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The Klamath Mountains Province of Northern California and southern Oregon, USA, consists of generally east-dipping terranes assembled via Paleozoic to Mesozoic subduction along the western margin of North America. The Klamath Mountains Province more than doubled in mass from Middle Jurassic to Early Cretaceous time, due to alternating episodes of extension (e.g., rifting and formation of the Josephine ophiolite) and shortening (e.g., Siskiyou and Nevadan events). However, the tectonic mechanisms driving this profound Mesozoic growth of the Klamath Mountains Province are poorly understood. In this paper, we show that formation of the Condrey Mountain schist (CMS) of the central Klamath Mountains Province spanned this critical time period and use the archive contained within the CMS as a key to deciphering the Mesozoic tectonics of the Klamath Mountains Province. Igneous samples from the outer CMS subunit yield U-Pb zircon ages of ca. 175–170 Ma, which reflect volcanic protolith eruptive timing. One detrital sample from the same subunit contains abundant (~54% of zircon grains analyzed) Middle Jurassic ages with Paleozoic and Proterozoic grains comprising the remainder and yields a maximum depositional age (MDA) of ca. 170 Ma. These ages, in the context of lithologic and thermochronologic relations, suggest that outer CMS protoliths accumulated in an outboard rift basin and subsequently underthrust the Klamath Mountains Province during the Late Jurassic Nevadan orogeny. Five samples of the chiefly metasedimentary inner CMS yield MDAs ranging from 160 Ma to 130 Ma, with younger ages corresponding to deeper structural levels. Such inverted age zonation is common in subduction complexes and, considering existing K-Ar ages, suggests that the inner CMS was assembled by progressive underplating over a >10 m.y. timespan. Despite this age zonation, age spectra derived from structurally shallow and deep portions of the inner CMS closely overlap those derived from the oldest section of the Franciscan subduction complex (South Fork Mountain schist). These relations suggest that the inner CMS is a composite of South Fork Mountain schist slices that were sequentially underplated beneath the Klamath Mountains Province. The age, inboard position, and structural position (i.e., the CMS resides directly beneath Jurassic arc assemblages with no intervening mantle) of the CMS suggest that these rocks were emplaced during one or more previously unrecognized episodes of shallow-angle subduction restricted to the Klamath Mountains Province. Furthermore, emplacement of the deepest portions of the CMS corresponds with the ca. 136 Ma termination of magmatism in the Klamath Mountains Province, which we relate to the disruption of asthenospheric flow during slab shallowing. The timing of shallow-angle subduction shortly precedes that of the westward translation of the Klamath Mountains Province relative to correlative rocks in the northern Sierra Nevada Range, which suggests that subduction dynamics were responsible for relocating the Klamath Mountains Province from the arc to the forearc. In aggregate, the above relations require at least three distinct phases of extension and/or rifting, each followed by an episode of shallow-angle underthrusting. The dynamic upper-plate deformation envisioned here is best interpreted in the context of tectonic switching, whereby slab steepening and trench retreat alternate with slab shallowing due to recurrent subduction of buoyant oceanic features. 

Abstract Members of the genusChondrusare well-known from temperate and cold waters.Chondrus ocellatusHolmes was reported from Hawai‘i Island (19° N latitude) in 1999 as a new record based on vegetative and tetrasporangial characteristics. The first specimens were collected by Setchell in 1900 in Hilo, HI. The presence of aChondrusspecies in the subtropics has been a phycological enigma for over 100 years. We addressed the question of species identity and biogeographic affinities of the HawaiianChondruswith fresh cystocarpic material, DNA samples, and phylogenetic analyses. Analysis and comparison of five genes (nuclear: EF2; plastid:psbA,rbcL, and 23S/UPA; mitochondrial: COI) from HawaiianChondrusand holotype and topotype material of 10 of the 11 acceptedChondrusspecies indicate that Hawaiian specimens areC. retortusMatsumotoetShimada. However, unlike type material, the Hawaiian specimens are commonly pinnulate, vary significantly in secondary medullary filament density, and have mature cystocarps filling the entire medullary space. This study shows the value of using multi-gene loci and comparing multiple sequences of several species to confirm taxonomic conclusions. Our findings suggest thatC. retortusmay have immigrated via rafting on natural floating material or on ships’ hulls. Solving this old puzzle adds new insight into Hawaiian phytogeography. 

Phymatolithon  Foslie is one of the most studied and ecologically important genera of crustose coralline algae (CCA) due to their dominant abundance in various marine ecosystems worldwide. The taxonomy of the genus is complex and has been revised and updated many times based on morphological and molecular analyses. We report on a crustose coralline algal species collected in June 2011 via snorkeling in the subtidal zone along the beach Abu Qir on the Mediterranean coast of Egypt, as part of a larger macroalgal diversity survey in the region. The species shows significant sequence divergences (3.5%–14.8% in rbc L; 2.9%–11% in psb A) from other closely related Phymatolithon taxa. Morpho-anatomically, this species possesses the characters considered collectively diagnostic of the genus Phymatolithon , namely, thalli non-geniculate epithelial cells and non-photosynthetic and domed-shaped meristematic cells, usually as short with progressive elongation of their perithallial derivatives. Based on molecular and morphological analyses, we determined that these specimens encompass a new, distinct species that we herein name Phymatolithon abuqirensis. Including this new species, the total number of described Phymatolithon species found in the Mediterranean Sea is now six. 

