Quaternary Origin Research Articles

The seasonally dry tropical forest species Cavanillesia chicamochae has a middle Quaternary origin

AbstractWe use DNA sequence data to understand the evolutionary history of the genus Cavanillesia (Malvaceae), with particular emphasis on C. chicamochae, an emblematic succulent‐trunked tree endemic to seasonally dry tropical forests (SDTFs) of the Chicamocha Canyon of Colombia, South America. Based on field sampling of multiple individuals from different populations, we inferred a phylogeny calibrated into absolute time using robust macrofossil information. We show strong support for a monophyletic Cavanillesia chicamochae, with a mean stem age of 1.46 Ma. Two different mechanisms could explain its origin, either a late uplift age of the eastern cordillera or increased dryness of the Chicamocha Canyon during the Middle Pleistocene Transition. We also find marked genetic differentiation of its populations within the Chicamocha Canyon, likely driven by a combination of climate change and local landscape processes. Our results suggest that within northern inter‐Andean SDTFs, as has been demonstrated in the central Andes, dispersal limitation leads to species and even population monophyly within individual valleys. The genetic differentiation of populations of C. chicamochae, together with the presence of other endemic and threatened species in the Chicamocha Canyon, calls for urgent management to conserve the unique biodiversity in the region.Abstract in Spanish is available with online material.

Les problèmes géologiques et typologiques des sites paléolithiques dans le Nord-Est du Japon

The northeastern area of Honshu is composed of six departments: Aomori, Iwate, Akita, Miyagi, Yamagata and Fukushima. The study of Paleolithic began in 1927 and has given place to the discovery of the site of Hanaizumi. Subsequently, one pushed the research below on land and the discovery of the first paleolithic site in Iwajyuku happened in 1946. Then, H. Nakagawa took back a success of survey of the geomorphological processes and the ordering of the fluviatile terraces with some layers from the volcano-sedimentary deposit of the Pleistocene in the basin of Kitakami and the one of Mabechi. Therefore, we understood that the archaeological levels of the region contain several sedimentary deposits volcano of quaternary origin from the Mounts Öu. In the basin of Kitakami, one noted the deposit of fall pyroclastic of Aiçra (AT) above the layer of the local volcanic ash from Kurosawajiri. Especially, it is one key of an important layer, the last horizon located under AT and above the tephra of Daïfudô from the local volcano, the pyroclastic stream of Towada and the involution of the layer of the volcanic ash from Kurosawajiri. More than 610 paleolithic sites has been counted in the Northeast.

Phylogeography and population genetics of Acanthophyllum squarrosum complex (Caryophyllaceae) in the Irano-Turanian region

Acanthophyllum squarrosum and two closely related species, A. heratense and A. laxiusculum (Caryophyllaceae), form a complex that covers parts of subalpine steppes of the Irano-Turanian (IT) region. In this study, we explored the genetic structure and phylogeography of this complex based on partial sequences of two chloroplasts (psbA–trnH and rpl32–trnL (UAG)) and two nuclear (EST24 and nrITS) DNA regions. We analysed 80 individuals from eight populations and detected 12 chloroplast haplotypes, 16 and eight nuclear alleles in EST24 and nrITS sequences, respectively. Phylogenetic trees and haplotype networks did not show distinct genetic groups in the complex and this could be explained by incomplete lineage sorting or introgression between species. Divergence time analysis revealed a Quaternary origin for A. squarrosum complex at approximately 1.8 million years ago (Mya) and the neutrality test results indicated that this complex experienced a recent population expansion. AMOVA analysis of the chloroplast regions showed a significant genetic differentiation among populations and low genetic differentiation within populations, but opposite results were found with nuclear markers, implying introgression between A. squarrosum complex populations.

