Evidence of Extreme Aridification Across the Jurassic/Cretaceous Boundary From North China

Jurassic–Cretaceous terrestrial transition red beds in northern North China and their implication on regional paleogeography, paleoecology, and tectonic evolution

Authors:

xu et al

Abstract:

Craton are associated with a number of major geological issues that remain controversial, such as paleogeography, biotic transition, and tectonic evolution. Based on previous studies and new progress related to stratigraphy, sedimentology, provenance, biotas, and tectonics, this paper performs a comprehensive review of the red beds in the northern North China Craton represented by the Tuchengzi/Houcheng/Daqingshan Formation (ca. 154–137 Ma) and offers some new perspectives. Based on the 15 measured sections, five facies units including alluvial fan, fluvial, delta, lacustrine, and eolian facies have been recognized and described in detail. Provenance analysis indicates that the red beds were derived from local sources. Deposits in the basins in the eastern Yinshan–Yanshan orogenic belt were derived mainly from volcanic rocks of the Middle–Late Jurassic Tiaojishan Formation and the Mesoproterozoic–Early Paleozoic carbonate, siliceous, and clastic rocks present around the basin, especially in the north. In contrast, sediments in the basins in the western Yinshan–Yanshan orogenic belt were provided predominantly by the Neoarchean–Paleoproterozoic metamorphic rocks exposed mainly in the north of the basin. Paleocurrent features in different regions show characteristics of a localized convergent paleo-drainage system, suggesting that a series of relatively independent small- to mid-scale basins developed in the northern North China Craton. The east–west-trending Yinshan–Yanshan orogenic belt, formed in the late Middle Jurassic, uplifted successively and constituted a paleogeographic highland in northern North China during the Jurassic–Cretaceous transition time. The presence of eolian deposits in the early Early Cretaceous indicates degradation of the severe arid and hot environment, which may have been an essential factor in the dying out of the Yanliao Biota. Combined with regional Late Jurassic–Early Cretaceous A-type granites, mafic dykes, and metamorphic core complexes and rift basins, this suggests that the Jurassic–Cretaceous transition red beds were formed in an extensional tectonic setting controlled by the post-orogenic collapse of the Mongol–Okhotsk orogenic belt.

Carbon cycle history across the Jurassic–Cretaceous boundary

Carbon cycle history through the Jurassic–Cretaceous boundary: A new global δ13C stack

Authors:

Price et al

Abstract:

We present new carbon and oxygen isotope curves from sections in the Bakony Mts. (Hungary), constrained by biostratigraphy and magnetostratigraphy in order to evaluate whether carbon isotopes can provide a tool to help establish and correlate the last system boundary remaining undefined in the Phanerozoic as well provide data to better understand the carbon cycle history and environmental drivers during the Jurassic–Cretaceous interval. We observe a gentle decrease in carbon isotope values through the Late Jurassic. A pronounced shift to more positive carbon isotope values does not occur until the Valanginian, corresponding to the Weissert event. In order to place the newly obtained stable isotope data into a global context, we compiled 31 published and stratigraphically constrained carbon isotope records from the Pacific, Tethyan, Atlantic, and Boreal realms, to produce a new global δ13C stack for the Late Oxfordian through Early Hauterivian interval. Our new data from Hungary is consistent with the global δ13C stack. The stack reveals a steady but slow decrease in carbon isotope values until the Early Valanginian. In comparison, the Late Jurassic–Early Cretaceous δ13C curve in GTS 2012 shows no slope and little variation. Aside from the well-defined Valanginian positive excursion, chemostratigraphic correlation durSchning the Jurassic–Cretaceous boundary interval is difficult, due to relatively stable δ13C values, compounded by a slope which is too slight. There is no clear isotopic marker event for the system boundary. The long-term gradual change towards more negative carbon isotope values through the Jurassic–Cretaceous transition has previously been explained by increasingly oligotrophic condition and lessened primary production. However, this contradicts the reported increase in 87Sr/86Sr ratios suggesting intensification of weathering (and a decreasing contribution of non-radiogenic hydrothermal Sr) and presumably a concomitant rise in nutrient input into the oceans. The concomitant rise of modern phytoplankton groups (dinoflagellates and coccolithophores) would have also led to increased primary productivity, making the negative carbon isotope trend even more notable. We suggest that gradual oceanographic changes, more effective connections and mixing between the Tethys, Atlantic and Pacific Oceans, would have promoted a shift towards enhanced burial of isotopically heavy carbonate carbon and effective recycling of isotopically light organic matter. These processes account for the observed long-term trend, interrupted only by the Weissert event in the Valanginian.

