Paleomagnetic Rotations in the Northeastern Caribbean Region Reveal Major Intraplate Deformation Since the Eocene

Relative Caribbean-North American plate motion is partitioned over the trench and intra-Caribbean plate faults that bound large scale tectonic blocks. Quantifying the kinematic evolution of this tectonic corridor is challenging because much of the region is submarine. We present an extensive regional paleomagnetic data set (1,330 cores from 136 sampling locations) from Eocene and younger rocks of the northern Lesser Antilles, the Virgin Islands, and Puerto Rico, and use a statistical bootstrapping approach to quantify vertical axis block rotations. Our results show that the Puerto Rico–Virgin Island (PRVI) block and the Northern Lesser Antilles (NoLA) block formed two coherently rotating domains that both underwent at least 45° counterclockwise rotation since the Eocene. The first ∼20° occurred in tandem in late Eocene and Oligocene time, after which the blocks were separated in the Miocene by the opening of the Anegada Passage. The last 25° of rotation of the PRVI block ended in the middle Miocene, whereas the NoLA block rotated slower, until the latest Miocene. The boundary between the NoLA block and a non-rotated Southern Lesser Antilles was likely the Monserrat-Harvers fault zone. These results require hundreds of kilometers of intra-Caribbean motions with oroclinal bending of the trench or forearc sliver motion along the curved plate boundary as endmembers. These data invite a critical re-evaluation of the kinematic reconstruction of Caribbean-North American plate motion. The consequent changes in paleogeography may provide a new view on the enigmatic eastern Caribbean paleo-biogeography and the Paleogene dispersal of South American mammals toward the Greater Antilles

Eocene intra-plate shortening responsible for the rise of a faunal pathway in the northeastern Caribbean realm

Intriguing latest Eocene land-faunal dispersals between South America and the Greater Antilles (northern Caribbean) has inspired the hypothesis of the GAARlandia (Greater Antilles Aves Ridge) land bridge. This landbridge, however, should have crossed the Caribbean oceanic plate, and the geological evolution of its rise and demise, or its geodynamic forcing, remain unknown. Here we present the results of a land-sea survey from the northeast Caribbean plate, combined with chronostratigraphic data, revealing a regional episode of mid to late Eocene, trench-normal, E-W shortening and crustal thickening by ∼25%. This shortening led to a regional late Eocene–early Oligocene hiatus in the sedimentary record revealing the location of an emerged land (the Greater Antilles-Northern Lesser Antilles, or GrANoLA, landmass), consistent with the GAARlandia hypothesis. Subsequent submergence is explained by combined trench-parallel extension and thermal relaxation following a shift of arc magmatism, expressed by a regional early Miocene transgression. We tentatively link the NE Caribbean intra-plate shortening to a well-known absolute and relative North American and Caribbean plate motion change, which may provide focus for the search of the remaining connection between ‘GrANoLA’ land and South America, through the Aves Ridge or Lesser Antilles island arc. Our study highlights the how regional geodynamic evolution may have driven paleogeographic change that is still reflected in current biology

Fish consumption and the risk of gastric cancer: systematic review and meta-analysis

<p>Abstract</p> <p>Background</p> <p>Gastric cancer is the fourth most frequently occurring malignancy after lung, breast, and colorectal cancer, and the second most common cause of death from cancer worldwide. Epidemiologic studies have examined the possible association between fish consumption and gastric cancer, but the results were inconclusive. We conducted a systematic review and meta-analysis to examine the association between fish intake and the risk of gastric cancer.</p> <p>Methods</p> <p>PubMed was searched for studies published in English-language journals from 1991 through 2009. We identified 17 epidemiologic studies (15 case-control and 2 cohort studies) that included relative risks (RRs) or odds ratios (ORs) estimates with 95% confidence intervals (CIs) of the relationship between gastric cancer and fish consumption. Data were extracted using standardized data forms. Summary RRs or ORs for the highest versus non/lowest fish consumption levels were calculated using random-effects model. Heterogeneity among studies was examined using Q and I²statistics.</p> <p>Results</p> <p>In this study, 5,323 cases of gastric cancer and over 130,000 non-cases were included. The combined results from all studies indicated that the association between high fish consumption and reduced gastric cancer risk was not statistically insignificant (RR = 0.87, 95% CI = 0.71-1.07).</p> <p>Conclusions</p> <p>Current evidence indicated that the association between fish consumption and risk of gastric cancer remains unclear.</p

