Palynology and sequence stratigraphy of the Cretaceous
of eastern Venezuela
J. Helenes and D. Somoza 1999 Cretaceous Research,
No. 20, 447–463
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This paper reports on
the stratigraphy and palynological content, particularly dinoflagellates, of Cretaceous
strata drilled in an allochthonous thrust block from the Eastern Basin of
Venezuela.
In the relatively
shallow marine environments of deposition commonly indicated in the sections studied,
dinoflagellates provide better biostratigraphic resolution than either
planktonic foraminifera or calcareous nannofossils. A Palynomorph Marine Index
is useful in identifying flooding surfaces and sequence boundaries within these
deposits.
Cretaceous strata in
the subsurface of eastern Venezuela have a maximum thickness of 3658 m and
encompass ages ranging from Barremian to Maastrichtian. Seven stratigraphic
sequences are recognized and correlated with Supercycles LZB-3 to TA-1 of Haq et
al. (1988).
The first important
flooding surface corresponds to the lower part of the El Cantil Formation, and represents
the Aptian transgression correlated to the condensed section dated at 111 Ma.
The Albian transgression found in the upper part of the El Cantil Formation is
correlatable to the condensed section dated at 98.5 Ma. After this transgression,
and for most of the Cenomanian, deposition in shallow marine environments, with
an input of large amounts of terrestrial palynomorphs, is indicated.
The most important
maximum flooding surface observed corresponds to the Turonian transgression (91.5
Ma) of the Querecual Formation, and can be correlated with sections in western
Venezuela and Colombia. The Santonian flooding surface in the lower part of the
San Antonio Formation is correlated with the condensed section dated at 86 Ma,
and the early Maastrichtian flooding surface in the upper part of the San
Antonio Formation with the condensed section dated at 73.5 Ma. The San Juan
Formation represents deposition after a sharp fall in sea level, corresponding to
the 68 Ma sequence boundary.
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