Submarine volcanic activity and giant amygdale formation along the Panama island arc as a precursor to 6000-year-old agate exploitation on Pedro González Island

An extensive deposit of agate occurs in Pedro González Island in the Gulf of Panama. Previous archaeological research showed that the agate was exploited between 6200 and 5600 cal BP to make stone tools found at the oldest known Preceramic human settlement in the Pearl Island archipelago. We constrain here the origin and geological context of the agate through a geological and geochemical study of the island. We show that it includes primary volcanic breccias, lavas, and tuffaceous marine deposits with sedimentary conglomerates and debris flow deposits, which we define as the Pedro González Formation. This formation records submarine to subaerial volcanic activity along an island arc during the Oligo-Miocene, confirming previous regional models that favour progressive emergence of the isthmus in the early Miocene. The igneous rocks have an extreme tholeiitic character that is interpreted to reflect magmatic cessation in eastern Panama during the early Miocene. The agate is hosted in andesitic lavas in unusually large amygdales up to 20–40 cm in diameter, as well as small amygdales (0.1–1.0 cm) in a bimodal distribution, and in veins. The large size of the agates made them suitable for tool manufacture. Field evidence suggests that the formation of large amygdales resulted from subaqueous lava–sediment interaction, in which water released from unconsolidated tuffaceous deposits at the base of lava flows rose through the lavas, coalesced, and accumulated below the chilled lava top, with subsequent hydrothermal mineralization. These amygdales could therefore be regarded as an unusual result of combined peperitic and hydrothermal processes.

New Ediacaran fossils from the Ukraine, some with a putative tunicate relationship

Sack-like body fossils Finkoella ukrainica gen. et sp. nov. and F. oblonga sp. nov., and reticulate fossil Pharyngomorpha reticulata gen. et sp. nov. are described from the upper Ediacaran shallow-marine deposits of Ukraine, which are no younger than 557 Ma. The first two resemble the flattened bodies of tunicates showing mainly the outline of tunica, while the third is considered as a fragment of the pharyngeal basket of a tunicate. F. ukrainica is represented by smaller individuals interpreted as juveniles, which may occur in clusters together with less numerous larger individuals. The larger forms are interpreted as adults, some of which show the preserved oral/atrial syphons and possible traces of internal organs bulging through the tunica. Moreover, Burykhia sp. from the uppermost Ediacaran of the same region is presented. This is the second and younger occurrence of the genus Burykhia, which is preserved as a possible fragment of the pharyngeal basket. All the fossils are preserved as the “death masks” between microbial mats, and their appearance depends partly on the relation to the parting surface on which they are observed. The presented new taxa along with the literature data reinforce the possibility that tunicates originated already in late Ediacaran.

Middle Miocene (Badenian) macroinvertebrates from Pécs-Danitzpuszta (Mecsek Mts, SW Hungary)

This paper examines Badenian (middle Miocene) macroinvertebrates – corals and molluscs – from the Pécs-Danitzpuszta sand pit (Mecsek Mts, SW Hungary) in order to extend our knowledge on Miocene normal marine deposits of the Mecsek region. Corals occur reworked in the upper Miocene sand that was deposited in the brackish Lake Pannon, and presumably originate either from the middle Badenian Pécsszabolcs or the upper Badenian Rákos Member of the Lajta Formation. A total of seven taxa were identified. These taxa suggest subtropical conditions and a lack of coral reefs in the Badenian. Molluscs were found in situ in the upper Badenian Szilágy Clay Marl Member of the Baden Formation and the Rákos Member of the Lajta Formation. They dominantly consist of bivalves and represent benthic assemblages typical of the middle Miocene Central Paratethys.

Various marginal marine environments in the Central Paratethys: Late Badenian and Sarmatian (middle Miocene) marine and non-marine microfossils from Pécs-Danitzpuszta, southern Hungary

The middle Miocene foraminifera and ostracod record of the Central Paratethys usually reflects stable normal marine epositional environments for the Badenian and more patchy, less stable restricted marine environments for the Sarmatian. A 17 m thick outcrop at Pécs-Danitzpuszta, Mecsek Mts, SW Hungary exposed an upper Badenian to Pannonian succession where foraminifers and ostracods document significant environmental changes. The basal layers of the section contain micro- and macrofossils indicating normal marine, shallow, warm, well-oxygenated habitat with relatively high-energy conditions and algal vegetation on the bottom, and represent the upper Badenian (13.82 to 12.65 Ma). The marine deposits are followed by coarse sandstone, breccia and siltstone layers barren of microfossils but containing rhizoliths. The sediments were probably subaerially exposed for some time. The following marine inundation, marked by the appearance of clays and limestones as well as fossils, was dated to the late Sarmatian (ca. 12 to 11.6 Ma) on the basis of the restricted marine microfossil assemblages from the upper part of the succession (Porosononion granosum Zone, Aurila notata Zone). This community is characterized by exclusively eurytopic forms indicating an unstable and vegetated marginal marine environment with fluctuations in salinity, as well as oxygen and food availability. Within the 5 m thick upper Sarmatian marine interval, a unique fresh- to oligohaline fauna characterizes a few layers in less than 1 m thickness. This fauna consists of highly euryhaline foraminifera and freshwater to oligohaline ostracod assemblages, indicating a temporary salinity reduction to 5–10 ‰. No similar freshwater fauna has been reported from the Sarmatian of the Central Partethys so far. The eventual disappearance of the foraminifera from the paleontological record coupled with a complete turnover in the ostracod fauna indicates the transition from the marginal marine Sarmatian Sea to the brackish Lake Pannon, marking the Sarmatian/Pannonian boundary (11.6 Ma).

