The Westernmost Tethys Blog

10/29/2019

Regional geology field trip to Teruel

Filed under: Iberian range,Paleozoic — Tags: , , — messinianalicante @ 6:36 PM

Students of the third course of Geology of the Alicante University within the subject of Regional Geology: visit Jarafuel triassic section, Aguaton jurassic section, Murero paleontological site, Fombuena section, Santa Cruz Paleozoic Seas Museum, Ojos Negros Mine, and Orea-Checa road Hirnatian section.

Student in the Aguatón “tunnel” section

The visit took place from 16 to 19 October of 2019 and the professors in charge were Juan Alberto Pérez-Valera and José Enrique Tent-Manclús.

Zoophycos found in the Devonian Santa Cruz de Nogueras Formation, near the village of Santa Cruz de Nogueras. The specimen is now in the Paleozoic Seas Museum.

10/25/2019

Tectonic breakup in the Eastern Betic zone

Six Paleogene-Aquitanian successions have been reconstructed in the Alicante area (eastern External Betic Zone). The lithofacies association evidences “catastrophic” syn-sedimentary tectonic processes consisting of slumps, mega-olisthostromes, “pillow-beds” and turbiditic deposits  (Figure 1).

Figure 1. Field photos of the main macro-tectofacies found in the study area (see text for details). (A) A typical Lower Eocene sequence of the Villafranqueza section. (B) Calcarenite turbidite with convolute bedding (Lower Eocene, Villafranqueza). (C) Two Oligocene carbonate turbiditic channelized bodies (Busot). (D) Oligocene conglomeratic bed with erosional base and reverse grading of clasts, typical of debris flow deposits (Busot). (E) Oligocene slumped level and pillow-beds (Busot). (F) Oligocene mega-flute casts indicating a northwestwards-directed paleocurrents (Relleu). (G) Oligocene pillow-beds (Relleu). (H) Oligocene mega-olisthostrome with huge blocks (Playa Nudista). (I) Slumped megabed (Playa Nudista).

This kind of sedimentation is related to unconformity surfaces delimiting sequence and para-sequence cycles in the stratigraphic record (Figure 2).

Figure 2. Unconformities, associated gaps of the Eocene and Oligocene-Miocene depositional sequences compared with the sedimentary cycles of (Vera, 2000). The figure shows a basement tectonic interpreted as folding during the Eocene and blind thrust during the Oligocene-Aquitanian. The different evolutionary trends are discussed in the text.

The data compiled have enabled the reconstruction of the Paleogene-Aquitanian paleogeographic and geodynamic evolution of this sector of the External Betics. During the Eocene the sedimentary basin is interpreted as a narrow trough affected by (growth) folding related to blind thrust faulting with a source area from the north-western margin, while the southeastern margin remained inactive. During the Oligocene-Aquitanian, the sourcing margin became the southeastern margin of the basin affected by a catastrophic tectonic (Figure 3).

Figure 3. Paleogeographic-geodynamic model of the Alicante Trough during Eocene and Oligocene-Miocene times.

The activity of the margins is identified from specific sediment sources area for the platform-slope-troughsystem and from tectofacies analysis. The southeastern South Iberian Margin is thought to be closer to the Internal Betic Zone, which was tectonically pushing towards the South Iberian Margin. This pushing could generate a lateral progressive elimination of subbetic paleogeographic domains in the eastern Betics (Figure 4).

Figure 4. Synthetic Oligocene-Aquitanian paleogeographic-geodynamic model proposed for the western.

This geodynamic frame could explain the development of such “catastrophic” tectono-sedimentary processes during the Late Oligocene-Early Miocene.

Cite as: Guerrera, F. and Martín-Martín, M. (2014): Paleogene-Aquitanian tectonic breakup in the Eastern External Betic Zone (Alicante, SE Spain). Revista de la Sociedad Geológica de España, 27(1): 271-285.

 

10/07/2019

Nearshore Mid-Triassic Zoophycos

Filed under: Iberian range,Tethys — Tags: , , — messinianalicante @ 12:53 PM

 Zoophycos is a well-known trace fossil common throughout the Phanerozoic. Paleozoic forms show important differences in morphology and habitat distribution with respect to the Jurassic, Cretaceous, and Cenozoic ones. Therefore, Early–Middle Triassic is considered a crucial time-span for the understanding of the evolution of this trace fossil. So far, Early Triassic  Zoophycos is unknown and Middle Triassic forms were recorded only in deposits from Thuringia. The morphology and paleoenvironment of  Zoophycos from the middle–upper Muschelkalk of the Iberian Range is herein described.

Zoophycos ichnoassemblage. Note the very small dimensions and poor vertical development of the trace fossils. Top view of a well-preserved Zoophycos. The flower-shaped outline is well visible as is the apex in the central part of the structure.

 

The best-preserved trace fossils occur in a dolomicritic bed Ladinian in age, and are represented by small forms with a subcircular, slightly lobed outline and very little penetration depth. They were deposited in a very shallow, quiet-water environment with transition to supratidal/emerged areas. The low diversity of both trace fossils and skeletal remains point to stressful conditions related to strong salinity variations and/or poor water circulation. A comparison was made with  Zoophycos from Anisian deposits of the Muschelkalk in Germany. This showed that both forms are quite simple and penetrate only the shallowest tiers, although they are different in whorl outline and lobe shape.

Reconstruction of the most common Zoophycos form of the Jarafuel section. W lobe width, L lobe length, H height of the whole structure.

This confirms that, notwithstanding the morphological variability of this group,  Zoophycos still maintained a quite simple structure in the Triassic. A shallow-water environment was deduced for both localities, confirming that at least until the Early Jurassic  Zoophycos had not definitively migrated toward deep-water areas.

Cite as: Giannetti, A., Tent-Manclús, J. E. y Baeza-Carratalá, J. F. (2017): New evidence of nearshore Mid-Triassic Zoophycos: morphological and paleoenvironmental characterization. Facies, 63,16: 1-12. DOI : 10.1007/s10347-017-0498-8

Powered by WordPress