A middle Miocene to Quaternary sedimentary and palaeoenvironmental record from the western continental shelf of South Africa

Dietary niche stability of equids across the mid-Miocene Climatic Optimum in Oregon, USA

Late Cenozoic phosphogenesis on the western shelf of South Africa in the vicinity of the Cape Canyon

BackgroundPhylogenetic analyses of the Annonaceae consistently identify four clades: a basal clade consisting of Anaxagorea, and a small 'ambavioid' clade that is sister to two main clades, the 'long branch clade' (LBC) and 'short branch clade' (SBC). Divergence times in the family have previously been estimated using non-parametric rate smoothing (NPRS) and penalized likelihood (PL). Here we use an uncorrelated lognormal (UCLD) relaxed molecular clock in BEAST to estimate diversification times of the main clades within the family with a focus on the Asian genus Pseuduvaria within the SBC. Two fossil calibration points are applied, including the first use of the recently discovered Annonaceae fossil Futabanthus. The taxonomy and morphology of Pseuduvaria have been well documented, although no previous dating or biogeographical studies have been undertaken. Ancestral areas at internal nodes within Pseuduvaria are determined using dispersal-vicariance analysis (DIVA) and weighted ancestral area analysis (WAAA).ResultsThe divergence times of the main clades within the Annonaceae were found to deviate slightly from previous estimates that used different calibration points and dating methods. In particular, our estimate for the SBC crown (55.2-26.9 Mya) is much younger than previous estimates (62.5-53.1 ± 3.6 Mya and ca. 58.76 Mya). Early diversification of Pseuduvaria was estimated to have occurred 15-8 Mya, possibly associated with the 'mid-Miocene climatic optimum.' Pseuduvaria is inferred to have originated in Sundaland in the late Miocene, ca. 8 Mya; subsequent migration events were predominantly eastwards towards New Guinea and Australia, although several migratory reversals are also postulated. Speciation of Pseuduvaria within New Guinea may have occurred after ca. 6.5 Mya, possibly coinciding with the formation of the Central Range orogeny from ca. 8 Mya.ConclusionOur divergence time estimates within the Annonaceae are likely to be more precise as we used a UCLD clock model and calibrated the phylogeny using new fossil evidence. Pseuduvaria is shown to have dispersed from Sundaland after the late Miocene. The present-day paleotropical distribution of Pseuduvaria may have been achieved by long-distance dispersal, and speciation events might be explained by global climatic oscillations, sea level fluctuations, and tectonic activity.

Winged fruits of Shorea (Dipterocarpaceae) from the Miocene of Southeast China: Evidence for the northward extension of dipterocarps during the Mid-Miocene Climatic Optimum

ABSTRACTSedimentary deposits north of the western Snake River Plain host Idaho’s first and only producing oil and gas field. They consist of the lower to middle Miocene Payette Formation, the middle to upper Miocene Poison Creek and Chalk Hills Formations, and the Pliocene to lower Pleistocene Glenns Ferry Formation. Using new geochronology, palynomorph biostratigraphy, and geologic mapping, we connect updip surface features to subsurface petroleum play elements. The Payette Formation is a likely main source of the hydrocarbons, and acts as one of the reservoirs in the unnamed basin. Here, we redefine the Payette Formation as 0 to ~3,500 ft (0 to ~1,000 m) of mudstone, with lesser amounts of sandstone overlying and interbedded with the Columbia River Basalt Group and Weiser volcanic field. Index palynomorphs, including Liquidambar and Pterocarya, present in Idaho during and immediately after the middle Miocene climatic optimum, and new U–Pb ages of 16.39 and 15.88 Ma, help establish the thickness and extent of the formation. For the first time, these biostratigraphic markers have been defined for the oil and gas wells. The Poison Creek Formation is sandstone interbedded with mudstone that is ~800–1,800 ft (250–550 m) thick. The Chalk Hills Formation is a tuffaceous siltstone, claystone, and sandstone that is as much as ~4,200 ft (1,280 m) thick. New U–Pb ages are 10.1, 9.04, and 9.00 for the Poison Creek Formation, along with maximum depositional ages of 10.7 to 9.9 Ma for four samples from the Poison Creek Formation. A single U–Pb age of 7.78 Ma was determined from pumice low in the Chalk Hills Formation. Like the Payette Formation, the Poison Creek Formation can be a reservoir, whereas the Chalk Hills Formation acts as a sealing mudstone facies. The overlying sandstone, siltstone, and conglomerate of the Glenns Ferry Formation act as the overburden to the petroleum system in the subsurface, and were important for burial and hydrocarbon maturation. The Glenns Ferry Formation is up to 500 ft (150 m) thick in the study area, as much has been eroded. Whereas the Payette and Poison Creek Formations were deposited during the mid-Miocene climatic optimum amongst and above volcanic flows, the Chalk Hills and Glenns Ferry Formations were deposited within ancient Lake Idaho during an overall increase in aridity and cooling after the mid-Miocene climatic optimum.