How Many Dinosaur Species Were There?

How many dinosaur species were there? Fossil bias and true richness estimated using a Poisson sampling model

Authors:

Starrfelt et al

Abstract:

The fossil record is a rich source of information about biological diversity in the past. However, the fossil record is not only incomplete but has also inherent biases due to geological, physical, chemical and biological factors. Our knowledge of past life is also biased because of differences in academic and amateur interests and sampling efforts. As a result, not all individuals or species that lived in the past are equally likely to be discovered at any point in time or space. To reconstruct temporal dynamics of diversity using the fossil record, biased sampling must be explicitly taken into account. Here, we introduce an approach that uses the variation in the number of times each species is observed in the fossil record to estimate both sampling bias and true richness. We term our technique TRiPS (True Richness estimated using a Poisson Sampling model) and explore its robustness to violation of its assumptions via simulations. We then venture to estimate sampling bias and absolute species richness of dinosaurs in the geological stages of the Mesozoic. Using TRiPS, we estimate that 1936 (1543–2468) species of dinosaurs roamed the Earth during the Mesozoic. We also present improved estimates of species richness trajectories of the three major dinosaur clades: the sauropodomorphs, ornithischians and theropods, casting doubt on the Jurassic–Cretaceous extinction event and demonstrating that all dinosaur groups are subject to considerable sampling bias throughout the Mesozoic.

What Environmental Factor Wiped out so Many Crocodyliforms Across the Jurassic-Cretaceous Boundary?

Environmental drivers of crocodyliform extinction across the Jurassic/Cretaceous transition

Authors:

Tennant et al

Abstract:

Crocodyliforms have a much richer evolutionary history than represented by their extant descendants, including several independent marine and terrestrial radiations during the Mesozoic. However, heterogeneous sampling of their fossil record has obscured their macroevolutionary dynamics, and obfuscated attempts to reconcile external drivers of these patterns. Here, we present a comprehensive analysis of crocodyliform biodiversity through the Jurassic/Cretaceous (J/K) transition using subsampling and phylogenetic approaches and apply maximum-likelihood methods to fit models of extrinsic variables to assess what mediated these patterns. A combination of fluctuations in sea-level and episodic perturbations to the carbon and sulfur cycles was primarily responsible for both a marine and non-marine crocodyliform biodiversity decline through the J/K boundary, primarily documented in Europe. This was tracked by high extinction rates at the boundary and suppressed origination rates throughout the Early Cretaceous. The diversification of Eusuchia and Notosuchia likely emanated from the easing of ecological pressure resulting from the biodiversity decline, which also culminated in the extinction of the marine thalattosuchians in the late Early Cretaceous. Through application of rigorous techniques for estimating biodiversity, our results demonstrate that it is possible to tease apart the complex array of controls on diversification patterns in major archosaur clades.

pop sci link.

Dinosaur Trackways of the Jurassic-Cretaceous Boundary in China

Theropod and possible ornithopod track assemblages from the Jurassic–Cretaceous boundary Houcheng Formation, Shangyi, northern Hebei, China

Authors:

Xing et al.

Abstract:

Dinosaur track assemblages from the Houcheng Formation in the small continental Shangyi Basin of northern Hebei Province, China bridge a gap in the record of vertebrates from this unit and enrich our knowledge of ichnofaunas from the Jurassic–Cretaceous boundary. Their stratigraphic position between the Middle Jurassic Yan-Liao Biota and the Lower Cretaceous Jehol Biota gives them a special importance. New discoveries allow a re-assessment of theropod and possible ornithopod tracks that are present with several trackways. Seventy-three footprints were examined and documented. Despite their smaller size, the tridactyl mesaxonic theropod tracks show morphological similarities with the ichnogenus Therangospodus known from the Upper Jurassic deposits of North America, Europe, and Central Asia. The possible ornithopod tracks lack an associated manus imprint, suggesting a bipedal trackmaker. These possible ornithopod tracks from the Houcheng Formation provide evidence for the presence of small basal ornithopods or basal Cerapoda in the Upper Jurassic–Lower Cretaceous in this region. The depositional environment was the margin of an extensive shallow lake with fluctuating water levels under seasonally dry climate.

