“The dominant geological unit exposed at Punta Carballo, Costa Rica, is part of the Nicoya Complex (Nicoya Ophiolite).”

“The oldest rocks in Costa Rica, the Nicoya Complex, crop out in an arcuate belt along the Pacific coast and outside the mapped area. The complex is an ophiolite assemblage… The Nicoya Complex forms the basement of the Nicoya and Osa peninsulas and nearby coastal areas, where it is widely exposed in sea cliffs and road cuts.”

“The pre-Tertiary oceanic crust exposed on the west coast of Costa Rica has been broadly referred to as the Nicoya Complex. Outcrops are generally limited to coastal peninsulas with the most extensive exposures on the Nicoya Peninsula… This project was designed to (1) determine the radiometric age of rocks from the Nicoya Complex… at the Nicoya Peninsula, Playa Jacó, and the Quepos Peninsula.”

“The oldest rocks in Costa Rica make up an ophiolite assemblage (Dengo, 1961, 1962a, b), the Nicoya Complex… A Late Cretaceous arc‑trench system, probably a southerly extension of the Middle America Trench, lay along and west of the present Pacific coast… Rocks of the Punta Carballo Formation (Dengo, 1962a, p. 38) on the flank of Cerro Turrucares in the Rio Grande quadrangle adjoining the Abra quadrangle on the west and on the Pacific coast near Puntarenas. The Punta Carballo on the Pacific coast consists predominantly of coarse sandstone and conglomerate derived from erosion of the Nicoya Complex ophiolite.”

The legend of the Punta Gorda geological sheet lists: "Complejo Nicoya (Basaltos)" and "Complejo de Nicoya (Radiolaritas)" among the mapped units. Punta Carballo is located within this 1:50 000 map sheet area, and the Nicoya Complex basalt and radiolarite units are shown along the coastal outcrops in that sector.

The paper states that the fossils were found at Doña Ana beaches near Puntarenas, Costa Rica, in the Punta Carballo Formation, which is described as a Miocene unit. It discusses the Punta Carballo Formation as the rock unit at the locality, but it does not identify the dominant exposed geological unit at Punta Carballo as part of the Nicoya Complex.

“The pre-Tertiary oceanic crust exposed on the west coast of Costa Rica has been broadly referred to as the Nicoya Complex. Outcrops are generally limited to coastal peninsulas with the most extensive exposures on the Nicoya Peninsula… The full extent of the obducted crust is not precisely known, but it is possible that the Nicoya Complex is part of a belt of accreted Mesozoic oceanic crust that extends southeastward through Panama into western Colombia and Ecuador.”

“At the Orotina plain, the Tiribí Tuff overlies sedimentary rocks of the Punta Carballo Formation, breccias of the Tivives Formation and ancient fluvial deposits… Most of the distal finger‑like deposits of Orotina facies flowed westward in the paleocanyon of the Grande de Tárcoles River, probably reaching the Pacific coast.” This description treats the Punta Carballo Formation as a sedimentary unit that is overlain by younger volcanic deposits, not as part of the Nicoya ophiolitic basement.

“Field mapping clearly shows that the Pacific coastal region in Costa Rica is underlain by deformed Mesozoic rocks (Upper Jurassic? to Upper Cretaceous) representing ocean crust. Although the structure of the Nicoya Complex is still uncertain, the presence in Santa Elena Peninsula of a complex involving a nappe of ultrabasic rocks… and the Nicoya Complex Mesozoic rocks (2) outcropping along the Pacific coast indicate a continuous belt of Nicoya Complex rocks in coastal Costa Rica.”

The description says that the regional basement corresponds to the Nicoya Ophiolitic Complex, on which the Tertiary rocks rest. In the southwest, turbiditic sediments and shallow marine deposits occur, and the Candelaria basin stratigraphy includes several younger formations above the Nicoya Complex.

“The outcroping stratigraphic sequence of the following quadrangles is shown: Belén, Carrillo Norte, Matapalo and Punta Gorda. We mapped the following geologic units: The Nicoya Ophiolitic Complex is constituted by basalts, radiolarites and the Potrero Intrusive…” The paper describes the northern Nicoya Peninsula coastal area (including Punta Gorda sheet, where Punta Carballo is located) as being underlain predominantly by the Nicoya Ophiolitic Complex.

“El Complejo de Nicoya, que cubre la mayor parte de la región estudiada, es una unidad compuesta por basaltos espilíticos, aglomerados, brechas de basalto y liditas, intrusiones de gabro, diabasa y diorita…” The study notes that in the Nicoya Peninsula coastal zone most outcrops belong to the Nicoya Complex, indicating that the dominant exposed rocks in many shoreline sectors are part of this ophiolitic unit.

