Carbonate intercalations in a terrigenous foredeep: late Miocene examples from the Simbruini Mts. and the Salto Valley (Central Apennines - Italy)

摘要: Resedimented calcarenites and hybrid arenites are commonly found interbedded with various Upper Miocene terrigenous units (hemipelagic marls, “brecce della Renga fm.”, siliciclastic turbidites) across the Simbruini Mts. neighbouring areas of Central Apennines. Their distribution provides evidence for a complex, rapidly evolving, paleogeography region that was experiencing transition from foreland to accretionary wedge conditions during Tortonian Messinian. The bio-sedimentological features indicate deposition through gravity flows (turbidity currents) sourced by active benthic, heterozoan-type carbonate production, locally lying at photic depth. Thin-section analysis >130 samples revealed resedimented levels mainly composed bioclastic calcarenites, fragments bivalves, echinoids, bryozoans, balanids, benthic foraminifera, anellids red algae, along subordinate planktonic foraminifera. calcareous turbidites in hemipelagic marls (Unita argilloso-marnosa) characterized presence Heterostegina sp., their main source area probably east, on undeformed foreland. In contrast, field mapping, common association Cretaceous lithoclasts, age encasing units, all suggest fm.” (“complesso torbiditico altomiocenico laziale-abruzzese”) could most likely have different source. ridge, corresponding today NW sector range, bordered normal faults exposing substrate, is proven mappable paleo-escarpment tracts onlapped clastic deposits. This ridge fed surrounding deeper mixture lithoclasts loose material, produced erosion exposed bedrock coupled export sediment being topping fringing footwall blocks marginal downsteps. Carbonate production apparently able survive limited time small productive until early Messinian, shedding into foredeep.