Modes of Pangean lake level cyclicity driven by astronomical climate pacing modulated by continental position and pCO[Formula: see text].

Orbital cyclicity is a fundamental pacemaker of Earth's climate system. The Newark-Hartford Basin (NHB) lake sediment record of eastern North America contains compelling geologic expressions of this cyclicity, reflecting variations of climatic conditions in tropical Pangea during the Late Triassic and earliest Jurassic (~233 to 199 Ma). Climate modeling enables a deeper mechanistic understanding of Earth system modulation during this unique greenhouse and supercontinent period. We link major features of the NHB record to the combined climatic effects of orbital forcing, paleogeographic changes, and atmospheric pCO[Formula: see text] variations. An ensemble of transient, orbitally driven climate simulations is assessed for nine time slices, three atmospheric pCO[Formula: see text] values, and two paleogeographic reconstructions. Climatic transitions from tropical humid to more seasonal and ultimately semiarid are associated with tectonic drift of the NHB from [Formula: see text] to [Formula: see text]. The modeled orbital modulation of the precipitation-evaporation balance is most pronounced during the 220 to 200 Ma interval, whereas it is limited by weak seasonality and increasing aridity before and after this interval. Lower pCO[Formula: see text] at around 205 Ma contributes to drier climates and could have led to the observed damping of sediment cyclicity. Eccentricity-modulated precession dominates the orbitally driven climate response in the NHB region. High obliquity further amplifies summer precipitation through the seasonal shifts in the tropical rainfall belt. Regions with other proxy records are also assessed, providing guidance toward an integrated picture of global astronomical climate forcing in the Late Triassic and ultimately of other periods in Earth history.

Investigating Mesozoic Climate Trends and Sensitivities With a Large Ensemble of Climate Model Simulations.

The Mesozoic era (∼252 to 66 million years ago) was a key interval in Earth's evolution toward its modern state, witnessing the breakup of the supercontinent Pangaea and significant biotic innovations like the early evolution of mammals. Plate tectonic dynamics drove a fundamental climatic transition from the early Mesozoic supercontinent toward the Late Cretaceous fragmented continental configuration. Here, key aspects of Mesozoic long-term environmental changes are assessed in a climate model ensemble framework. We analyze so far the most extended ensemble of equilibrium climate states simulated for evolving Mesozoic boundary conditions covering the period from 255 to 60 Ma in 5 Myr timesteps. Global mean temperatures are generally found to be elevated above the present and exhibit a baseline warming trend driven by rising sea levels and increasing solar luminosity. Warm (Triassic and mid-Cretaceous) and cool (Jurassic and end-Cretaceous) anomalies result from pCO2 changes indicated by different reconstructions. Seasonal and zonal temperature contrasts as well as continental aridity show an overall decrease from the Late Triassic-Early Jurassic to the Late Cretaceous. Meridional temperature gradients are reduced at higher global temperatures and less land area in the high latitudes. With systematic sensitivity experiments, the influence of paleogeography, sea level, vegetation patterns, pCO2, solar luminosity, and orbital configuration on these trends is investigated. For example, long-term seasonality trends are driven by paleogeography, but orbital cycles could have had similar-scale effects on shorter timescales. Global mean temperatures, continental humidity, and meridional temperature gradients are, however, also strongly affected by pCO2.

New record of podocopid ostracods from Cretaceous amber.

Burmese Cretaceous amber (∼99 Ma, Myanmar) is famous for the preservation of a wide range of fauna and flora, including representatives of marine, freshwater and terrestrial groups. Here, we report on three ostracod specimens, that came visible as syninclusions to an aquatic isopod. The three specimens represent three different taxa, that were found preserved in a single piece of amber. One of the described specimens was studied using µCT scanning data. On the basis of general carapace morphology we assign all three to the group Podocopida, and (tentatively) its ingroup Cypridocopina. A lack of visibility of more particular diagnostic features such as adductor muscle scars and details of the marginal zone precludes a further identification, but we discuss possible affinities with either the marine-brackish group Pontocypridoidea or the non-marine group Cypridoidea. The taphonomy indicates that the studied ostracods had been subject to limited (if any) post-mortem transport, which could be consistent with marginal marine environments.

A gigantic marine ostracod (Crustacea: Myodocopa) trapped in mid-Cretaceous Burmese amber.

The mid-Cretaceous Burmese amber (~99 Ma, Myanmar), widely known for exquisite preservation of theropods, also yields microfossils, which can provide important contextual information on paleoenvironment and amber formation. We report the first Cretaceous ostracod in amber-the gigantic (12.9 mm) right valve of an exclusively marine group (Myodocopa: Myodocopida) preserved in Burmese amber. Ostracods are usually small (0.5-2 mm), with well-calcified carapaces that provide an excellent fossil record extending to at least the Ordovician (~485 million years ago), but they are rarely encountered in amber. The new specimen effectively doubles the age of the ostracod amber record, offering the first representative of the Myodocopa, a weakly calcified group with a poor fossil record. Its carapace morphology is atypical and likely plesiomorphic. The preserved valve appears to be either a moulted exuvium or a dead and disarticulated specimen, and subsequent resin flows contain forest floor inclusions with terrestrial arthropods, i.e., fragmentary remains of spiders, and insect frass. These features resolve an enigmatic taphonomic pathway, and support a marginal marine setting for resin production.

Middle to Late Eocene paleoenvironmental changes in a marine transgressive sequence from the northern Tethyan margin (Adelholzen, Germany).

The northern Tethyan margin is a key region for determining environmental changes associated with the collision of continental and oceanic tectonic plates and Alpine orogeny. Herein we investigated Middle to Late Eocene neritic to bathyal sediments deposited during an interval of unstable climatic conditions. In order to quantify paleoenvironmental changes, we developed a detailed age model based on biozonations of planktic foraminifera, calcareous nannoplankton, and larger benthic foraminifera. The section at Adelholzen covers the almost complete Lutetian Stage (calcareous nannoplankton zones NP15a-16, planktic foraminifera zones E8-11, shallow benthic (foraminifera) zones SBZ13-15) and large parts of the Priabonian Stage (NP18-20, E14/15), while the intermediate Bartonian Stage (NP17) is completely missing. Foraminiferal, calcareous nannoplankton, and macrofossil assemblages were analyzed for changes in paleo-water depth, mixing and stratification, paleo-primary productivity (pPP), food supply, and bottom water oxygenation. Paleo-water depth estimates range from 50 m (middle neritic, early Lutetian) to nearly 500 m (upper bathyal, late Priabonian). The combination of assemblage composition, planktic and benthic foraminiferal accumulation rates, and derived parameters (carbon-flux to sea floor, pPP) enabled us to identify a series of distinct paleoceanographic events of at least regional significance. Such events are characterized by considerable changes in primary productivity or reduced bottom water ventilation. Calculated pPP-values indicate oligotrophic conditions throughout.