Coastal sediments from the Algarve: low-latitude climate archive for the Aptian-Albian |
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Authors: | Ulrich Heimhofer Thierry Adatte Peter A Hochuli Stefan Burla Helmut Weissert |
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Institution: | 1. Institute for Geology, Mineralogy and Geophysics, Ruhr-Universit?t Bochum, Universit?tsstr. 150, Bochum, 44801, Germany 2. Institute of Geology, University of Neuchatel, Emile-Argand 11, Case Postale 158, Neuchatel, CH2009, Switzerland 3. Palaeontological Institute, University of Zürich, Karl Schmid-Strasse 4, Zürich, 8006, Switzerland 4. Geological Institute, ETH Zürich, Sonneggstr. 5, Zürich, 8092, Switzerland
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Abstract: | The Late Aptian to Early Albian transition has previously been identified as a possible example of substantial climate cooling
within the mid-Cretaceous greenhouse period. To study the response of continental weathering and terrestrial vegetation to
this cooling episode at low- to mid-latitudes, marine nearshore deposits from the Algarve Basin (SW Portugal) have been investigated
with a combined approach including palynology, clay mineralogy and bulk-rock geochemistry. In the Lower Aptian part of the
succession, quartz-rich sandstone facies is accompanied by high abundances of early diagenetic kaolinite, which is interpreted
to reflect episodes of enhanced humidity and high meteoric flow-through. In contrast, the Late Aptian to Early Albian deposits
are characterized by high abundances of detrital clay minerals (mica and chlorite) indicating the dominance of physical weathering
processes in the source area, most probably related to low precipitation rates in conjunction with tectonically enhanced erosion.
Palynological data show a strong dominance of Classopollis pollen associated with low pteridophyte spore abundances, suggesting warm semi-arid to arid palaeoenvironments. Changes in
sedimentation patterns from varicoloured lagoonal marls to thick-bedded shallow-water carbonates are neither expressed in
the spore-pollen assemblages nor in the distributions of clay minerals which both remain essentially stable throughout the
Late Aptian to Early Albian. These relatively stable patterns are in contrast with various lines of evidence, predominantly
from high-latitude areas, that suggest a significant cooling during this time interval. Our study demonstrates that terrestrial
environments of low- to mid-latitude regions were not significantly affected by the Late Aptian - Early Albian “cold snap”. |
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Keywords: | Early Cretaceous Algarve Basin Palaeoclimate Palynology Clay mineralogy |
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