Search for: All records

Late Triassic marine macrofaunal assemblages of Aotearoa (New Zealand) exhibit remarkably low diversity, high endemism, and synchronous faunal turnover, and present a complicated array of bottom-water oxygenation indicators. Here we present the results of three bulk sampling campaigns representing marine communities across both the North and South Islands. Four biofacies are present, beginning with Halobia biofacies in the Oretian (lower Norian). The Otamitan (middle Norian) deposits are characterized by two successive biofacies, the Manticula/Hokonuia biofacies and the high diversity brachiopod biofacies of the upper Otamitan. The Warepan (upper Norian) deposits are recognized by the Monotis biofacies. The four biofacies persist across different regions, displaying nearly identical turnover events despite sedimentological variations. However, the bivalve and brachiopod genera exhibit differential shell bed-forming capabilities in different regions. Only the bivalve Monotis was observed in dense shell beds in all three regions sampled. In the northernmost region sampled (including Kiritehere Beach), shell beds are the primary presentation for fossils irrespective of the taxa. We present a comparison of the sedimentological characteristics between shell bed and non-shell bed deposits. Large and/or inflated bivalves are not uncommon, but essentially no burrowing organisms are present. These findings provide crucial insights into the dynamic nature of Triassic marine ecosystems, shedding light on the paleontological diversity patterns and ecological structure of high-latitude systems during hot-house intervals. The persistence of the same biofacies over a broad spatial extent emphasizes the strong influence of regional environmental conditions on the establishment and maintenance of marine communities. 

In the South Island of Aotearoa (New Zealand), the preservation of biogenic carbonate in Late Triassic sedimentary rocks is rare to non-existent; however, differential preservation modes between common phyla are commonly observed and serve to elucidate the stratigraphic and diagenetic history of these often poorly- exposed immature sandstone units. The Taringatura Group sandstones from Southland and Otago range from sandy siltstones to silty arkosic sandstones that commonly host molluscan and brachiopod macrofossils as well as rare echinoderms, bryozoans, and foraminifera. Additionally, there is a hypothesized unconformity between the lower Oretian and Otamitan age (227.7–217.0 Ma) and the overlying Warepan age (217–208.5 Ma) deposits indicated by an abrupt change in composition, grain size, and fossil assemblage. Molluscs from the Oretian and Otamitan deposits exhibit fine-detail preservation on external and internal molds. Thin-shelled taxa, such as Halobia, exhibit some shell replacement by clay minerals, likely from the dissolution of feldspars in the surrounding rock. Conversely, larger and thicker-shelled brachiopods and bivalves such as Manticula and Hokonuia do not present as casts. When preserved, foraminifera and rare bryozoans are typically silicified. The overlying Warepan sandstone beds frequently contain fossils of the bivalve Monotis which exhibit a similar preservation style to older molluscs, though lacking clay minerals. Presently, the fossiliferous Taringatura sandstones exhibit low porosity and low permeability, as is expected from the subsequent compaction of sandstones after burial. However, the dissolution of biogenic carbonate implies a past permeability. The presence of clay minerals in Oretian and Otamitan fossils may indicate a period of subaerial exposure and infiltration of meteoric water prior to the deposition of Warepan units. Notably, clay replacement occurs more frequently in the thinnest fossils. Original carbonate material may have persisted for longer in the more robust taxa, allowing them to resist most deformation from compaction prior to the final loss of carbonate. Differential diagenesis of biogenic carbonates supports the existence of a significant unconformity between Otamitan and Warepan units in the Taringatura sandstones. 

