scholarly journals Exploring Ichnofacies Distribution in Ancient Seaways: The Late Miocene Rifian Corridor as a Natural Laboratory

2020 ◽  
Author(s):  
Wouter de Weger ◽  
Francisco Rodríguez-Tovar ◽  
Olmo Miguez-Salas
Keyword(s):  
Ocean Circulation ◽  
Late Miocene ◽  
Trace Fossils ◽  
Shallow Marine ◽  
Climatic Variations ◽  
Fine Grain ◽  
Major Controlling Factor ◽  
Palaeoenvironmental Conditions ◽  
Natural Laboratory ◽  
Ophiomorpha Rudis

Abstract Oceanic gateways have modulated ocean circulation and have influenced climatic variations throughout the Earth´s history. During the Late Miocene (7.8 - 7.35 Ma), the Atlantic Ocean and the Mediterranean Sea were connected through the Rifian Corridor (Morocco). This gateway is one of the few examples of deep ancient seaways with a semi-continuous sedimentary record. Deposits comprise turbidites intercalated between deep-sea fine grain sediments (i.e., hemipelagites and drift deposits), channelized sandstone contourite facies, and shallow marine sandstones. Herein an ichnological analysis was conducted in these upper Miocene sediments to improve characterisation of palaeoenvironmental conditions. In addition, ichnofacies were analysed to elucidate how bottom currents control ichnofacies distribution and can modified their attributes. Turbidite deposits are typified by vertical trace fossils (i.e., Ophiomorpha), conforming the Ophiomorpha rudis ichnosubfacies. Contouritic sandstones exhibit high density and low diverse trace fossil assemblage, with predominant Macaronichnus and Scolicia, resembling a proximal expression of Cruziana ichnofacies. Shallow marine environments are dominated by vertical trace fossils (e.g., Conichnus, Ophiomorpha and Skolithos), allowing an assignation to Skolithos ichnofacies. This study reveals energy to be a major controlling factor determining ichnofacies attributes and distribution in ancient deep seaways. Within these seaways, highly energetic conditions typical of shallower settings are present in deeper environments (i.e., slope), contributing to ichnodiversity impoverishment in ichnofacies.

scholarly journals The Late Miocene Rifian corridor as a natural laboratory to explore a case of ichnofacies distribution in ancient gateways

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Olmo Miguez-Salas ◽  
Francisco J. Rodríguez-Tovar ◽  
Wouter de Weger
Keyword(s):  
Ocean Circulation ◽  
Late Miocene ◽  
Trace Fossils ◽  
Shallow Marine ◽  
Low Diversity ◽  
Shallow Marine Sediments ◽  
First Time ◽  
Palaeoenvironmental Conditions ◽  
Natural Laboratory ◽  
Ophiomorpha Rudis

AbstractOceanic gateways have modulated ocean circulation and have influenced climatic variations throughout the Earth´s history. During the late Miocene (7.8–7.35 Ma), the Atlantic Ocean and the Mediterranean Sea were connected through the Rifian Corridor (Morocco). This gateway is one of the few examples of deep ancient seaways with a semi-continuous sedimentary record. Deposits comprise turbidites intercalated between deep-sea mudstone (i.e., hemipelagites and drift deposits), channelized sandstone contourite facies, and shallow marine sandstone. Herein an ichnological analysis was conducted in these upper Miocene sediments to improve characterisation of palaeoenvironmental conditions. In addition, ichnofacies were analysed to elucidate how bottom currents control ichnofacies distribution and can modify their attributes. Turbidite deposits are typified by vertical trace fossils (i.e., Ophiomorpha), conforming the Ophiomorpha rudis ichnosubfacies. Contouritic sandstone exhibits high density and low diversity trace-fossil assemblage, with predominant Macaronichnus and Scolicia, resembling a proximal expression of the Cruziana ichnofacies. Shallow marine environments are dominated by vertical trace fossils (e.g., Conichnus, Ophiomorpha, Skolithos), allowing an assignation to the Skolithos ichnofacies. This study reveals for the first time a variability in ichnofacies attributes and distribution at the Rifian Corridor, associated with turbidites, contourite and shallow marine sediments. Hydrodynamic energy reveals as the major factor controlling trace maker communities in the studied seaway. Highly energetic conditions typical of shallower settings are present in deeper-water environments (i.e., slope), contributing to ichnodiversity impoverishment in ichnofacies.

