Huesser Horizon: A Lake and a Marine Incursion in Northwestern South America During the Early Miocene

Abstract

The Cenozoic stratigraphic sequence in the foothills of the Eastern Cordillera of Colombia is mostly fluvial in nature and very thick (ϳ8000 m), but it contains very few mollusk-bearing horizons. Recent fieldwork discovered a well-preserved molluscan assemblage that occurs near the top of the Carbonera Formation (lower Miocene) in the central foothills of the Eastern Cordillera. This level, named the Huesser horizon, is laterally extensive and can be followed for tens of kilometers. The horizon is 10 m thick and was divided into eight levels, five of them highly fossiliferous. Most of the levels are dominated by the freshwater gastropod Sheppardiconcha, with lower abundances of the bivalves Anodondites and Mytilopsis. The top level is dominated by specimens from the bivalve family Arcidae. The taxonomic composition of the assemblage is similar to that of the Magdalena and Amazonas Basins during the early-to-middle Miocene. Paleoecologic, taphonomic, and palynological analyses indicate that the Huesser accumulated in a freshwater lake system, capped by a marine incursion. The development of a large lake and the subsequent marine event could be related to increasing subsidence coincident with eustatic sea-level rise that has been identified for the basin during the early Miocene.

Episodic orogenic front migration in the northern Andes: Constraints from low‐temperature thermochronology in the Eastern Cordillera, Colombia

“…First, two‐dimensional flexural models require tectonic loads in the Quetame Massif to match the reconstructed middle Miocene flexural profile in the Llanos basin [ Bayona et al , 2008]. Second, an increase in the sediment accumulation rates recorded by the early to late Miocene Upper Carbonera Formation in the Medina wedge top basin [ Parra et al , 2007; Gómez et al , 2009; Parra et al , 2009] and the Llanos foredeep [ Bayona et al , 2008] suggest an eastward advance of the orogenic front and the corresponding loads from their position along the axial Eastern Cordillera during the late Eocene‐Oligocene. Finally, the offset of the basal Cretaceous unconformity across the Cenozoic faults, as noted by Mora et al [2006, 2009], illustrates that the Naranjal fault is one of many Mesozoic normal faults that have undergone only minor Cenozoic contractional reactivation (see Figure 7).…”

The Origin of the Modern Amazon Rainforest: Implications of the Palynological and Palaeobotanical Record

“…Mangrove fl oras dominated eastern Amazonia near Belen (Leite 2004), while fl uvial systems of local origin prevailed in western Amazonia (Hoorn 1994a), and scattered lacustrine settings existed near the incipient Andean Eastern Cordillera (Gomez et al 2009 Psilaperiporites minimus…”

A phylogenetic and morphologic context for the radiation of an endemic fauna in a long-lived lake: Corbulidae (Bivalvia; Myoida) in the Miocene Pebas Formation of western Amazonia

“…A close phylogenetic affinity between Pa leocene North American and Neogene South American freshwater corbulids requires a gap of about 50 Myr between stratigraphic occur rences. No freshwater corbulids of Eocene or Oligocene age are reported from the Amer icas, although several lacustrine faunas are well documented, including those of the Cretaceous to Eocene Sheep Pass Formation of Nevada (Good 1987), Paleocene Flagstaff Formation of Utah (La Rocque 1960), Eocene Green River and Wasatch Formations of Wyoming (Hanley 1977), Eocene/Oligocene Los Corros Formation of northern South America (Pilsbry and Olsson 1935), and lower Miocene Carbonera Formation of Colombia (Gomez et al 2009). A similar gap is seen between Eocene occurrences of freshwater rays in the Green River Formation and Miocene occurrences of Potamotrygonidae species in South America (Brito and Deynat 2004;Antoine et al 2007).…”