Investigating Sedimentological Architecture Using Electrical Resistivity Tomography: A Case Study from the Archaeological Open-Air Site Shën Mitri, Southern Albania

Large-scale and small-scale high-resolution electrical resistivity tomography (ERT) measurements were carried out to investigate the sedimentological architecture of the Shen Mitri hill and its close surroundings near the Butrint archaeological site in Albania. The ERT measurements were conducted in combination with archaeological excavations of an Upper Paleolithic/Mesolithic open-air site with the aim to better understand the early modern human migration history. The resulting inversion models are meaningful and span a wide range of subsurface resistivities. The Shen Mitri hill is mainly composed of low-resistive Pliocene clayey sediments less than 5 $$\Omega$$ m and is covered by resistive sandstone towards the hill-top reaching values more than 100 $$\Omega$$ m. The Vrina plain surrounding the hill consists of sediments of Quaternary origin with rather low resistivities. High-resistive features in the Vrina plain correspond to Pliocene units of sandstone and outcrops of evaporates with several hundred $$\Omega$$ m of resistivity. The results revealed that the neighboring hill Xarre is likely to be of older age than the hill Shen Mitri as it is composed of sediments from an older Pliocene unit with higher resistivities. The results improve the knowledge of the actual geological understanding of the hills and give detailed insight to their architecture, such as thickness and distribution of the occurring formations. Thus, not the main focus of the article, small-scale ERT results reveal zones with a high-resistive surface layer which is identified as a archaeological layer-containing stone artifacts and ceramic sherds. However, undisturbed archaeological layers were not identified yet and ERT measurements can help to clarify the taphonomic history of the Shen Mitri site. Prior to the inversion, an elaborate estimation of ERT data errors including geometrical errors and the data variation coefficient is presented. The estimated error model is meaningful and included in the two-dimensional error-weighted inversion scheme. Subsequently, the effect of surface topography on ERT data is estimated by a modeling study and, as a consequence, included in all the inversion models.

Last major gap in scydmaenine evolution filled (Coleoptera: Staphylinidae)

The tribe Scydmaenini represents one of the most successful modern groups of the ant-like stone beetles (Scydmaeninae), displaying a high degree of species diversity (>750 species) and morphological disparity. Surprisingly, direct fossil evidence crucial for elucidating the origin and early evolution of Scydmaenini is lacking. This gap of knowledge is of particular interest as the Cretaceous origin of other major scydmaenine lineages, e.g., Mastigini, Eutheiini, Cephenniini, and Glandulariini, were recently documented. Here, we report a new genus and species, Kuafu borealis gen. et sp. nov., from Cretaceous Burmese amber, pushing back the oldest definitive record of stem-group Scydmaenini to approximately 99 Ma. An affinity of the new taxon with recent Scydmaenini is strongly supported by the beetle's short, dome-like terminal (fourth) maxillary palpomeres, as well as an exposed metanepimera which are typical character states of the tribe. However, Kuafu possesses a plesiomorphic un-notched anterior margin of the scape, a character state unknown among living Scydmaenini, and suggesting a basal position of the fossil taxon. Our find provides firm evidence that stem-group Scydmaenini, like other major scydmaenine lineages, originated no later than the mid-Cretaceous, removing the possibility that Scydmaenini may had a young, Quaternary origin.

Molecular evidence in Diplotaxis (Brassicaceae) suggests a Quaternary origin of the Cape Verdean flora

In comparison with other Macaronesian Islands (e.g., the Canary Islands), the Cape Verde Islands have received little attention in terms of plant molecular phylogenetic studies, which might also elucidate the general floristic history of this archipelago. The Cape Verdean vascular plant flora (ca. 12% endemics) has traditionally been regarded as relict of a former subtropical Tertiary flora. In contrast, it has been postulated more recently that the flora is much younger and of Pleistocene origin. To test these hypotheses, we have produced molecular phylogenies associated with a molecular clock approach, sampling all nine Cape Verdean endemic Diplotaxis taxa and 21 accessions representing the D. harra complex from across its distributional range. Analyzing three molecular markers from the nuclear and chloroplast genome, we provide evidence that the Cape Verdean endemic Diplotaxis originated from North African D. harra populations in Pleistocene times, putatively linked to the genesis of the (western) Sahara. This adds to the emerging picture that the present Cape Verdean flora is of Pleistocene origin.

Allopatric hybrids as evidence for past range dynamics in Sempervivum (Crassulaceae), a western Eurasian high mountain oreophyte

