Geological stories from the journey of mollusks fossils in Java

The journey began in the Eocene with the presence of mollusk fossil in the Nanggulan Formation (near Yogyakarta) in Central Java. Many experts believe this was the early part of the Tethys system which might still be connected to the Tethys system in Europe.The oldest mollusk fossils type locality after Nanggulan is the Early Miocene Jonggrangan Formation in Kulon Progo near the city of Yogyakarta, which is dominated by the gastropod Haustator specimen. Molluscan paleontological studies of this type of locality reflect a restricted environment with less influence of the Tethyan system. Haustator are considered as the ancestor of the Turritellidae group, which is found mostly on Java Island, during the younger Tertiary to Quaternary Periods.The story continued to the Middle Miocene where the Tethyan realms indication was clearly observed by the presence of some typical Tethys species such as Volema and Babylonia from Nyalindung Formation, West Java. The regional sea level rise in this epoch (around 12 Ma) that was indicated by the presence of Vicarya as an index fossil, which occurrence was due to land submerging to become mangroves area. The fossil then quickly become extinct when the sea level dropped back.Late Miocene to Pliocene was like the transition period from the Tethyan realm to the Pacific realm, where the Tethyan fauna was no longer present. Only evolutional traces of the Middle Miocene mollusk fossils were observed. This continuous evolution is most clearly seen in Turritella cramatensis (late Miocene), Turritella acuticarinata (early Pliocene) and Turritella cikumpaiensis (late Pliocene) which was interpreted to have originated from Turritella angulata as their ancestors.Earth cooling environment that happened in the late Pliocene/early Pleistocene has led the diversity and evolution of a new group of mollusks, most clearly observed from the abundance of Turritella bantamensis in the Bojong Formation, Banten. The new Turritella group has a curved whorl that different from its predecessor with an angled whorl shape.Plio-Pleistocene tectonics event has ended the period of Java marine mollusks domination, then only freshwater mollusk fossils can be found in almost all Quaternary mollusks-bearing deposits.

