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Tectonic breakup in the Eastern Betic zone

10/25/2019 / Leave a comment

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.

Paleogene sedimentary evolution of the Alicante Trough

08/27/2019 / Leave a comment

A new work to illustrate a changes in the evolution of the Alicante Trough located to the southeastern part of the sudiberian paleomargin and north to the supposed elevated sea floor forming a marine platform. Here the link to the work in Repository of the UA.

The Paleogene Alicante Trough of the South-Iberian Margin (External Betic Zone) consists of a narrow sedimentary basin that has active margins located to the north-northwest (active mainly during the Eocene) and to the south-southeast (active during the Oligocene). Both margins, consisting of shallow unstable platforms, were the source areas for the external-platform slope (in the opposite margins) and deep-basin (in the middle) depositional realms. The southern margin, lost under the Mediterranean Sea, is recognized only by the reconstructed Oligocene slope sediments.

Geological sketch map of the Alicante region of the study area (External Betic Zone) within the Internal Prebetic (North-Northeast sector) and Intermediate sub-Domains (south-southwest sector).

The eight successions studied, on opposites external-platform-slope margins and the deep within the central part of the basin, lead us to divide the basin into two depositional realms: the subsident Western Depositional Area (WDA) and the not subsident Eastern Depositional Area (EDA). This study has also enabled us to divide the infilling of the basin into two depositional sequences: Eocene p.p. (EDS) and Oligocene p.p. (ODS) in age, respectively, bound by two sequence boundaries (unconformities) at the Early Eocene (P6 zone) and Early Oligocene (P19 zone). The EDSand ODSare comprised of turbiditic and olisthostromic deposits and frequently slumps, evidencing an active tectonic in the margin-basin system.

Stratigraphy, correlation, sampling localization and main sedimentary cycles recognized (Eocene p.p. and Oligocene p.p.) of the studied successions in the Western (WDA) and Eastern EDA) Depositional Areas.

Chronostragraphy of the studied successions.

The correlation of the Paleogene sedimentary reconstructed in the Alicante Trough with other four synthetic successions throughout the External (three in the Subbetic Domain) and one in the Internal Betic Zone indicate a Paleogene generalised deformational framework.

Main Eocene and Oligocene sedimentary realms and location of the studied successions in the Internal Prebetic and Intermediate sub-Domains.

Sedimentary record and new sequential stratigraphy in the study area.

In addition, this evolution is contemporaneous to the Pyrenean, Iberian and the Nevado-Filabride Alpine deformation. The Paleogene tectonic recognised in the External Betic Zone is younger since the main orogenic deformation took place in the late Burdigalian to early Tortonian.