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Michael Talbot, University of Bergen (Norway)
Camilla Thrana, StatoilHydro (Norway)
Catherine Baird, ConocoPhillips (Norway)
Kjersti Soltveit, University of Bergen (Norway)
Niels Bo Jensen, IRIS (Norway)
Ivar Grunnaleite, IRIS (Norway)
Gunnar Sælen, IRIS (Norway)
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The mid- to late Miocene was a time of significant tectonic activity in the Mediterranean region, related to the closing stages of the Betic and Alpine orogenies. One consequence of this activity was the development of fault-controlled straits or seaways along the southern margins of the Iberian and European plates Several of these straits were filled by keletal sands and gravels which today form significant volumes of bioclastic limestones or mixed carbonate-siliciclastic deposits with excellent poroperm properties. This poster presents two examples of such strait deposits from southeastern Spain. Both are dominated by warm-temperate bioclastic carbonates, but display contrasting large-scale facies.
The first example is from the Upper Tortonian Azagador Mbr. which accumulated in a ca. 1.5 to 3 km wide strait that joined the Sorbas and Vera basins. The strait deposits are dominated by large-scale mixed calcarenite and siliciclastic sand sheets cut by giant trough structures. The latter form "channels" up to 30 m deep and 100+ m in width filled by a mixture of coarse-grained, subaqueous dune deposits and intensely bioturbated (predominantly Thalassinoides and Scolicia) coarse, bioclastic sands. Marginal to the bioclastic dunes and troughs are debris-flow deposits, suggesting that mass flows played an important role in transporting bioclastic debris from factory areas along the adjacent coastline.
Our second example is from the Upper Serravalian La Escalera Fm. (informal name), west of Moratalla (Murcia). Here, a strait formed between fault-controlled ridges of Eocene and Palaeocene limestones within the Internal Prebetic Zone. Giant-scale trough structures are lacking, instead the initial coarse, bioclastic strait deposits are characterised by large-scale tabular cross-bedding with sets up to 5 m thick representing aqueous sandwaves. Rhodoliths are an important component of the sediments. Lenticular, coarse-grained debris-flow deposits containing large clasts of basement rocks shed from the steep strait margins occur at some localities. Succeeding the sandwave calcarenites is a 60-100 m thick, laterally extensive package of coarse, trough cross-bedded aqueous dune deposits with a typical set thickness of 1-2 m.
In both examples, the initial strait deposits are dominated by coarse to very coarse bioclastic limestones. Fine-grained deposits are virtually absent suggesting that sediment accumulation occurred in an environment dominated by consistently strong marine currents, possibly amplified by the narrow geometry of the strait. Substantial thicknesses (>100 m) of such limestones form linear sediment bodies extending several km. to 10's of km, suggesting that mid- to late Miocene strait deposits may form a previously unconsidered hydrocarbon play in the region.
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