Ichnology of the Miocene Jaraba Formation, Almazán Basin,NE Spain -Morphological characteristics and paleoenvironmental implications of distinct continental trace fossils

摘要

The Tertiary-age Almazán Basin is located in the western part of the Iberian Range, and formed during the Alpine Orogeny. The basin is a continental endorheic piggyback-basin, transported along the north-propagating Cameros Thrust, and was subjected to high subsidence rates resulting in a basin fill of more than 3500 m. The sediments comprise a deformed alluvial Paleogene succession with a maximum thickness of more than 3000 m as well as an extensive, sub-horizontally bedded alluvial Neogene-age succession that underwent exceptionally low deformation. High-resolution sedimentary facies analysis characterized the Jaraba Formation as a continental dryland succession. Three facies associations were identified, including (1) disorganized conglomerates associated with the facies association of alluvial fans spreading out from the SE' basin boundary, (2) organized channelized conglomerates and sandstones that are assigned to the facies association of the axial river system, and, (3) unchannelized fine-grained sediments, including structureless sandstones, corresponding to the facies associations of the flood plain and the sheetflood-subjected flood plain, respectively. The ichnocoenosis of the Jaraba Formation of the Almazán Basin contains a low-diversity ichnofossil assemblage, dominated by Skolithos, but also including Daimoniobarax, Macanopsis and Polychoredrites as well as abundant rhizoliths. A new ichnospecies, Polychoredrites cetinensis, is introduced. These traces can be linked to particular depositional subenvironments.