RT Journal Article
T1 The Upper Permian Boniches Conglomerates Formation:evolution from alluvial fan to fluvial system environments andaccompanying tectonic and climatic controlsin the southeast Iberian Ranges,central Spain
A1 López Gómez, José
A1 Arche, Alfredo
AB The Boniches Conglomerates Fm. (Upper Permian) represents the first episode of sedimentation in the southeastborder margin of the Iberian Basin, central Spain. The Iberian Basin commenced development as a rift basin runningmainly NW-SE during the Early Permian and underwent its first general extensional period during the Late Permian. TheBoniches Fm. was deposited as a small segment (less than 100 km long and 9-10 km wide) of the Iberian Basin thatextended in a northeast direction during this period.Detailed mapping and palaeocurrent analysis have shown that the Boniches Fm. is of a curvilinear, wedge-shapedmorphology. Sediments close to the southwest main faulted border are of a maximum thickness of 230 m. Clear lateralvariation in thickness controlled by the activity of secondary transfer faults perpendicular to the main NW-SE axis maybe observed. This network of faults permitted the formation of blocks, limited laterally by the transfer faults. Theseblocks experienced subsidence and rotation against the elevated southwest footwall block which resulted in the isolation ofreduced sub-basins with different sedimentary characteristics.Based on facies and facies association, the Boniches Fm. is thought to have evolved vertically from two main alluvialfan systems in the lowest part of the formation, into fluvial braided systems flowing southeast. As expected, no floworientations towards the footwall block are observed during the first episodes of the refill. This may be explained byerosion, or simply a lack of sedimentation due to the gentle slope. The change from alluvial fan to fluvial environments isinterpreted as a relatively sudden tectonic reorganization of the whole segment favouring new longitudinal fluvial drainagefrom a transfer zone located to the northwest. Three different reorganization episodes, clearly marked in the Boniches Fm.as 'main boundary surfaces' (MBS) separate four members subdivided into 4-5 levels (34 m thick). Each level consistsof fining-upward successions less than 1 m thick.Tectonics and climatic factors clearly controlled sedimentation. Tectonic activity was probably of greatest importanceand was conditioned by the movement of the main NW-SE and NE-SW transfer faults. The role of climate in ancientconglomerate sediments has not been well established. Palaeogeographical, mineralogical, sedimentological and clastanalyses suggest that the Boniches Fm. was deposited under humid conditions by running water. The differentiation between 'proper' alluvial fans and fluvial environments during the transition period of the BonichesFro. is not clear since, in many recent alluvial fans, braided fluvial systems are associated with fans.
PB Elsevier
SN 0037-0738
YR 1997
FD 1997
LK https://hdl.handle.net/20.500.14352/57797
UL https://hdl.handle.net/20.500.14352/57797
LA eng
DS Docta Complutense
RD 19 may 2024