<p>The Miocene experienced both, ice-house periods with continental ice-sheets covering both poles and warm greenhouse conditions with strongly increased global temperature, glacier retreat and sea-level rise. The Mid-Miocene Climatic Optimum (MMCO) is the most pronounced warming event in the last 24 Ma, standing out in a time of protracted cooling. The MMCO is marked by a period of intensive global warming between ca. 17 and 15 Ma. The subsequent Mid-Miocene Climate Transition (MMCT), in contrast, was affected by global temperature decline, growth of Antarctic ice sheets, sea level fall and marine biota overturn.</p><p>Miocene climate conditions were intensely studied on both, global and regional scales, based on i.a. marine isotope records and continental paleobotanical and mammalian fossil data sets. Despite the dense data sets continental Miocene temperature evolution still remains unclear owing to a large range of inferred temperatures and/or poor age constraints of the associated records.</p><p>Here, we present a long-term terrestrial climate record that covers the time interval between ~20 and ~13 Ma and is based on stable (δ<sup>18</sup>O) and clumped isotope (Δ<sub>47</sub>) geochemical data. We apply Δ<sub>47</sub> thermometry on terrestrial foreland basin sediments to reconstruct the Middle Miocene continental temperature evolution for central Europe. Pedogenic carbonates from well dated fossil soils from several sites in the Northern Alpine Foreland Basin (Switzerland) reveal warm and stable temperatures for the early Miocene (20 – 19 Ma), followed by overall strongly enhanced variability in temperatures with maximum values attained between ca. 17 and 14 Ma. We observe a highly dynamic transition to cooler climates at the end of the MMCO and a subsequent rapid temperature decline of approximately 20°C after 14 Ma during the MMCT. The highly variable temperature patterns during the cooling period coincide with phases of high seasonality in the precipitation pattern as derived from oxygen isotope compositions of soil water.</p>

Late Neogene foraminifera from the northern Namibian continental shelf and the transition to the Benguela Upwelling System

Modeling the effects of global cooling and the Tethyan Seaway closure on North African and South Asian climates during the Middle Miocene Climate Transition

Glirid dental material is described from the Middle Miocene channel fill of the Hambach open-cast lignite mine in northwestern Germany. The fauna Hambach 6C shows a high diversity with seven species in six genera: Glirudinus undosus, Muscardinus thaleri, Muscardinus sansaniensis, Miodyromys aegercii, Paraglirulus werenfelsi, Microdyromys koenigswaldi, and Paraglis astaracensis, which are characteristic taxa in Middle Miocene European localities. Regarding the faunal composition and high diversity, the Hambach 6C assemblage is closest to that of the MN 5 locality Schönenberg in southern Germany, but also shares many taxa with late Middle Miocene faunas. The species richness of glirids, combined with other vertebrate remains in Hambach 6C indicates a warm, humid forested environment during the Mid-Miocene Climate Optimum (MCO).

The Miocene palaeoenvironmental and palaeoceanographic evolution of the Gippsland Basin, Southeast Australia: a record of Southern Ocean change

A tropical forest of the middle Miocene of Fujian (SE China) reveals Sino-Indian biogeographic affinities

Paleoceanographic changes in the Northeast Indian Ocean during middle Miocene inferred from carbon and oxygen isotopes of foraminiferal fossil shells

Middle Miocene Climatic Optimum (MMCO) is widely distributed and associated with increasing temperature and CO2 content in the atmosphere. The effects of MMCO are identified in the mid-latitude region, with lack of examples from the low latitude areas. In this study, we aim to determine the effect of MMCO at Cibulakan Formation of Bogor Basin, Indonesia, which is situated in lower latitude. We took 58 samples from the Cibulakan Formation, which is exposed along Cileungsi River, for quantitative nannoplankton (the abundance of Helicosphaera carteri) analysis to mark increasing and decreasing salinity event, as they are sensitive to temperature. Temperature relates to the salinity of the seawater due to evaporation. From our analysis, we identified sea surface temperature change in Early Miocene which was presumably due to small scale Early Miocene glaciation and active tectonic during the period. The warmer temperature took place on Middle Miocene as the effect of a warm and open sea environment during Mid Miocene Climatic Optimum. Afterward, the temperature continued to rise until the late Miocene, as it had been triggered by the increasing global temperature at the Pacific Ocean and widely distributed clean water at North West Java Basin during the depositional period.