Pliocene glacial-interglacial sea-level change

<p>The mid- to late Pliocene (3.3-2.6 Ma) spans one of the most significant climatic transitions of the Cenozoic. It is characterised by global cooling from a climate with an atmospheric CO2 concentration of ~400 ppm and temperatures of 2-3°C warmer-than-present, to one marked by the progressive expansion of ice sheets on northern hemisphere. Consequently, the mid-Pliocene warm period (MPWP; 3.3-3.0 Ma) provides the most accessible and recent geological analogue for global sea-level variability relevant to future warming. Global mean sea level has been estimated at 22 ± 10 m above present-day for MPWP. However, recent re-evaluations of this estimate suggest that spatially-varying visco-elastic responses of the crust, local gravitational changes and dynamic topography from mantle processes may preclude ever being able to reconstruct peak Pliocene mean sea level. The Whanganui Basin, New Zealand, contains a ~5 km thick stratigraphic succession of Pliocene-Pleistocene (last 5 Ma), shallow-marine, cyclical sedimentary sequences demonstrated to record orbitally-paced, glacial-interglacial global sea-level fluctuations. A limitation of the Whanganui sea level record, to date, has been an inability to resolve the full amplitude of glacial-interglacial water depth change due to the occurrence of cycle bounding unconformities representing sub-aerial erosion during glacial lowstands. This thesis analyses a new ~900 m-thick, mid- (3.3-3.0 Ma) to late Pliocene (3.0-2.6 Ma), shallow-marine, cyclical sedimentary succession from a remote and relatively understudied part of Whanganui Basin. Unlike previous studies, these shelf sediments were continuously deposited, and were not eroded during sea-level lowstands, and thus provide the potential to reconstruct the full amplitude of glacial-interglacial sea-level change. On orbital timescales the influence of mantle dynamic processes is minimal. The approach taken applies lithofacies, sequence stratigraphy, and benthic foraminiferal analyses and a novel depth-dependent sediment grain size method to reconstruct the paleowater depths for, two continuously-cored drill holes, which are integrated with studies of outcropping sections. The thesis presents a new record of the amplitude and frequency of orbitally-paced, global sea-level changes from a wave-graded continental shelf, that is independent of the benthic δ¹⁸O proxy record of global ice-volume change. Paleobathymetric interpretations are underpinned by analysis of extant benthic foraminiferal census data and a statistical correlation with the distribution of modern taxa. In general, water depths derived from foraminiferal modern analogue technique are consistent with variability recorded by lithofacies. The inferred sea-level cycles co-vary with a qualitative climate record reconstructed from a census of extant pollen and spores, and a modern temperature relationship. A high-resolution age model is established using magnetostratigraphy constrained by biostratigraphy, and the dating and correlation of tephra. This integrated chronostratigraphy allows the recognition of 23 individual sedimentary cycles, that are correlated “one-to-one” across the paleo-shelf and are compared to the deep-ocean benthic oxygen isotope (δ ¹⁸O) record. A grain size-water depth technique was developed to quantify the paleobathymetry with more precision than the relatively insensitive benthic foraminifera approach. The method utilises a water depth threshold relationship between wave-induced near bed velocity and the velocity required to transport sand. The resulting paleobathymetric records of the most sensitive sites, the mid-Pliocene Siberia-1 drill core and the late Pliocene Rangitikei River section, were selected to compile a composite paleobathymetry. A one-dimensional backstripping method was then applied to remove the effects of tectonic subsidence, sediment and water loading on the record, to derive a relative sea level (RSL) curve. The contribution of glacio-hydro-isostatic (GIA) processes to the RSL record was evaluated using a process-based forward numerical solid Earth model for a range of plausible meltwater scenarios. The Whanganui Basin RSL record approximates eustatic sea level (ESL) in all scenarios when variability is dominated by Antarctic Ice Sheet meltwater source during the mid-Pliocene, but overestimates ESL once Northern Hemisphere ice sheet variability dominates in the late Pliocene. The RSL record displays 20 kyr precession-paced sea level variability during the MPWP with an average amplitude of ~15 ± 8 m, in-phase with southern high-latitude summer insolation. These are interpreted as ~20 m Antarctic Ice Sheet contributions, offset by ~ 5 m anti-phased Greenland Ice Sheet contribution, in the absence of a significant Northern Hemisphere ice sheets. This interpretation is supported by a previously published ice-proximal precession-paced, ice-berg-rafted debris record recovered off the coast of Wilkes Land. The Whanganui RSL record is not consistent with a dominant 40 kyr pacing observed the benthic oxygen isotope stack at this time. While the deep ocean benthic δ¹⁸O stack is of varying temporal and spatial resolution, during this time interval, the Whanganui RSL record implies a more complex relationship between ice-volume and oxygen isotope composition of sea water (δ¹⁸Oseawater). The relative influences of varying composition of the polar ice sheets, marine versus land based ice, the out-of-phase behaviour of polar ice sheet growth and retreat, and a potential decoupling of ocean bottom water temperature and δ¹⁸Oseawater are explored. The late Pliocene relative sea level record exhibits increasing ~40 kyr obliquity-paced amplitudes of ~20 ± 8 m. This is interpreted as a response to the expansion of Northern Hemisphere ice sheets after ~2.9 Ma. During this time the Antarctic proximal ice-berg rafted debris records display continuing precession-paced ice-volume fluctuations, but with decreasing amplitude suggesting cooling and stabilisation of the East Antarctic Ice Sheet. With the bipolar glaciation, the ocean δ¹⁸O signal became increasingly dominated by northern hemisphere ice-volume. However, the RSL record implies relatively limited ice-volume contributions (up to ~25 m sea level equivalent) prior to ~2.6 Ma. The large amplitude contribution of Antarctic Ice Sheets to global sea level during the MPWP has significant implications for the sensitivity of the Antarctica Ice Sheet to global temperatures 2-3°C above preindustrial levels, and atmospheric CO₂ forecast for the coming decades.</p>

