RT Journal Article
T1 Taphonomic analysis and sequence stratigraphy of the Albarracinites beds(lower Bajocian, Iberian range, Spain).An example of shallow condensed section
A1 Fernández López, Sixto Rafael
AB Several ammonite fossil assemblages from Sierra de Albarracín (Teruel, Castilian Branch) contain abundantspecimens of the Ovale and Laeviuscula zones (lower Bajocian, Middle Jurassic), including microconchs andmacroconchs of the characteristic genus Albarracinites. Over 1500 ammonites from the type horizon of the species A.albarraciniensis, in the outcrop of Masada Toyuela, have been studied.Ammonites are commonly preserved as phosphatized, calcareous, concretionary internal moulds (mean size =50.5 mm) of unflattened shells, partially or completely filled with relatively heterogeneous mudstone to wackestonesediment. Incomplete, fragmented phragmocones with calcitic septa are the dominant remains, generally bearing tracesof rounding, incrustation and bioerosion. Taphonomic data, such as the predominant taphonomic populations of type 3,composed of reelaborated, relatively heterogeneous concretionary internal moulds, isolated concretionary body chambersand hollow ammonites, bearing traces of abrasion, bioerosion and encrusting organisms, are indicative of low rateof sedimentation and occasional high rate of sediment accumulation, due to sedimentary winnowing and bypassing interruptedby storm depositional events, in shallow-water marine environments. The exceptional occurrence of taphonicpopulations of type 2 belonging to Albarracinites and Hebetoxyites, with dominant shells of pre-adults and absence ofjuveniles, suggests autochthonous biogenic production of shells by indigenous populations of Sub-Mediterranean taxaat the Iberian platform system.In the outcrop of Masada Toyuela, the Albarracinites beds correspond to a condensed section, developed in shallow-water, open-marine, carbonate environments of the External Castilian platform. The sharp, irregular base of bedsand the normal grading of reworked elements suggest these carbonate deposits were affected by tractive currents, scouringand redeposition. Limestone beds represent storm-related sedimentary events, whereas the local marly intervals representbackground-sedimentation time-intervals of winnowing and bypassing on the seafloor. This condensed sectionis composed of at least four, decimetric or centimetric, expanded-deposit intervals, stacked and showing an overall thinningupward, which constitute a deepening sequence developed during two biochrons. Taphonomic results also corroboratethe development of an incipient-deepening phase, which represents the first episode of a deepening half-cycle ofthird order, in the Albarracín area within the Castilian platform, during the Ovale and Laeviuscula biochrons (earlyBajocian).
PB Société géologique de France
SN 0037-9409
YR 2011
FD 2011
LK https://hdl.handle.net/20.500.14352/44123
UL https://hdl.handle.net/20.500.14352/44123
LA eng
DS Docta Complutense
RD 18 abr 2025