 |
| Titel |
Middle Cretaceous to Oligocene rise of the Middle American landbridge - documented by south-eastwards younging shallow water carbonates |
| VerfasserIn |
Claudia Baumgartner-Mora, Peter O. Baumgartner, Flore Barat |
| Konferenz |
EGU General Assembly 2013
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250083640
|
|
|
|
|
|
| Zusammenfassung |
| Basements of Southern Central America are oceanic in origin, including the southern half of
the classical “Chortis Block” formed by subduction/accretion mélanges named Mesquito
Composite Oceanic Terrane (MCOT). The rise of these oceanic basements into the photic
zone and eventual emergence was controlled by convergent, collision tectonics, and/or arc
development. In this context, shallow carbonate palaeo-environments were short-lived and
formed not only on uplifted basements and arcs, but also on (now accreted) volcanic edifices
of Pacific oceanic seamounts.
From Northern Nicaragua (NW) to Eastern Panama (SE) we observe a systematic younging
of the first shallow water carbonate facies encroaching on basements and/or older deep-water
formations:
In the Siuna area (NE-Nicaragua) Aptian-Albian shallow water limestones dated by rudists
and Orbitolina texana rest unconformably on the Jurassic/Early Cretaceous Siuna
Serpentinite Mélange, part of the MCOT. In N-Costa Rica, the assembly of several terranes
(Santa Elena Ultramafic Unit, Nicoya Complex s. s., Matambu and Manzanillo Terranes) is
overlapped by Late Campanian-Maastrichtian shallow water facies dated by rudists and
Larger Foraminifera, such as Pseudorbitoides rutteni, Pseudorbitoides israelski,
Sulcoperculina sp. and Sulcoperculina globosa. Reworked Campanian-Maastrichtian
shallow water material including Larger Foraminifera was found in the Herradura
Promontory (central Pacific coast of Costa Rica). It could be derived from an accreted
seamount.
No shallow carbonates are known so far from the early Palaeocene.
The Tempisque Basin (N-Costa Rica) hosts the Barra Honda carbonate Platform (originally
>900 km2) dated as late Palaeocene (Thanetian) by planktonic Foraminifera, 87Sr / 86Sr
ratios and Ranikothalia spp. Other late Palaeocene shallow carbonates documented in
S-Costa Rica/W-Panama (Quepos, Burica) are interpreted as insular carbonate shoals (atolls?)
on now accreted seamounts.
To the SE of the S-Nicoya fault line (Central Costa Rica) Late Cretaceous oceanic plateaus
may represent actual outcrops of the trailing edge of the Caribbean Large Igneous Province
(CLIP). These include the SE corner of the Herradura Promontory (Costa Rica) and the
Azuero Plateau cropping out in Coiba, Sona and Azuero (Panama). CLIP formation triggered
a new, E-dipping subduction zone and Campanian-Maastrichtian arc initiation on the CLIP
edge. By middle to late Eocene times this Middle American Arc and forearc areas reached the
photic zone leading to widespread formation of carbonate banks/ramps. They are dated by
many Larger Foraminifera of the genera Amphistegina, Asterocyclina, Discocyclina,
Euconoloides, Eofabiania, Fabiania, Gypsina, Helicolepidina, Heterostegina, ,
Lepidocyclina, Linderina, Neodiscocyclina, Nummulites, Operculina, Orthophragmina,
Polylepidina, Proporocyclina, and Sphareogypsina.
The first shallow carbonates that encroach on arc/forearc basements in Panama are
dated as Late Eocene in Azuero and the Canal Basin and as Oligocene, dated by
Lepidocyclina miraflorensis, L. giraudi, L. canellei around the Chucunaque Basin of Eastern
Panama.
Progressive shallowing of the trailing edge of the Caribbean plate from NW (middle/Late
Cretaceous) to SE (Late Eocene-Oligocene) implies a growing restriction of the Atlantic –
Caribbean – Pacific seaway that must have affected global circulation patterns, to be
considered in palaeo-oceanographic/palaeo-climatic models of the Late Cretaceous
–Tertiary. |
|
|
|
|
|
|