Summary

In the central part of the Ebro Basin, Latest Oligocene-Late Miocene lacustrine carbonate deposits include, among other facies, laminated limestones and stromatolitic limestones, which formed in low to moderate saline waters. Three subfacies are differentiated within facies L1: L1.1: with ripples, lenticular or wavy bedding; L1.2: with hummocky cross-stratification (HCS) and L1.3: with parallel or pseudoparallel lamination. All of them consist of alternating micrite laminae and detrital laminae and lenticules, organized as single, fining-upward units, mm to cm thick. Associated facies are stromatolitic limestones (Ls) and marls (M).

In a complete deepening-shallowing lacustrine sequence, laminated deposits show two vertical successions of facies: i) Erosive surface/Ls->L1.1 or L1,3->L1.2->L1.3->M, typical of deepening events, and ii) (L1.3)->L1.2->L1.3 or L1.1->Ls, present in shallowing events. Amalgamation of successive L1.2 or L1.3 layers is common. Gutter surfaces can be present in all three subfacies. Stromatolites occur as bioherms, biostromes and encrustations.

Subfacies L1.1 and L1.2 reflect the influence of storm waves above storm wave-base, HCS resulted from combined oscillatory flows and and unidirectional currents. Subfacies L1.3 could be formed both below storm wave-base by storm-induced bottom currents, and above storm wave-base, in marginal, shallow lacustrine areas from sheet inflows. All these deposits suggest that surge dynamics was a dominant factor during the development of carbonate saline lake-systems, where stromatolites represent periods of fair-weather conditions.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah