Geomorphic expression of active tectonics in a rapidly-deforming arc, Sila Massif, Calabria, southern Italy

We examine the tectonic geomorphology of La Sila, Calabria, southern Italy, a high-standing (1500 m) plateau surrounded by crustal extension, with map, DEM, and field data. These data are used to constrain a simple geodynamic model that describes short-wavelength deformation of the plateau rim. Topographic metrics including drainage patterns, river longitudinal profiles, and swath profiles are consistent with field stratigraphic relationships collectively suggesting that local tectonic deformation is embedded within a broader, regional uplift that has increased the mean elevation of the Sila Plateau during the Quaternary. The concavity, steepness, and length-gradient index of modeled river longitudinal profiles proved to be the most useful metrics for recording the effects of locally active faults. A previously unrecognized horst on the northeastern portion of the plateau was identified with these data. Nevertheless, the core of the Sila Plateau remains relatively undeformed with respect to its flanks which are characterized by steep, fault-bounded escarpments. Active extension has dropped base level for and unloaded the plateau rim, causing deep fluvial incision and associated flexural uplift of the footwall. This footwall uplift helps maintain a separate external, and nearly radial drainage away from the plateau along its flanks, and a nearly closed drainage for the plateau interior. A drainage divide roughly correlates with the plateau rim, inhibiting the process of drainage integration through the Sila interior and subsequent landscape dissection. As a result, geomorphic processes driving erosion of the Sila upland are lagging behind the tectonic processes that have driven rock uplift leading to an overall increase in mean surface elevation. These results underscore the importance of the lag times a landscape may endure in transforming from one tectonic and base level condition to another. We conclude that the Calabrian forearc has a similar geomorphic evolution as the more northern Apennines consistent with the emerging view that growth of Apennine topography has been recent (Quaternary), rapid, and possibly decoupled from rock deformation in the orogenic wedge

Palynology of the Bryn Mawr Formation (Miocene): insights on the age and genesis of Middle Atlantic margin fluvial deposits

The ages of fluvial deposits at the head of Chesapeake Bay, thought to be the updip, chronostratigraphic equivalents of a well-dated late Oligocene to Quaternary marine sequence in the Salisbury Embayment, are poorly known. We present data regarding a new occurrence of a palynoflora recovered from the Bryn Mawr Formation in Cecil County, Maryland. The floral assemblage for the Bryn Mawr Formation includes at least 40 taxa at the generic level where Quercus, Cupuliferae, Ilex, Carya, Taxodium, and Pinus are important elements. Most of the taxa identified from the Bryn Mawr Formation palynoflora are extant and occur within the modern middle Atlantic Coastal Plain; however, several important taxa such as Alangium, Engelhardia, Sciadopitys, Tricolporopollenites sp., and Cupuliferoidaepollenites sp. are at present either extinct or exotic to the middle Atlantic Coastal Plain. Comparison of the Bryn Mawr Formation palynoflora to well-dated marine deposits of the Salisbury Embayment suggests a late middle to early late Miocene age (late Serravallian-early Tortonian) for Bryn Mawr Formation phase-2 deposition, supporting previously proposed genetic links to the marine deposits of the Choptank Formation in the subsurface of the Delmarva Peninsula.Relative abundances of common, extant taxa such as Quercus, Carya, Pinus, and NAP (the total non-arboreal pollen) vary considerably throughout late Cenozoic deposits of the middle Atlantic Coastal Plain. We present data for common, extant taxa in a ternary diagram to define discrete palynofacies that discriminate among middle Miocene, late Miocene, Pliocene, and Pleistocene palynofloras. These results show that relative abundances of common, easily identifiable extant pollen may be as diagnostic as exotic taxa in assigning ages to middle Atlantic Coastal Plain deposits.The Bryn Mawr Formation palynoflora, like other middle to late Miocene palynofloras of the middle Atlantic Coastal Plain, suggests terrestrial climatic cooling. In the larger temporal scale of climate change throughout the Cenozoic, this change in Miocene climate is one of three major events that may have had a significant impact on the rate of sediment yield from the Appalachians as recorded in the volume of offshore basin sediments.</p

Colluvium supply in humid regions limits the frequency of storm-triggered landslides.

Shallow landslides, triggered by extreme rainfall, are a significant hazard in mountainous landscapes. The hazard posed by shallow landslides depends on the availability and strength of colluvial material in landslide source areas and the frequency and intensity of extreme rainfall events. Here we investigate how the time taken to accumulate colluvium affects landslide triggering rate in the Southern Appalachian Mountains, USA and how this may affect future landslide hazards. We calculated the failure potential of 283 hollows by comparing colluvium depths to the minimum (critical) soil depth required for landslide initiation in each hollow. Our data show that most hollow soil depths are close to their critical depth, with 62% of hollows having soils that are too thin to fail. Our results, supported by numerical modeling, reveal that landslide frequency in many humid landscapes may be insensitive to projected changes in the frequency of intense rainfall events