Pliocene glacial-interglacial sea-level change

<p>The mid- to late Pliocene (3.3-2.6 Ma) spans one of the most significant climatic transitions of the Cenozoic. It is characterised by global cooling from a climate with an atmospheric CO2 concentration of ~400 ppm and temperatures of 2-3°C warmer-than-present, to one marked by the progressive expansion of ice sheets on northern hemisphere. Consequently, the mid-Pliocene warm period (MPWP; 3.3-3.0 Ma) provides the most accessible and recent geological analogue for global sea-level variability relevant to future warming. Global mean sea level has been estimated at 22 ± 10 m above present-day for MPWP. However, recent re-evaluations of this estimate suggest that spatially-varying visco-elastic responses of the crust, local gravitational changes and dynamic topography from mantle processes may preclude ever being able to reconstruct peak Pliocene mean sea level. The Whanganui Basin, New Zealand, contains a ~5 km thick stratigraphic succession of Pliocene-Pleistocene (last 5 Ma), shallow-marine, cyclical sedimentary sequences demonstrated to record orbitally-paced, glacial-interglacial global sea-level fluctuations. A limitation of the Whanganui sea level record, to date, has been an inability to resolve the full amplitude of glacial-interglacial water depth change due to the occurrence of cycle bounding unconformities representing sub-aerial erosion during glacial lowstands. This thesis analyses a new ~900 m-thick, mid- (3.3-3.0 Ma) to late Pliocene (3.0-2.6 Ma), shallow-marine, cyclical sedimentary succession from a remote and relatively understudied part of Whanganui Basin. Unlike previous studies, these shelf sediments were continuously deposited, and were not eroded during sea-level lowstands, and thus provide the potential to reconstruct the full amplitude of glacial-interglacial sea-level change. On orbital timescales the influence of mantle dynamic processes is minimal. The approach taken applies lithofacies, sequence stratigraphy, and benthic foraminiferal analyses and a novel depth-dependent sediment grain size method to reconstruct the paleowater depths for, two continuously-cored drill holes, which are integrated with studies of outcropping sections. The thesis presents a new record of the amplitude and frequency of orbitally-paced, global sea-level changes from a wave-graded continental shelf, that is independent of the benthic δ¹⁸O proxy record of global ice-volume change. Paleobathymetric interpretations are underpinned by analysis of extant benthic foraminiferal census data and a statistical correlation with the distribution of modern taxa. In general, water depths derived from foraminiferal modern analogue technique are consistent with variability recorded by lithofacies. The inferred sea-level cycles co-vary with a qualitative climate record reconstructed from a census of extant pollen and spores, and a modern temperature relationship. A high-resolution age model is established using magnetostratigraphy constrained by biostratigraphy, and the dating and correlation of tephra. This integrated chronostratigraphy allows the recognition of 23 individual sedimentary cycles, that are correlated “one-to-one” across the paleo-shelf and are compared to the deep-ocean benthic oxygen isotope (δ ¹⁸O) record. A grain size-water depth technique was developed to quantify the paleobathymetry with more precision than the relatively insensitive benthic foraminifera approach. The method utilises a water depth threshold relationship between wave-induced near bed velocity and the velocity required to transport sand. The resulting paleobathymetric records of the most sensitive sites, the mid-Pliocene Siberia-1 drill core and the late Pliocene Rangitikei River section, were selected to compile a composite paleobathymetry. A one-dimensional backstripping method was then applied to remove the effects of tectonic subsidence, sediment and water loading on the record, to derive a relative sea level (RSL) curve. The contribution of glacio-hydro-isostatic (GIA) processes to the RSL record was evaluated using a process-based forward numerical solid Earth model for a range of plausible meltwater scenarios. The Whanganui Basin RSL record approximates eustatic sea level (ESL) in all scenarios when variability is dominated by Antarctic Ice Sheet meltwater source during the mid-Pliocene, but overestimates ESL once Northern Hemisphere ice sheet variability dominates in the late Pliocene. The RSL record displays 20 kyr precession-paced sea level variability during the MPWP with an average amplitude of ~15 ± 8 m, in-phase with southern high-latitude summer insolation. These are interpreted as ~20 m Antarctic Ice Sheet contributions, offset by ~ 5 m anti-phased Greenland Ice Sheet contribution, in the absence of a significant Northern Hemisphere ice sheets. This interpretation is supported by a previously published ice-proximal precession-paced, ice-berg-rafted debris record recovered off the coast of Wilkes Land. The Whanganui RSL record is not consistent with a dominant 40 kyr pacing observed the benthic oxygen isotope stack at this time. While the deep ocean benthic δ¹⁸O stack is of varying temporal and spatial resolution, during this time interval, the Whanganui RSL record implies a more complex relationship between ice-volume and oxygen isotope composition of sea water (δ¹⁸Oseawater). The relative influences of varying composition of the polar ice sheets, marine versus land based ice, the out-of-phase behaviour of polar ice sheet growth and retreat, and a potential decoupling of ocean bottom water temperature and δ¹⁸Oseawater are explored. The late Pliocene relative sea level record exhibits increasing ~40 kyr obliquity-paced amplitudes of ~20 ± 8 m. This is interpreted as a response to the expansion of Northern Hemisphere ice sheets after ~2.9 Ma. During this time the Antarctic proximal ice-berg rafted debris records display continuing precession-paced ice-volume fluctuations, but with decreasing amplitude suggesting cooling and stabilisation of the East Antarctic Ice Sheet. With the bipolar glaciation, the ocean δ¹⁸O signal became increasingly dominated by northern hemisphere ice-volume. However, the RSL record implies relatively limited ice-volume contributions (up to ~25 m sea level equivalent) prior to ~2.6 Ma. The large amplitude contribution of Antarctic Ice Sheets to global sea level during the MPWP has significant implications for the sensitivity of the Antarctica Ice Sheet to global temperatures 2-3°C above preindustrial levels, and atmospheric CO₂ forecast for the coming decades.</p>

