Paleolimnological Evaluation of Lake Chapala (Western Mexico) During the Past 10,000 Years (CONACYT CB2011, Grant 168685, In Progress). PHASE II: Laboratory Work: First Results.

Zarate, Pedro

PP13B-2281
Paleolimnological Evaluation of Lake Chapala (Western Mexico) During the Past 10,000 Years (CONACYT CB2011, Grant 168685, In Progress). PHASE II: Laboratory Work: First Results.

Monday, 14 December 2015

Poster Hall (Moscone South)

Pedro F Zarate¹, Isabel Israde-Alcantara², Walter Dorfler³, Ingmar Björn Unkel⁴, Gabriela Dominguez Vazquez², Oliver Nelle⁵, Ivan Rosario Espinoza Encinas⁶ and CHAPHOLO, (1)University of Guadalajara, Chemistry, Guadalajara, Jalisco, Mexico, (2)UMSNH Universidad Michoacana de San Nicolás de Hidalgo, Depto de Geología y Mineralogía, Edif. U-4. Instituto de Investigaciones Metalúrgicas, Michoacan, Mexico, (3)Christian Albrechts University, Institute of Pre and Protohistoric Archaeology, Kiel, Germany, (4)Christian Albrechts University, Institute for Ecosystem Research, Kiel, Germany, (5)State Conservation Office, Archaelogy, Gaienhofen-Hemmenhofen, Germany, (6)Autonomus National University of Mexico, Earth Sciences Postgraduate Program, Hermosillo, Sonora, Mexico

Abstract:

At Lake Chapala (103° 02'W, 20° 15’N) a linear sedimentation rate of 2 mm a^-1 for the last 12,000 years was deduced from ten ¹⁴C dates. Due to the presence of very old hydrothermal bitumen (¹⁴C date: >40,000 years BP) a reservoir effect of c. 2000 years must be taken into account. Pollen results indicate a generally increase in dry forest taxa with an interruption during the middle Holocene. Diatom results allow a zonation into 6 paleoenvironmental phases.

Zone 1: From 27 to 26m depth (c. 12,000 yBP), Stephanodiscus niagaraeis the dominant taxa in coincidence with high TOC percents; a transgression into moister conditions is indicated.

Zone 2: From 26 to 17m (10,310–8720 cal BP) it is characterized by Aulacoseira granulata indicating an increase in ionic conditions and turbidity in lake as result of a decrease in lacustrine levels.

Zone 3: From 17 to 13m (8720-5950 cal BP) it is dominated by C. aff. kuetzingiana and the presence of temperate pollen taxa at 12 m (ca. 5000 YBP) suggest an increase in humid conditions in this interval.

Zone 4: From 13 to 8.5m (5950-2840 cal BP) encompass the middle Holocene. Stephanodiscus medius alternating with Surirella ovalis characterize this period and indicate very fluctuant conditions in coincidence with at a decrease of low TOC percents.

Zone 5: From 8.5 to 4m (2840-1580 cal BP), mark the establishment of modern conditions until present, with a peak in S. ovalis in coincidence with the high A. granulata, indicating low lake, saline, turbid and more extreme conditions at the base and top of this interval.

Zone 6: From 4 to 0m (1580 cal BP to Present) S. medius (over 50%), C. aff. dubius (20 to 40%), perifitic diatoms in low percents (<5%), and A. granulata and S.ovallis in spite of few percents, are observed in concordance with a return of saline conditions of the lake, indicate a regressive phase. Magnetic (susceptibility and paleomagnetism), microprobe analyses on tephra levels, X-ray Fluorescence (XRF) and Difraction (XRD) and anthracological studies are in progress.

PP13B-2281 Paleolimnological Evaluation of Lake Chapala (Western Mexico) During the Past 10,000 Years (CONACYT CB2011, Grant 168685, In Progress). PHASE II: Laboratory Work: First Results.

Abstract:

PP13B-2281
Paleolimnological Evaluation of Lake Chapala (Western Mexico) During the Past 10,000 Years (CONACYT CB2011, Grant 168685, In Progress). PHASE II: Laboratory Work: First Results.