In the past, non-geniculate coralline algae in the northwestern Gulf of Mexico have been identified based primarily on comparative morpho-anatomy. Recent studies employing DNA sequencing techniques combined with morpho-anatomical studies using SEM have revealed a wealth of previously undocumented diversity of rhodolith-forming non-geniculate coralline algae in the Corallinales, Hapalidiales and Sporolithales from mesophotic hard bank communities at 45-90 meters depth. Although many advances in the last decade have been made in clarifying species names and describing new species of corallines from offshore Louisiana and Texas, total diversity estimates are still incomplete and many species remain to be described. Collections from offshore Louisiana at Parker Bank in the newly expanded Flower Garden Banks National Marine Sanctuary yielded thin, finely branched rhodoliths. DNA sequence analyses of plastid-encoded psb A and rbc L loci, and nuclear-encoded LSU rDNA of these rhodolith-forming specimens revealed that some belong to an unnamed species of Sporolithon (Sporolithales) that we herein newly describe. Additionally, comparative DNA sequence analyses of rhodolith collections from Ewing Bank and other hard banks offshore Louisiana were conducted to assess rhodolith diversity in these mesophotic communities. The results revealed new reports of taxa for the region, including new rhodolith-forming species of Roseolithon (Hapalidiales) to be described herein as well. Our new biodiversity findings will be compared with historical studies from the NW Gulf of Mexico. 

The Klamath Mountains province and adjacent Franciscan subduction complex (northern California–southern Oregon) together contain a world-class archive of subduction-related growth and stabilization of continental lithosphere. These key elements of the North American Cordillera expanded significantly from Middle Jurassic to Early Cretaceous time, apparently by a combination of tectonic accretion and continental arc– plus rift-related magmatic additions. The purpose of this field trip is twofold: to showcase the rock record of continental growth in this region and to discuss unresolved regional geologic problems. The latter include: (1) the extent to which Mesozoic orogenesis (e.g., Siskiyou and Nevadan events plus the onset of Franciscan accretion) was driven by collision of continental or oceanic fragments versus changes in plate motion, (2) whether growth involved “accordion tectonics” whereby marginal basins (and associated fringing arcs) repeatedly opened and closed or was driven by the accretion of significant volumes of material exotic to North America, and (3) the origin of the Condrey Mountain schist, a composite low-grade unit occupying an enigmatic structural window in the central Klamaths—at odds with the east-dipping thrust sheet regional structural “rule.” Respectively, we assert that (1) if collision drove orogenesis, the requisite exotic materials are missing (we cannot rule out the possibility that such materials were removed via subduction and/or strike slip faulting); (2) opening and closure of the Josephine ophiolite-floored and Galice Formation–filled basin demonstrably occurred adjacent to North America; and (3) the inner Condrey Mountain schist domain is equivalent to the oldest clastic Franciscan subunit (the South Fork Mountain schist) and therefore represents trench assemblages underplated >100 km inboard of the subduction margin, presumably during a previously unrecognized phase of shallow-angle subduction. In aggregate, these relations suggest that the Klamath Mountains and adjacent Franciscan complex represent telescoped arc and forearc upper plate domains of a dynamic Mesozoic subduction zone, wherein the downgoing oceanic plate took a variety of trajectories into the mantle. We speculate that the downgoing plate contained alternating tracts of smooth and dense versus rough and buoyant lithosphere—the former gliding into the mantle (facilitating slab rollback and upper plate extension) and the latter enhancing basal traction (driving upper plate compression and slab-shallowing). Modern snapshots of similarly complex convergent settings are abundant in the western Pacific Ocean, with subduction of the Australian plate beneath New Guinea and adjacent island groups providing perhaps the best analog. 

DNA sequence analysis of plastid-encoded psbA and UPA, mitochondrion-encoded COI, and nuclear-encoded LSU rDNA of rhodolith-forming crustose coralline algal specimens from the northwestern Gulf of Mexico reveals that Mesophyllum erubescens (Foslie) Me. Lemoine is present in mesophotic rhodolith beds offshore Louisiana and Texas at 39–57 m depth. Morpho-anatomical characters viewed with SEM support the identification of these specimens. Mesophyllum erubescens is reported for the first time offshore Louisiana at Ewing Bank, the Louisiana–Texas border at Bright Bank, and Texas in the Flower Garden Banks National Marine Sanctuary.