Nuevos sitios fosilíferos y evolución paleoambiental del cenozoico tardío del suroeste de Córdoba, Argentina

New fossil remains were found in Neogene and quaternary sedimentary sequences exposed in Alpa Corral and río San Bartolomé localities (Rio Cuarto Department, Córdoba, Argentina). They were assigned to Nopachtus cabrerai (Xenarthra, Cingulata, Glyptodontidae), Notiomastodon platensis (Proboscidea, Gomphotheriidae) and cf. Trigodon gaudryi (Notoungulata, Toxodontidae), and traces of the Scoyenia ichnofacies, as Taenidium barretti, were identified. Based on these findings, we conclude that: 1, the species Nopachtus cabrerai and cf. Trigodon gaudryi are registered for the first time in the Sierras Pampeanas region and support (along with the rest of the known taxa) a clear faunistic similarity to the Pampean region; 2, the beginning of the Neogene sedimentation in the Alpa Corral area (Las Barrancas river and San Bartolome river) would have started during the early Pliocene (Montehermosan Age); 3, the paleoenvironment would have been a fluvial system, with meandering canals interspersed with paleosols developed in floodplains with overflow deposits or abandoned meanders; 4, the paleontological and sedimentary record suggests a well-marked diachronism (from west-southwest to east-northeast) between the beginning of the Neogene sedimentation in the southern sector of San Alberto valley (late Miocene [Huayquerian Age]), the Alpa Corral region (early Pliocene [Monthermosan Age), and Río La Cruz valley (late Pliocene [Chapadmalalan Age]).