Basin Analysis of Tertiary Strata in Golden Bay, Nelson

<p>Eocene to Miocene strata comprise the Brunner Coal Measures (Ak-Ld), Takaka Limestone (Ld-Po), Tarakohe Mudstone (P1-S1) and Waitui Sandstone (Sc-Sl), and form a transgressive-regressive sequence on an essentially stable structural platform. Brunner Coal Measures in the Takaka valley (up to 350m thick) consist of cross-bedded sand and gravel, interlaminated sand and silt, bioturbated muddy sandstone, carbonaceous mudstone and coal. Five facies associations are recognized and interpreted as river/floodbasin, estuarine and shallow marine deposits. In the Aorere and Parapara River catchments, two new members are recognized: the Quartz Wash Member, comprising quartzose sand and conglomerate, and the Washbourn Limonite Member, a sedimentary iron-ore deposit. The Takaka Limestone (up to 100m thick), consists of bryozoan, bivalve or sandy grainstone or packstone, deposited on a tidal current-swept shallow-middle shelf with minimal terrigenous influx. Diagenesis was controlled by pressure-solution during deep burial, and resulted in a rightly cemented rock with dolomite and neomorphic features. The Tarakohe Mudstone (up to 900m thick) is dominated in its lower half by massive mudstone of hemipelagic and turbiditic origin, and in its upper half by shallow shelf-estuarine sandstones and mudstones. The Waitui Sandstone (160m thick) comprises shallow marine sandstone. Deposition of the Brunner Coal Measures took place in localized fault-angle depressions. The Takaka Limestone was deposited during a period of regional subsidence and minimal tectonic activity. The Tarakohe Mudstone and Waitui Sandstone were deposited in synclinal basins which were later modified by rising monoclinal boundaries.</p>

Basin Analysis of Tertiary Strata in Golden Bay, Nelson

<p>Eocene to Miocene strata comprise the Brunner Coal Measures (Ak-Ld), Takaka Limestone (Ld-Po), Tarakohe Mudstone (P1-S1) and Waitui Sandstone (Sc-Sl), and form a transgressive-regressive sequence on an essentially stable structural platform. Brunner Coal Measures in the Takaka valley (up to 350m thick) consist of cross-bedded sand and gravel, interlaminated sand and silt, bioturbated muddy sandstone, carbonaceous mudstone and coal. Five facies associations are recognized and interpreted as river/floodbasin, estuarine and shallow marine deposits. In the Aorere and Parapara River catchments, two new members are recognized: the Quartz Wash Member, comprising quartzose sand and conglomerate, and the Washbourn Limonite Member, a sedimentary iron-ore deposit. The Takaka Limestone (up to 100m thick), consists of bryozoan, bivalve or sandy grainstone or packstone, deposited on a tidal current-swept shallow-middle shelf with minimal terrigenous influx. Diagenesis was controlled by pressure-solution during deep burial, and resulted in a rightly cemented rock with dolomite and neomorphic features. The Tarakohe Mudstone (up to 900m thick) is dominated in its lower half by massive mudstone of hemipelagic and turbiditic origin, and in its upper half by shallow shelf-estuarine sandstones and mudstones. The Waitui Sandstone (160m thick) comprises shallow marine sandstone. Deposition of the Brunner Coal Measures took place in localized fault-angle depressions. The Takaka Limestone was deposited during a period of regional subsidence and minimal tectonic activity. The Tarakohe Mudstone and Waitui Sandstone were deposited in synclinal basins which were later modified by rising monoclinal boundaries.</p>

Late Pleistocene and early Holocene sea-level history and glacial retreat interpreted from shell-bearing marine deposits of southeastern Alaska, USA

We leverage a data set of &gt;720 shell-bearing marine deposits throughout southeastern Alaska (USA) to develop updated relative sea-level curves that span the past ~14,000 yr. This data set includes site location, elevation, description when available, and 436 14C ages, 45 of which are published here for the first time. Our sea-level curves suggest a peripheral forebulge developed west of the retreating Cordilleran Ice Sheet (CIS) margin between ca. 17,000 and 10,800 calibrated yr B.P. By 14,870 ± 630 to 12,820 ± 340 cal. yr B.P., CIS margins had retreated from all of southeastern Alaska’s fjords, channels, and passages. At this time, isolated or stranded ice caps existed on the islands, with alpine or tidewater glaciers in many valleys. Paleoshorelines up to 25 m above sea level mark the maximum elevation of transgression in the southern portion of the study region, which was achieved by 11,000 ± 390 to 10,500 ± 420 cal. yr B.P. The presence of Pacific sardine (Sardinops sagax) and the abundance of charcoal in sediments that date between 11,000 ± 390 and 7630 ± 90 cal. yr B.P. suggest that both ocean and air temperatures in southeastern Alaska were relatively warm in the early Holocene. The sea-level and paleoenvironmental reconstruction presented here can inform future investigations into the glacial, volcanic, and archaeological history of southeastern Alaska.