Palaeogeographic evolution of the eastern Iberian carbonate ramp during the Middle Oxfordian

• Autorzy: Ramajo J. , Bello J. , Melendez G. , Page K.
• Konferencja: International Congress on the Jurassic System (7 ; 06-18.09.2006 ; Kraków, Poland)
• Języki publikacji: EN

Abstrakty

EN

Sedimentation on the East Iberian carbonate platform during the Middle and early Late Oxfordian represents the onset of subtidal marine conditions after a long period (Middle Callovian - Early Oxfordian) where extremely shallow to temporarily emerged environments predominated, favouring the development of condensed deposits. A progressive deepening during the Middle Oxfordian led to the development of sponge and microbiolite buildups alternating with biostromes. Levels with inverted or fragmented sponges and bioclastic storm deposits mark the most energetic events. Ammonite assemblages comprise mainly drifted shells from open-marine areas with only short-lived episodes of colonisation. Five stages are distinguished in this Middle Oxfordian sequence. 1. Parandieri Subchronozone - Middle Oxfordian deepening begins. In deeper areas to the NW, carbonate sediments contain abundant, well-preserved sponges occasionally in upright position. In shallower distal areas (SE) across a palaeogeographic swell, sedimentation is limited to thin, condensed levels of iron-oolite limestones and sponge spicules. 2. Luciaeformis-Schilli Subchronozone interval - a widespread deepening event leads to the development of sponge limestone facies throughout the platform. Sponge biostromes and buildups are developed in the NW, and in distal areas (SE) biostromic levels with inverted sponges and tempestite levels with broken sponges are common. A brief ammonite colonisation event took place in the NW during the middle Schilli Subchronozone. 3. Rotoides Subchronozone - lower part forms a condensed sequence (representing a storm deposit interval) formed by bioclastic limestones with sponge fragments and ammonite internal moulds. In the SE this interval is represented by a centrimetic level of bioclastic and ferruginous pelloids, which grade laterally into layers with fragmented sponges and pellets. The upper, Wartae Horizon, is represented in NW areas by a more expanded sequence of well-bedded micritic sponge limestones. 4. Stenocycloides Subchronozone - a micritic limestone sequence containing fragmented and broken sponges occasionally in upright position develops in the NW. In the SE more condensed, pelloidal, glauconitic limestones with packed, inverted sponge fossils are present. Ammonite assemblages comprise mainly reelaborated moulds. 5. Grossouvrei Subchronozone - the lower part in the NW forms a homogeneous interbedding of micritic limestones and marls with an increasing quartz content upwards; sponges are generally inverted or fragmented. In the SE, pelloidal and glauconitic limestones are dominant. Facies analysis and taphonomic features of ammonites indicate that maximum depths were reached at around the Grossouvrei-Hypselum zone boundary.

Słowa kluczowe

EN

ammonites; taphonomy; environment reconstruction

• Wydawca: Państwowy Instytut Geologiczny - Państwowy Instytut Badawczy
• Czasopismo: Volumina Jurassica
• Rocznik: 2006
• Tom: Vol. 4, no. 1
• Strony: 103--104

Twórcy

autor

Ramajo J.

autor

Bello J.

autor

Melendez G.

autor

Page K.

• Departamento de Geologia (Estratigrafia), Univ. Zaragoza, Zaragoza 50009, Spain,