Sclerochronological evidence of pronounced seasonality from the late Pliocene of the southern North Sea Basin, and its implications

Oxygen isotope (δ18O) sclerochronology of benthic marine molluscs provides a means of reconstructing the seasonal range in seafloor temperature, subject to use of an appropriate equation relating shell δ18O to temperature and water δ18O, reasonably accurate estimation of water δ18O, and due consideration of growth-rate effects. Taking these factors into account, δ18O data from late Pliocene bivalves of the southern North Sea Basin (Belgium and the Netherlands) indicate a seasonal seafloor range at times larger than now in the area. Microgrowth-increment data from Aequipecten opercularis, together with the species-composition of the bivalve assemblage and aspects of preservation, suggest a setting below the summer thermocline for all but the latest material investigated. This implies a higher summer temperature at the surface than on the seafloor and consequently a greater seasonal range. A conservative (3 °C) estimate of the difference between maximum seafloor and surface temperature under circumstances of summer stratification points to seasonal surface ranges in excess of the present value (12.4 °C nearby). Using model-constrained estimates of water δ18O, summer surface temperature was initially in the cool temperate range (< 20 °C) and then (during the Mid-Piacenzian Warm Period; MPWP) increased into the warm temperate range (> 20 °C) before reverting to cool temperate values (in conjunction with shallowing and a loss of summer stratification). This pattern is in agreement with biotic-assemblage evidence. Winter temperature was firmly in the cool temperate range (< 10 °C) throughout, contrary to previous interpretations. Averaging of summer and winter surface temperatures for the MPWP provides a figure for mean annual sea-surface temperature that is 2–3 °C higher than the present value (10.9 °C nearby) and in close agreement with a figure obtained by averaging alkenone- and TEX86-temperatures for the MPWP from the Netherlands. These proxies, however, respectively underestimate summer temperature and overestimate winter temperature, giving an incomplete picture of seasonality. A higher mean annual temperature than now is consistent with the notion of global warmth in the MPWP, but a low winter temperature in the southern North Sea Basin suggests regional reduction in oceanic heat supply, contrasting with other interpretations of North Atlantic oceanography during the interval. Carbonate clumped isotope (Δ47) and biomineral unit thermometry offer means of checking the δ18O-based temperatures.

An assessment of the influence of orbital forcing on Late Pliocene global sea-level using a shallow-marine sedimentary record from the Wanganui Basin, New Zealand

<p>Classical Milankovitch Theory suggests variance in the orbital cycles of precession (21,000 year) modulated by eccentricity (~100,000 year) and obliquity (41,000 year) should have a profound influence on polar insolation and ice volume. However, the globally-integrated ice volume proxy record (benthic δ¹⁸O) during the Late Pliocene (3.0-2.6 Ma) is dominated by obliquity-paced cycles, and lacks a significant precession component. A number of conceptual hypotheses have been proposed to explain this “41,000 year problem”, but palaeoclimate records independent of the benthic δ¹⁸O record are required to test these hypotheses. The Wanganui Basin, New Zealand, contains a well-dated, shallow-marine Neogene sedimentary succession that is widely recognised as an important site for examining sea-level/ice volume changes at orbital frequencies. In this study, the shallow-marine Late Pliocene Mangaweka Mudstone is examined at an orbital-scale resolution (~3-5 kyr sampling) along a continuous 672 metre thick (true thickness) outcropping road section on Watershed Road between the Rangitikei and Turakina River valleys. Two modern analogue-calibrated water depth proxies were used to evaluate palaeobathymetric changes: (i) sediment texture and (ii) benthic foraminifera census data. An overall trend of shallowing to inner-shelf water depths occurs up-section, but is superimposed by higher frequency fluctuations. For the lowermost ~400 metres of the section, in situ benthic foraminifera assemblages indicate water depths >100 metres. As wave-induced sand transport does not occur on the modern Manawatu-Wanganui outer-shelf, and modern wave climates are assumed to be analogous to the Pliocene, it is concluded that the sediment grainsize approach is not an appropriate proxy for reconstruction water depth changes in the lower ~400 metres of section. An integrated magneto-, bio- and tephrostratigraphy was developed that constrains the outcrop succession to between ~3.0 Ma and 2.58 Ma. Nine distinct cycles spanning ~400,000 years are identified in the grainsize and benthic foraminifera assemblages. Within the uncertainty of the age model, the Mangaweka Mudstone grainsize cycles can be matched one-for-one to the δ¹⁸O glacial-interglacial cycles, as they display a similar pattern in terms of frequency and amplitude. The frequency of the Mangaweka Mudstone cycles (and the corresponding interval in the benthic δ¹⁸O record) are dominated by the ~40,000 year obliquity cycle, but with a subordinate eccentricity component. Therefore, the fluctuations in the grainsize and benthic foraminifera proxies likely represent an indirect response to global sea-level fluctuations via their effect on continental shelf sediment transport mechanisms (non-wave) with the orbitally-paced transgression and regression of the shoreline on a restricted palaeo- continental shelf. The implications for the orbital theory of the ice ages are that during the Late Pliocene, global ice volume changes responded primarily to obliquity, and the precession influences were either: (i) too low in amplitude to have influenced the grainsize and benthic foraminifera assemblages in the Mangaweka Mudstone depositional environment, or (ii) cancelled-out in global ice volume and sea-level changes because precession forcing is anti-phased between the hemispheres.</p>