Deep-sea panoramas: Progress and remaining challenges in late Miocene stratigraphy and climate

2021 ◽  
Author(s):  
Anna Joy Drury ◽  
Thomas Westerhold ◽  
David A. Hodell ◽  
Mitchell Lyle ◽  
Cédric M. John ◽  
...  
Keyword(s):  
High Resolution ◽  
Ocean Circulation ◽  
Late Miocene ◽  
Deep Sea ◽  
Deep Ocean ◽  
High Resolution Data ◽  
Ongoing Work ◽  
Climate Evolution ◽  
Deep Ocean Circulation ◽  
Geological Timescale

<p>During the late Miocene, meridional sea surface temperature gradients, deep ocean circulation patterns, and continental configurations evolved to a state similar to modern day. Deep-sea benthic foraminiferal stable oxygen (δ<sup>18</sup>O) and carbon (δ<sup>13</sup>C) isotope stratigraphy remains a fundamental tool for providing accurate chronologies and global correlations, both of which can be used to assess late Miocene climate dynamics. Until recently, late Miocene benthic δ<sup>18</sup>O and δ<sup>13</sup>C stratigraphies remained poorly constrained, due to relatively poor global high-resolution data coverage.</p><p>Here, I present ongoing work that uses high-resolution deep-sea foraminiferal stable isotope records to improve late Miocene (chrono)stratigraphy. Although challenges remain, the coverage of late Miocene benthic δ<sup>18</sup>O and δ<sup>13</sup>C stratigraphies has drastically improved in recent years, with high-resolution records now available across the Atlantic and Pacific Oceans. The recovery of these deep-sea records, including the first astronomically tuned, deep-sea integrated magneto-chemostratigraphy, has also helped to improve the late Miocene geological timescale. Finally, I will briefly touch upon how our understanding of late Miocene climate evolution has improved, based on the high-resolution deep-sea archives that are now available.</p>

Trace Fossils in Quaternary, Bahamian-Style Carbonate Environments: The Modern to Fossil Transition

1992 ◽  
Vol 5 ◽  
pp. 105-120 ◽  
Author(s):  
H. Allen Curran
Keyword(s):  
Fossil Record ◽  
Trace Fossils ◽  
Subtidal Zone ◽  
Carbonate Sediments ◽  
Shallow Marine ◽  
Shallow Subtidal ◽  
Dominant Process ◽  
Burrowing Activity

Tracemaking organisms are common and diverse components of the fauna and flora of tropical, shallow-marine and coastal carbonate environments. In the shallow subtidal zone, the burrowing activity of callianassid shrimp commonly is the dominant process in the modification of original depositional fabrics (Tudhope and Scoffin, 1984; Tedesco and Wanless, 1991). Both borers and burrowers have great potential to leave their mark in tropical carbonate sediments and rocks and to become part of the fossil record.

Geochemical and Geophysical Evidence for Late Miocene Onset of Tasman Leakage

2020 ◽  
Author(s):  
Beth Christensen ◽  
David DeVleeschouwer ◽  
Jeroen Groeneveld ◽  
Jorijntje Henderiks ◽  
Gerald Auer ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Southern Hemisphere ◽  
Ocean Circulation ◽  
Late Miocene ◽  
Return Flow ◽  
Intermediate Water ◽  
Isotope Data ◽  
The North ◽  
Tasman Sea ◽  
Intermediate Waters

