Abstract: Sedimentology of Outer-Fan Depositional Lobes of Upper Miocene-Pliocene Laga Formation, East-Central Italy

Emiliano Mutti, Tor H. Nilsen, Franco Ricci Lucchi

More than 3,000 m of Laga Formation turbidites fill an irregularly shaped northwest-southeast trending sedimentary basin approximately 100 km long and 50 km wide. Paleocurrents generally indicate sediment transport southeastward, primarily from older arenaceous deposits uplifted along the southwestern margin of the basin. Sediments were deposited rapidly at an average rate of 100 cm per 1,000 years in stratigraphic sequences indicative of deep-sea-fan deposition. Deposits begin generally with channelized, thickly bedded strata near the base and end in nonchannelized, more thinly bedded strata toward the top. During part of the Messinian (upper Miocene), turbidites composed of evaporitic detritus also were deposited.

Twenty sections were measured and beds were traced laterally in the field to study the geometry, stratigraphy, facies variations, sedimentary structures, and paleocurrent patterns of four prominent sandstone bodies interpreted as outer-fan depositional lobes from the upper part of the Laga Formation. Exceptionally good exposures permitted the bodies to be examined in detail for distances of 5 to 10 km in both downcurrent and crosscurrent directions. The lobes, which range from about 10 to 35 m in thickness, most commonly form thickening- and coarsening-upward cycles indicative of progradational sedimentation. However, individual lobes are observed to: (1) change markedly in thickness both downcurrent and crosscurrent; (2) pinch out laterally; (3) change from thickening-upward to thinn ng-upward or symmetrical cycles; (4) change from multiple or complex cycles to simple cycles; and (5) contain individual beds and groups of beds that can be traced long distances with little change in character or thickness. These last sequences may represent basin-plain intercalations.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA