Irbzer Formation

The Irbzer Formation is 100–440 m thick, that records the transition from marginal-marine to continental environments. It is divided into three members: Lower member (20–190 m): begins with marine-influenced phosphatic sandstones, sandy limestones and marly limestones rich in marine fossils (shark teeth, mosasaurs, bivalves), then passes upward into thick white-to-varicoloured marls, often gypsiferous, with charophytes, ostracods and dinosaur eggshell fragments. Middle member (2–55 m): sharp-based terrigenous interval resting on an erosive disconformity; composed of red sandstones, channelized polymictic conglomerates and siltstones with cross-bedding, ripples and bioturbation, reflecting fluvial-alluvial deposition. Finally, the Upper member (25–170 m): dominantly varicoloured or gray marls with basal gypsum in many sections, thin sandstones and occasional charophyte levels; deposited in restricted lacustrine–floodplain settings. == Paleoenvironment ==

During the Maastrichtian the inner area was situated within an anoxic marine setting, as revelated by bituminous, very oily and dolomitic black shells. Palynology of the underliying and coeval El Koubbat Formation has revelated an microbiota composed of Dinoflagellates, Pterospermopsis, Scolecodonts and Tasmanaceae. The formation reflects a shallow marine to lagoonal setting, transitioning from fine sands to marls and limestones. The presence of marine organisms, including bivalves and gastropods, along with phosphatic layers containing fish remains, indicates periodic marine incursions, with intermittent lagoonal or nearshore conditions. Oxidation and sedimentary discontinuities suggest episodes of exposure or subaerial erosion. The overall environment was likely a shallow, low-energy, marginal marine setting with occasional deeper marine influences. Marine Amniote fauna is known from coeval layers of the El Koubbat Formation, mostly Mosasaurs (Halisaurinae, Gavialimimus, Globidens, Mosasaurus, Prognathodontini) and Elasmosauridae plesiosaurs. == Biota ==

Charophytes Ostracods Echinoderms Fish Crocodylomorpha Sauropoda Theropoda == References ==