--> ABSTRACT: Anatomy of Fluvial Sequences in Medial-Distal Megafan Zones (Caspe Fm. Ebro Foreland Basin, NE Spain), by Mariano Marzo, Pau Arbues, Lluis Cabrera, Sandra Blasco, Jordi Corregidor, Santiago Sánchez-Villanueva, and Isabel Vila; #90906(2001)

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Mariano Marzo1, Pau Arbues2, Lluis Cabrera2, Sandra Blasco2, Jordi Corregidor3, Santiago Sánchez-Villanueva2, Isabel Vila4

(1) University of Barcelona, Barcelona, Spain
(2) University of Barcelona, Spain
(3) Independent Consultant
(4) University of Barcelona

ABSTRACT: Anatomy of fluvial sequences in medial-distal megafan zones (Caspe Fm. Ebro foreland basin, NE Spain)

The Caspe Formation represents the medial to distal parts of a Late Oligocene-Early Miocene fluvial megafan (the Guadalope-Matarranya System, GMS) which evolved in the SE Ebro foreland basin. The radius of the GMS ranges from 30 to 60 km. The proximal successions are characterized by laterally extensive, gravel-dominated bodies and sheet-like sandstone bodies, deposited in braided streams. The medial to distal zones grade from sandstone to mudstone-dominated facies assemblages and are loosely organized as active channelized axes, flanked by interaxes zones where channels were scarcer. A variety of channel-fills developed in the medial to distal axis zones together with overbank and flood-plain deposits. The largest channels in medial zones were several tens of meters wide, less than 10 m deep and straight to low sinuosity. Their fills are mainly aggradational, formed by vertically stacked storeys individually fining upwards from coarse to fine-grained sandstone. Alternate, bank-attached bars and crescent shaped dunes were the dominant bed forms. Nevertheless, in some cases and due to upstream node channel avulsion, the channel-fills are dominated by small scale, delta-like progradational fills, with downstream gradation from fine-grained cross-bedded sandstones to silts, this resulting in the development of meter scale coarsening upwards sequences. Channel fills in the mudstone-dominated distal zones are isolated, linear, a few meters wide and less than 5 m thick, fine to very fine-grained sandstone bodies which show vertically accreted fills and/or small-scale lateral accretion. Local development of small, meter-scaled lobes is also recorded in these distal zones.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado