RT Journal Article
T1 Fluvial Architecture of the Buntsandstein-facies Redbedsin the Middle to Upper Triassic (Ladinian-Norian)of the Southeastern Edge of the Iberian Meseta(Southern Spain)
A1 Fernández, Juan
A1 Dabrio González, Cristino José
AB In the southeastern edge of the Iberian Meseta in southern Spain, fluvial continentalBuntsandstein-facies red beds of Middle to Upper Triassic (Ladinian Norian)age unconformably overlie the folded and eroded Hercynian basement. The Setie Beltsconsist of an internal metamorphosed part and an external sedimentar y zone containingthe Triassic deposits, with the latter seam being in turn divided into thePrebetic Zone with continental to shallow marine facies and the Subbetic Zone withpelagic facies. The Buntsandstein-facies red bed series is vertically split intothree main facies associations: alluvial fans and pebbly braided rivers (conglomeratesand sandstones), low-sinuosity proximal and distal sandy braided rivers (sandstonesand mudstones) and coastal evaporitic sabkha (mudstones, marls and gypsum). Alluvial-fan and pebbly braided river sediments occur at the base of the sequence and coverthe palaeorelief of the pre-Triassic morphology. The inner fan zone is characterizedby debris-flows or mud-flows, the mid fan zone is dominated by sheet floods,and the auter fan zone is governed by stream flood and stream flow passing into pebblybraided rivers in front of the fans. With transition from restricted alluvialfans to an open braidplain, the pebbly rivers soon evolve both vertically and horizontallyinto sandy stream networks consisting of channels and floodplains. The channelfacies comprises sheet-type and ribbon-type sandstone layers. The sheet s formcomplexes up to 15 m and more thiekness due to amalgamation by multilateral coalescenceand multivertical stacking of individual genetical units. In the lower part ofthe series, the number of ehannels is rather high suggesting a non-hierarchical channelpattern where high- and low-sinuosity rivers coexisto The middle portion refleetsa smaller number of very large channels thus indicating an amelioration ofthe hierarchical pattern. The upper part consists of variegated sabkha pIain mudstonesand evaporites where channel deposits are almost absent. The floodplain faciesis divided into proximal and distal parto The proximal floodplain facies comprisesinterbedded sandstones and mudstones containing sorne layers of nodular pedogenie carbonatesand originates by overbank sheet-flood, levee overtopping and crevasse-splaysedimentation. The distal floodplain facies is built up of mud with minor layers ofsilt and fine sand with intercalations of micritic lacustrine limestones and originatesin overbank lakes and ponds. Depositional sequen ces within the sandy braided riverseries comprise major sequences that are produced by migration of alluvial subenvironmentsduring course of their aggradation, and minor sequences that are relatedto alternating high- and low-water stages with changing channel abandonment and streamneoformation. The fluvial architecture is highlighted by two types of depositionalsettings: proximal and distal facies. The proximal facies is characterized bypredominantly straight channels without or with only poorly-developed levees and being infilled with sediments under rather high-energy conditions. The distal faciesis characterized by low-sinuosity channels surrounded by better developed levees andbeing infilled under lower energy conditions than the proximal equivalents. With passage from the proximal to the distal facies, the floodplain sediments consist of increasinglymore backswamp, levee and crevasse-splay deposits as well as of sedimentsof small meandering channels operating in the overhank plain between the large maínstreams. The evaporitic complex at the top of the Triassic originates in en arid coastalintertidal belt and supratidal sahkha seam. Within the sandy braided river complexes,the different magnitudes and effectivities of currents in large channels,small watercourses and floodplain reaches are underlined by partially divergent, bimodalor even bipolar palaeocurrent directions. Copper mineralizations of mixed syngeneticand epigenetic type in the terrestrial red beds are associated with plantdebris in sediments of inactive to abandoned secondary channels and comprise azurite,chrysocolla and malachite. The Triassic palaeogeographical setting represents alarge bay between the European and African plates. Fluvio-lacustrine red beds ofBuntsandstein facies surrounded the bay and graded laterally into coastal and shallowmarine carbonates.
PB Springer Verlag
SN 0930-0317
YR 1985
FD 1985
LK https://hdl.handle.net/20.500.14352/64567
UL https://hdl.handle.net/20.500.14352/64567
LA eng
DS Docta Complutense
RD 9 abr 2025