<p>The recent documentation of the southern hemisphere “supergyre”, the coupled subtropical southern hemisphere gyres spanning the 3 ocean basins, leads to questions about its impact on Indian Ocean circulation. The Indonesian Throughflow (ITF) acts as a switchboard directing warm surface waters towards the Agulhas Current (AC) and return flow to the North Atlantic, but Tasman Leakage (TL) is another source of return flow, however, at intermediate water depths. Fed by a complex mixture of South Pacific (SP) western boundary current surface and intermediate waters, and Antarctic Intermediate Water (AAIW), today the topography forces it to flow in a westerly direction. The TL flows over the Broken Ridge towards Madagascar, joining the AC and ultimately Atlantic Meridional Circulation (AMOC).</p><p>Stable isotope data from 4 DSPD/ ODP Indian Ocean sites define the history of TL and constrain the timing of its onset to ~7 Ma.  A simple nannofossil- biostratigraphy age model applied to previously published benthic foraminiferal carbon isotope data ensures the 4 time-series (~11 – 2 Ma) are consistent. All 4 records (Sites 752 Broken Ridge, 590 Tasman Sea, 757 90 East Ridge, 751 Kerguelen Plateau) are similar from ~11 Ma to ~7 Ma, indicating the Tasman Sea intermediate water was sourced from the Southern Ocean (SO). A coeval shift at ~7 Ma at Sites 590 and 752 signals a SP contribution and the onset of TL. We do not observe TL at Sites 757 and 751 and so interpret the post-7 Ma divergence between the TL pair and the KP / 90E Ridge sites as a reflection of different intermediate water masses. The KP / 90E Ridge sites record a more fully SO signal, and these waters are constrained to the region west of the 90 East ridge.</p><p>The isotopic record of TL onset suggests important tectonic changes ~ 7 Ma: 1) opening of the Tasman Sea to the north and 2) Australia’s northward motion allowing westward flow around Tasmania. The former is supported by a change in sedimentation style on the Marion Plateau (ODP Site 1197). The latter is supported by unconformities on the South Australian Bight margin (Leg 182 Sites 1126 (784 m), 1134 (701 m), 1130 (488m) and coeval decreases in mud- sized sediments at the Broken Ridge sites, indicating winnowing associated with the onset of the TL. A divergence is also apparent between Broken Ridge and Mascarene Plateau Site 707 records at this time. These events, coupled with the temporal relationship between the onset of the TL and a change in the character of deposition in the Maldives indicate enhanced Indian Ocean circulation at intermediate depths coincident with the late Miocene global cooling. Combined, these observations suggest the Indian Ocean in general plays a larger role in the global ocean system than previously recognized, and intermediate waters in particular are a critical yet poorly understood component of AMOC.</p>

The Fish River Subgroup in Namibia: stratigraphy, depositional environments and the Proterozoic–Cambrian boundary problem revisited

2005 ◽  
Vol 142 (5) ◽  
pp. 465-498 ◽  
Author(s):  
G. GEYER
Keyword(s):  
Trace Fossils ◽  
Global Scale ◽  
Depositional Environments ◽  
Trace Fossil ◽  
Braided River ◽  
Shallow Marine ◽  
Sequence Stratigraphic ◽  
Marine Habitats ◽  
Short Period ◽  
Distinct Sequence