Fossil evidence, phylogeographic analyses, species distribution modelling and ancient DNA analyses have all shown that plant distributions have been highly dynamic through time. We use the geographical distribution of intra- and interspecific hybrids in Sempervivum, a western Eurasian high mountain oreophyte, as evidence for the past range dynamics of their parents. Sequences of the nuclear ribosomal internal transcribed spacer (ITS), parts of the nuclear ribosomal intergenic spacer region (IGS), and the three chloroplast markers atpI–atpH, rps16-intron and trnQ–rps16 were generated for 101 individuals of Sempervivum from across its entire distribution range. Hybrid individuals were identified by the presence of double base calls in direct sequencing of polymerase chain reaction products of ITS and IGS. Parentage was inferred from comparison with sequences without double base calls and with cpDNA sequences. We identified 27 hybrid individuals, which were found outside the current distribution range of one parent in 10 cases and with both (or all three) parents in eight cases. Geographical distance of hybrids and allopatric parents ranged from 25 to 2100 km. The distribution of hybrid individuals in relation to their parents provides evidence for past range dynamics and migration over sometimes large geographical distances. As all taxa involved had been postulated to be of Quaternary origin in an earlier study, we hypothesise that hybridisation took place in glacial refugia where the parental species came into contact.

Research Article Quaternary origin and genetic divergence of the endemic cactus Mammillaria pectinifera in a changing landscape in the Tehuacán Valley, Mexico

The endemic Mexican cactus, Mammillaria pectinifera, shows low dispersal capabilities and isolated populations within the highly dissected landscape of Tehuacán Valley. These characteristics can restrict gene flow and act upon the genetic divergence and speciation in arid plants. We conducted a phylogeographic study to determine if the origin, current distribution, and genetic structure of M. pectinifera were driven by Quaternary geomorphic processes. Sequences of the plastids psbA-trnH and trnT-trnL obtained from 66 individuals from seven populations were used to estimate genetic diversity. Population differentiation was assessed by an analysis of molecular variance. We applied a stepwise phylogenetic calibration test to determine whether species origin and genetic divergence among haplotypes were temporally concordant with recognizable episodes of geomorphic evolution. The combination of plastid markers yielded six haplotypes, with high levels of haplotype diversity (h = 0.622) and low nucleotide diversity (π = 0.00085). The populations were found to be genetically structured (F(ST) = 0.682; P < 0.00001), indicating that geographic isolation and limited dispersal were the primary causes of genetic population differentiation. The estimated origin and divergence time among haplotypes were 0.017-2.39 and 0.019-1.237 mya, respectively, which correlates with Pleistocene tectonics and erosion events, supporting a hypothesis of geomorphically-driven geographical isolation. Based on a Bayesian skyline plot, these populations showed long term demographic stability, indicating that persistence in confined habitats has been the main response of this species to landscape changes. We conclude that the origin and haplotype divergence of M. pectinifera were a response to local Quaternary geomorphic evolution.

Diversification ofCeanothus(Rhamnaceae) in the California Floristic Province

High diversity and endemism in the California Floristic Province (CFP) are an alleged response to the late Cenozoic advent of Mediterranean-type climate in this region. Ceanothus comprises two divergent subgenera with centers of diversity in the CFP. We reconstruct the evolution of Ceanothus by using DNA sequence data from the nuclear gene nitrate reductase. We find that the timing of diversification events is related to geological and climatic history. In both subgenera, diversification is characterized by recent divergence of extant taxa and geographically structured phylogenetic relationships. A strong north-south divergence of subgenus Cerastes across the Transverse Ranges indicates that phylogenetic relationships may be structured by climatically divergent regions of the CFP. Divergence-time estimation suggests that the age of extant diversification in both subgenera is ∼6 Ma. This agrees with the fossil record but predates the hypothesized Quaternary (2-Ma) origin of Mediterranean-type climate in the region.

Ephemeral Pleistocene woodlands connect the dots for highland rattlesnakes of the Crotalus intermedius group

Aim To test how Pleistocene climatic changes affected diversification of the Crotalus intermedius species complex. Location Highlands of Mexico and the south-western United States (Arizona). Methods We synthesize the matrilineal genealogy based on 2406 base pairs of mitochondrial DNA sequences, fossil-calibrated molecular dating, reconstruction of ancestral geographic ranges, and climate-based modelling of species distributions to evaluate the history of female dispersion. Results The presently fragmented distribution of the C. intermedius group is the result of both Neogene vicariance and Pleistocene pine–oak habitat fragmentation. Most lineages appear to have a Quaternary origin. The Sierra Madre del Sur and northern Sierra Madre Oriental are likely to have been colonized during this time. Species distribution models for the Last Glacial Maximum predict expansions of suitable habitat for taxa in the southern Sierra Madre Occidental and northern Sierra Madre Oriental. Main conclusions Lineage diversification in the C. intermedius group is a consequence of Pleistocene climate cycling. Distribution models for two sister taxa in the northern and southern Sierra Madre Occidental and northern Sierra Madre Oriental during the Last Glacial Maximum provide evidence for the expansion of pine–oak habitat across the Central Mexican Plateau. Downward displacement and subsequent expansions of highland vegetation across Mexico during cooler glacial cycles may have allowed dispersal between highlands, which resulted in contact between previously isolated taxa and the colonization of new habitats.

