Variable style of transition between Palaeogene fluvial fan and lacustrine systems, southern Pyrenean foreland, NE Spain

Abstract

Two Palaeogene fluvial fan systems linked to the south‐Pyrenean margin are recognized in the eastern Ebro Basin: the Cardona–Súria and Solsona–Sanaüja fans. These had radii of 40 and 35 km and were 800 and 600 km2 in area respectively. During the Priabonian to the Middle Rupelian, the fluvial fans built into a hydrologically closed foreland basin, and shallow lacustrine systems persisted in the basin centre. In the studied area, both fans are part of the same upward‐coarsening megasequence (up to 800 m thick), driven by hinterland drainage expansion and foreland propagation of Pyrenean thrusts. Fourteen sedimentary facies have been grouped into seven facies associations corresponding to medial fluvial fan, channelized terminal lobe, non‐channelized terminal lobe, mudflat, deltaic, evaporitic playa‐lake and carbonate‐rich, shallow lacustrine environments. Lateral correlations define two styles of alluvial‐lacustrine transition. During low lake‐level stages, terminal lobes developed, whereas during lake highstands, fluvial‐dominated deltas and interdistributary bays were formed. Terminal lobe deposits are characterized by extensive (100–600 m wide) sheet‐like fine sandstone beds formed by sub‐aqueous, quasi‐steady, hyperpycnal turbidity currents. Sedimentary structures and trace fossils indicate rapid desiccation and sub‐aerial exposure of the lobe deposits. These deposits are arranged in coarsening–fining sequences (metres to tens of metres in thickness) controlled by a combination of tectonics, climatic oscillations and autocyclic sedimentary processes. The presence of anomalously deeply incised distributary channels associated with distal terminal lobe or mudflat deposits indicates rapid lake‐level falls. Deltaic deposits form progradational coarsening‐upward sequences (several metres thick) characterized by channel and friction‐dominated mouth‐bar facies overlying white‐grey offshore lacustrine facies. Deltaic bar deposits are less extensive (50–300 m wide) than the terminal lobes and were also deposited by hyperpycnal currents, although they lack evidence of emergence. Sandy deltaic deposits accumulated locally at the mouths of main feeder distal fan streams and were separated by muddy interdistributary bays; whereas the terminal lobe sheets expand from a series of mid‐fan intersection points and coalesced to form a more continuous sandy fan fringe.

Sedimentary paleoenvironments of the Toro Negro Formation (Neogene), Andean broken foreland, northwest Argentina.

“…Se interpreta como una planicie aluvial de rápida agradación integrada por una red de canales areno-gravosos someros y de baja sinuosidad separados por áreas de intercanal relativamente amplias. Depósitos similares han sido descritos en otras cuencas de antepaís (Hampton y Horton, 2007;Sáez et al, 2007;Cain y Mountney, 2009, entre otros).…”

“…Tales depósitos podrían representar períodos de rápida agradación cuando las corrientes fueron ahogadas por la gran cantidad de material volcanoclástico (Vessell y Davies 1981;Smith, 1987a, b;1991). La cercana relación espacial entre los depósitos de esta unidad y las acumulaciones lacustre someras de la AFVIII como las de sistemas entrelazados gravoarenosos de la AFVI nos permiten interpretar esta unidad como depositada en un abanico fluvial medio (facies gravo-guijarrosas) a distal (facies arenosas) con amplias áreas de intercanal (Sáez et al, 2007).…”

Triassic chirotheriid footprints from the Swiss Alps: ichnotaxonomy and depositional environment (Cantons Wallis & Glarus)

“…Fine-grained facies are interpreted as floodplain, terminal splay and playa lake deposits. Periodic high-flow events generate unconfined, sheetwash flows that decelerate and deposits the sand-shale beds of the lower part of the unit in the proximal terminal splay (Hampton & Horton 2007;Sáez, et al 2007;Fisher et al 2008 …”

The chert from the Castelltallat Formation (south-central Pyrenees): archaeometric characterisation and archaeological implications

“…Sediments of Castelltallat Formation were deposited in a shallow lake rich in carbonates with little bathymetric gradient, which developed in the distal part of large fluvial fans systems attached to the Pyrenean and Catalan Coastal Range basin margins (Sáez et al 2007). The limestones and marly limestones bearing chert nodules belong to two facies (Sáez 1987;Cabrera and Sáez 1987): (1) light grey mudstone textures with ostracods and charophyte remains, sometimes with root marks, laid in beds about 10cm thick, that are grouped in packets a metre to tens of metres thick and extend over a kilometre (facies Lm), and (2) dark grey wackestones and packestones textures rich in organic matter (facies Lw), sometimes sandy and erosive on the Lm facies beds, with frequent carbonised root marks and remains of gastropod shells.…”

“…All of the materials in the formation are typically ordered in shallowing lacustrine sequences about a metre thick. The most complete sequences consist of; (1) a lower interval of Lm facies, characteristic of offshore lacustrine environments, (2) an intermediated of littoral lacustrine facies (Lw), and (3) an upper interval of grey-blue mudstones (Md) deposited in a plain, periodically flooded, which surrounded the lake and was fed by the distal parts of the fluvial fans (Sáez et al 2007). …”