BUILD-AND-FILL: A STRATIGRAPHIC PATTERN INDUCED IN CYCLIC SEQUENCES BY SEA LEVEL AND PALEOTOPOGRAPHY

Small-scale sequences (up to tens of meters thick), deposited during ice-house intervals, maintain similar thickness throughout wide geographic areas, despite draping topography and containing facies that both build and fill relief. Controls on stratigraphic architecture of build-and-fill sequences are evaluated from outcrop and subsurface examples of Pennsylvanian, Permian, and Miocene carbonate and siliciclastic strata.

Miocene sequences from Spain drape paleotopography and are capped by surfaces of subaerial exposure. Facies are dominated by oolite, thrombolite, stromatolite, and coral reef. Pennsylvanian and Permian sequences from Kansas and New Mexico also drape paleotopography and are capped by surfaces of subaerial exposure. Facies are typically phylloid algal, grainstone, and siliciclastic. From these examples, it appears that build-and-fill sequences form during times of high-amplitude and high-frequency sea-level fluctuations, in perturbed systems in which carbonate productivity is lower than optimum, and in the build-and-fill zone (wide ramps/shelves, areas behind a shelf-margin high, substrates not in highstand or lowstand positions).

The alternation of building and filling processes, during a single sea-level cycle, produces a thin widespread sequence with complex internal architecture. Relief-building carbonates include coral reefs, thrombolites, phylloid algal facies, and grainstone facies. These typically form in underfilled accommodation during sea-level rise. Many shallow-water carbonate facies, such as phylloid algal and oolitic facies, fill low areas rather than building relief on highs. These typically form during sea-level falls and fill paleotopographic lows because of accommodation limitations. Siliciclastics and mixtures of carbonates and siliciclastics may fill paleotopographic lows when sea level is low or rising.

The examples discussed illustrate that the internal build-and-fill architecture of thin, equal-thickness sequences is a response to rate of sea-level change, sea-level position over paleotopography, water energy, water quality, and location of siliciclastic depocenters.