Quaternary origin of the inverse latitudinal diversity gradient among southern Chilean mollusks

Mollusks along the Pacific coast of South America provide one of the main exceptions from the latitudinal diversity gradient of decreasing species numbers toward the poles. From 42 degrees S southward, coincident with the onset of the mosaic coastline of the southern Chilean fiord-lands, species numbers show a twofold to threefold increase compared to the central Chilean coast. Here we use the Neogene fossil record of central and southern Chile to test hypotheses on the origin of this unusual pattern. Contrary to previous suggestions, we did not find evidence for a buildup of biodiversity since the Eocene, or for the northward spread of Antarctic taxa into southern mid-latitudes. Rather, our data suggest that the mosaic coastline south of 42 degrees S was colonized after the retreat of the glaciers from their marine termini since the later Pleistocene, by taxa that were already present along the Chilean coast. The majority of the most species-rich genera in this area are shallow-water hardground inhabitants, suggesting a rapid adaptive radiation of these taxa. The unusually low present-day diversity to the north of 42 degrees S most likely results from the severe late Neogene extinction and only moderate subsequent origination in this area.

Weathering processes and Quaternary origin of an alpine blockfield in Arctic Sweden

The weathering and origin of an autochthonous blockfield in the northern Swedish mountains were investigated through an examination of fine matrix and clasts from two pits excavated across ridge‐top sorted circles; one on a summit, the other in a saddle. At the summit, fine matrix chemical weathering is limited to the production of poorly crystallized Al‐ and Fe‐oxyhydroxides, whereas some additional vermiculitization and gibbsite crystallization occurs in the saddle. In both locations, volumes of clay‐sized matrix are low, mass balance calculations indicate only minor elemental losses and no chemically etched grains are visible under a scanning electron microscope (SEM). In addition, soil horizons are absent and chemical weathering intensity is uniformly low across both excavated sorted circles. Minor clast chemical weathering consists of Fe oxidation, which dominates in the matrix‐rich circle centres, and some rind development, which increases in frequency in the clast‐rich rings. The dominance of physical weathering processes and the presence of only minor chemical weathering, in both fine matrix and clasts, indicate that the blockfield is not a Neogene weathering remnant. Rather, the blockfield has a Quaternary origin, developing during interglacials, interstadials and the Holocene, primarily through subsurface weathering processes.

Phylogeny and quaternary history of the European montane/alpine endemicSoldanella(Primulaceae) based on ITS and AFLP variation

Soldanella contains 16 species of herbaceous perennials that are endemic to the central and south European high mountains. The genus is ecogeographically subdivided into forest/montane and alpine species. Evolutionary relationships and large-scale biogeographic patterns were inferred from parsimony analyses of the internal transcribed spacer (ITS) regions of nuclear ribosomal DNA, and genetic distance analyses based on amplified fragment length polymorphism (AFLP) markers. The ITS region proved useful for examining subgeneric relationships and testing hypotheses on genus-wide divergence times, whereas the AFLP markers were suitable for studying relationships among closely related taxa and biogeographic patterns of divergence. Neither ITS nor AFLP data supported sectional delimitations, particularly those related to the grouping of S. alpina (sect. Soldanella) with S. pusilla (sect. Tubiflores), which may be the result of hybridization. Additional results and conclusions drawn are (1) Soldanella is derived from an ancestor of Asian origin with a montane ecology; (2) estimates of divergence times suggest a late Quaternary origin of the genus; (3) alpine species of sect. Tubiflores diverged from within a paraphyletic sect. Soldanella of mainly montane species; (4) alpine and montane species of Soldanella experienced different cycles of range expansion and contraction during late Quaternary climatic changes, resulting in differential patterns of geographic distribution; and (5) AFLP divergence among montane species from eastern Europe was lower than between alpine species; we hypothesize that the latter differentiated in allopatric regions of expansion during glacials, while the former experienced secondary contact at lower elevations in more southern refugia.

