Depositional Sequence Evolution, Paleozoic and Early Mesozoic of the Central Saharan Platform, North Africa

The outcrops of the Sierra de Albarracín (NE Spain) allow a precise reconstruction of the shallow sedimentary domains of a late Kimmeridgian carbonate ramp, developed in western marginal areas of the Iberian Basin. The sedimentary record shows a hierarchical sequence stratigraphic organization, which implies sea-level changes of different frequencies. The studied succession is arranged in a long-term transgressive–regressive sequence, which is likely to reflect local variation in the subsidence rates. This sequence includes four higher-order sequences A to D, which have variable thickness (from 3 to 21 m). The similar sedimentary evolution observed in distant localities suggests the existence of high-frequency sea-level fluctuations controlling the sequence development. The average amplitude of these cycles would range from 5 to 10 m. The precise estimation of their duration (some few hundreds of kyr) and their possible assignment to any of the long-term orbital cycles (the 100 or the 400 kyr eccentricity cycles) is uncertain. Sequences A and B, formed during the long-term transgressive interval, are relatively thin (from 3 to 9 m) give-up sequences that were never subaerially exposed. These sequences are locally formed by five shallowing-upward elementary sequences. Sequences C and D are catch-down sequences with evidence of emersion of subtidal facies. Sequence C, formed during the stage of maximum gain of long-term accommodation, is the thickest sequence (from 13 to 21 m) and includes coral–microbial reefs (pinnacles up to 16 m in height). The increased production rates were able to fill part of the accommodation created during the early stage of high-frequency sea-level rise and the shallow platform was eventually exposed to subaereal erosion and meteoric cementation.

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Limulitella tejraensis, a new species of limulid (Chelicerata, Xiphosura) from the Middle Triassic of southern Tunisia (Saharan Platform)

Journal of Paleontology ◽

10.1017/jpa.2017.29 ◽

2017 ◽

Vol 91 (5) ◽

pp. 960-967 ◽

Cited By ~ 7

Author(s):

Błażej Błażejowski ◽

Grzegorz Niedźwiedzki ◽

Kamel Boukhalfa ◽

Mohamed Soussi

Keyword(s):

New Species ◽

North Africa ◽

Type Species ◽

Middle Triassic ◽

Marine Transgression ◽

Stressful Environment ◽

Southern Tunisia ◽

Morphological Differences ◽

Saharan Platform ◽

A New Species

AbstractNumerous well-preserved remains of a new limulid species from the Anisian-lower Ladinian (Middle Triassic) of the Tejra section of southern Tunisia are described. Comparisons are made with limulids from the Triassic deposits of Europe and Australia. The new specimens are congeneric with the type species ofLimulitella, but show some morphological differences. Here we describeLimulitella tejraensisnew species, a small limulid with semicircular prosoma, small and triangular opisthosoma, well-defined axial ridge, and pleurae along both ridges of the opisthosoma. The TunisianLimulitellafossils are associated with conchostracans, bivalves, gastropods, and microconchids. Sedimentological and paleontological data from the Tejra section suggest freshwater to brackish-water conditions during the formation of the fossil-bearing interval and the influence of marine transgression into a playa-like environment. Supposed adaptation to the stressful environment sheds new light on the origin and survival of the extant limulines. This is the first report of limulid body fossils from the Triassic of North Africa and the first documentation ofLimulitellain the Middle Triassic of northern Gondwanaland.

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Depositional Sequence Evolution as a Result of Tectonism, Basin Subsidence, and Sea Level Change, Turonian to Santonian, West-Central Utah: ABSTRACT

AAPG Bulletin ◽

10.1306/948868e4-1704-11d7-8645000102c1865d ◽

1986 ◽

Vol 70 ◽

Author(s):

Peter Schwans

Keyword(s):

Sea Level ◽

Sea Level Change ◽

Sequence Evolution ◽

Depositional Sequence ◽

Level Change ◽

West Central ◽

Basin Subsidence ◽

And Sea Level

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Development of an Upper Triassic-Lower Jurassic Evaporite Basin on the Saharan Platform, North Africa

Permo-Triassic Salt Provinces of Europe, North Africa and the Atlantic Margins ◽

10.1016/b978-0-12-809417-4.00028-8 ◽

2017 ◽

pp. 581-599

Author(s):

P. Turner ◽

K. Pelz

Keyword(s):

North Africa ◽

Lower Jurassic ◽

Upper Triassic ◽

Saharan Platform

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The Infancy of Solar-Type Stars and its Relevance for the Origin of Life

International Astronomical Union Colloquium ◽

10.1017/s0252921100014780 ◽

1997 ◽

Vol 161 ◽

pp. 267-282 ◽

Cited By ~ 1

Author(s):

Thierry Montmerle

Keyword(s):

Main Sequence ◽

Solar Nebula ◽

Circumstellar Disks ◽

T Tauri Stars ◽

Necessary Condition ◽

Sequence Evolution ◽

T Tauri ◽

Solar Type ◽

Optical Domain ◽

The Origin Of Life

AbstractFor life to develop, planets are a necessary condition. Likewise, for planets to form, stars must be surrounded by circumstellar disks, at least some time during their pre-main sequence evolution. Much progress has been made recently in the study of young solar-like stars. In the optical domain, these stars are known as «T Tauri stars». A significant number show IR excess, and other phenomena indirectly suggesting the presence of circumstellar disks. The current wisdom is that there is an evolutionary sequence from protostars to T Tauri stars. This sequence is characterized by the initial presence of disks, with lifetimes ~ 1-10 Myr after the intial collapse of a dense envelope having given birth to a star. While they are present, about 30% of the disks have masses larger than the minimum solar nebula. Their disappearance may correspond to the growth of dust grains, followed by planetesimal and planet formation, but this is not yet demonstrated.

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