NEOGENE PALEO-ENVIRONMENTAL ANALYSIS OF QUEBRADA LA HIGUERA SECTION, BAHIA INLGESA, NORTHERN CHILE

Author

Anthony Stevens, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2010

Degree Name

Master of Science

Department

Geology

First Advisor

Ishman, Scott

Abstract

Marine sediment samples were collected from Quebrada la Higuera, Chile to provide a record of planktonic and benthic foraminifera as a means of reconstructing the paleo-bathymetry and paleo-environment of the Quebrada la Higuera basin. The research area is located in northern Chile, south of Caldera in Quebrada la Higuera (S 27° 16.443, W 70° 54.887). The Quebrada la Higuera basin rests unconformably atop Mesozoic gabbroic basement, which is locally exposed, representing fault-bounded horsts and grabens. At the base of the section, diatomaceous sediment within the sequence suggests intervals of high productivity. The co-occurrence of the shallower water benthic species Nonionella miocenica and Epistominella pulchella with deep-water species Bolivina tumida, Uvigerina peregrina, Globobulimina auriculata, and Bolivina subfusiformis, at 10-23 m above the base of the section and again at 44-62 m, within fining-upward sedimentary packages suggests possible turbidites caused by transgressive-regressive cycles. Additionally, the occurrence and high abundance of these species are indicative of high productivity. A 30-40 cm Late Miocene phosphatic bed consisting of vertebrate and invertebrate fossils lies unconformably atop a poorly consolidated sand ~42 m from the base of the section. This phosphatic bed suggests that upwelling was occurring off the coast of Chile earlier than previously believed. The hyperaridity of Chile's Atacama Desert has been the result of the cold upwelling Peru-Chile current, which is further intensified by the rain-shadow effect of the Andes and the cold, dry descending Hadley cell. The occurrence of planktonic foraminifer Globigerina bulloides at the base of the section establishes the maximum possible lower age limit of 15.97 Ma (Middle Miocene). At 47 m, the co-occurrence of Globorotalia margaritae, Globorotalia crassaformis, and Dentogloboquadrina altispira establishes a maximum age limit for that horizon of ~3.6 Ma (Early Pliocene), providing an age range for the Quebrada la Higuera section from Middle Miocene through Early Pliocene. This study provides a record of planktonic and benthic foraminifera as a means of reconstructing the paleohistory of Quebrada la Higuera and more broadly through the Caldera region. The analyses address interactions between uplift, atmospheric conditions, sea level, and upwelling within the region from interpretations of the composite section, including facies relationship between sediments and occurring foraminifera species. These observations, along with the foraminiferal record, help broaden the understanding and development of the Quebrada la Higuera Neogene record.