Quaternary Volcanism and Origin of the Kurile Basin (Sea of Okhotsk)

Quaternary Volcanism and Origin of the Kurile Basin (Sea of Okhotsk)

Paleomagnetic age of the central Missouri barite deposits and its genetic implications

In the Central Missouri barite district, barite samples were taken from four barite deposits and carbonate samples from the Lower Ordovician Jefferson City and Gasconade Dolomites in two road cuts and from the Mississippian Burlington Limestone in a quarry. The samples were tested paleomagnetically using detailed alternating field and thermal demagnetization and saturation isothermal remanent magnetization methods. An A magnetization direction of declination = 153.5 degrees , inclination = 17.6 degrees (N = 35, k = 17, alpha 95 = 4.8 degrees ) is carried by pseudosingle domain magnetite in the barite-rich zones of three open-pit mines as an ore-synchronous component, in the Jefferson City Dolomite as a secondary component, and in collapse breccia blocks of probable post-Middle Devonian age in the dolomite to give a negative conglomerate test. The A paleopole at 121.0 degrees E, 36.6 degrees N (dp = 2.6 degrees , dm = 4.9 degrees ) falls within the Kiaman reversed magnetic polarity interval on the Late Pennsylvanian to early Early Permian part of the apparent polar wander path for North America. A B magnetization direction of declination = 36.8 degrees , inclination = 77.8 degrees (N = 21, k = 13, alpha 95 = 92 degrees ) is found in the other units. It is a hybrid magnetization dominated by hematite produced by weathering and by viscous remanence in magnetite, both of Quaternary origin. The Kiaman magnetization in the barite ores and host rocks of the Central Missouri district agrees with known Kiaman magnetizations in the lead-zinc ores and host rocks of the adjacent Southeastern Missouri and Northern Arkansas districts. This agreement provides strong support for the Ouachita tectonic uplift model of genesis for the origin of the Mississippi Valley-type ore deposits in the midcontinental region of the United States.

THE ORIGIN AND RELATIONSHIPS OF SPELOBIA TENEBRARUM (ALDRICH), A TROGLOBITIC, EASTERN NORTH AMERICAN, SPHAEROCERID FLY

AbstractSpelobia tenebrarum is a troglobitic sphaerocerid restricted to a large number of isolated eastern North American caves. The Quaternary origin of this species from its sister species, S. semioculata, is discussed.

Th230-U234 dating of pedogenic carbonates in gravelly desert soils of Vidal Valley, southeastern California

Radioactive disequilibrium relationships among Th 230 , U 234 , and U 238 can be used to date pedogenic carbonates formed in regions of arid to semiarid climate. Samples suitable for dating consist of dense carbonate rinds around pebbles from the Cca soil horizon. Analytically, the method involves leaching the samples with dilute hydrochloric acid and measuring U 238 , U 234 , Th 230 , and Th 232 in both the leachate and residue fractions. As the soil carbonate commonly incorporates silicate mineral-bearing detritus, corrections are made to account for possible introduction of detrital Th 230 and U 234 into the acid leachate. The corrections are based on the assumptions that (1) the carbonate initially contains negligible amounts of Th 232 and Th 230 , or has a Th 230 /Th 232 ratio similar to that in detrital minerals, (2) U 238 , U 234 , and Th 230 in the detrital silicate phase are in secular equilibrium with each other, and (3) the thorium isotopes in the detrital phase are not fractionated by the acid leaching. Application of the method to calcareous soils developed on upper Quaternary alluvial deposits of the eastern Mojave Desert in southern California gives ages that are internally consistent and that agree with the geomorphic and stratigraphic relative age relationships. Fourteen samples from an upper Pleistocene geomorphic surface, Q2b, yielded an average age of 83,000 ± 10,000 yr. This age is confirmed by a different assessment of the data independent of the aforementioned assumptions. On one specimen two different layers of a pebble coating were dated, and a carbonate accumulation rate of about 1 mm/8,000 yr was obtained. It is hoped that this study will serve as a basis for further research into the absolute dating of various types of impure carbonates of late Quaternary origin.

