Way Group
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Way Group () is a
geologic group In geology, a group is a lithostratigraphic unit consisting of a series of related formations that have been classified together to form a group. Formations are the fundamental unit of stratigraphy. Groups may sometimes be combined into superg ...
of
Lower Cretaceous Lower may refer to: * ''Lower'' (album), 2025 album by Benjamin Booker * Lower (surname) * Lower Township, New Jersey *Lower Receiver (firearms) * Lower Wick Gloucestershire, England See also * Nizhny {{Disambiguation ...
age located in northern Chile. The sediments of the group deposited in Coloso Basin, a small
intra-arc basin In geology an intra-arc basin is a sedimentary basin that exists amidst a volcanic arc. Being located next to volcanoes intra-arc basins tend to host volcano-sedimentary sequences. Cura-Mallín at the border of Chile and Argentina is an example ...
made up by a
half graben A half-graben is a geological structure bounded by a fault along one side of its boundaries, unlike a full graben where a depressed block of land is bordered by parallel faults. Rift and fault structure A rift is a region where the lithosphere ...
. The now inactive Coloso Basin is elongated along a NNW-SSE oriented axis and has its southwestern border made up by faults. The Way Group is made up of the following arrangement from top to bottom the Tablado Formation made up chiefly of
limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
, the conglomerate-
gravel Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone. Gr ...
-
sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...
Lombriz Formation and the conglomerate and
breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...
dominated Caleta Coloso Formation.


Tabledo Formation

Tableado Formation is the uppermost member of Way Group. It is made up of limestone and shale deposited in the shallow marine conditions of the
continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an islan ...
. The limestones contains fossils. It rests conformably on top of Lombriz Formation.


Lombriz Formation

Clasts of epidotized lava are common in the conglomerates of Lombriz Formation. The clasts of Lombriz Formation are made up of
andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...
and
diorite Diorite ( ) is an intrusive rock, intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is Intermediate composition, inter ...
. The climate at the time of deposition of the Lombriz Formation was arid as evidenced by the
evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...
s that are part of the formation.


Coloso Formation

Caleta Coloso Formation or Coloso Formation is the lowermost formation of the Way Group. The breccias and conglomerates of Coloso Formation are the deposits of former alluvial fans. In particular, Coloso Formation represents the parts of the alluvial fan closer to the apex. Minas Conglomerate is the name of a group of conglomerate beds in upper Coloso Formation that contains what is known as Minas Conglomerate, a conglomerate rich in clasts with
copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
mineralization. The lower Coloso Formation contains a majority of
andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...
clasts while the upper Coloso Formation contains more
diorite Diorite ( ) is an intrusive rock, intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is Intermediate composition, inter ...
. Possibly, this difference indicates a sequence of erosion starting from more surficial volcanic rocks and then plutonic rocks. Diagenesis has formed
analcime Analcime (; ) or analcite is a white, gray, or colorless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is NaAlSi2O6 · H2O. Minor amounts of potassium and calcium ...
,
calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
and
hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
in the matrix of the lower Coloso Formation.


References

{{Geology of Chile Geologic groups of Chile Lower Cretaceous Series of South America Cretaceous Chile Geology of the Chilean Coast Range Geology of Antofagasta Region