GeoActa Special Publication 1
2008
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GeoActa
an international Journal of Earth Sciences
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Lucia Simone, Gabriele Carannante
Dipartimento di Scienze della Terra, Università degli Studi di Napoli "Federico II", Largo San Marcellino 10, 80138 Napoli, Italy. E-mail: lusimone@unina.it, gabcaran@unina.it
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Pery-Tethyan Cretaceous shallow-water carbonate systems: sedimentary patterns and lithofacies
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PDF (1,6 MB)
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Abstract
The Cretaceous shallow water limestones cropping out both in the Italian Peninsula (Apenninic Chain) and Sardinia (Nurra Region) record significant events that affected the peri-Tethyan Region during Cretaceous times. These limestones have been investigated in order to highlight the regional variability in the related depositional systems, developed along opposing Tethyan continental margins. In spite of some remarkable differences as regards the areal partitioning of the main palaeoecologic controlling factors, several stratigraphic similarities and common sedimentological features are demonstrated.
In the latest Jurassic-earliest Cretaceous time interval, significant regression events resulted in a widespread occurrence of non-marine, peritidal or restricted areas on the shallow peri-Tethyan carbonate platforms. Brackish, muddy deposits bearing ostracods and charophyte remains prevailed in the Sardinia carbonate depositional systems (north Tethyan margin), whereas schizohaline lagoonal/coastal lake systems, containing abundant radial-fibrous ooids, spread out largely along the southern Tethyan belt.
The subsequent lower Cretaceous limestone documents the inception of shallow-water carbonate factories, via a progressive stratification of the water column, in both the marginal Tethyan subsiding areas. The transgressive Lower Cretaceous limestone piled up in carbonate systems, which grew supporting mainly chlorozoan assemblages and non-skeletal, grain-rich deposits. Nevertheless, several crisis moments in the growth of the carbonate factories have been recognized.
Mid-Cretaceous tectonics and the consequent complex palaeotopography dramatically controlled the Albian-Turonian evolution of the analyzed areas. As a result of the complex interplay of tectonic, climatic and biothic factors, contrasting drowning episodes and continental exposures of different sectors of the peri-Tethyan carbonate platforms occurred. The carbonate factories experienced repeated crisis events during which cyanobacterial consortia, with variable contributions from rudists, largely prevailed in the shallow-water domains.
The latest Turonian-Coniacian p.p. recovering of the carbonate factories might testify ameliorated environmental conditions. Afterwards, a shift toward foramol depositional systems occurred with sciophilous and mesotrophic condition-adapted assemblages flourishing in the new shallow-water domains.
Rudist-bearing rhodalgal carbonate factories grew in the Sardinia domain. There, relatively cool and mesotrophic/tendentially eutrophic conditions became dominant in the water mass impinging on the marginal sectors of the carbonate system with demise of large sectors of the carbonate factory that underwent local drowning episodes in Santonian times.
In contrast, the studied transgressive Apennine sequences show persisting evidence of microbial-related carbonate deposition in stressed peritidal domains. These latter rapidly evolved to rudist-dominated foramol carbonate factories whose ecological meaning is difficult to define due to the impossibility of an actualistc approach. The sustained production of rudist bioclasts partially damped the typical drowning tendency of the foramol open shelves. In spite of this, limited aggradation and/or retrogradation occurred and local starvation episodes characterized the neighbouring slopes and basins in Santonian-Campanian times.
Unconformity surfaces generally end the Cretaceous sequences in the studied peri-Tethyan successions but, where present, the discontinuous outcrops of upper Campanian-Maastrichtian shallow-water limestone indicate that a very shallow paralic depositional setting with improved water conditions stimulated the flourishing of chlorozoan assemblages again.
Keywords: Peri-Tethyan carbonate platforms, Cretaceous, Northwestern Sardinia, Southern Apennines.
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