Tamu Massif is a Single, Massive Volcano the Size of the State of New Mexico

A University of Houston (UH) professor led a team of scientists to uncover the largest single volcano yet documented on Earth. Covering an area roughly equivalent to the British Isles or the state of New Mexico, this volcano, dubbed the Tamu Massif, is nearly as big as the giant volcanoes of Mars, placing it among the largest in the Solar System.

William Sager, a professor in the Department of Earth and Atmospheric Sciences at UH, first began studying the volcano about 20 years ago at Texas A&M's College of Geosciences. Sager and his team's findings appear in the Sept. 8 issue of Nature Geoscience, the monthly multi-disciplinary journal reflecting disciplines within the geosciences.

Located about 1,000 miles east of Japan, Tamu Massif is the largest feature of Shatsky Rise, an underwater mountain range formed 130 to 145 million years ago by the eruption of several underwater volcanoes. Until now, it was unclear whether Tamu Massif was a single volcano, or a composite of many eruption points. By integrating several sources of evidence, including core samples and data collected on board the JOIDES Resolution research ship, the authors have confirmed that the mass of basalt that constitutes Tamu Massif did indeed erupt from a single source near the center.

"Tamu Massif is the biggest single shield volcano ever discovered on Earth," Sager said. "There may be larger volcanoes, because there are bigger igneous features out there such as the Ontong Java Plateau, but we don't know if these features are one volcano or complexes of volcanoes."

Tamu Massif stands out among underwater volcanoes not just for its size, but also its shape. It is low and broad, meaning that the erupted lava flows must have traveled long distances compared to most other volcanoes on Earth. The seafloor is dotted with thousands of underwater volcanoes, or seamounts, most of which are small and steep compared to the low, broad expanse of Tamu Massif.

link.

That's a VERY interesting time frame.  Oh, about the J-K Boundary even.  Nothing happened then!

Carbon Isotope Excursions Across the Boreal Jurassic–Cretaceous Boundary

Carbon isotope excursions in Boreal Jurassic–Cretaceous boundary sections and their correlation potential

Authors:

1. Oksana S. Dzyuba (a)

2. Olga P. Izokh (b)

3. Boris N. Shurygin (a)

Affiliations:

a. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of RAS, Acad. Koptyug av., 3, Novosibirsk, 630090, Russia

b. Sobolev Institute of Geology and Mineralogy, Siberian Branch of RAS, Acad. Koptyug av., 3, Novosibirsk, 630090, Russia

Abstract:

The Jurassic–Cretaceous (J–K) boundary is one of the most problematic points on the geological timescale. The boundary is not defined by a Global Stratotype Section and Point (GSSP) because of the absence of well-defined (by significant faunal turnover), widely correlatable biostratigraphic levels to fix the base of the Berriasian. A distinct earliest Berriasian positive carbon isotope excursion is identified in the Boreal marine carbonate (belemnites) carbon records from the Maurynya River (Northern Urals) and the Nordvik Peninsula (northern East Siberia). The excursion is found within the top part of the upper Volgian Craspedites taimyrensis ammonite Zone, slightly above the J–K boundary, which was established by palaeomagnetic data. Because a significant positive δ13C shift was also observed immediately above the J–K boundary in the Tethyan Guppen-Heuberge pelagic-carbonate section (Switzerland), this positive carbon isotope event can be regarded as a useful marker for a Panboreal and Boreal–Tethyan correlation of J–K boundary beds. This δ13C excursion is interpreted as a record of increased rates of organic carbon burial. The δ13C data obtained previously for the upper Volgian and Ryazanian in different Boreal regions are also analysed in this paper. Other well-documented carbon isotope excursions with less global significance allow the creation of a composite carbon-isotope curve for Boreal regions that characterises the upper Volgian and Ryazanian in detail.