The ecology of Cenomanian lithistid sponge frameworks, Regensburg area, Germany

Upper Jurassic-Lower Cretaceous sponge biostromes and bafflestone mounds we re common and widespread in European temperate to tropical marine environme nts. They declined markedly during the Late Cretaceous. Most sponge framewo rks were paucispecific and ecologically simple, with only basic levels of s uccession or tiering. The occurrence of ecologically complex, lithistid spo nge biostromes and mounds in the Cenomanian Quadersandstein Member, Regensb urger Grunsandstein of the Saal Quarry, Bavaria, is therefore of special si gnificance. These are ecologically the most complex sponge frameworks yet r eported from the Cretaceous. Their size, morphology and ecological organiza tion compare favorably with shallow-water, sponge-dominated frameworks in m odern seas. The Saal Quarry sponge frameworks are generally associated with firmgrounds and condensed intervals in the transgressive systems tract of the Cenomanian-Turonian. tectonoeustatic supercycle UZA-2. The lowest spong e frameworks are up to Im high bafflestone mounds consisting of large, irre gular, sheet- and mound-like recumbent sponges overlain by diverse, cylindr ical, pyriform, upward-branching forms of Jerea and Siphonia. These biostro mes overlie a condensed interval or firmground which locally contains small , in situ pyriform sponges (Jerea pyriformis Lamouroux) as well as Middle C enomanian Inoceramus etheridgei Woods. The upper sponge frameworks consist of bafflestone mounds up to 4.4 m wide and 1.3 m high, composed of six lith istid sponge morphotypes, possibly representing several species of Jerea an d Siphonia. The occurrence of Rotalipora cushmanni in strata overlying the upper sponge framework indicates a Late Cenomanian age. Morphotypes preserv e internal sponge morphologies and partially dissolved spicules surrounded by a diagenetic halo of silicified, pelletoid grainstone and/or packstone. Silica cements were derived from spicule dissolution. Different combination s of these morphotypes dominate three to four successional stages of sponge framework growth, and show vertical ecological tiering within communities. This ecological zonation is consistent among frameworks, and is partially or wholly repeated between storm-related disturbance events.