Holocene and Upper Pleistocene stratigraphy of Xochimilco lake, central Mexico

Abstract

The lacustrine system developed in the basin of Mexico has been of great interest in studies of various geological and social disciplines. Its sediments preserve the history of the environmental changes that occurred during the late Quaternary. Between 2016 and 2018, a set of lacustrine sediment cores were collected in the Xochimilco sub-basin, located south of the basin of Mexico. From these sedimentary sequences, a master sequence was constructed that represents the upper 66.5 m of the lacustrine deposits. For the establishment of its stratigraphic column, 15 lithotypes were defined from their sedimentary components in which the clastic components made up of silicates dominate, mostly silt and clay in size. The most abundant biogenic fraction is diatoms that frequently form oozes, and ostracods are a common component in most of the sequence, which locally form hashes. Interbedded with the clastic and biogenic lithotypes are volcaniclastic deposits. Eight lithological units were defined based on their dominant lithotypes. The time scale of the sequence is still uncertain for the oldest sediments; however, it is estimated that it covers the last 300000 to 350000 years. From this temporality, environmental oscillations of millennial scales are inferred. Diatom-rich laminated sediments represent the deepest phases in the lake. The deposits with higher biogenic and authigenic calcareous components indicate the phases of higher ionic concentration during which the lake was shallower. The detailed analysis of the stratigraphy and the description of the sedimentary components in Xochimilco allows to establish an initial interpretation of the variations in the depositional environments, and provides the base from which the detailed studies of paleoclimatic indicators will be supported.

Response of diatom assemblages to orbital‐ and millennial‐scale climatic variability since the penultimate glacial maximum in the northern limit of the Neotropics

“…Both Lake Chalco and Lake Titicaca show ecosystem rearrangements that follow orbital‐scale climate changes. This reorganization of the diatom community between freshwater and salt‐tolerant taxa could be a useful tool to identify boundaries between previous glacial maxima when analyzing other long lacustrine sequences from the Basin of Mexico that have been recovered recently (Lozano‐García et al 2017, Brown et al 2019, Ortega‐Guerrero et al 2022).…”

Ruby Xenocrystals in Dacite from Central Mexico

“…As stated by Ortega-Gutiérrez et al (2008) the lower crust of the TMVB and surrounding setting to the south, must be at granulite facies, with a minimum temperature between 700 800 °C, a crustal thickness about 40 45 km, and with the presence of garnet at the deepest levels. Nonetheless, higher temperatures for the granulite facies (950 112 ⁰C) have been proposed for central Mexico (Hayob et al, 1989) and 990 1100 ⁰C for southern Mexico (Ortega-Gutiérrez et al, 2011).…”

“…It is accepted that the occurrence of granulitic outcrops and xenoliths coming from the lower crust have been reported in Mexico (Hayob et al, 1989;Roberts & Ruiz, 1989;Ruiz et al, 1988). In central Mexico (TMVB and surroundings) in five localities, granulite facies xenoliths have been thoroughly studied even though they can be present in several other places (e.g., Pico de Orizaba, Carrazco-Núñez et al, 2005) et al, 2011) andChalcatzingo (Ortega-Gutiérrez et al, 2012), which are pelitic granulites constituted by pyrope rich garnet, sillimanite, rutile, spinel, corundum, cordierite, orthopyroxene, and Fe-Ti oxides with less common quartz and feldspar.…”

“…While iron, titanium, and nickel trace contents in sapphires result in a wide range of colors -yellow, green, blue, orange, black and pink-ruby chromophores derive from trace chromium (Al 3 substituted by Cr 3 + in the crystalline structure) (García-Lastra et al, 2005) and are less common than rubies with traces of vanadium or iron (Dubinski et al, 2020) which result in rubies ranging in color from orange-red to purplish-red. In Mexico, the presence of sapphire xenocrystals has been documented in an Oligocene andesitic dike (K/Ar = 29.20±0.30 30.50±0.60 Ma; Ortega-Gutiérrez et al, 2011). However, up until now, the occurrence of rubies has not been reported in the Mexican territory (e. g. Cruz-Ocampo et al, 2007).…”

Estimation of Toxic Hexavalent Chromium (Cr6+) in Metal Components Present in Electronic and Electrical Materials with or without using Coordinating Ligands

“…The literature [32, [49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67] given above can be summarized to two conditions: a) aqueous or acidic (pH = 1 -6) Cr 6+ <10 -3 M solutions and b) aqueous or acidic (pH = 1 -6) Cr 6+ >10 -3 M solutions.…”