Seismic Reflection and Aeromagnetic Surveys of the Great Salt Lake, Utah

Seismic reflection surveys of the Great Salt Lake, Utah, have provided continuous profiles for more than 750 km (450 mi) using air-gun and sparker sources. Useful penetration to as much as 1,220 m (4,000 ft) has been obtained in an average water depth of 6 m (20 ft). The data were deconvolved, processed, and displayed using a computer graphics system. In addition, a total-field aeromagnetic survey, flown at a terrain clearance of 152 m (500 ft), provided 750 km (450 mi) of corresponding profile coverage. Interpretation of the seismic data indicates that the Tertiary and Quaternary sediments of the Great Salt Lake were deposited in north-trending basins characterized by gently east-dipping beds over most of the west and central areas. Rapid subsidence and secondary folding occurred adjacent to north-trending normal fault zones along the east side of the lake. Buried anticlines and faults along the east side suggest a pre–late Tertiary period of deformation characterized by normal faulting and basin development. The total thickness of Tertiary and Quaternary sediments ranges from ∼488 m (1,600 ft) in the north to more than 3,658 m (10,000 ft) in the south. The Quaternary sediments alone range in thickness from at least 152 m (500 ft) in the north to more than 396 m (1,300 ft) in the south. Interbedded volcanic rocks, probably basalt of late Tertiary age, occur as shallow flows beneath the northern portion of the lake. West of Promontory Point, restricted basins of Quaternary origin contain ∼8 m (25 ft) of unconsolidated mud and silt overlying 213 m (700 ft) of inter-bedded mirabilite, silt, and clay. In several locations along the causeway, the mirabilite has flowed into near-surface diapiric folds and small domes. This sequence suggests restricted deposition during cool climate near the end of Pleistocene time, followed by a rapid increase in mean annual temperature with widespread deposition of mud and clay.

The roussillon continental margin (Gulf of Lions): Plio-Quaternary paleogeographic interpretation

The paleographic evolution of the Roussillon continental margin during the Plio-Quaternary has been reconstructed on the basis of indirect methods of investigation (continuous seismic reflexion) and of analysis of core samples. Interpretation of the first group is based on the character of the reflectors, their position, morphology, and their correlation with outcrop equivalents. Evolution in this area can be integrated in the more general history of the Gulf of Lions and the western Mediterranean. A remarkable factor is the morphotectonic control played by the Paleozoic substratum until recently. The Quaternary origin of the canyon seems to be characteristic of submarine valleys in this part of the Mediterranean. The different studies confirm the importance of submarine phenomena in the shaping and maintaining their morphology. The following are defined in the Quaternary complex: alluvial deposits and the fossil channel of the early and mid-Quaternary; the major Tyrrhenian phase of filling; the recent eustatic oscillations. The latter have been defined in the light of analytical data. The oldest sequence reached by drilling for core samples is the transgressive neo-Tyrrhenian. The recent Würm is figured by two regressive phases (Würm III and Würm IV) and one positive interstadial. The Holocene facies enable us to measure the rise of Flandrian sea level at a rate of 10 m per 1,000 years.

Geologic history of the intersection of the pioneer fracture zone with the Delgada Deep-Sea Fan, Northeast Pacific

Continuous reflection profiles (ARCER) of the region where the Pioneer Fracture Zone intersects the Delgada Deep-Sea Fan (39°N 127°W) show that the top of the seismic second layer is displaced along the fracture zone, but that the overlying sediments are undisturbed by faulting. At the foot of the continental slope, 200 km east of this area (depth 30 m) the sediments are about 1·5 km thick and mask all relief on the top of the second layer. In this area of investigation (depth 4500 m) the fan sediments are only 0·5 km thick and the bottom topography is a subdued replica of the relief on the buried upper surface of the second layer: where the buried relief is rough, the bottom is hilly; where smooth, the bottom is likewise smooth. At the distal edge of the fan, abyssal hills and smooth areas, which continue up into the fan, are underlain by similar thicknesses of sediments which are mineralogically nearly indistinguishable. We therefore infer that sedimentation in the two contrasting physiographic areas in this distal portion of the fan is controlled mainly by the same mechanisms, predominantly pelagic, rather than turbidity-current, deposition of sediment.Preliminary isopaching of the total sediment between this region and the foot of the continental slope suggests that the Delgada and Monterey Deep-Sea Fans overlie and partially merge with an older continental rise. We conclude that some of the sediment of this continental rise and much of the sediment in the area of this investigation has been transported ultimately from sources to the North, including the Columbia River, by the south flowign California Current, starting at least in Late Tertiary time and continuing through the Quaternary. The fans are probably predominantly of Quaternary origin.