TITLE:
Fossil Stomatocysts in Upper Cretaceous Sedimentary Pyrite from Central Mexico
AUTHORS:
Carlos Castañeda-Posadas, Alberto Blanco-Piñón, Juan Hernández-Ávila, Silvia P. Ambrocio-Cruz, Liliana Lizárraga-Mendiola, Susana A. Ángeles-Trigueros
KEYWORDS:
Fossil Stomatocysts; Upper Cretaceous; Agua Nueva Formation; Mexico; Sedimentary Pyrite
JOURNAL NAME:
International Journal of Geosciences,
Vol.5 No.2,
February
26,
2014
ABSTRACT: In this paper six fossil forms of Chrysophycean stomatocysts
are described. The material was collected from sedimentary pyrite embedded in
well-laminated organic-rich limestone of the Upper Cretaceous Agua Nueva
Formation at the locality of Xilitla, Central Mexico. The stomatocysts are represented
by two spherical specimens with smooth surfaces lacking of ornamentation, three
ovoid forms with rugose textures, one of them exposing presence of pore without
collar, and one spherical specimen showing rugose texture and the presence of
two short and rounded projections. The specimens here described showed affinity
with some stomatocysts morphotypes described for brackish and fresh water, but
not for known marine specimens. The presence of these microfossils in the Agua
Nueva Formation represents the first formal description of fossil stomatocysts
in Upper Cretaceous sedimentary pyrite in Mexico. The occurrence of both micro
(planktonic foraminifera, calcispheres, radiolarians) and macrobiota
(ammonites, inoceramid bivalves and fishes) and the presence of the specimens
in sedimentary pyrite suggest that the stomatocysts were preserved under
oxygen-deficiency conditions in a low energy environment. This event could have
occurred in open marine waters in the Tampico-Misantla basin (Central Mexico) during
the late Cenomanian throughout the early Turonian.