The relationship between dietary fat intake and risk of colorectal cancer: evidence from the combined analysis of 13 case-control studies

The objective of this study was to examine the effects of the intakeof dietary fat upon colorectal cancer risk in a combined analysis of datafrom 13 case-control studies previously conducted in populations withdiffering colorectal cancer rates and dietary practices. Original datarecords for 5,287 cases of colorectal cancer and 10,470 controls werecombined. Logistic regression analysis was used to estimate odds ratios (OR)for intakes of total energy, total fat and its components, and cholesterol.Positive associations with energy intake were observed for 11 of the 13studies. However, there was little, if any, evidence of anyenergy-independent effect of either total fat with ORs of 1.00, 0.95, 1.01,1.02, and 0.92 for quintiles of residuals of total fat intake (P trend =0.67) or for saturated fat with ORs of 1.00, 1.08, 1.06, 1.21, and 1.06 (Ptrend = 0.39). The analysis suggests that, among these case-control studies,there is no energy-independent association between dietary fat intake andrisk of colorectal cancer. It also suggests that simple substitution of fatby other sources of calories is unlikely to reduce meaningfully the risk ofcolorectal cancer.Facultad de Ciencias Médica

Fossil assemblages associated with submerged beachrock beds as indicators of environmental changes in terrigenous sediments: Examples from the Gelasian (Early Pleistocene) of Rhodes, Greece

The lower Pleistocene Kritika Member of the Rhodes Formation is composed of predominantly siliciclastic deposits that are sometimes intercalated with hardbottoms formed by drowning of former beachrock beds. A wide variety of sclerobionts occur in this environment, very different from the poorest soft-bottom populations occurring in other levels of the Kritika Member. The most characteristic, abundant and frequently diverse are the encrusting forms: coralline algae, bivalves, serpulid worms, and bryozoans. Numerous other groups of sessile and vagile organisms are associated with these crust-forming communities. A number of skeletal organisms (sometimes including zooxanthellate coral colonies) formed small carbonate buildups on top of several beachrock beds. Boring organisms also occur. Evidence for a two-step deepening succession over the previously formed beachrock is provided by palaeontological and sedimentological data. The rapidly cemented sandy-conglomeratic beds were first colonised by a relatively shallow-water (around 20. m) biocoenosis of mostly encrusting organisms. Another association, with encrusting and erect organisms, was later established in a deeper environment (20-40. m). A comparison with Holocene beachrock occurring on the coast of Rhodes was also undertaken. Their submerged part provided habitat for poorer but similar biotas to those occurring in the Kritika Member. The lower Pleistocene beachrock and associated organogenic fossil assemblages indicate repeated drowning episodes during deposition of the Kritika Member and provide help in sequence stratigraphic interpretations of these siliciclastic deposits. Notably, they can be used as indicators of relative sea-level changes. © 2012 Elsevier B.V

Facies associations in warm-temperate siliciclastic deposits: Insights from early Pleistocene eastern Mediterranean (Rhodes, Greece)

Diverse, abundant and usually well-preserved communities of skeletal organisms occur in the lower Pleistocene (Gelasian) siliciclastic deposits of the Greek island of Rhodes. Benthic foraminifers, molluscs and bryozoans have been studied in four measured and sampled sections located in the northern part of the island. Among these bottom-dwelling organisms, numerous extant taxa are good environmental indicators and, combined with field observations and sedimentological data, they provide information on the probable conditions in which they developed. The siliciclastic deposits of the Kritika Formation have been divided into 14 different bio- and lithofacies, which have been further grouped into four facies associations corresponding to four different environmental settings: (1) continental to fluviatile; (2) brackish-water (lagoonal/deltaic); (3) infralittoral (0-20 m); and (4) upper circalittoral (depths of 20-40 m, but also down to c. 50-60 m). Among the marine facies associations, several characteristic biocoenoses have been recognized: soft-bottoms (fine to coarse sands and gravels); seagrass meadows; biogenic calcareous crusts on drowned beachrock slabs; red algal rhodoliths; and bivalve shell beds. In the studied sections, 13 superimposed genetic sequences have been documented. The repetition of similar facies associations within each sequence suggests: (1) a possibly eustasy-controlled, cyclic sedimentation; (2) a general subsidence of Rhodes during the deposition of the studied facies associations; and (3) a mostly constant range of environmental conditions (i.e. sedimentation rates and temperature) throughout the Gelasian. Copyright © Cambridge University Press 2015

