RT Journal Article
T1 Sedimentology, diagenesis and ichnology of Cretaceous and Palaeogene calcretes andpalustrine carbonates from Uruguay
A1 Alonso Zarza, Ana María
A1 Genise, Jorge F.
A1 Verde Cataldo, Mariano
AB The Cretaceous (Mercedes Formation) and Paleogene (Queguay Formation) deposits cropping out inWand SUruguay comprise two terrestrial limestone units that are very rich in trace fossils. The study of these unitspermits to propose a sedimentological model for palustrine limestones and calcretes in which the distributionof different types of trace fossils is considered. The study units include three main types of deposit: lacustrinelimestones, palustrine limestones and calcretes. The lacustrine limestones are relatively homogeneous andcontain gastropods, charophytes and ostracods, but no trace fossils. They were deposited in a relatively moreperennial lacustrine environment. The palustrine limestones include four different facies: desiccatedmudstones, nodular limestones, granular limestones and gravel-sheets. The desiccated mudstones indicatea lesser degree of pedogenic modification and the granular limestones a higher degree. The gravel-sheets arean indication of the reworking of previous limestones deposits during low lakewater levels. Most of thepalustrine limestones (except the gravel sheets) contain the same bioclasts as the lacustrine limestones plus avariety of trace fossils such as Rebuffoichnus sciuttoi, Fictovichnus gobiensis and different ichnospecies ofCelliforma. The calcretes are either massive (groundwater) or laminar. The massive calcretes are sandylimestones made up of a carbonate matrix and cements. The laminar calcretes (root mats), which containalveolar septal structures, occur as centimetre-thick layers and can be seen in all types of deposit. They containthe same trace fossil association as the palustrine limestones; the massive calcretes are poorer in such fossils.The distribution of trace fossils in these environments is under strong facies control and provides goodevidence of subaerial exposure and semi-arid climates. All the limestones are partially replaced and cementedby opal and quartz, but in all cases the primary structure is preserved. Silicification occurred undergroundwater meteoric conditions. Overall, the limestones facies (calcretes, palustrine and lacustrine) andtheir lateral distribution likely reflect the existence of wetland environments in semiarid to sub-humidclimates. These climatic conditions were interrupted by a period of increased precipitations, probably theEarly Eocene Climatic Optimum.
PB Elsevier
SN 0037-0738
YR 2011
FD 2011
LK https://hdl.handle.net/20.500.14352/44166
UL https://hdl.handle.net/20.500.14352/44166
LA eng
DS Docta Complutense
RD 7 abr 2025