Facies evolution and sequence chronostratigraphy of a “mid”-Cretaceous shallow-water carbonate succession of the Apulia Carbonate Platform from the northern Murge area (Apulia,southern Italy) |
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Authors: | Luigi Spalluto |
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Institution: | 1.Dipartimento di Geologia e Geofisica,Università degli Studi di Bari “Aldo Moro”,Bari,Italy |
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Abstract: | The “mid”-Cretaceous carbonate succession of the Apulia Carbonate Platform cropping out in northern Murge area (Apulia, southern
Italy) is composed of shallow-water carbonate rocks and is over 400 m in thickness. This paper focuses on the lithofacies
analysis of this carbonate succession, its paleoenvironmental interpretation, and its sequence-chronostratigraphic architecture.
Lithofacies analysis permitted to identify deposits which can be grouped into the following three facies belts: (1) terrestrial
facies belt formed by: intraclast-supported paleosoils; solution-collapse breccias; (2) restricted facies belt made up of
lithofacies deposited in protected peritidal environments; (3) normal-marine facies belt made up of lithofacies formed in
moderate- to high-energy subtidal environments. The detailed study both in outcrops and in thin-sections revealed that, at
the bed scale, lithofacies are cyclically arranged and form shallowing-upward small-scale depositional sequences comparable
to parasequences and/or simple sequences. The following three small-scale sequence types have been distinguished: (1) subtidal
sequences mostly made up of lithofacies formed in the normal-marine open subtidal domain; (2) peritidal sequences made up
of lithofacies formed in the restricted peritidal domain; (3) peritidal sequences showing a cap formed by paleosoils. Small-scale
sequences are not randomly arranged in the compiled succession but form discrete packages, or sets, that alternate in the
sedimentary record. The repetition of such small-scale sequence packages in the succession has been the key to recognize large-scale
sequences comparable to third-order depositional sequences. Although sedimentological data are often fragmentary due to late
dolomitization, four large-scale sequences have been distinguished. The data support a generalized landward-backstepping of
facies belts during transgression, which implies a gradual gain of accommodation culminating with the deposition of a package
of small-scale sequences formed by normal-marine subtidal deposits. These mark periods of maximum accommodation space and
form the maximum-flooding zones of large-scale sequences. A gradual seaward progradation of facies belts is recorded during
highstand conditions, which implies a gradual loss of accommodation culminating with the deposition of a package of peritidal
small-scale sequences capped by paleosoils or by solution-collapse breccias. The occurrence of terrestrial deposits marks
periods of minimum accommodation on the platform and determines the sequence boundary of large-scale sequences. The large-scale
sequences identified in this study fit with the main transgressive/regressive cycles published in the sequence-chronostratigraphic
chart of European basins. As a consequence, it is interpreted that changes of the sea level recorded at the scale of European
basins played an important role in determining the sequence-stratigraphic architecture of the studied succession. In spite
of this, the occurrence of solution-collapse breccias, which implies a significant gap in carbonate sedimentation in between
Early and Middle Cenomanian times, may also have an alternative interpretation. In particular, this deposit may represent
the local fingerprint of the well-known tectonic phase which, during Late Albian-Early/Middle Cenomanian times, determined
the subaerial exposure of large parts of Periadriatic carbonate platforms producing a marked regional unconformity. |
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