Fossilization of ammonites and sedimentary events in deep environments of carbonate platform (highest Middle to lowest Upper Oxfordian, Iberian Range, Spain).



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Fernández López, Sixto Rafael and Meléndez Hevia, Guillermo (2004) Fossilization of ammonites and sedimentary events in deep environments of carbonate platform (highest Middle to lowest Upper Oxfordian, Iberian Range, Spain). Rivista italiana di paleontologia e stratigrafia , 110 (1). pp. 219-230. ISSN 0035-6883

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In the Ricla area (Zaragoza, Aragonese Branch of
the Iberian Range), at the top of the Yátova Formation, grey-reddish
wackestone limestones grade into yellow-green siliciclastic limestones
of the Aldealpozo Formation. These changes of facies between the two
successive formations are associated with syndepositional palaeoreliefs
developed during the Late Oxfordian. The uppermost deposits of the
Yátova Formation represent an Oxfordian condensed section, from the
upper Bifurcatus Zone (Middle Oxfordian) and Hypselum Zone (Upper
Oxfordian). These deposits are interpreted as developed in an open
marine, moderately deep carbonate platform, showing uniform lowenergy
conditions with extremely reduced carbonate and terrigenous
background sedimentation, and very low sedimentation rates. The low
diversity of the benthic fauna, scarce development of sponge bioherms
and ammonite populations inhabiting the platform are palaeobiological
criteria which corroborate these palaeoenvironmental conditions.
Ammonite assemblages are composed of Sub-Mediterranean
taxa. Over 900 ammonite specimens have been collected from the upper
Bifurcatus and Hypselum zones. Oppeliidae (45,2%) and Perisphinctidae
(37,9 %) are dominant. Aspidoceratidae (14,3%) are common. Haploceratidae
(2,2%) are scarce. Two phylloceratids and a lytoceratid have
been found. Ammonoids are commonly preserved as concretionary calcareous
internal moulds of reelaborated elements. Resedimented shells
are scarce. The degree of packing of ammonite remains and the stratigraphical
persistence display high values. Taphonomic features indicative
of sedimentary starving in deep carbonate platform environments are: 1)
high concentrations of reelaborated ammonites, 2) taphonic population
of type two, 3) phragmocones completely filled with sediment, and 4)
homogeneous concretionary internal moulds, bearing no signs of abrasion,
bioerosion or dense encrusting by organisms (such as serpulids,
bryozoans or oysters). In conclusion, the occurrence of these ammonite
associations confirms the development of an advanced deepening
phase, within a 3rd order deepening/shallowing cycle, in the Aragonese
platform, during the late Bifurcatus to Hypselum zones.

Item Type:Article
Uncontrolled Keywords:Taphonomy, Facies analysis, Stratigraphic condensation, Sedimentary condensation, Sediment starvation, Sea-level change, Upper Jurassic, Western Tethys
Subjects:Sciences > Geology > Paleontology
ID Code:23086
Deposited On:09 Oct 2013 11:43
Last Modified:11 Dec 2018 08:42

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