Middle Eocene terrestrial paleoweathering and climate evolution in the midlatitude Bohai Bay Basin of eastern China

The middle Eocene climatic optimum(MECO,ca.-42 Ma)is a key time period for understanding Cenozoic cooling of the global climate.Still,midlatitude terrestrial records of climate evolution during MEcO epoch are rare.In this study,continuous high-resolution record of shale sediments in mid-Eocene Shahejie Formation(MES shales)in the Bohai Bay Basin were performed with major-element and wavelet analysis.The midlatitude paleoweathering and paleoclimatic evolution during MEcO epoch were analyzed in this study.The MES shales experienced weak-moderate paleoweathering under a subtropical monsoon paleoclimate with mean annual temperature of 8.3-12.9℃ and mean annual precipitation of 685-1100 mm/yr.The MES shales record a mixed provenance involving intermediate igneous rocks,and low compositional maturity.The nutrient-rich environment led to enrichment in organic matter in the MES shales.Wavelet analysis revealed good periodicity about the paleoclimate and weathering during MECO epoch.In the stage I of MES shales depositional process,the paleolake was high in nutrients,and the MES shales experienced high chemical weathering due to a relatively warmer and more humid climate.In contrast,the climate in stage II was relatively cold and dry,and the maturity of the MES shales was relatively high during this stage,suggesting a relatively stable tectonic background.This work provides more terrestrial records of MEco epoch for midlatitude region,and is benefit for better understanding of the palaeoenvironment when MES shales formed.The implication of organic matters enrichment in this study is meaningful for the shale oil/gas exploration in Nanpu Sag.

Stratigraphy of the Alveolina elliptica group from the Middle Eocene of Iran:Calibration with calcareous nannofossils biozones and description of Alveolina ozcani n. sp.

Precise taxonomy and the chronostratigraphic calibration of the Middle Eocene Alveolina from Central Iran is here undertaken from the Chah-Talkh section of the southern Sabzevar region(Central Iran). We have identified Alveolina kieli, Alveolina stercusmuris and Alveolina nuttalli along with the new species Alveolina ozcani n. sp. that we include into the Alveolina elliptica group. We have also found Nummulites uroniensis, Nummulites obesus and Nummulites cf. verneuili and associated calcareous nannofossils that look reliable to make thoughtful correlations with the Shallow Benthic Zones(SBZ). The foraminiferal biostratigraphy suggests an assignment to the upper part of the lower Lutetian-lower part of the middle Lutetian,SBZ13(Middle Eocene), further strengthened through the identification of the calcareous nannofossil NP14b-NP15b or CNE8-CNE10 biozones, providing a solid correlation with the global stratigraphic standards.

Competition between Coral and Algae in Tertiary and Quaternary Reefs: Greenhouse to Icehouse Transitions

The competition between coral and algae in marine reefs is pervasive through geologic time;that competition determines the structure and composition of reef communities, which we see in the fossil record. However, the relationships between coral and calcareous algae in reefs are poorly understood. To study this relationship, several hand samples and thin sections were examined from nine different foralgal reef localities around the world. Foralgal reefs typically extend from about 20 m depth or shallower on the seaward side of the reef. The first section is Salt Mountain, Alabama, which preserves a Paleocene reef. It contains a high percentage of red coralline algae with benthic foraminifera. The second section is IDOP-U1376, IIA Limestone, it is Middle Eocene, in the form of an isolated reef sandwiched between two igneous beds. The third section is the Utoe’ Limestone, New Caledonia, it is Middle Eocene in age and is composed mainly of grain-boundstone units with some igneous interlayered. The fourth section is the Darnah Formation in the West-Darnah roadcut section, Northeast Libya, it is Middle Eocene in age, it is composed of highly fossiliferous limestone (corals, red coralline algae, echinoids, mollusks, foraminifers, and bryozoans). The fifth section, the Al Bayda Formation (Algal Limestone Member) in Northeast Libya, is in the Drayanah—Al Abyar roadcut, Northeast Libya, it has several species of algae but also includes a high percentage of buildups of coral species. The sixth section is the Oligo-Miocene Al Faidiyah Formation (Al Fatayah Cement Quarry) limestone unit in Northeast Libya. The seventh section is (Core-core 20) late-early to middle Miocene Limestone Unit-Cicuco Field, NW Colombia. The eighth section is the Benghazi Formation at Benghazi Cement Quarry, in Northeast Libya, it is fossiliferous limestone, consisting of coral, algae, mollusks, and echinoids. The ninth and tenth sections are Quaternary reefs in the Bahamas and the Florida Keys, respectively. These reefs contain a high percentage of coral, red coralline algae, echinoids, mollusks, foraminifers, and ostracods. Based on the data and static analysis results on the thin sections and hand specimens, this study determines the occurrence and outcomes of coral-algal interactions among different coral growth forms (branching, upright, massive, encrusting, plating, and solitary). The Early Paleogene (Paleocene to Eocene) has the highest percentage of algae in two forms (crustose and frondose), which is a good indicator of a warm climate. In the Middle Eocene to Late Eocene, coral replaced algae in different localities in sections of that age. This change is an indicator of climatic cooling, especially in the western Lutetian Darnah section. In the Oligocene time, high-branching corals became abundant and escaped competition with the algae due to Icehouse conditions, as shown in the Al Bayda Formation. In the Miocene, coral species started to decline because of the return to Greenhouse conditions. Coral can lose its competitive edge when chemical and physical defense systems reduce growth and production due to warming. On the other hand, crustose-form algae attract the larvae of the coral. Algae induce them to get a more highly competitive frondose form, which is useful for corals as they decrease growth and production. Algae can quickly colonize the dead reef by using the firm substrate to rebuild themselves. This research may prove valuable when predicting the response of modern coral reef systems to future climatic warming conditions and provides a model for what future reefs may look like.

Lagoonal carbonate deposition preceding rifting-related uplift:evidence from the Bartonian-Priabonian(Eocene)of the northwestern Gulf of Suez(Egypt)

Sedimentary successions in the northwestern Gulf of Suez provide important clues to the understanding of the geological evolution of NE Africa during the middle and late Eocene.This study focuses on detailed facies analyses in order to characterize the depositional environments and system tracts of the Bartonian-Priabonian succession cropping out in this area.Bartonian-Priabonian carbonate deposits in five stratigraphic sections constitute,from base to top,the Gebel Hof,Observatory,Sannur,Qurn,and Wadi Hof Formations.These formations contain four local assemblage zones of larger benthic foraminifers.Analyses of litho-,bio-,and microfacies in the succession resulted in the recognition of 12 lithofacies types.These lithofacies are represented by packages of lime-mudstones,wackestones,packstones,pack-to grainstones,grainstones,rudstones,boundstones and dolomites.These lithofacies have been grouped into four geneticallyrelated facies associations that represent,respectively,tidal flats/shallow subtidal,restricted-shelf/lagoonal,shoal bar,and outer-shelf lagoon/reefal depositional environments in a downslope shallow-marine inner-ramp setting.The vertical transitions of these facies associations,representing facies changes through time,imply fluctuations of the regional sea level.The two peaks in the Bartonian correspond to well-known global eustatic sea-level rises;the pronounced Priabonian regression must be ascribed to the known global eustatic sea-level fall in combination with regional tectonic activity.The facies distribution suggests that the study area was located in the direct vicinity of some islands during the Bartonian-Priabonian.