FROM SHELF TO BASIN, ANATOMY OF A GLACIATION RECORD(UPPER ORDOVICIAN, MOROCCO; ANR SEQSTRAT-ICE PROJECT2013-2017)

International audienceWe investigated the Hirnantian glaciation record based on sedimentology, 3D architecture, palynology,carbon isotopes and provenance study. Four settings of the Moroccan Gondwana platform are documented:proximal and distal shelves, shelf canyons and “deep-water” fans; the three former experiencing subglacialerosion during the glaciation acme. Contrasted successions at the 100 km scale allow inspection of sedimentpartitioning through the glacial event.The proximal shelf shows storm-dominated highstand wedges eroded by poorly differentiated glacialsurfaces or deeply truncated by sand-filled tunnel valleys. The main part of the record however consists of asingle glacial retreat succession comprised of a glaciomarine wedge and an overlying forced regressive delta,both coeval with the final glacio-isostatic rebound (cf. presentation by P. Dietrich et al.).In the distal shelf, glacio-eustatic lowstand wedges bounded by flooding surfaces recorded the glaciationonset occurring more inland. Later, the glacial record s.s. is accommodated in shallow glacial incisions flooredby glaciofluvials. Prior to the glacial maximum, glaciomarine and tidal deposits constitute fingerprints ofsubordinate retreat phases. The glacial maximum-ice-sheet front at > 200 km beyond the study area-isrestricted to a single glacial surface and an ensuing glacio-isostatically forced progradation; the latter beinginterrupted by an ultimate glacial advance (an ice lobe?), which built a fold-and-thrust belt deforming outwashsands. Shelf canyons, 350 m) includes a single glaciomarine interval and two coarsergrainedsandsheets (50-75 m) representing oversupplied conditions. A 13C isotopic signal allows its correlationwith basins of intermediate latitudes. Whether the turbidites were issuing from a canyon or from a shelf apronis unknown but most of the succession relates to the glaciation acme. The poor development of glaciomarinedeposits suggests a buffer-in-canyon grounding-line fans or subaerial sandar, respectively between the ice frontand the deep-water depocenter. Detrital zircon geochronology suggests a significant contribution of reworkedpreglacial deposits remobilized at lowstand conditions. Actual glaciogenics tied to maximum glacial advancesrepresent less than 50% of the succession. Those are mature sandstones remobilized via subglacial erosionfrom the inner glaciated platform. None of the four settings offers a comprehensive glacial record, yet separately, each fairly documentsone particular stage within the glaciation development (e.g., glacial advances preceding the glaciation acme,early glacial retreat). Waiting for a refined Hirnantian chitinozoan biozonation, high-resolution correlationsfrom one setting to the other essentially rely on sequence stratigraphic inferences. A provenance study iscurrently in progress to corroborate the shelf-scale correlation framework. Correlations with glacial cyclespreserved over the inner platform (Mauritania, Algeria, Libya) remain controversial