The Fish River Subgroup of the Nama Group, southern Namibia, is restudied in terms of lithostratigraphy and depositional environment. The study is based on partly fine-scaled sections, particularly of the Nababis and Gross Aub Formation. The results are generally in accordance with earlier studies. However, braided river deposits appear to be less widely distributed in the studied area, and a considerable part of the formations of the middle and upper subgroup apparently were deposited under shallowest marine conditions including upper shore-face. Evidence comes partly from sedimentary features and facies distribution, and partly from trace fossils, particularly Skolithos and the characteristic Trichophycus pedum. Environmental conditions represented by layers with T. pedum suggest that the producer favoured shallow marine habitats and transgressive regimes. The successions represent two deepening-upward sequences, both starting as fluvial (braided river) systems and ending as shallow marine tidally dominated environments. The first sequence includes the traditional Stockdale, Breckhorn and lower Nababis formations (Zamnarib Member). The second sequence includes the upper Nababis (Haribes Member) and Gross Aub formations. As a result, the Nababis and Gross Aub formations require emendation: a new formation including the Haribes and Rosenhof and possibly also the Deurstamp members. In addition, four distinct sequence stratigraphic units are deter-minable for the Fish River Subgroup in the southern part of the basin. The Proterozoic–Cambrian transition in southern Namibia is most probably located as low as the middle Schwarzrand Subgroup. The environmentally controlled occurrence of Trichophycus pedum undermines the local stratigraphic significance of this trace fossil which is eponymous with the lowest Cambrian and Phanerozoic trace fossil assemblage on a global scale. However, occurrences of such trace fossils have to be regarded as positive evidence for Phanerozoic age regardless of co-occurring body fossils. Other suggestions strongly dispute the concept of the formal Proterozoic–Cambrian and Precambrian–Phanerozoic boundary. Carbon isotope excursions and radiometric datings for the Nama Group do not help to calibrate precisely the temporal extent of the Fish River Subgroup. Fossil content, sequence stratigraphy and inferred depositional developments suggest that this subgroup represents only a short period of late orogenic molasse sedimentation during the early sub-trilobitic Early Cambrian.

scholarly journals Diversity and biostratigraphy of the late Oligocene-late Miocene sand dollars (Echinoidea: Scutelliformes) of Argentina and Uruguay

2021 ◽  
Vol 69 (Suppl.1) ◽  
pp. 35-50
Author(s):  
Claudia-J. Del Río ◽  
Sergio Martínez
Keyword(s):  
South America ◽  
Late Miocene ◽  
Middle Miocene ◽  
Field Work ◽  
Early Miocene ◽  
Late Oligocene ◽  
Good Correspondence ◽  
Shallow Marine ◽  
Sand Dollars ◽  
Temporal Dimensions

Introduction: Scutelliforms were diverse and widespread in shallow marine environments during Neogene times in South America. Nevertheless, they have almost never been used as biostratigraphic tools. Objective: To provide a refined stratigraphic frame useful for calibrating temporal dimensions of scutelliform diversity from Argentina and Uruguay and its correlation with the molluscan assemblages previously proposed. Methods: A detailed survey of their geographic and stratigraphic provenance was carried out. We revised both the bibliography and collections (institutional and from our own field work). Results: The group is represented by 14 species belonging to six genera, and four assemblages were identified. Numerical dates of the Neogene marine rocks obtained recently allowed their placement in a chronological scheme: “Iheringiella” sp. A is restricted to the late Oligocene, the genera Camachoaster and “Eoscutella” and the species Monophoraster telfordi to the early Miocene, Abertella gualichensis and Abertella miskellyi to the middle Miocene, and Monophoraster duboisi, Amplaster coloniensis and Amplaster ellipticus to the late Miocene. Non-lunulate scutelliforms are not restricted to the late Oligocene as previously supposed. The oldest occurrence of the genus Monophoraster corresponds to the early Miocene, and along with Iheringiella are long-living taxa that embrace the 25.3 Ma-18.1 Ma (Iheringiella patagonensis) and approximately 15 Ma-6.48 Ma (Monophoraster darwini) intervals. The presence of Iheringiella in the early Miocene of northeastern Patagonia is corroborated, reaching there its northernmost distribution. Monophoraster darwini has a temporal range from the late Miocene (where it was previously thought to be restricted) back to the middle Miocene, since this is the species yielded in the well-known and discussed “Monophoraster and Venericor Beds”. Conclusions: The Paleogene-Neogene scutelliforms of Argentina and Uruguay range from the late Oligocene to the late Miocene. There is a good correspondence among the numerical ages, molluscan biozones and scutelliform assemblages.

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