Two recently discovered vertebrae collections from the Gabbs Formation in New York Canyon, Nevada, USA are among the first Late Triassic pistosauroid fossils reported from North America. Pistosauroidea were a group of long-necked secondarily aquatic reptiles that belong to the clade sauropterygia. Pistosauroids first evolved in the Triassic Period but later became an integral part of the Mesozoic marine ecosystem as the iconic plesiosaurs during the Jurassic and Cretaceous Periods. Our findings include a single small centrum from near the Triassic/Jurassic boundary and a block of similarly sized associated vertebrae from the early Rhaetian. The vertebrae exhibit a uniquely pistosauroid external morphology. The centrum is antero-posteriorly narrow but dorso-ventrally tall with gently amphicoelous faces. The histology revealed through micro-CT scanning, is also diagnostically pistosauroid. In sagittal cross-section, a denser layer of bone is visible along the faces of the centrum, while a unique V-shaped texture extending from the base of the neural canal is visible in transverse cross-section. The New York Canyon locality has long been renowned as a reference section for the Late Triassic and Triassic/Jurassic boundary but has only recently become a focus for vertebrate research. The Gabbs Formation at this locality is a relatively shallow marine environment and ranges from mid ramp to inner ramp. Vertebrate material has been noted throughout New York Canyon, nearly all of which has been identified as ichthyosaur, but these discoveries have shown the potential for the area as an important site for Late Triassic sauropterygians which have a poor record globally and were previously unknown from North America. Despite the limited nature of this new material, it is significant in providing evidence of the presence of pistosauroids in the Late Triassic of Eastern Panthalassa and helps fill in the exceptionally sparse history of sauropterygians in the Triassic of cordilleran North America. 

Although many sources of atmospheric CO2 have been identified, the major sinks are best understood in a deep-time context. Here, we focus on two Large Igneous Provinces (LIPs), the Central Atlantic Magmatic Province (CAMP) situated in the low latitude humid zone ~201.6 Ma and the Karoo-Ferrar located at high southern latitudes ~183 Ma. We use soil carbonate, lithologic, δD of n-alkanes, Sr data, and modeling to examine how these eruptions, hydrological cycling, and weathering impacted global atmospheric CO2, carbon cycling, and biotic extinction at the ETE and T-OAE hyperthermals. CAMP largely erupted in the tropics, doubled atmospheric CO2 from ~2,500 – 5,000 ppm at the ETE (observed in soil carbonates with an onset <1000 and a duration of <~20 ky) and rapidly sequestered CO2 (< 2,500 ppm) as recorded in Newark Supergroup basins (eastern US). These same strata preserve variations in the lake level expression of the climatic precession cycle based on lithology and δD. High cyclicity variance tracked high pCO2 (>~4000 ppm) and drove insolation-paced increases in precipitation. Leaf wax δD shows significant variability, reflecting an enhanced hydrological cycle at the ETE with repeated sudden shifts in relative evaporation for ~1 Myr. In marine strata, 87Sr/86Sr and 187Os/188Os values track changes in pCO2, suggesting a terrestrial/marine linkage through continental weathering, CO2, and runoff. Despite the northward movement of these basins into the arid belt, our data suggest lower evaporation relative to precipitation driven by lower temperatures, consistent with lower pCO2 due to CAMP weathering, which modeling estimates to have increased 6 to 10-fold for >1.6 Myr after the eruptive phase. Release of CO2 from the Karoo-Ferrar LIP similarly enhanced the hydrological cycle as evidenced from sedimentary observations (e.g., fine-scale turbidites and debris flow deposits) in Yorkshire (UK). The onset of the carbon isotope excursion at the T-OAE lasts 0.5 Myr with a 1.5 Myr duration modulated by astronomical pacing. Our leaf wax δD from the same strata show a transient enhancement in the hydrological cycle. Although the Karoo-Ferrar has a limited drawdown potential when compared with CAMP‐type basalts because of its higher latitude location, Toarcian weathering rates may have increased 2 to 5-fold, acting as a net sink 1–2 Myr after eruptions ceased. 

The latest Triassic was an interval of prolonged biotic extinction culminated by the end-Triassic Extinction, which is associated with a pronounced perturbation of the global carbon cycle that can be connected to extensive volcanism of the Central Atlantic Magmatic Province (CAMP). Earlier chaotic perturbations of the global carbon cycle can also be tied to the onset of declining latest Triassic diversity, which reached its maximum across the Norian-Rhaetian boundary (NRB). These perturbations are global across the Panthalassa Ocean to both sides of the Pangean supercontinent in both the Northern and Southern Hemispheres. The NRB witnessed the severe global extinctions of significant marine fossil groups, such as ammonoids, bivalves, conodonts and radiolarians. The onset of the stepwise Late Triassic extinctions coincided with the NRB carbon perturbation (d13Corg), indicating that the combined climate and environmental changes impacted the global biota. The trigger of this event is attributed to a volcanic event pre-dating the NRB, an alternative source of volcanogenic gas emissions, and/or a meteorite impact.