Preservation of Organic Fossils at the Las Hoyas Formation, Spain - Biopolymers: A Molecular Paleontology Approach - page 162

An alternative explanation for organic matter preservation is the incorporation of
labile lipids into a resistant aliphatic macromolecule via in situ polymerization (see
Briggs 1999 for review). This is based on evidence obtained from analyses of organ-
ically preserved macrofossils of plants, arthropods (Briggs 1999 ), graptolites and on
simple thermal maturation experiments (confi ned pyrolysis in gold tubes). Although
plant and insect cuticles have been studied extensively, little is known about the
organic preservation of fossil fi sh. This investigation considers the molecular pres-
ervation of fossils from the Las Hoyas Formation (Cretaceous, Barremian, c.
126 Ma) of Spain with emphasis on the organic preservation of fi sh in relation to
their modern counterparts.
Geological Setting and Fossil Material
The fossils of the Konservat-Lagerstätte of Las Hoyas (La Huérguina Limestones
Formation, Upper Barremian, Serranía de Cuenca, Spain) are preserved in fi nely
laminated limestones composed almost entirely of calcium carbonate with a small
fraction of clays and organic matter. These limestones were produced in the context
of a continental (freshwater) subtropical, seasonal summer wet, carbonate wetland
that overlay a low-relief karstic terrain. The wetland was drained by carbonate-rich
freshwater and comprised a typical environmental mosaic of swampy plains, ponds,
lakes, ephemeral channels and sloughs. Fossiliferous laminated sediments formed in
a pond covered by thick microbial mats (Fig. 11.1 ) that experienced strong cyclical
oscillations of water level. During seasonal fl ooding and prolonged wet periods
lacustrine sedimentation dominated including chemical and bioinduced precipitation
of calcium carbonate and accumulation of thin microbial mats. Microbial mats and
Fig. 11.1 Wet ( a ) and dry
( b ) microfacies from Las
Hoyas laminated limestones
(La Huérguina Formation,
Upper Barremian, Serranía de
Cuenca, Spain) (After
Fregenal-Martínez 1998 ).
Scale bar in millimeters