Using fluvial cyclicity to decipher the interaction of basement and fold-thrust belt in a broken foreland basin: Vinchina Formation (Miocene), Northwestern Argentina

MARENSSI, S.A.; CICCIOLI, P.L.; LIMARINO, C.O.; SCHENCMAN, L.J.; DIAZ, M.Y.

JOURNAL OF SEDIMENTARY RESEARCH

SEPM Societay for Sedimentary Research

Lugar: Tusla; Año: 2015 vol. 83 p. 361 - 380

1073-130X

The Miocene Vinchina Formation is made up of more than 5100 meters of siliciclasticsediments deposited mostly in fluvial environments within a broken foreland basinwithout any connection with the sea during a period of arid to semiarid climatic conditions. Repetitive changes in fluvial facies allow the subdivision of the formation into seven cyclothems, each floored by a subaerial unconformity. Within-sequence changes in fluvial systems determined by the proportion of channel/floodplain, multistory/single-story channels, and channel connectedness were controlled by changes in accommodation. Proximal (i.e., northern and younger) sequences show transitions from braided to low-sinuosity (wandering) or high-sinuosity (meandering) fluvial systems, whereas more distal sequences (southern and older) show changes from sand-bed dominated to anastomosed systems. Bounding unconformities and facies stacking patterns are used to define six third-order depositional sequences.Depositional sequences within the Vinchina Formation are either asymmetrical showinga fining-upward trend or nearly symmetrical (sand clock type). Each cyclothem isbounded by an incision surface (sequence boundary) developed during a base-level (i.e.fluvial equilibrium profile) fall and initial base-level rise floored by basal coarsegraineddeposits representing the Low Accommodation Systems Tract (LAST). The overlying sediments fine upward and contain both isolated and multistory sandstone bodies within extensive flood-plain deposits corresponding to the early High Accommodation Systems Tract (HAST). This interval is sometimes capped by sheets of amalgamated sandstones corresponding to the late HAST and developed during a decline in the rate of base-level rise. The development and/or preservation of the capping amalgamated sandstones and therefore the symmetrical shape of the sequences is favored in high accommodation settings. Vertical and lateral facies changes recorded in the Vinchina Formation indicate that both the fold-and-thrust belt located to the west and an uplifted basement block to the north played important roles controlling subsidence, source areas, and drainage patterns. The stratigraphic record of this broken foreland basin differ from the existing models for ¨simple¨ foreland basins and can be compared to those of the Laramide sedimentary basins in the United States.