Abstract. The Lower Jurassic platform and basinal deposits exposed in the
Montagna dei Fiori Anticline (Central Apennines, Italy) are pervasively
affected by dolomitization. Based on the integration of field work,
petrography, and geochemistry, two fault-related dolomitization events were
recognized and interpreted as having occurred before and during the
Apenninic orogeny. Fluid inclusion analysis indicates moderate
to elevated salinity values of 3.5 to 20.5 and 12.8 to 18.6 eq. wt % NaCl in the first and the second event, respectively. The estimated
salinities, in combination with δ18O values and 87Sr∕86Sr ratios,
suggest significant involvement of evaporitic fluids in both events, most
likely derived from the underlying Upper Triassic Burano Formation. In
addition, the 87Sr∕86Sr ratios up to 0.70963 suggest the circulation of
deep-sourced fluids that interacted with siliciclastic rocks and/or the
crystalline basement during the dolomitization events. Two major dolomite types (D1 and D2) were recognized as pertaining to the
first event, both postdated by high-amplitude bed-parallel stylolites,
supporting a syn-burial pre-layer-parallel shortening dolomitization. A
possible geodynamic framework for this dolomitization event is Early Jurassic to Late
Jurassic rift-related extensional tectonism. The second dolomitization event
(D3, D4, and D5) is characterized by a temperature upturn (up to
105 ∘C) and interpreted as associated with the inflow of
hydrothermal fluids, possibly related to major changes in the permeability
architecture of faults during early- to syn-thrusting and folding activity.
Based on the timing of deformation in the Montagna dei Fiori Anticline, the
second dolomitization event likely occurred in Late Miocene to Pliocene
times. The findings regarding characteristics and timing of dolomitization
here illustrates the long-term controlling role of the evaporitic
detachments in the dolomitization process. This study shows that the Mg-rich
fluids that were most likely derived from evaporites may prime the
tectonically involved successions for repeated dolomitization, and hence the
formation of potential reservoirs during sequential tectonic modifications
(extensional vs. compressional).
MESOZOIC RADIOLARIANS FROM RHYTHMICALLY LAYERED SEDIMENTS OF THE RIMSKY-KORSAKOV ISLANDS (PETER THE GREAT BAY, JAPAN SEA) AND THEIR SIGNIFICANCE FOR DETERMINING THE TRIASSIC-JURASSIC BOUNDARY
