CENOMANIAN TURONIAN SPONGE MICROBIALITE DEEP-WATER HARDGROUND COMMUNITY (LIENCRES, NORTHERN SPAIN)/

A benthic community of sessile metazoans dominated by coralline sponge s (e.g. Acanthochaetetes and Vaceletia) is found within a Cenomanian-T uronian deep water hardground succession cropping out at the coastal a rea of the Bay of Biscay neat Santander. The characteristic K-strategi c community exhibits a very close taxonomic relationship with modern c ommunities from the Pacific realm, which allows for a comparison with Recent environmental conditions. The sponge community was associated w ith automicrites, microbialites, and thin mineralized limonitic biofil ms, This biofacies is typically found in cryptic niches of reefal buil dups (''telescoping''). The iron-rich biofilms had a strong electroche mical corrosive ability which explains the distinct submarine dissolut ion patterns. The hardground conditions are controlled, in part, by st rong contour current regimes linked with extremely oligotrophic water masses. This system was established during the drowning of a distal ca rbonate ramp during the early Middle Cenomanian (A. rhotomagense zone) . In the uppermost portion of the hardground (Late Cenomanian, upper R . cushmani zone) the coralline sponge community was replaced by thick limonitic stromatolites with numerous encrusting foraminifera (Miniaci na-type) and by colonies of the problematic iron bacterium Frutexites. This event is accompanied by an increase of terrigenous influx and de trital glauconite, indicating a fundamental change in food web, and te rminates the sponge dominated basal hardground interval. The hardgroun d was buried by hemipelagic sediments during the Middle Turonian (uppe r R. kallesi zone).