An assessment of the influence of orbital forcing on Late Pliocene global sea-level using a shallow-marine sedimentary record from the Wanganui Basin, New Zealand

<p>Classical Milankovitch Theory suggests variance in the orbital cycles of precession (21,000 year) modulated by eccentricity (~100,000 year) and obliquity (41,000 year) should have a profound influence on polar insolation and ice volume. However, the globally-integrated ice volume proxy record (benthic δ¹⁸O) during the Late Pliocene (3.0-2.6 Ma) is dominated by obliquity-paced cycles, and lacks a significant precession component. A number of conceptual hypotheses have been proposed to explain this “41,000 year problem”, but palaeoclimate records independent of the benthic δ¹⁸O record are required to test these hypotheses. The Wanganui Basin, New Zealand, contains a well-dated, shallow-marine Neogene sedimentary succession that is widely recognised as an important site for examining sea-level/ice volume changes at orbital frequencies. In this study, the shallow-marine Late Pliocene Mangaweka Mudstone is examined at an orbital-scale resolution (~3-5 kyr sampling) along a continuous 672 metre thick (true thickness) outcropping road section on Watershed Road between the Rangitikei and Turakina River valleys. Two modern analogue-calibrated water depth proxies were used to evaluate palaeobathymetric changes: (i) sediment texture and (ii) benthic foraminifera census data. An overall trend of shallowing to inner-shelf water depths occurs up-section, but is superimposed by higher frequency fluctuations. For the lowermost ~400 metres of the section, in situ benthic foraminifera assemblages indicate water depths >100 metres. As wave-induced sand transport does not occur on the modern Manawatu-Wanganui outer-shelf, and modern wave climates are assumed to be analogous to the Pliocene, it is concluded that the sediment grainsize approach is not an appropriate proxy for reconstruction water depth changes in the lower ~400 metres of section. An integrated magneto-, bio- and tephrostratigraphy was developed that constrains the outcrop succession to between ~3.0 Ma and 2.58 Ma. Nine distinct cycles spanning ~400,000 years are identified in the grainsize and benthic foraminifera assemblages. Within the uncertainty of the age model, the Mangaweka Mudstone grainsize cycles can be matched one-for-one to the δ¹⁸O glacial-interglacial cycles, as they display a similar pattern in terms of frequency and amplitude. The frequency of the Mangaweka Mudstone cycles (and the corresponding interval in the benthic δ¹⁸O record) are dominated by the ~40,000 year obliquity cycle, but with a subordinate eccentricity component. Therefore, the fluctuations in the grainsize and benthic foraminifera proxies likely represent an indirect response to global sea-level fluctuations via their effect on continental shelf sediment transport mechanisms (non-wave) with the orbitally-paced transgression and regression of the shoreline on a restricted palaeo- continental shelf. The implications for the orbital theory of the ice ages are that during the Late Pliocene, global ice volume changes responded primarily to obliquity, and the precession influences were either: (i) too low in amplitude to have influenced the grainsize and benthic foraminifera assemblages in the Mangaweka Mudstone depositional environment, or (ii) cancelled-out in global ice volume and sea-level changes because precession forcing is anti-phased between the hemispheres.</p>