The nature of carbonate cycles and their stacking patterns have been interpreted to be related with global climate conditions through geologic history. Carbonate cycles formed during icehouse times (e.g., late Devonian – early Permian and Neogene) are laterally variable due to allocyclic controls in response to high amplitude, high frequency (fifthand fourth-order) sea-level fluctuations superposed on lower amplitude, low frequency (third-order) eustatic sea-level changes. Whereas cycles formed during greenhouse times (e.g., Mesoproterozoic, Ordovician-early Devonian and late Permian-early Tertiary) are commonly more laterally continuous due to the domination of lower frequency (thirdorder) eustatic sea-level fluctuations. During supergreenhouse climate conditions such as in the Furongian, carbonate cycles were less likely controlled by eustatic sea-level fluctuations. High levels of atmospheric CO2 (>4000 ppm) during this epoch would have prevented the development of polar ice sheet, thus limiting and/or minimizing glacio-eustatic sea-level changes. Tracing the cycles and cycle boundaries in continuous outcrop in the Great Basin, western United States reveals significant lateral variability of cycles. Cycle boundaries disappear within tens to hundreds of meters and component facies of individual cycles pinch out or interfinger with other component facies. Within a cycle set (i.e., cycle stacking patterns bounded by key surfaces), cycle numbers and thickness vary locally and regionally, suggesting dominant autogenic formation of cycles and stacking patterns in the warm Furongian carbonate platforms. Understanding the style of cycles and stacking patterns formation through time has implications to carbonate exploration activities in Southeast Asia and elsewhere. * University of Nevada ** ExxonMobil Indonesia INTRODUCTION About 60% of the world’s oil and 40% of the world’s gas reserves are held in carbonate reservoirs (Schlumberger, 2007). Yet, the very nature of carbonate cycles (i.e., meter-scale cycles and cycle stacking patterns) as the building blocks of these reservoirs remain unpredictable and debated (Spence and Tucker, 2007, Bosence et al., 2009). In a review paper on carbonate cyclostratigraphy, Lehrmann and Goldhammer (1999) concluded that carbonate cycles and their stacking patterns are related to the global climate conditions through geologic history (Figure 1). Icehouse carbonates are laterally variable due to allocyclic controls in response to high amplitude, high frequency (fifthand fourth-order) sea-level fluctuations superposed on lower amplitude, low frequency (third-order) eustatic sea-level changes (Lehrmann and Goldhammer, 1999; Bishop et al., 2010). Whereas greenhouse carbonates are commonly more laterally continuous due to the domination of lower frequency (third-order) eustatic sea-level fluctuations (e.g., Koerschner and Read, 1989; Lehrmann and Goldhammer, 1999; Miller et al., 2003; Saltzman et al., 2004). While giving insight to carbonate cycles studies, these models, however, may have been oversimplified. We hypothesize that carbonate successions formed during supergreenhouse times with high atmospheric CO2 (e.g., Mesoproterozoic, CambrianOrdovician and Cretaceous) should have less influence from glacio-eustatic sea-level changes than those that formed during other times. The Furongian (late Cambrian) carbonate platforms were noticeably formed under the highest atmospheric CO2 levels (~4000–7000 ppm; Berner and Kothavala, 2001) of the Phanerozoic. Such high atmospheric CO2 may have prevented the development of significant continental ice sheets, thus limiting or minimizing glacio-eustatic sea-level fluctuations. Under these conditions, carbonate accumulation was most likely controlled by the © IPA, 2012 35th Annual Convention Proceedings, 2011

Over the past 34 Million years, the Antarctic continental shelf has gradually deepened due to ice sheet loading, thermal subsidence, and erosion from repeated glaciations. The deepening that is recorded in the sedimentary deposits around the Antarctic margin indicates that after the mid-Miocene Climate Optimum (≈15 Ma), Antarctic Ice Sheet (AIS) dynamical response to climate conditions changed. We explore end-members for maximum AIS extent, based on ice-sheet simulations of a late-Pleistocene and a mid-Miocene glaciation. Fundamental dynamical differences emerge as a consequence of atmospheric forcing, eustatic sea level and continental shelf evolution. We show that the AIS contributed to the amplification of its own sensitivity to ocean forcing by gradually expanding and eroding the continental shelf, that probably changed its tipping points through time. The lack of past topographic and bathymetric reconstructions implies that so far, we still have an incomplete understanding of AIS fast response to past warm climate conditions, which is crucial to constrain its future evolution.