Unravelling hinterland and offshore palaeogeography from pre-to-syn-orogenic clastic sequences of the Betic Cordillera (Sierra Espuña), Spain

Abstract

The Malaguide Complex (Betic Cordillera) occurs in the Sierra Espuña area (SE Spain) providing a favorable setting to study a sedimentary successions from continental and shallow-marine to deep-marine environments using structural and stratigraphic relations, and petrological and geochemical signatures. The aim of this work is to outline the sedimentary evolution of the Malaguide Complex and the El Niño Fm. This succession is arranged into pre-orogenic (Paleocene-Early Oligocene) and syn-orogenic (Late Oligocene-Early Miocene) stages. The detrital modes of sandstones of the overall succession are heterogeneous and indicate a multi-source area, marked by exhumation till an unknown Malaguide basement and probably lower units of the Internal Betic Zone (e.g. Alpujarride Complex) in the case of the El Niño Fm. Pre-orogenic deposits are mainly carbonate with abundant skeletons of intrabasinal to extra-basinal larger foraminifera, calcareous lithic fragments and quartz grains, and metamorphic lithic fragments. Minor metamorphic lithic fragments occur in the Eocene deposits (i.e. Espuña Fm). Calcareous lithic fragments and extra-basinal fossils (lithoclastic bioclasts) are mostly present in the Early Oligocene pre-orogenic formations (i.e. As Fm) and were derived from the Paleocene-Eocene sedimentary successions of the Malaguide Complex. Syn-orogenic sandstones are quartzolithic with abundant metamorphic and sedimentary lithic fragments (slate, phyllite, fine-grained schist, ooidal grainstone, mudrock and quartz-rich siltstone fragments). Sedimentary lithic fragments were derived from the Mesozoic successions of the Malaguide Complex while metamorphic detritus is related to the Malaguide basement (probably also Alpujarride from Burdigalian on) that was exhumed starting from the Late Oligocene. Mudrocks of the syn-orogenic clastics, record an increase of phyllosilicate, quartz and feldspars and an abrupt decrease in calcite and dolomite. The abundance of calcite and dolomite, and traces of hematite occur dominantly in the pre-orogenic mudrocks. The geochemical signatures suggest a provenance mostly derived from felsic source rocks with a minor supply from mafic metavolcanic rocks in some samples of the syn-orogenic stage. The syn-orogenic formations (i.e. Rio Pliego Fm and El Niño Fm) are characterized by higher Cr/V values than the pre-orogenic formations suggesting a mafic supply for the syn-orogenic samples. In particular, the contents of Cr (average=85ppm) and Ni (average=48ppm) for the samples of the Rio Pliego and El Niño Formations are higher than those samples (Cr average=20ppm; Ni average=14ppm) of the pre-orogenic formations. Palaeoweathering indices suggest low to moderate weathering conditions for the source area(s). The Cenozoic studied succession played a key role in the geodynamic evolution of the Betic Cordillera, representing the key tectonic element of the western Mesomediterranean domains.