Evolution tectono-sédimentaire d'un bassin molassique postorogénique : l'exemple des séries conglomératiques stephano-triasiques de Mechra ben Abbou, Rehamna, Maroc

Tectonosedimentary evolution of a molassic and postorogenic basin : example from the Stephanian-Triassic conglomeratical sequences of Mechra Ben Abbou, Rehamna, Maroc. Postorogenic molassic and volcanic rocks of the Mechra Ben Abbou area include two formations separated by an unconformity. The first fills a half-graben controlled by an N80° E normal fault. After its deposition this formation was folded, slightly thrusted and faulted and then corved by the second formation which was subsequently flexured. The opening of the E-W trending half-graben and the deformation of the molassic sequences seem to be related to differential motions along N10° E to N40° E trending Hercynian faults of the paleozoic basement : the first motion occured along a N10° E dextral shear zone, later sinistral because of a rotation of the shortening sense.Les séquences molassiques et volcaniques postorogéniques de Mechra Ben Abbou comprennent deux formations séparées par une discordance angulaire. La première comble un demi-graben contrôlé par une faille vivante N80° E à regard sud ; elle est ensuite plissée, écaillée et fracturée. La seconde, qui fossilise l'ensemble sous-jacent, n'est que légèrement flexurée. L'ouverture du demi-graben et la structuration des molasses paraissent commandées par des mouvements différentiels le long de fractures hercyniennes N10° E et N40° E qui découpent le soubassement paléozoïque dans un régime de cisaillement N10° E d'abord dextre puis réactivé en senestre par suite de la rotation de la direction du raccourcissement.Muller J., Cornée Jean-Jacques, Kamel Fouad El. Evolution tectono-sédimentaire d'un bassin molassique postorogénique : l'exemple des séries conglomératiques stephano-triasiques de Mechra ben Abbou, Rehamna, Maroc. In: Géologie Méditerranéenne. Tome 18, numéro 1-2, 1991. Le paleozoïque du Maroc. II – Carbonifère – Permien (Paléontologie – Biostratigraphie – Aspects structuraux) pp. 109-122

Spectacular preservation of seagrasses and seagrass-associated communities from the Pliocene of Rhodes, Greece

An exceptionally well-preserved fossil seagrass community occurs in the late Pliocene of the Greek Island of Rhodes. The siliciclastic deposits of the Kritika section (Kritika Member, Rhodes Formation) contain several beds of clay and fine-grained sand with abundant remains of the leaves of Posidonia oceanica. A coarser sand bed with in situ rhizomes of the same endemic Mediterranean phanerogam also was found. Samples yield a diverse skeletal assemblage of 121 species of crustose coralline algae, foraminifers, annelids, gastropods, bivalves, encrusting bryozoans, and ostracodes, some of which also live exclusively on the leaves of present-day P. oceanica. The community of organisms associated with the rhizomes is slightly poorer (57 species), with bivalves appearing as distinctively abundant components of this assemblage (21 species). An analysis of the relationships between skeletal organisms and fossil leaves and rhizomes shows that the majority of them lived together in the same seagrass-vegetated environment, were transported a short distance from their natural habitat, and buried very rapidly in fine-grained sediments, thus preserving this remarkable assemblage almost intact. The rhizomes were preserved in growth position within a coarse-grained sand trapped by their horizontal and vertical network. The fossil assemblage compares well in terms of major skeletal components with modern shallow-water P. oceanica meadows. This study also provides evidence for the presence during the Pliocene of an already well-established and widespread seagrass community with biotopes comparable to those of the present-day Mediterranean. Copyright © 2007, SEPM (Society for Sedimentary Geology)