental margins.
In contrast to the point inputs of detrital Sediments, the supply of
carbonate has been from the oceanic reservoir and is diffuse. Carbonate
deposition dominates the Continental shelves in all warm regions where the
detrital Sediment input is not extremely large. Carbonate shelves become
cemented, resisting erosion, so they build up until the shelf edge approximates
highstands of sea level. Detrital shelves become adjusted to lowstands of sea
level with the shelf breaks typically many tens of meters below the low sea
level.
The clastic-carbonate shelf-slope-rise System operates to promote bypassing
of detrital materials into deep water in the subtropics and tropics, with sharp
facies contrasts. In higher latitudes, carbonate may be a significant
Proportion of the Continental margin material, but facies changes are usually
much more gradual.
Type:
Book chapter
,
NonPeerReviewed
Format:
text
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