Mathematics – Logic
Scientific paper
Jul 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997e%26psl.150...79l&link_type=abstract
Earth and Planetary Science Letters, Volume 150, Issue 1-2, p. 79-83.
Mathematics
Logic
2
Scientific paper
The carbonate platform margin of the Montagna della Maiella in the Abruzzi region of central Italy has a complex history of sedimentation, consisting of aggradational and progradational episodes along the shelf margin and pelagic deposition in the basin. A paleomagnetic study at 12 regionally distributed limestone sites of late Cretaceous to Miocene age in the Maiella anticline was unable to define stable magnetic directions at most sites, largely due to the weakness of the magnetizations. At the few usable sites inclinations agreed with reference values based on an African polar wander path. Declinations were inconsistent, indicating local tectonic rotations. Both normal and reversed polarities were preserved at some sites. A magnetostratigraphic section, consisting of 280 samples spaced at 1-1.5 m intervals, was sampled along a profile in the Valle delle Tre Grotte, near the village of Pennapiedimonte. Sequence stratigraphy, based on two-dimensional analysis of outcrops, formed the stratigraphic framework for the magnetostratigraphic study. Rock magnetic analyses showed that magnetite is the dominant ferromagnetic mineral in the limestones. Both alternating field and thermal demagnetization were satisfactory in defining two main components in the weak magnetizations. A component with low coercivity, low unblocking temperature and normal polarity was close in direction to the present axial dipole field direction at the site. A higher coercivity, higher unblocking temperature component with both polarities was interpreted as the characteristic remanent magnetization (ChRM). Although the mean directions of samples with normal and reversed polarity are not exactly antipodal, a stratigraphic sequence of magnetozones is very clearly defined. The Pennapiedimonte magnetostratigraphy correlates well with late Cretaceous Chrons C30r to C34n in the established polarity timescale; numerical ages can thus be allocated to the reversals. Correlation to the Gubbio section allows paleontological dates for the reversal sequence to be inferred. The correlations allow more precise dating of formational and sequence boundaries and a better evaluation of stratigraphic hiatuses. In particular, the boundary between the Tre Grotte Formation (Supersequence 1, Turonian to middle Campanian) and the Orfento Formation (Supersequence 2, upper Campanian to upper Maastrichtian) is shown to be associated with a significant hiatus, spanning most of the middle Campanian G. ventricosa zone. Likewise, the absence of Chron C29r at the top of the Orfento Formation (SS2) documents non-deposition during the latest Maastrichtian or subsequent erosion. Lower sedimentation rates in the Maastrichtian redeposited sediments than in the Gubbio section suggest that the Maastrichtian record in the Pennapiedimonte section is punctuated by submarine erosion.
Bernoulli Daniel
Hirt Ann M.
Lampert S. A.
Lowrie William
Mutti Maria
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