“The geology, geochemistry and emplacement of the Cretaceous–Tertiary ophiolitic Nicoya Complex of the Osa Peninsula, southern Costa Rica, are described. The Nicoya Ophiolite Complex is composed predominantly of basaltic pillow lavas, sheeted dikes, gabbros and ultramafic rocks, and represents obducted oceanic crust that forms the basement of large parts of the Pacific coast of Costa Rica.”

“Outcrops at Doña Ana beach (Punta Carballo Formation, Miocene) exhibit proximal tempestites that formed in a shallow platform environment (protected bay)… The Punta Carballo Formation is composed of shallow‑marine siliciclastic and bioclastic deposits.” This characterization of the Punta Carballo Formation as Miocene shallow‑marine tempestite‑bearing sediments contrasts with the ultramafic–mafic oceanic crustal rocks typical of the Nicoya Ophiolite.

“4.1.1 Complejo de Nicoya. El Complejo de Nicoya está constituido por rocas de origen ígneo y sedimentario, siendo las rocas ígneas son coladas de basaltos…” The report describes the Nicoya Complex as the principal basement unit along much of the Costa Rican Pacific margin, including the Nicoya Peninsula coastal sector where Punta Carballo is located.

“A continuación se describen las unidades geológicas… COMPLEJO DE NICOYA… Estratotipo: Para el Complejo de Nicoya, Dengo (1962) indica la localidad de Montezuma… Descripción: En los afloramiento vistos en la hoja Barranca se observaron basaltos, tanto masivos como con estructura en almohadilla y diabasas.” This article documents that along the adjacent Pacific coastal sheet (Barranca) the dominant coastal basement unit is the Nicoya Complex basalts, showing the same regional pattern of Nicoya Complex dominance along the coast as at Punta Carballo.

“Se presenta la estratigrafía generalizada de las hojas topográficas Belén, Carrillo Norte, Matapalo y Punta Gorda. En las cuales se cartografiaron las siguientes unidades: El Complejo de Nicoya, constituido por basaltos, radiolaritas y el Intrusivo Potrero…” The article emphasizes that in the Punta Gorda sheet the mapped basement is the Nicoya Complex, with only a sedimentary cover and ignimbrites locally overlying it.

The guide notes that the rugged interior of the Herradura block exposes primarily oceanic basalts of the Nicoya Complex. This supports the broader regional association between exposed coastal forearc rocks and the Nicoya Complex, though it does not specifically identify Punta Carballo itself.

The document lists the Nicoya Complex among the oldest volcanic rocks with oceanic affinity in Costa Rica and then places younger sedimentary units, including Punta Carballo, in a later stratigraphic sequence. This is consistent with Punta Carballo being a younger cover unit rather than the Nicoya Complex itself.

The thesis PDF references the Punta Carballo Formation in a stratigraphic context and cites the Nicoya Ophiolite Complex as a regional basement unit in Costa Rica. It provides background on the geology but does not directly state that the dominant unit exposed at Punta Carballo is the Nicoya Complex.

In Costa Rican coastal geology, Punta Carballo is commonly associated with the Punta Carballo Formation and nearby Miocene marine deposits, while the Nicoya Complex is the older oceanic basement that underlies much of the region. This makes the claim about the dominant exposed unit requiring site-specific confirmation rather than being automatically true from regional basement geology.

The indexed record includes references to the Punta Carballo Formation and regional Costa Rican stratigraphy, including San Miguel and other units. Because this is an index/metadata page rather than the original paper text, it is only indirect evidence and does not directly resolve the Punta Carballo exposure question.

“Today, the Cocos Plate is still pushing its way below the Caribbean Plate in what is considered a subduction megathrust fault, and it is happening directly below Costa Rica’s Nicoya Peninsula along the Pacific Coast. Off the Nicoya Peninsula, the Cocos Plate is subducting along the Middle America Trench under the Caribbean Plate… A major earthquake centered beneath the Nicoya Peninsula occurred on October 5, 1950… and on September 5 (2012) a major megathrust earthquake (7.6) ruptured the plate boundary under the Peninsula.”

In the talk, geologists Pablo Morales and Óscar Morales explain that the Nicoya Peninsula is largely formed by the Nicoya Complex (Nicoya ophiolite). Around timestamp 1830 s they describe how oceanic crustal blocks were accreted and uplifted to form the peninsula, and note that many coastal headlands and cliffs are exposures of these Nicoya Complex basalts and related rocks.

The atlas identifies Punta Carballo as 'Roca de Carballo' and a notable coastal landmark in the Gulf of Nicoya area. The page is useful for locality context, but it does not specify the exposed geological unit as the Nicoya Complex.