Microtaphonomy of bioclasts and paleoecology of microencrusters from Upper Jurassic spongiolithic limestones (External Prebetic,Southern Spain) |
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Authors: | Matías Reolid Christian Gaillard |
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Institution: | (1) Dept. Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, Fuentenueva s/n, 18002 Granada, Spain;(2) UMR 5125 Paléoenvironnements & Paléobiosphère, Université Claude Bernard Lyon-1, 2-rue Dubois 69622, Villeurbanne, France |
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Abstract: | Microencrusters and microtaphonomic features of the Oxfordian spongiolithic limestones of the External Prebetic were studied
using thin-section analysis. The spongiolithic limestone is a bioclastic-rich packstone with common echinoderm, mollusc and
brachiopod remains. The bioclasts show a high fragmentation index and frequent microborings. The encrustation index (E
i) is higher for fragments of serpulids, ammonoids and bivalves, and increases with the initial grain-size of bioclasts. The
main microencrusters consist of benthic microbial communities (BMC) and nubeculariids, as well as subordinate calcareous and
siliceous agglutinated foraminifera, serpulids and bryozoans. BMC are usually the first colonizers, and encrusting foraminifera
mainly appear on bioclasts larger than 2 mm. BMC dominate in well-developed encrustations on upward facing surfaces of larger
bioclasts that are also colonized by foraminifera (nubeculariids and Subdelloidina). Bullopora, serpulids and bryozoans are more common on lower surfaces. The fact that the values of encrustation index, encrustation
thickness and diversity of the microencrusters increase with the size of bioclasts is related to a higher stability and exposure
time of the available bioclastic substrate. The microencruster distribution on upper and lower surfaces of large bioclasts
may be related to photic control, space competition and/or predation avoidance. |
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Keywords: | Microencrusters Paleoecology Taphonomy Upper Jurassic Southern Iberia |
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