Disaster opportunists Guembelitrinidae: index for environmental catastrophes.

Abstract Blooms of the disaster opportunist Guembelitria species are proxies for environmental catastrophes, whether impact or volcanism, leading to severe biotic stress crises that may range from temporary exclusion of ecological specialists and generalists to mass extinctions. During the late Maastrichtian and early Danian (zones P0 and Pla), Guembelitria blooms show global distributions, but with the largest blooms (40 -80% Guembelitria) in low and middle latitudes and only minor blooms (10 -20%) in high latitudes. Late Maastrichtian Guembelitria blooms are, so far, known from the Indian Ocean and eastern Tethys. The most intense Guembelitria blooms (>60% Guembelitria) occurred in shallow continental shelf areas, slope/shelf margins and volcanic provinces of the Indian Ocean. What these environments have in common is high nutrient influx (eutrophication) either from continental runoff, upwelling along continental margins or volcanic input. At times of biotic crises, Guembelitria blooms may have spread rapidly to the exclusion of most or all other species, much like today's red tides, but with near global distributions. A simple model can explain the ecological succession and recovery phases that follow major biotic perturbations caused by impacts or volcanism that lead to exclusion of specialist and most generalist species. Within such highly stressed environments, Guembelitria is the only genus to thrive, and without competition, rapidly reproduce and exponentially increase their populations. When nutrients are depleted, populations rapidly decrease, leading to ecologic niches for other generalists and ecosystem recovery. Small low-O 2 -tolerant heterohelicid populations mark this second stage, followed by small trochospiral and planispiral species. With further environmental recovery, increasing competition, niche development and restoration of a well-stratified water mass, oligotrophic conditions are restored, opening habitats for the highly specialized and diverse species and a return to normal diverse assemblages. This ecological succession is observed in association with mantle plume volcanism in the Indian Ocean and eastern Tethys during the late Maastrichtian, and in association with the K -T impact and volcanism during the early Tertiary.

Disaster opportunists Guembelitrinidae: index for environmental catastrophes.

Abstract Blooms of the disaster opportunist Guembelitria species are proxies for environmental catastrophes, whether impact or volcanism, leading to severe biotic stress crises that may range from temporary exclusion of ecological specialists and generalists to mass extinctions. During the late Maastrichtian and early Danian (zones P0 and Pla), Guembelitria blooms show global distributions, but with the largest blooms (40 -80% Guembelitria) in low and middle latitudes and only minor blooms (10 -20%) in high latitudes. Late Maastrichtian Guembelitria blooms are, so far, known from the Indian Ocean and eastern Tethys. The most intense Guembelitria blooms (>60% Guembelitria) occurred in shallow continental shelf areas, slope/shelf margins and volcanic provinces of the Indian Ocean. What these environments have in common is high nutrient influx (eutrophication) either from continental runoff, upwelling along continental margins or volcanic input. At times of biotic crises, Guembelitria blooms may have spread rapidly to the exclusion of most or all other species, much like today's red tides, but with near global distributions. A simple model can explain the ecological succession and recovery phases that follow major biotic perturbations caused by impacts or volcanism that lead to exclusion of specialist and most generalist species. Within such highly stressed environments, Guembelitria is the only genus to thrive, and without competition, rapidly reproduce and exponentially increase their populations. When nutrients are depleted, populations rapidly decrease, leading to ecologic niches for other generalists and ecosystem recovery. Small low-O 2 -tolerant heterohelicid populations mark this second stage, followed by small trochospiral and planispiral species. With further environmental recovery, increasing competition, niche development and restoration of a well-stratified water mass, oligotrophic conditions are restored, opening habitats for the highly specialized and diverse species and a return to normal diverse assemblages. This ecological succession is observed in association with mantle plume volcanism in the Indian Ocean and eastern Tethys during the late Maastrichtian, and in association with the K -T impact and volcanism during the early Tertiary.

