Amaia Ordiales

BENTHIC FORAMINIFERA AND OSTRACODA FROM MIDDLE–UPPER MIOCENE SEQUENCES OF SOUTHERN ECUADOR

Abstract. The debate regarding a possible marine influence during the middle—late Miocene in the Loja, Malacatos-Vilcabamba and Catamayo-Gonzanamá Basins (southern Ecuador) continues. To shed light on this controversy, we present a detailed stratigraphic and micropaleontological (benthic foraminifers and ostracods) study of selected sections from these basins. The facies associations, together with the presence of several benthic foraminifer species from marginal marine and open-water environments and ostracod genera resistant to high salinity changes, verify a marine water influence and sporadic marginal marine conditions in this area during certain periods of the middle—late Miocene. Additionally, six new ostracod species are hereby described: Heterocypris ballentae, Cyprideis lojaensis, Cyprideis petersonae, Cyprideis pachamama, Cyprideis tumi and Cyprideis amaru.

ASOCIACIONES DE OSTRÁCODOS DEL MIOCENO TEMPRANO-MEDIO DE LOMA NEGRA (BARDENAS REALES DE NAVARRA, CUENCA DEL EBRO): EVOLUCIÓN PALEOAMBIENTAL DE UN MEDIO LACUSTRE

Abstract. LOWER—MIDDLE MIOCENE OSTRACOD ASSEMBLAGES OF LOMA NEGRA (BARDENAS REALES DE NAVARRA, EBRO BASIN): PALAEOENVIRONMENTAL EVOLUTION OF A LACUSTRINE SYSTEM. The palaeoenvironmental evolution of the Loma Negra section (Bardenas Reales de Navarra, Ebro Basin) during the lower—middle Miocene, is studied for the first time. The paleoenvironmental interpretation is based on the recovered ostracod assemblages and the sedimentology. The lower part of this section is composed by red, yellow and grey mudstones, and with Paralimnocythere sp. as the most abundant ostracod taxon. The lithological features and the faunistic assemblage allows the interpretation of a paleoenvironment with the development of shallow water bodies with stagnant, warm and fresh to oligohaline waters in distal alluvial flood plains for this section. The presence of some sandstone levels where the most abundant ostracod species is Cyclocypris laevis (Müller) marks punctual higher energy events inside this alluvial system and the presence of more saline waters. The upper part of the section is formed by grey limestones with interbedded fine grey mudstones. In this interval, Pseudocandona parallela Müller is the most abundant ostracod species, indicating the development of a stable lacustrine system with water currents, and temperate to cold and oligohaline to mesohaline waters. The transition between the alluvial and the lacustrine systems shows a gradual evolution.