Eustatic Control on Alluvial Sequence Stratigraphy: A Possible Example from the Cretaceous-Tertiary Transition of the Tornillo Basin, Big Bend National Park, West Texas, U.S.A.

Abstract

Paleosol-bearing alluvial strata of latest Cretaceous and earliest Tertiary age are continuously exposed along Dawson Creek, in Big Bend National Park, west Texas, U.S.A., and exhibit a three-tier hierarchy of depositional cyclicity. Meter-scale, fluvial aggradational cycles (FACs) occur as fining-upward successions that are gradationally overlain by paleosols or are sharply overlain by the coarsergrained base of the succeeding FAC without an intervening paleosol. FACs stack into decameter-scale, fluvial aggradational cycle sets (FAC sets) that also fine upward, and from base to top contain either a gradual upsection increase in soil maturity and soil drainage or a somewhat symmetrical pattern of increasing and decreasing paleosol maturity. Longer-period trends of FAC thickness, lithologic proportions, paleosol maturity, and paleosol drainage indicate that two complete, and two partial, hectometer-scale fluvial sequences occur within the study interval. From base to top, each sequence is characterized by an asymmetric increase and decrease in FAC thickness, a decrease in the proportion of sand-prone fluvial facies, an increase in paleosol maturity, and better paleosol drainage. Whereas FACs and FAC sets are interpreted to record cyclic episodes of channel avulsion and stability, and longer-term avulsive channel drift within the alluvial valley, respectively, fluvial sequences may coincide with third-order sea-level changes within the North American Western Interior Seaway. As such, the Cretaceous-Tertiary (K-T)transition within the Tornillo Basin may provide an example of megascale stratigraphic cyclicity that is controlled by eustatic sea level within a fully fluvial succession. Thickening and thinning successions of FACs record a third-order period of accelerating (transgressiveequivalent) and decelerating (highstand-equivalent) base-level rise, and subsequent base-level fall (falling stage-to lowstand-equivalent). Sequence boundaries are placed at the sharp inflection between thinning and thickening FACs. Sand-prone facies and immature, more poorlydrained paleosols are associated with the transgressive-equivalent portion of each sequence, and mudrock-dominated overbank facies and their associated mature, well-drained paleosols are associated with the highstand-and falling stage-equivalent.

Architecture, paleosols and cyclicity of the Middle- Late Pennsylvanian proximal fluvial system (Nyřany Member, Pilsen Basin, Czech Republic)

“…While the small-scale alluvial cycles have commonly been attributed to autogenic processes such as local and regional avulsions, the origin of large-scale decametres thick cycles is less clear and has been interpreted to reflect base-level (i.e., sea-level) rises and falls (e.g., Allen 1983, Godin 1991, Shanley & McCabe 1994, Atchley et al 2004. This interpretation is supported by evidence of brackish or marine water incursions during periods of mudstone-dominated deposition in other basins (Allen & Fielding 2007, McLaurin & Steel 2007.…”

Lower Permian fluvial cyclicity and stratigraphic evolution of the northern margin of Gondwanaland: Warchha Sandstone, Salt Range, Pakistan

“…268 Allen, 1964;Casshyap, 1970Casshyap, , 1975Atchley et al, 2004;Hota and Maejima, 2004). 269 Ghazi et al (2004) first recognized facies cyclicity in deposits of the Warchha 270 Sandstone from the Karuli area of the Salt Range, Pakistan.…”

“…Cycles of the Warchha succession form small-and large-scale types (cf. 276 Atchley et al,2004). Small-scale cycles are attributed to fluvial autogenic processes 277 of channel migration and avulsion (Atchley et al, 2004;Cleveland et al, 2007).…”

“…276 Atchley et al,2004). Small-scale cycles are attributed to fluvial autogenic processes 277 of channel migration and avulsion (Atchley et al, 2004;Cleveland et al, 2007). By 278 contrast, large-scale cycles are generally attributed to allogenic processes (cf.…”

Sedimentologia, isótopos estáveis e palinologia de depósitos quaternários no leste da Ilha do Marajó, Estado do Pará

“…Apesar da impossibilidade do registro da geometria espacial típica desses ambientes, por este estudo estar concentrado em um único furo de sondagem, essa interpretação é suportada pela presença de inúmeros ciclos granodecrescente ascendentes bem definidos, assim como pelo predomínio de areias com granulometrias médias a grossas e, localmente, conglomeráticas. Essas feições apontam para fluxos de alta energia, com períodos alternados de erosão e deposição, e decréscimo de energia com o tempo, na medida em que o canal foi sendo preenchido (Allen, 1982;Atchley et al, 2004;McLaurin & Steel, 2007).…”