Field guide to Cretaceous-tertiary boundary sections in northeastern Mexico

This guide was prepared for the field trip to the KT elastic sequence of northeastern Mexico, 5-8 February 1994, in conjunction with the Conference on New Developments Regarding the KT Event and Other Catastrophes in Earth History, held in Houston, Texas. The four-day excursion offers an invaluable opportunity to visit three key outcrops: Arroyo El Mimbral, La Lajilla, and El Pinon. These and other outcrops of this sequence have recently been interpreted as tsunami deposits produced by the meteorite impact event that produced the 200 to 300-km Chicxulub basin in Yucatan, and distributed ejecta around the world approximately 65 m.y. ago that today is recorded as a thin clay layer found at the K/T boundary. The impact tsunami interpretation for these rocks has not gone unchallenged, and others examining the outcrops arrive at quite different conclusions: not tsunami deposits but turbidites; not KT at all but 'upper Cretaceous.' Indeed, it is in hopes of resolving this debate through field discussion, outcrop evaluation, and sampling that led the organizers of the conference to sanction this field trip. This field guide provides participants with background information on the KT clastic sequence outcrops and is divided into two sections. The first section provides regional and logistical context for the outcrops and a description of the clastic sequence. The second section presents three representative interpretations of the outcrops by their advocates. There is clearly no way that these models can be reconciled and so two, if not all three, must be fundamentally wrong. Readers of this guide should keep in mind that many basic outcrop observations that these models are based upon remain unresolved. While great measures were taken to ensure that the information in the description section was as objective as possible, many observations are rooted in interpretations and the emphasis placed on certain observations depends to some degree upon the perspective of the author

Maastrichtian-Paleocene deposition in the Paraíba basin, NE Brazil

Abstrac

Chicxulub impact spherules in the North Atlantic and Caribbean: age constraints and Cretaceous-Tertiary boundary hiatus

The Chicxulub impact is commonly believed to have caused the Cretaceous-Tertiary boundary mass extinction and a thin impact spherule layer in the North Atlantic and Caribbean is frequently cited as proof. We evaluated this claim in the seven best North Atlantic and Caribbean Cretaceous-Tertiary boundary sequences based on high-resolution biostratigraphy, quantitative faunal analyses and stable isotopes. Results reveal a major Cretaceous-Tertiary boundary unconformity spanning most of Danian subzone P1a(1) and Maastrichtian zones CF1-CF2 (~400 ka) in the NW Atlantic Bass River core, ODP Sites 1049A, 1049C and 1050C. In the Caribbean ODP Sites 999B and 1001B the unconformity spans from the early Danian zone P1a(1) through to zones CF1-CF4 (~3 Ma). Only in the Demerara Rise ODP Site 1259B is erosion relatively minor and restricted to the earliest Danian zone P0 and most of subzone P1a(1) (~150 ka). In all sites examined, Chicxulub impact spherules are reworked into the early Danian subzone P1a(1) about 150-200 ka after the mass extinction. A similar pattern of erosion and redeposition of impact spherules in Danian sediments has previously been documented from Cuba, Haiti, Belize, Guatemala, south and central Mexico. This pattern can be explained by intensified Gulf stream circulation at times of climate cooling and sea level changes. The age of the Chicxulub impact cannot be determined from these reworked impact spherule layers, but can be evaluated based on the stratigraphically oldest spherule layer in NE Mexico and Texas, which indicates that this impact predates the Cretaceous-Tertiary boundary by about 130-150 k

CenomanianTuronian transition in a shallow water sequence of the Sinai, Egypt

Environmental and depositional changes across the Late Cenomanian oceanic anoxic event (OAE2) in the Sinai, Egypt, are examined based on biostratigraphy, mineralogy, δ13C values and phosphorus analyses. Comparison with the Pueblo, Colorado, stratotype section reveals the Whadi El Ghaib section as stratigraphically complete across the late Cenomanianearly Turonian. Foraminifera are dominated by high-stress planktic and benthic assemblages characterized by low diversity, low-oxygen and low-salinity tolerant species, which mark shallow-water oceanic dysoxic conditions during OAE2. Oyster biostromes suggest deposition occurred in less than 50 m depths in low-oxygen, brackish, and nutrient-rich waters. Their demise prior to the peak δ13C excursion is likely due to a rising sea-level. Characteristic OAE2 anoxic conditions reached this coastal region only at the end of the δ13C plateau in deeper waters near the end of the Cenomanian. Increased phosphorus accumulations before and after the δ13C excursion suggest higher oxic conditions and increased detrital input. Bulk-rock and clay mineralogy indicate humid climate conditions, increased continental runoff and a rising sea up to the first δ13C peak. Above this interval, a dryer and seasonally well-contrasted climate with intermittently dry conditions prevailed. These results reveal the globally synchronous δ13C shift, but delayed effects of OAE2 dependent on water depth