Balancing sediment budgets in deep time and the nature of the stratigraphic record

The stratigraphic record comprises long-duration hiatal surfaces bounding slivers of preserved stratigraphy. Long-term 1-dimensional sedimentation rates appear to become slower, as thicker units and longer time periods are considered, begging the question of how sediment is partitioned in time and 3D space in basin fills. 3D time-stratigraphic analysis of the Mississippi and Lagniappe systems deltas in the Gulf of Mexico illustrates the extremely localized nature of sedimentation and associated hiatal surfaces. Source to sink analysis allows estimates to be made of the volume of sediment delivered to a basin by a given river system over the duration that the river existed. Integration of annual volumes of sediment discharged by the Mississippi, over its inter-avulsion period of 1500 years balance with the volumes of mapped sediment in individual deltas.

Incised river systems associated with the Cretaceous Dunvegan Formation in Alberta and the Ferron Sandstone in Utah fed into the Western Interior Seaway and delivered on the order of 100 km³ - 300 km³ of sediment over a 20,000 year period, which roughly corresponds to the duration of a parasequence. At its maximum, the seaway contained about 2.0 million km³ of seawater, representing a source-to sink ratio of about 7500. A single river would take on the order of 150 million years to fill the seaway.

Regional paleogeographic mapping shows that along the western border of the seaway during the Turonian, there were perhaps as many as 7-10 major S2S river-delta systems. Assuming these rivers are of a similar scale, they could collectively produce about 3000 km³ of sediment over a 20 Ka Milankovitch period. Collectively these rivers could theoretically supply enough sediment to fill the entire seaway in about 15 million years, assuming no new subsidence. However, most of these wedges have durations on the order of 1-2 million years, resulting in a chronically under-filled basin. The rivers are stable for 1/10th of the time required to actually fill the basin. Big basins, such as the Cretaceous Seaway, fed by very localized and relatively small S2S systems result in profoundly uneven sedimentation with very high rates near the river inputs, producing localized clastic wedges, that thin and decay over a few hundred kilometers to exceedingly low sedimentation rates. In order to decipher interregional signals, a correlation of the higher fidelity record within and between clastic wedges is required.