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Synsedimentary Tectonics in Late Cretaceous-Early Tertiary Pelagic Basin of Northern Apennines, Italy

Alessandro Montanari, Lung S. Chan, Walter Alvarez

The sequence of Upper Cretaceous-Lower Tertiary pelagic limestones in the Umbria-Marches Apennines of Italy have recorded, with remarkable continuity, the geologic history of an epeiric sea on the eastern continental margin of the Ligurian Ocean during a time of widespread tectonism in the western Tethys domain. Sedimentary facies and paleocurrent analyses indicate that intrabasinal depocenters and structural highs have formed in response to extensional tectonic movements which started to affect the central part of the paleobasin in the early Turonian. The topography of the paleobasin was probably controlled by a complex pattern of buried fault blocks formed during the passive margin phase of the western Tethys and then reactivated in the Turonian after a prolonged time ( ptian to Cenomanian) of tectonic quiescence. Calcareous turbidites essentially made of remobilized pelagic mud were generated on the newly formed intrabasinal slopes and deposited in the adjacent depocenters. Conspicuous sedimentary events such as maxima in turbiditic deposition and soft-sediment slumps in these intrabasinal depocenters are attributed to major syndepositional earthquakes of regional extent. A detailed event-stratigraphy based on these sedimentary features indicates that the level of syndepositional tectonic activity reached a peak in the late Maastrichtian-early Paleocene and rapidly diminished in the Eocene.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.