Isotopic Variations of Oxygen (δ<sup>18</sup>O) in Benthic Foraminifera under Antiestuarine Conditions in the Colorado River Delta

• 作者: Ismael Yarbuh Karla Mejia-Pi?a Luis Antonio Cupul-Maga?a Miguel A. Santa Rosa-del Río Miguel Agustín Tellez-Duarte Raúl Herrera-Gutiérrez Rigoberto Guardado-France Ronald M. Spelz
• 来源期刊: 地质学期刊(英文)
• 学科: 医学
• 关键词: Stable ISOTOPES Living ASSEMBLAGES DEAD ASSEMBLAGES Upper GULF of California
• 年，卷（期）: 2018,（2）
• 页码范围: 104-123
• 页数: 20页
• 分类号: R73

摘要

Benthic foraminifera are excellent environmental indicators;CaCO3 test records the isotopic concentration of their surroundings and can be used to analyze environmental changes that occur during a certain time period. Stable isotopes, particularly those of oxygen (δ18O), are useful for interpreting ancient environments, given that they are used as “proxy” environmental variables (temperature and salinity). In this study, we provide ranges of isotopic variation in benthic foraminifera communities from the Colorado River delta. Four sampling campaigns were conducted in one year (2009-2010) in the adjacent subtidal zone of Baja California. Four transects with a total of sixteen sample station were drawn perpendicular to the coastline. Here, we recorded the following in situ: sand-type, salinity, and temperature. In the laboratory, 300 individuals per sample were separated, and sub-samples were taken for isotopic analysis. Data was processed using the software’s R 2.12.2, PAST 1.81 and Arc Map 9.3. Forty species were identified in the dead assemblages (Thanatocoenosis), whereas thirteen species were found in the living assemblages (Biocoenosis). The most abundant species in both communities belong to the genera Ammonia and Cribroelphidium. In the living assemblages, isotopic variation −2.15% to 5.94% within a temperature interval of 11°C, indicated antiestuarine conditions. In the dead assemblages, isotopic composition −3.04 to −0.74 served as a sign of estuarine conditions prior to damming.